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If any of the sign extended bits are demanded, the input sign bit is demanded

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for a sign extension.

This fixes InstCombine/2006-02-13-DemandedMiscompile.ll and Ptrdist/bc.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@26152 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-02-13 22:41:07 +00:00
parent 3fcb664dbc
commit f345fe4d9a
1 changed files with 9 additions and 3 deletions
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12
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -889,15 +889,21 @@ bool InstCombiner::SimplifyDemandedBits(Value *V, uint64_t DemandedMask,
KnownZero |= NewBits;
} else {
// Sign extension.
if (SimplifyDemandedBits(I->getOperand(0),
DemandedMask & SrcTy->getIntegralTypeMask(),
uint64_t InSignBit = 1ULL << (SrcTy->getPrimitiveSizeInBits()-1);
int64_t InputDemandedBits = DemandedMask & SrcTy->getIntegralTypeMask();
// If any of the sign extended bits are demanded, we know that the sign
// bit is demanded.
if (NewBits & DemandedMask)
InputDemandedBits |= InSignBit;
if (SimplifyDemandedBits(I->getOperand(0), InputDemandedBits,
KnownZero, KnownOne, Depth+1))
return true;
assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
// If the sign bit of the input is known set or clear, then we know the
// top bits of the result.
uint64_t InSignBit = 1ULL << (SrcTy->getPrimitiveSizeInBits()-1);
// If the input sign bit is known zero, or if the NewBits are not demanded
// convert this into a zero extension.