mercury/compiler/stack_layout.m

%---------------------------------------------------------------------------%
% Copyright (C) 1997-2001 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.
%---------------------------------------------------------------------------%
%
% File: stack_layout.m.
% Main authors: trd, zs.
%
% This module generates label, procedure, module and closure layout structures
% for code in the current module for the LLDS backend. Layout structures are
% used by the parts of the runtime system that need to look at the stacks
% (and sometimes the registers) and make sense of their contents. The parts
% of the runtime system that need to do this include exception handling,
% the debugger, and (eventually) the accurate garbage collector.
%
% The tables we generate are mostly of (Mercury) types defined in layout.m,
% which are turned into C code (global variable declarations and
% initializations) by layout_out.m. However, these data structures also have
% a number of `create' rvals within them; llds_common.m converts these into
% static data structures.
% 
% The C types of the structures we generate are defined and documented in
% runtime/mercury_stack_layout.h. 
%
%---------------------------------------------------------------------------%

:- module stack_layout.

:- interface.

:- import_module prog_data, continuation_info, hlds_module, llds.
:- import_module std_util, list, map, counter.

:- pred stack_layout__generate_llds(module_info::in, module_info::out,
	global_data::in, list(comp_gen_c_data)::out,
	list(comp_gen_c_data)::out, map(label, data_addr)::out) is det.

:- pred stack_layout__construct_closure_layout(proc_label::in, int::in,
	closure_layout_info::in, proc_label::in, module_name::in,
	string::in, int::in, string::in, list(maybe(rval))::out,
	create_arg_types::out, comp_gen_c_data::out,
	counter::in, counter::out) is det.

:- implementation.

:- import_module globals, options, llds_out, trace_params, trace.
:- import_module hlds_data, hlds_goal, hlds_pred.
:- import_module prog_util, prog_out, instmap.
:- import_module prog_rep, static_term, layout_out.
:- import_module rtti, layout, ll_pseudo_type_info, (inst), code_util.
:- import_module assoc_list, bool, string, int, require.
:- import_module map, term, set, varset.

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

	% Process all the continuation information stored in the HLDS,
	% converting it into LLDS data structures.

stack_layout__generate_llds(ModuleInfo0, ModuleInfo, GlobalData,
		PossiblyDynamicLayouts, StaticLayouts, LayoutLabels) :-
	global_data_get_all_proc_layouts(GlobalData, ProcLayoutList0),
	list__filter(stack_layout__valid_proc_layout, ProcLayoutList0,
		ProcLayoutList),

	module_info_globals(ModuleInfo0, Globals),
	globals__lookup_bool_option(Globals, agc_stack_layout, AgcLayout),
	globals__lookup_bool_option(Globals, trace_stack_layout, TraceLayout),
	globals__lookup_bool_option(Globals, procid_stack_layout,
		ProcIdLayout),
	globals__get_trace_level(Globals, TraceLevel),
	globals__get_trace_suppress(Globals, TraceSuppress),
	globals__have_static_code_addresses(Globals, StaticCodeAddr),
	map__init(LayoutLabels0),

	map__init(StringMap0),
	map__init(LabelTables0),
	StringTable0 = string_table(StringMap0, [], 0),
	LayoutInfo0 = stack_layout_info(ModuleInfo0,
		AgcLayout, TraceLayout, ProcIdLayout,
		TraceLevel, TraceSuppress,
		StaticCodeAddr, [], [], LayoutLabels0, [],
		StringTable0, LabelTables0, map__init),
	stack_layout__lookup_string_in_table("", _, LayoutInfo0, LayoutInfo1),
	stack_layout__lookup_string_in_table("<too many variables>", _,
		LayoutInfo1, LayoutInfo2),
	list__foldl(stack_layout__construct_layouts, ProcLayoutList,
		LayoutInfo2, LayoutInfo),
	ModuleInfo = LayoutInfo ^ module_info,
	ProcLayouts = LayoutInfo ^ proc_layouts,
	InternalLayouts = LayoutInfo ^ internal_layouts,
	LayoutLabels = LayoutInfo ^ label_set,
	ProcLayoutNames = LayoutInfo ^ proc_layout_name_list,
	StringTable = LayoutInfo ^ string_table,
	LabelTables = LayoutInfo ^ label_tables,
	StringTable = string_table(_, RevStringList, StringOffset),
	list__reverse(RevStringList, StringList),
	stack_layout__concat_string_list(StringList, StringOffset,
		ConcatStrings),

	PossiblyDynamicLayouts = ProcLayouts,
	( TraceLayout = yes ->
		module_info_name(ModuleInfo0, ModuleName),
		globals__lookup_bool_option(Globals, rtti_line_numbers,
			LineNumbers),
		(
			LineNumbers = yes,
			EffLabelTables = LabelTables
		;
			LineNumbers = no,
			map__init(EffLabelTables)
		),
		stack_layout__format_label_tables(EffLabelTables,
			SourceFileLayouts),
		ModuleLayout = layout_data(module_layout_data(ModuleName,
			StringOffset, ConcatStrings, ProcLayoutNames,
			SourceFileLayouts, TraceLevel)),
		StaticLayouts = [ModuleLayout | InternalLayouts]
	;
		StaticLayouts = InternalLayouts
	).

:- pred stack_layout__valid_proc_layout(proc_layout_info::in) is semidet.

stack_layout__valid_proc_layout(ProcLayoutInfo) :-
	EntryLabel = ProcLayoutInfo ^ entry_label,
	code_util__extract_proc_label_from_label(EntryLabel, ProcLabel),
	(
		ProcLabel = proc(_, _, DeclModule, Name, Arity, _),
		\+ no_type_info_builtin(DeclModule, Name, Arity)
	;
		ProcLabel = special_proc(_, _, _, _, _, _)
	).

:- pred stack_layout__data_addr_to_maybe_rval(data_addr::in, maybe(rval)::out)
	is det.

stack_layout__data_addr_to_maybe_rval(DataAddr, yes(Rval)) :-
	Rval = const(data_addr_const(DataAddr)).

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

:- pred stack_layout__concat_string_list(list(string)::in, int::in,
	string::out) is det.

:- pragma c_header_code("
	#include ""mercury_tags.h""	/* for MR_list_*() */
	#include ""mercury_heap.h""	/* for MR_incr_hp_atomic*() */
	#include ""mercury_misc.h""	/* for MR_fatal_error() */
").

:- pragma c_code(stack_layout__concat_string_list(StringList::in,
		ArenaSize::in, Arena::out),
		[will_not_call_mercury, thread_safe], "{
	MR_Word		cur_node;
	MR_Integer	cur_offset;
	MR_Word		tmp;

	MR_incr_hp_atomic(tmp,
		(ArenaSize + sizeof(MR_Word)) / sizeof(MR_Word));
	Arena = (char *) tmp;

	cur_offset = 0;
	cur_node = StringList;

	while (! MR_list_is_empty(cur_node)) {
		(void) strcpy(&Arena[cur_offset],
			(char *) MR_list_head(cur_node));
		cur_offset += strlen((char *) MR_list_head(cur_node)) + 1;
		cur_node = MR_list_tail(cur_node);
	}

	if (cur_offset != ArenaSize) {
		char	msg[256];

		sprintf(msg, ""internal error in creating string table;\\n""
			""cur_offset = %ld, ArenaSize = %ld\\n"",
			(long) cur_offset, (long) ArenaSize);
		MR_fatal_error(msg);
	}
}").

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

:- pred stack_layout__format_label_tables(map(string, label_table)::in, 
	list(file_layout_data)::out) is det.

stack_layout__format_label_tables(LabelTableMap, SourceFileLayouts) :-
	map__to_assoc_list(LabelTableMap, LabelTableList),
	list__map(stack_layout__format_label_table, LabelTableList,
		SourceFileLayouts).

:- pred stack_layout__format_label_table(pair(string, label_table)::in,
	file_layout_data::out) is det.

stack_layout__format_label_table(FileName - LineNoMap,
		file_layout_data(FileName, FilteredList)) :-
		% This step should produce a list ordered on line numbers.
	map__to_assoc_list(LineNoMap, LineNoList),
		% And this step should preserve that order.
	stack_layout__flatten_label_table(LineNoList, [], FlatLineNoList),
	Filter = (pred(LineNoInfo::in, FilteredLineNoInfo::out) is det :-
		LineNoInfo = LineNo - (Label - _IsReturn),
		FilteredLineNoInfo = LineNo - Label
	),
	list__map(Filter, FlatLineNoList, FilteredList).

