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/* Common block and equivalence list handling

   Copyright (C) 2000, 2003, 2004, 2005 Free Software Foundation, Inc.

   Contributed by Canqun Yang <canqun@nudt.edu.cn>

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it under

the terms of the GNU General Public License as published by the Free

Software Foundation; either version 2, or (at your option) any later

version.

GCC is distributed in the hope that it will be useful, but WITHOUT ANY

WARRANTY; without even the implied warranty of MERCHANTABILITY or

FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

for more details.

You should have received a copy of the GNU General Public License

along with GCC; see the file COPYING.  If not, write to the Free

Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA

02110-1301, USA.  */

/* The core algorithm is based on Andy Vaught's g95 tree.  Also the

   way to build UNION_TYPE is borrowed from Richard Henderson.

   Transform common blocks.  An integral part of this is processing

   equivalence variables.  Equivalenced variables that are not in a

   common block end up in a private block of their own.

   Each common block or local equivalence list is declared as a union.

   Variables within the block are represented as a field within the

   block with the proper offset.

   So if two variables are equivalenced, they just point to a common

   area in memory.

   Mathematically, laying out an equivalence block is equivalent to

   solving a linear system of equations.  The matrix is usually a

   sparse matrix in which each row contains all zero elements except

   for a +1 and a -1, a sort of a generalized Vandermonde matrix.  The

   matrix is usually block diagonal.  The system can be

   overdetermined, underdetermined or have a unique solution.  If the

   system is inconsistent, the program is not standard conforming.

   The solution vector is integral, since all of the pivots are +1 or -1.

   How we lay out an equivalence block is a little less complicated.

   In an equivalence list with n elements, there are n-1 conditions to

   be satisfied.  The conditions partition the variables into what we

   will call segments.  If A and B are equivalenced then A and B are

   in the same segment.  If B and C are equivalenced as well, then A,

   B and C are in a segment and so on.  Each segment is a block of

   memory that has one or more variables equivalenced in some way.  A

   common block is made up of a series of segments that are joined one

   after the other.  In the linear system, a segment is a block

   diagonal.

   To lay out a segment we first start with some variable and

   determine its length.  The first variable is assumed to start at

   offset one and extends to however long it is.  We then traverse the

   list of equivalences to find an unused condition that involves at

   least one of the variables currently in the segment.

   Each equivalence condition amounts to the condition B+b=C+c where B

   and C are the offsets of the B and C variables, and b and c are

   constants which are nonzero for array elements, substrings or

   structure components.  So for

     EQUIVALENCE(B(2), C(3))

   we have

     B + 2*size of B's elements = C + 3*size of C's elements.

   If B and C are known we check to see if the condition already

   holds.  If B is known we can solve for C.  Since we know the length

   of C, we can see if the minimum and maximum extents of the segment

   are affected.  Eventually, we make a full pass through the

   equivalence list without finding any new conditions and the segment

   is fully specified.

   At this point, the segment is added to the current common block.

   Since we know the minimum extent of the segment, everything in the

   segment is translated to its position in the common block.  The

   usual case here is that there are no equivalence statements and the

   common block is series of segments with one variable each, which is

   a diagonal matrix in the matrix formulation.

   Each segment is described by a chain of segment_info structures.  Each

   segment_info structure describes the extents of a single varible within

   the segment.  This list is maintained in the order the elements are

   positioned withing the segment.  If two elements have the same starting

   offset the smaller will come first.  If they also have the same size their

   ordering is undefined.

   Once all common blocks have been created, the list of equivalences

   is examined for still-unused equivalence conditions.  We create a

   block for each merged equivalence list.  */

#include "config.h"

#include "system.h"

#include "coretypes.h"

#include "tree.h"

#include "toplev.h"

#include "tm.h"

#include "gfortran.h"

#include "trans.h"

#include "trans-types.h"

#include "trans-const.h"

/* Holds a single variable in an equivalence set.  */

typedef struct segment_info

{

  gfc_symbol *sym;

  HOST_WIDE_INT offset;

  HOST_WIDE_INT length;

  /* This will contain the field type until the field is created.  */

  tree field;

  struct segment_info *next;

} segment_info;

static segment_info * current_segment;

static gfc_namespace *gfc_common_ns = NULL;

/* Make a segment_info based on a symbol.  */

static segment_info *

get_segment_info (gfc_symbol * sym, HOST_WIDE_INT offset)

{

  segment_info *s;

  /* Make sure we've got the character length.  */

  if (sym->ts.type == BT_CHARACTER)

    gfc_conv_const_charlen (sym->ts.cl);

