C++ ConstantRange::intersectWith方法代码示例

/// intersectWith - Return the range that results from the intersection of this
/// range with another range.  The resultant range is guaranteed to include all
/// elements contained in both input ranges, and to have the smallest possible
/// set size that does so.  Because there may be two intersections with the
/// same set size, A.intersectWith(B) might not be equal to B.intersectWith(A).
ConstantRange ConstantRange::intersectWith(const ConstantRange &CR) const {
  assert(getBitWidth() == CR.getBitWidth() && 
         "ConstantRange types don't agree!");

  // Handle common cases.
  if (   isEmptySet() || CR.isFullSet()) return *this;
  if (CR.isEmptySet() ||    isFullSet()) return CR;

  if (!isWrappedSet() && CR.isWrappedSet())
    return CR.intersectWith(*this);

  if (!isWrappedSet() && !CR.isWrappedSet()) {
    if (Lower.ult(CR.Lower)) {
      if (Upper.ule(CR.Lower))
        return ConstantRange(getBitWidth(), false);

      if (Upper.ult(CR.Upper))
        return ConstantRange(CR.Lower, Upper);

      return CR;
    }
    if (Upper.ult(CR.Upper))
      return *this;

    if (Lower.ult(CR.Upper))
      return ConstantRange(Lower, CR.Upper);

    return ConstantRange(getBitWidth(), false);
  }

  if (isWrappedSet() && !CR.isWrappedSet()) {
    if (CR.Lower.ult(Upper)) {
      if (CR.Upper.ult(Upper))
        return CR;

      if (CR.Upper.ule(Lower))
        return ConstantRange(CR.Lower, Upper);

      if (getSetSize().ult(CR.getSetSize()))
        return *this;
      return CR;
    }
    if (CR.Lower.ult(Lower)) {
      if (CR.Upper.ule(Lower))
        return ConstantRange(getBitWidth(), false);

      return ConstantRange(Lower, CR.Upper);
    }
    return CR;
  }

  if (CR.Upper.ult(Upper)) {
    if (CR.Lower.ult(Upper)) {
      if (getSetSize().ult(CR.getSetSize()))
        return *this;
      return CR;
    }

    if (CR.Lower.ult(Lower))
      return ConstantRange(Lower, CR.Upper);

    return CR;
  }
  if (CR.Upper.ule(Lower)) {
    if (CR.Lower.ult(Lower))
      return *this;

    return ConstantRange(CR.Lower, Upper);
  }
  if (getSetSize().ult(CR.getSetSize()))
    return *this;
  return CR;
}

/// getEdgeValue - This method attempts to infer more complex 
bool LazyValueInfoCache::getEdgeValue(Value *Val, BasicBlock *BBFrom,
                                      BasicBlock *BBTo, LVILatticeVal &Result) {
  // If already a constant, there is nothing to compute.
  if (Constant *VC = dyn_cast<Constant>(Val)) {
    Result = LVILatticeVal::get(VC);
    return true;
  }
  
  // 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 && ICI->getOperand(0) == Val &&
          isa<Constant>(ICI->getOperand(1))) {
        if (ICI->isEquality()) {
          // 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;
        }

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

          // If we're interested in the false dest, invert the condition.
          if (!isTrueDest) TrueValues = TrueValues.inverse();
          
          // Figure out the possible values of the query BEFORE this branch.  
          if (!hasBlockValue(Val, BBFrom)) {
            BlockValueStack.push(std::make_pair(BBFrom, Val));
            return false;
          }
          
          LVILatticeVal InBlock = getBlockValue(Val, BBFrom);
          if (!InBlock.isConstantRange()) {
            Result = LVILatticeVal::getRange(TrueValues);
            return true;
          }

          // Find all potential values that satisfy both the input and output
          // conditions.
          ConstantRange PossibleValues =
            TrueValues.intersectWith(InBlock.getConstantRange());

          Result = LVILatticeVal::getRange(PossibleValues);
          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) {
      // We don't know anything in the default case.
      if (SI->getDefaultDest() == BBTo) {
        Result.markOverdefined();
        return true;
      }
      
      // We only know something if there is exactly one value that goes from
      // BBFrom to BBTo.
      unsigned NumEdges = 0;
      ConstantInt *EdgeVal = 0;
      for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
        if (SI->getSuccessor(i) != BBTo) continue;
        if (NumEdges++) break;
        EdgeVal = SI->getCaseValue(i);
      }
      assert(EdgeVal && "Missing successor?");
      if (NumEdges == 1) {
        Result = LVILatticeVal::get(EdgeVal);
        return true;
      }
//.........这里部分代码省略.........

static bool canBeMerged(const ConstantRange &A, const ConstantRange &B) {
  return !A.intersectWith(B).isEmptySet() || isContiguous(A, B);
}

/// getPredicateOnEdge - Determine whether the specified value comparison
/// with a constant is known to be true or false on the specified CFG edge.
/// Pred is a CmpInst predicate.
LazyValueInfo::Tristate
LazyValueInfo::getPredicateOnEdge(unsigned Pred, Value *V, Constant *C,
                                  BasicBlock *FromBB, BasicBlock *ToBB) {
  LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB);
  
  // If we know the value is a constant, evaluate the conditional.
  Constant *Res = 0;
  if (Result.isConstant()) {
    Res = ConstantFoldCompareInstOperands(Pred, Result.getConstant(), C, TD);
    if (ConstantInt *ResCI = dyn_cast_or_null<ConstantInt>(Res))
      return ResCI->isZero() ? False : True;
    return Unknown;
  }
  
  if (Result.isConstantRange()) {
    ConstantInt *CI = dyn_cast<ConstantInt>(C);
    if (!CI) return Unknown;
    
    ConstantRange CR = Result.getConstantRange();
    if (Pred == ICmpInst::ICMP_EQ) {
      if (!CR.contains(CI->getValue()))
        return False;
      
      if (CR.isSingleElement() && CR.contains(CI->getValue()))
        return True;
    } else if (Pred == ICmpInst::ICMP_NE) {
      if (!CR.contains(CI->getValue()))
        return True;
      
      if (CR.isSingleElement() && CR.contains(CI->getValue()))
        return False;
    }
    
    // Handle more complex predicates.
    ConstantRange RHS(CI->getValue(), CI->getValue()+1);
    ConstantRange TrueValues = ConstantRange::makeICmpRegion(Pred, RHS);
    if (CR.intersectWith(TrueValues).isEmptySet())
      return False;
    else if (TrueValues.contains(CR))
      return True;
    
    return Unknown;
  }
  
  if (Result.isNotConstant()) {
    // If this is an equality comparison, we can try to fold it knowing that
    // "V != C1".
    if (Pred == ICmpInst::ICMP_EQ) {
      // !C1 == C -> false iff C1 == C.
      Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
                                            Result.getNotConstant(), C, TD);
      if (Res->isNullValue())
        return False;
    } else if (Pred == ICmpInst::ICMP_NE) {
      // !C1 != C -> true iff C1 == C.
      Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
                                            Result.getNotConstant(), C, TD);
      if (Res->isNullValue())
        return True;
    }
    return Unknown;
  }
  
  return Unknown;
}