[PATCH v2 01/10] x86: Set Prefer_No_VZEROUPPER and add Prefer_AVX2_STRCMP

["H.J. Lu" <hjl.tools@gmail.com>]

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.
---
 sysdeps/x86/cpu-features.c                    | 20 +++++++++++++++++--
 sysdeps/x86/cpu-tunables.c                    |  2 ++
 ...cpu-features-preferred_feature_index_1.def |  1 +
 3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
index d7248cbb45..d7808acb33 100644
--- a/sysdeps/x86/cpu-features.c
+++ b/sysdeps/x86/cpu-features.c
@@ -531,8 +531,24 @@ init_cpu_features (struct cpu_features *cpu_features)
 	cpu_features->preferred[index_arch_Prefer_No_VZEROUPPER]
 	  |= bit_arch_Prefer_No_VZEROUPPER;
       else
-	cpu_features->preferred[index_arch_Prefer_No_AVX512]
-	  |= bit_arch_Prefer_No_AVX512;
+	{
+	  cpu_features->preferred[index_arch_Prefer_No_AVX512]
+	    |= bit_arch_Prefer_No_AVX512;
+
+	  /* Avoid RTM abort triggered by VZEROUPPER inside a
+	     transactionally executing RTM region.  */
+	  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;
+	}
     }
   /* This spells out "AuthenticAMD" or "HygonGenuine".  */
   else if ((ebx == 0x68747541 && ecx == 0x444d4163 && edx == 0x69746e65)
diff --git a/sysdeps/x86/cpu-tunables.c b/sysdeps/x86/cpu-tunables.c
index 126896f41b..a90df39b78 100644
--- a/sysdeps/x86/cpu-tunables.c
+++ b/sysdeps/x86/cpu-tunables.c
@@ -238,6 +238,8 @@ 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 06af1a8dd5..133aab19f1 100644
--- a/sysdeps/x86/include/cpu-features-preferred_feature_index_1.def
+++ b/sysdeps/x86/include/cpu-features-preferred_feature_index_1.def
@@ -32,3 +32,4 @@ BIT (Prefer_ERMS)
 BIT (Prefer_No_AVX512)
 BIT (MathVec_Prefer_No_AVX512)
 BIT (Prefer_FSRM)
+BIT (Prefer_AVX2_STRCMP)
-- 
2.30.2