diff options
Diffstat (limited to 'llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp')
| -rw-r--r-- | llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 35 |
1 files changed, 35 insertions, 0 deletions
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp index 9d5b6ecb4be..3008bd75036 100644 --- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp +++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp @@ -2216,6 +2216,41 @@ SDValue DAGCombiner::visitADDCARRYLike(SDValue N0, SDValue N1, SDValue CarryIn, return DAG.getNode(ISD::ADDCARRY, SDLoc(N), N->getVTList(), N0.getOperand(0), N0.getOperand(1), CarryIn); + /** + * When one of the addcarry argument is itself a carry, we may be facing + * a diamond carry propagation. In which case we try to transform the DAG + * to ensure linear carry propagation if that is possible. + * + * We are trying to get: + * (addcarry X, 0, (addcarry A, B, Z):Carry) + */ + if (auto Y = getAsCarry(TLI, N1)) { + /** + * (uaddo A, B) + * / \ + * Carry Sum + * | \ + * | (addcarry *, 0, Z) + * | / + * \ Carry + * | / + * (addcarry X, *, *) + */ + if (Y.getOpcode() == ISD::UADDO && + CarryIn.getResNo() == 1 && + CarryIn.getOpcode() == ISD::ADDCARRY && + isNullConstant(CarryIn.getOperand(1)) && + CarryIn.getOperand(0) == Y.getValue(0)) { + auto NewY = DAG.getNode(ISD::ADDCARRY, SDLoc(N), Y->getVTList(), + Y.getOperand(0), Y.getOperand(1), + CarryIn.getOperand(2)); + AddToWorklist(NewY.getNode()); + return DAG.getNode(ISD::ADDCARRY, SDLoc(N), N->getVTList(), N0, + DAG.getConstant(0, SDLoc(N), N0.getValueType()), + NewY.getValue(1)); + } + } + return SDValue(); } |
