[DAGCombiner] Add node back in the worklist in topological order in CommitTargetLoweringOpt

[deadalnix]

Summary

Right now, DAGCombiner process the nodes in an iplementation defined order. This tends to be fragile as optimisation may or may not kick in depending on the traversal order.

This is part of a larger effort to get the DAGCombiner to process its node in topological order.

[deadalnix]

Ping, rebase

[lebedev.ri]

... where AddToWorklistWithUsers() calls those two functions in the opposite order.
Looks ok to me. Might be good to have a test case, but i don't expect that it would be easy to produce one.

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

 void DAGCombiner::
 CommitTargetLoweringOpt(const TargetLowering::TargetLoweringOpt &TLO) {
   // Replace all uses.  If any nodes become isomorphic to other nodes and
   // are deleted, make sure to remove them from our worklist.
   WorklistRemover DeadNodes(*this);
   DAG.ReplaceAllUsesOfValueWith(TLO.Old, TLO.New);
 
   // Push the new node and any (possibly new) users onto the worklist.
-  AddToWorklist(TLO.New.getNode());
-  AddUsersToWorklist(TLO.New.getNode());
+  AddToWorklistWithUsers(TLO.New.getNode());
 
   // Finally, if the node is now dead, remove it from the graph.  The node
   // may not be dead if the replacement process recursively simplified to
   // something else needing this node.
   if (TLO.Old.getNode()->use_empty())
     deleteAndRecombine(TLO.Old.getNode());
 }