[PATCH] D153453: [MemCpyOpt] implement single BB stack-move optimization which unify the static unescaped allocas

Fri Jul 14 21:41:16 PDT 2023

khei4 added a comment.

In D153453#4500670 <https://reviews.llvm.org/D153453#4500670>, @nikic wrote:

> In D153453#4500558 <https://reviews.llvm.org/D153453#4500558>, @serge-sans-paille wrote:
>
>> In D153453#4500396 <https://reviews.llvm.org/D153453#4500396>, @nikic wrote:
>>
>>> We shouldn't use dominates() in this patch, as it's not always semantically correct.
>>
>> Can you explain why?
>
> A lot of these comesBefore() are actually reachability queries. This reduces to comesBefore() within one block, but is not the same as dominates() across blocks.

Thank you for your explanation! Yes, that was precisely the reachability, and semantics will differ from domination on multi-bb. But that is at least sound and might be reasonable to restrict only dominated cases. I'm still finding the reasonable scope ;)

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