diff options
| -rw-r--r-- | lib/Transforms/Scalar/InstructionCombining.cpp | 12 |
1 files changed, 4 insertions, 8 deletions
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp index 6cc7bbe3dc..51141162bf 100644 --- a/lib/Transforms/Scalar/InstructionCombining.cpp +++ b/lib/Transforms/Scalar/InstructionCombining.cpp @@ -1361,14 +1361,10 @@ static bool MaskedValueIsZero(Value *V, ConstantIntegral *Mask) { break; } case Instruction::Shl: - // (shl X, C1) & C2 == 0 iff (-1 << C1) & C2 == 0 - if (ConstantUInt *SA = dyn_cast<ConstantUInt>(I->getOperand(1))) { - Constant *C1 = ConstantIntegral::getAllOnesValue(I->getType()); - C1 = ConstantExpr::getShl(C1, SA); - C1 = ConstantExpr::getAnd(C1, Mask); - if (C1->isNullValue()) - return true; - } + // (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0 + if (ConstantUInt *SA = dyn_cast<ConstantUInt>(I->getOperand(1))) + return MaskedValueIsZero(I->getOperand(0), + cast<ConstantIntegral>(ConstantExpr::getUShr(Mask, SA))); break; case Instruction::Shr: // (ushr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0 |