html/suif1_42.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 - Global Symbol Table</TITLE>
   7 <link href="suif1_43.html" rel=Next>
   8 <link href="suif1_41.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_41.html">previous</A>, <A HREF="suif1_43.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 <H3><A NAME="SEC42" HREF="suif1_toc.html#TOC42">The Global Symbol Table</A></H3>
  18 <P>
  19 <A NAME="IDX265"></A>
  20 <A NAME="IDX266"></A>
  21
  22 </P>
  23 <P>
  24 The global symbol table is at the top of the symbol table hierarchy and
  25 corresponds to the outermost global scope.  It contains objects that are
  26 visible across source files (i.e. shared types and global symbols with
  27 external linkage).  For this reason, it is associated with the
  28 <CODE>file_set</CODE> object.  See section <A HREF="suif1_8.html#SEC8">The File Set</A>.
  29
  30 </P>
  31 <P>
  32 The advantage of using a shared global symbol table appears when
  33 performing interprocedural analyses and transformations.  Without a
  34 common symbol table, it can be quite a burden to deal with references to
  35 symbols that are defined in some files but not in others.  Even trying
  36 to determine which symbols from different files correspond to the same
  37 objects is difficult.  In essence, each interprocedural pass would need
  38 to do the work of a linker!  The shared global symbol table avoids all
  39 of these problems and makes interprocedural optimization relatively
  40 easy.
  41
  42 </P>
  43 <P>
  44 Along with the benefits of the global symbol table come a few
  45 difficulties.  Sharing the global symbol table across files makes it
  46 difficult to support separate compilation.  Each file must contain a
  47 copy of the global symbol table, and if these files are manipulated
  48 individually, their copies of the global symbol table will not be
  49 consistent.  Thus, before a group of files can be combined in a SUIF
  50 file set, their global symbol tables must be "linked" together using
  51 the SUIF linker pass.  Whether this is preferable to just combining all
  52 of the source files into one big SUIF file is debatable.
  53
  54 </P>
  55 <P>
  56 <A NAME="IDX267"></A>
  57 The <CODE>global_symtab</CODE> class is used to represent the global symbol
  58 table.  It is also used as the base class for file symbol tables.
  59 Because procedure symbols may only be entered in global and file symbol
  60 tables, this class contains the methods to deal with them.  The
  61 <CODE>new_proc</CODE> method creates a new procedure symbol and enters it in
  62 the table (see section <A HREF="suif1_48.html#SEC48">Creating New Entries</A>), and the <CODE>lookup_proc</CODE>
  63 method searches for an existing procedure symbol (see section <A HREF="suif1_47.html#SEC47">Lookup Methods</A>).  The <CODE>number_globals</CODE> method in this class handles the
  64 task of assigning ID numbers to the symbols and types in global and file
  65 symbol tables (see section <A HREF="suif1_50.html#SEC50">Numbering Types and Symbols</A>).
  66
  67 </P>
  68
  69 <P><HR><P>
  70 <p>Go to the <A HREF="suif1_1.html">first</A>, <A HREF="suif1_41.html">previous</A>, <A HREF="suif1_43.html">next</A>, <A HREF="suif1_113.html">last</A> section, <A HREF="suif1_toc.html">table of contents</A>.
  71 </BODY>
  72 </HTML>