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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.

*/

/* 	$Id: tempdecs.c,v 1.1.1.1 1998/01/17 15:56:01 release Exp $	 */

#ifndef lint

static char vcid[] = "$Id: tempdecs.c,v 1.1.1.1 1998/01/17 15:56:01 release Exp $";

#endif /* lint */

/*  

  tempdec.c - is the value in the declaration required over  

  proc calls ?  If it isn't, declaration can be allocated 

  in t-reg, rather than s-reg.

*/

#include "config.h"

#include "tags.h"

#include "common_types.h"

#include "exp.h"

#include "const.h"

#include "expmacs.h"

#include "bitsmacs.h"

#include "tempdecs.h"

static int nouses;

static bool useinpar;

/* 

   reduces nouses for each non-assignment use of id encountered 

   in e; sets useinpar if use in actual parameter posn 

   terminates with 0 on applications or jumps terminates with 2 

   on assignment to id otherwise delivers 1

*/

int trace_uses

    PROTO_N ( ( e, id ) )

    PROTO_T ( exp e X exp id )

{

  Assert(e!=(exp)0);

  Assert(id!=(exp)0);

  switch(name(e)) {

    case name_tag: {

      nouses -=(son(e)==id);

      return (1);

    }	

    case apply_general_tag :

    case apply_tag :{

    int u = nouses;

    int p = 1;

    exp l = son(e);

    while( p==1 ) {

      p = trace_uses(l, id);	    	

      if (u!=nouses || p==2) { useinpar=1; }

      if (p==0) nouses = u;

      if (last(l)) break;

      l = bro(l);

    }

    return 0;

    }	

  case ident_tag: {

    exp f = son(e);

    exp s = bro(f);

    int a;

    if ( ( props(e) & defer_bit) != 0 ) {

      exp t = f;

      f = s;

      s = t;

    }

    a = trace_uses(f, id);

    if (a !=1) return a;

    return trace_uses(s, id);

  }	

  case case_tag:  {

    trace_uses(son(e), id);

    return 0;

  }

  case labst_tag: return 0;

  case seq_tag: {

     exp s = son(son(e));

     for(;;) {

       int el = trace_uses(s, id);

       if (el!=1 ) return el;

       if (last(s)) return trace_uses(bro(son(e)),id);

       s = bro(s);		

     }

   }

  case ass_tag: {

    if (isvar(id) && name(son(e))==name_tag && son(son(e))==id) {

      trace_uses(bro(son(e)),id);

      return 2;

    }

    else{

      int nu = nouses;

      if (trace_uses(son(e),id) != 1 ||

	  trace_uses(bro(son(e)), id) !=1 ){

	nouses = nu;

	return 0;

      }

      return 1;

    }

  }

  case goto_lv_tag:

  {

    int nu = nouses;

    if(trace_uses(son(e),id) != 1){

      nouses = nu;

    }

    return 0;

  }

  case test_tag:{

    int nu = nouses;

    if((trace_uses(son(e),id) != 1) || (trace_uses(bro(son(e)),id)!= 1)){

      nouses = nu;

    }	

    return 0;

   }

   case solve_tag:case cond_tag: {

     return trace_uses(son(e),id);

   }

   case goto_tag:case rep_tag:

     return 0;

   case current_env_tag:

     return 0;

   default: {

     exp s = son(e);

     int nu = nouses; /* s list can be done in any order ...*/

     if (s == nilexp) return 1;

     for(;;) {

       int el = trace_uses(s, id);

       if (el!=1 ) { /* ... so reset nouses if any terminate */

	 nouses = nu; 

	 return el; 

       }

       if (last(s)) return 1;

       s = bro(s);

     }

   }

  }

}

void after_a

    PROTO_N ( ( a, id ) )

    PROTO_T ( exp a X exp id )

{

  /* apply trace_uses to dynamic successors of a */

  exp dad ;

  exp l;

 tailrec: dad = father(a);

  if (nouses == 0) return;

  if (name(dad)==cond_tag || name(dad)==rep_tag || name(dad) == res_tag

      || name(dad) == solve_tag || name(dad) == labst_tag

      || name(dad) == case_tag || name(dad)== goto_lv_tag

      || name(dad) == test_tag ||  name(dad) == apply_tag) {

    /* dont try too hard ! */

    while (name(dad) != apply_tag && dad !=id) dad = father(dad);

    if (name(dad) == apply_tag) { useinpar =1;}

    return;

  }

  for (l=a; !last(l); l=bro(l)) {

    int u = trace_uses(bro(l), id);

    if (u!=1|| nouses==0) return;

  }

  a = dad;

  if (dad!=id) goto tailrec;	     

}

bool simple_seq

    PROTO_N ( ( e, id ) )

    PROTO_T ( exp e X exp id )

{

  exp dad = father(e);

  for(;;) {

    if (dad == id) return 1;

    if (name(dad)==seq_tag || name(dad)==0

	|| name(dad) == ident_tag) { dad = father(dad);}

    else return 0;

  }

}

bool tempdecopt = 0;		/* flag to allow this optimisation; -Tt

				   sets to 0 */

bool tempdec

    PROTO_N ( ( e, enoughs ) )

    PROTO_T ( exp e X bool enoughs )

{

  /* e is a local declaration; 'enoughs'

     is a misnomer to say whether there are

     t-regs available delivers 1 if e can be

     allocated into t-reg or par reg */

  exp p;

  if (!tempdecopt ) return 0;

  nouses = 0;

  useinpar = 0;

  if (isvar(e) ) {

    for (p=pt(e); p!=nilexp; p =pt(p)) {

      /* find no of uses which are not assignments to id ... */

      if (!last(p) && last(bro(p)) 

	  && name(bro(bro(p))) == ass_tag ) {

/*	if (!simple_seq(bro(bro(p)), e) ) return 0;*/

	/* ... in simple sequence */		 

	continue;

      }

      nouses++;

    }

  }

  else nouses = no(e);

  /* trace simple successors to assignmnts or init to id to find 

     if all uses occur before unpredictable change of control 

     (or another assignment to id) */

  if (name(son(e)) != clear_tag || isparam(e)) { after_a(son(e), e); }

  if (isvar(e)) {

    for (p=pt(e); p!=nilexp; p =pt(p)) {

      if (!last(p) && last(bro(p)) 

	  && name(bro(bro(p))) == ass_tag ) {	

	after_a(bro(bro(p)), e);

      }

    }

  }

  if (nouses ==0 &&(enoughs || !useinpar) ) {

    if (useinpar) props(e) |= notparreg; 

    /* don't allocate this into par reg */

    return 1;

  }

  return 0;

}