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   6 <TITLE>The SUIF Version 1 Library - Lookup Methods</TITLE>
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  17 <H2><A NAME="SEC47" HREF="suif1_toc.html#TOC47">Lookup Methods</A></H2>
  18 <P>
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  22 <P>
  23 SUIF symbol tables provide a number of methods to search for and
  24 retrieve particular types, symbols, and variable definitions.  Most of
  25 these lookup methods will optionally search all the ancestor symbol
  26 tables, making it easy to determine if an object is defined in the
  27 current scope.
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  30 <P>
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  32 The <CODE>lookup_type</CODE> method is available at all levels in the symbol
  33 table hierarchy to search for SUIF types.  Given an existing type, the
  34 method searches for a type that is the same.  It uses the <CODE>is_same</CODE>
  35 method from the <CODE>type_node</CODE> class to perform these comparisons.  If
  36 a matching type is not found within the current symbol table,
  37 <CODE>lookup_type</CODE> will continue searching in the ancestor symbol tables
  38 by default.  However, if the optional <CODE>up</CODE> parameter is set to
  39 <CODE>FALSE</CODE>, it will give up after searching the first table.
  40
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  47 Several methods are provided to lookup symbols.  Each different kind of
  48 symbol (variable, procedure, and label) has its own name space, so the
  49 <CODE>lookup_sym</CODE> method requires that you specify both the name and the
  50 kind of symbol for which to search.  This method may be used with all
  51 symbol tables.  For convenience, other methods are defined as wrappers
  52 around <CODE>lookup_sym</CODE>.  Each of these wrappers searches for a
  53 particular kind of symbol: <CODE>lookup_var</CODE> searches for variables,
  54 <CODE>lookup_proc</CODE> searches for procedures, and <CODE>lookup_label</CODE>
  55 searches for labels.  Because procedure symbols may only be defined in
  56 global symbol tables, the <CODE>lookup_proc</CODE> method is declared in the
  57 <CODE>global_symtab</CODE> class.  Similarly, the <CODE>lookup_label</CODE> method
  58 is declared in the <CODE>block_symtab</CODE> class, because labels may only be
  59 defined within procedures.  By default, all of these methods search the
  60 current symbol table and, if unsuccessful, proceed to search the
  61 ancestor symbol tables.  The optional <CODE>up</CODE> parameters may be set to
  62 <CODE>FALSE</CODE> to turn off this default behavior and only search the
  63 current symbol table.
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  66 <P>
  67 <A NAME="IDX298"></A>
  68 A symbol for a global variable is just a declaration of that variable
  69 and does not automatically have any storage allocated.  Variable
  70 definitions are required to allocate storage and to specify alignment
  71 requirements and any initial data for the variable.  Since the variable
  72 definitions are not directly connected to the variable symbols, the
  73 <CODE>lookup_var_def</CODE> method is provided to search a symbol table for
  74 the definition of a particular variable symbol.  This method does not
  75 search the parent symbol table.  In general the <CODE>definition</CODE> method
  76 in the <CODE>var_sym</CODE> class is a better way to locate a variable
  77 definition.
  78
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  80 <P>
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  83 Symbols and types are assigned ID numbers (see section <A HREF="suif1_50.html#SEC50">Numbering Types and Symbols</A>) that uniquely identify them within a particular context.  The
  84 <CODE>lookup_type_id</CODE> method searches the types defined within a symbol
  85 table and its ancestors for a type with the specified ID number.  The
  86 <CODE>lookup_sym_id</CODE> does the same thing for symbols.
  87
  88 </P>
  89 <P>
  90 <A NAME="IDX301"></A>
  91 Besides searching for one of the entries in a symbol table, you can also
  92 search for one of its children in the symbol table hierarchy.  The
  93 <CODE>lookup_child</CODE> method searches through the list of children for a
  94 symbol table with a given name.  This may not be very useful, but it is
  95 included for completeness.
  96
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