[PATCH] D136201: [InstCombine] Handle PHI nodes when eliminating constant memcpy

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added inline comments.


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Comment at: llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp:269
+      // Check if any of the incoming values of PHI is the destination of Copy
+      auto CopySrcAddrSpace = Copy->getSourceAddressSpace();
+      auto PHIAddrSpace = PHI->getType()->getPointerAddressSpace();
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Don't like auto for addrspace


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Comment at: llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp:111
       MemTransferInst *MI = dyn_cast<MemTransferInst>(I);
-      if (!MI)
+      if (!MI || isa<PHINode>(MI->getDest()))
         return false;
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gandhi21299 wrote:
> nikic wrote:
> > This is not sufficient: E.g. consider doing the memcpy to an addrspacecast of the phi or similar. I think what we'd need instead is that set `IsOffset=true` for phi nodes, so we'll recursively reject memcpys into it. Of course we would need a different name than IsOffset in that case. It would more generally indicate that the pointer is not equivalent to the base.
> @nikic What do you mean by "need a different name"? I could simply emplace_back a pair of the instruction and a true to `ValuesToInspect` vector right?
I think I'm getting lost in the different revisions of the patch; not sure what this comment is referring to anymore. There isn't anything about phi handling right here?


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  https://reviews.llvm.org/D136201/new/

https://reviews.llvm.org/D136201