From 14dbbf46a007ae5df36646b51ad0c9e5f5259f30 Mon Sep 17 00:00:00 2001 From: "H.J. Lu" Date: Fri, 29 Oct 2021 12:56:53 -0700 Subject: 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. --- sysdeps/x86/cpu-features.c | 8 -------- 1 file changed, 8 deletions(-) (limited to 'sysdeps/x86/cpu-features.c') diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c index 645bba6314..be2498b2e7 100644 --- a/sysdeps/x86/cpu-features.c +++ b/sysdeps/x86/cpu-features.c @@ -546,14 +546,6 @@ 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; } /* Avoid avoid short distance REP MOVSB on processor with FSRM. */ -- cgit 1.4.1