mercury/compiler/cse_detection.m

%-----------------------------------------------------------------------------%
% Copyright (C) 1995-2005 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.
%-----------------------------------------------------------------------------%
%
% Common subexpression detection - hoist common subexpression goals out of
% branched structures. This can enable us to find more indexing opportunities
% and hence can make the code more deterministic.
% This code is switched on/off with the `--common-goal' option.
%
% Main author: zs.
% Much of the code is based on switch_detection.m by fjh.
%
%-----------------------------------------------------------------------------%

:- module check_hlds__cse_detection.

:- interface.

:- import_module hlds__hlds_module.
:- import_module hlds__hlds_pred.

:- import_module io.

:- pred detect_cse(module_info::in, module_info::out, io::di, io::uo) is det.

:- pred detect_cse_in_proc(proc_id::in, pred_id::in,
	module_info::in, module_info::out, io::di, io::uo) is det.

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

:- implementation.

:- import_module check_hlds__det_util.
:- import_module check_hlds__inst_match.
:- import_module check_hlds__mode_util.
:- import_module check_hlds__modes.
:- import_module check_hlds__switch_detection.
:- import_module check_hlds__switch_detection.
:- import_module check_hlds__type_util.
:- import_module hlds__goal_util.
:- import_module hlds__hlds_data.
:- import_module hlds__hlds_goal.
:- import_module hlds__hlds_out.
:- import_module hlds__instmap.
:- import_module hlds__quantification.
:- import_module libs__globals.
:- import_module libs__options.
:- import_module parse_tree__prog_data.

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

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

	% Traverse the module structure, calling `detect_cse_in_goal'
	% for each procedure body.

detect_cse(!ModuleInfo, !IO) :-
	module_info_predids(!.ModuleInfo, PredIds),
	detect_cse_in_preds(PredIds, !ModuleInfo, !IO).

:- pred detect_cse_in_preds(list(pred_id)::in,
	module_info::in, module_info::out, io::di, io::uo) is det.

detect_cse_in_preds([], !ModuleInfo, !IO).
detect_cse_in_preds([PredId | PredIds], !ModuleInfo, !IO) :-
	module_info_preds(!.ModuleInfo, PredTable),
	map__lookup(PredTable, PredId, PredInfo),
	detect_cse_in_pred(PredId, PredInfo, !ModuleInfo, !IO),
	detect_cse_in_preds(PredIds, !ModuleInfo, !IO).

:- pred detect_cse_in_pred(pred_id::in, pred_info::in,
	module_info::in, module_info::out, io::di, io::uo) is det.

detect_cse_in_pred(PredId, PredInfo0, !ModuleInfo, !IO) :-
	ProcIds = pred_info_non_imported_procids(PredInfo0),
	detect_cse_in_procs(ProcIds, PredId, !ModuleInfo, !IO).

:- pred detect_cse_in_procs(list(proc_id)::in, pred_id::in,
	module_info::in, module_info::out, io::di, io::uo) is det.

detect_cse_in_procs([], _PredId, !ModuleInfo, !IO).
detect_cse_in_procs([ProcId | ProcIds], PredId, !ModuleInfo, !IO) :-
	detect_cse_in_proc(ProcId, PredId, !ModuleInfo, !IO),
	detect_cse_in_procs(ProcIds, PredId, !ModuleInfo, !IO).

detect_cse_in_proc(ProcId, PredId, !ModuleInfo, !IO) :-
	detect_cse_in_proc_2(ProcId, PredId, Redo, !ModuleInfo),
	(
		Redo = no
	;
		Redo = yes,
		globals__io_lookup_bool_option(very_verbose, VeryVerbose, !IO),
		(
			VeryVerbose = yes,
			io__write_string("% Repeating mode check for ", !IO),
			hlds_out__write_pred_id(!.ModuleInfo, PredId, !IO),
			io__write_string("\n", !IO)
		;
			VeryVerbose = no
		),
		modecheck_proc(ProcId, PredId, !ModuleInfo, Errs, _Changed,
			!IO),
		( Errs > 0 ->
			error("mode check fails when repeated")
		;
			true
		),
		(
			VeryVerbose = yes,
			io__write_string("% Repeating switch detection for ",
				!IO),
			hlds_out__write_pred_id(!.ModuleInfo, PredId, !IO),
			io__write_string("\n", !IO)
		;
			VeryVerbose = no
		),
		detect_switches_in_proc(ProcId, PredId, !ModuleInfo),
		(
			VeryVerbose = yes,
			io__write_string("% Repeating common " ++
				"deconstruction detection for ", !IO),
			hlds_out__write_pred_id(!.ModuleInfo, PredId, !IO),
			io__write_string("\n", !IO)
		;
			VeryVerbose = no
		),
		detect_cse_in_proc(ProcId, PredId, !ModuleInfo, !IO)
	).

:- type cse_info
	--->	cse_info(
			varset			:: prog_varset,
			vartypes		:: vartypes,
			type_info_varmap	:: type_info_varmap,
			typeclass_info_varmap	:: typeclass_info_varmap,
			module_info		:: module_info
		).

:- pred detect_cse_in_proc_2(proc_id::in, pred_id::in, bool::out,
	module_info::in, module_info::out) is det.

detect_cse_in_proc_2(ProcId, PredId, Redo, ModuleInfo0, ModuleInfo) :-
	module_info_preds(ModuleInfo0, PredTable0),
	map__lookup(PredTable0, PredId, PredInfo0),
	pred_info_procedures(PredInfo0, ProcTable0),
	map__lookup(ProcTable0, ProcId, ProcInfo0),

		% To process each ProcInfo, we get the goal,
		% initialize the instmap based on the modes of the head vars,
		% and pass these to `detect_cse_in_goal'.

	proc_info_goal(ProcInfo0, Goal0),
	proc_info_get_initial_instmap(ProcInfo0, ModuleInfo0, InstMap0),
	proc_info_varset(ProcInfo0, Varset0),
	proc_info_vartypes(ProcInfo0, VarTypes0),
	proc_info_typeinfo_varmap(ProcInfo0, TypeInfoVarMap0),
	proc_info_typeclass_info_varmap(ProcInfo0, TypeClassInfoVarMap0),
	CseInfo0 = cse_info(Varset0, VarTypes0,
		TypeInfoVarMap0, TypeClassInfoVarMap0, ModuleInfo0),
	detect_cse_in_goal(Goal0, InstMap0, CseInfo0, CseInfo, Redo, Goal1),

	(
		Redo = no,
		ModuleInfo = ModuleInfo0
	;
		Redo = yes,

		% ModuleInfo should not be changed by detect_cse_in_goal
		CseInfo = cse_info(VarSet1, VarTypes1,
			TypeInfoVarMap, TypeClassInfoVarMap, _),
		proc_info_headvars(ProcInfo0, HeadVars),

		implicitly_quantify_clause_body(HeadVars, _Warnings,
			Goal1, Goal, VarSet1, VarSet, VarTypes1, VarTypes),

		proc_info_set_goal(Goal, ProcInfo0, ProcInfo1),
		proc_info_set_varset(VarSet, ProcInfo1, ProcInfo2),
		proc_info_set_vartypes(VarTypes, ProcInfo2, ProcInfo3),
		proc_info_set_typeinfo_varmap(TypeInfoVarMap,
			ProcInfo3, ProcInfo4),
		proc_info_set_typeclass_info_varmap(TypeClassInfoVarMap,
			ProcInfo4, ProcInfo),

		map__det_update(ProcTable0, ProcId, ProcInfo, ProcTable),
		pred_info_set_procedures(ProcTable, PredInfo0, PredInfo),
		map__det_update(PredTable0, PredId, PredInfo, PredTable),
		module_info_set_preds(PredTable, ModuleInfo0, ModuleInfo)
	).

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

	% Given a goal, and the instmap on entry to that goal,
	% find disjunctions that contain common subexpressions
	% and hoist these out of the disjunction. At the moment
	% we only look for cses that are deconstruction unifications.

:- pred detect_cse_in_goal(hlds_goal::in, instmap::in, cse_info::in,
	cse_info::out, bool::out, hlds_goal::out) is det.

detect_cse_in_goal(Goal0, InstMap0, !CseInfo, Redo, Goal) :-
	detect_cse_in_goal_1(Goal0, InstMap0, !CseInfo, Redo, Goal, _InstMap).

	% This version is the same as the above except that it returns
	% the resulting instmap on exit from the goal, which is
	% computed by applying the instmap delta specified in the
	% goal's goalinfo.

:- pred detect_cse_in_goal_1(hlds_goal::in, instmap::in, cse_info::in,
	cse_info::out, bool::out, hlds_goal::out, instmap::out) is det.

detect_cse_in_goal_1(Goal0 - GoalInfo, InstMap0, !CseInfo, Redo,
		Goal - GoalInfo, InstMap) :-
	detect_cse_in_goal_2(Goal0, GoalInfo, InstMap0, !CseInfo, Redo, Goal),
	goal_info_get_instmap_delta(GoalInfo, InstMapDelta),
	instmap__apply_instmap_delta(InstMap0, InstMapDelta, InstMap).

	% Here we process each of the different sorts of goals.

:- pred detect_cse_in_goal_2(hlds_goal_expr::in, hlds_goal_info::in,
	instmap::in, cse_info::in, cse_info::out, bool::out,
	hlds_goal_expr::out) is det.

