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Make MergeBlockIntoPredecessor conformant to the precondition of calling DTU.applyUpdates 

Summary:
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.

Reviewers: kuhar, brzycki, chandlerc

Reviewed By: brzycki

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58444

llvm-svn: 355105
This commit is contained in:
Chijun Sima 2019-02-28 16:47:18 +00:00
parent 85c3afd7f6
commit 586187639a
1 changed files with 3 additions and 1 deletions
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4
llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
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@ -186,7 +186,9 @@ bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, DomTreeUpdater *DTU,
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});
}
}