/// Rebuild a new instruction just like 'I' but with the new operands given.
/// In the event of type mismatch, the type of the operands is correct.
static Value *BuildNew(Instruction *I, ArrayRef<Value*> NewOps) {
  // We don't want to use the IRBuilder here because we want the replacement
  // instructions to appear next to 'I', not the builder's insertion point.
  switch (I->getOpcode()) {
    case Instruction::Add:
    case Instruction::FAdd:
    case Instruction::Sub:
    case Instruction::FSub:
    case Instruction::Mul:
    case Instruction::FMul:
    case Instruction::UDiv:
    case Instruction::SDiv:
    case Instruction::FDiv:
    case Instruction::URem:
    case Instruction::SRem:
    case Instruction::FRem:
    case Instruction::Shl:
    case Instruction::LShr:
    case Instruction::AShr:
    case Instruction::And:
    case Instruction::Or:
    case Instruction::Xor: {
      BinaryOperator *BO = cast<BinaryOperator>(I);
      assert(NewOps.size() == 2 && "binary operator with #ops != 2");
      BinaryOperator *New =
          BinaryOperator::Create(cast<BinaryOperator>(I)->getOpcode(),
                                 NewOps[0], NewOps[1], "", BO);
      if (isa<OverflowingBinaryOperator>(BO)) {
        New->setHasNoUnsignedWrap(BO->hasNoUnsignedWrap());
        New->setHasNoSignedWrap(BO->hasNoSignedWrap());
      }
      if (isa<PossiblyExactOperator>(BO)) {
        New->setIsExact(BO->isExact());
      }
      return New;
    }
    case Instruction::ICmp:
      assert(NewOps.size() == 2 && "icmp with #ops != 2");
      return new ICmpInst(I, cast<ICmpInst>(I)->getPredicate(),
                          NewOps[0], NewOps[1]);
    case Instruction::FCmp:
      assert(NewOps.size() == 2 && "fcmp with #ops != 2");
      return new FCmpInst(I, cast<FCmpInst>(I)->getPredicate(),
                          NewOps[0], NewOps[1]);
    case Instruction::Trunc:
    case Instruction::ZExt:
    case Instruction::SExt:
    case Instruction::FPToUI:
    case Instruction::FPToSI:
    case Instruction::UIToFP:
    case Instruction::SIToFP:
    case Instruction::FPTrunc:
    case Instruction::FPExt: {
      // It's possible that the mask has a different number of elements from
      // the original cast. We recompute the destination type to match the mask.
      Type *DestTy =
          VectorType::get(I->getType()->getScalarType(),
                          NewOps[0]->getType()->getVectorNumElements());
      assert(NewOps.size() == 1 && "cast with #ops != 1");
      return CastInst::Create(cast<CastInst>(I)->getOpcode(), NewOps[0], DestTy,
                              "", I);
    }
    case Instruction::GetElementPtr: {
      Value *Ptr = NewOps[0];
      ArrayRef<Value*> Idx = NewOps.slice(1);
      GetElementPtrInst *GEP = GetElementPtrInst::Create(Ptr, Idx, "", I);
      GEP->setIsInBounds(cast<GetElementPtrInst>(I)->isInBounds());
      return GEP;
    }
  }
  llvm_unreachable("failed to rebuild vector instructions");
}
Example #2
0
Instruction *InstCombiner::FoldShiftByConstant(Value *Op0, Constant *Op1,
                                               BinaryOperator &I) {
  bool isLeftShift = I.getOpcode() == Instruction::Shl;

  ConstantInt *COp1 = nullptr;
  if (ConstantDataVector *CV = dyn_cast<ConstantDataVector>(Op1))
    COp1 = dyn_cast_or_null<ConstantInt>(CV->getSplatValue());
  else if (ConstantVector *CV = dyn_cast<ConstantVector>(Op1))
    COp1 = dyn_cast_or_null<ConstantInt>(CV->getSplatValue());
  else
    COp1 = dyn_cast<ConstantInt>(Op1);

  if (!COp1)
    return nullptr;

  // 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, COp1->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, COp1->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();

  assert(!COp1->uge(TypeBits) &&
         "Shift over the type width should have been removed already");

  // ((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(COp1, 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 <<= COp1->getZExtValue();
      else {
        assert(I.getOpcode() == Instruction::LShr && "Unknown logical shift");
        MaskV = MaskV.lshr(COp1->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 = COp1->getLimitedValue(TypeBits);

          APInt Bits = APInt::getHighBitsSet(TypeBits, TypeBits - Op1Val);
          Constant *Mask = ConstantInt::get(I.getContext(), Bits);
          if (VectorType *VT = dyn_cast<VectorType>(X->getType()))
            Mask = ConstantVector::getSplat(VT->getNumElements(), Mask);
          return BinaryOperator::CreateAnd(X, Mask);
        }

        // 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 = COp1->getLimitedValue(TypeBits);

          APInt Bits = APInt::getHighBitsSet(TypeBits, TypeBits - Op1Val);
          Constant *Mask = ConstantInt::get(I.getContext(), Bits);
          if (VectorType *VT = dyn_cast<VectorType>(X->getType()))
            Mask = ConstantVector::getSplat(VT->getNumElements(), Mask);
          return BinaryOperator::CreateAnd(X, Mask);
        }

        // 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 = nullptr;

  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 = COp1->getLimitedValue(TypeBits);
    assert(ShiftAmt2 != 0 && "Should have been simplified earlier");
    if (ShiftAmt1 == 0) return nullptr;  // 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 nullptr;
}