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Reimplement r114460 in target-independent DAGCombine rather than target-dependent, by using

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the predicate to discover the number of sign bits.  Enhance X86's target lowering to provide
a useful response to this query.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@114473 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Owen Anderson 2010-09-21 20:42:50 +00:00
parent 78d3af47f5
commit bc146b0a4d
3 changed files with 29 additions and 23 deletions
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14
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@ -1424,6 +1424,20 @@ SDValue DAGCombiner::visitADD(SDNode *N) {
N0.getOperand(0).getOperand(1),
N0.getOperand(1)));
if (N1.getOpcode() == ISD::AND) {
SDValue AndOp0 = N1.getOperand(0);
ConstantSDNode *AndOp1 = dyn_cast<ConstantSDNode>(N1->getOperand(1));
unsigned NumSignBits = DAG.ComputeNumSignBits(AndOp0);
unsigned DestBits = VT.getScalarType().getSizeInBits();
// (add z, (and (sbbl x, x), 1)) -> (sub z, (sbbl x, x))
// and similar xforms where the inner op is either ~0 or 0.
if (NumSignBits == DestBits && AndOp1 && AndOp1->isOne()) {
DebugLoc DL = N->getDebugLoc();
return DAG.getNode(ISD::SUB, DL, VT, N->getOperand(0), AndOp0);
}
}
return SDValue();
}

33
lib/Target/X86/X86ISelLowering.cpp
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@ -1021,7 +1021,6 @@ X86TargetLowering::X86TargetLowering(X86TargetMachine &TM)
setTargetDAGCombine(ISD::OR);
setTargetDAGCombine(ISD::STORE);
setTargetDAGCombine(ISD::ZERO_EXTEND);
setTargetDAGCombine(ISD::ADD);
if (Subtarget->is64Bit())
setTargetDAGCombine(ISD::MUL);
@ -9980,6 +9979,16 @@ void X86TargetLowering::computeMaskedBitsForTargetNode(const SDValue Op,
}
}
unsigned X86TargetLowering::ComputeNumSignBitsForTargetNode(SDValue Op,
unsigned Depth) const {
// SETCC_CARRY sets the dest to ~0 for true or 0 for false.
if (Op.getOpcode() == X86ISD::SETCC_CARRY)
return Op.getValueType().getScalarType().getSizeInBits();
// Fallback case.
return 1;
}
/// isGAPlusOffset - Returns true (and the GlobalValue and the offset) if the
/// node is a GlobalAddress + offset.
bool X86TargetLowering::isGAPlusOffset(SDNode *N,
@ -10454,27 +10463,6 @@ static SDValue PerformCMOVCombine(SDNode *N, SelectionDAG &DAG,
return SDValue();
}
/// PerformAddCombine - Optimize ADD when combined with X86 opcodes.
static SDValue PerformAddCombine(SDNode *N, SelectionDAG &DAG,
TargetLowering::DAGCombinerInfo &DCI) {
if (DCI.isBeforeLegalize() || DCI.isCalledByLegalizer())
return SDValue();
EVT VT = N->getValueType(0);
SDValue Op1 = N->getOperand(1);
if (Op1->getOpcode() == ISD::AND) {
SDValue AndOp0 = Op1->getOperand(0);
ConstantSDNode *AndOp1 = dyn_cast<ConstantSDNode>(Op1->getOperand(1));
// (add z, (and (sbbl x, x), 1)) -> (sub z, (sbbl x, x))
if (AndOp0->getOpcode() == X86ISD::SETCC_CARRY &&
AndOp1 && AndOp1->getZExtValue() == 1) {
DebugLoc DL = N->getDebugLoc();
return DAG.getNode(ISD::SUB, DL, VT, N->getOperand(0), AndOp0);
}
}
return SDValue();
}
/// PerformMulCombine - Optimize a single multiply with constant into two
/// in order to implement it with two cheaper instructions, e.g.
@ -10961,7 +10949,6 @@ SDValue X86TargetLowering::PerformDAGCombine(SDNode *N,
return PerformEXTRACT_VECTOR_ELTCombine(N, DAG, *this);
case ISD::SELECT: return PerformSELECTCombine(N, DAG, Subtarget);
case X86ISD::CMOV: return PerformCMOVCombine(N, DAG, DCI);
case ISD::ADD: return PerformAddCombine(N, DAG, DCI);
case ISD::MUL: return PerformMulCombine(N, DAG, DCI);
case ISD::SHL:
case ISD::SRA:

5
lib/Target/X86/X86ISelLowering.h
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@ -523,6 +523,11 @@ namespace llvm {
const SelectionDAG &DAG,
unsigned Depth = 0) const;
// ComputeNumSignBitsForTargetNode - Determine the number of bits in the
// operation that are sign bits.
virtual unsigned ComputeNumSignBitsForTargetNode(SDValue Op,
unsigned Depth) const;
virtual bool
isGAPlusOffset(SDNode *N, const GlobalValue* &GA, int64_t &Offset) const;