[PATCH] D41587: [AArch64] Change order of candidate FMLS patterns
Matthew Simpson via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Tue Dec 26 12:45:14 PST 2017
mssimpso added a comment.
In https://reviews.llvm.org/D41587#964226, @fhahn wrote:
> Thanks for spotting this!
> The reordering looks good to me, give the current behavior of the MachineCombiner it makes sense to move up the more profitable patterns.
>
> > However, the order in which we add the patterns to the list of candidates determines the transformation that takes place, since only the first pattern that matches will be used.
>
> This behavior is not ideal though, especially as some order of patterns might be good for one micro architecture, whereas a different order is better for a different micro architecture.
>
> I'll try to look into this. Maybe it's worth to change the MachineCombiner to try all available patterns.
Thanks Florian! Yes, I agree with your comment. There's actually a note about the limitations of the current behavior in `MachineCombiner::combineInstructions`.
https://reviews.llvm.org/D41587
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