%---------------------------------------------------------------------------% % vim: ft=mercury ts=4 sw=4 et %---------------------------------------------------------------------------% % Copyright (C) 1995-2012 The University of Melbourne. % Copyright (C) 2015 The Mercury team. % This file may only be copied under the terms of the GNU General % Public License - see the file COPYING in the Mercury distribution. %---------------------------------------------------------------------------% % % File: common.m. % Original author: squirrel (Jane Anna Langley). % Other authors: fjh, zs, stayl. % % The main task of this module is to look for conjoined goals that involve % the same structure (the "common" structure the module is named after), % and to optimize those goals. The reason why we created this module was % code like this: % % X => f(A, B, C), % ... % Y <= f(A, B, C) % % This module replaces this code with % % X => f(A, B, C), % ... % Y := X % % since this allocates less memory on the heap. % % We want to perform this optimization even if the deconstruction of X and % the construction of Y are not in the same conjunction, but are nevertheless % conjoined (e.g. because the construction of Y is inside an if-then-else % or a disjunction that is inside the conjunction containing the deconstruction % of X). We also want to do it if the two argument lists are not equal % syntactically, but instead look like this: % % X => f(A, B, C1), % ... % C2 := C1 % ... % Y <= f(A, B, C2) % % We therefore have to keep track of pretty much all unifications in the body % of the procedure being optimized. Since we have this information laying % around anyway, we also use to for two other purposes. The first is % to eliminate unnecessary tests of function symbols, replacing % % X => f(A1, B1, C1), % ... % X => f(A2, B2, C2) % % with % % X => f(A1, B1, C1), % ... % A2 := A1, % B2 := B1, % C2 := C1 % % provided that this does not increase the number of variables that % have to be saved across calls and other stack flushes. % % The other is to detect and optimize duplicate calls, replacing % % p(InA, InB, OutC1, OutD1), % ... % p(InA, InB, OutC2, OutD2) % % with % % p(InA, InB, OutC1, OutD1), % ... % OutC2 := OutC1, % OutD2 := OutD1 % % Since the author probably did not mean to write duplicate calls, we also % generate a warning for such code, if the option asking for such warnings % is set. % % IMPORTANT: This module does a small subset of the job of compile-time % garbage collection, but it does so without paying attention to uniqueness % information, since the compiler does not yet have such information. % Once we implement ctgc, the assumptions made by this module % will have to be revisited. % % NOTE: There is another compiler module, cse_detection.m, that looks for % unifications involving common structures in *disjoined*, not *conjoined* % goals. Its purpose is not optimization, but the generation of more precise % determinism information. % %---------------------------------------------------------------------------% :- module check_hlds.simplify.common. :- interface. :- import_module check_hlds.simplify.simplify_info. :- import_module hlds. :- import_module hlds.hlds_goal. :- import_module hlds.hlds_pred. :- import_module parse_tree. :- import_module parse_tree.prog_data. :- import_module list. :- import_module maybe. %---------------------------------------------------------------------------% % Assorted stuff used here that the rest of the simplify package % does not need to know about. % :- type common_info. :- func common_info_init = common_info. % Clear the list of structs seen since the last stack flush. % :- pred common_info_clear_structs(common_info::in, common_info::out) is det. % If we find a construction that constructs a cell identical to one we % have seen before, replace the construction with an assignment from the % variable that already holds that cell. % % If we find a deconstruction or a construction we cannot optimize, record % the details of the memory cell in the updated common_info. % :- pred common_optimise_unification(unification::in, unify_mode::in, hlds_goal_expr::in, hlds_goal_expr::out, hlds_goal_info::in, hlds_goal_info::out, common_info::in, common_info::out, simplify_info::in, simplify_info::out) is det. % Check whether this call has been seen before and is replaceable. % If it is, generate assignment unifications for the