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Add a select_cc optimization for recognizing abs(int). This speeds up an

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integer MPEG encoding loop by a factor of two.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@22758 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nate Begeman 2005-08-11 02:18:13 +00:00
parent e5d63829fd
commit e1fae4a3ae
1 changed files with 16 additions and 0 deletions
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16
lib/CodeGen/SelectionDAG/SelectionDAG.cpp
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@ -1495,6 +1495,22 @@ SDOperand SelectionDAG::getNode(unsigned Opcode, MVT::ValueType VT,
return getNode(ISD::AND, AType, Shift, N3);
}
}
// Check to see if this is an integer abs. select_cc setl[te] X, 0, -X, X ->
// Y = sra (X, size(X)-1); xor (add (X, Y), Y)
if (N2C && N2C->isNullValue() && (CC == ISD::SETLT || CC == ISD::SETLE) &&
N1 == N4 && N3.getOpcode() == ISD::SUB && N1 == N3.getOperand(1)) {
if (ConstantSDNode *SubC = dyn_cast<ConstantSDNode>(N3.getOperand(0))) {
MVT::ValueType XType = N1.getValueType();
if (SubC->isNullValue() && MVT::isInteger(XType)) {
SDOperand Shift = getNode(ISD::SRA, XType, N1,
getConstant(MVT::getSizeInBits(XType)-1,
TLI.getShiftAmountTy()));
return getNode(ISD::XOR, XType, getNode(ISD::ADD, XType, N1, Shift),
Shift);
}
}
}
}
std::vector<SDOperand> Ops;