:- pred stack_layout__flatten_label_table(
	assoc_list(int, list(line_no_info))::in,
	assoc_list(int, line_no_info)::in,
	assoc_list(int, line_no_info)::out) is det.

stack_layout__flatten_label_table([], RevList, List) :-
	list__reverse(RevList, List).
stack_layout__flatten_label_table([LineNo - LinesInfos | Lines],
		RevList0, List) :-
	list__foldl(stack_layout__add_line_no(LineNo), LinesInfos,
		RevList0, RevList1),
	stack_layout__flatten_label_table(Lines, RevList1, List).

:- pred stack_layout__add_line_no(int::in, line_no_info::in,
	assoc_list(int, line_no_info)::in,
	assoc_list(int, line_no_info)::out) is det.

stack_layout__add_line_no(LineNo, LineInfo, RevList0, RevList) :-
	RevList = [LineNo - LineInfo | RevList0].

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

	% Construct the layouts that concern a single procedure:
	% the procedure-specific layout and the layouts of the labels
	% inside that procedure. Also update the module-wide label table
	% with the labels defined in this procedure.

:- pred stack_layout__construct_layouts(proc_layout_info::in,
	stack_layout_info::in, stack_layout_info::out) is det.

stack_layout__construct_layouts(ProcLayoutInfo) -->
	{ ProcLayoutInfo = proc_layout_info(EntryLabel, Detism, StackSlots,
		SuccipLoc, EvalMethod, MaybeCallLabel, MaxTraceReg,
		Goal, InstMap, TraceSlotInfo, ForceProcIdLayout,
		VarSet, VarTypes, InternalMap) },
	{ map__to_assoc_list(InternalMap, Internals) },
	stack_layout__set_cur_proc_named_vars(map__init),

	{ code_util__extract_proc_label_from_label(EntryLabel, ProcLabel) },
	stack_layout__get_procid_stack_layout(ProcIdLayout0),
	{ bool__or(ProcIdLayout0, ForceProcIdLayout, ProcIdLayout) },
	( { ProcIdLayout = yes } ->
		{ UserOrCompiler = proc_label_user_or_compiler(ProcLabel) },
		stack_layout__get_trace_stack_layout(TraceLayout),
		{
			TraceLayout = yes,
			Kind = proc_layout_exec_trace(UserOrCompiler)
		;
			TraceLayout = no,
			Kind = proc_layout_proc_id(UserOrCompiler)
		}
	;
		{ Kind = proc_layout_traversal }
	),

	{ ProcLayoutName = proc_layout(ProcLabel, Kind) },

	list__foldl2(stack_layout__construct_internal_layout(ProcLayoutName),
		Internals, [], InternalLayouts),
	stack_layout__get_cur_proc_named_vars(NamedVars),
	stack_layout__get_label_tables(LabelTables0),
	{ list__foldl(stack_layout__update_label_table, InternalLayouts,
		LabelTables0, LabelTables) },
	stack_layout__set_label_tables(LabelTables),
	stack_layout__construct_proc_layout(EntryLabel, ProcLabel, Detism,
		StackSlots, SuccipLoc, EvalMethod, MaybeCallLabel, MaxTraceReg,
		Goal, InstMap, TraceSlotInfo, VarSet, VarTypes, NamedVars,
		Kind).

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

	% Add the given label layout to the module-wide label tables.

:- pred stack_layout__update_label_table(
	pair(pair(label, label_vars), internal_layout_info)::in,
	map(string, label_table)::in, map(string, label_table)::out) is det.

stack_layout__update_label_table((Label - LabelVars) - InternalInfo,
		LabelTables0, LabelTables) :-
	InternalInfo = internal_layout_info(Port, _, Return),
	(
		Return = yes(return_layout_info(TargetsContexts, _)),
		stack_layout__find_valid_return_context(TargetsContexts,
			Target, Context, _GoalPath)
	->
		( Target = label(TargetLabel) ->
			IsReturn = known_callee(TargetLabel)
		;
			IsReturn = unknown_callee
		),
		stack_layout__update_label_table_2(Label, LabelVars,
			Context, IsReturn, LabelTables0, LabelTables)
	;
		Port = yes(trace_port_layout_info(Context, _, _, _)),
		stack_layout__context_is_valid(Context)
	->
		stack_layout__update_label_table_2(Label, LabelVars,
			Context, not_a_return, LabelTables0, LabelTables)
	;
		LabelTables = LabelTables0
	).

:- pred stack_layout__update_label_table_2(label::in, label_vars::in,
	context::in, is_label_return::in,
	map(string, label_table)::in, map(string, label_table)::out) is det.

stack_layout__update_label_table_2(Label, LabelVars, Context, IsReturn,
		LabelTables0, LabelTables) :-
	term__context_file(Context, File),
	term__context_line(Context, Line),
	( map__search(LabelTables0, File, LabelTable0) ->
		LabelLayout = label_layout(Label, LabelVars),
		( map__search(LabelTable0, Line, LineInfo0) ->
			LineInfo = [LabelLayout - IsReturn | LineInfo0],
			map__det_update(LabelTable0, Line, LineInfo,
				LabelTable),
			map__det_update(LabelTables0, File, LabelTable,
				LabelTables)
		;
			LineInfo = [LabelLayout - IsReturn],
			map__det_insert(LabelTable0, Line, LineInfo,
				LabelTable),
			map__det_update(LabelTables0, File, LabelTable,
				LabelTables)
		)
	; stack_layout__context_is_valid(Context) ->
		map__init(LabelTable0),
		LabelLayout = label_layout(Label, LabelVars),
		LineInfo = [LabelLayout - IsReturn],
		map__det_insert(LabelTable0, Line, LineInfo, LabelTable),
		map__det_insert(LabelTables0, File, LabelTable, LabelTables)
	;
			% We don't have a valid context for this label,
			% so we don't enter it into any tables.
		LabelTables = LabelTables0
	).

:- pred stack_layout__find_valid_return_context(
	assoc_list(code_addr, pair(prog_context, goal_path))::in,
	code_addr::out, prog_context::out, goal_path::out) is semidet.

stack_layout__find_valid_return_context([Target - (Context - GoalPath)
		| TargetContexts], ValidTarget, ValidContext, ValidGoalPath) :-
	( stack_layout__context_is_valid(Context) ->
		ValidTarget = Target,
		ValidContext = Context,
		ValidGoalPath = GoalPath
	;
		stack_layout__find_valid_return_context(TargetContexts,
			ValidTarget, ValidContext, ValidGoalPath)
	).

:- pred stack_layout__context_is_valid(prog_context::in) is semidet.

stack_layout__context_is_valid(Context) :-
	term__context_file(Context, File),
	term__context_line(Context, Line),
	File \= "",
	Line > 0.

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

	% Construct a procedure-specific layout.

:- pred stack_layout__construct_proc_layout(label::in, proc_label::in,
	determinism::in, int::in, maybe(int)::in, eval_method::in,
	maybe(label)::in, int::in, hlds_goal::in, instmap::in,
	trace_slot_info::in, prog_varset::in, vartypes::in,
	map(int, string)::in, proc_layout_kind::in,
	stack_layout_info::in, stack_layout_info::out) is det.

stack_layout__construct_proc_layout(EntryLabel, ProcLabel, Detism, StackSlots,
		MaybeSuccipLoc, EvalMethod, MaybeCallLabel, MaxTraceReg, Goal,
		InstMap, TraceSlotInfo, VarSet, VarTypes, UsedVarNames, Kind)
		-->
	{
		MaybeSuccipLoc = yes(Location)
	->
		( determinism_components(Detism, _, at_most_many) ->
			SuccipLval = framevar(Location)
		;
			SuccipLval = stackvar(Location)
		),
		stack_layout__represent_locn_as_int(direct(SuccipLval),
			SuccipInt),
		MaybeSuccipInt = yes(SuccipInt)
	;
			% Use a dummy location 1 if there is no succip slot
			% on the stack.
			%
			% This case can arise in two circumstances.
			% First, procedures that use the nondet stack
			% have a special slot for the succip, so the
			% succip is not stored in a general purpose
			% slot. Second, procedures that use the det stack
			% but which do not call other procedures
			% do not save the succip on the stack.
			%
			% The tracing system does not care about the
			% location of the saved succip. The accurate
			% garbage collector does. It should know from
			% the determinism that the procedure uses the
			% nondet stack, which takes care of the first
			% possibility above. Procedures that do not call
			% other procedures do not establish resumption
			% points and thus agc is not interested in them.
			% As far as stack dumps go, calling error counts
			% as a call, so any procedure that may call error
			% (directly or indirectly) will have its saved succip
			% location recorded, so the stack dump will work.
			%
			% Future uses of stack layouts will have to have
			% similar constraints.
		MaybeSuccipInt = no
	},
	stack_layout__get_static_code_addresses(StaticCodeAddr),
	{ StaticCodeAddr = yes ->
		MaybeEntryLabel = yes(EntryLabel)
	;
		MaybeEntryLabel = no
	},
	{ TraversalGroup = proc_layout_stack_traversal(MaybeEntryLabel,
		MaybeSuccipInt, StackSlots, Detism) },
	(
		{ Kind = proc_layout_traversal },
		{ MaybeRest = no_proc_id }
	;
		{ Kind = proc_layout_proc_id(_) },
		{ MaybeRest = proc_id_only }
	;
		{ Kind = proc_layout_exec_trace(_) },
		stack_layout__construct_trace_layout(EvalMethod, MaybeCallLabel,
			MaxTraceReg, Goal, InstMap, TraceSlotInfo, VarSet,
			VarTypes, UsedVarNames, ExecTrace),
		{ MaybeRest = proc_id_and_exec_trace(ExecTrace) }
	),

	{ ProcLayout = proc_layout_data(ProcLabel, TraversalGroup, MaybeRest) },
	{ Data = layout_data(ProcLayout) },
	{ LayoutName = proc_layout(ProcLabel, Kind) },
	stack_layout__add_proc_layout_data(Data, LayoutName, EntryLabel).

