[llvm] 0699da1 - [NFCI][Local] MergeBasicBlockIntoOnlyPred(): improve Dominator Tree updating

[Roman Lebedev via llvm-commits]

Author: Roman Lebedev
Date: 2021-04-11T23:56:23+03:00
New Revision: 0699da1569870a4f7cf26534b87ca3c3b14caf3b

URL: https://github.com/llvm/llvm-project/commit/0699da1569870a4f7cf26534b87ca3c3b14caf3b
DIFF: https://github.com/llvm/llvm-project/commit/0699da1569870a4f7cf26534b87ca3c3b14caf3b.diff

LOG: [NFCI][Local] MergeBasicBlockIntoOnlyPred(): improve Dominator Tree updating

Same as with TryToSimplifyUncondBranchFromEmptyBlock()/MergeBlockIntoPredecessor() patch.

Added: 
    

Modified: 
    llvm/lib/Transforms/Utils/Local.cpp

Removed: 
    


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diff  --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 10e185956a49..e285f8aa7a20 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -738,12 +738,15 @@ void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB,
   SmallVector<DominatorTree::UpdateType, 32> Updates;
 
   if (DTU) {
-    for (BasicBlock *PredPredBB : predecessors(PredBB)) {
+    SmallPtrSet<BasicBlock *, 2> PredsOfPredBB(pred_begin(PredBB),
+                                               pred_end(PredBB));
+    Updates.reserve(Updates.size() + 2 * PredsOfPredBB.size() + 1);
+    for (BasicBlock *PredOfPredBB : PredsOfPredBB)
       // This predecessor of PredBB may already have DestBB as a successor.
-      if (!llvm::is_contained(successors(PredPredBB), DestBB))
-        Updates.push_back({DominatorTree::Insert, PredPredBB, DestBB});
-      Updates.push_back({DominatorTree::Delete, PredPredBB, PredBB});
-    }
+      if (PredOfPredBB != PredBB)
+        Updates.push_back({DominatorTree::Insert, PredOfPredBB, DestBB});
+    for (BasicBlock *PredOfPredBB : PredsOfPredBB)
+      Updates.push_back({DominatorTree::Delete, PredOfPredBB, PredBB});
     Updates.push_back({DominatorTree::Delete, PredBB, DestBB});
   }