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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;
}