postgres.git / summary / log / commit / refs

commit    8a934d6778331f2ac04a40f4f22178a56a232315
Author:   Andres Freund <andres@anarazel.de>
Date:     Wed Mar 28 19:45:32 2018 +0000
First released in: 11.0

    Use isinf builtin for clang, for performance.
    
    When compiling with clang glibc's definition of isinf() ends up
    leading to and external libc function call. That's because there was a
    bug in the builtin in an old gcc version, and clang claims
    compatibility with an older version.  That causes clang to be
    measurably slower for floating point heavy workloads than gcc.
    
    To fix simply redirect isinf when using clang and clang confirms it
    has __builtin_isinf().


 src/include/port.h | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/src/include/port.h b/src/include/port.h
index 3e528fa1725..a514ab758b5 100644
--- a/src/include/port.h
+++ b/src/include/port.h
@@ -343,7 +343,20 @@ extern int	getpeereid(int sock, uid_t *uid, gid_t *gid);
 
 #ifndef HAVE_ISINF
 extern int	isinf(double x);
-#endif
+#else
+/*
+ * Glibc doesn't use the builtin for clang due to a *gcc* bug in a version
+ * newer than the gcc compatibility clang claims to have. This would cause a
+ * *lot* of superflous function calls, therefore revert when using clang.
+ */
+#ifdef __clang__
+/* needs to be separate to not confuse other compilers */
+#if __has_builtin(__builtin_isinf)
+#undef isinf
+#define isinf __builtin_isinf
+#endif							/* __has_builtin(isinf) */
+#endif							/* __clang__ */
+#endif							/* !HAVE_ISINF */
 
 #ifndef HAVE_MKDTEMP
 extern char *mkdtemp(char *path);


[parent: 266b6acb312f]