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 aebef3daafc73565e4829744bb09abadaee9217c..fec8790c1156718656c1e87a89701fae5d74838f 100644 (file)
--- a/sysdeps/x86_64/multiarch/ifunc-impl-list.c
+++ b/sysdeps/x86_64/multiarch/ifunc-impl-list.c
@@ -810,10 +810,12 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
                                      && CPU_FEATURE_USABLE (BMI2)),
                                     __wcscmp_evex)
              X86_IFUNC_IMPL_ADD_V3 (array, i, wcscmp,
-                                    CPU_FEATURE_USABLE (AVX2),
+                                    (CPU_FEATURE_USABLE (AVX2)
+                                     && CPU_FEATURE_USABLE (BMI2)),
                                     __wcscmp_avx2)
              X86_IFUNC_IMPL_ADD_V3 (array, i, wcscmp,
                                     (CPU_FEATURE_USABLE (AVX2)
+                                     && CPU_FEATURE_USABLE (BMI2)
                                      && CPU_FEATURE_USABLE (RTM)),
                                     __wcscmp_avx2_rtm)
              /* ISA V2 wrapper for SSE2 implementation because the SSE2
@@ -830,10 +832,12 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
                                      && CPU_FEATURE_USABLE (BMI2)),
                                     __wcsncmp_evex)
              X86_IFUNC_IMPL_ADD_V3 (array, i, wcsncmp,
-                                    CPU_FEATURE_USABLE (AVX2),
+                                    (CPU_FEATURE_USABLE (AVX2)
+                                     && CPU_FEATURE_USABLE (BMI2)),
                                     __wcsncmp_avx2)
              X86_IFUNC_IMPL_ADD_V3 (array, i, wcsncmp,
                                     (CPU_FEATURE_USABLE (AVX2)
+                                     && CPU_FEATURE_USABLE (BMI2)
                                      && CPU_FEATURE_USABLE (RTM)),
                                     __wcsncmp_avx2_rtm)
              /* ISA V2 wrapper for GENERIC implementation because the