[m-rev.] Bugfix in solver type variable initialisation

[Ralph Becket]

Estimated hours taken: 5
Branches: main, release

Fix a bug in solver type variable initialisation reported by Peter Hawkins.

compiler/modes.m:
	When searching for a subset of solver type variables to initialise to
	allow a deterministic schedule, also take into account var/lambda
	unifications and non-solver-type non-locals in the conditions of
	if-then-else goals.

Index: compiler/modes.m
===================================================================
RCS file: /home/mercury1/repository/mercury/compiler/modes.m,v
retrieving revision 1.301
diff -u -r1.301 modes.m
--- compiler/modes.m	10 Jun 2005 06:17:20 -0000	1.301
+++ compiler/modes.m	4 Aug 2005 05:05:59 -0000
@@ -2314,6 +2314,21 @@
     !:CandidateVars = set__insert_list(!.CandidateVars, Args).
 
 candidate_init_vars_3(_ModeInfo, Goal, !NonFree, !CandidateVars) :-
+        % A var/lambda unification, which can only be deterministic
+        % if it's a construction.  The non-locals in the lambda are
+        % *not* candidates for initialisation because that could
+        % permit violations of referential transparency (executing
+        % the lambda could otherwise further constrain a solver
+        % variable that was not supplied as an argument).
+        %
+    Goal = unify(X, RHS, _, _, _) - _GoalInfo,
+    RHS  = lambda_goal(_, _, _, _, _, _, _, _, _),
+        % If this is a construction then X must be free.
+    not set__member(X, !.NonFree),
+        % But X becomes instantiated.
+    !:NonFree = set__insert(!.NonFree, X).
+
+candidate_init_vars_3(_ModeInfo, Goal, !NonFree, !CandidateVars) :-
         % Disjunctions are tricky, because we don't perform
         % switch analysis until after mode analysis.  So
         % here we assume that the disjunction is a det switch
@@ -2322,12 +2337,22 @@
     Goal = disj(_Goals) - _GoalInfo.
 
 candidate_init_vars_3(ModeInfo, Goal, !NonFree, !CandidateVars) :-
-        % We ignore the conditions of if-then-else goals,
-        % but proceed on the assumption that the then and else
-        % arms are det.  This isn't very accurate and may
+        % We ignore the condition of an if-then-else goal,
+        % other than to assume that it binds its non-solver-type
+        % non-locals, but proceed on the assumption that the then
+        % and else arms are det.  This isn't very accurate and may
         % need refinement.
         %
-    Goal = if_then_else(_LocalVars, _CondGoal, ThenGoal, ElseGoal) - _GoalInfo,
+    Goal = if_then_else(_LocalVars, CondGoal, ThenGoal, ElseGoal) - _GoalInfo,
+
+    CondGoal = _CondGoalExpr - CondGoalInfo,
+    hlds_goal__goal_info_get_nonlocals(CondGoalInfo, NonLocals),
+    mode_info_get_module_info(ModeInfo, ModuleInfo),
+    mode_info_get_var_types(ModeInfo, VarTypes),
+    NonSolverNonLocals =
+        set__filter(non_solver_var(ModuleInfo, VarTypes), NonLocals),
+    !:NonFree = set__union(NonSolverNonLocals, !.NonFree),
+
     candidate_init_vars_3(ModeInfo, ThenGoal, !.NonFree, NonFreeThen,
         !CandidateVars),
     candidate_init_vars_3(ModeInfo, ElseGoal, !.NonFree, NonFreeElse,
@@ -2382,11 +2407,19 @@
     ( DeclaredDetism = (det) ; DeclaredDetism = (cc_multidet) ),
         % Find the argument modes.
         %
-    proc_info_maybe_declared_argmodes(ProcInfo, yes(ArgModes)),
+    proc_info_argmodes(ProcInfo, ArgModes),
         % Process the call args.
         %
     candidate_init_vars_call(ModeInfo, Args, ArgModes,
         !NonFree, !CandidateVars).
+
+    % Filter pred succeeding if a variable does not have a solver type.
+    %
+:- pred non_solver_var(module_info::in, vartypes::in, prog_var::in) is semidet.
+
+non_solver_var(ModuleInfo, VarTypes, Var) :-
+    VarType = VarTypes ^ det_elem(Var),
+    not type_util__type_is_solver_type(ModuleInfo, VarType).
 
     % Update !NonFree and !CandidateVars given the args and modes for
     % a call.
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