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6. Extensions to the C Language Family

GNU C provides several language features not found in ISO standard C. (The `-pedantic' option directs GCC to print a warning message if any of these features is used.) To test for the availability of these features in conditional compilation, check for a predefined macro __GNUC__, which is always defined under GCC.

These extensions are available in C and Objective-C. Most of them are also available in C++. See section Extensions to the C++ Language, for extensions that apply only to C++.

Some features that are in ISO C99 but not C90 or C++ are also, as extensions, accepted by GCC in C90 mode and in C++.

6.1 Statements and Declarations in Expressions  Putting statements and declarations inside expressions.
6.2 Locally Declared Labels  Labels local to a block.
6.3 Labels as Values  Getting pointers to labels, and computed gotos.
6.4 Nested Functions  As in Algol and Pascal, lexical scoping of functions.
6.5 Constructing Function Calls  Dispatching a call to another function.
6.6 Referring to a Type with typeof  typeof: referring to the type of an expression.
6.7 Conditionals with Omitted Operands  Omitting the middle operand of a `?:' expression.
6.8 Double-Word Integers  Double-word integers---long long int.
6.9 Complex Numbers  Data types for complex numbers.
6.10 Additional Floating Types  
6.11 Half-Precision Floating Point  
6.12 Decimal Floating Types  
6.13 Hex Floats  Hexadecimal floating-point constants.
6.14 Fixed-Point Types  
6.15 Named address spaces  
6.16 Arrays of Length Zero  Zero-length arrays.
6.18 Arrays of Variable Length  Arrays whose length is computed at run time.
6.17 Structures With No Members  Structures with no members.
6.19 Macros with a Variable Number of Arguments.  Macros with a variable number of arguments.
6.20 Slightly Looser Rules for Escaped Newlines  Slightly looser rules for escaped newlines.
6.21 Non-Lvalue Arrays May Have Subscripts  Any array can be subscripted, even if not an lvalue.
6.22 Arithmetic on void- and Function-Pointers  Arithmetic on void-pointers and function pointers.
6.23 Non-Constant Initializers  Non-constant initializers.
6.24 Compound Literals  Compound literals give structures, unions or arrays as values.
6.25 Designated Initializers  Labeling elements of initializers.
6.27 Cast to a Union Type  Casting to union type from any member of the union.
6.26 Case Ranges  `case 1 ... 9' and such.
6.28 Mixed Declarations and Code  Mixing declarations and code.
6.29 Declaring Attributes of Functions  Declaring that functions have no side effects, or that they can never return.
6.30 Attribute Syntax  Formal syntax for attributes.
6.31 Prototypes and Old-Style Function Definitions  Prototype declarations and old-style definitions.
6.32 C++ Style Comments  C++ comments are recognized.
6.33 Dollar Signs in Identifier Names  Dollar sign is allowed in identifiers.
6.34 The Character ESC in Constants  `\e' stands for the character ESC.
6.35 Specifying Attributes of Variables  Specifying attributes of variables.
6.36 Specifying Attributes of Types  Specifying attributes of types.
6.37 Inquiring on Alignment of Types or Variables  Inquiring about the alignment of a type or variable.
6.38 An Inline Function is As Fast As a Macro  Defining inline functions (as fast as macros).
6.39 Assembler Instructions with C Expression Operands  Assembler instructions with C expressions as operands.

                        (With them you can define "built-in" functions.)
6.40 Constraints for asm Operands  Constraints for asm operands
6.41 Controlling Names Used in Assembler Code  Specifying the assembler name to use for a C symbol.
6.42 Variables in Specified Registers  Defining variables residing in specified registers.
6.43 Alternate Keywords  __const__, __asm__, etc., for header files.
6.44 Incomplete enum Types  enum foo;, with details to follow.
6.45 Function Names as Strings  Printable strings which are the name of the current function.
6.46 Getting the Return or Frame Address of a Function  Getting the return or frame address of a function.
6.47 Using vector instructions through built-in functions  
6.48 Offsetof  Special syntax for implementing offsetof.
6.49 Built-in functions for atomic memory access  
6.51 Object Size Checking Builtins  Built-in functions for limited buffer overflow checking.
6.52 Other built-in functions provided by GCC  Other built-in functions.
6.53 Built-in Functions Specific to Particular Target Machines  Built-in functions specific to particular targets.
6.54 Format Checks Specific to Particular Target Machines  Format checks specific to particular targets.
6.55 Pragmas Accepted by GCC  Pragmas accepted by GCC.
6.56 Unnamed struct/union fields within structs/unions  
6.57 Thread-Local Storage  Per-thread variables.
6.58 Binary constants using the `0b' prefix  


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6.1 Statements and Declarations in Expressions

A compound statement enclosed in parentheses may appear as an expression in GNU C. This allows you to use loops, switches, and local variables within an expression.

Recall that a compound statement is a sequence of statements surrounded by braces; in this construct, parentheses go around the braces. For example:

 
({ int y = foo (); int z;
   if (y > 0) z = y;
   else z = - y;
   z; })

is a valid (though slightly more complex than necessary) expression for the absolute value of foo ().

The last thing in the compound statement should be an expression followed by a semicolon; the value of this subexpression serves as the value of the entire construct. (If you use some other kind of statement last within the braces, the construct has type void, and thus effectively no value.)

This feature is especially useful in making macro definitions "safe" (so that they evaluate each operand exactly once). For example, the "maximum" function is commonly defined as a macro in standard C as follows:

 
#define max(a,b) ((a) > (b) ? (a) : (b))

But this definition computes either a or b twice, with bad results if the operand has side effects. In GNU C, if you know the type of the operands (here taken as int), you can define the macro safely as follows:

 
#define maxint(a,b) \
  ({int _a = (a), _b = (b); _a > _b ? _a : _b; })

Embedded statements are not allowed in constant expressions, such as the value of an enumeration constant, the width of a bit-field, or the initial value of a static variable.

If you don't know the type of the operand, you can still do this, but you must use typeof (see section 6.6 Referring to a Type with typeof).

In G++, the result value of a statement expression undergoes array and function pointer decay, and is returned by value to the enclosing expression. For instance, if A is a class, then

 
        A a;

        ({a;}).Foo ()

will construct a temporary A object to hold the result of the statement expression, and that will be used to invoke Foo. Therefore the this pointer observed by Foo will not be the address of a.

Any temporaries created within a statement within a statement expression will be destroyed at the statement's end. This makes statement expressions inside macros slightly different from function calls. In the latter case temporaries introduced during argument evaluation will be destroyed at the end of the statement that includes the function call. In the statement expression case they will be destroyed during the statement expression. For instance,

 
#define macro(a)  ({__typeof__(a) b = (a); b + 3; })
template<typename T> T function(T a) { T b = a; return b + 3; }

void foo ()
{
  macro (X ());
  function (X ());
}

will have different places where temporaries are destroyed. For the macro case, the temporary X will be destroyed just after the initialization of b. In the function case that temporary will be destroyed when the function returns.

These considerations mean that it is probably a bad idea to use statement-expressions of this form in header files that are designed to work with C++. (Note that some versions of the GNU C Library contained header files using statement-expression that lead to precisely this bug.)

Jumping into a statement expression with goto or using a switch statement outside the statement expression with a case or default label inside the statement expression is not permitted. Jumping into a statement expression with a computed goto (see section 6.3 Labels as Values) yields undefined behavior. Jumping out of a statement expression is permitted, but if the statement expression is part of a larger expression then it is unspecified which other subexpressions of that expression have been evaluated except where the language definition requires certain subexpressions to be evaluated before or after the statement expression. In any case, as with a function call the evaluation of a statement expression is not interleaved with the evaluation of other parts of the containing expression. For example,

 
  foo (), (({ bar1 (); goto a; 0; }) + bar2 ()), baz();

will call foo and bar1 and will not call baz but may or may not call bar2. If bar2 is called, it will be called after foo and before bar1


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6.2 Locally Declared Labels

GCC allows you to declare local labels in any nested block scope. A local label is just like an ordinary label, but you can only reference it (with a goto statement, or by taking its address) within the block in which it was declared.

A local label declaration looks like this:

 
__label__ label;

or

 
__label__ label1, label2, /* ... */;

Local label declarations must come at the beginning of the block, before any ordinary declarations or statements.

The label declaration defines the label name, but does not define the label itself. You must do this in the usual way, with label:, within the statements of the statement expression.

The local label feature is useful for complex macros. If a macro contains nested loops, a goto can be useful for breaking out of them. However, an ordinary label whose scope is the whole function cannot be used: if the macro can be expanded several times in one function, the label will be multiply defined in that function. A local label avoids this problem. For example:

 
#define SEARCH(value, array, target)              \
do {                                              \
  __label__ found;                                \
  typeof (target) _SEARCH_target = (target);      \
  typeof (*(array)) *_SEARCH_array = (array);     \
  int i, j;                                       \
  int value;                                      \
  for (i = 0; i < max; i++)                       \
    for (j = 0; j < max; j++)                     \
      if (_SEARCH_array[i][j] == _SEARCH_target)  \
        { (value) = i; goto found; }              \
  (value) = -1;                                   \
 found:;                                          \
} while (0)

This could also be written using a statement-expression:

 
#define SEARCH(array, target)                     \
({                                                \
  __label__ found;                                \
  typeof (target) _SEARCH_target = (target);      \
  typeof (*(array)) *_SEARCH_array = (array);     \
  int i, j;                                       \
  int value;                                      \
  for (i = 0; i < max; i++)                       \
    for (j = 0; j < max; j++)                     \
      if (_SEARCH_array[i][j] == _SEARCH_target)  \
        { value = i; goto found; }                \
  value = -1;                                     \
 found:                                           \
  value;                                          \
})

Local label declarations also make the labels they declare visible to nested functions, if there are any. See section 6.4 Nested Functions, for details.


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6.3 Labels as Values

You can get the address of a label defined in the current function (or a containing function) with the unary operator `&&'. The value has type void *. This value is a constant and can be used wherever a constant of that type is valid. For example:

 
void *ptr;
/* ... */
ptr = &&foo;

To use these values, you need to be able to jump to one. This is done with the computed goto statement(3), goto *exp;. For example,

 
goto *ptr;

Any expression of type void * is allowed.

One way of using these constants is in initializing a static array that will serve as a jump table:

 
static void *array[] = { &&foo, &&bar, &&hack };

Then you can select a label with indexing, like this:

 
goto *array[i];

Note that this does not check whether the subscript is in bounds--array indexing in C never does that.

Such an array of label values serves a purpose much like that of the switch statement. The switch statement is cleaner, so use that rather than an array unless the problem does not fit a switch statement very well.

Another use of label values is in an interpreter for threaded code. The labels within the interpreter function can be stored in the threaded code for super-fast dispatching.

You may not use this mechanism to jump to code in a different function. If you do that, totally unpredictable things will happen. The best way to avoid this is to store the label address only in automatic variables and never pass it as an argument.

An alternate way to write the above example is

 
static const int array[] = { &&foo - &&foo, &&bar - &&foo,
                             &&hack - &&foo };
goto *(&&foo + array[i]);

This is more friendly to code living in shared libraries, as it reduces the number of dynamic relocations that are needed, and by consequence, allows the data to be read-only.

The &&foo expressions for the same label might have different values if the containing function is inlined or cloned. If a program relies on them being always the same, __attribute__((__noinline__,__noclone__)) should be used to prevent inlining and cloning. If &&foo is used in a static variable initializer, inlining and cloning is forbidden.


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6.4 Nested Functions

A nested function is a function defined inside another function. (Nested functions are not supported for GNU C++.) The nested function's name is local to the block where it is defined. For example, here we define a nested function named square, and call it twice:

 
foo (double a, double b)
{
  double square (double z) { return z * z; }

  return square (a) + square (b);
}

The nested function can access all the variables of the containing function that are visible at the point of its definition. This is called lexical scoping. For example, here we show a nested function which uses an inherited variable named offset:

 
bar (int *array, int offset, int size)
{
  int access (int *array, int index)
    { return array[index + offset]; }
  int i;
  /* ... */
  for (i = 0; i < size; i++)
    /* ... */ access (array, i) /* ... */
}

Nested function definitions are permitted within functions in the places where variable definitions are allowed; that is, in any block, mixed with the other declarations and statements in the block.

It is possible to call the nested function from outside the scope of its name by storing its address or passing the address to another function:

 
hack (int *array, int size)
{
  void store (int index, int value)
    { array[index] = value; }

  intermediate (store, size);
}

Here, the function intermediate receives the address of store as an argument. If intermediate calls store, the arguments given to store are used to store into array. But this technique works only so long as the containing function (hack, in this example) does not exit.

If you try to call the nested function through its address after the containing function has exited, all hell will break loose. If you try to call it after a containing scope level has exited, and if it refers to some of the variables that are no longer in scope, you may be lucky, but it's not wise to take the risk. If, however, the nested function does not refer to anything that has gone out of scope, you should be safe.

GCC implements taking the address of a nested function using a technique called trampolines. This technique was described in Lexical Closures for C++ (Thomas M. Breuel, USENIX C++ Conference Proceedings, October 17-21, 1988).

A nested function can jump to a label inherited from a containing function, provided the label was explicitly declared in the containing function (see section 6.2 Locally Declared Labels). Such a jump returns instantly to the containing function, exiting the nested function which did the goto and any intermediate functions as well. Here is an example:

 
bar (int *array, int offset, int size)
{
  __label__ failure;
  int access (int *array, int index)
    {
      if (index > size)
        goto failure;
      return array[index + offset];
    }
  int i;
  /* ... */
  for (i = 0; i < size; i++)
    /* ... */ access (array, i) /* ... */
  /* ... */
  return 0;

 /* Control comes here from access
    if it detects an error.  */
 failure:
  return -1;
}

A nested function always has no linkage. Declaring one with extern or static is erroneous. If you need to declare the nested function before its definition, use auto (which is otherwise meaningless for function declarations).

 
bar (int *array, int offset, int size)
{
  __label__ failure;
  auto int access (int *, int);
  /* ... */
  int access (int *array, int index)
    {
      if (index > size)
        goto failure;
      return array[index + offset];
    }
  /* ... */
}


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6.5 Constructing Function Calls

Using the built-in functions described below, you can record the arguments a function received, and call another function with the same arguments, without knowing the number or types of the arguments.

You can also record the return value of that function call, and later return that value, without knowing what data type the function tried to return (as long as your caller expects that data type).

However, these built-in functions may interact badly with some sophisticated features or other extensions of the language. It is, therefore, not recommended to use them outside very simple functions acting as mere forwarders for their arguments.

Built-in Function: void * __builtin_apply_args ()
This built-in function returns a pointer to data describing how to perform a call with the same arguments as were passed to the current function.

The function saves the arg pointer register, structure value address, and all registers that might be used to pass arguments to a function into a block of memory allocated on the stack. Then it returns the address of that block.

Built-in Function: void * __builtin_apply (void (*function)(), void *arguments, size_t size)
This built-in function invokes function with a copy of the parameters described by arguments and size.

The value of arguments should be the value returned by __builtin_apply_args. The argument size specifies the size of the stack argument data, in bytes.

This function returns a pointer to data describing how to return whatever value was returned by function. The data is saved in a block of memory allocated on the stack.

It is not always simple to compute the proper value for size. The value is used by __builtin_apply to compute the amount of data that should be pushed on the stack and copied from the incoming argument area.

Built-in Function: void __builtin_return (void *result)
This built-in function returns the value described by result from the containing function. You should specify, for result, a value returned by __builtin_apply.

Built-in Function: __builtin_va_arg_pack ()
This built-in function represents all anonymous arguments of an inline function. It can be used only in inline functions which will be always inlined, never compiled as a separate function, such as those using __attribute__ ((__always_inline__)) or __attribute__ ((__gnu_inline__)) extern inline functions. It must be only passed as last argument to some other function with variable arguments. This is useful for writing small wrapper inlines for variable argument functions, when using preprocessor macros is undesirable. For example:
 
extern int myprintf (FILE *f, const char *format, ...);
extern inline __attribute__ ((__gnu_inline__)) int
myprintf (FILE *f, const char *format, ...)
{
  int r = fprintf (f, "myprintf: ");
  if (r < 0)
    return r;
  int s = fprintf (f, format, __builtin_va_arg_pack ());
  if (s < 0)
    return s;
  return r + s;
}

Built-in Function: __builtin_va_arg_pack_len ()
This built-in function returns the number of anonymous arguments of an inline function. It can be used only in inline functions which will be always inlined, never compiled as a separate function, such as those using __attribute__ ((__always_inline__)) or __attribute__ ((__gnu_inline__)) extern inline functions. For example following will do link or runtime checking of open arguments for optimized code:
 
#ifdef __OPTIMIZE__
extern inline __attribute__((__gnu_inline__)) int
myopen (const char *path, int oflag, ...)
{
  if (__builtin_va_arg_pack_len () > 1)
    warn_open_too_many_arguments ();

  if (__builtin_constant_p (oflag))
    {
      if ((oflag & O_CREAT) != 0 && __builtin_va_arg_pack_len () < 1)
        {
          warn_open_missing_mode ();
          return __open_2 (path, oflag);
        }
      return open (path, oflag, __builtin_va_arg_pack ());
    }
    
  if (__builtin_va_arg_pack_len () < 1)
    return __open_2 (path, oflag);

  return open (path, oflag, __builtin_va_arg_pack ());
}
#endif


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6.6 Referring to a Type with typeof

Another way to refer to the type of an expression is with typeof. The syntax of using of this keyword looks like sizeof, but the construct acts semantically like a type name defined with typedef.

There are two ways of writing the argument to typeof: with an expression or with a type. Here is an example with an expression:

 
typeof (x[0](1))

This assumes that x is an array of pointers to functions; the type described is that of the values of the functions.

Here is an example with a typename as the argument:

 
typeof (int *)

Here the type described is that of pointers to int.

If you are writing a header file that must work when included in ISO C programs, write __typeof__ instead of typeof. See section 6.43 Alternate Keywords.

A typeof-construct can be used anywhere a typedef name could be used. For example, you can use it in a declaration, in a cast, or inside of sizeof or typeof.

The operand of typeof is evaluated for its side effects if and only if it is an expression of variably modified type or the name of such a type.

typeof is often useful in conjunction with the statements-within-expressions feature. Here is how the two together can be used to define a safe "maximum" macro that operates on any arithmetic type and evaluates each of its arguments exactly once:

 
#define max(a,b) \
  ({ typeof (a) _a = (a); \
      typeof (b) _b = (b); \
    _a > _b ? _a : _b; })

The reason for using names that start with underscores for the local variables is to avoid conflicts with variable names that occur within the expressions that are substituted for a and b. Eventually we hope to design a new form of declaration syntax that allows you to declare variables whose scopes start only after their initializers; this will be a more reliable way to prevent such conflicts.

Some more examples of the use of typeof:

Compatibility Note: In addition to typeof, GCC 2 supported a more limited extension which permitted one to write

 
typedef T = expr;

with the effect of declaring T to have the type of the expression expr. This extension does not work with GCC 3 (versions between 3.0 and 3.2 will crash; 3.2.1 and later give an error). Code which relies on it should be rewritten to use typeof:

 
typedef typeof(expr) T;

This will work with all versions of GCC.


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6.7 Conditionals with Omitted Operands

The middle operand in a conditional expression may be omitted. Then if the first operand is nonzero, its value is the value of the conditional expression.

Therefore, the expression

 
x ? : y

has the value of x if that is nonzero; otherwise, the value of y.

This example is perfectly equivalent to

 
x ? x : y

In this simple case, the ability to omit the middle operand is not especially useful. When it becomes useful is when the first operand does, or may (if it is a macro argument), contain a side effect. Then repeating the operand in the middle would perform the side effect twice. Omitting the middle operand uses the value already computed without the undesirable effects of recomputing it.


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6.8 Double-Word Integers

ISO C99 supports data types for integers that are at least 64 bits wide, and as an extension GCC supports them in C90 mode and in C++. Simply write long long int for a signed integer, or unsigned long long int for an unsigned integer. To make an integer constant of type long long int, add the suffix `LL' to the integer. To make an integer constant of type unsigned long long int, add the suffix `ULL' to the integer.

You can use these types in arithmetic like any other integer types. Addition, subtraction, and bitwise boolean operations on these types are open-coded on all types of machines. Multiplication is open-coded if the machine supports fullword-to-doubleword a widening multiply instruction. Division and shifts are open-coded only on machines that provide special support. The operations that are not open-coded use special library routines that come with GCC.

There may be pitfalls when you use long long types for function arguments, unless you declare function prototypes. If a function expects type int for its argument, and you pass a value of type long long int, confusion will result because the caller and the subroutine will disagree about the number of bytes for the argument. Likewise, if the function expects long long int and you pass int. The best way to avoid such problems is to use prototypes.


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6.9 Complex Numbers

ISO C99 supports complex floating data types, and as an extension GCC supports them in C90 mode and in C++, and supports complex integer data types which are not part of ISO C99. You can declare complex types using the keyword _Complex. As an extension, the older GNU keyword __complex__ is also supported.

For example, `_Complex double x;' declares x as a variable whose real part and imaginary part are both of type double. `_Complex short int y;' declares y to have real and imaginary parts of type short int; this is not likely to be useful, but it shows that the set of complex types is complete.

To write a constant with a complex data type, use the suffix `i' or `j' (either one; they are equivalent). For example, 2.5fi has type _Complex float and 3i has type _Complex int. Such a constant always has a pure imaginary value, but you can form any complex value you like by adding one to a real constant. This is a GNU extension; if you have an ISO C99 conforming C library (such as GNU libc), and want to construct complex constants of floating type, you should include <complex.h> and use the macros I or _Complex_I instead.

To extract the real part of a complex-valued expression exp, write __real__ exp. Likewise, use __imag__ to extract the imaginary part. This is a GNU extension; for values of floating type, you should use the ISO C99 functions crealf, creal, creall, cimagf, cimag and cimagl, declared in <complex.h> and also provided as built-in functions by GCC.

The operator `~' performs complex conjugation when used on a value with a complex type. This is a GNU extension; for values of floating type, you should use the ISO C99 functions conjf, conj and conjl, declared in <complex.h> and also provided as built-in functions by GCC.

GCC can allocate complex automatic variables in a noncontiguous fashion; it's even possible for the real part to be in a register while the imaginary part is on the stack (or vice-versa). Only the DWARF2 debug info format can represent this, so use of DWARF2 is recommended. If you are using the stabs debug info format, GCC describes a noncontiguous complex variable as if it were two separate variables of noncomplex type. If the variable's actual name is foo, the two fictitious variables are named foo$real and foo$imag. You can examine and set these two fictitious variables with your debugger.


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6.10 Additional Floating Types

As an extension, the GNU C compiler supports additional floating types, __float80 and __float128 to support 80bit (XFmode) and 128 bit (TFmode) floating types. Support for additional types includes the arithmetic operators: add, subtract, multiply, divide; unary arithmetic operators; relational operators; equality operators; and conversions to and from integer and other floating types. Use a suffix `w' or `W' in a literal constant of type __float80 and `q' or `Q' for _float128. You can declare complex types using the corresponding internal complex type, XCmode for __float80 type and TCmode for __float128 type:

 
typedef _Complex float __attribute__((mode(TC))) _Complex128;
typedef _Complex float __attribute__((mode(XC))) _Complex80;

Not all targets support additional floating point types. __float80 and __float128 types are supported on i386, x86_64 and ia64 targets.


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6.11 Half-Precision Floating Point

On ARM targets, GCC supports half-precision (16-bit) floating point via the __fp16 type. You must enable this type explicitly with the `-mfp16-format' command-line option in order to use it.

ARM supports two incompatible representations for half-precision floating-point values. You must choose one of the representations and use it consistently in your program.

Specifying `-mfp16-format=ieee' selects the IEEE 754-2008 format. This format can represent normalized values in the range of 2^{-14} to 65504. There are 11 bits of significand precision, approximately 3 decimal digits.

Specifying `-mfp16-format=alternative' selects the ARM alternative format. This representation is similar to the IEEE format, but does not support infinities or NaNs. Instead, the range of exponents is extended, so that this format can represent normalized values in the range of 2^{-14} to 131008.

The __fp16 type is a storage format only. For purposes of arithmetic and other operations, __fp16 values in C or C++ expressions are automatically promoted to float. In addition, you cannot declare a function with a return value or parameters of type __fp16.

Note that conversions from double to __fp16 involve an intermediate conversion to float. Because of rounding, this can sometimes produce a different result than a direct conversion.

ARM provides hardware support for conversions between __fp16 and float values as an extension to VFP and NEON (Advanced SIMD). GCC generates code using these hardware instructions if you compile with options to select an FPU that provides them; for example, `-mfpu=neon-fp16 -mfloat-abi=softfp', in addition to the `-mfp16-format' option to select a half-precision format.

Language-level support for the __fp16 data type is independent of whether GCC generates code using hardware floating-point instructions. In cases where hardware support is not specified, GCC implements conversions between __fp16 and float values as library calls.


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6.12 Decimal Floating Types

As an extension, the GNU C compiler supports decimal floating types as defined in the N1312 draft of ISO/IEC WDTR24732. Support for decimal floating types in GCC will evolve as the draft technical report changes. Calling conventions for any target might also change. Not all targets support decimal floating types.

The decimal floating types are _Decimal32, _Decimal64, and _Decimal128. They use a radix of ten, unlike the floating types float, double, and long double whose radix is not specified by the C standard but is usually two.

Support for decimal floating types includes the arithmetic operators add, subtract, multiply, divide; unary arithmetic operators; relational operators; equality operators; and conversions to and from integer and other floating types. Use a suffix `df' or `DF' in a literal constant of type _Decimal32, `dd' or `DD' for _Decimal64, and `dl' or `DL' for _Decimal128.

GCC support of decimal float as specified by the draft technical report is incomplete:

Types _Decimal32, _Decimal64, and _Decimal128 are supported by the DWARF2 debug information format.


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6.13 Hex Floats

ISO C99 supports floating-point numbers written not only in the usual decimal notation, such as 1.55e1, but also numbers such as 0x1.fp3 written in hexadecimal format. As a GNU extension, GCC supports this in C90 mode (except in some cases when strictly conforming) and in C++. In that format the `0x' hex introducer and the `p' or `P' exponent field are mandatory. The exponent is a decimal number that indicates the power of 2 by which the significant part will be multiplied. Thus `0x1.f' is 1 15/16, `p3' multiplies it by 8, and the value of 0x1.fp3 is the same as 1.55e1.

Unlike for floating-point numbers in the decimal notation the exponent is always required in the hexadecimal notation. Otherwise the compiler would not be able to resolve the ambiguity of, e.g., 0x1.f. This could mean 1.0f or 1.9375 since `f' is also the extension for floating-point constants of type float.


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6.14 Fixed-Point Types

As an extension, the GNU C compiler supports fixed-point types as defined in the N1169 draft of ISO/IEC DTR 18037. Support for fixed-point types in GCC will evolve as the draft technical report changes. Calling conventions for any target might also change. Not all targets support fixed-point types.

The fixed-point types are short _Fract, _Fract, long _Fract, long long _Fract, unsigned short _Fract, unsigned _Fract, unsigned long _Fract, unsigned long long _Fract, _Sat short _Fract, _Sat _Fract, _Sat long _Fract, _Sat long long _Fract, _Sat unsigned short _Fract, _Sat unsigned _Fract, _Sat unsigned long _Fract, _Sat unsigned long long _Fract, short _Accum, _Accum, long _Accum, long long _Accum, unsigned short _Accum, unsigned _Accum, unsigned long _Accum, unsigned long long _Accum, _Sat short _Accum, _Sat _Accum, _Sat long _Accum, _Sat long long _Accum, _Sat unsigned short _Accum, _Sat unsigned _Accum, _Sat unsigned long _Accum, _Sat unsigned long long _Accum.

Fixed-point data values contain fractional and optional integral parts. The format of fixed-point data varies and depends on the target machine.

Support for fixed-point types includes:

Use a suffix in a fixed-point literal constant:

GCC support of fixed-point types as specified by the draft technical report is incomplete:

Fixed-point types are supported by the DWARF2 debug information format.


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6.15 Named address spaces

As an extension, the GNU C compiler supports named address spaces as defined in the N1275 draft of ISO/IEC DTR 18037. Support for named address spaces in GCC will evolve as the draft technical report changes. Calling conventions for any target might also change. At present, only the SPU target supports other address spaces. On the SPU target, for example, variables may be declared as belonging to another address space by qualifying the type with the __ea address space identifier:

 
extern int __ea i;

When the variable i is accessed, the compiler will generate special code to access this variable. It may use runtime library support, or generate special machine instructions to access that address space.

The __ea identifier may be used exactly like any other C type qualifier (e.g., const or volatile). See the N1275 document for more details.


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6.16 Arrays of Length Zero

Zero-length arrays are allowed in GNU C. They are very useful as the last element of a structure which is really a header for a variable-length object:

 
struct line {
  int length;
  char contents[0];
};

struct line *thisline = (struct line *)
  malloc (sizeof (struct line) + this_length);
thisline->length = this_length;

In ISO C90, you would have to give contents a length of 1, which means either you waste space or complicate the argument to malloc.

In ISO C99, you would use a flexible array member, which is slightly different in syntax and semantics:

GCC versions before 3.0 allowed zero-length arrays to be statically initialized, as if they were flexible arrays. In addition to those cases that were useful, it also allowed initializations in situations that would corrupt later data. Non-empty initialization of zero-length arrays is now treated like any case where there are more initializer elements than the array holds, in that a suitable warning about "excess elements in array" is given, and the excess elements (all of them, in this case) are ignored.

Instead GCC allows static initialization of flexible array members. This is equivalent to defining a new structure containing the original structure followed by an array of sufficient size to contain the data. I.e. in the following, f1 is constructed as if it were declared like f2.

 
struct f1 {
  int x; int y[];
} f1 = { 1, { 2, 3, 4 } };

struct f2 {
  struct f1 f1; int data[3];
} f2 = { { 1 }, { 2, 3, 4 } };

The convenience of this extension is that f1 has the desired type, eliminating the need to consistently refer to f2.f1.

This has symmetry with normal static arrays, in that an array of unknown size is also written with [].

Of course, this extension only makes sense if the extra data comes at the end of a top-level object, as otherwise we would be overwriting data at subsequent offsets. To avoid undue complication and confusion with initialization of deeply nested arrays, we simply disallow any non-empty initialization except when the structure is the top-level object. For example:

 
struct foo { int x; int y[]; };
struct bar { struct foo z; };

struct foo a = { 1, { 2, 3, 4 } };        // Valid.
struct bar b = { { 1, { 2, 3, 4 } } };    // Invalid.
struct bar c = { { 1, { } } };            // Valid.
struct foo d[1] = { { 1 { 2, 3, 4 } } };  // Invalid.


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6.17 Structures With No Members

GCC permits a C structure to have no members:

 
struct empty {
};

The structure will have size zero. In C++, empty structures are part of the language. G++ treats empty structures as if they had a single member of type char.


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6.18 Arrays of Variable Length

Variable-length automatic arrays are allowed in ISO C99, and as an extension GCC accepts them in C90 mode and in C++. These arrays are declared like any other automatic arrays, but with a length that is not a constant expression. The storage is allocated at the point of declaration and deallocated when the brace-level is exited. For example:

 
FILE *
concat_fopen (char *s1, char *s2, char *mode)
{
  char str[strlen (s1) + strlen (s2) + 1];
  strcpy (str, s1);
  strcat (str, s2);
  return fopen (str, mode);
}

Jumping or breaking out of the scope of the array name deallocates the storage. Jumping into the scope is not allowed; you get an error message for it.

You can use the function alloca to get an effect much like variable-length arrays. The function alloca is available in many other C implementations (but not in all). On the other hand, variable-length arrays are more elegant.

There are other differences between these two methods. Space allocated with alloca exists until the containing function returns. The space for a variable-length array is deallocated as soon as the array name's scope ends. (If you use both variable-length arrays and alloca in the same function, deallocation of a variable-length array will also deallocate anything more recently allocated with alloca.)

You can also use variable-length arrays as arguments to functions:

 
struct entry
tester (int len, char data[len][len])
{
  /* ... */
}

The length of an array is computed once when the storage is allocated and is remembered for the scope of the array in case you access it with sizeof.

If you want to pass the array first and the length afterward, you can use a forward declaration in the parameter list--another GNU extension.

 
struct entry
tester (int len; char data[len][len], int len)
{
  /* ... */
}

The `int len' before the semicolon is a parameter forward declaration, and it serves the purpose of making the name len known when the declaration of data is parsed.

You can write any number of such parameter forward declarations in the parameter list. They can be separated by commas or semicolons, but the last one must end with a semicolon, which is followed by the "real" parameter declarations. Each forward declaration must match a "real" declaration in parameter name and data type. ISO C99 does not support parameter forward declarations.


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6.19 Macros with a Variable Number of Arguments.

In the ISO C standard of 1999, a macro can be declared to accept a variable number of arguments much as a function can. The syntax for defining the macro is similar to that of a function. Here is an example:

 
#define debug(format, ...) fprintf (stderr, format, __VA_ARGS__)

Here `...' is a variable argument. In the invocation of such a macro, it represents the zero or more tokens until the closing parenthesis that ends the invocation, including any commas. This set of tokens replaces the identifier __VA_ARGS__ in the macro body wherever it appears. See the CPP manual for more information.

GCC has long supported variadic macros, and used a different syntax that allowed you to give a name to the variable arguments just like any other argument. Here is an example:

 
#define debug(format, args...) fprintf (stderr, format, args)

This is in all ways equivalent to the ISO C example above, but arguably more readable and descriptive.

GNU CPP has two further variadic macro extensions, and permits them to be used with either of the above forms of macro definition.

In standard C, you are not allowed to leave the variable argument out entirely; but you are allowed to pass an empty argument. For example, this invocation is invalid in ISO C, because there is no comma after the string:

 
debug ("A message")

GNU CPP permits you to completely omit the variable arguments in this way. In the above examples, the compiler would complain, though since the expansion of the macro still has the extra comma after the format string.

To help solve this problem, CPP behaves specially for variable arguments used with the token paste operator, `##'. If instead you write

 
#define debug(format, ...) fprintf (stderr, format, ## __VA_ARGS__)

and if the variable arguments are omitted or empty, the `##' operator causes the preprocessor to remove the comma before it. If you do provide some variable arguments in your macro invocation, GNU CPP does not complain about the paste operation and instead places the variable arguments after the comma. Just like any other pasted macro argument, these arguments are not macro expanded.


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6.20 Slightly Looser Rules for Escaped Newlines

Recently, the preprocessor has relaxed its treatment of escaped newlines. Previously, the newline had to immediately follow a backslash. The current implementation allows whitespace in the form of spaces, horizontal and vertical tabs, and form feeds between the backslash and the subsequent newline. The preprocessor issues a warning, but treats it as a valid escaped newline and combines the two lines to form a single logical line. This works within comments and tokens, as well as between tokens. Comments are not treated as whitespace for the purposes of this relaxation, since they have not yet been replaced with spaces.


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6.21 Non-Lvalue Arrays May Have Subscripts

In ISO C99, arrays that are not lvalues still decay to pointers, and may be subscripted, although they may not be modified or used after the next sequence point and the unary `&' operator may not be applied to them. As an extension, GCC allows such arrays to be subscripted in C90 mode, though otherwise they do not decay to pointers outside C99 mode. For example, this is valid in GNU C though not valid in C90:

 
struct foo {int a[4];};

struct foo f();

bar (int index)
{
  return f().a[index];
}


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6.22 Arithmetic on void- and Function-Pointers

In GNU C, addition and subtraction operations are supported on pointers to void and on pointers to functions. This is done by treating the size of a void or of a function as 1.

A consequence of this is that sizeof is also allowed on void and on function types, and returns 1.

The option `-Wpointer-arith' requests a warning if these extensions are used.


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6.23 Non-Constant Initializers

As in standard C++ and ISO C99, the elements of an aggregate initializer for an automatic variable are not required to be constant expressions in GNU C. Here is an example of an initializer with run-time varying elements:

 
foo (float f, float g)
{
  float beat_freqs[2] = { f-g, f+g };
  /* ... */
}


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6.24 Compound Literals

ISO C99 supports compound literals. A compound literal looks like a cast containing an initializer. Its value is an object of the type specified in the cast, containing the elements specified in the initializer; it is an lvalue. As an extension, GCC supports compound literals in C90 mode and in C++.

Usually, the specified type is a structure. Assume that struct foo and structure are declared as shown:

 
struct foo {int a; char b[2];} structure;

Here is an example of constructing a struct foo with a compound literal:

 
structure = ((struct foo) {x + y, 'a', 0});

This is equivalent to writing the following:

 
{
  struct foo temp = {x + y, 'a', 0};
  structure = temp;
}

You can also construct an array. If all the elements of the compound literal are (made up of) simple constant expressions, suitable for use in initializers of objects of static storage duration, then the compound literal can be coerced to a pointer to its first element and used in such an initializer, as shown here:

 
char **foo = (char *[]) { "x", "y", "z" };

Compound literals for scalar types and union types are is also allowed, but then the compound literal is equivalent to a cast.

As a GNU extension, GCC allows initialization of objects with static storage duration by compound literals (which is not possible in ISO C99, because the initializer is not a constant). It is handled as if the object was initialized only with the bracket enclosed list if the types of the compound literal and the object match. The initializer list of the compound literal must be constant. If the object being initialized has array type of unknown size, the size is determined by compound literal size.

 
static struct foo x = (struct foo) {1, 'a', 'b'};
static int y[] = (int []) {1, 2, 3};
static int z[] = (int [3]) {1};

The above lines are equivalent to the following:
 
static struct foo x = {1, 'a', 'b'};
static int y[] = {1, 2, 3};
static int z[] = {1, 0, 0};


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6.25 Designated Initializers

Standard C90 requires the elements of an initializer to appear in a fixed order, the same as the order of the elements in the array or structure being initialized.

In ISO C99 you can give the elements in any order, specifying the array indices or structure field names they apply to, and GNU C allows this as an extension in C90 mode as well. This extension is not implemented in GNU C++.

To specify an array index, write `[index] =' before the element value. For example,

 
int a[6] = { [4] = 29, [2] = 15 };

is equivalent to

 
int a[6] = { 0, 0, 15, 0, 29, 0 };

The index values must be constant expressions, even if the array being initialized is automatic.

An alternative syntax for this which has been obsolete since GCC 2.5 but GCC still accepts is to write `[index]' before the element value, with no `='.

To initialize a range of elements to the same value, write `[first ... last] = value'. This is a GNU extension. For example,

 
int widths[] = { [0 ... 9] = 1, [10 ... 99] = 2, [100] = 3 };

If the value in it has side-effects, the side-effects will happen only once, not for each initialized field by the range initializer.

Note that the length of the array is the highest value specified plus one.

In a structure initializer, specify the name of a field to initialize with `.fieldname =' before the element value. For example, given the following structure,

 
struct point { int x, y; };

the following initialization

 
struct point p = { .y = yvalue, .x = xvalue };

is equivalent to

 
struct point p = { xvalue, yvalue };

Another syntax which has the same meaning, obsolete since GCC 2.5, is `fieldname:', as shown here:

 
struct point p = { y: yvalue, x: xvalue };

The `[index]' or `.fieldname' is known as a designator. You can also use a designator (or the obsolete colon syntax) when initializing a union, to specify which element of the union should be used. For example,

 
union foo { int i; double d; };

union foo f = { .d = 4 };

will convert 4 to a double to store it in the union using the second element. By contrast, casting 4 to type union foo would store it into the union as the integer i, since it is an integer. (See section 6.27 Cast to a Union Type.)

You can combine this technique of naming elements with ordinary C initialization of successive elements. Each initializer element that does not have a designator applies to the next consecutive element of the array or structure. For example,

 
int a[6] = { [1] = v1, v2, [4] = v4 };

is equivalent to

 
int a[6] = { 0, v1, v2, 0, v4, 0 };

Labeling the elements of an array initializer is especially useful when the indices are characters or belong to an enum type. For example:

 
int whitespace[256]
  = { [' '] = 1, ['\t'] = 1, ['\h'] = 1,
      ['\f'] = 1, ['\n'] = 1, ['\r'] = 1 };

You can also write a series of `.fieldname' and `[index]' designators before an `=' to specify a nested subobject to initialize; the list is taken relative to the subobject corresponding to the closest surrounding brace pair. For example, with the `struct point' declaration above:

 
struct point ptarray[10] = { [2].y = yv2, [2].x = xv2, [0].x = xv0 };

If the same field is initialized multiple times, it will have value from the last initialization. If any such overridden initialization has side-effect, it is unspecified whether the side-effect happens or not. Currently, GCC will discard them and issue a warning.


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6.26 Case Ranges

You can specify a range of consecutive values in a single case label, like this:

 
case low ... high:

This has the same effect as the proper number of individual case labels, one for each integer value from low to high, inclusive.

This feature is especially useful for ranges of ASCII character codes:

 
case 'A' ... 'Z':

Be careful: Write spaces around the ..., for otherwise it may be parsed wrong when you use it with integer values. For example, write this:

 
case 1 ... 5:

rather than this:

 
case 1...5:


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6.27 Cast to a Union Type

A cast to union type is similar to other casts, except that the type specified is a union type. You can specify the type either with union tag or with a typedef name. A cast to union is actually a constructor though, not a cast, and hence does not yield an lvalue like normal casts. (See section 6.24 Compound Literals.)

The types that may be cast to the union type are those of the members of the union. Thus, given the following union and variables:

 
union foo { int i; double d; };
int x;
double y;

both x and y can be cast to type union foo.

Using the cast as the right-hand side of an assignment to a variable of union type is equivalent to storing in a member of the union:

 
union foo u;
/* ... */
u = (union foo) x  ==  u.i = x
u = (union foo) y  ==  u.d = y

You can also use the union cast as a function argument:

 
void hack (union foo);
/* ... */
hack ((union foo) x);


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6.28 Mixed Declarations and Code

ISO C99 and ISO C++ allow declarations and code to be freely mixed within compound statements. As an extension, GCC also allows this in C90 mode. For example, you could do:

 
int i;
/* ... */
i++;
int j = i + 2;

Each identifier is visible from where it is declared until the end of the enclosing block.


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6.29 Declaring Attributes of Functions

In GNU C, you declare certain things about functions called in your program which help the compiler optimize function calls and check your code more carefully.

The keyword __attribute__ allows you to specify special attributes when making a declaration. This keyword is followed by an attribute specification inside double parentheses. The following attributes are currently defined for functions on all targets: aligned, alloc_size, noreturn, returns_twice, noinline, noclone, always_inline, flatten, pure, const, nothrow, sentinel, format, format_arg, no_instrument_function, section, constructor, destructor, used, unused, deprecated, weak, malloc, alias, warn_unused_result, nonnull, gnu_inline, externally_visible, hot, cold, artificial, error and warning. Several other attributes are defined for functions on particular target systems. Other attributes, including section are supported for variables declarations (see section 6.35 Specifying Attributes of Variables) and for types (see section 6.36 Specifying Attributes of Types).

GCC plugins may provide their own attributes.

You may also specify attributes with `__' preceding and following each keyword. This allows you to use them in header files without being concerned about a possible macro of the same name. For example, you may use __noreturn__ instead of noreturn.

See section 6.30 Attribute Syntax, for details of the exact syntax for using attributes.

alias ("target")
The alias attribute causes the declaration to be emitted as an alias for another symbol, which must be specified. For instance,

 
void __f () { /* Do something. */; }
void f () __attribute__ ((weak, alias ("__f")));

defines `f' to be a weak alias for `__f'. In C++, the mangled name for the target must be used. It is an error if `__f' is not defined in the same translation unit.

Not all target machines support this attribute.

aligned (alignment)
This attribute specifies a minimum alignment for the function, measured in bytes.

You cannot use this attribute to decrease the alignment of a function, only to increase it. However, when you explicitly specify a function alignment this will override the effect of the `-falign-functions' (see section 3.10 Options That Control Optimization) option for this function.

Note that the effectiveness of aligned attributes may be limited by inherent limitations in your linker. On many systems, the linker is only able to arrange for functions to be aligned up to a certain maximum alignment. (For some linkers, the maximum supported alignment may be very very small.) See your linker documentation for further information.

The aligned attribute can also be used for variables and fields (see section 6.35 Specifying Attributes of Variables.)

alloc_size
The alloc_size attribute is used to tell the compiler that the function return value points to memory, where the size is given by one or two of the functions parameters. GCC uses this information to improve the correctness of __builtin_object_size.

The function parameter(s) denoting the allocated size are specified by one or two integer arguments supplied to the attribute. The allocated size is either the value of the single function argument specified or the product of the two function arguments specified. Argument numbering starts at one.

For instance,

 
void* my_calloc(size_t, size_t) __attribute__((alloc_size(1,2)))
void my_realloc(void*, size_t) __attribute__((alloc_size(2)))

declares that my_calloc will return memory of the size given by the product of parameter 1 and 2 and that my_realloc will return memory of the size given by parameter 2.

always_inline
Generally, functions are not inlined unless optimization is specified. For functions declared inline, this attribute inlines the function even if no optimization level was specified.

gnu_inline
This attribute should be used with a function which is also declared with the inline keyword. It directs GCC to treat the function as if it were defined in gnu90 mode even when compiling in C99 or gnu99 mode.

If the function is declared extern, then this definition of the function is used only for inlining. In no case is the function compiled as a standalone function, not even if you take its address explicitly. Such an address becomes an external reference, as if you had only declared the function, and had not defined it. This has almost the effect of a macro. The way to use this is to put a function definition in a header file with this attribute, and put another copy of the function, without extern, in a library file. The definition in the header file will cause most calls to the function to be inlined. If any uses of the function remain, they will refer to the single copy in the library. Note that the two definitions of the functions need not be precisely the same, although if they do not have the same effect your program may behave oddly.

In C, if the function is neither extern nor static, then the function is compiled as a standalone function, as well as being inlined where possible.

This is how GCC traditionally handled functions declared inline. Since ISO C99 specifies a different semantics for inline, this function attribute is provided as a transition measure and as a useful feature in its own right. This attribute is available in GCC 4.1.3 and later. It is available if either of the preprocessor macros __GNUC_GNU_INLINE__ or __GNUC_STDC_INLINE__ are defined. See section An Inline Function is As Fast As a Macro.

In C++, this attribute does not depend on extern in any way, but it still requires the inline keyword to enable its special behavior.

artificial
This attribute is useful for small inline wrappers which if possible should appear during debugging as a unit, depending on the debug info format it will either mean marking the function as artificial or using the caller location for all instructions within the inlined body.

bank_switch
When added to an interrupt handler with the M32C port, causes the prologue and epilogue to use bank switching to preserve the registers rather than saving them on the stack.

flatten
Generally, inlining into a function is limited. For a function marked with this attribute, every call inside this function will be inlined, if possible. Whether the function itself is considered for inlining depends on its size and the current inlining parameters.

error ("message")
If this attribute is used on a function declaration and a call to such a function is not eliminated through dead code elimination or other optimizations, an error which will include message will be diagnosed. This is useful for compile time checking, especially together with __builtin_constant_p and inline functions where checking the inline function arguments is not possible through extern char [(condition) ? 1 : -1]; tricks. While it is possible to leave the function undefined and thus invoke a link failure, when using this attribute the problem will be diagnosed earlier and with exact location of the call even in presence of inline functions or when not emitting debugging information.

warning ("message")
If this attribute is used on a function declaration and a call to such a function is not eliminated through dead code elimination or other optimizations, a warning which will include message will be diagnosed. This is useful for compile time checking, especially together with __builtin_constant_p and inline functions. While it is possible to define the function with a message in .gnu.warning* section, when using this attribute the problem will be diagnosed earlier and with exact location of the call even in presence of inline functions or when not emitting debugging information.

cdecl
On the Intel 386, the cdecl attribute causes the compiler to assume that the calling function will pop off the stack space used to pass arguments. This is useful to override the effects of the `-mrtd' switch.

const
Many functions do not examine any values except their arguments, and have no effects except the return value. Basically this is just slightly more strict class than the pure attribute below, since function is not allowed to read global memory.

Note that a function that has pointer arguments and examines the data pointed to must not be declared const. Likewise, a function that calls a non-const function usually must not be const. It does not make sense for a const function to return void.

The attribute const is not implemented in GCC versions earlier than 2.5. An alternative way to declare that a function has no side effects, which works in the current version and in some older versions, is as follows:

 
typedef int intfn ();

extern const intfn square;

This approach does not work in GNU C++ from 2.6.0 on, since the language specifies that the `const' must be attached to the return value.

constructor
destructor
constructor (priority)
destructor (priority)
The constructor attribute causes the function to be called automatically before execution enters main (). Similarly, the destructor attribute causes the function to be called automatically after main () has completed or exit () has been called. Functions with these attributes are useful for initializing data that will be used implicitly during the execution of the program.

You may provide an optional integer priority to control the order in which constructor and destructor functions are run. A constructor with a smaller priority number runs before a constructor with a larger priority number; the opposite relationship holds for destructors. So, if you have a constructor that allocates a resource and a destructor that deallocates the same resource, both functions typically have the same priority. The priorities for constructor and destructor functions are the same as those specified for namespace-scope C++ objects (see section 7.7 C++-Specific Variable, Function, and Type Attributes).

These attributes are not currently implemented for Objective-C.

deprecated
deprecated (msg)
The deprecated attribute results in a warning if the function is used anywhere in the source file. This is useful when identifying functions that are expected to be removed in a future version of a program. The warning also includes the location of the declaration of the deprecated function, to enable users to easily find further information about why the function is deprecated, or what they should do instead. Note that the warnings only occurs for uses:

 
int old_fn () __attribute__ ((deprecated));
int old_fn ();
int (*fn_ptr)() = old_fn;

results in a warning on line 3 but not line 2. The optional msg argument, which must be a string, will be printed in the warning if present.

The deprecated attribute can also be used for variables and types (see section 6.35 Specifying Attributes of Variables, see section 6.36 Specifying Attributes of Types.)

disinterrupt
On MeP targets, this attribute causes the compiler to emit instructions to disable interrupts for the duration of the given function.

dllexport
On Microsoft Windows targets and Symbian OS targets the dllexport attribute causes the compiler to provide a global pointer to a pointer in a DLL, so that it can be referenced with the dllimport attribute. On Microsoft Windows targets, the pointer name is formed by combining _imp__ and the function or variable name.

You can use __declspec(dllexport) as a synonym for __attribute__ ((dllexport)) for compatibility with other compilers.

On systems that support the visibility attribute, this attribute also implies "default" visibility. It is an error to explicitly specify any other visibility.

Currently, the dllexport attribute is ignored for inlined functions, unless the `-fkeep-inline-functions' flag has been used. The attribute is also ignored for undefined symbols.

When applied to C++ classes, the attribute marks defined non-inlined member functions and static data members as exports. Static consts initialized in-class are not marked unless they are also defined out-of-class.

For Microsoft Windows targets there are alternative methods for including the symbol in the DLL's export table such as using a `.def' file with an EXPORTS section or, with GNU ld, using the `--export-all' linker flag.

dllimport
On Microsoft Windows and Symbian OS targets, the dllimport attribute causes the compiler to reference a function or variable via a global pointer to a pointer that is set up by the DLL exporting the symbol. The attribute implies extern. On Microsoft Windows targets, the pointer name is formed by combining _imp__ and the function or variable name.

You can use __declspec(dllimport) as a synonym for __attribute__ ((dllimport)) for compatibility with other compilers.

On systems that support the visibility attribute, this attribute also implies "default" visibility. It is an error to explicitly specify any other visibility.

Currently, the attribute is ignored for inlined functions. If the attribute is applied to a symbol definition, an error is reported. If a symbol previously declared dllimport is later defined, the attribute is ignored in subsequent references, and a warning is emitted. The attribute is also overridden by a subsequent declaration as dllexport.

When applied to C++ classes, the attribute marks non-inlined member functions and static data members as imports. However, the attribute is ignored for virtual methods to allow creation of vtables using thunks.

On the SH Symbian OS target the dllimport attribute also has another affect--it can cause the vtable and run-time type information for a class to be exported. This happens when the class has a dllimport'ed constructor or a non-inline, non-pure virtual function and, for either of those two conditions, the class also has an inline constructor or destructor and has a key function that is defined in the current translation unit.

For Microsoft Windows based targets the use of the dllimport attribute on functions is not necessary, but provides a small performance benefit by eliminating a thunk in the DLL. The use of the dllimport attribute on imported variables was required on older versions of the GNU linker, but can now be avoided by passing the `--enable-auto-import' switch to the GNU linker. As with functions, using the attribute for a variable eliminates a thunk in the DLL.

One drawback to using this attribute is that a pointer to a variable marked as dllimport cannot be used as a constant address. However, a pointer to a function with the dllimport attribute can be used as a constant initializer; in this case, the address of a stub function in the import lib is referenced. On Microsoft Windows targets, the attribute can be disabled for functions by setting the `-mnop-fun-dllimport' flag.

eightbit_data
Use this attribute on the H8/300, H8/300H, and H8S to indicate that the specified variable should be placed into the eight bit data section. The compiler will generate more efficient code for certain operations on data in the eight bit data area. Note the eight bit data area is limited to 256 bytes of data.

You must use GAS and GLD from GNU binutils version 2.7 or later for this attribute to work correctly.

exception_handler
Use this attribute on the Blackfin to indicate that the specified function is an exception handler. The compiler will generate function entry and exit sequences suitable for use in an exception handler when this attribute is present.

externally_visible
This attribute, attached to a global variable or function, nullifies the effect of the `-fwhole-program' command-line option, so the object remains visible outside the current compilation unit.

far
On 68HC11 and 68HC12 the far attribute causes the compiler to use a calling convention that takes care of switching memory banks when entering and leaving a function. This calling convention is also the default when using the `-mlong-calls' option.

On 68HC12 the compiler will use the call and rtc instructions to call and return from a function.

On 68HC11 the compiler will generate a sequence of instructions to invoke a board-specific routine to switch the memory bank and call the real function. The board-specific routine simulates a call. At the end of a function, it will jump to a board-specific routine instead of using rts. The board-specific return routine simulates the rtc.

On MeP targets this causes the compiler to use a calling convention which assumes the called function is too far away for the built-in addressing modes.

fast_interrupt
Use this attribute on the M32C and RX ports to indicate that the specified function is a fast interrupt handler. This is just like the interrupt attribute, except that freit is used to return instead of reit.

fastcall
On the Intel 386, the fastcall attribute causes the compiler to pass the first argument (if of integral type) in the register ECX and the second argument (if of integral type) in the register EDX. Subsequent and other typed arguments are passed on the stack. The called function will pop the arguments off the stack. If the number of arguments is variable all arguments are pushed on the stack.

format (archetype, string-index, first-to-check)
The format attribute specifies that a function takes printf, scanf, strftime or strfmon style arguments which should be type-checked against a format string. For example, the declaration:

 
extern int
my_printf (void *my_object, const char *my_format, ...)
      __attribute__ ((format (printf, 2, 3)));

causes the compiler to check the arguments in calls to my_printf for consistency with the printf style format string argument my_format.

The parameter archetype determines how the format string is interpreted, and should be printf, scanf, strftime, gnu_printf, gnu_scanf, gnu_strftime or strfmon. (You can also use __printf__, __scanf__, __strftime__ or __strfmon__.) On MinGW targets, ms_printf, ms_scanf, and ms_strftime are also present. archtype values such as printf refer to the formats accepted by the system's C run-time library, while gnu_ values always refer to the formats accepted by the GNU C Library. On Microsoft Windows targets, ms_ values refer to the formats accepted by the `msvcrt.dll' library. The parameter string-index specifies which argument is the format string argument (starting from 1), while first-to-check is the number of the first argument to check against the format string. For functions where the arguments are not available to be checked (such as vprintf), specify the third parameter as zero. In this case the compiler only checks the format string for consistency. For strftime formats, the third parameter is required to be zero. Since non-static C++ methods have an implicit this argument, the arguments of such methods should be counted from two, not one, when giving values for string-index and first-to-check.

In the example above, the format string (my_format) is the second argument of the function my_print, and the arguments to check start with the third argument, so the correct parameters for the format attribute are 2 and 3.

The format attribute allows you to identify your own functions which take format strings as arguments, so that GCC can check the calls to these functions for errors. The compiler always (unless `-ffreestanding' or `-fno-builtin' is used) checks formats for the standard library functions printf, fprintf, sprintf, scanf, fscanf, sscanf, strftime, vprintf, vfprintf and vsprintf whenever such warnings are requested (using `-Wformat'), so there is no need to modify the header file `stdio.h'. In C99 mode, the functions snprintf, vsnprintf, vscanf, vfscanf and vsscanf are also checked. Except in strictly conforming C standard modes, the X/Open function strfmon is also checked as are printf_unlocked and fprintf_unlocked. See section Options Controlling C Dialect.

The target may provide additional types of format checks. See section Format Checks Specific to Particular Target Machines.

format_arg (string-index)
The format_arg attribute specifies that a function takes a format string for a printf, scanf, strftime or strfmon style function and modifies it (for example, to translate it into another language), so the result can be passed to a printf, scanf, strftime or strfmon style function (with the remaining arguments to the format function the same as they would have been for the unmodified string). For example, the declaration:

 
extern char *
my_dgettext (char *my_domain, const char *my_format)
      __attribute__ ((format_arg (2)));

causes the compiler to check the arguments in calls to a printf, scanf, strftime or strfmon type function, whose format string argument is a call to the my_dgettext function, for consistency with the format string argument my_format. If the format_arg attribute had not been specified, all the compiler could tell in such calls to format functions would be that the format string argument is not constant; this would generate a warning when `-Wformat-nonliteral' is used, but the calls could not be checked without the attribute.

The parameter string-index specifies which argument is the format string argument (starting from one). Since non-static C++ methods have an implicit this argument, the arguments of such methods should be counted from two.

The format-arg attribute allows you to identify your own functions which modify format strings, so that GCC can check the calls to printf, scanf, strftime or strfmon type function whose operands are a call to one of your own function. The compiler always treats gettext, dgettext, and dcgettext in this manner except when strict ISO C support is requested by `-ansi' or an appropriate `-std' option, or `-ffreestanding' or `-fno-builtin' is used. See section Options Controlling C Dialect.

function_vector
Use this attribute on the H8/300, H8/300H, and H8S to indicate that the specified function should be called through the function vector. Calling a function through the function vector will reduce code size, however; the function vector has a limited size (maximum 128 entries on the H8/300 and 64 entries on the H8/300H and H8S) and shares space with the interrupt vector.

In SH2A target, this attribute declares a function to be called using the TBR relative addressing mode. The argument to this attribute is the entry number of the same function in a vector table containing all the TBR relative addressable functions. For the successful jump, register TBR should contain the start address of this TBR relative vector table. In the startup routine of the user application, user needs to care of this TBR register initialization. The TBR relative vector table can have at max 256 function entries. The jumps to these functions will be generated using a SH2A specific, non delayed branch instruction JSR/N @(disp8,TBR). You must use GAS and GLD from GNU binutils version 2.7 or later for this attribute to work correctly.

Please refer the example of M16C target, to see the use of this attribute while declaring a function,

In an application, for a function being called once, this attribute will save at least 8 bytes of code; and if other successive calls are being made to the same function, it will save 2 bytes of code per each of these calls.

On M16C/M32C targets, the function_vector attribute declares a special page subroutine call function. Use of this attribute reduces the code size by 2 bytes for each call generated to the subroutine. The argument to the attribute is the vector number entry from the special page vector table which contains the 16 low-order bits of the subroutine's entry address. Each vector table has special page number (18 to 255) which are used in jsrs instruction. Jump addresses of the routines are generated by adding 0x0F0000 (in case of M16C targets) or 0xFF0000 (in case of M32C targets), to the 2 byte addresses set in the vector table. Therefore you need to ensure that all the special page vector routines should get mapped within the address range 0x0F0000 to 0x0FFFFF (for M16C) and 0xFF0000 to 0xFFFFFF (for M32C).

In the following example 2 bytes will be saved for each call to function foo.

 
void foo (void) __attribute__((function_vector(0x18)));
void foo (void)
{
}

void bar (void)
{
    foo();
}

If functions are defined in one file and are called in another file, then be sure to write this declaration in both files.

This attribute is ignored for R8C target.

interrupt
Use this attribute on the ARM, AVR, CRX, M32C, M32R/D, m68k, MeP, MIPS, RX and Xstormy16 ports to indicate that the specified function is an interrupt handler. The compiler will generate function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.

Note, interrupt handlers for the Blackfin, H8/300, H8/300H, H8S, and SH processors can be specified via the interrupt_handler attribute.

Note, on the AVR, interrupts will be enabled inside the function.

Note, for the ARM, you can specify the kind of interrupt to be handled by adding an optional parameter to the interrupt attribute like this:

 
void f () __attribute__ ((interrupt ("IRQ")));

Permissible values for this parameter are: IRQ, FIQ, SWI, ABORT and UNDEF.

On ARMv7-M the interrupt type is ignored, and the attribute means the function may be called with a word aligned stack pointer.

On MIPS targets, you can use the following attributes to modify the behavior of an interrupt handler:

use_shadow_register_set
Assume that the handler uses a shadow register set, instead of the main general-purpose registers.

keep_interrupts_masked
Keep interrupts masked for the whole function. Without this attribute, GCC tries to reenable interrupts for as much of the function as it can.

use_debug_exception_return
Return using the deret instruction. Interrupt handlers that don't have this attribute return using eret instead.

You can use any combination of these attributes, as shown below:
 
void __attribute__ ((interrupt)) v0 ();
void __attribute__ ((interrupt, use_shadow_register_set)) v1 ();
void __attribute__ ((interrupt, keep_interrupts_masked)) v2 ();
void __attribute__ ((interrupt, use_debug_exception_return)) v3 ();
void __attribute__ ((interrupt, use_shadow_register_set,
                     keep_interrupts_masked)) v4 ();
void __attribute__ ((interrupt, use_shadow_register_set,
                     use_debug_exception_return)) v5 ();
void __attribute__ ((interrupt, keep_interrupts_masked,
                     use_debug_exception_return)) v6 ();
void __attribute__ ((interrupt, use_shadow_register_set,
                     keep_interrupts_masked,
                     use_debug_exception_return)) v7 ();

interrupt_handler
Use this attribute on the Blackfin, m68k, H8/300, H8/300H, H8S, and SH to indicate that the specified function is an interrupt handler. The compiler will generate function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.

interrupt_thread
Use this attribute on fido, a subarchitecture of the m68k, to indicate that the specified function is an interrupt handler that is designed to run as a thread. The compiler omits generate prologue/epilogue sequences and replaces the return instruction with a sleep instruction. This attribute is available only on fido.

isr
Use this attribute on ARM to write Interrupt Service Routines. This is an alias to the interrupt attribute above.

kspisusp
When used together with interrupt_handler, exception_handler or nmi_handler, code will be generated to load the stack pointer from the USP register in the function prologue.

l1_text
This attribute specifies a function to be placed into L1 Instruction SRAM. The function will be put into a specific section named .l1.text. With `-mfdpic', function calls with a such function as the callee or caller will use inlined PLT.

l2
On the Blackfin, this attribute specifies a function to be placed into L2 SRAM. The function will be put into a specific section named .l1.text. With `-mfdpic', callers of such functions will use an inlined PLT.

long_call/short_call
This attribute specifies how a particular function is called on ARM. Both attributes override the `-mlong-calls' (see section 3.17.2 ARM Options) command line switch and #pragma long_calls settings. The long_call attribute indicates that the function might be far away from the call site and require a different (more expensive) calling sequence. The short_call attribute always places the offset to the function from the call site into the `BL' instruction directly.

longcall/shortcall
On the Blackfin, RS/6000 and PowerPC, the longcall attribute indicates that the function might be far away from the call site and require a different (more expensive) calling sequence. The shortcall attribute indicates that the function is always close enough for the shorter calling sequence to be used. These attributes override both the `-mlongcall' switch and, on the RS/6000 and PowerPC, the #pragma longcall setting.

See section 3.17.32 IBM RS/6000 and PowerPC Options, for more information on whether long calls are necessary.

long_call/near/far
These attributes specify how a particular function is called on MIPS. The attributes override the `-mlong-calls' (see section 3.17.26 MIPS Options) command-line switch. The long_call and far attributes are synonyms, and cause the compiler to always call the function by first loading its address into a register, and then using the contents of that register. The near attribute has the opposite effect; it specifies that non-PIC calls should be made using the more efficient jal instruction.

malloc
The malloc attribute is used to tell the compiler that a function may be treated as if any non-NULL pointer it returns cannot alias any other pointer valid when the function returns. This will often improve optimization. Standard functions with this property include malloc and calloc. realloc-like functions have this property as long as the old pointer is never referred to (including comparing it to the new pointer) after the function returns a non-NULL value.

mips16/nomips16

On MIPS targets, you can use the mips16 and nomips16 function attributes to locally select or turn off MIPS16 code generation. A function with the mips16 attribute is emitted as MIPS16 code, while MIPS16 code generation is disabled for functions with the nomips16 attribute. These attributes override the `-mips16' and `-mno-mips16' options on the command line (see section 3.17.26 MIPS Options).

When compiling files containing mixed MIPS16 and non-MIPS16 code, the preprocessor symbol __mips16 reflects the setting on the command line, not that within individual functions. Mixed MIPS16 and non-MIPS16 code may interact badly with some GCC extensions such as __builtin_apply (see section 6.5 Constructing Function Calls).

model (model-name)

On the M32R/D, use this attribute to set the addressability of an object, and of the code generated for a function. The identifier model-name is one of small, medium, or large, representing each of the code models.

Small model objects live in the lower 16MB of memory (so that their addresses can be loaded with the ld24 instruction), and are callable with the bl instruction.

Medium model objects may live anywhere in the 32-bit address space (the compiler will generate seth/add3 instructions to load their addresses), and are callable with the bl instruction.

Large model objects may live anywhere in the 32-bit address space (the compiler will generate seth/add3 instructions to load their addresses), and may not be reachable with the bl instruction (the compiler will generate the much slower seth/add3/jl instruction sequence).

On IA-64, use this attribute to set the addressability of an object. At present, the only supported identifier for model-name is small, indicating addressability via "small" (22-bit) addresses (so that their addresses can be loaded with the addl instruction). Caveat: such addressing is by definition not position independent and hence this attribute must not be used for objects defined by shared libraries.

ms_abi/sysv_abi

On 64-bit x86_64-*-* targets, you can use an ABI attribute to indicate which calling convention should be used for a function. The ms_abi attribute tells the compiler to use the Microsoft ABI, while the sysv_abi attribute tells the compiler to use the ABI used on GNU/Linux and other systems. The default is to use the Microsoft ABI when targeting Windows. On all other systems, the default is the AMD ABI.

Note, the ms_abi attribute for Windows targets currently requires the `-maccumulate-outgoing-args' option.

ms_hook_prologue

On 32 bit i[34567]86-*-* targets, you can use this function attribute to make gcc generate the "hot-patching" function prologue used in Win32 API functions in Microsoft Windows XP Service Pack 2 and newer. This requires support for the swap suffix in the assembler. (GNU Binutils 2.19.51 or later)

naked
Use this attribute on the ARM, AVR, IP2K, RX and SPU ports to indicate that the specified function does not need prologue/epilogue sequences generated by the compiler. It is up to the programmer to provide these sequences. The only statements that can be safely included in naked functions are asm statements that do not have operands. All other statements, including declarations of local variables, if statements, and so forth, should be avoided. Naked functions should be used to implement the body of an assembly function, while allowing the compiler to construct the requisite function declaration for the assembler.

near
On 68HC11 and 68HC12 the near attribute causes the compiler to use the normal calling convention based on jsr and rts. This attribute can be used to cancel the effect of the `-mlong-calls' option.

On MeP targets this attribute causes the compiler to assume the called function is close enough to use the normal calling convention, overriding the -mtf command line option.

nesting
Use this attribute together with interrupt_handler, exception_handler or nmi_handler to indicate that the function entry code should enable nested interrupts or exceptions.

nmi_handler
Use this attribute on the Blackfin to indicate that the specified function is an NMI handler. The compiler will generate function entry and exit sequences suitable for use in an NMI handler when this attribute is present.

no_instrument_function
If `-finstrument-functions' is given, profiling function calls will be generated at entry and exit of most user-compiled functions. Functions with this attribute will not be so instrumented.

noinline
This function attribute prevents a function from being considered for inlining. If the function does not have side-effects, there are optimizations other than inlining that causes function calls to be optimized away, although the function call is live. To keep such calls from being optimized away, put
 
asm ("");
(see section 6.39 Assembler Instructions with C Expression Operands) in the called function, to serve as a special side-effect.

noclone
This function attribute prevents a function from being considered for cloning - a mechanism which produces specialized copies of functions and which is (currently) performed by interprocedural constant propagation.

nonnull (arg-index, ...)
The nonnull attribute specifies that some function parameters should be non-null pointers. For instance, the declaration:

 
extern void *
my_memcpy (void *dest, const void *src, size_t len)
        __attribute__((nonnull (1, 2)));

causes the compiler to check that, in calls to my_memcpy, arguments dest and src are non-null. If the compiler determines that a null pointer is passed in an argument slot marked as non-null, and the `-Wnonnull' option is enabled, a warning is issued. The compiler may also choose to make optimizations based on the knowledge that certain function arguments will not be null.

If no argument index list is given to the nonnull attribute, all pointer arguments are marked as non-null. To illustrate, the following declaration is equivalent to the previous example:

 
extern void *
my_memcpy (void *dest, const void *src, size_t len)
        __attribute__((nonnull));

noreturn
A few standard library functions, such as abort and exit, cannot return. GCC knows this automatically. Some programs define their own functions that never return. You can declare them noreturn to tell the compiler this fact. For example,

 
void fatal () __attribute__ ((noreturn));

void
fatal (/* ... */)
{
  /* ... */ /* Print error message. */ /* ... */
  exit (1);
}

The noreturn keyword tells the compiler to assume that fatal cannot return. It can then optimize without regard to what would happen if fatal ever did return. This makes slightly better code. More importantly, it helps avoid spurious warnings of uninitialized variables.

The noreturn keyword does not affect the exceptional path when that applies: a noreturn-marked function may still return to the caller by throwing an exception or calling longjmp.

Do not assume that registers saved by the calling function are restored before calling the noreturn function.

It does not make sense for a noreturn function to have a return type other than void.

The attribute noreturn is not implemented in GCC versions earlier than 2.5. An alternative way to declare that a function does not return, which works in the current version and in some older versions, is as follows:

 
typedef void voidfn ();

volatile voidfn fatal;

This approach does not work in GNU C++.

nothrow
The nothrow attribute is used to inform the compiler that a function cannot throw an exception. For example, most functions in the standard C library can be guaranteed not to throw an exception with the notable exceptions of qsort and bsearch that take function pointer arguments. The nothrow attribute is not implemented in GCC versions earlier than 3.3.

optimize
The optimize attribute is used to specify that a function is to be compiled with different optimization options than specified on the command line. Arguments can either be numbers or strings. Numbers are assumed to be an optimization level. Strings that begin with O are assumed to be an optimization option, while other options are assumed to be used with a -f prefix. You can also use the `#pragma GCC optimize' pragma to set the optimization options that affect more than one function. See section 6.55.13 Function Specific Option Pragmas, for details about the `#pragma GCC optimize' pragma.

This can be used for instance to have frequently executed functions compiled with more aggressive optimization options that produce faster and larger code, while other functions can be called with less aggressive options.

pcs

The pcs attribute can be used to control the calling convention used for a function on ARM. The attribute takes an argument that specifies the calling convention to use.

When compiling using the AAPCS ABI (or a variant of that) then valid values for the argument are "aapcs" and "aapcs-vfp". In order to use a variant other than "aapcs" then the compiler must be permitted to use the appropriate co-processor registers (i.e., the VFP registers must be available in order to use "aapcs-vfp"). For example,

 
/* Argument passed in r0, and result returned in r0+r1.  */
double f2d (float) __attribute__((pcs("aapcs")));

Variadic functions always use the "aapcs" calling convention and the compiler will reject attempts to specify an alternative.

pure
Many functions have no effects except the return value and their return value depends only on the parameters and/or global variables. Such a function can be subject to common subexpression elimination and loop optimization just as an arithmetic operator would be. These functions should be declared with the attribute pure. For example,

 
int square (int) __attribute__ ((pure));

says that the hypothetical function square is safe to call fewer times than the program says.

Some of common examples of pure functions are strlen or memcmp. Interesting non-pure functions are functions with infinite loops or those depending on volatile memory or other system resource, that may change between two consecutive calls (such as feof in a multithreading environment).

The attribute pure is not implemented in GCC versions earlier than 2.96.

hot
The hot attribute is used to inform the compiler that a function is a hot spot of the compiled program. The function is optimized more aggressively and on many target it is placed into special subsection of the text section so all hot functions appears close together improving locality.

When profile feedback is available, via `-fprofile-use', hot functions are automatically detected and this attribute is ignored.

The hot attribute is not implemented in GCC versions earlier than 4.3.

cold
The cold attribute is used to inform the compiler that a function is unlikely executed. The function is optimized for size rather than speed and on many targets it is placed into special subsection of the text section so all cold functions appears close together improving code locality of non-cold parts of program. The paths leading to call of cold functions within code are marked as unlikely by the branch prediction mechanism. It is thus useful to mark functions used to handle unlikely conditions, such as perror, as cold to improve optimization of hot functions that do call marked functions in rare occasions.

When profile feedback is available, via `-fprofile-use', hot functions are automatically detected and this attribute is ignored.

The cold attribute is not implemented in GCC versions earlier than 4.3.

regparm (number)
On the Intel 386, the regparm attribute causes the compiler to pass arguments number one to number if they are of integral type in registers EAX, EDX, and ECX instead of on the stack. Functions that take a variable number of arguments will continue to be passed all of their arguments on the stack.

Beware that on some ELF systems this attribute is unsuitable for global functions in shared libraries with lazy binding (which is the default). Lazy binding will send the first call via resolving code in the loader, which might assume EAX, EDX and ECX can be clobbered, as per the standard calling conventions. Solaris 8 is affected by this. GNU systems with GLIBC 2.1 or higher, and FreeBSD, are believed to be safe since the loaders there save EAX, EDX and ECX. (Lazy binding can be disabled with the linker or the loader if desired, to avoid the problem.)

sseregparm
On the Intel 386 with SSE support, the sseregparm attribute causes the compiler to pass up to 3 floating point arguments in SSE registers instead of on the stack. Functions that take a variable number of arguments will continue to pass all of their floating point arguments on the stack.

force_align_arg_pointer
On the Intel x86, the force_align_arg_pointer attribute may be applied to individual function definitions, generating an alternate prologue and epilogue that realigns the runtime stack if necessary. This supports mixing legacy codes that run with a 4-byte aligned stack with modern codes that keep a 16-byte stack for SSE compatibility.

resbank
On the SH2A target, this attribute enables the high-speed register saving and restoration using a register bank for interrupt_handler routines. Saving to the bank is performed automatically after the CPU accepts an interrupt that uses a register bank.

The nineteen 32-bit registers comprising general register R0 to R14, control register GBR, and system registers MACH, MACL, and PR and the vector table address offset are saved into a register bank. Register banks are stacked in first-in last-out (FILO) sequence. Restoration from the bank is executed by issuing a RESBANK instruction.

returns_twice
The returns_twice attribute tells the compiler that a function may return more than one time. The compiler will ensure that all registers are dead before calling such a function and will emit a warning about the variables that may be clobbered after the second return from the function. Examples of such functions are setjmp and vfork. The longjmp-like counterpart of such function, if any, might need to be marked with the noreturn attribute.

saveall
Use this attribute on the Blackfin, H8/300, H8/300H, and H8S to indicate that all registers except the stack pointer should be saved in the prologue regardless of whether they are used or not.

section ("section-name")
Normally, the compiler places the code it generates in the text section. Sometimes, however, you need additional sections, or you need certain particular functions to appear in special sections. The section attribute specifies that a function lives in a particular section. For example, the declaration:

 
extern void foobar (void) __attribute__ ((section ("bar")));

puts the function foobar in the bar section.

Some file formats do not support arbitrary sections so the section attribute is not available on all platforms. If you need to map the entire contents of a module to a particular section, consider using the facilities of the linker instead.

sentinel
This function attribute ensures that a parameter in a function call is an explicit NULL. The attribute is only valid on variadic functions. By default, the sentinel is located at position zero, the last parameter of the function call. If an optional integer position argument P is supplied to the attribute, the sentinel must be located at position P counting backwards from the end of the argument list.

 
__attribute__ ((sentinel))
is equivalent to
__attribute__ ((sentinel(0)))

The attribute is automatically set with a position of 0 for the built-in functions execl and execlp. The built-in function execle has the attribute set with a position of 1.

A valid NULL in this context is defined as zero with any pointer type. If your system defines the NULL macro with an integer type then you need to add an explicit cast. GCC replaces stddef.h with a copy that redefines NULL appropriately.

The warnings for missing or incorrect sentinels are enabled with `-Wformat'.

short_call
See long_call/short_call.

shortcall
See longcall/shortcall.

signal
Use this attribute on the AVR to indicate that the specified function is a signal handler. The compiler will generate function entry and exit sequences suitable for use in a signal handler when this attribute is present. Interrupts will be disabled inside the function.

sp_switch
Use this attribute on the SH to indicate an interrupt_handler function should switch to an alternate stack. It expects a string argument that names a global variable holding the address of the alternate stack.

 
void *alt_stack;
void f () __attribute__ ((interrupt_handler,
                          sp_switch ("alt_stack")));

stdcall
On the Intel 386, the stdcall attribute causes the compiler to assume that the called function will pop off the stack space used to pass arguments, unless it takes a variable number of arguments.

syscall_linkage
This attribute is used to modify the IA64 calling convention by marking all input registers as live at all function exits. This makes it possible to restart a system call after an interrupt without having to save/restore the input registers. This also prevents kernel data from leaking into application code.

target
The target attribute is used to specify that a function is to be compiled with different target options than specified on the command line. This can be used for instance to have functions compiled with a different ISA (instruction set architecture) than the default. You can also use the `#pragma GCC target' pragma to set more than one function to be compiled with specific target options. See section 6.55.13 Function Specific Option Pragmas, for details about the `#pragma GCC target' pragma.

For instance on a 386, you could compile one function with target("sse4.1,arch=core2") and another with target("sse4a,arch=amdfam10") that would be equivalent to compiling the first function with `-msse4.1' and `-march=core2' options, and the second function with `-msse4a' and `-march=amdfam10' options. It is up to the user to make sure that a function is only invoked on a machine that supports the particular ISA it was compiled for (for example by using cpuid on 386 to determine what feature bits and architecture family are used).

 
int core2_func (void) __attribute__ ((__target__ ("arch=core2")));
int sse3_func (void) __attribute__ ((__target__ ("sse3")));

On the 386, the following options are allowed:

`abm'
`no-abm'
Enable/disable the generation of the advanced bit instructions.

`aes'
`no-aes'
Enable/disable the generation of the AES instructions.

`mmx'
`no-mmx'
Enable/disable the generation of the MMX instructions.

`pclmul'
`no-pclmul'
Enable/disable the generation of the PCLMUL instructions.

`popcnt'
`no-popcnt'
Enable/disable the generation of the POPCNT instruction.

`sse'
`no-sse'
Enable/disable the generation of the SSE instructions.

`sse2'
`no-sse2'
Enable/disable the generation of the SSE2 instructions.

`sse3'
`no-sse3'
Enable/disable the generation of the SSE3 instructions.

`sse4'
`no-sse4'
Enable/disable the generation of the SSE4 instructions (both SSE4.1 and SSE4.2).

`sse4.1'
`no-sse4.1'
Enable/disable the generation of the sse4.1 instructions.

`sse4.2'
`no-sse4.2'
Enable/disable the generation of the sse4.2 instructions.

`sse4a'
`no-sse4a'
Enable/disable the generation of the SSE4A instructions.

`fma4'
`no-fma4'
Enable/disable the generation of the FMA4 instructions.

`xop'
`no-xop'
Enable/disable the generation of the XOP instructions.

`lwp'
`no-lwp'
Enable/disable the generation of the LWP instructions.

`ssse3'
`no-ssse3'
Enable/disable the generation of the SSSE3 instructions.

`cld'
`no-cld'
Enable/disable the generation of the CLD before string moves.

`fancy-math-387'
`no-fancy-math-387'
Enable/disable the generation of the sin, cos, and sqrt instructions on the 387 floating point unit.

`fused-madd'
`no-fused-madd'
Enable/disable the generation of the fused multiply/add instructions.

`ieee-fp'
`no-ieee-fp'
Enable/disable the generation of floating point that depends on IEEE arithmetic.

`inline-all-stringops'
`no-inline-all-stringops'
Enable/disable inlining of string operations.

`inline-stringops-dynamically'
`no-inline-stringops-dynamically'
Enable/disable the generation of the inline code to do small string operations and calling the library routines for large operations.

`align-stringops'
`no-align-stringops'
Do/do not align destination of inlined string operations.

`recip'
`no-recip'
Enable/disable the generation of RCPSS, RCPPS, RSQRTSS and RSQRTPS instructions followed an additional Newton-Raphson step instead of doing a floating point division.

`arch=ARCH'
Specify the architecture to generate code for in compiling the function.

`tune=TUNE'
Specify the architecture to tune for in compiling the function.

`fpmath=FPMATH'
Specify which floating point unit to use. The target("fpmath=sse,387") option must be specified as target("fpmath=sse+387") because the comma would separate different options.

On the 386, you can use either multiple strings to specify multiple options, or you can separate the option with a comma (,).

On the 386, the inliner will not inline a function that has different target options than the caller, unless the callee has a subset of the target options of the caller. For example a function declared with target("sse3") can inline a function with target("sse2"), since -msse3 implies -msse2.

The target attribute is not implemented in GCC versions earlier than 4.4, and at present only the 386 uses it.

tiny_data
Use this attribute on the H8/300H and H8S to indicate that the specified variable should be placed into the tiny data section. The compiler will generate more efficient code for loads and stores on data in the tiny data section. Note the tiny data area is limited to slightly under 32kbytes of data.

trap_exit
Use this attribute on the SH for an interrupt_handler to return using trapa instead of rte. This attribute expects an integer argument specifying the trap number to be used.

unused
This attribute, attached to a function, means that the function is meant to be possibly unused. GCC will not produce a warning for this function.

used
This attribute, attached to a function, means that code must be emitted for the function even if it appears that the function is not referenced. This is useful, for example, when the function is referenced only in inline assembly.

version_id
This IA64 HP-UX attribute, attached to a global variable or function, renames a symbol to contain a version string, thus allowing for function level versioning. HP-UX system header files may use version level functioning for some system calls.

 
extern int foo () __attribute__((version_id ("20040821")));

Calls to foo will be mapped to calls to foo{20040821}.

visibility ("visibility_type")
This attribute affects the linkage of the declaration to which it is attached. There are four supported visibility_type values: default, hidden, protected or internal visibility.

 
void __attribute__ ((visibility ("protected")))
f () { /* Do something. */; }
int i __attribute__ ((visibility ("hidden")));

The possible values of visibility_type correspond to the visibility settings in the ELF gABI.

default
Default visibility is the normal case for the object file format. This value is available for the visibility attribute to override other options that may change the assumed visibility of entities.

On ELF, default visibility means that the declaration is visible to other modules and, in shared libraries, means that the declared entity may be overridden.

On Darwin, default visibility means that the declaration is visible to other modules.

Default visibility corresponds to "external linkage" in the language.

hidden
Hidden visibility indicates that the entity declared will have a new form of linkage, which we'll call "hidden linkage". Two declarations of an object with hidden linkage refer to the same object if they are in the same shared object.

internal
Internal visibility is like hidden visibility, but with additional processor specific semantics. Unless otherwise specified by the psABI, GCC defines internal visibility to mean that a function is never called from another module. Compare this with hidden functions which, while they cannot be referenced directly by other modules, can be referenced indirectly via function pointers. By indicating that a function cannot be called from outside the module, GCC may for instance omit the load of a PIC register since it is known that the calling function loaded the correct value.

protected
Protected visibility is like default visibility except that it indicates that references within the defining module will bind to the definition in that module. That is, the declared entity cannot be overridden by another module.

All visibilities are supported on many, but not all, ELF targets (supported when the assembler supports the `.visibility' pseudo-op). Default visibility is supported everywhere. Hidden visibility is supported on Darwin targets.

The visibility attribute should be applied only to declarations which would otherwise have external linkage. The attribute should be applied consistently, so that the same entity should not be declared with different settings of the attribute.

In C++, the visibility attribute applies to types as well as functions and objects, because in C++ types have linkage. A class must not have greater visibility than its non-static data member types and bases, and class members default to the visibility of their class. Also, a declaration without explicit visibility is limited to the visibility of its type.

In C++, you can mark member functions and static member variables of a class with the visibility attribute. This is useful if you know a particular method or static member variable should only be used from one shared object; then you can mark it hidden while the rest of the class has default visibility. Care must be taken to avoid breaking the One Definition Rule; for example, it is usually not useful to mark an inline method as hidden without marking the whole class as hidden.

A C++ namespace declaration can also have the visibility attribute. This attribute applies only to the particular namespace body, not to other definitions of the same namespace; it is equivalent to using `#pragma GCC visibility' before and after the namespace definition (see section 6.55.11 Visibility Pragmas).

In C++, if a template argument has limited visibility, this restriction is implicitly propagated to the template instantiation. Otherwise, template instantiations and specializations default to the visibility of their template.

If both the template and enclosing class have explicit visibility, the visibility from the template is used.

vliw
On MeP, the vliw attribute tells the compiler to emit instructions in VLIW mode instead of core mode. Note that this attribute is not allowed unless a VLIW coprocessor has been configured and enabled through command line options.

warn_unused_result
The warn_unused_result attribute causes a warning to be emitted if a caller of the function with this attribute does not use its return value. This is useful for functions where not checking the result is either a security problem or always a bug, such as realloc.

 
int fn () __attribute__ ((warn_unused_result));
int foo ()
{
  if (fn () < 0) return -1;
  fn ();
  return 0;
}

results in warning on line 5.

weak
The weak attribute causes the declaration to be emitted as a weak symbol rather than a global. This is primarily useful in defining library functions which can be overridden in user code, though it can also be used with non-function declarations. Weak symbols are supported for ELF targets, and also for a.out targets when using the GNU assembler and linker.

weakref
weakref ("target")
The weakref attribute marks a declaration as a weak reference. Without arguments, it should be accompanied by an alias attribute naming the target symbol. Optionally, the target may be given as an argument to weakref itself. In either case, weakref implicitly marks the declaration as weak. Without a target, given as an argument to weakref or to alias, weakref is equivalent to weak.

 
static int x() __attribute__ ((weakref ("y")));
/* is equivalent to... */
static int x() __attribute__ ((weak, weakref, alias ("y")));
/* and to... */
static int x() __attribute__ ((weakref));
static int x() __attribute__ ((alias ("y")));

A weak reference is an alias that does not by itself require a definition to be given for the target symbol. If the target symbol is only referenced through weak references, then the becomes a weak undefined symbol. If it is directly referenced, however, then such strong references prevail, and a definition will be required for the symbol, not necessarily in the same translation unit.

The effect is equivalent to moving all references to the alias to a separate translation unit, renaming the alias to the aliased symbol, declaring it as weak, compiling the two separate translation units and performing a reloadable link on them.

At present, a declaration to which weakref is attached can only be static.

You can specify multiple attributes in a declaration by separating them by commas within the double parentheses or by immediately following an attribute declaration with another attribute declaration.

Some people object to the __attribute__ feature, suggesting that ISO C's #pragma should be used instead. At the time __attribute__ was designed, there were two reasons for not doing this.

  1. It is impossible to generate #pragma commands from a macro.

  2. There is no telling what the same #pragma might mean in another compiler.

These two reasons applied to almost any application that might have been proposed for #pragma. It was basically a mistake to use #pragma for anything.

The ISO C99 standard includes _Pragma, which now allows pragmas to be generated from macros. In addition, a #pragma GCC namespace is now in use for GCC-specific pragmas. However, it has been found convenient to use __attribute__ to achieve a natural attachment of attributes to their corresponding declarations, whereas #pragma GCC is of use for constructs that do not naturally form part of the grammar. See section `Miscellaneous Preprocessing Directives' in The GNU C Preprocessor.


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6.30 Attribute Syntax

This section describes the syntax with which __attribute__ may be used, and the constructs to which attribute specifiers bind, for the C language. Some details may vary for C++ and Objective-C. Because of infelicities in the grammar for attributes, some forms described here may not be successfully parsed in all cases.

There are some problems with the semantics of attributes in C++. For example, there are no manglings for attributes, although they may affect code generation, so problems may arise when attributed types are used in conjunction with templates or overloading. Similarly, typeid does not distinguish between types with different attributes. Support for attributes in C++ may be restricted in future to attributes on declarations only, but not on nested declarators.

See section 6.29 Declaring Attributes of Functions, for details of the semantics of attributes applying to functions. See section 6.35 Specifying Attributes of Variables, for details of the semantics of attributes applying to variables. See section 6.36 Specifying Attributes of Types, for details of the semantics of attributes applying to structure, union and enumerated types.

An attribute specifier is of the form __attribute__ ((attribute-list)). An attribute list is a possibly empty comma-separated sequence of attributes, where each attribute is one of the following:

An attribute specifier list is a sequence of one or more attribute specifiers, not separated by any other tokens.

In GNU C, an attribute specifier list may appear after the colon following a label, other than a case or default label. The only attribute it makes sense to use after a label is unused. This feature is intended for code generated by programs which contains labels that may be unused but which is compiled with `-Wall'. It would not normally be appropriate to use in it human-written code, though it could be useful in cases where the code that jumps to the label is contained within an #ifdef conditional. GNU C++ only permits attributes on labels if the attribute specifier is immediately followed by a semicolon (i.e., the label applies to an empty statement). If the semicolon is missing, C++ label attributes are ambiguous, as it is permissible for a declaration, which could begin with an attribute list, to be labelled in C++. Declarations cannot be labelled in C90 or C99, so the ambiguity does not arise there.

An attribute specifier list may appear as part of a struct, union or enum specifier. It may go either immediately after the struct, union or enum keyword, or after the closing brace. The former syntax is preferred. Where attribute specifiers follow the closing brace, they are considered to relate to the structure, union or enumerated type defined, not to any enclosing declaration the type specifier appears in, and the type defined is not complete until after the attribute specifiers.

Otherwise, an attribute specifier appears as part of a declaration, counting declarations of unnamed parameters and type names, and relates to that declaration (which may be nested in another declaration, for example in the case of a parameter declaration), or to a particular declarator within a declaration. Where an attribute specifier is applied to a parameter declared as a function or an array, it should apply to the function or array rather than the pointer to which the parameter is implicitly converted, but this is not yet correctly implemented.

Any list of specifiers and qualifiers at the start of a declaration may contain attribute specifiers, whether or not such a list may in that context contain storage class specifiers. (Some attributes, however, are essentially in the nature of storage class specifiers, and only make sense where storage class specifiers may be used; for example, section.) There is one necessary limitation to this syntax: the first old-style parameter declaration in a function definition cannot begin with an attribute specifier, because such an attribute applies to the function instead by syntax described below (which, however, is not yet implemented in this case). In some other cases, attribute specifiers are permitted by this grammar but not yet supported by the compiler. All attribute specifiers in this place relate to the declaration as a whole. In the obsolescent usage where a type of int is implied by the absence of type specifiers, such a list of specifiers and qualifiers may be an attribute specifier list with no other specifiers or qualifiers.

At present, the first parameter in a function prototype must have some type specifier which is not an attribute specifier; this resolves an ambiguity in the interpretation of void f(int (__attribute__((foo)) x)), but is subject to change. At present, if the parentheses of a function declarator contain only attributes then those attributes are ignored, rather than yielding an error or warning or implying a single parameter of type int, but this is subject to change.

An attribute specifier list may appear immediately before a declarator (other than the first) in a comma-separated list of declarators in a declaration of more than one identifier using a single list of specifiers and qualifiers. Such attribute specifiers apply only to the identifier before whose declarator they appear. For example, in

 
__attribute__((noreturn)) void d0 (void),
    __attribute__((format(printf, 1, 2))) d1 (const char *, ...),
     d2 (void)

the noreturn attribute applies to all the functions declared; the format attribute only applies to d1.

An attribute specifier list may appear immediately before the comma, = or semicolon terminating the declaration of an identifier other than a function definition. Such attribute specifiers apply to the declared object or function. Where an assembler name for an object or function is specified (see section 6.41 Controlling Names Used in Assembler Code), the attribute must follow the asm specification.

An attribute specifier list may, in future, be permitted to appear after the declarator in a function definition (before any old-style parameter declarations or the function body).

Attribute specifiers may be mixed with type qualifiers appearing inside the [] of a parameter array declarator, in the C99 construct by which such qualifiers are applied to the pointer to which the array is implicitly converted. Such attribute specifiers apply to the pointer, not to the array, but at present this is not implemented and they are ignored.

An attribute specifier list may appear at the start of a nested declarator. At present, there are some limitations in this usage: the attributes correctly apply to the declarator, but for most individual attributes the semantics this implies are not implemented. When attribute specifiers follow the * of a pointer declarator, they may be mixed with any type qualifiers present. The following describes the formal semantics of this syntax. It will make the most sense if you are familiar with the formal specification of declarators in the ISO C standard.

Consider (as in C99 subclause 6.7.5 paragraph 4) a declaration T D1, where T contains declaration specifiers that specify a type Type (such as int) and D1 is a declarator that contains an identifier ident. The type specified for ident for derived declarators whose type does not include an attribute specifier is as in the ISO C standard.

If D1 has the form ( attribute-specifier-list D ), and the declaration T D specifies the type "derived-declarator-type-list Type" for ident, then T D1 specifies the type "derived-declarator-type-list attribute-specifier-list Type" for ident.

If D1 has the form * type-qualifier-and-attribute-specifier-list D, and the declaration T D specifies the type "derived-declarator-type-list Type" for ident, then T D1 specifies the type "derived-declarator-type-list type-qualifier-and-attribute-specifier-list Type" for ident.

For example,

 
void (__attribute__((noreturn)) ****f) (void);

specifies the type "pointer to pointer to pointer to pointer to non-returning function returning void". As another example,

 
char *__attribute__((aligned(8))) *f;

specifies the type "pointer to 8-byte-aligned pointer to char". Note again that this does not work with most attributes; for example, the usage of `aligned' and `noreturn' attributes given above is not yet supported.

For compatibility with existing code written for compiler versions that did not implement attributes on nested declarators, some laxity is allowed in the placing of attributes. If an attribute that only applies to types is applied to a declaration, it will be treated as applying to the type of that declaration. If an attribute that only applies to declarations is applied to the type of a declaration, it will be treated as applying to that declaration; and, for compatibility with code placing the attributes immediately before the identifier declared, such an attribute applied to a function return type will be treated as applying to the function type, and such an attribute applied to an array element type will be treated as applying to the array type. If an attribute that only applies to function types is applied to a pointer-to-function type, it will be treated as applying to the pointer target type; if such an attribute is applied to a function return type that is not a pointer-to-function type, it will be treated as applying to the function type.


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6.31 Prototypes and Old-Style Function Definitions

GNU C extends ISO C to allow a function prototype to override a later old-style non-prototype definition. Consider the following example:

 
/* Use prototypes unless the compiler is old-fashioned.  */
#ifdef __STDC__
#define P(x) x
#else
#define P(x) ()
#endif

/* Prototype function declaration.  */
int isroot P((uid_t));

/* Old-style function definition.  */
int
isroot (x)   /* ??? lossage here ??? */
     uid_t x;
{
  return x == 0;
}

Suppose the type uid_t happens to be short. ISO C does not allow this example, because subword arguments in old-style non-prototype definitions are promoted. Therefore in this example the function definition's argument is really an int, which does not match the prototype argument type of short.

