Hi all,
This patch supersedes yesterday's; it impements autoconf-based
detection of compiler builtins.
The purpose of this feature is to give explicit hints to compilers
supporting them about the likely outcome of an if() clause; thus
allowing the compiler to do explicit optimizations (CPU predictor
hinting, code layout optimizations) based on the predicted outcome.
The obvious case is the singleton pattern, where the existence check
will always be true except for the first time.
This work is not correlated to Alex's SMP-inspired cachemgr work.
Kinkie
# Bazaar merge directive format 2 (Bazaar 0.90)
# revision_id: kin...@squid-cache.org-20101013160855-lmi2vbrokh7e64yl
# target_branch: file:///home/kinkie/squid/workspace/squid-trunk-co/
# testament_sha1: 4c48469579bcf0502e4769dd550e3fea76e1e29a
# timestamp: 2010-10-13 18:09:02 +0200
# base_revision_id: amosjeffr...@squid-cache.org-20101006130311-\
# xnwwkgwnuhy5oj0r
#
# Begin patch
=== modified file 'acinclude/os-deps.m4'
--- acinclude/os-deps.m4 2010-08-29 14:07:18 +0000
+++ acinclude/os-deps.m4 2010-10-13 16:08:55 +0000
@@ -814,3 +814,17 @@
squid_cv_resuid_works="no" ],[:])
)
])
+
+
+dnl check compiler support for gcc-style conditional branch hinting
+dnl set squid_cv_branch_hints to either "no" or "yes"
+AC_DEFUN([SQUID_CHECK_GCC_COMPILER_BRANCH_HINTS],[
+ AC_CACHE_CHECK(if the compiler supports branch hints, squid_cv_branch_hints,
+ AC_LINK_IFELSE([AC_LANG_PROGRAM([],[[
+ int foo=1;
+ if (__builtin_expect(!!(foo==1), 1)) {
+ foo=2;
+ }
+ ]])],[squid_cv_branch_hints=yes],[squid_cv_branch_hints=no])
+ )
+])
=== modified file 'configure.in'
--- configure.in 2010-10-06 13:03:11 +0000
+++ configure.in 2010-10-13 16:08:55 +0000
@@ -79,6 +79,10 @@
AC_USE_SYSTEM_EXTENSIONS
fi
+SQUID_CHECK_GCC_COMPILER_BRANCH_HINTS
+SQUID_DEFINE_BOOL(HAVE_GCC_BRANCH_HINTS,$squid_cv_branch_hints,
+ [Defined if the compiler supports gcc-style conditional branch hinting])
+
AC_ARG_ENABLE(strict-error-checking,
AS_HELP_STRING([--disable-strict-error-checking],[By default squid is compiled
with all possible static compiler error-checks enabled.
=== added file 'include/branch-hints.h'
--- include/branch-hints.h 1970-01-01 00:00:00 +0000
+++ include/branch-hints.h 2010-10-13 16:08:55 +0000
@@ -0,0 +1,45 @@
+/*
+ * branch-hints.h (C) 2009 Francesco Chemolli <kin...@squid-cache.org>
+ *
+ * SQUID Web Proxy Cache http://www.squid-cache.org/
+ * ----------------------------------------------------------
+ *
+ * Squid is the result of efforts by numerous individuals from
+ * the Internet community; see the CONTRIBUTORS file for full
+ * details. Many organizations have provided support for Squid's
+ * development; see the SPONSORS file for full details. Squid is
+ * Copyrighted (C) 2001 by the Regents of the University of
+ * California; see the COPYRIGHT file for full details. Squid
+ * incorporates software developed and/or copyrighted by other
+ * sources; see the CREDITS file for full details.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA.
+ *
+ */
+
+#ifndef BRANCHHINTS_H_
+#define BRANCHHINTS_H_
+
+#include "config.h"
+
+#if HAVE_GCC_BRANCH_HINTS
+#define likely(x) __builtin_expect(!!(x), 1)
+#define unlikely(x) __builtin_expect(!!(x), 0)
+#else
+#define likely(x) (x)
+#define unlikely(x) (x)
+#endif /* __GNUC__ */
+
+#endif /* BRANCHHINTS_H_ */
=== modified file 'src/cache_manager.cc'
--- src/cache_manager.cc 2010-08-16 11:35:40 +0000
+++ src/cache_manager.cc 2010-10-12 15:42:26 +0000
@@ -33,6 +33,7 @@
*
*/
+#include "branch-hints.h"
#include "CacheManager.h"
#include "errorpage.h"
#include "HttpReply.h"
@@ -478,7 +479,7 @@
CacheManager*
CacheManager::GetInstance()
{
- if (instance == 0) {
+ if (unlikely(instance == 0)) {
debugs(16, 6, "CacheManager::GetInstance: starting cachemanager up");
instance = new CacheManager;
}
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