[glibc] x86-64: Require BMI2 for AVX2 strcmp implementation

[glibc] x86-64: Require BMI2 for AVX2 strcmp implementation

[Aurelien Jarno]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=4d64c6445735e9b34e2ac8e369312cbfc2f88e17

commit 4d64c6445735e9b34e2ac8e369312cbfc2f88e17
Author: Aurelien Jarno <aurelien@aurel32.net>
Date:   Mon Oct 3 23:46:11 2022 +0200

    x86-64: Require BMI2 for AVX2 strcmp implementation
    
    The AVX2 strcmp implementation uses the 'bzhi' instruction, which
    belongs to the BMI2 CPU feature.
    
    NB: It also uses the 'tzcnt' BMI1 instruction, but it is executed as BSF
    as BSF if the CPU doesn't support TZCNT, and produces the same result
    for non-zero input.
    
    Partially fixes: b77b06e0e296 ("x86: Optimize strcmp-avx2.S")
    Partially resolves: BZ #29611
    
    Reviewed-by: Noah Goldstein  <goldstein.w.n@gmail.com>

Diff:
---
 sysdeps/x86_64/multiarch/ifunc-impl-list.c | 4 +++-
 sysdeps/x86_64/multiarch/strcmp.c          | 4 ++--
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/sysdeps/x86_64/multiarch/ifunc-impl-list.c b/sysdeps/x86_64/multiarch/ifunc-impl-list.c
index d208fae4bf..a42b0a4620 100644
--- a/sysdeps/x86_64/multiarch/ifunc-impl-list.c
+++ b/sysdeps/x86_64/multiarch/ifunc-impl-list.c
@@ -591,10 +591,12 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
 				      && CPU_FEATURE_USABLE (BMI2)),
 				     __strcmp_evex)
 	      X86_IFUNC_IMPL_ADD_V3 (array, i, strcmp,
-				     CPU_FEATURE_USABLE (AVX2),
+				     (CPU_FEATURE_USABLE (AVX2)
+				      && CPU_FEATURE_USABLE (BMI2)),
 				     __strcmp_avx2)
 	      X86_IFUNC_IMPL_ADD_V3 (array, i, strcmp,
 				     (CPU_FEATURE_USABLE (AVX2)
+				      && CPU_FEATURE_USABLE (BMI2)
 				      && CPU_FEATURE_USABLE (RTM)),
 				     __strcmp_avx2_rtm)
 	      X86_IFUNC_IMPL_ADD_V2 (array, i, strcmp,
diff --git a/sysdeps/x86_64/multiarch/strcmp.c b/sysdeps/x86_64/multiarch/strcmp.c
index fdd5afe3af..9d6c9f66ba 100644
--- a/sysdeps/x86_64/multiarch/strcmp.c
+++ b/sysdeps/x86_64/multiarch/strcmp.c
@@ -45,12 +45,12 @@ IFUNC_SELECTOR (void)
   const struct cpu_features *cpu_features = __get_cpu_features ();
 
   if (X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, AVX2)
+      && X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, BMI2)
       && X86_ISA_CPU_FEATURES_ARCH_P (cpu_features,
 				      AVX_Fast_Unaligned_Load, ))
     {
       if (X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, AVX512VL)
-	  && X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, AVX512BW)
-	  && X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, BMI2))
+	  && X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, AVX512BW))
 	return OPTIMIZE (evex);
 
       if (CPU_FEATURE_USABLE_P (cpu_features, RTM))