This restriction of ISO C makes it hard to write code that is portable to traditional C compilers, because the programmer does not know whether the uid_t type is short, int, or long. Therefore, in cases like these GNU C allows a prototype to override a later old-style definition. More precisely, in GNU C, a function prototype argument type overrides the argument type specified by a later old-style definition if the former type is the same as the latter type before promotion. Thus in GNU C the above example is equivalent to the following:

 
int isroot (uid_t);

int
isroot (uid_t x)
{
  return x == 0;
}

GNU C++ does not support old-style function definitions, so this extension is irrelevant.


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6.32 C++ Style Comments

In GNU C, you may use C++ style comments, which start with `//' and continue until the end of the line. Many other C implementations allow such comments, and they are included in the 1999 C standard. However, C++ style comments are not recognized if you specify an `-std' option specifying a version of ISO C before C99, or `-ansi' (equivalent to `-std=c90').


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6.33 Dollar Signs in Identifier Names

In GNU C, you may normally use dollar signs in identifier names. This is because many traditional C implementations allow such identifiers. However, dollar signs in identifiers are not supported on a few target machines, typically because the target assembler does not allow them.


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6.34 The Character ESC in Constants

You can use the sequence `\e' in a string or character constant to stand for the ASCII character ESC.


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6.35 Specifying Attributes of Variables

The keyword __attribute__ allows you to specify special attributes of variables or structure fields. This keyword is followed by an attribute specification inside double parentheses. Some attributes are currently defined generically for variables. Other attributes are defined for variables on particular target systems. Other attributes are available for functions (see section 6.29 Declaring Attributes of Functions) and for types (see section 6.36 Specifying Attributes of Types). Other front ends might define more attributes (see section Extensions to the C++ Language).

You may also specify attributes with `__' preceding and following each keyword. This allows you to use them in header files without being concerned about a possible macro of the same name. For example, you may use __aligned__ instead of aligned.

See section 6.30 Attribute Syntax, for details of the exact syntax for using attributes.

aligned (alignment)
This attribute specifies a minimum alignment for the variable or structure field, measured in bytes. For example, the declaration:

 
int x __attribute__ ((aligned (16))) = 0;

causes the compiler to allocate the global variable x on a 16-byte boundary. On a 68040, this could be used in conjunction with an asm expression to access the move16 instruction which requires 16-byte aligned operands.

You can also specify the alignment of structure fields. For example, to create a double-word aligned int pair, you could write:

 
struct foo { int x[2] __attribute__ ((aligned (8))); };

This is an alternative to creating a union with a double member that forces the union to be double-word aligned.

As in the preceding examples, you can explicitly specify the alignment (in bytes) that you wish the compiler to use for a given variable or structure field. Alternatively, you can leave out the alignment factor and just ask the compiler to align a variable or field to the default alignment for the target architecture you are compiling for. The default alignment is sufficient for all scalar types, but may not be enough for all vector types on a target which supports vector operations. The default alignment is fixed for a particular target ABI.

Gcc also provides a target specific macro __BIGGEST_ALIGNMENT__, which is the largest alignment ever used for any data type on the target machine you are compiling for. For example, you could write:

 
short array[3] __attribute__ ((aligned (__BIGGEST_ALIGNMENT__)));

The compiler automatically sets the alignment for the declared variable or field to __BIGGEST_ALIGNMENT__. Doing this can often make copy operations more efficient, because the compiler can use whatever instructions copy the biggest chunks of memory when performing copies to or from the variables or fields that you have aligned this way. Note that the value of __BIGGEST_ALIGNMENT__ may change depending on command line options.

When used on a struct, or struct member, the aligned attribute can only increase the alignment; in order to decrease it, the packed attribute must be specified as well. When used as part of a typedef, the aligned attribute can both increase and decrease alignment, and specifying the packed attribute will generate a warning.

Note that the effectiveness of aligned attributes may be limited by inherent limitations in your linker. On many systems, the linker is only able to arrange for variables to be aligned up to a certain maximum alignment. (For some linkers, the maximum supported alignment may be very very small.) If your linker is only able to align variables up to a maximum of 8 byte alignment, then specifying aligned(16) in an __attribute__ will still only provide you with 8 byte alignment. See your linker documentation for further information.

The aligned attribute can also be used for functions (see section 6.29 Declaring Attributes of Functions.)

cleanup (cleanup_function)
The cleanup attribute runs a function when the variable goes out of scope. This attribute can only be applied to auto function scope variables; it may not be applied to parameters or variables with static storage duration. The function must take one parameter, a pointer to a type compatible with the variable. The return value of the function (if any) is ignored.

If `-fexceptions' is enabled, then cleanup_function will be run during the stack unwinding that happens during the processing of the exception. Note that the cleanup attribute does not allow the exception to be caught, only to perform an action. It is undefined what happens if cleanup_function does not return normally.

common
nocommon
The common attribute requests GCC to place a variable in "common" storage. The nocommon attribute requests the opposite--to allocate space for it directly.

These attributes override the default chosen by the `-fno-common' and `-fcommon' flags respectively.

deprecated
deprecated (msg)
The deprecated attribute results in a warning if the variable is used anywhere in the source file. This is useful when identifying variables that are expected to be removed in a future version of a program. The warning also includes the location of the declaration of the deprecated variable, to enable users to easily find further information about why the variable is deprecated, or what they should do instead. Note that the warning only occurs for uses:

 
extern int old_var __attribute__ ((deprecated));
extern int old_var;
int new_fn () { return old_var; }

results in a warning on line 3 but not line 2. The optional msg argument, which must be a string, will be printed in the warning if present.

The deprecated attribute can also be used for functions and types (see section 6.29 Declaring Attributes of Functions, see section 6.36 Specifying Attributes of Types.)

mode (mode)
This attribute specifies the data type for the declaration--whichever type corresponds to the mode mode. This in effect lets you request an integer or floating point type according to its width.

You may also specify a mode of `byte' or `__byte__' to indicate the mode corresponding to a one-byte integer, `word' or `__word__' for the mode of a one-word integer, and `pointer' or `__pointer__' for the mode used to represent pointers.

packed
The packed attribute specifies that a variable or structure field should have the smallest possible alignment--one byte for a variable, and one bit for a field, unless you specify a larger value with the aligned attribute.

Here is a structure in which the field x is packed, so that it immediately follows a:

 
struct foo
{
  char a;
  int x[2] __attribute__ ((packed));
};

Note: The 4.1, 4.2 and 4.3 series of GCC ignore the packed attribute on bit-fields of type char. This has been fixed in GCC 4.4 but the change can lead to differences in the structure layout. See the documentation of `-Wpacked-bitfield-compat' for more information.

section ("section-name")
Normally, the compiler places the objects it generates in sections like data and bss. Sometimes, however, you need additional sections, or you need certain particular variables to appear in special sections, for example to map to special hardware. The section attribute specifies that a variable (or function) lives in a particular section. For example, this small program uses several specific section names:

 
struct duart a __attribute__ ((section ("DUART_A"))) = { 0 };
struct duart b __attribute__ ((section ("DUART_B"))) = { 0 };
char stack[10000] __attribute__ ((section ("STACK"))) = { 0 };
int init_data __attribute__ ((section ("INITDATA")));

main()
{
  /* Initialize stack pointer */
  init_sp (stack + sizeof (stack));

  /* Initialize initialized data */
  memcpy (&init_data, &data, &edata - &data);

  /* Turn on the serial ports */
  init_duart (&a);
  init_duart (&b);
}

Use the section attribute with global variables and not local variables, as shown in the example.

You may use the section attribute with initialized or uninitialized global variables but the linker requires each object be defined once, with the exception that uninitialized variables tentatively go in the common (or bss) section and can be multiply "defined". Using the section attribute will change what section the variable goes into and may cause the linker to issue an error if an uninitialized variable has multiple definitions. You can force a variable to be initialized with the `-fno-common' flag or the nocommon attribute.

Some file formats do not support arbitrary sections so the section attribute is not available on all platforms. If you need to map the entire contents of a module to a particular section, consider using the facilities of the linker instead.

shared
On Microsoft Windows, in addition to putting variable definitions in a named section, the section can also be shared among all running copies of an executable or DLL. For example, this small program defines shared data by putting it in a named section shared and marking the section shareable:

 
int foo __attribute__((section ("shared"), shared)) = 0;

int
main()
{
  /* Read and write foo.  All running
     copies see the same value.  */
  return 0;
}

You may only use the shared attribute along with section attribute with a fully initialized global definition because of the way linkers work. See section attribute for more information.

The shared attribute is only available on Microsoft Windows.

tls_model ("tls_model")
The tls_model attribute sets thread-local storage model (see section 6.57 Thread-Local Storage) of a particular __thread variable, overriding `-ftls-model=' command line switch on a per-variable basis. The tls_model argument should be one of global-dynamic, local-dynamic, initial-exec or local-exec.

Not all targets support this attribute.

unused
This attribute, attached to a variable, means that the variable is meant to be possibly unused. GCC will not produce a warning for this variable.

used
This attribute, attached to a variable, means that the variable must be emitted even if it appears that the variable is not referenced.

vector_size (bytes)
This attribute specifies the vector size for the variable, measured in bytes. For example, the declaration:

 
int foo __attribute__ ((vector_size (16)));

causes the compiler to set the mode for foo, to be 16 bytes, divided into int sized units. Assuming a 32-bit int (a vector of 4 units of 4 bytes), the corresponding mode of foo will be V4SI.

This attribute is only applicable to integral and float scalars, although arrays, pointers, and function return values are allowed in conjunction with this construct.

Aggregates with this attribute are invalid, even if they are of the same size as a corresponding scalar. For example, the declaration:

 
struct S { int a; };
struct S  __attribute__ ((vector_size (16))) foo;

is invalid even if the size of the structure is the same as the size of the int.

selectany
The selectany attribute causes an initialized global variable to have link-once semantics. When multiple definitions of the variable are encountered by the linker, the first is selected and the remainder are discarded. Following usage by the Microsoft compiler, the linker is told not to warn about size or content differences of the multiple definitions.

Although the primary usage of this attribute is for POD types, the attribute can also be applied to global C++ objects that are initialized by a constructor. In this case, the static initialization and destruction code for the object is emitted in each translation defining the object, but the calls to the constructor and destructor are protected by a link-once guard variable.

The selectany attribute is only available on Microsoft Windows targets. You can use __declspec (selectany) as a synonym for __attribute__ ((selectany)) for compatibility with other compilers.

weak
The weak attribute is described in 6.29 Declaring Attributes of Functions.

dllimport
The dllimport attribute is described in 6.29 Declaring Attributes of Functions.

dllexport
The dllexport attribute is described in 6.29 Declaring Attributes of Functions.


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6.35.1 Blackfin Variable Attributes

Three attributes are currently defined for the Blackfin.

l1_data
l1_data_A
l1_data_B
Use these attributes on the Blackfin to place the variable into L1 Data SRAM. Variables with l1_data attribute will be put into the specific section named .l1.data. Those with l1_data_A attribute will be put into the specific section named .l1.data.A. Those with l1_data_B attribute will be put into the specific section named .l1.data.B.

l2
Use this attribute on the Blackfin to place the variable into L2 SRAM. Variables with l2 attribute will be put into the specific section named .l2.data.


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6.35.2 M32R/D Variable Attributes

One attribute is currently defined for the M32R/D.

model (model-name)
Use this attribute on the M32R/D to set the addressability of an object. The identifier model-name is one of small, medium, or large, representing each of the code models.

Small model objects live in the lower 16MB of memory (so that their addresses can be loaded with the ld24 instruction).

Medium and large model objects may live anywhere in the 32-bit address space (the compiler will generate seth/add3 instructions to load their addresses).


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6.35.3 MeP Variable Attributes

The MeP target has a number of addressing modes and busses. The near space spans the standard memory space's first 16 megabytes (24 bits). The far space spans the entire 32-bit memory space. The based space is a 128 byte region in the memory space which is addressed relative to the $tp register. The tiny space is a 65536 byte region relative to the $gp register. In addition to these memory regions, the MeP target has a separate 16-bit control bus which is specified with cb attributes.

based
Any variable with the based attribute will be assigned to the .based section, and will be accessed with relative to the $tp register.

tiny
Likewise, the tiny attribute assigned variables to the .tiny section, relative to the $gp register.

near
Variables with the near attribute are assumed to have addresses that fit in a 24-bit addressing mode. This is the default for large variables (-mtiny=4 is the default) but this attribute can override -mtiny= for small variables, or override -ml.

far
Variables with the far attribute are addressed using a full 32-bit address. Since this covers the entire memory space, this allows modules to make no assumptions about where variables might be stored.

io
io (addr)
Variables with the io attribute are used to address memory-mapped peripherals. If an address is specified, the variable is assigned that address, else it is not assigned an address (it is assumed some other module will assign an address). Example:

 
int timer_count __attribute__((io(0x123)));

cb
cb (addr)
Variables with the cb attribute are used to access the control bus, using special instructions. addr indicates the control bus address. Example:

 
int cpu_clock __attribute__((cb(0x123)));


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6.35.4 i386 Variable Attributes

Two attributes are currently defined for i386 configurations: ms_struct and gcc_struct

ms_struct
gcc_struct

If packed is used on a structure, or if bit-fields are used it may be that the Microsoft ABI packs them differently than GCC would normally pack them. Particularly when moving packed data between functions compiled with GCC and the native Microsoft compiler (either via function call or as data in a file), it may be necessary to access either format.

Currently `-m[no-]ms-bitfields' is provided for the Microsoft Windows X86 compilers to match the native Microsoft compiler.

The Microsoft structure layout algorithm is fairly simple with the exception of the bitfield packing:

The padding and alignment of members of structures and whether a bit field can straddle a storage-unit boundary

  1. Structure members are stored sequentially in the order in which they are declared: the first member has the lowest memory address and the last member the highest.

  2. Every data object has an alignment-requirement. The alignment-requirement for all data except structures, unions, and arrays is either the size of the object or the current packing size (specified with either the aligned attribute or the pack pragma), whichever is less. For structures, unions, and arrays, the alignment-requirement is the largest alignment-requirement of its members. Every object is allocated an offset so that:

    offset % alignment-requirement == 0

  3. Adjacent bit fields are packed into the same 1-, 2-, or 4-byte allocation unit if the integral types are the same size and if the next bit field fits into the current allocation unit without crossing the boundary imposed by the common alignment requirements of the bit fields.

Handling of zero-length bitfields:

MSVC interprets zero-length bitfields in the following ways:

  1. If a zero-length bitfield is inserted between two bitfields that would normally be coalesced, the bitfields will not be coalesced.

    For example:

     
    struct
     {
       unsigned long bf_1 : 12;
       unsigned long : 0;
       unsigned long bf_2 : 12;
     } t1;
    

    The size of t1 would be 8 bytes with the zero-length bitfield. If the zero-length bitfield were removed, t1's size would be 4 bytes.

  2. If a zero-length bitfield is inserted after a bitfield, foo, and the alignment of the zero-length bitfield is greater than the member that follows it, bar, bar will be aligned as the type of the zero-length bitfield.

    For example:

     
    struct
     {
       char foo : 4;
       short : 0;
       char bar;
     } t2;
    
    struct
     {
       char foo : 4;
       short : 0;
       double bar;
     } t3;
    

    For t2, bar will be placed at offset 2, rather than offset 1. Accordingly, the size of t2 will be 4. For t3, the zero-length bitfield will not affect the alignment of bar or, as a result, the size of the structure.

    Taking this into account, it is important to note the following:

    1. If a zero-length bitfield follows a normal bitfield, the type of the zero-length bitfield may affect the alignment of the structure as whole. For example, t2 has a size of 4 bytes, since the zero-length bitfield follows a normal bitfield, and is of type short.

    2. Even if a zero-length bitfield is not followed by a normal bitfield, it may still affect the alignment of the structure:

       
      struct
       {
         char foo : 6;
         long : 0;
       } t4;
      

      Here, t4 will take up 4 bytes.

  3. Zero-length bitfields following non-bitfield members are ignored:

     
    struct
     {
       char foo;
       long : 0;
       char bar;
     } t5;
    

    Here, t5 will take up 2 bytes.


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6.35.5 PowerPC Variable Attributes

Three attributes currently are defined for PowerPC configurations: altivec, ms_struct and gcc_struct.

For full documentation of the struct attributes please see the documentation in i386 Variable Attributes.

For documentation of altivec attribute please see the documentation in PowerPC Type Attributes.


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6.35.6 SPU Variable Attributes

The SPU supports the spu_vector attribute for variables. For documentation of this attribute please see the documentation in SPU Type Attributes.


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6.35.7 Xstormy16 Variable Attributes

One attribute is currently defined for xstormy16 configurations: below100.

below100

If a variable has the below100 attribute (BELOW100 is allowed also), GCC will place the variable in the first 0x100 bytes of memory and use special opcodes to access it. Such variables will be placed in either the .bss_below100 section or the .data_below100 section.


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6.35.8 AVR Variable Attributes

progmem
The progmem attribute is used on the AVR to place data in the Program Memory address space. The AVR is a Harvard Architecture processor and data normally resides in the Data Memory address space.


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6.36 Specifying Attributes of Types

The keyword __attribute__ allows you to specify special attributes of struct and union types when you define such types. This keyword is followed by an attribute specification inside double parentheses. Seven attributes are currently defined for types: aligned, packed, transparent_union, unused, deprecated, visibility, and may_alias. Other attributes are defined for functions (see section 6.29 Declaring Attributes of Functions) and for variables (see section 6.35 Specifying Attributes of Variables).

You may also specify any one of these attributes with `__' preceding and following its keyword. This allows you to use these attributes in header files without being concerned about a possible macro of the same name. For example, you may use __aligned__ instead of aligned.

You may specify type attributes in an enum, struct or union type declaration or definition, or for other types in a typedef declaration.

For an enum, struct or union type, you may specify attributes either between the enum, struct or union tag and the name of the type, or just past the closing curly brace of the definition. The former syntax is preferred.

See section 6.30 Attribute Syntax, for details of the exact syntax for using attributes.

aligned (alignment)
This attribute specifies a minimum alignment (in bytes) for variables of the specified type. For example, the declarations:

 
struct S { short f[3]; } __attribute__ ((aligned (8)));
typedef int more_aligned_int __attribute__ ((aligned (8)));

force the compiler to insure (as far as it can) that each variable whose type is struct S or more_aligned_int will be allocated and aligned at least on a 8-byte boundary. On a SPARC, having all variables of type struct S aligned to 8-byte boundaries allows the compiler to use the ldd and std (doubleword load and store) instructions when copying one variable of type struct S to another, thus improving run-time efficiency.

Note that the alignment of any given struct or union type is required by the ISO C standard to be at least a perfect multiple of the lowest common multiple of the alignments of all of the members of the struct or union in question. This means that you can effectively adjust the alignment of a struct or union type by attaching an aligned attribute to any one of the members of such a type, but the notation illustrated in the example above is a more obvious, intuitive, and readable way to request the compiler to adjust the alignment of an entire struct or union type.

As in the preceding example, you can explicitly specify the alignment (in bytes) that you wish the compiler to use for a given struct or union type. Alternatively, you can leave out the alignment factor and just ask the compiler to align a type to the maximum useful alignment for the target machine you are compiling for. For example, you could write:

 
struct S { short f[3]; } __attribute__ ((aligned));

Whenever you leave out the alignment factor in an aligned attribute specification, the compiler automatically sets the alignment for the type to the largest alignment which is ever used for any data type on the target machine you are compiling for. Doing this can often make copy operations more efficient, because the compiler can use whatever instructions copy the biggest chunks of memory when performing copies to or from the variables which have types that you have aligned this way.

In the example above, if the size of each short is 2 bytes, then the size of the entire struct S type is 6 bytes. The smallest power of two which is greater than or equal to that is 8, so the compiler sets the alignment for the entire struct S type to 8 bytes.

Note that although you can ask the compiler to select a time-efficient alignment for a given type and then declare only individual stand-alone objects of that type, the compiler's ability to select a time-efficient alignment is primarily useful only when you plan to create arrays of variables having the relevant (efficiently aligned) type. If you declare or use arrays of variables of an efficiently-aligned type, then it is likely that your program will also be doing pointer arithmetic (or subscripting, which amounts to the same thing) on pointers to the relevant type, and the code that the compiler generates for these pointer arithmetic operations will often be more efficient for efficiently-aligned types than for other types.

The aligned attribute can only increase the alignment; but you can decrease it by specifying packed as well. See below.

Note that the effectiveness of aligned attributes may be limited by inherent limitations in your linker. On many systems, the linker is only able to arrange for variables to be aligned up to a certain maximum alignment. (For some linkers, the maximum supported alignment may be very very small.) If your linker is only able to align variables up to a maximum of 8 byte alignment, then specifying aligned(16) in an __attribute__ will still only provide you with 8 byte alignment. See your linker documentation for further information.

packed
This attribute, attached to struct or union type definition, specifies that each member (other than zero-width bitfields) of the structure or union is placed to minimize the memory required. When attached to an enum definition, it indicates that the smallest integral type should be used.

Specifying this attribute for struct and union types is equivalent to specifying the packed attribute on each of the structure or union members. Specifying the `-fshort-enums' flag on the line is equivalent to specifying the packed attribute on all enum definitions.

In the following example struct my_packed_struct's members are packed closely together, but the internal layout of its s member is not packed--to do that, struct my_unpacked_struct would need to be packed too.

 
struct my_unpacked_struct
 {
    char c;
    int i;
 };

struct __attribute__ ((__packed__)) my_packed_struct
  {
     char c;
     int  i;
     struct my_unpacked_struct s;
  };

You may only specify this attribute on the definition of an enum, struct or union, not on a typedef which does not also define the enumerated type, structure or union.

transparent_union
This attribute, attached to a union type definition, indicates that any function parameter having that union type causes calls to that function to be treated in a special way.

First, the argument corresponding to a transparent union type can be of any type in the union; no cast is required. Also, if the union contains a pointer type, the corresponding argument can be a null pointer constant or a void pointer expression; and if the union contains a void pointer type, the corresponding argument can be any pointer expression. If the union member type is a pointer, qualifiers like const on the referenced type must be respected, just as with normal pointer conversions.

Second, the argument is passed to the function using the calling conventions of the first member of the transparent union, not the calling conventions of the union itself. All members of the union must have the same machine representation; this is necessary for this argument passing to work properly.

Transparent unions are designed for library functions that have multiple interfaces for compatibility reasons. For example, suppose the wait function must accept either a value of type int * to comply with Posix, or a value of type union wait * to comply with the 4.1BSD interface. If wait's parameter were void *, wait would accept both kinds of arguments, but it would also accept any other pointer type and this would make argument type checking less useful. Instead, <sys/wait.h> might define the interface as follows:

 
typedef union __attribute__ ((__transparent_union__))
  {
    int *__ip;
    union wait *__up;
  } wait_status_ptr_t;

pid_t wait (wait_status_ptr_t);

This interface allows either int * or union wait * arguments to be passed, using the int * calling convention. The program can call wait with arguments of either type:

 
int w1 () { int w; return wait (&w); }
int w2 () { union wait w; return wait (&w); }

With this interface, wait's implementation might look like this:

 
pid_t wait (wait_status_ptr_t p)
{
  return waitpid (-1, p.__ip, 0);
}

unused
When attached to a type (including a union or a struct), this attribute means that variables of that type are meant to appear possibly unused. GCC will not produce a warning for any variables of that type, even if the variable appears to do nothing. This is often the case with lock or thread classes, which are usually defined and then not referenced, but contain constructors and destructors that have nontrivial bookkeeping functions.

deprecated
deprecated (msg)
The deprecated attribute results in a warning if the type is used anywhere in the source file. This is useful when identifying types that are expected to be removed in a future version of a program. If possible, the warning also includes the location of the declaration of the deprecated type, to enable users to easily find further information about why the type is deprecated, or what they should do instead. Note that the warnings only occur for uses and then only if the type is being applied to an identifier that itself is not being declared as deprecated.

 
typedef int T1 __attribute__ ((deprecated));
T1 x;
typedef T1 T2;
T2 y;
typedef T1 T3 __attribute__ ((deprecated));
T3 z __attribute__ ((deprecated));

results in a warning on line 2 and 3 but not lines 4, 5, or 6. No warning is issued for line 4 because T2 is not explicitly deprecated. Line 5 has no warning because T3 is explicitly deprecated. Similarly for line 6. The optional msg argument, which must be a string, will be printed in the warning if present.

The deprecated attribute can also be used for functions and variables (see section 6.29 Declaring Attributes of Functions, see section 6.35 Specifying Attributes of Variables.)

may_alias
Accesses through pointers to types with this attribute are not subject to type-based alias analysis, but are instead assumed to be able to alias any other type of objects. In the context of 6.5/7 an lvalue expression dereferencing such a pointer is treated like having a character type. See `-fstrict-aliasing' for more information on aliasing issues. This extension exists to support some vector APIs, in which pointers to one vector type are permitted to alias pointers to a different vector type.

Note that an object of a type with this attribute does not have any special semantics.

Example of use:

 
typedef short __attribute__((__may_alias__)) short_a;

int
main (void)
{
  int a = 0x12345678;
  short_a *b = (short_a *) &a;

  b[1] = 0;

  if (a == 0x12345678)
    abort();

  exit(0);
}

If you replaced short_a with short in the variable declaration, the above program would abort when compiled with `-fstrict-aliasing', which is on by default at `-O2' or above in recent GCC versions.

visibility
In C++, attribute visibility (see section 6.29 Declaring Attributes of Functions) can also be applied to class, struct, union and enum types. Unlike other type attributes, the attribute must appear between the initial keyword and the name of the type; it cannot appear after the body of the type.

Note that the type visibility is applied to vague linkage entities associated with the class (vtable, typeinfo node, etc.). In particular, if a class is thrown as an exception in one shared object and caught in another, the class must have default visibility. Otherwise the two shared objects will be unable to use the same typeinfo node and exception handling will break.


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6.36.1 ARM Type Attributes

On those ARM targets that support dllimport (such as Symbian OS), you can use the notshared attribute to indicate that the virtual table and other similar data for a class should not be exported from a DLL. For example:

 
class __declspec(notshared) C {
public:
  __declspec(dllimport) C();
  virtual void f();
}

__declspec(dllexport)
C::C() {}

In this code, C::C is exported from the current DLL, but the virtual table for C is not exported. (You can use __attribute__ instead of __declspec if you prefer, but most Symbian OS code uses __declspec.)


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6.36.2 MeP Type Attributes

Many of the MeP variable attributes may be applied to types as well. Specifically, the based, tiny, near, and far attributes may be applied to either. The io and cb attributes may not be applied to types.


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6.36.3 i386 Type Attributes

Two attributes are currently defined for i386 configurations: ms_struct and gcc_struct.

ms_struct
gcc_struct

If packed is used on a structure, or if bit-fields are used it may be that the Microsoft ABI packs them differently than GCC would normally pack them. Particularly when moving packed data between functions compiled with GCC and the native Microsoft compiler (either via function call or as data in a file), it may be necessary to access either format.

Currently `-m[no-]ms-bitfields' is provided for the Microsoft Windows X86 compilers to match the native Microsoft compiler.

To specify multiple attributes, separate them by commas within the double parentheses: for example, `__attribute__ ((aligned (16), packed))'.


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6.36.4 PowerPC Type Attributes

Three attributes currently are defined for PowerPC configurations: altivec, ms_struct and gcc_struct.

For full documentation of the ms_struct and gcc_struct attributes please see the documentation in i386 Type Attributes.

The altivec attribute allows one to declare AltiVec vector data types supported by the AltiVec Programming Interface Manual. The attribute requires an argument to specify one of three vector types: vector__, pixel__ (always followed by unsigned short), and bool__ (always followed by unsigned).

 
__attribute__((altivec(vector__)))
__attribute__((altivec(pixel__))) unsigned short
__attribute__((altivec(bool__))) unsigned

These attributes mainly are intended to support the __vector, __pixel, and __bool AltiVec keywords.


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6.36.5 SPU Type Attributes

The SPU supports the spu_vector attribute for types. This attribute allows one to declare vector data types supported by the Sony/Toshiba/IBM SPU Language Extensions Specification. It is intended to support the __vector keyword.


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6.37 Inquiring on Alignment of Types or Variables

The keyword __alignof__ allows you to inquire about how an object is aligned, or the minimum alignment usually required by a type. Its syntax is just like sizeof.

For example, if the target machine requires a double value to be aligned on an 8-byte boundary, then __alignof__ (double) is 8. This is true on many RISC machines. On more traditional machine designs, __alignof__ (double) is 4 or even 2.

Some machines never actually require alignment; they allow reference to any data type even at an odd address. For these machines, __alignof__ reports the smallest alignment that GCC will give the data type, usually as mandated by the target ABI.

If the operand of __alignof__ is an lvalue rather than a type, its value is the required alignment for its type, taking into account any minimum alignment specified with GCC's __attribute__ extension (see section 6.35 Specifying Attributes of Variables). For example, after this declaration:

 
struct foo { int x; char y; } foo1;

the value of __alignof__ (foo1.y) is 1, even though its actual alignment is probably 2 or 4, the same as __alignof__ (int).

It is an error to ask for the alignment of an incomplete type.


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6.38 An Inline Function is As Fast As a Macro

By declaring a function inline, you can direct GCC to make calls to that function faster. One way GCC can achieve this is to integrate that function's code into the code for its callers. This makes execution faster by eliminating the function-call overhead; in addition, if any of the actual argument values are constant, their known values may permit simplifications at compile time so that not all of the inline function's code needs to be included. The effect on code size is less predictable; object code may be larger or smaller with function inlining, depending on the particular case. You can also direct GCC to try to integrate all "simple enough" functions into their callers with the option `-finline-functions'.

GCC implements three different semantics of declaring a function inline. One is available with `-std=gnu89' or `-fgnu89-inline' or when gnu_inline attribute is present on all inline declarations, another when `-std=c99' or `-std=gnu99' (without `-fgnu89-inline'), and the third is used when compiling C++.

To declare a function inline, use the inline keyword in its declaration, like this:

 
static inline int
inc (int *a)
{
  (*a)++;
}

If you are writing a header file to be included in ISO C90 programs, write __inline__ instead of inline. See section 6.43 Alternate Keywords.

The three types of inlining behave similarly in two important cases: when the inline keyword is used on a static function, like the example above, and when a function is first declared without using the inline keyword and then is defined with inline, like this:

 
extern int inc (int *a);
inline int
inc (int *a)
{
  (*a)++;
}

In both of these common cases, the program behaves the same as if you had not used the inline keyword, except for its speed.

When a function is both inline and static, if all calls to the function are integrated into the caller, and the function's address is never used, then the function's own assembler code is never referenced. In this case, GCC does not actually output assembler code for the function, unless you specify the option `-fkeep-inline-functions'. Some calls cannot be integrated for various reasons (in particular, calls that precede the function's definition cannot be integrated, and neither can recursive calls within the definition). If there is a nonintegrated call, then the function is compiled to assembler code as usual. The function must also be compiled as usual if the program refers to its address, because that can't be inlined.

Note that certain usages in a function definition can make it unsuitable for inline substitution. Among these usages are: use of varargs, use of alloca, use of variable sized data types (see section 6.18 Arrays of Variable Length), use of computed goto (see section 6.3 Labels as Values), use of nonlocal goto, and nested functions (see section 6.4 Nested Functions). Using `-Winline' will warn when a function marked inline could not be substituted, and will give the reason for the failure.

As required by ISO C++, GCC considers member functions defined within the body of a class to be marked inline even if they are not explicitly declared with the inline keyword. You can override this with `-fno-default-inline'; see section Options Controlling C++ Dialect.

GCC does not inline any functions when not optimizing unless you specify the `always_inline' attribute for the function, like this:

 
/* Prototype.  */
inline void foo (const char) __attribute__((always_inline));

The remainder of this section is specific to GNU C90 inlining.

When an inline function is not static, then the compiler must assume that there may be calls from other source files; since a global symbol can be defined only once in any program, the function must not be defined in the other source files, so the calls therein cannot be integrated. Therefore, a non-static inline function is always compiled on its own in the usual fashion.

If you specify both inline and extern in the function definition, then the definition is used only for inlining. In no case is the function compiled on its own, not even if you refer to its address explicitly. Such an address becomes an external reference, as if you had only declared the function, and had not defined it.

This combination of inline and extern has almost the effect of a macro. The way to use it is to put a function definition in a header file with these keywords, and put another copy of the definition (lacking inline and extern) in a library file. The definition in the header file will cause most calls to the function to be inlined. If any uses of the function remain, they will refer to the single copy in the library.


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6.39 Assembler Instructions with C Expression Operands

In an assembler instruction using asm, you can specify the operands of the instruction using C expressions. This means you need not guess which registers or memory locations will contain the data you want to use.

You must specify an assembler instruction template much like what appears in a machine description, plus an operand constraint string for each operand.

For example, here is how to use the 68881's fsinx instruction:

 
asm ("fsinx %1,%0" : "=f" (result) : "f" (angle));

Here angle is the C expression for the input operand while result is that of the output operand. Each has `"f"' as its operand constraint, saying that a floating point register is required. The `=' in `=f' indicates that the operand is an output; all output operands' constraints must use `='. The constraints use the same language used in the machine description (see section 6.40 Constraints for asm Operands).

Each operand is described by an operand-constraint string followed by the C expression in parentheses. A colon separates the assembler template from the first output operand and another separates the last output operand from the first input, if any. Commas separate the operands within each group. The total number of operands is currently limited to 30; this limitation may be lifted in some future version of GCC.

If there are no output operands but there are input operands, you must place two consecutive colons surrounding the place where the output operands would go.

As of GCC version 3.1, it is also possible to specify input and output operands using symbolic names which can be referenced within the assembler code. These names are specified inside square brackets preceding the constraint string, and can be referenced inside the assembler code using %[name] instead of a percentage sign followed by the operand number. Using named operands the above example could look like:

 
asm ("fsinx %[angle],%[output]"
     : [output] "=f" (result)
     : [angle] "f" (angle));

Note that the symbolic operand names have no relation whatsoever to other C identifiers. You may use any name you like, even those of existing C symbols, but you must ensure that no two operands within the same assembler construct use the same symbolic name.

Output operand expressions must be lvalues; the compiler can check this. The input operands need not be lvalues. The compiler cannot check whether the operands have data types that are reasonable for the instruction being executed. It does not parse the assembler instruction template and does not know what it means or even whether it is valid assembler input. The extended asm feature is most often used for machine instructions the compiler itself does not know exist. If the output expression cannot be directly addressed (for example, it is a bit-field), your constraint must allow a register. In that case, GCC will use the register as the output of the asm, and then store that register into the output.

The ordinary output operands must be write-only; GCC will assume that the values in these operands before the instruction are dead and need not be generated. Extended asm supports input-output or read-write operands. Use the constraint character `+' to indicate such an operand and list it with the output operands. You should only use read-write operands when the constraints for the operand (or the operand in which only some of the bits are to be changed) allow a register.

You may, as an alternative, logically split its function into two separate operands, one input operand and one write-only output operand. The connection between them is expressed by constraints which say they need to be in the same location when the instruction executes. You can use the same C expression for both operands, or different expressions. For example, here we write the (fictitious) `combine' instruction with bar as its read-only source operand and foo as its read-write destination:

 
asm ("combine %2,%0" : "=r" (foo) : "0" (foo), "g" (bar));

The constraint `"0"' for operand 1 says that it must occupy the same location as operand 0. A number in constraint is allowed only in an input operand and it must refer to an output operand.

Only a number in the constraint can guarantee that one operand will be in the same place as another. The mere fact that foo is the value of both operands is not enough to guarantee that they will be in the same place in the generated assembler code. The following would not work reliably:

 
asm ("combine %2,%0" : "=r" (foo) : "r" (foo), "g" (bar));

Various optimizations or reloading could cause operands 0 and 1 to be in different registers; GCC knows no reason not to do so. For example, the compiler might find a copy of the value of foo in one register and use it for operand 1, but generate the output operand 0 in a different register (copying it afterward to foo's own address). Of course, since the register for operand 1 is not even mentioned in the assembler code, the result will not work, but GCC can't tell that.

As of GCC version 3.1, one may write [name] instead of the operand number for a matching constraint. For example:

 
asm ("cmoveq %1,%2,%[result]"
     : [result] "=r"(result)
     : "r" (test), "r"(new), "[result]"(old));

Sometimes you need to make an asm operand be a specific register, but there's no matching constraint letter for that register by itself. To force the operand into that register, use a local variable for the operand and specify the register in the variable declaration. See section 6.42 Variables in Specified Registers. Then for the asm operand, use any register constraint letter that matches the register:

 
register int *p1 asm ("r0") = ...;
register int *p2 asm ("r1") = ...;
register int *result asm ("r0");
asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2));

In the above example, beware that a register that is call-clobbered by the target ABI will be overwritten by any function call in the assignment, including library calls for arithmetic operators. Also a register may be clobbered when generating some operations, like variable shift, memory copy or memory move on x86. Assuming it is a call-clobbered register, this may happen to r0 above by the assignment to p2. If you have to use such a register, use temporary variables for expressions between the register assignment and use:

 
int t1 = ...;
register int *p1 asm ("r0") = ...;
register int *p2 asm ("r1") = t1;
register int *result asm ("r0");
asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2));

Some instructions clobber specific hard registers. To describe this, write a third colon after the input operands, followed by the names of the clobbered hard registers (given as strings). Here is a realistic example for the VAX:

 
asm volatile ("movc3 %0,%1,%2"
              : /* no outputs */
              : "g" (from), "g" (to), "g" (count)
              : "r0", "r1", "r2", "r3", "r4", "r5");

You may not write a clobber description in a way that overlaps with an input or output operand. For example, you may not have an operand describing a register class with one member if you mention that register in the clobber list. Variables declared to live in specific registers (see section 6.42 Variables in Specified Registers), and used as asm input or output operands must have no part mentioned in the clobber description. There is no way for you to specify that an input operand is modified without also specifying it as an output operand. Note that if all the output operands you specify are for this purpose (and hence unused), you will then also need to specify volatile for the asm construct, as described below, to prevent GCC from deleting the asm statement as unused.

If you refer to a particular hardware register from the assembler code, you will probably have to list the register after the third colon to tell the compiler the register's value is modified. In some assemblers, the register names begin with `%'; to produce one `%' in the assembler code, you must write `%%' in the input.

If your assembler instruction can alter the condition code register, add `cc' to the list of clobbered registers. GCC on some machines represents the condition codes as a specific hardware register; `cc' serves to name this register. On other machines, the condition code is handled differently, and specifying `cc' has no effect. But it is valid no matter what the machine.

If your assembler instructions access memory in an unpredictable fashion, add `memory' to the list of clobbered registers. This will cause GCC to not keep memory values cached in registers across the assembler instruction and not optimize stores or loads to that memory. You will also want to add the volatile keyword if the memory affected is not listed in the inputs or outputs of the asm, as the `memory' clobber does not count as a side-effect of the asm. If you know how large the accessed memory is, you can add it as input or output but if this is not known, you should add `memory'. As an example, if you access ten bytes of a string, you can use a memory input like:

 
{"m"( ({ struct { char x[10]; } *p = (void *)ptr ; *p; }) )}.

Note that in the following example the memory input is necessary, otherwise GCC might optimize the store to x away:
 
int foo ()
{
  int x = 42;
  int *y = &x;
  int result;
  asm ("magic stuff accessing an 'int' pointed to by '%1'"
        "=&d" (r) : "a" (y), "m" (*y));
  return result;
}

You can put multiple assembler instructions together in a single asm template, separated by the characters normally used in assembly code for the system. A combination that works in most places is a newline to break the line, plus a tab character to move to the instruction field (written as `\n\t'). Sometimes semicolons can be used, if the assembler allows semicolons as a line-breaking character. Note that some assembler dialects use semicolons to start a comment. The input operands are guaranteed not to use any of the clobbered registers, and neither will the output operands' addresses, so you can read and write the clobbered registers as many times as you like. Here is an example of multiple instructions in a template; it assumes the subroutine _foo accepts arguments in registers 9 and 10:

 
asm ("movl %0,r9\n\tmovl %1,r10\n\tcall _foo"
     : /* no outputs */
     : "g" (from), "g" (to)
     : "r9", "r10");

Unless an output operand has the `&' constraint modifier, GCC may allocate it in the same register as an unrelated input operand, on the assumption the inputs are consumed before the outputs are produced. This assumption may be false if the assembler code actually consists of more than one instruction. In such a case, use `&' for each output operand that may not overlap an input. See section 6.40.3 Constraint Modifier Characters.

If you want to test the condition code produced by an assembler instruction, you must include a branch and a label in the asm construct, as follows:

 
asm ("clr %0\n\tfrob %1\n\tbeq 0f\n\tmov #1,%0\n0:"
     : "g" (result)
     : "g" (input));

This assumes your assembler supports local labels, as the GNU assembler and most Unix assemblers do.

Speaking of labels, jumps from one asm to another are not supported. The compiler's optimizers do not know about these jumps, and therefore they cannot take account of them when deciding how to optimize. See Extended asm with goto.

Usually the most convenient way to use these asm instructions is to encapsulate them in macros that look like functions. For example,

 
#define sin(x)       \
({ double __value, __arg = (x);   \
   asm ("fsinx %1,%0": "=f" (__value): "f" (__arg));  \
   __value; })

Here the variable __arg is used to make sure that the instruction operates on a proper double value, and to accept only those arguments x which can convert automatically to a double.

Another way to make sure the instruction operates on the correct data type is to use a cast in the asm. This is different from using a variable __arg in that it converts more different types. For example, if the desired type were int, casting the argument to int would accept a pointer with no complaint, while assigning the argument to an int variable named __arg would warn about using a pointer unless the caller explicitly casts it.

If an asm has output operands, GCC assumes for optimization purposes the instruction has no side effects except to change the output operands. This does not mean instructions with a side effect cannot be used, but you must be careful, because the compiler may eliminate them if the output operands aren't used, or move them out of loops, or replace two with one if they constitute a common subexpression. Also, if your instruction does have a side effect on a variable that otherwise appears not to change, the old value of the variable may be reused later if it happens to be found in a register.

You can prevent an asm instruction from being deleted by writing the keyword volatile after the asm. For example:

 
#define get_and_set_priority(new)              \
({ int __old;                                  \
   asm volatile ("get_and_set_priority %0, %1" \
                 : "=g" (__old) : "g" (new));  \
   __old; })

The volatile keyword indicates that the instruction has important side-effects. GCC will not delete a volatile asm if it is reachable. (The instruction can still be deleted if GCC can prove that control-flow will never reach the location of the instruction.) Note that even a volatile asm instruction can be moved relative to other code, including across jump instructions. For example, on many targets there is a system register which can be set to control the rounding mode of floating point operations. You might try setting it with a volatile asm, like this PowerPC example:

 
       asm volatile("mtfsf 255,%0" : : "f" (fpenv));
       sum = x + y;

This will not work reliably, as the compiler may move the addition back before the volatile asm. To make it work you need to add an artificial dependency to the asm referencing a variable in the code you don't want moved, for example:

 
    asm volatile ("mtfsf 255,%1" : "=X"(sum): "f"(fpenv));
    sum = x + y;

Similarly, you can't expect a sequence of volatile asm instructions to remain perfectly consecutive. If you want consecutive output, use a single asm. Also, GCC will perform some optimizations across a volatile asm instruction; GCC does not "forget everything" when it encounters a volatile asm instruction the way some other compilers do.

An asm instruction without any output operands will be treated identically to a volatile asm instruction.

It is a natural idea to look for a way to give access to the condition code left by the assembler instruction. However, when we attempted to implement this, we found no way to make it work reliably. The problem is that output operands might need reloading, which would result in additional following "store" instructions. On most machines, these instructions would alter the condition code before there was time to test it. This problem doesn't arise for ordinary "test" and "compare" instructions because they don't have any output operands.

For reasons similar to those described above, it is not possible to give an assembler instruction access to the condition code left by previous instructions.

As of GCC version 4.5, asm goto may be used to have the assembly jump to one or more C labels. In this form, a fifth section after the clobber list contains a list of all C labels to which the assembly may jump. Each label operand is implicitly self-named. The asm is also assumed to fall through to the next statement.

This form of asm is restricted to not have outputs. This is due to a internal restriction in the compiler that control transfer instructions cannot have outputs. This restriction on asm goto may be lifted in some future version of the compiler. In the mean time, asm goto may include a memory clobber, and so leave outputs in memory.

 
int frob(int x)
{
  int y;
  asm goto ("frob %%r5, %1; jc %l[error]; mov (%2), %%r5"
            : : "r"(x), "r"(&y) : "r5", "memory" : error);
  return y;
 error:
  return -1;
}

In this (inefficient) example, the frob instruction sets the carry bit to indicate an error. The jc instruction detects this and branches to the error label. Finally, the output of the frob instruction (%r5) is stored into the memory for variable y, which is later read by the return statement.

 
void doit(void)
{
  int i = 0;
  asm goto ("mfsr %%r1, 123; jmp %%r1;"
            ".pushsection doit_table;"
            ".long %l0, %l1, %l2, %l3;"
            ".popsection"
            : : : "r1" : label1, label2, label3, label4);
  __builtin_unreachable ();

 label1:
  f1();
  return;
 label2:
  f2();
  return;
 label3:
  i = 1;
 label4:
  f3(i);
}

In this (also inefficient) example, the mfsr instruction reads an address from some out-of-band machine register, and the following jmp instruction branches to that address. The address read by the mfsr instruction is assumed to have been previously set via some application-specific mechanism to be one of the four values stored in the doit_table section. Finally, the asm is followed by a call to __builtin_unreachable to indicate that the asm does not in fact fall through.

 
#define TRACE1(NUM)                         \
  do {                                      \
    asm goto ("0: nop;"                     \
              ".pushsection trace_table;"   \
              ".long 0b, %l0;"              \
              ".popsection"                 \
              : : : : trace#NUM);           \
    if (0) { trace#NUM: trace(); }          \
  } while (0)
#define TRACE  TRACE1(__COUNTER__)

In this example (which in fact inspired the asm goto feature) we want on rare occasions to call the trace function; on other occasions we'd like to keep the overhead to the absolute minimum. The normal code path consists of a single nop instruction. However, we record the address of this nop together with the address of a label that calls the trace function. This allows the nop instruction to be patched at runtime to be an unconditional branch to the stored label. It is assumed that an optimizing compiler will move the labeled block out of line, to optimize the fall through path from the asm.

If you are writing a header file that should be includable in ISO C programs, write __asm__ instead of asm. See section 6.43 Alternate Keywords.


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6.39.1 Size of an asm

Some targets require that GCC track the size of each instruction used in order to generate correct code. Because the final length of an asm is only known by the assembler, GCC must make an estimate as to how big it will be. The estimate is formed by counting the number of statements in the pattern of the asm and multiplying that by the length of the longest instruction on that processor. Statements in the asm are identified by newline characters and whatever statement separator characters are supported by the assembler; on most processors this is the `;' character.

Normally, GCC's estimate is perfectly adequate to ensure that correct code is generated, but it is possible to confuse the compiler if you use pseudo instructions or assembler macros that expand into multiple real instructions or if you use assembler directives that expand to more space in the object file than would be needed for a single instruction. If this happens then the assembler will produce a diagnostic saying that a label is unreachable.


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6.39.2 i386 floating point asm operands

There are several rules on the usage of stack-like regs in asm_operands insns. These rules apply only to the operands that are stack-like regs:

  1. Given a set of input regs that die in an asm_operands, it is necessary to know which are implicitly popped by the asm, and which must be explicitly popped by gcc.

    An input reg that is implicitly popped by the asm must be explicitly clobbered, unless it is constrained to match an output operand.

