[glibc/release/2.34/master] x86-64: Remove Prefer_AVX2_STRCMP

[glibc/release/2.34/master] x86-64: Remove Prefer_AVX2_STRCMP

[Sunil Pandey]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=a182bb7a3922404f79def09d79ef89678b4049f0

commit a182bb7a3922404f79def09d79ef89678b4049f0
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Fri Oct 29 12:56:53 2021 -0700

    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)

Diff:
---
 sysdeps/x86/cpu-features.c                                     | 8 --------
 sysdeps/x86/cpu-tunables.c                                     | 2 --
 sysdeps/x86/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 de4e3c3b72..f4d4049e39 100644
--- a/sysdeps/x86/cpu-features.c
+++ b/sysdeps/x86/cpu-features.c
@@ -574,14 +574,6 @@ disable_tsx:
 	  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.  */
diff --git a/sysdeps/x86/cpu-tunables.c b/sysdeps/x86/cpu-tunables.c
index 00fe5045eb..61b05e5b1d 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 d7c93f00c5..1530d594b3 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_No_AVX512)
 BIT (MathVec_Prefer_No_AVX512)
 BIT (Prefer_FSRM)
-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 62b7abeeee..7c2901bf44 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 60ba0fe356..f94a421784 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))