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Diffstat (limited to 'contrib/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp')
| -rw-r--r-- | contrib/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp | 813 |
1 files changed, 813 insertions, 0 deletions
diff --git a/contrib/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp b/contrib/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp new file mode 100644 index 0000000..4bb2403 --- /dev/null +++ b/contrib/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp @@ -0,0 +1,813 @@ +//===- 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->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.getTargetData(), + 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_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))) { + + // 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; +} + |
