mercury/trace/mercury_trace_declarative.c

/*
** Copyright (C) 1998-2003 The University of Melbourne.
** This file may only be copied under the terms of the GNU Library General
** Public License - see the file COPYING.LIB in the Mercury distribution.
*/

/*
** Main author: Mark Brown
**
** This file implements the back end of the declarative debugger.  The
** back end is an extension to the internal debugger which collects
** related trace events and builds them into an annotated trace.  Once
** built, the structure is passed to the front end where it can be
** analysed to find bugs.  The front end is implemented in
** browse/declarative_debugger.m.
**
** The interface between the front and back ends is via the
** annotated_trace/2 typeclass, which is documented in
** browse/declarative_debugger.m.  It would be possible to replace
** the front end or the back end with an alternative implementation
** which also conforms to the typeclass constraints.  For example:
** 	- An alternative back end could generate the same tree
** 	  structure in a different way, such as via program
** 	  transformation.
** 	- An alternative front end could graphically display the
** 	  generated trees as part of a visualization tool rather
** 	  than analyzing them for bugs.
*/

#include "mercury_imp.h"
#include "mercury_trace_declarative.h"

#include "mercury_trace.h"
#include "mercury_trace_browse.h"
#include "mercury_trace_internal.h"
#include "mercury_trace_tables.h"
#include "mercury_trace_util.h"
#include "mercury_trace_vars.h"

#include "mercury_layout_util.h"
#include "mercury_deep_copy.h"
#include "mercury_stack_trace.h"
#include "mercury_string.h"
#include "mercury_trace_base.h"

#include "mdb.declarative_debugger.mh"
#include "mdb.declarative_execution.mh"

#include "std_util.mh"

#include <errno.h>

/*
** We only build the annotated trace for events down to a certain
** depth.  The following macro gives the default depth limit (relative
** to the starting depth).  In future it would be nice to dynamically
** adjust this factor based on profiling information.
*/

#define MR_EDT_DEPTH_STEP_SIZE		3

/*
** These macros are to aid debugging of the code which constructs
** the annotated trace.
*/

#ifdef MR_DEBUG_DD_BACK_END

#define MR_decl_checkpoint_event(event_info)				\
		MR_decl_checkpoint_event_imp("EVENT", event_info)

#define MR_decl_checkpoint_filter(event_info)				\
		MR_decl_checkpoint_event_imp("FILTER", event_info)

#define MR_decl_checkpoint_find(location)				\
		MR_decl_checkpoint_loc("FIND", location)

#define MR_decl_checkpoint_step(location)				\
		MR_decl_checkpoint_loc("STEP", location)

#define MR_decl_checkpoint_match(location)				\
		MR_decl_checkpoint_loc("MATCH", location)

#define MR_decl_checkpoint_alloc(location)				\
		MR_decl_checkpoint_loc("ALLOC", location)

#else /* !MR_DEBUG_DD_BACK_END */

#define MR_decl_checkpoint_event(event_info)
#define MR_decl_checkpoint_filter(event_info)
#define MR_decl_checkpoint_find(location)
#define MR_decl_checkpoint_step(location)
#define MR_decl_checkpoint_match(location)
#define MR_decl_checkpoint_alloc(location)

#endif

/*
** The declarative debugger back end is controlled by the
** settings of the following variables.  They are set in
** MR_trace_start_decl_debug when the back end is started.  They
** are used by MR_trace_decl_debug to decide what action to
** take for a particular trace event.
**
** Events that are deeper than the maximum depth, or which are
** outside the top call being debugged, are ignored.  Events which
** are beyond the given last event cause the internal debugger to
** be switched back into interactive mode.
*/

static	MR_Unsigned	MR_edt_max_depth;
static	MR_Unsigned	MR_edt_last_event;
static	MR_bool		MR_edt_inside;
static	MR_Unsigned	MR_edt_start_seqno;
static	MR_Unsigned	MR_edt_start_io_counter;

/*
** The declarative debugger ignores modules that were not compiled with
** the required information.  However, this may result in incorrect
** assumptions being made about the code, so the debugger gives a warning
** if this happens.  The following flag indicates whether a warning
** should be printed before calling the front end.
*/

static	MR_bool		MR_edt_compiler_flag_warning;

/*
** This is used as the abstract map from node identifiers to nodes
** in the data structure passed to the front end.  It should be
** incremented each time the data structure is destructively
** updated, before being passed to Mercury code again.
*/

static	MR_Unsigned	MR_trace_node_store;

/*
** The front end state is stored here in between calls to it.
** MR_trace_decl_ensure_init should be called before using the state.
*/

static	MR_Word		MR_trace_front_end_state;

static	void
MR_trace_decl_ensure_init(void);

/*
** MR_trace_current_node always contains the last node allocated,
** or NULL if the collection has just started.
*/

static	MR_Trace_Node	MR_trace_current_node;

/*
** When in test mode, MR_trace_store_file points to an open file to
** which the store should be written when built.  This global is
** set in MR_trace_start_decl_debug, and keeps the same value
** throughout the declarative debugging session.
*/

static	FILE		*MR_trace_store_file;

