[PATCH] D120033: [SCEV] Fully invalidate SCEVUnknown on RAUW

[Nikita Popov via Phabricator via llvm-commits]

nikic created this revision.
nikic added reviewers: reames, lebedev.ri, mkazantsev.
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When a SCEVUnknown gets RAUWd, we currently drop it from the value map, but we don't forget memoized values. I believe we should be treating RAUW the same way as deletion here and invalidate all caches and dependent expressions.

I don't have any specific cases where this causes issues right now. This patch is inspired by the FIXME in https://reviews.llvm.org/D119488.


https://reviews.llvm.org/D120033

Files:
  llvm/lib/Analysis/ScalarEvolution.cpp


Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -519,13 +519,9 @@
 }
 
 void SCEVUnknown::allUsesReplacedWith(Value *New) {
-  // Remove this SCEVUnknown from the uniquing map.
-  SE->UniqueSCEVs.RemoveNode(this);
-
-  // Update this SCEVUnknown to point to the new value. This is needed
-  // because there may still be outstanding SCEVs which still point to
-  // this SCEVUnknown.
-  setValPtr(New);
+  // Treat this the same way as the value being deleted, to force
+  // recomputation of dependent expressions.
+  deleted();
 }
 
 bool SCEVUnknown::isSizeOf(Type *&AllocTy) const {


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