:- pred stack_layout__construct_trace_layout(eval_method::in, maybe(label)::in,
	int::in, hlds_goal::in, instmap::in, trace_slot_info::in,
	prog_varset::in, vartypes::in, map(int, string)::in,
	proc_layout_exec_trace::out,
	stack_layout_info::in, stack_layout_info::out) is det.

stack_layout__construct_trace_layout(EvalMethod, MaybeCallLabel, MaxTraceReg,
		Goal, InstMap, TraceSlotInfo, VarSet, VarTypes, UsedVarNameMap,
		ExecTrace) -->
	stack_layout__construct_var_name_vector(VarSet, UsedVarNameMap,
		MaxVarNum, VarNameVector),
	stack_layout__get_trace_level(TraceLevel),
	stack_layout__get_trace_suppress(TraceSuppress),
	{ trace_needs_proc_body_reps(TraceLevel, TraceSuppress)
		= BodyReps },
	(
		{ BodyReps = no },
		{ MaybeGoalRepRval = no }
	;
		{ BodyReps = yes },
		stack_layout__get_module_info(ModuleInfo),
		{ prog_rep__represent_goal(Goal, InstMap, VarTypes,
			ModuleInfo, GoalRep) },
		{ type_to_univ(GoalRep, GoalRepUniv) },
		stack_layout__get_cell_counter(CellCounter0),
		{ static_term__term_to_rval(GoalRepUniv, MaybeGoalRepRval,
			CellCounter0, CellCounter) },
		stack_layout__set_cell_counter(CellCounter)
	),
	{ MaybeCallLabel = yes(CallLabelPrime) ->
		CallLabel = CallLabelPrime
	;
		error("stack_layout__construct_trace_layout: call label not present")
	},
	{ TraceSlotInfo = trace_slot_info(MaybeFromFullSlot,
		MaybeIoSeqSlot, MaybeTrailSlots, MaybeMaxfrSlot,
		MaybeCallTableSlot, MaybeDeclSlots) },
		% The label associated with an event must have variable info.
	{ CallLabelLayout = label_layout(CallLabel, label_has_var_info) },
	{ ExecTrace = proc_layout_exec_trace(CallLabelLayout, MaybeGoalRepRval,
		VarNameVector, MaxVarNum, MaxTraceReg,
		MaybeFromFullSlot, MaybeIoSeqSlot, MaybeTrailSlots,
		MaybeMaxfrSlot, EvalMethod, MaybeCallTableSlot,
		MaybeDeclSlots) }.

:- pred stack_layout__construct_var_name_vector(prog_varset::in,
	map(int, string)::in, int::out, list(int)::out,
	stack_layout_info::in, stack_layout_info::out) is det.

stack_layout__construct_var_name_vector(VarSet, UsedVarNameMap, Count, Offsets)
		-->
	stack_layout__get_trace_level(TraceLevel),
	stack_layout__get_trace_suppress(TraceSuppress),
	{ trace_needs_all_var_names(TraceLevel, TraceSuppress)
		= NeedsAllNames },
	(
		{ NeedsAllNames = yes },
		{ varset__var_name_list(VarSet, VarNameList) },
		{ list__map(stack_layout__convert_var_name_to_int,
			VarNameList, VarNames) }
	;
		{ NeedsAllNames = no },
		{ map__to_assoc_list(UsedVarNameMap, VarNames) }
	),
	( { VarNames = [FirstVar - _ | _] } ->
		stack_layout__construct_var_name_rvals(VarNames, 1,
			FirstVar, Count, Offsets)
	;
		{ Count = 0 },
		{ Offsets = [] }
	).

:- pred stack_layout__construct_var_name_rvals(assoc_list(int, string)::in,
	int::in, int::in, int::out, list(int)::out,
	stack_layout_info::in, stack_layout_info::out) is det.

stack_layout__construct_var_name_rvals([], _CurNum, MaxNum, MaxNum, []) --> [].
stack_layout__construct_var_name_rvals([Var - Name | VarNames1], CurNum,
		MaxNum0, MaxNum, [Offset | Offsets1]) -->
	( { Var = CurNum } ->
		stack_layout__lookup_string_in_table(Name, Offset),
		{ MaxNum1 = Var },
		{ VarNames = VarNames1 }
	;
		{ Offset = 0 },
		{ MaxNum1 = MaxNum0 },
		{ VarNames = [Var - Name | VarNames1] }
	),
	stack_layout__construct_var_name_rvals(VarNames, CurNum + 1,
		MaxNum1, MaxNum, Offsets1).

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

	% Construct the layout describing a single internal label
	% for accurate GC and/or execution tracing.

:- pred stack_layout__construct_internal_layout(layout_name::in,
	pair(label, internal_layout_info)::in,
	assoc_list(pair(label, label_vars), internal_layout_info)::in,
	assoc_list(pair(label, label_vars), internal_layout_info)::out,
	stack_layout_info::in, stack_layout_info::out) is det.

stack_layout__construct_internal_layout(ProcLayoutName, Label - Internal,
		LabelLayouts, [(Label - LabelVars) - Internal | LabelLayouts])
		-->
	{ Internal = internal_layout_info(Trace, Resume, Return) },
	(
		{ Trace = no },
		{ set__init(TraceLiveVarSet) },
		{ map__init(TraceTypeVarMap) }
	;
		{ Trace = yes(trace_port_layout_info(_, _, _, TraceLayout)) },
		{ TraceLayout = layout_label_info(TraceLiveVarSet,
			TraceTypeVarMap) }
	),
	{
		Resume = no,
		set__init(ResumeLiveVarSet),
		map__init(ResumeTypeVarMap)
	;
		Resume = yes(ResumeLayout),
		ResumeLayout = layout_label_info(ResumeLiveVarSet,
			ResumeTypeVarMap)
	},
	(
		{ Trace = yes(trace_port_layout_info(_, Port, GoalPath, _)) },
		{ Return = no },
		{ MaybePort = yes(Port) },
		{ trace__path_to_string(GoalPath, GoalPathStr) },
		stack_layout__lookup_string_in_table(GoalPathStr, GoalPathNum),
		{ MaybeGoalPath = yes(GoalPathNum) }
	;
		{ Trace = no },
		{ Return = yes(ReturnInfo) },
			% We only ever use the port fields of these layout
			% structures when we process exception events.
			% (Since exception events are interface events,
			% the goal path field is not meaningful then.)
		{ MaybePort = yes(exception) },
			% We only ever use the goal path fields of these
			% layout structures when we process "fail" commands
			% in the debugger.
		{ ReturnInfo = return_layout_info(TargetsContexts, _) },
		(
			{ stack_layout__find_valid_return_context(
				TargetsContexts, _, _, GoalPath) }
		->
			{ trace__path_to_string(GoalPath, GoalPathStr) },
			stack_layout__lookup_string_in_table(GoalPathStr,
				GoalPathNum),
			{ MaybeGoalPath = yes(GoalPathNum) }
		;
				% If tracing is enabled, then exactly one of
				% the calls for which this label is a return
				% site would have had a valid context. If none
				% do, then tracing is not enabled, and
				% therefore the goal path of this label will
				% not be accessed.
			{ MaybeGoalPath = no }
		)
	;
		{ Trace = no },
		{ Return = no },
		{ MaybePort = no },
		{ MaybeGoalPath = no }
	;
		{ Trace = yes(_) },
		{ Return = yes(_) },
		{ error("label has both trace and return layout info") }
	),
	stack_layout__get_agc_stack_layout(AgcStackLayout),
	{
		Return = no,
		set__init(ReturnLiveVarSet),
		map__init(ReturnTypeVarMap)
	;
		Return = yes(return_layout_info(_, ReturnLayout)),
		ReturnLayout = layout_label_info(ReturnLiveVarSet0,
			ReturnTypeVarMap0),
		(
			AgcStackLayout = yes,
			ReturnLiveVarSet = ReturnLiveVarSet0,
			ReturnTypeVarMap = ReturnTypeVarMap0
		;
			AgcStackLayout = no,
			% This set of variables must be for uplevel printing
			% in execution tracing, so we are interested only
			% in (a) variables, not temporaries, (b) only named
			% variables, and (c) only those on the stack, not
			% the return values.
			set__to_sorted_list(ReturnLiveVarSet0,
				ReturnLiveVarList0),
			stack_layout__select_trace_return(
				ReturnLiveVarList0, ReturnTypeVarMap0,
				ReturnLiveVarList, ReturnTypeVarMap),
			set__list_to_set(ReturnLiveVarList, ReturnLiveVarSet)
		)
	},
	(
		{ Trace = no },
		{ Resume = no },
		{ Return = no }
	->
		{ MaybeVarInfo = no },
		{ LabelVars = label_has_no_var_info }
	;
			% XXX ignore differences in insts inside var_infos
		{ set__union(TraceLiveVarSet, ResumeLiveVarSet, LiveVarSet0) },
		{ set__union(LiveVarSet0, ReturnLiveVarSet, LiveVarSet) },
		{ map__union(set__intersect, TraceTypeVarMap, ResumeTypeVarMap,
			TypeVarMap0) },
		{ map__union(set__intersect, TypeVarMap0, ReturnTypeVarMap,
			TypeVarMap) },
		stack_layout__construct_livelval_rvals(LiveVarSet, TypeVarMap,
			EncodedLength, LiveValRval, NamesRval, TypeParamRval),
		{ VarInfo = label_var_info(EncodedLength, 
			LiveValRval, NamesRval, TypeParamRval) },
		{ MaybeVarInfo = yes(VarInfo) },
		{ LabelVars = label_has_var_info }
	),

