anchor.diff:        return false;
       }
       if (!atUseSite) define(phi);
  -    visitBasicBlock(node.joinBlock);
  +    continueSubGraph(node.joinBlock);
       return true;
     }
   
  
positive.code:     // (e.g., return/throw/break) there can be any number of these.
      List<HBasicBlock> dominated = node.block.dominatedBlocks;
      for (int i = 2; i < dominated.length; i++) {
        visitBasicBlock(dominated[i]);
      }
    }
  
  
negative.code:   // if branches.
    SubGraph subGraph;
  
    // Pending blocks than need to be visited as part of current subgraph.
    Queue<HBasicBlock> blockQueue;
  
    SsaCodeGenerator(
        this._options,
        this._emitter,
  