62 lines
2.5 KiB
Diff
62 lines
2.5 KiB
Diff
From 7afbd1e56acb721031bffd876f275dcb1af7e530 Mon Sep 17 00:00:00 2001
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From: Aurelien Jarno <aurelien@aurel32.net>
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Date: Mon, 3 Oct 2022 23:46:11 +0200
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Subject: [PATCH 51/81] 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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---
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sysdeps/x86_64/multiarch/ifunc-impl-list.c | 4 +++-
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sysdeps/x86_64/multiarch/strcmp.c | 4 ++--
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2 files changed, 5 insertions(+), 3 deletions(-)
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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 d208fae4bf..a42b0a4620 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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@@ -591,10 +591,12 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
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&& CPU_FEATURE_USABLE (BMI2)),
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__strcmp_evex)
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X86_IFUNC_IMPL_ADD_V3 (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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X86_IFUNC_IMPL_ADD_V3 (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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X86_IFUNC_IMPL_ADD_V2 (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 fdd5afe3af..9d6c9f66ba 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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@@ -45,12 +45,12 @@ IFUNC_SELECTOR (void)
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const struct cpu_features *cpu_features = __get_cpu_features ();
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if (X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, AVX2)
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+ && X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, BMI2)
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&& X86_ISA_CPU_FEATURES_ARCH_P (cpu_features,
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AVX_Fast_Unaligned_Load, ))
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{
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if (X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, AVX512VL)
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- && X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, AVX512BW)
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- && X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, BMI2))
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+ && X86_ISA_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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--
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2.19.1.6.gb485710b
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