[PATCH] D62392: [DAGCombine][ARM] (sub Carry, X) -> (addcarry (sub 0, X), 0, Carry) fold

[Amaury SECHET via Phabricator via llvm-commits]

deadalnix added a comment.

Maybe it is worth adding some platform dependent check to actually make sure turning the carry into a scalar is expensive? Or is it a reasonable assumption to make that it expensive on all plateforms?

In any case, this is more likely than not that this will optimize better down the road anyways, so maybe, if such plateform exist, we may want to delegate the cleanup to plateform specific transforms.

I think it would be beneficial to have an X86 test case for this pattern.


Repository:
  rL LLVM

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https://reviews.llvm.org/D62392