if (ConstantInt *CUI = dyn_cast<ConstantInt>(Op1))
if (Instruction *Res = FoldShiftByConstant(Op0, CUI, I))
return Res;
+
+ // X shift (A srem B) -> X shift (A urem B) iff B is positive.
+ // Because shifts by negative values are undefined.
+ if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Op1))
+ if (BO->getOpcode() == Instruction::SRem && BO->getType()->isIntegerTy()) {
+ // Make sure the divisor's sign bit is zero.
+ APInt Mask = APInt::getSignBit(BO->getType()->getPrimitiveSizeInBits());
+ if (MaskedValueIsZero(BO->getOperand(1), Mask)) {
+ Value *URem = Builder->CreateURem(BO->getOperand(0), BO->getOperand(1),
+ BO->getName());
+ I.setOperand(1, URem);
+ return &I;
+ }
+ }
+
return 0;
}