static	MR_Trace_Node	MR_trace_decl_call(MR_Event_Info *event_info,
				MR_Trace_Node prev);
static	MR_Trace_Node	MR_trace_decl_exit(MR_Event_Info *event_info,
				MR_Trace_Node prev);
static	MR_Trace_Node	MR_trace_decl_redo(MR_Event_Info *event_info,
				MR_Trace_Node prev);
static	MR_Trace_Node	MR_trace_decl_fail(MR_Event_Info *event_info,
				MR_Trace_Node prev);
static	MR_Trace_Node	MR_trace_decl_excp(MR_Event_Info *event_info,
				MR_Trace_Node prev);
static	MR_Trace_Node	MR_trace_decl_switch(MR_Event_Info *event_info,
				MR_Trace_Node prev);
static	MR_Trace_Node	MR_trace_decl_disj(MR_Event_Info *event_info,
				MR_Trace_Node prev);
static	MR_Trace_Node	MR_trace_decl_cond(MR_Event_Info *event_info,
				MR_Trace_Node prev);
static	MR_Trace_Node	MR_trace_decl_then(MR_Event_Info *event_info,
				MR_Trace_Node prev);
static	MR_Trace_Node	MR_trace_decl_else(MR_Event_Info *event_info,
				MR_Trace_Node prev);
static	MR_Trace_Node	MR_trace_decl_neg_enter(MR_Event_Info *event_info,
				MR_Trace_Node prev);
static	MR_Trace_Node	MR_trace_decl_neg_success(MR_Event_Info *event_info,
				MR_Trace_Node prev);
static	MR_Trace_Node	MR_trace_decl_neg_failure(MR_Event_Info *event_info,
				MR_Trace_Node prev);
static	MR_Trace_Node	MR_trace_matching_call(MR_Trace_Node node);
static	MR_bool		MR_trace_first_disjunct(MR_Event_Info *event_info);
static	MR_bool		MR_trace_matching_cond(const char *path,
				MR_Trace_Node node);
static	MR_bool		MR_trace_matching_neg(const char *path,
				MR_Trace_Node node);
static	MR_bool		MR_trace_matching_disj(const char *path,
				MR_Trace_Node node);
static	MR_bool		MR_trace_same_construct(const char *p1,
				const char *p2);
static	MR_bool		MR_trace_single_component(const char *path);
static	MR_Word		MR_decl_make_atom(const MR_Label_Layout *layout,
				MR_Word *saved_regs, MR_Trace_Port port);
static	MR_ConstString	MR_decl_atom_name(const MR_Proc_Layout *entry);
static	MR_Word		MR_decl_atom_args(const MR_Label_Layout *layout,
				MR_Word *saved_regs);
static	const char	*MR_trace_start_collecting(MR_Unsigned event,
				MR_Unsigned seqno, MR_Unsigned maxdepth,
				MR_Trace_Cmd_Info *cmd,
				MR_Event_Info *event_info,
				MR_Event_Details *event_details,
				MR_Code **jumpaddr);
static	MR_Code		*MR_trace_restart_decl_debug(MR_Unsigned event,
				MR_Unsigned seqno, MR_Trace_Cmd_Info *cmd,
				MR_Event_Info *event_info,
				MR_Event_Details *event_details);
static	MR_Code		*MR_decl_diagnosis(MR_Trace_Node root,
				MR_Trace_Cmd_Info *cmd,
				MR_Event_Info *event_info,
				MR_Event_Details *event_details);
static	MR_Code		*MR_decl_go_to_selected_event(MR_Unsigned event,
				MR_Trace_Cmd_Info *cmd,
				MR_Event_Info *event_info,
				MR_Event_Details *event_details);
static	MR_String	MR_trace_node_path(MR_Trace_Node node);
static	MR_Trace_Port	MR_trace_node_port(MR_Trace_Node node);
static	MR_Unsigned	MR_trace_node_seqno(MR_Trace_Node node);
static	MR_Trace_Node	MR_trace_node_first_disj(MR_Trace_Node node);
static	MR_Trace_Node	MR_trace_step_left_in_contour(MR_Trace_Node node);
static	MR_Trace_Node	MR_trace_find_prev_contour(MR_Trace_Node node);
static	void		MR_decl_checkpoint_event_imp(const char *str,
				MR_Event_Info *event_info);
static	void		MR_decl_checkpoint_loc(const char *str,
				MR_Trace_Node node);

MR_bool MR_trace_decl_assume_all_io_is_tabled = MR_FALSE;

MR_Code *
MR_trace_decl_debug(MR_Trace_Cmd_Info *cmd, MR_Event_Info *event_info)
{
	const MR_Proc_Layout 	*entry;
	MR_Unsigned		depth;
	MR_Trace_Node		trace;
	MR_Event_Details	event_details;
	MR_Integer		trace_suppress;

	entry = event_info->MR_event_sll->MR_sll_entry;
	depth = event_info->MR_call_depth;

	if (event_info->MR_event_number > MR_edt_last_event) {
		/* This shouldn't ever be reached. */
		fprintf(MR_mdb_err, "Warning: missed final event.\n");
		fprintf(MR_mdb_err, "event %lu\nlast event %lu\n",
				(unsigned long) event_info->MR_event_number,
				(unsigned long) MR_edt_last_event);
		MR_trace_decl_mode = MR_TRACE_INTERACTIVE;
		return MR_trace_event_internal(cmd, MR_TRUE, event_info);
	}

	if (!MR_PROC_LAYOUT_HAS_EXEC_TRACE(entry)) {
		/* XXX this should be handled better. */
		MR_fatal_error("layout has no execution tracing");
	}

	if (depth > MR_edt_max_depth) {
		/*
		** We filter out events which are deeper than a certain
		** limit given by MR_edt_max_depth.  These events are
		** implicitly represented in the structure being built.
		*/
		return NULL;
	}

	if (MR_edt_inside) {
		if (event_info->MR_call_seqno == MR_edt_start_seqno &&
			MR_port_is_final(event_info->MR_trace_port))
		{
			/*
			** We are leaving the topmost call.
			*/
			MR_edt_inside = MR_FALSE;
		}
	} else {
		if (event_info->MR_call_seqno == MR_edt_start_seqno) {
			/*
			** The port must be either CALL or REDO;
			** we are (re)entering the topmost call.
			*/
			MR_edt_inside = MR_TRUE;
		} else {
			/*
			** Ignore this event---it is outside the
			** topmost call.
			*/
			MR_decl_checkpoint_filter(event_info);
			return NULL;
		}
	}

	if (MR_PROC_LAYOUT_COMPILER_GENERATED(entry)) {
		/*
		** Filter out events for compiler generated procedures.
		*/
		return NULL;
	}

	trace_suppress = entry->MR_sle_module_layout->MR_ml_suppressed_events;
	if (trace_suppress != 0) {
		/*
		** We ignore events from modules that were not compiled
		** with the necessary information.  Procedures in those
		** modules are effectively assumed correct, so we give
		** the user a warning.
		*/
		MR_edt_compiler_flag_warning = MR_TRUE;
		return NULL;
	}

	event_details.MR_call_seqno = MR_trace_call_seqno;
	event_details.MR_call_depth = MR_trace_call_depth;
	event_details.MR_event_number = MR_trace_event_number;

