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BLD: fallback to __builtin_prefetch on clang-cl with -mno-mmx #2742

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Merged
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Oct 1, 2025
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BLD: fallback to __builtin_prefetch on clang-cl with -mno-mmx #2742

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5 changes: 3 additions & 2 deletions hwy/cache_control.h
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Original file line number Diff line number Diff line change
Expand Up @@ -98,9 +98,10 @@ template <typename T>
HWY_INLINE HWY_ATTR_CACHE void Prefetch(const T* p) {
(void)p;
#ifndef HWY_DISABLE_CACHE_CONTROL
#if HWY_ARCH_X86
// Use _mm_prefetch on x86/x64, except when clang-cl is compiled with -mno-mmx.
#if HWY_ARCH_X86 && !(HWY_COMPILER_CLANGCL && !defined(__MMX__))
_mm_prefetch(reinterpret_cast<const char*>(p), _MM_HINT_T0);
#elif HWY_COMPILER_GCC // includes clang
#elif HWY_COMPILER_GCC || HWY_COMPILER_CLANGCL // includes clang
// Hint=0 (NTA) behavior differs, but skipping outer caches is probably not
// desirable, so use the default 3 (keep in caches).
__builtin_prefetch(p, /*write=*/0, /*hint=*/3);
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