mercury/compiler/accumulator.m

%-----------------------------------------------------------------------------%
% Copyright (C) 1999 The University of Melbourne.
% This file may only be copied under the terms of the GNU General
% Public License - see the file COPYING in the Mercury distribution.
%-----------------------------------------------------------------------------%
%
% Module:	accumulator
% Main authors: petdr
%
% Attempts to transform a single proc to a tail recursive form by
% introducing accumlators.
%
% The transformation is described more fully in the paper
% "Making Mercury programs tail recursive", which will be available 
% from the Mercury web site.
%
% Basically the transformation is to locate predicates in the following
% form.  The transformation also handles if-then-elses since they can
% conceptually be treated like a switch, we just need to be a little bit
% more careful about what happens in the condition.
%
% p(X,Ys) :-
%         minimal(X),
%         base(Ys).
% p(X, Ys) :-
%         decompose(X, Xhead, Xrest),
%         process(Xhead, Hs),
%         p(Xrest, Y0s),
%         compose(Hs, Y0s, Ys).
%
% and transform them into this form
%
% p(X,Ys) :-
%         minimal(X),
%         base(Ys).
% p(X, Ys) :-
%         decompose(X, Xhead, Xrest),
%         process(Xhead, Hs),
%         p'(Xrest, Ys, Hs).
% 
% p'(X, Ys, As) :-
%         minimal(X),
%         base(Y0s),
%         compose(As, Y0s, Ys).
% p'(X, Ys, As) :-
%         decompose(X, Xhead, Xrest),
%         process(Xhead, Hs),
%         compose(As, Hs, A1s),
%         p'(Xrest, Ys, A1s).
%
% Any variable that ends with an 's' represents a set of variables.
% The constraint on the transformation is that the compose goal must
% obey the following law
%      
%	some [BC] (compose(I, B, C, BC), compose(I, A, BC, ABC))
%		<=> some [AB] (compose(I, A, B, AB), compose(I, AB, C, ABC))
%
% The above law denotes that the compose goal must be associative, or
% maybe more intuitively the compose goal can construct an answer processing
% in a right to left manner or a left to right manner.
%
% Currently the knowledge of which goals are associative is hard-wired
% into this module, at a later date we should add the ability to add
% pragmas to supply this information.
%
% Another subtlety is that making the code tail recursive doesn't
% necessarily improve the efficiency of code.  Note that the call 
% to compose in the accumulator version of the code has Hs located
% in a different position.  For append(in, in, out) it is the first
% argument which controls the complexity of append.  So if the compose
% goal was append, the complexity of the predicate as a whole will
% change.  This problem is dealt with by ensuring that only a variable
% that is a member of Hs ends up in the first position of append,
% because in general the variables in Hs are smaller then those in As.
%
% Note that the transformation will leave construction unifications
% after the recursive call if '--optimize-constructor-last-call' is
% enabled.
%
%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%

:- module accumulator.

:- interface.

:- import_module hlds_module, hlds_pred, io.

:- pred accumulator__process_proc(pred_id::in, proc_id::in, proc_info::in,
		proc_info::out, module_info::in, module_info::out,
		io__state::di, io__state::uo) is det.

%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%

:- implementation.

:- import_module goal_util, globals, hlds_data, hlds_goal, hlds_out.
:- import_module inst_match, instmap, mode_util, options, prog_data, prog_util.

:- import_module assoc_list, bool, list, map, multi_map.
:- import_module require, set, std_util, term, varset.

%-----------------------------------------------------------------------------%

:- type base_goal
	--->	base(
			hlds_goals
		).

:- type rec_goal
	--->	recursive(
			a_goals,	% Goals inside the condition of an
					% if/then/else
			a_goals,	% Decompose, Process
			a_goal,		% Recursive call
			a_goals		% Compose calls
		).

:- type split_result
	--->	recursive(
			hlds_goals,	% Decompose, Process
			hlds_goal,	% Recursive call
			hlds_goals	% Compose calls
		).

:- type a_goal  == goal(hlds_goal).
:- type a_goals == goal(hlds_goals).

:- type goal(T)
	--->	goal(
			T,		% goal/s
			instmap		% instmap at the start of the goal
		).

:- type top_level
	--->	switch_base_rec
	;	switch_rec_base
	;	disj_base_rec
	;	disj_rec_base
	;	ite_base_rec
	;	ite_rec_base.

:- type subst == map(prog_var, prog_var).

:- type assoc_info
	--->	assoc_info(
			set(prog_var),	% Static set
					% A static variable is one whose
					% value is set before the
					% recursive call.

			set(prog_var),	% Dynamic set
					% The dynamic set is initialised
					% to Y0s.  At the end of the
					% process it will contain all
					% the variables that are
					% constructed using another
					% dynamic variable.
			module_info,
			prev_call_map,
			orig_dynvar_map,
			subst,		% Y0s -> As
			subst,		% Hs -> As
			set(prog_var)	% Ys
		).

	% is the pred commutative?
:- type commutative == bool.

:- type prev_call
	--->	prev_call(
			pred_id,
			proc_id,
			commutative
		).

	% If a variable is constructed from a chain of calls, what are
	% the details of the previous call in the chain.
:- type prev_call_map == map(prog_var, prev_call).
	
	% Given a dynamic variable, from which dynamic variable was it
	% descended (ie which variable in Y0s).
	%
	% For the following call
	%
	% append(R0, ListH, R)
	%
	% The variable ListH is static and R0 is dynamic, therefore R is
	% descended from R0.
	%
:- type orig_dynvar_map == map(prog_var, prog_var).

%-----------------------------------------------------------------------------%


	%
	% accumulator__process_proc
	%
	% Attempt to transform one procedure into a accumulator
	% recursive form.
	%
accumulator__process_proc(PredId, ProcId, ProcInfo0, ProcInfo, 
		ModuleInfo0, ModuleInfo) -->
	globals__io_lookup_bool_option(optimize_constructor_last_call, DoLCO),
	globals__io_lookup_bool_option(fully_strict, FullyStrict),
	(
		{ module_info_pred_info(ModuleInfo0, PredId, PredInfo) },
		{ accumulator__attempt_transform(ProcId, ProcInfo0, PredId,
				PredInfo, DoLCO, FullyStrict, ModuleInfo0,
				ProcInfo1, ModuleInfo1) }
	->
		globals__io_lookup_bool_option(very_verbose, VeryVerbose),
		( 
			{ VeryVerbose = yes }
		->
			io__write_string("% Accumulators introduced into "),
			hlds_out__write_pred_id(ModuleInfo1, PredId),
			io__write_string("\n")
		;
			[]
		),

		{ ProcInfo   = ProcInfo1 },
		{ ModuleInfo = ModuleInfo1 }
	;
		{ ProcInfo   = ProcInfo0 },
		{ ModuleInfo = ModuleInfo0 }
	).

	%
	% accumulator__attempt_transform is only true if the current
	% proc has been transformed to call the newly created
	% accumulator proc.
	%
:- pred accumulator__attempt_transform(proc_id::in, proc_info::in,
		pred_id::in, pred_info::in, bool::in, bool::in, module_info::in,
		proc_info::out, module_info::out) is semidet.

accumulator__attempt_transform(ProcId, ProcInfo0, PredId, PredInfo0, DoLCO,
		FullyStrict, ModuleInfo0, ProcInfo, ModuleInfo) :-
	proc_info_goal(ProcInfo0, Goal0),
	proc_info_headvars(ProcInfo0, HeadVars),
	proc_info_get_initial_instmap(ProcInfo0, ModuleInfo0, InitialInstMap),

	accumulator__simplify(Goal0, Goal),
	accumulator__rearrange_goal(PredId, ProcId, Goal, InitialInstMap,
			ModuleInfo0, FullyStrict, GoalType, Base, Rec),

	accumulator__create_accumulator_pred(Rec, PredInfo0, ProcInfo0,
			HstoAs_Subst, NewPredId, NewProcId, NewPredName,
			ModuleInfo0, ModuleInfo1),

	accumulator__transform(GoalType, Base, Rec, Goal, DoLCO, FullyStrict,
			ModuleInfo1, HeadVars, HstoAs_Subst, NewPredId,
			NewProcId, NewPredName, OrigGoal, AccGoal),

	accumulator__update_accumulator_pred(NewPredId, NewProcId, AccGoal,
			ModuleInfo1, ModuleInfo),

	proc_info_set_goal(ProcInfo0, OrigGoal, ProcInfo).

%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%

	%
	% accumulator__simplify
	%
	% Simplify the goal to make it more amenable to introducing
	% accumulators.
	%
	% At the moment all this does is remove any extra disj/conj
	% wrappers around the top level goal.
	%
	% Future work is for this code to rearrange code with multiple
	% base and recursive cases into a single base and recursive
	% case.
	%
:- pred accumulator__simplify(hlds_goal, hlds_goal).
:- mode accumulator__simplify(in, out) is det.

accumulator__simplify(Goal0, Goal) :-
	(
		(
			Goal0 = conj([Goal1]) - _
		;
			Goal0 = disj([Goal1], _) - _
		)
	->
		accumulator__simplify(Goal1, Goal)
	;
		Goal = Goal0
	).


%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%

	%
	% This predicate is meant to take the original goal and
	% rearrange it into a standard form that can be used in the rest
	% of module.
	%
:- pred accumulator__rearrange_goal(pred_id::in, proc_id::in,
		hlds_goal::in, instmap::in, module_info::in, bool::in,
		top_level::out, base_goal::out, rec_goal::out) is semidet.

accumulator__rearrange_goal(PredId, ProcId, Goal, InitialInstMap, ModuleInfo,
		FullyStrict, Type, Base, Rec) :-
	(
		Goal = switch(_Var, _CanFail, Cases, _StoreMap) - _GoalInfo,
		Cases = [case(_IdA, GoalA), case(_IdB, GoalB)],
		goal_to_conj_list(GoalA, GoalAList),
		goal_to_conj_list(GoalB, GoalBList)
	->
		(
			accumulator__split_recursive_case(PredId, ProcId,
					InitialInstMap, [],
					InitialInstMap, ModuleInfo, FullyStrict,
					GoalAList, Rec0),

				% Make sure that the base case doesn't
				% contain a recursive call.
			\+ accumulator__split_recursive_case(PredId, ProcId,
					InitialInstMap, [],
					InitialInstMap, ModuleInfo, FullyStrict,
					GoalBList, _)
		->
			Type = switch_rec_base,
			Base = base(GoalBList),
			Rec = Rec0
		;
			accumulator__split_recursive_case(PredId, ProcId,
					InitialInstMap, [],
					InitialInstMap, ModuleInfo, FullyStrict,
					GoalBList, Rec0),

				% Make sure that the base case doesn't
				% contain a recursive call.
			\+ accumulator__split_recursive_case(PredId, ProcId,
					InitialInstMap, [],
					InitialInstMap, ModuleInfo, FullyStrict,
					GoalAList, _)
		->
			Type = switch_base_rec,
			Base = base(GoalAList),
			Rec = Rec0
		;
			fail
		)
	;
		Goal = disj(Goals, _SM) - _GoalInfo,
		Goals = [GoalA, GoalB],
		goal_to_conj_list(GoalA, GoalAList),
		goal_to_conj_list(GoalB, GoalBList)
	->
		(
			accumulator__split_recursive_case(PredId, ProcId,
					InitialInstMap, [],
					InitialInstMap, ModuleInfo, FullyStrict,
					GoalAList, Rec0),

				% Make sure that the base case doesn't
				% contain a recursive call.
			\+ accumulator__split_recursive_case(PredId, ProcId,
					InitialInstMap, [],
					InitialInstMap, ModuleInfo, FullyStrict,
					GoalBList, _)
		->
			Type = disj_rec_base,
			Base = base(GoalBList),
			Rec = Rec0
		;
			accumulator__split_recursive_case(PredId, ProcId,
					InitialInstMap, [],
					InitialInstMap, ModuleInfo, FullyStrict,
					GoalBList, Rec0),

				% Make sure that the base case doesn't
				% contain a recursive call.
			\+ accumulator__split_recursive_case(PredId, ProcId,
					InitialInstMap, [],
					InitialInstMap, ModuleInfo, FullyStrict,
					GoalAList, _)
		->
			Type = disj_base_rec,
			Base = base(GoalAList),
			Rec = Rec0
		;
			fail
		)
	;
		Goal = if_then_else(_Vars, If, Then, Else, _SM) - _GoalInfo,

		If = _ - IfGoalInfo,
		goal_info_get_instmap_delta(IfGoalInfo, IMDelta),
		instmap__apply_instmap_delta(InitialInstMap, IMDelta,
				BeforeThenInstMap),

		goal_to_conj_list(If, IfList),
		goal_to_conj_list(Then, ThenList),
		goal_to_conj_list(Else, ElseList)
	->
		(
			accumulator__split_recursive_case(PredId, ProcId,
					InitialInstMap, IfList,
					BeforeThenInstMap, ModuleInfo,
					FullyStrict, ThenList, Rec0),

				% Make sure that the base case doesn't
				% contain a recursive call.
			\+ accumulator__split_recursive_case(PredId, ProcId,
					InitialInstMap, [],
					InitialInstMap, ModuleInfo, FullyStrict,
					ElseList, _)
		->
			Type = ite_rec_base,
			Base = base(ElseList),
			Rec = Rec0
		;
			accumulator__split_recursive_case(PredId, ProcId,
					InitialInstMap, [],
					InitialInstMap, ModuleInfo, FullyStrict,
					ElseList, Rec0),

				% Make sure that the base case doesn't
				% contain a recursive call.
			\+ accumulator__split_recursive_case(PredId, ProcId,
					InitialInstMap, [],
					InitialInstMap, ModuleInfo, FullyStrict,
					ThenList, _)
		->
			Type = ite_base_rec,
			Base = base(ThenList),
			Rec = Rec0
		;
			fail
		)
		
	;
		fail
	).

%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%

	%
	% accumulator__create_accumulator_pred
	%
	% Create a new predicate which is an accumulator version of the
	% current proc being looked at.
	%
:- pred accumulator__create_accumulator_pred(rec_goal::in, pred_info::in,
		proc_info::in, subst::out, pred_id::out, proc_id::out,
		sym_name::out, module_info::in, module_info::out) is det.

accumulator__create_accumulator_pred(RecGoal, PredInfo, ProcInfo, HstoAs_Subst,
		NewPredId, NewProcId, NewPredName, ModuleInfo0, ModuleInfo) :-

	proc_info_get_initial_instmap(ProcInfo, ModuleInfo0, InstMap0),

	accumulator__acc_proc_info(RecGoal, InstMap0, ProcInfo, HstoAs_Subst,
			NewTypes, NewProcInfo),
	accumulator__acc_pred_info(NewTypes, NewProcInfo, PredInfo, NewProcId,
			NewPredInfo),

	pred_info_name(NewPredInfo, NewPredName0),
	NewPredName = unqualified(NewPredName0),

	module_info_get_predicate_table(ModuleInfo0, PredTable0),
	predicate_table_insert(PredTable0, NewPredInfo, NewPredId, PredTable),
	module_info_set_predicate_table(ModuleInfo0, PredTable, ModuleInfo).


	%
	% accumulator__acc_proc_info
	%
	% Construct a proc_info for the introduced predicate, it also
	% creates the substitutions that maps between each variable that
	% is a member of Hs and those in As.
	%
:- pred accumulator__acc_proc_info(rec_goal::in, instmap::in, proc_info::in,
		subst::out, list(type)::out, proc_info::out) is det.

accumulator__acc_proc_info(recursive(PreDP, DP, _R, C), InstMap0,
		ProcInfo, HstoAs_Subst, NewTypes, NewProcInfo) :-

		% ProcInfo Stuff that must change.
	proc_info_varset(ProcInfo, VarSet0),
	proc_info_vartypes(ProcInfo, VarTypes0),
	proc_info_headvars(ProcInfo, HeadVars0),
	proc_info_argmodes(ProcInfo, HeadModes0),

	proc_info_inferred_determinism(ProcInfo, Detism),
	proc_info_goal(ProcInfo, Goal),
	proc_info_context(ProcInfo, Context),
	proc_info_typeinfo_varmap(ProcInfo, TVarMap),
	proc_info_typeclass_info_varmap(ProcInfo, TCVarsMap),
	proc_info_is_address_taken(ProcInfo, IsAddressTaken),

	accumulator__extra_vars_for_recursive_call(PreDP, DP, C, Vars),

	DP = goal(DPGoals, _DPInstMap),
	goal_list_instmap_delta(DPGoals, InstMapDelta),
	instmap__apply_instmap_delta(InstMap0, InstMapDelta, InstMap),

	accumulator__new_acc_var(Vars, InstMap, VarSet0, VarTypes0,
			HstoAs_Subst, NewHeadVars, VarSet,
			VarTypes, NewHeadModes),

	list__append(HeadVars0, NewHeadVars, HeadVars),
	list__append(HeadModes0, NewHeadModes, HeadModes),

	list__map(map__lookup(VarTypes), NewHeadVars, NewTypes),
	
	proc_info_create(VarSet, VarTypes, HeadVars, HeadModes, Detism, Goal,
	                Context, TVarMap, TCVarsMap, IsAddressTaken,
			NewProcInfo).

	%
	% accumulator__new_acc_var(Hs, IM, VS0, VT0, HstoAs0, HstoAs,
	% 		As, VS, VT, Ms)
	%
	% For each variable, Hs, that needs to be accumulated create a
	% corresponding variable in As updating the varset, VS, var-type
	% mapping, VT, and recording the mode in Ms.  Also record the
	% mapping from each H to A in HstoAs.
	%
:- pred accumulator__new_acc_var(prog_vars::in, instmap::in,
		prog_varset::in, map(prog_var, type)::in,
		map(prog_var, prog_var)::out, prog_vars::out, prog_varset::out,
		map(prog_var, type)::out, list(mode)::out) is det.

accumulator__new_acc_var([], _InstMap, VarSet, VarTypes,
		Subst, [], VarSet, VarTypes, []) :-
	map__init(Subst).
accumulator__new_acc_var([Var | Vars], InstMap, VarSet0, VarTypes0,
		Subst, HeadVars, VarSet, VarTypes, Modes) :-
	accumulator__new_acc_var(Vars, InstMap, VarSet0, VarTypes0,
			Subst0, HeadVars0, VarSet1, VarTypes1, Modes0),

	varset__new_var(VarSet1, NewVar, VarSet),

	map__det_insert(Subst0, Var, NewVar, Subst),

	HeadVars = [NewVar | HeadVars0],

	map__lookup(VarTypes0, Var, Type),
	map__det_insert(VarTypes1, NewVar, Type, VarTypes),

	instmap__lookup_var(InstMap, Var, Inst),
	inst_lists_to_mode_list([Inst], [Inst], Mode),
	list__append(Mode, Modes0, Modes).

