x86-64: Require BMI2 for AVX2 wcs(n)cmp implementations

The AVX2 wcs(n)cmp implementations use 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>
(cherry picked from commit f31a5a884ed84bd37032729d4d1eb9d06c9f3c29)

diff --git a/sysdeps/x86_64/multiarch/ifunc-impl-list.c b/sysdeps/x86_64/multiarch/ifunc-impl-list.c
index b27ae975e4d09c36744231419c3b281f897135c3..5824554b4edc58e585b121cbe737bfe7ef720aa0 100644 (file)
--- a/sysdeps/x86_64/multiarch/ifunc-impl-list.c
+++ b/sysdeps/x86_64/multiarch/ifunc-impl-list.c
@@ -711,10 +711,12 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
   /* Support sysdeps/x86_64/multiarch/wcscmp.c.  */
   IFUNC_IMPL (i, name, wcscmp,
              IFUNC_IMPL_ADD (array, i, wcscmp,
-                             CPU_FEATURE_USABLE (AVX2),
+                             (CPU_FEATURE_USABLE (AVX2)
+                              && CPU_FEATURE_USABLE (BMI2)),
                              __wcscmp_avx2)
              IFUNC_IMPL_ADD (array, i, wcscmp,
                              (CPU_FEATURE_USABLE (AVX2)
+                              && CPU_FEATURE_USABLE (BMI2)
                               && CPU_FEATURE_USABLE (RTM)),
                              __wcscmp_avx2_rtm)
              IFUNC_IMPL_ADD (array, i, wcscmp,
@@ -727,10 +729,12 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
   /* Support sysdeps/x86_64/multiarch/wcsncmp.c.  */
   IFUNC_IMPL (i, name, wcsncmp,
              IFUNC_IMPL_ADD (array, i, wcsncmp,
-                             CPU_FEATURE_USABLE (AVX2),
+                             (CPU_FEATURE_USABLE (AVX2)
+                              && CPU_FEATURE_USABLE (BMI2)),
                              __wcsncmp_avx2)
              IFUNC_IMPL_ADD (array, i, wcsncmp,
                              (CPU_FEATURE_USABLE (AVX2)
+                              && CPU_FEATURE_USABLE (BMI2)
                               && CPU_FEATURE_USABLE (RTM)),
                              __wcsncmp_avx2_rtm)
              IFUNC_IMPL_ADD (array, i, wcsncmp,