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commit e1561d8cf005a23bcaf514802854b493829a25b1
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Author: Aurelien Jarno <aurelien@aurel32.net>
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Date: Mon Oct 3 23:16:46 2022 +0200
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x86-64: Require BMI2 for AVX2 strcmp implementation
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The AVX2 strcmp implementation uses the 'bzhi' instruction, which
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belongs to the BMI2 CPU feature.
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NB: It also uses the 'tzcnt' BMI1 instruction, but it is executed as BSF
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as BSF if the CPU doesn't support TZCNT, and produces the same result
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for non-zero input.
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Partially fixes: b77b06e0e296 ("x86: Optimize strcmp-avx2.S")
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Partially resolves: BZ #29611
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Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>
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(cherry picked from commit 4d64c6445735e9b34e2ac8e369312cbfc2f88e17)
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diff --git a/sysdeps/x86_64/multiarch/ifunc-impl-list.c b/sysdeps/x86_64/multiarch/ifunc-impl-list.c
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index ca64b34c146a76f9..70931f15985334af 100644
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--- a/sysdeps/x86_64/multiarch/ifunc-impl-list.c
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+++ b/sysdeps/x86_64/multiarch/ifunc-impl-list.c
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@@ -503,10 +503,12 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
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/* Support sysdeps/x86_64/multiarch/strcmp.c. */
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IFUNC_IMPL (i, name, strcmp,
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IFUNC_IMPL_ADD (array, i, strcmp,
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- CPU_FEATURE_USABLE (AVX2),
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+ (CPU_FEATURE_USABLE (AVX2)
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+ && CPU_FEATURE_USABLE (BMI2)),
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__strcmp_avx2)
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IFUNC_IMPL_ADD (array, i, strcmp,
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(CPU_FEATURE_USABLE (AVX2)
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+ && CPU_FEATURE_USABLE (BMI2)
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&& CPU_FEATURE_USABLE (RTM)),
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__strcmp_avx2_rtm)
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IFUNC_IMPL_ADD (array, i, strcmp,
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diff --git a/sysdeps/x86_64/multiarch/strcmp.c b/sysdeps/x86_64/multiarch/strcmp.c
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index b457fb4c150e4407..0c0cd20a03278a2b 100644
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--- a/sysdeps/x86_64/multiarch/strcmp.c
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+++ b/sysdeps/x86_64/multiarch/strcmp.c
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@@ -40,11 +40,11 @@ IFUNC_SELECTOR (void)
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const struct cpu_features* cpu_features = __get_cpu_features ();
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if (CPU_FEATURE_USABLE_P (cpu_features, AVX2)
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+ && CPU_FEATURE_USABLE_P (cpu_features, BMI2)
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&& CPU_FEATURES_ARCH_P (cpu_features, AVX_Fast_Unaligned_Load))
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{
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if (CPU_FEATURE_USABLE_P (cpu_features, AVX512VL)
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- && CPU_FEATURE_USABLE_P (cpu_features, AVX512BW)
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- && CPU_FEATURE_USABLE_P (cpu_features, BMI2))
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+ && CPU_FEATURE_USABLE_P (cpu_features, AVX512BW))
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return OPTIMIZE (evex);
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if (CPU_FEATURE_USABLE_P (cpu_features, RTM))
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