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/*

    		 Crown Copyright (c) 1997

    This TenDRA(r) Computer Program is subject to Copyright

    owned by the United Kingdom Secretary of State for Defence

    acting through the Defence Evaluation and Research Agency

    (DERA).  It is made available to Recipients with a

    royalty-free licence for its use, reproduction, transfer

    to other parties and amendment for any purpose not excluding

    product development provided that any such use et cetera

    shall be deemed to be acceptance of the following conditions:-

        (1) Its Recipients shall ensure that this Notice is

        reproduced upon any copies or amended versions of it;

        (2) Any amended version of it shall be clearly marked to

        show both the nature of and the organisation responsible

        for the relevant amendment or amendments;

        (3) Its onward transfer from a recipient to another

        party shall be deemed to be that party's acceptance of

        these conditions;

        (4) DERA gives no warranty or assurance as to its

        quality or suitability for any purpose and DERA accepts

        no liability whatsoever in relation to any use to which

        it may be put.

*/

/*** rule-tail.c --- Tail recursion elimination routines.

 *

 ** Author: Steve Folkes <smf@hermes.mod.uk>

 *

 *** Commentary:

 *

 * This file implements the SID inlining routines.

 *

 * There are five separate phases implemented in this file.

 *

 * The first phase is to find and eliminate all tail recursive cycles that

 * each rule is involved in.  The cycles are detected by the

 * ``grammar_compute_inlining'' function in the file "grammar.c".  For each

 * cyclic group that is found, the ``rule_handle_tails'' function is called to

 * remove the cycle.  All rules in the cycle are marked as being cyclic, and

 * are given a unique identification that is the same for all members of the

 * cycle (but different for members of different cycles).  The tail recursive

 * calls are marked as inlinable and tail recursive, and the rules' call

 * graphs are computed (this is the set of rules that will make tail calls).

 * This phase is only performed if tail recursion inlining is enabled.

 *

 * The second phase is implemented by the ``rule_compute_all_basics''

 * function.  This marks a rule that only contains basics as such.  This phase

 * is only performed if all basic inlining is enabled.

 *

 * The third phase is implemented by the ``rule_compute_inlining'' function.

 * This marks all calls to all basic rules as inlinable.  If single

 * alternative rule inlining is enabled, then all calls to single alternative

 * rules are marked as inlinable.  If non tail recursion inlining is enabled,

 * it also marks all other calls as inlinable, and computes their call count

 * if functions that are called more than once are not to be inlined (the

 * output routines won't inline rules with a call count greater than one).

 *

 * The fourth phase is implemented by the ``rule_compute_needed_functions''

 * function.  It marks all required functions, and functions that are called

 * from a non-inlinable position as requiring function implementations.

 *

 * The final phase is implemented by the ``rule_handle_need_functions''

 * function.  The cycle detection routines are used in the

 * ``grammar_compute_inlining'' function to find cycles in the function call

 * graph.  If any such cycles are found, then all of the rules in the cycle

 * are marked as needing a function implementation.

 *

 *** Change Log:

 * $Log: rule-tail.c,v $

 * Revision 1.1.1.1  1998/01/17  15:57:47  release

 * First version to be checked into rolling release.

 *

 * Revision 1.3  1994/12/15  09:58:53  smf

 * Brought into line with OSSG C Coding Standards Document, as per

 * "CR94_178.sid+tld-update".

 *

 * Revision 1.2  1994/11/11  11:47:09  smf

 * Fixed a bug in the tail recursion elimination, for bug fix

 * CR94_127.sid-tail-rec.

 * There was a problem with tail calls that had reference parameters in an

 * earlier version of SID, and they had been disabled.  This should have been

 * fixed when the output routines were fixed to do references properly, but the

 * check wasn't removed.  It has been now.

 *

 * Revision 1.1.1.1  1994/07/25  16:04:41  smf

 * Initial import of SID 1.8 non shared files.

 *

**/

/****************************************************************************/

#include "rule.h"

#include "action.h"

#include "basic.h"

#include "entry-list.h"

#include "name.h"

#include "type.h"

/*--------------------------------------------------------------------------*/

typedef struct CycleHeadT {

    RuleP			head;

    RuleP		       *tail;

} CycleHeadT, *CycleHeadP;

typedef struct RuleStackT {

    struct RuleStackT	       *next;

    RuleP			rule;

} RuleStackT, *RuleStackP;

/*--------------------------------------------------------------------------*/

static BoolT			rule_do_inline_tail_calls     = TRUE;

static BoolT			rule_do_inline_all_basics     = TRUE;

static BoolT			rule_do_inline_singles        = FALSE;

static BoolT			rule_do_inline_non_tail_calls = FALSE;

static BoolT			rule_do_multiple_inlining     = FALSE;

