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Willy Tarreaucc05fba2009-10-27 21:40:18 +01001/*
2 * include/common/compiler.h
3 * This files contains some compiler-specific settings.
4 *
5 * Copyright (C) 2000-2009 Willy Tarreau - w@1wt.eu
6 *
7 * This library is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation, version 2.1
10 * exclusively.
11 *
12 * This library is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
16 *
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with this library; if not, write to the Free Software
Willy Tarreauf3bfede2011-07-25 11:38:17 +020019 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
Willy Tarreaucc05fba2009-10-27 21:40:18 +010020 */
21
22#ifndef _COMMON_COMPILER_H
23#define _COMMON_COMPILER_H
24
25
26/*
27 * Gcc before 3.0 needs [0] to declare a variable-size array
28 */
29#ifndef VAR_ARRAY
30#if __GNUC__ < 3
31#define VAR_ARRAY 0
32#else
33#define VAR_ARRAY
34#endif
35#endif
36
37
38/* Support passing function parameters in registers. For this, the
39 * CONFIG_REGPARM macro has to be set to the maximal number of registers
40 * allowed. Some functions have intentionally received a regparm lower than
41 * their parameter count, it is in order to avoid register clobbering where
42 * they are called.
43 */
44#ifndef REGPRM1
45#if CONFIG_REGPARM >= 1 && __GNUC__ >= 3
46#define REGPRM1 __attribute__((regparm(1)))
47#else
48#define REGPRM1
49#endif
50#endif
51
52#ifndef REGPRM2
53#if CONFIG_REGPARM >= 2 && __GNUC__ >= 3
54#define REGPRM2 __attribute__((regparm(2)))
55#else
56#define REGPRM2 REGPRM1
57#endif
58#endif
59
60#ifndef REGPRM3
61#if CONFIG_REGPARM >= 3 && __GNUC__ >= 3
62#define REGPRM3 __attribute__((regparm(3)))
63#else
64#define REGPRM3 REGPRM2
65#endif
66#endif
67
68
69/* By default, gcc does not inline large chunks of code, but we want it to
70 * respect our choices.
71 */
72#if !defined(forceinline)
73#if __GNUC__ < 3
74#define forceinline inline
75#else
76#define forceinline inline __attribute__((always_inline))
77#endif
78#endif
79
80
81/*
82 * Gcc >= 3 provides the ability for the programme to give hints to the
83 * compiler about what branch of an if is most likely to be taken. This
84 * helps the compiler produce the most compact critical paths, which is
85 * generally better for the cache and to reduce the number of jumps.
86 */
87#if !defined(likely)
88#if __GNUC__ < 3
89#define __builtin_expect(x,y) (x)
90#define likely(x) (x)
91#define unlikely(x) (x)
Willy Tarreauc9398352017-10-08 22:26:03 +020092#elif __GNUC__ < 4 || __GNUC__ >= 5
93/* gcc 3.x and 5.x do the best job at this */
Willy Tarreaucc05fba2009-10-27 21:40:18 +010094#define likely(x) (__builtin_expect((x) != 0, 1))
95#define unlikely(x) (__builtin_expect((x) != 0, 0))
96#else
97/* GCC 4.x is stupid, it performs the comparison then compares it to 1,
98 * so we cheat in a dirty way to prevent it from doing this. This will
99 * only work with ints and booleans though.
100 */
101#define likely(x) (x)
102#define unlikely(x) (__builtin_expect((unsigned long)(x), 0))
103#endif
104#endif
105
106
107#endif /* _COMMON_COMPILER_H */