	MR_trace_enabled = MR_FALSE;
	MR_decl_checkpoint_event(event_info);
	trace = MR_trace_current_node;
	switch (event_info->MR_trace_port) {
		case MR_PORT_CALL:
			trace = MR_trace_decl_call(event_info, trace);
			break;
		case MR_PORT_EXIT:
			trace = MR_trace_decl_exit(event_info, trace);
			break;
		case MR_PORT_REDO:
			trace = MR_trace_decl_redo(event_info, trace);
			break;
		case MR_PORT_FAIL:
			trace = MR_trace_decl_fail(event_info, trace);
			break;
		case MR_PORT_DISJ:
			trace = MR_trace_decl_disj(event_info, trace);
			break;
		case MR_PORT_SWITCH:
			trace = MR_trace_decl_switch(event_info, trace);
			break;
		case MR_PORT_COND:
			trace = MR_trace_decl_cond(event_info, trace);
			break;
		case MR_PORT_THEN:
			trace = MR_trace_decl_then(event_info, trace);
			break;
		case MR_PORT_ELSE:
			trace = MR_trace_decl_else(event_info, trace);
			break;
		case MR_PORT_NEG_ENTER:
			trace = MR_trace_decl_neg_enter(event_info, trace);
			break;
		case MR_PORT_NEG_SUCCESS:
			trace = MR_trace_decl_neg_success(event_info, trace);
			break;
		case MR_PORT_NEG_FAILURE:
			trace = MR_trace_decl_neg_failure(event_info, trace);
			break;
		case MR_PORT_PRAGMA_FIRST:
		case MR_PORT_PRAGMA_LATER:
			MR_fatal_error("MR_trace_decl_debug: "
				"foreign language code is not handled (yet)");
		case MR_PORT_EXCEPTION:
			trace = MR_trace_decl_excp(event_info, trace);
			break;
		default:
			MR_fatal_error("MR_trace_decl_debug: unknown port");
	}
	MR_decl_checkpoint_alloc(trace);
	MR_trace_current_node = trace;
	
	/*
	** Restore globals from the saved copies.
	*/
	MR_trace_call_seqno = event_details.MR_call_seqno;
	MR_trace_call_depth = event_details.MR_call_depth;
	MR_trace_event_number = event_details.MR_event_number;

	if (MR_trace_event_number == MR_edt_last_event) {
		/*
		** Call the front end.
		*/
		return MR_decl_diagnosis(MR_trace_current_node, cmd,
				event_info, &event_details);
	}

	MR_trace_enabled = MR_TRUE;
	return NULL;
}

static	MR_Trace_Node
MR_trace_decl_call(MR_Event_Info *event_info, MR_Trace_Node prev)
{
	MR_Trace_Node			node;
	MR_Word				atom;
	MR_bool				at_depth_limit;
	const MR_Label_Layout		*event_label_layout;
	const MR_Proc_Layout		*event_proc_layout;
	const MR_Label_Layout		*return_label_layout;
	MR_Word				proc_rep;
	MR_Stack_Walk_Step_Result	result;
	MR_ConstString			problem;
	MR_String			goal_path;
	MR_Word				*base_sp;
	MR_Word				*base_curfr;

	if (event_info->MR_call_depth == MR_edt_max_depth) {
		at_depth_limit = MR_TRUE;
	} else {
		at_depth_limit = MR_FALSE;
	}

	event_label_layout = event_info->MR_event_sll;
	event_proc_layout = event_label_layout->MR_sll_entry;
	proc_rep = (MR_Word) event_proc_layout->MR_sle_proc_rep;
	atom = MR_decl_make_atom(event_label_layout, event_info->MR_saved_regs,
			MR_PORT_CALL);
	base_sp = MR_saved_sp(event_info->MR_saved_regs);
	base_curfr = MR_saved_curfr(event_info->MR_saved_regs);
	result = MR_stack_walk_step(event_proc_layout, &return_label_layout,
			&base_sp, &base_curfr, &problem);

	/*
	** We pass goal_path to Mercury code, which expects its type to be
	** MR_String, not MR_ConstString, even though it treats the string as
	** constant.
	**
	** return_label_layout may be NULL even if result is MR_STEP_OK, if
	** the current event is inside the code of main/2.
	*/

	if (result == MR_STEP_OK && return_label_layout != NULL) {
		goal_path = (MR_String) (MR_Integer)
			MR_label_goal_path(return_label_layout);
	} else {
		goal_path = (MR_String) (MR_Integer) "";
	}

	MR_TRACE_CALL_MERCURY(
		if (proc_rep) {
			node = (MR_Trace_Node)
				MR_DD_construct_call_node_with_goal(
					(MR_Word) prev, atom,
					(MR_Word) event_info->MR_call_seqno,
					(MR_Word) event_info->MR_event_number,
					(MR_Word) at_depth_limit, proc_rep,
					goal_path, MR_io_tabling_counter);
		} else {
			node = (MR_Trace_Node)
				MR_DD_construct_call_node((MR_Word) prev, atom,
					(MR_Word) event_info->MR_call_seqno,
					(MR_Word) event_info->MR_event_number,
					(MR_Word) at_depth_limit, goal_path,
					MR_io_tabling_counter);
		}
	);

	return node;
}
	
static	MR_Trace_Node
MR_trace_decl_exit(MR_Event_Info *event_info, MR_Trace_Node prev)
{
	MR_Trace_Node		node;
	MR_Trace_Node		call;
	MR_Word			last_interface;
	MR_Word			atom;

	atom = MR_decl_make_atom(event_info->MR_event_sll,
				event_info->MR_saved_regs,
				MR_PORT_EXIT);

	call = MR_trace_matching_call(prev);
	MR_decl_checkpoint_match(call);
	MR_TRACE_CALL_MERCURY(
		last_interface = MR_DD_call_node_get_last_interface(
				(MR_Word) call);
		node = (MR_Trace_Node) MR_DD_construct_exit_node(
				(MR_Word) prev, (MR_Word) call, last_interface,
				atom, (MR_Word) event_info->MR_event_number,
				MR_io_tabling_counter);
		MR_DD_call_node_set_last_interface((MR_Word) call,
				(MR_Word) node);
	);

	return node;
}

static	MR_Trace_Node
MR_trace_decl_redo(MR_Event_Info *event_info, MR_Trace_Node prev)
{
	MR_Trace_Node		node;
	MR_Trace_Node		call;
	MR_Trace_Node		next;
	MR_Word			last_interface;

	/*
	** Search through previous contour for a matching EXIT event.
	*/
	next = MR_trace_find_prev_contour(prev);
	while (MR_trace_node_port(next) != MR_PORT_EXIT
		|| MR_trace_node_seqno(next) != event_info->MR_call_seqno)
	{
		next = MR_trace_step_left_in_contour(next);
	}
	MR_decl_checkpoint_match(next);

	MR_TRACE_CALL_MERCURY(
		MR_trace_node_store++;
		if (!MR_DD_trace_node_call(MR_trace_node_store, (MR_Word) next,
					(MR_Word *) &call))
		{
			MR_fatal_error("MR_trace_decl_redo: no matching EXIT");
		}
	);

