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commit a182bb7a3922404f79def09d79ef89678b4049f0
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Author: H.J. Lu <hjl.tools@gmail.com>
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Date: Fri Oct 29 12:56:53 2021 -0700
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x86-64: Remove Prefer_AVX2_STRCMP
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Remove Prefer_AVX2_STRCMP to enable EVEX strcmp. When comparing 2 32-byte
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strings, EVEX strcmp has been improved to require 1 load, 1 VPTESTM, 1
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VPCMP, 1 KMOVD and 1 INCL instead of 2 loads, 3 VPCMPs, 2 KORDs, 1 KMOVD
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and 1 TESTL while AVX2 strcmp requires 1 load, 2 VPCMPEQs, 1 VPMINU, 1
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VPMOVMSKB and 1 TESTL. EVEX strcmp is now faster than AVX2 strcmp by up
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to 40% on Tiger Lake and Ice Lake.
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(cherry picked from commit 14dbbf46a007ae5df36646b51ad0c9e5f5259f30)
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diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
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index de4e3c3b7258120d..f4d4049e391cbabd 100644
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--- a/sysdeps/x86/cpu-features.c
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+++ b/sysdeps/x86/cpu-features.c
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@@ -574,14 +574,6 @@ disable_tsx:
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if (CPU_FEATURE_USABLE_P (cpu_features, RTM))
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cpu_features->preferred[index_arch_Prefer_No_VZEROUPPER]
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|= bit_arch_Prefer_No_VZEROUPPER;
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-
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- /* Since to compare 2 32-byte strings, 256-bit EVEX strcmp
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- requires 2 loads, 3 VPCMPs and 2 KORDs while AVX2 strcmp
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- requires 1 load, 2 VPCMPEQs, 1 VPMINU and 1 VPMOVMSKB,
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- AVX2 strcmp is faster than EVEX strcmp. */
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- if (CPU_FEATURE_USABLE_P (cpu_features, AVX2))
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- cpu_features->preferred[index_arch_Prefer_AVX2_STRCMP]
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- |= bit_arch_Prefer_AVX2_STRCMP;
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}
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/* Avoid avoid short distance REP MOVSB on processor with FSRM. */
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diff --git a/sysdeps/x86/cpu-tunables.c b/sysdeps/x86/cpu-tunables.c
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index 58f2fad4323d5d91..957db3ad229ba39f 100644
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--- a/sysdeps/x86/cpu-tunables.c
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+++ b/sysdeps/x86/cpu-tunables.c
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@@ -239,8 +239,6 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
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CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features,
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Fast_Copy_Backward,
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disable, 18);
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- CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH
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- (n, cpu_features, Prefer_AVX2_STRCMP, AVX2, disable, 18);
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}
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break;
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case 19:
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diff --git a/sysdeps/x86/include/cpu-features-preferred_feature_index_1.def b/sysdeps/x86/include/cpu-features-preferred_feature_index_1.def
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index 3bdc76cf71007948..8250bfcbecd29a9f 100644
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--- a/sysdeps/x86/include/cpu-features-preferred_feature_index_1.def
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+++ b/sysdeps/x86/include/cpu-features-preferred_feature_index_1.def
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@@ -31,5 +31,4 @@ BIT (Prefer_ERMS)
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BIT (Prefer_No_AVX512)
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BIT (MathVec_Prefer_No_AVX512)
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BIT (Prefer_FSRM)
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-BIT (Prefer_AVX2_STRCMP)
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BIT (Avoid_Short_Distance_REP_MOVSB)
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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 62b7abeeee646ab4..7c2901bf44456259 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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@@ -43,8 +43,7 @@ IFUNC_SELECTOR (void)
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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_FEATURES_ARCH_P (cpu_features, Prefer_AVX2_STRCMP))
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+ && CPU_FEATURE_USABLE_P (cpu_features, BMI2))
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return OPTIMIZE (evex);
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if (CPU_FEATURE_USABLE_P (cpu_features, RTM))
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diff --git a/sysdeps/x86_64/multiarch/strncmp.c b/sysdeps/x86_64/multiarch/strncmp.c
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index 60ba0fe356b31779..f94a421784bfe923 100644
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--- a/sysdeps/x86_64/multiarch/strncmp.c
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+++ b/sysdeps/x86_64/multiarch/strncmp.c
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@@ -43,8 +43,7 @@ IFUNC_SELECTOR (void)
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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_FEATURES_ARCH_P (cpu_features, Prefer_AVX2_STRCMP))
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+ && CPU_FEATURE_USABLE_P (cpu_features, BMI2))
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return OPTIMIZE (evex);
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if (CPU_FEATURE_USABLE_P (cpu_features, RTM))
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