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Check RHS simplification before LHS simplification to avoid infinitely looping

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on PowerPC/small-arguments.ll


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@26389 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-02-27 00:36:27 +00:00
parent 5f0c658aa4
commit 81cd35586f
1 changed files with 17 additions and 18 deletions
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35
lib/CodeGen/SelectionDAG/TargetLowering.cpp
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@ -201,7 +201,23 @@ bool TargetLowering::SimplifyDemandedBits(SDOperand Op, uint64_t DemandedMask,
KnownZero = ~KnownOne & DemandedMask;
return false; // Don't fall through, will infinitely loop.
case ISD::AND:
// If either the LHS or the RHS are Zero, the result is zero.
// If the RHS is a constant, check to see if the LHS would be zero without
// using the bits from the RHS. Below, we use knowledge about the RHS to
// simplify the LHS, here we're using information from the LHS to simplify
// the RHS.
if (ConstantSDNode *RHSC = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
uint64_t LHSZero, LHSOne;
ComputeMaskedBits(Op.getOperand(0), DemandedMask,
LHSZero, LHSOne, Depth+1);
// If the LHS already has zeros where RHSC does, this and is dead.
if ((LHSZero & DemandedMask) == (~RHSC->getValue() & DemandedMask))
return TLO.CombineTo(Op, Op.getOperand(0));
// If any of the set bits in the RHS are known zero on the LHS, shrink
// the constant.
if (TLO.ShrinkDemandedConstant(Op, ~LHSZero & DemandedMask))
return true;
}
if (SimplifyDemandedBits(Op.getOperand(1), DemandedMask, KnownZero,
KnownOne, TLO, Depth+1))
return true;
@ -224,23 +240,6 @@ bool TargetLowering::SimplifyDemandedBits(SDOperand Op, uint64_t DemandedMask,
if (TLO.ShrinkDemandedConstant(Op, DemandedMask & ~KnownZero2))
return true;
// If the RHS is a constant, check to see if the LHS would be zero without
// using the bits from the RHS. Above, we used knowledge about the RHS to
// simplify the LHS, here we're using information from the LHS to simplify
// the RHS.
if (ConstantSDNode *RHSC = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
uint64_t LHSZero, LHSOne;
ComputeMaskedBits(Op.getOperand(0), DemandedMask,
LHSZero, LHSOne, Depth+1);
// If the LHS already has zeros where RHSC does, this and is dead.
if ((LHSZero & DemandedMask) == (~RHSC->getValue() & DemandedMask))
return TLO.CombineTo(Op, Op.getOperand(0));
// If any of the set bits in the RHS are known zero on the LHS, shrink
// the constant.
if (TLO.ShrinkDemandedConstant(Op, ~LHSZero & DemandedMask))
return true;
}
// Output known-1 bits are only known if set in both the LHS & RHS.
KnownOne &= KnownOne2;
// Output known-0 are known to be clear if zero in either the LHS | RHS.