C++ LVILatticeVal::isUndefined方法代码示例

LVILatticeVal LVIQuery::getBlockValue(BasicBlock *BB) {
  // See if we already have a value for this block.
  LVILatticeVal BBLV = getCachedEntryForBlock(BB);
  
  // If we've already computed this block's value, return it.
  if (!BBLV.isUndefined()) {
    DEBUG(dbgs() << "  reuse BB '" << BB->getName() << "' val=" << BBLV <<'\n');
    return BBLV;
  }

  // Otherwise, this is the first time we're seeing this block.  Reset the
  // lattice value to overdefined, so that cycles will terminate and be
  // conservatively correct.
  BBLV.markOverdefined();
  Cache[BB] = BBLV;
  
  Instruction *BBI = dyn_cast<Instruction>(Val);
  if (BBI == 0 || BBI->getParent() != BB) {
    LVILatticeVal Result;  // Start Undefined.
    
    // If this is a pointer, and there's a load from that pointer in this BB,
    // then we know that the pointer can't be NULL.
    bool NotNull = false;
    if (Val->getType()->isPointerTy()) {
      for (BasicBlock::iterator BI = BB->begin(), BE = BB->end();BI != BE;++BI){
        LoadInst *L = dyn_cast<LoadInst>(BI);
        if (L && L->getPointerAddressSpace() == 0 &&
            L->getPointerOperand()->getUnderlyingObject() ==
              Val->getUnderlyingObject()) {
          NotNull = true;
          break;
        }
      }
    }
    
    unsigned NumPreds = 0;    
    // Loop over all of our predecessors, merging what we know from them into
    // result.
    for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
      Result.mergeIn(getEdgeValue(*PI, BB));
      
      // If we hit overdefined, exit early.  The BlockVals entry is already set
      // to overdefined.
      if (Result.isOverdefined()) {
        DEBUG(dbgs() << " compute BB '" << BB->getName()
                     << "' - overdefined because of pred.\n");
        // If we previously determined that this is a pointer that can't be null
        // then return that rather than giving up entirely.
        if (NotNull) {
          const PointerType *PTy = cast<PointerType>(Val->getType());
          Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
        }
        
        return Result;
      }
      ++NumPreds;
    }
    
    
    // If this is the entry block, we must be asking about an argument.  The
    // value is overdefined.
    if (NumPreds == 0 && BB == &BB->getParent()->front()) {
      assert(isa<Argument>(Val) && "Unknown live-in to the entry block");
      Result.markOverdefined();
      return Result;
    }
    
    // Return the merged value, which is more precise than 'overdefined'.
    assert(!Result.isOverdefined());
    return Cache[BB] = Result;
  }
  
  // If this value is defined by an instruction in this block, we have to
  // process it here somehow or return overdefined.
  if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
    LVILatticeVal Result;  // Start Undefined.
    
    // Loop over all of our predecessors, merging what we know from them into
    // result.
    for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
      Value* PhiVal = PN->getIncomingValueForBlock(*PI);
      Result.mergeIn(Parent.getValueOnEdge(PhiVal, *PI, BB));
      
      // If we hit overdefined, exit early.  The BlockVals entry is already set
      // to overdefined.
      if (Result.isOverdefined()) {
        DEBUG(dbgs() << " compute BB '" << BB->getName()
                     << "' - overdefined because of pred.\n");
        return Result;
      }
    }
    
    // Return the merged value, which is more precise than 'overdefined'.
    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
//.........这里部分代码省略.........