  2. For any input reg that is implicitly popped by an asm, it is necessary to know how to adjust the stack to compensate for the pop. If any non-popped input is closer to the top of the reg-stack than the implicitly popped reg, it would not be possible to know what the stack looked like--it's not clear how the rest of the stack "slides up".

    All implicitly popped input regs must be closer to the top of the reg-stack than any input that is not implicitly popped.

    It is possible that if an input dies in an insn, reload might use the input reg for an output reload. Consider this example:

     
    asm ("foo" : "=t" (a) : "f" (b));
    

    This asm says that input B is not popped by the asm, and that the asm pushes a result onto the reg-stack, i.e., the stack is one deeper after the asm than it was before. But, it is possible that reload will think that it can use the same reg for both the input and the output, if input B dies in this insn.

    If any input operand uses the f constraint, all output reg constraints must use the & earlyclobber.

    The asm above would be written as

     
    asm ("foo" : "=&t" (a) : "f" (b));
    

  3. Some operands need to be in particular places on the stack. All output operands fall in this category--there is no other way to know which regs the outputs appear in unless the user indicates this in the constraints.

    Output operands must specifically indicate which reg an output appears in after an asm. =f is not allowed: the operand constraints must select a class with a single reg.

  4. Output operands may not be "inserted" between existing stack regs. Since no 387 opcode uses a read/write operand, all output operands are dead before the asm_operands, and are pushed by the asm_operands. It makes no sense to push anywhere but the top of the reg-stack.

    Output operands must start at the top of the reg-stack: output operands may not "skip" a reg.

  5. Some asm statements may need extra stack space for internal calculations. This can be guaranteed by clobbering stack registers unrelated to the inputs and outputs.

Here are a couple of reasonable asms to want to write. This asm takes one input, which is internally popped, and produces two outputs.

 
asm ("fsincos" : "=t" (cos), "=u" (sin) : "0" (inp));

This asm takes two inputs, which are popped by the fyl2xp1 opcode, and replaces them with one output. The user must code the st(1) clobber for reg-stack.c to know that fyl2xp1 pops both inputs.

 
asm ("fyl2xp1" : "=t" (result) : "0" (x), "u" (y) : "st(1)");


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6.40 Constraints for asm Operands

Here are specific details on what constraint letters you can use with asm operands. Constraints can say whether an operand may be in a register, and which kinds of register; whether the operand can be a memory reference, and which kinds of address; whether the operand may be an immediate constant, and which possible values it may have. Constraints can also require two operands to match.

6.40.1 Simple Constraints  Basic use of constraints.
6.40.2 Multiple Alternative Constraints  When an insn has two alternative constraint-patterns.
6.40.3 Constraint Modifier Characters  More precise control over effects of constraints.
6.40.4 Constraints for Particular Machines  Special constraints for some particular machines.


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6.40.1 Simple Constraints

The simplest kind of constraint is a string full of letters, each of which describes one kind of operand that is permitted. Here are the letters that are allowed:

whitespace
Whitespace characters are ignored and can be inserted at any position except the first. This enables each alternative for different operands to be visually aligned in the machine description even if they have different number of constraints and modifiers.

`m'
A memory operand is allowed, with any kind of address that the machine supports in general. Note that the letter used for the general memory constraint can be re-defined by a back end using the TARGET_MEM_CONSTRAINT macro.

`o'
A memory operand is allowed, but only if the address is offsettable. This means that adding a small integer (actually, the width in bytes of the operand, as determined by its machine mode) may be added to the address and the result is also a valid memory address.

For example, an address which is constant is offsettable; so is an address that is the sum of a register and a constant (as long as a slightly larger constant is also within the range of address-offsets supported by the machine); but an autoincrement or autodecrement address is not offsettable. More complicated indirect/indexed addresses may or may not be offsettable depending on the other addressing modes that the machine supports.

Note that in an output operand which can be matched by another operand, the constraint letter `o' is valid only when accompanied by both `<' (if the target machine has predecrement addressing) and `>' (if the target machine has preincrement addressing).

`V'
A memory operand that is not offsettable. In other words, anything that would fit the `m' constraint but not the `o' constraint.

`<'
A memory operand with autodecrement addressing (either predecrement or postdecrement) is allowed.

`>'
A memory operand with autoincrement addressing (either preincrement or postincrement) is allowed.

`r'
A register operand is allowed provided that it is in a general register.

`i'
An immediate integer operand (one with constant value) is allowed. This includes symbolic constants whose values will be known only at assembly time or later.

`n'
An immediate integer operand with a known numeric value is allowed. Many systems cannot support assembly-time constants for operands less than a word wide. Constraints for these operands should use `n' rather than `i'.

`I', `J', `K', ... `P'
Other letters in the range `I' through `P' may be defined in a machine-dependent fashion to permit immediate integer operands with explicit integer values in specified ranges. For example, on the 68000, `I' is defined to stand for the range of values 1 to 8. This is the range permitted as a shift count in the shift instructions.

`E'
An immediate floating operand (expression code const_double) is allowed, but only if the target floating point format is the same as that of the host machine (on which the compiler is running).

`F'
An immediate floating operand (expression code const_double or const_vector) is allowed.

`G', `H'
`G' and `H' may be defined in a machine-dependent fashion to permit immediate floating operands in particular ranges of values.

`s'
An immediate integer operand whose value is not an explicit integer is allowed.

This might appear strange; if an insn allows a constant operand with a value not known at compile time, it certainly must allow any known value. So why use `s' instead of `i'? Sometimes it allows better code to be generated.

For example, on the 68000 in a fullword instruction it is possible to use an immediate operand; but if the immediate value is between -128 and 127, better code results from loading the value into a register and using the register. This is because the load into the register can be done with a `moveq' instruction. We arrange for this to happen by defining the letter `K' to mean "any integer outside the range -128 to 127", and then specifying `Ks' in the operand constraints.

`g'
Any register, memory or immediate integer operand is allowed, except for registers that are not general registers.

`X'
Any operand whatsoever is allowed.

`0', `1', `2', ... `9'
An operand that matches the specified operand number is allowed. If a digit is used together with letters within the same alternative, the digit should come last.

This number is allowed to be more than a single digit. If multiple digits are encountered consecutively, they are interpreted as a single decimal integer. There is scant chance for ambiguity, since to-date it has never been desirable that `10' be interpreted as matching either operand 1 or operand 0. Should this be desired, one can use multiple alternatives instead.

This is called a matching constraint and what it really means is that the assembler has only a single operand that fills two roles which asm distinguishes. For example, an add instruction uses two input operands and an output operand, but on most CISC machines an add instruction really has only two operands, one of them an input-output operand:

 
addl #35,r12

Matching constraints are used in these circumstances. More precisely, the two operands that match must include one input-only operand and one output-only operand. Moreover, the digit must be a smaller number than the number of the operand that uses it in the constraint.

`p'
An operand that is a valid memory address is allowed. This is for "load address" and "push address" instructions.

`p' in the constraint must be accompanied by address_operand as the predicate in the match_operand. This predicate interprets the mode specified in the match_operand as the mode of the memory reference for which the address would be valid.

other-letters
Other letters can be defined in machine-dependent fashion to stand for particular classes of registers or other arbitrary operand types. `d', `a' and `f' are defined on the 68000/68020 to stand for data, address and floating point registers.


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6.40.2 Multiple Alternative Constraints

Sometimes a single instruction has multiple alternative sets of possible operands. For example, on the 68000, a logical-or instruction can combine register or an immediate value into memory, or it can combine any kind of operand into a register; but it cannot combine one memory location into another.

These constraints are represented as multiple alternatives. An alternative can be described by a series of letters for each operand. The overall constraint for an operand is made from the letters for this operand from the first alternative, a comma, the letters for this operand from the second alternative, a comma, and so on until the last alternative.

If all the operands fit any one alternative, the instruction is valid. Otherwise, for each alternative, the compiler counts how many instructions must be added to copy the operands so that that alternative applies. The alternative requiring the least copying is chosen. If two alternatives need the same amount of copying, the one that comes first is chosen. These choices can be altered with the `?' and `!' characters:

?
Disparage slightly the alternative that the `?' appears in, as a choice when no alternative applies exactly. The compiler regards this alternative as one unit more costly for each `?' that appears in it.

!
Disparage severely the alternative that the `!' appears in. This alternative can still be used if it fits without reloading, but if reloading is needed, some other alternative will be used.


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6.40.3 Constraint Modifier Characters

Here are constraint modifier characters.

`='
Means that this operand is write-only for this instruction: the previous value is discarded and replaced by output data.

`+'
Means that this operand is both read and written by the instruction.

When the compiler fixes up the operands to satisfy the constraints, it needs to know which operands are inputs to the instruction and which are outputs from it. `=' identifies an output; `+' identifies an operand that is both input and output; all other operands are assumed to be input only.

If you specify `=' or `+' in a constraint, you put it in the first character of the constraint string.

`&'
Means (in a particular alternative) that this operand is an earlyclobber operand, which is modified before the instruction is finished using the input operands. Therefore, this operand may not lie in a register that is used as an input operand or as part of any memory address.

`&' applies only to the alternative in which it is written. In constraints with multiple alternatives, sometimes one alternative requires `&' while others do not. See, for example, the `movdf' insn of the 68000.

An input operand can be tied to an earlyclobber operand if its only use as an input occurs before the early result is written. Adding alternatives of this form often allows GCC to produce better code when only some of the inputs can be affected by the earlyclobber. See, for example, the `mulsi3' insn of the ARM.

`&' does not obviate the need to write `='.

`%'
Declares the instruction to be commutative for this operand and the following operand. This means that the compiler may interchange the two operands if that is the cheapest way to make all operands fit the constraints. GCC can only handle one commutative pair in an asm; if you use more, the compiler may fail. Note that you need not use the modifier if the two alternatives are strictly identical; this would only waste time in the reload pass. The modifier is not operational after register allocation, so the result of define_peephole2 and define_splits performed after reload cannot rely on `%' to make the intended insn match.

`#'
Says that all following characters, up to the next comma, are to be ignored as a constraint. They are significant only for choosing register preferences.

`*'
Says that the following character should be ignored when choosing register preferences. `*' has no effect on the meaning of the constraint as a constraint, and no effect on reloading.


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6.40.4 Constraints for Particular Machines

Whenever possible, you should use the general-purpose constraint letters in asm arguments, since they will convey meaning more readily to people reading your code. Failing that, use the constraint letters that usually have very similar meanings across architectures. The most commonly used constraints are `m' and `r' (for memory and general-purpose registers respectively; see section 6.40.1 Simple Constraints), and `I', usually the letter indicating the most common immediate-constant format.

Each architecture defines additional constraints. These constraints are used by the compiler itself for instruction generation, as well as for asm statements; therefore, some of the constraints are not particularly useful for asm. Here is a summary of some of the machine-dependent constraints available on some particular machines; it includes both constraints that are useful for asm and constraints that aren't. The compiler source file mentioned in the table heading for each architecture is the definitive reference for the meanings of that architecture's constraints.

ARM family---`config/arm/arm.h'
f
Floating-point register

w
VFP floating-point register

F
One of the floating-point constants 0.0, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0 or 10.0

G
Floating-point constant that would satisfy the constraint `F' if it were negated

I
Integer that is valid as an immediate operand in a data processing instruction. That is, an integer in the range 0 to 255 rotated by a multiple of 2

J
Integer in the range -4095 to 4095

K
Integer that satisfies constraint `I' when inverted (ones complement)

L
Integer that satisfies constraint `I' when negated (twos complement)

M
Integer in the range 0 to 32

Q
A memory reference where the exact address is in a single register (``m'' is preferable for asm statements)

R
An item in the constant pool

S
A symbol in the text segment of the current file

Uv
A memory reference suitable for VFP load/store insns (reg+constant offset)

Uy
A memory reference suitable for iWMMXt load/store instructions.

Uq
A memory reference suitable for the ARMv4 ldrsb instruction.

AVR family---`config/avr/constraints.md'
l
Registers from r0 to r15

a
Registers from r16 to r23

d
Registers from r16 to r31

w
Registers from r24 to r31. These registers can be used in `adiw' command

e
Pointer register (r26--r31)

b
Base pointer register (r28--r31)

q
Stack pointer register (SPH:SPL)

t
Temporary register r0

x
Register pair X (r27:r26)

y
Register pair Y (r29:r28)

z
Register pair Z (r31:r30)

I
Constant greater than -1, less than 64

J
Constant greater than -64, less than 1

K
Constant integer 2

L
Constant integer 0

M
Constant that fits in 8 bits

N
Constant integer -1

O
Constant integer 8, 16, or 24

P
Constant integer 1

G
A floating point constant 0.0

R
Integer constant in the range -6 ... 5.

Q
A memory address based on Y or Z pointer with displacement.

CRX Architecture---`config/crx/crx.h'
b
Registers from r0 to r14 (registers without stack pointer)

l
Register r16 (64-bit accumulator lo register)

h
Register r17 (64-bit accumulator hi register)

k
Register pair r16-r17. (64-bit accumulator lo-hi pair)

I
Constant that fits in 3 bits

J
Constant that fits in 4 bits

K
Constant that fits in 5 bits

L
Constant that is one of -1, 4, -4, 7, 8, 12, 16, 20, 32, 48

G
Floating point constant that is legal for store immediate

Hewlett-Packard PA-RISC---`config/pa/pa.h'
a
General register 1

f
Floating point register

q
Shift amount register

x
Floating point register (deprecated)

y
Upper floating point register (32-bit), floating point register (64-bit)

Z
Any register

I
Signed 11-bit integer constant

J
Signed 14-bit integer constant

K
Integer constant that can be deposited with a zdepi instruction

L
Signed 5-bit integer constant

M
Integer constant 0

N
Integer constant that can be loaded with a ldil instruction

O
Integer constant whose value plus one is a power of 2

P
Integer constant that can be used for and operations in depi and extru instructions

S
Integer constant 31

U
Integer constant 63

G
Floating-point constant 0.0

A
A lo_sum data-linkage-table memory operand

Q
A memory operand that can be used as the destination operand of an integer store instruction

R
A scaled or unscaled indexed memory operand

T
A memory operand for floating-point loads and stores

W
A register indirect memory operand

picoChip family---`picochip.h'
k
Stack register.

f
Pointer register. A register which can be used to access memory without supplying an offset. Any other register can be used to access memory, but will need a constant offset. In the case of the offset being zero, it is more efficient to use a pointer register, since this reduces code size.

t
A twin register. A register which may be paired with an adjacent register to create a 32-bit register.

a
Any absolute memory address (e.g., symbolic constant, symbolic constant + offset).

I
4-bit signed integer.

J
4-bit unsigned integer.

K
8-bit signed integer.

M
Any constant whose absolute value is no greater than 4-bits.

N
10-bit signed integer

O
16-bit signed integer.

PowerPC and IBM RS6000---`config/rs6000/rs6000.h'
b
Address base register

d
Floating point register (containing 64-bit value)

f
Floating point register (containing 32-bit value)

v
Altivec vector register

wd
VSX vector register to hold vector double data

wf
VSX vector register to hold vector float data

ws
VSX vector register to hold scalar float data

wa
Any VSX register

h
`MQ', `CTR', or `LINK' register

q
`MQ' register

c
`CTR' register

l
`LINK' register

x
`CR' register (condition register) number 0

y
`CR' register (condition register)

z
`FPMEM' stack memory for FPR-GPR transfers

I
Signed 16-bit constant

J
Unsigned 16-bit constant shifted left 16 bits (use `L' instead for SImode constants)

K
Unsigned 16-bit constant

L
Signed 16-bit constant shifted left 16 bits

M
Constant larger than 31

N
Exact power of 2

O
Zero

P
Constant whose negation is a signed 16-bit constant

G
Floating point constant that can be loaded into a register with one instruction per word

H
Integer/Floating point constant that can be loaded into a register using three instructions

m
Memory operand. Note that on PowerPC targets, m can include addresses that update the base register. It is therefore only safe to use `m' in an asm statement if that asm statement accesses the operand exactly once. The asm statement must also use `%U<opno>' as a placeholder for the "update" flag in the corresponding load or store instruction. For example:

 
asm ("st%U0 %1,%0" : "=m" (mem) : "r" (val));

is correct but:

 
asm ("st %1,%0" : "=m" (mem) : "r" (val));

is not. Use es rather than m if you don't want the base register to be updated.

es
A "stable" memory operand; that is, one which does not include any automodification of the base register. Unlike `m', this constraint can be used in asm statements that might access the operand several times, or that might not access it at all.

Q
Memory operand that is an offset from a register (it is usually better to use `m' or `es' in asm statements)

Z
Memory operand that is an indexed or indirect from a register (it is usually better to use `m' or `es' in asm statements)

R
AIX TOC entry

a
Address operand that is an indexed or indirect from a register (`p' is preferable for asm statements)

S
Constant suitable as a 64-bit mask operand

T
Constant suitable as a 32-bit mask operand

U
System V Release 4 small data area reference

t
AND masks that can be performed by two rldic{l, r} instructions

W
Vector constant that does not require memory

j
Vector constant that is all zeros.

Intel 386---`config/i386/constraints.md'
R
Legacy register--the eight integer registers available on all i386 processors (a, b, c, d, si, di, bp, sp).

q
Any register accessible as rl. In 32-bit mode, a, b, c, and d; in 64-bit mode, any integer register.

Q
Any register accessible as rh: a, b, c, and d.

a
The a register.

b
The b register.

c
The c register.

d
The d register.

S
The si register.

D
The di register.

A
The a and d registers, as a pair (for instructions that return half the result in one and half in the other).

f
Any 80387 floating-point (stack) register.

t
Top of 80387 floating-point stack (%st(0)).

u
Second from top of 80387 floating-point stack (%st(1)).

y
Any MMX register.

x
Any SSE register.

Yz
First SSE register (%xmm0).

I
Integer constant in the range 0 ... 31, for 32-bit shifts.

J
Integer constant in the range 0 ... 63, for 64-bit shifts.

K
Signed 8-bit integer constant.

L
0xFF or 0xFFFF, for andsi as a zero-extending move.

M
0, 1, 2, or 3 (shifts for the lea instruction).

N
Unsigned 8-bit integer constant (for in and out instructions).

G
Standard 80387 floating point constant.

C
Standard SSE floating point constant.

e
32-bit signed integer constant, or a symbolic reference known to fit that range (for immediate operands in sign-extending x86-64 instructions).

Z
32-bit unsigned integer constant, or a symbolic reference known to fit that range (for immediate operands in zero-extending x86-64 instructions).

Intel IA-64---`config/ia64/ia64.h'
a
General register r0 to r3 for addl instruction

b
Branch register

c
Predicate register (`c' as in "conditional")

d
Application register residing in M-unit

e
Application register residing in I-unit

f
Floating-point register

m
Memory operand. Remember that `m' allows postincrement and postdecrement which require printing with `%Pn' on IA-64. Use `S' to disallow postincrement and postdecrement.

G
Floating-point constant 0.0 or 1.0

I
14-bit signed integer constant

J
22-bit signed integer constant

K
8-bit signed integer constant for logical instructions

L
8-bit adjusted signed integer constant for compare pseudo-ops

M
6-bit unsigned integer constant for shift counts

N
9-bit signed integer constant for load and store postincrements

O
The constant zero

P
0 or -1 for dep instruction

Q
Non-volatile memory for floating-point loads and stores

R
Integer constant in the range 1 to 4 for shladd instruction

S
Memory operand except postincrement and postdecrement

FRV---`config/frv/frv.h'
a
Register in the class ACC_REGS (acc0 to acc7).

b
Register in the class EVEN_ACC_REGS (acc0 to acc7).

c
Register in the class CC_REGS (fcc0 to fcc3 and icc0 to icc3).

d
Register in the class GPR_REGS (gr0 to gr63).

e
Register in the class EVEN_REGS (gr0 to gr63). Odd registers are excluded not in the class but through the use of a machine mode larger than 4 bytes.

f
Register in the class FPR_REGS (fr0 to fr63).

h
Register in the class FEVEN_REGS (fr0 to fr63). Odd registers are excluded not in the class but through the use of a machine mode larger than 4 bytes.

l
Register in the class LR_REG (the lr register).

q
Register in the class QUAD_REGS (gr2 to gr63). Register numbers not divisible by 4 are excluded not in the class but through the use of a machine mode larger than 8 bytes.

t
Register in the class ICC_REGS (icc0 to icc3).

u
Register in the class FCC_REGS (fcc0 to fcc3).

v
Register in the class ICR_REGS (cc4 to cc7).

w
Register in the class FCR_REGS (cc0 to cc3).

x
Register in the class QUAD_FPR_REGS (fr0 to fr63). Register numbers not divisible by 4 are excluded not in the class but through the use of a machine mode larger than 8 bytes.

z
Register in the class SPR_REGS (lcr and lr).

A
Register in the class QUAD_ACC_REGS (acc0 to acc7).

B
Register in the class ACCG_REGS (accg0 to accg7).

C
Register in the class CR_REGS (cc0 to cc7).

G
Floating point constant zero

I
6-bit signed integer constant

J
10-bit signed integer constant

L
16-bit signed integer constant

M
16-bit unsigned integer constant

N
12-bit signed integer constant that is negative--i.e. in the range of -2048 to -1

O
Constant zero

P
12-bit signed integer constant that is greater than zero--i.e. in the range of 1 to 2047.

Blackfin family---`config/bfin/constraints.md'
a
P register

d
D register

z
A call clobbered P register.

qn
A single register. If n is in the range 0 to 7, the corresponding D register. If it is A, then the register P0.

D
Even-numbered D register

W
Odd-numbered D register

e
Accumulator register.

A
Even-numbered accumulator register.

B
Odd-numbered accumulator register.

b
I register

v
B register

f
M register

c
Registers used for circular buffering, i.e. I, B, or L registers.

C
The CC register.

t
LT0 or LT1.

k
LC0 or LC1.

u
LB0 or LB1.

x
Any D, P, B, M, I or L register.

y
Additional registers typically used only in prologues and epilogues: RETS, RETN, RETI, RETX, RETE, ASTAT, SEQSTAT and USP.

w
Any register except accumulators or CC.

Ksh
Signed 16 bit integer (in the range -32768 to 32767)

Kuh
Unsigned 16 bit integer (in the range 0 to 65535)

Ks7
Signed 7 bit integer (in the range -64 to 63)

Ku7
Unsigned 7 bit integer (in the range 0 to 127)

Ku5
Unsigned 5 bit integer (in the range 0 to 31)

Ks4
Signed 4 bit integer (in the range -8 to 7)

Ks3
Signed 3 bit integer (in the range -3 to 4)

Ku3
Unsigned 3 bit integer (in the range 0 to 7)

Pn
Constant n, where n is a single-digit constant in the range 0 to 4.

PA
An integer equal to one of the MACFLAG_XXX constants that is suitable for use with either accumulator.

PB
An integer equal to one of the MACFLAG_XXX constants that is suitable for use only with accumulator A1.

M1
Constant 255.

M2
Constant 65535.

J
An integer constant with exactly a single bit set.

L
An integer constant with all bits set except exactly one.

H

Q
Any SYMBOL_REF.

M32C---`config/m32c/m32c.c'
Rsp
Rfb
Rsb
`$sp', `$fb', `$sb'.

Rcr
Any control register, when they're 16 bits wide (nothing if control registers are 24 bits wide)

Rcl
Any control register, when they're 24 bits wide.

R0w
R1w
R2w
R3w
$r0, $r1, $r2, $r3.

R02
$r0 or $r2, or $r2r0 for 32 bit values.

R13
$r1 or $r3, or $r3r1 for 32 bit values.

Rdi
A register that can hold a 64 bit value.

Rhl
$r0 or $r1 (registers with addressable high/low bytes)

R23
$r2 or $r3

Raa
Address registers

Raw
Address registers when they're 16 bits wide.

Ral
Address registers when they're 24 bits wide.

Rqi
Registers that can hold QI values.

Rad
Registers that can be used with displacements ($a0, $a1, $sb).

Rsi
Registers that can hold 32 bit values.

Rhi
Registers that can hold 16 bit values.

Rhc
Registers chat can hold 16 bit values, including all control registers.

Rra
$r0 through R1, plus $a0 and $a1.

Rfl
The flags register.

Rmm
The memory-based pseudo-registers $mem0 through $mem15.

Rpi
Registers that can hold pointers (16 bit registers for r8c, m16c; 24 bit registers for m32cm, m32c).

Rpa
Matches multiple registers in a PARALLEL to form a larger register. Used to match function return values.

Is3
-8 ... 7

IS1
-128 ... 127

IS2
-32768 ... 32767

IU2
0 ... 65535

In4
-8 ... -1 or 1 ... 8

In5
-16 ... -1 or 1 ... 16

In6
-32 ... -1 or 1 ... 32

IM2
-65536 ... -1

Ilb
An 8 bit value with exactly one bit set.

Ilw
A 16 bit value with exactly one bit set.

Sd
The common src/dest memory addressing modes.

Sa
Memory addressed using $a0 or $a1.

Si
Memory addressed with immediate addresses.

Ss
Memory addressed using the stack pointer ($sp).

Sf
Memory addressed using the frame base register ($fb).

Ss
Memory addressed using the small base register ($sb).

S1
$r1h

MeP---`config/mep/constraints.md'
a
The $sp register.

b
The $tp register.

c
Any control register.

d
Either the $hi or the $lo register.

em
Coprocessor registers that can be directly loaded ($c0-$c15).

ex
Coprocessor registers that can be moved to each other.

er
Coprocessor registers that can be moved to core registers.

h
The $hi register.

j
The $rpc register.

l
The $lo register.

t
Registers which can be used in $tp-relative addressing.

v
The $gp register.

x
The coprocessor registers.

y
The coprocessor control registers.

z
The $0 register.

A
User-defined register set A.

B
User-defined register set B.

C
User-defined register set C.

D
User-defined register set D.

I
Offsets for $gp-rel addressing.

J
Constants that can be used directly with boolean insns.

K
Constants that can be moved directly to registers.

L
Small constants that can be added to registers.

M
Long shift counts.

N
Small constants that can be compared to registers.

O
Constants that can be loaded into the top half of registers.

S
Signed 8-bit immediates.

T
Symbols encoded for $tp-rel or $gp-rel addressing.

U
Non-constant addresses for loading/saving coprocessor registers.

W
The top half of a symbol's value.

Y
A register indirect address without offset.

Z
Symbolic references to the control bus.

MIPS---`config/mips/constraints.md'
d
An address register. This is equivalent to r unless generating MIPS16 code.

f
A floating-point register (if available).

h
Formerly the hi register. This constraint is no longer supported.

l
The lo register. Use this register to store values that are no bigger than a word.

x
The concatenated hi and lo registers. Use this register to store doubleword values.

c
A register suitable for use in an indirect jump. This will always be $25 for `-mabicalls'.

v
Register $3. Do not use this constraint in new code; it is retained only for compatibility with glibc.

y
Equivalent to r; retained for backwards compatibility.

z
A floating-point condition code register.

I
A signed 16-bit constant (for arithmetic instructions).

J
Integer zero.

K
An unsigned 16-bit constant (for logic instructions).

L
A signed 32-bit constant in which the lower 16 bits are zero. Such constants can be loaded using lui.

M
A constant that cannot be loaded using lui, addiu or ori.

N
A constant in the range -65535 to -1 (inclusive).

O
A signed 15-bit constant.

P
A constant in the range 1 to 65535 (inclusive).

G
Floating-point zero.

R
An address that can be used in a non-macro load or store.

Motorola 680x0---`config/m68k/constraints.md'
a
Address register

d
Data register

f
68881 floating-point register, if available

I
Integer in the range 1 to 8

J
16-bit signed number

K
Signed number whose magnitude is greater than 0x80

L
Integer in the range -8 to -1

M
Signed number whose magnitude is greater than 0x100

N
Range 24 to 31, rotatert:SI 8 to 1 expressed as rotate

O
16 (for rotate using swap)

P
Range 8 to 15, rotatert:HI 8 to 1 expressed as rotate

R
Numbers that mov3q can handle

G
Floating point constant that is not a 68881 constant

S
Operands that satisfy 'm' when -mpcrel is in effect

T
Operands that satisfy 's' when -mpcrel is not in effect

Q
Address register indirect addressing mode

U
Register offset addressing

W
const_call_operand

Cs
symbol_ref or const

Ci
const_int

C0
const_int 0

Cj
Range of signed numbers that don't fit in 16 bits

Cmvq
Integers valid for mvq

Capsw
Integers valid for a moveq followed by a swap

Cmvz
Integers valid for mvz

Cmvs
Integers valid for mvs

Ap
push_operand

Ac
Non-register operands allowed in clr

Motorola 68HC11 & 68HC12 families---`config/m68hc11/m68hc11.h'
a
Register `a'

b
Register `b'

d
Register `d'

q
An 8-bit register

t
Temporary soft register _.tmp

u
A soft register _.d1 to _.d31

w
Stack pointer register

x
Register `x'

y
Register `y'

z
Pseudo register `z' (replaced by `x' or `y' at the end)

A
An address register: x, y or z

B
An address register: x or y

D
Register pair (x:d) to form a 32-bit value

L
Constants in the range -65536 to 65535

M
Constants whose 16-bit low part is zero

N
Constant integer 1 or -1

O
Constant integer 16

P
Constants in the range -8 to 2

Moxie---`config/moxie/constraints.md'
A
An absolute address

B
An offset address

W
A register indirect memory operand

I
A constant in the range of 0 to 255.

N
A constant in the range of 0 to -255.

RX---`config/rx/constraints.md'
Q
An address which does not involve register indirect addressing or pre/post increment/decrement addressing.

Symbol
A symbol reference.

Int08
A constant in the range -256 to 255, inclusive.

Sint08
A constant in the range -128 to 127, inclusive.

Sint16
A constant in the range -32768 to 32767, inclusive.

Sint24
A constant in the range -8388608 to 8388607, inclusive.

Uint04
A constant in the range 0 to 15, inclusive.

SPARC---`config/sparc/sparc.h'
f
Floating-point register on the SPARC-V8 architecture and lower floating-point register on the SPARC-V9 architecture.

e
Floating-point register. It is equivalent to `f' on the SPARC-V8 architecture and contains both lower and upper floating-point registers on the SPARC-V9 architecture.

c
Floating-point condition code register.

d
Lower floating-point register. It is only valid on the SPARC-V9 architecture when the Visual Instruction Set is available.

b
Floating-point register. It is only valid on the SPARC-V9 architecture when the Visual Instruction Set is available.

h
64-bit global or out register for the SPARC-V8+ architecture.

D
A vector constant

I
Signed 13-bit constant

J
Zero

K
32-bit constant with the low 12 bits clear (a constant that can be loaded with the sethi instruction)

L
A constant in the range supported by movcc instructions

M
A constant in the range supported by movrcc instructions

N
Same as `K', except that it verifies that bits that are not in the lower 32-bit range are all zero. Must be used instead of `K' for modes wider than SImode

O
The constant 4096

G
Floating-point zero

H
Signed 13-bit constant, sign-extended to 32 or 64 bits

Q
Floating-point constant whose integral representation can be moved into an integer register using a single sethi instruction

R
Floating-point constant whose integral representation can be moved into an integer register using a single mov instruction

S
Floating-point constant whose integral representation can be moved into an integer register using a high/lo_sum instruction sequence

T
Memory address aligned to an 8-byte boundary

U
Even register

W
Memory address for `e' constraint registers

Y
Vector zero

SPU---`config/spu/spu.h'
a
An immediate which can be loaded with the il/ila/ilh/ilhu instructions. const_int is treated as a 64 bit value.

c
An immediate for and/xor/or instructions. const_int is treated as a 64 bit value.

d
An immediate for the iohl instruction. const_int is treated as a 64 bit value.

f
An immediate which can be loaded with fsmbi.

A
An immediate which can be loaded with the il/ila/ilh/ilhu instructions. const_int is treated as a 32 bit value.

B
An immediate for most arithmetic instructions. const_int is treated as a 32 bit value.

C
An immediate for and/xor/or instructions. const_int is treated as a 32 bit value.

D
An immediate for the iohl instruction. const_int is treated as a 32 bit value.

I
A constant in the range [-64, 63] for shift/rotate instructions.

J
An unsigned 7-bit constant for conversion/nop/channel instructions.

K
A signed 10-bit constant for most arithmetic instructions.

M
A signed 16 bit immediate for stop.

N
An unsigned 16-bit constant for iohl and fsmbi.

O
An unsigned 7-bit constant whose 3 least significant bits are 0.

P
An unsigned 3-bit constant for 16-byte rotates and shifts

R
Call operand, reg, for indirect calls

S
Call operand, symbol, for relative calls.

T
Call operand, const_int, for absolute calls.

U
An immediate which can be loaded with the il/ila/ilh/ilhu instructions. const_int is sign extended to 128 bit.

W
An immediate for shift and rotate instructions. const_int is treated as a 32 bit value.

Y
An immediate for and/xor/or instructions. const_int is sign extended as a 128 bit.

Z
An immediate for the iohl instruction. const_int is sign extended to 128 bit.

S/390 and zSeries---`config/s390/s390.h'
a
Address register (general purpose register except r0)

c
Condition code register

d
Data register (arbitrary general purpose register)

f
Floating-point register

I
Unsigned 8-bit constant (0--255)

J
Unsigned 12-bit constant (0--4095)

K
Signed 16-bit constant (-32768--32767)

L
Value appropriate as displacement.
(0..4095)
for short displacement
(-524288..524287)
for long displacement

M
Constant integer with a value of 0x7fffffff.

N
Multiple letter constraint followed by 4 parameter letters.
0..9:
number of the part counting from most to least significant
H,Q:
mode of the part
D,S,H:
mode of the containing operand
0,F:
value of the other parts (F--all bits set)
The constraint matches if the specified part of a constant has a value different from its other parts.

Q
Memory reference without index register and with short displacement.

R
Memory reference with index register and short displacement.

S
Memory reference without index register but with long displacement.

T
Memory reference with index register and long displacement.

U
Pointer with short displacement.

W
Pointer with long displacement.

Y
Shift count operand.

Score family---`config/score/score.h'
d
Registers from r0 to r32.

e
Registers from r0 to r16.

t
r8--r11 or r22--r27 registers.

h
hi register.

l
lo register.

x
hi + lo register.

q
cnt register.

y
lcb register.

z
scb register.

a
cnt + lcb + scb register.

c
cr0--cr15 register.

b
cp1 registers.

f
cp2 registers.

i
cp3 registers.

j
cp1 + cp2 + cp3 registers.

I
High 16-bit constant (32-bit constant with 16 LSBs zero).

J
Unsigned 5 bit integer (in the range 0 to 31).

K
Unsigned 16 bit integer (in the range 0 to 65535).

L
Signed 16 bit integer (in the range -32768 to 32767).

M
Unsigned 14 bit integer (in the range 0 to 16383).

N
Signed 14 bit integer (in the range -8192 to 8191).

Z
Any SYMBOL_REF.

Xstormy16---`config/stormy16/stormy16.h'
a
Register r0.

b
Register r1.

c
Register r2.

d
Register r8.

e
Registers r0 through r7.

t
Registers r0 and r1.

y
The carry register.

z
Registers r8 and r9.

I
A constant between 0 and 3 inclusive.

J
A constant that has exactly one bit set.

K
A constant that has exactly one bit clear.

L
A constant between 0 and 255 inclusive.

M
A constant between -255 and 0 inclusive.

N
A constant between -3 and 0 inclusive.

O
A constant between 1 and 4 inclusive.

P
A constant between -4 and -1 inclusive.

Q
A memory reference that is a stack push.

R
A memory reference that is a stack pop.

S
A memory reference that refers to a constant address of known value.

T
The register indicated by Rx (not implemented yet).

U
A constant that is not between 2 and 15 inclusive.

Z
The constant 0.

Xtensa---`config/xtensa/constraints.md'
a
General-purpose 32-bit register

b
One-bit boolean register

A
MAC16 40-bit accumulator register

I
Signed 12-bit integer constant, for use in MOVI instructions

J
Signed 8-bit integer constant, for use in ADDI instructions

K
Integer constant valid for BccI instructions

L
Unsigned constant valid for BccUI instructions


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6.41 Controlling Names Used in Assembler Code

You can specify the name to be used in the assembler code for a C function or variable by writing the asm (or __asm__) keyword after the declarator as follows:

 
int foo asm ("myfoo") = 2;

This specifies that the name to be used for the variable foo in the assembler code should be `myfoo' rather than the usual `_foo'.

On systems where an underscore is normally prepended to the name of a C function or variable, this feature allows you to define names for the linker that do not start with an underscore.

It does not make sense to use this feature with a non-static local variable since such variables do not have assembler names. If you are trying to put the variable in a particular register, see 6.42 Variables in Specified Registers. GCC presently accepts such code with a warning, but will probably be changed to issue an error, rather than a warning, in the future.

You cannot use asm in this way in a function definition; but you can get the same effect by writing a declaration for the function before its definition and putting asm there, like this:

 
extern func () asm ("FUNC");

func (x, y)
     int x, y;
/* ... */

It is up to you to make sure that the assembler names you choose do not conflict with any other assembler symbols. Also, you must not use a register name; that would produce completely invalid assembler code. GCC does not as yet have the ability to store static variables in registers. Perhaps that will be added.


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6.42 Variables in Specified Registers

GNU C allows you to put a few global variables into specified hardware registers. You can also specify the register in which an ordinary register variable should be allocated.

6.42.1 Defining Global Register Variables  
6.42.2 Specifying Registers for Local Variables  


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6.42.1 Defining Global Register Variables

You can define a global register variable in GNU C like this:

 
register int *foo asm ("a5");

Here a5 is the name of the register which should be used. Choose a register which is normally saved and restored by function calls on your machine, so that library routines will not clobber it.

Naturally the register name is cpu-dependent, so you would need to conditionalize your program according to cpu type. The register a5 would be a good choice on a 68000 for a variable of pointer type. On machines with register windows, be sure to choose a "global" register that is not affected magically by the function call mechanism.

In addition, operating systems on one type of cpu may differ in how they name the registers; then you would need additional conditionals. For example, some 68000 operating systems call this register %a5.

Eventually there may be a way of asking the compiler to choose a register automatically, but first we need to figure out how it should choose and how to enable you to guide the choice. No solution is evident.

Defining a global register variable in a certain register reserves that register entirely for this use, at least within the current compilation. The register will not be allocated for any other purpose in the functions in the current compilation. The register will not be saved and restored by these functions. Stores into this register are never deleted even if they would appear to be dead, but references may be deleted or moved or simplified.

It is not safe to access the global register variables from signal handlers, or from more than one thread of control, because the system library routines may temporarily use the register for other things (unless you recompile them specially for the task at hand).

It is not safe for one function that uses a global register variable to call another such function foo by way of a third function lose that was compiled without knowledge of this variable (i.e. in a different source file in which the variable wasn't declared). This is because lose might save the register and put some other value there. For example, you can't expect a global register variable to be available in the comparison-function that you pass to qsort, since qsort might have put something else in that register. (If you are prepared to recompile qsort with the same global register variable, you can solve this problem.)

If you want to recompile qsort or other source files which do not actually use your global register variable, so that they will not use that register for any other purpose, then it suffices to specify the compiler option `-ffixed-reg'. You need not actually add a global register declaration to their source code.

A function which can alter the value of a global register variable cannot safely be called from a function compiled without this variable, because it could clobber the value the caller expects to find there on return. Therefore, the function which is the entry point into the part of the program that uses the global register variable must explicitly save and restore the value which belongs to its caller.

On most machines, longjmp will restore to each global register variable the value it had at the time of the setjmp. On some machines, however, longjmp will not change the value of global register variables. To be portable, the function that called setjmp should make other arrangements to save the values of the global register variables, and to restore them in a longjmp. This way, the same thing will happen regardless of what longjmp does.

All global register variable declarations must precede all function definitions. If such a declaration could appear after function definitions, the declaration would be too late to prevent the register from being used for other purposes in the preceding functions.

Global register variables may not have initial values, because an executable file has no means to supply initial contents for a register.

On the SPARC, there are reports that g3 ... g7 are suitable registers, but certain library functions, such as getwd, as well as the subroutines for division and remainder, modify g3 and g4. g1 and g2 are local temporaries.

On the 68000, a2 ... a5 should be suitable, as should d2 ... d7. Of course, it will not do to use more than a few of those.


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6.42.2 Specifying Registers for Local Variables

You can define a local register variable with a specified register like this:

 
register int *foo asm ("a5");

Here a5 is the name of the register which should be used. Note that this is the same syntax used for defining global register variables, but for a local variable it would appear within a function.

Naturally the register name is cpu-dependent, but this is not a problem, since specific registers are most often useful with explicit assembler instructions (see section 6.39 Assembler Instructions with C Expression Operands). Both of these things generally require that you conditionalize your program according to cpu type.

In addition, operating systems on one type of cpu may differ in how they name the registers; then you would need additional conditionals. For example, some 68000 operating systems call this register %a5.

Defining such a register variable does not reserve the register; it remains available for other uses in places where flow control determines the variable's value is not live.

This option does not guarantee that GCC will generate code that has this variable in the register you specify at all times. You may not code an explicit reference to this register in the assembler instruction template part of an asm statement and assume it will always refer to this variable. However, using the variable as an asm operand guarantees that the specified register is used for the operand.

Stores into local register variables may be deleted when they appear to be dead according to dataflow analysis. References to local register variables may be deleted or moved or simplified.

As for global register variables, it's recommended that you choose a register which is normally saved and restored by function calls on your machine, so that library routines will not clobber it. A common pitfall is to initialize multiple call-clobbered registers with arbitrary expressions, where a function call or library call for an arithmetic operator will overwrite a register value from a previous assignment, for example r0 below:
 
register int *p1 asm ("r0") = ...;
register int *p2 asm ("r1") = ...;
In those cases, a solution is to use a temporary variable for each arbitrary expression. See Example of asm with clobbered asm reg.


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6.43 Alternate Keywords

`-ansi' and the various `-std' options disable certain keywords. This causes trouble when you want to use GNU C extensions, or a general-purpose header file that should be usable by all programs, including ISO C programs. The keywords asm, typeof and inline are not available in programs compiled with `-ansi' or `-std' (although inline can be used in a program compiled with `-std=c99'). The ISO C99 keyword restrict is only available when `-std=gnu99' (which will eventually be the default) or `-std=c99' (or the equivalent `-std=iso9899:1999') is used.

The way to solve these problems is to put `__' at the beginning and end of each problematical keyword. For example, use __asm__ instead of asm, and __inline__ instead of inline.

Other C compilers won't accept these alternative keywords; if you want to compile with another compiler, you can define the alternate keywords as macros to replace them with the customary keywords. It looks like this:

 
#ifndef __GNUC__
#define __asm__ asm
#endif

`-pedantic' and other options cause warnings for many GNU C extensions. You can prevent such warnings within one expression by writing __extension__ before the expression. __extension__ has no effect aside from this.


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6.44 Incomplete enum Types

You can define an enum tag without specifying its possible values. This results in an incomplete type, much like what you get if you write struct foo without describing the elements. A later declaration which does specify the possible values completes the type.

You can't allocate variables or storage using the type while it is incomplete. However, you can work with pointers to that type.

This extension may not be very useful, but it makes the handling of enum more consistent with the way struct and union are handled.

This extension is not supported by GNU C++.


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6.45 Function Names as Strings

GCC provides three magic variables which hold the name of the current function, as a string. The first of these is __func__, which is part of the C99 standard:

The identifier __func__ is implicitly declared by the translator as if, immediately following the opening brace of each function definition, the declaration

 
static const char __func__[] = "function-name";

appeared, where function-name is the name of the lexically-enclosing function. This name is the unadorned name of the function.

__FUNCTION__ is another name for __func__. Older versions of GCC recognize only this name. However, it is not standardized. For maximum portability, we recommend you use __func__, but provide a fallback definition with the preprocessor:

 
#if __STDC_VERSION__ < 199901L
# if __GNUC__ >= 2
#  define __func__ __FUNCTION__
# else
#  define __func__ "<unknown>"
# endif
#endif

In C, __PRETTY_FUNCTION__ is yet another name for __func__. However, in C++, __PRETTY_FUNCTION__ contains the type signature of the function as well as its bare name. For example, this program:

 
extern "C" {
extern int printf (char *, ...);
}

class a {
 public:
  void sub (int i)
    {
      printf ("__FUNCTION__ = %s\n", __FUNCTION__);
      printf ("__PRETTY_FUNCTION__ = %s\n", __PRETTY_FUNCTION__);
    }
};

int
main (void)
{
  a ax;
  ax.sub (0);
  return 0;
}

gives this output:

 
__FUNCTION__ = sub
__PRETTY_FUNCTION__ = void a::sub(int)

These identifiers are not preprocessor macros. In GCC 3.3 and earlier, in C only, __FUNCTION__ and __PRETTY_FUNCTION__ were treated as string literals; they could be used to initialize char arrays, and they could be concatenated with other string literals. GCC 3.4 and later treat them as variables, like __func__. In C++, __FUNCTION__ and __PRETTY_FUNCTION__ have always been variables.


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6.46 Getting the Return or Frame Address of a Function

These functions may be used to get information about the callers of a function.

Built-in Function: void * __builtin_return_address (unsigned int level)
This function returns the return address of the current function, or of one of its callers. The level argument is number of frames to scan up the call stack. A value of 0 yields the return address of the current function, a value of 1 yields the return address of the caller of the current function, and so forth. When inlining the expected behavior is that the function will return the address of the function that will be returned to. To work around this behavior use the noinline function attribute.

The level argument must be a constant integer.

On some machines it may be impossible to determine the return address of any function other than the current one; in such cases, or when the top of the stack has been reached, this function will return 0 or a random value. In addition, __builtin_frame_address may be used to determine if the top of the stack has been reached.

Additional post-processing of the returned value may be needed, see __builtin_extract_return_address.

This function should only be used with a nonzero argument for debugging purposes.

Built-in Function: void * __builtin_extract_return_address (void *addr)
The address as returned by __builtin_return_address may have to be fed through this function to get the actual encoded address. For example, on the 31-bit S/390 platform the highest bit has to be masked out, or on SPARC platforms an offset has to be added for the true next instruction to be executed.

If no fixup is needed, this function simply passes through addr.

Built-in Function: void * __builtin_frob_return_address (void *addr)
This function does the reverse of __builtin_extract_return_address.

Built-in Function: void * __builtin_frame_address (unsigned int level)
This function is similar to __builtin_return_address, but it returns the address of the function frame rather than the return address of the function. Calling __builtin_frame_address with a value of 0 yields the frame address of the current function, a value of 1 yields the frame address of the caller of the current function, and so forth.

The frame is the area on the stack which holds local variables and saved registers. The frame address is normally the address of the first word pushed on to the stack by the function. However, the exact definition depends upon the processor and the calling convention. If the processor has a dedicated frame pointer register, and the function has a frame, then __builtin_frame_address will return the value of the frame pointer register.

On some machines it may be impossible to determine the frame address of any function other than the current one; in such cases, or when the top of the stack has been reached, this function will return 0 if the first frame pointer is properly initialized by the startup code.

This function should only be used with a nonzero argument for debugging purposes.


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6.47 Using vector instructions through built-in functions

On some targets, the instruction set contains SIMD vector instructions that operate on multiple values contained in one large register at the same time. For example, on the i386 the MMX, 3DNow! and SSE extensions can be used this way.

The first step in using these extensions is to provide the necessary data types. This should be done using an appropriate typedef:

 
typedef int v4si __attribute__ ((vector_size (16)));

The int type specifies the base type, while the attribute specifies the vector size for the variable, measured in bytes. For example, the declaration above causes the compiler to set the mode for the v4si type to be 16 bytes wide and divided into int sized units. For a 32-bit int this means a vector of 4 units of 4 bytes, and the corresponding mode of foo will be V4SI.

The vector_size attribute is only applicable to integral and float scalars, although arrays, pointers, and function return values are allowed in conjunction with this construct.

