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Fold shifts into subsequent SHL's. These shifts often arise due to addrses

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arithmetic lowering.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@21818 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2005-05-09 17:06:45 +00:00
parent 7516255795
commit 57aa5961a9
1 changed files with 28 additions and 0 deletions
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28
lib/CodeGen/SelectionDAG/SelectionDAG.cpp
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@ -946,6 +946,34 @@ SDOperand SelectionDAG::getNode(unsigned Opcode, MVT::ValueType VT,
return getNode(ISD::UNDEF, N1.getValueType()); return getNode(ISD::UNDEF, N1.getValueType());
} }
if (C2 == 0) return N1; if (C2 == 0) return N1;
if (Opcode == ISD::SHL && N1.getNumOperands() == 2)
if (ConstantSDNode *OpSA = dyn_cast<ConstantSDNode>(N1.getOperand(1))) {
unsigned OpSAC = OpSA->getValue();
if (N1.getOpcode() == ISD::SHL) {
if (C2+OpSAC >= MVT::getSizeInBits(N1.getValueType()))
return getConstant(0, N1.getValueType());
return getNode(ISD::SHL, N1.getValueType(), N1.getOperand(0),
getConstant(C2+OpSAC, N2.getValueType()));
} else if (N1.getOpcode() == ISD::SRL) {
// (X >> C1) << C2: if C2 > C1, ((X & ~0<<C1) << C2-C1)
SDOperand Mask = getNode(ISD::AND, VT, N1.getOperand(0),
getConstant(~0ULL << OpSAC, VT));
if (C2 > OpSAC) {
return getNode(ISD::SHL, VT, Mask,
getConstant(C2-OpSAC, N2.getValueType()));
} else {
// (X >> C1) << C2: if C2 <= C1, ((X & ~0<<C1) >> C1-C2)
return getNode(ISD::SRL, VT, Mask,
getConstant(OpSAC-C2, N2.getValueType()));
}
} else if (N1.getOpcode() == ISD::SRA) {
// if C1 == C2, just mask out low bits.
if (C2 == OpSAC)
return getNode(ISD::AND, VT, N1.getOperand(0),
getConstant(~0ULL << C2, VT));
}
}
break; break;
case ISD::AND: case ISD::AND: