[SDAG] Fix a case where we would iteratively legalize a node during

combining by replacing it with something else but not re-process the
node afterward to remove it.

In a truly remarkable stroke of bad luck, this would (in the test case
attached) end up getting some other node combined into it without ever
getting re-processed. By adding it back on to the worklist, in addition
to deleting the dead nodes more quickly we also ensure that if it
*stops* being dead for any reason it makes it back through the
legalizer. Without this, the test case will end up failing during
instruction selection due to an and node with a type we don't have an
instruction pattern for.

It took many million runs of the shuffle fuzz tester to find this.

llvm-svn: 215611

1 files changed, 2 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
index d689630f72c..232cbd81f76 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -156,6 +156,8 @@ public:
   // Node replacement helpers
   void ReplacedNode(SDNode *N) {
     LegalizedNodes.erase(N);
+    if (UpdatedNodes)
+      UpdatedNodes->insert(N);
   }
   void ReplaceNode(SDNode *Old, SDNode *New) {
     DEBUG(dbgs() << " ... replacing: "; Old->dump(&DAG);