[m-dev.] for review: type specialisation round 2

[Simon Taylor]

> > +		% A constraint says nothing if the types are all ground.
> > +		list__member(Type, Types),
> > +		\+ term__is_ground(Type)
> 
> This is not always true.  Constraints on ground types can make sense
> if the instance declaration is visible in the caller but not in the
> callee.

OK, I'll remove the elimination of ground constraints -- it can't hurt
to have them lying around even if they aren't needed. 

> > +		(
> > +			list__member(ConstrainedType, ConstrainedTypes),
> > +			\+ term__is_ground(ConstrainedType)
> > +		->
> > +			true
> > +		;
> > +			fail
> > +		)
> 
> Hmm, `(A -> true ; fail)' is the same as `A'.
> I don't think the if-then-else improves readability here, does it?

What I meant was 
	some([ConstrainedType],
		list__member(ConstrainedType, ConstrainedTypes),
		\+ term__is_ground(ConstrainedType)
	)

Here's a relative diff addressing your comments:

===================================================================
RCS file: RCS/higher_order.m,v
retrieving revision 1.6
diff -u -r1.6 higher_order.m
--- higher_order.m	1998/09/08 23:03:13	1.6
+++ higher_order.m	1998/09/09 00:35:19
@@ -1598,9 +1598,9 @@
 
 %-----------------------------------------------------------------------------%
 
-	% Collect the list class_constraints from the list of argument types.
-	% The typeclass_info for universal constraints is input, output for
-	% existential constraints.
+	% Collect the list of class_constraints from the list of argument
+	% types. The typeclass_info for universal constraints is input,
+	% output for existential constraints.
 :- pred find_class_context(module_info::in, list(type)::in, list(mode)::in,
 	list(class_constraint)::in, list(class_constraint)::in,
 	class_constraints::out) is det.
@@ -1637,12 +1637,8 @@
 	strip_term_contexts(Types0, Types),
 	Constraint = constraint(ClassName, Types),
 	(
-		% Remove duplicates
-		\+ list__member(Constraint, Constraints0),
-
-		% A constraint says nothing if the types are all ground.
-		list__member(Type, Types),
-		\+ term__is_ground(Type)
+		% Remove duplicates.
+		\+ list__member(Constraint, Constraints0)
 	->
 		Constraints = [Constraint | Constraints0]	
 	;
@@ -1672,20 +1668,7 @@
 add_extra_typeclass_infos_2([Var | Vars], [Type0 | Types],
 		TCVarMap0, TCVarMap) :-
 	strip_term_context(Type0, Type),
-	(
-		polymorphism__typeclass_info_class_constraint(Type,
-			Constraint),
-		Constraint = constraint(_, ConstrainedTypes),
-
-		(
-			list__member(ConstrainedType, ConstrainedTypes),
-			\+ term__is_ground(ConstrainedType)
-		->
-			true
-		;
-			fail
-		)
-	->
+	( polymorphism__typeclass_info_class_constraint(Type, Constraint) ->
 		map__set(TCVarMap0, Constraint, Var, TCVarMap1)
 	;
 		TCVarMap1 = TCVarMap0
===================================================================
RCS file: RCS/type_util.m,v
retrieving revision 1.4
diff -u -r1.4 type_util.m
--- type_util.m	1998/09/08 23:03:13	1.4
+++ type_util.m	1998/09/09 00:39:04
@@ -158,8 +158,9 @@
 :- mode apply_rec_substitution_to_type_map(in, in, out) is det.
 
 	% Update a map from tvar to type_info_locn, using the type renaming
-	% and substitution to rename tvars and a variable substition to
-	% rename vars.
+	% and substitution to rename tvars and a variable substitution to
+	% rename vars. The type renaming is applied before the type
+	% substitution.
 	%
 	% If tvar maps to a another type variable, we keep the new
 	% variable, if it maps to a type, we remove it from the map.
@@ -170,10 +171,8 @@
 
 	% Update a map from class_constraint to var, using the type renaming
 	% and substitution to rename tvars and a variable substition to
-	% rename vars.
-	%
-	% If the constraint no longer constraints any type variables,
-	% we remove it from the map.
+	% rename vars. The type renaming is applied before the type
+	% substitution.
 
