Fix a bug in the DAGCombiner's handling of multiple linked

MERGE_VALUES nodes. Replacing the result values with the
operands in one MERGE_VALUES node may cause another
MERGE_VALUES node be CSE'd with the first one, and bring
its uses along, so that the first one isn't dead, as this
code expects. Fix this by iterating until the node is
really dead. This fixes PR4699.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78619 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 8 insertions, 3 deletions

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 42d163f79b..d4d13884cb 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -924,9 +924,14 @@ SDValue DAGCombiner::visitTokenFactor(SDNode *N) {
 /// MERGE_VALUES can always be eliminated.
 SDValue DAGCombiner::visitMERGE_VALUES(SDNode *N) {
   WorkListRemover DeadNodes(*this);
-  for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i)
-    DAG.ReplaceAllUsesOfValueWith(SDValue(N, i), N->getOperand(i),
-                                  &DeadNodes);
+  // Replacing results may cause a different MERGE_VALUES to suddenly
+  // be CSE'd with N, and carry its uses with it. Iterate until no
+  // uses remain, to ensure that the node can be safely deleted.
+  do {
+    for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i)
+      DAG.ReplaceAllUsesOfValueWith(SDValue(N, i), N->getOperand(i),
+                                    &DeadNodes);
+  } while (!N->use_empty());
   removeFromWorkList(N);
   DAG.DeleteNode(N);
   return SDValue(N, 0);   // Return N so it doesn't get rechecked!