[PATCH] D87965: [InstCombine] replace phi values from unreachable blocks with 'undef'

[Nikita Popov via Phabricator via llvm-commits]

nikic added a comment.

I don't think this fully addresses the problem, in that this relies on the phi getting processed before the unreachable, which is not a given. This would have to happen prior to the main InstCombine run, at the same time we remove instructions in unreachable blocks. It's probably not worth it. I think we should fix this the direct way, by performing a `replaceInstUsesWith(*Prev, UndefValue(Prev->getType())` before the `eraseInstFromFunction()` in the unreachable transform.


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