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[X86][EVEX512] Restrict attaching EVEX512 for default CPU only, NFCI #65920

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Merged
merged 1 commit into from
Sep 11, 2023
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[X86][EVEX512] Restrict attaching EVEX512 for default CPU only, NFCI #65920

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29 changes: 17 additions & 12 deletions llvm/lib/Target/X86/X86Subtarget.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -268,18 +268,23 @@ void X86Subtarget::initSubtargetFeatures(StringRef CPU, StringRef TuneCPU,
if (!FS.empty())
FullFS = (Twine(FullFS) + "," + FS).str();

// Attach EVEX512 feature when we have AVX512 features and EVEX512 is not set.
size_t posNoEVEX512 = FS.rfind("-evex512");
// Make sure we won't be cheated by "-avx512fp16".
size_t posNoAVX512F = FS.endswith("-avx512f") ? FS.size() - 8
: FS.rfind("-avx512f,");
size_t posEVEX512 = FS.rfind("+evex512");
size_t posAVX512F = FS.rfind("+avx512"); // Any AVX512XXX will enable AVX512F.

if (posAVX512F != StringRef::npos &&
(posNoAVX512F == StringRef::npos || posNoAVX512F < posAVX512F))
if (posEVEX512 == StringRef::npos && posNoEVEX512 == StringRef::npos)
FullFS += ",+evex512";
// Attach EVEX512 feature when we have AVX512 features with a default CPU.
// "pentium4" is default CPU for 32-bit targets.
// "x86-64" is default CPU for 64-bit targets.
if (CPU == "generic" || CPU == "pentium4" || CPU == "x86-64") {
size_t posNoEVEX512 = FS.rfind("-evex512");
// Make sure we won't be cheated by "-avx512fp16".
size_t posNoAVX512F = FS.endswith("-avx512f") ? FS.size() - 8
: FS.rfind("-avx512f,");
size_t posEVEX512 = FS.rfind("+evex512");
// Any AVX512XXX will enable AVX512F.
size_t posAVX512F = FS.rfind("+avx512");

if (posAVX512F != StringRef::npos &&
(posNoAVX512F == StringRef::npos || posNoAVX512F < posAVX512F))
if (posEVEX512 == StringRef::npos && posNoEVEX512 == StringRef::npos)
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Combine two if to one?

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I think keeping it separate is friendly to understand. This outer logic is for AVX512 and inner is for EVEX512.

FullFS += ",+evex512";
}

// Parse features string and set the CPU.
ParseSubtargetFeatures(CPU, TuneCPU, FullFS);
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