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   6 <TITLE>The SUIF Version 1 Library - Tree Nodes</TITLE>
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  17 <H2><A NAME="SEC11" HREF="suif1_toc.html#TOC11">Tree Nodes</A></H2>
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  25 The different kinds of AST nodes are represented by objects derived from
  26 the <CODE>tree_node</CODE> class.  This base class includes features, such as
  27 ID numbers, that are shared by all kinds of tree nodes.
  28
  29 </P>
  30 <P>
  31 The simplest kind of tree node is a <CODE>tree_instr</CODE>.  Each of these is
  32 a leaf node that contains a single instruction or expression.
  33
  34 </P>
  35 <P>
  36 Conditional structures may be represented by <CODE>tree_if</CODE> nodes.
  37
  38 </P>
  39 <P>
  40 The ASTs include two different kinds of loop nodes.  The
  41 <CODE>tree_loop</CODE> nodes just record the control-flow structure of the
  42 loops and are used to represent generic "do-while" loops.  Many
  43 optimizations, however, only apply to certain well-behaved types of
  44 loops.  Thus, the trees may also contain <CODE>tree_for</CODE> nodes to
  45 represent loops with scalar indices that vary from their initial to
  46 final values, being incremented or decremented on every iteration, and
  47 that meet various other requirements.  Most Fortran <CODE>DO</CODE> loops
  48 qualify as <CODE>tree_for</CODE> nodes.  Those loops which do not meet the
  49 requirements for <CODE>tree_for</CODE> nodes are represented by
  50 <CODE>tree_loop</CODE> nodes instead.
  51
  52 </P>
  53 <P>
  54 Nested scopes are represented by <CODE>tree_block</CODE> nodes.  A
  55 <CODE>tree_block</CODE> contains a list of tree nodes and a symbol table.  The
  56 symbols and types in the table may only be referenced from within the
  57 block.  The node at the root of an AST is a special kind of
  58 <CODE>tree_block</CODE> called a <CODE>tree_proc</CODE>.  The <CODE>tree_proc</CODE>
  59 objects use a slightly different kind of symbol table and include some
  60 extra methods but are otherwise the same as the <CODE>tree_block</CODE>
  61 objects.
  62
  63 </P>
  64
  65 <UL>
  66 <LI><A HREF="suif1_12.html#SEC12">ID Numbers</A>: ID numbers for tree nodes and instructions.
  67 <LI><A HREF="suif1_13.html#SEC13">Other Node Features</A>: Other features shared by all tree nodes.
  68 <LI><A HREF="suif1_14.html#SEC14">Instruction Nodes</A>: Leaf nodes: instructions and expressions.
  69 <LI><A HREF="suif1_15.html#SEC15">If Nodes</A>: Conditionals.
  70 <LI><A HREF="suif1_16.html#SEC16">Loop Nodes</A>: General do-while loops.
  71 <LI><A HREF="suif1_17.html#SEC17">For Nodes</A>: Nicely-structured FOR loops.
  72 <LI><A HREF="suif1_18.html#SEC18">Block Nodes</A>: Nested scopes.
  73 <LI><A HREF="suif1_19.html#SEC19">Procedure Nodes</A>: Root nodes for procedure bodies.
  74 </UL>
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