LANGUAGES revision 117395 
1Right now there is no documentation for the GCC tree -> rtl interfaces
2(or more generally the interfaces for adding new languages).
3
4Such documentation would be of great benefit to the project.  Until such
5time as we can formally start documenting the interface this file will
6serve as a repository for information on these interface and any incompatable
7changes we've made.
8
92001-02-26:
10  A DECL_INITIAL of NULL_TREE or error_mark_node in a VAR_DECL is no longer
11  taken to signify a tentative definition which should not be emitted until
12  end-of-file.  Frontends which want that behavior should set
13  DECL_DEFER_OUTPUT before calling rest_of_decl_compilation.
14
15Aug 31, 1998:
16  The interface to HANDLE_PRAGMA has changed.  It now takes three arguments.
17  The first two are pointers to functions that should be used to read characters
18  from the input stream, and to push them back into the input stream respectively.
19  The third argument is a pointer to a null terminate string which is the first
20  word after #pragma.  The expression supplied by HANDLE_PRAGMA should return
21  nonzero if it parsed and implemented the pragma.  Otherwise it should return
22  zero, and leave the input stream as it was before the expression was evaluated.
23
24  A new back-end definable macro has been added: INSERT_ATTRIBUTES.  This macro
25  allows backend to add attributes to decls as they are created.
26
27Jun 10, 1998:
28  The interface to lang_decode_option has changed. It now uses and argc/argv
29  interface to allow for options that use more than one input string. The new
30  declaration is: int lang_decode_option (int argc, char** argv). It now
31  returns the number of input strings processed, or 0 if the option is
32  unknown.
33
34Jun  7, 1998:
35  Front-ends must now define lang_init_options.  It is safe for this
36  function to do nothing.  See c-lang.c.
37
38Apr 21, 1998:
39  Front ends which link with c-common or other files from the C/C++
40  front-ends may need to handle TI types.  Look for references to
41  [unsigned]int_DI_type_node in your front end.  If you have references
42  to these variables, you'll need up update the front end.
43
44  To update the front end you must mirror all the code which currently
45  deals with intDI_type_node to also handle intTI_type_node.
46
47
48Apr 7, 1998:
49  The interface between toplev.c and the language front ends for opening the
50  source file has changed:
51
52  o init_lex() has been renamed to init_parse (char *filename) where filename
53    is the name of the source file.
54  o The code in toplev.c which opened the source file should be moved to
55    the new init_parse function.
56  o toplev.c now calls finish_parse() instead of closing the source file
57    using fclose(). This should now be done in finish_parse, if necessary.
58
59Apr 1, 1998:
60  Front-ends must now define lang_print_xnode.  It is safe for this
61  function to do nothing.  See c-lang.c.
62
63Feb 1, 1998:
64
65  GCC used to store structure sizes & offsets to elements as bitsize
66  quantities.  This causes problems because a structure can only be
67  (target memsize / 8) bytes long (this may effect arrays too).  This
68  is particularly problematical on machines with small address spaces.
69
70  So:
71
72    All trees that represent sizes in bits should have a TREE_TYPE of
73    bitsizetype (rather than sizetype).
74
75    Accordingly, when such values are computed / initialized, care has to
76    be takes to use / compute the proper type.
77
78    When a size in bits is converted into a size in bytes, which is expressed
79    in trees, care should be taken to change the tree's type again to sizetype.
80
81    We've updated C, C++, Fortran & Objective-C to work with the new
82    scheme.  Other languages will need to be updated accordingly.
83    Contact amylaar@cygnus.com for additional information.
84
85?? 1997:
86
87  In an effort to decrease cache thrashing and useless loads we've changed the
88  third argument to the DEFTREECODE macro to be a single char.  This will
89  affect languages that defined their own tree codes (usually in a .def file).
90
91  Old way:
92
93    DEFTREECODE (CLASS_METHOD_DECL, "class_method_decl", "d", 0)
94
95  New way:
96
97    DEFTREECODE (CLASS_METHOD_DECL, "class_method_decl", 'd', 0)
98