All the basic integer types can be used as base types, both as signed and as unsigned: char, short, int, long, long long. In addition, float and double can be used to build floating-point vector types.

Specifying a combination that is not valid for the current architecture will cause GCC to synthesize the instructions using a narrower mode. For example, if you specify a variable of type V4SI and your architecture does not allow for this specific SIMD type, GCC will produce code that uses 4 SIs.

The types defined in this manner can be used with a subset of normal C operations. Currently, GCC will allow using the following operators on these types: +, -, *, /, unary minus, ^, |, &, ~, %.

The operations behave like C++ valarrays. Addition is defined as the addition of the corresponding elements of the operands. For example, in the code below, each of the 4 elements in a will be added to the corresponding 4 elements in b and the resulting vector will be stored in c.

 
typedef int v4si __attribute__ ((vector_size (16)));

v4si a, b, c;

c = a + b;

Subtraction, multiplication, division, and the logical operations operate in a similar manner. Likewise, the result of using the unary minus or complement operators on a vector type is a vector whose elements are the negative or complemented values of the corresponding elements in the operand.

You can declare variables and use them in function calls and returns, as well as in assignments and some casts. You can specify a vector type as a return type for a function. Vector types can also be used as function arguments. It is possible to cast from one vector type to another, provided they are of the same size (in fact, you can also cast vectors to and from other datatypes of the same size).

You cannot operate between vectors of different lengths or different signedness without a cast.

A port that supports hardware vector operations, usually provides a set of built-in functions that can be used to operate on vectors. For example, a function to add two vectors and multiply the result by a third could look like this:

 
v4si f (v4si a, v4si b, v4si c)
{
  v4si tmp = __builtin_addv4si (a, b);
  return __builtin_mulv4si (tmp, c);
}


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6.48 Offsetof

GCC implements for both C and C++ a syntactic extension to implement the offsetof macro.

 
primary:
        "__builtin_offsetof" "(" typename "," offsetof_member_designator ")"

offsetof_member_designator:
          identifier
        | offsetof_member_designator "." identifier
        | offsetof_member_designator "[" expr "]"

This extension is sufficient such that

 
#define offsetof(type, member)  __builtin_offsetof (type, member)

is a suitable definition of the offsetof macro. In C++, type may be dependent. In either case, member may consist of a single identifier, or a sequence of member accesses and array references.


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6.49 Built-in functions for atomic memory access

The following builtins are intended to be compatible with those described in the Intel Itanium Processor-specific Application Binary Interface, section 7.4. As such, they depart from the normal GCC practice of using the "__builtin_" prefix, and further that they are overloaded such that they work on multiple types.

The definition given in the Intel documentation allows only for the use of the types int, long, long long as well as their unsigned counterparts. GCC will allow any integral scalar or pointer type that is 1, 2, 4 or 8 bytes in length.

Not all operations are supported by all target processors. If a particular operation cannot be implemented on the target processor, a warning will be generated and a call an external function will be generated. The external function will carry the same name as the builtin, with an additional suffix `_n' where n is the size of the data type.

In most cases, these builtins are considered a full barrier. That is, no memory operand will be moved across the operation, either forward or backward. Further, instructions will be issued as necessary to prevent the processor from speculating loads across the operation and from queuing stores after the operation.

All of the routines are described in the Intel documentation to take "an optional list of variables protected by the memory barrier". It's not clear what is meant by that; it could mean that only the following variables are protected, or it could mean that these variables should in addition be protected. At present GCC ignores this list and protects all variables which are globally accessible. If in the future we make some use of this list, an empty list will continue to mean all globally accessible variables.

type __sync_fetch_and_add (type *ptr, type value, ...)
type __sync_fetch_and_sub (type *ptr, type value, ...)
type __sync_fetch_and_or (type *ptr, type value, ...)
type __sync_fetch_and_and (type *ptr, type value, ...)
type __sync_fetch_and_xor (type *ptr, type value, ...)
type __sync_fetch_and_nand (type *ptr, type value, ...)
These builtins perform the operation suggested by the name, and returns the value that had previously been in memory. That is,

 
{ tmp = *ptr; *ptr op= value; return tmp; }
{ tmp = *ptr; *ptr = ~(tmp & value); return tmp; }   // nand

Note: GCC 4.4 and later implement __sync_fetch_and_nand builtin as *ptr = ~(tmp & value) instead of *ptr = ~tmp & value.

type __sync_add_and_fetch (type *ptr, type value, ...)
type __sync_sub_and_fetch (type *ptr, type value, ...)
type __sync_or_and_fetch (type *ptr, type value, ...)
type __sync_and_and_fetch (type *ptr, type value, ...)
type __sync_xor_and_fetch (type *ptr, type value, ...)
type __sync_nand_and_fetch (type *ptr, type value, ...)
These builtins perform the operation suggested by the name, and return the new value. That is,

 
{ *ptr op= value; return *ptr; }
{ *ptr = ~(*ptr & value); return *ptr; }   // nand

Note: GCC 4.4 and later implement __sync_nand_and_fetch builtin as *ptr = ~(*ptr & value) instead of *ptr = ~*ptr & value.

bool __sync_bool_compare_and_swap (type *ptr, type oldval type newval, ...)
type __sync_val_compare_and_swap (type *ptr, type oldval type newval, ...)
These builtins perform an atomic compare and swap. That is, if the current value of *ptr is oldval, then write newval into *ptr.

The "bool" version returns true if the comparison is successful and newval was written. The "val" version returns the contents of *ptr before the operation.

__sync_synchronize (...)
This builtin issues a full memory barrier.

type __sync_lock_test_and_set (type *ptr, type value, ...)
This builtin, as described by Intel, is not a traditional test-and-set operation, but rather an atomic exchange operation. It writes value into *ptr, and returns the previous contents of *ptr.

Many targets have only minimal support for such locks, and do not support a full exchange operation. In this case, a target may support reduced functionality here by which the only valid value to store is the immediate constant 1. The exact value actually stored in *ptr is implementation defined.

This builtin is not a full barrier, but rather an acquire barrier. This means that references after the builtin cannot move to (or be speculated to) before the builtin, but previous memory stores may not be globally visible yet, and previous memory loads may not yet be satisfied.

void __sync_lock_release (type *ptr, ...)
This builtin releases the lock acquired by __sync_lock_test_and_set. Normally this means writing the constant 0 to *ptr.

This builtin is not a full barrier, but rather a release barrier. This means that all previous memory stores are globally visible, and all previous memory loads have been satisfied, but following memory reads are not prevented from being speculated to before the barrier.


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6.50 Built-in functions for memory model aware atomic operations.

The following builtins approximately match the requirements for C++1x memory model. Many are similar to the "__sync" prefixed builtins, but all also have a memory model parameter. These are all identified by being prefixed with "__atomic", and most are overloaded such that they work with multiple types.

GCC will allow any integral scalar or pointer type that is 1, 2, 4, or 8 bytes in length. 16 bytes integral types are also allowed if __int128_t is supported by the architecture.

Target architectures are encouraged to provide their own patterns for each of these builtins. If no target is provided, the original non-memory model set of "__sync" atomic builtins will be utilized, along with any required synchronization fences surrounding it in order to achieve the proper behaviour. Execution in this case is subject to the same restrictions as those builtins.

There are 6 different memory models which can be specified. These map to the same names in the C++1x standard. Refer there or to the GCC wiki on atomics for more detailed definitions. These memory models integrate both barriers to code motion as well as synchronization requirements with other threads. These are listed in approximately ascending order of strength.

__ATOMIC_RELAXED
No barriers or synchronization.
__ATOMIC_CONSUME
Data dependency only for both barrier and synchronization with another thread.
__ATOMIC_ACQUIRE
Barrier to hoisting of code and synchronizes with release (or stronger) semantic stores from another thread.
__ATOMIC_RELEASE
Barrier to sinking of code and synchronizes with acquire (or stronger) semantic loads from another thread.
__ATOMIC_ACQ_REL
Full barrier in both directions and synchronizes with acquire loads and release stores in another thread.
__ATOMIC_SEQ_CST
Full barrier in both directions and synchronizes with acquire loads and release stores in all threads.

When implementing patterns for these builtins, the memory model parameter can be ignored as long as the pattern implements the most restrictive __ATOMIC_SEQ_CST model. Any of the other memory models will execute correctly with this memory model but they may not execute as efficiently as they could with a more appropriate implemention of the relaxed requirements.

Note that the C++11 standard allows for the memory model parameter to be determined at runtime rather than at compile time. These builtins will map any runtime value to __ATOMIC_SEQ_CST rather than invoke a runtime library call or inline a switch statement. This is standard compliant, safe, and the simplest approach for now.

  • type __atomic_load (type *ptr, int memmodel) This builtin implements an atomic load operation. It returns the contents of *ptr.

    The valid memory model variants are __ATOMIC_RELAXED, __ATOMIC_SEQ_CST, __ATOMIC_ACQUIRE, and __ATOMIC_CONSUME.

  • void __atomic_store (type *ptr, type val, int memmodel) This builtin implements an atomic store operation. It writes val into *ptr. On targets which are limited, 0 may be the only valid value. This mimics the behaviour of __sync_lock_release on such hardware.

    The valid memory model variants are __ATOMIC_RELAXED, __ATOMIC_SEQ_CST, and __ATOMIC_RELEASE.

  • type __atomic_exchange (type *ptr, type val, int memmodel) This builtin implements an atomic exchange operation. It writes val into *ptr, and returns the previous contents of *ptr.

    On targets which are limited, a value of 1 may be the only valid value written. This mimics the behaviour of __sync_lock_test_and_set on such hardware.

    The valid memory model variants are __ATOMIC_RELAXED, __ATOMIC_SEQ_CST, __ATOMIC_ACQUIRE, __ATOMIC_RELEASE, and __ATOMIC_ACQ_REL.

  • bool __atomic_compare_exchange (type *ptr, type *expected, type desired, int success_memmodel, int failure_memmodel) This builtin implements an atomic compare_exchange operation. This compares the contents of *ptr with the contents of *expected and if equal, writes desired into *ptr. If they are not equal, the current contents of *ptr is written into *expected.

    True is returned if *desired is written into *ptr and the execution is considered to conform to the memory model specified by success_memmodel. There are no restrictions on what memory model can be used here.

    False is returned otherwise, and the execution is considered to conform to failure_memmodel. This memory model cannot be __ATOMIC_RELEASE nor __ATOMIC_ACQ_REL. It also cannot be a stronger model than that specified by success_memmodel.

  • type __atomic_add_fetch (type *ptr, type val, int memmodel)
  • type __atomic_sub_fetch (type *ptr, type val, int memmodel)
  • type __atomic_and_fetch (type *ptr, type val, int memmodel)
  • type __atomic_xor_fetch (type *ptr, type val, int memmodel)
  • type __atomic_or_fetch (type *ptr, type val, int memmodel) These builtins perform the operation suggested by the name, and return the result of the operation. That is,

     
    { *ptr op= val; return *ptr; }
    

    All memory models are valid.

  • type __atomic_fetch_add (type *ptr, type val, int memmodel)
  • type __atomic_fetch_sub (type *ptr, type val, int memmodel)
  • type __atomic_fetch_and (type *ptr, type val, int memmodel)
  • type __atomic_fetch_xor (type *ptr, type val, int memmodel)
  • type __atomic_fetch_or (type *ptr, type val, int memmodel) These builtins perform the operation suggested by the name, and return the value that had previously been in *ptr . That is,

     
    { tmp = *ptr; *ptr op= val; return tmp; }
    

    All memory models are valid.

  • void __atomic_thread_fence (int memmodel)

    This builtin acts as a synchronization fence between threads based on the specified memory model.

    All memory orders are valid.

  • void __atomic_signal_fence (int memmodel)

    This builtin acts as a synchronization fence between a thread and signal handlers based in the same thread.

    All memory orders are valid.

  • bool __atomic_always_lock_free (size_t size)

    This builtin returns true if objects of size bytes will always generate lock free atomic instructions for the target architecture. Otherwise false is returned.

    size must resolve to a compile time constant.

     
    if (_atomic_always_lock_free (sizeof (long long)))
    

  • bool __atomic_is_lock_free (size_t size)

    This builtin returns true if objects of size bytes will always generate lock free atomic instructions for the target architecture. If it is not known to be lock free a call is made to a runtime routine named __atomic_is_lock_free.


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    6.51 Object Size Checking Builtins

    GCC implements a limited buffer overflow protection mechanism that can prevent some buffer overflow attacks.

    Built-in Function: size_t __builtin_object_size (void * ptr, int type)
    is a built-in construct that returns a constant number of bytes from ptr to the end of the object ptr pointer points to (if known at compile time). __builtin_object_size never evaluates its arguments for side-effects. If there are any side-effects in them, it returns (size_t) -1 for type 0 or 1 and (size_t) 0 for type 2 or 3. If there are multiple objects ptr can point to and all of them are known at compile time, the returned number is the maximum of remaining byte counts in those objects if type & 2 is 0 and minimum if nonzero. If it is not possible to determine which objects ptr points to at compile time, __builtin_object_size should return (size_t) -1 for type 0 or 1 and (size_t) 0 for type 2 or 3.

    type is an integer constant from 0 to 3. If the least significant bit is clear, objects are whole variables, if it is set, a closest surrounding subobject is considered the object a pointer points to. The second bit determines if maximum or minimum of remaining bytes is computed.

     
    struct V { char buf1[10]; int b; char buf2[10]; } var;
    char *p = &var.buf1[1], *q = &var.b;
    
    /* Here the object p points to is var.  */
    assert (__builtin_object_size (p, 0) == sizeof (var) - 1);
    /* The subobject p points to is var.buf1.  */
    assert (__builtin_object_size (p, 1) == sizeof (var.buf1) - 1);
    /* The object q points to is var.  */
    assert (__builtin_object_size (q, 0)
            == (char *) (&var + 1) - (char *) &var.b);
    /* The subobject q points to is var.b.  */
    assert (__builtin_object_size (q, 1) == sizeof (var.b));
    

    There are built-in functions added for many common string operation functions, e.g., for memcpy __builtin___memcpy_chk built-in is provided. This built-in has an additional last argument, which is the number of bytes remaining in object the dest argument points to or (size_t) -1 if the size is not known.

    The built-in functions are optimized into the normal string functions like memcpy if the last argument is (size_t) -1 or if it is known at compile time that the destination object will not be overflown. If the compiler can determine at compile time the object will be always overflown, it issues a warning.

    The intended use can be e.g.

     
    #undef memcpy
    #define bos0(dest) __builtin_object_size (dest, 0)
    #define memcpy(dest, src, n) \
      __builtin___memcpy_chk (dest, src, n, bos0 (dest))
    
    char *volatile p;
    char buf[10];
    /* It is unknown what object p points to, so this is optimized
       into plain memcpy - no checking is possible.  */
    memcpy (p, "abcde", n);
    /* Destination is known and length too.  It is known at compile
       time there will be no overflow.  */
    memcpy (&buf[5], "abcde", 5);
    /* Destination is known, but the length is not known at compile time.
       This will result in __memcpy_chk call that can check for overflow
       at runtime.  */
    memcpy (&buf[5], "abcde", n);
    /* Destination is known and it is known at compile time there will
       be overflow.  There will be a warning and __memcpy_chk call that
       will abort the program at runtime.  */
    memcpy (&buf[6], "abcde", 5);
    

    Such built-in functions are provided for memcpy, mempcpy, memmove, memset, strcpy, stpcpy, strncpy, strcat and strncat.

    There are also checking built-in functions for formatted output functions.
     
    int __builtin___sprintf_chk (char *s, int flag, size_t os, const char *fmt, ...);
    int __builtin___snprintf_chk (char *s, size_t maxlen, int flag, size_t os,
                                  const char *fmt, ...);
    int __builtin___vsprintf_chk (char *s, int flag, size_t os, const char *fmt,
                                  va_list ap);
    int __builtin___vsnprintf_chk (char *s, size_t maxlen, int flag, size_t os,
                                   const char *fmt, va_list ap);
    

    The added flag argument is passed unchanged to __sprintf_chk etc. functions and can contain implementation specific flags on what additional security measures the checking function might take, such as handling %n differently.

    The os argument is the object size s points to, like in the other built-in functions. There is a small difference in the behavior though, if os is (size_t) -1, the built-in functions are optimized into the non-checking functions only if flag is 0, otherwise the checking function is called with os argument set to (size_t) -1.

    In addition to this, there are checking built-in functions __builtin___printf_chk, __builtin___vprintf_chk, __builtin___fprintf_chk and __builtin___vfprintf_chk. These have just one additional argument, flag, right before format string fmt. If the compiler is able to optimize them to fputc etc. functions, it will, otherwise the checking function should be called and the flag argument passed to it.


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    6.52 Other built-in functions provided by GCC

    GCC provides a large number of built-in functions other than the ones mentioned above. Some of these are for internal use in the processing of exceptions or variable-length argument lists and will not be documented here because they may change from time to time; we do not recommend general use of these functions.

    The remaining functions are provided for optimization purposes.

    GCC includes built-in versions of many of the functions in the standard C library. The versions prefixed with __builtin_ will always be treated as having the same meaning as the C library function even if you specify the `-fno-builtin' option. (see section 3.4 Options Controlling C Dialect) Many of these functions are only optimized in certain cases; if they are not optimized in a particular case, a call to the library function will be emitted.

    Outside strict ISO C mode (`-ansi', `-std=c90' or `-std=c99'), the functions _exit, alloca, bcmp, bzero, dcgettext, dgettext, dremf, dreml, drem, exp10f, exp10l, exp10, ffsll, ffsl, ffs, fprintf_unlocked, fputs_unlocked, gammaf, gammal, gamma, gammaf_r, gammal_r, gamma_r, gettext, index, isascii, j0f, j0l, j0, j1f, j1l, j1, jnf, jnl, jn, lgammaf_r, lgammal_r, lgamma_r, mempcpy, pow10f, pow10l, pow10, printf_unlocked, rindex, scalbf, scalbl, scalb, signbit, signbitf, signbitl, signbitd32, signbitd64, signbitd128, significandf, significandl, significand, sincosf, sincosl, sincos, stpcpy, stpncpy, strcasecmp, strdup, strfmon, strncasecmp, strndup, toascii, y0f, y0l, y0, y1f, y1l, y1, ynf, ynl and yn may be handled as built-in functions. All these functions have corresponding versions prefixed with __builtin_, which may be used even in strict C90 mode.

    The ISO C99 functions _Exit, acoshf, acoshl, acosh, asinhf, asinhl, asinh, atanhf, atanhl, atanh, cabsf, cabsl, cabs, cacosf, cacoshf, cacoshl, cacosh, cacosl, cacos, cargf, cargl, carg, casinf, casinhf, casinhl, casinh, casinl, casin, catanf, catanhf, catanhl, catanh, catanl, catan, cbrtf, cbrtl, cbrt, ccosf, ccoshf, ccoshl, ccosh, ccosl, ccos, cexpf, cexpl, cexp, cimagf, cimagl, cimag, clogf, clogl, clog, conjf, conjl, conj, copysignf, copysignl, copysign, cpowf, cpowl, cpow, cprojf, cprojl, cproj, crealf, creall, creal, csinf, csinhf, csinhl, csinh, csinl, csin, csqrtf, csqrtl, csqrt, ctanf, ctanhf, ctanhl, ctanh, ctanl, ctan, erfcf, erfcl, erfc, erff, erfl, erf, exp2f, exp2l, exp2, expm1f, expm1l, expm1, fdimf, fdiml, fdim, fmaf, fmal, fmaxf, fmaxl, fmax, fma, fminf, fminl, fmin, hypotf, hypotl, hypot, ilogbf, ilogbl, ilogb, imaxabs, isblank, iswblank, lgammaf, lgammal, lgamma, llabs, llrintf, llrintl, llrint, llroundf, llroundl, llround, log1pf, log1pl, log1p, log2f, log2l, log2, logbf, logbl, logb, lrintf, lrintl, lrint, lroundf, lroundl, lround, nearbyintf, nearbyintl, nearbyint, nextafterf, nextafterl, nextafter, nexttowardf, nexttowardl, nexttoward, remainderf, remainderl, remainder, remquof, remquol, remquo, rintf, rintl, rint, roundf, roundl, round, scalblnf, scalblnl, scalbln, scalbnf, scalbnl, scalbn, snprintf, tgammaf, tgammal, tgamma, truncf, truncl, trunc, vfscanf, vscanf, vsnprintf and vsscanf are handled as built-in functions except in strict ISO C90 mode (`-ansi' or `-std=c90').

    There are also built-in versions of the ISO C99 functions acosf, acosl, asinf, asinl, atan2f, atan2l, atanf, atanl, ceilf, ceill, cosf, coshf, coshl, cosl, expf, expl, fabsf, fabsl, floorf, floorl, fmodf, fmodl, frexpf, frexpl, ldexpf, ldexpl, log10f, log10l, logf, logl, modfl, modf, powf, powl, sinf, sinhf, sinhl, sinl, sqrtf, sqrtl, tanf, tanhf, tanhl and tanl that are recognized in any mode since ISO C90 reserves these names for the purpose to which ISO C99 puts them. All these functions have corresponding versions prefixed with __builtin_.

    The ISO C94 functions iswalnum, iswalpha, iswcntrl, iswdigit, iswgraph, iswlower, iswprint, iswpunct, iswspace, iswupper, iswxdigit, towlower and towupper are handled as built-in functions except in strict ISO C90 mode (`-ansi' or `-std=c90').

    The ISO C90 functions abort, abs, acos, asin, atan2, atan, calloc, ceil, cosh, cos, exit, exp, fabs, floor, fmod, fprintf, fputs, frexp, fscanf, isalnum, isalpha, iscntrl, isdigit, isgraph, islower, isprint, ispunct, isspace, isupper, isxdigit, tolower, toupper, labs, ldexp, log10, log, malloc, memchr, memcmp, memcpy, memset, modf, pow, printf, putchar, puts, scanf, sinh, sin, snprintf, sprintf, sqrt, sscanf, strcat, strchr, strcmp, strcpy, strcspn, strlen, strncat, strncmp, strncpy, strpbrk, strrchr, strspn, strstr, tanh, tan, vfprintf, vprintf and vsprintf are all recognized as built-in functions unless `-fno-builtin' is specified (or `-fno-builtin-function' is specified for an individual function). All of these functions have corresponding versions prefixed with __builtin_.

    GCC provides built-in versions of the ISO C99 floating point comparison macros that avoid raising exceptions for unordered operands. They have the same names as the standard macros ( isgreater, isgreaterequal, isless, islessequal, islessgreater, and isunordered) , with __builtin_ prefixed. We intend for a library implementor to be able to simply #define each standard macro to its built-in equivalent. In the same fashion, GCC provides fpclassify, isfinite, isinf_sign and isnormal built-ins used with __builtin_ prefixed. The isinf and isnan builtins appear both with and without the __builtin_ prefix.

    Built-in Function: int __builtin_types_compatible_p (type1, type2)

    You can use the built-in function __builtin_types_compatible_p to determine whether two types are the same.

    This built-in function returns 1 if the unqualified versions of the types type1 and type2 (which are types, not expressions) are compatible, 0 otherwise. The result of this built-in function can be used in integer constant expressions.

    This built-in function ignores top level qualifiers (e.g., const, volatile). For example, int is equivalent to const int.

    The type int[] and int[5] are compatible. On the other hand, int and char * are not compatible, even if the size of their types, on the particular architecture are the same. Also, the amount of pointer indirection is taken into account when determining similarity. Consequently, short * is not similar to short **. Furthermore, two types that are typedefed are considered compatible if their underlying types are compatible.

    An enum type is not considered to be compatible with another enum type even if both are compatible with the same integer type; this is what the C standard specifies. For example, enum {foo, bar} is not similar to enum {hot, dog}.

    You would typically use this function in code whose execution varies depending on the arguments' types. For example:

     
    #define foo(x)                                                  \
      ({                                                           \
        typeof (x) tmp = (x);                                       \
        if (__builtin_types_compatible_p (typeof (x), long double)) \
          tmp = foo_long_double (tmp);                              \
        else if (__builtin_types_compatible_p (typeof (x), double)) \
          tmp = foo_double (tmp);                                   \
        else if (__builtin_types_compatible_p (typeof (x), float))  \
          tmp = foo_float (tmp);                                    \
        else                                                        \
          abort ();                                                 \
        tmp;                                                        \
      })
    

    Note: This construct is only available for C.

    Built-in Function: type __builtin_choose_expr (const_exp, exp1, exp2)

    You can use the built-in function __builtin_choose_expr to evaluate code depending on the value of a constant expression. This built-in function returns exp1 if const_exp, which is an integer constant expression, is nonzero. Otherwise it returns 0.

    This built-in function is analogous to the `? :' operator in C, except that the expression returned has its type unaltered by promotion rules. Also, the built-in function does not evaluate the expression that was not chosen. For example, if const_exp evaluates to true, exp2 is not evaluated even if it has side-effects.

    This built-in function can return an lvalue if the chosen argument is an lvalue.

    If exp1 is returned, the return type is the same as exp1's type. Similarly, if exp2 is returned, its return type is the same as exp2.

    Example:

     
    #define foo(x)                                                    \
      __builtin_choose_expr (                                         \
        __builtin_types_compatible_p (typeof (x), double),            \
        foo_double (x),                                               \
        __builtin_choose_expr (                                       \
          __builtin_types_compatible_p (typeof (x), float),           \
          foo_float (x),                                              \
          /* The void expression results in a compile-time error  \
             when assigning the result to something.  */          \
          (void)0))
    

    Note: This construct is only available for C. Furthermore, the unused expression (exp1 or exp2 depending on the value of const_exp) may still generate syntax errors. This may change in future revisions.

    Built-in Function: int __builtin_constant_p (exp)
    You can use the built-in function __builtin_constant_p to determine if a value is known to be constant at compile-time and hence that GCC can perform constant-folding on expressions involving that value. The argument of the function is the value to test. The function returns the integer 1 if the argument is known to be a compile-time constant and 0 if it is not known to be a compile-time constant. A return of 0 does not indicate that the value is not a constant, but merely that GCC cannot prove it is a constant with the specified value of the `-O' option.

    You would typically use this function in an embedded application where memory was a critical resource. If you have some complex calculation, you may want it to be folded if it involves constants, but need to call a function if it does not. For example:

     
    #define Scale_Value(X)      \
      (__builtin_constant_p (X) \
      ? ((X) * SCALE + OFFSET) : Scale (X))
    

    You may use this built-in function in either a macro or an inline function. However, if you use it in an inlined function and pass an argument of the function as the argument to the built-in, GCC will never return 1 when you call the inline function with a string constant or compound literal (see section 6.24 Compound Literals) and will not return 1 when you pass a constant numeric value to the inline function unless you specify the `-O' option.

    You may also use __builtin_constant_p in initializers for static data. For instance, you can write

     
    static const int table[] = {
       __builtin_constant_p (EXPRESSION) ? (EXPRESSION) : -1,
       /* ... */
    };
    

    This is an acceptable initializer even if EXPRESSION is not a constant expression, including the case where __builtin_constant_p returns 1 because EXPRESSION can be folded to a constant but EXPRESSION contains operands that would not otherwise be permitted in a static initializer (for example, 0 && foo ()). GCC must be more conservative about evaluating the built-in in this case, because it has no opportunity to perform optimization.

    Previous versions of GCC did not accept this built-in in data initializers. The earliest version where it is completely safe is 3.0.1.

    Built-in Function: long __builtin_expect (long exp, long c)
    You may use __builtin_expect to provide the compiler with branch prediction information. In general, you should prefer to use actual profile feedback for this (`-fprofile-arcs'), as programmers are notoriously bad at predicting how their programs actually perform. However, there are applications in which this data is hard to collect.

    The return value is the value of exp, which should be an integral expression. The semantics of the built-in are that it is expected that exp == c. For example:

     
    if (__builtin_expect (x, 0))
      foo ();
    

    would indicate that we do not expect to call foo, since we expect x to be zero. Since you are limited to integral expressions for exp, you should use constructions such as

     
    if (__builtin_expect (ptr != NULL, 1))
      error ();
    

    when testing pointer or floating-point values.

    Built-in Function: void __builtin_trap (void)
    This function causes the program to exit abnormally. GCC implements this function by using a target-dependent mechanism (such as intentionally executing an illegal instruction) or by calling abort. The mechanism used may vary from release to release so you should not rely on any particular implementation.

    Built-in Function: void __builtin_unreachable (void)
    If control flow reaches the point of the __builtin_unreachable, the program is undefined. It is useful in situations where the compiler cannot deduce the unreachability of the code.

    One such case is immediately following an asm statement that will either never terminate, or one that transfers control elsewhere and never returns. In this example, without the __builtin_unreachable, GCC would issue a warning that control reaches the end of a non-void function. It would also generate code to return after the asm.

     
    int f (int c, int v)
    {
      if (c)
        {
          return v;
        }
      else
        {
          asm("jmp error_handler");
          __builtin_unreachable ();
        }
    }
    

    Because the asm statement unconditionally transfers control out of the function, control will never reach the end of the function body. The __builtin_unreachable is in fact unreachable and communicates this fact to the compiler.

    Another use for __builtin_unreachable is following a call a function that never returns but that is not declared __attribute__((noreturn)), as in this example:

     
    void function_that_never_returns (void);
    
    int g (int c)
    {
      if (c)
        {
          return 1;
        }
      else
        {
          function_that_never_returns ();
          __builtin_unreachable ();
        }
    }
    

    Built-in Function: void __builtin___clear_cache (char *begin, char *end)
    This function is used to flush the processor's instruction cache for the region of memory between begin inclusive and end exclusive. Some targets require that the instruction cache be flushed, after modifying memory containing code, in order to obtain deterministic behavior.

    If the target does not require instruction cache flushes, __builtin___clear_cache has no effect. Otherwise either instructions are emitted in-line to clear the instruction cache or a call to the __clear_cache function in libgcc is made.

    Built-in Function: void __builtin_prefetch (const void *addr, ...)
    This function is used to minimize cache-miss latency by moving data into a cache before it is accessed. You can insert calls to __builtin_prefetch into code for which you know addresses of data in memory that is likely to be accessed soon. If the target supports them, data prefetch instructions will be generated. If the prefetch is done early enough before the access then the data will be in the cache by the time it is accessed.

    The value of addr is the address of the memory to prefetch. There are two optional arguments, rw and locality. The value of rw is a compile-time constant one or zero; one means that the prefetch is preparing for a write to the memory address and zero, the default, means that the prefetch is preparing for a read. The value locality must be a compile-time constant integer between zero and three. A value of zero means that the data has no temporal locality, so it need not be left in the cache after the access. A value of three means that the data has a high degree of temporal locality and should be left in all levels of cache possible. Values of one and two mean, respectively, a low or moderate degree of temporal locality. The default is three.

     
    for (i = 0; i < n; i++)
      {
        a[i] = a[i] + b[i];
        __builtin_prefetch (&a[i+j], 1, 1);
        __builtin_prefetch (&b[i+j], 0, 1);
        /* ... */
      }
    

    Data prefetch does not generate faults if addr is invalid, but the address expression itself must be valid. For example, a prefetch of p->next will not fault if p->next is not a valid address, but evaluation will fault if p is not a valid address.

    If the target does not support data prefetch, the address expression is evaluated if it includes side effects but no other code is generated and GCC does not issue a warning.

    Built-in Function: double __builtin_huge_val (void)
    Returns a positive infinity, if supported by the floating-point format, else DBL_MAX. This function is suitable for implementing the ISO C macro HUGE_VAL.

    Built-in Function: float __builtin_huge_valf (void)
    Similar to __builtin_huge_val, except the return type is float.

    Built-in Function: long double __builtin_huge_vall (void)
    Similar to __builtin_huge_val, except the return type is long double.

    Built-in Function: int __builtin_fpclassify (int, int, int, int, int, ...)
    This built-in implements the C99 fpclassify functionality. The first five int arguments should be the target library's notion of the possible FP classes and are used for return values. They must be constant values and they must appear in this order: FP_NAN, FP_INFINITE, FP_NORMAL, FP_SUBNORMAL and FP_ZERO. The ellipsis is for exactly one floating point value to classify. GCC treats the last argument as type-generic, which means it does not do default promotion from float to double.

    Built-in Function: double __builtin_inf (void)
    Similar to __builtin_huge_val, except a warning is generated if the target floating-point format does not support infinities.

    Built-in Function: _Decimal32 __builtin_infd32 (void)
    Similar to __builtin_inf, except the return type is _Decimal32.

    Built-in Function: _Decimal64 __builtin_infd64 (void)
    Similar to __builtin_inf, except the return type is _Decimal64.

    Built-in Function: _Decimal128 __builtin_infd128 (void)
    Similar to __builtin_inf, except the return type is _Decimal128.

    Built-in Function: float __builtin_inff (void)
    Similar to __builtin_inf, except the return type is float. This function is suitable for implementing the ISO C99 macro INFINITY.

    Built-in Function: long double __builtin_infl (void)
    Similar to __builtin_inf, except the return type is long double.

    Built-in Function: int __builtin_isinf_sign (...)
    Similar to isinf, except the return value will be negative for an argument of -Inf. Note while the parameter list is an ellipsis, this function only accepts exactly one floating point argument. GCC treats this parameter as type-generic, which means it does not do default promotion from float to double.

    Built-in Function: double __builtin_nan (const char *str)
    This is an implementation of the ISO C99 function nan.

    Since ISO C99 defines this function in terms of strtod, which we do not implement, a description of the parsing is in order. The string is parsed as by strtol; that is, the base is recognized by leading `0' or `0x' prefixes. The number parsed is placed in the significand such that the least significant bit of the number is at the least significant bit of the significand. The number is truncated to fit the significand field provided. The significand is forced to be a quiet NaN.

    This function, if given a string literal all of which would have been consumed by strtol, is evaluated early enough that it is considered a compile-time constant.

    Built-in Function: _Decimal32 __builtin_nand32 (const char *str)
    Similar to __builtin_nan, except the return type is _Decimal32.

    Built-in Function: _Decimal64 __builtin_nand64 (const char *str)
    Similar to __builtin_nan, except the return type is _Decimal64.

    Built-in Function: _Decimal128 __builtin_nand128 (const char *str)
    Similar to __builtin_nan, except the return type is _Decimal128.

    Built-in Function: float __builtin_nanf (const char *str)
    Similar to __builtin_nan, except the return type is float.

    Built-in Function: long double __builtin_nanl (const char *str)
    Similar to __builtin_nan, except the return type is long double.

    Built-in Function: double __builtin_nans (const char *str)
    Similar to __builtin_nan, except the significand is forced to be a signaling NaN. The nans function is proposed by WG14 N965.

    Built-in Function: float __builtin_nansf (const char *str)
    Similar to __builtin_nans, except the return type is float.

    Built-in Function: long double __builtin_nansl (const char *str)
    Similar to __builtin_nans, except the return type is long double.

    Built-in Function: int __builtin_ffs (unsigned int x)
    Returns one plus the index of the least significant 1-bit of x, or if x is zero, returns zero.

    Built-in Function: int __builtin_clz (unsigned int x)
    Returns the number of leading 0-bits in x, starting at the most significant bit position. If x is 0, the result is undefined.

    Built-in Function: int __builtin_ctz (unsigned int x)
    Returns the number of trailing 0-bits in x, starting at the least significant bit position. If x is 0, the result is undefined.

    Built-in Function: int __builtin_popcount (unsigned int x)
    Returns the number of 1-bits in x.

    Built-in Function: int __builtin_parity (unsigned int x)
    Returns the parity of x, i.e. the number of 1-bits in x modulo 2.

    Built-in Function: int __builtin_ffsl (unsigned long)
    Similar to __builtin_ffs, except the argument type is unsigned long.

    Built-in Function: int __builtin_clzl (unsigned long)
    Similar to __builtin_clz, except the argument type is unsigned long.

    Built-in Function: int __builtin_ctzl (unsigned long)
    Similar to __builtin_ctz, except the argument type is unsigned long.

    Built-in Function: int __builtin_popcountl (unsigned long)
    Similar to __builtin_popcount, except the argument type is unsigned long.

    Built-in Function: int __builtin_parityl (unsigned long)
    Similar to __builtin_parity, except the argument type is unsigned long.

    Built-in Function: int __builtin_ffsll (unsigned long long)
    Similar to __builtin_ffs, except the argument type is unsigned long long.

    Built-in Function: int __builtin_clzll (unsigned long long)
    Similar to __builtin_clz, except the argument type is unsigned long long.

    Built-in Function: int __builtin_ctzll (unsigned long long)
    Similar to __builtin_ctz, except the argument type is unsigned long long.

    Built-in Function: int __builtin_popcountll (unsigned long long)
    Similar to __builtin_popcount, except the argument type is unsigned long long.

    Built-in Function: int __builtin_parityll (unsigned long long)
    Similar to __builtin_parity, except the argument type is unsigned long long.

    Built-in Function: double __builtin_powi (double, int)
    Returns the first argument raised to the power of the second. Unlike the pow function no guarantees about precision and rounding are made.

    Built-in Function: float __builtin_powif (float, int)
    Similar to __builtin_powi, except the argument and return types are float.

    Built-in Function: long double __builtin_powil (long double, int)
    Similar to __builtin_powi, except the argument and return types are long double.

    Built-in Function: int32_t __builtin_bswap32 (int32_t x)
    Returns x with the order of the bytes reversed; for example, 0xaabbccdd becomes 0xddccbbaa. Byte here always means exactly 8 bits.

    Built-in Function: int64_t __builtin_bswap64 (int64_t x)
    Similar to __builtin_bswap32, except the argument and return types are 64-bit.


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    6.53 Built-in Functions Specific to Particular Target Machines

    On some target machines, GCC supports many built-in functions specific to those machines. Generally these generate calls to specific machine instructions, but allow the compiler to schedule those calls.

    6.53.1 Alpha Built-in Functions  
    6.53.2 ARM iWMMXt Built-in Functions  
    6.53.3 ARM NEON Intrinsics  
    6.53.4 Blackfin Built-in Functions  
    6.53.5 FR-V Built-in Functions  
    6.53.6 X86 Built-in Functions  
    6.53.7 MIPS DSP Built-in Functions  
    6.53.8 MIPS Paired-Single Support  
    6.53.9 MIPS Loongson Built-in Functions  
    6.53.11 Other MIPS Built-in Functions  
    6.53.10 picoChip Built-in Functions  
    6.53.12 PowerPC AltiVec Built-in Functions  
    6.53.13 RX Built-in Functions  
    6.53.14 SPARC VIS Built-in Functions  
    6.53.15 SPU Built-in Functions  


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    6.53.1 Alpha Built-in Functions

    These built-in functions are available for the Alpha family of processors, depending on the command-line switches used.

    The following built-in functions are always available. They all generate the machine instruction that is part of the name.

     
    long __builtin_alpha_implver (void)
    long __builtin_alpha_rpcc (void)
    long __builtin_alpha_amask (long)
    long __builtin_alpha_cmpbge (long, long)
    long __builtin_alpha_extbl (long, long)
    long __builtin_alpha_extwl (long, long)
    long __builtin_alpha_extll (long, long)
    long __builtin_alpha_extql (long, long)
    long __builtin_alpha_extwh (long, long)
    long __builtin_alpha_extlh (long, long)
    long __builtin_alpha_extqh (long, long)
    long __builtin_alpha_insbl (long, long)
    long __builtin_alpha_inswl (long, long)
    long __builtin_alpha_insll (long, long)
    long __builtin_alpha_insql (long, long)
    long __builtin_alpha_inswh (long, long)
    long __builtin_alpha_inslh (long, long)
    long __builtin_alpha_insqh (long, long)
    long __builtin_alpha_mskbl (long, long)
    long __builtin_alpha_mskwl (long, long)
    long __builtin_alpha_mskll (long, long)
    long __builtin_alpha_mskql (long, long)
    long __builtin_alpha_mskwh (long, long)
    long __builtin_alpha_msklh (long, long)
    long __builtin_alpha_mskqh (long, long)
    long __builtin_alpha_umulh (long, long)
    long __builtin_alpha_zap (long, long)
    long __builtin_alpha_zapnot (long, long)
    

    The following built-in functions are always with `-mmax' or `-mcpu=cpu' where cpu is pca56 or later. They all generate the machine instruction that is part of the name.

     
    long __builtin_alpha_pklb (long)
    long __builtin_alpha_pkwb (long)
    long __builtin_alpha_unpkbl (long)
    long __builtin_alpha_unpkbw (long)
    long __builtin_alpha_minub8 (long, long)
    long __builtin_alpha_minsb8 (long, long)
    long __builtin_alpha_minuw4 (long, long)
    long __builtin_alpha_minsw4 (long, long)
    long __builtin_alpha_maxub8 (long, long)
    long __builtin_alpha_maxsb8 (long, long)
    long __builtin_alpha_maxuw4 (long, long)
    long __builtin_alpha_maxsw4 (long, long)
    long __builtin_alpha_perr (long, long)
    

    The following built-in functions are always with `-mcix' or `-mcpu=cpu' where cpu is ev67 or later. They all generate the machine instruction that is part of the name.

     
    long __builtin_alpha_cttz (long)
    long __builtin_alpha_ctlz (long)
    long __builtin_alpha_ctpop (long)
    

    The following builtins are available on systems that use the OSF/1 PALcode. Normally they invoke the rduniq and wruniq PAL calls, but when invoked with `-mtls-kernel', they invoke rdval and wrval.

     
    void *__builtin_thread_pointer (void)
    void __builtin_set_thread_pointer (void *)
    


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    6.53.2 ARM iWMMXt Built-in Functions

    These built-in functions are available for the ARM family of processors when the `-mcpu=iwmmxt' switch is used:

     
    typedef int v2si __attribute__ ((vector_size (8)));
    typedef short v4hi __attribute__ ((vector_size (8)));
    typedef char v8qi __attribute__ ((vector_size (8)));
    
    int __builtin_arm_getwcx (int)
    void __builtin_arm_setwcx (int, int)
    int __builtin_arm_textrmsb (v8qi, int)
    int __builtin_arm_textrmsh (v4hi, int)
    int __builtin_arm_textrmsw (v2si, int)
    int __builtin_arm_textrmub (v8qi, int)
    int __builtin_arm_textrmuh (v4hi, int)
    int __builtin_arm_textrmuw (v2si, int)
    v8qi __builtin_arm_tinsrb (v8qi, int)
    v4hi __builtin_arm_tinsrh (v4hi, int)
    v2si __builtin_arm_tinsrw (v2si, int)
    long long __builtin_arm_tmia (long long, int, int)
    long long __builtin_arm_tmiabb (long long, int, int)
    long long __builtin_arm_tmiabt (long long, int, int)
    long long __builtin_arm_tmiaph (long long, int, int)
    long long __builtin_arm_tmiatb (long long, int, int)
    long long __builtin_arm_tmiatt (long long, int, int)
    int __builtin_arm_tmovmskb (v8qi)
    int __builtin_arm_tmovmskh (v4hi)
    int __builtin_arm_tmovmskw (v2si)
    long long __builtin_arm_waccb (v8qi)
    long long __builtin_arm_wacch (v4hi)
    long long __builtin_arm_waccw (v2si)
    v8qi __builtin_arm_waddb (v8qi, v8qi)
    v8qi __builtin_arm_waddbss (v8qi, v8qi)
    v8qi __builtin_arm_waddbus (v8qi, v8qi)
    v4hi __builtin_arm_waddh (v4hi, v4hi)
    v4hi __builtin_arm_waddhss (v4hi, v4hi)
    v4hi __builtin_arm_waddhus (v4hi, v4hi)
    v2si __builtin_arm_waddw (v2si, v2si)
    v2si __builtin_arm_waddwss (v2si, v2si)
    v2si __builtin_arm_waddwus (v2si, v2si)
    v8qi __builtin_arm_walign (v8qi, v8qi, int)
    long long __builtin_arm_wand(long long, long long)
    long long __builtin_arm_wandn (long long, long long)
    v8qi __builtin_arm_wavg2b (v8qi, v8qi)
    v8qi __builtin_arm_wavg2br (v8qi, v8qi)
    v4hi __builtin_arm_wavg2h (v4hi, v4hi)
    v4hi __builtin_arm_wavg2hr (v4hi, v4hi)
    v8qi __builtin_arm_wcmpeqb (v8qi, v8qi)
    v4hi __builtin_arm_wcmpeqh (v4hi, v4hi)
    v2si __builtin_arm_wcmpeqw (v2si, v2si)
    v8qi __builtin_arm_wcmpgtsb (v8qi, v8qi)
    v4hi __builtin_arm_wcmpgtsh (v4hi, v4hi)
    v2si __builtin_arm_wcmpgtsw (v2si, v2si)
    v8qi __builtin_arm_wcmpgtub (v8qi, v8qi)
    v4hi __builtin_arm_wcmpgtuh (v4hi, v4hi)
    v2si __builtin_arm_wcmpgtuw (v2si, v2si)
    long long __builtin_arm_wmacs (long long, v4hi, v4hi)
    long long __builtin_arm_wmacsz (v4hi, v4hi)
    long long __builtin_arm_wmacu (long long, v4hi, v4hi)
    long long __builtin_arm_wmacuz (v4hi, v4hi)
    v4hi __builtin_arm_wmadds (v4hi, v4hi)
    v4hi __builtin_arm_wmaddu (v4hi, v4hi)
    v8qi __builtin_arm_wmaxsb (v8qi, v8qi)
    v4hi __builtin_arm_wmaxsh (v4hi, v4hi)
    v2si __builtin_arm_wmaxsw (v2si, v2si)
    v8qi __builtin_arm_wmaxub (v8qi, v8qi)
    v4hi __builtin_arm_wmaxuh (v4hi, v4hi)
    v2si __builtin_arm_wmaxuw (v2si, v2si)
    v8qi __builtin_arm_wminsb (v8qi, v8qi)
    v4hi __builtin_arm_wminsh (v4hi, v4hi)
    v2si __builtin_arm_wminsw (v2si, v2si)
    v8qi __builtin_arm_wminub (v8qi, v8qi)
    v4hi __builtin_arm_wminuh (v4hi, v4hi)
    v2si __builtin_arm_wminuw (v2si, v2si)
    v4hi __builtin_arm_wmulsm (v4hi, v4hi)
    v4hi __builtin_arm_wmulul (v4hi, v4hi)
    v4hi __builtin_arm_wmulum (v4hi, v4hi)
    long long __builtin_arm_wor (long long, long long)
    v2si __builtin_arm_wpackdss (long long, long long)
    v2si __builtin_arm_wpackdus (long long, long long)
    v8qi __builtin_arm_wpackhss (v4hi, v4hi)
    v8qi __builtin_arm_wpackhus (v4hi, v4hi)
    v4hi __builtin_arm_wpackwss (v2si, v2si)
    v4hi __builtin_arm_wpackwus (v2si, v2si)
    long long __builtin_arm_wrord (long long, long long)
    long long __builtin_arm_wrordi (long long, int)
    v4hi __builtin_arm_wrorh (v4hi, long long)
    v4hi __builtin_arm_wrorhi (v4hi, int)
    v2si __builtin_arm_wrorw (v2si, long long)
    v2si __builtin_arm_wrorwi (v2si, int)
    v2si __builtin_arm_wsadb (v8qi, v8qi)
    v2si __builtin_arm_wsadbz (v8qi, v8qi)
    v2si __builtin_arm_wsadh (v4hi, v4hi)
    v2si __builtin_arm_wsadhz (v4hi, v4hi)
    v4hi __builtin_arm_wshufh (v4hi, int)
    long long __builtin_arm_wslld (long long, long long)
    long long __builtin_arm_wslldi (long long, int)
    v4hi __builtin_arm_wsllh (v4hi, long long)
    v4hi __builtin_arm_wsllhi (v4hi, int)
    v2si __builtin_arm_wsllw (v2si, long long)
    v2si __builtin_arm_wsllwi (v2si, int)
    long long __builtin_arm_wsrad (long long, long long)
    long long __builtin_arm_wsradi (long long, int)
    v4hi __builtin_arm_wsrah (v4hi, long long)
    v4hi __builtin_arm_wsrahi (v4hi, int)
    v2si __builtin_arm_wsraw (v2si, long long)
    v2si __builtin_arm_wsrawi (v2si, int)
    long long __builtin_arm_wsrld (long long, long long)
    long long __builtin_arm_wsrldi (long long, int)
    v4hi __builtin_arm_wsrlh (v4hi, long long)
    v4hi __builtin_arm_wsrlhi (v4hi, int)
    v2si __builtin_arm_wsrlw (v2si, long long)
    v2si __builtin_arm_wsrlwi (v2si, int)
    v8qi __builtin_arm_wsubb (v8qi, v8qi)
    v8qi __builtin_arm_wsubbss (v8qi, v8qi)
    v8qi __builtin_arm_wsubbus (v8qi, v8qi)
    v4hi __builtin_arm_wsubh (v4hi, v4hi)
    v4hi __builtin_arm_wsubhss (v4hi, v4hi)
    v4hi __builtin_arm_wsubhus (v4hi, v4hi)
    v2si __builtin_arm_wsubw (v2si, v2si)
    v2si __builtin_arm_wsubwss (v2si, v2si)
    v2si __builtin_arm_wsubwus (v2si, v2si)
    v4hi __builtin_arm_wunpckehsb (v8qi)
    v2si __builtin_arm_wunpckehsh (v4hi)
    long long __builtin_arm_wunpckehsw (v2si)
    v4hi __builtin_arm_wunpckehub (v8qi)
    v2si __builtin_arm_wunpckehuh (v4hi)
    long long __builtin_arm_wunpckehuw (v2si)
    v4hi __builtin_arm_wunpckelsb (v8qi)
    v2si __builtin_arm_wunpckelsh (v4hi)
    long long __builtin_arm_wunpckelsw (v2si)
    v4hi __builtin_arm_wunpckelub (v8qi)
    v2si __builtin_arm_wunpckeluh (v4hi)
    long long __builtin_arm_wunpckeluw (v2si)
    v8qi __builtin_arm_wunpckihb (v8qi, v8qi)
    v4hi __builtin_arm_wunpckihh (v4hi, v4hi)
    v2si __builtin_arm_wunpckihw (v2si, v2si)
    v8qi __builtin_arm_wunpckilb (v8qi, v8qi)
    v4hi __builtin_arm_wunpckilh (v4hi, v4hi)
    v2si __builtin_arm_wunpckilw (v2si, v2si)
    long long __builtin_arm_wxor (long long, long long)
    long long __builtin_arm_wzero ()
    


