[DAGCombiner] Add node to the worklist in topological order in scalarizeExtractedVectorLoad

[deadalnix]

Summary

As per title.

[lebedev.ri]

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

16639

Won't this cause the node to be revisited, before AddToWorklist(EVE); ?

[deadalnix]

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

1696

When the node itself is returned, it is not added back to the worklist.

16639

No. The only difference between this and just returning an empty value is that it increment the counter of transform that has been done. The main loop assumes that whatever transform does this has handled the worklist properly.

[lebedev.ri]

Appears to have test coverage as per https://llvm.org/reports/coverage/lib/CodeGen/SelectionDAG/DAGCombiner.cpp.gcov.html
LG, @RKSimon ?

[RKSimon]

LGTM

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

while (SDNode *N = getNextWorklistEntry()) {
 
     ++NodesCombined;
 
     // If we get back the same node we passed in, rather than a new node or
     // zero, we know that the node must have defined multiple values and
     // CombineTo was used.  Since CombineTo takes care of the worklist
     // mechanics for us, we have no work to do in this case.
     if (RV.getNode() == N)
       continue;
 
     assert(N->getOpcode() != ISD::DELETED_NODE &&
            RV.getOpcode() != ISD::DELETED_NODE &&
            "Node was deleted but visit returned new node!");
 
     LLVM_DEBUG(dbgs() << " ... into: "; RV.getNode()->dump(&DAG));
 
     if (N->getNumValues() == RV.getNode()->getNumValues())
if (ResultVT.bitsLT(VecEltVT))
       Load = DAG.getNode(ISD::TRUNCATE, SDLoc(EVE), ResultVT, Load);
     else
       Load = DAG.getBitcast(ResultVT, Load);
   }
   WorklistRemover DeadNodes(*this);
   SDValue From[] = { SDValue(EVE, 0), SDValue(OriginalLoad, 1) };
   SDValue To[] = { Load, Chain };
   DAG.ReplaceAllUsesOfValuesWith(From, To, 2);
+  // Make sure to revisit this node to clean it up; it will usually be dead.
+  AddToWorklist(EVE);
   // Since we're explicitly calling ReplaceAllUses, add the new node to the
   // worklist explicitly as well.
-  AddToWorklist(Load.getNode());
   AddUsersToWorklist(Load.getNode()); // Add users too
-  // Make sure to revisit this node to clean it up; it will usually be dead.
-  AddToWorklist(EVE);
+  AddToWorklist(Load.getNode());
   ++OpsNarrowed;
   return SDValue(EVE, 0);
 }
 
 /// Transform a vector binary operation into a scalar binary operation by moving
 /// the math/logic after an extract element of a vector.
 static SDValue scalarizeExtractedBinop(SDNode *ExtElt, SelectionDAG &DAG,
                                        bool LegalOperations) {
   const TargetLowering &TLI = DAG.getTargetLoweringInfo();
   SDValue Vec = ExtElt->getOperand(0);