From: Aurelien Jarno <aurelien@aurel32.net>
Date: Mon, 3 Oct 2022 21:16:46 +0000 (+0200)
Subject: x86-64: Require BMI2 and LZCNT for AVX2 memrchr implementation
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=38e321f4ac70b6aecb35a8af7d1a2fbe366ab482;p=thirdparty%2Fglibc.git

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 --git a/sysdeps/x86_64/multiarch/ifunc-avx2.h b/sysdeps/x86_64/multiarch/ifunc-avx2.h
index 6de72f72724..52bd00ea5ca 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 81640cf0066..d1fc1e75d67 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))