detect_cse_in_goal_2(Goal @ foreign_proc(_, _, _, _, _, _), _, _, !CseInfo,
		no, Goal).
detect_cse_in_goal_2(Goal @ generic_call(_, _, _, _), _, _, !CseInfo,
		no, Goal).
detect_cse_in_goal_2(Goal @ call(_, _, _, _, _, _), _, _, !CseInfo, no, Goal).
detect_cse_in_goal_2(unify(LHS, RHS0, Mode, Unify,  UnifyContext), _, InstMap0,
		!CseInfo, Redo, unify(LHS, RHS, Mode,Unify, UnifyContext)) :-
	(
		RHS0 = lambda_goal(Purity, PredOrFunc, EvalMethod, FixModes,
			NonLocalVars, Vars, Modes, Det, Goal0)
	->
		ModuleInfo = !.CseInfo ^ module_info,
		instmap__pre_lambda_update(ModuleInfo,
			Vars, Modes, InstMap0, InstMap),
		detect_cse_in_goal(Goal0, InstMap, !CseInfo, Redo, Goal),
		RHS = lambda_goal(Purity, PredOrFunc, EvalMethod, FixModes,
			NonLocalVars, Vars, Modes, Det, Goal)
	;
		RHS = RHS0,
		Redo = no
	).
detect_cse_in_goal_2(not(Goal0), _GoalInfo, InstMap, !CseInfo, Redo,
		not(Goal)) :-
	detect_cse_in_goal(Goal0, InstMap, !CseInfo, Redo, Goal).
detect_cse_in_goal_2(scope(Reason, Goal0), _GoalInfo, InstMap,
		!CseInfo, Redo, scope(Reason, Goal)) :-
	detect_cse_in_goal(Goal0, InstMap, !CseInfo, Redo, Goal).
detect_cse_in_goal_2(conj(Goals0), _GoalInfo, InstMap, !CseInfo, Redo,
		conj(Goals)) :-
	detect_cse_in_conj(Goals0, InstMap, !CseInfo, Redo, Goals).
detect_cse_in_goal_2(par_conj(Goals0), _, InstMap, !CseInfo, Redo,
		par_conj(Goals)) :-
	detect_cse_in_par_conj(Goals0, InstMap, !CseInfo, Redo, Goals).
detect_cse_in_goal_2(disj(Goals0), GoalInfo, InstMap, !CseInfo, Redo, Goal) :-
	( Goals0 = [] ->
		Redo = no,
		Goal = disj([])
	;
		goal_info_get_nonlocals(GoalInfo, NonLocals),
		set__to_sorted_list(NonLocals, NonLocalsList),
		detect_cse_in_disj(NonLocalsList, Goals0, GoalInfo,
			InstMap, !CseInfo, Redo, Goal)
	).
detect_cse_in_goal_2(switch(Var, CanFail, Cases0), GoalInfo, InstMap,
		!CseInfo, Redo, Goal) :-
	goal_info_get_nonlocals(GoalInfo, NonLocals),
	set__to_sorted_list(NonLocals, NonLocalsList),
	detect_cse_in_cases(NonLocalsList, Var, CanFail, Cases0, GoalInfo,
		InstMap, !CseInfo, Redo, Goal).
detect_cse_in_goal_2(if_then_else(Vars, Cond0, Then0, Else0), GoalInfo,
		InstMap, !CseInfo, Redo, Goal) :-
	goal_info_get_nonlocals(GoalInfo, NonLocals),
	set__to_sorted_list(NonLocals, NonLocalsList),
	detect_cse_in_ite(NonLocalsList, Vars, Cond0, Then0, Else0, GoalInfo,
		InstMap, !CseInfo, Redo, Goal).

detect_cse_in_goal_2(shorthand(_), _, _, _, _, _, _) :-
	% these should have been expanded out by now
	error("detect_cse_in_goal_2: unexpected shorthand").

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

:- pred detect_cse_in_conj(list(hlds_goal)::in, instmap::in, cse_info::in,
	cse_info::out, bool::out, list(hlds_goal)::out) is det.

detect_cse_in_conj([], _InstMap, !CseInfo, no, []).
detect_cse_in_conj([Goal0 | Goals0], InstMap0, !CseInfo,
		Redo, Goals) :-
	detect_cse_in_goal_1(Goal0, InstMap0, !CseInfo, Redo1, Goal1,
		InstMap1),
	detect_cse_in_conj(Goals0, InstMap1, !CseInfo, Redo2, Goals1),
	( Goal1 = conj(ConjGoals) - _ ->
		list__append(ConjGoals, Goals1, Goals)
	;
		Goals = [Goal1 | Goals1]
	),
	bool__or(Redo1, Redo2, Redo).

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

:- pred detect_cse_in_par_conj(list(hlds_goal)::in, instmap::in, cse_info::in,
	cse_info::out, bool::out, list(hlds_goal)::out) is det.

detect_cse_in_par_conj([], _InstMap, !CseInfo, no, []).
detect_cse_in_par_conj([Goal0 | Goals0], InstMap0, !CseInfo, Redo,
		[Goal | Goals]) :-
	detect_cse_in_goal(Goal0, InstMap0, !CseInfo, Redo1, Goal),
	detect_cse_in_par_conj(Goals0, InstMap0, !CseInfo, Redo2, Goals),
	bool__or(Redo1, Redo2, Redo).

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

	% These are the interesting bits - we've found a non-empty branched
	% structure, and we've got a list of the non-local variables of that
	% structure. Now for each non-local variable, we check whether each
	% branch matches that variable against the same functor.

