diff options
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/Transforms/InstCombine/InstCombineShifts.cpp | 16 |
1 files changed, 11 insertions, 5 deletions
diff --git a/lib/Transforms/InstCombine/InstCombineShifts.cpp b/lib/Transforms/InstCombine/InstCombineShifts.cpp index 702e0f2ee8..6779e4076c 100644 --- a/lib/Transforms/InstCombine/InstCombineShifts.cpp +++ b/lib/Transforms/InstCombine/InstCombineShifts.cpp @@ -536,12 +536,11 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantInt *Op1, if (ShiftAmt1 == 0) return 0; // Will be simplified in the future. Value *X = ShiftOp->getOperand(0); - uint32_t AmtSum = ShiftAmt1+ShiftAmt2; // Fold into one big shift. - IntegerType *Ty = cast<IntegerType>(I.getType()); // Check for (X << c1) << c2 and (X >> c1) >> c2 if (I.getOpcode() == ShiftOp->getOpcode()) { + uint32_t AmtSum = ShiftAmt1+ShiftAmt2; // Fold into one big shift. // If this is oversized composite shift, then unsigned shifts get 0, ashr // saturates. if (AmtSum >= TypeBits) { @@ -603,9 +602,16 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantInt *Op1, // (X >>? C1) << C2 --> X >>? (C1-C2) & (-1 << C2) if (I.getOpcode() == Instruction::Shl && ShiftOp->getOpcode() != Instruction::Shl) { - Value *Shift = Builder->CreateBinOp(ShiftOp->getOpcode(), X, - ConstantInt::get(Ty, ShiftDiff)); - + ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff); + if (ShiftOp->isExact()) { + // (X >>?exact C1) << C2 --> X >>?exact (C1-C2) + BinaryOperator *NewShr = BinaryOperator::Create(ShiftOp->getOpcode(), + X, ShiftDiffCst); + NewShr->setIsExact(true); + return NewShr; + } + Value *Shift = Builder->CreateBinOp(ShiftOp->getOpcode(), + X, ShiftDiffCst); APInt Mask(APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt2)); return BinaryOperator::CreateAnd(Shift, ConstantInt::get(I.getContext(),Mask)); |