x86-64: Optimize memrchr with AVX2

Optimize memrchr with AVX2 to search 32 bytes with a single vector
compare instruction.  It is as fast as SSE2 memrchr for small data
sizes and up to 1X faster for large data sizes on Haswell.  Select
AVX2 memrchr on AVX2 machines where vzeroupper is preferred and AVX
unaligned load is fast.

	* sysdeps/x86_64/multiarch/Makefile (sysdep_routines): Add
	memrchr-sse2 and memrchr-avx2.
	* sysdeps/x86_64/multiarch/ifunc-impl-list.c
	(__libc_ifunc_impl_list): Add tests for __memrchr_avx2 and
	__memrchr_sse2.
	* sysdeps/x86_64/multiarch/memrchr-avx2.S: New file.
	* sysdeps/x86_64/multiarch/memrchr-sse2.S: Likewise.
	* sysdeps/x86_64/multiarch/memrchr.c: Likewise.

1 files changed, 26 insertions, 0 deletions

diff --git a/sysdeps/x86_64/multiarch/memrchr-sse2.S b/sysdeps/x86_64/multiarch/memrchr-sse2.S
new file mode 100644
index 0000000000..f518819c87
--- /dev/null
+++ b/sysdeps/x86_64/multiarch/memrchr-sse2.S
@@ -0,0 +1,26 @@
+/* memrchr optimized with SSE2.
+   Copyright (C) 2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#if IS_IN (libc)
+# define __memrchr __memrchr_sse2
+
+# undef weak_alias
+# define weak_alias(__memrchr, memrchr)
+#endif
+
+#include "../memrchr.S"