/**
     * Determines whether this block is guaranteed to begin executing before the given block does.
     */
    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();
    }
    /** @return Whether the variable is only assigned a value once for its lifetime. */
    boolean isAssignedOnceInLifetime() {
      Reference ref = getOneAndOnlyAssignment();
      if (ref == null) {
        return false;
      }

      // Make sure this assignment is not in a loop.
      for (BasicBlock block = ref.getBasicBlock(); block != null; block = block.getParent()) {
        if (block.isFunction) {
          if (ref.getSymbol().getScope() != ref.scope) {
            return false;
          }
          break;
        } else if (block.isLoop) {
          return false;
        }
      }

      return true;
    }