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 4289df29ecbbb7211f6b48d8d113f24bb1394b80..5cc1e4b0bc32abd1a0082b63805286232a7a65da 100644 (file)
--- 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 9959f7b2286bef2413a16205365841f61cfbbc47..a7c8ebbe850d654dd0dede6df1b5fc20e97fad4b 100644 (file)
--- 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))