	MR_TRACE_CALL_MERCURY(
		last_interface = MR_DD_call_node_get_last_interface(
					(MR_Word) call);
		node = (MR_Trace_Node) MR_DD_construct_redo_node(
					(MR_Word) prev,
					last_interface);
		MR_DD_call_node_set_last_interface((MR_Word) call,
					(MR_Word) node);
	);

	return node;
}

static	MR_Trace_Node
MR_trace_decl_fail(MR_Event_Info *event_info, MR_Trace_Node prev)
{
	MR_Trace_Node		node;
	MR_Trace_Node		next;
	MR_Trace_Node		call;
	MR_Word			redo;

	if (MR_trace_node_port(prev) == MR_PORT_CALL) {
		/*
		** We are already at the corresponding call, so there
		** is no need to search for it.
		*/
		call = prev;
	} else {
		next = MR_trace_find_prev_contour(prev);
		call = MR_trace_matching_call(next);
	}
	MR_decl_checkpoint_match(call);

	MR_TRACE_CALL_MERCURY(
		redo = MR_DD_call_node_get_last_interface((MR_Word) call);
		node = (MR_Trace_Node) MR_DD_construct_fail_node(
					(MR_Word) prev, (MR_Word) call,
					(MR_Word) redo,
					(MR_Word) event_info->MR_event_number);
		MR_DD_call_node_set_last_interface((MR_Word) call,
					(MR_Word) node);
	);
	return node;
}

static	MR_Trace_Node
MR_trace_decl_excp(MR_Event_Info *event_info, MR_Trace_Node prev)
{
	MR_Trace_Node		node;
	MR_Trace_Node		call;
	MR_Word			last_interface;

	call = MR_trace_matching_call(prev);
	MR_decl_checkpoint_match(call);

	MR_TRACE_CALL_MERCURY(
		last_interface = MR_DD_call_node_get_last_interface(
				(MR_Word) call);
		node = (MR_Trace_Node) MR_DD_construct_excp_node(
				(MR_Word) prev, (MR_Word) call, last_interface,
				MR_trace_get_exception_value(),
				(MR_Word) event_info->MR_event_number);
		MR_DD_call_node_set_last_interface(
				(MR_Word) call, (MR_Word) node);
	);

	return node;
}

static	MR_Trace_Node
MR_trace_decl_cond(MR_Event_Info *event_info, MR_Trace_Node prev)
{
	MR_Trace_Node		node;

	MR_TRACE_CALL_MERCURY(
		node = (MR_Trace_Node) MR_DD_construct_cond_node(
					(MR_Word) prev,
					(MR_String) event_info->MR_event_path);
	);
	return node;
}

static	MR_Trace_Node
MR_trace_decl_then(MR_Event_Info *event_info, MR_Trace_Node prev)
{
	MR_Trace_Node		node;
	MR_Trace_Node		next;
	MR_Trace_Node		cond;
	const char		*path = event_info->MR_event_path;

	/*
	** Search through current contour for a matching COND event.
	*/
	next = prev;
	while (!MR_trace_matching_cond(path, next))
	{
		next = MR_trace_step_left_in_contour(next);
	}
	cond = next;
	MR_decl_checkpoint_match(cond);
	
	MR_TRACE_CALL_MERCURY(
		MR_DD_cond_node_set_status((MR_Word) cond,
					MR_TRACE_STATUS_SUCCEEDED);
		node = (MR_Trace_Node) MR_DD_construct_then_node(
					(MR_Word) prev,
					(MR_Word) cond);
	);
	return node;
}

static	MR_Trace_Node
MR_trace_decl_else(MR_Event_Info *event_info, MR_Trace_Node prev)
{
	MR_Trace_Node		node;
	MR_Trace_Node		cond;
	const char		*path = event_info->MR_event_path;

	/*
	** Search through previous contour for a matching COND event.
	*/
	if (MR_trace_matching_cond(path, prev))
	{
		cond = prev;
	}
	else
	{
		MR_Trace_Node		next;

		next = prev;
		while (!MR_trace_matching_cond(path, next))
		{
			next = MR_trace_step_left_in_contour(next);
		}
		cond = next;
	}
	MR_decl_checkpoint_match(cond);
	
	MR_TRACE_CALL_MERCURY(
		MR_DD_cond_node_set_status((MR_Word) cond,
					MR_TRACE_STATUS_FAILED);
		node = (MR_Trace_Node) MR_DD_construct_else_node(
					(MR_Word) prev,
					(MR_Word) cond);
	);
	return node;
}

static	MR_Trace_Node
MR_trace_decl_neg_enter(MR_Event_Info *event_info, MR_Trace_Node prev)
{
	MR_Trace_Node		node;

	MR_TRACE_CALL_MERCURY(
		node = (MR_Trace_Node) MR_DD_construct_neg_node(
					(MR_Word) prev,
					(MR_String) event_info->MR_event_path);
	);
	return node;
}

static	MR_Trace_Node
MR_trace_decl_neg_success(MR_Event_Info *event_info, MR_Trace_Node prev)
{
	MR_Trace_Node		node;
	MR_Trace_Node		nege;
	const char		*path = event_info->MR_event_path;

	/*
	** Search through previous contour for a matching NEGE event.
	*/
	if (MR_trace_matching_neg(path, prev))
	{
		nege = MR_trace_current_node;
	}
	else
	{
		MR_Trace_Node		next;

		next = prev;
		while (!MR_trace_matching_neg(path, next))
		{
			next = MR_trace_step_left_in_contour(next);
		}
		nege = next;
	}
	MR_decl_checkpoint_match(nege);
	
	MR_TRACE_CALL_MERCURY(
		MR_DD_neg_node_set_status((MR_Word) nege,
					MR_TRACE_STATUS_SUCCEEDED);
		node = (MR_Trace_Node) MR_DD_construct_neg_succ_node(
						(MR_Word) prev,
						(MR_Word) nege);
	);
	return node;
}

static	MR_Trace_Node
MR_trace_decl_neg_failure(MR_Event_Info *event_info, MR_Trace_Node prev)
{
	MR_Trace_Node		node;
	MR_Trace_Node		next;

	/*
	** Search through current contour for a matching NEGE event.
	*/
	next = prev;
	while (!MR_trace_matching_neg(event_info->MR_event_path, next))
	{
		next = MR_trace_step_left_in_contour(next);
	}
	MR_decl_checkpoint_match(next);
	
