C++ ConstantRange::subtract方法代码示例

bool getValueFromFromCondition(Value *Val, ICmpInst *ICI,
                               LVILatticeVal &Result, bool isTrueDest) {
  if (ICI && isa<Constant>(ICI->getOperand(1))) {
    if (ICI->isEquality() && ICI->getOperand(0) == Val) {
      // We know that V has the RHS constant if this is a true SETEQ or
      // false SETNE.
      if (isTrueDest == (ICI->getPredicate() == ICmpInst::ICMP_EQ))
        Result = LVILatticeVal::get(cast<Constant>(ICI->getOperand(1)));
      else
        Result = LVILatticeVal::getNot(cast<Constant>(ICI->getOperand(1)));
      return true;
    }

    // Recognize the range checking idiom that InstCombine produces.
    // (X-C1) u< C2 --> [C1, C1+C2)
    ConstantInt *NegOffset = nullptr;
    if (ICI->getPredicate() == ICmpInst::ICMP_ULT)
      match(ICI->getOperand(0), m_Add(m_Specific(Val),
                                      m_ConstantInt(NegOffset)));

    ConstantInt *CI = dyn_cast<ConstantInt>(ICI->getOperand(1));
    if (CI && (ICI->getOperand(0) == Val || NegOffset)) {
      // Calculate the range of values that would satisfy the comparison.
      ConstantRange CmpRange(CI->getValue());
      ConstantRange TrueValues =
        ConstantRange::makeICmpRegion(ICI->getPredicate(), CmpRange);

      if (NegOffset) // Apply the offset from above.
        TrueValues = TrueValues.subtract(NegOffset->getValue());

      // If we're interested in the false dest, invert the condition.
      if (!isTrueDest) TrueValues = TrueValues.inverse();

      Result = LVILatticeVal::getRange(TrueValues);
      return true;
    }
  }

  return false;
}

/// \brief Compute the value of Val on the edge BBFrom -> BBTo. Returns false if
/// Val is not constrained on the edge.
static bool getEdgeValueLocal(Value *Val, BasicBlock *BBFrom,
                              BasicBlock *BBTo, LVILatticeVal &Result) {
  // TODO: Handle more complex conditionals.  If (v == 0 || v2 < 1) is false, we
  // know that v != 0.
  if (BranchInst *BI = dyn_cast<BranchInst>(BBFrom->getTerminator())) {
    // If this is a conditional branch and only one successor goes to BBTo, then
    // we maybe able to infer something from the condition. 
    if (BI->isConditional() &&
        BI->getSuccessor(0) != BI->getSuccessor(1)) {
      bool isTrueDest = BI->getSuccessor(0) == BBTo;
      assert(BI->getSuccessor(!isTrueDest) == BBTo &&
             "BBTo isn't a successor of BBFrom");
      
      // If V is the condition of the branch itself, then we know exactly what
      // it is.
      if (BI->getCondition() == Val) {
        Result = LVILatticeVal::get(ConstantInt::get(
                              Type::getInt1Ty(Val->getContext()), isTrueDest));
        return true;
      }
      
      // If the condition of the branch is an equality comparison, we may be
      // able to infer the value.
      ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition());
      if (ICI && isa<Constant>(ICI->getOperand(1))) {
        if (ICI->isEquality() && ICI->getOperand(0) == Val) {
          // We know that V has the RHS constant if this is a true SETEQ or
          // false SETNE. 
          if (isTrueDest == (ICI->getPredicate() == ICmpInst::ICMP_EQ))
            Result = LVILatticeVal::get(cast<Constant>(ICI->getOperand(1)));
          else
            Result = LVILatticeVal::getNot(cast<Constant>(ICI->getOperand(1)));
          return true;
        }

        // Recognize the range checking idiom that InstCombine produces.
        // (X-C1) u< C2 --> [C1, C1+C2)
        ConstantInt *NegOffset = 0;
        if (ICI->getPredicate() == ICmpInst::ICMP_ULT)
          match(ICI->getOperand(0), m_Add(m_Specific(Val),
                                          m_ConstantInt(NegOffset)));

        ConstantInt *CI = dyn_cast<ConstantInt>(ICI->getOperand(1));
        if (CI && (ICI->getOperand(0) == Val || NegOffset)) {
          // Calculate the range of values that would satisfy the comparison.
          ConstantRange CmpRange(CI->getValue());
          ConstantRange TrueValues =
            ConstantRange::makeICmpRegion(ICI->getPredicate(), CmpRange);

          if (NegOffset) // Apply the offset from above.
            TrueValues = TrueValues.subtract(NegOffset->getValue());

          // If we're interested in the false dest, invert the condition.
          if (!isTrueDest) TrueValues = TrueValues.inverse();

          Result = LVILatticeVal::getRange(TrueValues);
          return true;
        }
      }
    }
  }

  // If the edge was formed by a switch on the value, then we may know exactly
  // what it is.
  if (SwitchInst *SI = dyn_cast<SwitchInst>(BBFrom->getTerminator())) {
    if (SI->getCondition() != Val)
      return false;

    bool DefaultCase = SI->getDefaultDest() == BBTo;
    unsigned BitWidth = Val->getType()->getIntegerBitWidth();
    ConstantRange EdgesVals(BitWidth, DefaultCase/*isFullSet*/);

    for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
         i != e; ++i) {
      ConstantRange EdgeVal(i.getCaseValue()->getValue());
      if (DefaultCase) {
        // It is possible that the default destination is the destination of
        // some cases. There is no need to perform difference for those cases.
        if (i.getCaseSuccessor() != BBTo)
          EdgesVals = EdgesVals.difference(EdgeVal);
      } else if (i.getCaseSuccessor() == BBTo)
        EdgesVals = EdgesVals.unionWith(EdgeVal);
    }
    Result = LVILatticeVal::getRange(EdgesVals);
    return true;
  }
  return false;
}