[PATCH] D36947: [x86] Teach the "generic" x86 CPU to avoid patterns that are slow on widely used processors.

[Chandler Carruth via Phabricator via llvm-commits]

chandlerc added a comment.

In https://reviews.llvm.org/D36947#847139, @echristo wrote:

> Seems reasonable to add a comment as to what microarch features we're attempting to target as modern here.
>
> Definitely starting to hit the point where we should verify for amd processors though - I'm not sure how any of the new zen based fare here.


Yeah, I actually looked and this is as good as LLVM's existing information allows.

For example, btver2 up through znver1 have SlowSHLD, and so not including FastSHLDRotate is probably good here to produce "least bad" x86 across architectures.

Other than that though, I couldn't find any FastFoo or SlowFoo features in LLVM's AMD processor feature sets that would make sense here and aren't already covered. Really just SlowBTMem on Barcelona and fam10, and that's been long covered.


https://reviews.llvm.org/D36947