	MR_TRACE_CALL_MERCURY(
		MR_DD_neg_node_set_status((MR_Word) next,
					MR_TRACE_STATUS_FAILED);
		node = (MR_Trace_Node) MR_DD_construct_neg_fail_node(
						(MR_Word) prev,
						(MR_Word) next);
	);
	return node;
}

static	MR_Trace_Node
MR_trace_decl_switch(MR_Event_Info *event_info, MR_Trace_Node prev)
{
	MR_Trace_Node		node;

	MR_TRACE_CALL_MERCURY(
		node = (MR_Trace_Node) MR_DD_construct_switch_node(
					(MR_Word) prev,
					(MR_String) event_info->MR_event_path);
	);
	return node;
}

static	MR_Trace_Node
MR_trace_decl_disj(MR_Event_Info *event_info, MR_Trace_Node prev)
{
	MR_Trace_Node		node;
	const char		*path = event_info->MR_event_path;

	if (MR_trace_first_disjunct(event_info))
	{
		MR_TRACE_CALL_MERCURY(
			node = (MR_Trace_Node) MR_DD_construct_first_disj_node(
					(MR_Word) prev,
					(MR_String) path);
		);
	}
	else
	{
		MR_Trace_Node		next;
		MR_Trace_Node		first;

		/*
		** Search through previous nodes for a matching DISJ event.
		*/
		next = MR_trace_find_prev_contour(prev);
		while (!MR_trace_matching_disj(path, next))
		{
			next = MR_trace_step_left_in_contour(next);
		}
		MR_decl_checkpoint_match(next);

		/*
		** Find the first disj event of this disjunction.
		*/
		first = MR_trace_node_first_disj(next);
		if (first == (MR_Trace_Node) NULL)
		{
			first = next;
		}

		MR_TRACE_CALL_MERCURY(
			node = (MR_Trace_Node) MR_DD_construct_later_disj_node(
						MR_trace_node_store,
						(MR_Word) prev,
						(MR_String) path,
						(MR_Word) first);
		);
	}

	return node;
}

static	MR_Trace_Node
MR_trace_matching_call(MR_Trace_Node node)
{
	MR_Trace_Node		next;

	/*
	** Search through contour for any CALL event.  Since there
	** is only one CALL event which can be reached, we assume it
	** is the correct one.
	*/
	next = node;
	while (MR_trace_node_port(next) != MR_PORT_CALL)
	{
		next = MR_trace_step_left_in_contour(next);
	}
	return next;
}

static	MR_bool
MR_trace_first_disjunct(MR_Event_Info *event_info)
{
	const char		*path;

	/*
	** Return MR_TRUE iff the last component of the path is "d1;".
	*/
	path = event_info->MR_event_path;
	while (*path)
	{
		if (MR_string_equal(path, "d1;"))
		{
			return MR_TRUE;
		}
		path++;
	}

	return MR_FALSE;
}
	
static	MR_bool
MR_trace_matching_cond(const char *path, MR_Trace_Node node)
{
	MR_Trace_Port		port;
	const char		*node_path;

	MR_TRACE_CALL_MERCURY(
		port = (MR_Trace_Port) MR_DD_trace_node_port(node);
	);
	if (port != MR_PORT_COND)
	{
		return MR_FALSE;
	}
	node_path = MR_trace_node_path(node);

	return MR_trace_same_construct(path, node_path);
}

static	MR_bool
MR_trace_matching_neg(const char *path, MR_Trace_Node node)
{
	MR_Trace_Port		port;
	const char		*node_path;

	MR_TRACE_CALL_MERCURY(
		port = (MR_Trace_Port) MR_DD_trace_node_port(node);
	);
	if (port != MR_PORT_NEG_ENTER) {
		return MR_FALSE;
	}
	node_path = MR_trace_node_path(node);

	return MR_trace_same_construct(path, node_path);
}

static	MR_bool
MR_trace_matching_disj(const char *path, MR_Trace_Node node)
{
	MR_Trace_Port		port;
	const char		*node_path;

	MR_TRACE_CALL_MERCURY(
		port = (MR_Trace_Port) MR_DD_trace_node_port(node);
	);
	if (port == MR_PORT_DISJ) {
		node_path = MR_trace_node_path(node);
		return MR_trace_same_construct(path, node_path);
	} else {
		return MR_FALSE;
	}
}

static	MR_bool
MR_trace_same_construct(const char *p1, const char *p2)
{
	/*
	** Checks if the two arguments represent goals in the same
	** construct.  If both strings are identical up to the last
	** component, return MR_TRUE, otherwise return MR_FALSE.
	** If the arguments point to identical strings, return MR_TRUE.
	*/
	while (*p1 == *p2) {
		if (*p1 == '\0' && *p2 == '\0') {
			return MR_TRUE;	/* They are identical. */
		}
		if (*p1 == '\0' || *p2 == '\0') {
			return MR_FALSE;  /* Different number of elements. */
		}

		p1++;
		p2++;
	}

	/*
	** If there is exactly one component left in each string, then
	** the goal paths match, otherwise they don't.
	*/
	return MR_trace_single_component(p1) && MR_trace_single_component(p2);
}

static	MR_bool
MR_trace_single_component(const char *path)
{
	while (*path != ';') {
		if (*path == '\0') {
			return MR_FALSE;
		}
		path++;
	}
	path++;
	return (*path == '\0');
}

static	MR_Word
MR_decl_make_atom(const MR_Label_Layout *layout, MR_Word *saved_regs,
		MR_Trace_Port port)
{
	MR_PredFunc			pred_or_func;
	MR_ConstString			name;
	int				arity;
	MR_Word				atom;
	int				hv;   /* any head variable */
	int				num_added_args;
	MR_TypeInfoParams		type_params;
	const MR_Proc_Layout		*entry = layout->MR_sll_entry;

	MR_trace_init_point_vars(layout, saved_regs, port, MR_TRUE);

	name = MR_decl_atom_name(entry);
	MR_proc_id_arity_addedargs_predfunc(entry, &arity, &num_added_args,
		&pred_or_func);

