[PATCH] D58444: Make MergeBlockIntoPredecessor conformant to the precondition of calling DTU.applyUpdates

[Chijun Sima via Phabricator via llvm-commits]

NutshellySima created this revision.
NutshellySima added reviewers: kuhar, brzycki, chandlerc.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.

It is mentioned in the document of DTU that "It is illegal to submit any update that has already been submitted, i.e., you are supposed not to insert an existent edge or delete a nonexistent edge." It is dangerous to violet this rule because DomTree and PostDomTree occasionally crash on this scenario.

This patch fixes `MergeBlockIntoPredecessor`, making it conformant to this precondition.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D58444

Files:
  llvm/lib/Transforms/Utils/BasicBlockUtils.cpp


Index: llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
===================================================================
--- llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -186,7 +186,9 @@
     Updates.push_back({DominatorTree::Delete, PredBB, BB});
     for (auto I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
       Updates.push_back({DominatorTree::Delete, BB, *I});
-      Updates.push_back({DominatorTree::Insert, PredBB, *I});
+      // This successor of BB may already have PredBB as a predecessor.
+      if (llvm::find(successors(PredBB), *I) == succ_end(PredBB))
+        Updates.push_back({DominatorTree::Insert, PredBB, *I});
     }
   }
 


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