:- pred detect_cse_in_disj(list(prog_var)::in, list(hlds_goal)::in,
	hlds_goal_info::in, instmap::in, cse_info::in,
	cse_info::out, bool::out, hlds_goal_expr::out) is det.

detect_cse_in_disj([], Goals0, _, InstMap, !CseInfo, Redo, disj(Goals)) :-
	detect_cse_in_disj_2(Goals0, InstMap, !CseInfo, Redo, Goals).
detect_cse_in_disj([Var | Vars], Goals0, GoalInfo0, InstMap,
		!CseInfo, Redo, Goal) :-
	(
		instmap__lookup_var(InstMap, Var, VarInst0),
		ModuleInfo = !.CseInfo ^ module_info,
		% XXX we only need inst_is_bound, but leave this as it is
		% until mode analysis can handle aliasing between free
		% variables.
		inst_is_ground_or_any(ModuleInfo, VarInst0),
		common_deconstruct(Goals0, Var, !CseInfo, Unify,
			FirstOldNew, LaterOldNew, Goals)
	->
		maybe_update_existential_data_structures(Unify,
			FirstOldNew, LaterOldNew, !CseInfo),
		Goal = conj([Unify, disj(Goals) - GoalInfo0]),
		Redo = yes
	;
		detect_cse_in_disj(Vars, Goals0, GoalInfo0, InstMap,
			!CseInfo, Redo, Goal)
	).

:- pred detect_cse_in_disj_2(list(hlds_goal)::in, instmap::in, cse_info::in,
	cse_info::out, bool::out, list(hlds_goal)::out) is det.

detect_cse_in_disj_2([], _InstMap, !CseInfo, no, []).
detect_cse_in_disj_2([Goal0 | Goals0], InstMap0, !CseInfo, Redo,
		[Goal | Goals]) :-
	detect_cse_in_goal(Goal0, InstMap0, !CseInfo, Redo1, Goal),
	detect_cse_in_disj_2(Goals0, InstMap0, !CseInfo, Redo2, Goals),
	bool__or(Redo1, Redo2, Redo).

:- pred detect_cse_in_cases(list(prog_var)::in, prog_var::in, can_fail::in,
	list(case)::in, hlds_goal_info::in, instmap::in,
	cse_info::in, cse_info::out, bool::out, hlds_goal_expr::out) is det.

detect_cse_in_cases([], SwitchVar, CanFail, Cases0, _GoalInfo, InstMap,
		!CseInfo, Redo, switch(SwitchVar, CanFail, Cases)) :-
	detect_cse_in_cases_2(Cases0, InstMap, !CseInfo, Redo, Cases).
detect_cse_in_cases([Var | Vars], SwitchVar, CanFail, Cases0, GoalInfo,
		InstMap, !CseInfo, Redo, Goal) :-
	(
		Var \= SwitchVar,
		instmap__lookup_var(InstMap, Var, VarInst0),
		ModuleInfo = !.CseInfo ^ module_info,
		% XXX we only need inst_is_bound, but leave this as it is
		% until mode analysis can handle aliasing between free
		% variables.
		inst_is_ground_or_any(ModuleInfo, VarInst0),
		common_deconstruct_cases(Cases0, Var, !CseInfo,
			Unify, FirstOldNew, LaterOldNew, Cases)
	->
		maybe_update_existential_data_structures(Unify,
			FirstOldNew, LaterOldNew, !CseInfo),
		Goal = conj([Unify, switch(SwitchVar, CanFail, Cases)
			- GoalInfo]),
		Redo = yes
	;
		detect_cse_in_cases(Vars, SwitchVar, CanFail, Cases0, GoalInfo,
			InstMap, !CseInfo, Redo, Goal)
	).

:- pred detect_cse_in_cases_2(list(case)::in, instmap::in, cse_info::in,
	cse_info::out, bool::out, list(case)::out) is det.

detect_cse_in_cases_2([], _, !CseInfo, no, []).
detect_cse_in_cases_2([Case0 | Cases0], InstMap, !CseInfo, Redo,
		[Case | Cases]) :-
	Case0 = case(Functor, Goal0),
	detect_cse_in_goal(Goal0, InstMap, !CseInfo, Redo1, Goal),
	Case = case(Functor, Goal),
	detect_cse_in_cases_2(Cases0, InstMap, !CseInfo, Redo2, Cases),
	bool__or(Redo1, Redo2, Redo).

:- pred detect_cse_in_ite(list(prog_var)::in, list(prog_var)::in,
	hlds_goal::in, hlds_goal::in, hlds_goal::in, hlds_goal_info::in,
	instmap::in, cse_info::in, cse_info::out, bool::out,
	hlds_goal_expr::out) is det.

detect_cse_in_ite([], IfVars, Cond0, Then0, Else0, _, InstMap, !CseInfo,
		Redo, if_then_else(IfVars, Cond, Then, Else)) :-
	detect_cse_in_ite_2(Cond0, Then0, Else0, InstMap, !CseInfo, Redo,
		Cond, Then, Else).
detect_cse_in_ite([Var | Vars], IfVars, Cond0, Then0, Else0, GoalInfo,
		InstMap, !CseInfo, Redo, Goal) :-
	(
		ModuleInfo = !.CseInfo ^ module_info,
		instmap__lookup_var(InstMap, Var, VarInst0),
		% XXX we only need inst_is_bound, but leave this as it is
		% until mode analysis can handle aliasing between free
		% variables.
		inst_is_ground_or_any(ModuleInfo, VarInst0),
		common_deconstruct([Then0, Else0], Var, !CseInfo,
			Unify, FirstOldNew, LaterOldNew, Goals),
		Goals = [Then, Else]
	->
		maybe_update_existential_data_structures(Unify,
			FirstOldNew, LaterOldNew, !CseInfo),
		Goal = conj([Unify, if_then_else(IfVars, Cond0, Then, Else)
			- GoalInfo]),
		Redo = yes
	;
		detect_cse_in_ite(Vars, IfVars, Cond0, Then0, Else0, GoalInfo,
			InstMap, !CseInfo, Redo, Goal)
	).

