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

[deadalnix]

Summary

As per title.

[lebedev.ri]

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

16639 ↗

(On Diff #216871)

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

[deadalnix]

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

1696 ↗

(On Diff #216871)

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

16639 ↗

(On Diff #216871)

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

llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

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) {