[PATCH] D105462: [X86] Add CRC32 feature.

[Wang Tianqing via Phabricator via llvm-commits]

tianqing added inline comments.


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Comment at: llvm/lib/Support/X86TargetParser.cpp:531
 constexpr FeatureBitset ImpliedFeaturesSSSE3 = FeatureSSE3;
 constexpr FeatureBitset ImpliedFeaturesSSE4_1 = FeatureSSSE3;
 constexpr FeatureBitset ImpliedFeaturesSSE4_2 = FeatureSSE4_1;
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pengfei wrote:
> hjl.tools wrote:
> > pengfei wrote:
> > > Can we let `ImpliedFeaturesSSE4_1 = FeatureSSSE3 | FeaturesCRC32` so that we don't need to add `crc32` on sse4.1 and above?
> > SSE4.1 implies CRC32.  But CRC32 shouldn't imply SSE4.1.
> Yes. The constexpr here means `FeaturesSSE4_1` implies both `FeatureSSSE3` and `FeaturesCRC32`.
CRC32 was added in SSE4.2.

In LLVM this implication relationship is bidirectional, that is:

* -msse4.2 implies -mcrc32
* -mcrc32 doesn't implies -msse4.2.
* -mno-sse4.2 doesn't implies -mno-crc32.
* But -mno-crc32 also implies -mno-sse4.2.


Repository:
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  https://reviews.llvm.org/D105462/new/

https://reviews.llvm.org/D105462