/*--------------------------------------------------------------------------*/

static void

rule_inline_tail_calls_1 PROTO_N ((rule, alt, tail_group))

			 PROTO_T (RuleP rule X

				  AltP  alt X

				  RuleP tail_group)

{

    ItemP item = alt_item_head (alt);

    ItemP next;

    while ((next = item_next (item)) != NIL (ItemP)) {

	item = next;

    }

    if (item_is_rule (item)) {

	RuleP item_rule = entry_get_rule (item_entry (item));

	if ((rule_get_tail_group (item_rule) == tail_group) &&

	    (types_equal_names (rule_result (rule), item_result (item)))) {

	    item_inlinable (item);

	    item_tail_call (item);

	}

    }

}

static void

rule_inline_tail_calls PROTO_N ((rule))

		       PROTO_T (RuleP rule)

{

    RuleP tail_group = rule_get_tail_group (rule);

    AltP  alt;

    if ((alt = rule_get_handler (rule)) != NIL (AltP)) {

	rule_inline_tail_calls_1 (rule, alt, tail_group);

    }

    for (alt = rule_alt_head (rule); alt; alt = alt_next (alt)) {

	rule_inline_tail_calls_1 (rule, alt, tail_group);

    }

}

static void			rule_compute_call_graph

	PROTO_S ((RuleP, EntryListP, RuleStackP));

static void

rule_compute_call_graph_1 PROTO_N ((alt, call_list, next))

			  PROTO_T (AltP       alt X

				   EntryListP call_list X

				   RuleStackP next)

{

    ItemP item = alt_item_head (alt);

    ItemP next_item;

    while ((next_item = item_next (item)) != NIL (ItemP)) {

	item = next_item;

    }

    if (item_is_tail_call (item)) {

	EntryP entry     = item_entry (item);

	RuleP  item_rule = entry_get_rule (entry);

	rule_compute_call_graph (item_rule, call_list, next);

    }

}

static void

rule_compute_call_graph PROTO_N ((rule, call_list, next))

			PROTO_T (RuleP      rule X

				 EntryListP call_list X

				 RuleStackP next)

{

    RuleStackT stack;

    AltP       alt;

    stack.rule = rule;

    stack.next = next;

    while (next) {

	if (next->rule == rule) {

	    entry_list_add_if_missing (call_list, rule_entry (rule));

	    return;

	}

	next = next->next;

    }

    if ((alt = rule_get_handler (rule)) != NIL (AltP)) {

	rule_compute_call_graph_1 (alt, call_list, &stack);

    }

    for (alt = rule_alt_head (rule); alt; alt = alt_next (alt)) {

	rule_compute_call_graph_1 (alt, call_list, &stack);

    }

}

static void

rule_compute_all_basics_1 PROTO_N ((rule))

			  PROTO_T (RuleP rule)

{

    if ((!rule_has_empty_alt (rule)) &&

	(rule_get_handler (rule) == NIL (AltP))) {

	AltP alt;

	for (alt = rule_alt_head (rule); alt; alt = alt_next (alt)) {

	    ItemP item;

	    for (item = alt_item_head (alt); item; item = item_next (item)) {

		if (!item_is_basic (item)) {

		    return;

		}

	    }

	}

	rule_all_basics (rule);

    }

}

static void			rule_compute_inlining_1

	PROTO_S ((RuleP));

static void

rule_compute_inlining_2 PROTO_N ((alt))

			PROTO_T (AltP alt)

{

    ItemP item;

    for (item = alt_item_head (alt); item; item = item_next (item)) {

	if ((item_is_rule (item)) && (!item_is_tail_call (item))) {

	    EntryP entry     = item_entry (item);

	    RuleP  item_rule = entry_get_rule (entry);

	    if (rule_is_all_basics (item_rule)) {

		item_inlinable (item);

	    } else if (rule_do_inline_singles &&

		       rule_has_one_alt (item_rule)) {

		item_inlinable (item);

	    } else if (!rule_do_multiple_inlining) {

		rule_inc_call_count (item_rule);

	    }

	    if (rule_do_inline_non_tail_calls) {

		item_inlinable (item);

	    }

	    rule_compute_inlining_1 (item_rule);

	}

    }

}

static void

rule_compute_inlining_1 PROTO_N ((rule))

			PROTO_T (RuleP rule)

{

    if (!rule_is_checked_for_inlining (rule)) {

	if (!rule_is_being_inlined (rule)) {

	    AltP alt;

	    rule_being_inlined (rule);

	    if ((alt = rule_get_handler (rule)) != NIL (AltP)) {

		rule_compute_inlining_2 (alt);