	%
	% accumulator__acc_pred_info
	%
	% Construct the pred_info for the introduced predicate
	%
:- pred accumulator__acc_pred_info(list(type)::in, proc_info::in, pred_info::in,
		proc_id::out, pred_info::out) is det.

accumulator__acc_pred_info(NewTypes, NewProcInfo, PredInfo,
		NewProcId, NewPredInfo) :-
		
		% PredInfo stuff that must change.
	pred_info_arg_types(PredInfo, TypeVarSet, ExistQVars, Types0),

	pred_info_module(PredInfo, ModuleName),
	pred_info_name(PredInfo, Name),
	Cond = true,
	pred_info_context(PredInfo, PredContext),
	pred_info_get_markers(PredInfo, Markers),
	pred_info_get_is_pred_or_func(PredInfo, PredOrFunc),
	pred_info_get_class_context(PredInfo, ClassContext),
	pred_info_get_aditi_owner(PredInfo, Owner),

	set__init(Assertions),

	proc_info_context(NewProcInfo, Context),
	term__context_line(Context, Line),
	Counter = 0,

	list__append(Types0, NewTypes, Types),

	make_pred_name_with_context(ModuleName, "AccFrom", PredOrFunc, Name,
		Line, Counter, SymName),

	pred_info_create(ModuleName, SymName, TypeVarSet, ExistQVars, Types,
			Cond, PredContext, local, Markers, PredOrFunc,
			ClassContext, Owner, Assertions, NewProcInfo, NewProcId,
			NewPredInfo).

%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%

	%
	% accumulator__transform
	%
	% Actually do the transformation.  This predicate may fail if
	% for some reason the transformation cannot be completed.
	%
:- pred accumulator__transform(top_level::in, base_goal::in, rec_goal::in,
		hlds_goal::in, bool::in, bool::in, module_info::in,
		prog_vars::in, subst::in, pred_id::in,
		proc_id::in, sym_name::in,
		hlds_goal::out, hlds_goal::out) is semidet.

accumulator__transform(TopLevel, base(BaseGoalList), recursive(PreDP, DP, R, C),
		Goal, DoLCO, FullyStrict, ModuleInfo, HeadVars, HstoAs_Subst,
		NewPredId, NewProcId, NewPredName, OrigGoal, NewGoal) :-

	accumulator__Ys_descended_from_Y0s(HeadVars, DP, ModuleInfo),

	accumulator__orig_base_case(BaseGoalList, OrigBaseGoal),

	accumulator__extra_vars_for_recursive_call(PreDP, DP, C, Vars),
	accumulator__orig_recursive_case(DP, R, HeadVars, NewPredId, NewProcId,
			NewPredName, Vars, Y0stoYs_Subst, OrigRecGoal),

	accumulator__new_base_case(BaseGoalList, C,
			Y0stoYs_Subst, HstoAs_Subst, NewBaseGoal),
	accumulator__new_recursive_case(DP, C, R, DoLCO, FullyStrict,
			ModuleInfo, NewPredId, NewProcId, NewPredName,
			Vars, HeadVars,
			Y0stoYs_Subst, HstoAs_Subst, NewRecGoal),

	accumulator__top_level(TopLevel, Goal, OrigBaseGoal, OrigRecGoal,
			NewBaseGoal, NewRecGoal, OrigGoal, NewGoal).


:- pred accumulator__top_level(top_level::in, hlds_goal::in,
		hlds_goal::in, hlds_goal::in, hlds_goal::in,
		hlds_goal::in, hlds_goal::out, hlds_goal::out) is det.

accumulator__top_level(switch_base_rec, Goal, OrigBaseGoal, OrigRecGoal,
		NewBaseGoal, NewRecGoal, OrigGoal, NewGoal) :-
	(
		Goal = switch(Var, CanFail, Cases0, StoreMap) - GoalInfo,
		Cases0 = [case(IdA, _), case(IdB, _)]
	->
		OrigCases = [case(IdA, OrigBaseGoal), case(IdB, OrigRecGoal)],
		OrigGoal = switch(Var, CanFail, OrigCases, StoreMap) - GoalInfo,

		NewCases = [case(IdA, NewBaseGoal), case(IdB, NewRecGoal)],
		NewGoal = switch(Var, CanFail, NewCases, StoreMap) - GoalInfo
	;
		error("accumulator__top_level: not the correct top level")
	).
accumulator__top_level(switch_rec_base, Goal, OrigBaseGoal, OrigRecGoal,
		NewBaseGoal, NewRecGoal, OrigGoal, NewGoal) :-
	(
		Goal = switch(Var, CanFail, Cases0, StoreMap) - GoalInfo,
		Cases0 = [case(IdA, _), case(IdB, _)]
	->
		OrigCases = [case(IdA, OrigRecGoal), case(IdB, OrigBaseGoal)],
		OrigGoal = switch(Var, CanFail, OrigCases, StoreMap) - GoalInfo,

		NewCases = [case(IdA, NewRecGoal), case(IdB, NewBaseGoal)],
		NewGoal = switch(Var, CanFail, NewCases, StoreMap) - GoalInfo
	;
		error("accumulator__top_level: not the correct top level")
	).
accumulator__top_level(disj_base_rec, Goal, OrigBaseGoal,
		OrigRecGoal, NewBaseGoal, NewRecGoal, OrigGoal, NewGoal) :-
	(
		Goal = disj(Goals, StoreMap) - GoalInfo,
		Goals = [_, _]
	->
		OrigGoals = [OrigBaseGoal, OrigRecGoal],
		OrigGoal = disj(OrigGoals, StoreMap) - GoalInfo,

		NewGoals = [NewBaseGoal, NewRecGoal],
		NewGoal = disj(NewGoals, StoreMap) - GoalInfo
	;
		error("accumulator__top_level: not the correct top level")
	).
accumulator__top_level(disj_rec_base, Goal, OrigBaseGoal,
		OrigRecGoal, NewBaseGoal, NewRecGoal, OrigGoal, NewGoal) :-
	(
		Goal = disj(Goals, StoreMap) - GoalInfo,
		Goals = [_, _]
	->
		OrigGoals = [OrigRecGoal, OrigBaseGoal],
		OrigGoal = disj(OrigGoals, StoreMap) - GoalInfo,

		NewGoals = [NewRecGoal, NewBaseGoal],
		NewGoal = disj(NewGoals, StoreMap) - GoalInfo
	;
		error("accumulator__top_level: not the correct top level")
	).
accumulator__top_level(ite_base_rec, Goal, OrigBaseGoal,
		OrigRecGoal, NewBaseGoal, NewRecGoal, OrigGoal, NewGoal) :-
	(
		Goal = if_then_else(Vars, If, _, _, StoreMap) - GoalInfo
	->
		OrigGoal = if_then_else(Vars, If,
				OrigBaseGoal, OrigRecGoal, StoreMap) - GoalInfo,

		NewGoal = if_then_else(Vars, If,
				NewBaseGoal, NewRecGoal, StoreMap) - GoalInfo
	;
		error("accumulator__top_level: not the correct top level")
	).
accumulator__top_level(ite_rec_base, Goal, OrigBaseGoal,
		OrigRecGoal, NewBaseGoal, NewRecGoal, OrigGoal, NewGoal) :-
	(
		Goal = if_then_else(Vars, If, _, _, StoreMap) - GoalInfo
	->
		OrigGoal = if_then_else(Vars, If,
				OrigRecGoal, OrigBaseGoal, StoreMap) - GoalInfo,

		NewGoal = if_then_else(Vars, If,
				NewRecGoal, NewBaseGoal, StoreMap) - GoalInfo
	;
		error("accumulator__top_level: not the correct top level")
	).

%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%

	%
	% accumulator__update_accumulator_pred
	%
	% Place the accumulator version of the predicate in the
	% module_info structure.
	%
:- pred accumulator__update_accumulator_pred(pred_id::in, proc_id::in,
		hlds_goal::in, module_info::in, module_info::out) is det.

accumulator__update_accumulator_pred(NewPredId, NewProcId, AccGoal,
		ModuleInfo0, ModuleInfo) :-
	module_info_pred_proc_info(ModuleInfo0, NewPredId, NewProcId,
			PredInfo, ProcInfo0),
	proc_info_set_goal(ProcInfo0, AccGoal, ProcInfo),
	module_info_set_pred_proc_info(ModuleInfo0, NewPredId, NewProcId,
			PredInfo, ProcInfo, ModuleInfo).

%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%

	%
	% accumulator__split_recursive_case(PredId, ProcId, IM0, MI, FS, Gs, R)
	%
	% Split the goals, Gs, which make up the recursive case into the
	% decompose and process list of goals, the compose goals and the 
	% recursive goal and place the components in the rec_goal
	% structure, R.
	%
:- pred accumulator__split_recursive_case(pred_id::in, proc_id::in,
		instmap::in, hlds_goals::in,
		instmap::in, module_info::in, bool::in,
		hlds_goals::in, rec_goal::out) is semidet.

accumulator__split_recursive_case(PredId, ProcId,
		PreInstMap, PreGoals,
		InitialInstMap, ModuleInfo, FullyStrict, Goals, RecGoal) :-
	solutions(accumulator__split_goals(Goals, PredId, ProcId), Solns),
	Solns = [recursive(DP0, R, C0)],
	calculate_instmap(DP0, InitialInstMap, InitialInstMapBeforeR),

		% Any goal which doesn't depend on the recursive call is
		% moved before the recursive call, because this means
		% that only goals which contain dynamic variables are
		% left after the recursive call, simplifying the latter
		% stages.
	move_goals(R, InitialInstMapBeforeR, ModuleInfo, FullyStrict,
			C0, PreC0, PostC0),
	list__append(DP0, PreC0, DP),
	C = PostC0,

	calculate_instmap(DP, InitialInstMap, InstMapBeforeR),
	calculate_instmap([R], InstMapBeforeR, InstMapBeforeC),

	Pre		 = goal(PreGoals, PreInstMap),
	DecomposeProcess = goal(DP, InitialInstMap),
	Recursive 	 = goal(R, InstMapBeforeR),
	Compose 	 = goal(C, InstMapBeforeC),

	RecGoal = recursive(Pre, DecomposeProcess, Recursive, Compose).

