[PATCH] D125712: [SLP][X86] Improve reordering to consider alternate instruction bundles

[Vasileios Porpodas via Phabricator via llvm-commits]

vporpo added a comment.

I understand your concerns, but I feel that this pattern is not as tricky as folded loads. We can accurately detect the add-sub pattern within the SLP pass itself, since it matches the AltShuffle TreeEntry. So we can even make the tree cost more accurate (this is in a follow up patch). The only issue that I see is perhaps with cost modeling of this pattern from within a different pass, other than SLP, since that would require special logic to skip the cost of the vector add and vector sub. But given the current infrastructure I don't think we can do anything about this, but that shouldn't stop us from making getShuffleCost() more accurate, even if it will only benefit SLP.


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https://reviews.llvm.org/D125712