diff options
Diffstat (limited to 'llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp')
| -rw-r--r-- | llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 29 |
1 files changed, 29 insertions, 0 deletions
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp index fd7d5917359..5c7c0290f0d 100644 --- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp +++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp @@ -7346,6 +7346,35 @@ SDValue DAGCombiner::visitSELECT(SDNode *N) { CC, TLI, DAG)) return FMinMax; + // Use 'unsigned add with overflow' to optimize an unsigned saturating add. + // This is conservatively limited to pre-legal-operations to give targets + // a chance to reverse the transform if they want to do that. Also, it is + // unlikely that the pattern would be formed late, so it's probably not + // worth going through the other checks. + if (!LegalOperations && TLI.isOperationLegalOrCustom(ISD::UADDO, VT) && + CC == ISD::SETUGT && N0.hasOneUse() && isAllOnesConstant(N1) && + N2.getOpcode() == ISD::ADD && Cond0 == N2.getOperand(0)) { + auto *C = dyn_cast<ConstantSDNode>(N2.getOperand(1)); + auto *NotC = dyn_cast<ConstantSDNode>(Cond1); + if (C && NotC && C->getAPIntValue() == ~NotC->getAPIntValue()) { + // select (setcc Cond0, ~C, ugt), -1, (add Cond0, C) --> + // uaddo Cond0, C; select uaddo.1, -1, uaddo.0 + // + // The IR equivalent of this transform would have this form: + // %a = add %x, C + // %c = icmp ugt %x, ~C + // %r = select %c, -1, %a + // => + // %u = call {iN,i1} llvm.uadd.with.overflow(%x, C) + // %u0 = extractvalue %u, 0 + // %u1 = extractvalue %u, 1 + // %r = select %u1, -1, %u0 + SDVTList VTs = DAG.getVTList(VT, VT0); + SDValue UAO = DAG.getNode(ISD::UADDO, DL, VTs, Cond0, N2.getOperand(1)); + return DAG.getSelect(DL, VT, UAO.getValue(1), N1, UAO.getValue(0)); + } + } + if (TLI.isOperationLegal(ISD::SELECT_CC, VT) || (!LegalOperations && TLI.isOperationLegalOrCustom(ISD::SELECT_CC, VT))) return DAG.getNode(ISD::SELECT_CC, DL, VT, Cond0, Cond1, N1, N2, |
