html/suif1_46.html

   1 <HTML>
   2 <HEAD>
   3 <!-- This HTML file has been created by texi2html 1.54
   4      from suif1.texi on 28 April 1999 -->
   5
   6 <TITLE>The SUIF Version 1 Library - Basic Symtab Features</TITLE>
   7 <link href="suif1_47.html" rel=Next>
   8 <link href="suif1_45.html" rel=Previous>
   9 <link href="suif1_toc.html" rel=ToC>
  10
  11 </HEAD>
  12 <BODY>
  13 <p>Go to the <A HREF="suif1_1.html">first</A>, <A HREF="suif1_45.html">previous</A>, <A HREF="suif1_47.html">next</A>, <A HREF="suif1_113.html">last</A> section, <A HREF="suif1_toc.html">table of contents</A>.
  14 <P><HR><P>
  15
  16
  17 <H2><A NAME="SEC46" HREF="suif1_toc.html#TOC46">Basic Features</A></H2>
  18 <P>
  19 <A NAME="IDX282"></A>
  20
  21 </P>
  22 <P>
  23 Symbol tables contain three different kinds of objects: types, symbols,
  24 and variable definitions.  The entries within a symbol table may only be
  25 referenced within the corresponding scope.  This includes references
  26 within registered annotations.  Violating this condition may lead to
  27 strange and unexpected errors.
  28
  29 </P>
  30 <P>
  31 <A NAME="IDX283"></A>
  32 <A NAME="IDX284"></A>
  33 <A NAME="IDX285"></A>
  34 For simplicity, the symbol table entries are stored on lists instead of
  35 using hash tables.  In theory, the actual implementation (lists or hash
  36 tables) should not be visible in the symbol table interface.
  37 Unfortunately that is not completely true for the current implementation
  38 of SUIF--the lists can be accessed directly.  The <CODE>types</CODE>,
  39 <CODE>symbols</CODE>, and <CODE>var_defs</CODE> methods return pointers to the
  40 lists.  However, these lists should only be accessed to examine the
  41 entries and should never be modified directly.  The symbol table classes
  42 provide other methods to add and remove entries from the lists and those
  43 methods should always be used.  If the list implementation becomes a
  44 performance bottleneck, we may need to switch to hash tables, and code
  45 that modifies the lists directly will be relatively hard to convert.
  46
  47 </P>
  48 <P>
  49 <A NAME="IDX286"></A>
  50 <A NAME="IDX287"></A>
  51 <A NAME="IDX288"></A>
  52 To distinguish the symbol tables nested within a particular scope, each
  53 table is given a name.  The <CODE>name</CODE> and <CODE>set_name</CODE> methods
  54 retrieve and modify this name.  If a scope in the source program has a
  55 name associated with it, that name may be used for the corresponding
  56 symbol table.  For example, the name of a procedure-level symbol table
  57 should generally be the same as the name of the procedure.  On the other
  58 hand, nested scopes within procedures are typically unnamed, and names
  59 must be generated for the corresponding symbol tables.
  60
  61 </P>
  62 <P>
  63 <A NAME="IDX289"></A>
  64 <A NAME="IDX290"></A>
  65 The symbol table names are used when printing a reference to a symbol or
  66 named type.  Because the symbol or type name alone may not be sufficient
  67 to identify it uniquely, the <CODE>chain_name</CODE> method is used to
  68 identify the symbol table.  The chain name of a symbol table includes
  69 the names of all of the symbol tables from the procedure-level downward,
  70 separated by slashes (as in a Unix path).  The file-level name is not
  71 included since it should always be clear from the context.  The chain
  72 name for a global or file symbol table is the empty string.
  73
  74 </P>
  75 <P>
  76 <A NAME="IDX291"></A>
  77 Duplicate names within a symbol table should be avoided whenever
  78 possible.  Each kind of symbol has a separate name space.  A variable,
  79 for example, may have the same name as a label in the same symbol table.
  80 Named types and child symbol table names are also in separate name
  81 spaces.  Duplicate names may be temporarily introduced but to avoid
  82 problems they should be renamed as soon as possible.  The
  83 <CODE>rename_duplicates</CODE> method is provided to check for and rename any
  84 duplicates in a symbol table.  This method is automatically called
  85 before writing out each symbol table.
  86
  87 </P>
  88
  89 <P><HR><P>
  90 <p>Go to the <A HREF="suif1_1.html">first</A>, <A HREF="suif1_45.html">previous</A>, <A HREF="suif1_47.html">next</A>, <A HREF="suif1_113.html">last</A> section, <A HREF="suif1_toc.html">table of contents</A>.
  91 </BODY>
  92 </HTML>