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

Summary:
This enables further transforms.

Depends on D32916

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

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D32925

llvm-svn: 304401

1 files changed, 49 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index a54ca4d32cd..9d5b6ecb4be 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -1970,6 +1970,44 @@ SDValue DAGCombiner::visitADD(SDNode *N) {
   return SDValue();
 }
 
+static SDValue getAsCarry(const TargetLowering &TLI, SDValue V) {
+  bool Masked = false;
+
+  // First, peel away TRUNCATE/ZERO_EXTEND/AND nodes due to legalization.
+  while (true) {
+    if (V.getOpcode() == ISD::TRUNCATE || V.getOpcode() == ISD::ZERO_EXTEND) {
+      V = V.getOperand(0);
+      continue;
+    }
+
+    if (V.getOpcode() == ISD::AND && isOneConstant(V.getOperand(1))) {
+      Masked = true;
+      V = V.getOperand(0);
+      continue;
+    }
+
+    break;
+  }
+
+  // If this is not a carry, return.
+  if (V.getResNo() != 1)
+    return SDValue();
+
+  if (V.getOpcode() != ISD::ADDCARRY && V.getOpcode() != ISD::SUBCARRY &&
+      V.getOpcode() != ISD::UADDO && V.getOpcode() != ISD::USUBO)
+    return SDValue();
+
+  // If the result is masked, then no matter what kind of bool it is we can
+  // return. If it isn't, then we need to make sure the bool type is either 0 or
+  // 1 and not other values.
+  if (Masked ||
+      TLI.getBooleanContents(V.getValueType()) ==
+          TargetLoweringBase::ZeroOrOneBooleanContent)
+    return V;
+
+  return SDValue();
+}
+
 SDValue DAGCombiner::visitADDLike(SDValue N0, SDValue N1, SDNode *LocReference) {
   EVT VT = N0.getValueType();
   SDLoc DL(LocReference);
@@ -2017,6 +2055,12 @@ SDValue DAGCombiner::visitADDLike(SDValue N0, SDValue N1, SDNode *LocReference)
     return DAG.getNode(ISD::ADDCARRY, DL, N1->getVTList(),
                        N0, N1.getOperand(0), N1.getOperand(2));
 
+  // (add X, Carry) -> (addcarry X, 0, Carry)
+  if (SDValue Carry = getAsCarry(TLI, N1))
+    return DAG.getNode(ISD::ADDCARRY, DL,
+                       DAG.getVTList(VT, Carry.getValueType()), N0,
+                       DAG.getConstant(0, DL, VT), Carry);
+
   return SDValue();
 }
 
@@ -2100,6 +2144,11 @@ SDValue DAGCombiner::visitUADDOLike(SDValue N0, SDValue N1, SDNode *N) {
                          N1.getOperand(2));
   }
 
+  // (uaddo X, Carry) -> (addcarry X, 0, Carry)
+  if (SDValue Carry = getAsCarry(TLI, N1))
+    return DAG.getNode(ISD::ADDCARRY, SDLoc(N), N->getVTList(), N0,
+                       DAG.getConstant(0, SDLoc(N), N0.getValueType()), Carry);
+
   return SDValue();
 }