fold away addc nodes when we know there cannot be a carry-out.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@34913 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 9fdbe26..fdcf99e 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -754,7 +754,7 @@
// If the flag result is dead, turn this into an ADD.
if (N->hasNUsesOfValue(0, 1))
return CombineTo(N, DAG.getNode(ISD::ADD, VT, N1, N0),
- SDOperand(N, 1));
+ DAG.getNode(ISD::CARRY_FALSE, MVT::Flag));
// canonicalize constant to RHS.
if (N0C && !N1C) {
@@ -762,9 +762,25 @@
return DAG.getNode(ISD::ADDC, N->getVTList(), Ops, 2);
}
- // fold (add x, 0) -> x + no carry out
- //if (N1C && N1C->isNullValue())
- // return N0;
+ // fold (addc x, 0) -> x + no carry out
+ if (N1C && N1C->isNullValue())
+ return CombineTo(N, N0, DAG.getNode(ISD::CARRY_FALSE, MVT::Flag));
+
+ // fold (addc a, b) -> (or a, b), CARRY_FALSE iff a and b share no bits.
+ uint64_t LHSZero, LHSOne;
+ uint64_t RHSZero, RHSOne;
+ uint64_t Mask = MVT::getIntVTBitMask(VT);
+ TLI.ComputeMaskedBits(N0, Mask, LHSZero, LHSOne);
+ if (LHSZero) {
+ TLI.ComputeMaskedBits(N1, Mask, RHSZero, RHSOne);
+
+ // If all possibly-set bits on the LHS are clear on the RHS, return an OR.
+ // If all possibly-set bits on the RHS are clear on the LHS, return an OR.
+ if ((RHSZero & (~LHSZero & Mask)) == (~LHSZero & Mask) ||
+ (LHSZero & (~RHSZero & Mask)) == (~RHSZero & Mask))
+ return CombineTo(N, DAG.getNode(ISD::OR, VT, N0, N1),
+ DAG.getNode(ISD::CARRY_FALSE, MVT::Flag));
+ }
return SDOperand();
}
@@ -772,19 +788,22 @@
SDOperand DAGCombiner::visitADDE(SDNode *N) {
SDOperand N0 = N->getOperand(0);
SDOperand N1 = N->getOperand(1);
+ SDOperand CarryIn = N->getOperand(2);
ConstantSDNode *N0C = dyn_cast<ConstantSDNode>(N0);
ConstantSDNode *N1C = dyn_cast<ConstantSDNode>(N1);
//MVT::ValueType VT = N0.getValueType();
// canonicalize constant to RHS
if (N0C && !N1C) {
- SDOperand Ops[] = { N1, N0, N->getOperand(2) };
+ SDOperand Ops[] = { N1, N0, CarryIn };
return DAG.getNode(ISD::ADDE, N->getVTList(), Ops, 3);
}
- // fold (add x, 0) -> x
- //if (N1C && N1C->isNullValue())
- // return N0;
+ // fold (adde x, y, false) -> (addc x, y)
+ if (CarryIn.getOpcode() == ISD::CARRY_FALSE) {
+ SDOperand Ops[] = { N1, N0 };
+ return DAG.getNode(ISD::ADDC, N->getVTList(), Ops, 2);
+ }
return SDOperand();
}