:- pred detect_cse_in_ite_2(hlds_goal::in, hlds_goal::in, hlds_goal::in,
	instmap::in, cse_info::in, cse_info::out, bool::out,
	hlds_goal::out, hlds_goal::out, hlds_goal::out) is det.

detect_cse_in_ite_2(Cond0, Then0, Else0, InstMap0, !CseInfo, Redo,
		Cond, Then, Else) :-
	detect_cse_in_goal_1(Cond0, InstMap0, !CseInfo, Redo1, Cond, InstMap1),
	detect_cse_in_goal(Then0, InstMap1, !CseInfo, Redo2, Then),
	detect_cse_in_goal(Else0, InstMap0, !CseInfo, Redo3, Else),
	bool__or(Redo1, Redo2, Redo12),
	bool__or(Redo12, Redo3, Redo).

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

% common_deconstruct(Goals0, Var, !CseInfo, Unify, Goals):
% input vars:
%	Goals0 is a list of parallel goals in a branched structure
%	(disjunction, if-then-else, or switch).
%	Var is the variable we are looking for a common deconstruction on.
%	!.CseInfo contains the original varset and type map.
% output vars:
%	!:CseInfo has a varset and a type map reflecting the new variables
%	we have introduced.
%	Goals is the modified version of Goals0 after the common deconstruction
%	has been hoisted out, with the new variables as the functor arguments.
%	Unify is the unification that was hoisted out.

:- pred common_deconstruct(list(hlds_goal)::in, prog_var::in, cse_info::in,
	cse_info::out, hlds_goal::out, assoc_list(prog_var)::out,
	list(assoc_list(prog_var))::out, list(hlds_goal)::out) is semidet.

common_deconstruct(Goals0, Var, !CseInfo, Unify, FirstOldNew, LaterOldNew,
		Goals) :-
	common_deconstruct_2(Goals0, Var, before_candidate,
		have_candidate(Unify, FirstOldNew, LaterOldNew),
		!CseInfo, Goals),
	LaterOldNew = [_ | _].

:- pred common_deconstruct_2(list(hlds_goal)::in, prog_var::in,
	cse_state::in, cse_state::out, cse_info::in, cse_info::out,
	list(hlds_goal)::out) is semidet.

common_deconstruct_2([], _Var, !CseState, !CseInfo, []).
common_deconstruct_2([Goal0 | Goals0], Var, !CseState, !CseInfo,
		[Goal | Goals]) :-
	find_bind_var(Var, find_bind_var_for_cse_in_deconstruct, Goal0, Goal,
		!CseState, !CseInfo, yes),
	!.CseState = have_candidate(_, _, _),
	common_deconstruct_2(Goals0, Var, !CseState, !CseInfo, Goals).

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

:- pred common_deconstruct_cases(list(case)::in, prog_var::in,
	cse_info::in, cse_info::out, hlds_goal::out, assoc_list(prog_var)::out,
	list(assoc_list(prog_var))::out, list(case)::out) is semidet.

common_deconstruct_cases(Cases0, Var, !CseInfo, Unify,
		FirstOldNew, LaterOldNew, Cases) :-
	common_deconstruct_cases_2(Cases0, Var, before_candidate,
		have_candidate(Unify, FirstOldNew, LaterOldNew),
		!CseInfo, Cases),
	LaterOldNew = [_ | _].

:- pred common_deconstruct_cases_2(list(case)::in, prog_var::in,
	cse_state::in, cse_state::out, cse_info::in, cse_info::out,
	list(case)::out) is semidet.

common_deconstruct_cases_2([], _Var, !CseState, !CseInfo, []).
common_deconstruct_cases_2([case(ConsId, Goal0) | Cases0], Var,
		!CseState, !CseInfo, [case(ConsId, Goal) | Cases]) :-
	find_bind_var(Var, find_bind_var_for_cse_in_deconstruct, Goal0, Goal,
		!CseState, !CseInfo, yes),
	!.CseState = have_candidate(_, _, _),
	common_deconstruct_cases_2(Cases0, Var, !CseState,
		!CseInfo, Cases).

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

	% This data structure represents the state of the search for
	% deconstructions in all the branches of a branched control structure
	% that deconstruct a given variable with the same functor.
	% Initially, we don't know what unification we will hoist out, so the
	% state is before_candidate. When we find a unification we want to
	% hoist out, this fixes the functor, and the state is have_candidate.
	% If we find that some branches unify that variable with some other
	% functor, we have multiple_candidates, which means that we don't hoist
	% out any of them. (Although our caller may try again with another
	% variable.)
	%
	% The goal field contains the unification we are proposing to put
	% before the branched control structure. The first_old_new field
	% gives the mapping from argument variables in the old unification
	% in the first branch to the freshly created variables in the goal
	% being hoisted before the branched control structure. The
	% later_old_new field contains the same information for the second
	% and later branches.
:- type cse_state
	--->	before_candidate
	;	have_candidate(
			goal		::	hlds_goal,
			first_old_new	::	assoc_list(prog_var),
			later_old_new	::	list(assoc_list(prog_var))
		)
	;	multiple_candidates.