	MR_TRACE_CALL_MERCURY(
		atom = MR_DD_construct_trace_atom(
				(MR_Word) pred_or_func,
				(MR_String) name,
				(MR_Word) entry->MR_sle_num_head_vars);
	);

	for (hv = 0; hv < entry->MR_sle_num_head_vars; hv++) {
		int		hlds_num;
		MR_Word		arg;
		MR_TypeInfo	arg_type;
		MR_Word		arg_value;
		MR_bool		is_prog_visible_headvar;
		const char	*problem;

		hlds_num = entry->MR_sle_head_var_nums[hv];

		is_prog_visible_headvar =
				hv >= num_added_args ? MR_TRUE : MR_FALSE;

		problem = MR_trace_return_hlds_var_info(hlds_num, &arg_type,
				&arg_value);
		if (problem != NULL) {
			/* this head variable is not live at this port */

			MR_TRACE_CALL_MERCURY(
				atom = MR_DD_add_trace_atom_arg_no_value(atom,
					(MR_Word) hv + 1, hlds_num,
					is_prog_visible_headvar);
			);
		} else {
			MR_TRACE_USE_HP(
				MR_new_univ_on_hp(arg, arg_type, arg_value);
			);

			MR_TRACE_CALL_MERCURY(
				atom = MR_DD_add_trace_atom_arg_value(atom,
					(MR_Word) hv + 1, hlds_num,
					is_prog_visible_headvar, arg);
			);
		}
	}

	return atom;
}

static	MR_ConstString
MR_decl_atom_name(const MR_Proc_Layout *entry)
{
	MR_ConstString		name;

	if (MR_PROC_LAYOUT_HAS_PROC_ID(entry)) {
		if (MR_PROC_LAYOUT_COMPILER_GENERATED(entry)) {
			MR_TRACE_USE_HP(
				MR_make_aligned_string(name, "<<internal>>");
			);
		} else {
			name = entry->MR_sle_proc_id.MR_proc_user.MR_user_name;
		}
	} else {
		MR_TRACE_USE_HP(
			MR_make_aligned_string(name, "<<unknown>>");
		);
	}

	return name;
}

static	void
MR_trace_decl_ensure_init(void)
{
	static MR_bool		done = MR_FALSE;
	static MercuryFile	mdb_in;
	static MercuryFile	mdb_out;

	MR_mercuryfile_init(MR_mdb_in, 1, &mdb_in);
	MR_mercuryfile_init(MR_mdb_out, 1, &mdb_out);

	if (! done) {
		MR_TRACE_CALL_MERCURY(
			MR_trace_node_store = 0;
			MR_DD_decl_diagnosis_state_init(
					(MR_Word) &mdb_in,
					(MR_Word) &mdb_out,
					&MR_trace_front_end_state);
		);
		done = MR_TRUE;
	}
}

MR_bool
MR_trace_start_decl_debug(MR_Trace_Mode trace_mode, const char *outfile,
	MR_Trace_Cmd_Info *cmd, MR_Event_Info *event_info,
	MR_Event_Details *event_details, MR_Code **jumpaddr)
{
	MR_Retry_Result		result;
	const MR_Proc_Layout 	*entry;
	FILE			*out;
	MR_Unsigned		depth_limit;
	const char		*message;
	MR_Trace_Level		trace_level;

	if (!MR_port_is_final(event_info->MR_trace_port)) {
		fflush(MR_mdb_out);
		fprintf(MR_mdb_err,
			"mdb: declarative debugging is only available"
			" from EXIT, FAIL or EXCP events.\n");
		return MR_FALSE;
	}

	entry = event_info->MR_event_sll->MR_sll_entry;
	if (!MR_PROC_LAYOUT_HAS_EXEC_TRACE(entry)) {
		fflush(MR_mdb_out);
		fprintf(MR_mdb_err,
			"mdb: cannot start declarative debugging, "
			"because this procedure was not\n"
			"compiled with execution tracing enabled.\n");
		return MR_FALSE;
	}

	if (MR_PROC_LAYOUT_COMPILER_GENERATED(entry)) {
		fflush(MR_mdb_out);
		fprintf(MR_mdb_err,
			"mdb: cannot start declarative debugging "
			"at compiler generated procedures.\n");
		return MR_FALSE;
	}

	trace_level = entry->MR_sle_module_layout->MR_ml_trace_level;
	if (trace_level != MR_TRACE_LEVEL_DEEP
		&& trace_level != MR_TRACE_LEVEL_DECL_REP)
	{
		fflush(MR_mdb_out);
		fprintf(MR_mdb_err,
			"mdb: cannot start declarative debugging, "
			"because this procedure was not\n"
			"compiled with trace level `deep' or `rep'.\n");
		return MR_FALSE;
	}

	if (entry->MR_sle_module_layout->MR_ml_suppressed_events != 0) {
		fflush(MR_mdb_out);
		fprintf(MR_mdb_err,
			"mdb: cannot start declarative debugging, "
			"because some event types were\n"
			"suppressed when this procedure was compiled.\n");
		return MR_FALSE;
	}

	if (trace_mode == MR_TRACE_DECL_DEBUG_DUMP) {
		out = fopen(outfile, "w");
		if (out == NULL) {
			fflush(MR_mdb_out);
			fprintf(MR_mdb_err,
				"mdb: cannot open file `%s' for output: %s.\n",
				outfile, strerror(errno));
			return MR_FALSE;
		} else {
			MR_trace_store_file = out;
		}
	}

	MR_trace_decl_mode = trace_mode;

	MR_trace_decl_ensure_init();
	depth_limit = event_info->MR_call_depth + MR_EDT_DEPTH_STEP_SIZE;
	message = MR_trace_start_collecting(event_info->MR_event_number,
			event_info->MR_call_seqno, depth_limit, cmd, event_info,
			event_details, jumpaddr);

	if (message == NULL) {
		return MR_TRUE;
	} else {
		fflush(MR_mdb_out);
		fprintf(MR_mdb_err,
			"mdb: failed to start collecting events:\n%s\n",
			message);

		return MR_FALSE;
	}
}

static	MR_Code *
MR_trace_restart_decl_debug(MR_Unsigned event, MR_Unsigned seqno,
	MR_Trace_Cmd_Info *cmd, MR_Event_Info *event_info,
	MR_Event_Details *event_details)
{
	MR_Unsigned		depth_limit;
	const char		*message;
	MR_Code			*jumpaddr;

	depth_limit = MR_edt_max_depth + MR_EDT_DEPTH_STEP_SIZE;
	message = MR_trace_start_collecting(event, seqno, depth_limit,
			cmd, event_info, event_details, &jumpaddr);

	if (message != NULL) {
		fflush(MR_mdb_out);
		fprintf(MR_mdb_err, "mdb: diagnosis aborted:\n%s\n", message);
		MR_trace_decl_mode = MR_TRACE_INTERACTIVE;
		MR_trace_enabled = MR_TRUE;
		return MR_trace_event_internal(cmd, MR_TRUE, event_info);
	}

	return jumpaddr;
}

static	const char *
MR_trace_start_collecting(MR_Unsigned event, MR_Unsigned seqno,
	MR_Unsigned maxdepth, MR_Trace_Cmd_Info *cmd, MR_Event_Info *event_info,
	MR_Event_Details *event_details, MR_Code **jumpaddr)
{
	const char		*problem;
	MR_Retry_Result		retry_result;

