[DAGCombine] (addcarry (add|uaddo X, Y), 0, Carry) -> (addcarry X, Y, Carry)

Summary: Do the transform when the carry isn't used. It's a pattern exposed when legalizing large integers.

Reviewers: jyknight, nemanjai, mkuper, spatel, RKSimon, zvi, bkramer

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D32755

llvm-svn: 302047

1 files changed, 19 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 3cd5573d9d2..03698ac862a 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -242,6 +242,7 @@ namespace {
     SDValue visitUSUBO(SDNode *N);
     SDValue visitADDE(SDNode *N);
     SDValue visitADDCARRY(SDNode *N);
+    SDValue visitADDCARRYLike(SDValue N0, SDValue N1, SDValue CarryIn, SDNode *N);
     SDValue visitSUBE(SDNode *N);
     SDValue visitSUBCARRY(SDNode *N);
     SDValue visitMUL(SDNode *N);
@@ -2142,6 +2143,24 @@ SDValue DAGCombiner::visitADDCARRY(SDNode *N) {
   if (isNullConstant(CarryIn))
     return DAG.getNode(ISD::UADDO, SDLoc(N), N->getVTList(), N0, N1);
 
+  if (SDValue Combined = visitADDCARRYLike(N0, N1, CarryIn, N))
+    return Combined;
+
+  if (SDValue Combined = visitADDCARRYLike(N1, N0, CarryIn, N))
+    return Combined;
+
+  return SDValue();
+}
+
+SDValue DAGCombiner::visitADDCARRYLike(SDValue N0, SDValue N1, SDValue CarryIn,
+                                       SDNode *N) {
+  // Iff the flag result is dead:
+  // (addcarry (add|uaddo X, Y), 0, Carry) -> (addcarry X, Y, Carry)
+  if ((N0.getOpcode() == ISD::ADD || N0.getOpcode() == ISD::UADDO) &&
+      isNullConstant(N1) && !N->hasAnyUseOfValue(1))
+    return DAG.getNode(ISD::ADDCARRY, SDLoc(N), N->getVTList(),
+                       N0.getOperand(0), N0.getOperand(1), CarryIn);
+
   return SDValue();
 }