[pf3gnuchains/gcc-fork.git] / gcc / cp / pt.c

/* Handle parameterized types (templates) for GNU C++.
   Copyright (C) 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
   2001, 2002, 2003, 2004, 2005  Free Software Foundation, Inc.
   Written by Ken Raeburn (raeburn@cygnus.com) while at Watchmaker Computing.
   Rewritten by Jason Merrill (jason@cygnus.com).

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GCC is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING.  If not, write to
the Free Software Foundation, 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */

/* Known bugs or deficiencies include:

     all methods must be provided in header files; can't use a source
     file that contains only the method templates and "just win".  */

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "obstack.h"
#include "tree.h"
#include "pointer-set.h"
#include "flags.h"
#include "c-common.h"
#include "cp-tree.h"
#include "cp-objcp-common.h"
#include "tree-inline.h"
#include "decl.h"
#include "output.h"
#include "except.h"
#include "toplev.h"
#include "rtl.h"
#include "timevar.h"
#include "tree-iterator.h"

/* The type of functions taking a tree, and some additional data, and
   returning an int.  */
typedef int (*tree_fn_t) (tree, void*);

/* The PENDING_TEMPLATES is a TREE_LIST of templates whose
   instantiations have been deferred, either because their definitions
   were not yet available, or because we were putting off doing the work.
   The TREE_PURPOSE of each entry is either a DECL (for a function or
   static data member), or a TYPE (for a class) indicating what we are
   hoping to instantiate.  The TREE_VALUE is not used.  */
static GTY(()) tree pending_templates;
static GTY(()) tree last_pending_template;

int processing_template_parmlist;
static int template_header_count;

static GTY(()) tree saved_trees;
static GTY(()) varray_type inline_parm_levels;
static size_t inline_parm_levels_used;

static GTY(()) tree current_tinst_level;

static GTY(()) tree saved_access_scope;

/* Live only within one (recursive) call to tsubst_expr.  We use
   this to pass the statement expression node from the STMT_EXPR
   to the EXPR_STMT that is its result.  */
static tree cur_stmt_expr;

/* A map from local variable declarations in the body of the template
   presently being instantiated to the corresponding instantiated
   local variables.  */
static htab_t local_specializations;

#define UNIFY_ALLOW_NONE 0
#define UNIFY_ALLOW_MORE_CV_QUAL 1
#define UNIFY_ALLOW_LESS_CV_QUAL 2
#define UNIFY_ALLOW_DERIVED 4
#define UNIFY_ALLOW_INTEGER 8
#define UNIFY_ALLOW_OUTER_LEVEL 16
#define UNIFY_ALLOW_OUTER_MORE_CV_QUAL 32
#define UNIFY_ALLOW_OUTER_LESS_CV_QUAL 64

static void push_access_scope (tree);
static void pop_access_scope (tree);
static int resolve_overloaded_unification (tree, tree, tree, tree,
                                           unification_kind_t, int);
static int try_one_overload (tree, tree, tree, tree, tree,
                             unification_kind_t, int, bool);
static int unify (tree, tree, tree, tree, int);
static void add_pending_template (tree);
static void reopen_tinst_level (tree);
static tree classtype_mangled_name (tree);
static char* mangle_class_name_for_template (const char *, tree, tree);
static tree tsubst_initializer_list (tree, tree);
static tree get_class_bindings (tree, tree, tree);
static tree coerce_template_parms (tree, tree, tree, tsubst_flags_t, int);
static void tsubst_enum (tree, tree, tree);
static tree add_to_template_args (tree, tree);
static tree add_outermost_template_args (tree, tree);
static bool check_instantiated_args (tree, tree, tsubst_flags_t);
static int maybe_adjust_types_for_deduction (unification_kind_t, tree*, tree*); 
static int  type_unification_real (tree, tree, tree, tree,
                                   int, unification_kind_t, int);
static void note_template_header (int);
static tree convert_nontype_argument_function (tree, tree);
static tree convert_nontype_argument (tree, tree);
static tree convert_template_argument (tree, tree, tree,
                                       tsubst_flags_t, int, tree);
static int for_each_template_parm (tree, tree_fn_t, void*,
                                   struct pointer_set_t*);
static tree build_template_parm_index (int, int, int, tree, tree);
static int inline_needs_template_parms (tree);
static void push_inline_template_parms_recursive (tree, int);
static tree retrieve_local_specialization (tree);
static void register_local_specialization (tree, tree);
static tree reduce_template_parm_level (tree, tree, int);
static int mark_template_parm (tree, void *);
static int template_parm_this_level_p (tree, void *);
static tree tsubst_friend_function (tree, tree);
static tree tsubst_friend_class (tree, tree);
static int can_complete_type_without_circularity (tree);
static tree get_bindings (tree, tree, tree, bool);
static int template_decl_level (tree);
static int check_cv_quals_for_unify (int, tree, tree);
static tree tsubst_template_arg (tree, tree, tsubst_flags_t, tree);
static tree tsubst_template_args (tree, tree, tsubst_flags_t, tree);
static tree tsubst_template_parms (tree, tree, tsubst_flags_t);
static void regenerate_decl_from_template (tree, tree);
static tree most_specialized (tree, tree, tree);
static tree most_specialized_class (tree, tree);
static int template_class_depth_real (tree, int);
static tree tsubst_aggr_type (tree, tree, tsubst_flags_t, tree, int);
static tree tsubst_arg_types (tree, tree, tsubst_flags_t, tree);
static tree tsubst_function_type (tree, tree, tsubst_flags_t, tree);
static void check_specialization_scope (void);
static tree process_partial_specialization (tree);
static void set_current_access_from_decl (tree);
static void check_default_tmpl_args (tree, tree, int, int);
static tree tsubst_call_declarator_parms (tree, tree, tsubst_flags_t, tree);
static tree get_template_base (tree, tree, tree, tree);
static int verify_class_unification (tree, tree, tree);
static tree try_class_unification (tree, tree, tree, tree);
static int coerce_template_template_parms (tree, tree, tsubst_flags_t,
                                           tree, tree);
static tree determine_specialization (tree, tree, tree *, int, int);
static int template_args_equal (tree, tree);
static void tsubst_default_arguments (tree);
static tree for_each_template_parm_r (tree *, int *, void *);
static tree copy_default_args_to_explicit_spec_1 (tree, tree);
static void copy_default_args_to_explicit_spec (tree);
static int invalid_nontype_parm_type_p (tree, tsubst_flags_t);
static int eq_local_specializations (const void *, const void *);
static bool dependent_type_p_r (tree);
static tree tsubst (tree, tree, tsubst_flags_t, tree);
static tree tsubst_expr (tree, tree, tsubst_flags_t, tree);
static tree tsubst_copy (tree, tree, tsubst_flags_t, tree);

