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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.

*/

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

$Author: release $

$Date: 1998/01/17 15:55:47 $

$Revision: 1.1.1.1 $

$Log: label_ops.c,v $

 * Revision 1.1.1.1  1998/01/17  15:55:47  release

 * First version to be checked into rolling release.

 *

 * Revision 1.5  1997/08/06  10:58:32  currie

 * Catch overflowed constants, PlumHall requirement

 *

 * Revision 1.4  1997/04/18  10:58:47  currie

 * another pathelogical case

 *

 * Revision 1.3  1996/05/21  12:53:54  currie

 * Pathological gotos

 *

 * Revision 1.2  1995/10/11  17:10:07  currie

 * avs errors

 *

 * Revision 1.1  1995/04/06  10:44:05  currie

 * Initial revision

 *

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

#include "config.h"

#include "common_types.h"

#include "expmacs.h"

#include "tags.h"

#include "label_ops.h"

#include "check.h"

#include "externs.h"

#include "exp.h"

#include "installglob.h"

#include "shapemacs.h"

/* label_is_next returns 1 if lab is a labst which immediately

   follows e, otherwise 0. e will not be nilexp

*/

int label_is_next

    PROTO_N ( (lab, e) )

    PROTO_T ( exp lab X exp e )

{

  if (!indirect_jumps)

    return 0;

  while (last(e)) {

    e = bro(e);

    if (e == nilexp || name(e) >= ass_tag || name(sh(e)) != bothd)

      return 0;

  };

  if (name(bro(e)) == labst_tag)

    return bro(e) == lab;

  return 0;

}

static exp is_jumper

    PROTO_N ( (e) )

    PROTO_T ( exp e )

{

  if (name(e) == test_tag || name(e) == goto_tag ||

	name(e) == testbit_tag || name(e) == res_tag)

    return e;

  return nilexp;

}

static exp down

    PROTO_N ( (e) )

    PROTO_T ( exp e )

{

  if (name(e) == seq_tag)

    return down(son(son(e)));

  if (name(e) == cond_tag)

    return down(son(e));

  return e;

}

/* next_jump delivers a goto, res, test or testbit exp if this

   is certain to be the next thing obeyed after e. nilexp

   otherwise.

*/

static exp next_jump

    PROTO_N ( (e) )

    PROTO_T ( exp e )

{

  if (!indirect_jumps)

    return nilexp;

  do {

    while (last(e)) {

      e = bro(e);

      if (e == nilexp || name(e) >= goto_tag)

        return nilexp;

    };

    e = bro(e);

  } while (name(e) == labst_tag && (e = father(e), name(e)!=rep_tag));

  if (is_jumper(e))

    return e;

  if (name(e) == seq_tag || name(e) == cond_tag)

    return is_jumper(down(e));

  if (name(e) == top_tag)

    return next_jump(e);

  return nilexp;

}

/* next_jump delivers a goto, res, test or testbit exp if this

   is certain to be the next thing obeyed after e and there is no

   other route to the goto (etc.). nilexp otherwise.

*/

exp short_next_jump

    PROTO_N ( (e) )

    PROTO_T ( exp e )

{

  if (!indirect_jumps)

    return nilexp;

    while (last(e)) {

      e = bro(e);

      if (e == nilexp || name(e) >= cond_tag)

        return nilexp;

    };

    e = bro(e);

  if (is_jumper(e))

    return e;

  if (name(e) == seq_tag || name(e) == cond_tag)

    return is_jumper(down(e));

  if (name(e) == top_tag)

    return short_next_jump(e);

  return nilexp;

}

exp jump_dest

    PROTO_N ( (lab) )

    PROTO_T ( exp lab )

{

  return next_jump(son(lab));

}

exp final_dest

    PROTO_N ( (lab) )

    PROTO_T ( exp lab )

{

  exp final = lab;

  exp temp, ll;

  while (name(final) == labst_tag) {

    temp = jump_dest(final);

    if (temp != nilexp && name(temp) == goto_tag && pt(temp) != final) {

      ll = lab;

      while (ll != final) {

	if (pt(temp) == ll)

	  return final;		/* pathological loop */

	ll = pt(jump_dest(ll));

      }

      final = pt(temp);

    }

    else

      break;

  };

  return final;

}

/* delivers 1 iff when a jumps, b also jumps

   a and b will be test or testbit

*/

static int subsumes

    PROTO_N ( (a, b) )

    PROTO_T ( exp a X exp b )

{

  if (name(a) == name(b) &&

	test_number(a) == test_number(b) &&

	eq_exp(son(a), son(b)) &&

	eq_exp(bro(son(a)), bro(son(b))))

    return 1;

  return 0;

}

exp final_dest_test

    PROTO_N ( (lab, e) )

    PROTO_T ( exp lab X exp e )

{

  exp final = lab;

  exp temp, ll;

  while (name(final) == labst_tag) {

    temp = jump_dest(final);

    if (temp == nilexp || final == pt(temp))

      return final;

    if (name(temp) == goto_tag || (name(temp) == name(e) && subsumes(e, temp))) {

      ll = lab;

      while (ll != final) {

	if (pt(temp) == ll)

	  return final;		/* pathological loop */

	ll = pt(jump_dest(ll));

      }

      final = pt(temp);

    }

    else

      break;

  };

  return final;

}