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    6.53.3 ARM NEON Intrinsics

    These built-in intrinsics for the ARM Advanced SIMD extension are available when the `-mfpu=neon' switch is used:


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    6.53.3.1 Addition


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    6.53.3.2 Multiplication


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    6.53.3.3 Multiply-accumulate


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    6.53.3.4 Multiply-subtract


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    6.53.3.5 Subtraction


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    6.53.3.6 Comparison (equal-to)


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    6.53.3.7 Comparison (greater-than-or-equal-to)


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    6.53.3.8 Comparison (less-than-or-equal-to)


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    6.53.3.9 Comparison (greater-than)


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    6.53.3.10 Comparison (less-than)


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    6.53.3.11 Comparison (absolute greater-than-or-equal-to)


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    6.53.3.12 Comparison (absolute less-than-or-equal-to)


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    6.53.3.13 Comparison (absolute greater-than)


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    6.53.3.14 Comparison (absolute less-than)


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    6.53.3.15 Test bits


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    6.53.3.16 Absolute difference


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    6.53.3.17 Absolute difference and accumulate


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    6.53.3.18 Maximum


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    6.53.3.19 Minimum


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    6.53.3.20 Pairwise add


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    6.53.3.21 Pairwise add, single_opcode widen and accumulate


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    6.53.3.22 Folding maximum


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    6.53.3.23 Folding minimum


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    6.53.3.24 Reciprocal step


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    6.53.3.25 Vector shift left


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    6.53.3.26 Vector shift left by constant


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    6.53.3.27 Vector shift right by constant


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    6.53.3.28 Vector shift right by constant and accumulate


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    6.53.3.29 Vector shift right and insert


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    6.53.3.30 Vector shift left and insert


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    6.53.3.31 Absolute value


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    6.53.3.32 Negation


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    6.53.3.33 Bitwise not


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    6.53.3.34 Count leading sign bits


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    6.53.3.35 Count leading zeros


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    6.53.3.36 Count number of set bits


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    6.53.3.37 Reciprocal estimate


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    6.53.3.38 Reciprocal square-root estimate


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    6.53.3.39 Get lanes from a vector


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    6.53.3.40 Set lanes in a vector


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    6.53.3.41 Create vector from literal bit pattern


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    6.53.3.42 Set all lanes to the same value


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    6.53.3.43 Combining vectors


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    6.53.3.44 Splitting vectors


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    6.53.3.45 Conversions


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    6.53.3.46 Move, single_opcode narrowing


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    6.53.3.47 Move, single_opcode long


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    6.53.3.48 Table lookup


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    6.53.3.49 Extended table lookup


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    6.53.3.50 Multiply, lane


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    6.53.3.51 Long multiply, lane


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    6.53.3.52 Saturating doubling long multiply, lane


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    6.53.3.53 Saturating doubling multiply high, lane


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    6.53.3.54 Multiply-accumulate, lane


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    6.53.3.55 Multiply-subtract, lane


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    6.53.3.56 Vector multiply by scalar


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    6.53.3.57 Vector long multiply by scalar


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    6.53.3.58 Vector saturating doubling long multiply by scalar


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    6.53.3.59 Vector saturating doubling multiply high by scalar


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    6.53.3.60 Vector multiply-accumulate by scalar


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    6.53.3.61 Vector multiply-subtract by scalar


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    6.53.3.62 Vector extract


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    6.53.3.63 Reverse elements


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    6.53.3.64 Bit selection


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    6.53.3.65 Transpose elements


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    6.53.3.66 Zip elements


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    6.53.3.67 Unzip elements


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    6.53.3.68 Element/structure loads, VLD1 variants


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    6.53.3.69 Element/structure stores, VST1 variants


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    6.53.3.70 Element/structure loads, VLD2 variants


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    6.53.3.71 Element/structure stores, VST2 variants


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    6.53.3.72 Element/structure loads, VLD3 variants


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    6.53.3.73 Element/structure stores, VST3 variants


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    6.53.3.74 Element/structure loads, VLD4 variants


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    6.53.3.75 Element/structure stores, VST4 variants


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    6.53.3.76 Logical operations (AND)


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    6.53.3.77 Logical operations (OR)


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    6.53.3.78 Logical operations (exclusive OR)


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    6.53.3.79 Logical operations (AND-NOT)


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    6.53.3.80 Logical operations (OR-NOT)


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    6.53.3.81 Reinterpret casts


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    6.53.4 Blackfin Built-in Functions

    Currently, there are two Blackfin-specific built-in functions. These are used for generating CSYNC and SSYNC machine insns without using inline assembly; by using these built-in functions the compiler can automatically add workarounds for hardware errata involving these instructions. These functions are named as follows:

     
    void __builtin_bfin_csync (void)
    void __builtin_bfin_ssync (void)
    


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    6.53.5 FR-V Built-in Functions

    GCC provides many FR-V-specific built-in functions. In general, these functions are intended to be compatible with those described by FR-V Family, Softune C/C++ Compiler Manual (V6), Fujitsu Semiconductor. The two exceptions are __MDUNPACKH and __MBTOHE, the gcc forms of which pass 128-bit values by pointer rather than by value.

    Most of the functions are named after specific FR-V instructions. Such functions are said to be "directly mapped" and are summarized here in tabular form.

    6.53.5.1 Argument Types  
    6.53.5.2 Directly-mapped Integer Functions  
    6.53.5.3 Directly-mapped Media Functions  
    6.53.5.4 Raw read/write Functions  
    6.53.5.5 Other Built-in Functions  


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    6.53.5.1 Argument Types

    The arguments to the built-in functions can be divided into three groups: register numbers, compile-time constants and run-time values. In order to make this classification clear at a glance, the arguments and return values are given the following pseudo types:

    Pseudo type Real C type Constant? Description
    uh unsigned short No an unsigned halfword
    uw1 unsigned int No an unsigned word
    sw1 int No a signed word
    uw2 unsigned long long No an unsigned doubleword
    sw2 long long No a signed doubleword
    const int Yes an integer constant
    acc int Yes an ACC register number
    iacc int Yes an IACC register number

    These pseudo types are not defined by GCC, they are simply a notational convenience used in this manual.

    Arguments of type uh, uw1, sw1, uw2 and sw2 are evaluated at run time. They correspond to register operands in the underlying FR-V instructions.

    const arguments represent immediate operands in the underlying FR-V instructions. They must be compile-time constants.

    acc arguments are evaluated at compile time and specify the number of an accumulator register. For example, an acc argument of 2 will select the ACC2 register.

    iacc arguments are similar to acc arguments but specify the number of an IACC register. See see section 6.53.5.5 Other Built-in Functions for more details.


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    6.53.5.2 Directly-mapped Integer Functions

    The functions listed below map directly to FR-V I-type instructions.

    Function prototype Example usage Assembly output
    sw1 __ADDSS (sw1, sw1) c = __ADDSS (a, b) ADDSS a,b,c
    sw1 __SCAN (sw1, sw1) c = __SCAN (a, b) SCAN a,b,c
    sw1 __SCUTSS (sw1) b = __SCUTSS (a) SCUTSS a,b
    sw1 __SLASS (sw1, sw1) c = __SLASS (a, b) SLASS a,b,c
    void __SMASS (sw1, sw1) __SMASS (a, b) SMASS a,b
    void __SMSSS (sw1, sw1) __SMSSS (a, b) SMSSS a,b
    void __SMU (sw1, sw1) __SMU (a, b) SMU a,b
    sw2 __SMUL (sw1, sw1) c = __SMUL (a, b) SMUL a,b,c
    sw1 __SUBSS (sw1, sw1) c = __SUBSS (a, b) SUBSS a,b,c
    uw2 __UMUL (uw1, uw1) c = __UMUL (a, b) UMUL a,b,c


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    6.53.5.3 Directly-mapped Media Functions

    The functions listed below map directly to FR-V M-type instructions.

    Function prototype Example usage Assembly output
    uw1 __MABSHS (sw1) b = __MABSHS (a) MABSHS a,b
    void __MADDACCS (acc, acc) __MADDACCS (b, a) MADDACCS a,b
    sw1 __MADDHSS (sw1, sw1) c = __MADDHSS (a, b) MADDHSS a,b,c
    uw1 __MADDHUS (uw1, uw1) c = __MADDHUS (a, b) MADDHUS a,b,c
    uw1 __MAND (uw1, uw1) c = __MAND (a, b) MAND a,b,c
    void __MASACCS (acc, acc) __MASACCS (b, a) MASACCS a,b
    uw1 __MAVEH (uw1, uw1) c = __MAVEH (a, b) MAVEH a,b,c
    uw2 __MBTOH (uw1) b = __MBTOH (a) MBTOH a,b
    void __MBTOHE (uw1 *, uw1) __MBTOHE (&b, a) MBTOHE a,b
    void __MCLRACC (acc) __MCLRACC (a) MCLRACC a
    void __MCLRACCA (void) __MCLRACCA () MCLRACCA
    uw1 __Mcop1 (uw1, uw1) c = __Mcop1 (a, b) Mcop1 a,b,c
    uw1 __Mcop2 (uw1, uw1) c = __Mcop2 (a, b) Mcop2 a,b,c
    uw1 __MCPLHI (uw2, const) c = __MCPLHI (a, b) MCPLHI a,#b,c
    uw1 __MCPLI (uw2, const) c = __MCPLI (a, b) MCPLI a,#b,c
    void __MCPXIS (acc, sw1, sw1) __MCPXIS (c, a, b) MCPXIS a,b,c
    void __MCPXIU (acc, uw1, uw1) __MCPXIU (c, a, b) MCPXIU a,b,c
    void __MCPXRS (acc, sw1, sw1) __MCPXRS (c, a, b) MCPXRS a,b,c
    void __MCPXRU (acc, uw1, uw1) __MCPXRU (c, a, b) MCPXRU a,b,c
    uw1 __MCUT (acc, uw1) c = __MCUT (a, b) MCUT a,b,c
    uw1 __MCUTSS (acc, sw1) c = __MCUTSS (a, b) MCUTSS a,b,c
    void __MDADDACCS (acc, acc) __MDADDACCS (b, a) MDADDACCS a,b
    void __MDASACCS (acc, acc) __MDASACCS (b, a) MDASACCS a,b
    uw2 __MDCUTSSI (acc, const) c = __MDCUTSSI (a, b) MDCUTSSI a,#b,c
    uw2 __MDPACKH (uw2, uw2) c = __MDPACKH (a, b) MDPACKH a,b,c
    uw2 __MDROTLI (uw2, const) c = __MDROTLI (a, b) MDROTLI a,#b,c
    void __MDSUBACCS (acc, acc) __MDSUBACCS (b, a) MDSUBACCS a,b
    void __MDUNPACKH (uw1 *, uw2) __MDUNPACKH (&b, a) MDUNPACKH a,b
    uw2 __MEXPDHD (uw1, const) c = __MEXPDHD (a, b) MEXPDHD a,#b,c
    uw1 __MEXPDHW (uw1, const) c = __MEXPDHW (a, b) MEXPDHW a,#b,c
    uw1 __MHDSETH (uw1, const) c = __MHDSETH (a, b) MHDSETH a,#b,c
    sw1 __MHDSETS (const) b = __MHDSETS (a) MHDSETS #a,b
    uw1 __MHSETHIH (uw1, const) b = __MHSETHIH (b, a) MHSETHIH #a,b
    sw1 __MHSETHIS (sw1, const) b = __MHSETHIS (b, a) MHSETHIS #a,b
    uw1 __MHSETLOH (uw1, const) b = __MHSETLOH (b, a) MHSETLOH #a,b
    sw1 __MHSETLOS (sw1, const) b = __MHSETLOS (b, a) MHSETLOS #a,b
    uw1 __MHTOB (uw2) b = __MHTOB (a) MHTOB a,b
    void __MMACHS (acc, sw1, sw1) __MMACHS (c, a, b) MMACHS a,b,c
    void __MMACHU (acc, uw1, uw1) __MMACHU (c, a, b) MMACHU a,b,c
    void __MMRDHS (acc, sw1, sw1) __MMRDHS (c, a, b) MMRDHS a,b,c
    void __MMRDHU (acc, uw1, uw1) __MMRDHU (c, a, b) MMRDHU a,b,c
    void __MMULHS (acc, sw1, sw1) __MMULHS (c, a, b) MMULHS a,b,c
    void __MMULHU (acc, uw1, uw1) __MMULHU (c, a, b) MMULHU a,b,c
    void __MMULXHS (acc, sw1, sw1) __MMULXHS (c, a, b) MMULXHS a,b,c
    void __MMULXHU (acc, uw1, uw1) __MMULXHU (c, a, b) MMULXHU a,b,c
    uw1 __MNOT (uw1) b = __MNOT (a) MNOT a,b
    uw1 __MOR (uw1, uw1) c = __MOR (a, b) MOR a,b,c
    uw1 __MPACKH (uh, uh) c = __MPACKH (a, b) MPACKH a,b,c
    sw2 __MQADDHSS (sw2, sw2) c = __MQADDHSS (a, b) MQADDHSS a,b,c
    uw2 __MQADDHUS (uw2, uw2) c = __MQADDHUS (a, b) MQADDHUS a,b,c
    void __MQCPXIS (acc, sw2, sw2) __MQCPXIS (c, a, b) MQCPXIS a,b,c
    void __MQCPXIU (acc, uw2, uw2) __MQCPXIU (c, a, b) MQCPXIU a,b,c
    void __MQCPXRS (acc, sw2, sw2) __MQCPXRS (c, a, b) MQCPXRS a,b,c
    void __MQCPXRU (acc, uw2, uw2) __MQCPXRU (c, a, b) MQCPXRU a,b,c
    sw2 __MQLCLRHS (sw2, sw2) c = __MQLCLRHS (a, b) MQLCLRHS a,b,c
    sw2 __MQLMTHS (sw2, sw2) c = __MQLMTHS (a, b) MQLMTHS a,b,c
    void __MQMACHS (acc, sw2, sw2) __MQMACHS (c, a, b) MQMACHS a,b,c
    void __MQMACHU (acc, uw2, uw2) __MQMACHU (c, a, b) MQMACHU a,b,c
    void __MQMACXHS (acc, sw2, sw2) __MQMACXHS (c, a, b) MQMACXHS a,b,c
    void __MQMULHS (acc, sw2, sw2) __MQMULHS (c, a, b) MQMULHS a,b,c
    void __MQMULHU (acc, uw2, uw2) __MQMULHU (c, a, b) MQMULHU a,b,c
    void __MQMULXHS (acc, sw2, sw2) __MQMULXHS (c, a, b) MQMULXHS a,b,c
    void __MQMULXHU (acc, uw2, uw2) __MQMULXHU (c, a, b) MQMULXHU a,b,c
    sw2 __MQSATHS (sw2, sw2) c = __MQSATHS (a, b) MQSATHS a,b,c
    uw2 __MQSLLHI (uw2, int) c = __MQSLLHI (a, b) MQSLLHI a,b,c
    sw2 __MQSRAHI (sw2, int) c = __MQSRAHI (a, b) MQSRAHI a,b,c
    sw2 __MQSUBHSS (sw2, sw2) c = __MQSUBHSS (a, b) MQSUBHSS a,b,c
    uw2 __MQSUBHUS (uw2, uw2) c = __MQSUBHUS (a, b) MQSUBHUS a,b,c
    void __MQXMACHS (acc, sw2, sw2) __MQXMACHS (c, a, b) MQXMACHS a,b,c
    void __MQXMACXHS (acc, sw2, sw2) __MQXMACXHS (c, a, b) MQXMACXHS a,b,c
    uw1 __MRDACC (acc) b = __MRDACC (a) MRDACC a,b
    uw1 __MRDACCG (acc) b = __MRDACCG (a) MRDACCG a,b
    uw1 __MROTLI (uw1, const) c = __MROTLI (a, b) MROTLI a,#b,c
    uw1 __MROTRI (uw1, const) c = __MROTRI (a, b) MROTRI a,#b,c
    sw1 __MSATHS (sw1, sw1) c = __MSATHS (a, b) MSATHS a,b,c
    uw1 __MSATHU (uw1, uw1) c = __MSATHU (a, b) MSATHU a,b,c
    uw1 __MSLLHI (uw1, const) c = __MSLLHI (a, b) MSLLHI a,#b,c
    sw1 __MSRAHI (sw1, const) c = __MSRAHI (a, b) MSRAHI a,#b,c
    uw1 __MSRLHI (uw1, const) c = __MSRLHI (a, b) MSRLHI a,#b,c
    void __MSUBACCS (acc, acc) __MSUBACCS (b, a) MSUBACCS a,b
    sw1 __MSUBHSS (sw1, sw1) c = __MSUBHSS (a, b) MSUBHSS a,b,c
    uw1 __MSUBHUS (uw1, uw1) c = __MSUBHUS (a, b) MSUBHUS a,b,c
    void __MTRAP (void) __MTRAP () MTRAP
    uw2 __MUNPACKH (uw1) b = __MUNPACKH (a) MUNPACKH a,b
    uw1 __MWCUT (uw2, uw1) c = __MWCUT (a, b) MWCUT a,b,c
    void __MWTACC (acc, uw1) __MWTACC (b, a) MWTACC a,b
    void __MWTACCG (acc, uw1) __MWTACCG (b, a) MWTACCG a,b
    uw1 __MXOR (uw1, uw1) c = __MXOR (a, b) MXOR a,b,c


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    6.53.5.4 Raw read/write Functions

    This sections describes built-in functions related to read and write instructions to access memory. These functions generate membar instructions to flush the I/O load and stores where appropriate, as described in Fujitsu's manual described above.

    unsigned char __builtin_read8 (void *data)
    unsigned short __builtin_read16 (void *data)
    unsigned long __builtin_read32 (void *data)
    unsigned long long __builtin_read64 (void *data)

    void __builtin_write8 (void *data, unsigned char datum)
    void __builtin_write16 (void *data, unsigned short datum)
    void __builtin_write32 (void *data, unsigned long datum)
    void __builtin_write64 (void *data, unsigned long long datum)


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    6.53.5.5 Other Built-in Functions

    This section describes built-in functions that are not named after a specific FR-V instruction.

    sw2 __IACCreadll (iacc reg)
    Return the full 64-bit value of IACC0. The reg argument is reserved for future expansion and must be 0.

    sw1 __IACCreadl (iacc reg)
    Return the value of IACC0H if reg is 0 and IACC0L if reg is 1. Other values of reg are rejected as invalid.

    void __IACCsetll (iacc reg, sw2 x)
    Set the full 64-bit value of IACC0 to x. The reg argument is reserved for future expansion and must be 0.

    void __IACCsetl (iacc reg, sw1 x)
    Set IACC0H to x if reg is 0 and IACC0L to x if reg is 1. Other values of reg are rejected as invalid.

    void __data_prefetch0 (const void *x)
    Use the dcpl instruction to load the contents of address x into the data cache.

    void __data_prefetch (const void *x)
    Use the nldub instruction to load the contents of address x into the data cache. The instruction will be issued in slot I1.


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    6.53.6 X86 Built-in Functions

    These built-in functions are available for the i386 and x86-64 family of computers, depending on the command-line switches used.

    Note that, if you specify command-line switches such as `-msse', the compiler could use the extended instruction sets even if the built-ins are not used explicitly in the program. For this reason, applications which perform runtime CPU detection must compile separate files for each supported architecture, using the appropriate flags. In particular, the file containing the CPU detection code should be compiled without these options.

    The following machine modes are available for use with MMX built-in functions (see section 6.47 Using vector instructions through built-in functions): V2SI for a vector of two 32-bit integers, V4HI for a vector of four 16-bit integers, and V8QI for a vector of eight 8-bit integers. Some of the built-in functions operate on MMX registers as a whole 64-bit entity, these use V1DI as their mode.

    If 3DNow! extensions are enabled, V2SF is used as a mode for a vector of two 32-bit floating point values.

    If SSE extensions are enabled, V4SF is used for a vector of four 32-bit floating point values. Some instructions use a vector of four 32-bit integers, these use V4SI. Finally, some instructions operate on an entire vector register, interpreting it as a 128-bit integer, these use mode TI.

    In 64-bit mode, the x86-64 family of processors uses additional built-in functions for efficient use of TF (__float128) 128-bit floating point and TC 128-bit complex floating point values.

    The following floating point built-in functions are available in 64-bit mode. All of them implement the function that is part of the name.

     
    __float128 __builtin_fabsq (__float128)
    __float128 __builtin_copysignq (__float128, __float128)
    

    The following floating point built-in functions are made available in the 64-bit mode.

    __float128 __builtin_infq (void)
    Similar to __builtin_inf, except the return type is __float128.

    __float128 __builtin_huge_valq (void)
    Similar to __builtin_huge_val, except the return type is __float128.

    The following built-in functions are made available by `-mmmx'. All of them generate the machine instruction that is part of the name.

     
    v8qi __builtin_ia32_paddb (v8qi, v8qi)
    v4hi __builtin_ia32_paddw (v4hi, v4hi)
    v2si __builtin_ia32_paddd (v2si, v2si)
    v8qi __builtin_ia32_psubb (v8qi, v8qi)
    v4hi __builtin_ia32_psubw (v4hi, v4hi)
    v2si __builtin_ia32_psubd (v2si, v2si)
    v8qi __builtin_ia32_paddsb (v8qi, v8qi)
    v4hi __builtin_ia32_paddsw (v4hi, v4hi)
    v8qi __builtin_ia32_psubsb (v8qi, v8qi)
    v4hi __builtin_ia32_psubsw (v4hi, v4hi)
    v8qi __builtin_ia32_paddusb (v8qi, v8qi)
    v4hi __builtin_ia32_paddusw (v4hi, v4hi)
    v8qi __builtin_ia32_psubusb (v8qi, v8qi)
    v4hi __builtin_ia32_psubusw (v4hi, v4hi)
    v4hi __builtin_ia32_pmullw (v4hi, v4hi)
    v4hi __builtin_ia32_pmulhw (v4hi, v4hi)
    di __builtin_ia32_pand (di, di)
    di __builtin_ia32_pandn (di,di)
    di __builtin_ia32_por (di, di)
    di __builtin_ia32_pxor (di, di)
    v8qi __builtin_ia32_pcmpeqb (v8qi, v8qi)
    v4hi __builtin_ia32_pcmpeqw (v4hi, v4hi)
    v2si __builtin_ia32_pcmpeqd (v2si, v2si)
    v8qi __builtin_ia32_pcmpgtb (v8qi, v8qi)
    v4hi __builtin_ia32_pcmpgtw (v4hi, v4hi)
    v2si __builtin_ia32_pcmpgtd (v2si, v2si)
    v8qi __builtin_ia32_punpckhbw (v8qi, v8qi)
    v4hi __builtin_ia32_punpckhwd (v4hi, v4hi)
    v2si __builtin_ia32_punpckhdq (v2si, v2si)
    v8qi __builtin_ia32_punpcklbw (v8qi, v8qi)
    v4hi __builtin_ia32_punpcklwd (v4hi, v4hi)
    v2si __builtin_ia32_punpckldq (v2si, v2si)
    v8qi __builtin_ia32_packsswb (v4hi, v4hi)
    v4hi __builtin_ia32_packssdw (v2si, v2si)
    v8qi __builtin_ia32_packuswb (v4hi, v4hi)
    
    v4hi __builtin_ia32_psllw (v4hi, v4hi)
    v2si __builtin_ia32_pslld (v2si, v2si)
    v1di __builtin_ia32_psllq (v1di, v1di)
    v4hi __builtin_ia32_psrlw (v4hi, v4hi)
    v2si __builtin_ia32_psrld (v2si, v2si)
    v1di __builtin_ia32_psrlq (v1di, v1di)
    v4hi __builtin_ia32_psraw (v4hi, v4hi)
    v2si __builtin_ia32_psrad (v2si, v2si)
    v4hi __builtin_ia32_psllwi (v4hi, int)
    v2si __builtin_ia32_pslldi (v2si, int)
    v1di __builtin_ia32_psllqi (v1di, int)
    v4hi __builtin_ia32_psrlwi (v4hi, int)
    v2si __builtin_ia32_psrldi (v2si, int)
    v1di __builtin_ia32_psrlqi (v1di, int)
    v4hi __builtin_ia32_psrawi (v4hi, int)
    v2si __builtin_ia32_psradi (v2si, int)
    
    

    The following built-in functions are made available either with `-msse', or with a combination of `-m3dnow' and `-march=athlon'. All of them generate the machine instruction that is part of the name.

     
    v4hi __builtin_ia32_pmulhuw (v4hi, v4hi)
    v8qi __builtin_ia32_pavgb (v8qi, v8qi)
    v4hi __builtin_ia32_pavgw (v4hi, v4hi)
    v1di __builtin_ia32_psadbw (v8qi, v8qi)
    v8qi __builtin_ia32_pmaxub (v8qi, v8qi)
    v4hi __builtin_ia32_pmaxsw (v4hi, v4hi)
    v8qi __builtin_ia32_pminub (v8qi, v8qi)
    v4hi __builtin_ia32_pminsw (v4hi, v4hi)
    int __builtin_ia32_pextrw (v4hi, int)
    v4hi __builtin_ia32_pinsrw (v4hi, int, int)
    int __builtin_ia32_pmovmskb (v8qi)
    void __builtin_ia32_maskmovq (v8qi, v8qi, char *)
    void __builtin_ia32_movntq (di *, di)
    void __builtin_ia32_sfence (void)
    

    The following built-in functions are available when `-msse' is used. All of them generate the machine instruction that is part of the name.

     
    int __builtin_ia32_comieq (v4sf, v4sf)
    int __builtin_ia32_comineq (v4sf, v4sf)
    int __builtin_ia32_comilt (v4sf, v4sf)
    int __builtin_ia32_comile (v4sf, v4sf)
    int __builtin_ia32_comigt (v4sf, v4sf)
    int __builtin_ia32_comige (v4sf, v4sf)
    int __builtin_ia32_ucomieq (v4sf, v4sf)
    int __builtin_ia32_ucomineq (v4sf, v4sf)
    int __builtin_ia32_ucomilt (v4sf, v4sf)
    int __builtin_ia32_ucomile (v4sf, v4sf)
    int __builtin_ia32_ucomigt (v4sf, v4sf)
    int __builtin_ia32_ucomige (v4sf, v4sf)
    v4sf __builtin_ia32_addps (v4sf, v4sf)
    v4sf __builtin_ia32_subps (v4sf, v4sf)
    v4sf __builtin_ia32_mulps (v4sf, v4sf)
    v4sf __builtin_ia32_divps (v4sf, v4sf)
    v4sf __builtin_ia32_addss (v4sf, v4sf)
    v4sf __builtin_ia32_subss (v4sf, v4sf)
    v4sf __builtin_ia32_mulss (v4sf, v4sf)
    v4sf __builtin_ia32_divss (v4sf, v4sf)
    v4si __builtin_ia32_cmpeqps (v4sf, v4sf)
    v4si __builtin_ia32_cmpltps (v4sf, v4sf)
    v4si __builtin_ia32_cmpleps (v4sf, v4sf)
    v4si __builtin_ia32_cmpgtps (v4sf, v4sf)
    v4si __builtin_ia32_cmpgeps (v4sf, v4sf)
    v4si __builtin_ia32_cmpunordps (v4sf, v4sf)
    v4si __builtin_ia32_cmpneqps (v4sf, v4sf)
    v4si __builtin_ia32_cmpnltps (v4sf, v4sf)
    v4si __builtin_ia32_cmpnleps (v4sf, v4sf)
    v4si __builtin_ia32_cmpngtps (v4sf, v4sf)
    v4si __builtin_ia32_cmpngeps (v4sf, v4sf)
    v4si __builtin_ia32_cmpordps (v4sf, v4sf)
    v4si __builtin_ia32_cmpeqss (v4sf, v4sf)
    v4si __builtin_ia32_cmpltss (v4sf, v4sf)
    v4si __builtin_ia32_cmpless (v4sf, v4sf)
    v4si __builtin_ia32_cmpunordss (v4sf, v4sf)
    v4si __builtin_ia32_cmpneqss (v4sf, v4sf)
    v4si __builtin_ia32_cmpnlts (v4sf, v4sf)
    v4si __builtin_ia32_cmpnless (v4sf, v4sf)
    v4si __builtin_ia32_cmpordss (v4sf, v4sf)
    v4sf __builtin_ia32_maxps (v4sf, v4sf)
    v4sf __builtin_ia32_maxss (v4sf, v4sf)
    v4sf __builtin_ia32_minps (v4sf, v4sf)
    v4sf __builtin_ia32_minss (v4sf, v4sf)
    v4sf __builtin_ia32_andps (v4sf, v4sf)
    v4sf __builtin_ia32_andnps (v4sf, v4sf)
    v4sf __builtin_ia32_orps (v4sf, v4sf)
    v4sf __builtin_ia32_xorps (v4sf, v4sf)
    v4sf __builtin_ia32_movss (v4sf, v4sf)
    v4sf __builtin_ia32_movhlps (v4sf, v4sf)
    v4sf __builtin_ia32_movlhps (v4sf, v4sf)
    v4sf __builtin_ia32_unpckhps (v4sf, v4sf)
    v4sf __builtin_ia32_unpcklps (v4sf, v4sf)
    v4sf __builtin_ia32_cvtpi2ps (v4sf, v2si)
    v4sf __builtin_ia32_cvtsi2ss (v4sf, int)
    v2si __builtin_ia32_cvtps2pi (v4sf)
    int __builtin_ia32_cvtss2si (v4sf)
    v2si __builtin_ia32_cvttps2pi (v4sf)
    int __builtin_ia32_cvttss2si (v4sf)
    v4sf __builtin_ia32_rcpps (v4sf)
    v4sf __builtin_ia32_rsqrtps (v4sf)
    v4sf __builtin_ia32_sqrtps (v4sf)
    v4sf __builtin_ia32_rcpss (v4sf)
    v4sf __builtin_ia32_rsqrtss (v4sf)
    v4sf __builtin_ia32_sqrtss (v4sf)
    v4sf __builtin_ia32_shufps (v4sf, v4sf, int)
    void __builtin_ia32_movntps (float *, v4sf)
    int __builtin_ia32_movmskps (v4sf)
    

    The following built-in functions are available when `-msse' is used.

    v4sf __builtin_ia32_loadaps (float *)
    Generates the movaps machine instruction as a load from memory.
    void __builtin_ia32_storeaps (float *, v4sf)
    Generates the movaps machine instruction as a store to memory.
    v4sf __builtin_ia32_loadups (float *)
    Generates the movups machine instruction as a load from memory.
    void __builtin_ia32_storeups (float *, v4sf)
    Generates the movups machine instruction as a store to memory.
    v4sf __builtin_ia32_loadsss (float *)
    Generates the movss machine instruction as a load from memory.
    void __builtin_ia32_storess (float *, v4sf)
    Generates the movss machine instruction as a store to memory.
    v4sf __builtin_ia32_loadhps (v4sf, const v2sf *)
    Generates the movhps machine instruction as a load from memory.
    v4sf __builtin_ia32_loadlps (v4sf, const v2sf *)
    Generates the movlps machine instruction as a load from memory
    void __builtin_ia32_storehps (v2sf *, v4sf)
    Generates the movhps machine instruction as a store to memory.
    void __builtin_ia32_storelps (v2sf *, v4sf)
    Generates the movlps machine instruction as a store to memory.

    The following built-in functions are available when `-msse2' is used. All of them generate the machine instruction that is part of the name.

     
    int __builtin_ia32_comisdeq (v2df, v2df)
    int __builtin_ia32_comisdlt (v2df, v2df)
    int __builtin_ia32_comisdle (v2df, v2df)
    int __builtin_ia32_comisdgt (v2df, v2df)
    int __builtin_ia32_comisdge (v2df, v2df)
    int __builtin_ia32_comisdneq (v2df, v2df)
    int __builtin_ia32_ucomisdeq (v2df, v2df)
    int __builtin_ia32_ucomisdlt (v2df, v2df)
    int __builtin_ia32_ucomisdle (v2df, v2df)
    int __builtin_ia32_ucomisdgt (v2df, v2df)
    int __builtin_ia32_ucomisdge (v2df, v2df)
    int __builtin_ia32_ucomisdneq (v2df, v2df)
    v2df __builtin_ia32_cmpeqpd (v2df, v2df)
    v2df __builtin_ia32_cmpltpd (v2df, v2df)
    v2df __builtin_ia32_cmplepd (v2df, v2df)
    v2df __builtin_ia32_cmpgtpd (v2df, v2df)
    v2df __builtin_ia32_cmpgepd (v2df, v2df)
    v2df __builtin_ia32_cmpunordpd (v2df, v2df)
    v2df __builtin_ia32_cmpneqpd (v2df, v2df)
    v2df __builtin_ia32_cmpnltpd (v2df, v2df)
    v2df __builtin_ia32_cmpnlepd (v2df, v2df)
    v2df __builtin_ia32_cmpngtpd (v2df, v2df)
    v2df __builtin_ia32_cmpngepd (v2df, v2df)
    v2df __builtin_ia32_cmpordpd (v2df, v2df)
    v2df __builtin_ia32_cmpeqsd (v2df, v2df)
    v2df __builtin_ia32_cmpltsd (v2df, v2df)
    v2df __builtin_ia32_cmplesd (v2df, v2df)
    v2df __builtin_ia32_cmpunordsd (v2df, v2df)
    v2df __builtin_ia32_cmpneqsd (v2df, v2df)
    v2df __builtin_ia32_cmpnltsd (v2df, v2df)
    v2df __builtin_ia32_cmpnlesd (v2df, v2df)
    v2df __builtin_ia32_cmpordsd (v2df, v2df)
    v2di __builtin_ia32_paddq (v2di, v2di)
    v2di __builtin_ia32_psubq (v2di, v2di)
    v2df __builtin_ia32_addpd (v2df, v2df)
    v2df __builtin_ia32_subpd (v2df, v2df)
    v2df __builtin_ia32_mulpd (v2df, v2df)
    v2df __builtin_ia32_divpd (v2df, v2df)
    v2df __builtin_ia32_addsd (v2df, v2df)
    v2df __builtin_ia32_subsd (v2df, v2df)
    v2df __builtin_ia32_mulsd (v2df, v2df)
    v2df __builtin_ia32_divsd (v2df, v2df)
    v2df __builtin_ia32_minpd (v2df, v2df)
    v2df __builtin_ia32_maxpd (v2df, v2df)
    v2df __builtin_ia32_minsd (v2df, v2df)
    v2df __builtin_ia32_maxsd (v2df, v2df)
    v2df __builtin_ia32_andpd (v2df, v2df)
    v2df __builtin_ia32_andnpd (v2df, v2df)
    v2df __builtin_ia32_orpd (v2df, v2df)
    v2df __builtin_ia32_xorpd (v2df, v2df)
    v2df __builtin_ia32_movsd (v2df, v2df)
    v2df __builtin_ia32_unpckhpd (v2df, v2df)
    v2df __builtin_ia32_unpcklpd (v2df, v2df)
    v16qi __builtin_ia32_paddb128 (v16qi, v16qi)
    v8hi __builtin_ia32_paddw128 (v8hi, v8hi)
    v4si __builtin_ia32_paddd128 (v4si, v4si)
    v2di __builtin_ia32_paddq128 (v2di, v2di)
    v16qi __builtin_ia32_psubb128 (v16qi, v16qi)
    v8hi __builtin_ia32_psubw128 (v8hi, v8hi)
    v4si __builtin_ia32_psubd128 (v4si, v4si)
    v2di __builtin_ia32_psubq128 (v2di, v2di)
    v8hi __builtin_ia32_pmullw128 (v8hi, v8hi)
    v8hi __builtin_ia32_pmulhw128 (v8hi, v8hi)
    v2di __builtin_ia32_pand128 (v2di, v2di)
    v2di __builtin_ia32_pandn128 (v2di, v2di)
    v2di __builtin_ia32_por128 (v2di, v2di)
    v2di __builtin_ia32_pxor128 (v2di, v2di)
    v16qi __builtin_ia32_pavgb128 (v16qi, v16qi)
    v8hi __builtin_ia32_pavgw128 (v8hi, v8hi)
    v16qi __builtin_ia32_pcmpeqb128 (v16qi, v16qi)
    v8hi __builtin_ia32_pcmpeqw128 (v8hi, v8hi)
    v4si __builtin_ia32_pcmpeqd128 (v4si, v4si)
    v16qi __builtin_ia32_pcmpgtb128 (v16qi, v16qi)
    v8hi __builtin_ia32_pcmpgtw128 (v8hi, v8hi)
    v4si __builtin_ia32_pcmpgtd128 (v4si, v4si)
    v16qi __builtin_ia32_pmaxub128 (v16qi, v16qi)
    v8hi __builtin_ia32_pmaxsw128 (v8hi, v8hi)
    v16qi __builtin_ia32_pminub128 (v16qi, v16qi)
    v8hi __builtin_ia32_pminsw128 (v8hi, v8hi)
    v16qi __builtin_ia32_punpckhbw128 (v16qi, v16qi)
    v8hi __builtin_ia32_punpckhwd128 (v8hi, v8hi)
    v4si __builtin_ia32_punpckhdq128 (v4si, v4si)
    v2di __builtin_ia32_punpckhqdq128 (v2di, v2di)
    v16qi __builtin_ia32_punpcklbw128 (v16qi, v16qi)
    v8hi __builtin_ia32_punpcklwd128 (v8hi, v8hi)
    v4si __builtin_ia32_punpckldq128 (v4si, v4si)
    v2di __builtin_ia32_punpcklqdq128 (v2di, v2di)
    v16qi __builtin_ia32_packsswb128 (v8hi, v8hi)
    v8hi __builtin_ia32_packssdw128 (v4si, v4si)
    v16qi __builtin_ia32_packuswb128 (v8hi, v8hi)
    v8hi __builtin_ia32_pmulhuw128 (v8hi, v8hi)
    void __builtin_ia32_maskmovdqu (v16qi, v16qi)
    v2df __builtin_ia32_loadupd (double *)
    void __builtin_ia32_storeupd (double *, v2df)
    v2df __builtin_ia32_loadhpd (v2df, double const *)
    v2df __builtin_ia32_loadlpd (v2df, double const *)
    int __builtin_ia32_movmskpd (v2df)
    int __builtin_ia32_pmovmskb128 (v16qi)
    void __builtin_ia32_movnti (int *, int)
    void __builtin_ia32_movntpd (double *, v2df)
    void __builtin_ia32_movntdq (v2df *, v2df)
    v4si __builtin_ia32_pshufd (v4si, int)
    v8hi __builtin_ia32_pshuflw (v8hi, int)
    v8hi __builtin_ia32_pshufhw (v8hi, int)
    v2di __builtin_ia32_psadbw128 (v16qi, v16qi)
    v2df __builtin_ia32_sqrtpd (v2df)
    v2df __builtin_ia32_sqrtsd (v2df)
    v2df __builtin_ia32_shufpd (v2df, v2df, int)
    v2df __builtin_ia32_cvtdq2pd (v4si)
    v4sf __builtin_ia32_cvtdq2ps (v4si)
    v4si __builtin_ia32_cvtpd2dq (v2df)
    v2si __builtin_ia32_cvtpd2pi (v2df)
    v4sf __builtin_ia32_cvtpd2ps (v2df)
    v4si __builtin_ia32_cvttpd2dq (v2df)
    v2si __builtin_ia32_cvttpd2pi (v2df)
    v2df __builtin_ia32_cvtpi2pd (v2si)
    int __builtin_ia32_cvtsd2si (v2df)
    int __builtin_ia32_cvttsd2si (v2df)
    long long __builtin_ia32_cvtsd2si64 (v2df)
    long long __builtin_ia32_cvttsd2si64 (v2df)
    v4si __builtin_ia32_cvtps2dq (v4sf)
    v2df __builtin_ia32_cvtps2pd (v4sf)
    v4si __builtin_ia32_cvttps2dq (v4sf)
    v2df __builtin_ia32_cvtsi2sd (v2df, int)
    v2df __builtin_ia32_cvtsi642sd (v2df, long long)
    v4sf __builtin_ia32_cvtsd2ss (v4sf, v2df)
    v2df __builtin_ia32_cvtss2sd (v2df, v4sf)
    void __builtin_ia32_clflush (const void *)
    void __builtin_ia32_lfence (void)
    void __builtin_ia32_mfence (void)
    v16qi __builtin_ia32_loaddqu (const char *)
    void __builtin_ia32_storedqu (char *, v16qi)
    v1di __builtin_ia32_pmuludq (v2si, v2si)
    v2di __builtin_ia32_pmuludq128 (v4si, v4si)
    v8hi __builtin_ia32_psllw128 (v8hi, v8hi)
    v4si __builtin_ia32_pslld128 (v4si, v4si)
    v2di __builtin_ia32_psllq128 (v2di, v2di)
    v8hi __builtin_ia32_psrlw128 (v8hi, v8hi)
    v4si __builtin_ia32_psrld128 (v4si, v4si)
    v2di __builtin_ia32_psrlq128 (v2di, v2di)
    v8hi __builtin_ia32_psraw128 (v8hi, v8hi)
    v4si __builtin_ia32_psrad128 (v4si, v4si)
    v2di __builtin_ia32_pslldqi128 (v2di, int)
    v8hi __builtin_ia32_psllwi128 (v8hi, int)
    v4si __builtin_ia32_pslldi128 (v4si, int)
    v2di __builtin_ia32_psllqi128 (v2di, int)
    v2di __builtin_ia32_psrldqi128 (v2di, int)
    v8hi __builtin_ia32_psrlwi128 (v8hi, int)
    v4si __builtin_ia32_psrldi128 (v4si, int)
    v2di __builtin_ia32_psrlqi128 (v2di, int)
    v8hi __builtin_ia32_psrawi128 (v8hi, int)
    v4si __builtin_ia32_psradi128 (v4si, int)
    v4si __builtin_ia32_pmaddwd128 (v8hi, v8hi)
    v2di __builtin_ia32_movq128 (v2di)
    

    The following built-in functions are available when `-msse3' is used. All of them generate the machine instruction that is part of the name.

     
    v2df __builtin_ia32_addsubpd (v2df, v2df)
    v4sf __builtin_ia32_addsubps (v4sf, v4sf)
    v2df __builtin_ia32_haddpd (v2df, v2df)
    v4sf __builtin_ia32_haddps (v4sf, v4sf)
    v2df __builtin_ia32_hsubpd (v2df, v2df)
    v4sf __builtin_ia32_hsubps (v4sf, v4sf)
    v16qi __builtin_ia32_lddqu (char const *)
    void __builtin_ia32_monitor (void *, unsigned int, unsigned int)
    v2df __builtin_ia32_movddup (v2df)
    v4sf __builtin_ia32_movshdup (v4sf)
    v4sf __builtin_ia32_movsldup (v4sf)
    void __builtin_ia32_mwait (unsigned int, unsigned int)
    

    The following built-in functions are available when `-msse3' is used.

    v2df __builtin_ia32_loadddup (double const *)
    Generates the movddup machine instruction as a load from memory.

