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Re: [PATCH v2] Do not transform strchr into rawmemchr
- From: Wilco Dijkstra <Wilco dot Dijkstra at arm dot com>
- To: "libc-alpha at sourceware dot org" <libc-alpha at sourceware dot org>
- Cc: nd <nd at arm dot com>
- Date: Thu, 9 Feb 2017 15:28:35 +0000
- Subject: Re: [PATCH v2] Do not transform strchr into rawmemchr
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From: Wilco Dijkstra
Sent: 23 November 2016 17:19
To: libc-alpha@sourceware.org
Cc: nd
Subject: [PATCH v2] Do not transform strchr into rawmemchr
Version 2 of the patch removes the strchr define completely as
suggested:
GLIBC uses strchr (s, '\0') as an idiom to find the end of a string.
This is transformed into rawmemchr by the bits/string2.h header.
However this is generally slower than strlen on most targets, even when
an optimized rawmemchr implementation exists. Since GCC7 optimizes
strchr (s, '\0') to strlen (s) + s, the GLIBC headers should not
transform this to rawmemchr. As GCC recognizes strchr as a builtin,
defining strchr as the builtin is not useful.
Regress passes, OK for commit?
ChangeLog:
2015-11-23 Wilco Dijkstra <wdijkstr@arm.com>
* string/bits/string2.h (strchr): Remove define.
--
diff --git a/string/bits/string2.h b/string/bits/string2.h
index e39d4f1a85c25a4f47418e6a5613b27177ca6cbb..de426b47cae09933b2dc53e0956d63b4c93aebc0 100644
--- a/string/bits/string2.h
+++ b/string/bits/string2.h
@@ -58,16 +58,6 @@
#endif
-#ifndef _HAVE_STRING_ARCH_strchr
-extern void *__rawmemchr (const void *__s, int __c);
-# define strchr(s, c) \
- (__extension__ (__builtin_constant_p (c) && !__builtin_constant_p (s) \
- && (c) == '\0' \
- ? (char *) __rawmemchr (s, c) \
- : __builtin_strchr (s, c)))
-#endif
-
-
/* Copy SRC to DEST, returning pointer to final NUL byte. */
#ifdef __USE_GNU
# ifndef _HAVE_STRING_ARCH_stpcpy