nonlocal output % variables (to remove the redundant call), and a warning (since the % programmer probably did not mean to write a redundant call). % % A call is considered replaceable if it is pure, and it has neither % destructive inputs nor uniquely moded outputs. % :- pred common_optimise_call(pred_id::in, proc_id::in, list(prog_var)::in, purity::in, hlds_goal_info::in, hlds_goal_expr::in, maybe(hlds_goal_expr)::out, common_info::in, common_info::out, simplify_info::in, simplify_info::out) is det. :- pred common_optimise_higher_order_call(prog_var::in, list(prog_var)::in, list(mer_mode)::in, determinism::in, purity::in, hlds_goal_info::in, hlds_goal_expr::in, maybe(hlds_goal_expr)::out, common_info::in, common_info::out, simplify_info::in, simplify_info::out) is det. % Succeeds if the two variables are equivalent according to the % information in the specified common_info. % :- pred common_vars_are_equivalent(common_info::in, prog_var::in, prog_var::in) is semidet. %---------------------------------------------------------------------------% %---------------------------------------------------------------------------% :- implementation. :- import_module check_hlds.det_report. :- import_module check_hlds.inst_match. :- import_module check_hlds.inst_test. :- import_module check_hlds.mode_util. :- import_module hlds.hlds_module. :- import_module hlds.hlds_rtti. :- import_module hlds.instmap. :- import_module hlds.vartypes. :- import_module libs. :- import_module libs.options. :- import_module parse_tree.error_util. :- import_module parse_tree.prog_type. :- import_module parse_tree.set_of_var. :- import_module transform_hlds. :- import_module transform_hlds.pd_cost. :- import_module bool. :- import_module eqvclass. :- import_module map. :- import_module pair. :- import_module require. :- import_module term. %---------------------------------------------------------------------------% % The var_eqv field records information about which sets of variables are % known to be equivalent, usually because they have been unified. This is % useful when eliminating duplicate unifications and when eliminating % duplicate calls. % % The all_structs and since_call_structs fields record information about % the memory cells available for reuse. The all_structs field has info % about all the cells available at the current program point. The % since_call_structs field contains info about the subset of these cells % that have been seen since the last stack flush, which is usually a call. % % The reason why we make the distinction between structs seen before the % last call and structs seen after is best explained by these two program % fragments: % % fragment 1: % X => f(A1, A2, A3, A4), % X => f(B1, B2, B3, B4), % % fragment 2: % X => f(A1, A2, A3, A4), % p(...), % X => f(B1, B2, B3, B4), % % In fragment 1, we want to replace the second deconstruction with % the assignments B1 = A1, ... B4 = A4, since this can avoid the % second check of X's function symbol. (If the inst of X at the start % of the second unification is `bound(f(...))', we can dispense with % this test anyway, but if the two unifications are brought together % by inlining, then X's inst then may simply be `ground'.) % % In fragment 2, we don't want make the same transformation, because % doing so would require storing A1 ... A4 across the call instead of % just X. % % If the second unification were a construction instead of a % deconstruction, we want to make the transformation in both cases, % because the heap allocation we thus avoid is quite expensive, % and because it actually reduces the number of stack slots we need % across the call (X instead of A1 .. A4). The exception is % constructions using function symbols of arity zero, which we % never need to eliminate. We process unifications with constants % only to update our information about variable equivalences: after % X = c and Y = c, X and Y are equivalent. % % The seen_calls field records which calls we have seen, which we use % to eliminate duplicate calls. :- type common_info ---> common_info( var_eqv :: eqvclass(prog_var), all_structs :: struct_map, since_call_structs :: struct_map, seen_calls :: seen_calls ). % A struct_map maps a principal type constructor and a cons_id of that % type to information about cells involving that cons_id. % % The reason why we need the principal type constructors is that % two syntactically identical