[m-rev.] for review: new termination analyser (part 6 of 6)

[Mark Brown]

On 24-Mar-2005, Julien Fischer <juliensf at cs.mu.OZ.AU> wrote:
> Index: compiler/termination2.m
> ===================================================================
> RCS file: compiler/termination2.m
> diff -N compiler/termination2.m
> --- /dev/null	1 Jan 1970 00:00:00 -0000
> +++ compiler/termination2.m	24 Mar 2005 04:17:13 -0000
> @@ -0,0 +1,736 @@
> +%-----------------------------------------------------------------------------%
> +% vim: ft=mercury ts=4 sw=4 et
> +%-----------------------------------------------------------------------------%
> +% Copyright (C) 1997,2002-2005 The University of Melbourne.

The copyright years are wrong.

> +%   (b) Perform fixpoint calculation to derive IR information.
> +%       ( See term_constr_fixpoint.m.)

There's an extra space.

> +:- interface.
> +
> +:- import_module hlds.hlds_module.
> +:- import_module hlds.hlds_pred.
> +
> +:- import_module parse_tree.prog_data.
> +
> +:- import_module libs.polyhedron.
> +
> +:- import_module mdbcomp.prim_data.
> +
> +:- import_module transform_hlds.term_constr_data.
> +:- import_module transform_hlds.term_constr_errors.

According to the current coding standards, you should remove the above
blank lines (and similarly elsewhere).

> +    % Why does the termination analyser think that a procedure is
> +    % terminating?  This is useful for debugging purposes.
> +    %
> +:- type term_reason
> +    --->    builtin             % procedure was a builtin.
> +
> +    ;       pragma_supplied     % procedure has pramga terminates decl.
> +
> +    ;       foreign_supplied    % procedure has foreign code attribute.
> +
> +    ;       import_supplied     % This procedure was imported and it's

s/it's/its/

> +                                % termination info. was read in from a .opt

Probably should s/info./info/ (and elsewhere).

> +                                % or .trans_opt file.
> +
> +    ;       analysis.           % Termination info. was derived via analysis.
> +

> +%------------------------------------------------------------------------------%
> +%
> +% The termination2_info structure.
> +%
> +
> +:- type termination2_info
> +    --->    term2_info(
> +            size_var_map :: size_var_map,
> +                % Map between prog_vars and size_vars.
> +                % Each procedure should have one of these.

That second sentence applies to the whole termination2_info structure,
so is redundant here.

(Upon further inspection, perhaps you mean that this field should be filled
in for each procedure, regardless of whether other fields are.  If so, you
should make that clearer.)

> +
> +            head_vars :: list(size_var),
> +                % These are the size variables that occur in argument
> +                % size constraints.  For procedures that are imported
> +                % via a `.opt' or `.trans_opt' file we set these during
> +                % the initial pass, for procedures in the module we are
> +                % analysing, pass 1 sets it.
> +
> +            import_headvarids :: maybe(list(int)),
> +            import_success   :: maybe(pragma_constr_arg_size_info),
> +            import_failure   :: maybe(pragma_constr_arg_size_info),
> +                % Arg size info. imported from another module via a
> +                % `.opt' or `.trans_opt' file.  The preprocessing pass
> +                % needs to convert these to the proper form.  These
> +                % particular fields are of no use after that.

By the "preprocessing" pass I take it you mean the initial pass, aka pass 0.
If so, you should stick to one of those names.

> +
> +            success_constrs :: maybe(constr_arg_size_info),
> +                % The interargument size relationships
> +                % (expressed as convex constraints)
> +                % obtained during pass 1.
> +
> +            failure_constrs :: maybe(constr_arg_size_info),
> +                % Failure constraints for predicates that
> +                % can fail (set by pass 1).
> +
> +            term_status :: maybe(constr_termination_info),
> +                % The termination status of the procedure as determined
> +                % by pass 2.
> +
> +            intermod_status :: maybe(intermod_status),
> +                % Is this procedure (possibly) involved in mutual
> +                % recursion across module boundaries. Set by pass 1.

s/boundaries/boundaries?/

> +
> +            abstract_rep :: maybe(abstract_proc)
> +                % The abstract representation of this
> +                % proc. Set by term_constr_build.m.
> +        ).
> +
> +term2_info_init = term2_info(map.init, [], no, no, no, no, no, no, no, no).
> +
> +%----------------------------------------------------------------------------%
> +%
> +% Main pass.
> +%
> +
> +% The analysis proceeds as follows:
> +%
> +% * Preprocess the module:
> +%   - setup information from termination pragmas
> +%   - setup information from foreign proc attributes
> +%   - setup information about imported procedures
> +%   - setup termination information for builtin predicates
> +%
> +% * Analyse the module - process SCCs bottom-up.
> +%
> +% * Optionally write out termination information to the `.opt' and
> +%   `.trans_opt' files.
> +%

You should refer to these stages by the pass names mentioned above.
Providing more detail would also be good, eg breaking pass 1 into build pass
and whatever else, since the build pass is mentioned just below.

> +analyse_scc(DepOrder, BuildOpts, FixpointOpts, Pass2Opts, SCC, !ModuleInfo,
> +        !IO) :-
> +    %
> +    % Since all of the passes are potentially optional we need to
> +    % initialise the size_var_maps separately.  If they are left
> +    % uninitialised intermodule optimization will not work.
> +    %
> +    NeedsAR = list.filter(proc_needs_ar_built(!.ModuleInfo), SCC),
> +    %
> +    % Build the abstract representation for those procedures that
> +    % require it. (those that do not already have both arg_size_info and
> +    % termination info).
> +    %
> +    term_constr_build.build_abstract_scc(DepOrder, NeedsAR, BuildOpts,
> +        BuildErrors, !ModuleInfo, !IO),
> +    %
> +    % We only perform the fixpoint computation for those procedures
> +    % where we can gain meaningful information from it.  We do not
> +    % do it when:
> +    % - the information is already known.

s/./, or/

(or maybe that should be "and".)

> +%------------------------------------------------------------------------------%
> +
> +:- func this_file = string.
> +
> +this_file = "termination2.m".

Do you still need this?  It isn't used at the moment.

To be continued...

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