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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
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.
This commit is contained in:
H.J. Lu
2021-10-29 12:56:53 -07:00
parent c46e9afb2d
commit 14dbbf46a0
5 changed files with 2 additions and 15 deletions
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8
sysdeps/x86/cpu-features.c
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@ -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. */