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Pull in r189672 from upstream llvm trunk:

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InstCombine: Check for zero shift amounts before subtracting one
  causing integer overflow.

  PR17026. Also avoid undefined shifts and shift amounts larger than 64
  bits (those are always undef because we can't represent integer types
  that large).

This should fix assertion failures when building the emulators/xmame
port.

Reported by:	bapt
This commit is contained in:
Dimitry Andric 2013-08-30 18:29:25 +00:00
parent 40a827b6f0
commit 89a53411d4
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=255076
1 changed files with 15 additions and 10 deletions
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25
contrib/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
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@ -845,21 +845,26 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
Value *InstCombiner::SimplifyShrShlDemandedBits(Instruction *Shr,
Instruction *Shl, APInt DemandedMask, APInt &KnownZero, APInt &KnownOne) {
unsigned ShlAmt = cast<ConstantInt>(Shl->getOperand(1))->getZExtValue();
unsigned ShrAmt = cast<ConstantInt>(Shr->getOperand(1))->getZExtValue();
const APInt &ShlOp1 = cast<ConstantInt>(Shl->getOperand(1))->getValue();
const APInt &ShrOp1 = cast<ConstantInt>(Shr->getOperand(1))->getValue();
if (!ShlOp1 || !ShrOp1)
return 0; // Noop.
Value *VarX = Shr->getOperand(0);
Type *Ty = VarX->getType();
unsigned BitWidth = Ty->getIntegerBitWidth();
if (ShlOp1.uge(BitWidth) || ShrOp1.uge(BitWidth))
return 0; // Undef.
unsigned ShlAmt = ShlOp1.getZExtValue();
unsigned ShrAmt = ShrOp1.getZExtValue();
KnownOne.clearAllBits();
KnownZero = APInt::getBitsSet(KnownZero.getBitWidth(), 0, ShlAmt-1);
KnownZero &= DemandedMask;
if (ShlAmt == 0 || ShrAmt == 0)
return 0;
Value *VarX = Shr->getOperand(0);
Type *Ty = VarX->getType();
APInt BitMask1(APInt::getAllOnesValue(Ty->getIntegerBitWidth()));
APInt BitMask2(APInt::getAllOnesValue(Ty->getIntegerBitWidth()));
APInt BitMask1(APInt::getAllOnesValue(BitWidth));
APInt BitMask2(APInt::getAllOnesValue(BitWidth));
bool isLshr = (Shr->getOpcode() == Instruction::LShr);
BitMask1 = isLshr ? (BitMask1.lshr(ShrAmt) << ShlAmt) :