[PATCH] D83595: [Draft][MSAN] Optimize away poisoning allocas that are always written before load

[Florian Hahn via Phabricator via llvm-commits]

fhahn added a comment.

> If we know that every path from an alloca leads to a store, we can optimize away poisoning its shadow (it'll be overwritten anyway).
> 
>> ! In D83595#2145347 <https://reviews.llvm.org/D83595#2145347>, @lebedev.ri wrote:
> 
> Perhaps MemSSA-based DCE can be taught about it?

MemorySSA-based DSE has similar logic (check that a store is either overwritten or never read on all paths to a function exit), but it uses a MemorySSA traversal to do so. I don't think alloca are modeled directly in MemorySSA though, so the approach cannot be directly applied I think. It might be possible to add a pseudo-memorydef writing to the alloca directly after its definition. Then the MemorySSA based logic may apply.


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