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| author | H.J. Lu <hjl.tools@gmail.com> | 2017-06-05 12:52:41 -0700 |
|---|---|---|
| committer | H.J. Lu <hjl.tools@gmail.com> | 2017-06-05 12:52:55 -0700 |
| commit | 935971ba6b4eaf67a34e4651434ba9b61e7355cc (patch) | |
| tree | 6daa389845c92adc076839582eb94871347b6779 /sysdeps/x86 | |
| parent | ef9c4cb6c7abb6340b52e19de31d2a56c8de5844 (diff) | |
x86-64: Optimize memcmp/wmemcmp with AVX2 and MOVBE
Optimize x86-64 memcmp/wmemcmp with AVX2. It uses vector compare as
much as possible. It is as fast as SSE4 memcmp for size <= 16 bytes
and up to 2X faster for size > 16 bytes on Haswell and Skylake. Select
AVX2 memcmp/wmemcmp on AVX2 machines where vzeroupper is preferred and
AVX unaligned load is fast.
NB: It uses TZCNT instead of BSF since TZCNT produces the same result
as BSF for non-zero input. TZCNT is faster than BSF and is executed
as BSF if machine doesn't support TZCNT.
Key features:
1. For size from 2 to 7 bytes, load as big endian with movbe and bswap
to avoid branches.
2. Use overlapping compare to avoid branch.
3. Use vector compare when size >= 4 bytes for memcmp or size >= 8
bytes for wmemcmp.
4. If size is 8 * VEC_SIZE or less, unroll the loop.
5. Compare 4 * VEC_SIZE at a time with the aligned first memory area.
6. Use 2 vector compares when size is 2 * VEC_SIZE or less.
7. Use 4 vector compares when size is 4 * VEC_SIZE or less.
8. Use 8 vector compares when size is 8 * VEC_SIZE or less.
* sysdeps/x86/cpu-features.h (index_cpu_MOVBE): New.
* sysdeps/x86_64/multiarch/Makefile (sysdep_routines): Add
memcmp-avx2 and wmemcmp-avx2.
* sysdeps/x86_64/multiarch/ifunc-impl-list.c
(__libc_ifunc_impl_list): Test __memcmp_avx2 and __wmemcmp_avx2.
* sysdeps/x86_64/multiarch/memcmp-avx2.S: New file.
* sysdeps/x86_64/multiarch/wmemcmp-avx2.S: Likewise.
* sysdeps/x86_64/multiarch/memcmp.S: Use __memcmp_avx2 on AVX
2 machines if AVX unaligned load is fast and vzeroupper is
preferred.
* sysdeps/x86_64/multiarch/wmemcmp.S: Use __wmemcmp_avx2 on AVX
2 machines if AVX unaligned load is fast and vzeroupper is
preferred.
Diffstat (limited to 'sysdeps/x86')
| -rw-r--r-- | sysdeps/x86/cpu-features.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/sysdeps/x86/cpu-features.h b/sysdeps/x86/cpu-features.h index 31c7c8023e..f2329ea696 100644 --- a/sysdeps/x86/cpu-features.h +++ b/sysdeps/x86/cpu-features.h @@ -102,6 +102,7 @@ # define index_cpu_AVX COMMON_CPUID_INDEX_1*CPUID_SIZE+CPUID_ECX_OFFSET # define index_cpu_AVX2 COMMON_CPUID_INDEX_7*CPUID_SIZE+CPUID_EBX_OFFSET # define index_cpu_ERMS COMMON_CPUID_INDEX_7*CPUID_SIZE+CPUID_EBX_OFFSET +# define index_cpu_MOVBE COMMON_CPUID_INDEX_1*CPUID_SIZE+CPUID_ECX_OFFSET # define index_arch_Fast_Rep_String FEATURE_INDEX_1*FEATURE_SIZE # define index_arch_Fast_Copy_Backward FEATURE_INDEX_1*FEATURE_SIZE |