Re: GM2 on Darwin 20.4.0/M1

[Gaius Mulley]

Benjamin Kowarsch <trijezdci@gmail.com> writes:

> On Sat, 22 Jul 2023 at 15:05, Gaius Mulley <gaiusmod2@gmail.com> wrote:
>
>  it would be possible to write a gcc tree to C99 "backend" - probably post
>  gimplification and replacing the call to lowering the trees with the new
>  C99 "backend".
>
> I am not sure that this would produce readable C output. If you let the GCC 
> middle infrastructure do transformations on the syntax tree, there will most 
> likely be significant changes relative to the original input. The
> resulting code would likely be very low level and thus difficult to read and 
> debug. For example it would probably split up expressions into smaller and 
> smaller sub-expressions. It may even turn WHILE and REPEAT and FOR
> loops into label and goto based equivalents.
>
> I still consider the approach of transforming the syntax tree in its
> original form from Modula-2 to C as close as possible and as often as
> possible in a 1:1 manner to be superior.
>
> regards
> benjamin

Ah yes - generating the C at that point would be less readable.  Perhaps
generating C pre-gimplification would be better.  (Just prior to
gimplify_function_tree in the gcc code base).  Ironically I use this
technique to debug gm2 - there is a m2pp.cc pretty printer which
attempts to generate M2 from the gcc trees.


Here is an example working on this source code:

MODULE testnew5 ;

FROM Storage IMPORT ALLOCATE ;

TYPE
   ptr = POINTER TO RECORD
                       a, b: CARDINAL ;
                    END ;

(*
   test -
*)

PROCEDURE test (VAR p: ptr) ;
BEGIN
   NEW (p) ;
   WITH p^ DO
      a := 1 ;
   END
END test ;


VAR
   n: ptr ;
BEGIN
   test (n)
END testnew5.


$ gdb cc1gm2 etc
(gdb) break gimplify_function_tree
(gdb) run
(gdb) print modula2::pf(fndecl)


(*
   test - static,
*)

PROCEDURE test (VAR p: (* <!g> *) POINTER TO (* <!g> *) RECORD
                                                           a : (* <!g> *) 
CARDINAL;
                                                           b : (* <!g> *) 
CARDINAL;
                                                        END) ; 
(* variables in function_decl (decl_initial) *)
VAR
   (* block variables *)
   _T103 : (* <!g> *) POINTER TO (* <!g> *) RECORD
                                               a : (* <!g> *) CARDINAL;
                                               b : (* <!g> *) CARDINAL;
                                            END ;
   _T102 : (* <!g> *) POINTER TO (* <!g> *) RECORD
                                               a : (* <!g> *) CARDINAL;
                                               b : (* <!g> *) CARDINAL;
                                            END ;
   _T100 : (* <!g> *) POINTER TO ADDRESS ;
   (* testnew5.mod:14 *)
   (* variables in bind_expr *)
   _T103 : (* <!g> *) POINTER TO (* <!g> *) RECORD
                                               a : (* <!g> *) CARDINAL;
                                               b : (* <!g> *) CARDINAL;
                                            END ;
   _T102 : (* <!g> *) POINTER TO (* <!g> *) RECORD
                                               a : (* <!g> *) CARDINAL;
                                               b : (* <!g> *) CARDINAL;
                                            END ;
   _T100 : (* <!g> *) POINTER TO ADDRESS ;
   (* bind_expr_block *)
    ; 
   (* statement list *)
   (* testnew5.mod:16 *)
   (* variable in decl_expr *)
   _T100 : (* <!g> *) POINTER TO ADDRESS ;
   (* testnew5.mod:17 *)
   (* variable in decl_expr *)
   _T102 : (* <!g> *) POINTER TO (* <!g> *) RECORD
                                               a : (* <!g> *) CARDINAL;
                                               b : (* <!g> *) CARDINAL;
                                            END ;
   (* testnew5.mod:17 *)
   (* variable in decl_expr *)
   _T103 : (* <!g> *) POINTER TO (* <!g> *) RECORD
                                               a : (* <!g> *) CARDINAL;
                                               b : (* <!g> *) CARDINAL;
                                            END ;
   (* testnew5.mod:16 *)
BEGIN
   _T100 := CAST ((* <!g> *) POINTER TO ADDRESS, p) ;
   (* testnew5.mod:16 *)
   m2pim_Storage_ALLOCATE( _T100, 8) ;
   (* testnew5.mod:17 *)
   _T102 := ( CAST ((* <!g> *) POINTER TO (* <!g> *) POINTER TO (* <!g> *) 
RECORD
                                                                              a 
: (* <!g> *) CARDINAL;
                                                                              b 
: (* <!g> *) CARDINAL;
                                                                           END, 
p))^ ;
   (* testnew5.mod:17 *)
   _T103 := _T102 ;
   (* testnew5.mod:18 *)
   (_T103)^.a := 1 ;
END test ;


ok so still pretty verbose and unpleasant :-).  But with a little work I
suspect it could look much neater (declaring a global type and reducing
clutter/tempories etc).  I guess the major attraction is portability
rather than language conversion,

regards,
Gaius