structures are guaranteed to have % compatible representations if and ONLY if their principal type % constructors are the same. For example, if we have: % % :- type maybe_err(T) ---> ok(T) ; err(string). % % :- pred p(maybe_err(foo)::in, maybe_err(bar)::out) is semidet. % p(err(X), err(X)). % % then we want to reuse the `err(X)' in the first arg rather than % constructing a new copy of it for the second arg. % The two occurrences of `err(X)' have types `maybe_err(int)' and % `maybe(float)', but we know that they have the same representation. % % Instead of a simple map whose keys are pairs, % we use a two-stage map, with the keys being type_ctors in the first stage % and cons_ids in the second. Having two stages makes the comparisons % cheaper, and we put the type_ctors first to avoid mixing together % cons_ids from different type constructors. :- type struct_map == map(type_ctor, cons_id_map). :- type cons_id_map == map(cons_id, structures). % Given a unification X = f(Y1, ... Yn), we record its availability for % reuse by creating structure(X, [Y1, ... Yn]), and putting it at the % front of the list of structures for the entry for f and X's type_ctor. :- type structures == list(structure). :- type structure ---> structure(prog_var, list(prog_var)). :- type seen_calls == map(seen_call_id, list(call_args)). :- type call_args ---> call_args( % The context of the call, for use in warnings about % duplicate calls. prog_context, % The input arguments. For higher-order calls, the closure % is the first input argument. list(prog_var), % The output arguments. list(prog_var) ). %---------------------------------------------------------------------------% common_info_init = CommonInfo :- eqvclass.init(VarEqv0), map.init(StructMap0), map.init(SeenCalls0), CommonInfo = common_info(VarEqv0, StructMap0, StructMap0, SeenCalls0). common_info_clear_structs(!Info) :- !Info ^ since_call_structs := map.init. %---------------------------------------------------------------------------% common_optimise_unification(Unification0, Mode, !GoalExpr, !GoalInfo, !Common, !Info) :- ( Unification0 = construct(Var, ConsId, ArgVars, _, _, _, SubInfo), ( if SubInfo = construct_sub_info(MaybeTakeAddr, _), MaybeTakeAddr = yes(_) then true else common_optimise_construct(Var, ConsId, ArgVars, Mode, !GoalExpr, !GoalInfo, !Common, !Info) ) ; Unification0 = deconstruct(Var, ConsId, ArgVars, ArgModes, CanFail, _), common_optimise_deconstruct(Var, ConsId, ArgVars, ArgModes, CanFail, Mode, !GoalExpr, !GoalInfo, !Common, !Info) ; ( Unification0 = assign(Var1, Var2) ; Unification0 = simple_test(Var1, Var2) ), record_equivalence(Var1, Var2, !Common) ; Unification0 = complicated_unify(_, _, _) ). :- pred common_optimise_construct(prog_var::in, cons_id::in, list(prog_var)::in, unify_mode::in, hlds_goal_expr::in, hlds_goal_expr::out, hlds_goal_info::in, hlds_goal_info::out, common_info::in, common_info::out, simplify_info::in, simplify_info::out) is det. common_optimise_construct(Var, ConsId, ArgVars, UnifyMode, GoalExpr0, GoalExpr, GoalInfo0, GoalInfo, !Common, !Info) :- simplify_info_get_module_info(!.Info, ModuleInfo), UnifyMode = unify_modes_li_lf_ri_rf(_, LVarFinalInst, _, _), % Don't optimise partially instantiated construction unifications, % because it would be tricky to work out how to mode the replacement % assignment unifications. In the vast majority of cases, the variable % is ground. ( if inst_is_ground(ModuleInfo, LVarFinalInst) then TypeCtor = lookup_var_type_ctor(!.Info, Var), VarEqv0 = !.Common ^ var_eqv, list.map_foldl(eqvclass.ensure_element_partition_id, ArgVars, ArgVarIds, VarEqv0, VarEqv1), AllStructMap0 = !.Common ^ all_structs, ( if % generate_assign assumes that the output variable % is in the instmap_delta, which will not be true if the % variable is local to the unification. The optimization % is pointless in that case. InstMapDelta = goal_info_get_instmap_delta(GoalInfo0), instmap_delta_search_var(InstMapDelta, Var, _), map.search(AllStructMap0, TypeCtor, ConsIdMap0), map.search(ConsIdMap0, ConsId, Structs), find_matching_cell_construct(Structs, VarEqv1, ArgVarIds, OldStruct) then OldStruct = structure(OldVar, _), eqvclass.ensure_equivalence(Var, OldVar, VarEqv1, VarEqv), !Common ^ var_eqv := VarEqv, ( ArgVars = [], % Constants don't use memory, so there is no point in % optimizing away their construction; in fact, doing so % could cause more stack