  /* Create the segment_info and fill it in.  */

  s = (segment_info *) gfc_getmem (sizeof (segment_info));

  s->sym = sym;

  /* We will use this type when building the segment aggregate type.  */

  s->field = gfc_sym_type (sym);

  s->length = int_size_in_bytes (s->field);

  s->offset = offset;

  return s;

}

/* Add a copy of a segment list to the namespace.  This is specifically for

   equivalence segments, so that dependency checking can be done on

   equivalence group members.  */

static void

copy_equiv_list_to_ns (segment_info *c)

{

  segment_info *f;

  gfc_equiv_info *s;

  gfc_equiv_list *l;

  l = (gfc_equiv_list *) gfc_getmem (sizeof (gfc_equiv_list));

  l->next = c->sym->ns->equiv_lists;

  c->sym->ns->equiv_lists = l;

  for (f = c; f; f = f->next)

    {

      s = (gfc_equiv_info *) gfc_getmem (sizeof (gfc_equiv_info));

      s->next = l->equiv;

      l->equiv = s;

      s->sym = f->sym;

      s->offset = f->offset;

    }

}

/* Add combine segment V and segment LIST.  */

static segment_info *

add_segments (segment_info *list, segment_info *v)

{

  segment_info *s;

  segment_info *p;

  segment_info *next;

  p = NULL;

  s = list;

  while (v)

    {

      /* Find the location of the new element.  */

      while (s)

        {

          if (v->offset < s->offset)

            break;

          if (v->offset == s->offset

              && v->length <= s->length)

            break;

          p = s;

          s = s->next;

        }

      /* Insert the new element in between p and s.  */

      next = v->next;

      v->next = s;

      if (p == NULL)

        list = v;

      else

        p->next = v;

      p = v;

      v = next;

    }

  return list;

}

/* Construct mangled common block name from symbol name.  */

static tree

gfc_sym_mangled_common_id (const char  *name)

{

  int has_underscore;

  char mangled_name[GFC_MAX_MANGLED_SYMBOL_LEN + 1];

  if (strcmp (name, BLANK_COMMON_NAME) == 0)

    return get_identifier (name);

  if (gfc_option.flag_underscoring)

    {

      has_underscore = strchr (name, '_') != 0;

      if (gfc_option.flag_second_underscore && has_underscore)

        snprintf (mangled_name, sizeof mangled_name, "%s__", name);

      else

        snprintf (mangled_name, sizeof mangled_name, "%s_", name);

      return get_identifier (mangled_name);

    }

  else

    return get_identifier (name);

}

/* Build a field declaration for a common variable or a local equivalence

   object.  */

static void

build_field (segment_info *h, tree union_type, record_layout_info rli)

{

  tree field;

  tree name;

  HOST_WIDE_INT offset = h->offset;

  unsigned HOST_WIDE_INT desired_align, known_align;

  name = get_identifier (h->sym->name);

  field = build_decl (FIELD_DECL, name, h->field);

  gfc_set_decl_location (field, &h->sym->declared_at);

  known_align = (offset & -offset) * BITS_PER_UNIT;

  if (known_align == 0 || known_align > BIGGEST_ALIGNMENT)

    known_align = BIGGEST_ALIGNMENT;

  desired_align = update_alignment_for_field (rli, field, known_align);

  if (desired_align > known_align)

    DECL_PACKED (field) = 1;

  DECL_FIELD_CONTEXT (field) = union_type;

  DECL_FIELD_OFFSET (field) = size_int (offset);

  DECL_FIELD_BIT_OFFSET (field) = bitsize_zero_node;

  SET_DECL_OFFSET_ALIGN (field, known_align);

  rli->offset = size_binop (MAX_EXPR, rli->offset,

                            size_binop (PLUS_EXPR,

                                        DECL_FIELD_OFFSET (field),

                                        DECL_SIZE_UNIT (field)));

  /* If this field is assigned to a label, we create another two variables.

     One will hold the address of target label or format label. The other will

     hold the length of format label string.  */

  if (h->sym->attr.assign)

    {

      tree len;

      tree addr;

      gfc_allocate_lang_decl (field);

      GFC_DECL_ASSIGN (field) = 1;

      len = gfc_create_var_np (gfc_charlen_type_node,h->sym->name);

      addr = gfc_create_var_np (pvoid_type_node, h->sym->name);

      TREE_STATIC (len) = 1;

      TREE_STATIC (addr) = 1;

      DECL_INITIAL (len) = build_int_cst (NULL_TREE, -2);

      gfc_set_decl_location (len, &h->sym->declared_at);

      gfc_set_decl_location (addr, &h->sym->declared_at);

      GFC_DECL_STRING_LEN (field) = pushdecl_top_level (len);

      GFC_DECL_ASSIGN_ADDR (field) = pushdecl_top_level (addr);

    }

  h->field = field;

}

/* Get storage for local equivalence.  */

static tree

build_equiv_decl (tree union_type, bool is_init, bool is_saved)

{

  tree decl;

  char name[15];

  static int serial = 0;

  if (is_init)

    {

      decl = gfc_create_var (union_type, "equiv");

      TREE_STATIC (decl) = 1;

      return decl;

    }

  snprintf (name, sizeof (name), "equiv.%d", serial++);

  decl = build_decl (VAR_DECL, get_identifier (name), union_type);

  DECL_ARTIFICIAL (decl) = 1;

  DECL_IGNORED_P (decl) = 1;

  if (!gfc_can_put_var_on_stack (DECL_SIZE_UNIT (decl))

      || is_saved)

    TREE_STATIC (decl) = 1;

  TREE_ADDRESSABLE (decl) = 1;

  TREE_USED (decl) = 1;

  /* The source location has been lost, and doesn't really matter.

     We need to set it to something though.  */

  gfc_set_decl_location (decl, &gfc_current_locus);

  gfc_add_decl_to_function (decl);

  return decl;

}

/* Get storage for common block.  */

static tree

build_common_decl (gfc_common_head *com, tree union_type, bool is_init)

{

  gfc_symbol *common_sym;

  tree decl;

  /* Create a namespace to store symbols for common blocks.  */

  if (gfc_common_ns == NULL)

    gfc_common_ns = gfc_get_namespace (NULL, 0);

  gfc_get_symbol (com->name, gfc_common_ns, &common_sym);

  decl = common_sym->backend_decl;

  /* Update the size of this common block as needed.  */

  if (decl != NULL_TREE)

    {

      tree size = TYPE_SIZE_UNIT (union_type);

      if (tree_int_cst_lt (DECL_SIZE_UNIT (decl), size))

        {

          /* Named common blocks of the same name shall be of the same size

             in all scoping units of a program in which they appear, but

             blank common blocks may be of different sizes.  */

          if (strcmp (com->name, BLANK_COMMON_NAME))

            gfc_warning ("Named COMMON block '%s' at %L shall be of the "

                         "same size", com->name, &com->where);

          DECL_SIZE_UNIT (decl) = size;

        }

     }

  /* If this common block has been declared in a previous program unit,

     and either it is already initialized or there is no new initialization

     for it, just return.  */

  if ((decl != NULL_TREE) && (!is_init || DECL_INITIAL (decl)))

    return decl;

  /* If there is no backend_decl for the common block, build it.  */

  if (decl == NULL_TREE)

    {

      decl = build_decl (VAR_DECL, get_identifier (com->name), union_type);

      SET_DECL_ASSEMBLER_NAME (decl, gfc_sym_mangled_common_id (com->name));

      TREE_PUBLIC (decl) = 1;

      TREE_STATIC (decl) = 1;

      DECL_ALIGN (decl) = BIGGEST_ALIGNMENT;

      DECL_USER_ALIGN (decl) = 0;

      gfc_set_decl_location (decl, &com->where);

      /* Place the back end declaration for this common block in

         GLOBAL_BINDING_LEVEL.  */

      common_sym->backend_decl = pushdecl_top_level (decl);

    }

  /* Has no initial values.  */

  if (!is_init)

    {

      DECL_INITIAL (decl) = NULL_TREE;

      DECL_COMMON (decl) = 1;

      DECL_DEFER_OUTPUT (decl) = 1;

    }

  else

    {

      DECL_INITIAL (decl) = error_mark_node;

      DECL_COMMON (decl) = 0;

      DECL_DEFER_OUTPUT (decl) = 0;

    }

  return decl;

}

/* Declare memory for the common block or local equivalence, and create

   backend declarations for all of the elements.  */

static void

create_common (gfc_common_head *com, segment_info * head, bool saw_equiv)

{

  segment_info *s, *next_s;

  tree union_type;

  tree *field_link;

  record_layout_info rli;

  tree decl;

  bool is_init = false;

  bool is_saved = false;

  /* Declare the variables inside the common block.