	{ LayoutData = label_layout_data(Label, ProcLayoutName,
		MaybePort, MaybeGoalPath, MaybeVarInfo) },
	{ CData = layout_data(LayoutData) },
	{ LayoutName = label_layout(Label, LabelVars) },
	stack_layout__add_internal_layout_data(CData, Label, LayoutName).

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

:- pred stack_layout__construct_livelval_rvals(set(var_info)::in,
	map(tvar, set(layout_locn))::in, int::out, rval::out, rval::out,
	rval::out, stack_layout_info::in, stack_layout_info::out) is det.

stack_layout__construct_livelval_rvals(LiveLvalSet, TVarLocnMap, EncodedLength,
		LiveValRval, NamesRval, TypeParamRval) -->
	{ set__to_sorted_list(LiveLvalSet, LiveLvals) },
	{ stack_layout__sort_livevals(LiveLvals, SortedLiveLvals) },
	stack_layout__construct_liveval_arrays(SortedLiveLvals,
		EncodedLength, LiveValRval, NamesRval),
	stack_layout__get_cell_counter(C0),
	{ stack_layout__construct_tvar_vector(TVarLocnMap,
		TypeParamRval, C0, C) },
	stack_layout__set_cell_counter(C).

:- pred stack_layout__construct_tvar_vector(map(tvar, set(layout_locn))::in,
	rval::out, counter::in, counter::out) is det.

stack_layout__construct_tvar_vector(TVarLocnMap, TypeParamRval, C0, C) :-
	( map__is_empty(TVarLocnMap) ->
		TypeParamRval = const(int_const(0)),
		C = C0
	;
		stack_layout__construct_tvar_rvals(TVarLocnMap,
			Vector, VectorTypes),
		counter__allocate(CNum, C0, C),
		Reuse = no,
		TypeParamRval = create(0, Vector, VectorTypes,
			must_be_static, CNum,
			"stack_layout_type_param_locn_vector", Reuse)
	).

:- pred stack_layout__construct_tvar_rvals(map(tvar, set(layout_locn))::in,
	list(maybe(rval))::out, create_arg_types::out) is det.

stack_layout__construct_tvar_rvals(TVarLocnMap, Vector, VectorTypes) :-
	map__to_assoc_list(TVarLocnMap, TVarLocns),
	stack_layout__construct_type_param_locn_vector(TVarLocns, 1,
		TypeParamLocs),
	list__length(TypeParamLocs, TypeParamsLength),
	LengthRval = const(int_const(TypeParamsLength)),
	Vector = [yes(LengthRval) | TypeParamLocs],
	VectorTypes = uniform(yes(uint_least32)).

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

	% Given a list of var_infos and the type variables that occur in them,
	% select only the var_infos that may be required by up-level printing
	% in the trace-based debugger. At the moment the typeinfo list we
	% return may be bigger than necessary, but this does not compromise
	% correctness; we do this to avoid having to scan the types of all
	% the selected var_infos.

:- pred stack_layout__select_trace_return(
	list(var_info)::in, map(tvar, set(layout_locn))::in,
	list(var_info)::out, map(tvar, set(layout_locn))::out) is det.

stack_layout__select_trace_return(Infos, TVars, TraceReturnInfos, TVars) :-
	IsNamedReturnVar = (pred(LocnInfo::in) is semidet :-
		LocnInfo = var_info(Locn, LvalType),
		LvalType = var(_, Name, _, _),
		Name \= "",
		( Locn = direct(Lval) ; Locn = indirect(Lval, _)),
		( Lval = stackvar(_) ; Lval = framevar(_) )
	),
	list__filter(IsNamedReturnVar, Infos, TraceReturnInfos).

	% Given a list of var_infos, put the ones that tracing can be
	% interested in (whether at an internal port or for uplevel printing)
	% in a block at the start, and both this block and the remaining
	% block. The division into two blocks can make the job of the
	% debugger somewhat easier, the sorting of the named var block makes
	% the output of the debugger look nicer, and the sorting of the both
	% blocks makes it more likely that different labels' layout structures
	% will have common parts (e.g. name vectors) that can be optimized
	% by llds_common.m.

:- pred stack_layout__sort_livevals(list(var_info)::in, list(var_info)::out)
	is det.

stack_layout__sort_livevals(OrigInfos, FinalInfos) :-
	IsNamedVar = (pred(LvalInfo::in) is semidet :-
		LvalInfo = var_info(_Lval, LvalType),
		LvalType = var(_, Name, _, _),
		Name \= ""
	),
	list__filter(IsNamedVar, OrigInfos, NamedVarInfos0, OtherInfos0),
	CompareVarInfos = (pred(Var1::in, Var2::in, Result::out) is det :-
		Var1 = var_info(Lval1, LiveType1),
		Var2 = var_info(Lval2, LiveType2),
		stack_layout__get_name_from_live_value_type(LiveType1, Name1),
		stack_layout__get_name_from_live_value_type(LiveType2, Name2),
		compare(NameResult, Name1, Name2),
		( NameResult = (=) ->
			compare(Result, Lval1, Lval2)
		;
			Result = NameResult
		)
	),
	list__sort(CompareVarInfos, NamedVarInfos0, NamedVarInfos),
	list__sort(CompareVarInfos, OtherInfos0, OtherInfos),
	list__append(NamedVarInfos, OtherInfos, FinalInfos).

:- pred stack_layout__get_name_from_live_value_type(live_value_type::in,
	string::out) is det.

stack_layout__get_name_from_live_value_type(LiveType, Name) :-
	( LiveType = var(_, NamePrime, _, _) ->
		Name = NamePrime
	;
		Name = ""
	).

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

	% Given a association list of type variables and their locations
	% sorted on the type variables, represent them in an array of
	% location descriptions indexed by the type variable. The next
	% slot to fill is given by the second argument.

:- pred stack_layout__construct_type_param_locn_vector(
	assoc_list(tvar, set(layout_locn))::in,
	int::in, list(maybe(rval))::out) is det.

stack_layout__construct_type_param_locn_vector([], _, []).
stack_layout__construct_type_param_locn_vector([TVar - Locns | TVarLocns],
		CurSlot, Vector) :-
	term__var_to_int(TVar, TVarNum),
	NextSlot is CurSlot + 1,
	( TVarNum = CurSlot ->
		( set__remove_least(Locns, LeastLocn, _) ->
			Locn = LeastLocn
		;
			error("tvar has empty set of locations")
		),
		stack_layout__represent_locn_as_int_rval(Locn, Rval),
		stack_layout__construct_type_param_locn_vector(TVarLocns,
			NextSlot, VectorTail),
		Vector = [yes(Rval) | VectorTail]
	; TVarNum > CurSlot ->
		stack_layout__construct_type_param_locn_vector(
			[TVar - Locns | TVarLocns], NextSlot, VectorTail),
			% This slot will never be referred to.
		Vector = [yes(const(int_const(0))) | VectorTail]
	;
		error("unsorted tvars in construct_type_param_locn_vector")
	).

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

:- type liveval_array_info
	--->	live_array_info(
			rval,	% Rval describing the location of a live value.
				% Always of llds type uint_least8 if the cell
				% is in the byte array, and uint_least32 if it
				% is in the int array.
			rval,	% Rval describing the type of a live value.
			llds_type, % The llds type of the rval describing the
				% type.
			rval	% Rval describing the variable number of a
				% live value. Always of llds type uint_least16.
				% Contains zero if the live value is not
				% a variable. Contains the hightest possible
				% uint_least16 value if the variable number
				% does not fit in 16 bits.
		).

	% Construct a vector of (locn, live_value_type) pairs,
	% and a corresponding vector of variable names.

:- pred stack_layout__construct_liveval_arrays(list(var_info)::in,
	int::out, rval::out, rval::out,
	stack_layout_info::in, stack_layout_info::out) is det.

stack_layout__construct_liveval_arrays(VarInfos, EncodedLength,
		TypeLocnVector, NumVector) -->
	{ int__pow(2, stack_layout__short_count_bits, BytesLimit) },
	stack_layout__construct_liveval_array_infos(VarInfos,
		0, BytesLimit, IntArrayInfo, ByteArrayInfo),

	{ list__length(IntArrayInfo, IntArrayLength) },
	{ list__length(ByteArrayInfo, ByteArrayLength) },
	{ list__append(IntArrayInfo, ByteArrayInfo, AllArrayInfo) },

	{ EncodedLength = IntArrayLength << stack_layout__short_count_bits
		+ ByteArrayLength },

	{ SelectLocns = (pred(ArrayInfo::in, MaybeLocnRval::out) is det :-
		ArrayInfo = live_array_info(LocnRval, _, _, _),
		MaybeLocnRval = yes(LocnRval)
	) },
	{ SelectTypes = (pred(ArrayInfo::in, MaybeTypeRval::out) is det :-
		ArrayInfo = live_array_info(_, TypeRval, _, _),
		MaybeTypeRval = yes(TypeRval)
	) },
	{ SelectTypeTypes = (pred(ArrayInfo::in, CountTypeType::out) is det :-
		ArrayInfo = live_array_info(_, _, TypeType, _),
		CountTypeType = 1 - yes(TypeType)
	) },
	{ AddRevNums = (pred(ArrayInfo::in, NumRvals0::in, NumRvals::out)
			is det :-
		ArrayInfo = live_array_info(_, _, _, NumRval),
		NumRvals = [yes(NumRval) | NumRvals0]
	) },

	{ list__map(SelectTypes, AllArrayInfo, AllTypes) },
	{ list__map(SelectTypeTypes, AllArrayInfo, AllTypeTypes) },
	{ list__map(SelectLocns, IntArrayInfo, IntLocns) },
	{ list__map(SelectLocns, ByteArrayInfo, ByteLocns) },
	{ list__append(IntLocns, ByteLocns, AllLocns) },
	{ list__append(AllTypes, AllLocns, TypeLocnVectorRvals) },
	{ LocnArgTypes = [IntArrayLength - yes(uint_least32),
			ByteArrayLength - yes(uint_least8)] },
	{ list__append(AllTypeTypes, LocnArgTypes, ArgTypes) },
	stack_layout__get_next_cell_number(CNum1),
	{ Reuse = no },
	{ TypeLocnVector = create(0, TypeLocnVectorRvals,
		initial(ArgTypes, none), must_be_static, CNum1,
		"stack_layout_locn_vector", Reuse) },

	stack_layout__get_trace_stack_layout(TraceStackLayout),
	( { TraceStackLayout = yes } ->
		{ list__foldl(AddRevNums, AllArrayInfo,
			[], RevVarNumRvals) },
		{ list__reverse(RevVarNumRvals, VarNumRvals) },
		stack_layout__get_next_cell_number(CNum2),
		{ NumVector = create(0, VarNumRvals,
			uniform(yes(uint_least16)), must_be_static,
			CNum2, "stack_layout_num_name_vector", Reuse) }
	;
		{ NumVector = const(int_const(0)) }
	).

:- pred stack_layout__construct_liveval_array_infos(list(var_info)::in,
	int::in, int::in,
	list(liveval_array_info)::out, list(liveval_array_info)::out,
	stack_layout_info::in, stack_layout_info::out) is det.

stack_layout__construct_liveval_array_infos([], _, _, [], []) --> [].
stack_layout__construct_liveval_array_infos([VarInfo | VarInfos],
		BytesSoFar, BytesLimit, IntVars, ByteVars) -->
	{ VarInfo = var_info(Locn, LiveValueType) },
	stack_layout__represent_live_value_type(LiveValueType, TypeRval,
		TypeRvalType),
	stack_layout__construct_liveval_num_rval(VarInfo, VarNumRval),
	(
		{ BytesSoFar < BytesLimit },
		{ stack_layout__represent_locn_as_byte(Locn, LocnByteRval) }
	->
		{ Var = live_array_info(LocnByteRval, TypeRval, TypeRvalType,
			VarNumRval) },
		stack_layout__construct_liveval_array_infos(VarInfos,
			BytesSoFar + 1, BytesLimit, IntVars, ByteVars0),
		{ ByteVars = [Var | ByteVars0] }
	;
		{ stack_layout__represent_locn_as_int_rval(Locn, LocnRval) },
		{ Var = live_array_info(LocnRval, TypeRval, TypeRvalType,
			VarNumRval) },
		stack_layout__construct_liveval_array_infos(VarInfos,
			BytesSoFar, BytesLimit, IntVars0, ByteVars),
		{ IntVars = [Var | IntVars0] }
	).

:- pred stack_layout__construct_liveval_num_rval(var_info::in, rval::out,
	stack_layout_info::in, stack_layout_info::out) is det.

stack_layout__construct_liveval_num_rval(var_info(_, LiveValueType),
		VarNumRval, SLI0, SLI) :-
	( LiveValueType = var(Var, Name, _, _) ->
		stack_layout__convert_var_to_int(Var, VarNum),
		VarNumRval = const(int_const(VarNum)),
		stack_layout__get_cur_proc_named_vars(NamedVars0, SLI0, SLI1),
		( map__insert(NamedVars0, VarNum, Name, NamedVars) ->
			stack_layout__set_cur_proc_named_vars(NamedVars,
				SLI1, SLI)
		;
			% The variable has been put into the map already at
			% another label.
			SLI = SLI1
		)
	;
		VarNumRval = const(int_const(0)),
		SLI = SLI0
	).

:- pred stack_layout__convert_var_name_to_int(pair(prog_var, string)::in,
	pair(int, string)::out) is det.

stack_layout__convert_var_name_to_int(Var - Name, VarNum - Name) :-
	stack_layout__convert_var_to_int(Var, VarNum).

:- pred stack_layout__convert_var_to_int(prog_var::in, int::out) is det.

stack_layout__convert_var_to_int(Var, VarNum) :-
	term__var_to_int(Var, VarNum0),
		% The variable number has to fit into two bytes.
		% We reserve the largest such number (Limit)
		% to mean that the variable number is too large
		% to be represented. This ought not to happen,
		% since compilation would be glacial at best
		% for procedures with that many variables.
	Limit = (1 << (2 * stack_layout__byte_bits)) - 1,
	int__min(VarNum0, Limit, VarNum).

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

	% The representation we build here should be kept in sync
	% with runtime/mercury_ho_call.h, which contains macros to access
	% the data structures we build here.

stack_layout__construct_closure_layout(CallerProcLabel, SeqNo,
		ClosureLayoutInfo, ClosureProcLabel,
		ModuleName, FileName, LineNumber, GoalPath,
		Rvals, ArgTypes, Data, C0, C) :-
	DataAddr = layout_addr(
		closure_proc_id(CallerProcLabel, SeqNo, ClosureProcLabel)),
	Data = layout_data(closure_proc_id_data(CallerProcLabel, SeqNo,
		ClosureProcLabel, ModuleName, FileName, LineNumber, GoalPath)),
	MaybeProcIdRval = yes(const(data_addr_const(DataAddr))),
	ProcIdType = 1 - yes(data_ptr),
	ClosureLayoutInfo = closure_layout_info(ClosureArgs, TVarLocnMap),
	stack_layout__construct_closure_arg_rvals(ClosureArgs,
		MaybeClosureArgRvals, ClosureArgTypes, C0, C1),
	stack_layout__construct_tvar_vector(TVarLocnMap, TVarVectorRval,
		C1, C),
	MaybeTVarVectorRval = yes(TVarVectorRval),
	TVarVectorType = 1 - yes(data_ptr),
	Rvals = [MaybeProcIdRval, MaybeTVarVectorRval | MaybeClosureArgRvals],
	ArgTypes = initial([ProcIdType, TVarVectorType | ClosureArgTypes],
		none).

:- pred stack_layout__construct_closure_arg_rvals(list(closure_arg_info)::in,
	list(maybe(rval))::out, initial_arg_types::out,
	counter::in, counter::out) is det.

stack_layout__construct_closure_arg_rvals(ClosureArgs, ClosureArgRvals,
		ClosureArgTypes, C0, C) :-
	list__map_foldl(stack_layout__construct_closure_arg_rval,
		ClosureArgs, MaybeArgRvalsTypes, C0, C),
	assoc_list__keys(MaybeArgRvalsTypes, MaybeArgRvals),
	AddOne = (pred(Pair::in, CountLldsType::out) is det :-
		Pair = _ - LldsType,
		CountLldsType = 1 - yes(LldsType)
	),
	list__map(AddOne, MaybeArgRvalsTypes, ArgRvalTypes),
	list__length(MaybeArgRvals, Length),
	ClosureArgRvals = [yes(const(int_const(Length))) | MaybeArgRvals],
	ClosureArgTypes = [1 - yes(integer) | ArgRvalTypes].

:- pred stack_layout__construct_closure_arg_rval(closure_arg_info::in,
	pair(maybe(rval), llds_type)::out, counter::in, counter::out) is det.

stack_layout__construct_closure_arg_rval(ClosureArg,
		yes(ArgRval) - ArgRvalType, C0, C) :-
	ClosureArg = closure_arg_info(Type, _Inst),

		% For a stack layout, we can treat all type variables as
		% universally quantified. This is not the argument of a
		% constructor, so we do not need to distinguish between type
		% variables that are and aren't in scope; we can take the
		% variable number directly from the procedure's tvar set.
	ExistQTvars = [],
	NumUnivQTvars = -1,

	ll_pseudo_type_info__construct_typed_llds_pseudo_type_info(Type,
		NumUnivQTvars, ExistQTvars, ArgRval, ArgRvalType, C0, C).

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

	% Construct a representation of the type of a value.
	%
	% For values representing variables, this will be a pseudo_type_info
	% describing the type of the variable.
	%
	% For the kinds of values used internally by the compiler,
	% this will be a pointer to a specific type_ctor_info (acting as a
	% type_info) defined by hand in builtin.m to stand for values of
	% each such kind; one for succips, one for hps, etc.

:- pred stack_layout__represent_live_value_type(live_value_type, rval,
	llds_type, stack_layout_info, stack_layout_info).
:- mode stack_layout__represent_live_value_type(in, out, out, in, out) is det.

stack_layout__represent_live_value_type(succip, Rval, data_ptr) -->
	{ RttiTypeId = rtti_type_id(unqualified(""), "succip", 0) },
	{ DataAddr = rtti_addr(RttiTypeId, type_ctor_info) },
	{ Rval = const(data_addr_const(DataAddr)) }.
stack_layout__represent_live_value_type(hp, Rval, data_ptr) -->
	{ RttiTypeId = rtti_type_id(unqualified(""), "hp", 0) },
	{ DataAddr = rtti_addr(RttiTypeId, type_ctor_info) },
	{ Rval = const(data_addr_const(DataAddr)) }.
stack_layout__represent_live_value_type(curfr, Rval, data_ptr) -->
	{ RttiTypeId = rtti_type_id(unqualified(""), "curfr", 0) },
	{ DataAddr = rtti_addr(RttiTypeId, type_ctor_info) },
	{ Rval = const(data_addr_const(DataAddr)) }.
stack_layout__represent_live_value_type(maxfr, Rval, data_ptr) -->
	{ RttiTypeId = rtti_type_id(unqualified(""), "maxfr", 0) },
	{ DataAddr = rtti_addr(RttiTypeId, type_ctor_info) },
	{ Rval = const(data_addr_const(DataAddr)) }.
stack_layout__represent_live_value_type(redofr, Rval, data_ptr) -->
	{ RttiTypeId = rtti_type_id(unqualified(""), "redofr", 0) },
	{ DataAddr = rtti_addr(RttiTypeId, type_ctor_info) },
	{ Rval = const(data_addr_const(DataAddr)) }.
stack_layout__represent_live_value_type(redoip, Rval, data_ptr) -->
	{ RttiTypeId = rtti_type_id(unqualified(""), "redoip", 0) },
	{ DataAddr = rtti_addr(RttiTypeId, type_ctor_info) },
	{ Rval = const(data_addr_const(DataAddr)) }.
stack_layout__represent_live_value_type(trail_ptr, Rval, data_ptr) -->
	{ RttiTypeId = rtti_type_id(unqualified(""), "trail_ptr", 0) },
	{ DataAddr = rtti_addr(RttiTypeId, type_ctor_info) },
	{ Rval = const(data_addr_const(DataAddr)) }.
stack_layout__represent_live_value_type(ticket, Rval, data_ptr) -->
	{ RttiTypeId = rtti_type_id(unqualified(""), "ticket", 0) },
	{ DataAddr = rtti_addr(RttiTypeId, type_ctor_info) },
	{ Rval = const(data_addr_const(DataAddr)) }.
stack_layout__represent_live_value_type(unwanted, Rval, data_ptr) -->
	{ RttiTypeId = rtti_type_id(unqualified(""), "unwanted", 0) },
	{ DataAddr = rtti_addr(RttiTypeId, type_ctor_info) },
	{ Rval = const(data_addr_const(DataAddr)) }.
stack_layout__represent_live_value_type(var(_, _, Type, _), Rval, LldsType)
		-->
	stack_layout__get_cell_counter(C0),

		% For a stack layout, we can treat all type variables as
		% universally quantified. This is not the argument of a
		% constructor, so we do not need to distinguish between type
		% variables that are and aren't in scope; we can take the
		% variable number directly from the procedure's tvar set.
	{ ExistQTvars = [] },
	{ NumUnivQTvars = -1 },
	{ ll_pseudo_type_info__construct_typed_llds_pseudo_type_info(Type,
		NumUnivQTvars, ExistQTvars,
		Rval, LldsType, C0, C) },
	stack_layout__set_cell_counter(C).

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

	% Construct a representation of a variable location as a 32-bit
	% integer.
	%
	% Most of the time, a layout specifies a location as an lval.
	% However, a type_info variable may be hidden inside a typeclass_info,
	% In this case, accessing the type_info requires indirection.
	% The address of the typeclass_info is given as an lval, and
	% the location of the typeinfo within the typeclass_info as an index;
	% private_builtin:type_info_from_typeclass_info interprets the index.
	%
	% This one level of indirection is sufficient, since type_infos
	% cannot be nested inside typeclass_infos any deeper than this.
	% A more general representation that would allow more indirection
	% would be much harder to fit into one machine word.

:- pred stack_layout__represent_locn_as_int_rval(layout_locn::in, rval::out)
	is det.

stack_layout__represent_locn_as_int_rval(Locn, Rval) :-
	stack_layout__represent_locn_as_int(Locn, Word),
	Rval = const(int_const(Word)).

:- pred stack_layout__represent_locn_as_int(layout_locn::in, int::out) is det.

stack_layout__represent_locn_as_int(direct(Lval), Word) :-
	stack_layout__represent_lval(Lval, Word).
stack_layout__represent_locn_as_int(indirect(Lval, Offset), Word) :-
	stack_layout__represent_lval(Lval, BaseWord),
	require((1 << stack_layout__long_lval_offset_bits) > Offset,
	"stack_layout__represent_locn: offset too large to be represented"),
	BaseAndOffset is (BaseWord << stack_layout__long_lval_offset_bits)
		+ Offset,
	stack_layout__make_tagged_word(lval_indirect, BaseAndOffset, Word).

	% Construct a four byte representation of an lval.

:- pred stack_layout__represent_lval(lval::in, int::out) is det.

stack_layout__represent_lval(reg(r, Num), Word) :-
	stack_layout__make_tagged_word(lval_r_reg, Num, Word).
stack_layout__represent_lval(reg(f, Num), Word) :-
	stack_layout__make_tagged_word(lval_f_reg, Num, Word).

stack_layout__represent_lval(stackvar(Num), Word) :-
	stack_layout__make_tagged_word(lval_stackvar, Num, Word).
stack_layout__represent_lval(framevar(Num), Word) :-
	stack_layout__make_tagged_word(lval_framevar, Num, Word).

stack_layout__represent_lval(succip, Word) :-
	stack_layout__make_tagged_word(lval_succip, 0, Word).
stack_layout__represent_lval(maxfr, Word) :-
	stack_layout__make_tagged_word(lval_maxfr, 0, Word).
stack_layout__represent_lval(curfr, Word) :-
	stack_layout__make_tagged_word(lval_curfr, 0, Word).
stack_layout__represent_lval(hp, Word) :-
	stack_layout__make_tagged_word(lval_hp, 0, Word).
stack_layout__represent_lval(sp, Word) :-
	stack_layout__make_tagged_word(lval_sp, 0, Word).

stack_layout__represent_lval(temp(_, _), _) :-
	error("stack_layout: continuation live value stored in temp register").

stack_layout__represent_lval(succip(_), _) :-
	error("stack_layout: continuation live value stored in fixed slot").
stack_layout__represent_lval(redoip(_), _) :-
	error("stack_layout: continuation live value stored in fixed slot").
stack_layout__represent_lval(redofr(_), _) :-
	error("stack_layout: continuation live value stored in fixed slot").
stack_layout__represent_lval(succfr(_), _) :-
	error("stack_layout: continuation live value stored in fixed slot").
stack_layout__represent_lval(prevfr(_), _) :-
	error("stack_layout: continuation live value stored in fixed slot").

stack_layout__represent_lval(field(_, _, _), _) :-
	error("stack_layout: continuation live value stored in field").
stack_layout__represent_lval(mem_ref(_), _) :-
	error("stack_layout: continuation live value stored in mem_ref").
stack_layout__represent_lval(lvar(_), _) :-
	error("stack_layout: continuation live value stored in lvar").

	% Some things in this module are encoded using a low tag.
	% This is not done using the normal compiler mkword, but by
	% doing the bit shifting here.
	%
	% This allows us to use more than the usual 2 or 3 bits, but
	% we have to use low tags and cannot tag pointers this way.

:- pred stack_layout__make_tagged_word(locn_type::in, int::in, int::out) is det.

stack_layout__make_tagged_word(Locn, Value, TaggedValue) :-
	stack_layout__locn_type_code(Locn, Tag),
	TaggedValue is (Value << stack_layout__long_lval_tag_bits) + Tag.

:- type locn_type
	--->	lval_r_reg
	;	lval_f_reg
	;	lval_stackvar
	;	lval_framevar
	;	lval_succip
	;	lval_maxfr
	;	lval_curfr
	;	lval_hp
	;	lval_sp
	;	lval_indirect.

:- pred stack_layout__locn_type_code(locn_type::in, int::out) is det.

stack_layout__locn_type_code(lval_r_reg,    0).
stack_layout__locn_type_code(lval_f_reg,    1).
stack_layout__locn_type_code(lval_stackvar, 2).
stack_layout__locn_type_code(lval_framevar, 3).
stack_layout__locn_type_code(lval_succip,   4).
stack_layout__locn_type_code(lval_maxfr,    5).
stack_layout__locn_type_code(lval_curfr,    6).
stack_layout__locn_type_code(lval_hp,       7).
stack_layout__locn_type_code(lval_sp,       8).
stack_layout__locn_type_code(lval_indirect, 9).

:- func stack_layout__long_lval_tag_bits = int.

% This number of tag bits must be able to encode all values of
% stack_layout__locn_type_code.

stack_layout__long_lval_tag_bits = 4.

% This number of tag bits must be able to encode the largest offset
% of a type_info within a typeclass_info.

:- func stack_layout__long_lval_offset_bits = int.

stack_layout__long_lval_offset_bits = 6.

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

	% Construct a representation of a variable location as a byte,
	% if this is possible.

:- pred stack_layout__represent_locn_as_byte(layout_locn::in, rval::out)
	is semidet.

stack_layout__represent_locn_as_byte(LayoutLocn, Rval) :-
	LayoutLocn = direct(Lval),
	stack_layout__represent_lval_as_byte(Lval, Byte),
	Rval = const(int_const(Byte)).

	% Construct a representation of an lval in a byte, if possible.

:- pred stack_layout__represent_lval_as_byte(lval::in, int::out) is semidet.

stack_layout__represent_lval_as_byte(reg(r, Num), Byte) :-
	stack_layout__make_tagged_byte(0, Num, Byte).

stack_layout__represent_lval_as_byte(stackvar(Num), Byte) :-
	stack_layout__make_tagged_byte(1, Num, Byte).
stack_layout__represent_lval_as_byte(framevar(Num), Byte) :-
	stack_layout__make_tagged_byte(2, Num, Byte).

stack_layout__represent_lval_as_byte(succip, Byte) :-
	stack_layout__locn_type_code(lval_succip, Val),
	stack_layout__make_tagged_byte(3, Val, Byte).
stack_layout__represent_lval_as_byte(maxfr, Byte) :-
	stack_layout__locn_type_code(lval_maxfr, Val),
	stack_layout__make_tagged_byte(3, Val, Byte).
stack_layout__represent_lval_as_byte(curfr, Byte) :-
	stack_layout__locn_type_code(lval_curfr, Val),
	stack_layout__make_tagged_byte(3, Val, Byte).
stack_layout__represent_lval_as_byte(hp, Byte) :-
	stack_layout__locn_type_code(lval_hp, Val),
	stack_layout__make_tagged_byte(3, Val, Byte).
stack_layout__represent_lval_as_byte(sp, Byte) :-
	stack_layout__locn_type_code(lval_succip, Val),
	stack_layout__make_tagged_byte(3, Val, Byte).

:- pred stack_layout__make_tagged_byte(int::in, int::in, int::out) is semidet.

stack_layout__make_tagged_byte(Tag, Value, TaggedValue) :-
	Limit = 1 << (stack_layout__byte_bits -
		stack_layout__short_lval_tag_bits),
	Value < Limit,
	TaggedValue is unchecked_left_shift(Value,
		stack_layout__short_lval_tag_bits) + Tag.

:- func stack_layout__short_lval_tag_bits = int.

stack_layout__short_lval_tag_bits = 2.

:- func stack_layout__short_count_bits = int.

stack_layout__short_count_bits = 10.

:- func stack_layout__byte_bits = int.

stack_layout__byte_bits = 8.

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

	% Construct a representation of the interface determinism of a
	% procedure. The code we have chosen is not sequential; instead
	% it encodes the various properties of each determinism.
	%
	% The 8 bit is set iff the context is first_solution.
	% The 4 bit is set iff the min number of solutions is more than zero.
	% The 2 bit is set iff the max number of solutions is more than zero.
	% The 1 bit is set iff the max number of solutions is more than one.

:- pred stack_layout__represent_determinism_rval(determinism::in, rval::out)
	is det.

stack_layout__represent_determinism_rval(Detism, const(int_const(Code))) :-
	stack_layout__represent_determinism(Detism, Code).

:- pred stack_layout__represent_determinism(determinism::in, int::out) is det.

stack_layout__represent_determinism(Detism, Code) :-
	(
		Detism = det,
		Code = 6		/* 0110 */
	;
		Detism = semidet,	/* 0010 */
		Code = 2
	;
		Detism = nondet,
		Code = 3		/* 0011 */
	;
		Detism = multidet,
		Code = 7		/* 0111 */
	;
		Detism = erroneous,
		Code = 4		/* 0100 */
	;
		Detism = failure,
		Code = 0		/* 0000 */
	;
		Detism = cc_nondet,
		Code = 10 		/* 1010 */
	;
		Detism = cc_multidet,
		Code = 14		/* 1110 */
	).

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

	% Access to the stack_layout data structure.

	% The per-sourcefile label table maps line numbers to the list of
	% labels that correspond to that line. Each label is accompanied
	% by a flag that says whether the label is the return site of a call
	% or not, and if it is, whether the called procedure is known.

:- type is_label_return
	--->	known_callee(label)
	;	unknown_callee
	;	not_a_return.

:- type line_no_info == pair(layout_name, is_label_return).

:- type label_table == map(int, list(line_no_info)).

:- type stack_layout_info 	--->
	stack_layout_info(
		module_info		:: module_info,
		agc_stack_layout	:: bool, % generate agc info?
		trace_stack_layout	:: bool, % generate tracing info?
		procid_stack_layout	:: bool, % generate proc id info?
		trace_level		:: trace_level,
		trace_suppress_items	:: trace_suppress_items,
		static_code_addresses	:: bool, % have static code addresses?
		proc_layouts		:: list(comp_gen_c_data),
		internal_layouts	:: list(comp_gen_c_data),
		label_set		:: map(label, data_addr),
					   % The set of labels (both entry
					   % and internal) with layouts.
		proc_layout_name_list	:: list(layout_name),
					   % The list of proc_layouts in
					   % the module.
		string_table		:: string_table,
		label_tables		:: map(string, label_table),
					   % Maps each filename that
					   % contributes labels to this module
					   % to a table describing those
					   % labels.
		cur_proc_named_vars	:: map(int, string)
					   % Maps the number of each variable
					   % in the current procedure whose
					   % name is of interest in an internal
					   % label's layout structure to the
					   % name of that variable.
	).

:- pred stack_layout__get_module_info(module_info::out,
	stack_layout_info::in, stack_layout_info::out) is det.

:- pred stack_layout__get_agc_stack_layout(bool::out,
	stack_layout_info::in, stack_layout_info::out) is det.

:- pred stack_layout__get_trace_stack_layout(bool::out,
	stack_layout_info::in, stack_layout_info::out) is det.

:- pred stack_layout__get_procid_stack_layout(bool::out,
	stack_layout_info::in, stack_layout_info::out) is det.

:- pred stack_layout__get_trace_level(trace_level::out,
	stack_layout_info::in, stack_layout_info::out) is det.

:- pred stack_layout__get_trace_suppress(trace_suppress_items::out,
	stack_layout_info::in, stack_layout_info::out) is det.

:- pred stack_layout__get_static_code_addresses(bool::out,
	stack_layout_info::in, stack_layout_info::out) is det.

:- pred stack_layout__get_proc_layout_data(list(comp_gen_c_data)::out,
	stack_layout_info::in, stack_layout_info::out) is det.

:- pred stack_layout__get_internal_layout_data(list(comp_gen_c_data)::out,
	stack_layout_info::in, stack_layout_info::out) is det.

:- pred stack_layout__get_label_set(map(label, data_addr)::out,
	stack_layout_info::in, stack_layout_info::out) is det.

:- pred stack_layout__get_string_table(string_table::out,
	stack_layout_info::in, stack_layout_info::out) is det.

:- pred stack_layout__get_label_tables(map(string, label_table)::out,
	stack_layout_info::in, stack_layout_info::out) is det.

:- pred stack_layout__get_cur_proc_named_vars(map(int, string)::out,
	stack_layout_info::in, stack_layout_info::out) is det.

stack_layout__get_module_info(LI ^ module_info, LI, LI).
stack_layout__get_agc_stack_layout(LI ^ agc_stack_layout, LI, LI).
stack_layout__get_trace_stack_layout(LI ^ trace_stack_layout, LI, LI).
stack_layout__get_procid_stack_layout(LI ^ procid_stack_layout, LI, LI).
stack_layout__get_trace_level(LI ^ trace_level, LI, LI).
stack_layout__get_trace_suppress(LI ^ trace_suppress_items, LI, LI).
stack_layout__get_static_code_addresses(LI ^ static_code_addresses, LI, LI).
stack_layout__get_proc_layout_data(LI ^ proc_layouts, LI, LI).
stack_layout__get_internal_layout_data(LI ^ internal_layouts, LI, LI).
stack_layout__get_label_set(LI ^ label_set, LI, LI).
stack_layout__get_string_table(LI ^ string_table, LI, LI).
stack_layout__get_label_tables(LI ^ label_tables, LI, LI).
stack_layout__get_cur_proc_named_vars(LI ^ cur_proc_named_vars, LI, LI).

:- pred stack_layout__get_module_name(module_name::out,
	stack_layout_info::in, stack_layout_info::out) is det.

stack_layout__get_module_name(ModuleName) -->
	stack_layout__get_module_info(ModuleInfo),
	{ module_info_name(ModuleInfo, ModuleName) }.

:- pred stack_layout__get_cell_counter(counter::out,
	stack_layout_info::in, stack_layout_info::out) is det.

stack_layout__get_cell_counter(CellCounter) -->
	stack_layout__get_module_info(ModuleInfo),
	{ module_info_get_cell_counter(ModuleInfo, CellCounter) }.

:- pred stack_layout__add_proc_layout_data(comp_gen_c_data::in,
	layout_name::in, label::in,
	stack_layout_info::in, stack_layout_info::out) is det.

stack_layout__add_proc_layout_data(ProcLayout, ProcLayoutName, Label,
		LI0, LI) :-
	ProcLayouts0 = LI0 ^ proc_layouts,
	ProcLayouts = [ProcLayout | ProcLayouts0],
	LabelSet0 = LI0 ^ label_set,
	map__det_insert(LabelSet0, Label, layout_addr(ProcLayoutName),
		LabelSet),
	ProcLayoutNames0 = LI0 ^ proc_layout_name_list,
	ProcLayoutNames = [ProcLayoutName | ProcLayoutNames0],
	LI = (((LI0 ^ proc_layouts := ProcLayouts)
		^ label_set := LabelSet)
		^ proc_layout_name_list := ProcLayoutNames).

:- pred stack_layout__add_internal_layout_data(comp_gen_c_data::in,
	label::in, layout_name::in, stack_layout_info::in,
	stack_layout_info::out) is det.

stack_layout__add_internal_layout_data(InternalLayout, Label, LayoutName,
		LI0, LI) :-
	InternalLayouts0 = LI0 ^ internal_layouts,
	InternalLayouts = [InternalLayout | InternalLayouts0],
	LabelSet0 = LI0 ^ label_set,
	map__det_insert(LabelSet0, Label, layout_addr(LayoutName), LabelSet),
	LI = ((LI0 ^ internal_layouts := InternalLayouts)
		^ label_set := LabelSet).

:- pred stack_layout__get_next_cell_number(int::out,
	stack_layout_info::in, stack_layout_info::out) is det.

stack_layout__get_next_cell_number(CellNum) -->
	stack_layout__get_cell_counter(CellCounter0),
	{ counter__allocate(CellNum, CellCounter0, CellCounter) },
	stack_layout__set_cell_counter(CellCounter).

:- pred stack_layout__set_cell_counter(counter::in,
	stack_layout_info::in, stack_layout_info::out) is det.

stack_layout__set_cell_counter(CellCounter) -->
	stack_layout__get_module_info(ModuleInfo0),
	{ module_info_set_cell_counter(ModuleInfo0, CellCounter,
		ModuleInfo) },
	stack_layout__set_module_info(ModuleInfo).

:- pred stack_layout__set_module_info(module_info::in,
	stack_layout_info::in, stack_layout_info::out) is det.

:- pred stack_layout__set_string_table(string_table::in,
	stack_layout_info::in, stack_layout_info::out) is det.

:- pred stack_layout__set_label_tables(map(string, label_table)::in,
	stack_layout_info::in, stack_layout_info::out) is det.

:- pred stack_layout__set_cur_proc_named_vars(map(int, string)::in,
	stack_layout_info::in, stack_layout_info::out) is det.

stack_layout__set_module_info(MI, LI0, LI0 ^ module_info := MI).
stack_layout__set_string_table(ST, LI0, LI0 ^ string_table := ST).
stack_layout__set_label_tables(LT, LI0, LI0 ^ label_tables := LT).
stack_layout__set_cur_proc_named_vars(NV, LI0,
	LI0 ^ cur_proc_named_vars := NV).

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

	% Access to the string_table data structure.

:- type string_table 	--->
	string_table(
		map(string, int),	% Maps strings to their offsets.
		list(string),		% List of strings so far,
					% in reverse order.
		int			% Next available offset
	).

:- pred stack_layout__lookup_string_in_table(string::in, int::out,
	stack_layout_info::in, stack_layout_info::out) is det.

stack_layout__lookup_string_in_table(String, Offset) -->
	stack_layout__get_string_table(StringTable0),
	{ StringTable0 = string_table(TableMap0, TableList0, TableOffset0) },
	(
		{ map__search(TableMap0, String, OldOffset) }
	->
		{ Offset = OldOffset }
	;
		{ string__length(String, Length) },
		{ TableOffset is TableOffset0 + Length + 1 },
		{ TableOffset < (1 << (2 * stack_layout__byte_bits)) }
	->
		{ Offset = TableOffset0 },
		{ map__det_insert(TableMap0, String, TableOffset0,
			TableMap) },
		{ TableList = [String | TableList0] },
		{ StringTable = string_table(TableMap, TableList,
			TableOffset) },
		stack_layout__set_string_table(StringTable)
	;
		% Says that the name of the variable is "TOO_MANY_VARIABLES".
		{ Offset = 1 }
	).