:- pred find_bind_var_for_cse_in_deconstruct(prog_var::in, hlds_goal::in,
	list(hlds_goal)::out, cse_state::in, cse_state::out,
	cse_info::in, cse_info::out) is det.

find_bind_var_for_cse_in_deconstruct(Var, Goal0, Goals,
		!CseState, !CseInfo) :-
	(
		!.CseState = before_candidate,
		construct_common_unify(Var, Goal0, !CseInfo,
			OldNewVars, HoistedGoal, Goals),
		!:CseState = have_candidate(HoistedGoal, OldNewVars, [])
	;
		!.CseState = have_candidate(HoistedGoal,
			FirstOldNewVars, LaterOldNewVars0),
		Goal0 = _ - GoalInfo,
		goal_info_get_context(GoalInfo, Context),
		(
			find_similar_deconstruct(HoistedGoal,
				Goal0, Context, OldNewVars, Goals0)
		->
			Goals = Goals0,
			LaterOldNewVars = [OldNewVars | LaterOldNewVars0],
			!:CseState = have_candidate(HoistedGoal,
				FirstOldNewVars, LaterOldNewVars)
		;
			Goals = [Goal0],
			!:CseState = multiple_candidates
		)
	;
		!.CseState = multiple_candidates,
		Goals = [Goal0],
		!:CseState = multiple_candidates
	).

:- pred construct_common_unify(prog_var::in, hlds_goal::in,
	cse_info::in, cse_info::out, assoc_list(prog_var)::out,
	hlds_goal::out, list(hlds_goal)::out) is det.

construct_common_unify(Var, GoalExpr0 - GoalInfo, !CseInfo, OldNewVars,
		HoistedGoal, Replacements) :-
	(
		GoalExpr0 = unify(_, Term, Umode, Unif0, Ucontext),
		Unif0 = deconstruct(_, Consid, Args, Submodes, CanFail, CanCGC)
	->
		Unif = deconstruct(Var, Consid, Args, Submodes, CanFail,
			CanCGC),
		( Term = functor(_, _, _) ->
			GoalExpr1 = unify(Var, Term, Umode, Unif, Ucontext)
		;
			error("non-functor unify in construct_common_unify")
		),
		goal_info_get_context(GoalInfo, Context),
		create_parallel_subterms(Args, Context, Ucontext,
			!CseInfo, OldNewVars, Replacements),
		map__from_assoc_list(OldNewVars, Sub),
		goal_util__rename_vars_in_goal(GoalExpr1 - GoalInfo, Sub,
			HoistedGoal)
	;
		error("non-unify goal in construct_common_unify")
	).

:- pred create_parallel_subterms(list(prog_var)::in, prog_context::in,
	unify_context::in, cse_info::in, cse_info::out,
	assoc_list(prog_var)::out, list(hlds_goal)::out) is det.

create_parallel_subterms([], _, _, !CseInfo, [], []).
create_parallel_subterms([OFV | OFV0], Context, UnifyContext, !CseInfo,
		OldNewVars, Replacements) :-
	create_parallel_subterms(OFV0, Context, UnifyContext, !CseInfo,
		OldNewVars1, Replacements1),
	create_parallel_subterm(OFV, Context, UnifyContext, !CseInfo,
		OldNewVars1, OldNewVars, Goal),
	Replacements = [Goal | Replacements1].

:- pred create_parallel_subterm(prog_var::in, prog_context::in,
	unify_context::in, cse_info::in, cse_info::out,
	assoc_list(prog_var)::in, assoc_list(prog_var)::out,
	hlds_goal::out) is det.

create_parallel_subterm(OFV, Context, UnifyContext, !CseInfo, !OldNewVar,
		Goal) :-
	VarSet0 = !.CseInfo ^ varset,
	VarTypes0 = !.CseInfo ^ vartypes,
	varset__new_var(VarSet0, NFV, VarSet),
	map__lookup(VarTypes0, OFV, Type),
	map__det_insert(VarTypes0, NFV, Type, VarTypes),
	!:OldNewVar = [OFV - NFV | !.OldNewVar],
	UnifyContext = unify_context(MainCtxt, SubCtxt),
	create_atomic_unification(OFV, var(NFV),
		Context, MainCtxt, SubCtxt, Goal),
	!:CseInfo = (!.CseInfo ^ varset := VarSet) ^ vartypes := VarTypes.

