diff options
Diffstat (limited to 'llvm/lib')
| -rw-r--r-- | llvm/lib/Target/X86/X86ISelLowering.cpp | 22 |
1 files changed, 19 insertions, 3 deletions
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp index 679fa81f7f8..2b51137901f 100644 --- a/llvm/lib/Target/X86/X86ISelLowering.cpp +++ b/llvm/lib/Target/X86/X86ISelLowering.cpp @@ -34897,13 +34897,29 @@ static SDValue combineAddOrSubToADCOrSBB(SDNode *N, SelectionDAG &DAG) { !Cmp.getOperand(0).getValueType().isInteger()) return SDValue(); - // (cmp Z, 1) sets the carry flag if Z is 0. SDValue Z = Cmp.getOperand(0); + SDVTList VTs = DAG.getVTList(N->getValueType(0), MVT::i32); + + // If X is -1 or 0, then we have an opportunity to avoid constants required by + // the cmp transform below. 'neg' sets the carry flag when Z != 0, so create 0 + // or -1 using 'sbb' with fake operands: + // 0 - (Z != 0) --> sbb %eax, %eax, (neg Z) + // -1 + (Z == 0) --> sbb %eax, %eax, (neg Z) + if (auto *ConstantX = dyn_cast<ConstantSDNode>(X)) { + if ((IsSub && CC == X86::COND_NE && ConstantX->isNullValue()) || + (!IsSub && CC == X86::COND_E && ConstantX->isAllOnesValue())) { + SDValue Zero = DAG.getConstant(0, DL, VT); + SDValue Neg = DAG.getNode(X86ISD::SUB, DL, VTs, Zero, Z); + return DAG.getNode(X86ISD::SETCC_CARRY, DL, VT, + DAG.getConstant(X86::COND_B, DL, MVT::i8), + SDValue(Neg.getNode(), 1)); + } + } + + // (cmp Z, 1) sets the carry flag if Z is 0. SDValue NewCmp = DAG.getNode(X86ISD::CMP, DL, MVT::i32, Z, DAG.getConstant(1, DL, Z.getValueType())); - SDVTList VTs = DAG.getVTList(N->getValueType(0), MVT::i32); - // X - (Z != 0) --> sub X, (zext(setne Z, 0)) --> adc X, -1, (cmp Z, 1) // X + (Z != 0) --> add X, (zext(setne Z, 0)) --> sbb X, -1, (cmp Z, 1) if (CC == X86::COND_NE) |