usage. GoalExpr = GoalExpr0, GoalInfo = GoalInfo0 ; ArgVars = [_ | _], VarFromToInsts = from_to_insts(LVarFinalInst, LVarFinalInst), generate_assign(Var, OldVar, VarFromToInsts, GoalInfo0, GoalExpr, GoalInfo, !Common, !Info), simplify_info_set_should_requantify(!Info), goal_cost(hlds_goal(GoalExpr0, GoalInfo0), Cost), simplify_info_incr_cost_delta(Cost, !Info) ) else GoalExpr = GoalExpr0, GoalInfo = GoalInfo0, Struct = structure(Var, ArgVars), record_cell_in_maps(TypeCtor, ConsId, Struct, VarEqv1, !Common) ) else GoalExpr = GoalExpr0, GoalInfo = GoalInfo0 ). :- pred common_optimise_deconstruct(prog_var::in, cons_id::in, list(prog_var)::in, list(unify_mode)::in, can_fail::in, unify_mode::in, hlds_goal_expr::in, hlds_goal_expr::out, hlds_goal_info::in, hlds_goal_info::out, common_info::in, common_info::out, simplify_info::in, simplify_info::out) is det. common_optimise_deconstruct(Var, ConsId, ArgVars, ArgModes, CanFail, UnifyMode, GoalExpr0, GoalExpr, GoalInfo0, GoalInfo, !Common, !Info) :- simplify_info_get_module_info(!.Info, ModuleInfo), ( if % Don't optimise partially instantiated deconstruction unifications, % because it would be tricky to work out how to mode the replacement % assignment unifications. In the vast majority of cases, the variable % is ground. UnifyMode = unify_modes_li_lf_ri_rf(LVarInitInst, _, _, _), not inst_is_ground(ModuleInfo, LVarInitInst) then GoalExpr = GoalExpr0 else TypeCtor = lookup_var_type_ctor(!.Info, Var), VarEqv0 = !.Common ^ var_eqv, eqvclass.ensure_element_partition_id(Var, VarId, VarEqv0, VarEqv1), SinceCallStructMap0 = !.Common ^ since_call_structs, ( if % Do not delete deconstruction unifications inserted by % stack_opt.m or tupling.m, which have done a more comprehensive % cost analysis than common.m can do. not goal_info_has_feature(GoalInfo, feature_stack_opt), not goal_info_has_feature(GoalInfo, feature_tuple_opt), map.search(SinceCallStructMap0, TypeCtor, ConsIdMap0), map.search(ConsIdMap0, ConsId, Structs), find_matching_cell_deconstruct(Structs, VarEqv1, VarId, OldStruct) then OldStruct = structure(_, OldArgVars), eqvclass.ensure_corresponding_equivalences(ArgVars, OldArgVars, VarEqv1, VarEqv), !Common ^ var_eqv := VarEqv, RHSFromToInsts = list.map(unify_modes_to_rhs_from_to_insts, ArgModes), create_output_unifications(GoalInfo0, ArgVars, OldArgVars, RHSFromToInsts, Goals, !Common, !Info), GoalExpr = conj(plain_conj, Goals), goal_cost(hlds_goal(GoalExpr0, GoalInfo0), Cost), simplify_info_incr_cost_delta(Cost, !Info), simplify_info_set_should_requantify(!Info), ( CanFail = can_fail, simplify_info_set_should_rerun_det(!Info) ; CanFail = cannot_fail ) else GoalExpr = GoalExpr0, Struct = structure(Var, ArgVars), record_cell_in_maps(TypeCtor, ConsId, Struct, VarEqv1, !Common) ) ), GoalInfo = GoalInfo0. :- func lookup_var_type_ctor(simplify_info, prog_var) = type_ctor. lookup_var_type_ctor(Info, Var) = TypeCtor :- simplify_info_get_var_types(Info, VarTypes), lookup_var_type(VarTypes, Var, Type), % If we unify a variable with a function symbol, we *must* know % what the principal type constructor of its type is. type_to_ctor_det(Type, TypeCtor). %---------------------------------------------------------------------------% :- pred find_matching_cell_construct(structures::in, eqvclass(prog_var)::in, list(partition_id)::in, structure::out) is semidet. find_matching_cell_construct([Struct | Structs], VarEqv, ArgVarIds, Match) :- Struct = structure(_Var, Vars), ( if ids_vars_match(ArgVarIds, Vars, VarEqv) then Match = Struct else find_matching_cell_construct(Structs, VarEqv, ArgVarIds, Match) ). :- pred find_matching_cell_deconstruct(structures::in, eqvclass(prog_var)::in, partition_id::in, structure::out) is semidet. find_matching_cell_deconstruct([Struct | Structs], VarEqv, VarId, Match) :- Struct = structure(Var, _Vars), ( if id_var_match(VarId, Var, VarEqv) then Match = Struct else find_matching_cell_deconstruct(Structs, VarEqv, VarId, Match) ). :- pred ids_vars_match(list(partition_id)::in, list(prog_var)::in, eqvclass(prog_var)::in) is semidet. ids_vars_match([], [], _VarEqv). ids_vars_match([Id | Ids], [Var | Vars], VarEqv) :- id_var_match(Id, Var, VarEqv), ids_vars_match(Ids, Vars, VarEqv). :- pred id_var_match(partition_id::in, prog_var::in, eqvclass(prog_var)::in) is semidet. :- pragma inline(id_var_match/3). id_var_match(Id, Var, VarEqv) :- eqvclass.partition_id(VarEqv, Var, VarId), Id = VarId. %---------------------------------------------------------------------------% :- pred record_cell_in_maps(type_ctor::in, cons_id::in, structure::in, eqvclass(prog_var)::in, common_info::in, common_info::out) is det. record_cell_in_maps(TypeCtor, ConsId, Struct, VarEqv, !Common) :- AllStructMap0 = !.Common ^ all_structs, SinceCallStructMap0 = !.Common ^ since_call_structs, do_record_cell_in_struct_map(TypeCtor, ConsId, Struct, AllStructMap0, AllStructMap), do_record_cell_in_struct_map(TypeCtor, ConsId, Struct, SinceCallStructMap0, SinceCallStructMap), !Common ^ var_eqv := VarEqv, !Common ^ all_structs := AllStructMap, !Common ^ since_call_structs := SinceCallStructMap. :- pred do_record_cell_in_struct_map(type_ctor::in, cons_id::in, structure::in, struct_map::in, struct_map::out) is det. do_record_cell_in_struct_map(TypeCtor, ConsId, Struct, !StructMap) :- ( if map.search(!.StructMap, TypeCtor, ConsIdMap0) then ( if map.search(ConsIdMap0, ConsId, Structs0) then Structs = [Struct | Structs0], map.det_update(ConsId, Structs, ConsIdMap0, ConsIdMap) else map.det_insert(ConsId, [Struct], ConsIdMap0, ConsIdMap) ), map.det_update(TypeCtor, ConsIdMap, !StructMap) else ConsIdMap = map.singleton(ConsId, [Struct]), map.det_insert(TypeCtor, ConsIdMap, !StructMap) ). %---------------------------------------------------------------------------% :- pred record_equivalence(prog_var::in, prog_var::in, common_info::in, common_info::out) is det. record_equivalence(VarA, VarB, !Common) :- VarEqv0 = !.Common ^ var_eqv, eqvclass.ensure_equivalence(VarA, VarB, VarEqv0, VarEqv), !Common ^ var_eqv := VarEqv. %---------------------------------------------------------------------------% %---------------------------------------------------------------------------% common_optimise_call(PredId, ProcId, Args, Purity, GoalInfo, GoalExpr0, MaybeAssignsGoalExpr, !Common, !Info) :- ( if Purity = purity_pure, Det = goal_info_get_determinism(GoalInfo), check_call_detism(Det), simplify_info_get_var_types(!.Info, VarTypes), simplify_info_get_module_info(!.Info, ModuleInfo), module_info_pred_proc_info(ModuleInfo, PredId, ProcId, _, ProcInfo), proc_info_get_argmodes(ProcInfo, ArgModes), partition_call_args(VarTypes, ModuleInfo, ArgModes, Args, InputArgs, OutputArgs, OutputModes) then common_optimise_call_2(seen_call(PredId, ProcId), InputArgs, OutputArgs, OutputModes, GoalInfo, GoalExpr0, MaybeAssignsGoalExpr, !Common, !Info) else MaybeAssignsGoalExpr = no ). common_optimise_higher_order_call(Closure, Args, Modes, Det, Purity, GoalInfo, GoalExpr0, MaybeAssignsGoalExpr, !Common, !Info) :- ( if Purity = purity_pure, check_call_detism(Det), simplify_info_get_var_types(!.Info, VarTypes), simplify_info_get_module_info(!.Info, ModuleInfo), partition_call_args(VarTypes, ModuleInfo, Modes, Args, InputArgs, OutputArgs, OutputModes) then common_optimise_call_2(higher_order_call, [Closure | InputArgs], OutputArgs, OutputModes, GoalInfo, GoalExpr0, MaybeAssignsGoalExpr, !Common, !Info) else MaybeAssignsGoalExpr = no ). :- pred check_call_detism(determinism::in) is semidet. check_call_detism(Det) :- determinism_components(Det, _, SolnCount), % Replacing nondet or multi calls would cause loss of solutions. ( SolnCount = at_most_one ; SolnCount = at_most_many_cc ). :- pred common_optimise_call_2(seen_call_id::in, list(prog_var)::in, list(prog_var)::in, list(mer_mode)::in, hlds_goal_info::in, hlds_goal_expr::in, maybe(hlds_goal_expr)::out, common_info::in, common_info::out, simplify_info::in, simplify_info::out) is det. common_optimise_call_2(SeenCall, InputArgs, OutputArgs, Modes, GoalInfo, GoalExpr0, MaybeAssignsGoalExpr, Common0, Common, !Info) :- Eqv0 = Common0 ^ var_eqv, SeenCalls0 = Common0 ^ seen_calls, ( if map.search(SeenCalls0, SeenCall, SeenCallsList0) then ( if find_previous_call(SeenCallsList0, InputArgs, Eqv0, OutputArgs2, PrevContext) then simplify_info_get_module_info(!.Info, ModuleInfo), list.map(mode_get_from_to_insts(ModuleInfo), Modes, FromToInsts), create_output_unifications(GoalInfo, OutputArgs, OutputArgs2, FromToInsts, AssignGoals, Common0, Common, !Info), ( if AssignGoals = [hlds_goal(OnlyGoalExpr, _OnlyGoalInfo)] then AssignsGoalExpr = OnlyGoalExpr else AssignsGoalExpr = conj(plain_conj, AssignGoals) ), MaybeAssignsGoalExpr = yes(AssignsGoalExpr), simplify_info_get_var_types(!.Info, VarTypes), ( if simplify_do_warn_duplicate_calls(!.Info), % Don't warn for cases such as: % set.init(Set1 : set(int)), % set.init(Set2 : set(float)). lookup_var_types(VarTypes, OutputArgs, OutputArgTypes1), lookup_var_types(VarTypes, OutputArgs2, OutputArgTypes2), types_match_exactly_list(OutputArgTypes1, OutputArgTypes2) then Context = goal_info_get_context(GoalInfo), CallPieces = det_report_seen_call_id(ModuleInfo, SeenCall), CurPieces = [words("Warning: redundant") | CallPieces] ++ [suffix(".")], PrevPieces = [words("Here is the previous") | CallPieces] ++ [suffix(".")], Severity = severity_conditional(warn_duplicate_calls, yes, severity_warning, no), Msg = simple_msg(Context, [option_is_set(warn_duplicate_calls, yes, [always(CurPieces)])]), PrevMsg = error_msg(yes(PrevContext), treat_as_first, 0, [option_is_set(warn_duplicate_calls, yes, [always(PrevPieces)])]), Spec = error_spec(Severity, phase_simplify(report_in_any_mode), [Msg, PrevMsg]), simplify_info_add_message(Spec, !Info) else true ), goal_cost(hlds_goal(GoalExpr0, GoalInfo), Cost), simplify_info_incr_cost_delta(Cost, !Info), simplify_info_set_should_requantify(!Info), Detism0 = goal_info_get_determinism(GoalInfo), ( Detism0 = detism_det ; ( Detism0 = detism_semi ; Detism0 = detism_non ; Detism0 = detism_multi ; Detism0 = detism_failure ; Detism0 = detism_erroneous ; Detism0 = detism_cc_non ; Detism0 = detism_cc_multi ), simplify_info_set_should_rerun_det(!Info) ) else Context = goal_info_get_context(GoalInfo), ThisCall = call_args(Context, InputArgs, OutputArgs), map.det_update(SeenCall, [ThisCall | SeenCallsList0], SeenCalls0, SeenCalls), Common = Common0 ^ seen_calls := SeenCalls, MaybeAssignsGoalExpr = no ) else Context = goal_info_get_context(GoalInfo), ThisCall = call_args(Context, InputArgs, OutputArgs), map.det_insert(SeenCall, [ThisCall], SeenCalls0, SeenCalls), Common = Common0 ^ seen_calls := SeenCalls, MaybeAssignsGoalExpr = no ). %---------------------------------------------------------------------------% % Partition the arguments of a call into inputs and outputs, % failing if any of the outputs have a unique component % or if any of the outputs contain any `any' insts. % :- pred partition_call_args(vartypes::in, module_info::in, list(mer_mode)::in, list(prog_var)::in, list(prog_var)::out, list(prog_var)::out, list(mer_mode)::out) is semidet. partition_call_args(_, _, [], [], [], [], []). partition_call_args(_, _, [], [_ | _], _, _, _) :- unexpected($pred, "length mismatch (1)"). partition_call_args(_, _, [_ | _], [], _, _, _) :- unexpected($pred, "length mismatch (2)"). partition_call_args(VarTypes, ModuleInfo, [ArgMode | ArgModes], [Arg | Args], InputArgs, OutputArgs, OutputModes) :- partition_call_args(VarTypes, ModuleInfo, ArgModes, Args, InputArgs1, OutputArgs1, OutputModes1), mode_get_insts(ModuleInfo, ArgMode, InitialInst, FinalInst), lookup_var_type(VarTypes, Arg, Type), ( if inst_matches_binding(InitialInst, FinalInst, Type, ModuleInfo) then InputArgs = [Arg | InputArgs1], OutputArgs = OutputArgs1, OutputModes = OutputModes1 else % Calls with partly unique outputs cannot be replaced, % since a unique copy of the outputs must be produced. inst_is_not_partly_unique(ModuleInfo, FinalInst), % Don't optimize calls whose outputs include any `any' insts, since % that would create false aliasing between the different variables. % (inst_matches_binding applied to identical insts fails only for % `any' insts.) inst_matches_binding(FinalInst, FinalInst, Type, ModuleInfo), % Don't optimize calls where a partially instantiated variable is % further instantiated. That case is difficult to test properly % because mode analysis currently rejects most potential test cases. inst_is_free(ModuleInfo, InitialInst), InputArgs = InputArgs1, OutputArgs = [Arg | OutputArgs1], OutputModes = [ArgMode | OutputModes1] ). %---------------------------------------------------------------------------% :- pred find_previous_call(list(call_args)::in, list(prog_var)::in, eqvclass(prog_var)::in, list(prog_var)::out, prog_context::out) is semidet. find_previous_call([SeenCall | SeenCalls], InputArgs, Eqv, OutputArgs, PrevContext) :- SeenCall = call_args(PrevContext, InputArgs1, OutputArgs1), ( if common_var_lists_are_equiv(Eqv, InputArgs, InputArgs1) then OutputArgs = OutputArgs1 else find_previous_call(SeenCalls, InputArgs, Eqv, OutputArgs, PrevContext) ). %---------------------------------------------------------------------------% % Succeeds if the two lists of variables are