:- pred accumulator__split_goals(hlds_goals::in, pred_id::in, proc_id::in,
		split_result::out) is nondet.

accumulator__split_goals(Goals, PredId, ProcId, RecGoal) :-
	list__append(DecomposeProcess, [RecursiveCall | Compose], Goals),
	RecursiveCall = call(PredId, ProcId, _, _, _, _) - _,

		% An empty compose means the predicate is already tail
		% recursive.
	Compose \= [],
	RecGoal = recursive(DecomposeProcess, RecursiveCall, Compose).


	%
	% Given a list of goals and an instmap before the list of goals,
	% work out what the instmap at the end of the goals is.
	%
:- pred calculate_instmap(hlds_goals::in, instmap::in, instmap::out) is det.

calculate_instmap(Goals, InstMap0, InstMap) :-
	goal_list_instmap_delta(Goals, InstMapDelta),
	instmap__apply_instmap_delta(InstMap0, InstMapDelta, InstMap).


%-----------------------------------------------------------------------------%

	%
	% move_goals(G, IM, MI, FS, Gs, BGs, AGs)
	%
	% Seperate the list of Goals, Gs, into the goals, BGs, that can be
	% placed before the goal, G, and the goals, AGs, which must be
	% placed after the goal, G.  IM is the instmap before the goal
	% G.
	%
	% XXX This should be able to be transformed to accumulator
	% recursive form, much harder to do though.  Look into this
	% later. NB you need LCO for the else case.
	%
:- pred move_goals(hlds_goal::in, instmap::in, module_info::in, bool::in,
		hlds_goals::in, hlds_goals::out, hlds_goals::out) is det.

move_goals(_StartGoal, _IMBeforeStartGoal, _MI, _FullyStrict, [], [], []).
move_goals(StartGoal, InstMapBeforeStartGoal, ModuleInfo, FullyStrict,
		[Goal|Goals], PreGoals, PostGoals) :-

	StartGoal = _GoalExpr - GoalInfo,
	goal_info_get_instmap_delta(GoalInfo, InstMapDelta),
	instmap__apply_instmap_delta(InstMapBeforeStartGoal,
			InstMapDelta, InstMapBeforeGoal),
	(
		goal_util__can_reorder_goals(ModuleInfo, FullyStrict,
				InstMapBeforeStartGoal, StartGoal,
				InstMapBeforeGoal, Goal)
	->
		move_goals(StartGoal, InstMapBeforeStartGoal, ModuleInfo,
				FullyStrict, Goals, PreGoals0, PostGoals),
		PreGoals = [Goal | PreGoals0]
	;
		move_goals(Goal, InstMapBeforeGoal, ModuleInfo, FullyStrict,
				Goals, PreGoalsForGoal, PostGoalsForGoal),
		move_goals(StartGoal, InstMapBeforeStartGoal,
				ModuleInfo, FullyStrict, PreGoalsForGoal,
				PreGoals, PostGoalsForStartGoal),
		
		list__append(PostGoalsForStartGoal, [Goal | PostGoalsForGoal],
				PostGoals)
	).


%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%

	%
	% accumulator__Ys_descended_from_Y0s(HV, DP)
	%
	% If any head variable is calculated in the decompose/process,
	% DP, list of goals then it cannot be descended from the Y0s.
	%
:- pred accumulator__Ys_descended_from_Y0s(prog_vars::in,
		a_goals::in, module_info::in) is semidet.

accumulator__Ys_descended_from_Y0s(HeadVars, DecomposeProcess, ModuleInfo) :-
	accumulator__vars_to_accumulate(HeadVars, DecomposeProcess,
			ModuleInfo, ChangedHeadVars),

	ChangedHeadVars = [].

%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%

	%
	% accumulator__vars_to_accumulate(HV, C, VA)
	%
	% Given the list of goals, C, which represent the compose
	% goal and the list of the head variables, HV, determine the
	% head variables that will need to be accumulated, VA.
	%
	% The variables that will need to be accumulated are simply
	% those whose instantiatedness change in the compose goals and
	% that are headvars.
	%
:- pred accumulator__vars_to_accumulate(prog_vars::in, a_goals::in,
		module_info::in, prog_vars::out) is det.

accumulator__vars_to_accumulate(HeadVars, C, ModuleInfo, VarsToAccumulate) :-
	C = goal(ComposeGoals, InstMapBeforeCompose),
		
	goal_list_instmap_delta(ComposeGoals, InstMapDelta),
	instmap__apply_instmap_delta(InstMapBeforeCompose,
			InstMapDelta,InstMapAfterCompose),

	instmap_changed_vars(InstMapBeforeCompose,
			InstMapAfterCompose, ModuleInfo, ChangedVars),

	Member = (pred(M::in) is semidet :- set__member(M, ChangedVars)),
	list__filter(Member, HeadVars, VarsToAccumulate).

%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%

	%
	% accumulator__extra_vars_for_recursive_call(DP, C, Hs)
	%
	% If the decompose/process list of goals, DP, produce a value
	% that is needed in the compose list of goals, C, then that
	% value will need to be passed via the introduced recursive
	% call.  This predicate identifies these variables, Hs.
	%
:- pred accumulator__extra_vars_for_recursive_call(a_goals::in, a_goals::in,
		a_goals::in, prog_vars::out) is det.

accumulator__extra_vars_for_recursive_call(
		goal(PreDecomposeProcess, _InstMapBeforePreDecomposeProcess),
		goal(DecomposeProcess, _InstMapBeforeDecomposeProcess),
		goal(Compose, _InstMapBeforeCompose), Vars) :-

	goal_list_nonlocals(PreDecomposeProcess, PreDPNonLocalsSet),
	goal_list_nonlocals(DecomposeProcess, DPNonLocalsSet),
	set__union(PreDPNonLocalsSet, DPNonLocalsSet, NonLocals),

	goal_list_nonlocals(Compose, CNonLocalsSet),

	set__intersect(NonLocals, CNonLocalsSet, VarsSet),
	set__to_sorted_list(VarsSet, Vars).

%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%

	%
	% accumulator__static_vars_in_recursive_call
	%
	% Identify the variables which are static and only appear in the
	% recursive call.
	%
	% This predicate is currently unused.
	%
:- pred accumulator__static_vars_in_recursive_call(a_goal::in,
		a_goals::in, module_info::in, prog_vars::out) is det.

accumulator__static_vars_in_recursive_call(Recursive, Compose,
		ModuleInfo, Vars) :-

	Recursive = goal(_RecGoalExpr - RecGoalInfo, InstMapBeforeRec),
	Compose = goal(ComposeGoals, _InstMapBeforeCompose),

	goal_info_get_instmap_delta(RecGoalInfo, RecInstMapDelta),
	goal_info_get_nonlocals(RecGoalInfo, RecNonLocals),
	instmap__apply_instmap_delta(InstMapBeforeRec, RecInstMapDelta,
			InstMapAfterRec),
	instmap_changed_vars(InstMapBeforeRec, InstMapAfterRec,
			ModuleInfo, ChangedVars),

	set__difference(RecNonLocals, ChangedVars, PossibleStaticVars),

	goal_list_nonlocals(ComposeGoals, CNonLocalsSet),

	set__intersect(CNonLocalsSet, PossibleStaticVars, VarsSet),
	set__to_sorted_list(VarsSet, Vars).

%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%

	%
	% accumulator__orig_base_case
	%
	% Determine the base case of the original goal.
	%
:- pred accumulator__orig_base_case(hlds_goals::in, hlds_goal::out) is det.

accumulator__orig_base_case(BaseGoalList, BaseGoal) :-
		
		% Note the the goal_info constructed should be identical
		% to the original goal_info.  It is just that it is no
		% longer easily accessible.
	calculate_goal_info(conj(BaseGoalList), BaseGoal).

%-----------------------------------------------------------------------------%

	%
	% accumulator__orig_recursive_case
	%
	% Work out a new recursive case for the original predicate
	% which replaces the recursive call with a call to the new
	% accumulator predicate.
	%
:- pred accumulator__orig_recursive_case(a_goals::in, a_goal::in,
		prog_vars::in, pred_id::in, proc_id::in, sym_name::in,
		prog_vars::in, subst::out, hlds_goal::out) is det.

accumulator__orig_recursive_case(DP, R0, HeadVars, PredId, ProcId, Name,
		ExtraVars, Y0stoYs_Subst, Goal) :-
	DP = goal(DecomposeProcess, _InstMapBeforeDecomposeProcess),
	R0 = goal(Recursive, _InstMapBeforeRecursive),
	(
		Recursive = GoalExpr0 - GoalInfo,
		GoalExpr0 = call(_, _, Vars, Builtin, Context, _)
	->
			% Calculate what vars the new call should use.
		goal_list_nonlocals(DecomposeProcess, NonLocals),
		assoc_list__from_corresponding_lists(HeadVars, Vars, Pairs),
		list__map(accumulator__which_var(NonLocals), Pairs, CallVars0),
		list__append(CallVars0, ExtraVars, CallVars),
		GoalExpr = call(PredId, ProcId, CallVars,
				Builtin, Context, Name),

			% Rename the variables in the goal.
		map__init(Subst0),
		map__det_insert_from_corresponding_lists(Subst0, Vars,
				CallVars0, Y0stoYs_Subst),
		goal_util__rename_vars_in_goal(GoalExpr - GoalInfo,
				Y0stoYs_Subst, R),
				

		list__append(DecomposeProcess, [R], GoalList),
		calculate_goal_info(conj(GoalList), Goal)
	;
		error("accumulator__orig_recursive_case: Not a call.")
	).


	%
	% If a var is a member of the nonlocal set of variables then it
	% must be that variable we are to use in the call, otherwise we
	% use the corresponding head variable.
	%
:- pred accumulator__which_var(set(prog_var)::in,
		pair(prog_var, prog_var)::in, prog_var::out) is det.

accumulator__which_var(NonLocals, HeadVar - CallVar, Var) :-
	(
		set__member(CallVar, NonLocals)
	->
		Var = CallVar
	;
		Var = HeadVar
	).


%-----------------------------------------------------------------------------%

	%
	% accumulator__new_base_case
	%
	% Determine the base case of the introduced predicate.
	%
:- pred accumulator__new_base_case(hlds_goals::in, a_goals::in,
		subst::in, subst::in, hlds_goal::out) is det.

accumulator__new_base_case(Base, C, Y0stoYs_Subst, HstoAs_Subst, Goal) :-
	C = goal(Compose, _InstMapBeforeCompose),

	reverse_subst(Y0stoYs_Subst, YstoY0s_Subst0),

	goal_list_nonlocals(Compose, NonLocals),
	map__select(YstoY0s_Subst0, NonLocals, YstoY0s_Subst),

	goal_util__rename_vars_in_goals(Base, no, YstoY0s_Subst, NewBase),
	goal_util__rename_vars_in_goals(Compose, no, HstoAs_Subst, NewCompose),

	list__append(NewBase, NewCompose, GoalList),
	calculate_goal_info(conj(GoalList), Goal).

%-----------------------------------------------------------------------------%

	%
	% accumulator__new_recursive_case
	%
	% Determine the recursive case of the introduced predicate.
	%
:- pred accumulator__new_recursive_case(a_goals::in, a_goals::in,
		a_goal::in, bool::in, bool::in,
		module_info::in, pred_id::in, proc_id::in,
		sym_name::in, prog_vars::in, prog_vars::in, subst::in,
		subst::in, hlds_goal::out) is semidet.

accumulator__new_recursive_case(DP, C, R0, DoLCO, FullyStrict,
		ModuleInfo, PredId, ProcId, Name, Hs, HeadVars,
		Y0stoYs_Subst, HstoAs_Subst, Goal) :-
	DP = goal(DecomposeProcess, _InstMapBeforeDecomposeProcess),
	C  = goal(Compose, InstMapBeforeCompose),
	R0 = goal(Recursive0, _InstMapBeforeRecursive0),

	assoc_info_init(ModuleInfo, HeadVars, DP, C, R0,
		Y0stoYs_Subst, HstoAs_Subst, AssocInfo0),
	accumulator__check_assoc(Compose, InstMapBeforeCompose, ModuleInfo,
			FullyStrict, PreRecGoal0, PostRecGoal0,
			AssocInfo0, AssocInfo),

	(
		DoLCO = yes,

			% If there are no goals that can be moved before
			% the recursive call, then there is nothing to
			% accumulate so fail.
		PreRecGoal0 \= [],

		map__init(LCO_Subst0),
		assoc_info_dynamic_set(DynamicSet, AssocInfo, _),
		accumulator__check_post_rec_goals(PostRecGoal0, DynamicSet,
				LCO_Subst0, LCO_Subst)
	;
		DoLCO = no,
		map__init(LCO_Subst),
		PostRecGoal0 = []
	),

	assoc_info_Y0stoAs(Y0stoAs_Subst, AssocInfo, _),

	accumulator__rename_prerec_goals(PreRecGoal0, Y0stoAs_Subst,
			Y0stoYs_Subst, LCO_Subst, HstoAs_Subst, PreRecGoal),

	accumulator__rename_recursive_goal(Recursive0, Hs, PredId, ProcId,
			Name, HstoAs_Subst, Y0stoAs_Subst,
			Y0stoYs_Subst, LCO_Subst, Recursive),

	accumulator__rename_postrec_goals(PostRecGoal0, HstoAs_Subst,
			PostRecGoal),

	list__append(PreRecGoal, [Recursive | PostRecGoal], GoalList0),
	list__append(DecomposeProcess, GoalList0, GoalList),
	calculate_goal_info(conj(GoalList), Goal).

%-----------------------------------------------------------------------------%


	%
	% accumulator__check_post_rec_goals
	%
	% Ensure that each goal which is to be placed after the
	% recursive goal is a construction unification.
	%
	% Also create a substition which records from which dynamic var
	% each headvar is descended.
	%
:- pred accumulator__check_post_rec_goals(hlds_goals::in, set(prog_var)::in,
		subst::in, subst::out) is semidet.

accumulator__check_post_rec_goals([], _DynamicSet, Subst, Subst).
accumulator__check_post_rec_goals([Goal | Goals], DynamicSet, Subst0, Subst) :-
	Goal = unify(_TermL, _TermR, _Mode, Unify, _Context) - _GoalInfo,
	Unify = construct(Var, _ConsId, Vars, _Modes, _, _, _),
	set__list_to_set(Vars, VarsSet),
	set__intersect(VarsSet, DynamicSet, DynamicVarsSet),
	set__singleton_set(DynamicVarsSet, DynamicVar),
	(
		map__search(Subst0, DynamicVar, DescendedFrom)
	->
		map__delete(Subst0, DynamicVar, Subst1),
		map__insert(Subst1, Var, DescendedFrom, Subst2)
	;
		map__insert(Subst0, Var, DynamicVar, Subst2)
	),
	accumulator__check_post_rec_goals(Goals, DynamicSet, Subst2, Subst).
	

%-----------------------------------------------------------------------------%

:- pred accumulator__rename_prerec_goals(hlds_goals::in, subst::in,
		subst::in, subst::in, subst::in, hlds_goals::out) is det.

accumulator__rename_prerec_goals(Goal0, Y0stoAs_Subst, Y0stoYs_Subst,
		LCO_Subst, HstoAs_Subst0, Goal) :-
	reverse_subst(Y0stoYs_Subst, YstoY0s_Subst),
	reverse_subst(LCO_Subst, LCOtoYs_Subst),
	chain_subst(LCOtoYs_Subst, YstoY0s_Subst, LCOtoY0s_Subst),

	delete_used_as(HstoAs_Subst0, Y0stoAs_Subst, HstoAs_Subst),

	goal_util__rename_vars_in_goals(Goal0, no, Y0stoAs_Subst, Goal1),
	goal_util__rename_vars_in_goals(Goal1, no, LCOtoY0s_Subst, Goal2),
	goal_util__rename_vars_in_goals(Goal2, no, YstoY0s_Subst, Goal3),
	goal_util__rename_vars_in_goals(Goal3, no, HstoAs_Subst, Goal).

:- pred delete_used_as(subst::in, subst::in, subst::out) is det.
delete_used_as(HstoAs_Subst0, Y0stoAs_Subst, HstoAs_Subst) :-
	reverse_subst(HstoAs_Subst0, AstoHs_Subst0),
	reverse_subst(Y0stoAs_Subst, AstoY0s_Subst),

	map__keys(AstoY0s_Subst, AstoDelete),
	map__delete_list(AstoHs_Subst0, AstoDelete, AstoHs_Subst),

	reverse_subst(AstoHs_Subst, HstoAs_Subst).

:- pred accumulator__rename_recursive_goal(hlds_goal::in, prog_vars::in,
		pred_id::in, proc_id::in, sym_name::in, subst::in, subst::in,
		subst::in, subst::in, hlds_goal::out) is det.

accumulator__rename_recursive_goal(Goal0, Hs, PredId, ProcId, Name,
		HstoAs_Subst, Y0stoAs_Subst, Y0stoYs_Subst, LCO_Subst, Goal) :-

	Goal0 = GoalExpr0 - GoalInfo0,
	(
		GoalExpr0 = call(_, _, Args0, Builtin, Context, _)
	->
		reverse_subst(Y0stoAs_Subst, AstoY0s_Subst),
		reverse_subst(HstoAs_Subst, AstoHs_Subst),

		list__append(Args0, Hs, Args),
		GoalExpr1 = call(PredId, ProcId, Args, Builtin, Context, Name),

		goal_info_get_nonlocals(GoalInfo0, NonLocals0),
		set__list_to_set(Args, ArgsSet),
		set__union(ArgsSet, NonLocals0, NonLocals),
		goal_info_set_nonlocals(GoalInfo0, NonLocals, GoalInfo1),

		Goal1 = GoalExpr1 - GoalInfo1,

		goal_util__rename_vars_in_goal(Goal1, Y0stoYs_Subst, Goal2),
		goal_util__rename_vars_in_goal(Goal2, HstoAs_Subst, Goal3),
		goal_util__rename_vars_in_goal(Goal3, AstoY0s_Subst, Goal4),
		goal_util__rename_vars_in_goal(Goal4, LCO_Subst, Goal5),
		goal_util__rename_vars_in_goal(Goal5, AstoHs_Subst, Goal)
	;
		error("accumulator__rename_recursive_goal: to make det.")
	).

:- pred accumulator__rename_postrec_goals(hlds_goals::in, subst::in,
		hlds_goals::out) is det.

accumulator__rename_postrec_goals(Goals0, HstoAs_Subst, Goals) :-
	goal_util__rename_vars_in_goals(Goals0, no, HstoAs_Subst, Goals).
	
