[m-dev.] for review: type specialisation

[Simon Taylor]

> > 	Added polymorphism__typeclass_info_class_constraint to get the
> > 	class_constraint from a typeclass_info's type. This isn't used yet.
> > 	In extract_type_info, an entry in the type_info_var_map
> > 	was being overwritten using an entry from a dummy typevarset.
> 
> Does the last sentence describe a change unrelated to the other stuff?
> If so, it would be helpful to seperate it a bit more clearly in the
> log message, e.g. make it a new paragraph and insert "Also, fix a bug: "
> at the start.

OK.

> 
> > compiler/higher_order.m:
> ...
> > 	Specialize calls to unify/2, index/2 and compare/3.
> > 	Specialize class_method_calls.
> > 	Interpret the predicates in private_builtin.m which manipulate
> > 	typeclass_infos.
> 
> "Interpret" is a bit unclear here.  Do you mean "Specialize calls to"?
> If so, I think that way of phrasing it would be clearer.

OK.

> The role of higher_order.m seems to be a bit more general now.
> Perhaps higher_order.m should be renamed specialize.m?

If you want, although the name specialize.m suggests something a bit
more general than what higher_order.m does, and there will be other
modules to perform different types of specialization such as constraint
propagation and partial deduction.

> 
> > Index: compiler/higher_order.m
> > +:- pred specialize_higher_order(bool::in, bool::in,
> > +                module_info::in, module_info::out,
> > +                io__state::di, io__state::uo) is det.
> 
> You should document the meaning of the `bool' arguments here.

+        % specialize_higher_order(DoHigherOrder, DoTypeInfos, Module0, Module).
+        % DoHigherOrder is the value of `--optimize-higher-order'.
+        % DoTypeInfos is the value of `--type-specialization'

> 
> > +traverse_goal_0(Goal0, Goal, Info0, Info) :-
> > +        Info0 = info(_, B, NewPreds0, PredProcId, E, F, G, H, I),
> > +        NewPreds0 = new_preds(_, PredVarMap),
> > +        % Lookup the initial known bindings of the variables if this
> > +        % procedure is a specialised version..
> 
> s/.././  ?
> 
> > @@ -586,63 +653,67 @@
> >          ;
> >                  error("higher_order.m: call expected")
> >          ),
> > -        module_info_pred_info(Module, CalledPred, PredInfo),
> > +        module_info_pred_info(Module, CalledPred, CalleePredInfo),
> >          (
> > -                pred_info_is_imported(PredInfo)
> > +                % Look for calls to unify/2 and compare/3 which can
> > +                % be specialized.
> > +                specialize_builtin(Info0, CalledPred, CalledProc,
> > +                        Args0, MaybeContext, Goal1) 
> 
> The predicates unify/2, compare/3, and index are generally called
> "special preds" rather than "builtins", so I suggest `specialize_builtin'
> be renamed `specialize_special_pred'.

OK.

> 
> > +        % Interpret a call to `type_info_from_typeclass_info' or
> > +        % `superclass_from_typeclass_info'. Currently they both have
> > +        % the same definition. This should be kept in sync with
> > +        % compiler/polymorphism.m and runtime/mercury_type_info.h.
> > +:- pred interpret_typeclass_info_manipulator(typeclass_info_manipulator::in,
> 
> You should put comments in both of those places too,
> saying that they should be kept in sync with this.
> 

compiler/polymorphism.m:
 %
 % IMPORTANT: ANY CHANGES TO THE DOCUMENTATION HERE MUST BE REFLECTED BY
-% SIMILAR CHANGES TO THE #defines IN "runtime/type_info.h"
-% AND VICE VERSA.
+% SIMILAR CHANGES TO THE #defines IN "runtime/mercury_type_info.h" AND
+% TO THE TYPE SPECIALIZATION CODE IN "compiler/higher_order.m".

library/private_builtin.m:
@@ -35,6 +35,8 @@
 
 % The following are used by the compiler, to implement polymorphism.
 % They should not be used in programs.
+% Changes here may also require changes in compiler/polymorphism.m,
+% compiler/higher_order.m and runtime/mercury_type_info.{c,h}.

runtime/mercury_type_info.h:
+**      Changes here may also require changes in compiler/polymorphism.m,
+**      compiler/higher_order.m and library/private_builtin.m.

Simon.