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[ARM] Remove redundant computeKnownBits helper.

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Move the BFI logic to computeKnownBitsForTargetNode, and delete
the redundant CMOV logic.

This is intended as a cleanup, but it's probably possible to construct
a case where moving the BFI logic allows more combines.

Differential Revision: https://reviews.llvm.org/D31795

llvm-svn: 300752
This commit is contained in:
Eli Friedman 2017-04-19 20:50:57 +00:00
parent 528682bdac
commit 7a7eb8d03b
1 changed files with 14 additions and 29 deletions
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43
lib/Target/ARM/ARMISelLowering.cpp
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@ -11694,34 +11694,6 @@ static SDValue PerformExtendCombine(SDNode *N, SelectionDAG &DAG,
return SDValue();
}
static void computeKnownBits(SelectionDAG &DAG, SDValue Op, APInt &KnownZero,
APInt &KnownOne) {
if (Op.getOpcode() == ARMISD::BFI) {
// Conservatively, we can recurse down the first operand
// and just mask out all affected bits.
computeKnownBits(DAG, Op.getOperand(0), KnownZero, KnownOne);
// The operand to BFI is already a mask suitable for removing the bits it
// sets.
ConstantSDNode *CI = cast<ConstantSDNode>(Op.getOperand(2));
const APInt &Mask = CI->getAPIntValue();
KnownZero &= Mask;
KnownOne &= Mask;
return;
}
if (Op.getOpcode() == ARMISD::CMOV) {
APInt KZ2(KnownZero.getBitWidth(), 0);
APInt KO2(KnownOne.getBitWidth(), 0);
computeKnownBits(DAG, Op.getOperand(0), KnownZero, KnownOne);
computeKnownBits(DAG, Op.getOperand(1), KZ2, KO2);
KnownZero &= KZ2;
KnownOne &= KO2;
return;
}
return DAG.computeKnownBits(Op, KnownZero, KnownOne);
}
SDValue ARMTargetLowering::PerformCMOVToBFICombine(SDNode *CMOV, SelectionDAG &DAG) const {
// If we have a CMOV, OR and AND combination such as:
// if (x & CN)
@ -11783,7 +11755,7 @@ SDValue ARMTargetLowering::PerformCMOVToBFICombine(SDNode *CMOV, SelectionDAG &D
// Lastly, can we determine that the bits defined by OrCI
// are zero in Y?
APInt KnownZero, KnownOne;
computeKnownBits(DAG, Y, KnownZero, KnownOne);
DAG.computeKnownBits(Y, KnownZero, KnownOne);
if ((OrCI & KnownZero) != OrCI)
return SDValue();
@ -12663,6 +12635,19 @@ void ARMTargetLowering::computeKnownBitsForTargetNode(const SDValue Op,
}
}
}
case ARMISD::BFI: {
// Conservatively, we can recurse down the first operand
// and just mask out all affected bits.
DAG.computeKnownBits(Op.getOperand(0), KnownZero, KnownOne, Depth + 1);
// The operand to BFI is already a mask suitable for removing the bits it
// sets.
ConstantSDNode *CI = cast<ConstantSDNode>(Op.getOperand(2));
const APInt &Mask = CI->getAPIntValue();
KnownZero &= Mask;
KnownOne &= Mask;
return;
}
}
}