[PATCH] D123174: [TypePromotion] Promote undef by converting to 0.

[Sam Parker via Phabricator via llvm-commits]

samparker added a comment.

Hi @craig.topper, so this is interesting because the AArch64 trunc-zext-chain.ll test file is a reproducer for a bug that I couldn't solve. The test function has two versions, because I couldn't figure out if having an undef was the underlying issue. I //think// it was causing some trouble with GetDemandedBits, but I was unable to figure it out with some very dense logic in the AArch64 backend. So I'm certainly happy to entertain this idea and matching the behaviour of InstCombine/InstSimplify sounds good to me.


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  https://reviews.llvm.org/D123174/new/

https://reviews.llvm.org/D123174