[PATCH] D87149: [InstCombine] erase instructions leading up to unreachable

[Johannes Doerfert via Phabricator via llvm-commits]

jdoerfert added a comment.

In D87149#2263725 <https://reviews.llvm.org/D87149#2263725>, @lebedev.ri wrote:

> In D87149#2263708 <https://reviews.llvm.org/D87149#2263708>, @nikic wrote:
>
>> @lebedev.ri I don't think the printf() case is any different. Keep in mind that undefined behavior acts retroactively, so if we know that unreachable will be executed later, we are free to optimize away side-effects before it as well. (If printf is not considered willreturn, then we cannot optimize it away, and won't.)
>
> IOW you are saying that in https://godbolt.org/z/TEo6oj `tail call void @_Z5errorv()` should ideally be optimized out?

If `_Z5errorv` was `willreturn` and `nounwind`, yes. Otherwise, no. Basically, if `isGuaranteedToTransferExecutionToSuccessor` given the call returns true.


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