 :- pred apply_substitutions_to_typeclass_var_map(map(class_constraint, var),
 	tsubst, map(tvar, type), map(var, var), map(class_constraint, var)).
@@ -782,33 +781,20 @@
 apply_substitutions_to_typeclass_var_map(VarMap0,
 		TRenaming, TSubst, Subst, VarMap) :-
 	map__to_assoc_list(VarMap0, VarAL0),
-	list__filter_map(
-		apply_substitutions_to_typeclass_var_map_2(TRenaming,
-			TSubst, Subst),
-		VarAL0, VarAL),
+	list__map(apply_substitutions_to_typeclass_var_map_2(TRenaming,
+		TSubst, Subst), VarAL0, VarAL),
 	map__from_assoc_list(VarAL, VarMap).
 
 :- pred apply_substitutions_to_typeclass_var_map_2(tsubst, map(tvar, type),
 		map(var, var), pair(class_constraint, var),
 		pair(class_constraint, var)).
 :- mode apply_substitutions_to_typeclass_var_map_2(in, in,
-		in, in, out) is semidet.
+		in, in, out) is det.
 	
 apply_substitutions_to_typeclass_var_map_2(TRenaming, TSubst, VarRenaming,
 		Constraint0 - Var0, Constraint - Var) :-
 	apply_subst_to_constraint(TRenaming, Constraint0, Constraint1),
 	apply_rec_subst_to_constraint(TSubst, Constraint1, Constraint),
-
-	% Check that the constraint still constrains some type variables.
-	Constraint = constraint(_, Types),
-	( 
-		list__member(Type, Types),
-		\+ term__is_ground(Type)
-	->
-		true
-	;
-		fail
-	),
 
 	( map__search(VarRenaming, Var0, Var1) ->
 		Var = Var1
===================================================================
RCS file: RCS/options.m,v
retrieving revision 1.1
diff -u -r1.1 options.m
--- options.m	1998/09/08 00:08:40	1.1
+++ options.m	1998/09/09 00:35:42
@@ -1751,7 +1751,10 @@
 		"--no-disable-opt-for-trace",
 		"\tEnabling tracing usually disables optimizations which could",
 		"\tmake it difficult to relate the trace to the source code.",
-		"\tThis option is useful when debugging those optimizations."
+		"\t`--no-disable-opt-for-trace' results in only those", 
+		"\toptimizations which don't work with tracing being disabled.",
+		"\tThis is useful for debugging the optimization passes of",
+		"\tthe compiler."
 	]).
 
 :- pred options_help_hlds_hlds_optimization(io__state::di, io__state::uo)


Index: user_guide.texi
===================================================================
RCS file: /home/staff/zs/imp/mercury/doc/user_guide.texi,v
retrieving revision 1.133
diff -u -t -u -r1.133 user_guide.texi
--- user_guide.texi	1998/08/10 07:17:09	1.133
+++ user_guide.texi	1998/09/09 00:33:21
@@ -2390,6 +2390,15 @@
 @samp{@var{MODULE}.split} target, i.e. type @samp{mmake foo.split}
 rather than @samp{mmake foo}.
 
+ at sp 1
+ at item --no-disable-opt-for-trace
+Enabling tracing usually disables optimizations which could
+make it difficult to relate the trace to the source code.
+ at samp{--no-disable-opt-for-trace} results in only those
+optimizations which don't work with tracing being disabled.
+This is useful for debugging the optimization passes of
+the compiler.
+
 @end table
 
 @node High-level (HLDS -> HLDS) optimization options