libc: replace generic memcmp with atom impl
This 'atom' impl is optimized with sse2, whereas the baseline is very
conservative. Since we use SSE-optimized builtins for ... everything
else, do that here, too.
To be clear, the atom impl for this is ssse3, which is required for x86
by the ABI.
Bug: 358360849
Test: mma
Change-Id: I3ba1e89987b75249ca5dc996e0450cff9cdfc8cb
diff --git a/libc/arch-x86/dynamic_function_dispatch.cpp b/libc/arch-x86/dynamic_function_dispatch.cpp
index db64237..98d7ec2 100644
--- a/libc/arch-x86/dynamic_function_dispatch.cpp
+++ b/libc/arch-x86/dynamic_function_dispatch.cpp
@@ -33,9 +33,8 @@
DEFINE_IFUNC_FOR(memcmp) {
__builtin_cpu_init();
- if (__builtin_cpu_is("atom")) RETURN_FUNC(memcmp_func_t, memcmp_atom);
if (__builtin_cpu_supports("sse4.1")) RETURN_FUNC(memcmp_func_t, memcmp_sse4);
- RETURN_FUNC(memcmp_func_t, memcmp_generic);
+ RETURN_FUNC(memcmp_func_t, memcmp_atom);
}
MEMCMP_SHIM()
diff --git a/libc/arch-x86/generic/string/memcmp.S b/libc/arch-x86/generic/string/memcmp.S
deleted file mode 100644
index 1d327c7..0000000
--- a/libc/arch-x86/generic/string/memcmp.S
+++ /dev/null
@@ -1,44 +0,0 @@
-/* $OpenBSD: memcmp.S,v 1.4 2005/08/07 11:30:38 espie Exp $ */
-/*
- * Written by J.T. Conklin <jtc@netbsd.org>.
- * Public domain.
- */
-
-#include <private/bionic_asm.h>
-
-ENTRY(memcmp_generic)
- pushl %edi
- pushl %esi
- movl 12(%esp),%edi
- movl 16(%esp),%esi
- cld /* set compare direction forward */
-
- movl 20(%esp),%ecx /* compare by words */
- shrl $2,%ecx
- repe
- cmpsl
- jne L5 /* do we match so far? */
-
- movl 20(%esp),%ecx /* compare remainder by bytes */
- andl $3,%ecx
- repe
- cmpsb
- jne L6 /* do we match? */
-
- xorl %eax,%eax /* we match, return zero */
- popl %esi
- popl %edi
- ret
-
-L5: movl $4,%ecx /* We know that one of the next */
- subl %ecx,%edi /* four pairs of bytes do not */
- subl %ecx,%esi /* match. */
- repe
- cmpsb
-L6: movzbl -1(%edi),%eax /* Perform unsigned comparison */
- movzbl -1(%esi),%edx
- subl %edx,%eax
- popl %esi
- popl %edi
- ret
-END(memcmp_generic)