    The following built-in functions are available when `-mssse3' is used. All of them generate the machine instruction that is part of the name with MMX registers.

     
    v2si __builtin_ia32_phaddd (v2si, v2si)
    v4hi __builtin_ia32_phaddw (v4hi, v4hi)
    v4hi __builtin_ia32_phaddsw (v4hi, v4hi)
    v2si __builtin_ia32_phsubd (v2si, v2si)
    v4hi __builtin_ia32_phsubw (v4hi, v4hi)
    v4hi __builtin_ia32_phsubsw (v4hi, v4hi)
    v4hi __builtin_ia32_pmaddubsw (v8qi, v8qi)
    v4hi __builtin_ia32_pmulhrsw (v4hi, v4hi)
    v8qi __builtin_ia32_pshufb (v8qi, v8qi)
    v8qi __builtin_ia32_psignb (v8qi, v8qi)
    v2si __builtin_ia32_psignd (v2si, v2si)
    v4hi __builtin_ia32_psignw (v4hi, v4hi)
    v1di __builtin_ia32_palignr (v1di, v1di, int)
    v8qi __builtin_ia32_pabsb (v8qi)
    v2si __builtin_ia32_pabsd (v2si)
    v4hi __builtin_ia32_pabsw (v4hi)
    

    The following built-in functions are available when `-mssse3' is used. All of them generate the machine instruction that is part of the name with SSE registers.

     
    v4si __builtin_ia32_phaddd128 (v4si, v4si)
    v8hi __builtin_ia32_phaddw128 (v8hi, v8hi)
    v8hi __builtin_ia32_phaddsw128 (v8hi, v8hi)
    v4si __builtin_ia32_phsubd128 (v4si, v4si)
    v8hi __builtin_ia32_phsubw128 (v8hi, v8hi)
    v8hi __builtin_ia32_phsubsw128 (v8hi, v8hi)
    v8hi __builtin_ia32_pmaddubsw128 (v16qi, v16qi)
    v8hi __builtin_ia32_pmulhrsw128 (v8hi, v8hi)
    v16qi __builtin_ia32_pshufb128 (v16qi, v16qi)
    v16qi __builtin_ia32_psignb128 (v16qi, v16qi)
    v4si __builtin_ia32_psignd128 (v4si, v4si)
    v8hi __builtin_ia32_psignw128 (v8hi, v8hi)
    v2di __builtin_ia32_palignr128 (v2di, v2di, int)
    v16qi __builtin_ia32_pabsb128 (v16qi)
    v4si __builtin_ia32_pabsd128 (v4si)
    v8hi __builtin_ia32_pabsw128 (v8hi)
    

    The following built-in functions are available when `-msse4.1' is used. All of them generate the machine instruction that is part of the name.

     
    v2df __builtin_ia32_blendpd (v2df, v2df, const int)
    v4sf __builtin_ia32_blendps (v4sf, v4sf, const int)
    v2df __builtin_ia32_blendvpd (v2df, v2df, v2df)
    v4sf __builtin_ia32_blendvps (v4sf, v4sf, v4sf)
    v2df __builtin_ia32_dppd (v2df, v2df, const int)
    v4sf __builtin_ia32_dpps (v4sf, v4sf, const int)
    v4sf __builtin_ia32_insertps128 (v4sf, v4sf, const int)
    v2di __builtin_ia32_movntdqa (v2di *);
    v16qi __builtin_ia32_mpsadbw128 (v16qi, v16qi, const int)
    v8hi __builtin_ia32_packusdw128 (v4si, v4si)
    v16qi __builtin_ia32_pblendvb128 (v16qi, v16qi, v16qi)
    v8hi __builtin_ia32_pblendw128 (v8hi, v8hi, const int)
    v2di __builtin_ia32_pcmpeqq (v2di, v2di)
    v8hi __builtin_ia32_phminposuw128 (v8hi)
    v16qi __builtin_ia32_pmaxsb128 (v16qi, v16qi)
    v4si __builtin_ia32_pmaxsd128 (v4si, v4si)
    v4si __builtin_ia32_pmaxud128 (v4si, v4si)
    v8hi __builtin_ia32_pmaxuw128 (v8hi, v8hi)
    v16qi __builtin_ia32_pminsb128 (v16qi, v16qi)
    v4si __builtin_ia32_pminsd128 (v4si, v4si)
    v4si __builtin_ia32_pminud128 (v4si, v4si)
    v8hi __builtin_ia32_pminuw128 (v8hi, v8hi)
    v4si __builtin_ia32_pmovsxbd128 (v16qi)
    v2di __builtin_ia32_pmovsxbq128 (v16qi)
    v8hi __builtin_ia32_pmovsxbw128 (v16qi)
    v2di __builtin_ia32_pmovsxdq128 (v4si)
    v4si __builtin_ia32_pmovsxwd128 (v8hi)
    v2di __builtin_ia32_pmovsxwq128 (v8hi)
    v4si __builtin_ia32_pmovzxbd128 (v16qi)
    v2di __builtin_ia32_pmovzxbq128 (v16qi)
    v8hi __builtin_ia32_pmovzxbw128 (v16qi)
    v2di __builtin_ia32_pmovzxdq128 (v4si)
    v4si __builtin_ia32_pmovzxwd128 (v8hi)
    v2di __builtin_ia32_pmovzxwq128 (v8hi)
    v2di __builtin_ia32_pmuldq128 (v4si, v4si)
    v4si __builtin_ia32_pmulld128 (v4si, v4si)
    int __builtin_ia32_ptestc128 (v2di, v2di)
    int __builtin_ia32_ptestnzc128 (v2di, v2di)
    int __builtin_ia32_ptestz128 (v2di, v2di)
    v2df __builtin_ia32_roundpd (v2df, const int)
    v4sf __builtin_ia32_roundps (v4sf, const int)
    v2df __builtin_ia32_roundsd (v2df, v2df, const int)
    v4sf __builtin_ia32_roundss (v4sf, v4sf, const int)
    

    The following built-in functions are available when `-msse4.1' is used.

    v4sf __builtin_ia32_vec_set_v4sf (v4sf, float, const int)
    Generates the insertps machine instruction.
    int __builtin_ia32_vec_ext_v16qi (v16qi, const int)
    Generates the pextrb machine instruction.
    v16qi __builtin_ia32_vec_set_v16qi (v16qi, int, const int)
    Generates the pinsrb machine instruction.
    v4si __builtin_ia32_vec_set_v4si (v4si, int, const int)
    Generates the pinsrd machine instruction.
    v2di __builtin_ia32_vec_set_v2di (v2di, long long, const int)
    Generates the pinsrq machine instruction in 64bit mode.

    The following built-in functions are changed to generate new SSE4.1 instructions when `-msse4.1' is used.

    float __builtin_ia32_vec_ext_v4sf (v4sf, const int)
    Generates the extractps machine instruction.
    int __builtin_ia32_vec_ext_v4si (v4si, const int)
    Generates the pextrd machine instruction.
    long long __builtin_ia32_vec_ext_v2di (v2di, const int)
    Generates the pextrq machine instruction in 64bit mode.

    The following built-in functions are available when `-msse4.2' is used. All of them generate the machine instruction that is part of the name.

     
    v16qi __builtin_ia32_pcmpestrm128 (v16qi, int, v16qi, int, const int)
    int __builtin_ia32_pcmpestri128 (v16qi, int, v16qi, int, const int)
    int __builtin_ia32_pcmpestria128 (v16qi, int, v16qi, int, const int)
    int __builtin_ia32_pcmpestric128 (v16qi, int, v16qi, int, const int)
    int __builtin_ia32_pcmpestrio128 (v16qi, int, v16qi, int, const int)
    int __builtin_ia32_pcmpestris128 (v16qi, int, v16qi, int, const int)
    int __builtin_ia32_pcmpestriz128 (v16qi, int, v16qi, int, const int)
    v16qi __builtin_ia32_pcmpistrm128 (v16qi, v16qi, const int)
    int __builtin_ia32_pcmpistri128 (v16qi, v16qi, const int)
    int __builtin_ia32_pcmpistria128 (v16qi, v16qi, const int)
    int __builtin_ia32_pcmpistric128 (v16qi, v16qi, const int)
    int __builtin_ia32_pcmpistrio128 (v16qi, v16qi, const int)
    int __builtin_ia32_pcmpistris128 (v16qi, v16qi, const int)
    int __builtin_ia32_pcmpistriz128 (v16qi, v16qi, const int)
    v2di __builtin_ia32_pcmpgtq (v2di, v2di)
    

    The following built-in functions are available when `-msse4.2' is used.

    unsigned int __builtin_ia32_crc32qi (unsigned int, unsigned char)
    Generates the crc32b machine instruction.
    unsigned int __builtin_ia32_crc32hi (unsigned int, unsigned short)
    Generates the crc32w machine instruction.
    unsigned int __builtin_ia32_crc32si (unsigned int, unsigned int)
    Generates the crc32l machine instruction.
    unsigned long long __builtin_ia32_crc32di (unsigned long long, unsigned long long)
    Generates the crc32q machine instruction.

    The following built-in functions are changed to generate new SSE4.2 instructions when `-msse4.2' is used.

    int __builtin_popcount (unsigned int)
    Generates the popcntl machine instruction.
    int __builtin_popcountl (unsigned long)
    Generates the popcntl or popcntq machine instruction, depending on the size of unsigned long.
    int __builtin_popcountll (unsigned long long)
    Generates the popcntq machine instruction.

    The following built-in functions are available when `-mavx' is used. All of them generate the machine instruction that is part of the name.

     
    v4df __builtin_ia32_addpd256 (v4df,v4df)
    v8sf __builtin_ia32_addps256 (v8sf,v8sf)
    v4df __builtin_ia32_addsubpd256 (v4df,v4df)
    v8sf __builtin_ia32_addsubps256 (v8sf,v8sf)
    v4df __builtin_ia32_andnpd256 (v4df,v4df)
    v8sf __builtin_ia32_andnps256 (v8sf,v8sf)
    v4df __builtin_ia32_andpd256 (v4df,v4df)
    v8sf __builtin_ia32_andps256 (v8sf,v8sf)
    v4df __builtin_ia32_blendpd256 (v4df,v4df,int)
    v8sf __builtin_ia32_blendps256 (v8sf,v8sf,int)
    v4df __builtin_ia32_blendvpd256 (v4df,v4df,v4df)
    v8sf __builtin_ia32_blendvps256 (v8sf,v8sf,v8sf)
    v2df __builtin_ia32_cmppd (v2df,v2df,int)
    v4df __builtin_ia32_cmppd256 (v4df,v4df,int)
    v4sf __builtin_ia32_cmpps (v4sf,v4sf,int)
    v8sf __builtin_ia32_cmpps256 (v8sf,v8sf,int)
    v2df __builtin_ia32_cmpsd (v2df,v2df,int)
    v4sf __builtin_ia32_cmpss (v4sf,v4sf,int)
    v4df __builtin_ia32_cvtdq2pd256 (v4si)
    v8sf __builtin_ia32_cvtdq2ps256 (v8si)
    v4si __builtin_ia32_cvtpd2dq256 (v4df)
    v4sf __builtin_ia32_cvtpd2ps256 (v4df)
    v8si __builtin_ia32_cvtps2dq256 (v8sf)
    v4df __builtin_ia32_cvtps2pd256 (v4sf)
    v4si __builtin_ia32_cvttpd2dq256 (v4df)
    v8si __builtin_ia32_cvttps2dq256 (v8sf)
    v4df __builtin_ia32_divpd256 (v4df,v4df)
    v8sf __builtin_ia32_divps256 (v8sf,v8sf)
    v8sf __builtin_ia32_dpps256 (v8sf,v8sf,int)
    v4df __builtin_ia32_haddpd256 (v4df,v4df)
    v8sf __builtin_ia32_haddps256 (v8sf,v8sf)
    v4df __builtin_ia32_hsubpd256 (v4df,v4df)
    v8sf __builtin_ia32_hsubps256 (v8sf,v8sf)
    v32qi __builtin_ia32_lddqu256 (pcchar)
    v32qi __builtin_ia32_loaddqu256 (pcchar)
    v4df __builtin_ia32_loadupd256 (pcdouble)
    v8sf __builtin_ia32_loadups256 (pcfloat)
    v2df __builtin_ia32_maskloadpd (pcv2df,v2df)
    v4df __builtin_ia32_maskloadpd256 (pcv4df,v4df)
    v4sf __builtin_ia32_maskloadps (pcv4sf,v4sf)
    v8sf __builtin_ia32_maskloadps256 (pcv8sf,v8sf)
    void __builtin_ia32_maskstorepd (pv2df,v2df,v2df)
    void __builtin_ia32_maskstorepd256 (pv4df,v4df,v4df)
    void __builtin_ia32_maskstoreps (pv4sf,v4sf,v4sf)
    void __builtin_ia32_maskstoreps256 (pv8sf,v8sf,v8sf)
    v4df __builtin_ia32_maxpd256 (v4df,v4df)
    v8sf __builtin_ia32_maxps256 (v8sf,v8sf)
    v4df __builtin_ia32_minpd256 (v4df,v4df)
    v8sf __builtin_ia32_minps256 (v8sf,v8sf)
    v4df __builtin_ia32_movddup256 (v4df)
    int __builtin_ia32_movmskpd256 (v4df)
    int __builtin_ia32_movmskps256 (v8sf)
    v8sf __builtin_ia32_movshdup256 (v8sf)
    v8sf __builtin_ia32_movsldup256 (v8sf)
    v4df __builtin_ia32_mulpd256 (v4df,v4df)
    v8sf __builtin_ia32_mulps256 (v8sf,v8sf)
    v4df __builtin_ia32_orpd256 (v4df,v4df)
    v8sf __builtin_ia32_orps256 (v8sf,v8sf)
    v2df __builtin_ia32_pd_pd256 (v4df)
    v4df __builtin_ia32_pd256_pd (v2df)
    v4sf __builtin_ia32_ps_ps256 (v8sf)
    v8sf __builtin_ia32_ps256_ps (v4sf)
    int __builtin_ia32_ptestc256 (v4di,v4di,ptest)
    int __builtin_ia32_ptestnzc256 (v4di,v4di,ptest)
    int __builtin_ia32_ptestz256 (v4di,v4di,ptest)
    v8sf __builtin_ia32_rcpps256 (v8sf)
    v4df __builtin_ia32_roundpd256 (v4df,int)
    v8sf __builtin_ia32_roundps256 (v8sf,int)
    v8sf __builtin_ia32_rsqrtps_nr256 (v8sf)
    v8sf __builtin_ia32_rsqrtps256 (v8sf)
    v4df __builtin_ia32_shufpd256 (v4df,v4df,int)
    v8sf __builtin_ia32_shufps256 (v8sf,v8sf,int)
    v4si __builtin_ia32_si_si256 (v8si)
    v8si __builtin_ia32_si256_si (v4si)
    v4df __builtin_ia32_sqrtpd256 (v4df)
    v8sf __builtin_ia32_sqrtps_nr256 (v8sf)
    v8sf __builtin_ia32_sqrtps256 (v8sf)
    void __builtin_ia32_storedqu256 (pchar,v32qi)
    void __builtin_ia32_storeupd256 (pdouble,v4df)
    void __builtin_ia32_storeups256 (pfloat,v8sf)
    v4df __builtin_ia32_subpd256 (v4df,v4df)
    v8sf __builtin_ia32_subps256 (v8sf,v8sf)
    v4df __builtin_ia32_unpckhpd256 (v4df,v4df)
    v8sf __builtin_ia32_unpckhps256 (v8sf,v8sf)
    v4df __builtin_ia32_unpcklpd256 (v4df,v4df)
    v8sf __builtin_ia32_unpcklps256 (v8sf,v8sf)
    v4df __builtin_ia32_vbroadcastf128_pd256 (pcv2df)
    v8sf __builtin_ia32_vbroadcastf128_ps256 (pcv4sf)
    v4df __builtin_ia32_vbroadcastsd256 (pcdouble)
    v4sf __builtin_ia32_vbroadcastss (pcfloat)
    v8sf __builtin_ia32_vbroadcastss256 (pcfloat)
    v2df __builtin_ia32_vextractf128_pd256 (v4df,int)
    v4sf __builtin_ia32_vextractf128_ps256 (v8sf,int)
    v4si __builtin_ia32_vextractf128_si256 (v8si,int)
    v4df __builtin_ia32_vinsertf128_pd256 (v4df,v2df,int)
    v8sf __builtin_ia32_vinsertf128_ps256 (v8sf,v4sf,int)
    v8si __builtin_ia32_vinsertf128_si256 (v8si,v4si,int)
    v4df __builtin_ia32_vperm2f128_pd256 (v4df,v4df,int)
    v8sf __builtin_ia32_vperm2f128_ps256 (v8sf,v8sf,int)
    v8si __builtin_ia32_vperm2f128_si256 (v8si,v8si,int)
    v2df __builtin_ia32_vpermil2pd (v2df,v2df,v2di,int)
    v4df __builtin_ia32_vpermil2pd256 (v4df,v4df,v4di,int)
    v4sf __builtin_ia32_vpermil2ps (v4sf,v4sf,v4si,int)
    v8sf __builtin_ia32_vpermil2ps256 (v8sf,v8sf,v8si,int)
    v2df __builtin_ia32_vpermilpd (v2df,int)
    v4df __builtin_ia32_vpermilpd256 (v4df,int)
    v4sf __builtin_ia32_vpermilps (v4sf,int)
    v8sf __builtin_ia32_vpermilps256 (v8sf,int)
    v2df __builtin_ia32_vpermilvarpd (v2df,v2di)
    v4df __builtin_ia32_vpermilvarpd256 (v4df,v4di)
    v4sf __builtin_ia32_vpermilvarps (v4sf,v4si)
    v8sf __builtin_ia32_vpermilvarps256 (v8sf,v8si)
    int __builtin_ia32_vtestcpd (v2df,v2df,ptest)
    int __builtin_ia32_vtestcpd256 (v4df,v4df,ptest)
    int __builtin_ia32_vtestcps (v4sf,v4sf,ptest)
    int __builtin_ia32_vtestcps256 (v8sf,v8sf,ptest)
    int __builtin_ia32_vtestnzcpd (v2df,v2df,ptest)
    int __builtin_ia32_vtestnzcpd256 (v4df,v4df,ptest)
    int __builtin_ia32_vtestnzcps (v4sf,v4sf,ptest)
    int __builtin_ia32_vtestnzcps256 (v8sf,v8sf,ptest)
    int __builtin_ia32_vtestzpd (v2df,v2df,ptest)
    int __builtin_ia32_vtestzpd256 (v4df,v4df,ptest)
    int __builtin_ia32_vtestzps (v4sf,v4sf,ptest)
    int __builtin_ia32_vtestzps256 (v8sf,v8sf,ptest)
    void __builtin_ia32_vzeroall (void)
    void __builtin_ia32_vzeroupper (void)
    v4df __builtin_ia32_xorpd256 (v4df,v4df)
    v8sf __builtin_ia32_xorps256 (v8sf,v8sf)
    

    The following built-in functions are available when `-maes' is used. All of them generate the machine instruction that is part of the name.

     
    v2di __builtin_ia32_aesenc128 (v2di, v2di)
    v2di __builtin_ia32_aesenclast128 (v2di, v2di)
    v2di __builtin_ia32_aesdec128 (v2di, v2di)
    v2di __builtin_ia32_aesdeclast128 (v2di, v2di)
    v2di __builtin_ia32_aeskeygenassist128 (v2di, const int)
    v2di __builtin_ia32_aesimc128 (v2di)
    

    The following built-in function is available when `-mpclmul' is used.

    v2di __builtin_ia32_pclmulqdq128 (v2di, v2di, const int)
    Generates the pclmulqdq machine instruction.

    The following built-in functions are available when `-msse4a' is used. All of them generate the machine instruction that is part of the name.

     
    void __builtin_ia32_movntsd (double *, v2df)
    void __builtin_ia32_movntss (float *, v4sf)
    v2di __builtin_ia32_extrq  (v2di, v16qi)
    v2di __builtin_ia32_extrqi (v2di, const unsigned int, const unsigned int)
    v2di __builtin_ia32_insertq (v2di, v2di)
    v2di __builtin_ia32_insertqi (v2di, v2di, const unsigned int, const unsigned int)
    

    The following built-in functions are available when `-mxop' is used.
     
    v2df __builtin_ia32_vfrczpd (v2df)
    v4sf __builtin_ia32_vfrczps (v4sf)
    v2df __builtin_ia32_vfrczsd (v2df, v2df)
    v4sf __builtin_ia32_vfrczss (v4sf, v4sf)
    v4df __builtin_ia32_vfrczpd256 (v4df)
    v8sf __builtin_ia32_vfrczps256 (v8sf)
    v2di __builtin_ia32_vpcmov (v2di, v2di, v2di)
    v2di __builtin_ia32_vpcmov_v2di (v2di, v2di, v2di)
    v4si __builtin_ia32_vpcmov_v4si (v4si, v4si, v4si)
    v8hi __builtin_ia32_vpcmov_v8hi (v8hi, v8hi, v8hi)
    v16qi __builtin_ia32_vpcmov_v16qi (v16qi, v16qi, v16qi)
    v2df __builtin_ia32_vpcmov_v2df (v2df, v2df, v2df)
    v4sf __builtin_ia32_vpcmov_v4sf (v4sf, v4sf, v4sf)
    v4di __builtin_ia32_vpcmov_v4di256 (v4di, v4di, v4di)
    v8si __builtin_ia32_vpcmov_v8si256 (v8si, v8si, v8si)
    v16hi __builtin_ia32_vpcmov_v16hi256 (v16hi, v16hi, v16hi)
    v32qi __builtin_ia32_vpcmov_v32qi256 (v32qi, v32qi, v32qi)
    v4df __builtin_ia32_vpcmov_v4df256 (v4df, v4df, v4df)
    v8sf __builtin_ia32_vpcmov_v8sf256 (v8sf, v8sf, v8sf)
    v16qi __builtin_ia32_vpcomeqb (v16qi, v16qi)
    v8hi __builtin_ia32_vpcomeqw (v8hi, v8hi)
    v4si __builtin_ia32_vpcomeqd (v4si, v4si)
    v2di __builtin_ia32_vpcomeqq (v2di, v2di)
    v16qi __builtin_ia32_vpcomequb (v16qi, v16qi)
    v4si __builtin_ia32_vpcomequd (v4si, v4si)
    v2di __builtin_ia32_vpcomequq (v2di, v2di)
    v8hi __builtin_ia32_vpcomequw (v8hi, v8hi)
    v8hi __builtin_ia32_vpcomeqw (v8hi, v8hi)
    v16qi __builtin_ia32_vpcomfalseb (v16qi, v16qi)
    v4si __builtin_ia32_vpcomfalsed (v4si, v4si)
    v2di __builtin_ia32_vpcomfalseq (v2di, v2di)
    v16qi __builtin_ia32_vpcomfalseub (v16qi, v16qi)
    v4si __builtin_ia32_vpcomfalseud (v4si, v4si)
    v2di __builtin_ia32_vpcomfalseuq (v2di, v2di)
    v8hi __builtin_ia32_vpcomfalseuw (v8hi, v8hi)
    v8hi __builtin_ia32_vpcomfalsew (v8hi, v8hi)
    v16qi __builtin_ia32_vpcomgeb (v16qi, v16qi)
    v4si __builtin_ia32_vpcomged (v4si, v4si)
    v2di __builtin_ia32_vpcomgeq (v2di, v2di)
    v16qi __builtin_ia32_vpcomgeub (v16qi, v16qi)
    v4si __builtin_ia32_vpcomgeud (v4si, v4si)
    v2di __builtin_ia32_vpcomgeuq (v2di, v2di)
    v8hi __builtin_ia32_vpcomgeuw (v8hi, v8hi)
    v8hi __builtin_ia32_vpcomgew (v8hi, v8hi)
    v16qi __builtin_ia32_vpcomgtb (v16qi, v16qi)
    v4si __builtin_ia32_vpcomgtd (v4si, v4si)
    v2di __builtin_ia32_vpcomgtq (v2di, v2di)
    v16qi __builtin_ia32_vpcomgtub (v16qi, v16qi)
    v4si __builtin_ia32_vpcomgtud (v4si, v4si)
    v2di __builtin_ia32_vpcomgtuq (v2di, v2di)
    v8hi __builtin_ia32_vpcomgtuw (v8hi, v8hi)
    v8hi __builtin_ia32_vpcomgtw (v8hi, v8hi)
    v16qi __builtin_ia32_vpcomleb (v16qi, v16qi)
    v4si __builtin_ia32_vpcomled (v4si, v4si)
    v2di __builtin_ia32_vpcomleq (v2di, v2di)
    v16qi __builtin_ia32_vpcomleub (v16qi, v16qi)
    v4si __builtin_ia32_vpcomleud (v4si, v4si)
    v2di __builtin_ia32_vpcomleuq (v2di, v2di)
    v8hi __builtin_ia32_vpcomleuw (v8hi, v8hi)
    v8hi __builtin_ia32_vpcomlew (v8hi, v8hi)
    v16qi __builtin_ia32_vpcomltb (v16qi, v16qi)
    v4si __builtin_ia32_vpcomltd (v4si, v4si)
    v2di __builtin_ia32_vpcomltq (v2di, v2di)
    v16qi __builtin_ia32_vpcomltub (v16qi, v16qi)
    v4si __builtin_ia32_vpcomltud (v4si, v4si)
    v2di __builtin_ia32_vpcomltuq (v2di, v2di)
    v8hi __builtin_ia32_vpcomltuw (v8hi, v8hi)
    v8hi __builtin_ia32_vpcomltw (v8hi, v8hi)
    v16qi __builtin_ia32_vpcomneb (v16qi, v16qi)
    v4si __builtin_ia32_vpcomned (v4si, v4si)
    v2di __builtin_ia32_vpcomneq (v2di, v2di)
    v16qi __builtin_ia32_vpcomneub (v16qi, v16qi)
    v4si __builtin_ia32_vpcomneud (v4si, v4si)
    v2di __builtin_ia32_vpcomneuq (v2di, v2di)
    v8hi __builtin_ia32_vpcomneuw (v8hi, v8hi)
    v8hi __builtin_ia32_vpcomnew (v8hi, v8hi)
    v16qi __builtin_ia32_vpcomtrueb (v16qi, v16qi)
    v4si __builtin_ia32_vpcomtrued (v4si, v4si)
    v2di __builtin_ia32_vpcomtrueq (v2di, v2di)
    v16qi __builtin_ia32_vpcomtrueub (v16qi, v16qi)
    v4si __builtin_ia32_vpcomtrueud (v4si, v4si)
    v2di __builtin_ia32_vpcomtrueuq (v2di, v2di)
    v8hi __builtin_ia32_vpcomtrueuw (v8hi, v8hi)
    v8hi __builtin_ia32_vpcomtruew (v8hi, v8hi)
    v4si __builtin_ia32_vphaddbd (v16qi)
    v2di __builtin_ia32_vphaddbq (v16qi)
    v8hi __builtin_ia32_vphaddbw (v16qi)
    v2di __builtin_ia32_vphadddq (v4si)
    v4si __builtin_ia32_vphaddubd (v16qi)
    v2di __builtin_ia32_vphaddubq (v16qi)
    v8hi __builtin_ia32_vphaddubw (v16qi)
    v2di __builtin_ia32_vphaddudq (v4si)
    v4si __builtin_ia32_vphadduwd (v8hi)
    v2di __builtin_ia32_vphadduwq (v8hi)
    v4si __builtin_ia32_vphaddwd (v8hi)
    v2di __builtin_ia32_vphaddwq (v8hi)
    v8hi __builtin_ia32_vphsubbw (v16qi)
    v2di __builtin_ia32_vphsubdq (v4si)
    v4si __builtin_ia32_vphsubwd (v8hi)
    v4si __builtin_ia32_vpmacsdd (v4si, v4si, v4si)
    v2di __builtin_ia32_vpmacsdqh (v4si, v4si, v2di)
    v2di __builtin_ia32_vpmacsdql (v4si, v4si, v2di)
    v4si __builtin_ia32_vpmacssdd (v4si, v4si, v4si)
    v2di __builtin_ia32_vpmacssdqh (v4si, v4si, v2di)
    v2di __builtin_ia32_vpmacssdql (v4si, v4si, v2di)
    v4si __builtin_ia32_vpmacsswd (v8hi, v8hi, v4si)
    v8hi __builtin_ia32_vpmacssww (v8hi, v8hi, v8hi)
    v4si __builtin_ia32_vpmacswd (v8hi, v8hi, v4si)
    v8hi __builtin_ia32_vpmacsww (v8hi, v8hi, v8hi)
    v4si __builtin_ia32_vpmadcsswd (v8hi, v8hi, v4si)
    v4si __builtin_ia32_vpmadcswd (v8hi, v8hi, v4si)
    v16qi __builtin_ia32_vpperm (v16qi, v16qi, v16qi)
    v16qi __builtin_ia32_vprotb (v16qi, v16qi)
    v4si __builtin_ia32_vprotd (v4si, v4si)
    v2di __builtin_ia32_vprotq (v2di, v2di)
    v8hi __builtin_ia32_vprotw (v8hi, v8hi)
    v16qi __builtin_ia32_vpshab (v16qi, v16qi)
    v4si __builtin_ia32_vpshad (v4si, v4si)
    v2di __builtin_ia32_vpshaq (v2di, v2di)
    v8hi __builtin_ia32_vpshaw (v8hi, v8hi)
    v16qi __builtin_ia32_vpshlb (v16qi, v16qi)
    v4si __builtin_ia32_vpshld (v4si, v4si)
    v2di __builtin_ia32_vpshlq (v2di, v2di)
    v8hi __builtin_ia32_vpshlw (v8hi, v8hi)
    

    The following built-in functions are available when `-mfma4' is used. All of them generate the machine instruction that is part of the name with MMX registers.

     
    v2df __builtin_ia32_fmaddpd (v2df, v2df, v2df)
    v4sf __builtin_ia32_fmaddps (v4sf, v4sf, v4sf)
    v2df __builtin_ia32_fmaddsd (v2df, v2df, v2df)
    v4sf __builtin_ia32_fmaddss (v4sf, v4sf, v4sf)
    v2df __builtin_ia32_fmsubpd (v2df, v2df, v2df)
    v4sf __builtin_ia32_fmsubps (v4sf, v4sf, v4sf)
    v2df __builtin_ia32_fmsubsd (v2df, v2df, v2df)
    v4sf __builtin_ia32_fmsubss (v4sf, v4sf, v4sf)
    v2df __builtin_ia32_fnmaddpd (v2df, v2df, v2df)
    v4sf __builtin_ia32_fnmaddps (v4sf, v4sf, v4sf)
    v2df __builtin_ia32_fnmaddsd (v2df, v2df, v2df)
    v4sf __builtin_ia32_fnmaddss (v4sf, v4sf, v4sf)
    v2df __builtin_ia32_fnmsubpd (v2df, v2df, v2df)
    v4sf __builtin_ia32_fnmsubps (v4sf, v4sf, v4sf)
    v2df __builtin_ia32_fnmsubsd (v2df, v2df, v2df)
    v4sf __builtin_ia32_fnmsubss (v4sf, v4sf, v4sf)
    v2df __builtin_ia32_fmaddsubpd  (v2df, v2df, v2df)
    v4sf __builtin_ia32_fmaddsubps  (v4sf, v4sf, v4sf)
    v2df __builtin_ia32_fmsubaddpd  (v2df, v2df, v2df)
    v4sf __builtin_ia32_fmsubaddps  (v4sf, v4sf, v4sf)
    v4df __builtin_ia32_fmaddpd256 (v4df, v4df, v4df)
    v8sf __builtin_ia32_fmaddps256 (v8sf, v8sf, v8sf)
    v4df __builtin_ia32_fmsubpd256 (v4df, v4df, v4df)
    v8sf __builtin_ia32_fmsubps256 (v8sf, v8sf, v8sf)
    v4df __builtin_ia32_fnmaddpd256 (v4df, v4df, v4df)
    v8sf __builtin_ia32_fnmaddps256 (v8sf, v8sf, v8sf)
    v4df __builtin_ia32_fnmsubpd256 (v4df, v4df, v4df)
    v8sf __builtin_ia32_fnmsubps256 (v8sf, v8sf, v8sf)
    v4df __builtin_ia32_fmaddsubpd256 (v4df, v4df, v4df)
    v8sf __builtin_ia32_fmaddsubps256 (v8sf, v8sf, v8sf)
    v4df __builtin_ia32_fmsubaddpd256 (v4df, v4df, v4df)
    v8sf __builtin_ia32_fmsubaddps256 (v8sf, v8sf, v8sf)
    
    

    The following built-in functions are available when `-mlwp' is used.

     
    void __builtin_ia32_llwpcb16 (void *);
    void __builtin_ia32_llwpcb32 (void *);
    void __builtin_ia32_llwpcb64 (void *);
    void * __builtin_ia32_llwpcb16 (void);
    void * __builtin_ia32_llwpcb32 (void);
    void * __builtin_ia32_llwpcb64 (void);
    void __builtin_ia32_lwpval16 (unsigned short, unsigned int, unsigned short)
    void __builtin_ia32_lwpval32 (unsigned int, unsigned int, unsigned int)
    void __builtin_ia32_lwpval64 (unsigned __int64, unsigned int, unsigned int)
    unsigned char __builtin_ia32_lwpins16 (unsigned short, unsigned int, unsigned short)
    unsigned char __builtin_ia32_lwpins32 (unsigned int, unsigned int, unsigned int)
    unsigned char __builtin_ia32_lwpins64 (unsigned __int64, unsigned int, unsigned int)
    

    The following built-in functions are available when `-m3dnow' is used. All of them generate the machine instruction that is part of the name.

     
    void __builtin_ia32_femms (void)
    v8qi __builtin_ia32_pavgusb (v8qi, v8qi)
    v2si __builtin_ia32_pf2id (v2sf)
    v2sf __builtin_ia32_pfacc (v2sf, v2sf)
    v2sf __builtin_ia32_pfadd (v2sf, v2sf)
    v2si __builtin_ia32_pfcmpeq (v2sf, v2sf)
    v2si __builtin_ia32_pfcmpge (v2sf, v2sf)
    v2si __builtin_ia32_pfcmpgt (v2sf, v2sf)
    v2sf __builtin_ia32_pfmax (v2sf, v2sf)
    v2sf __builtin_ia32_pfmin (v2sf, v2sf)
    v2sf __builtin_ia32_pfmul (v2sf, v2sf)
    v2sf __builtin_ia32_pfrcp (v2sf)
    v2sf __builtin_ia32_pfrcpit1 (v2sf, v2sf)
    v2sf __builtin_ia32_pfrcpit2 (v2sf, v2sf)
    v2sf __builtin_ia32_pfrsqrt (v2sf)
    v2sf __builtin_ia32_pfrsqrtit1 (v2sf, v2sf)
    v2sf __builtin_ia32_pfsub (v2sf, v2sf)
    v2sf __builtin_ia32_pfsubr (v2sf, v2sf)
    v2sf __builtin_ia32_pi2fd (v2si)
    v4hi __builtin_ia32_pmulhrw (v4hi, v4hi)
    

    The following built-in functions are available when both `-m3dnow' and `-march=athlon' are used. All of them generate the machine instruction that is part of the name.

     
    v2si __builtin_ia32_pf2iw (v2sf)
    v2sf __builtin_ia32_pfnacc (v2sf, v2sf)
    v2sf __builtin_ia32_pfpnacc (v2sf, v2sf)
    v2sf __builtin_ia32_pi2fw (v2si)
    v2sf __builtin_ia32_pswapdsf (v2sf)
    v2si __builtin_ia32_pswapdsi (v2si)
    


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    6.53.7 MIPS DSP Built-in Functions

    The MIPS DSP Application-Specific Extension (ASE) includes new instructions that are designed to improve the performance of DSP and media applications. It provides instructions that operate on packed 8-bit/16-bit integer data, Q7, Q15 and Q31 fractional data.

    GCC supports MIPS DSP operations using both the generic vector extensions (see section 6.47 Using vector instructions through built-in functions) and a collection of MIPS-specific built-in functions. Both kinds of support are enabled by the `-mdsp' command-line option.

    Revision 2 of the ASE was introduced in the second half of 2006. This revision adds extra instructions to the original ASE, but is otherwise backwards-compatible with it. You can select revision 2 using the command-line option `-mdspr2'; this option implies `-mdsp'.

    The SCOUNT and POS bits of the DSP control register are global. The WRDSP, EXTPDP, EXTPDPV and MTHLIP instructions modify the SCOUNT and POS bits. During optimization, the compiler will not delete these instructions and it will not delete calls to functions containing these instructions.

    At present, GCC only provides support for operations on 32-bit vectors. The vector type associated with 8-bit integer data is usually called v4i8, the vector type associated with Q7 is usually called v4q7, the vector type associated with 16-bit integer data is usually called v2i16, and the vector type associated with Q15 is usually called v2q15. They can be defined in C as follows:

     
    typedef signed char v4i8 __attribute__ ((vector_size(4)));
    typedef signed char v4q7 __attribute__ ((vector_size(4)));
    typedef short v2i16 __attribute__ ((vector_size(4)));
    typedef short v2q15 __attribute__ ((vector_size(4)));
    

    v4i8, v4q7, v2i16 and v2q15 values are initialized in the same way as aggregates. For example:

     
    v4i8 a = {1, 2, 3, 4};
    v4i8 b;
    b = (v4i8) {5, 6, 7, 8};
    
    v2q15 c = {0x0fcb, 0x3a75};
    v2q15 d;
    d = (v2q15) {0.1234 * 0x1.0p15, 0.4567 * 0x1.0p15};
    

    Note: The CPU's endianness determines the order in which values are packed. On little-endian targets, the first value is the least significant and the last value is the most significant. The opposite order applies to big-endian targets. For example, the code above will set the lowest byte of a to 1 on little-endian targets and 4 on big-endian targets.

    Note: Q7, Q15 and Q31 values must be initialized with their integer representation. As shown in this example, the integer representation of a Q7 value can be obtained by multiplying the fractional value by 0x1.0p7. The equivalent for Q15 values is to multiply by 0x1.0p15. The equivalent for Q31 values is to multiply by 0x1.0p31.

    The table below lists the v4i8 and v2q15 operations for which hardware support exists. a and b are v4i8 values, and c and d are v2q15 values.

    C code MIPS instruction
    a + b addu.qb
    c + d addq.ph
    a - b subu.qb
    c - d subq.ph

    The table below lists the v2i16 operation for which hardware support exists for the DSP ASE REV 2. e and f are v2i16 values.

    C code MIPS instruction
    e * f mul.ph

    It is easier to describe the DSP built-in functions if we first define the following types:

     
    typedef int q31;
    typedef int i32;
    typedef unsigned int ui32;
    typedef long long a64;
    

    q31 and i32 are actually the same as int, but we use q31 to indicate a Q31 fractional value and i32 to indicate a 32-bit integer value. Similarly, a64 is the same as long long, but we use a64 to indicate values that will be placed in one of the four DSP accumulators ($ac0, $ac1, $ac2 or $ac3).

    Also, some built-in functions prefer or require immediate numbers as parameters, because the corresponding DSP instructions accept both immediate numbers and register operands, or accept immediate numbers only. The immediate parameters are listed as follows.

     
    imm0_3: 0 to 3.
    imm0_7: 0 to 7.
    imm0_15: 0 to 15.
    imm0_31: 0 to 31.
    imm0_63: 0 to 63.
    imm0_255: 0 to 255.
    imm_n32_31: -32 to 31.
    imm_n512_511: -512 to 511.
    

    The following built-in functions map directly to a particular MIPS DSP instruction. Please refer to the architecture specification for details on what each instruction does.

     
    v2q15 __builtin_mips_addq_ph (v2q15, v2q15)
    v2q15 __builtin_mips_addq_s_ph (v2q15, v2q15)
    q31 __builtin_mips_addq_s_w (q31, q31)
    v4i8 __builtin_mips_addu_qb (v4i8, v4i8)
    v4i8 __builtin_mips_addu_s_qb (v4i8, v4i8)
    v2q15 __builtin_mips_subq_ph (v2q15, v2q15)
    v2q15 __builtin_mips_subq_s_ph (v2q15, v2q15)
    q31 __builtin_mips_subq_s_w (q31, q31)
    v4i8 __builtin_mips_subu_qb (v4i8, v4i8)
    v4i8 __builtin_mips_subu_s_qb (v4i8, v4i8)
    i32 __builtin_mips_addsc (i32, i32)
    i32 __builtin_mips_addwc (i32, i32)
    i32 __builtin_mips_modsub (i32, i32)
    i32 __builtin_mips_raddu_w_qb (v4i8)
    v2q15 __builtin_mips_absq_s_ph (v2q15)
    q31 __builtin_mips_absq_s_w (q31)
    v4i8 __builtin_mips_precrq_qb_ph (v2q15, v2q15)
    v2q15 __builtin_mips_precrq_ph_w (q31, q31)
    v2q15 __builtin_mips_precrq_rs_ph_w (q31, q31)
    v4i8 __builtin_mips_precrqu_s_qb_ph (v2q15, v2q15)
    q31 __builtin_mips_preceq_w_phl (v2q15)
    q31 __builtin_mips_preceq_w_phr (v2q15)
    v2q15 __builtin_mips_precequ_ph_qbl (v4i8)
    v2q15 __builtin_mips_precequ_ph_qbr (v4i8)
    v2q15 __builtin_mips_precequ_ph_qbla (v4i8)
    v2q15 __builtin_mips_precequ_ph_qbra (v4i8)
    v2q15 __builtin_mips_preceu_ph_qbl (v4i8)
    v2q15 __builtin_mips_preceu_ph_qbr (v4i8)
    v2q15 __builtin_mips_preceu_ph_qbla (v4i8)
    v2q15 __builtin_mips_preceu_ph_qbra (v4i8)
    v4i8 __builtin_mips_shll_qb (v4i8, imm0_7)
    v4i8 __builtin_mips_shll_qb (v4i8, i32)
    v2q15 __builtin_mips_shll_ph (v2q15, imm0_15)
    v2q15 __builtin_mips_shll_ph (v2q15, i32)
    v2q15 __builtin_mips_shll_s_ph (v2q15, imm0_15)
    v2q15 __builtin_mips_shll_s_ph (v2q15, i32)
    q31 __builtin_mips_shll_s_w (q31, imm0_31)
    q31 __builtin_mips_shll_s_w (q31, i32)
    v4i8 __builtin_mips_shrl_qb (v4i8, imm0_7)
    v4i8 __builtin_mips_shrl_qb (v4i8, i32)
    v2q15 __builtin_mips_shra_ph (v2q15, imm0_15)
    v2q15 __builtin_mips_shra_ph (v2q15, i32)
    v2q15 __builtin_mips_shra_r_ph (v2q15, imm0_15)
    v2q15 __builtin_mips_shra_r_ph (v2q15, i32)
    q31 __builtin_mips_shra_r_w (q31, imm0_31)
    q31 __builtin_mips_shra_r_w (q31, i32)
    v2q15 __builtin_mips_muleu_s_ph_qbl (v4i8, v2q15)
    v2q15 __builtin_mips_muleu_s_ph_qbr (v4i8, v2q15)
    v2q15 __builtin_mips_mulq_rs_ph (v2q15, v2q15)
    q31 __builtin_mips_muleq_s_w_phl (v2q15, v2q15)
    q31 __builtin_mips_muleq_s_w_phr (v2q15, v2q15)
    a64 __builtin_mips_dpau_h_qbl (a64, v4i8, v4i8)
    a64 __builtin_mips_dpau_h_qbr (a64, v4i8, v4i8)
    a64 __builtin_mips_dpsu_h_qbl (a64, v4i8, v4i8)
    a64 __builtin_mips_dpsu_h_qbr (a64, v4i8, v4i8)
    a64 __builtin_mips_dpaq_s_w_ph (a64, v2q15, v2q15)
    a64 __builtin_mips_dpaq_sa_l_w (a64, q31, q31)
    a64 __builtin_mips_dpsq_s_w_ph (a64, v2q15, v2q15)
    a64 __builtin_mips_dpsq_sa_l_w (a64, q31, q31)
    a64 __builtin_mips_mulsaq_s_w_ph (a64, v2q15, v2q15)
    a64 __builtin_mips_maq_s_w_phl (a64, v2q15, v2q15)
    a64 __builtin_mips_maq_s_w_phr (a64, v2q15, v2q15)
    a64 __builtin_mips_maq_sa_w_phl (a64, v2q15, v2q15)
    a64 __builtin_mips_maq_sa_w_phr (a64, v2q15, v2q15)
    i32 __builtin_mips_bitrev (i32)
    i32 __builtin_mips_insv (i32, i32)
    v4i8 __builtin_mips_repl_qb (imm0_255)
    v4i8 __builtin_mips_repl_qb (i32)
    v2q15 __builtin_mips_repl_ph (imm_n512_511)
    v2q15 __builtin_mips_repl_ph (i32)
    void __builtin_mips_cmpu_eq_qb (v4i8, v4i8)
    void __builtin_mips_cmpu_lt_qb (v4i8, v4i8)
    void __builtin_mips_cmpu_le_qb (v4i8, v4i8)
    i32 __builtin_mips_cmpgu_eq_qb (v4i8, v4i8)
    i32 __builtin_mips_cmpgu_lt_qb (v4i8, v4i8)
    i32 __builtin_mips_cmpgu_le_qb (v4i8, v4i8)
    void __builtin_mips_cmp_eq_ph (v2q15, v2q15)
    void __builtin_mips_cmp_lt_ph (v2q15, v2q15)
    void __builtin_mips_cmp_le_ph (v2q15, v2q15)
    v4i8 __builtin_mips_pick_qb (v4i8, v4i8)
    v2q15 __builtin_mips_pick_ph (v2q15, v2q15)
    v2q15 __builtin_mips_packrl_ph (v2q15, v2q15)
    i32 __builtin_mips_extr_w (a64, imm0_31)
    i32 __builtin_mips_extr_w (a64, i32)
    i32 __builtin_mips_extr_r_w (a64, imm0_31)
    i32 __builtin_mips_extr_s_h (a64, i32)
    i32 __builtin_mips_extr_rs_w (a64, imm0_31)
    i32 __builtin_mips_extr_rs_w (a64, i32)
    i32 __builtin_mips_extr_s_h (a64, imm0_31)
    i32 __builtin_mips_extr_r_w (a64, i32)
    i32 __builtin_mips_extp (a64, imm0_31)
    i32 __builtin_mips_extp (a64, i32)
    i32 __builtin_mips_extpdp (a64, imm0_31)
    i32 __builtin_mips_extpdp (a64, i32)
    a64 __builtin_mips_shilo (a64, imm_n32_31)
    a64 __builtin_mips_shilo (a64, i32)
    a64 __builtin_mips_mthlip (a64, i32)
    void __builtin_mips_wrdsp (i32, imm0_63)
    i32 __builtin_mips_rddsp (imm0_63)
    i32 __builtin_mips_lbux (void *, i32)
    i32 __builtin_mips_lhx (void *, i32)
    i32 __builtin_mips_lwx (void *, i32)
    i32 __builtin_mips_bposge32 (void)
    

    The following built-in functions map directly to a particular MIPS DSP REV 2 instruction. Please refer to the architecture specification for details on what each instruction does.

     
    v4q7 __builtin_mips_absq_s_qb (v4q7);
    v2i16 __builtin_mips_addu_ph (v2i16, v2i16);
    v2i16 __builtin_mips_addu_s_ph (v2i16, v2i16);
    v4i8 __builtin_mips_adduh_qb (v4i8, v4i8);
    v4i8 __builtin_mips_adduh_r_qb (v4i8, v4i8);
    i32 __builtin_mips_append (i32, i32, imm0_31);
    i32 __builtin_mips_balign (i32, i32, imm0_3);
    i32 __builtin_mips_cmpgdu_eq_qb (v4i8, v4i8);
    i32 __builtin_mips_cmpgdu_lt_qb (v4i8, v4i8);
    i32 __builtin_mips_cmpgdu_le_qb (v4i8, v4i8);
    a64 __builtin_mips_dpa_w_ph (a64, v2i16, v2i16);
    a64 __builtin_mips_dps_w_ph (a64, v2i16, v2i16);
    a64 __builtin_mips_madd (a64, i32, i32);
    a64 __builtin_mips_maddu (a64, ui32, ui32);
    a64 __builtin_mips_msub (a64, i32, i32);
    a64 __builtin_mips_msubu (a64, ui32, ui32);
    v2i16 __builtin_mips_mul_ph (v2i16, v2i16);
    v2i16 __builtin_mips_mul_s_ph (v2i16, v2i16);
    q31 __builtin_mips_mulq_rs_w (q31, q31);
    v2q15 __builtin_mips_mulq_s_ph (v2q15, v2q15);
    q31 __builtin_mips_mulq_s_w (q31, q31);
    a64 __builtin_mips_mulsa_w_ph (a64, v2i16, v2i16);
    a64 __builtin_mips_mult (i32, i32);
    a64 __builtin_mips_multu (ui32, ui32);
    v4i8 __builtin_mips_precr_qb_ph (v2i16, v2i16);
    v2i16 __builtin_mips_precr_sra_ph_w (i32, i32, imm0_31);
    v2i16 __builtin_mips_precr_sra_r_ph_w (i32, i32, imm0_31);
    i32 __builtin_mips_prepend (i32, i32, imm0_31);
    v4i8 __builtin_mips_shra_qb (v4i8, imm0_7);
    v4i8 __builtin_mips_shra_r_qb (v4i8, imm0_7);
    v4i8 __builtin_mips_shra_qb (v4i8, i32);
    v4i8 __builtin_mips_shra_r_qb (v4i8, i32);
    v2i16 __builtin_mips_shrl_ph (v2i16, imm0_15);
    v2i16 __builtin_mips_shrl_ph (v2i16, i32);
    v2i16 __builtin_mips_subu_ph (v2i16, v2i16);
    v2i16 __builtin_mips_subu_s_ph (v2i16, v2i16);
    v4i8 __builtin_mips_subuh_qb (v4i8, v4i8);
    v4i8 __builtin_mips_subuh_r_qb (v4i8, v4i8);
    v2q15 __builtin_mips_addqh_ph (v2q15, v2q15);
    v2q15 __builtin_mips_addqh_r_ph (v2q15, v2q15);
    q31 __builtin_mips_addqh_w (q31, q31);
    q31 __builtin_mips_addqh_r_w (q31, q31);
    v2q15 __builtin_mips_subqh_ph (v2q15, v2q15);
    v2q15 __builtin_mips_subqh_r_ph (v2q15, v2q15);
    q31 __builtin_mips_subqh_w (q31, q31);
    q31 __builtin_mips_subqh_r_w (q31, q31);
    a64 __builtin_mips_dpax_w_ph (a64, v2i16, v2i16);
    a64 __builtin_mips_dpsx_w_ph (a64, v2i16, v2i16);
    a64 __builtin_mips_dpaqx_s_w_ph (a64, v2q15, v2q15);
    a64 __builtin_mips_dpaqx_sa_w_ph (a64, v2q15, v2q15);
    a64 __builtin_mips_dpsqx_s_w_ph (a64, v2q15, v2q15);
    a64 __builtin_mips_dpsqx_sa_w_ph (a64, v2q15, v2q15);
    


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    6.53.8 MIPS Paired-Single Support

    The MIPS64 architecture includes a number of instructions that operate on pairs of single-precision floating-point values. Each pair is packed into a 64-bit floating-point register, with one element being designated the "upper half" and the other being designated the "lower half".

