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From: Aurelien Jarno <aurel32@sourceware.org> To: glibc-cvs@sourceware.org Subject: [glibc/release/2.34/master] x86-64: Require BMI2 for AVX2 strcmp implementation Date: Mon, 3 Oct 2022 22:02:16 +0000 (GMT) [thread overview] Message-ID: <20221003220216.400BC3857C7D@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=e1561d8cf005a23bcaf514802854b493829a25b1 commit e1561d8cf005a23bcaf514802854b493829a25b1 Author: Aurelien Jarno <aurelien@aurel32.net> Date: Mon Oct 3 23:16:46 2022 +0200 x86-64: Require BMI2 for AVX2 strcmp implementation The AVX2 strcmp implementation uses the 'bzhi' instruction, which belongs to the BMI2 CPU feature. NB: It also uses the 'tzcnt' BMI1 instruction, but it is executed as BSF as BSF if the CPU doesn't support TZCNT, and produces the same result for non-zero input. Partially fixes: b77b06e0e296 ("x86: Optimize strcmp-avx2.S") Partially resolves: BZ #29611 Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com> (cherry picked from commit 4d64c6445735e9b34e2ac8e369312cbfc2f88e17) Diff: --- sysdeps/x86_64/multiarch/ifunc-impl-list.c | 4 +++- sysdeps/x86_64/multiarch/strcmp.c | 4 ++-- 2 files changed, 5 insertions(+), 3 deletions(-) diff --git a/sysdeps/x86_64/multiarch/ifunc-impl-list.c b/sysdeps/x86_64/multiarch/ifunc-impl-list.c index ca64b34c14..70931f1598 100644 --- a/sysdeps/x86_64/multiarch/ifunc-impl-list.c +++ b/sysdeps/x86_64/multiarch/ifunc-impl-list.c @@ -503,10 +503,12 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array, /* Support sysdeps/x86_64/multiarch/strcmp.c. */ IFUNC_IMPL (i, name, strcmp, IFUNC_IMPL_ADD (array, i, strcmp, - CPU_FEATURE_USABLE (AVX2), + (CPU_FEATURE_USABLE (AVX2) + && CPU_FEATURE_USABLE (BMI2)), __strcmp_avx2) IFUNC_IMPL_ADD (array, i, strcmp, (CPU_FEATURE_USABLE (AVX2) + && CPU_FEATURE_USABLE (BMI2) && CPU_FEATURE_USABLE (RTM)), __strcmp_avx2_rtm) IFUNC_IMPL_ADD (array, i, strcmp, diff --git a/sysdeps/x86_64/multiarch/strcmp.c b/sysdeps/x86_64/multiarch/strcmp.c index b457fb4c15..0c0cd20a03 100644 --- a/sysdeps/x86_64/multiarch/strcmp.c +++ b/sysdeps/x86_64/multiarch/strcmp.c @@ -40,11 +40,11 @@ IFUNC_SELECTOR (void) const struct cpu_features* cpu_features = __get_cpu_features (); if (CPU_FEATURE_USABLE_P (cpu_features, AVX2) + && CPU_FEATURE_USABLE_P (cpu_features, BMI2) && CPU_FEATURES_ARCH_P (cpu_features, AVX_Fast_Unaligned_Load)) { if (CPU_FEATURE_USABLE_P (cpu_features, AVX512VL) - && CPU_FEATURE_USABLE_P (cpu_features, AVX512BW) - && CPU_FEATURE_USABLE_P (cpu_features, BMI2)) + && CPU_FEATURE_USABLE_P (cpu_features, AVX512BW)) return OPTIMIZE (evex); if (CPU_FEATURE_USABLE_P (cpu_features, RTM))
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