C++ LVILatticeVal::getConstantRange方法代码示例

/// \brief Compute the value of Val on the edge BBFrom -> BBTo or the value at
/// the basic block if the edge does not constrain Val.
bool LazyValueInfoCache::getEdgeValue(Value *Val, BasicBlock *BBFrom,
                                      BasicBlock *BBTo, LVILatticeVal &Result,
                                      Instruction *CxtI) {
  // If already a constant, there is nothing to compute.
  if (Constant *VC = dyn_cast<Constant>(Val)) {
    Result = LVILatticeVal::get(VC);
    return true;
  }

  if (getEdgeValueLocal(Val, BBFrom, BBTo, Result)) {
    if (!Result.isConstantRange() ||
        Result.getConstantRange().getSingleElement())
      return true;

    // FIXME: this check should be moved to the beginning of the function when
    // LVI better supports recursive values. Even for the single value case, we
    // can intersect to detect dead code (an empty range).
    if (!hasBlockValue(Val, BBFrom)) {
      if (pushBlockValue(std::make_pair(BBFrom, Val)))
        return false;
      Result.markOverdefined();
      return true;
    }

    // Try to intersect ranges of the BB and the constraint on the edge.
    LVILatticeVal InBlock = getBlockValue(Val, BBFrom);
    mergeAssumeBlockValueConstantRange(Val, InBlock, BBFrom->getTerminator());
    // See note on the use of the CxtI with mergeAssumeBlockValueConstantRange,
    // and caching, below.
    mergeAssumeBlockValueConstantRange(Val, InBlock, CxtI);
    if (!InBlock.isConstantRange())
      return true;

    ConstantRange Range =
      Result.getConstantRange().intersectWith(InBlock.getConstantRange());
    Result = LVILatticeVal::getRange(Range);
    return true;
  }

  if (!hasBlockValue(Val, BBFrom)) {
    if (pushBlockValue(std::make_pair(BBFrom, Val)))
      return false;
    Result.markOverdefined();
    return true;
  }

  // If we couldn't compute the value on the edge, use the value from the BB.
  Result = getBlockValue(Val, BBFrom);
  mergeAssumeBlockValueConstantRange(Val, Result, BBFrom->getTerminator());
  // We can use the context instruction (generically the ultimate instruction
  // the calling pass is trying to simplify) here, even though the result of
  // this function is generally cached when called from the solve* functions
  // (and that cached result might be used with queries using a different
  // context instruction), because when this function is called from the solve*
  // functions, the context instruction is not provided. When called from
  // LazyValueInfoCache::getValueOnEdge, the context instruction is provided,
  // but then the result is not cached.
  mergeAssumeBlockValueConstantRange(Val, Result, CxtI);
  return true;
}

/// \brief Compute the value of Val on the edge BBFrom -> BBTo, or the value at
/// the basic block if the edge does not constraint Val.
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;
  }

  if (getEdgeValueLocal(Val, BBFrom, BBTo, Result)) {
    if (!Result.isConstantRange() ||
      Result.getConstantRange().getSingleElement())
      return true;

    // FIXME: this check should be moved to the beginning of the function when
    // LVI better supports recursive values. Even for the single value case, we
    // can intersect to detect dead code (an empty range).
    if (!hasBlockValue(Val, BBFrom)) {
      BlockValueStack.push(std::make_pair(BBFrom, Val));
      return false;
    }

    // Try to intersect ranges of the BB and the constraint on the edge.
    LVILatticeVal InBlock = getBlockValue(Val, BBFrom);
    if (!InBlock.isConstantRange())
      return true;

    ConstantRange Range =
      Result.getConstantRange().intersectWith(InBlock.getConstantRange());
    Result = LVILatticeVal::getRange(Range);
    return true;
  }

  if (!hasBlockValue(Val, BBFrom)) {
    BlockValueStack.push(std::make_pair(BBFrom, Val));
    return false;
  }

  // if we couldn't compute the value on the edge, use the value from the BB
  Result = getBlockValue(Val, BBFrom);
  return true;
}

Constant *LazyValueInfo::getConstant(Value *V, BasicBlock *BB) {
  LVILatticeVal Result = getCache(PImpl).getValueInBlock(V, BB);
  
  if (Result.isConstant())
    return Result.getConstant();
  if (Result.isConstantRange()) {
    ConstantRange CR = Result.getConstantRange();
    if (const APInt *SingleVal = CR.getSingleElement())
      return ConstantInt::get(V->getContext(), *SingleVal);
  }
  return 0;
}

Constant *LazyValueInfo::getConstant(Value *V, BasicBlock *BB,
                                     Instruction *CxtI) {
  LVILatticeVal Result =
      getCache(PImpl, AC, DL, DT).getValueInBlock(V, BB, CxtI);

  if (Result.isConstant())
    return Result.getConstant();
  if (Result.isConstantRange()) {
    ConstantRange CR = Result.getConstantRange();
    if (const APInt *SingleVal = CR.getSingleElement())
      return ConstantInt::get(V->getContext(), *SingleVal);
  }
  return nullptr;
}

