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[Support] Don't check XCR0 when detecting avx512 on Darwin.

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Darwin lazily saves the AVX512 context on first use [1]: instead of checking
that it already does to figure out if the OS supports AVX512, trust that
the kernel will do the right thing and always assume the context save
support is available.

[1] https://github.com/apple/darwin-xnu/blob/xnu-4903.221.2/osfmk/i386/fpu.c#L174

Reviewers: ab, RKSimon, craig.topper

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D70453
This commit is contained in:
Florian Hahn 2019-11-21 09:03:16 +00:00
parent ba35e653b7
commit ee8bfe440e
1 changed files with 15 additions and 0 deletions
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15
lib/Support/Host.cpp
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@ -1027,7 +1027,15 @@ static void getAvailableFeatures(unsigned ECX, unsigned EDX, unsigned MaxLeaf,
const unsigned AVXBits = (1 << 27) | (1 << 28);
bool HasAVX = ((ECX & AVXBits) == AVXBits) && !getX86XCR0(&EAX, &EDX) &&
((EAX & 0x6) == 0x6);
#if defined(__APPLE__)
// Darwin lazily saves the AVX512 context on first use: trust that the OS will
// save the AVX512 context if we use AVX512 instructions, even the bit is not
// set right now.
bool HasAVX512Save = true;
#else
// AVX512 requires additional context to be saved by the OS.
bool HasAVX512Save = HasAVX && ((EAX & 0xe0) == 0xe0);
#endif
if (HasAVX)
setFeature(X86::FEATURE_AVX);
@ -1364,8 +1372,15 @@ bool sys::getHostCPUFeatures(StringMap<bool> &Features) {
// switch, then we have full AVX support.
bool HasAVXSave = ((ECX >> 27) & 1) && ((ECX >> 28) & 1) &&
!getX86XCR0(&EAX, &EDX) && ((EAX & 0x6) == 0x6);
#if defined(__APPLE__)
// Darwin lazily saves the AVX512 context on first use: trust that the OS will
// save the AVX512 context if we use AVX512 instructions, even the bit is not
// set right now.
bool HasAVX512Save = true;
#else
// AVX512 requires additional context to be saved by the OS.
bool HasAVX512Save = HasAVXSave && ((EAX & 0xe0) == 0xe0);
#endif
Features["avx"] = HasAVXSave;
Features["fma"] = ((ECX >> 12) & 1) && HasAVXSave;