================
@@ -14935,6 +14936,52 @@ SDValue SITargetLowering::performAddCombine(SDNode *N,
return SDValue();
}
+SDValue SITargetLowering::performPtrAddCombine(SDNode *N,
+ DAGCombinerInfo &DCI) const {
+ SelectionDAG &DAG = DCI.DAG;
+ EVT VT = N->getValueType(0);
+ SDLoc DL(N);
+ SDValue N0 = N->getOperand(0);
+ SDValue N1 = N->getOperand(1);
+
+ if (N1.getOpcode() == ISD::ADD) {
+ // (ptradd x, (add y, z)) -> (ptradd (ptradd x, y), z) if z is a constant,
+ // y is not, and (add y, z) is used only once.
+ // (ptradd x, (add y, z)) -> (ptradd (ptradd x, z), y) if y is a constant,
+ // z is not, and (add y, z) is used only once.
+ // The goal is to move constant offsets to the outermost ptradd, to create
+ // more opportunities to fold offsets into memory instructions.
+ // Together with the generic combines in DAGCombiner.cpp, this also
+ // implements (ptradd (ptradd x, y), z) -> (ptradd (ptradd x, z), y)).
+ //
+ // This transform is here instead of in the general DAGCombiner as it can
+ // turn in-bounds pointer arithmetic out-of-bounds, which is problematic
for
+ // AArch64's CPA.
----------------
arichardson wrote:
I think having it here is fine, it explains why it can't be moved to a generic
fold.
https://github.com/llvm/llvm-project/pull/142739
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