%-----------------------------------------------------------------------------%

:- pred calculate_goal_info(hlds_goal_expr::in, hlds_goal::out) is det.

calculate_goal_info(GoalExpr, GoalExpr - GoalInfo) :-
	(
		GoalExpr = conj(GoalList)
	->
		goal_list_nonlocals(GoalList, NonLocals),
		goal_list_instmap_delta(GoalList, InstMapDelta),
		goal_list_determinism(GoalList, Determinism),

		goal_info_init(NonLocals, InstMapDelta, Determinism, GoalInfo)
	;
		error("calculate_goal_info: not a conj.")
	).
	
%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%

	%
	% accumulator__check_assoc(Gs, MGs, AGs)
	%
	% Given a list of goals, Gs, check to ensure that the list of
	% goals Gs is associative rearranging a goal if necessary to
	% ensure associativity.  These goals are placed into MGs.
	%
	% It is not possible for construction unfications to be
	% associative.  However if only construction unfications remain
	% after the recursive call, it is possible to do the lco (see
	% lco.m) optimisation.  So whenever the predicate encounters a
	% construction unfication, it places it any goals that depend on
	% that goal into AGs.
	%
:- pred accumulator__check_assoc(hlds_goals::in, instmap::in,
		module_info::in, bool::in, hlds_goals::out,
		hlds_goals::out, assoc_info::in, assoc_info::out) is semidet.

accumulator__check_assoc([], _InstMap, _MI, _FullyStrict, [], []) --> [].
accumulator__check_assoc([Goal0 | Goal0s], InstMapBeforeGoal0,
		ModuleInfo, FullyStrict, MovedGoals, AfterGoals) -->
	(
		{ goal_is_construction_unification(Goal0) }
	->
		{ move_goals(Goal0, InstMapBeforeGoal0, ModuleInfo, FullyStrict,
				Goal0s, PreGoal0s, PostGoal0s) },
		accumulator__check_assoc(PreGoal0s, InstMapBeforeGoal0,
				ModuleInfo, FullyStrict,
				MovedGoals, AfterGoal0s),
		{ list__append(AfterGoal0s, [Goal0 | PostGoal0s], AfterGoals) }
	;
		{ Goal0 = _ - GoalInfo0 },
		{ goal_info_get_instmap_delta(GoalInfo0, InstMapDelta) },
		{ instmap__apply_instmap_delta(InstMapBeforeGoal0 ,
				InstMapDelta, InstMapBeforeGoal0s) },


		accumulator__check_goal(Goal0, Goal),
		accumulator__check_assoc(Goal0s, InstMapBeforeGoal0s,
				ModuleInfo, FullyStrict,
				MovedGoal0s, AfterGoals),
		{ MovedGoals = [Goal | MovedGoal0s] }
	).


%-----------------------------------------------------------------------------%

	%
	% Is the goal a construction unification?
	%
:- pred goal_is_construction_unification(hlds_goal::in) is semidet.

goal_is_construction_unification(Goal - _GoalInfo) :-
	Goal = unify(_, _, _, Unification, _),
	Unification = construct(_, _, _, _, _, _, _).

%-----------------------------------------------------------------------------%

	%
	% Is the current goal associative?
	%
:- pred accumulator__check_goal(hlds_goal::in, hlds_goal::out,
		assoc_info::in, assoc_info::out) is semidet.

accumulator__check_goal(conj(Goals0) - GoalInfo, conj(Goals) - GoalInfo) -->
	accumulator__check_goallist(Goals0, Goals).

accumulator__check_goal(par_conj(_, _) - _, _) -->
	{ fail }.

	% Branched Goals
	%
	% XXX the previous version of accumulator ensured the condition
	% that each arm of the disjunct only updated static variables.
	% However this will not handle the vectorising case.
accumulator__check_goal(disj(_, _) - _, _) --> { fail }.
accumulator__check_goal(switch(_, _, _, _) - _, _) --> { fail }.
accumulator__check_goal(if_then_else(_, _, _, _, _) - _, _) --> { fail }.

accumulator__check_goal(not(_) - _, _) --> { fail }.

accumulator__check_goal(some(Vars, CanRemove, Goal0) - GoalInfo,
		some(Vars, CanRemove, Goal) - GoalInfo) -->
	accumulator__check_goal(Goal0, Goal).

	% All of these must fail because there is no way we can know
	% whether or not these calls are associative.
	% XXX this may not be true for class_method_call, it may be
	% possible to make it a condition that this method is always
	% associative.
accumulator__check_goal(generic_call(_,_,_,_) - _, _) --> { fail }.
accumulator__check_goal(pragma_c_code(_,_,_,_,_,_,_) - _, _) --> { fail }.

accumulator__check_goal(unify(TermL, TermR, Mode, Unify, Context) - GoalInfo, 
		unify(TermL, TermR, Mode, Unify, Context) - GoalInfo) -->
	{ accumulator__check_assoc_unify_rhs(TermR) },
	accumulator__check_assoc_unify(Unify).

accumulator__check_goal(call(PredId, ProcId, Arg0s, Builtin, Context, Sym)
			- GoalInfo,
		call(PredId, ProcId, Args, Builtin, Context, Sym)
			- GoalInfo) -->
	assoc_info_module_info(ModuleInfo),
	accumulator__call_dynamic_var(Arg0s, DynamicCallVar),

	{ accumulator__is_associative(PredId, ProcId, ModuleInfo, Arg0s, Args,
		PossibleStaticVars, Commutative) },

	(
			% Make sure that after rearrangement of the
			% arguments the new proc will be at least as
			% efficient as the old pred.
		{ Commutative = no },
		assoc_info_static_set(StaticSet),
		{ accumulator__obey_heuristic(PredId, ModuleInfo,
				Args, StaticSet) }
	;
		{ Commutative = yes }
	),

	accumulator__check_previous_calls(DynamicCallVar,
			PredId, ProcId, Commutative),
	accumulator__new_dynamic_var(Arg0s, DynamicCallVar, NewDynamicVar),
	accumulator__update_orig_var_map(DynamicCallVar, NewDynamicVar),
	accumulator__update_Y0stoAs_subst(DynamicCallVar, [PossibleStaticVars]).

%-----------------------------------------------------------------------------%

:- pred accumulator__check_goallist(hlds_goals::in, hlds_goals::out,
		assoc_info::in, assoc_info::out) is semidet.

accumulator__check_goallist([], []) --> [].
accumulator__check_goallist([Goal0 | Goals0], [Goal | Goals]) -->
	accumulator__check_goal(Goal0, Goal),
	accumulator__check_goallist(Goals0, Goals).

%-----------------------------------------------------------------------------%

	%
	% This predicate is meant to fail if the rhs of the unification
	% is a lambda goal, because I am not convinced that I know how
	% to handle this correctly.
	%
:- pred accumulator__check_assoc_unify_rhs(unify_rhs::in) is semidet.

accumulator__check_assoc_unify_rhs(var(_)).
accumulator__check_assoc_unify_rhs(functor(_, _)).
accumulator__check_assoc_unify_rhs(lambda_goal(_, _, _, _, _, _, _, _)) :-
		%
		% For the moment just fail, as I am not sure how to
		% handle this.
		%
	fail.

	%
	% accumulator__check_assoc_unify_rhs
	%
	% The only safe unifications are assignment unifications.
	%
:- pred accumulator__check_assoc_unify(unification::in,
		assoc_info::in, assoc_info::out) is semidet.

accumulator__check_assoc_unify(
		construct(_Var, _ConsId, _Vars, _Modes, _, _, _)) -->
		%
		% We shouldn't fail if we have this case as all the
		% construction unification does is put a wrapper 
		% around the dynamic variables.  What we need to
		% recognise is that the construction/deconstruction
		% pair do nothing.
		%
		% f(X,Y) :-
		% 	decompose(X,Xh,Xr),
		% 	f(Xr,Y0),
		% 	Y0 = c(A0, B0),
		%	composeA(Xh,A0,A),
		%	composeB(Xh,B0,B),
		%	Y = c(A, B).
		%
		% I think that the way to recognise these
		% situations is when the type of Y is flat
		% (non-recursive).
		%
	{ fail }.
accumulator__check_assoc_unify(
		deconstruct(_Var, _ConsId, _Vars, _Modes, _Cat)) -->
		% see comment in construct
	{ fail }.
accumulator__check_assoc_unify(assign(L, _R)) -->
	assoc_info_dynamic_set(DynamicSet0),
	{ set__insert(DynamicSet0, L, DynamicSet) },
	assoc_info_set_dynamic_set(DynamicSet).
accumulator__check_assoc_unify(simple_test(_L, _R)) --> 
	{ fail }.
accumulator__check_assoc_unify(complicated_unify(_Modes, _Cat, _)) -->
	{ fail }.	% XXX not sure what this should be.

%-----------------------------------------------------------------------------%

	%
	% accumulator__call_dynamic_var(As, DV)
	%
	% Given the list of arguments to a call try and determine which
	% of the arguments is the current dynamic variable.
	%
	% Fails if there is more then one dynamic variable in a call.
	% This is because in general more then one dynamic variable
	% being used in a call prevents the goals from being
	% associative.
	%
:- pred accumulator__call_dynamic_var(prog_vars::in, prog_var::out,
		assoc_info::in, assoc_info::out) is semidet.

accumulator__call_dynamic_var(Args, DynamicCallVar) -->
	assoc_info_dynamic_set(DynamicSet),
	{ set__list_to_set(Args, ArgSet) },
	{ set__intersect(ArgSet, DynamicSet, DynamicCallArgs) },
	{ set__singleton_set(DynamicCallArgs, DynamicCallVar) }.