	/*
	** Go back to an event before the topmost call.
	*/
	retry_result = MR_trace_retry(event_info, event_details, 0,
		MR_RETRY_IO_ONLY_IF_SAFE,
		MR_trace_decl_assume_all_io_is_tabled, &problem, NULL, NULL,
		jumpaddr);
	if (retry_result != MR_RETRY_OK_DIRECT) {
		if (retry_result == MR_RETRY_ERROR) {
			return problem;
		} else {
			return "internal error: direct retry impossible";
		}
	}

	/*
	** Clear any warnings.
	*/
	MR_edt_compiler_flag_warning = MR_FALSE;

	/*
	** Start collecting the trace from the desired call, with the
	** desired depth bound.
	*/
	MR_edt_last_event = event;
	MR_edt_inside = MR_FALSE;
	MR_edt_start_seqno = seqno;
	MR_edt_start_io_counter = MR_io_tabling_counter;
	MR_edt_max_depth = maxdepth;
	MR_trace_current_node = (MR_Trace_Node) NULL;

	/*
	** Restore globals from the saved copies.
	*/
        MR_trace_call_seqno = event_details->MR_call_seqno;
	MR_trace_call_depth = event_details->MR_call_depth;
	MR_trace_event_number = event_details->MR_event_number;

	/*
	** Single step through every event.
	*/
	cmd->MR_trace_cmd = MR_CMD_GOTO;
	cmd->MR_trace_stop_event = 0;
	cmd->MR_trace_strict = MR_TRUE;
	cmd->MR_trace_print_level = MR_PRINT_LEVEL_NONE;
	cmd->MR_trace_must_check = MR_FALSE;

	MR_trace_enabled = MR_TRUE;
	return NULL;
}

static MR_bool		MR_io_action_map_cache_is_valid = MR_FALSE;
static MR_Unsigned	MR_io_action_map_cache_start;
static MR_Unsigned	MR_io_action_map_cache_end;

static	MR_Code *
MR_decl_diagnosis(MR_Trace_Node root, MR_Trace_Cmd_Info *cmd,
	MR_Event_Info *event_info, MR_Event_Details *event_details)
{
	MR_Word			response;
	MR_bool			bug_found;
	MR_bool			symptom_found;
	MR_bool			no_bug_found;
	MR_bool			require_subtree;
	MR_Unsigned		bug_event;
	MR_Unsigned		symptom_event;
	MR_Unsigned		final_event;
	MR_Unsigned		topmost_seqno;
	MercuryFile		stream;
	MR_Integer		use_old_io_map;
	MR_Unsigned		io_start;
	MR_Unsigned		io_end;

	event_details->MR_call_seqno = MR_trace_call_seqno;
	event_details->MR_call_depth = MR_trace_call_depth;
	event_details->MR_event_number = MR_trace_event_number;

	if (MR_edt_compiler_flag_warning) {
		fflush(MR_mdb_out);
		fprintf(MR_mdb_err, "Warning: some modules were compiled with"
				" a trace level lower than `decl'.\n"
				"This may result in calls being omitted from"
				" the debugging tree.\n");
	}

	if (MR_trace_decl_mode == MR_TRACE_DECL_DEBUG_DUMP) {
		MR_mercuryfile_init(MR_trace_store_file, 1, &stream);

		MR_TRACE_CALL_MERCURY(
			MR_DD_save_trace((MR_Word) &stream,
						MR_trace_node_store, root);
		);

		fclose(MR_trace_store_file);
		MR_trace_decl_mode = MR_TRACE_INTERACTIVE;
		MR_trace_enabled = MR_TRUE;
		MR_trace_call_seqno = event_details->MR_call_seqno;
		MR_trace_call_depth = event_details->MR_call_depth;
		MR_trace_event_number = event_details->MR_event_number;

		return MR_trace_event_internal(cmd, MR_TRUE, event_info);
	}

	if (MR_trace_decl_mode == MR_TRACE_DECL_DEBUG_DEBUG) {
		/*
		** This is a quick and dirty way to debug the front end.
		*/
		MR_trace_enabled = MR_TRUE;
		MR_trace_decl_mode = MR_TRACE_INTERACTIVE;
	}

	io_start = MR_edt_start_io_counter;
	io_end = MR_io_tabling_counter;

	if (MR_io_action_map_cache_is_valid
		&& MR_io_action_map_cache_start <= io_start
		&& io_end <= MR_io_action_map_cache_end)
	{
		use_old_io_map = MR_TRUE;
	} else {
		use_old_io_map = MR_FALSE;

		MR_io_action_map_cache_is_valid = MR_TRUE;
		MR_io_action_map_cache_start = io_start;
		MR_io_action_map_cache_end = io_end;
	}

	MR_TRACE_CALL_MERCURY(
		MR_DD_decl_diagnosis(MR_trace_node_store, root, use_old_io_map,
				MR_io_action_map_cache_start,
				MR_io_action_map_cache_end,
				&response, MR_trace_front_end_state,
				&MR_trace_front_end_state
			);
		bug_found = MR_DD_diagnoser_bug_found(response,
				(MR_Integer *) &bug_event);
		symptom_found = MR_DD_diagnoser_symptom_found(response,
				(MR_Integer *) &symptom_event);
		no_bug_found = MR_DD_diagnoser_no_bug_found(response);
		require_subtree = MR_DD_diagnoser_require_subtree(response,
				(MR_Integer *) &final_event,
				(MR_Integer *) &topmost_seqno);
	);