     If the current common block contains any equivalence object, then

     make a UNION_TYPE node, otherwise RECORD_TYPE. This will let the

     alias analyzer work well when there is no address overlapping for

     common variables in the current common block.  */

  if (saw_equiv)

    union_type = make_node (UNION_TYPE);

  else

    union_type = make_node (RECORD_TYPE);

  rli = start_record_layout (union_type);

  field_link = &TYPE_FIELDS (union_type);

  for (s = head; s; s = s->next)

    {

      build_field (s, union_type, rli);

      /* Link the field into the type.  */

      *field_link = s->field;

      field_link = &TREE_CHAIN (s->field);

      /* Has initial value.  */

      if (s->sym->value)

        is_init = true;

      /* Has SAVE attribute.  */

      if (s->sym->attr.save)

        is_saved = true;

    }

  finish_record_layout (rli, true);

  if (com)

    decl = build_common_decl (com, union_type, is_init);

  else

    decl = build_equiv_decl (union_type, is_init, is_saved);

  if (is_init)

    {

      tree ctor, tmp;

      HOST_WIDE_INT offset = 0;

      VEC(constructor_elt,gc) *v = NULL;

      for (s = head; s; s = s->next)

        {

          if (s->sym->value)

            {

              if (s->offset < offset)

                {

                    /* We have overlapping initializers.  It could either be

                       partially initialized arrays (legal), or the user

                       specified multiple initial values (illegal).

                       We don't implement this yet, so bail out.  */

                  gfc_todo_error ("Initialization of overlapping variables");

                }

              /* Add the initializer for this field.  */

              tmp = gfc_conv_initializer (s->sym->value, &s->sym->ts,

                  TREE_TYPE (s->field), s->sym->attr.dimension,

                  s->sym->attr.pointer || s->sym->attr.allocatable);

              CONSTRUCTOR_APPEND_ELT (v, s->field, tmp);

              offset = s->offset + s->length;

            }

        }

      gcc_assert (!VEC_empty (constructor_elt, v));

      ctor = build_constructor (union_type, v);

      TREE_CONSTANT (ctor) = 1;

      TREE_INVARIANT (ctor) = 1;

      TREE_STATIC (ctor) = 1;

      DECL_INITIAL (decl) = ctor;

#ifdef ENABLE_CHECKING

      {

        tree field, value;

        unsigned HOST_WIDE_INT idx;

        FOR_EACH_CONSTRUCTOR_ELT (CONSTRUCTOR_ELTS (ctor), idx, field, value)

          gcc_assert (TREE_CODE (field) == FIELD_DECL);

      }

#endif

    }

  /* Build component reference for each variable.  */

  for (s = head; s; s = next_s)

    {

      tree var_decl;

      var_decl = build_decl (VAR_DECL, DECL_NAME (s->field),

                             TREE_TYPE (s->field));

      gfc_set_decl_location (var_decl, &s->sym->declared_at);

      TREE_PUBLIC (var_decl) = TREE_PUBLIC (decl);

      TREE_STATIC (var_decl) = TREE_STATIC (decl);

      TREE_USED (var_decl) = TREE_USED (decl);

      if (s->sym->attr.target)

        TREE_ADDRESSABLE (var_decl) = 1;

      /* This is a fake variable just for debugging purposes.  */

      TREE_ASM_WRITTEN (var_decl) = 1;

      if (com)

        var_decl = pushdecl_top_level (var_decl);

      else

        gfc_add_decl_to_function (var_decl);

      SET_DECL_VALUE_EXPR (var_decl,

                           build3 (COMPONENT_REF, TREE_TYPE (s->field),

                                   decl, s->field, NULL_TREE));

      DECL_HAS_VALUE_EXPR_P (var_decl) = 1;

      if (s->sym->attr.assign)

        {

          gfc_allocate_lang_decl (var_decl);

          GFC_DECL_ASSIGN (var_decl) = 1;

          GFC_DECL_STRING_LEN (var_decl) = GFC_DECL_STRING_LEN (s->field);

          GFC_DECL_ASSIGN_ADDR (var_decl) = GFC_DECL_ASSIGN_ADDR (s->field);

        }

      s->sym->backend_decl = var_decl;

      next_s = s->next;

      gfc_free (s);

    }

}

/* Given a symbol, find it in the current segment list. Returns NULL if

   not found.  */

static segment_info *

find_segment_info (gfc_symbol *symbol)

{

  segment_info *n;

  for (n = current_segment; n; n = n->next)

    {

      if (n->sym == symbol)

        return n;

    }

  return NULL;

