[PATCH] D119929: [MemCpyOpt] Check uses of found Clobber in writtenBetween.

[Florian Hahn via Phabricator via llvm-commits]

fhahn updated this revision to Diff 409338.
fhahn added a comment.



In D119929#3326038 <https://reviews.llvm.org/D119929#3326038>, @nikic wrote:

> I'm not sure this is the right approach. The `getDefininingAccess()` here is essentially only supposed to skip over End itself during the clobber walk. As you correctly note, this is not correct if End is a MemoryUse. But shouldn't we be able to still do basically the same thing, but with the previous def in the block? Something like stepping one back on `getReverseDefsIterator()`?

I wasn't aware of the available reverse iterators for defs/accesses. I updated the code to recursively walk over the previous accesses. Because the iterator is block-only, we'd need to also go through the predecessors manually I think which makes it a bit trickier, unless there's already some existing functionaltiy I missed

I think we also need to do that for MemoryDefs, if End doesn't clobber Loc, because then the defining access could be optimized by skipping any accesses to Loc unless I am missing something.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D119929/new/

https://reviews.llvm.org/D119929

Files:
  llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
  llvm/test/Transforms/MemCpyOpt/memcpy-byval-forwarding-clobbers.ll

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