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* [glibc/release/2.33/master] x86-64: Require BMI2 and LZCNT for AVX2 memrchr implementation
@ 2022-10-03 22:05 Aurelien Jarno
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From: Aurelien Jarno @ 2022-10-03 22:05 UTC (permalink / raw)
  To: glibc-cvs

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=38e321f4ac70b6aecb35a8af7d1a2fbe366ab482

commit 38e321f4ac70b6aecb35a8af7d1a2fbe366ab482
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 6de72f7272..52bd00ea5c 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 81640cf006..d1fc1e75d6 100644
--- a/sysdeps/x86_64/multiarch/ifunc-impl-list.c
+++ b/sysdeps/x86_64/multiarch/ifunc-impl-list.c
@@ -174,15 +174,21 @@ __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))

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