}

/* Given an expression node, make sure it is a constant integer and return

   the mpz_t value.  */

static mpz_t *

get_mpz (gfc_expr *e)

{

  if (e->expr_type != EXPR_CONSTANT)

    gfc_internal_error ("get_mpz(): Not an integer constant");

  return &e->value.integer;

}

/* Given an array specification and an array reference, figure out the

   array element number (zero based). Bounds and elements are guaranteed

   to be constants.  If something goes wrong we generate an error and

   return zero.  */

static HOST_WIDE_INT

element_number (gfc_array_ref *ar)

{

  mpz_t multiplier, offset, extent, n;

  gfc_array_spec *as;

  HOST_WIDE_INT i, rank;

  as = ar->as;

  rank = as->rank;

  mpz_init_set_ui (multiplier, 1);

  mpz_init_set_ui (offset, 0);

  mpz_init (extent);

  mpz_init (n);

  for (i = 0; i < rank; i++)

    {

      if (ar->dimen_type[i] != DIMEN_ELEMENT)

        gfc_internal_error ("element_number(): Bad dimension type");

      mpz_sub (n, *get_mpz (ar->start[i]), *get_mpz (as->lower[i]));

      mpz_mul (n, n, multiplier);

      mpz_add (offset, offset, n);

      mpz_sub (extent, *get_mpz (as->upper[i]), *get_mpz (as->lower[i]));

      mpz_add_ui (extent, extent, 1);

      if (mpz_sgn (extent) < 0)

        mpz_set_ui (extent, 0);

      mpz_mul (multiplier, multiplier, extent);

    }

  i = mpz_get_ui (offset);

  mpz_clear (multiplier);

  mpz_clear (offset);

  mpz_clear (extent);

  mpz_clear (n);

  return i;

}

/* Given a single element of an equivalence list, figure out the offset

   from the base symbol.  For simple variables or full arrays, this is

   simply zero.  For an array element we have to calculate the array

   element number and multiply by the element size. For a substring we

   have to calculate the further reference.  */

static HOST_WIDE_INT

calculate_offset (gfc_expr *e)

{

  HOST_WIDE_INT n, element_size, offset;

  gfc_typespec *element_type;

  gfc_ref *reference;

  offset = 0;

  element_type = &e->symtree->n.sym->ts;

  for (reference = e->ref; reference; reference = reference->next)

    switch (reference->type)

      {

      case REF_ARRAY:

        switch (reference->u.ar.type)

          {

          case AR_FULL:

            break;

          case AR_ELEMENT:

            n = element_number (&reference->u.ar);

            if (element_type->type == BT_CHARACTER)

              gfc_conv_const_charlen (element_type->cl);

            element_size =

              int_size_in_bytes (gfc_typenode_for_spec (element_type));

            offset += n * element_size;

            break;

          default:

            gfc_error ("Bad array reference at %L", &e->where);

          }

        break;

      case REF_SUBSTRING:

        if (reference->u.ss.start != NULL)

          offset += mpz_get_ui (*get_mpz (reference->u.ss.start)) - 1;

        break;

      default:

        gfc_error ("Illegal reference type at %L as EQUIVALENCE object",

                   &e->where);

    }

  return offset;

}

/* Add a new segment_info structure to the current segment.  eq1 is already

   in the list, eq2 is not.  */

static void

new_condition (segment_info *v, gfc_equiv *eq1, gfc_equiv *eq2)

{

  HOST_WIDE_INT offset1, offset2;

  segment_info *a;

  offset1 = calculate_offset (eq1->expr);

  offset2 = calculate_offset (eq2->expr);

  a = get_segment_info (eq2->expr->symtree->n.sym,

                        v->offset + offset1 - offset2);

  current_segment = add_segments (current_segment, a);

}

/* Given two equivalence structures that are both already in the list, make

   sure that this new condition is not violated, generating an error if it

   is.  */

static void

confirm_condition (segment_info *s1, gfc_equiv *eq1, segment_info *s2,

                   gfc_equiv *eq2)

{

  HOST_WIDE_INT offset1, offset2;

  offset1 = calculate_offset (eq1->expr);

  offset2 = calculate_offset (eq2->expr);

  if (s1->offset + offset1 != s2->offset + offset2)

    gfc_error ("Inconsistent equivalence rules involving '%s' at %L and "

               "'%s' at %L", s1->sym->name, &s1->sym->declared_at,

               s2->sym->name, &s2->sym->declared_at);

}

/* Process a new equivalence condition. eq1 is know to be in segment f.