From 69ce2769234e36e62c2db82e1e638124f076e82e Mon Sep 17 00:00:00 2001 From: "H.J. Lu" Date: Wed, 2 Mar 2022 15:42:47 -0800 Subject: [PATCH] x86-64: Remove Prefer_AVX2_STRCMP Remove Prefer_AVX2_STRCMP to enable EVEX strcmp. When comparing 2 32-byte strings, EVEX strcmp has been improved to require 1 load, 1 VPTESTM, 1 VPCMP, 1 KMOVD and 1 INCL instead of 2 loads, 3 VPCMPs, 2 KORDs, 1 KMOVD and 1 TESTL while AVX2 strcmp requires 1 load, 2 VPCMPEQs, 1 VPMINU, 1 VPMOVMSKB and 1 TESTL. EVEX strcmp is now faster than AVX2 strcmp by up to 40% on Tiger Lake and Ice Lake. (cherry picked from commit 14dbbf46a007ae5df36646b51ad0c9e5f5259f30) --- sysdeps/x86/cpu-features.c | 8 -------- sysdeps/x86/cpu-tunables.c | 2 -- .../include/cpu-features-preferred_feature_index_1.def | 1 - sysdeps/x86_64/multiarch/strcmp.c | 3 +-- sysdeps/x86_64/multiarch/strncmp.c | 3 +-- 5 files changed, 2 insertions(+), 15 deletions(-) diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c index 8885b48e..956bfb4f 100644 --- a/sysdeps/x86/cpu-features.c +++ b/sysdeps/x86/cpu-features.c @@ -533,14 +533,6 @@ init_cpu_features (struct cpu_features *cpu_features) if (CPU_FEATURE_USABLE_P (cpu_features, RTM)) cpu_features->preferred[index_arch_Prefer_No_VZEROUPPER] |= bit_arch_Prefer_No_VZEROUPPER; - - /* Since to compare 2 32-byte strings, 256-bit EVEX strcmp - requires 2 loads, 3 VPCMPs and 2 KORDs while AVX2 strcmp - requires 1 load, 2 VPCMPEQs, 1 VPMINU and 1 VPMOVMSKB, - AVX2 strcmp is faster than EVEX strcmp. */ - if (CPU_FEATURE_USABLE_P (cpu_features, AVX2)) - cpu_features->preferred[index_arch_Prefer_AVX2_STRCMP] - |= bit_arch_Prefer_AVX2_STRCMP; } } /* This spells out "AuthenticAMD". */ diff --git a/sysdeps/x86/cpu-tunables.c b/sysdeps/x86/cpu-tunables.c index 73adbaba..3173b2b9 100644 --- a/sysdeps/x86/cpu-tunables.c +++ b/sysdeps/x86/cpu-tunables.c @@ -239,8 +239,6 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp) CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features, Fast_Copy_Backward, disable, 18); - CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH - (n, cpu_features, Prefer_AVX2_STRCMP, AVX2, disable, 18); } break; case 19: diff --git a/sysdeps/x86/include/cpu-features-preferred_feature_index_1.def b/sysdeps/x86/include/cpu-features-preferred_feature_index_1.def index f2340624..e7277b33 100644 --- a/sysdeps/x86/include/cpu-features-preferred_feature_index_1.def +++ b/sysdeps/x86/include/cpu-features-preferred_feature_index_1.def @@ -32,5 +32,4 @@ BIT (Prefer_ERMS) BIT (Prefer_FSRM) BIT (Prefer_No_AVX512) BIT (MathVec_Prefer_No_AVX512) -BIT (Prefer_AVX2_STRCMP) BIT (Avoid_Short_Distance_REP_MOVSB) diff --git a/sysdeps/x86_64/multiarch/strcmp.c b/sysdeps/x86_64/multiarch/strcmp.c index 11bbea2b..f8a7220e 100644 --- a/sysdeps/x86_64/multiarch/strcmp.c +++ b/sysdeps/x86_64/multiarch/strcmp.c @@ -43,8 +43,7 @@ IFUNC_SELECTOR (void) { if (CPU_FEATURE_USABLE_P (cpu_features, AVX512VL) && CPU_FEATURE_USABLE_P (cpu_features, AVX512BW) - && CPU_FEATURE_USABLE_P (cpu_features, BMI2) - && !CPU_FEATURES_ARCH_P (cpu_features, Prefer_AVX2_STRCMP)) + && CPU_FEATURE_USABLE_P (cpu_features, BMI2)) return OPTIMIZE (evex); if (CPU_FEATURE_USABLE_P (cpu_features, RTM)) diff --git a/sysdeps/x86_64/multiarch/strncmp.c b/sysdeps/x86_64/multiarch/strncmp.c index 44c85116..7903f807 100644 --- a/sysdeps/x86_64/multiarch/strncmp.c +++ b/sysdeps/x86_64/multiarch/strncmp.c @@ -43,8 +43,7 @@ IFUNC_SELECTOR (void) { if (CPU_FEATURE_USABLE_P (cpu_features, AVX512VL) && CPU_FEATURE_USABLE_P (cpu_features, AVX512BW) - && CPU_FEATURE_USABLE_P (cpu_features, BMI2) - && !CPU_FEATURES_ARCH_P (cpu_features, Prefer_AVX2_STRCMP)) + && CPU_FEATURE_USABLE_P (cpu_features, BMI2)) return OPTIMIZE (evex); if (CPU_FEATURE_USABLE_P (cpu_features, RTM)) -- GitLab