[glibc/release/2.34/master] x86: Add sse42 implementation to strcmp's ifunc

[glibc/release/2.34/master] x86: Add sse42 implementation to strcmp's ifunc

[Sunil Pandey]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=9d50e162eef88e1f870a941b0a973060e984e7ca

commit 9d50e162eef88e1f870a941b0a973060e984e7ca
Author: Noah Goldstein <goldstein.w.n@gmail.com>
Date:   Tue Jun 14 15:37:28 2022 -0700

    x86: Add sse42 implementation to strcmp's ifunc
    
    This has been missing since the the ifuncs where added.
    
    The performance of SSE4.2 is preferable to to SSE2.
    
    Measured on Tigerlake with N = 20 runs.
    Geometric Mean of all benchmarks SSE4.2 / SSE2: 0.906
    
    (cherry picked from commit ff439c47173565fbff4f0f78d07b0f14e4a7db05)

Diff:
---
 sysdeps/x86_64/multiarch/strcmp.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/sysdeps/x86_64/multiarch/strcmp.c b/sysdeps/x86_64/multiarch/strcmp.c
index 7c2901bf44..b457fb4c15 100644
--- a/sysdeps/x86_64/multiarch/strcmp.c
+++ b/sysdeps/x86_64/multiarch/strcmp.c
@@ -29,6 +29,7 @@
 extern __typeof (REDIRECT_NAME) OPTIMIZE (sse2) attribute_hidden;
 extern __typeof (REDIRECT_NAME) OPTIMIZE (sse2_unaligned) attribute_hidden;
 extern __typeof (REDIRECT_NAME) OPTIMIZE (ssse3) attribute_hidden;
+extern __typeof (REDIRECT_NAME) OPTIMIZE (sse42) attribute_hidden;
 extern __typeof (REDIRECT_NAME) OPTIMIZE (avx2) attribute_hidden;
 extern __typeof (REDIRECT_NAME) OPTIMIZE (avx2_rtm) attribute_hidden;
 extern __typeof (REDIRECT_NAME) OPTIMIZE (evex) attribute_hidden;
@@ -53,6 +54,10 @@ IFUNC_SELECTOR (void)
 	return OPTIMIZE (avx2);
     }
 
+  if (CPU_FEATURE_USABLE_P (cpu_features, SSE4_2)
+      && !CPU_FEATURES_ARCH_P (cpu_features, Slow_SSE4_2))
+    return OPTIMIZE (sse42);
+
   if (CPU_FEATURES_ARCH_P (cpu_features, Fast_Unaligned_Load))
     return OPTIMIZE (sse2_unaligned);