[m-dev.] fix for simplify.m

[Simon TAYLOR]

Hi Fergus

> 
> >  	; Disjuncts0 = [SingleGoal0] ->
> >  		% a singleton disjunction is equivalent to the goal itself
> > -		simplify__goal(SingleGoal0, Goal - _, Info0, Info) 
> > +		simplify__goal(SingleGoal0, Goal - GoalInfo, Info0, Info) 
> 
> This change is not described in your log message.
> Here you are changing the goal_info used when simplifying a
> singleton disjunction; previously the outer goal_info was used,
> now the inner one is used.  Are you sure that this will not
> cause any problems?

I think it could if the determinisms are different, as with inlining
of erroneous procedures. Here's an updated diff.

Simon

Index: simplify.m
===================================================================
@@ -248,14 +246,32 @@
 		)
 	).
 
-simplify__goal_2(disj(Disjuncts0, SM), GoalInfo,
+simplify__goal_2(disj(Disjuncts0, SM), GoalInfo0,
 		Goal, GoalInfo, Info0, Info) :-
 	( Disjuncts0 = [] ->
 		Goal = disj([], SM),
+		GoalInfo = GoalInfo0,
 		Info = Info0
 	; Disjuncts0 = [SingleGoal0] ->
 		% a singleton disjunction is equivalent to the goal itself
-		simplify__goal(SingleGoal0, Goal - _, Info0, Info) 
+		simplify__goal(SingleGoal0, Goal1 - GoalInfo1, Info0, Info),
+		(
+			% If the determinisms are not the same, we really
+			% need to rerun determinism analysis on the
+			% procedure. I think this is a similar situation
+			% to inlining of erroneous goals. The safe thing
+			% to do is to disable the optimisation if the
+			% inner and outer determinisms are not the same.
+			% It probably won't happen that often.
+			goal_info_get_determinism(GoalInfo0, Det),
+			goal_info_get_determinism(GoalInfo1, Det)
+		->
+			Goal = Goal1,
+			GoalInfo = GoalInfo1
+		;
+			Goal = disj([Goal1 - GoalInfo1], SM),
+			GoalInfo = GoalInfo0
+		)
 	;
 		simplify__disj(Disjuncts0, Disjuncts, [], InstMaps,
 			Info0, Info0, Info1),