C++ BinaryOperator::use_empty方法代码示例

/// OptimizeAdd - Optimize a series of operands to an 'add' instruction.  This
/// optimizes based on identities.  If it can be reduced to a single Value, it
/// is returned, otherwise the Ops list is mutated as necessary.
Value *Reassociate::OptimizeAdd(Instruction *I,
                                SmallVectorImpl<ValueEntry> &Ops) {
  // Scan the operand lists looking for X and -X pairs.  If we find any, we
  // can simplify the expression. X+-X == 0.  While we're at it, scan for any
  // duplicates.  We want to canonicalize Y+Y+Y+Z -> 3*Y+Z.
  //
  // TODO: We could handle "X + ~X" -> "-1" if we wanted, since "-X = ~X+1".
  //
  for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
    Value *TheOp = Ops[i].Op;
    // Check to see if we've seen this operand before.  If so, we factor all
    // instances of the operand together.  Due to our sorting criteria, we know
    // that these need to be next to each other in the vector.
    if (i+1 != Ops.size() && Ops[i+1].Op == TheOp) {
      // Rescan the list, remove all instances of this operand from the expr.
      unsigned NumFound = 0;
      do {
        Ops.erase(Ops.begin()+i);
        ++NumFound;
      } while (i != Ops.size() && Ops[i].Op == TheOp);
      
      DEBUG(errs() << "\nFACTORING [" << NumFound << "]: " << *TheOp << '\n');
      ++NumFactor;
      
      // Insert a new multiply.
      Value *Mul = ConstantInt::get(cast<IntegerType>(I->getType()), NumFound);
      Mul = BinaryOperator::CreateMul(TheOp, Mul, "factor", I);
      
      // Now that we have inserted a multiply, optimize it. This allows us to
      // handle cases that require multiple factoring steps, such as this:
      // (X*2) + (X*2) + (X*2) -> (X*2)*3 -> X*6
      RedoInsts.push_back(Mul);
      
      // If every add operand was a duplicate, return the multiply.
      if (Ops.empty())
        return Mul;
      
      // Otherwise, we had some input that didn't have the dupe, such as
      // "A + A + B" -> "A*2 + B".  Add the new multiply to the list of
      // things being added by this operation.
      Ops.insert(Ops.begin(), ValueEntry(getRank(Mul), Mul));
      
      --i;
      e = Ops.size();
      continue;
    }
    
    // Check for X and -X in the operand list.
    if (!BinaryOperator::isNeg(TheOp))
      continue;
    
    Value *X = BinaryOperator::getNegArgument(TheOp);
    unsigned FoundX = FindInOperandList(Ops, i, X);
    if (FoundX == i)
      continue;
    
    // Remove X and -X from the operand list.
    if (Ops.size() == 2)
      return Constant::getNullValue(X->getType());
    
    Ops.erase(Ops.begin()+i);
    if (i < FoundX)
      --FoundX;
    else
      --i;   // Need to back up an extra one.
    Ops.erase(Ops.begin()+FoundX);
    ++NumAnnihil;
    --i;     // Revisit element.
    e -= 2;  // Removed two elements.
  }
  
  // Scan the operand list, checking to see if there are any common factors
  // between operands.  Consider something like A*A+A*B*C+D.  We would like to
  // reassociate this to A*(A+B*C)+D, which reduces the number of multiplies.
  // To efficiently find this, we count the number of times a factor occurs
  // for any ADD operands that are MULs.
  DenseMap<Value*, unsigned> FactorOccurrences;
  
  // Keep track of each multiply we see, to avoid triggering on (X*4)+(X*4)
  // where they are actually the same multiply.
  unsigned MaxOcc = 0;
  Value *MaxOccVal = 0;
  for (unsigned i = 0, e = Ops.size(); i != e; ++i) {
    BinaryOperator *BOp = dyn_cast<BinaryOperator>(Ops[i].Op);
    if (BOp == 0 || BOp->getOpcode() != Instruction::Mul || !BOp->use_empty())
      continue;
    
    // Compute all of the factors of this added value.
    SmallVector<Value*, 8> Factors;
    FindSingleUseMultiplyFactors(BOp, Factors, Ops, true);
    assert(Factors.size() > 1 && "Bad linearize!");
    
    // Add one to FactorOccurrences for each unique factor in this op.
    SmallPtrSet<Value*, 8> Duplicates;
    for (unsigned i = 0, e = Factors.size(); i != e; ++i) {
      Value *Factor = Factors[i];
      if (!Duplicates.insert(Factor)) continue;
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