[PATCH v2 1/2] x86: Add comment explaining no Slow_SSE4_2 check in ifunc-sse4_2

[Noah Goldstein]

Just for clarities sake and so that if a future implementation is
added we remember to add the check.
---
 sysdeps/x86_64/multiarch/ifunc-sse4_2.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/sysdeps/x86_64/multiarch/ifunc-sse4_2.h b/sysdeps/x86_64/multiarch/ifunc-sse4_2.h
index ee36525bcf..973041d23b 100644
--- a/sysdeps/x86_64/multiarch/ifunc-sse4_2.h
+++ b/sysdeps/x86_64/multiarch/ifunc-sse4_2.h
@@ -27,7 +27,11 @@ IFUNC_SELECTOR (void)
 {
   const struct cpu_features* cpu_features = __get_cpu_features ();
 
-  if (CPU_FEATURE_USABLE_P (cpu_features, SSE4_2))
+  /* This function uses slow sse4.2 instructions (pcmpstri) but since
+     there is no other optimized implementation keep using.  If an
+     optimized fallback is added add a X86_ISA_CPU_FEATURE_ARCH_P
+     (cpu_features, Slow_SSE4_2) check.  */
+  if (ISA_CPU_FEATURE_USABLE_P (cpu_features, SSE4_2))
     return OPTIMIZE (sse42);
 
   return OPTIMIZE (generic);
-- 
2.34.1