    GCC supports paired-single operations using both the generic vector extensions (see section 6.47 Using vector instructions through built-in functions) and a collection of MIPS-specific built-in functions. Both kinds of support are enabled by the `-mpaired-single' command-line option.

    The vector type associated with paired-single values is usually called v2sf. It can be defined in C as follows:

     
    typedef float v2sf __attribute__ ((vector_size (8)));
    

    v2sf values are initialized in the same way as aggregates. For example:

     
    v2sf a = {1.5, 9.1};
    v2sf b;
    float e, f;
    b = (v2sf) {e, f};
    

    Note: The CPU's endianness determines which value is stored in the upper half of a register and which value is stored in the lower half. On little-endian targets, the first value is the lower one and the second value is the upper one. The opposite order applies to big-endian targets. For example, the code above will set the lower half of a to 1.5 on little-endian targets and 9.1 on big-endian targets.


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    6.53.9 MIPS Loongson Built-in Functions

    GCC provides intrinsics to access the SIMD instructions provided by the ST Microelectronics Loongson-2E and -2F processors. These intrinsics, available after inclusion of the loongson.h header file, operate on the following 64-bit vector types:

    The intrinsics provided are listed below; each is named after the machine instruction to which it corresponds, with suffixes added as appropriate to distinguish intrinsics that expand to the same machine instruction yet have different argument types. Refer to the architecture documentation for a description of the functionality of each instruction.

     
    int16x4_t packsswh (int32x2_t s, int32x2_t t);
    int8x8_t packsshb (int16x4_t s, int16x4_t t);
    uint8x8_t packushb (uint16x4_t s, uint16x4_t t);
    uint32x2_t paddw_u (uint32x2_t s, uint32x2_t t);
    uint16x4_t paddh_u (uint16x4_t s, uint16x4_t t);
    uint8x8_t paddb_u (uint8x8_t s, uint8x8_t t);
    int32x2_t paddw_s (int32x2_t s, int32x2_t t);
    int16x4_t paddh_s (int16x4_t s, int16x4_t t);
    int8x8_t paddb_s (int8x8_t s, int8x8_t t);
    uint64_t paddd_u (uint64_t s, uint64_t t);
    int64_t paddd_s (int64_t s, int64_t t);
    int16x4_t paddsh (int16x4_t s, int16x4_t t);
    int8x8_t paddsb (int8x8_t s, int8x8_t t);
    uint16x4_t paddush (uint16x4_t s, uint16x4_t t);
    uint8x8_t paddusb (uint8x8_t s, uint8x8_t t);
    uint64_t pandn_ud (uint64_t s, uint64_t t);
    uint32x2_t pandn_uw (uint32x2_t s, uint32x2_t t);
    uint16x4_t pandn_uh (uint16x4_t s, uint16x4_t t);
    uint8x8_t pandn_ub (uint8x8_t s, uint8x8_t t);
    int64_t pandn_sd (int64_t s, int64_t t);
    int32x2_t pandn_sw (int32x2_t s, int32x2_t t);
    int16x4_t pandn_sh (int16x4_t s, int16x4_t t);
    int8x8_t pandn_sb (int8x8_t s, int8x8_t t);
    uint16x4_t pavgh (uint16x4_t s, uint16x4_t t);
    uint8x8_t pavgb (uint8x8_t s, uint8x8_t t);
    uint32x2_t pcmpeqw_u (uint32x2_t s, uint32x2_t t);
    uint16x4_t pcmpeqh_u (uint16x4_t s, uint16x4_t t);
    uint8x8_t pcmpeqb_u (uint8x8_t s, uint8x8_t t);
    int32x2_t pcmpeqw_s (int32x2_t s, int32x2_t t);
    int16x4_t pcmpeqh_s (int16x4_t s, int16x4_t t);
    int8x8_t pcmpeqb_s (int8x8_t s, int8x8_t t);
    uint32x2_t pcmpgtw_u (uint32x2_t s, uint32x2_t t);
    uint16x4_t pcmpgth_u (uint16x4_t s, uint16x4_t t);
    uint8x8_t pcmpgtb_u (uint8x8_t s, uint8x8_t t);
    int32x2_t pcmpgtw_s (int32x2_t s, int32x2_t t);
    int16x4_t pcmpgth_s (int16x4_t s, int16x4_t t);
    int8x8_t pcmpgtb_s (int8x8_t s, int8x8_t t);
    uint16x4_t pextrh_u (uint16x4_t s, int field);
    int16x4_t pextrh_s (int16x4_t s, int field);
    uint16x4_t pinsrh_0_u (uint16x4_t s, uint16x4_t t);
    uint16x4_t pinsrh_1_u (uint16x4_t s, uint16x4_t t);
    uint16x4_t pinsrh_2_u (uint16x4_t s, uint16x4_t t);
    uint16x4_t pinsrh_3_u (uint16x4_t s, uint16x4_t t);
    int16x4_t pinsrh_0_s (int16x4_t s, int16x4_t t);
    int16x4_t pinsrh_1_s (int16x4_t s, int16x4_t t);
    int16x4_t pinsrh_2_s (int16x4_t s, int16x4_t t);
    int16x4_t pinsrh_3_s (int16x4_t s, int16x4_t t);
    int32x2_t pmaddhw (int16x4_t s, int16x4_t t);
    int16x4_t pmaxsh (int16x4_t s, int16x4_t t);
    uint8x8_t pmaxub (uint8x8_t s, uint8x8_t t);
    int16x4_t pminsh (int16x4_t s, int16x4_t t);
    uint8x8_t pminub (uint8x8_t s, uint8x8_t t);
    uint8x8_t pmovmskb_u (uint8x8_t s);
    int8x8_t pmovmskb_s (int8x8_t s);
    uint16x4_t pmulhuh (uint16x4_t s, uint16x4_t t);
    int16x4_t pmulhh (int16x4_t s, int16x4_t t);
    int16x4_t pmullh (int16x4_t s, int16x4_t t);
    int64_t pmuluw (uint32x2_t s, uint32x2_t t);
    uint8x8_t pasubub (uint8x8_t s, uint8x8_t t);
    uint16x4_t biadd (uint8x8_t s);
    uint16x4_t psadbh (uint8x8_t s, uint8x8_t t);
    uint16x4_t pshufh_u (uint16x4_t dest, uint16x4_t s, uint8_t order);
    int16x4_t pshufh_s (int16x4_t dest, int16x4_t s, uint8_t order);
    uint16x4_t psllh_u (uint16x4_t s, uint8_t amount);
    int16x4_t psllh_s (int16x4_t s, uint8_t amount);
    uint32x2_t psllw_u (uint32x2_t s, uint8_t amount);
    int32x2_t psllw_s (int32x2_t s, uint8_t amount);
    uint16x4_t psrlh_u (uint16x4_t s, uint8_t amount);
    int16x4_t psrlh_s (int16x4_t s, uint8_t amount);
    uint32x2_t psrlw_u (uint32x2_t s, uint8_t amount);
    int32x2_t psrlw_s (int32x2_t s, uint8_t amount);
    uint16x4_t psrah_u (uint16x4_t s, uint8_t amount);
    int16x4_t psrah_s (int16x4_t s, uint8_t amount);
    uint32x2_t psraw_u (uint32x2_t s, uint8_t amount);
    int32x2_t psraw_s (int32x2_t s, uint8_t amount);
    uint32x2_t psubw_u (uint32x2_t s, uint32x2_t t);
    uint16x4_t psubh_u (uint16x4_t s, uint16x4_t t);
    uint8x8_t psubb_u (uint8x8_t s, uint8x8_t t);
    int32x2_t psubw_s (int32x2_t s, int32x2_t t);
    int16x4_t psubh_s (int16x4_t s, int16x4_t t);
    int8x8_t psubb_s (int8x8_t s, int8x8_t t);
    uint64_t psubd_u (uint64_t s, uint64_t t);
    int64_t psubd_s (int64_t s, int64_t t);
    int16x4_t psubsh (int16x4_t s, int16x4_t t);
    int8x8_t psubsb (int8x8_t s, int8x8_t t);
    uint16x4_t psubush (uint16x4_t s, uint16x4_t t);
    uint8x8_t psubusb (uint8x8_t s, uint8x8_t t);
    uint32x2_t punpckhwd_u (uint32x2_t s, uint32x2_t t);
    uint16x4_t punpckhhw_u (uint16x4_t s, uint16x4_t t);
    uint8x8_t punpckhbh_u (uint8x8_t s, uint8x8_t t);
    int32x2_t punpckhwd_s (int32x2_t s, int32x2_t t);
    int16x4_t punpckhhw_s (int16x4_t s, int16x4_t t);
    int8x8_t punpckhbh_s (int8x8_t s, int8x8_t t);
    uint32x2_t punpcklwd_u (uint32x2_t s, uint32x2_t t);
    uint16x4_t punpcklhw_u (uint16x4_t s, uint16x4_t t);
    uint8x8_t punpcklbh_u (uint8x8_t s, uint8x8_t t);
    int32x2_t punpcklwd_s (int32x2_t s, int32x2_t t);
    int16x4_t punpcklhw_s (int16x4_t s, int16x4_t t);
    int8x8_t punpcklbh_s (int8x8_t s, int8x8_t t);
    

    6.53.9.1 Paired-Single Arithmetic  
    6.53.9.2 Paired-Single Built-in Functions  
    6.53.9.3 MIPS-3D Built-in Functions  


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    6.53.9.1 Paired-Single Arithmetic

    The table below lists the v2sf operations for which hardware support exists. a, b and c are v2sf values and x is an integral value.

    C code MIPS instruction
    a + b add.ps
    a - b sub.ps
    -a neg.ps
    a * b mul.ps
    a * b + c madd.ps
    a * b - c msub.ps
    -(a * b + c) nmadd.ps
    -(a * b - c) nmsub.ps
    x ? a : b movn.ps/movz.ps

    Note that the multiply-accumulate instructions can be disabled using the command-line option -mno-fused-madd.


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    6.53.9.2 Paired-Single Built-in Functions

    The following paired-single functions map directly to a particular MIPS instruction. Please refer to the architecture specification for details on what each instruction does.

    v2sf __builtin_mips_pll_ps (v2sf, v2sf)
    Pair lower lower (pll.ps).

    v2sf __builtin_mips_pul_ps (v2sf, v2sf)
    Pair upper lower (pul.ps).

    v2sf __builtin_mips_plu_ps (v2sf, v2sf)
    Pair lower upper (plu.ps).

    v2sf __builtin_mips_puu_ps (v2sf, v2sf)
    Pair upper upper (puu.ps).

    v2sf __builtin_mips_cvt_ps_s (float, float)
    Convert pair to paired single (cvt.ps.s).

    float __builtin_mips_cvt_s_pl (v2sf)
    Convert pair lower to single (cvt.s.pl).

    float __builtin_mips_cvt_s_pu (v2sf)
    Convert pair upper to single (cvt.s.pu).

    v2sf __builtin_mips_abs_ps (v2sf)
    Absolute value (abs.ps).

    v2sf __builtin_mips_alnv_ps (v2sf, v2sf, int)
    Align variable (alnv.ps).

    Note: The value of the third parameter must be 0 or 4 modulo 8, otherwise the result will be unpredictable. Please read the instruction description for details.

    The following multi-instruction functions are also available. In each case, cond can be any of the 16 floating-point conditions: f, un, eq, ueq, olt, ult, ole, ule, sf, ngle, seq, ngl, lt, nge, le or ngt.

    v2sf __builtin_mips_movt_c_cond_ps (v2sf a, v2sf b, v2sf c, v2sf d)
    v2sf __builtin_mips_movf_c_cond_ps (v2sf a, v2sf b, v2sf c, v2sf d)
    Conditional move based on floating point comparison (c.cond.ps, movt.ps/movf.ps).

    The movt functions return the value x computed by:

     
    c.cond.ps cc,a,b
    mov.ps x,c
    movt.ps x,d,cc
    

    The movf functions are similar but use movf.ps instead of movt.ps.

    int __builtin_mips_upper_c_cond_ps (v2sf a, v2sf b)
    int __builtin_mips_lower_c_cond_ps (v2sf a, v2sf b)
    Comparison of two paired-single values (c.cond.ps, bc1t/bc1f).

    These functions compare a and b using c.cond.ps and return either the upper or lower half of the result. For example:

     
    v2sf a, b;
    if (__builtin_mips_upper_c_eq_ps (a, b))
      upper_halves_are_equal ();
    else
      upper_halves_are_unequal ();
    
    if (__builtin_mips_lower_c_eq_ps (a, b))
      lower_halves_are_equal ();
    else
      lower_halves_are_unequal ();
    


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    6.53.9.3 MIPS-3D Built-in Functions

    The MIPS-3D Application-Specific Extension (ASE) includes additional paired-single instructions that are designed to improve the performance of 3D graphics operations. Support for these instructions is controlled by the `-mips3d' command-line option.

    The functions listed below map directly to a particular MIPS-3D instruction. Please refer to the architecture specification for more details on what each instruction does.

    v2sf __builtin_mips_addr_ps (v2sf, v2sf)
    Reduction add (addr.ps).

    v2sf __builtin_mips_mulr_ps (v2sf, v2sf)
    Reduction multiply (mulr.ps).

    v2sf __builtin_mips_cvt_pw_ps (v2sf)
    Convert paired single to paired word (cvt.pw.ps).

    v2sf __builtin_mips_cvt_ps_pw (v2sf)
    Convert paired word to paired single (cvt.ps.pw).

    float __builtin_mips_recip1_s (float)
    double __builtin_mips_recip1_d (double)
    v2sf __builtin_mips_recip1_ps (v2sf)
    Reduced precision reciprocal (sequence step 1) (recip1.fmt).

    float __builtin_mips_recip2_s (float, float)
    double __builtin_mips_recip2_d (double, double)
    v2sf __builtin_mips_recip2_ps (v2sf, v2sf)
    Reduced precision reciprocal (sequence step 2) (recip2.fmt).

    float __builtin_mips_rsqrt1_s (float)
    double __builtin_mips_rsqrt1_d (double)
    v2sf __builtin_mips_rsqrt1_ps (v2sf)
    Reduced precision reciprocal square root (sequence step 1) (rsqrt1.fmt).

    float __builtin_mips_rsqrt2_s (float, float)
    double __builtin_mips_rsqrt2_d (double, double)
    v2sf __builtin_mips_rsqrt2_ps (v2sf, v2sf)
    Reduced precision reciprocal square root (sequence step 2) (rsqrt2.fmt).

    The following multi-instruction functions are also available. In each case, cond can be any of the 16 floating-point conditions: f, un, eq, ueq, olt, ult, ole, ule, sf, ngle, seq, ngl, lt, nge, le or ngt.

    int __builtin_mips_cabs_cond_s (float a, float b)
    int __builtin_mips_cabs_cond_d (double a, double b)
    Absolute comparison of two scalar values (cabs.cond.fmt, bc1t/bc1f).

    These functions compare a and b using cabs.cond.s or cabs.cond.d and return the result as a boolean value. For example:

     
    float a, b;
    if (__builtin_mips_cabs_eq_s (a, b))
      true ();
    else
      false ();
    

    int __builtin_mips_upper_cabs_cond_ps (v2sf a, v2sf b)
    int __builtin_mips_lower_cabs_cond_ps (v2sf a, v2sf b)
    Absolute comparison of two paired-single values (cabs.cond.ps, bc1t/bc1f).

    These functions compare a and b using cabs.cond.ps and return either the upper or lower half of the result. For example:

     
    v2sf a, b;
    if (__builtin_mips_upper_cabs_eq_ps (a, b))
      upper_halves_are_equal ();
    else
      upper_halves_are_unequal ();
    
    if (__builtin_mips_lower_cabs_eq_ps (a, b))
      lower_halves_are_equal ();
    else
      lower_halves_are_unequal ();
    

    v2sf __builtin_mips_movt_cabs_cond_ps (v2sf a, v2sf b, v2sf c, v2sf d)
    v2sf __builtin_mips_movf_cabs_cond_ps (v2sf a, v2sf b, v2sf c, v2sf d)
    Conditional move based on absolute comparison (cabs.cond.ps, movt.ps/movf.ps).

    The movt functions return the value x computed by:

     
    cabs.cond.ps cc,a,b
    mov.ps x,c
    movt.ps x,d,cc
    

    The movf functions are similar but use movf.ps instead of movt.ps.

    int __builtin_mips_any_c_cond_ps (v2sf a, v2sf b)
    int __builtin_mips_all_c_cond_ps (v2sf a, v2sf b)
    int __builtin_mips_any_cabs_cond_ps (v2sf a, v2sf b)
    int __builtin_mips_all_cabs_cond_ps (v2sf a, v2sf b)
    Comparison of two paired-single values (c.cond.ps/cabs.cond.ps, bc1any2t/bc1any2f).

    These functions compare a and b using c.cond.ps or cabs.cond.ps. The any forms return true if either result is true and the all forms return true if both results are true. For example:

     
    v2sf a, b;
    if (__builtin_mips_any_c_eq_ps (a, b))
      one_is_true ();
    else
      both_are_false ();
    
    if (__builtin_mips_all_c_eq_ps (a, b))
      both_are_true ();
    else
      one_is_false ();
    

    int __builtin_mips_any_c_cond_4s (v2sf a, v2sf b, v2sf c, v2sf d)
    int __builtin_mips_all_c_cond_4s (v2sf a, v2sf b, v2sf c, v2sf d)
    int __builtin_mips_any_cabs_cond_4s (v2sf a, v2sf b, v2sf c, v2sf d)
    int __builtin_mips_all_cabs_cond_4s (v2sf a, v2sf b, v2sf c, v2sf d)
    Comparison of four paired-single values (c.cond.ps/cabs.cond.ps, bc1any4t/bc1any4f).

    These functions use c.cond.ps or cabs.cond.ps to compare a with b and to compare c with d. The any forms return true if any of the four results are true and the all forms return true if all four results are true. For example:

     
    v2sf a, b, c, d;
    if (__builtin_mips_any_c_eq_4s (a, b, c, d))
      some_are_true ();
    else
      all_are_false ();
    
    if (__builtin_mips_all_c_eq_4s (a, b, c, d))
      all_are_true ();
    else
      some_are_false ();
    


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    6.53.10 picoChip Built-in Functions

    GCC provides an interface to selected machine instructions from the picoChip instruction set.

    int __builtin_sbc (int value)
    Sign bit count. Return the number of consecutive bits in value which have the same value as the sign-bit. The result is the number of leading sign bits minus one, giving the number of redundant sign bits in value.

    int __builtin_byteswap (int value)
    Byte swap. Return the result of swapping the upper and lower bytes of value.

    int __builtin_brev (int value)
    Bit reversal. Return the result of reversing the bits in value. Bit 15 is swapped with bit 0, bit 14 is swapped with bit 1, and so on.

    int __builtin_adds (int x, int y)
    Saturating addition. Return the result of adding x and y, storing the value 32767 if the result overflows.

    int __builtin_subs (int x, int y)
    Saturating subtraction. Return the result of subtracting y from x, storing the value -32768 if the result overflows.

    void __builtin_halt (void)
    Halt. The processor will stop execution. This built-in is useful for implementing assertions.


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    6.53.11 Other MIPS Built-in Functions

    GCC provides other MIPS-specific built-in functions:

    void __builtin_mips_cache (int op, const volatile void *addr)
    Insert a `cache' instruction with operands op and addr. GCC defines the preprocessor macro ___GCC_HAVE_BUILTIN_MIPS_CACHE when this function is available.


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    6.53.12 PowerPC AltiVec Built-in Functions

    GCC provides an interface for the PowerPC family of processors to access the AltiVec operations described in Motorola's AltiVec Programming Interface Manual. The interface is made available by including <altivec.h> and using `-maltivec' and `-mabi=altivec'. The interface supports the following vector types.

     
    vector unsigned char
    vector signed char
    vector bool char
    
    vector unsigned short
    vector signed short
    vector bool short
    vector pixel
    
    vector unsigned int
    vector signed int
    vector bool int
    vector float
    

    If `-mvsx' is used the following additional vector types are implemented.

     
    vector unsigned long
    vector signed long
    vector double
    

    The long types are only implemented for 64-bit code generation, and the long type is only used in the floating point/integer conversion instructions.

    GCC's implementation of the high-level language interface available from C and C++ code differs from Motorola's documentation in several ways.

    Note: Only the <altivec.h> interface is supported. Internally, GCC uses built-in functions to achieve the functionality in the aforementioned header file, but they are not supported and are subject to change without notice.

    The following interfaces are supported for the generic and specific AltiVec operations and the AltiVec predicates. In cases where there is a direct mapping between generic and specific operations, only the generic names are shown here, although the specific operations can also be used.

    Arguments that are documented as const int require literal integral values within the range required for that operation.

     
    vector signed char vec_abs (vector signed char);
    vector signed short vec_abs (vector signed short);
    vector signed int vec_abs (vector signed int);
    vector float vec_abs (vector float);
    
    vector signed char vec_abss (vector signed char);
    vector signed short vec_abss (vector signed short);
    vector signed int vec_abss (vector signed int);
    
    vector signed char vec_add (vector bool char, vector signed char);
    vector signed char vec_add (vector signed char, vector bool char);
    vector signed char vec_add (vector signed char, vector signed char);
    vector unsigned char vec_add (vector bool char, vector unsigned char);
    vector unsigned char vec_add (vector unsigned char, vector bool char);
    vector unsigned char vec_add (vector unsigned char,
                                  vector unsigned char);
    vector signed short vec_add (vector bool short, vector signed short);
    vector signed short vec_add (vector signed short, vector bool short);
    vector signed short vec_add (vector signed short, vector signed short);
    vector unsigned short vec_add (vector bool short,
                                   vector unsigned short);
    vector unsigned short vec_add (vector unsigned short,
                                   vector bool short);
    vector unsigned short vec_add (vector unsigned short,
                                   vector unsigned short);
    vector signed int vec_add (vector bool int, vector signed int);
    vector signed int vec_add (vector signed int, vector bool int);
    vector signed int vec_add (vector signed int, vector signed int);
    vector unsigned int vec_add (vector bool int, vector unsigned int);
    vector unsigned int vec_add (vector unsigned int, vector bool int);
    vector unsigned int vec_add (vector unsigned int, vector unsigned int);
    vector float vec_add (vector float, vector float);
    
    vector float vec_vaddfp (vector float, vector float);
    
    vector signed int vec_vadduwm (vector bool int, vector signed int);
    vector signed int vec_vadduwm (vector signed int, vector bool int);
    vector signed int vec_vadduwm (vector signed int, vector signed int);
    vector unsigned int vec_vadduwm (vector bool int, vector unsigned int);
    vector unsigned int vec_vadduwm (vector unsigned int, vector bool int);
    vector unsigned int vec_vadduwm (vector unsigned int,
                                     vector unsigned int);
    
    vector signed short vec_vadduhm (vector bool short,
                                     vector signed short);
    vector signed short vec_vadduhm (vector signed short,
                                     vector bool short);
    vector signed short vec_vadduhm (vector signed short,
                                     vector signed short);
    vector unsigned short vec_vadduhm (vector bool short,
                                       vector unsigned short);
    vector unsigned short vec_vadduhm (vector unsigned short,
                                       vector bool short);
    vector unsigned short vec_vadduhm (vector unsigned short,
                                       vector unsigned short);
    
    vector signed char vec_vaddubm (vector bool char, vector signed char);
    vector signed char vec_vaddubm (vector signed char, vector bool char);
    vector signed char vec_vaddubm (vector signed char, vector signed char);
    vector unsigned char vec_vaddubm (vector bool char,
                                      vector unsigned char);
    vector unsigned char vec_vaddubm (vector unsigned char,
                                      vector bool char);
    vector unsigned char vec_vaddubm (vector unsigned char,
                                      vector unsigned char);
    
    vector unsigned int vec_addc (vector unsigned int, vector unsigned int);
    
    vector unsigned char vec_adds (vector bool char, vector unsigned char);
    vector unsigned char vec_adds (vector unsigned char, vector bool char);
    vector unsigned char vec_adds (vector unsigned char,
                                   vector unsigned char);
    vector signed char vec_adds (vector bool char, vector signed char);
    vector signed char vec_adds (vector signed char, vector bool char);
    vector signed char vec_adds (vector signed char, vector signed char);
    vector unsigned short vec_adds (vector bool short,
                                    vector unsigned short);
    vector unsigned short vec_adds (vector unsigned short,
                                    vector bool short);
    vector unsigned short vec_adds (vector unsigned short,
                                    vector unsigned short);
    vector signed short vec_adds (vector bool short, vector signed short);
    vector signed short vec_adds (vector signed short, vector bool short);
    vector signed short vec_adds (vector signed short, vector signed short);
    vector unsigned int vec_adds (vector bool int, vector unsigned int);
    vector unsigned int vec_adds (vector unsigned int, vector bool int);
    vector unsigned int vec_adds (vector unsigned int, vector unsigned int);
    vector signed int vec_adds (vector bool int, vector signed int);
    vector signed int vec_adds (vector signed int, vector bool int);
    vector signed int vec_adds (vector signed int, vector signed int);
    
    vector signed int vec_vaddsws (vector bool int, vector signed int);
    vector signed int vec_vaddsws (vector signed int, vector bool int);
    vector signed int vec_vaddsws (vector signed int, vector signed int);
    
    vector unsigned int vec_vadduws (vector bool int, vector unsigned int);
    vector unsigned int vec_vadduws (vector unsigned int, vector bool int);
    vector unsigned int vec_vadduws (vector unsigned int,
                                     vector unsigned int);
    
    vector signed short vec_vaddshs (vector bool short,
                                     vector signed short);
    vector signed short vec_vaddshs (vector signed short,
                                     vector bool short);
    vector signed short vec_vaddshs (vector signed short,
                                     vector signed short);
    
    vector unsigned short vec_vadduhs (vector bool short,
                                       vector unsigned short);
    vector unsigned short vec_vadduhs (vector unsigned short,
                                       vector bool short);
    vector unsigned short vec_vadduhs (vector unsigned short,
                                       vector unsigned short);
    
    vector signed char vec_vaddsbs (vector bool char, vector signed char);
    vector signed char vec_vaddsbs (vector signed char, vector bool char);
    vector signed char vec_vaddsbs (vector signed char, vector signed char);
    
    vector unsigned char vec_vaddubs (vector bool char,
                                      vector unsigned char);
    vector unsigned char vec_vaddubs (vector unsigned char,
                                      vector bool char);
    vector unsigned char vec_vaddubs (vector unsigned char,
                                      vector unsigned char);
    
    vector float vec_and (vector float, vector float);
    vector float vec_and (vector float, vector bool int);
    vector float vec_and (vector bool int, vector float);
    vector bool int vec_and (vector bool int, vector bool int);
    vector signed int vec_and (vector bool int, vector signed int);
    vector signed int vec_and (vector signed int, vector bool int);
    vector signed int vec_and (vector signed int, vector signed int);
    vector unsigned int vec_and (vector bool int, vector unsigned int);
    vector unsigned int vec_and (vector unsigned int, vector bool int);
    vector unsigned int vec_and (vector unsigned int, vector unsigned int);
    vector bool short vec_and (vector bool short, vector bool short);
    vector signed short vec_and (vector bool short, vector signed short);
    vector signed short vec_and (vector signed short, vector bool short);
    vector signed short vec_and (vector signed short, vector signed short);
    vector unsigned short vec_and (vector bool short,
                                   vector unsigned short);
    vector unsigned short vec_and (vector unsigned short,
                                   vector bool short);
    vector unsigned short vec_and (vector unsigned short,
                                   vector unsigned short);
    vector signed char vec_and (vector bool char, vector signed char);
    vector bool char vec_and (vector bool char, vector bool char);
    vector signed char vec_and (vector signed char, vector bool char);
    vector signed char vec_and (vector signed char, vector signed char);
    vector unsigned char vec_and (vector bool char, vector unsigned char);
    vector unsigned char vec_and (vector unsigned char, vector bool char);
    vector unsigned char vec_and (vector unsigned char,
                                  vector unsigned char);
    
    vector float vec_andc (vector float, vector float);
    vector float vec_andc (vector float, vector bool int);
    vector float vec_andc (vector bool int, vector float);
    vector bool int vec_andc (vector bool int, vector bool int);
    vector signed int vec_andc (vector bool int, vector signed int);
    vector signed int vec_andc (vector signed int, vector bool int);
    vector signed int vec_andc (vector signed int, vector signed int);
    vector unsigned int vec_andc (vector bool int, vector unsigned int);
    vector unsigned int vec_andc (vector unsigned int, vector bool int);
    vector unsigned int vec_andc (vector unsigned int, vector unsigned int);
    vector bool short vec_andc (vector bool short, vector bool short);
    vector signed short vec_andc (vector bool short, vector signed short);
    vector signed short vec_andc (vector signed short, vector bool short);
    vector signed short vec_andc (vector signed short, vector signed short);
    vector unsigned short vec_andc (vector bool short,
                                    vector unsigned short);
    vector unsigned short vec_andc (vector unsigned short,
                                    vector bool short);
    vector unsigned short vec_andc (vector unsigned short,
                                    vector unsigned short);
    vector signed char vec_andc (vector bool char, vector signed char);
    vector bool char vec_andc (vector bool char, vector bool char);
    vector signed char vec_andc (vector signed char, vector bool char);
    vector signed char vec_andc (vector signed char, vector signed char);
    vector unsigned char vec_andc (vector bool char, vector unsigned char);
    vector unsigned char vec_andc (vector unsigned char, vector bool char);
    vector unsigned char vec_andc (vector unsigned char,
                                   vector unsigned char);
    
    vector unsigned char vec_avg (vector unsigned char,
                                  vector unsigned char);
    vector signed char vec_avg (vector signed char, vector signed char);
    vector unsigned short vec_avg (vector unsigned short,
                                   vector unsigned short);
    vector signed short vec_avg (vector signed short, vector signed short);
    vector unsigned int vec_avg (vector unsigned int, vector unsigned int);
    vector signed int vec_avg (vector signed int, vector signed int);
    
    vector signed int vec_vavgsw (vector signed int, vector signed int);
    
    vector unsigned int vec_vavguw (vector unsigned int,
                                    vector unsigned int);
    
    vector signed short vec_vavgsh (vector signed short,
                                    vector signed short);
    
    vector unsigned short vec_vavguh (vector unsigned short,
                                      vector unsigned short);
    
    vector signed char vec_vavgsb (vector signed char, vector signed char);
    
    vector unsigned char vec_vavgub (vector unsigned char,
                                     vector unsigned char);
    
    vector float vec_copysign (vector float);
    
    vector float vec_ceil (vector float);
    
    vector signed int vec_cmpb (vector float, vector float);
    
    vector bool char vec_cmpeq (vector signed char, vector signed char);
    vector bool char vec_cmpeq (vector unsigned char, vector unsigned char);
    vector bool short vec_cmpeq (vector signed short, vector signed short);
    vector bool short vec_cmpeq (vector unsigned short,
                                 vector unsigned short);
    vector bool int vec_cmpeq (vector signed int, vector signed int);
    vector bool int vec_cmpeq (vector unsigned int, vector unsigned int);
    vector bool int vec_cmpeq (vector float, vector float);
    
    vector bool int vec_vcmpeqfp (vector float, vector float);
    
    vector bool int vec_vcmpequw (vector signed int, vector signed int);
    vector bool int vec_vcmpequw (vector unsigned int, vector unsigned int);
    
    vector bool short vec_vcmpequh (vector signed short,
                                    vector signed short);
    vector bool short vec_vcmpequh (vector unsigned short,
                                    vector unsigned short);
    
    vector bool char vec_vcmpequb (vector signed char, vector signed char);
    vector bool char vec_vcmpequb (vector unsigned char,
                                   vector unsigned char);
    
    vector bool int vec_cmpge (vector float, vector float);
    
    vector bool char vec_cmpgt (vector unsigned char, vector unsigned char);
    vector bool char vec_cmpgt (vector signed char, vector signed char);
    vector bool short vec_cmpgt (vector unsigned short,
                                 vector unsigned short);
    vector bool short vec_cmpgt (vector signed short, vector signed short);
    vector bool int vec_cmpgt (vector unsigned int, vector unsigned int);
    vector bool int vec_cmpgt (vector signed int, vector signed int);
    vector bool int vec_cmpgt (vector float, vector float);
    
    vector bool int vec_vcmpgtfp (vector float, vector float);
    
    vector bool int vec_vcmpgtsw (vector signed int, vector signed int);
    
    vector bool int vec_vcmpgtuw (vector unsigned int, vector unsigned int);
    
    vector bool short vec_vcmpgtsh (vector signed short,
                                    vector signed short);
    
    vector bool short vec_vcmpgtuh (vector unsigned short,
                                    vector unsigned short);
    
    vector bool char vec_vcmpgtsb (vector signed char, vector signed char);
    
    vector bool char vec_vcmpgtub (vector unsigned char,
                                   vector unsigned char);
    
    vector bool int vec_cmple (vector float, vector float);
    
    vector bool char vec_cmplt (vector unsigned char, vector unsigned char);
    vector bool char vec_cmplt (vector signed char, vector signed char);
    vector bool short vec_cmplt (vector unsigned short,
                                 vector unsigned short);
    vector bool short vec_cmplt (vector signed short, vector signed short);
    vector bool int vec_cmplt (vector unsigned int, vector unsigned int);
    vector bool int vec_cmplt (vector signed int, vector signed int);
    vector bool int vec_cmplt (vector float, vector float);
    
    vector float vec_ctf (vector unsigned int, const int);
    vector float vec_ctf (vector signed int, const int);
    
    vector float vec_vcfsx (vector signed int, const int);
    
    vector float vec_vcfux (vector unsigned int, const int);
    
    vector signed int vec_cts (vector float, const int);
    
    vector unsigned int vec_ctu (vector float, const int);
    
    void vec_dss (const int);
    
    void vec_dssall (void);
    
    void vec_dst (const vector unsigned char *, int, const int);
    void vec_dst (const vector signed char *, int, const int);
    void vec_dst (const vector bool char *, int, const int);
    void vec_dst (const vector unsigned short *, int, const int);
    void vec_dst (const vector signed short *, int, const int);
    void vec_dst (const vector bool short *, int, const int);
    void vec_dst (const vector pixel *, int, const int);
    void vec_dst (const vector unsigned int *, int, const int);
    void vec_dst (const vector signed int *, int, const int);
    void vec_dst (const vector bool int *, int, const int);
    void vec_dst (const vector float *, int, const int);
    void vec_dst (const unsigned char *, int, const int);
    void vec_dst (const signed char *, int, const int);
    void vec_dst (const unsigned short *, int, const int);
    void vec_dst (const short *, int, const int);
    void vec_dst (const unsigned int *, int, const int);
    void vec_dst (const int *, int, const int);
    void vec_dst (const unsigned long *, int, const int);
    void vec_dst (const long *, int, const int);
    void vec_dst (const float *, int, const int);
    
    void vec_dstst (const vector unsigned char *, int, const int);
    void vec_dstst (const vector signed char *, int, const int);
    void vec_dstst (const vector bool char *, int, const int);
    void vec_dstst (const vector unsigned short *, int, const int);
    void vec_dstst (const vector signed short *, int, const int);
    void vec_dstst (const vector bool short *, int, const int);
    void vec_dstst (const vector pixel *, int, const int);
    void vec_dstst (const vector unsigned int *, int, const int);
    void vec_dstst (const vector signed int *, int, const int);
    void vec_dstst (const vector bool int *, int, const int);
    void vec_dstst (const vector float *, int, const int);
    void vec_dstst (const unsigned char *, int, const int);
    void vec_dstst (const signed char *, int, const int);
    void vec_dstst (const unsigned short *, int, const int);
    void vec_dstst (const short *, int, const int);
    void vec_dstst (const unsigned int *, int, const int);
    void vec_dstst (const int *, int, const int);
    void vec_dstst (const unsigned long *, int, const int);
    void vec_dstst (const long *, int, const int);
    void vec_dstst (const float *, int, const int);
    
    void vec_dststt (const vector unsigned char *, int, const int);
    void vec_dststt (const vector signed char *, int, const int);
    void vec_dststt (const vector bool char *, int, const int);
    void vec_dststt (const vector unsigned short *, int, const int);
    void vec_dststt (const vector signed short *, int, const int);
    void vec_dststt (const vector bool short *, int, const int);
    void vec_dststt (const vector pixel *, int, const int);
    void vec_dststt (const vector unsigned int *, int, const int);
    void vec_dststt (const vector signed int *, int, const int);
    void vec_dststt (const vector bool int *, int, const int);
    void vec_dststt (const vector float *, int, const int);
    void vec_dststt (const unsigned char *, int, const int);
    void vec_dststt (const signed char *, int, const int);
    void vec_dststt (const unsigned short *, int, const int);
    void vec_dststt (const short *, int, const int);
    void vec_dststt (const unsigned int *, int, const int);
    void vec_dststt (const int *, int, const int);
    void vec_dststt (const unsigned long *, int, const int);
    void vec_dststt (const long *, int, const int);
    void vec_dststt (const float *, int, const int);
    
    void vec_dstt (const vector unsigned char *, int, const int);
    void vec_dstt (const vector signed char *, int, const int);
    void vec_dstt (const vector bool char *, int, const int);
    void vec_dstt (const vector unsigned short *, int, const int);
    void vec_dstt (const vector signed short *, int, const int);
    void vec_dstt (const vector bool short *, int, const int);
    void vec_dstt (const vector pixel *, int, const int);
    void vec_dstt (const vector unsigned int *, int, const int);
    void vec_dstt (const vector signed int *, int, const int);
    void vec_dstt (const vector bool int *, int, const int);
    void vec_dstt (const vector float *, int, const int);
    void vec_dstt (const unsigned char *, int, const int);
    void vec_dstt (const signed char *, int, const int);
    void vec_dstt (const unsigned short *, int, const int);
    void vec_dstt (const short *, int, const int);
    void vec_dstt (const unsigned int *, int, const int);
    void vec_dstt (const int *, int, const int);
    void vec_dstt (const unsigned long *, int, const int);
    void vec_dstt (const long *, int, const int);
    void vec_dstt (const float *, int, const int);
    
    vector float vec_expte (vector float);
    
    vector float vec_floor (vector float);
    
    vector float vec_ld (int, const vector float *);
    vector float vec_ld (int, const float *);
    vector bool int vec_ld (int, const vector bool int *);
    vector signed int vec_ld (int, const vector signed int *);
    vector signed int vec_ld (int, const int *);
    vector signed int vec_ld (int, const long *);
    vector unsigned int vec_ld (int, const vector unsigned int *);
    vector unsigned int vec_ld (int, const unsigned int *);
    vector unsigned int vec_ld (int, const unsigned long *);
    vector bool short vec_ld (int, const vector bool short *);
    vector pixel vec_ld (int, const vector pixel *);
    vector signed short vec_ld (int, const vector signed short *);
    vector signed short vec_ld (int, const short *);
    vector unsigned short vec_ld (int, const vector unsigned short *);
    vector unsigned short vec_ld (int, const unsigned short *);
    vector bool char vec_ld (int, const vector bool char *);
    vector signed char vec_ld (int, const vector signed char *);
    vector signed char vec_ld (int, const signed char *);
    vector unsigned char vec_ld (int, const vector unsigned char *);
    vector unsigned char vec_ld (int, const unsigned char *);
    
    vector signed char vec_lde (int, const signed char *);
    vector unsigned char vec_lde (int, const unsigned char *);
    vector signed short vec_lde (int, const short *);
    vector unsigned short vec_lde (int, const unsigned short *);
    vector float vec_lde (int, const float *);
    vector signed int vec_lde (int, const int *);
    vector unsigned int vec_lde (int, const unsigned int *);
    vector signed int vec_lde (int, const long *);
    vector unsigned int vec_lde (int, const unsigned long *);
    
    vector float vec_lvewx (int, float *);
    vector signed int vec_lvewx (int, int *);
    vector unsigned int vec_lvewx (int, unsigned int *);
    vector signed int vec_lvewx (int, long *);
    vector unsigned int vec_lvewx (int, unsigned long *);
    
    vector signed short vec_lvehx (int, short *);
    vector unsigned short vec_lvehx (int, unsigned short *);
    
    vector signed char vec_lvebx (int, char *);
    vector unsigned char vec_lvebx (int, unsigned char *);
    
    vector float vec_ldl (int, const vector float *);
    vector float vec_ldl (int, const float *);
    vector bool int vec_ldl (int, const vector bool int *);
    vector signed int vec_ldl (int, const vector signed int *);
    vector signed int vec_ldl (int, const int *);
    vector signed int vec_ldl (int, const long *);
    vector unsigned int vec_ldl (int, const vector unsigned int *);
    vector unsigned int vec_ldl (int, const unsigned int *);
    vector unsigned int vec_ldl (int, const unsigned long *);
    vector bool short vec_ldl (int, const vector bool short *);
    vector pixel vec_ldl (int, const vector pixel *);
    vector signed short vec_ldl (int, const vector signed short *);
    vector signed short vec_ldl (int, const short *);
    vector unsigned short vec_ldl (int, const vector unsigned short *);
    vector unsigned short vec_ldl (int, const unsigned short *);
    vector bool char vec_ldl (int, const vector bool char *);
    vector signed char vec_ldl (int, const vector signed char *);
    vector signed char vec_ldl (int, const signed char *);
    vector unsigned char vec_ldl (int, const vector unsigned char *);
    vector unsigned char vec_ldl (int, const unsigned char *);
    
    vector float vec_loge (vector float);
    
    vector unsigned char vec_lvsl (int, const volatile unsigned char *);
    vector unsigned char vec_lvsl (int, const volatile signed char *);
    vector unsigned char vec_lvsl (int, const volatile unsigned short *);
    vector unsigned char vec_lvsl (int, const volatile short *);
    vector unsigned char vec_lvsl (int, const volatile unsigned int *);
    vector unsigned char vec_lvsl (int, const volatile int *);
    vector unsigned char vec_lvsl (int, const volatile unsigned long *);
    vector unsigned char vec_lvsl (int, const volatile long *);
    vector unsigned char vec_lvsl (int, const volatile float *);
    
    vector unsigned char vec_lvsr (int, const volatile unsigned char *);
    vector unsigned char vec_lvsr (int, const volatile signed char *);
    vector unsigned char vec_lvsr (int, const volatile unsigned short *);
    vector unsigned char vec_lvsr (int, const volatile short *);
    vector unsigned char vec_lvsr (int, const volatile unsigned int *);
    vector unsigned char vec_lvsr (int, const volatile int *);
    vector unsigned char vec_lvsr (int, const volatile unsigned long *);
    vector unsigned char vec_lvsr (int, const volatile long *);
    vector unsigned char vec_lvsr (int, const volatile float *);
    
    vector float vec_madd (vector float, vector float, vector float);
    
    vector signed short vec_madds (vector signed short,
                                   vector signed short,
                                   vector signed short);
    
    vector unsigned char vec_max (vector bool char, vector unsigned char);
    vector unsigned char vec_max (vector unsigned char, vector bool char);
    vector unsigned char vec_max (vector unsigned char,
                                  vector unsigned char);
    vector signed char vec_max (vector bool char, vector signed char);
    vector signed char vec_max (vector signed char, vector bool char);
    vector signed char vec_max (vector signed char, vector signed char);
    vector unsigned short vec_max (vector bool short,
                                   vector unsigned short);
    vector unsigned short vec_max (vector unsigned short,
                                   vector bool short);
    vector unsigned short vec_max (vector unsigned short,
                                   vector unsigned short);
    vector signed short vec_max (vector bool short, vector signed short);
    vector signed short vec_max (vector signed short, vector bool short);
    vector signed short vec_max (vector signed short, vector signed short);
    vector unsigned int vec_max (vector bool int, vector unsigned int);
    vector unsigned int vec_max (vector unsigned int, vector bool int);
    vector unsigned int vec_max (vector unsigned int, vector unsigned int);
    vector signed int vec_max (vector bool int, vector signed int);
    vector signed int vec_max (vector signed int, vector bool int);
    vector signed int vec_max (vector signed int, vector signed int);
    vector float vec_max (vector float, vector float);
    
    vector float vec_vmaxfp (vector float, vector float);
    
    vector signed int vec_vmaxsw (vector bool int, vector signed int);
    vector signed int vec_vmaxsw (vector signed int, vector bool int);
    vector signed int vec_vmaxsw (vector signed int, vector signed int);
    
    vector unsigned int vec_vmaxuw (vector bool int, vector unsigned int);
    vector unsigned int vec_vmaxuw (vector unsigned int, vector bool int);
    vector unsigned int vec_vmaxuw (vector unsigned int,
                                    vector unsigned int);
    
    vector signed short vec_vmaxsh (vector bool short, vector signed short);
    vector signed short vec_vmaxsh (vector signed short, vector bool short);
    vector signed short vec_vmaxsh (vector signed short,
                                    vector signed short);
    
    vector unsigned short vec_vmaxuh (vector bool short,
                                      vector unsigned short);
    vector unsigned short vec_vmaxuh (vector unsigned short,
                                      vector bool short);
    vector unsigned short vec_vmaxuh (vector unsigned short,
                                      vector unsigned short);
    
    vector signed char vec_vmaxsb (vector bool char, vector signed char);
    vector signed char vec_vmaxsb (vector signed char, vector bool char);
    vector signed char vec_vmaxsb (vector signed char, vector signed char);
    
    vector unsigned char vec_vmaxub (vector bool char,
                                     vector unsigned char);
    vector unsigned char vec_vmaxub (vector unsigned char,
                                     vector bool char);
    vector unsigned char vec_vmaxub (vector unsigned char,
                                     vector unsigned char);
    
    vector bool char vec_mergeh (vector bool char, vector bool char);
    vector signed char vec_mergeh (vector signed char, vector signed char);
    vector unsigned char vec_mergeh (vector unsigned char,
                                     vector unsigned char);
    vector bool short vec_mergeh (vector bool short, vector bool short);
    vector pixel vec_mergeh (vector pixel, vector pixel);
    vector signed short vec_mergeh (vector signed short,
                                    vector signed short);
    vector unsigned short vec_mergeh (vector unsigned short,
                                      vector unsigned short);
    vector float vec_mergeh (vector float, vector float);
    vector bool int vec_mergeh (vector bool int, vector bool int);
    vector signed int vec_mergeh (vector signed int, vector signed int);
    vector unsigned int vec_mergeh (vector unsigned int,
                                    vector unsigned int);
    
    vector float vec_vmrghw (vector float, vector float);
    vector bool int vec_vmrghw (vector bool int, vector bool int);
    vector signed int vec_vmrghw (vector signed int, vector signed int);
    vector unsigned int vec_vmrghw (vector unsigned int,
                                    vector unsigned int);
    
    vector bool short vec_vmrghh (vector bool short, vector bool short);
    vector signed short vec_vmrghh (vector signed short,
                                    vector signed short);
    vector unsigned short vec_v