/// Determine whether the specified value is known to be a
/// constant on the specified edge. Return null if not.
Constant *LazyValueInfo::getConstantOnEdge(Value *V, BasicBlock *FromBB,
                                           BasicBlock *ToBB,
                                           Instruction *CxtI) {
  const DataLayout &DL = FromBB->getModule()->getDataLayout();
  LVILatticeVal Result =
      getCache(PImpl, AC, &DL, DT).getValueOnEdge(V, FromBB, ToBB, CxtI);

  if (Result.isConstant())
    return Result.getConstant();
  if (Result.isConstantRange()) {
    ConstantRange CR = Result.getConstantRange();
    if (const APInt *SingleVal = CR.getSingleElement())
      return ConstantInt::get(V->getContext(), *SingleVal);
  }
  return nullptr;
}

bool LazyValueInfoCache::solveBlockValueConstantRange(LVILatticeVal &BBLV,
                                                      Instruction *BBI,
                                                      BasicBlock *BB) {
  // Figure out the range of the LHS.  If that fails, bail.
  if (!hasBlockValue(BBI->getOperand(0), BB)) {
    BlockValueStack.push(std::make_pair(BB, BBI->getOperand(0)));
    return false;
  }

  LVILatticeVal LHSVal = getBlockValue(BBI->getOperand(0), BB);
  if (!LHSVal.isConstantRange()) {
    BBLV.markOverdefined();
    return true;
  }
  
  ConstantRange LHSRange = LHSVal.getConstantRange();
  ConstantRange RHSRange(1);
  IntegerType *ResultTy = cast<IntegerType>(BBI->getType());
  if (isa<BinaryOperator>(BBI)) {
    if (ConstantInt *RHS = dyn_cast<ConstantInt>(BBI->getOperand(1))) {
      RHSRange = ConstantRange(RHS->getValue());
    } else {
      BBLV.markOverdefined();
      return true;
    }
  }

  // NOTE: We're currently limited by the set of operations that ConstantRange
  // can evaluate symbolically.  Enhancing that set will allows us to analyze
  // more definitions.
  LVILatticeVal Result;
  switch (BBI->getOpcode()) {
  case Instruction::Add:
    Result.markConstantRange(LHSRange.add(RHSRange));
    break;
  case Instruction::Sub:
    Result.markConstantRange(LHSRange.sub(RHSRange));
    break;
  case Instruction::Mul:
    Result.markConstantRange(LHSRange.multiply(RHSRange));
    break;
  case Instruction::UDiv:
    Result.markConstantRange(LHSRange.udiv(RHSRange));
    break;
  case Instruction::Shl:
    Result.markConstantRange(LHSRange.shl(RHSRange));
    break;
  case Instruction::LShr:
    Result.markConstantRange(LHSRange.lshr(RHSRange));
    break;
  case Instruction::Trunc:
    Result.markConstantRange(LHSRange.truncate(ResultTy->getBitWidth()));
    break;
  case Instruction::SExt:
    Result.markConstantRange(LHSRange.signExtend(ResultTy->getBitWidth()));
    break;
  case Instruction::ZExt:
    Result.markConstantRange(LHSRange.zeroExtend(ResultTy->getBitWidth()));
    break;
  case Instruction::BitCast:
    Result.markConstantRange(LHSRange);
    break;
  case Instruction::And:
    Result.markConstantRange(LHSRange.binaryAnd(RHSRange));
    break;
  case Instruction::Or:
    Result.markConstantRange(LHSRange.binaryOr(RHSRange));
    break;
  
  // Unhandled instructions are overdefined.
  default:
    DEBUG(dbgs() << " compute BB '" << BB->getName()
                 << "' - overdefined because inst def found.\n");
    Result.markOverdefined();
    break;
  }
  
  BBLV = Result;
  return true;
}

/// 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,
                                          TLI);
    if (ConstantInt *ResCI = dyn_cast<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 TrueValues =
        ICmpInst::makeConstantRange((ICmpInst::Predicate)Pred, CI->getValue());
    if (TrueValues.contains(CR))
      return True;
    if (TrueValues.inverse().contains(CR))
      return False;
    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,
                                            TLI);
      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,
                                            TLI);
      if (Res->isNullValue())
        return True;
    }
    return Unknown;
  }
  
  return Unknown;
}

static LazyValueInfo::Tristate
getPredicateResult(unsigned Pred, Constant *C, LVILatticeVal &Result,
                   const DataLayout *DL, TargetLibraryInfo *TLI) {

  // If we know the value is a constant, evaluate the conditional.
  Constant *Res = nullptr;
  if (Result.isConstant()) {
    Res = ConstantFoldCompareInstOperands(Pred, Result.getConstant(), C, DL,
                                          TLI);
    if (ConstantInt *ResCI = dyn_cast<ConstantInt>(Res))
      return ResCI->isZero() ? LazyValueInfo::False : LazyValueInfo::True;
    return LazyValueInfo::Unknown;
  }

  if (Result.isConstantRange()) {
    ConstantInt *CI = dyn_cast<ConstantInt>(C);
    if (!CI) return LazyValueInfo::Unknown;

