[SelectionDAG] Refactor use of getMemBasePlusOffset() where applicable

Reduce complexity of PTRADD usage logic by harnessing
getMemBasePlusOffset().
Not all uses are applicable, as ADD's order of operands might be inverted
(PTRADD should always have pointer first, offset second).

Author: rgwott

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -4304,12 +4304,6 @@ void SelectionDAGBuilder::visitGetElementPtr(const User &I) {
   SDLoc dl = getCurSDLoc();
   auto &TLI = DAG.getTargetLoweringInfo();
   GEPNoWrapFlags NW = cast<GEPOperator>(I).getNoWrapFlags();
-  unsigned int AddOpcode = ISD::PTRADD;
-
-  if (!DAG.getTarget().shouldPreservePtrArith(
-          DAG.getMachineFunction().getFunction())) {
-    AddOpcode = ISD::ADD;
-  }
 
   // Normalize Vector GEP - all scalar operands should be converted to the
   // splat vector.
@@ -4341,8 +4335,8 @@ void SelectionDAGBuilder::visitGetElementPtr(const User &I) {
             (int64_t(Offset) >= 0 && NW.hasNoUnsignedSignedWrap()))
           Flags |= SDNodeFlags::NoUnsignedWrap;
 
-        N = DAG.getNode(AddOpcode, dl, N.getValueType(), N,
-                        DAG.getConstant(Offset, dl, N.getValueType()), Flags);
+        N = DAG.getMemBasePlusOffset(
+            N, DAG.getConstant(Offset, dl, N.getValueType()), dl, Flags);
       }
     } else {
       // IdxSize is the width of the arithmetic according to IR semantics.
@@ -4386,7 +4380,7 @@ void SelectionDAGBuilder::visitGetElementPtr(const User &I) {
 
         OffsVal = DAG.getSExtOrTrunc(OffsVal, dl, N.getValueType());
 
-        N = DAG.getNode(AddOpcode, dl, N.getValueType(), N, OffsVal, Flags);
+        N = DAG.getMemBasePlusOffset(N, OffsVal, dl, Flags);
         continue;
       }
 
@@ -4446,7 +4440,7 @@ void SelectionDAGBuilder::visitGetElementPtr(const User &I) {
       SDNodeFlags AddFlags;
       AddFlags.setNoUnsignedWrap(NW.hasNoUnsignedWrap());
 
-      N = DAG.getNode(AddOpcode, dl, N.getValueType(), N, IdxN, AddFlags);
+      N = DAG.getMemBasePlusOffset(N, IdxN, dl, AddFlags);
     }
   }
 
@@ -4515,7 +4509,7 @@ void SelectionDAGBuilder::visitAlloca(const AllocaInst &I) {
   } else {
     AllocSize = DAG.getNode(ISD::ADD, dl, AllocSize.getValueType(), AllocSize,
                             DAG.getConstant(StackAlignMask, dl, IntPtr),
-			    SDNodeFlags::NoUnsignedWrap);
+                            SDNodeFlags::NoUnsignedWrap);
   }
 
   // Mask out the low bits for alignment purposes.
@@ -9214,13 +9208,8 @@ bool SelectionDAGBuilder::visitMemPCpyCall(const CallInst &I) {
   Size = DAG.getSExtOrTrunc(Size, sdl, Dst.getValueType());
 
   // Adjust return pointer to point just past the last dst byte.
-  unsigned int AddOpcode = ISD::PTRADD;
-  if (!DAG.getTarget().shouldPreservePtrArith(
-          DAG.getMachineFunction().getFunction())) {
-    AddOpcode = ISD::ADD;
-  }
-  SDValue DstPlusSize =
-      DAG.getNode(AddOpcode, sdl, Dst.getValueType(), Dst, Size);
+  SDNodeFlags Flags;
+  SDValue DstPlusSize = DAG.getMemBasePlusOffset(Dst, Size, sdl, Flags);
   setValue(&I, DstPlusSize);
   return true;
 }
@@ -11317,15 +11306,9 @@ TargetLowering::LowerCallTo(TargetLowering::CallLoweringInfo &CLI) const {
     MachineFunction &MF = CLI.DAG.getMachineFunction();
     Align HiddenSRetAlign = MF.getFrameInfo().getObjectAlign(DemoteStackIdx);
     for (unsigned i = 0; i < NumValues; ++i) {
-      unsigned int AddOpcode = ISD::PTRADD;
-      if (!CLI.DAG.getTarget().shouldPreservePtrArith(
-              CLI.DAG.getMachineFunction().getFunction())) {
-        AddOpcode = ISD::ADD;
-      }
-      SDValue Add = CLI.DAG.getNode(
-          AddOpcode, CLI.DL, PtrVT, DemoteStackSlot,
-          CLI.DAG.getConstant(Offsets[i], CLI.DL, PtrVT),
-	  SDNodeFlags::NoUnisgnedWrap);
+      SDValue Add = CLI.DAG.getMemBasePlusOffset(
+          DemoteStackSlot, CLI.DAG.getConstant(Offsets[i], CLI.DL, PtrVT),
+          CLI.DL, SDNodeFlags::NoUnsignedWrap);
       SDValue L = CLI.DAG.getLoad(
           RetTys[i], CLI.DL, CLI.Chain, Add,
           MachinePointerInfo::getFixedStack(CLI.DAG.getMachineFunction(),