DWARF and GDB Algol 68 support - notes

[Jose E. Marchesi]

> Hi Cuper.
>
> These are the notes from the discussion we have just had over jitsi
> about adding support for Algol 68 to GDB.
>
>   begin int x := 20; (*)
>         prio > = 4;
>         real i = (x_1>10 | 10 | x_2);
>                                 { Without -g: real(x) }
>                                 { With -g: (real x_2 = real(x); x) }
>         puts (fixed(1) + "'n")
>   end

I just noticed that creating var_decls for the applied identifiers x_1,
x_2, etc, doesn't mean that the var_decl for the defining identifier x
goes away: it is still there.

This is very good, because it means that, given a listing:

  10  begin int x := 20;
  11        prio > = 4;
  12        real i = (x_1>10 | 10 | x_2);
  13        puts (fixed(1) + "'n")
  14  end

When we breakpoint at line 13, we have:

  (gdb) print x
  x = 20
  (gdb) print x_1
  x_1 = 20
  (gdb) print x_2
  x_2 = 20.0

Therefore, we can document that using a non-subscripted identifier
refers to the defining identifier, i.e. the object x, whereas using a
subscripted version of x refers to some particular applied identifier,
in its role as coercee.

This is looking good :)

>
>                 unit
>                   |
>                 widen
>                   |
>   deref         deref
>     |             |
>     x             x
>
>   (gdb) print x_2 + 10
>
> For unit_is_applied_identifier (p)
>
>   Skip zero or more nodes:
>
>      WIDENING
>      VOIDING
>      ROWING
>      UNITING
>      DEREFERENCING
>      DEPROCEDURING
>
>   If next node is IDENTIFIER, return TREE_DECL (TAX (node))
>   Otherwise, return NULL_TREE
>
> Code sketch:
>
> diff --git a/gcc/algol68/a68-low-units.cc b/gcc/algol68/a68-low-units.cc
> index 3cbf131112b..831fd509c2f 100644
> --- a/gcc/algol68/a68-low-units.cc
> +++ b/gcc/algol68/a68-low-units.cc
> @@ -1371,5 +1371,27 @@ a68_lower_formal_hole (NODE_T *p, LOW_CTX_T ctx ATTRIBUTE_UNUSED)
>  tree
>  a68_lower_unit (NODE_T *p, LOW_CTX_T ctx)
>  {
> -  return a68_lower_tree (SUB (p), ctx);
> +  tree unit = a68_lower_tree (SUB (p), ctx);
> +
> +  if (debug_info)
> +    {
> +      tree *id_decl = unit_is_applied_identifier (p);
> +
> +      /* If the unit is an applied identifier after zero or more coercions.  */
> +      if (id_decl != NULL_TREE)
> +	{
> +	  /* Return a compound_stmt
> +
> +	     (var_decl for an object named ID_N, and value UNIT,
> +	     ID_N)
> +	  */
> +	  unit = save_expr (unit);
> +	  return fold_build2 (COMPOUND_EXPR, TREE_TYPE (unit),
> +			      build_decl (LOC (unit),
> +					  VAR_DECL,
> +					  DECL_NAME (id_decl) + "_" + ++(NAMECNT (TAX (id_decl))),
> +					  unit),
> +			      unit);
> +	}
> +    }
>  }
> diff --git a/gcc/algol68/a68-types.h b/gcc/algol68/a68-types.h
> index 9dc3d006e9f..6736c51ca18 100644
> --- a/gcc/algol68/a68-types.h
> +++ b/gcc/algol68/a68-types.h
> @@ -638,6 +638,7 @@ struct GTY((chain_next ("%h.next"))) TAG_T
>    LOWERER_T lowerer;
>    TAG_T *next, *body;
>    const char *extern_symbol;
> +  int name_counter;
>  };
>  #define NO_TAG ((TAG_T *) 0)
>  
> @@ -1021,6 +1022,7 @@ struct GTY(()) A68_T
>  #define MULTIPLE(p) ((p)->multiple_mode)
>  #define MULTIPLE_MODE(p) ((p)->multiple_mode)
>  #define NAME(p) ((p)->name)
> +#define NAMECNT(p) ((p)->name_counter)
>  #define NEST(p) ((p)->nest)
>  #define NEST_PROC(p) ((p)->nest_proc)
>  #define NEXT(p) ((p)->next)
>