[glibc/release/2.35/master] x86-64: Require BMI2 and LZCNT for AVX2 memrchr implementation

[glibc/release/2.35/master] x86-64: Require BMI2 and LZCNT for AVX2 memrchr implementation

[Aurelien Jarno]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=02aa1f4a5b6955f2cb384daa4e520d9c8078a078

commit 02aa1f4a5b6955f2cb384daa4e520d9c8078a078
Author: Aurelien Jarno <aurelien@aurel32.net>
Date:   Mon Oct 3 23:16:46 2022 +0200

    x86-64: Require BMI2 and LZCNT for AVX2 memrchr implementation
    
    The AVX2 memrchr implementation uses the 'shlxl' instruction, which
    belongs to the BMI2 CPU feature and uses the 'lzcnt' instruction, which
    belongs to the LZCNT CPU feature.
    
    Fixes: af5306a735eb ("x86: Optimize memrchr-avx2.S")
    Partially resolves: BZ #29611
    
    Reviewed-by: Noah Goldstein  <goldstein.w.n@gmail.com>
    (cherry picked from commit 3c0c78afabfed4b6fc161c159e628fbf14ff370b)

Diff:
---
 sysdeps/x86_64/multiarch/ifunc-avx2.h      |  1 +
 sysdeps/x86_64/multiarch/ifunc-impl-list.c | 10 ++++++++--
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/sysdeps/x86_64/multiarch/ifunc-avx2.h b/sysdeps/x86_64/multiarch/ifunc-avx2.h
index 4289df29ec..5cc1e4b0bc 100644
--- a/sysdeps/x86_64/multiarch/ifunc-avx2.h
+++ b/sysdeps/x86_64/multiarch/ifunc-avx2.h
@@ -31,6 +31,7 @@ IFUNC_SELECTOR (void)
 
   if (CPU_FEATURE_USABLE_P (cpu_features, AVX2)
       && CPU_FEATURE_USABLE_P (cpu_features, BMI2)
+      && CPU_FEATURE_USABLE_P (cpu_features, LZCNT)
       && CPU_FEATURES_ARCH_P (cpu_features, AVX_Fast_Unaligned_Load))
     {
       if (CPU_FEATURE_USABLE_P (cpu_features, AVX512VL)
diff --git a/sysdeps/x86_64/multiarch/ifunc-impl-list.c b/sysdeps/x86_64/multiarch/ifunc-impl-list.c
index 9959f7b228..a7c8ebbe85 100644
--- a/sysdeps/x86_64/multiarch/ifunc-impl-list.c
+++ b/sysdeps/x86_64/multiarch/ifunc-impl-list.c
@@ -192,15 +192,21 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
   /* Support sysdeps/x86_64/multiarch/memrchr.c.  */
   IFUNC_IMPL (i, name, memrchr,
 	      IFUNC_IMPL_ADD (array, i, memrchr,
-			      CPU_FEATURE_USABLE (AVX2),
+			      (CPU_FEATURE_USABLE (AVX2)
+			       && CPU_FEATURE_USABLE (BMI2)
+			       && CPU_FEATURE_USABLE (LZCNT)),
 			      __memrchr_avx2)
 	      IFUNC_IMPL_ADD (array, i, memrchr,
 			      (CPU_FEATURE_USABLE (AVX2)
+			       && CPU_FEATURE_USABLE (BMI2)
+			       && CPU_FEATURE_USABLE (LZCNT)
 			       && CPU_FEATURE_USABLE (RTM)),
 			      __memrchr_avx2_rtm)
 	      IFUNC_IMPL_ADD (array, i, memrchr,
 			      (CPU_FEATURE_USABLE (AVX512VL)
-			       && CPU_FEATURE_USABLE (AVX512BW)),
+			       && CPU_FEATURE_USABLE (AVX512BW)
+			       && CPU_FEATURE_USABLE (BMI2)
+			       && CPU_FEATURE_USABLE (LZCNT)),
 			      __memrchr_evex)
 
 	      IFUNC_IMPL_ADD (array, i, memrchr, 1, __memrchr_sse2))