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 --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
index 4c24ba7c3143f3ab472432e4e179243cec3d3d04..eb554b6d141676715bcc41348ede73ac1a06de80 100644 (file)
--- a/sysdeps/x86/cpu-features.c
+++ b/sysdeps/x86/cpu-features.c
@@ -546,8 +546,24 @@ 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-features.h b/sysdeps/x86/cpu-features.h
index a0b9b9177c827b75f1405714851286cebd90e5e0..72ea74d083e6e2d026b3f7f5172a58b7c5a1e389 100644 (file)
--- a/sysdeps/x86/cpu-features.h
+++ b/sysdeps/x86/cpu-features.h
@@ -804,6 +804,7 @@ 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             PREFERRED_FEATURE_INDEX_1
 #define index_arch_Fast_Copy_Backward          PREFERRED_FEATURE_INDEX_1
@@ -821,6 +822,7 @@ extern const struct cpu_features *__get_cpu_features (void)
 #define index_arch_Prefer_No_AVX512            PREFERRED_FEATURE_INDEX_1
 #define index_arch_MathVec_Prefer_No_AVX512    PREFERRED_FEATURE_INDEX_1
 #define index_arch_Prefer_FSRM                 PREFERRED_FEATURE_INDEX_1
+#define index_arch_Prefer_AVX2_STRCMP          PREFERRED_FEATURE_INDEX_1
 
 /* XCR0 Feature flags.  */
 #define bit_XMM_state          (1u << 1)

diff --git a/sysdeps/x86/cpu-tunables.c b/sysdeps/x86/cpu-tunables.c
index 588bbf9448bd6a44497818651ca3cfeaa84c8701..b251a91af3fe5202fe378823e33eee45332291fa 100644 (file)
--- 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: