gcc_hints.h

Go to the documentation of this file.

//Be very careful with some of these.
//Their use is described at
//http://blog.rlove.org/2005_10_01_archive.html

#ifndef _GCC_HINTS_H
#define _GCC_HINTS_H


//Primarily, likely and unlikely are often used.

#if __GNUC__ >= 3
# define ___always_inline   inline __attribute__ ((always_inline))
# define ___pure    __attribute__ ((pure))
# define ___const __attribute__ ((const))
# define ___noreturn  __attribute__ ((noreturn))
# define ___malloc  __attribute__ ((malloc))
# define ___must_check  __attribute__ ((warn_unused_result))
# define ___deprecated  __attribute__ ((deprecated))
# define ___used    __attribute__ ((used))
# define ___unused  __attribute__ ((unused))
# define ___packed  __attribute__ ((packed))
# define likely(x)  __builtin_expect (!!(x), 1)
# define unlikely(x)  __builtin_expect (!!(x), 0)
#else
# define ___always_inline inline  /* inline when possible */
# define ___pure    /* no pure */
# define ___const /* no const */
# define ___noreturn  /* no noreturn */
# define ___malloc  /* no malloc */
# define ___must_check  /* no warn_unused_result */
# define ___deprecated  /* no deprecated */
# define ___used    /* no used */
# define ___unused  /* no unused */
# define ___packed  /* no packed */
# define likely(x)  (x)
# define unlikely(x)  (x)
#endif

//Cool new optimizing things for GNU compiler collection 4.3 and later
#if __GNUC__ >= 4 && __GNUC_MINOR__ >= 3
/*For functions that are hotspots (i.e. called a lot and should be
 *  more agressively optimized for speed) vs functions that are cold
 *  and should be optimized for space over speed.  This also affects
 *  where the functions are stored in the final binary, to try to hit
 *  the cache more often (i.e. cold functions are pushed away from
 *  everything else, while hot functions are clustered together.)
 */
#define hotfunc __attribute__((hot))
#define coldfunc __attribute__((cold))
#else
#define hotfunc 
#define coldfunc
#endif

#endif