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c939835f77
After some tests, gcc 5.x produces better code with likely() than without, contrary to gcc 4.x where it was better to disable it. Let's re-enable it for 5 and above.
108 lines
2.9 KiB
C
108 lines
2.9 KiB
C
/*
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* include/common/compiler.h
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* This files contains some compiler-specific settings.
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*
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* Copyright (C) 2000-2009 Willy Tarreau - w@1wt.eu
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation, version 2.1
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* exclusively.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#ifndef _COMMON_COMPILER_H
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#define _COMMON_COMPILER_H
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/*
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* Gcc before 3.0 needs [0] to declare a variable-size array
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*/
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#ifndef VAR_ARRAY
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#if __GNUC__ < 3
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#define VAR_ARRAY 0
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#else
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#define VAR_ARRAY
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#endif
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#endif
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/* Support passing function parameters in registers. For this, the
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* CONFIG_REGPARM macro has to be set to the maximal number of registers
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* allowed. Some functions have intentionally received a regparm lower than
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* their parameter count, it is in order to avoid register clobbering where
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* they are called.
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*/
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#ifndef REGPRM1
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#if CONFIG_REGPARM >= 1 && __GNUC__ >= 3
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#define REGPRM1 __attribute__((regparm(1)))
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#else
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#define REGPRM1
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#endif
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#endif
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#ifndef REGPRM2
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#if CONFIG_REGPARM >= 2 && __GNUC__ >= 3
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#define REGPRM2 __attribute__((regparm(2)))
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#else
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#define REGPRM2 REGPRM1
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#endif
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#endif
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#ifndef REGPRM3
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#if CONFIG_REGPARM >= 3 && __GNUC__ >= 3
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#define REGPRM3 __attribute__((regparm(3)))
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#else
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#define REGPRM3 REGPRM2
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#endif
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#endif
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/* By default, gcc does not inline large chunks of code, but we want it to
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* respect our choices.
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*/
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#if !defined(forceinline)
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#if __GNUC__ < 3
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#define forceinline inline
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#else
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#define forceinline inline __attribute__((always_inline))
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#endif
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#endif
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/*
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* Gcc >= 3 provides the ability for the programme to give hints to the
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* compiler about what branch of an if is most likely to be taken. This
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* helps the compiler produce the most compact critical paths, which is
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* generally better for the cache and to reduce the number of jumps.
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*/
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#if !defined(likely)
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#if __GNUC__ < 3
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#define __builtin_expect(x,y) (x)
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#define likely(x) (x)
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#define unlikely(x) (x)
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#elif __GNUC__ < 4 || __GNUC__ >= 5
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/* gcc 3.x and 5.x do the best job at this */
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#define likely(x) (__builtin_expect((x) != 0, 1))
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#define unlikely(x) (__builtin_expect((x) != 0, 0))
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#else
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/* GCC 4.x is stupid, it performs the comparison then compares it to 1,
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* so we cheat in a dirty way to prevent it from doing this. This will
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* only work with ints and booleans though.
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*/
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#define likely(x) (x)
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#define unlikely(x) (__builtin_expect((unsigned long)(x), 0))
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#endif
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#endif
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#endif /* _COMMON_COMPILER_H */
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