[llvm-branch-commits] [llvm] [AMDGPU][SDAG] Add ISD::PTRADD DAG combines (PR #142739)

[Matt Arsenault via llvm-branch-commits]

================
@@ -2628,6 +2630,87 @@ SDValue DAGCombiner::foldSubToAvg(SDNode *N, const SDLoc &DL) {
   return SDValue();
 }
 
+/// Try to fold a pointer arithmetic node.
+/// This needs to be done separately from normal addition, because pointer
+/// addition is not commutative.
+SDValue DAGCombiner::visitPTRADD(SDNode *N) {
+  SDValue N0 = N->getOperand(0);
+  SDValue N1 = N->getOperand(1);
+  EVT PtrVT = N0.getValueType();
+  EVT IntVT = N1.getValueType();
+  SDLoc DL(N);
+
+  // This is already ensured by an assert in SelectionDAG::getNode(). Several
+  // combines here depend on this assumption.
+  assert(PtrVT == IntVT &&
+         "PTRADD with different operand types is not supported");
+
+  // fold (ptradd x, 0) -> x
+  if (isNullConstant(N1))
+    return N0;
+
+  // fold (ptradd 0, x) -> x
+  if (isNullConstant(N0) && PtrVT == IntVT)
+    return N1;
----------------
arsenm wrote:

```suggestion
  // fold (ptradd 0, x) -> x
  if (PtrVT == IntVT && isNullConstant(N0))
    return N1;
```

But PtrVT == IntVT was already asserted above? 

https://github.com/llvm/llvm-project/pull/142739