//===- 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/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); // shl X, 0 == X and shr X, 0 == X // shl 0, X == 0 and shr 0, X == 0 if (Op1 == Constant::getNullValue(Op1->getType()) || Op0 == Constant::getNullValue(Op0->getType())) return ReplaceInstUsesWith(I, Op0); if (isa(Op0)) { if (I.getOpcode() == Instruction::AShr) // undef >>s X -> undef return ReplaceInstUsesWith(I, Op0); else // undef << X -> 0, undef >>u X -> 0 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType())); } if (isa(Op1)) { if (I.getOpcode() == Instruction::AShr) // X >>s undef -> X return ReplaceInstUsesWith(I, Op0); else // X << undef, X >>u undef -> 0 return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType())); } // See if we can fold away this shift. if (SimplifyDemandedInstructionBits(I)) return &I; // Try to fold constant and into select arguments. if (isa(Op0)) if (SelectInst *SI = dyn_cast(Op1)) if (Instruction *R = FoldOpIntoSelect(I, SI)) return R; if (ConstantInt *CUI = dyn_cast(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 are undefined. if (BinaryOperator *BO = dyn_cast(Op1)) if (BO->hasOneUse() && BO->getOpcode() == Instruction::SRem) if (ConstantInt *CI = dyn_cast(BO->getOperand(1))) if (CI->getValue().isPowerOf2()) { Constant *C = ConstantInt::get(BO->getType(), CI->getValue()-1); Value *Rem = Builder->CreateAnd(BO->getOperand(0), C, BO->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(V)) return true; Instruction *I = dyn_cast(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; 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(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(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) { if (MaskedValueIsZero(I->getOperand(0), APInt::getLowBitsSet(TypeWidth, NumBits))) return true; } return false; } case Instruction::Select: { SelectInst *SI = cast(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(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(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(V)) V = ConstantFoldConstantExpression(CE, IC.getTargetData()); return V; } Instruction *I = cast(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: { unsigned TypeWidth = I->getType()->getScalarSizeInBits(); // We only accept shifts-by-a-constant in CanEvaluateShifted. ConstantInt *CI = cast(I->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()); I->setOperand(1, ConstantInt::get(I->getType(), NewShAmt)); 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(I->getOperand(0), ConstantInt::get(I->getContext(), Mask)); if (Instruction *VI = dyn_cast(V)) { VI->moveBefore(I); VI->takeName(I); } 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); I->setOperand(1, ConstantInt::get(I->getType(), CI->getZExtValue() - NumBits)); return I; } case Instruction::LShr: { unsigned TypeWidth = I->getType()->getScalarSizeInBits(); // We only accept shifts-by-a-constant in CanEvaluateShifted. ConstantInt *CI = cast(I->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(I->getType()); I->setOperand(1, ConstantInt::get(I->getType(), NewShAmt)); 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(I->getContext(), Mask)); if (Instruction *VI = dyn_cast(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); I->setOperand(1, ConstantInt::get(I->getType(), CI->getZExtValue() - NumBits)); return I; } 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(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(Op0)) if (BO->getOpcode() == Instruction::Mul && isLeftShift) if (Constant *BOOp = dyn_cast(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(Op0)) if (Instruction *R = FoldOpIntoSelect(I, SI)) return R; if (isa(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(Op0)) { Instruction *TrOp = dyn_cast(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(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(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(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(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(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(Op0); if (ShiftOp && !ShiftOp->isShift()) ShiftOp = 0; if (ShiftOp && isa(ShiftOp->getOperand(1))) { ConstantInt *ShiftAmt1C = cast(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. const IntegerType *Ty = cast(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) { return commonShiftTransforms(I); } Instruction *InstCombiner::visitLShr(BinaryOperator &I) { if (Instruction *R = commonShiftTransforms(I)) return R; Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); if (ConstantInt *Op1C = dyn_cast(Op1)) if (IntrinsicInst *II = dyn_cast(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) == Op1C->getZExtValue()){ 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()); } } return 0; } Instruction *InstCombiner::visitAShr(BinaryOperator &I) { if (Instruction *R = commonShiftTransforms(I)) return R; Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1); if (ConstantInt *CSI = dyn_cast(Op0)) { // ashr int -1, X = -1 (for any arithmetic shift rights of ~0) if (CSI->isAllOnesValue()) return ReplaceInstUsesWith(I, CSI); } if (ConstantInt *Op1C = dyn_cast(Op1)) { // 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 input value is known to already be sign extended enough, delete // the extension. if (ComputeNumSignBits(X) > Op1C->getZExtValue()) 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(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()); } } } // 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; }