[PATCH v1 1/1] x86: wmemset ifunc: fix stray '!' causing SSE2 fallback

Jiamei Xie xiejiamei@hygon.cn
Mon Oct 13 13:02:22 GMT 2025


From: xiejiamei <xiejiamei@hygon.com>

The ifunc selector for wmemset had a stray '!' in the
X86_ISA_CPU_FEATURES_ARCH_P(...) check:

  if (X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, AVX2)
      && X86_ISA_CPU_FEATURES_ARCH_P (cpu_features,
                                      AVX_Fast_Unaligned_Load, !))

This effectively negated the predicate and caused the AVX2/AVX512
paths to be skipped, making the dispatcher fall back to the SSE2
implementation even on CPUs where AVX2/AVX512 are available. The
regression leads to noticeable throughput loss for wmemset.

Remove the stray '!' so the AVX_Fast_Unaligned_Load capability is
tested as intended and the correct AVX2/EVEX variants are selected.

Impact:
- On AVX2/AVX512-capable x86_64, wmemset no longer incorrectly
  falls back to SSE2; perf now shows __wmemset_evex/avx2 variants.

Testing:
- benchtests/bench-wmemset shows improved bandwidth across sizes.
- perf confirm the selected symbol is no longer SSE2.

Signed-off-by: xiejiamei <xiejiamei@hygon.com>
Signed-off-by: Li jing <lijing@hygon.cn>
---
 sysdeps/x86_64/multiarch/ifunc-wmemset.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sysdeps/x86_64/multiarch/ifunc-wmemset.h b/sysdeps/x86_64/multiarch/ifunc-wmemset.h
index f95cca6ae5..50af138230 100644
--- a/sysdeps/x86_64/multiarch/ifunc-wmemset.h
+++ b/sysdeps/x86_64/multiarch/ifunc-wmemset.h
@@ -35,7 +35,7 @@ IFUNC_SELECTOR (void)
 
   if (X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, AVX2)
       && X86_ISA_CPU_FEATURES_ARCH_P (cpu_features,
-				      AVX_Fast_Unaligned_Load, !))
+				      AVX_Fast_Unaligned_Load,))
     {
       if (X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, AVX512VL))
 	{
-- 
2.42.0




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