Author: danielsh
Date: Mon Jul 29 18:35:25 2013
New Revision: 1508170
URL: http://svn.apache.org/r1508170
Log:
Follow-up to r1507366: svn_hash_gets: compute the length of string literal
keys (common case) at compile-time, without multiply-evaluating dynamically-
computed keys.
Review by: philip
breser
* build/ac-macros/svn-macros.m4
(SVN_CHECK_FOR_DUNDER_BUILTINS): New macro.
* configure.ac:
Call SVN_CHECK_FOR_DUNDER_BUILTINS() and set -D SVN_HAS_DUNDER_BUILTINS.
* subversion/include/svn_hash.h
(svn_hash_gets): Use __builtin_choose_expr() and __builtin_constant_p(),
when available.
Modified:
subversion/trunk/build/ac-macros/svn-macros.m4
subversion/trunk/configure.ac
subversion/trunk/subversion/include/svn_hash.h
Modified: subversion/trunk/build/ac-macros/svn-macros.m4
URL:
http://svn.apache.org/viewvc/subversion/trunk/build/ac-macros/svn-macros.m4?rev=1508170&r1=1508169&r2=1508170&view=diff
==============================================================================
--- subversion/trunk/build/ac-macros/svn-macros.m4 (original)
+++ subversion/trunk/build/ac-macros/svn-macros.m4 Mon Jul 29 18:35:25 2013
@@ -163,3 +163,26 @@ AC_DEFUN([SVN_CHECK_FOR_ATOMIC_BUILTINS]
return 0;
}], [svn_cv_atomic_builtins=yes], [svn_cv_atomic_builtins=no],
[svn_cv_atomic_builtins=no])])
])
+
+AC_DEFUN([SVN_CHECK_FOR_DUNDER_BUILTINS],
+[
+ AC_CACHE_CHECK([whether the compiler provides dunder builtins],
[svn_cv_dunder_builtins],
+ [
+ AC_RUN_IFELSE([AC_LANG_SOURCE([[
+ int main(int argc)
+ {
+ return (!__builtin_choose_expr(__builtin_constant_p(argc), 1, 0)
+ && __builtin_choose_expr(__builtin_constant_p("foobar"), 1, 0))
+ ? 0 /* EXIT_SUCCESS */ : 1 /* EXIT_FAILURE */;
+ }]])],
+ svn_cv_dunder_builtins="yes",
+ svn_cv_dunder_builtins="no",
+ [AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
+ int main(void){
+ return __builtin_choose_expr(__builtin_constant_p("foobar"), 0, 1);
+ }]])],
+ svn_cv_dunder_builtins="yes",
+ svn_cv_dunder_builtins="no")
+ ])
+ ])
+])
Modified: subversion/trunk/configure.ac
URL:
http://svn.apache.org/viewvc/subversion/trunk/configure.ac?rev=1508170&r1=1508169&r2=1508170&view=diff
==============================================================================
--- subversion/trunk/configure.ac (original)
+++ subversion/trunk/configure.ac Mon Jul 29 18:35:25 2013
@@ -167,11 +167,15 @@ if test -n "$sqlite_compat_ver" && test
fi
SVN_CHECK_FOR_ATOMIC_BUILTINS
-
if test "$svn_cv_atomic_builtins" = "yes"; then
AC_DEFINE(SVN_HAS_ATOMIC_BUILTINS, 1, [Define if compiler provides atomic
builtins])
fi
+SVN_CHECK_FOR_DUNDER_BUILTINS
+if test "$svn_cv_dunder_builtins" = "yes"; then
+ AC_DEFINE(SVN_HAS_DUNDER_BUILTINS, 1, [Define if compiler provides
__builtin_constant_p and __builtin_choose_expr])
+fi
+
dnl Set up a number of directories ---------------------
dnl Create SVN_BINDIR for proper substitution
Modified: subversion/trunk/subversion/include/svn_hash.h
URL:
http://svn.apache.org/viewvc/subversion/trunk/subversion/include/svn_hash.h?rev=1508170&r1=1508169&r2=1508170&view=diff
==============================================================================
--- subversion/trunk/subversion/include/svn_hash.h (original)
+++ subversion/trunk/subversion/include/svn_hash.h Mon Jul 29 18:35:25 2013
@@ -244,8 +244,25 @@ svn_hash_from_cstring_keys(apr_hash_t **
*
* @since New in 1.8.
*/
-#define svn_hash_gets(ht, key) \
+#if SVN_HAS_DUNDER_BUILTINS
+/* We have two use-cases:
+ 1. (common) KEY is a string literal.
+ 2. (rare) KEY is the result of an expensive function call.
+ For the former, we want to evaluate the string length at compile time. (We
+ use strlen(), which gets optimized to a constant.) For the latter, however,
+ we want to avoid having the macro multiply-evaluate KEY. So, if our
+ compiler is smart enough (that includes at least gcc and clang), we use
+ __builtin_constant_p() to have our cake and eat it too: */
+# define svn_hash_gets(ht, key) \
+ apr_hash_get(ht, key, \
+ __builtin_constant_p(strlen(key)) \
+ ? strlen(key) : APR_HASH_KEY_STRING)
+#else
+/* ... and when our compiler is anything else, we take the hit and compute the
+ length of string literals at run-time. */
+# define svn_hash_gets(ht, key) \
apr_hash_get(ht, key, APR_HASH_KEY_STRING)
+#endif
/** Shortcut for apr_hash_set() with a const char * key.
*