equivalent % according to the specified equivalence class. % :- pred common_var_lists_are_equiv(eqvclass(prog_var)::in, list(prog_var)::in, list(prog_var)::in) is semidet. common_var_lists_are_equiv(_VarEqv, [], []). common_var_lists_are_equiv(VarEqv, [X | Xs], [Y | Ys]) :- common_vars_are_equiv(VarEqv, X, Y), common_var_lists_are_equiv(VarEqv, Xs, Ys). common_vars_are_equivalent(CommonInfo, X, Y) :- EqvVars = CommonInfo ^ var_eqv, common_vars_are_equiv(EqvVars, X, Y). % Succeeds if the two variables are equivalent according to the % specified equivalence class. % :- pred common_vars_are_equiv(eqvclass(prog_var)::in, prog_var::in, prog_var::in) is semidet. common_vars_are_equiv(VarEqv, X, Y) :- ( X = Y ; eqvclass.partition_id(VarEqv, X, Id), eqvclass.partition_id(VarEqv, Y, Id) ). %---------------------------------------------------------------------------% % Create unifications to assign the vars in OutputArgs from the % corresponding var in OldOutputArgs. This needs to be done even if % OutputArg is not a nonlocal in the original goal, because later goals % in the conjunction may match against the cell and need all the output % arguments. Any unneeded assignments will be removed later. % :- pred create_output_unifications(hlds_goal_info::in, list(prog_var)::in, list(prog_var)::in, list(from_to_insts)::in, list(hlds_goal)::out, common_info::in, common_info::out, simplify_info::in, simplify_info::out) is det. create_output_unifications(OldGoalInfo, OutputArgs, OldOutputArgs, FromToInsts, AssignGoals, !Common, !Info) :- ( if OutputArgs = [HeadOutputArg | TailOutputArgs], OldOutputArgs = [HeadOldOutputArg | TailOldOutputArgs], FromToInsts = [HeadFromToInsts | TailFromToInsts] then ( if HeadOutputArg = HeadOldOutputArg then % This can happen if the first cell was created % with a partially instantiated deconstruction. create_output_unifications(OldGoalInfo, TailOutputArgs, TailOldOutputArgs, TailFromToInsts, AssignGoals, !Common, !Info) else generate_assign(HeadOutputArg, HeadOldOutputArg, HeadFromToInsts, OldGoalInfo, HeadAssignGoalExpr, HeadAssignGoalInfo, !Common, !Info), HeadAssignGoal = hlds_goal(HeadAssignGoalExpr, HeadAssignGoalInfo), create_output_unifications(OldGoalInfo, TailOutputArgs, TailOldOutputArgs, TailFromToInsts, TailAssignGoals, !Common, !Info), AssignGoals = [HeadAssignGoal | TailAssignGoals] ) else if OutputArgs = [], OldOutputArgs = [], FromToInsts = [] then AssignGoals = [] else unexpected($pred, "mode mismatch") ). %---------------------------------------------------------------------------% :- pred generate_assign(prog_var::in, prog_var::in, from_to_insts::in, hlds_goal_info::in, hlds_goal_expr::out, hlds_goal_info::out, common_info::in, common_info::out, simplify_info::in, simplify_info::out) is det. generate_assign(ToVar, FromVar, ToVarMode, OldGoalInfo, GoalExpr, GoalInfo, !Common, !Info) :- apply_induced_substitutions(ToVar, FromVar, !Info), simplify_info_get_var_types(!.Info, VarTypes), lookup_var_type(VarTypes, ToVar, ToVarType), lookup_var_type(VarTypes, FromVar, FromVarType), set_of_var.list_to_set([ToVar, FromVar], NonLocals), ToVarMode = from_to_insts(ToVarInit, ToVarFinal), ( if types_match_exactly(ToVarType, FromVarType) then UnifyMode = unify_modes_li_lf_ri_rf(ToVarInit, ToVarFinal, ToVarFinal, ToVarFinal), UnifyContext = unify_context(umc_explicit, []), GoalExpr = unify(ToVar, rhs_var(FromVar), UnifyMode, assign(ToVar, FromVar), UnifyContext) else % If the cells we are optimizing don't have exactly the same type, % we insert explicit type casts to ensure type correctness. % This avoids problems with HLDS optimizations such as inlining % which expect the HLDS to be well-typed. Unfortunately, this loses % information for other optimizations, since the cast hides the % equivalence of the input and output. Modes = [from_to_mode(ToVarFinal, ToVarFinal), from_to_mode(free, ToVarFinal)], GoalExpr = generic_call(cast(unsafe_type_cast), [FromVar, ToVar], Modes, arg_reg_types_unset, detism_det) ), % `ToVar' may not appear in the original instmap_delta, so we can't just % use instmap_delta_restrict on the original instmap_delta here. InstMapDelta = instmap_delta_from_assoc_list([ToVar - ToVarFinal]), goal_info_init(NonLocals, InstMapDelta, detism_det, purity_pure, GoalInfo0), Context = goal_info_get_context(OldGoalInfo), goal_info_set_context(Context, GoalInfo0, GoalInfo), record_equivalence(ToVar, FromVar, !Common). :- pred types_match_exactly(mer_type::in, mer_type::in) is semidet. types_match_exactly(type_variable(TVar, _), type_variable(TVar, _)). types_match_exactly(defined_type(Name, As, _), defined_type(Name, Bs, _)) :- types_match_exactly_list(As, Bs). types_match_exactly(builtin_type(BuiltinType), builtin_type(BuiltinType)). types_match_exactly(higher_order_type(PorF, As, H, P, E), higher_order_type(PorF, Bs, H, P, E)) :- types_match_exactly_list(As, Bs). types_match_exactly(tuple_type(As, _), tuple_type(Bs, _)) :- types_match_exactly_list(As, Bs). types_match_exactly(apply_n_type(TVar, As, _), apply_n_type(TVar, Bs, _)) :- types_match_exactly_list(As, Bs). types_match_exactly(kinded_type(_, _), _) :- unexpected($pred, "kind annotation"). :- pred types_match_exactly_list(list(mer_type)::in, list(mer_type)::in) is semidet. types_match_exactly_list([], []). types_match_exactly_list([Type1 | Types1], [Type2 | Types2]) :- types_match_exactly(Type1, Type2), types_match_exactly_list(Types1, Types2). %---------------------------------------------------------------------------% % Two existentially quantified type variables may become aliased if two % calls or two deconstructions are merged together. We detect this % situation here and apply the appropriate tsubst to the vartypes and % rtti_varmaps. This allows us to avoid an unsafe cast, and also may % allow more opportunities for simplification. % % If we do need to apply a type substitution, then we also apply the % substitution ToVar -> FromVar to the RttiVarMaps, then duplicate % FromVar's information for ToVar. This ensures we always refer to the % "original" variables, not the copies created by generate_assign. % % Note that this relies on the assignments for type_infos and % typeclass_infos to be generated before other arguments with these % existential types are processed. In other words, the arguments of % calls and deconstructions must be processed in left to right order. % :- pred apply_induced_substitutions(prog_var::in, prog_var::in, simplify_info::in, simplify_info::out) is det. apply_induced_substitutions(ToVar, FromVar, !Info) :- simplify_info_get_rtti_varmaps(!.Info, RttiVarMaps0), rtti_varmaps_var_info(RttiVarMaps0, FromVar, FromVarRttiInfo), rtti_varmaps_var_info(RttiVarMaps0, ToVar, ToVarRttiInfo), ( if calculate_induced_tsubst(ToVarRttiInfo, FromVarRttiInfo, TSubst) then ( if map.is_empty(TSubst) then true else simplify_info_apply_substitutions_and_duplicate(ToVar, FromVar, TSubst, !Info) ) else % Update the rtti_varmaps with new information if only one of the % variables has rtti_var_info recorded. This can happen if a new % variable has been introduced, eg in quantification, without % being recorded in the rtti_varmaps. ( FromVarRttiInfo = non_rtti_var, rtti_var_info_duplicate(ToVar, FromVar, RttiVarMaps0, RttiVarMaps), simplify_info_set_rtti_varmaps(RttiVarMaps, !Info) ; ( FromVarRttiInfo = type_info_var(_) ; FromVarRttiInfo = typeclass_info_var(_) ), ( ToVarRttiInfo = non_rtti_var, rtti_var_info_duplicate(FromVar, ToVar, RttiVarMaps0, RttiVarMaps), simplify_info_set_rtti_varmaps(RttiVarMaps, !Info) ; ( ToVarRttiInfo = type_info_var(_) ; ToVarRttiInfo = typeclass_info_var(_) ), % Calculate_induced_tsubst failed for a different reason, % either because unification failed or because one variable % was a type_info and the other was a typeclass_info. unexpected($pred, "inconsistent info") ) ) ). % Calculate the induced substitution by unifying the types or constraints, % if they exist. Fail if given non-matching rtti_var_infos. % :- pred calculate_induced_tsubst(rtti_var_info::in, rtti_var_info::in, tsubst::out) is semidet. calculate_induced_tsubst(ToVarRttiInfo, FromVarRttiInfo, TSubst) :- ( FromVarRttiInfo = type_info_var(FromVarTypeInfoType), ToVarRttiInfo = type_info_var(ToVarTypeInfoType), type_subsumes(ToVarTypeInfoType, FromVarTypeInfoType, TSubst) ; FromVarRttiInfo = typeclass_info_var(FromVarConstraint), ToVarRttiInfo = typeclass_info_var(ToVarConstraint), FromVarConstraint = constraint(Name, FromArgs), ToVarConstraint = constraint(Name, ToArgs), type_list_subsumes(ToArgs, FromArgs, TSubst) ; FromVarRttiInfo = non_rtti_var, ToVarRttiInfo = non_rtti_var, map.init(TSubst) ). %---------------------------------------------------------------------------% :- end_module check_hlds.simplify.common. %---------------------------------------------------------------------------%