	MR_trace_call_seqno = event_details->MR_call_seqno;
	MR_trace_call_depth = event_details->MR_call_depth;
	MR_trace_event_number = event_details->MR_event_number;

	if (bug_found) {
		return MR_decl_go_to_selected_event(bug_event, cmd,
				event_info, event_details);
	}

	if (symptom_found) {
		return MR_decl_go_to_selected_event(symptom_event, cmd,
				event_info, event_details);
	}

	if (no_bug_found) {
		/*
		** No bug found.  Return to the procedural debugger at the
		** current event, which was the event it was left from.
		*/
		MR_trace_decl_mode = MR_TRACE_INTERACTIVE;
		MR_trace_enabled = MR_TRUE;
		return MR_trace_event_internal(cmd, MR_TRUE, event_info);
	}

	if (require_subtree) {
		/*
		** Front end requires a subtree to be made explicit.
		** Restart the declarative debugger with deeper
		** depth limit.
		*/
		return MR_trace_restart_decl_debug(final_event, topmost_seqno,
				cmd, event_info, event_details);
	}

	/* We shouldn't ever get here. */
	MR_fatal_error("unknown diagnoser response");
}

static	MR_Code *
MR_decl_go_to_selected_event(MR_Unsigned event, MR_Trace_Cmd_Info *cmd,
		MR_Event_Info *event_info, MR_Event_Details *event_details)
{
	const char		*problem;
	MR_Retry_Result		retry_result;
	MR_Code			*jumpaddr;

	/*
	** Perform a retry to get to somewhere before the
	** bug event.  Then set the command to go to the bug
	** event and return to interactive mode.
	*/
#ifdef	MR_DEBUG_RETRY
	MR_print_stack_regs(stdout, event_info->MR_saved_regs);
	MR_print_succip_reg(stdout, event_info->MR_saved_regs);
#endif
	retry_result = MR_trace_retry(event_info, event_details, 0,
		MR_RETRY_IO_ONLY_IF_SAFE,
		MR_trace_decl_assume_all_io_is_tabled,
		&problem, NULL, NULL, &jumpaddr);
#ifdef	MR_DEBUG_RETRY
	MR_print_stack_regs(stdout, event_info->MR_saved_regs);
	MR_print_succip_reg(stdout, event_info->MR_saved_regs);
	MR_print_r_regs(stdout, event_info->MR_saved_regs);
#endif
	if (retry_result != MR_RETRY_OK_DIRECT) {
		fflush(MR_mdb_out);
		fprintf(MR_mdb_err, "mdb: diagnosis aborted:\n");
		if (retry_result == MR_RETRY_ERROR) {
			fprintf(MR_mdb_err, "%s\n", problem);
		} else {
			fprintf(MR_mdb_err, "direct retry impossible\n");
		}
		MR_trace_decl_mode = MR_TRACE_INTERACTIVE;
		MR_trace_enabled = MR_TRUE;
		return MR_trace_event_internal(cmd, MR_TRUE, event_info);
	}

	cmd->MR_trace_cmd = MR_CMD_GOTO;
	cmd->MR_trace_stop_event = event;
	cmd->MR_trace_print_level = MR_PRINT_LEVEL_NONE;
	cmd->MR_trace_strict = MR_TRUE;
	cmd->MR_trace_must_check = MR_FALSE;
	MR_trace_decl_mode = MR_TRACE_INTERACTIVE;
	MR_trace_enabled = MR_TRUE;
	return jumpaddr;
}

static	MR_String
MR_trace_node_path(MR_Trace_Node node)
{
	MR_String			path;

	MR_trace_node_store++;
	MR_TRACE_CALL_MERCURY(
		path = MR_DD_trace_node_path(MR_trace_node_store,
				(MR_Word) node);
	);
	return path;
}

static	MR_Trace_Port
MR_trace_node_port(MR_Trace_Node node)
{
	MR_Trace_Port		port;

	MR_TRACE_CALL_MERCURY(
		port = (MR_Trace_Port) MR_DD_trace_node_port((MR_Word) node);
	);
	return port;
}

static	MR_Unsigned
MR_trace_node_seqno(MR_Trace_Node node)
{
	MR_Unsigned		seqno;

	MR_trace_node_store++;
	MR_TRACE_CALL_MERCURY(
		if (!MR_DD_trace_node_seqno(MR_trace_node_store,
					(MR_Word) node,
					(MR_Integer *) &seqno))
		{
			MR_fatal_error("MR_trace_node_seqno: "
				"not an interface event");
		}
	);
	return seqno;
}

static	MR_Trace_Node
MR_trace_node_first_disj(MR_Trace_Node node)
{
	MR_Trace_Node		first;

	MR_TRACE_CALL_MERCURY(
		if (!MR_DD_trace_node_first_disj((MR_Word) node,
				(MR_Word *) &first))
		{
			MR_fatal_error("MR_trace_node_first_disj: "
				"not a DISJ event");
		}
	);
	return first;
}

static	MR_Trace_Node
MR_trace_step_left_in_contour(MR_Trace_Node node)
{
	MR_Trace_Node		next;

	MR_decl_checkpoint_step(node);

	MR_trace_node_store++;
	MR_TRACE_CALL_MERCURY(
		next = (MR_Trace_Node) MR_DD_step_left_in_contour(
						MR_trace_node_store, node);
	);
	return next;
}

static	MR_Trace_Node
MR_trace_find_prev_contour(MR_Trace_Node node)
{
	MR_Trace_Node		next;

	MR_decl_checkpoint_find(node);

	MR_trace_node_store++;
	MR_TRACE_CALL_MERCURY(
		next = (MR_Trace_Node) MR_DD_find_prev_contour(
						MR_trace_node_store, node);
	);
	return next;
}

#ifdef MR_DEBUG_DD_BACK_END

static	void
MR_decl_checkpoint_event_imp(const char *str, MR_Event_Info *event_info)
{
	fprintf(MR_mdb_out, "DD %s %ld: #%ld %ld %s ",
			str,
			(long) event_info->MR_event_number,
			(long) event_info->MR_call_seqno,
			(long) event_info->MR_call_depth,
			MR_port_names[event_info->MR_trace_port]);
	MR_print_proc_id(MR_mdb_out, event_info->MR_event_sll->MR_sll_entry);
	fprintf(MR_mdb_out, "\n");
}

static	void
MR_decl_checkpoint_loc(const char *str, MR_Trace_Node node)
{
	MercuryFile mdb_out;

	MR_mercuryfile_init(MR_mdb_out, 1, &mdb_out);

	fprintf(MR_mdb_out, "DD %s: %ld ", str, (long) node);
	MR_TRACE_CALL_MERCURY(
		MR_DD_print_trace_node((MR_Word) &mdb_out, (MR_Word) node);
	);
	fprintf(MR_mdb_out, "\n");
}

#endif /* MR_DEBUG_DD_BACK_END */