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   6 <TITLE>The SUIF Version 1 Library - Mapping Subtrees</TITLE>
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  17 <H2><A NAME="SEC21" HREF="suif1_toc.html#TOC21">Mapping Functions Over Subtrees</A></H2>
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  19 <A NAME="IDX128"></A>
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  25 Many SUIF programs contain code that visits all of the nodes in an AST
  26 to perform various operations.  Rather than having every programmer
  27 duplicate the code for this traversal, the SUIF library includes methods
  28 to map functions over ASTs.  The <CODE>tree_node</CODE> and
  29 <CODE>tree_node_list</CODE> classes both provide these <CODE>map</CODE> methods.
  30
  31 </P>
  32 <P>
  33 The function to be mapped must be of type <CODE>tree_map_f</CODE>.  For a tree
  34 node, the <CODE>map</CODE> method applies the function to the tree node and
  35 all of its children.  The <CODE>preorder</CODE> parameter is used to select
  36 either preorder or postorder traversals; the default is preorder.  For
  37 preorder traversals, the function is applied to the tree node before it
  38 is applied to the children.  For postorder, the function is first
  39 applied to the tree_node's children and descendants and then last
  40 applied to the tree node itself.
  41
  42 </P>
  43 <P>
  44 The <CODE>map</CODE> method for a tree node list calls <CODE>map</CODE> for each
  45 node in the list.  The nodes are visited in order from first to last
  46 regardless of the <CODE>preorder</CODE> parameter.  The <CODE>tree_node_list</CODE>
  47 version of the <CODE>map</CODE> method has an extra optional parameter that
  48 allows you to only map the function over the entries in the list without
  49 recursively visiting their children.
  50
  51 </P>
  52 <P>
  53 The <CODE>tree_map_f</CODE> functions have two parameters: a pointer to the
  54 tree node and a <CODE>void*</CODE> value passed on from the <CODE>map</CODE> method.
  55 Additional parameters can be passed by making the <CODE>void*</CODE> value a
  56 pointer to a structure containing the parameters.  For example, the
  57 following code counts the number of <CODE>tree_for</CODE> and <CODE>tree_loop</CODE>
  58 nodes in a procedure:
  59
  60 </P>
  61
  62 <PRE>
  63 struct count_result {
  64     int num_fors;
  65     int num_loops;
  66 };
  67
  68 void count_loops (tree_node *t, void *x)
  69 {
  70     count_result *results = (count_result *)x;
  71
  72     if (t-&#62;kind() == TREE_FOR) results-&#62;num_fors++;
  73     else if (t-&#62;kind() == TREE_LOOP) results-&#62;num_loops++;
  74 }
  75
  76 /*
  77  *  Return the number of tree_fors and tree_loops in the procedure.
  78  */
  79
  80 void counter (tree_proc *p, int *for_count, int *loop_count)
  81 {
  82     count_result results;
  83     results.num_fors = 0;
  84     results.num_loops = 0;
  85
  86     p-&#62;map(count_loops, (void *)&#38;results);
  87
  88     *for_count =  results.num_fors;
  89     *loop_count = results.num_loops;
  90 }
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