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

:- pred find_similar_deconstruct(hlds_goal::in, hlds_goal::in,
	prog_context::in, assoc_list(prog_var)::out, list(hlds_goal)::out)
	is semidet.

find_similar_deconstruct(HoistedUnifyGoal, OldUnifyGoal, Context,
		OldHoistedVars, Replacements) :-
	(
		HoistedUnifyGoal = unify(_, _, _, HoistedUnifyInfo, OC) - _,
		HoistedUnifyInfo = deconstruct(_, HoistedFunctor,
			HoistedVars, _, _, _),
		OldUnifyGoal = unify(_, _, _, OldUnifyInfo, _NC) - _,
		OldUnifyInfo = deconstruct(_, OldFunctor, OldVars, _, _, _)
	->
		HoistedFunctor = OldFunctor,
		list__length(HoistedVars, HoistedVarsCount),
		list__length(OldVars, OldVarsCount),
		HoistedVarsCount = OldVarsCount,
		assoc_list__from_corresponding_lists(OldVars, HoistedVars,
			OldHoistedVars),
		pair_subterms(OldHoistedVars, Context, OC, Replacements)
	;
		error("find_similar_deconstruct: non-deconstruct unify")
	).

:- pred pair_subterms(assoc_list(prog_var)::in, prog_context::in,
	unify_context::in, list(hlds_goal)::out) is det.

pair_subterms([], _Context, _UnifyContext, []).
pair_subterms([OldVar - HoistedVar | OldHoistedVars], Context, UnifyContext,
		Replacements) :-
	pair_subterms(OldHoistedVars, Context, UnifyContext, Replacements1),
	( OldVar = HoistedVar ->
		Replacements = Replacements1
	;
		UnifyContext = unify_context(MainCtxt, SubCtxt),
		create_atomic_unification(HoistedVar, var(OldVar),
			Context, MainCtxt, SubCtxt, Goal),
		Replacements = [Goal | Replacements1]
	).

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

% This section handles the case where the functor involved in the
% common subexpression contains existentially typed arguments,
% whether or not they are constrained to belong to a typeclass.
% In such cases, what the compiler used to consider several distinct
% types (the types of say the first the existentially typed argument
% in the deconstructions in the different branches) become one (in this
% case, the type of the first existentially typed argument in the
% hoisted out deconstruction). The prog_vars describing the types
% of the existentially typed arguments (i.e. containing their
% typeinfos) change as well, from being some of the variables in
% in the original deconstructions to being the corresponding variables
% in the hoisted out deconstruction.
%
% As an example, consider a disjunction such as
%
%	(
%		HeadVar__2_2 = x:u(TypeClassInfo_for_v_8, V_4),
%		...
%	;
%		HeadVar__2_2 = x:u(TypeClassInfo_for_v_14, V_6)
%		...
%	)
%
% The main part of cse_detection will replace this with
%
%	HeadVar__2_2 = x:u(V_17, V_16)
%	(
%		TypeClassInfo_for_v_8 = V_17,
%		V_4 = V_16,
%		...
%	;
%		TypeClassInfo_for_v_14 = V_17,
%		V_6 = V_16,
%		...
%	)
%
% However, this is not enough. Since TypeClassInfo_for_v_8 and
% TypeClassInfo_for_v_14 may (and probably will) be eliminated later,
% it is imperative that the data structures in the proc_info that refer
% to them be updated to eliminate references to those variables.
% Those data structures may originally contain something like this:
%
% type_info varmap:
% T_1 (number 1) -> typeclass_info(TypeClassInfo_for_v_8, 1)
% T_3 (number 3) -> typeclass_info(TypeClassInfo_for_v_14, 1)
% typeclass_info varmap:
% x:v(T_1) -> TypeClassInfo_for_v_8
% x:v(T_3) -> TypeClassInfo_for_v_14
% variable types map:
% V_4 (number 4) :: T_1
% V_6 (number 6) :: T_3
%
% They must be updated like this:
%
% type_info varmap:
% T_1 (number 1) -> typeclass_info(V_17, 1)
% typeclass_info varmap:
% x:v(T_1) -> V_17
% variable types map:
% V_4 (number 4) :: T_1
% V_6 (number 6) :: T_1

:- pred maybe_update_existential_data_structures(hlds_goal::in,
	assoc_list(prog_var)::in, list(assoc_list(prog_var))::in,
	cse_info::in, cse_info::out) is det.

maybe_update_existential_data_structures(Unify, FirstOldNew, LaterOldNew,
		!CseInfo) :-
	(
		Unify = unify(_, _, _, UnifyInfo, _) - _,
		UnifyInfo = deconstruct(Var, ConsId, _, _, _, _),
		ModuleInfo = !.CseInfo ^ module_info,
		VarTypes = !.CseInfo ^ vartypes,
		map__lookup(VarTypes, Var, Type),
		type_util__is_existq_cons(ModuleInfo, Type, ConsId)
	->
		update_existential_data_structures(FirstOldNew, LaterOldNew,
			!CseInfo)
	;
		true
	).