	
	%
	% accumulator__new_dynamic_var(As, DV, O)
	%
	% Given the original arguments to a call, As, and the dynamic
	% var, DV, determine the new dynamic var, O, also update the
	% dynamic set at the same time.
	%
:- pred accumulator__new_dynamic_var(prog_vars::in, prog_var::in,
		prog_var::out, assoc_info::in, assoc_info::out) is semidet.

accumulator__new_dynamic_var(Args0, DynamicCallVar, NewDynamicVar) -->
	assoc_info_static_set(StaticSet0),
	assoc_info_dynamic_set(DynamicSet0),

	{ set__list_to_set(Args0, ArgSet) },
	{ set__difference(ArgSet, StaticSet0, ArgDynamicSet) },
	{ set__union(ArgDynamicSet, DynamicSet0, DynamicSet) },

	assoc_info_set_dynamic_set(DynamicSet),

	{ set__delete(ArgDynamicSet, DynamicCallVar, OutputDynamicCallArgs) },
	{ set__singleton_set(OutputDynamicCallArgs, NewDynamicVar) }.

	%
	% accumulator__check_previous_calls
	%
	% Ensure that the previous calls have been commutative and calling
	% the same procedure, or if it is associative that there has
	% been no previous calls.
	%
:- pred accumulator__check_previous_calls(prog_var::in,
		pred_id::in, proc_id::in, commutative::in,
		assoc_info::in, assoc_info::out) is semidet.

accumulator__check_previous_calls(DynamicCallVar,
		PredId, ProcId, Commutative) -->
	assoc_info_orig_dynvar_map(OrigDynMap),
	assoc_info_prev_call_map(PrevCallMap0),

	{ map__lookup(OrigDynMap, DynamicCallVar, OrigVar) },
	{ accumulator__check_prevcalls(OrigVar, PredId, ProcId, Commutative,
		PrevCallMap0, PrevCallMap) },

	assoc_info_set_prev_call_map(PrevCallMap).

	%
	% accumulator__update_orig_var_map(DV, Ns)
	%
	% Record for each variable Ns which variable that variable
	% is descended from.
	%
:- pred accumulator__update_orig_var_map(prog_var::in, prog_var::in,
		assoc_info::in, assoc_info::out) is det.

accumulator__update_orig_var_map(DynamicCallVar, NewDynamicVar) -->
	assoc_info_orig_dynvar_map(OrigDynMap0),

	{ map__lookup(OrigDynMap0, DynamicCallVar, OrigVar) },
	{ map__det_insert(OrigDynMap0, NewDynamicVar, OrigVar, OrigDynMap) },

	assoc_info_set_orig_dynvar_map(OrigDynMap).

	%
	% accumulator__update_Y0stoAs_subst
	%
	% Update the Y0s -> As Substitution.
	%
:- pred accumulator__update_Y0stoAs_subst(prog_var::in, list(set(prog_var))::in,
		assoc_info::in, assoc_info::out) is semidet.

accumulator__update_Y0stoAs_subst(DynamicCallVar, PossibleStaticVarsList) -->
	assoc_info_orig_dynvar_map(OrigDynVarMap),
	assoc_info_static_set(StaticSet),
	assoc_info_HstoAs(HstoAs_Subst),

	{ map__lookup(OrigDynVarMap, DynamicCallVar, OrigDynVar) },

	assoc_info_Y0stoAs(Y0stoAs_Subst0),
	{ accumulator__update_Y0stoAs_subst_2(PossibleStaticVarsList,
			OrigDynVar, StaticSet, HstoAs_Subst,
			Y0stoAs_Subst0, Y0stoAs_Subst) },
	assoc_info_set_Y0stoAs(Y0stoAs_Subst).


:- pred accumulator__update_Y0stoAs_subst_2(list(set(prog_var))::in,
		prog_var::in, set(prog_var)::in,
		subst::in, subst::in, subst::out) is semidet.

accumulator__update_Y0stoAs_subst_2([], _, _, _, Y0stoAs_Subst, Y0stoAs_Subst).
accumulator__update_Y0stoAs_subst_2([PossibleStaticVars | T], OrigDynVar,
		StaticSet, HstoAs_Subst, Y0stoAs_Subst0, Y0stoAs_Subst) :-

	set__intersect(PossibleStaticVars, StaticSet, StaticVarSet),
	set__to_sorted_list(StaticVarSet, StaticVar),
	list__map(map__lookup(HstoAs_Subst), StaticVar, As),

		% There should only be one variable that is being
		% accumulated.
	As = [AccVar],

		%
		% If you have a chain of commutative calls,
		% only the first one will need to have the
		% accumulator placed in the call.
		%
	(
		map__insert(Y0stoAs_Subst0, OrigDynVar, AccVar,
				Y0stoAs_Subst1)
	->
		Y0stoAs_Subst2 = Y0stoAs_Subst1
	;
		Y0stoAs_Subst2 = Y0stoAs_Subst0
	),

	accumulator__update_Y0stoAs_subst_2(T, OrigDynVar, StaticSet,
			HstoAs_Subst, Y0stoAs_Subst2, Y0stoAs_Subst).


%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%

	%
	% accumulator__check_prevcalls
	%
	% We must ensure that if the dynamic variables which the current
	% variable is descended from have been used in any other
	% calls previously that all these calls have been commutative
	% including the current call.
	%
	% If this is true update the prev call map.
	%
:- pred accumulator__check_prevcalls(prog_var::in,
		pred_id::in, proc_id::in, commutative::in,
		prev_call_map::in, prev_call_map::out) is semidet.

accumulator__check_prevcalls(OrigVar, PredId, ProcId, Commutative,
		PrevCallMap0, PrevCallMap) :-
	(
		map__search(PrevCallMap0, OrigVar, PrevCall)
	->
			%
			% Only succeed if the current call is
			% commutative and all the previous calls are
			% commutative and to the same procedure.
			%
		PrevCall = prev_call(PredId, ProcId, yes),
		PrevCallMap = PrevCallMap0
	;
			%
			% There are no previous calls so set whether or
			% not the current call is commutative for all
			% the original variables.
			%
		map__det_insert(PrevCallMap0, OrigVar,
				prev_call(PredId, ProcId, Commutative),
				PrevCallMap)
	).


%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%

	%
	% If accumulator_is_associative is true, it returns a reordering
	% of the args to make it associative when executed left to right
	% and an indicator of whether or not the predicate is
	% commutative.
	%
:- pred accumulator__is_associative(pred_id::in, proc_id::in, module_info::in,
		prog_vars::in, prog_vars::out, set(prog_var)::out,
		commutative::out) is semidet.

accumulator__is_associative(PredId, ProcId, ModuleInfo,
		Args0, Args, PossibleStaticVars, Commutative):-
	module_info_pred_proc_info(ModuleInfo, PredId, ProcId, 
			PredInfo, ProcInfo),
	pred_info_module(PredInfo, ModuleName),
	pred_info_name(PredInfo, PredName),
	pred_info_arity(PredInfo, Arity),
	proc_info_argmodes(ProcInfo, Modes),
	assoc_fact(ModuleName, PredName, Arity, Modes, ModuleInfo, Args0, Args,
		PossibleStaticVars, Reordered),
	bool__not(Reordered, Commutative).

	%
	% XXX this fact table is only a temporary solution to whether or
	% not a particular procedure is associative.  In the long term
	% the user should be able to annotate their code to indicate
	% which predicates are associative.
	%
	% The set is simply the set of vars that must be static.  It is
	% a simple heuristic to ensure that the O() behaviour only
	% improves.  ie for append after swapping the arguments the
	% static variable must be in the first location.
	%
:- pred assoc_fact(module_name::in, string::in, arity::in,
		list(mode)::in, module_info::in, prog_vars::in,
		prog_vars::out, set(prog_var)::out, bool::out) is semidet.

assoc_fact(unqualified("int"), "+", 3, [In, In, Out], ModuleInfo, 
		[A, B, C], [A, B, C], PossibleStaticVars, no) :-
	set__list_to_set([A, B], PossibleStaticVars),
	mode_is_input(ModuleInfo, In),
	mode_is_output(ModuleInfo, Out).

assoc_fact(unqualified("int"), "*", 3, [In, In, Out], ModuleInfo, 
		[A, B, C], [A, B, C], PossibleStaticVars, no) :-
	set__list_to_set([A, B], PossibleStaticVars),
	mode_is_input(ModuleInfo, In),
	mode_is_output(ModuleInfo, Out).

assoc_fact(unqualified("list"), "append", 3, [TypeInfoIn, In, In, Out], 
		ModuleInfo, [TypeInfo, A, B, C], 
		[TypeInfo, B, A, C], PossibleStaticVars, yes) :-
	set__list_to_set([A, B], PossibleStaticVars),
	mode_is_input(ModuleInfo, TypeInfoIn),
	mode_is_input(ModuleInfo, In),
	mode_is_output(ModuleInfo, Out).



/* XXX introducing accumulators for floating point numbers can be bad.
assoc_fact(unqualified("float"), "+", 3, [In, In, Out], ModuleInfo, 
		[A, B, C], [A, B, C], PossibleStaticVars, no) :-
	set__list_to_set([A, B], PossibleStaticVars),
	mode_is_input(ModuleInfo, In),
	mode_is_output(ModuleInfo, Out).

assoc_fact(unqualified("float"), "*", 3, [In, In, Out], ModuleInfo, 
		[A, B, C], [A, B, C], PossibleStaticVars, no) :-
	set__list_to_set([A, B], PossibleStaticVars),
	mode_is_input(ModuleInfo, In),
	mode_is_output(ModuleInfo, Out).
*/
/*
	XXX this no longer works, because set__insert isn't associative.

