diff options
Diffstat (limited to 'lib/Transforms')
| -rw-r--r-- | lib/Transforms/InstCombine/InstCombineShifts.cpp | 74 |
1 files changed, 39 insertions, 35 deletions
diff --git a/lib/Transforms/InstCombine/InstCombineShifts.cpp b/lib/Transforms/InstCombine/InstCombineShifts.cpp index 4c14509..b31049e 100644 --- a/lib/Transforms/InstCombine/InstCombineShifts.cpp +++ b/lib/Transforms/InstCombine/InstCombineShifts.cpp @@ -529,19 +529,6 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantInt *Op1, ShiftOp = 0; if (ShiftOp && isa<ConstantInt>(ShiftOp->getOperand(1))) { - - // This is a constant shift of a constant shift. Be careful about hiding - // shl instructions behind bit masks. They are used to represent multiplies - // by a constant, and it is important that simple arithmetic expressions - // are still recognizable by scalar evolution. - // - // The transforms applied to shl are very similar to the transforms applied - // to mul by constant. We can be more aggressive about optimizing right - // shifts. - // - // Combinations of right and left shifts will still be optimized in - // DAGCombine where scalar evolution no longer applies. - ConstantInt *ShiftAmt1C = cast<ConstantInt>(ShiftOp->getOperand(1)); uint32_t ShiftAmt1 = ShiftAmt1C->getLimitedValue(TypeBits); uint32_t ShiftAmt2 = Op1->getLimitedValue(TypeBits); @@ -567,6 +554,13 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantInt *Op1, } if (ShiftAmt1 == ShiftAmt2) { + // If we have ((X >>? C) << C), turn this into X & (-1 << C). + if (I.getOpcode() == Instruction::Shl && + ShiftOp->getOpcode() != Instruction::Shl) { + APInt Mask(APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt1)); + return BinaryOperator::CreateAnd(X, + ConstantInt::get(I.getContext(),Mask)); + } // If we have ((X << C) >>u C), turn this into X & (-1 >>u C). if (I.getOpcode() == Instruction::LShr && ShiftOp->getOpcode() == Instruction::Shl) { @@ -576,23 +570,28 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantInt *Op1, } } else if (ShiftAmt1 < ShiftAmt2) { uint32_t ShiftDiff = ShiftAmt2-ShiftAmt1; - - // (X >>?,exact C1) << C2 --> X << (C2-C1) - // The inexact version is deferred to DAGCombine so we don't hide shl - // behind a bit mask. + + // (X >>? C1) << C2 --> X << (C2-C1) & (-1 << C2) if (I.getOpcode() == Instruction::Shl && - ShiftOp->getOpcode() != Instruction::Shl && - ShiftOp->isExact()) { + ShiftOp->getOpcode() != Instruction::Shl) { assert(ShiftOp->getOpcode() == Instruction::LShr || ShiftOp->getOpcode() == Instruction::AShr); ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff); - BinaryOperator *NewShl = BinaryOperator::Create(Instruction::Shl, - X, ShiftDiffCst); - NewShl->setHasNoUnsignedWrap(I.hasNoUnsignedWrap()); - NewShl->setHasNoSignedWrap(I.hasNoSignedWrap()); - return NewShl; + if (ShiftOp->isExact()) { + // (X >>?,exact C1) << C2 --> X << (C2-C1) + BinaryOperator *NewShl = BinaryOperator::Create(Instruction::Shl, + X, ShiftDiffCst); + NewShl->setHasNoUnsignedWrap(I.hasNoUnsignedWrap()); + NewShl->setHasNoSignedWrap(I.hasNoSignedWrap()); + return NewShl; + } + Value *Shift = Builder->CreateShl(X, ShiftDiffCst); + + APInt Mask(APInt::getHighBitsSet(TypeBits, TypeBits - ShiftAmt2)); + return BinaryOperator::CreateAnd(Shift, + ConstantInt::get(I.getContext(),Mask)); } - + // (X << C1) >>u C2 --> X >>u (C2-C1) & (-1 >> C2) if (I.getOpcode() == Instruction::LShr && ShiftOp->getOpcode() == Instruction::Shl) { @@ -628,19 +627,24 @@ Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantInt *Op1, assert(ShiftAmt2 < ShiftAmt1); uint32_t ShiftDiff = ShiftAmt1-ShiftAmt2; - // (X >>?exact C1) << C2 --> X >>?exact (C1-C2) - // The inexact version is deferred to DAGCombine so we don't hide shl - // behind a bit mask. + // (X >>? C1) << C2 --> X >>? (C1-C2) & (-1 << C2) if (I.getOpcode() == Instruction::Shl && - ShiftOp->getOpcode() != Instruction::Shl && - ShiftOp->isExact()) { + ShiftOp->getOpcode() != Instruction::Shl) { ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff); - BinaryOperator *NewShr = BinaryOperator::Create(ShiftOp->getOpcode(), - X, ShiftDiffCst); - NewShr->setIsExact(true); - return NewShr; + 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)); } - + // (X << C1) >>u C2 --> X << (C1-C2) & (-1 >> C2) if (I.getOpcode() == Instruction::LShr && ShiftOp->getOpcode() == Instruction::Shl) { |