[PATCH] D57033: [LCSSA] Handle case with single new PHI faster.

Thu Jan 24 13:50:59 PST 2019

efriedma added inline comments.

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Comment at: llvm/lib/Transforms/Utils/LCSSA.cpp:205
+        if (UseToRewrite->get()->hasValueHandle())
+          ValueHandleBase::ValueIsRAUWd(*UseToRewrite, AddedPHIs[0]);
+        UseToRewrite->set(AddedPHIs[0]);
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Maybe worth mentioning that this can call ValueIsRAUWd multiple times for the same value.  (I don't think it's a problem, but took me a minute to understand what this is doing.)

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Comment at: llvm/lib/Transforms/Utils/LCSSA.cpp:226
+      Value *V = AddedPHIs.size() == 1 ? AddedPHIs[0]
+                                       : SSAUpdate.FindValueForBlock(UserBB);
+      DVI->setOperand(0, MetadataAsValue::get(Ctx, ValueAsMetadata::get(V)));
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I'm not sure I understand why you're changing the logic here for the `AddedPHIs.size() != 1` case.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D57033/new/

https://reviews.llvm.org/D57033