    ConstantRange CR = Result.getConstantRange();
    if (Pred == ICmpInst::ICMP_EQ) {
      if (!CR.contains(CI->getValue()))
        return LazyValueInfo::False;

      if (CR.isSingleElement() && CR.contains(CI->getValue()))
        return LazyValueInfo::True;
    } else if (Pred == ICmpInst::ICMP_NE) {
      if (!CR.contains(CI->getValue()))
        return LazyValueInfo::True;

      if (CR.isSingleElement() && CR.contains(CI->getValue()))
        return LazyValueInfo::False;
    }

    // Handle more complex predicates.
    ConstantRange TrueValues =
        ICmpInst::makeConstantRange((ICmpInst::Predicate)Pred, CI->getValue());
    if (TrueValues.contains(CR))
      return LazyValueInfo::True;
    if (TrueValues.inverse().contains(CR))
      return LazyValueInfo::False;
    return LazyValueInfo::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, DL,
                                            TLI);
      if (Res->isNullValue())
        return LazyValueInfo::False;
    } else if (Pred == ICmpInst::ICMP_NE) {
      // !C1 != C -> true iff C1 == C.
      Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
                                            Result.getNotConstant(), C, DL,
                                            TLI);
      if (Res->isNullValue())
        return LazyValueInfo::True;
    }
    return LazyValueInfo::Unknown;
  }

  return LazyValueInfo::Unknown;
}

/// 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.........

//.........这里部分代码省略.........
    assert(!Result.isOverdefined());
    return Cache[BB] = Result;
  }

  assert(Cache[BB].isOverdefined() && "Recursive query changed our cache?");

  // We can only analyze the definitions of certain classes of instructions
  // (integral binops and casts at the moment), so bail if this isn't one.
  LVILatticeVal Result;
  if ((!isa<BinaryOperator>(BBI) && !isa<CastInst>(BBI)) ||
     !BBI->getType()->isIntegerTy()) {
    DEBUG(dbgs() << " compute BB '" << BB->getName()
                 << "' - overdefined because inst def found.\n");
    Result.markOverdefined();
    return Result;
  }
   
  // FIXME: We're currently limited to binops with a constant RHS.  This should
  // be improved.
  BinaryOperator *BO = dyn_cast<BinaryOperator>(BBI);
  if (BO && !isa<ConstantInt>(BO->getOperand(1))) { 
    DEBUG(dbgs() << " compute BB '" << BB->getName()
                 << "' - overdefined because inst def found.\n");

    Result.markOverdefined();
    return Result;
  }  

  // Figure out the range of the LHS.  If that fails, bail.
  LVILatticeVal LHSVal = Parent.getValueInBlock(BBI->getOperand(0), BB);
  if (!LHSVal.isConstantRange()) {
    Result.markOverdefined();
    return Result;
  }
  
  ConstantInt *RHS = 0;
  ConstantRange LHSRange = LHSVal.getConstantRange();
  ConstantRange RHSRange(1);
  const IntegerType *ResultTy = cast<IntegerType>(BBI->getType());
  if (isa<BinaryOperator>(BBI)) {
    RHS = dyn_cast<ConstantInt>(BBI->getOperand(1));
    if (!RHS) {
      Result.markOverdefined();
      return Result;
    }
    
    RHSRange = ConstantRange(RHS->getValue(), RHS->getValue()+1);
  }
      
  // NOTE: We're currently limited by the set of operations that ConstantRange
  // can evaluate symbolically.  Enhancing that set will allows us to analyze
  // more definitions.
  switch (BBI->getOpcode()) {
  case Instruction::Add:
    Result.markConstantRange(LHSRange.add(RHSRange));
    break;
  case Instruction::Sub:
    Result.markConstantRange(LHSRange.sub(RHSRange));
    break;
  case Instruction::Mul:
    Result.markConstantRange(LHSRange.multiply(RHSRange));
    break;
  case Instruction::UDiv:
    Result.markConstantRange(LHSRange.udiv(RHSRange));
    break;
  case Instruction::Shl:
    Result.markConstantRange(LHSRange.shl(RHSRange));
    break;
  case Instruction::LShr:
    Result.markConstantRange(LHSRange.lshr(RHSRange));
    break;
  case Instruction::Trunc:
    Result.markConstantRange(LHSRange.truncate(ResultTy->getBitWidth()));
    break;
  case Instruction::SExt:
    Result.markConstantRange(LHSRange.signExtend(ResultTy->getBitWidth()));
    break;
  case Instruction::ZExt:
    Result.markConstantRange(LHSRange.zeroExtend(ResultTy->getBitWidth()));
    break;
  case Instruction::BitCast:
    Result.markConstantRange(LHSRange);
    break;
  case Instruction::And:
    Result.markConstantRange(LHSRange.binaryAnd(RHSRange));
    break;
  case Instruction::Or:
    Result.markConstantRange(LHSRange.binaryOr(RHSRange));
    break;
  
  // Unhandled instructions are overdefined.
  default:
    DEBUG(dbgs() << " compute BB '" << BB->getName()
                 << "' - overdefined because inst def found.\n");
    Result.markOverdefined();
    break;
  }
  
  return Cache[BB] = Result;
}