	    }

	    for (alt = rule_alt_head (rule); alt; alt = alt_next (alt)) {

		rule_compute_inlining_2 (alt);

	    }

	    rule_checked_for_inlining (rule);

	}

    }

}

static void

rule_compute_needed_functions_2 PROTO_N ((alt))

				PROTO_T (AltP alt)

{

    ItemP item;

    for (item = alt_item_head (alt); item; item = item_next (item)) {

	if (item_is_rule (item)) {

	    RuleP item_rule = entry_get_rule (item_entry (item));

	    if ((!item_is_inlinable (item)) ||

		(rule_get_call_count (item_rule) > 1)) {

		rule_will_need_function (item_rule);

	    }

	}

    }

}

static void

rule_compute_needed_functions_1 PROTO_N ((rule))

				PROTO_T (RuleP rule)

{

    AltP     alt;

    if ((alt = rule_get_handler (rule)) != NIL (AltP)) {

	rule_compute_needed_functions_2 (alt);

    }

    for (alt = rule_alt_head (rule); alt; alt = alt_next (alt)) {

	rule_compute_needed_functions_2 (alt);

    }

}

/*--------------------------------------------------------------------------*/

void

rule_handle_tails PROTO_N ((rule_list))

		  PROTO_T (RuleP rule_list)

{

    RuleP rule;

    for (rule = rule_list; rule; rule = rule_get_next_in_reverse_dfs (rule)) {

	rule_set_tail_group (rule, rule_list);

	rule_no_cycles (rule);

    }

    for (rule = rule_list; rule; rule = rule_get_next_in_reverse_dfs (rule)) {

	rule_inline_tail_calls (rule);

    }

    for (rule = rule_list; rule; rule = rule_get_next_in_reverse_dfs (rule)) {

	rule_compute_call_graph (rule, rule_call_list (rule),

				 NIL (RuleStackP));

    }

}

void

rule_compute_all_basics PROTO_N ((entry, gclosure))

			PROTO_T (EntryP   entry X

				 GenericP gclosure)

{

    UNUSED (gclosure);

    if (rule_do_inline_all_basics && entry_is_rule (entry)) {

	RuleP rule = entry_get_rule (entry);

	rule_compute_all_basics_1 (rule);

    }

}

void

rule_compute_inlining PROTO_N ((entry, gclosure))

		      PROTO_T (EntryP   entry X

			       GenericP gclosure)

{

    UNUSED (gclosure);

    if (entry_is_rule (entry)) {

	RuleP rule = entry_get_rule (entry);

	rule_compute_inlining_1 (rule);

    }

}

void

rule_compute_needed_functions PROTO_N ((entry, gclosure))

			      PROTO_T (EntryP   entry X

				       GenericP gclosure)

{

    UNUSED (gclosure);

    if (entry_is_rule (entry)) {

	RuleP rule = entry_get_rule (entry);

	rule_compute_needed_functions_1 (rule);

    }

}

void

rule_handle_need_functions PROTO_N ((rule_list))

			   PROTO_T (RuleP rule_list)

{

    RuleP rule;

    for (rule = rule_list; rule; rule = rule_get_next_in_reverse_dfs (rule)) {

	rule_will_need_function (rule);

    }

}

BoolT

rule_get_inline_tail_calls PROTO_Z ()

{

    return (rule_do_inline_tail_calls);

}

void

rule_set_inline_tail_calls PROTO_N ((enable))

			   PROTO_T (BoolT enable)

{

    rule_do_inline_tail_calls = enable;

}

void

rule_set_inline_all_basics PROTO_N ((enable))

			   PROTO_T (BoolT enable)

{

    rule_do_inline_all_basics = enable;

}

void

rule_set_inline_singles PROTO_N ((enable))

			PROTO_T (BoolT enable)

{

    rule_do_inline_singles = enable;

}

void

rule_set_inline_non_tail_calls PROTO_N ((enable))

			       PROTO_T (BoolT enable)

{

    if (enable) {

	rule_do_inline_non_tail_calls = TRUE;

    } else {

	rule_do_inline_non_tail_calls = FALSE;

	rule_do_multiple_inlining     = FALSE;

    }

}

void

rule_set_multiple_inlining PROTO_N ((enable))

			   PROTO_T (BoolT enable)

{

    if (enable) {

	rule_do_inline_non_tail_calls = TRUE;

	rule_do_multiple_inlining     = TRUE;

    } else {

	rule_do_multiple_inlining     = FALSE;

    }

}

/*

 * Local variables(smf):

 * eval: (include::add-path-entry "../os-interface" "../library")

 * eval: (include::add-path-entry "../generated")

 * end:

**/