[SelectionDAG][PowerPC] Remove setTruncatingStore from StoreSDNode. (llvm#137667)

Mutating a node after it has been created isn't a good idea. After
e17f07c, we have a version of setStore
that can create a truncating indexed store. Use that instead of
MorphNodeTo+setTruncatingStore in PowerPC.

Unfortunately, if we return the newly created node, DAGCombiner will
visit the node and change the constant. To prevent this, we use
DCI.CombineTo and avoid adding the new node to the worklist.

Author: topperc

llvm/include/llvm/CodeGen/SelectionDAGNodes.h

@@ -2533,9 +2533,6 @@ class StoreSDNode : public LSBaseSDNode {
   /// For integers this is the same as doing a TRUNCATE and storing the result.
   /// For floats, it is the same as doing an FP_ROUND and storing the result.
   bool isTruncatingStore() const { return StoreSDNodeBits.IsTruncating; }
-  void setTruncatingStore(bool Truncating) {
-    StoreSDNodeBits.IsTruncating = Truncating;
-  }
 
   const SDValue &getValue() const { return getOperand(1); }
   const SDValue &getBasePtr() const { return getOperand(2); }

llvm/lib/Target/PowerPC/PPCISelLowering.cpp

@@ -16562,13 +16562,16 @@ SDValue PPCTargetLowering::PerformDAGCombine(SDNode *N,
                                     MemVT.getSizeInBits());
       SDValue Const64 = DAG.getConstant(Val64, dl, MVT::i64);
 
-      // DAG.getTruncStore() can't be used here because it doesn't accept
-      // the general (base + offset) addressing mode.
-      // So we use UpdateNodeOperands and setTruncatingStore instead.
-      DAG.UpdateNodeOperands(N, N->getOperand(0), Const64, N->getOperand(2),
-                             N->getOperand(3));
-      cast<StoreSDNode>(N)->setTruncatingStore(true);
-      return SDValue(N, 0);
+      auto *ST = cast<StoreSDNode>(N);
+      SDValue NewST = DAG.getStore(ST->getChain(), dl, Const64,
+                                   ST->getBasePtr(), ST->getOffset(), MemVT,
+                                   ST->getMemOperand(), ST->getAddressingMode(),
+                                   /*IsTruncating=*/true);
+      // Note we use CombineTo here to prevent DAGCombiner from visiting the
+      // new store which will change the constant by removing non-demanded bits.
+      return ST->isUnindexed()
+                 ? DCI.CombineTo(N, NewST, /*AddTo=*/false)
+                 : DCI.CombineTo(N, NewST, NewST.getValue(1), /*AddTo=*/false);
     }
 
     // For little endian, VSX stores require generating xxswapd/lxvd2x.