UpdatePHINodes in BasicBlockUtils should not crash on duplicate predecessors

UpdatePHINodes has an optimization to reuse an existing PHI node, where it
first deletes all of its entries and then replaces them. Unfortunately, in the
case where we had duplicate predecessors (which are allowed so long as the
associated PHI entries have the same value), the loop removing the existing PHI
entries from the to-be-reused PHI would assert (if that PHI was not the one
which had the duplicates).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192001 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 6 insertions, 2 deletions

diff --git a/lib/Transforms/Utils/BasicBlockUtils.cpp b/lib/Transforms/Utils/BasicBlockUtils.cpp
index a2e82f337b..12de9eed4b 100644
--- a/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -400,8 +400,12 @@ static void UpdatePHINodes(BasicBlock *OrigBB, BasicBlock *NewBB,
       // If all incoming values for the new PHI would be the same, just don't
       // make a new PHI.  Instead, just remove the incoming values from the old
       // PHI.
-      for (unsigned i = 0, e = Preds.size(); i != e; ++i)
-        PN->removeIncomingValue(Preds[i], false);
+      for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
+        // Explicitly check the BB index here to handle duplicates in Preds.
+        int Idx = PN->getBasicBlockIndex(Preds[i]);
+        if (Idx >= 0)
+          PN->removeIncomingValue(Idx, false);
+      }
     } else {
       // If the values coming into the block are not the same, we need a PHI.
       // Create the new PHI node, insert it into NewBB at the end of the block