The dag combiner is missing revisiting nodes that it really should, and thus leaving

dead stuff around.  This gets fed into the isel pass and causes certain foldings from
happening because nodes have extraneous uses floating around.  For example, if we turned
foo(bar(x)) -> baz(x), we sometimes left bar(x) around.

llvm-svn: 46305

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -606,6 +606,11 @@ void DAGCombiner::Run(bool RunningAfterLegalize) {
         // Push the new node and any users onto the worklist
         AddToWorkList(RV.Val);
         AddUsersToWorkList(RV.Val);
+        
+        // Add any uses of the old node to the worklist if they have a single
+        // use.  They may be dead after this node is deleted.
+        for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i)
+          AddToWorkList(N->getOperand(i).Val);
           
         // Nodes can be reintroduced into the worklist.  Make sure we do not
         // process a node that has been replaced.