if (!isa<SExtInst>(OpA) && !isa<ZExtInst>(OpA))
return false;
+ bool Signed = isa<SExtInst>(OpA);
+
OpA = dyn_cast<Instruction>(OpA->getOperand(0));
OpB = dyn_cast<Instruction>(OpB->getOperand(0));
if (!OpA || !OpB || OpA->getType() != OpB->getType())
return false;
// Now we need to prove that adding 1 to OpA won't overflow.
+ bool Safe = false;
+ // First attempt: if OpB is an add with NSW/NUW, and OpB is 1 added to OpA,
+ // we're okay.
+ if (OpB->getOpcode() == Instruction::Add &&
+ isa<ConstantInt>(OpB->getOperand(1)) &&
+ cast<ConstantInt>(OpB->getOperand(1))->getSExtValue() > 0) {
+ if (Signed)
+ Safe = cast<BinaryOperator>(OpB)->hasNoSignedWrap();
+ else
+ Safe = cast<BinaryOperator>(OpB)->hasNoUnsignedWrap();
+ }
+
unsigned BitWidth = OpA->getType()->getScalarSizeInBits();
- APInt KnownZero = APInt(BitWidth, 0);
- APInt KnownOne = APInt(BitWidth, 0);
- computeKnownBits(OpA, KnownZero, KnownOne, DL, 0, nullptr, OpA, &DT);
+
+ // Second attempt:
// If any bits are known to be zero other than the sign bit in OpA, we can
// add 1 to it while guaranteeing no overflow of any sort.
- KnownZero &= ~APInt::getHighBitsSet(BitWidth, 1);
- if (KnownZero == 0)
+ if (!Safe) {
+ APInt KnownZero(BitWidth, 0);
+ APInt KnownOne(BitWidth, 0);
+ computeKnownBits(OpA, KnownZero, KnownOne, DL, 0, nullptr, OpA, &DT);
+ KnownZero &= ~APInt::getHighBitsSet(BitWidth, 1);
+ if (KnownZero != 0)
+ Safe = true;
+ }
+
+ if (!Safe)
return false;
const SCEV *OffsetSCEVA = SE.getSCEV(OpA);