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<a name="9.7"></a>9.7 对下面的程序片段作出其程序流图并计算：<br>
（1）各基本块的到达_定值集IN[B]；<br>
（2）各基本块中各变量引用点的ud链；<br>
（3）各基本块出口的活跃变量集V_OUT[B]；<br>
（4）各基本块中变量定值点的du链。<br>
N := 0<br>
L1: I := 2<br>
L2: <font color="#0000FF">if</font><b> </b>I < N <font color="#0000FF">goto</font> L4<br>
<font color="#0000FF">write</font> N<br>
L3: N := N+1<br>
<font color="#0000FF">goto</font> L1<br>
L4: J := N/I<br>
<font color="#0000FF">if </font>J = 0 <font color="#0000FF">goto</font> L3<br>
I := I=1<br>
<font color="#0000FF">goto</font> L2<br>
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<a name="9.8"></a>9.8 填空题<p>在对编译程序产生的中间代码进行优化时，就实施优化的范围来说，分<font class="emphasize"><u> A </u></font>优化和<font class="emphasize"><u> B </u></font>优化。循环优化属于<font class="emphasize"><u> B </u></font>优化，它对于提高目标代码的运行速度是非常有效的。循环优化主要采用的三项优化措施是<font class="emphasize"><u> C </u></font>、<font class="emphasize"><u> D </u></font>、<font class="emphasize"><u> E </u></font>。<br>
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