code: boolean provablyExecutesBefore(BasicBlock thatBlock) {
      // If thatBlock is a descendant of this block, and there are no hoisted
      // blocks between them, then this block must start before thatBlock.
      BasicBlock currentBlock;
      for (currentBlock = thatBlock;
          currentBlock != null && currentBlock != this;
          currentBlock = currentBlock.getParent()) {}
  
      if (currentBlock == this) {
        return true;
      }
      return isGlobalScopeBlock() && thatBlock.isGlobalScopeBlock();
    }
docs: Determines whether this block is guaranteed to begin executing before the given block does.