[glibc/release/2.31/master] x86: Set Prefer_No_VZEROUPPER and add Prefer_AVX2_STRCMP

[H.J. Lu <hjl@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=2d612b2c5f16ffa859e2567365f20ce3de695fa3

commit 2d612b2c5f16ffa859e2567365f20ce3de695fa3
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Fri Feb 26 05:36:59 2021 -0800

    x86: Set Prefer_No_VZEROUPPER and add Prefer_AVX2_STRCMP
    
    1. Set Prefer_No_VZEROUPPER if RTM is usable to avoid RTM abort triggered
    by VZEROUPPER inside a transactionally executing RTM region.
    2. 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.  Add
    Prefer_AVX2_STRCMP to prefer AVX2 strcmp family functions.
    
    (cherry picked from commit 1da50d4bda07f04135dca39f40e79fc9eabed1f8)

Diff:
---
 sysdeps/x86/cpu-features.c | 20 ++++++++++++++++++--
 sysdeps/x86/cpu-features.h |  2 ++
 sysdeps/x86/cpu-tunables.c |  3 +++
 3 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
index 81a170a819..ffd1bdb10c 100644
--- a/sysdeps/x86/cpu-features.c
+++ b/sysdeps/x86/cpu-features.c
@@ -424,8 +424,24 @@ init_cpu_features (struct cpu_features *cpu_features)
 	cpu_features->feature[index_arch_Prefer_No_VZEROUPPER]
 	  |= bit_arch_Prefer_No_VZEROUPPER;
       else
-	cpu_features->feature[index_arch_Prefer_No_AVX512]
-	  |= bit_arch_Prefer_No_AVX512;
+	{
+	  cpu_features->feature[index_arch_Prefer_No_AVX512]
+	    |= bit_arch_Prefer_No_AVX512;
+
+	  /* Avoid RTM abort triggered by VZEROUPPER inside a
+	     transactionally executing RTM region.  */
+	  if (CPU_FEATURES_CPU_P (cpu_features, RTM))
+	    cpu_features->feature[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_FEATURES_ARCH_P (cpu_features, AVX2_Usable))
+	    cpu_features->feature[index_arch_Prefer_AVX2_STRCMP]
+	      |= bit_arch_Prefer_AVX2_STRCMP;
+	}
     }
   /* This spells out "AuthenticAMD" or "HygonGenuine".  */
   else if ((ebx == 0x68747541 && ecx == 0x444d4163 && edx == 0x69746e65)
diff --git a/sysdeps/x86/cpu-features.h b/sysdeps/x86/cpu-features.h
index aea83e6e31..94e3cf8774 100644
--- a/sysdeps/x86/cpu-features.h
+++ b/sysdeps/x86/cpu-features.h
@@ -897,6 +897,7 @@ extern const struct cpu_features *__get_cpu_features (void)
 #define bit_arch_Prefer_FSRM			(1u << 13)
 #define bit_arch_Prefer_No_AVX512		(1u << 14)
 #define bit_arch_MathVec_Prefer_No_AVX512	(1u << 15)
+#define bit_arch_Prefer_AVX2_STRCMP		(1u << 16)
 
 #define index_arch_Fast_Rep_String		FEATURE_INDEX_2
 #define index_arch_Fast_Copy_Backward		FEATURE_INDEX_2
@@ -914,6 +915,7 @@ extern const struct cpu_features *__get_cpu_features (void)
 #define index_arch_Prefer_No_AVX512		FEATURE_INDEX_2
 #define index_arch_MathVec_Prefer_No_AVX512	FEATURE_INDEX_2
 #define index_arch_Prefer_FSRM			FEATURE_INDEX_2
+#define index_arch_Prefer_AVX2_STRCMP		FEATURE_INDEX_2
 
 /* XCR0 Feature flags.  */
 #define bit_XMM_state		(1u << 1)
diff --git a/sysdeps/x86/cpu-tunables.c b/sysdeps/x86/cpu-tunables.c
index 861bd7bcaa..cb83ecc3b2 100644
--- a/sysdeps/x86/cpu-tunables.c
+++ b/sysdeps/x86/cpu-tunables.c
@@ -282,6 +282,9 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
 	      CHECK_GLIBC_IFUNC_ARCH_BOTH (n, cpu_features,
 					   Fast_Copy_Backward, disable,
 					   18);
+	      CHECK_GLIBC_IFUNC_ARCH_NEED_ARCH_BOTH
+		(n, cpu_features, Prefer_AVX2_STRCMP, AVX2_Usable,
+		 disable, 18);
 	    }
 	  break;
 	case 19: