| //===- 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/IntrinsicInst.h" | |
| #include "llvm/Analysis/ConstantFolding.h" | |
| #include "llvm/Analysis/InstructionSimplify.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->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.getTargetData()); | |
| return V; | |
| } | |
| Instruction *I = cast<Instruction>(V); | |
| IC.Worklist.Add(I); | |
| switch (I->getOpcode()) { | |
| default: assert(0 && "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_Shr(m_Value(V1), m_Specific(Op1)), | |
| m_ConstantInt(CC))) && | |
| cast<BinaryOperator>(Op0BOOp1)->getOperand(0)->hasOneUse()) { | |
| 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_Shr(m_Value(V1), m_Value(V2)), | |
| m_ConstantInt(CC))) && V2 == Op1 && | |
| cast<BinaryOperator>(Op0BO->getOperand(0)) | |
| ->getOperand(0)->hasOneUse()) { | |
| 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))) { | |
| 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); | |
| 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()) { | |
| // 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) << 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) { | |
| 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 >>? C1) << C2 --> X << (C2-C1) & (-1 << C2) | |
| if (I.getOpcode() == Instruction::Shl && | |
| ShiftOp->getOpcode() != Instruction::Shl) { | |
| assert(ShiftOp->getOpcode() == Instruction::LShr || | |
| ShiftOp->getOpcode() == Instruction::AShr); | |
| Value *Shift = Builder->CreateShl(X, ConstantInt::get(Ty, ShiftDiff)); | |
| 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) { | |
| assert(ShiftOp->getOpcode() == Instruction::Shl); | |
| Value *Shift = Builder->CreateLShr(X, ConstantInt::get(Ty, ShiftDiff)); | |
| 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. | |
| } else { | |
| assert(ShiftAmt2 < ShiftAmt1); | |
| uint32_t ShiftDiff = ShiftAmt1-ShiftAmt2; | |
| // (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)); | |
| 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) { | |
| Value *Shift = Builder->CreateShl(X, ConstantInt::get(Ty, ShiftDiff)); | |
| APInt Mask(APInt::getLowBitsSet(TypeBits, TypeBits - ShiftAmt2)); | |
| return BinaryOperator::CreateAnd(Shift, | |
| ConstantInt::get(I.getContext(),Mask)); | |
| } | |
| // We can't handle (X << C1) >>a C2, it shifts arbitrary bits in. | |
| } | |
| } | |
| 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; | |
| } | |