[glibc/release/2.28/master] x86: Set Prefer_No_VZEROUPPER and add Prefer_AVX2_STRCMP

[glibc/release/2.28/master] x86: Set Prefer_No_VZEROUPPER and add Prefer_AVX2_STRCMP

[H.J. Lu]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=b2e59f87ae10e5874bb150bd87f3b92b47b1090e

commit b2e59f87ae10e5874bb150bd87f3b92b47b1090e
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 4695ac80d4..5ddc8eebf4 100644
--- a/sysdeps/x86/cpu-features.c
+++ b/sysdeps/x86/cpu-features.c
@@ -347,8 +347,24 @@ 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".  */
   else if (ebx == 0x68747541 && ecx == 0x444d4163 && edx == 0x69746e65)
diff --git a/sysdeps/x86/cpu-features.h b/sysdeps/x86/cpu-features.h
index 347a4b118d..1f60296e7b 100644
--- a/sysdeps/x86/cpu-features.h
+++ b/sysdeps/x86/cpu-features.h
@@ -41,6 +41,7 @@
 #define bit_arch_MathVec_Prefer_No_AVX512	(1 << 21)
 #define bit_arch_XSAVEC_Usable			(1 << 22)
 #define bit_arch_Prefer_FSRM			(1 << 23)
+#define bit_arch_Prefer_AVX2_STRCMP		(1 << 24)
 
 /* CPUID Feature flags.  */
 
@@ -266,6 +267,7 @@ extern const struct cpu_features *__get_cpu_features (void)
 # define index_arch_MathVec_Prefer_No_AVX512 FEATURE_INDEX_1
 # define index_arch_XSAVEC_Usable	FEATURE_INDEX_1
 # define index_arch_Prefer_FSRM		FEATURE_INDEX_1
+# define index_arch_Prefer_AVX2_STRCMP	FEATURE_INDEX_1
 
 #endif	/* !__ASSEMBLER__ */
 
diff --git a/sysdeps/x86/cpu-tunables.c b/sysdeps/x86/cpu-tunables.c
index 69155a8f44..824ee76b1a 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: