re PR fortran/40453 ([F95] Enhanced (recursive) argument checking)

[thirdparty/gcc.git] / gcc / fortran / interface.c

/* Deal with interfaces.
   Copyright (C) 2000, 2001, 2002, 2004, 2005, 2006, 2007, 2008, 2009,
   2010, 2011, 2012
   Free Software Foundation, Inc.
   Contributed by Andy Vaught

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 3, 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 COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */


/* Deal with interfaces.  An explicit interface is represented as a
   singly linked list of formal argument structures attached to the
   relevant symbols.  For an implicit interface, the arguments don't
   point to symbols.  Explicit interfaces point to namespaces that
   contain the symbols within that interface.

   Implicit interfaces are linked together in a singly linked list
   along the next_if member of symbol nodes.  Since a particular
   symbol can only have a single explicit interface, the symbol cannot
   be part of multiple lists and a single next-member suffices.

   This is not the case for general classes, though.  An operator
   definition is independent of just about all other uses and has it's
   own head pointer.

   Nameless interfaces:
     Nameless interfaces create symbols with explicit interfaces within
     the current namespace.  They are otherwise unlinked.

   Generic interfaces:
     The generic name points to a linked list of symbols.  Each symbol
     has an explicit interface.  Each explicit interface has its own
     namespace containing the arguments.  Module procedures are symbols in
     which the interface is added later when the module procedure is parsed.

   User operators:
     User-defined operators are stored in a their own set of symtrees
     separate from regular symbols.  The symtrees point to gfc_user_op
     structures which in turn head up a list of relevant interfaces.

   Extended intrinsics and assignment:
     The head of these interface lists are stored in the containing namespace.

   Implicit interfaces:
     An implicit interface is represented as a singly linked list of
     formal argument list structures that don't point to any symbol
     nodes -- they just contain types.


   When a subprogram is defined, the program unit's name points to an
   interface as usual, but the link to the namespace is NULL and the
   formal argument list points to symbols within the same namespace as
   the program unit name.  */

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "gfortran.h"
#include "match.h"
#include "arith.h"

/* The current_interface structure holds information about the
   interface currently being parsed.  This structure is saved and
   restored during recursive interfaces.  */

gfc_interface_info current_interface;


/* Free a singly linked list of gfc_interface structures.  */

void
gfc_free_interface (gfc_interface *intr)
{
  gfc_interface *next;

  for (; intr; intr = next)
    {
      next = intr->next;
      free (intr);
    }
}


/* Change the operators unary plus and minus into binary plus and
   minus respectively, leaving the rest unchanged.  */

static gfc_intrinsic_op
fold_unary_intrinsic (gfc_intrinsic_op op)
{
  switch (op)
    {
    case INTRINSIC_UPLUS:
      op = INTRINSIC_PLUS;
      break;
    case INTRINSIC_UMINUS:
      op = INTRINSIC_MINUS;
      break;
    default:
      break;
    }

  return op;
}


/* Match a generic specification.  Depending on which type of
   interface is found, the 'name' or 'op' pointers may be set.
   This subroutine doesn't return MATCH_NO.  */

match
gfc_match_generic_spec (interface_type *type,
                        char *name,
                        gfc_intrinsic_op *op)
{
  char buffer[GFC_MAX_SYMBOL_LEN + 1];
  match m;
  gfc_intrinsic_op i;

  if (gfc_match (" assignment ( = )") == MATCH_YES)
    {
      *type = INTERFACE_INTRINSIC_OP;
      *op = INTRINSIC_ASSIGN;
      return MATCH_YES;
    }

  if (gfc_match (" operator ( %o )", &i) == MATCH_YES)
    {                           /* Operator i/f */
      *type = INTERFACE_INTRINSIC_OP;
      *op = fold_unary_intrinsic (i);
      return MATCH_YES;
    }

  *op = INTRINSIC_NONE;
  if (gfc_match (" operator ( ") == MATCH_YES)
    {
      m = gfc_match_defined_op_name (buffer, 1);
      if (m == MATCH_NO)
        goto syntax;
      if (m != MATCH_YES)
        return MATCH_ERROR;

      m = gfc_match_char (')');
      if (m == MATCH_NO)
        goto syntax;
      if (m != MATCH_YES)
        return MATCH_ERROR;

      strcpy (name, buffer);
      *type = INTERFACE_USER_OP;
      return MATCH_YES;
    }

  if (gfc_match_name (buffer) == MATCH_YES)
    {
      strcpy (name, buffer);
      *type = INTERFACE_GENERIC;
      return MATCH_YES;
    }

  *type = INTERFACE_NAMELESS;
  return MATCH_YES;

syntax:
  gfc_error ("Syntax error in generic specification at %C");
  return MATCH_ERROR;
}


/* Match one of the five F95 forms of an interface statement.  The
   matcher for the abstract interface follows.  */

match
gfc_match_interface (void)
{
  char name[GFC_MAX_SYMBOL_LEN + 1];
  interface_type type;
  gfc_symbol *sym;
  gfc_intrinsic_op op;
  match m;

  m = gfc_match_space ();

  if (gfc_match_generic_spec (&type, name, &op) == MATCH_ERROR)
    return MATCH_ERROR;

  /* If we're not looking at the end of the statement now, or if this
     is not a nameless interface but we did not see a space, punt.  */
  if (gfc_match_eos () != MATCH_YES
      || (type != INTERFACE_NAMELESS && m != MATCH_YES))
    {
      gfc_error ("Syntax error: Trailing garbage in INTERFACE statement "
                 "at %C");
      return MATCH_ERROR;
    }

  current_interface.type = type;

  switch (type)
    {
    case INTERFACE_GENERIC:
      if (gfc_get_symbol (name, NULL, &sym))
        return MATCH_ERROR;

      if (!sym->attr.generic 
          && gfc_add_generic (&sym->attr, sym->name, NULL) == FAILURE)
        return MATCH_ERROR;

      if (sym->attr.dummy)
        {
          gfc_error ("Dummy procedure '%s' at %C cannot have a "
                     "generic interface", sym->name);
          return MATCH_ERROR;
        }

      current_interface.sym = gfc_new_block = sym;
      break;

    case INTERFACE_USER_OP:
      current_interface.uop = gfc_get_uop (name);
      break;

    case INTERFACE_INTRINSIC_OP:
      current_interface.op = op;
      break;

    case INTERFACE_NAMELESS:
    case INTERFACE_ABSTRACT:
      break;
    }

  return MATCH_YES;
}



/* Match a F2003 abstract interface.  */

match
gfc_match_abstract_interface (void)
{
  match m;

  if (gfc_notify_std (GFC_STD_F2003, "ABSTRACT INTERFACE at %C")
                      == FAILURE)
    return MATCH_ERROR;

  m = gfc_match_eos ();

  if (m != MATCH_YES)
    {
      gfc_error ("Syntax error in ABSTRACT INTERFACE statement at %C");
      return MATCH_ERROR;
    }

  current_interface.type = INTERFACE_ABSTRACT;

  return m;
}


/* Match the different sort of generic-specs that can be present after
   the END INTERFACE itself.  */

match
gfc_match_end_interface (void)
{
  char name[GFC_MAX_SYMBOL_LEN + 1];
  interface_type type;
  gfc_intrinsic_op op;
  match m;

  m = gfc_match_space ();

  if (gfc_match_generic_spec (&type, name, &op) == MATCH_ERROR)
    return MATCH_ERROR;

  /* If we're not looking at the end of the statement now, or if this
     is not a nameless interface but we did not see a space, punt.  */
  if (gfc_match_eos () != MATCH_YES
      || (type != INTERFACE_NAMELESS && m != MATCH_YES))
    {
      gfc_error ("Syntax error: Trailing garbage in END INTERFACE "
                 "statement at %C");
      return MATCH_ERROR;
    }

  m = MATCH_YES;

  switch (current_interface.type)
    {
    case INTERFACE_NAMELESS:
    case INTERFACE_ABSTRACT:
      if (type != INTERFACE_NAMELESS)
        {
          gfc_error ("Expected a nameless interface at %C");
          m = MATCH_ERROR;
        }

      break;

    case INTERFACE_INTRINSIC_OP:
      if (type != current_interface.type || op != current_interface.op)
        {

          if (current_interface.op == INTRINSIC_ASSIGN)
            {
              m = MATCH_ERROR;
              gfc_error ("Expected 'END INTERFACE ASSIGNMENT (=)' at %C");
            }
          else
            {
              const char *s1, *s2;
              s1 = gfc_op2string (current_interface.op);
              s2 = gfc_op2string (op);

              /* The following if-statements are used to enforce C1202
                 from F2003.  */
              if ((strcmp(s1, "==") == 0 && strcmp(s2, ".eq.") == 0)
                  || (strcmp(s1, ".eq.") == 0 && strcmp(s2, "==") == 0))
                break;
              if ((strcmp(s1, "/=") == 0 && strcmp(s2, ".ne.") == 0)
                  || (strcmp(s1, ".ne.") == 0 && strcmp(s2, "/=") == 0))
                break;
              if ((strcmp(s1, "<=") == 0 && strcmp(s2, ".le.") == 0)
                  || (strcmp(s1, ".le.") == 0 && strcmp(s2, "<=") == 0))
                break;
              if ((strcmp(s1, "<") == 0 && strcmp(s2, ".lt.") == 0)
                  || (strcmp(s1, ".lt.") == 0 && strcmp(s2, "<") == 0))
                break;
              if ((strcmp(s1, ">=") == 0 && strcmp(s2, ".ge.") == 0)
                  || (strcmp(s1, ".ge.") == 0 && strcmp(s2, ">=") == 0))
                break;
              if ((strcmp(s1, ">") == 0 && strcmp(s2, ".gt.") == 0)
                  || (strcmp(s1, ".gt.") == 0 && strcmp(s2, ">") == 0))
                break;

              m = MATCH_ERROR;
              gfc_error ("Expecting 'END INTERFACE OPERATOR (%s)' at %C, "
                         "but got %s", s1, s2);
            }
                
        }

      break;

    case INTERFACE_USER_OP:
      /* Comparing the symbol node names is OK because only use-associated
         symbols can be renamed.  */
      if (type != current_interface.type
          || strcmp (current_interface.uop->name, name) != 0)
        {
          gfc_error ("Expecting 'END INTERFACE OPERATOR (.%s.)' at %C",
                     current_interface.uop->name);
          m = MATCH_ERROR;
        }

      break;

    case INTERFACE_GENERIC:
      if (type != current_interface.type
          || strcmp (current_interface.sym->name, name) != 0)
        {
          gfc_error ("Expecting 'END INTERFACE %s' at %C",
                     current_interface.sym->name);
          m = MATCH_ERROR;
        }

      break;
    }

  return m;
}


/* Compare two derived types using the criteria in 4.4.2 of the standard,
   recursing through gfc_compare_types for the components.  */

int
gfc_compare_derived_types (gfc_symbol *derived1, gfc_symbol *derived2)
{
  gfc_component *dt1, *dt2;

  if (derived1 == derived2)
    return 1;

  gcc_assert (derived1 && derived2);

  /* Special case for comparing derived types across namespaces.  If the
     true names and module names are the same and the module name is
     nonnull, then they are equal.  */
  if (strcmp (derived1->name, derived2->name) == 0
      && derived1->module != NULL && derived2->module != NULL
      && strcmp (derived1->module, derived2->module) == 0)
    return 1;

  /* Compare type via the rules of the standard.  Both types must have
     the SEQUENCE or BIND(C) attribute to be equal.  */

  if (strcmp (derived1->name, derived2->name))
    return 0;

  if (derived1->component_access == ACCESS_PRIVATE
      || derived2->component_access == ACCESS_PRIVATE)
    return 0;

  if (!(derived1->attr.sequence && derived2->attr.sequence)
      && !(derived1->attr.is_bind_c && derived2->attr.is_bind_c))
    return 0;

  dt1 = derived1->components;
  dt2 = derived2->components;

  /* Since subtypes of SEQUENCE types must be SEQUENCE types as well, a
     simple test can speed things up.  Otherwise, lots of things have to
     match.  */
  for (;;)
    {
      if (strcmp (dt1->name, dt2->name) != 0)
        return 0;

      if (dt1->attr.access != dt2->attr.access)
        return 0;

      if (dt1->attr.pointer != dt2->attr.pointer)
        return 0;

      if (dt1->attr.dimension != dt2->attr.dimension)
        return 0;

     if (dt1->attr.allocatable != dt2->attr.allocatable)
        return 0;

      if (dt1->attr.dimension && gfc_compare_array_spec (dt1->as, dt2->as) == 0)
        return 0;

      /* Make sure that link lists do not put this function into an 
         endless recursive loop!  */
      if (!(dt1->ts.type == BT_DERIVED && derived1 == dt1->ts.u.derived)
            && !(dt2->ts.type == BT_DERIVED && derived2 == dt2->ts.u.derived)
            && gfc_compare_types (&dt1->ts, &dt2->ts) == 0)
        return 0;

      else if ((dt1->ts.type == BT_DERIVED && derived1 == dt1->ts.u.derived)
                && !(dt1->ts.type == BT_DERIVED && derived1 == dt1->ts.u.derived))
        return 0;

      else if (!(dt1->ts.type == BT_DERIVED && derived1 == dt1->ts.u.derived)
                && (dt1->ts.type == BT_DERIVED && derived1 == dt1->ts.u.derived))
        return 0;

      dt1 = dt1->next;
      dt2 = dt2->next;

      if (dt1 == NULL && dt2 == NULL)
        break;
      if (dt1 == NULL || dt2 == NULL)
        return 0;
    }

  return 1;
}


/* Compare two typespecs, recursively if necessary.  */

int
gfc_compare_types (gfc_typespec *ts1, gfc_typespec *ts2)
{
  /* See if one of the typespecs is a BT_VOID, which is what is being used
     to allow the funcs like c_f_pointer to accept any pointer type.
     TODO: Possibly should narrow this to just the one typespec coming in
     that is for the formal arg, but oh well.  */
  if (ts1->type == BT_VOID || ts2->type == BT_VOID)
    return 1;
   
  if (ts1->type != ts2->type
      && ((ts1->type != BT_DERIVED && ts1->type != BT_CLASS)
          || (ts2->type != BT_DERIVED && ts2->type != BT_CLASS)))
    return 0;
  if (ts1->type != BT_DERIVED && ts1->type != BT_CLASS)
    return (ts1->kind == ts2->kind);

  /* Compare derived types.  */
  if (gfc_type_compatible (ts1, ts2))
    return 1;

  return gfc_compare_derived_types (ts1->u.derived ,ts2->u.derived);
}


/* Given two symbols that are formal arguments, compare their ranks
   and types.  Returns nonzero if they have the same rank and type,
   zero otherwise.  */

static int
compare_type_rank (gfc_symbol *s1, gfc_symbol *s2)
{
  gfc_array_spec *as1, *as2;
  int r1, r2;

  as1 = (s1->ts.type == BT_CLASS) ? CLASS_DATA (s1)->as : s1->as;
  as2 = (s2->ts.type == BT_CLASS) ? CLASS_DATA (s2)->as : s2->as;

  r1 = as1 ? as1->rank : 0;
  r2 = as2 ? as2->rank : 0;

  if (r1 != r2
      && (!as1 || as1->type != AS_ASSUMED_RANK)
      && (!as2 || as2->type != AS_ASSUMED_RANK))
    return 0;                   /* Ranks differ.  */

  return gfc_compare_types (&s1->ts, &s2->ts)
         || s1->ts.type == BT_ASSUMED || s2->ts.type == BT_ASSUMED; 
}


/* Given two symbols that are formal arguments, compare their types
   and rank and their formal interfaces if they are both dummy
   procedures.  Returns nonzero if the same, zero if different.  */

static int
compare_type_rank_if (gfc_symbol *s1, gfc_symbol *s2)
{
  if (s1 == NULL || s2 == NULL)
    return s1 == s2 ? 1 : 0;

  if (s1 == s2)
    return 1;

  if (s1->attr.flavor != FL_PROCEDURE && s2->attr.flavor != FL_PROCEDURE)
    return compare_type_rank (s1, s2);

  if (s1->attr.flavor != FL_PROCEDURE || s2->attr.flavor != FL_PROCEDURE)
    return 0;

  /* At this point, both symbols are procedures.  It can happen that
     external procedures are compared, where one is identified by usage
     to be a function or subroutine but the other is not.  Check TKR
     nonetheless for these cases.  */
  if (s1->attr.function == 0 && s1->attr.subroutine == 0)
    return s1->attr.external == 1 ? compare_type_rank (s1, s2) : 0;

  if (s2->attr.function == 0 && s2->attr.subroutine == 0)
    return s2->attr.external == 1 ? compare_type_rank (s1, s2) : 0;

  /* Now the type of procedure has been identified.  */
  if (s1->attr.function != s2->attr.function
      || s1->attr.subroutine != s2->attr.subroutine)
    return 0;

  if (s1->attr.function && compare_type_rank (s1, s2) == 0)
    return 0;

  /* Originally, gfortran recursed here to check the interfaces of passed
     procedures.  This is explicitly not required by the standard.  */
  return 1;
}


/* Given a formal argument list and a keyword name, search the list
   for that keyword.  Returns the correct symbol node if found, NULL
   if not found.  */

static gfc_symbol *
find_keyword_arg (const char *name, gfc_formal_arglist *f)
{
  for (; f; f = f->next)
    if (strcmp (f->sym->name, name) == 0)
      return f->sym;

  return NULL;
}


/******** Interface checking subroutines **********/


/* Given an operator interface and the operator, make sure that all
   interfaces for that operator are legal.  */

bool
gfc_check_operator_interface (gfc_symbol *sym, gfc_intrinsic_op op,
                              locus opwhere)
{
  gfc_formal_arglist *formal;
  sym_intent i1, i2;
  bt t1, t2;
  int args, r1, r2, k1, k2;

  gcc_assert (sym);

  args = 0;
  t1 = t2 = BT_UNKNOWN;
  i1 = i2 = INTENT_UNKNOWN;
  r1 = r2 = -1;
  k1 = k2 = -1;

  for (formal = sym->formal; formal; formal = formal->next)
    {
      gfc_symbol *fsym = formal->sym;
      if (fsym == NULL)
        {
          gfc_error ("Alternate return cannot appear in operator "
                     "interface at %L", &sym->declared_at);
          return false;
        }
      if (args == 0)
        {
          t1 = fsym->ts.type;
          i1 = fsym->attr.intent;
          r1 = (fsym->as != NULL) ? fsym->as->rank : 0;
          k1 = fsym->ts.kind;
        }
      if (args == 1)
        {
          t2 = fsym->ts.type;
          i2 = fsym->attr.intent;
          r2 = (fsym->as != NULL) ? fsym->as->rank : 0;
          k2 = fsym->ts.kind;
        }
      args++;
    }

  /* Only +, - and .not. can be unary operators.
     .not. cannot be a binary operator.  */
  if (args == 0 || args > 2 || (args == 1 && op != INTRINSIC_PLUS
                                && op != INTRINSIC_MINUS
                                && op != INTRINSIC_NOT)
      || (args == 2 && op == INTRINSIC_NOT))
    {
      if (op == INTRINSIC_ASSIGN)
        gfc_error ("Assignment operator interface at %L must have "
                   "two arguments", &sym->declared_at);
      else
        gfc_error ("Operator interface at %L has the wrong number of arguments",
                   &sym->declared_at);
      return false;
    }

  /* Check that intrinsics are mapped to functions, except
     INTRINSIC_ASSIGN which should map to a subroutine.  */
  if (op == INTRINSIC_ASSIGN)
    {
      if (!sym->attr.subroutine)
        {
          gfc_error ("Assignment operator interface at %L must be "
                     "a SUBROUTINE", &sym->declared_at);
          return false;
        }

      /* Allowed are (per F2003, 12.3.2.1.2 Defined assignments):
         - First argument an array with different rank than second,
         - First argument is a scalar and second an array,
         - Types and kinds do not conform, or
         - First argument is of derived type.  */
      if (sym->formal->sym->ts.type != BT_DERIVED
          && sym->formal->sym->ts.type != BT_CLASS
          && (r2 == 0 || r1 == r2)
          && (sym->formal->sym->ts.type == sym->formal->next->sym->ts.type
              || (gfc_numeric_ts (&sym->formal->sym->ts)
                  && gfc_numeric_ts (&sym->formal->next->sym->ts))))
        {
          gfc_error ("Assignment operator interface at %L must not redefine "
                     "an INTRINSIC type assignment", &sym->declared_at);
          return false;
        }
    }
  else
    {
      if (!sym->attr.function)
        {
          gfc_error ("Intrinsic operator interface at %L must be a FUNCTION",
                     &sym->declared_at);
          return false;
        }
    }

  /* Check intents on operator interfaces.  */
  if (op == INTRINSIC_ASSIGN)
    {
      if (i1 != INTENT_OUT && i1 != INTENT_INOUT)
        {
          gfc_error ("First argument of defined assignment at %L must be "
                     "INTENT(OUT) or INTENT(INOUT)", &sym->declared_at);
          return false;
        }

      if (i2 != INTENT_IN)
        {
          gfc_error ("Second argument of defined assignment at %L must be "
                     "INTENT(IN)", &sym->declared_at);
          return false;
        }
    }
  else
    {
      if (i1 != INTENT_IN)
        {
          gfc_error ("First argument of operator interface at %L must be "
                     "INTENT(IN)", &sym->declared_at);
          return false;
        }

      if (args == 2 && i2 != INTENT_IN)
        {
          gfc_error ("Second argument of operator interface at %L must be "
                     "INTENT(IN)", &sym->declared_at);
          return false;
        }
    }

  /* From now on, all we have to do is check that the operator definition
     doesn't conflict with an intrinsic operator. The rules for this
     game are defined in 7.1.2 and 7.1.3 of both F95 and F2003 standards,
     as well as 12.3.2.1.1 of Fortran 2003:

     "If the operator is an intrinsic-operator (R310), the number of
     function arguments shall be consistent with the intrinsic uses of
     that operator, and the types, kind type parameters, or ranks of the
     dummy arguments shall differ from those required for the intrinsic
     operation (7.1.2)."  */

#define IS_NUMERIC_TYPE(t) \
  ((t) == BT_INTEGER || (t) == BT_REAL || (t) == BT_COMPLEX)

  /* Unary ops are easy, do them first.  */
  if (op == INTRINSIC_NOT)
    {
      if (t1 == BT_LOGICAL)
        goto bad_repl;
      else
        return true;
    }

  if (args == 1 && (op == INTRINSIC_PLUS || op == INTRINSIC_MINUS))
    {
      if (IS_NUMERIC_TYPE (t1))
        goto bad_repl;
      else
        return true;
    }

  /* Character intrinsic operators have same character kind, thus
     operator definitions with operands of different character kinds
     are always safe.  */
  if (t1 == BT_CHARACTER && t2 == BT_CHARACTER && k1 != k2)
    return true;

  /* Intrinsic operators always perform on arguments of same rank,
     so different ranks is also always safe.  (rank == 0) is an exception
     to that, because all intrinsic operators are elemental.  */
  if (r1 != r2 && r1 != 0 && r2 != 0)
    return true;

  switch (op)
  {
    case INTRINSIC_EQ:
    case INTRINSIC_EQ_OS:
    case INTRINSIC_NE:
    case INTRINSIC_NE_OS:
      if (t1 == BT_CHARACTER && t2 == BT_CHARACTER)
        goto bad_repl;
      /* Fall through.  */

    case INTRINSIC_PLUS:
    case INTRINSIC_MINUS:
    case INTRINSIC_TIMES:
    case INTRINSIC_DIVIDE:
    case INTRINSIC_POWER:
      if (IS_NUMERIC_TYPE (t1) && IS_NUMERIC_TYPE (t2))
        goto bad_repl;
      break;

    case INTRINSIC_GT:
    case INTRINSIC_GT_OS:
    case INTRINSIC_GE:
    case INTRINSIC_GE_OS:
    case INTRINSIC_LT:
    case INTRINSIC_LT_OS:
    case INTRINSIC_LE:
    case INTRINSIC_LE_OS:
      if (t1 == BT_CHARACTER && t2 == BT_CHARACTER)
        goto bad_repl;
      if ((t1 == BT_INTEGER || t1 == BT_REAL)
          && (t2 == BT_INTEGER || t2 == BT_REAL))
        goto bad_repl;
      break;

    case INTRINSIC_CONCAT:
      if (t1 == BT_CHARACTER && t2 == BT_CHARACTER)
        goto bad_repl;
      break;

    case INTRINSIC_AND:
    case INTRINSIC_OR:
    case INTRINSIC_EQV:
    case INTRINSIC_NEQV:
      if (t1 == BT_LOGICAL && t2 == BT_LOGICAL)
        goto bad_repl;
      break;

    default:
      break;
  }

  return true;

#undef IS_NUMERIC_TYPE

bad_repl:
  gfc_error ("Operator interface at %L conflicts with intrinsic interface",
             &opwhere);
  return false;
}


/* Given a pair of formal argument lists, we see if the two lists can
   be distinguished by counting the number of nonoptional arguments of
   a given type/rank in f1 and seeing if there are less then that
   number of those arguments in f2 (including optional arguments).
   Since this test is asymmetric, it has to be called twice to make it
   symmetric. Returns nonzero if the argument lists are incompatible
   by this test. This subroutine implements rule 1 of section F03:16.2.3.
   'p1' and 'p2' are the PASS arguments of both procedures (if applicable).  */

static int
count_types_test (gfc_formal_arglist *f1, gfc_formal_arglist *f2,
                  const char *p1, const char *p2)
{
  int rc, ac1, ac2, i, j, k, n1;
  gfc_formal_arglist *f;

  typedef struct
  {
    int flag;
    gfc_symbol *sym;
  }
  arginfo;

  arginfo *arg;

  n1 = 0;

  for (f = f1; f; f = f->next)
    n1++;

  /* Build an array of integers that gives the same integer to
     arguments of the same type/rank.  */
  arg = XCNEWVEC (arginfo, n1);

  f = f1;
  for (i = 0; i < n1; i++, f = f->next)
    {
      arg[i].flag = -1;
      arg[i].sym = f->sym;
    }

  k = 0;

  for (i = 0; i < n1; i++)
    {
      if (arg[i].flag != -1)
        continue;

      if (arg[i].sym && (arg[i].sym->attr.optional
                         || (p1 && strcmp (arg[i].sym->name, p1) == 0)))
        continue;               /* Skip OPTIONAL and PASS arguments.  */

      arg[i].flag = k;

      /* Find other non-optional, non-pass arguments of the same type/rank.  */
      for (j = i + 1; j < n1; j++)
        if ((arg[j].sym == NULL
             || !(arg[j].sym->attr.optional
                  || (p1 && strcmp (arg[j].sym->name, p1) == 0)))
            && (compare_type_rank_if (arg[i].sym, arg[j].sym)
                || compare_type_rank_if (arg[j].sym, arg[i].sym)))
          arg[j].flag = k;

      k++;
    }

  /* Now loop over each distinct type found in f1.  */
  k = 0;
  rc = 0;

  for (i = 0; i < n1; i++)
    {
      if (arg[i].flag != k)
        continue;

      ac1 = 1;
      for (j = i + 1; j < n1; j++)
        if (arg[j].flag == k)
          ac1++;

      /* Count the number of non-pass arguments in f2 with that type,
         including those that are optional.  */
      ac2 = 0;

      for (f = f2; f; f = f->next)
        if ((!p2 || strcmp (f->sym->name, p2) != 0)
            && (compare_type_rank_if (arg[i].sym, f->sym)
                || compare_type_rank_if (f->sym, arg[i].sym)))
          ac2++;

      if (ac1 > ac2)
        {
          rc = 1;
          break;
        }

      k++;
    }

  free (arg);

  return rc;
}


/* Perform the correspondence test in rule (3) of F08:C1215.
   Returns zero if no argument is found that satisfies this rule,
   nonzero otherwise. 'p1' and 'p2' are the PASS arguments of both procedures
   (if applicable).

   This test is also not symmetric in f1 and f2 and must be called
   twice.  This test finds problems caused by sorting the actual
   argument list with keywords.  For example:

   INTERFACE FOO
     SUBROUTINE F1(A, B)
       INTEGER :: A ; REAL :: B
     END SUBROUTINE F1

     SUBROUTINE F2(B, A)
       INTEGER :: A ; REAL :: B
     END SUBROUTINE F1
   END INTERFACE FOO

   At this point, 'CALL FOO(A=1, B=1.0)' is ambiguous.  */

static int
generic_correspondence (gfc_formal_arglist *f1, gfc_formal_arglist *f2,
                        const char *p1, const char *p2)
{
  gfc_formal_arglist *f2_save, *g;
  gfc_symbol *sym;

  f2_save = f2;

  while (f1)
    {
      if (f1->sym->attr.optional)
        goto next;

      if (p1 && strcmp (f1->sym->name, p1) == 0)
        f1 = f1->next;
      if (f2 && p2 && strcmp (f2->sym->name, p2) == 0)
        f2 = f2->next;

      if (f2 != NULL && (compare_type_rank (f1->sym, f2->sym)
                         || compare_type_rank (f2->sym, f1->sym))
          && !((gfc_option.allow_std & GFC_STD_F2008)
               && ((f1->sym->attr.allocatable && f2->sym->attr.pointer)
                   || (f2->sym->attr.allocatable && f1->sym->attr.pointer))))
        goto next;

      /* Now search for a disambiguating keyword argument starting at
         the current non-match.  */
      for (g = f1; g; g = g->next)
        {
          if (g->sym->attr.optional || (p1 && strcmp (g->sym->name, p1) == 0))
            continue;

          sym = find_keyword_arg (g->sym->name, f2_save);
          if (sym == NULL || !compare_type_rank (g->sym, sym)
              || ((gfc_option.allow_std & GFC_STD_F2008)
                  && ((sym->attr.allocatable && g->sym->attr.pointer)
                      || (sym->attr.pointer && g->sym->attr.allocatable))))
            return 1;
        }

    next:
      if (f1 != NULL)
        f1 = f1->next;
      if (f2 != NULL)
        f2 = f2->next;
    }

  return 0;
}


/* Check if the characteristics of two dummy arguments match,
   cf. F08:12.3.2.  */

static gfc_try
check_dummy_characteristics (gfc_symbol *s1, gfc_symbol *s2,
                             bool type_must_agree, char *errmsg, int err_len)
{
  /* Check type and rank.  */
  if (type_must_agree && !compare_type_rank (s2, s1))
    {
      snprintf (errmsg, err_len, "Type/rank mismatch in argument '%s'",
                s1->name);
      return FAILURE;
    }

  /* Check INTENT.  */
  if (s1->attr.intent != s2->attr.intent)
    {
      snprintf (errmsg, err_len, "INTENT mismatch in argument '%s'",
                s1->name);
      return FAILURE;
    }

  /* Check OPTIONAL attribute.  */
  if (s1->attr.optional != s2->attr.optional)
    {
      snprintf (errmsg, err_len, "OPTIONAL mismatch in argument '%s'",
                s1->name);
      return FAILURE;
    }

  /* Check ALLOCATABLE attribute.  */
  if (s1->attr.allocatable != s2->attr.allocatable)
    {
      snprintf (errmsg, err_len, "ALLOCATABLE mismatch in argument '%s'",
                s1->name);
      return FAILURE;
    }

  /* Check POINTER attribute.  */
  if (s1->attr.pointer != s2->attr.pointer)
    {
      snprintf (errmsg, err_len, "POINTER mismatch in argument '%s'",
                s1->name);
      return FAILURE;
    }

  /* Check TARGET attribute.  */
  if (s1->attr.target != s2->attr.target)
    {
      snprintf (errmsg, err_len, "TARGET mismatch in argument '%s'",
                s1->name);
      return FAILURE;
    }

  /* FIXME: Do more comprehensive testing of attributes, like e.g.
            ASYNCHRONOUS, CONTIGUOUS, VALUE, VOLATILE, etc.  */

  /* Check interface of dummy procedures.  */
  if (s1->attr.flavor == FL_PROCEDURE)
    {
      char err[200];
      if (!gfc_compare_interfaces (s1, s2, s2->name, 0, 1, err, sizeof(err),
                                   NULL, NULL))
        {
          snprintf (errmsg, err_len, "Interface mismatch in dummy procedure "
                    "'%s': %s", s1->name, err);
          return FAILURE;
        }
    }

  /* Check string length.  */
  if (s1->ts.type == BT_CHARACTER
      && s1->ts.u.cl && s1->ts.u.cl->length
      && s2->ts.u.cl && s2->ts.u.cl->length)
    {
      int compval = gfc_dep_compare_expr (s1->ts.u.cl->length,
                                          s2->ts.u.cl->length);
      switch (compval)
      {
        case -1:
        case  1:
        case -3:
          snprintf (errmsg, err_len, "Character length mismatch "
                    "in argument '%s'", s1->name);
          return FAILURE;

        case -2:
          /* FIXME: Implement a warning for this case.
          gfc_warning ("Possible character length mismatch in argument '%s'",
                       s1->name);*/
          break;

        case 0:
          break;

        default:
          gfc_internal_error ("check_dummy_characteristics: Unexpected result "
                              "%i of gfc_dep_compare_expr", compval);
          break;
      }
    }

  /* Check array shape.  */
  if (s1->as && s2->as)
    {
      int i, compval;
      gfc_expr *shape1, *shape2;

      if (s1->as->type != s2->as->type)
        {
          snprintf (errmsg, err_len, "Shape mismatch in argument '%s'",
                    s1->name);
          return FAILURE;
        }

      if (s1->as->type == AS_EXPLICIT)
        for (i = 0; i < s1->as->rank + s1->as->corank; i++)
          {
            shape1 = gfc_subtract (gfc_copy_expr (s1->as->upper[i]),
                                  gfc_copy_expr (s1->as->lower[i]));
            shape2 = gfc_subtract (gfc_copy_expr (s2->as->upper[i]),
                                  gfc_copy_expr (s2->as->lower[i]));
            compval = gfc_dep_compare_expr (shape1, shape2);
            gfc_free_expr (shape1);
            gfc_free_expr (shape2);
            switch (compval)
            {
              case -1:
              case  1:
              case -3:
                snprintf (errmsg, err_len, "Shape mismatch in dimension %i of "
                          "argument '%s'", i + 1, s1->name);
                return FAILURE;

              case -2:
                /* FIXME: Implement a warning for this case.
                gfc_warning ("Possible shape mismatch in argument '%s'",
                            s1->name);*/
                break;

              case 0:
                break;

              default:
                gfc_internal_error ("check_dummy_characteristics: Unexpected "
                                    "result %i of gfc_dep_compare_expr",
                                    compval);
                break;
            }
          }
    }
    
  return SUCCESS;
}


/* Check if the characteristics of two function results match,
   cf. F08:12.3.3.  */

static gfc_try
check_result_characteristics (gfc_symbol *s1, gfc_symbol *s2,
                              char *errmsg, int err_len)
{
  gfc_symbol *r1, *r2;

  r1 = s1->result ? s1->result : s1;
  r2 = s2->result ? s2->result : s2;

  if (r1->ts.type == BT_UNKNOWN)
    return SUCCESS;

  /* Check type and rank.  */
  if (!compare_type_rank (r1, r2))
    {
      snprintf (errmsg, err_len, "Type/rank mismatch in function result");
      return FAILURE;
    }

  /* Check ALLOCATABLE attribute.  */
  if (r1->attr.allocatable != r2->attr.allocatable)
    {
      snprintf (errmsg, err_len, "ALLOCATABLE attribute mismatch in "
                "function result");
      return FAILURE;
    }

  /* Check POINTER attribute.  */
  if (r1->attr.pointer != r2->attr.pointer)
    {
      snprintf (errmsg, err_len, "POINTER attribute mismatch in "
                "function result");
      return FAILURE;
    }

  /* Check CONTIGUOUS attribute.  */
  if (r1->attr.contiguous != r2->attr.contiguous)
    {
      snprintf (errmsg, err_len, "CONTIGUOUS attribute mismatch in "
                "function result");
      return FAILURE;
    }

  /* Check PROCEDURE POINTER attribute.  */
  if (r1 != s1 && r1->attr.proc_pointer != r2->attr.proc_pointer)
    {
      snprintf (errmsg, err_len, "PROCEDURE POINTER mismatch in "
                "function result");
      return FAILURE;
    }

  /* Check string length.  */
  if (r1->ts.type == BT_CHARACTER && r1->ts.u.cl && r2->ts.u.cl)
    {
      if (r1->ts.deferred != r2->ts.deferred)
        {
          snprintf (errmsg, err_len, "Character length mismatch "
                    "in function result");
          return FAILURE;
        }

      if (r1->ts.u.cl->length)
        {
          int compval = gfc_dep_compare_expr (r1->ts.u.cl->length,
                                              r2->ts.u.cl->length);
          switch (compval)
          {
            case -1:
            case  1:
            case -3:
              snprintf (errmsg, err_len, "Character length mismatch "
                        "in function result");
              return FAILURE;

            case -2:
              /* FIXME: Implement a warning for this case.
              snprintf (errmsg, err_len, "Possible character length mismatch "
                        "in function result");*/
              break;

            case 0:
              break;

            default:
              gfc_internal_error ("check_result_characteristics (1): Unexpected "
                                  "result %i of gfc_dep_compare_expr", compval);
              break;
          }
        }
    }

  /* Check array shape.  */
  if (!r1->attr.allocatable && !r1->attr.pointer && r1->as && r2->as)
    {
      int i, compval;
      gfc_expr *shape1, *shape2;

      if (r1->as->type != r2->as->type)
        {
          snprintf (errmsg, err_len, "Shape mismatch in function result");
          return FAILURE;
        }

      if (r1->as->type == AS_EXPLICIT)
        for (i = 0; i < r1->as->rank + r1->as->corank; i++)
          {
            shape1 = gfc_subtract (gfc_copy_expr (r1->as->upper[i]),
                                   gfc_copy_expr (r1->as->lower[i]));
            shape2 = gfc_subtract (gfc_copy_expr (r2->as->upper[i]),
                                   gfc_copy_expr (r2->as->lower[i]));
            compval = gfc_dep_compare_expr (shape1, shape2);
            gfc_free_expr (shape1);
            gfc_free_expr (shape2);
            switch (compval)
            {
              case -1:
              case  1:
              case -3:
                snprintf (errmsg, err_len, "Shape mismatch in dimension %i of "
                          "function result", i + 1);
                return FAILURE;

              case -2:
                /* FIXME: Implement a warning for this case.
                gfc_warning ("Possible shape mismatch in return value");*/
                break;

              case 0:
                break;

              default:
                gfc_internal_error ("check_result_characteristics (2): "
                                    "Unexpected result %i of "
                                    "gfc_dep_compare_expr", compval);
                break;
            }
          }
    }

  return SUCCESS;
}


/* 'Compare' two formal interfaces associated with a pair of symbols.
   We return nonzero if there exists an actual argument list that
   would be ambiguous between the two interfaces, zero otherwise.
   'strict_flag' specifies whether all the characteristics are
   required to match, which is not the case for ambiguity checks.
   'p1' and 'p2' are the PASS arguments of both procedures (if applicable).  */

int
gfc_compare_interfaces (gfc_symbol *s1, gfc_symbol *s2, const char *name2,
                        int generic_flag, int strict_flag,
                        char *errmsg, int err_len,
                        const char *p1, const char *p2)
{
  gfc_formal_arglist *f1, *f2;

  gcc_assert (name2 != NULL);

  if (s1->attr.function && (s2->attr.subroutine
      || (!s2->attr.function && s2->ts.type == BT_UNKNOWN
          && gfc_get_default_type (name2, s2->ns)->type == BT_UNKNOWN)))
    {
      if (errmsg != NULL)
        snprintf (errmsg, err_len, "'%s' is not a function", name2);
      return 0;
    }

  if (s1->attr.subroutine && s2->attr.function)
    {
      if (errmsg != NULL)
        snprintf (errmsg, err_len, "'%s' is not a subroutine", name2);
      return 0;
    }

  /* Do strict checks on all characteristics
     (for dummy procedures and procedure pointer assignments).  */
  if (!generic_flag && strict_flag)
    {
      if (s1->attr.function && s2->attr.function)
        {
          /* If both are functions, check result characteristics.  */
          if (check_result_characteristics (s1, s2, errmsg, err_len)
              == FAILURE)
            return 0;
        }

      if (s1->attr.pure && !s2->attr.pure)
        {
          snprintf (errmsg, err_len, "Mismatch in PURE attribute");
          return 0;
        }
      if (s1->attr.elemental && !s2->attr.elemental)
        {
          snprintf (errmsg, err_len, "Mismatch in ELEMENTAL attribute");
          return 0;
        }
    }

  if (s1->attr.if_source == IFSRC_UNKNOWN
      || s2->attr.if_source == IFSRC_UNKNOWN)
    return 1;

  f1 = s1->formal;
  f2 = s2->formal;

  if (f1 == NULL && f2 == NULL)
    return 1;                   /* Special case: No arguments.  */

  if (generic_flag)
    {
      if (count_types_test (f1, f2, p1, p2)
          || count_types_test (f2, f1, p2, p1))
        return 0;
      if (generic_correspondence (f1, f2, p1, p2)
          || generic_correspondence (f2, f1, p2, p1))
        return 0;
    }
  else
    /* Perform the abbreviated correspondence test for operators (the
       arguments cannot be optional and are always ordered correctly).
       This is also done when comparing interfaces for dummy procedures and in
       procedure pointer assignments.  */

    for (;;)
      {
        /* Check existence.  */
        if (f1 == NULL && f2 == NULL)
          break;
        if (f1 == NULL || f2 == NULL)
          {
            if (errmsg != NULL)
              snprintf (errmsg, err_len, "'%s' has the wrong number of "
                        "arguments", name2);
            return 0;
          }

        if (strict_flag)
          {
            /* Check all characteristics.  */
            if (check_dummy_characteristics (f1->sym, f2->sym,
                                             true, errmsg, err_len) == FAILURE)
              return 0;
          }
        else if (!compare_type_rank (f2->sym, f1->sym))
          {
            /* Only check type and rank.  */
            if (errmsg != NULL)
              snprintf (errmsg, err_len, "Type/rank mismatch in argument '%s'",
                        f1->sym->name);
            return 0;
          }

        f1 = f1->next;
        f2 = f2->next;
      }

  return 1;
}


/* Given a pointer to an interface pointer, remove duplicate
   interfaces and make sure that all symbols are either functions
   or subroutines, and all of the same kind.  Returns nonzero if
   something goes wrong.  */

static int
check_interface0 (gfc_interface *p, const char *interface_name)
{
  gfc_interface *psave, *q, *qlast;

  psave = p;
  for (; p; p = p->next)
    {
      /* Make sure all symbols in the interface have been defined as
         functions or subroutines.  */
      if (((!p->sym->attr.function && !p->sym->attr.subroutine)
           || !p->sym->attr.if_source)
          && p->sym->attr.flavor != FL_DERIVED)
        {
          if (p->sym->attr.external)
            gfc_error ("Procedure '%s' in %s at %L has no explicit interface",
                       p->sym->name, interface_name, &p->sym->declared_at);
          else
            gfc_error ("Procedure '%s' in %s at %L is neither function nor "
                       "subroutine", p->sym->name, interface_name,
                      &p->sym->declared_at);
          return 1;
        }

      /* Verify that procedures are either all SUBROUTINEs or all FUNCTIONs.  */
      if ((psave->sym->attr.function && !p->sym->attr.function
           && p->sym->attr.flavor != FL_DERIVED)
          || (psave->sym->attr.subroutine && !p->sym->attr.subroutine))
        {
          if (p->sym->attr.flavor != FL_DERIVED)
            gfc_error ("In %s at %L procedures must be either all SUBROUTINEs"
                       " or all FUNCTIONs", interface_name,
                       &p->sym->declared_at);
          else
            gfc_error ("In %s at %L procedures must be all FUNCTIONs as the "
                       "generic name is also the name of a derived type",
                       interface_name, &p->sym->declared_at);
          return 1;
        }

      /* F2003, C1207. F2008, C1207.  */
      if (p->sym->attr.proc == PROC_INTERNAL
          && gfc_notify_std (GFC_STD_F2008, "Internal procedure "
                             "'%s' in %s at %L", p->sym->name, interface_name,
                             &p->sym->declared_at) == FAILURE)
        return 1;
    }
  p = psave;

  /* Remove duplicate interfaces in this interface list.  */
  for (; p; p = p->next)
    {
      qlast = p;

      for (q = p->next; q;)
        {
          if (p->sym != q->sym)
            {
              qlast = q;
              q = q->next;
            }
          else
            {
              /* Duplicate interface.  */
              qlast->next = q->next;
              free (q);
              q = qlast->next;
            }
        }
    }

  return 0;
}


/* Check lists of interfaces to make sure that no two interfaces are
   ambiguous.  Duplicate interfaces (from the same symbol) are OK here.  */

static int
check_interface1 (gfc_interface *p, gfc_interface *q0,
                  int generic_flag, const char *interface_name,
                  bool referenced)
{
  gfc_interface *q;
  for (; p; p = p->next)
    for (q = q0; q; q = q->next)
      {
        if (p->sym == q->sym)
          continue;             /* Duplicates OK here.  */

        if (p->sym->name == q->sym->name && p->sym->module == q->sym->module)
          continue;

        if (p->sym->attr.flavor != FL_DERIVED
            && q->sym->attr.flavor != FL_DERIVED
            && gfc_compare_interfaces (p->sym, q->sym, q->sym->name,
                                       generic_flag, 0, NULL, 0, NULL, NULL))
          {
            if (referenced)
              gfc_error ("Ambiguous interfaces '%s' and '%s' in %s at %L",
                         p->sym->name, q->sym->name, interface_name,
                         &p->where);
            else if (!p->sym->attr.use_assoc && q->sym->attr.use_assoc)
              gfc_warning ("Ambiguous interfaces '%s' and '%s' in %s at %L",
                           p->sym->name, q->sym->name, interface_name,
                           &p->where);
            else
              gfc_warning ("Although not referenced, '%s' has ambiguous "
                           "interfaces at %L", interface_name, &p->where);
            return 1;
          }
      }
  return 0;
}


/* Check the generic and operator interfaces of symbols to make sure
   that none of the interfaces conflict.  The check has to be done
   after all of the symbols are actually loaded.  */

static void
check_sym_interfaces (gfc_symbol *sym)
{
  char interface_name[100];
  gfc_interface *p;

  if (sym->ns != gfc_current_ns)
    return;

  if (sym->generic != NULL)
    {
      sprintf (interface_name, "generic interface '%s'", sym->name);
      if (check_interface0 (sym->generic, interface_name))
        return;

      for (p = sym->generic; p; p = p->next)
        {
          if (sym->attr.access != ACCESS_PRIVATE)
            p->sym->attr.public_used = 1;

          if (p->sym->attr.mod_proc
              && (p->sym->attr.if_source != IFSRC_DECL
                  || p->sym->attr.procedure))
            {
              gfc_error ("'%s' at %L is not a module procedure",
                         p->sym->name, &p->where);
              return;
            }
        }

      /* Originally, this test was applied to host interfaces too;
         this is incorrect since host associated symbols, from any
         source, cannot be ambiguous with local symbols.  */
      check_interface1 (sym->generic, sym->generic, 1, interface_name,
                        sym->attr.referenced || !sym->attr.use_assoc);
    }
}


static void
check_uop_interfaces (gfc_user_op *uop)
{
  char interface_name[100];
  gfc_user_op *uop2;
  gfc_namespace *ns;
  gfc_interface *p;

  sprintf (interface_name, "operator interface '%s'", uop->name);
  if (check_interface0 (uop->op, interface_name))
    return;

  if (uop->access != ACCESS_PRIVATE)
    for (p = uop->op; p; p = p->next)
      p->sym->attr.public_used = 1;

  for (ns = gfc_current_ns; ns; ns = ns->parent)
    {
      uop2 = gfc_find_uop (uop->name, ns);
      if (uop2 == NULL)
        continue;

      check_interface1 (uop->op, uop2->op, 0,
                        interface_name, true);
    }
}

/* Given an intrinsic op, return an equivalent op if one exists,
   or INTRINSIC_NONE otherwise.  */

gfc_intrinsic_op
gfc_equivalent_op (gfc_intrinsic_op op)
{
  switch(op)
    {
    case INTRINSIC_EQ:
      return INTRINSIC_EQ_OS;

    case INTRINSIC_EQ_OS:
      return INTRINSIC_EQ;

    case INTRINSIC_NE:
      return INTRINSIC_NE_OS;

    case INTRINSIC_NE_OS:
      return INTRINSIC_NE;

    case INTRINSIC_GT:
      return INTRINSIC_GT_OS;

    case INTRINSIC_GT_OS:
      return INTRINSIC_GT;

    case INTRINSIC_GE:
      return INTRINSIC_GE_OS;

    case INTRINSIC_GE_OS:
      return INTRINSIC_GE;

    case INTRINSIC_LT:
      return INTRINSIC_LT_OS;

    case INTRINSIC_LT_OS:
      return INTRINSIC_LT;

    case INTRINSIC_LE:
      return INTRINSIC_LE_OS;

    case INTRINSIC_LE_OS:
      return INTRINSIC_LE;

    default:
      return INTRINSIC_NONE;
    }
}

/* For the namespace, check generic, user operator and intrinsic
   operator interfaces for consistency and to remove duplicate
   interfaces.  We traverse the whole namespace, counting on the fact
   that most symbols will not have generic or operator interfaces.  */

void
gfc_check_interfaces (gfc_namespace *ns)
{
  gfc_namespace *old_ns, *ns2;
  gfc_interface *p;
  char interface_name[100];
  int i;

  old_ns = gfc_current_ns;
  gfc_current_ns = ns;

  gfc_traverse_ns (ns, check_sym_interfaces);

  gfc_traverse_user_op (ns, check_uop_interfaces);

  for (i = GFC_INTRINSIC_BEGIN; i != GFC_INTRINSIC_END; i++)
    {
      if (i == INTRINSIC_USER)
        continue;

      if (i == INTRINSIC_ASSIGN)
        strcpy (interface_name, "intrinsic assignment operator");
      else
        sprintf (interface_name, "intrinsic '%s' operator",
                 gfc_op2string ((gfc_intrinsic_op) i));

      if (check_interface0 (ns->op[i], interface_name))
        continue;

      for (p = ns->op[i]; p; p = p->next)
        p->sym->attr.public_used = 1;


      if (ns->op[i])
        gfc_check_operator_interface (ns->op[i]->sym, (gfc_intrinsic_op) i,
                                      ns->op[i]->where);

      for (ns2 = ns; ns2; ns2 = ns2->parent)
        {
          gfc_intrinsic_op other_op;
          
          if (check_interface1 (ns->op[i], ns2->op[i], 0,
                                interface_name, true))
            goto done;

          /* i should be gfc_intrinsic_op, but has to be int with this cast
             here for stupid C++ compatibility rules.  */
          other_op = gfc_equivalent_op ((gfc_intrinsic_op) i);
          if (other_op != INTRINSIC_NONE
            &&  check_interface1 (ns->op[i], ns2->op[other_op],
                                  0, interface_name, true))
            goto done;
        }
    }

done:
  gfc_current_ns = old_ns;
}


static int
symbol_rank (gfc_symbol *sym)
{
  if (sym->ts.type == BT_CLASS && CLASS_DATA (sym)->as)
    return CLASS_DATA (sym)->as->rank;

  return (sym->as == NULL) ? 0 : sym->as->rank;
}


/* Given a symbol of a formal argument list and an expression, if the
   formal argument is allocatable, check that the actual argument is
   allocatable. Returns nonzero if compatible, zero if not compatible.  */

static int
compare_allocatable (gfc_symbol *formal, gfc_expr *actual)
{
  symbol_attribute attr;

  if (formal->attr.allocatable
      || (formal->ts.type == BT_CLASS && CLASS_DATA (formal)->attr.allocatable))
    {
      attr = gfc_expr_attr (actual);
      if (!attr.allocatable)
        return 0;
    }

  return 1;
}


/* Given a symbol of a formal argument list and an expression, if the
   formal argument is a pointer, see if the actual argument is a
   pointer. Returns nonzero if compatible, zero if not compatible.  */

static int
compare_pointer (gfc_symbol *formal, gfc_expr *actual)
{
  symbol_attribute attr;

  if (formal->attr.pointer
      || (formal->ts.type == BT_CLASS && CLASS_DATA (formal)
          && CLASS_DATA (formal)->attr.class_pointer))
    {
      attr = gfc_expr_attr (actual);

      /* Fortran 2008 allows non-pointer actual arguments.  */
      if (!attr.pointer && attr.target && formal->attr.intent == INTENT_IN)
        return 2;

      if (!attr.pointer)
        return 0;
    }

  return 1;
}


/* Emit clear error messages for rank mismatch.  */

static void
argument_rank_mismatch (const char *name, locus *where,
                        int rank1, int rank2)
{

  /* TS 29113, C407b.  */
  if (rank2 == -1)
    {
      gfc_error ("The assumed-rank array at %L requires that the dummy argument"
                 " '%s' has assumed-rank", where, name);
    }
  else if (rank1 == 0)
    {
      gfc_error ("Rank mismatch in argument '%s' at %L "
                 "(scalar and rank-%d)", name, where, rank2);
    }
  else if (rank2 == 0)
    {
      gfc_error ("Rank mismatch in argument '%s' at %L "
                 "(rank-%d and scalar)", name, where, rank1);
    }
  else
    {    
      gfc_error ("Rank mismatch in argument '%s' at %L "
                 "(rank-%d and rank-%d)", name, where, rank1, rank2);
    }
}


/* Given a symbol of a formal argument list and an expression, see if
   the two are compatible as arguments.  Returns nonzero if
   compatible, zero if not compatible.  */

static int
compare_parameter (gfc_symbol *formal, gfc_expr *actual,
                   int ranks_must_agree, int is_elemental, locus *where)
{
  gfc_ref *ref;
  bool rank_check, is_pointer;

  /* If the formal arg has type BT_VOID, it's to one of the iso_c_binding
     procs c_f_pointer or c_f_procpointer, and we need to accept most
     pointers the user could give us.  This should allow that.  */
  if (formal->ts.type == BT_VOID)
    return 1;

  if (formal->ts.type == BT_DERIVED
      && formal->ts.u.derived && formal->ts.u.derived->ts.is_iso_c
      && actual->ts.type == BT_DERIVED
      && actual->ts.u.derived && actual->ts.u.derived->ts.is_iso_c)
    return 1;

  if (formal->ts.type == BT_CLASS && actual->ts.type == BT_DERIVED)
    /* Make sure the vtab symbol is present when
       the module variables are generated.  */
    gfc_find_derived_vtab (actual->ts.u.derived);

  if (actual->ts.type == BT_PROCEDURE)
    {
      char err[200];
      gfc_symbol *act_sym = actual->symtree->n.sym;

      if (formal->attr.flavor != FL_PROCEDURE)
        {
          if (where)
            gfc_error ("Invalid procedure argument at %L", &actual->where);
          return 0;
        }

      if (!gfc_compare_interfaces (formal, act_sym, act_sym->name, 0, 1, err,
                                   sizeof(err), NULL, NULL))
        {
          if (where)
            gfc_error ("Interface mismatch in dummy procedure '%s' at %L: %s",
                       formal->name, &actual->where, err);
          return 0;
        }

      if (formal->attr.function && !act_sym->attr.function)
        {
          gfc_add_function (&act_sym->attr, act_sym->name,
          &act_sym->declared_at);
          if (act_sym->ts.type == BT_UNKNOWN
              && gfc_set_default_type (act_sym, 1, act_sym->ns) == FAILURE)
            return 0;
        }
      else if (formal->attr.subroutine && !act_sym->attr.subroutine)
        gfc_add_subroutine (&act_sym->attr, act_sym->name,
                            &act_sym->declared_at);

      return 1;
    }

  /* F2008, C1241.  */
  if (formal->attr.pointer && formal->attr.contiguous
      && !gfc_is_simply_contiguous (actual, true))
    {
      if (where)
        gfc_error ("Actual argument to contiguous pointer dummy '%s' at %L "
                   "must be simply contiguous", formal->name, &actual->where);
      return 0;
    }

  if ((actual->expr_type != EXPR_NULL || actual->ts.type != BT_UNKNOWN)
      && actual->ts.type != BT_HOLLERITH
      && formal->ts.type != BT_ASSUMED
      && !gfc_compare_types (&formal->ts, &actual->ts)
      && !(formal->ts.type == BT_DERIVED && actual->ts.type == BT_CLASS
           && gfc_compare_derived_types (formal->ts.u.derived, 
                                         CLASS_DATA (actual)->ts.u.derived)))
    {
      if (where)
        gfc_error ("Type mismatch in argument '%s' at %L; passed %s to %s",
                   formal->name, &actual->where, gfc_typename (&actual->ts),
                   gfc_typename (&formal->ts));
      return 0;
    }

  /* F2008, 12.5.2.5; IR F08/0073.  */
  if (formal->ts.type == BT_CLASS && actual->expr_type != EXPR_NULL
      && ((CLASS_DATA (formal)->attr.class_pointer
           && !formal->attr.intent == INTENT_IN)
          || CLASS_DATA (formal)->attr.allocatable))
    {
      if (actual->ts.type != BT_CLASS)
        {
          if (where)
            gfc_error ("Actual argument to '%s' at %L must be polymorphic",
                        formal->name, &actual->where);
          return 0;
        }
      if (!gfc_compare_derived_types (CLASS_DATA (actual)->ts.u.derived,
                                      CLASS_DATA (formal)->ts.u.derived))
        {
          if (where)
            gfc_error ("Actual argument to '%s' at %L must have the same "
                       "declared type", formal->name, &actual->where);
          return 0;
        }
    }

  if (formal->attr.codimension && !gfc_is_coarray (actual))
    {
      if (where)
        gfc_error ("Actual argument to '%s' at %L must be a coarray",
                       formal->name, &actual->where);
      return 0;
    }

  if (formal->attr.codimension && formal->attr.allocatable)
    {
      gfc_ref *last = NULL;

      for (ref = actual->ref; ref; ref = ref->next)
        if (ref->type == REF_COMPONENT)
          last = ref;

      /* F2008, 12.5.2.6.  */
      if ((last && last->u.c.component->as->corank != formal->as->corank)
          || (!last
              && actual->symtree->n.sym->as->corank != formal->as->corank))
        {
          if (where)
            gfc_error ("Corank mismatch in argument '%s' at %L (%d and %d)",
                   formal->name, &actual->where, formal->as->corank,
                   last ? last->u.c.component->as->corank
                        : actual->symtree->n.sym->as->corank);
          return 0;
        }
    }

  if (formal->attr.codimension)
    {
      /* F2008, 12.5.2.8.  */
      if (formal->attr.dimension
          && (formal->attr.contiguous || formal->as->type != AS_ASSUMED_SHAPE)
          && gfc_expr_attr (actual).dimension
          && !gfc_is_simply_contiguous (actual, true))
        {
          if (where)
            gfc_error ("Actual argument to '%s' at %L must be simply "
                       "contiguous", formal->name, &actual->where);
          return 0;
        }

      /* F2008, C1303 and C1304.  */
      if (formal->attr.intent != INTENT_INOUT
          && (((formal->ts.type == BT_DERIVED || formal->ts.type == BT_CLASS)
               && formal->ts.u.derived->from_intmod == INTMOD_ISO_FORTRAN_ENV
               && formal->ts.u.derived->intmod_sym_id == ISOFORTRAN_LOCK_TYPE)
              || formal->attr.lock_comp))

        {
          if (where)
            gfc_error ("Actual argument to non-INTENT(INOUT) dummy '%s' at %L, "
                       "which is LOCK_TYPE or has a LOCK_TYPE component",
                       formal->name, &actual->where);
          return 0;
        }
    }

  /* F2008, C1239/C1240.  */
  if (actual->expr_type == EXPR_VARIABLE
      && (actual->symtree->n.sym->attr.asynchronous
         || actual->symtree->n.sym->attr.volatile_)
      &&  (formal->attr.asynchronous || formal->attr.volatile_)
      && actual->rank && !gfc_is_simply_contiguous (actual, true)
      && ((formal->as->type != AS_ASSUMED_SHAPE && !formal->attr.pointer)
          || formal->attr.contiguous))
    {
      if (where)
        gfc_error ("Dummy argument '%s' has to be a pointer or assumed-shape "
                   "array without CONTIGUOUS attribute - as actual argument at"
                   " %L is not simply contiguous and both are ASYNCHRONOUS "
                   "or VOLATILE", formal->name, &actual->where);
      return 0;
    }

  if (formal->attr.allocatable && !formal->attr.codimension
      && gfc_expr_attr (actual).codimension)
    {
      if (formal->attr.intent == INTENT_OUT)
        {
          if (where)
            gfc_error ("Passing coarray at %L to allocatable, noncoarray, "
                       "INTENT(OUT) dummy argument '%s'", &actual->where,
                       formal->name);
            return 0;
        }
      else if (gfc_option.warn_surprising && where
               && formal->attr.intent != INTENT_IN)
        gfc_warning ("Passing coarray at %L to allocatable, noncoarray dummy "
                     "argument '%s', which is invalid if the allocation status"
                     " is modified",  &actual->where, formal->name);
    }

  /* If the rank is the same or the formal argument has assumed-rank.  */
  if (symbol_rank (formal) == actual->rank || symbol_rank (formal) == -1)
    return 1;

  if (actual->ts.type == BT_CLASS && CLASS_DATA (actual)->as
        && CLASS_DATA (actual)->as->rank == symbol_rank (formal))
    return 1;

  rank_check = where != NULL && !is_elemental && formal->as
               && (formal->as->type == AS_ASSUMED_SHAPE
                   || formal->as->type == AS_DEFERRED)
               && actual->expr_type != EXPR_NULL;

  /* Scalar & coindexed, see: F2008, Section 12.5.2.4.  */
  if (rank_check || ranks_must_agree
      || (formal->attr.pointer && actual->expr_type != EXPR_NULL)
      || (actual->rank != 0 && !(is_elemental || formal->attr.dimension))
      || (actual->rank == 0
          && ((formal->ts.type == BT_CLASS
               && CLASS_DATA (formal)->as->type == AS_ASSUMED_SHAPE)
              || (formal->ts.type != BT_CLASS
                   && formal->as->type == AS_ASSUMED_SHAPE))
          && actual->expr_type != EXPR_NULL)
      || (actual->rank == 0 && formal->attr.dimension
          && gfc_is_coindexed (actual)))
    {
      if (where)
        argument_rank_mismatch (formal->name, &actual->where,
                                symbol_rank (formal), actual->rank);
      return 0;
    }
  else if (actual->rank != 0 && (is_elemental || formal->attr.dimension))
    return 1;

  /* At this point, we are considering a scalar passed to an array.   This
     is valid (cf. F95 12.4.1.1, F2003 12.4.1.2, and F2008 12.5.2.4),
     - if the actual argument is (a substring of) an element of a
       non-assumed-shape/non-pointer/non-polymorphic array; or
     - (F2003) if the actual argument is of type character of default/c_char
       kind.  */

  is_pointer = actual->expr_type == EXPR_VARIABLE
               ? actual->symtree->n.sym->attr.pointer : false;

  for (ref = actual->ref; ref; ref = ref->next)
    {
      if (ref->type == REF_COMPONENT)
        is_pointer = ref->u.c.component->attr.pointer;
      else if (ref->type == REF_ARRAY && ref->u.ar.type == AR_ELEMENT
               && ref->u.ar.dimen > 0
               && (!ref->next 
                   || (ref->next->type == REF_SUBSTRING && !ref->next->next)))
        break;
    }

  if (actual->ts.type == BT_CLASS && actual->expr_type != EXPR_NULL)
    {
      if (where)
        gfc_error ("Polymorphic scalar passed to array dummy argument '%s' "
                   "at %L", formal->name, &actual->where);
      return 0;
    }

  if (actual->expr_type != EXPR_NULL && ref && actual->ts.type != BT_CHARACTER
      && (is_pointer || ref->u.ar.as->type == AS_ASSUMED_SHAPE))
    {
      if (where)
        gfc_error ("Element of assumed-shaped or pointer "
                   "array passed to array dummy argument '%s' at %L",
                   formal->name, &actual->where);
      return 0;
    }

  if (actual->ts.type == BT_CHARACTER && actual->expr_type != EXPR_NULL
      && (!ref || is_pointer || ref->u.ar.as->type == AS_ASSUMED_SHAPE))
    {
      if (formal->ts.kind != 1 && (gfc_option.allow_std & GFC_STD_GNU) == 0)
        {
          if (where)
            gfc_error ("Extension: Scalar non-default-kind, non-C_CHAR-kind "
                       "CHARACTER actual argument with array dummy argument "
                       "'%s' at %L", formal->name, &actual->where);
          return 0;
        }

      if (where && (gfc_option.allow_std & GFC_STD_F2003) == 0)
        {
          gfc_error ("Fortran 2003: Scalar CHARACTER actual argument with "
                     "array dummy argument '%s' at %L",
                     formal->name, &actual->where);
          return 0;
        }
      else if ((gfc_option.allow_std & GFC_STD_F2003) == 0)
        return 0;
      else
        return 1;
    }

  if (ref == NULL && actual->expr_type != EXPR_NULL)
    {
      if (where)
        argument_rank_mismatch (formal->name, &actual->where,
                                symbol_rank (formal), actual->rank);
      return 0;
    }

  return 1;
}


/* Returns the storage size of a symbol (formal argument) or
   zero if it cannot be determined.  */

static unsigned long
get_sym_storage_size (gfc_symbol *sym)
{
  int i;
  unsigned long strlen, elements;

  if (sym->ts.type == BT_CHARACTER)
    {
      if (sym->ts.u.cl && sym->ts.u.cl->length
          && sym->ts.u.cl->length->expr_type == EXPR_CONSTANT)
        strlen = mpz_get_ui (sym->ts.u.cl->length->value.integer);
      else
        return 0;
    }
  else
    strlen = 1; 

  if (symbol_rank (sym) == 0)
    return strlen;

  elements = 1;
  if (sym->as->type != AS_EXPLICIT)
    return 0;
  for (i = 0; i < sym->as->rank; i++)
    {
      if (sym->as->upper[i]->expr_type != EXPR_CONSTANT
          || sym->as->lower[i]->expr_type != EXPR_CONSTANT)
        return 0;

      elements *= mpz_get_si (sym->as->upper[i]->value.integer)
                  - mpz_get_si (sym->as->lower[i]->value.integer) + 1L;
    }

  return strlen*elements;
}


/* Returns the storage size of an expression (actual argument) or
   zero if it cannot be determined. For an array element, it returns
   the remaining size as the element sequence consists of all storage
   units of the actual argument up to the end of the array.  */

static unsigned long
get_expr_storage_size (gfc_expr *e)
{
  int i;
  long int strlen, elements;
  long int substrlen = 0;
  bool is_str_storage = false;
  gfc_ref *ref;

  if (e == NULL)
    return 0;
  
  if (e->ts.type == BT_CHARACTER)
    {
      if (e->ts.u.cl && e->ts.u.cl->length
          && e->ts.u.cl->length->expr_type == EXPR_CONSTANT)
        strlen = mpz_get_si (e->ts.u.cl->length->value.integer);
      else if (e->expr_type == EXPR_CONSTANT
               && (e->ts.u.cl == NULL || e->ts.u.cl->length == NULL))
        strlen = e->value.character.length;
      else
        return 0;
    }
  else
    strlen = 1; /* Length per element.  */

  if (e->rank == 0 && !e->ref)
    return strlen;

  elements = 1;
  if (!e->ref)
    {
      if (!e->shape)
        return 0;
      for (i = 0; i < e->rank; i++)
        elements *= mpz_get_si (e->shape[i]);
      return elements*strlen;
    }

  for (ref = e->ref; ref; ref = ref->next)
    {
      if (ref->type == REF_SUBSTRING && ref->u.ss.start
          && ref->u.ss.start->expr_type == EXPR_CONSTANT)
        {
          if (is_str_storage)
            {
              /* The string length is the substring length.
                 Set now to full string length.  */
              if (!ref->u.ss.length || !ref->u.ss.length->length
                  || ref->u.ss.length->length->expr_type != EXPR_CONSTANT)
                return 0;

              strlen = mpz_get_ui (ref->u.ss.length->length->value.integer);
            }
          substrlen = strlen - mpz_get_ui (ref->u.ss.start->value.integer) + 1;
          continue;
        }

      if (ref->type == REF_ARRAY && ref->u.ar.type == AR_SECTION)
        for (i = 0; i < ref->u.ar.dimen; i++)
          {
            long int start, end, stride;
            stride = 1;

            if (ref->u.ar.stride[i])
              {
                if (ref->u.ar.stride[i]->expr_type == EXPR_CONSTANT)
                  stride = mpz_get_si (ref->u.ar.stride[i]->value.integer);
                else
                  return 0;
              }

            if (ref->u.ar.start[i])
              {
                if (ref->u.ar.start[i]->expr_type == EXPR_CONSTANT)
                  start = mpz_get_si (ref->u.ar.start[i]->value.integer);
                else
                  return 0;
              }
            else if (ref->u.ar.as->lower[i]
                     && ref->u.ar.as->lower[i]->expr_type == EXPR_CONSTANT)
              start = mpz_get_si (ref->u.ar.as->lower[i]->value.integer);
            else
              return 0;

            if (ref->u.ar.end[i])
              {
                if (ref->u.ar.end[i]->expr_type == EXPR_CONSTANT)
                  end = mpz_get_si (ref->u.ar.end[i]->value.integer);
                else
                  return 0;
              }
            else if (ref->u.ar.as->upper[i]
                     && ref->u.ar.as->upper[i]->expr_type == EXPR_CONSTANT)
              end = mpz_get_si (ref->u.ar.as->upper[i]->value.integer);
            else
              return 0;

            elements *= (end - start)/stride + 1L;
          }
      else if (ref->type == REF_ARRAY && ref->u.ar.type == AR_FULL)
        for (i = 0; i < ref->u.ar.as->rank; i++)
          {
            if (ref->u.ar.as->lower[i] && ref->u.ar.as->upper[i]
                && ref->u.ar.as->lower[i]->expr_type == EXPR_CONSTANT
                && ref->u.ar.as->upper[i]->expr_type == EXPR_CONSTANT)
              elements *= mpz_get_si (ref->u.ar.as->upper[i]->value.integer)
                          - mpz_get_si (ref->u.ar.as->lower[i]->value.integer)
                          + 1L;
            else
              return 0;
          }
      else if (ref->type == REF_ARRAY && ref->u.ar.type == AR_ELEMENT
               && e->expr_type == EXPR_VARIABLE)
        {
          if (ref->u.ar.as->type == AS_ASSUMED_SHAPE
              || e->symtree->n.sym->attr.pointer)
            {
              elements = 1;
              continue;
            }

          /* Determine the number of remaining elements in the element
             sequence for array element designators.  */
          is_str_storage = true;
          for (i = ref->u.ar.dimen - 1; i >= 0; i--)
            {
              if (ref->u.ar.start[i] == NULL
                  || ref->u.ar.start[i]->expr_type != EXPR_CONSTANT
                  || ref->u.ar.as->upper[i] == NULL
                  || ref->u.ar.as->lower[i] == NULL
                  || ref->u.ar.as->upper[i]->expr_type != EXPR_CONSTANT
                  || ref->u.ar.as->lower[i]->expr_type != EXPR_CONSTANT)
                return 0;

              elements
                   = elements
                     * (mpz_get_si (ref->u.ar.as->upper[i]->value.integer)
                        - mpz_get_si (ref->u.ar.as->lower[i]->value.integer)
                        + 1L)
                     - (mpz_get_si (ref->u.ar.start[i]->value.integer)
                        - mpz_get_si (ref->u.ar.as->lower[i]->value.integer));
            }
        }
    }

  if (substrlen)
    return (is_str_storage) ? substrlen + (elements-1)*strlen
                            : elements*strlen;
  else
    return elements*strlen;
}


/* Given an expression, check whether it is an array section
   which has a vector subscript. If it has, one is returned,
   otherwise zero.  */

int
gfc_has_vector_subscript (gfc_expr *e)
{
  int i;
  gfc_ref *ref;

  if (e == NULL || e->rank == 0 || e->expr_type != EXPR_VARIABLE)
    return 0;

  for (ref = e->ref; ref; ref = ref->next)
    if (ref->type == REF_ARRAY && ref->u.ar.type == AR_SECTION)
      for (i = 0; i < ref->u.ar.dimen; i++)
        if (ref->u.ar.dimen_type[i] == DIMEN_VECTOR)
          return 1;

  return 0;
}


/* Given formal and actual argument lists, see if they are compatible.
   If they are compatible, the actual argument list is sorted to
   correspond with the formal list, and elements for missing optional
   arguments are inserted. If WHERE pointer is nonnull, then we issue
   errors when things don't match instead of just returning the status
   code.  */

static int
compare_actual_formal (gfc_actual_arglist **ap, gfc_formal_arglist *formal,
                       int ranks_must_agree, int is_elemental, locus *where)
{
  gfc_actual_arglist **new_arg, *a, *actual, temp;
  gfc_formal_arglist *f;
  int i, n, na;
  unsigned long actual_size, formal_size;
  bool full_array = false;

  actual = *ap;

  if (actual == NULL && formal == NULL)
    return 1;

  n = 0;
  for (f = formal; f; f = f->next)
    n++;

  new_arg = XALLOCAVEC (gfc_actual_arglist *, n);

  for (i = 0; i < n; i++)
    new_arg[i] = NULL;

  na = 0;
  f = formal;
  i = 0;

  for (a = actual; a; a = a->next, f = f->next)
    {
      /* Look for keywords but ignore g77 extensions like %VAL.  */
      if (a->name != NULL && a->name[0] != '%')
        {
          i = 0;
          for (f = formal; f; f = f->next, i++)
            {
              if (f->sym == NULL)
                continue;
              if (strcmp (f->sym->name, a->name) == 0)
                break;
            }

          if (f == NULL)
            {
              if (where)
                gfc_error ("Keyword argument '%s' at %L is not in "
                           "the procedure", a->name, &a->expr->where);
              return 0;
            }

          if (new_arg[i] != NULL)
            {
              if (where)
                gfc_error ("Keyword argument '%s' at %L is already associated "
                           "with another actual argument", a->name,
                           &a->expr->where);
              return 0;
            }
        }

      if (f == NULL)
        {
          if (where)
            gfc_error ("More actual than formal arguments in procedure "
                       "call at %L", where);

          return 0;
        }

      if (f->sym == NULL && a->expr == NULL)
        goto match;

      if (f->sym == NULL)
        {
          if (where)
            gfc_error ("Missing alternate return spec in subroutine call "
                       "at %L", where);
          return 0;
        }

      if (a->expr == NULL)
        {
          if (where)
            gfc_error ("Unexpected alternate return spec in subroutine "
                       "call at %L", where);
          return 0;
        }

      if (a->expr->expr_type == EXPR_NULL
          && ((f->sym->ts.type != BT_CLASS && !f->sym->attr.pointer
               && (f->sym->attr.allocatable || !f->sym->attr.optional
                   || (gfc_option.allow_std & GFC_STD_F2008) == 0))
              || (f->sym->ts.type == BT_CLASS
                  && !CLASS_DATA (f->sym)->attr.class_pointer
                  && (CLASS_DATA (f->sym)->attr.allocatable
                      || !f->sym->attr.optional
                      || (gfc_option.allow_std & GFC_STD_F2008) == 0))))
        {
          if (where
              && (!f->sym->attr.optional
                  || (f->sym->ts.type != BT_CLASS && f->sym->attr.allocatable)
                  || (f->sym->ts.type == BT_CLASS
                         && CLASS_DATA (f->sym)->attr.allocatable)))
            gfc_error ("Unexpected NULL() intrinsic at %L to dummy '%s'",
                       where, f->sym->name);
          else if (where)
            gfc_error ("Fortran 2008: Null pointer at %L to non-pointer "
                       "dummy '%s'", where, f->sym->name);

          return 0;
        }
      
      if (!compare_parameter (f->sym, a->expr, ranks_must_agree,
                              is_elemental, where))
        return 0;

      /* TS 29113, 6.3p2.  */
      if (f->sym->ts.type == BT_ASSUMED
          && (a->expr->ts.type == BT_DERIVED
              || (a->expr->ts.type == BT_CLASS && CLASS_DATA (a->expr))))
        {
          gfc_namespace *f2k_derived;

          f2k_derived = a->expr->ts.type == BT_DERIVED
                        ? a->expr->ts.u.derived->f2k_derived
                        : CLASS_DATA (a->expr)->ts.u.derived->f2k_derived;

          if (f2k_derived
              && (f2k_derived->finalizers || f2k_derived->tb_sym_root))
            {
              gfc_error ("Actual argument at %L to assumed-type dummy is of "
                         "derived type with type-bound or FINAL procedures",
                         &a->expr->where);
              return FAILURE;
            }
        }

      /* Special case for character arguments.  For allocatable, pointer
         and assumed-shape dummies, the string length needs to match
         exactly.  */
      if (a->expr->ts.type == BT_CHARACTER
           && a->expr->ts.u.cl && a->expr->ts.u.cl->length
           && a->expr->ts.u.cl->length->expr_type == EXPR_CONSTANT
           && f->sym->ts.u.cl && f->sym->ts.u.cl && f->sym->ts.u.cl->length
           && f->sym->ts.u.cl->length->expr_type == EXPR_CONSTANT
           && (f->sym->attr.pointer || f->sym->attr.allocatable
               || (f->sym->as && f->sym->as->type == AS_ASSUMED_SHAPE))
           && (mpz_cmp (a->expr->ts.u.cl->length->value.integer,
                        f->sym->ts.u.cl->length->value.integer) != 0))
         {
           if (where && (f->sym->attr.pointer || f->sym->attr.allocatable))
             gfc_warning ("Character length mismatch (%ld/%ld) between actual "
                          "argument and pointer or allocatable dummy argument "
                          "'%s' at %L",
                          mpz_get_si (a->expr->ts.u.cl->length->value.integer),
                          mpz_get_si (f->sym->ts.u.cl->length->value.integer),
                          f->sym->name, &a->expr->where);
           else if (where)
             gfc_warning ("Character length mismatch (%ld/%ld) between actual "
                          "argument and assumed-shape dummy argument '%s' "
                          "at %L",
                          mpz_get_si (a->expr->ts.u.cl->length->value.integer),
                          mpz_get_si (f->sym->ts.u.cl->length->value.integer),
                          f->sym->name, &a->expr->where);
           return 0;
         }

      if ((f->sym->attr.pointer || f->sym->attr.allocatable)
            && f->sym->ts.deferred != a->expr->ts.deferred
            && a->expr->ts.type == BT_CHARACTER)
        {
          if (where)
            gfc_error ("Actual argument at %L to allocatable or "
                       "pointer dummy argument '%s' must have a deferred "
                       "length type parameter if and only if the dummy has one",
                       &a->expr->where, f->sym->name);
          return 0;
        }

      if (f->sym->ts.type == BT_CLASS)
        goto skip_size_check;

      actual_size = get_expr_storage_size (a->expr);
      formal_size = get_sym_storage_size (f->sym);
      if (actual_size != 0 && actual_size < formal_size
          && a->expr->ts.type != BT_PROCEDURE
          && f->sym->attr.flavor != FL_PROCEDURE)
        {
          if (a->expr->ts.type == BT_CHARACTER && !f->sym->as && where)
            gfc_warning ("Character length of actual argument shorter "
                         "than of dummy argument '%s' (%lu/%lu) at %L",
                         f->sym->name, actual_size, formal_size,
                         &a->expr->where);
          else if (where)
            gfc_warning ("Actual argument contains too few "
                         "elements for dummy argument '%s' (%lu/%lu) at %L",
                         f->sym->name, actual_size, formal_size,
                         &a->expr->where);
          return  0;
        }

     skip_size_check:

      /* Satisfy F03:12.4.1.3 by ensuring that a procedure pointer actual
         argument is provided for a procedure pointer formal argument.  */
      if (f->sym->attr.proc_pointer
          && !((a->expr->expr_type == EXPR_VARIABLE
                && a->expr->symtree->n.sym->attr.proc_pointer)
               || (a->expr->expr_type == EXPR_FUNCTION
                   && a->expr->symtree->n.sym->result->attr.proc_pointer)
               || gfc_is_proc_ptr_comp (a->expr)))
        {
          if (where)
            gfc_error ("Expected a procedure pointer for argument '%s' at %L",
                       f->sym->name, &a->expr->where);
          return 0;
        }

      /* Satisfy F03:12.4.1.3 by ensuring that a procedure actual argument is
         provided for a procedure formal argument.  */
      if (f->sym->attr.flavor == FL_PROCEDURE
          && gfc_expr_attr (a->expr).flavor != FL_PROCEDURE)
        {
          if (where)
            gfc_error ("Expected a procedure for argument '%s' at %L",
                       f->sym->name, &a->expr->where);
          return 0;
        }

      if (f->sym->as && f->sym->as->type == AS_ASSUMED_SHAPE
          && a->expr->expr_type == EXPR_VARIABLE
          && a->expr->symtree->n.sym->as
          && a->expr->symtree->n.sym->as->type == AS_ASSUMED_SIZE
          && (a->expr->ref == NULL
              || (a->expr->ref->type == REF_ARRAY
                  && a->expr->ref->u.ar.type == AR_FULL)))
        {
          if (where)
            gfc_error ("Actual argument for '%s' cannot be an assumed-size"
                       " array at %L", f->sym->name, where);
          return 0;
        }

      if (a->expr->expr_type != EXPR_NULL
          && compare_pointer (f->sym, a->expr) == 0)
        {
          if (where)
            gfc_error ("Actual argument for '%s' must be a pointer at %L",
                       f->sym->name, &a->expr->where);
          return 0;
        }

      if (a->expr->expr_type != EXPR_NULL
          && (gfc_option.allow_std & GFC_STD_F2008) == 0
          && compare_pointer (f->sym, a->expr) == 2)
        {
          if (where)
            gfc_error ("Fortran 2008: Non-pointer actual argument at %L to "
                       "pointer dummy '%s'", &a->expr->where,f->sym->name);
          return 0;
        }
        

      /* Fortran 2008, C1242.  */
      if (f->sym->attr.pointer && gfc_is_coindexed (a->expr))
        {
          if (where)
            gfc_error ("Coindexed actual argument at %L to pointer "
                       "dummy '%s'",
                       &a->expr->where, f->sym->name);
          return 0;
        }

      /* Fortran 2008, 12.5.2.5 (no constraint).  */
      if (a->expr->expr_type == EXPR_VARIABLE
          && f->sym->attr.intent != INTENT_IN
          && f->sym->attr.allocatable
          && gfc_is_coindexed (a->expr))
        {
          if (where)
            gfc_error ("Coindexed actual argument at %L to allocatable "
                       "dummy '%s' requires INTENT(IN)",
                       &a->expr->where, f->sym->name);
          return 0;
        }

      /* Fortran 2008, C1237.  */
      if (a->expr->expr_type == EXPR_VARIABLE
          && (f->sym->attr.asynchronous || f->sym->attr.volatile_)
          && gfc_is_coindexed (a->expr)
          && (a->expr->symtree->n.sym->attr.volatile_
              || a->expr->symtree->n.sym->attr.asynchronous))
        {
          if (where)
            gfc_error ("Coindexed ASYNCHRONOUS or VOLATILE actual argument at "
                       "%L requires that dummy '%s' has neither "
                       "ASYNCHRONOUS nor VOLATILE", &a->expr->where,
                       f->sym->name);
          return 0;
        }

      /* Fortran 2008, 12.5.2.4 (no constraint).  */
      if (a->expr->expr_type == EXPR_VARIABLE
          && f->sym->attr.intent != INTENT_IN && !f->sym->attr.value
          && gfc_is_coindexed (a->expr)
          && gfc_has_ultimate_allocatable (a->expr))
        {
          if (where)
            gfc_error ("Coindexed actual argument at %L with allocatable "
                       "ultimate component to dummy '%s' requires either VALUE "
                       "or INTENT(IN)", &a->expr->where, f->sym->name);
          return 0;
        }

     if (f->sym->ts.type == BT_CLASS
           && CLASS_DATA (f->sym)->attr.allocatable
           && gfc_is_class_array_ref (a->expr, &full_array)
           && !full_array)
        {
          if (where)
            gfc_error ("Actual CLASS array argument for '%s' must be a full "
                       "array at %L", f->sym->name, &a->expr->where);
          return 0;
        }


      if (a->expr->expr_type != EXPR_NULL
          && compare_allocatable (f->sym, a->expr) == 0)
        {
          if (where)
            gfc_error ("Actual argument for '%s' must be ALLOCATABLE at %L",
                       f->sym->name, &a->expr->where);
          return 0;
        }

      /* Check intent = OUT/INOUT for definable actual argument.  */
      if ((f->sym->attr.intent == INTENT_OUT
          || f->sym->attr.intent == INTENT_INOUT))
        {
          const char* context = (where
                                 ? _("actual argument to INTENT = OUT/INOUT")
                                 : NULL);

          if (((f->sym->ts.type == BT_CLASS && f->sym->attr.class_ok
                && CLASS_DATA (f->sym)->attr.class_pointer)
               || (f->sym->ts.type != BT_CLASS && f->sym->attr.pointer))
              && gfc_check_vardef_context (a->expr, true, false, context)
                   == FAILURE)
            return 0;
          if (gfc_check_vardef_context (a->expr, false, false, context)
                == FAILURE)
            return 0;
        }

      if ((f->sym->attr.intent == INTENT_OUT
           || f->sym->attr.intent == INTENT_INOUT
           || f->sym->attr.volatile_
           || f->sym->attr.asynchronous)
          && gfc_has_vector_subscript (a->expr))
        {
          if (where)
            gfc_error ("Array-section actual argument with vector "
                       "subscripts at %L is incompatible with INTENT(OUT), "
                       "INTENT(INOUT), VOLATILE or ASYNCHRONOUS attribute "
                       "of the dummy argument '%s'",
                       &a->expr->where, f->sym->name);
          return 0;
        }

      /* C1232 (R1221) For an actual argument which is an array section or
         an assumed-shape array, the dummy argument shall be an assumed-
         shape array, if the dummy argument has the VOLATILE attribute.  */

      if (f->sym->attr.volatile_
          && a->expr->symtree->n.sym->as
          && a->expr->symtree->n.sym->as->type == AS_ASSUMED_SHAPE
          && !(f->sym->as && f->sym->as->type == AS_ASSUMED_SHAPE))
        {
          if (where)
            gfc_error ("Assumed-shape actual argument at %L is "
                       "incompatible with the non-assumed-shape "
                       "dummy argument '%s' due to VOLATILE attribute",
                       &a->expr->where,f->sym->name);
          return 0;
        }

      if (f->sym->attr.volatile_
          && a->expr->ref && a->expr->ref->u.ar.type == AR_SECTION
          && !(f->sym->as && f->sym->as->type == AS_ASSUMED_SHAPE))
        {
          if (where)
            gfc_error ("Array-section actual argument at %L is "
                       "incompatible with the non-assumed-shape "
                       "dummy argument '%s' due to VOLATILE attribute",
                       &a->expr->where,f->sym->name);
          return 0;
        }

      /* C1233 (R1221) For an actual argument which is a pointer array, the
         dummy argument shall be an assumed-shape or pointer array, if the
         dummy argument has the VOLATILE attribute.  */

      if (f->sym->attr.volatile_
          && a->expr->symtree->n.sym->attr.pointer
          && a->expr->symtree->n.sym->as
          && !(f->sym->as
               && (f->sym->as->type == AS_ASSUMED_SHAPE
                   || f->sym->attr.pointer)))
        {
          if (where)
            gfc_error ("Pointer-array actual argument at %L requires "
                       "an assumed-shape or pointer-array dummy "
                       "argument '%s' due to VOLATILE attribute",
                       &a->expr->where,f->sym->name);
          return 0;
        }

    match:
      if (a == actual)
        na = i;

      new_arg[i++] = a;
    }

  /* Make sure missing actual arguments are optional.  */
  i = 0;
  for (f = formal; f; f = f->next, i++)
    {
      if (new_arg[i] != NULL)
        continue;
      if (f->sym == NULL)
        {
          if (where)
            gfc_error ("Missing alternate return spec in subroutine call "
                       "at %L", where);
          return 0;
        }
      if (!f->sym->attr.optional)
        {
          if (where)
            gfc_error ("Missing actual argument for argument '%s' at %L",
                       f->sym->name, where);
          return 0;
        }
    }

  /* The argument lists are compatible.  We now relink a new actual
     argument list with null arguments in the right places.  The head
     of the list remains the head.  */
  for (i = 0; i < n; i++)
    if (new_arg[i] == NULL)
      new_arg[i] = gfc_get_actual_arglist ();

  if (na != 0)
    {
      temp = *new_arg[0];
      *new_arg[0] = *actual;
      *actual = temp;

      a = new_arg[0];
      new_arg[0] = new_arg[na];
      new_arg[na] = a;
    }

  for (i = 0; i < n - 1; i++)
    new_arg[i]->next = new_arg[i + 1];

  new_arg[i]->next = NULL;

  if (*ap == NULL && n > 0)
    *ap = new_arg[0];

  /* Note the types of omitted optional arguments.  */
  for (a = *ap, f = formal; a; a = a->next, f = f->next)
    if (a->expr == NULL && a->label == NULL)
      a->missing_arg_type = f->sym->ts.type;

  return 1;
}


typedef struct
{
  gfc_formal_arglist *f;
  gfc_actual_arglist *a;
}
argpair;

/* qsort comparison function for argument pairs, with the following
   order:
    - p->a->expr == NULL
    - p->a->expr->expr_type != EXPR_VARIABLE
    - growing p->a->expr->symbol.  */

static int
pair_cmp (const void *p1, const void *p2)
{
  const gfc_actual_arglist *a1, *a2;

  /* *p1 and *p2 are elements of the to-be-sorted array.  */
  a1 = ((const argpair *) p1)->a;
  a2 = ((const argpair *) p2)->a;
  if (!a1->expr)
    {
      if (!a2->expr)
        return 0;
      return -1;
    }
  if (!a2->expr)
    return 1;
  if (a1->expr->expr_type != EXPR_VARIABLE)
    {
      if (a2->expr->expr_type != EXPR_VARIABLE)
        return 0;
      return -1;
    }
  if (a2->expr->expr_type != EXPR_VARIABLE)
    return 1;
  return a1->expr->symtree->n.sym < a2->expr->symtree->n.sym;
}


/* Given two expressions from some actual arguments, test whether they
   refer to the same expression. The analysis is conservative.
   Returning FAILURE will produce no warning.  */

static gfc_try
compare_actual_expr (gfc_expr *e1, gfc_expr *e2)
{
  const gfc_ref *r1, *r2;

  if (!e1 || !e2
      || e1->expr_type != EXPR_VARIABLE
      || e2->expr_type != EXPR_VARIABLE
      || e1->symtree->n.sym != e2->symtree->n.sym)
    return FAILURE;

  /* TODO: improve comparison, see expr.c:show_ref().  */
  for (r1 = e1->ref, r2 = e2->ref; r1 && r2; r1 = r1->next, r2 = r2->next)
    {
      if (r1->type != r2->type)
        return FAILURE;
      switch (r1->type)
        {
        case REF_ARRAY:
          if (r1->u.ar.type != r2->u.ar.type)
            return FAILURE;
          /* TODO: At the moment, consider only full arrays;
             we could do better.  */
          if (r1->u.ar.type != AR_FULL || r2->u.ar.type != AR_FULL)
            return FAILURE;
          break;

        case REF_COMPONENT:
          if (r1->u.c.component != r2->u.c.component)
            return FAILURE;
          break;

        case REF_SUBSTRING:
          return FAILURE;

        default:
          gfc_internal_error ("compare_actual_expr(): Bad component code");
        }
    }
  if (!r1 && !r2)
    return SUCCESS;
  return FAILURE;
}


/* Given formal and actual argument lists that correspond to one
   another, check that identical actual arguments aren't not
   associated with some incompatible INTENTs.  */

static gfc_try
check_some_aliasing (gfc_formal_arglist *f, gfc_actual_arglist *a)
{
  sym_intent f1_intent, f2_intent;
  gfc_formal_arglist *f1;
  gfc_actual_arglist *a1;
  size_t n, i, j;
  argpair *p;
  gfc_try t = SUCCESS;

  n = 0;
  for (f1 = f, a1 = a;; f1 = f1->next, a1 = a1->next)
    {
      if (f1 == NULL && a1 == NULL)
        break;
      if (f1 == NULL || a1 == NULL)
        gfc_internal_error ("check_some_aliasing(): List mismatch");
      n++;
    }
  if (n == 0)
    return t;
  p = XALLOCAVEC (argpair, n);

  for (i = 0, f1 = f, a1 = a; i < n; i++, f1 = f1->next, a1 = a1->next)
    {
      p[i].f = f1;
      p[i].a = a1;
    }

  qsort (p, n, sizeof (argpair), pair_cmp);

  for (i = 0; i < n; i++)
    {
      if (!p[i].a->expr
          || p[i].a->expr->expr_type != EXPR_VARIABLE
          || p[i].a->expr->ts.type == BT_PROCEDURE)
        continue;
      f1_intent = p[i].f->sym->attr.intent;
      for (j = i + 1; j < n; j++)
        {
          /* Expected order after the sort.  */
          if (!p[j].a->expr || p[j].a->expr->expr_type != EXPR_VARIABLE)
            gfc_internal_error ("check_some_aliasing(): corrupted data");

          /* Are the expression the same?  */
          if (compare_actual_expr (p[i].a->expr, p[j].a->expr) == FAILURE)
            break;
          f2_intent = p[j].f->sym->attr.intent;
          if ((f1_intent == INTENT_IN && f2_intent == INTENT_OUT)
              || (f1_intent == INTENT_OUT && f2_intent == INTENT_IN))
            {
              gfc_warning ("Same actual argument associated with INTENT(%s) "
                           "argument '%s' and INTENT(%s) argument '%s' at %L",
                           gfc_intent_string (f1_intent), p[i].f->sym->name,
                           gfc_intent_string (f2_intent), p[j].f->sym->name,
                           &p[i].a->expr->where);
              t = FAILURE;
            }
        }
    }

  return t;
}


/* Given formal and actual argument lists that correspond to one
   another, check that they are compatible in the sense that intents
   are not mismatched.  */

static gfc_try
check_intents (gfc_formal_arglist *f, gfc_actual_arglist *a)
{
  sym_intent f_intent;

  for (;; f = f->next, a = a->next)
    {
      if (f == NULL && a == NULL)
        break;
      if (f == NULL || a == NULL)
        gfc_internal_error ("check_intents(): List mismatch");

      if (a->expr == NULL || a->expr->expr_type != EXPR_VARIABLE)
        continue;

      f_intent = f->sym->attr.intent;

      if (gfc_pure (NULL) && gfc_impure_variable (a->expr->symtree->n.sym))
        {
          if ((f->sym->ts.type == BT_CLASS && f->sym->attr.class_ok
               && CLASS_DATA (f->sym)->attr.class_pointer)
              || (f->sym->ts.type != BT_CLASS && f->sym->attr.pointer))
            {
              gfc_error ("Procedure argument at %L is local to a PURE "
                         "procedure and has the POINTER attribute",
                         &a->expr->where);
              return FAILURE;
            }
        }

       /* Fortran 2008, C1283.  */
       if (gfc_pure (NULL) && gfc_is_coindexed (a->expr))
        {
          if (f_intent == INTENT_INOUT || f_intent == INTENT_OUT)
            {
              gfc_error ("Coindexed actual argument at %L in PURE procedure "
                         "is passed to an INTENT(%s) argument",
                         &a->expr->where, gfc_intent_string (f_intent));
              return FAILURE;
            }

          if ((f->sym->ts.type == BT_CLASS && f->sym->attr.class_ok
               && CLASS_DATA (f->sym)->attr.class_pointer)
              || (f->sym->ts.type != BT_CLASS && f->sym->attr.pointer))
            {
              gfc_error ("Coindexed actual argument at %L in PURE procedure "
                         "is passed to a POINTER dummy argument",
                         &a->expr->where);
              return FAILURE;
            }
        }

       /* F2008, Section 12.5.2.4.  */
       if (a->expr->ts.type == BT_CLASS && f->sym->ts.type == BT_CLASS
           && gfc_is_coindexed (a->expr))
         {
           gfc_error ("Coindexed polymorphic actual argument at %L is passed "
                      "polymorphic dummy argument '%s'",
                         &a->expr->where, f->sym->name);
           return FAILURE;
         }
    }

  return SUCCESS;
}


/* Check how a procedure is used against its interface.  If all goes
   well, the actual argument list will also end up being properly
   sorted.  */

gfc_try
gfc_procedure_use (gfc_symbol *sym, gfc_actual_arglist **ap, locus *where)
{
  /* Warn about calls with an implicit interface.  Special case
     for calling a ISO_C_BINDING becase c_loc and c_funloc
     are pseudo-unknown.  Additionally, warn about procedures not
     explicitly declared at all if requested.  */
  if (sym->attr.if_source == IFSRC_UNKNOWN && ! sym->attr.is_iso_c)
    {
      if (gfc_option.warn_implicit_interface)
        gfc_warning ("Procedure '%s' called with an implicit interface at %L",
                     sym->name, where);
      else if (gfc_option.warn_implicit_procedure
               && sym->attr.proc == PROC_UNKNOWN)
        gfc_warning ("Procedure '%s' called at %L is not explicitly declared",
                     sym->name, where);
    }

  if (sym->attr.if_source == IFSRC_UNKNOWN)
    {
      gfc_actual_arglist *a;

      if (sym->attr.pointer)
        {
          gfc_error("The pointer object '%s' at %L must have an explicit "
                    "function interface or be declared as array",
                    sym->name, where);
          return FAILURE;
        }

      if (sym->attr.allocatable && !sym->attr.external)
        {
          gfc_error("The allocatable object '%s' at %L must have an explicit "
                    "function interface or be declared as array",
                    sym->name, where);
          return FAILURE;
        }

      if (sym->attr.allocatable)
        {
          gfc_error("Allocatable function '%s' at %L must have an explicit "
                    "function interface", sym->name, where);
          return FAILURE;
        }

      for (a = *ap; a; a = a->next)
        {
          /* Skip g77 keyword extensions like %VAL, %REF, %LOC.  */
          if (a->name != NULL && a->name[0] != '%')
            {
              gfc_error("Keyword argument requires explicit interface "
                        "for procedure '%s' at %L", sym->name, &a->expr->where);
              break;
            }

          /* TS 29113, 6.2.  */
          if (a->expr && a->expr->ts.type == BT_ASSUMED
              && sym->intmod_sym_id != ISOCBINDING_LOC)
            {
              gfc_error ("Assumed-type argument %s at %L requires an explicit "
                         "interface", a->expr->symtree->n.sym->name,
                         &a->expr->where);
              break;
            }

          /* F2008, C1303 and C1304.  */
          if (a->expr
              && (a->expr->ts.type == BT_DERIVED || a->expr->ts.type == BT_CLASS)
              && ((a->expr->ts.u.derived->from_intmod == INTMOD_ISO_FORTRAN_ENV
                   && a->expr->ts.u.derived->intmod_sym_id == ISOFORTRAN_LOCK_TYPE)
                  || gfc_expr_attr (a->expr).lock_comp))
            {
              gfc_error("Actual argument of LOCK_TYPE or with LOCK_TYPE "
                        "component at %L requires an explicit interface for "
                        "procedure '%s'", &a->expr->where, sym->name);
              break;
            }

          if (a->expr && a->expr->expr_type == EXPR_NULL
              && a->expr->ts.type == BT_UNKNOWN)
            {
              gfc_error ("MOLD argument to NULL required at %L", &a->expr->where);
              return FAILURE;
            }

          /* TS 29113, C407b.  */
          if (a->expr && a->expr->expr_type == EXPR_VARIABLE
              && symbol_rank (a->expr->symtree->n.sym) == -1)
            {
              gfc_error ("Assumed-rank argument requires an explicit interface "
                         "at %L", &a->expr->where);
              return FAILURE;
            }
        }

      return SUCCESS;
    }

  if (!compare_actual_formal (ap, sym->formal, 0, sym->attr.elemental, where))
    return FAILURE;

  if (check_intents (sym->formal, *ap) == FAILURE)
    return FAILURE;

  if (gfc_option.warn_aliasing)
    check_some_aliasing (sym->formal, *ap);

  return SUCCESS;
}


/* Check how a procedure pointer component is used against its interface.
   If all goes well, the actual argument list will also end up being properly
   sorted. Completely analogous to gfc_procedure_use.  */

void
gfc_ppc_use (gfc_component *comp, gfc_actual_arglist **ap, locus *where)
{

  /* Warn about calls with an implicit interface.  Special case
     for calling a ISO_C_BINDING becase c_loc and c_funloc
     are pseudo-unknown.  */
  if (gfc_option.warn_implicit_interface
      && comp->attr.if_source == IFSRC_UNKNOWN
      && !comp->attr.is_iso_c)
    gfc_warning ("Procedure pointer component '%s' called with an implicit "
                 "interface at %L", comp->name, where);

  if (comp->attr.if_source == IFSRC_UNKNOWN)
    {
      gfc_actual_arglist *a;
      for (a = *ap; a; a = a->next)
        {
          /* Skip g77 keyword extensions like %VAL, %REF, %LOC.  */
          if (a->name != NULL && a->name[0] != '%')
            {
              gfc_error("Keyword argument requires explicit interface "
                        "for procedure pointer component '%s' at %L",
                        comp->name, &a->expr->where);
              break;
            }
        }

      return;
    }

  if (!compare_actual_formal (ap, comp->formal, 0, comp->attr.elemental, where))
    return;

  check_intents (comp->formal, *ap);
  if (gfc_option.warn_aliasing)
    check_some_aliasing (comp->formal, *ap);
}


/* Try if an actual argument list matches the formal list of a symbol,
   respecting the symbol's attributes like ELEMENTAL.  This is used for
   GENERIC resolution.  */

bool
gfc_arglist_matches_symbol (gfc_actual_arglist** args, gfc_symbol* sym)
{
  bool r;

  gcc_assert (sym->attr.flavor == FL_PROCEDURE);

  r = !sym->attr.elemental;
  if (compare_actual_formal (args, sym->formal, r, !r, NULL))
    {
      check_intents (sym->formal, *args);
      if (gfc_option.warn_aliasing)
        check_some_aliasing (sym->formal, *args);
      return true;
    }

  return false;
}


/* Given an interface pointer and an actual argument list, search for
   a formal argument list that matches the actual.  If found, returns
   a pointer to the symbol of the correct interface.  Returns NULL if
   not found.  */

gfc_symbol *
gfc_search_interface (gfc_interface *intr, int sub_flag,
                      gfc_actual_arglist **ap)
{
  gfc_symbol *elem_sym = NULL;
  gfc_symbol *null_sym = NULL;
  locus null_expr_loc;
  gfc_actual_arglist *a;
  bool has_null_arg = false;

  for (a = *ap; a; a = a->next)
    if (a->expr && a->expr->expr_type == EXPR_NULL
        && a->expr->ts.type == BT_UNKNOWN)
      {
        has_null_arg = true;
        null_expr_loc = a->expr->where;
        break;
      } 

  for (; intr; intr = intr->next)
    {
      if (intr->sym->attr.flavor == FL_DERIVED)
        continue;
      if (sub_flag && intr->sym->attr.function)
        continue;
      if (!sub_flag && intr->sym->attr.subroutine)
        continue;

      if (gfc_arglist_matches_symbol (ap, intr->sym))
        {
          if (has_null_arg && null_sym)
            {
              gfc_error ("MOLD= required in NULL() argument at %L: Ambiguity "
                         "between specific functions %s and %s",
                         &null_expr_loc, null_sym->name, intr->sym->name);
              return NULL;
            }
          else if (has_null_arg)
            {
              null_sym = intr->sym;
              continue;
            }

          /* Satisfy 12.4.4.1 such that an elemental match has lower
             weight than a non-elemental match.  */ 
          if (intr->sym->attr.elemental)
            {
              elem_sym = intr->sym;
              continue;
            }
          return intr->sym;
        }
    }

  if (null_sym)
    return null_sym;

  return elem_sym ? elem_sym : NULL;
}


/* Do a brute force recursive search for a symbol.  */

static gfc_symtree *
find_symtree0 (gfc_symtree *root, gfc_symbol *sym)
{
  gfc_symtree * st;

  if (root->n.sym == sym)
    return root;

  st = NULL;
  if (root->left)
    st = find_symtree0 (root->left, sym);
  if (root->right && ! st)
    st = find_symtree0 (root->right, sym);
  return st;
}


/* Find a symtree for a symbol.  */

gfc_symtree *
gfc_find_sym_in_symtree (gfc_symbol *sym)
{
  gfc_symtree *st;
  gfc_namespace *ns;

  /* First try to find it by name.  */
  gfc_find_sym_tree (sym->name, gfc_current_ns, 1, &st);
  if (st && st->n.sym == sym)
    return st;

  /* If it's been renamed, resort to a brute-force search.  */
  /* TODO: avoid having to do this search.  If the symbol doesn't exist
     in the symtree for the current namespace, it should probably be added.  */
  for (ns = gfc_current_ns; ns; ns = ns->parent)
    {
      st = find_symtree0 (ns->sym_root, sym);
      if (st)
        return st;
    }
  gfc_internal_error ("Unable to find symbol %s", sym->name);
  /* Not reached.  */
}


/* See if the arglist to an operator-call contains a derived-type argument
   with a matching type-bound operator.  If so, return the matching specific
   procedure defined as operator-target as well as the base-object to use
   (which is the found derived-type argument with operator).  The generic
   name, if any, is transmitted to the final expression via 'gname'.  */

static gfc_typebound_proc*
matching_typebound_op (gfc_expr** tb_base,
                       gfc_actual_arglist* args,
                       gfc_intrinsic_op op, const char* uop,
                       const char ** gname)
{
  gfc_actual_arglist* base;

  for (base = args; base; base = base->next)
    if (base->expr->ts.type == BT_DERIVED || base->expr->ts.type == BT_CLASS)
      {
        gfc_typebound_proc* tb;
        gfc_symbol* derived;
        gfc_try result;

        while (base->expr->expr_type == EXPR_OP
               && base->expr->value.op.op == INTRINSIC_PARENTHESES)
          base->expr = base->expr->value.op.op1;

        if (base->expr->ts.type == BT_CLASS)
          {
            if (CLASS_DATA (base->expr) == NULL
                || !gfc_expr_attr (base->expr).class_ok)
              continue;
            derived = CLASS_DATA (base->expr)->ts.u.derived;
          }
        else
          derived = base->expr->ts.u.derived;

        if (op == INTRINSIC_USER)
          {
            gfc_symtree* tb_uop;

            gcc_assert (uop);
            tb_uop = gfc_find_typebound_user_op (derived, &result, uop,
                                                 false, NULL);

            if (tb_uop)
              tb = tb_uop->n.tb;
            else
              tb = NULL;
          }
        else
          tb = gfc_find_typebound_intrinsic_op (derived, &result, op,
                                                false, NULL);

        /* This means we hit a PRIVATE operator which is use-associated and
           should thus not be seen.  */
        if (result == FAILURE)
          tb = NULL;

        /* Look through the super-type hierarchy for a matching specific
           binding.  */
        for (; tb; tb = tb->overridden)
          {
            gfc_tbp_generic* g;

            gcc_assert (tb->is_generic);
            for (g = tb->u.generic; g; g = g->next)
              {
                gfc_symbol* target;
                gfc_actual_arglist* argcopy;
                bool matches;

                gcc_assert (g->specific);
                if (g->specific->error)
                  continue;

                target = g->specific->u.specific->n.sym;

                /* Check if this arglist matches the formal.  */
                argcopy = gfc_copy_actual_arglist (args);
                matches = gfc_arglist_matches_symbol (&argcopy, target);
                gfc_free_actual_arglist (argcopy);

                /* Return if we found a match.  */
                if (matches)
                  {
                    *tb_base = base->expr;
                    *gname = g->specific_st->name;
                    return g->specific;
                  }
              }
          }
      }

  return NULL;
}


/* For the 'actual arglist' of an operator call and a specific typebound
   procedure that has been found the target of a type-bound operator, build the
   appropriate EXPR_COMPCALL and resolve it.  We take this indirection over
   type-bound procedures rather than resolving type-bound operators 'directly'
   so that we can reuse the existing logic.  */

static void
build_compcall_for_operator (gfc_expr* e, gfc_actual_arglist* actual,
                             gfc_expr* base, gfc_typebound_proc* target,
                             const char *gname)
{
  e->expr_type = EXPR_COMPCALL;
  e->value.compcall.tbp = target;
  e->value.compcall.name = gname ? gname : "$op";
  e->value.compcall.actual = actual;
  e->value.compcall.base_object = base;
  e->value.compcall.ignore_pass = 1;
  e->value.compcall.assign = 0;
  if (e->ts.type == BT_UNKNOWN
        && target->function)
    {
      if (target->is_generic)
        e->ts = target->u.generic->specific->u.specific->n.sym->ts;
      else
        e->ts = target->u.specific->n.sym->ts;
    }
}


/* This subroutine is called when an expression is being resolved.
   The expression node in question is either a user defined operator
   or an intrinsic operator with arguments that aren't compatible
   with the operator.  This subroutine builds an actual argument list
   corresponding to the operands, then searches for a compatible
   interface.  If one is found, the expression node is replaced with
   the appropriate function call. We use the 'match' enum to specify
   whether a replacement has been made or not, or if an error occurred.  */

match
gfc_extend_expr (gfc_expr *e)
{
  gfc_actual_arglist *actual;
  gfc_symbol *sym;
  gfc_namespace *ns;
  gfc_user_op *uop;
  gfc_intrinsic_op i;
  const char *gname;

  sym = NULL;

  actual = gfc_get_actual_arglist ();
  actual->expr = e->value.op.op1;

  gname = NULL;

  if (e->value.op.op2 != NULL)
    {
      actual->next = gfc_get_actual_arglist ();
      actual->next->expr = e->value.op.op2;
    }

  i = fold_unary_intrinsic (e->value.op.op);

  if (i == INTRINSIC_USER)
    {
      for (ns = gfc_current_ns; ns; ns = ns->parent)
        {
          uop = gfc_find_uop (e->value.op.uop->name, ns);
          if (uop == NULL)
            continue;

          sym = gfc_search_interface (uop->op, 0, &actual);
          if (sym != NULL)
            break;
        }
    }
  else
    {
      for (ns = gfc_current_ns; ns; ns = ns->parent)
        {
          /* Due to the distinction between '==' and '.eq.' and friends, one has
             to check if either is defined.  */
          switch (i)
            {
#define CHECK_OS_COMPARISON(comp) \
  case INTRINSIC_##comp: \
  case INTRINSIC_##comp##_OS: \
    sym = gfc_search_interface (ns->op[INTRINSIC_##comp], 0, &actual); \
    if (!sym) \
      sym = gfc_search_interface (ns->op[INTRINSIC_##comp##_OS], 0, &actual); \
    break;
              CHECK_OS_COMPARISON(EQ)
              CHECK_OS_COMPARISON(NE)
              CHECK_OS_COMPARISON(GT)
              CHECK_OS_COMPARISON(GE)
              CHECK_OS_COMPARISON(LT)
              CHECK_OS_COMPARISON(LE)
#undef CHECK_OS_COMPARISON

              default:
                sym = gfc_search_interface (ns->op[i], 0, &actual);
            }

          if (sym != NULL)
            break;
        }
    }

  /* TODO: Do an ambiguity-check and error if multiple matching interfaces are
     found rather than just taking the first one and not checking further.  */

  if (sym == NULL)
    {
      gfc_typebound_proc* tbo;
      gfc_expr* tb_base;

      /* See if we find a matching type-bound operator.  */
      if (i == INTRINSIC_USER)
        tbo = matching_typebound_op (&tb_base, actual,
                                     i, e->value.op.uop->name, &gname);
      else
        switch (i)
          {
#define CHECK_OS_COMPARISON(comp) \
  case INTRINSIC_##comp: \
  case INTRINSIC_##comp##_OS: \
    tbo = matching_typebound_op (&tb_base, actual, \
                                 INTRINSIC_##comp, NULL, &gname); \
    if (!tbo) \
      tbo = matching_typebound_op (&tb_base, actual, \
                                   INTRINSIC_##comp##_OS, NULL, &gname); \
    break;
            CHECK_OS_COMPARISON(EQ)
            CHECK_OS_COMPARISON(NE)
            CHECK_OS_COMPARISON(GT)
            CHECK_OS_COMPARISON(GE)
            CHECK_OS_COMPARISON(LT)
            CHECK_OS_COMPARISON(LE)
#undef CHECK_OS_COMPARISON

            default:
              tbo = matching_typebound_op (&tb_base, actual, i, NULL, &gname);
              break;
          }
              
      /* If there is a matching typebound-operator, replace the expression with
         a call to it and succeed.  */
      if (tbo)
        {
          gfc_try result;

          gcc_assert (tb_base);
          build_compcall_for_operator (e, actual, tb_base, tbo, gname);

          result = gfc_resolve_expr (e);
          if (result == FAILURE)
            return MATCH_ERROR;

          return MATCH_YES;
        }

      /* Don't use gfc_free_actual_arglist().  */
      free (actual->next);
      free (actual);

      return MATCH_NO;
    }

  /* Change the expression node to a function call.  */
  e->expr_type = EXPR_FUNCTION;
  e->symtree = gfc_find_sym_in_symtree (sym);
  e->value.function.actual = actual;
  e->value.function.esym = NULL;
  e->value.function.isym = NULL;
  e->value.function.name = NULL;
  e->user_operator = 1;

  if (gfc_resolve_expr (e) == FAILURE)
    return MATCH_ERROR;

  return MATCH_YES;
}


/* Tries to replace an assignment code node with a subroutine call to
   the subroutine associated with the assignment operator.  Return
   SUCCESS if the node was replaced.  On FAILURE, no error is
   generated.  */

gfc_try
gfc_extend_assign (gfc_code *c, gfc_namespace *ns)
{
  gfc_actual_arglist *actual;
  gfc_expr *lhs, *rhs;
  gfc_symbol *sym;
  const char *gname;

  gname = NULL;

  lhs = c->expr1;
  rhs = c->expr2;

  /* Don't allow an intrinsic assignment to be replaced.  */
  if (lhs->ts.type != BT_DERIVED && lhs->ts.type != BT_CLASS
      && (rhs->rank == 0 || rhs->rank == lhs->rank)
      && (lhs->ts.type == rhs->ts.type
          || (gfc_numeric_ts (&lhs->ts) && gfc_numeric_ts (&rhs->ts))))
    return FAILURE;

  actual = gfc_get_actual_arglist ();
  actual->expr = lhs;

  actual->next = gfc_get_actual_arglist ();
  actual->next->expr = rhs;

  sym = NULL;

  for (; ns; ns = ns->parent)
    {
      sym = gfc_search_interface (ns->op[INTRINSIC_ASSIGN], 1, &actual);
      if (sym != NULL)
        break;
    }

  /* TODO: Ambiguity-check, see above for gfc_extend_expr.  */

  if (sym == NULL)
    {
      gfc_typebound_proc* tbo;
      gfc_expr* tb_base;

      /* See if we find a matching type-bound assignment.  */
      tbo = matching_typebound_op (&tb_base, actual,
                                   INTRINSIC_ASSIGN, NULL, &gname);
              
      /* If there is one, replace the expression with a call to it and
         succeed.  */
      if (tbo)
        {
          gcc_assert (tb_base);
          c->expr1 = gfc_get_expr ();
          build_compcall_for_operator (c->expr1, actual, tb_base, tbo, gname);
          c->expr1->value.compcall.assign = 1;
          c->expr1->where = c->loc;
          c->expr2 = NULL;
          c->op = EXEC_COMPCALL;

          /* c is resolved from the caller, so no need to do it here.  */

          return SUCCESS;
        }

      free (actual->next);
      free (actual);
      return FAILURE;
    }

  /* Replace the assignment with the call.  */
  c->op = EXEC_ASSIGN_CALL;
  c->symtree = gfc_find_sym_in_symtree (sym);
  c->expr1 = NULL;
  c->expr2 = NULL;
  c->ext.actual = actual;

  return SUCCESS;
}


/* Make sure that the interface just parsed is not already present in
   the given interface list.  Ambiguity isn't checked yet since module
   procedures can be present without interfaces.  */

gfc_try
gfc_check_new_interface (gfc_interface *base, gfc_symbol *new_sym, locus loc)
{
  gfc_interface *ip;

  for (ip = base; ip; ip = ip->next)
    {
      if (ip->sym == new_sym)
        {
          gfc_error ("Entity '%s' at %L is already present in the interface",
                     new_sym->name, &loc);
          return FAILURE;
        }
    }

  return SUCCESS;
}


/* Add a symbol to the current interface.  */

gfc_try
gfc_add_interface (gfc_symbol *new_sym)
{
  gfc_interface **head, *intr;
  gfc_namespace *ns;
  gfc_symbol *sym;

  switch (current_interface.type)
    {
    case INTERFACE_NAMELESS:
    case INTERFACE_ABSTRACT:
      return SUCCESS;

    case INTERFACE_INTRINSIC_OP:
      for (ns = current_interface.ns; ns; ns = ns->parent)
        switch (current_interface.op)
          {
            case INTRINSIC_EQ:
            case INTRINSIC_EQ_OS:
              if (gfc_check_new_interface (ns->op[INTRINSIC_EQ], new_sym,
                                           gfc_current_locus) == FAILURE
                  || gfc_check_new_interface (ns->op[INTRINSIC_EQ_OS], new_sym,
                                              gfc_current_locus) == FAILURE)
                return FAILURE;
              break;

            case INTRINSIC_NE:
            case INTRINSIC_NE_OS:
              if (gfc_check_new_interface (ns->op[INTRINSIC_NE], new_sym,
                                           gfc_current_locus) == FAILURE
                  || gfc_check_new_interface (ns->op[INTRINSIC_NE_OS], new_sym,
                                              gfc_current_locus) == FAILURE)
                return FAILURE;
              break;

            case INTRINSIC_GT:
            case INTRINSIC_GT_OS:
              if (gfc_check_new_interface (ns->op[INTRINSIC_GT], new_sym,
                                           gfc_current_locus) == FAILURE
                  || gfc_check_new_interface (ns->op[INTRINSIC_GT_OS], new_sym,
                                              gfc_current_locus) == FAILURE)
                return FAILURE;
              break;

            case INTRINSIC_GE:
            case INTRINSIC_GE_OS:
              if (gfc_check_new_interface (ns->op[INTRINSIC_GE], new_sym,
                                           gfc_current_locus) == FAILURE
                  || gfc_check_new_interface (ns->op[INTRINSIC_GE_OS], new_sym,
                                              gfc_current_locus) == FAILURE)
                return FAILURE;
              break;

            case INTRINSIC_LT:
            case INTRINSIC_LT_OS:
              if (gfc_check_new_interface (ns->op[INTRINSIC_LT], new_sym,
                                           gfc_current_locus) == FAILURE
                  || gfc_check_new_interface (ns->op[INTRINSIC_LT_OS], new_sym,
                                              gfc_current_locus) == FAILURE)
                return FAILURE;
              break;

            case INTRINSIC_LE:
            case INTRINSIC_LE_OS:
              if (gfc_check_new_interface (ns->op[INTRINSIC_LE], new_sym,
                                           gfc_current_locus) == FAILURE
                  || gfc_check_new_interface (ns->op[INTRINSIC_LE_OS], new_sym,
                                              gfc_current_locus) == FAILURE)
                return FAILURE;
              break;

            default:
              if (gfc_check_new_interface (ns->op[current_interface.op], new_sym,
                                           gfc_current_locus) == FAILURE)
                return FAILURE;
          }

      head = &current_interface.ns->op[current_interface.op];
      break;

    case INTERFACE_GENERIC:
      for (ns = current_interface.ns; ns; ns = ns->parent)
        {
          gfc_find_symbol (current_interface.sym->name, ns, 0, &sym);
          if (sym == NULL)
            continue;

          if (gfc_check_new_interface (sym->generic, new_sym, gfc_current_locus)
              == FAILURE)
            return FAILURE;
        }

      head = &current_interface.sym->generic;
      break;

    case INTERFACE_USER_OP:
      if (gfc_check_new_interface (current_interface.uop->op, new_sym,
                                   gfc_current_locus) == FAILURE)
        return FAILURE;

      head = &current_interface.uop->op;
      break;

    default:
      gfc_internal_error ("gfc_add_interface(): Bad interface type");
    }

  intr = gfc_get_interface ();
  intr->sym = new_sym;
  intr->where = gfc_current_locus;

  intr->next = *head;
  *head = intr;

  return SUCCESS;
}


gfc_interface *
gfc_current_interface_head (void)
{
  switch (current_interface.type)
    {
      case INTERFACE_INTRINSIC_OP:
        return current_interface.ns->op[current_interface.op];
        break;

      case INTERFACE_GENERIC:
        return current_interface.sym->generic;
        break;

      case INTERFACE_USER_OP:
        return current_interface.uop->op;
        break;

      default:
        gcc_unreachable ();
    }
}


void
gfc_set_current_interface_head (gfc_interface *i)
{
  switch (current_interface.type)
    {
      case INTERFACE_INTRINSIC_OP:
        current_interface.ns->op[current_interface.op] = i;
        break;

      case INTERFACE_GENERIC:
        current_interface.sym->generic = i;
        break;

      case INTERFACE_USER_OP:
        current_interface.uop->op = i;
        break;

      default:
        gcc_unreachable ();
    }
}


/* Gets rid of a formal argument list.  We do not free symbols.
   Symbols are freed when a namespace is freed.  */

void
gfc_free_formal_arglist (gfc_formal_arglist *p)
{
  gfc_formal_arglist *q;

  for (; p; p = q)
    {
      q = p->next;
      free (p);
    }
}


/* Check that it is ok for the type-bound procedure 'proc' to override the
   procedure 'old', cf. F08:4.5.7.3.  */

gfc_try
gfc_check_typebound_override (gfc_symtree* proc, gfc_symtree* old)
{
  locus where;
  gfc_symbol *proc_target, *old_target;
  unsigned proc_pass_arg, old_pass_arg, argpos;
  gfc_formal_arglist *proc_formal, *old_formal;
  bool check_type;
  char err[200];

  /* This procedure should only be called for non-GENERIC proc.  */
  gcc_assert (!proc->n.tb->is_generic);

  /* If the overwritten procedure is GENERIC, this is an error.  */
  if (old->n.tb->is_generic)
    {
      gfc_error ("Can't overwrite GENERIC '%s' at %L",
                 old->name, &proc->n.tb->where);
      return FAILURE;
    }

  where = proc->n.tb->where;
  proc_target = proc->n.tb->u.specific->n.sym;
  old_target = old->n.tb->u.specific->n.sym;

  /* Check that overridden binding is not NON_OVERRIDABLE.  */
  if (old->n.tb->non_overridable)
    {
      gfc_error ("'%s' at %L overrides a procedure binding declared"
                 " NON_OVERRIDABLE", proc->name, &where);
      return FAILURE;
    }

  /* It's an error to override a non-DEFERRED procedure with a DEFERRED one.  */
  if (!old->n.tb->deferred && proc->n.tb->deferred)
    {
      gfc_error ("'%s' at %L must not be DEFERRED as it overrides a"
                 " non-DEFERRED binding", proc->name, &where);
      return FAILURE;
    }

  /* If the overridden binding is PURE, the overriding must be, too.  */
  if (old_target->attr.pure && !proc_target->attr.pure)
    {
      gfc_error ("'%s' at %L overrides a PURE procedure and must also be PURE",
                 proc->name, &where);
      return FAILURE;
    }

  /* If the overridden binding is ELEMENTAL, the overriding must be, too.  If it
     is not, the overriding must not be either.  */
  if (old_target->attr.elemental && !proc_target->attr.elemental)
    {
      gfc_error ("'%s' at %L overrides an ELEMENTAL procedure and must also be"
                 " ELEMENTAL", proc->name, &where);
      return FAILURE;
    }
  if (!old_target->attr.elemental && proc_target->attr.elemental)
    {
      gfc_error ("'%s' at %L overrides a non-ELEMENTAL procedure and must not"
                 " be ELEMENTAL, either", proc->name, &where);
      return FAILURE;
    }

  /* If the overridden binding is a SUBROUTINE, the overriding must also be a
     SUBROUTINE.  */
  if (old_target->attr.subroutine && !proc_target->attr.subroutine)
    {
      gfc_error ("'%s' at %L overrides a SUBROUTINE and must also be a"
                 " SUBROUTINE", proc->name, &where);
      return FAILURE;
    }

  /* If the overridden binding is a FUNCTION, the overriding must also be a
     FUNCTION and have the same characteristics.  */
  if (old_target->attr.function)
    {
      if (!proc_target->attr.function)
        {
          gfc_error ("'%s' at %L overrides a FUNCTION and must also be a"
                     " FUNCTION", proc->name, &where);
          return FAILURE;
        }
        
      if (check_result_characteristics (proc_target, old_target,
                                        err, sizeof(err)) == FAILURE)
        {
          gfc_error ("Result mismatch for the overriding procedure "
                     "'%s' at %L: %s", proc->name, &where, err);
          return FAILURE;
        }
    }

  /* If the overridden binding is PUBLIC, the overriding one must not be
     PRIVATE.  */
  if (old->n.tb->access == ACCESS_PUBLIC
      && proc->n.tb->access == ACCESS_PRIVATE)
    {
      gfc_error ("'%s' at %L overrides a PUBLIC procedure and must not be"
                 " PRIVATE", proc->name, &where);
      return FAILURE;
    }

  /* Compare the formal argument lists of both procedures.  This is also abused
     to find the position of the passed-object dummy arguments of both
     bindings as at least the overridden one might not yet be resolved and we
     need those positions in the check below.  */
  proc_pass_arg = old_pass_arg = 0;
  if (!proc->n.tb->nopass && !proc->n.tb->pass_arg)
    proc_pass_arg = 1;
  if (!old->n.tb->nopass && !old->n.tb->pass_arg)
    old_pass_arg = 1;
  argpos = 1;
  for (proc_formal = proc_target->formal, old_formal = old_target->formal;
       proc_formal && old_formal;
       proc_formal = proc_formal->next, old_formal = old_formal->next)
    {
      if (proc->n.tb->pass_arg
          && !strcmp (proc->n.tb->pass_arg, proc_formal->sym->name))
        proc_pass_arg = argpos;
      if (old->n.tb->pass_arg
          && !strcmp (old->n.tb->pass_arg, old_formal->sym->name))
        old_pass_arg = argpos;

      /* Check that the names correspond.  */
      if (strcmp (proc_formal->sym->name, old_formal->sym->name))
        {
          gfc_error ("Dummy argument '%s' of '%s' at %L should be named '%s' as"
                     " to match the corresponding argument of the overridden"
                     " procedure", proc_formal->sym->name, proc->name, &where,
                     old_formal->sym->name);
          return FAILURE;
        }

      check_type = proc_pass_arg != argpos && old_pass_arg != argpos;
      if (check_dummy_characteristics (proc_formal->sym, old_formal->sym,
                                       check_type, err, sizeof(err)) == FAILURE)
        {
          gfc_error ("Argument mismatch for the overriding procedure "
                     "'%s' at %L: %s", proc->name, &where, err);
          return FAILURE;
        }

      ++argpos;
    }
  if (proc_formal || old_formal)
    {
      gfc_error ("'%s' at %L must have the same number of formal arguments as"
                 " the overridden procedure", proc->name, &where);
      return FAILURE;
    }

  /* If the overridden binding is NOPASS, the overriding one must also be
     NOPASS.  */
  if (old->n.tb->nopass && !proc->n.tb->nopass)
    {
      gfc_error ("'%s' at %L overrides a NOPASS binding and must also be"
                 " NOPASS", proc->name, &where);
      return FAILURE;
    }

  /* If the overridden binding is PASS(x), the overriding one must also be
     PASS and the passed-object dummy arguments must correspond.  */
  if (!old->n.tb->nopass)
    {
      if (proc->n.tb->nopass)
        {
          gfc_error ("'%s' at %L overrides a binding with PASS and must also be"
                     " PASS", proc->name, &where);
          return FAILURE;
        }

      if (proc_pass_arg != old_pass_arg)
        {
          gfc_error ("Passed-object dummy argument of '%s' at %L must be at"
                     " the same position as the passed-object dummy argument of"
                     " the overridden procedure", proc->name, &where);
          return FAILURE;
        }
    }

  return SUCCESS;
}