:- pred update_existential_data_structures(
	assoc_list(prog_var)::in, list(assoc_list(prog_var))::in,
	cse_info::in, cse_info::out) is det.

update_existential_data_structures(FirstOldNew, LaterOldNews, !CseInfo) :-
	list__condense(LaterOldNews, LaterOldNew),
	list__append(FirstOldNew, LaterOldNew, OldNew),
	map__from_assoc_list(OldNew, OldNewMap),
	map__from_assoc_list(FirstOldNew, FirstOldNewMap),

	TypeInfoVarMap0 = !.CseInfo ^ type_info_varmap,
	TypeClassInfoVarMap0 = !.CseInfo ^ typeclass_info_varmap,
	VarTypes0 = !.CseInfo ^ vartypes,

	map__to_assoc_list(TypeInfoVarMap0, TypeInfoVarList0),
	list__foldl(find_type_info_locn_tvar_map(FirstOldNewMap),
		TypeInfoVarList0, map__init, NewTvarMap),

	list__foldl2(reconstruct_type_info_varmap(OldNewMap, NewTvarMap),
		TypeInfoVarList0, map__init, TypeInfoVarMap1,
		map__init, TvarSub),
	map__keys(TvarSub, ElimTvars),
	map__delete_list(TypeInfoVarMap1, ElimTvars, TypeInfoVarMap),

	map__to_assoc_list(TypeClassInfoVarMap0, TypeClassInfoVarList0),
	list__foldl(reconstruct_typeclass_info_varmap(OldNewMap, TvarSub),
		TypeClassInfoVarList0, map__init, TypeClassInfoVarMap),

	map__map_values(apply_tvar_rename(TvarSub), VarTypes0, VarTypes),

	!:CseInfo = !.CseInfo ^ type_info_varmap := TypeInfoVarMap,
	!:CseInfo = !.CseInfo ^ typeclass_info_varmap := TypeClassInfoVarMap,
	!:CseInfo = !.CseInfo ^ vartypes := VarTypes.

:- pred apply_tvar_rename(map(tvar, tvar)::in, prog_var::in,
	(type)::in, (type)::out) is det.

apply_tvar_rename(TvarSub, _Var, Type0, Type) :-
	Type = term__apply_variable_renaming(Type0, TvarSub).

:- pred find_type_info_locn_tvar_map(map(prog_var, prog_var)::in,
	pair(tvar, type_info_locn)::in,
 	map(type_info_locn, tvar)::in, map(type_info_locn, tvar)::out) is det.

find_type_info_locn_tvar_map(FirstOldNewMap, Tvar - TypeInfoLocn0,
		NewTvarMap0, NewTvarMap) :-
 	type_info_locn_var(TypeInfoLocn0, Old),
 	( map__search(FirstOldNewMap, Old, New) ->
  		type_info_locn_set_var(New, TypeInfoLocn0, TypeInfoLocn),
 		map__det_insert(NewTvarMap0, TypeInfoLocn, Tvar, NewTvarMap)
 	;
 		NewTvarMap = NewTvarMap0
 	).

:- pred reconstruct_type_info_varmap(map(prog_var, prog_var)::in,
	map(type_info_locn, tvar)::in, pair(tvar, type_info_locn)::in,
 	map(tvar, type_info_locn)::in, map(tvar, type_info_locn)::out,
	map(tvar, tvar)::in, map(tvar, tvar)::out) is det.

reconstruct_type_info_varmap(FirstOldNewMap, NewTvarMap, Tvar - TypeInfoLocn0,
		TypeInfoVarMap0, TypeInfoVarMap, TvarSub0, TvarSub) :-
 	type_info_locn_var(TypeInfoLocn0, Old),
 	( map__search(FirstOldNewMap, Old, New) ->
  		type_info_locn_set_var(New, TypeInfoLocn0, TypeInfoLocn),
 		map__det_insert(TypeInfoVarMap0, Tvar, TypeInfoLocn,
			TypeInfoVarMap),
		map__lookup(NewTvarMap, TypeInfoLocn, NewTvar),
		( Tvar = NewTvar ->
			TvarSub = TvarSub0
		;
			map__det_insert(TvarSub0, Tvar, NewTvar, TvarSub)
		)
 	;
		map__det_insert(TypeInfoVarMap0, Tvar, TypeInfoLocn0,
			TypeInfoVarMap),
		TvarSub = TvarSub0
 	).

:- pred reconstruct_typeclass_info_varmap(map(prog_var, prog_var)::in,
	map(tvar, tvar)::in, pair(class_constraint, prog_var)::in,
	typeclass_info_varmap::in, typeclass_info_varmap::out) is det.

reconstruct_typeclass_info_varmap(OldNewMap, TvarSub,
		Constraint0 - TypeClassInfoVar0,
		TypeClassInfoVarMap0, TypeClassInfoVarMap) :-
	type_util__apply_variable_renaming_to_constraint(TvarSub,
		Constraint0, Constraint),
	( map__search(OldNewMap, TypeClassInfoVar0, TypeClassInfoVar1) ->
		TypeClassInfoVar = TypeClassInfoVar1
	;
		TypeClassInfoVar = TypeClassInfoVar0
	),
	( map__search(TypeClassInfoVarMap0, Constraint, OldTypeClassInfoVar) ->
		require(unify(OldTypeClassInfoVar, TypeClassInfoVar),
			"reconstruct_typeclass_info_varmap: mismatch"),
		TypeClassInfoVarMap = TypeClassInfoVarMap0
	;
		map__det_insert(TypeClassInfoVarMap0, Constraint,
			TypeClassInfoVar, TypeClassInfoVarMap)
	).

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