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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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2
sysdeps/x86/cpu-tunables.c
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@@ -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: