| //===- InstCombineShifts.cpp ----------------------------------------------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file implements the visitShl, visitLShr, and visitAShr functions. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "InstCombine.h" |
| #include "llvm/Analysis/ConstantFolding.h" |
| #include "llvm/Analysis/InstructionSimplify.h" |
| #include "llvm/IR/IntrinsicInst.h" |
| #include "llvm/Support/PatternMatch.h" |
| using namespace llvm; |
| using namespace PatternMatch; |
| |
| Instruction *InstCombiner::commonShiftTransforms(BinaryOperator &I) { |
| assert(I.getOperand(1)->getType() == I.getOperand(0)->getType()); |
| Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); |
| |
| // See if we can fold away this shift. |
| if (SimplifyDemandedInstructionBits(I)) |
| return &I; |
| |
| // Try to fold constant and into select arguments. |
| if (isa<Constant>(Op0)) |
| if (SelectInst *SI = dyn_cast<SelectInst>(Op1)) |
| if (Instruction *R = FoldOpIntoSelect(I, SI)) |
| return R; |
| |
| if (ConstantInt *CUI = dyn_cast<ConstantInt>(Op1)) |
| if (Instruction *Res = FoldShiftByConstant(Op0, CUI, I)) |
| return Res; |
| |
| // X shift (A srem B) -> X shift (A and B-1) iff B is a power of 2. |
| // Because shifts by negative values (which could occur if A were negative) |
| // are undefined. |
| Value *A; const APInt *B; |
| if (Op1->hasOneUse() && match(Op1, m_SRem(m_Value(A), m_Power2(B)))) { |
| // FIXME: Should this get moved into SimplifyDemandedBits by saying we don't |
| // demand the sign bit (and many others) here?? |
| Value *Rem = Builder->CreateAnd(A, ConstantInt::get(I.getType(), *B-1), |
| Op1->getName()); |
| I.setOperand(1, Rem); |
| return &I; |
| } |
| |
| return 0; |
| } |
| |
| /// CanEvaluateShifted - See if we can compute the specified value, but shifted |
| /// logically to the left or right by some number of bits. This should return |
| /// true if the expression can be computed for the same cost as the current |
| /// expression tree. This is used to eliminate extraneous shifting from things |
| /// like: |
| /// %C = shl i128 %A, 64 |
| /// %D = shl i128 %B, 96 |
| /// %E = or i128 %C, %D |
| /// %F = lshr i128 %E, 64 |
| /// where the client will ask if E can be computed shifted right by 64-bits. If |
| /// this succeeds, the GetShiftedValue function will be called to produce the |
| /// value. |
| static bool CanEvaluateShifted(Value *V, unsigned NumBits, bool isLeftShift, |
| InstCombiner &IC) { |
| // We can always evaluate constants shifted. |
| if (isa<Constant>(V)) |
| return true; |
| |
| Instruction *I = dyn_cast<Instruction>(V); |
| if (!I) return false; |
| |
| // If this is the opposite shift, we can directly reuse the input of the shift |
| // if the needed bits are already zero in the input. This allows us to reuse |
| // the value which means that we don't care if the shift has multiple uses. |
| // TODO: Handle opposite shift by exact value. |
| ConstantInt *CI = 0; |
| if ((isLeftShift && match(I, m_LShr(m_Value(), m_ConstantInt(CI)))) || |
| (!isLeftShift && match(I, m_Shl(m_Value(), m_ConstantInt(CI))))) { |
| if (CI->getZExtValue() == NumBits) { |
| // TODO: Check that the input bits are already zero with MaskedValueIsZero |
| #if 0 |
| // If this is a truncate of a logical shr, we can truncate it to a smaller |
| // lshr iff we know that the bits we would otherwise be shifting in are |
| // already zeros. |
| uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits(); |
| uint32_t BitWidth = Ty->getScalarSizeInBits(); |
| if (MaskedValueIsZero(I->getOperand(0), |
| APInt::getHighBitsSet(OrigBitWidth, OrigBitWidth-BitWidth)) && |
| CI->getLimitedValue(BitWidth) < BitWidth) { |
| return CanEvaluateTruncated(I->getOperand(0), Ty); |
| } |
| #endif |
| |
| } |
| } |
| |
| // We can't mutate something that has multiple uses: doing so would |
| // require duplicating the instruction in general, which isn't profitable. |
| if (!I->hasOneUse()) return false; |
| |
| switch (I->getOpcode()) { |
| default: return false; |
| case Instruction::And: |
| case Instruction::Or: |
| case Instruction::Xor: |
| // Bitwise operators can all arbitrarily be arbitrarily evaluated shifted. |
| return CanEvaluateShifted(I->getOperand(0), NumBits, isLeftShift, IC) && |
| CanEvaluateShifted(I->getOperand(1), NumBits, isLeftShift, IC); |
| |
| case Instruction::Shl: { |
| // We can often fold the shift into shifts-by-a-constant. |
| CI = dyn_cast<ConstantInt>(I->getOperand(1)); |
| if (CI == 0) return false; |
| |
| // We can always fold shl(c1)+shl(c2) -> shl(c1+c2). |
| if (isLeftShift) return true; |
| |
| // We can always turn shl(c)+shr(c) -> and(c2). |
| if (CI->getValue() == NumBits) return true; |
| |
| unsigned TypeWidth = I->getType()->getScalarSizeInBits(); |
| |
| // We can turn shl(c1)+shr(c2) -> shl(c3)+and(c4), but it isn't |
| // profitable unless we know the and'd out bits are already zero. |
| if (CI->getZExtValue() > NumBits) { |
| unsigned LowBits = TypeWidth - CI->getZExtValue(); |
| if (MaskedValueIsZero(I->getOperand(0), |
| APInt::getLowBitsSet(TypeWidth, NumBits) << LowBits)) |
| return true; |
| } |
| |
| return false; |
| } |
| case Instruction::LShr: { |
| // We can often fold the shift into shifts-by-a-constant. |
| CI = dyn_cast<ConstantInt>(I->getOperand(1)); |
| if (CI == 0) return false; |
| |
| // We can always fold lshr(c1)+lshr(c2) -> lshr(c1+c2). |
| if (!isLeftShift) return true; |
| |
| // We can always turn lshr(c)+shl(c) -> and(c2). |
| if (CI->getValue() == NumBits) return true; |
| |
| unsigned TypeWidth = I->getType()->getScalarSizeInBits(); |
| |
| // We can always turn lshr(c1)+shl(c2) -> lshr(c3)+and(c4), but it isn't |
| // profitable unless we know the and'd out bits are already zero. |
| if (CI->getValue().ult(TypeWidth) && CI->getZExtValue() > NumBits) { |
| unsigned LowBits = CI->getZExtValue() - NumBits; |
| if (MaskedValueIsZero(I->getOperand(0), |
| APInt::getLowBitsSet(TypeWidth, NumBits) << LowBits)) |
| return true; |
| } |
| |
| return false; |
| } |
| case Instruction::Select: { |
| SelectInst *SI = cast<SelectInst>(I); |
| return CanEvaluateShifted(SI->getTrueValue(), NumBits, isLeftShift, IC) && |
| CanEvaluateShifted(SI->getFalseValue(), NumBits, isLeftShift, IC); |
| } |
| case Instruction::PHI: { |
| // We can change a phi if we can change all operands. Note that we never |
| // get into trouble with cyclic PHIs here because we only consider |
| // instructions with a single use. |
| PHINode *PN = cast<PHINode>(I); |
| for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) |
| if (!CanEvaluateShifted(PN->getIncomingValue(i), NumBits, isLeftShift,IC)) |
| return false; |
| return true; |
| } |
| } |
| } |
| |
| /// GetShiftedValue - When CanEvaluateShifted returned true for an expression, |
| /// this value inserts the new computation that produces the shifted value. |
| static Value *GetShiftedValue(Value *V, unsigned NumBits, bool isLeftShift, |
| InstCombiner &IC) { |
| // We can always evaluate constants shifted. |
| if (Constant *C = dyn_cast<Constant>(V)) { |
| if (isLeftShift) |
| V = IC.Builder->CreateShl(C, NumBits); |
| else |
| V = IC.Builder->CreateLShr(C, NumBits); |
| // If we got a constantexpr back, try to simplify it with TD info. |
| if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) |
| V = ConstantFoldConstantExpression(CE, IC.getDataLayout(), |
| IC.getTargetLibraryInfo()); |
| return V; |
| } |
| |
| Instruction *I = cast<Instruction>(V); |
| IC.Worklist.Add(I); |
| |
| switch (I->getOpcode()) { |
| default: llvm_unreachable("Inconsistency with CanEvaluateShifted"); |
| case Instruction::And: |
| case Instruction::Or: |
| case Instruction::Xor: |
| // Bitwise operators can all arbitrarily be arbitrarily evaluated shifted. |
| I->setOperand(0, GetShiftedValue(I->getOperand(0), NumBits,isLeftShift,IC)); |
| I->setOperand(1, GetShiftedValue(I->getOperand(1), NumBits,isLeftShift,IC)); |
| return I; |
| |
| case Instruction::Shl: { |
| BinaryOperator *BO = cast<BinaryOperator>(I); |
| unsigned TypeWidth = BO->getType()->getScalarSizeInBits(); |
| |
| // We only accept shifts-by-a-constant in CanEvaluateShifted. |
| ConstantInt *CI = cast<ConstantInt>(BO->getOperand(1)); |
| |
| // We can always fold shl(c1)+shl(c2) -> shl(c1+c2). |
| if (isLeftShift) { |
| // If this is oversized composite shift, then unsigned shifts get 0. |
| unsigned NewShAmt = NumBits+CI->getZExtValue(); |
| if (NewShAmt >= TypeWidth) |
| return Constant::getNullValue(I->getType()); |
| |
| BO->setOperand(1, ConstantInt::get(BO->getType(), NewShAmt)); |
| BO->setHasNoUnsignedWrap(false); |
| BO->setHasNoSignedWrap(false); |
| return I; |
| } |
| |
| // We turn shl(c)+lshr(c) -> and(c2) if the input doesn't already have |
| // zeros. |
| if (CI->getValue() == NumBits) { |
| APInt Mask(APInt::getLowBitsSet(TypeWidth, TypeWidth - NumBits)); |
| V = IC.Builder->CreateAnd(BO->getOperand(0), |
| ConstantInt::get(BO->getContext(), Mask)); |
| if (Instruction *VI = dyn_cast<Instruction>(V)) { |
| VI->moveBefore(BO); |
| VI->takeName(BO); |
| } |
| return V; |
| } |
| |
| // We turn shl(c1)+shr(c2) -> shl(c3)+and(c4), but only when we know that |
| // the and won't be needed. |
| assert(CI->getZExtValue() > NumBits); |
| BO->setOperand(1, ConstantInt::get(BO->getType(), |
| CI->getZExtValue() - NumBits)); |
| BO->setHasNoUnsignedWrap(false); |
| BO->setHasNoSignedWrap(false); |
| return BO; |
| } |
| case Instruction::LShr: { |
| BinaryOperator *BO = cast<BinaryOperator>(I); |
| unsigned TypeWidth = BO->getType()->getScalarSizeInBits(); |
| // We only accept shifts-by-a-constant in CanEvaluateShifted. |
| ConstantInt *CI = cast<ConstantInt>(BO->getOperand(1)); |
| |
| // We can always fold lshr(c1)+lshr(c2) -> lshr(c1+c2). |
| if (!isLeftShift) { |
| // If this is oversized composite shift, then unsigned shifts get 0. |
| unsigned NewShAmt = NumBits+CI->getZExtValue(); |
| if (NewShAmt >= TypeWidth) |
| return Constant::getNullValue(BO->getType()); |
| |
| BO->setOperand(1, ConstantInt::get(BO->getType(), NewShAmt)); |
| BO->setIsExact(false); |
| return I; |
| } |
| |
| // We turn lshr(c)+shl(c) -> and(c2) if the input doesn't already have |
| // zeros. |
| if (CI->getValue() == NumBits) { |
| APInt Mask(APInt::getHighBitsSet(TypeWidth, TypeWidth - NumBits)); |
| V = IC.Builder->CreateAnd(I->getOperand(0), |
| ConstantInt::get(BO->getContext(), Mask)); |
| if (Instruction *VI = dyn_cast<Instruction>(V)) { |
| VI->moveBefore(I); |
| VI->takeName(I); |
| } |
| return V; |
| } |
| |
| // We turn lshr(c1)+shl(c2) -> lshr(c3)+and(c4), but only when we know that |
| // the and won't be needed. |
| assert(CI->getZExtValue() > NumBits); |
| BO->setOperand(1, ConstantInt::get(BO->getType(), |
| CI->getZExtValue() - NumBits)); |
| BO->setIsExact(false); |
| return BO; |
| } |
| |
| case Instruction::Select: |
| I->setOperand(1, GetShiftedValue(I->getOperand(1), NumBits,isLeftShift,IC)); |
| I->setOperand(2, GetShiftedValue(I->getOperand(2), NumBits,isLeftShift,IC)); |
| return I; |
| case Instruction::PHI: { |
| // We can change a phi if we can change all operands. Note that we never |
| // get into trouble with cyclic PHIs here because we only consider |
| // instructions with a single use. |
| PHINode *PN = cast<PHINode>(I); |
| for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) |
| PN->setIncomingValue(i, GetShiftedValue(PN->getIncomingValue(i), |
| NumBits, isLeftShift, IC)); |
| return PN; |
| } |
| } |
| } |
| |
| |
| |
| Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, ConstantInt *Op1, |
| BinaryOperator &I) { |
| bool isLeftShift = I.getOpcode() == Instruction::Shl; |
| |
| |
| // See if we can propagate this shift into the input, this covers the trivial |
| // cast of lshr(shl(x,c1),c2) as well as other more complex cases. |
| if (I.getOpcode() != Instruction::AShr && |
| CanEvaluateShifted(Op0, Op1->getZExtValue(), isLeftShift, *this)) { |
| DEBUG(dbgs() << "ICE: GetShiftedValue propagating shift through expression" |
| " to eliminate shift:\n IN: " << *Op0 << "\n SH: " << I <<"\n"); |
| |
| return ReplaceInstUsesWith(I, |
| GetShiftedValue(Op0, Op1->getZExtValue(), isLeftShift, *this)); |
| } |
| |
| |
| // See if we can simplify any instructions used by the instruction whose sole |
| // purpose is to compute bits we don't care about. |
| uint32_t TypeBits = Op0->getType()->getScalarSizeInBits(); |
| |
| // shl i32 X, 32 = 0 and srl i8 Y, 9 = 0, ... just don't eliminate |
| // a signed shift. |
| // |
| if (Op1->uge(TypeBits)) { |
| if (I.getOpcode() != Instruction::AShr) |
| return ReplaceInstUsesWith(I, Constant::getNullValue(Op0->getType())); |
| // ashr i32 X, 32 --> ashr i32 X, 31 |
| I.setOperand(1, ConstantInt::get(I.getType(), TypeBits-1)); |
| return &I; |
| } |
| |
| // ((X*C1) << C2) == (X * (C1 << C2)) |
| if (BinaryOperator *BO = dyn_cast<BinaryOperator>(Op0)) |
| if (BO->getOpcode() == Instruction::Mul && isLeftShift) |
| if (Constant *BOOp = dyn_cast<Constant>(BO->getOperand(1))) |
| return BinaryOperator::CreateMul(BO->getOperand(0), |
| ConstantExpr::getShl(BOOp, Op1)); |
| |
| // Try to fold constant and into select arguments. |
| if (SelectInst *SI = dyn_cast<SelectInst>(Op0)) |
| if (Instruction *R = FoldOpIntoSelect(I, SI)) |
| return R; |
| if (isa<PHINode>(Op0)) |
| if (Instruction *NV = FoldOpIntoPhi(I)) |
| return NV; |
| |
| // Fold shift2(trunc(shift1(x,c1)), c2) -> trunc(shift2(shift1(x,c1),c2)) |
| if (TruncInst *TI = dyn_cast<TruncInst>(Op0)) { |
| Instruction *TrOp = dyn_cast<Instruction>(TI->getOperand(0)); |
| // If 'shift2' is an ashr, we would have to get the sign bit into a funny |
| // place. Don't try to do this transformation in this case. Also, we |
| // require that the input operand is a shift-by-constant so that we have |
| // confidence that the shifts will get folded together. We could do this |
| // xform in more cases, but it is unlikely to be profitable. |
| if (TrOp && I.isLogicalShift() && TrOp->isShift() && |
| isa<ConstantInt>(TrOp->getOperand(1))) { |
| // Okay, we'll do this xform. Make the shift of shift. |
| Constant *ShAmt = ConstantExpr::getZExt(Op1, TrOp->getType()); |
| // (shift2 (shift1 & 0x00FF), c2) |
| Value *NSh = Builder->CreateBinOp(I.getOpcode(), TrOp, ShAmt,I.getName()); |
| |
| // For logical shifts, the truncation has the effect of making the high |
| // part of the register be zeros. Emulate this by inserting an AND to |
| // clear the top bits as needed. This 'and' will usually be zapped by |
| // other xforms later if dead. |
| unsigned SrcSize = TrOp->getType()->getScalarSizeInBits(); |
| unsigned DstSize = TI->getType()->getScalarSizeInBits(); |
| APInt MaskV(APInt::getLowBitsSet(SrcSize, DstSize)); |
| |
| // The mask we constructed says what the trunc would do if occurring |
| // between the shifts. We want to know the effect *after* the second |
| // shift. We know that it is a logical shift by a constant, so adjust the |
| // mask as appropriate. |
| if (I.getOpcode() == Instruction::Shl) |
| MaskV <<= Op1->getZExtValue(); |
| else { |
| assert(I.getOpcode() == Instruction::LShr && "Unknown logical shift"); |
| MaskV = MaskV.lshr(Op1->getZExtValue()); |
| } |
| |
| // shift1 & 0x00FF |
| Value *And = Builder->CreateAnd(NSh, |
| ConstantInt::get(I.getContext(), MaskV), |
| TI->getName()); |
| |
| // Return the value truncated to the interesting size. |
| return new TruncInst(And, I.getType()); |
| } |
| } |
| |
| if (Op0->hasOneUse()) { |
| if (BinaryOperator *Op0BO = dyn_cast<BinaryOperator>(Op0)) { |
| // Turn ((X >> C) + Y) << C -> (X + (Y << C)) & (~0 << C) |
| Value *V1, *V2; |
| ConstantInt *CC; |
| switch (Op0BO->getOpcode()) { |
| default: break; |
| case Instruction::Add: |
| case Instruction::And: |
| case Instruction::Or: |
| case Instruction::Xor: { |
| // These operators commute. |
| // Turn (Y + (X >> C)) << C -> (X + (Y << C)) & (~0 << C) |
| if (isLeftShift && Op0BO->getOperand(1)->hasOneUse() && |
| match(Op0BO->getOperand(1), m_Shr(m_Value(V1), |
| m_Specific(Op1)))) { |
| Value *YS = // (Y << C) |
| Builder->CreateShl(Op0BO->getOperand(0), Op1, Op0BO->getName()); |
| // (X + (Y << C)) |
| Value *X = Builder->CreateBinOp(Op0BO->getOpcode(), YS, V1, |
| Op0BO->getOperand(1)->getName()); |
| uint32_t Op1Val = Op1->getLimitedValue(TypeBits); |
| return BinaryOperator::CreateAnd(X, ConstantInt::get(I.getContext(), |
| APInt::getHighBitsSet(TypeBits, TypeBits-Op1Val))); |
| } |
| |
| // Turn (Y + ((X >> C) & CC)) << C -> ((X & (CC << C)) + (Y << C)) |
| Value *Op0BOOp1 = Op0BO->getOperand(1); |
| if (isLeftShift && Op0BOOp1->hasOneUse() && |
| match(Op0BOOp1, |
| m_And(m_OneUse(m_Shr(m_Value(V1), m_Specific(Op1))), |
| m_ConstantInt(CC)))) { |
| Value *YS = // (Y << C) |
| Builder->CreateShl(Op0BO->getOperand(0), Op1, |
| Op0BO->getName()); |
| // X & (CC << C) |
| Value *XM = Builder->CreateAnd(V1, ConstantExpr::getShl(CC, Op1), |
| V1->getName()+".mask"); |
| return BinaryOperator::Create(Op0BO->getOpcode(), YS, XM); |
| } |
| } |
| |
| // FALL THROUGH. |
| case Instruction::Sub: { |
| // Turn ((X >> C) + Y) << C -> (X + (Y << C)) & (~0 << C) |
| if (isLeftShift && Op0BO->getOperand(0)->hasOneUse() && |
| match(Op0BO->getOperand(0), m_Shr(m_Value(V1), |
| m_Specific(Op1)))) { |
| Value *YS = // (Y << C) |
| Builder->CreateShl(Op0BO->getOperand(1), Op1, Op0BO->getName()); |
| // (X + (Y << C)) |
| Value *X = Builder->CreateBinOp(Op0BO->getOpcode(), V1, YS, |
| Op0BO->getOperand(0)->getName()); |
| uint32_t Op1Val = Op1->getLimitedValue(TypeBits); |
| return BinaryOperator::CreateAnd(X, ConstantInt::get(I.getContext(), |
| APInt::getHighBitsSet(TypeBits, TypeBits-Op1Val))); |
| } |
| |
| // Turn (((X >> C)&CC) + Y) << C -> (X + (Y << C)) & (CC << C) |
| if (isLeftShift && Op0BO->getOperand(0)->hasOneUse() && |
| match(Op0BO->getOperand(0), |
| m_And(m_OneUse(m_Shr(m_Value(V1), m_Value(V2))), |
| m_ConstantInt(CC))) && V2 == Op1) { |
| Value *YS = // (Y << C) |
| Builder->CreateShl(Op0BO->getOperand(1), Op1, Op0BO->getName()); |
| // X & (CC << C) |
| Value *XM = Builder->CreateAnd(V1, ConstantExpr::getShl(CC, Op1), |
| V1->getName()+".mask"); |
| |
| return BinaryOperator::Create(Op0BO->getOpcode(), XM, YS); |
| } |
| |
| break; |
| } |
| } |
| |
| |
| // If the operand is an bitwise operator with a constant RHS, and the |
| // shift is the only use, we can pull it out of the shift. |
| if (ConstantInt *Op0C = dyn_cast<ConstantInt>(Op0BO->getOperand(1))) { |
| bool isValid = true; // Valid only for And, Or, Xor |
| bool highBitSet = false; // Transform if high bit of constant set? |
| |
| switch (Op0BO->getOpcode()) { |
| default: isValid = false; break; // Do not perform transform! |
| case Instruction::Add: |
| isValid = isLeftShift; |
| break; |
| case Instruction::Or: |
| case Instruction::Xor: |
| highBitSet = false; |
| break; |
| case Instruction::And: |
| highBitSet = true; |
| break; |
| } |
| |
| // If this is a signed shift right, and the high bit is modified |
| // by the logical operation, do not perform the transformation. |
| // The highBitSet boolean indicates the value of the high bit of |
| // the constant which would cause it to be modified for this |
| // operation. |
| // |
| if (isValid && I.getOpcode() == Instruction::AShr) |
| isValid = Op0C->getValue()[TypeBits-1] == highBitSet; |
| |
| if (isValid) { |
| Constant *NewRHS = ConstantExpr::get(I.getOpcode(), Op0C, Op1); |
| |
| Value *NewShift = |
| Builder->CreateBinOp(I.getOpcode(), Op0BO->getOperand(0), Op1); |
| NewShift->takeName(Op0BO); |
| |
| return BinaryOperator::Create(Op0BO->getOpcode(), NewShift, |
| NewRHS); |
| } |
| } |
| } |
| } |
| |
| // Find out if this is a shift of a shift by a constant. |
| BinaryOperator *ShiftOp = dyn_cast<BinaryOperator>(Op0); |
| if (ShiftOp && !ShiftOp->isShift()) |
| 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); |
| assert(ShiftAmt2 != 0 && "Should have been simplified earlier"); |
| if (ShiftAmt1 == 0) return 0; // Will be simplified in the future. |
| Value *X = ShiftOp->getOperand(0); |
| |
| 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) { |
| if (I.getOpcode() != Instruction::AShr) |
| return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType())); |
| AmtSum = TypeBits-1; // Saturate to 31 for i32 ashr. |
| } |
| |
| return BinaryOperator::Create(I.getOpcode(), X, |
| ConstantInt::get(Ty, AmtSum)); |
| } |
| |
| if (ShiftAmt1 == ShiftAmt2) { |
| // If we have ((X << C) >>u C), turn this into X & (-1 >>u C). |
| if (I.getOpcode() == Instruction::LShr && |
| ShiftOp->getOpcode() == Instruction::Shl) { |
| APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt1)); |
| return BinaryOperator::CreateAnd(X, |
| ConstantInt::get(I.getContext(), Mask)); |
| } |
| } 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. |
| if (I.getOpcode() == Instruction::Shl && |
| ShiftOp->getOpcode() != Instruction::Shl && |
| ShiftOp->isExact()) { |
| 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; |
| } |
| |
| // (X << C1) >>u C2 --> X >>u (C2-C1) & (-1 >> C2) |
| if (I.getOpcode() == Instruction::LShr && |
| ShiftOp->getOpcode() == Instruction::Shl) { |
| ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff); |
| // (X <<nuw C1) >>u C2 --> X >>u (C2-C1) |
| if (ShiftOp->hasNoUnsignedWrap()) { |
| BinaryOperator *NewLShr = BinaryOperator::Create(Instruction::LShr, |
| X, ShiftDiffCst); |
| NewLShr->setIsExact(I.isExact()); |
| return NewLShr; |
| } |
| Value *Shift = Builder->CreateLShr(X, ShiftDiffCst); |
| |
| APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt2)); |
| return BinaryOperator::CreateAnd(Shift, |
| ConstantInt::get(I.getContext(),Mask)); |
| } |
| |
| // We can't handle (X << C1) >>s C2, it shifts arbitrary bits in. However, |
| // we can handle (X <<nsw C1) >>s C2 since it only shifts in sign bits. |
| if (I.getOpcode() == Instruction::AShr && |
| ShiftOp->getOpcode() == Instruction::Shl) { |
| if (ShiftOp->hasNoSignedWrap()) { |
| // (X <<nsw C1) >>s C2 --> X >>s (C2-C1) |
| ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff); |
| BinaryOperator *NewAShr = BinaryOperator::Create(Instruction::AShr, |
| X, ShiftDiffCst); |
| NewAShr->setIsExact(I.isExact()); |
| return NewAShr; |
| } |
| } |
| } else { |
| 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. |
| if (I.getOpcode() == Instruction::Shl && |
| ShiftOp->getOpcode() != Instruction::Shl && |
| ShiftOp->isExact()) { |
| ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff); |
| BinaryOperator *NewShr = BinaryOperator::Create(ShiftOp->getOpcode(), |
| X, ShiftDiffCst); |
| NewShr->setIsExact(true); |
| return NewShr; |
| } |
| |
| // (X << C1) >>u C2 --> X << (C1-C2) & (-1 >> C2) |
| if (I.getOpcode() == Instruction::LShr && |
| ShiftOp->getOpcode() == Instruction::Shl) { |
| ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff); |
| if (ShiftOp->hasNoUnsignedWrap()) { |
| // (X <<nuw C1) >>u C2 --> X <<nuw (C1-C2) |
| BinaryOperator *NewShl = BinaryOperator::Create(Instruction::Shl, |
| X, ShiftDiffCst); |
| NewShl->setHasNoUnsignedWrap(true); |
| return NewShl; |
| } |
| Value *Shift = Builder->CreateShl(X, ShiftDiffCst); |
| |
| APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt2)); |
| return BinaryOperator::CreateAnd(Shift, |
| ConstantInt::get(I.getContext(),Mask)); |
| } |
| |
| // We can't handle (X << C1) >>s C2, it shifts arbitrary bits in. However, |
| // we can handle (X <<nsw C1) >>s C2 since it only shifts in sign bits. |
| if (I.getOpcode() == Instruction::AShr && |
| ShiftOp->getOpcode() == Instruction::Shl) { |
| if (ShiftOp->hasNoSignedWrap()) { |
| // (X <<nsw C1) >>s C2 --> X <<nsw (C1-C2) |
| ConstantInt *ShiftDiffCst = ConstantInt::get(Ty, ShiftDiff); |
| BinaryOperator *NewShl = BinaryOperator::Create(Instruction::Shl, |
| X, ShiftDiffCst); |
| NewShl->setHasNoSignedWrap(true); |
| return NewShl; |
| } |
| } |
| } |
| } |
| return 0; |
| } |
| |
| Instruction *InstCombiner::visitShl(BinaryOperator &I) { |
| if (Value *V = SimplifyShlInst(I.getOperand(0), I.getOperand(1), |
| I.hasNoSignedWrap(), I.hasNoUnsignedWrap(), |
| TD)) |
| return ReplaceInstUsesWith(I, V); |
| |
| if (Instruction *V = commonShiftTransforms(I)) |
| return V; |
| |
| if (ConstantInt *Op1C = dyn_cast<ConstantInt>(I.getOperand(1))) { |
| unsigned ShAmt = Op1C->getZExtValue(); |
| |
| // If the shifted-out value is known-zero, then this is a NUW shift. |
| if (!I.hasNoUnsignedWrap() && |
| MaskedValueIsZero(I.getOperand(0), |
| APInt::getHighBitsSet(Op1C->getBitWidth(), ShAmt))) { |
| I.setHasNoUnsignedWrap(); |
| return &I; |
| } |
| |
| // If the shifted out value is all signbits, this is a NSW shift. |
| if (!I.hasNoSignedWrap() && |
| ComputeNumSignBits(I.getOperand(0)) > ShAmt) { |
| I.setHasNoSignedWrap(); |
| return &I; |
| } |
| } |
| |
| // (C1 << A) << C2 -> (C1 << C2) << A |
| Constant *C1, *C2; |
| Value *A; |
| if (match(I.getOperand(0), m_OneUse(m_Shl(m_Constant(C1), m_Value(A)))) && |
| match(I.getOperand(1), m_Constant(C2))) |
| return BinaryOperator::CreateShl(ConstantExpr::getShl(C1, C2), A); |
| |
| return 0; |
| } |
| |
| Instruction *InstCombiner::visitLShr(BinaryOperator &I) { |
| if (Value *V = SimplifyLShrInst(I.getOperand(0), I.getOperand(1), |
| I.isExact(), TD)) |
| return ReplaceInstUsesWith(I, V); |
| |
| if (Instruction *R = commonShiftTransforms(I)) |
| return R; |
| |
| Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); |
| |
| if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) { |
| unsigned ShAmt = Op1C->getZExtValue(); |
| |
| if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Op0)) { |
| unsigned BitWidth = Op0->getType()->getScalarSizeInBits(); |
| // ctlz.i32(x)>>5 --> zext(x == 0) |
| // cttz.i32(x)>>5 --> zext(x == 0) |
| // ctpop.i32(x)>>5 --> zext(x == -1) |
| if ((II->getIntrinsicID() == Intrinsic::ctlz || |
| II->getIntrinsicID() == Intrinsic::cttz || |
| II->getIntrinsicID() == Intrinsic::ctpop) && |
| isPowerOf2_32(BitWidth) && Log2_32(BitWidth) == ShAmt) { |
| bool isCtPop = II->getIntrinsicID() == Intrinsic::ctpop; |
| Constant *RHS = ConstantInt::getSigned(Op0->getType(), isCtPop ? -1:0); |
| Value *Cmp = Builder->CreateICmpEQ(II->getArgOperand(0), RHS); |
| return new ZExtInst(Cmp, II->getType()); |
| } |
| } |
| |
| // If the shifted-out value is known-zero, then this is an exact shift. |
| if (!I.isExact() && |
| MaskedValueIsZero(Op0,APInt::getLowBitsSet(Op1C->getBitWidth(),ShAmt))){ |
| I.setIsExact(); |
| return &I; |
| } |
| } |
| |
| return 0; |
| } |
| |
| Instruction *InstCombiner::visitAShr(BinaryOperator &I) { |
| if (Value *V = SimplifyAShrInst(I.getOperand(0), I.getOperand(1), |
| I.isExact(), TD)) |
| return ReplaceInstUsesWith(I, V); |
| |
| if (Instruction *R = commonShiftTransforms(I)) |
| return R; |
| |
| Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); |
| |
| if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) { |
| unsigned ShAmt = Op1C->getZExtValue(); |
| |
| // If the input is a SHL by the same constant (ashr (shl X, C), C), then we |
| // have a sign-extend idiom. |
| Value *X; |
| if (match(Op0, m_Shl(m_Value(X), m_Specific(Op1)))) { |
| // If the left shift is just shifting out partial signbits, delete the |
| // extension. |
| if (cast<OverflowingBinaryOperator>(Op0)->hasNoSignedWrap()) |
| return ReplaceInstUsesWith(I, X); |
| |
| // If the input is an extension from the shifted amount value, e.g. |
| // %x = zext i8 %A to i32 |
| // %y = shl i32 %x, 24 |
| // %z = ashr %y, 24 |
| // then turn this into "z = sext i8 A to i32". |
| if (ZExtInst *ZI = dyn_cast<ZExtInst>(X)) { |
| uint32_t SrcBits = ZI->getOperand(0)->getType()->getScalarSizeInBits(); |
| uint32_t DestBits = ZI->getType()->getScalarSizeInBits(); |
| if (Op1C->getZExtValue() == DestBits-SrcBits) |
| return new SExtInst(ZI->getOperand(0), ZI->getType()); |
| } |
| } |
| |
| // If the shifted-out value is known-zero, then this is an exact shift. |
| if (!I.isExact() && |
| MaskedValueIsZero(Op0,APInt::getLowBitsSet(Op1C->getBitWidth(),ShAmt))){ |
| I.setIsExact(); |
| return &I; |
| } |
| } |
| |
| // See if we can turn a signed shr into an unsigned shr. |
| if (MaskedValueIsZero(Op0, |
| APInt::getSignBit(I.getType()->getScalarSizeInBits()))) |
| return BinaryOperator::CreateLShr(Op0, Op1); |
| |
| // Arithmetic shifting an all-sign-bit value is a no-op. |
| unsigned NumSignBits = ComputeNumSignBits(Op0); |
| if (NumSignBits == Op0->getType()->getScalarSizeInBits()) |
| return ReplaceInstUsesWith(I, Op0); |
| |
| return 0; |
| } |
| |