	However set__insert obeys the following axiom, providing that you 
	use user-defined equality (set__equals), not structural equality 
	for S.

		some [SA] (p(A, S0, SA), p(B, SA, S)) <=>
			some [SB] (p(B, S0, SB), p(A, SB, S))

	My previous attempt at this transformation handled this case 
	and I thought the current one did as well.  I was wrong.  I need
	to reintegrate my old code.

assoc_fact(unqualified("set"), "insert", 3, [TypeInfoIn, In, In, Out], 
		Moduleinfo, [TypeInfo, A, B, C], 
		[TypeInfo, A, B, C], PossibleStaticVars, no) :-
	set__list_to_set([A, B], PossibleStaticVars),
	mode_is_input(Moduleinfo, TypeInfoIn),
	mode_is_input(Moduleinfo, In),
	mode_is_output(Moduleinfo, Out).
*/

%-----------------------------------------------------------------------------%
%-----------------------------------------------------------------------------%

	% 
	% accumulator__obey_heuristic
	%
	% for calls which rearrange the order of variables ensure that
	% the call obeys the heuristic that the static variables are in 
	% certain positions.
	%
	% For example, a call to append in the forward mode will have
	% the following types of variables: (static, dynamic, dynamic).
	% After rearrangment that order will be (dynamic, static, dynamic).
	% Having a dynamic variable in the first position will probably
	% take O(N) time to process while having a static variable will 
	% probably take O(1) time.  Therefore the complexity of the
	% predicate as a whole will change, we must ensure that it
	% changes for the better.
	%
:- pred accumulator__obey_heuristic(pred_id::in, module_info::in,
		prog_vars::in, set(prog_var)::in) is semidet.

accumulator__obey_heuristic(Predid, ModuleInfo, Args, StaticSet) :-
	module_info_pred_info(ModuleInfo, Predid, PredInfo),
	pred_info_module(PredInfo, ModuleName),
	pred_info_name(PredInfo, PredName),
	pred_info_arity(PredInfo, Arity),
	heuristic(ModuleName, PredName, Arity, Args, MustBeStaticVars),
	set__intersect(StaticSet, MustBeStaticVars, Intersection),
	set__equal(MustBeStaticVars, Intersection).

:- pred heuristic(module_name::in, string::in, arity::in, prog_vars::in,
		set(prog_var)::out) is semidet.

heuristic(unqualified("list"), "append", 3, [_Typeinfo, A, _B, _C], Set) :-
	set__list_to_set([A], Set).

%-----------------------------------------------------------------------------%

:- pred assoc_info_init(module_info::in, prog_vars::in, a_goals::in,
		a_goals::in, a_goal::in,
		subst::in, subst::in, assoc_info::out) is det.

assoc_info_init(ModuleInfo, HeadVars, DP, Compose, R, Y0stoYs_Subst,
		HstoAs_Subst, AssocInfo) :-
	DP = goal(Decompose, _InstMapBeforeDecomposeProcess),
	R = goal(_RecGoalExpr - RecGoalInfo, _InstMapBeforeRecursive),

	map__init(PrevCallMap),

		%
		% Set up the OrigDynVarMap
		%
	reverse_subst(Y0stoYs_Subst, YstoY0s_Subst),
	accumulator__vars_to_accumulate(HeadVars, Compose, ModuleInfo, Ys),
	list__map(map__lookup(YstoY0s_Subst), Ys, Y0s),

	assoc_list__from_corresponding_lists(Y0s, Y0s, AssocDynamicList),
	map__from_assoc_list(AssocDynamicList, OrigDynVarMap),

		%
		% Dynamic Set
		%
	set__list_to_set(Y0s, DynamicSet),

		%
		% Static Set
		%
	GetGoalInfos = (pred(Goal::in, GoalInfo::out) is det :-
				Goal = _ - GoalInfo),
	list__map(GetGoalInfos, Decompose, DPGoalInfos),
	list__map(goal_info_get_nonlocals, DPGoalInfos, DPNonLocals),
	set__list_to_set(DPNonLocals, DPNonLocalsPowerSet),
	set__power_union(DPNonLocalsPowerSet, StaticSet0),

	goal_info_get_nonlocals(RecGoalInfo, RecNonLocals),
	set__delete_list(RecNonLocals, Y0s, StaticSet1),

	set__union(StaticSet0, StaticSet1, StaticSet),

		%
		% Y0stoAs
		%
	map__init(Y0stoAs_Subst),

		%
		% Ys
		%
	set__list_to_set(Ys, YsSet),

	AssocInfo = assoc_info(StaticSet, DynamicSet,
			ModuleInfo, PrevCallMap, OrigDynVarMap,
			Y0stoAs_Subst, HstoAs_Subst, YsSet).

:- pred assoc_info_static_set(set(prog_var)::out,
		assoc_info::in, assoc_info::out) is det.
assoc_info_static_set(StaticSet, AssocInfo, AssocInfo) :-
	AssocInfo = assoc_info(StaticSet, _, _, _, _, _, _, _).

:- pred assoc_info_dynamic_set(set(prog_var)::out,
		assoc_info::in, assoc_info::out) is det.
assoc_info_dynamic_set(DynamicSet, AssocInfo, AssocInfo) :-
	AssocInfo = assoc_info(_, DynamicSet, _, _, _, _, _, _).

:- pred assoc_info_module_info(module_info::out,
		assoc_info::in, assoc_info::out) is det.
assoc_info_module_info(ModuleInfo, AssocInfo, AssocInfo) :-
	AssocInfo = assoc_info(_, _, ModuleInfo, _, _, _, _, _).

:- pred assoc_info_prev_call_map(prev_call_map::out,
		assoc_info::in, assoc_info::out) is det.
assoc_info_prev_call_map(PrevCallMap, AssocInfo, AssocInfo) :-
	AssocInfo = assoc_info(_, _, _, PrevCallMap, _, _, _, _).

:- pred assoc_info_orig_dynvar_map(orig_dynvar_map::out,
		assoc_info::in, assoc_info::out) is det.
assoc_info_orig_dynvar_map(OrigDynVarMap, AssocInfo, AssocInfo) :-
	AssocInfo = assoc_info(_, _, _, _, OrigDynVarMap, _, _, _).

:- pred assoc_info_Y0stoAs(subst::out,
		assoc_info::in, assoc_info::out) is det.
assoc_info_Y0stoAs(Y0stoAs_Subst, AssocInfo, AssocInfo) :-
	AssocInfo = assoc_info(_, _, _, _, _, Y0stoAs_Subst, _, _).

:- pred assoc_info_HstoAs(subst::out,
		assoc_info::in, assoc_info::out) is det.
assoc_info_HstoAs(HstoAs_Subst, AssocInfo, AssocInfo) :-
	AssocInfo = assoc_info(_, _, _, _, _, _, HstoAs_Subst, _).

:- pred assoc_info_Ys(set(prog_var)::out,
		assoc_info::in, assoc_info::out) is det.
assoc_info_Ys(Ys, AssocInfo, AssocInfo) :-
	AssocInfo = assoc_info(_, _, _, _, _, _, _, Ys).

/*
:- pred assoc_info_set_static_set(set(prog_var)::in, assoc_info::in,
		assoc_info::out) is det.
assoc_info_set_static_set(StaticSet, assoc_info(_, B, C, D, E, F, G, H),
		assoc_info(StaticSet, B, C, D, E, F, G, H)).
*/

:- pred assoc_info_set_dynamic_set(set(prog_var)::in, assoc_info::in,
		assoc_info::out) is det.
assoc_info_set_dynamic_set(DynamicSet, assoc_info(A, _, C, D, E, F, G, H),
		assoc_info(A, DynamicSet, C, D, E, F, G, H)).

:- pred assoc_info_set_prev_call_map(prev_call_map::in, assoc_info::in,
		assoc_info::out) is det.
assoc_info_set_prev_call_map(PrevCallMap, assoc_info(A, B, C, _, E, F, G, H),
		assoc_info(A, B, C, PrevCallMap, E, F, G, H)).

:- pred assoc_info_set_orig_dynvar_map(orig_dynvar_map::in, assoc_info::in,
		assoc_info::out) is det.
assoc_info_set_orig_dynvar_map(OrigDynMap, assoc_info(A, B, C, D, _, F, G, H),
		assoc_info(A, B, C, D, OrigDynMap, F, G, H)).

:- pred assoc_info_set_Y0stoAs(subst::in, assoc_info::in,
		assoc_info::out) is det.
assoc_info_set_Y0stoAs(Y0stoAs_Subst, assoc_info(A, B, C, D, E, _, G, H),
		assoc_info(A, B, C, D, E, Y0stoAs_Subst, G, H)).

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%-----------------------------------------------------------------------------%

:- pred reverse_subst(subst::in, subst::out) is det.

reverse_subst(Subst0, Subst) :-
	map__to_assoc_list(Subst0, List0),
	assoc_list__reverse_members(List0, List),
	map__from_assoc_list(List, Subst).

:- pred chain_subst(subst::in, subst::in, subst::out) is det.

chain_subst(AtoB, BtoC, AtoC) :-
	map__keys(AtoB, Keys),
	chain_subst_2(Keys, AtoB, BtoC, AtoC).

:- pred chain_subst_2(list(A)::in, map(A, B)::in, map(B, C)::in,
		map(A, C)::out) is det.

chain_subst_2([], _, _, AtoC) :-
	map__init(AtoC).
chain_subst_2([A|As], AtoB, BtoC, AtoC) :-
	chain_subst_2(As, AtoB, BtoC, AtoC0),
	map__lookup(AtoB, A, B),
	map__lookup(BtoC, B, C),
	map__det_insert(AtoC0, A, C, AtoC).

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