/* Make the current scope suitable for access checking when we are
   processing T.  T can be FUNCTION_DECL for instantiated function
   template, or VAR_DECL for static member variable (need by
   instantiate_decl).  */

static void
push_access_scope (tree t)
{
  gcc_assert (TREE_CODE (t) == FUNCTION_DECL
              || TREE_CODE (t) == VAR_DECL);

  if (DECL_FRIEND_CONTEXT (t))
    push_nested_class (DECL_FRIEND_CONTEXT (t));
  else if (DECL_CLASS_SCOPE_P (t))
    push_nested_class (DECL_CONTEXT (t));
  else
    push_to_top_level ();
    
  if (TREE_CODE (t) == FUNCTION_DECL)
    {
      saved_access_scope = tree_cons
        (NULL_TREE, current_function_decl, saved_access_scope);
      current_function_decl = t;
    }
}

/* Restore the scope set up by push_access_scope.  T is the node we
   are processing.  */

static void
pop_access_scope (tree t)
{
  if (TREE_CODE (t) == FUNCTION_DECL)
    {
      current_function_decl = TREE_VALUE (saved_access_scope);
      saved_access_scope = TREE_CHAIN (saved_access_scope);
    }

  if (DECL_FRIEND_CONTEXT (t) || DECL_CLASS_SCOPE_P (t))
    pop_nested_class ();
  else
    pop_from_top_level ();
}

/* Do any processing required when DECL (a member template
   declaration) is finished.  Returns the TEMPLATE_DECL corresponding
   to DECL, unless it is a specialization, in which case the DECL
   itself is returned.  */

tree
finish_member_template_decl (tree decl)
{
  if (decl == error_mark_node)
    return error_mark_node;

  gcc_assert (DECL_P (decl));

  if (TREE_CODE (decl) == TYPE_DECL)
    {
      tree type;

      type = TREE_TYPE (decl);
      if (IS_AGGR_TYPE (type) 
          && CLASSTYPE_TEMPLATE_INFO (type)
          && !CLASSTYPE_TEMPLATE_SPECIALIZATION (type))
        {
          tree tmpl = CLASSTYPE_TI_TEMPLATE (type);
          check_member_template (tmpl);
          return tmpl;
        }
      return NULL_TREE;
    }
  else if (TREE_CODE (decl) == FIELD_DECL)
    error ("data member %qD cannot be a member template", decl);
  else if (DECL_TEMPLATE_INFO (decl))
    {
      if (!DECL_TEMPLATE_SPECIALIZATION (decl))
        {
          check_member_template (DECL_TI_TEMPLATE (decl));
          return DECL_TI_TEMPLATE (decl);
        }
      else
        return decl;
    } 
  else
    error ("invalid member template declaration %qD", decl);

  return error_mark_node;
}

/* Returns the template nesting level of the indicated class TYPE.
   
   For example, in:
     template <class T>
     struct A
     {
       template <class U>
       struct B {};
     };

   A<T>::B<U> has depth two, while A<T> has depth one.  
   Both A<T>::B<int> and A<int>::B<U> have depth one, if
   COUNT_SPECIALIZATIONS is 0 or if they are instantiations, not
   specializations.  

   This function is guaranteed to return 0 if passed NULL_TREE so
   that, for example, `template_class_depth (current_class_type)' is
   always safe.  */

static int 
template_class_depth_real (tree type, int count_specializations)
{
  int depth;

  for (depth = 0; 
       type && TREE_CODE (type) != NAMESPACE_DECL;
       type = (TREE_CODE (type) == FUNCTION_DECL) 
         ? CP_DECL_CONTEXT (type) : TYPE_CONTEXT (type))
    {
      if (TREE_CODE (type) != FUNCTION_DECL)
        {
          if (CLASSTYPE_TEMPLATE_INFO (type)
              && PRIMARY_TEMPLATE_P (CLASSTYPE_TI_TEMPLATE (type))
              && ((count_specializations
                   && CLASSTYPE_TEMPLATE_SPECIALIZATION (type))
                  || uses_template_parms (CLASSTYPE_TI_ARGS (type))))
            ++depth;
        }
      else 
        {
          if (DECL_TEMPLATE_INFO (type)
              && PRIMARY_TEMPLATE_P (DECL_TI_TEMPLATE (type))
              && ((count_specializations
                   && DECL_TEMPLATE_SPECIALIZATION (type))
                  || uses_template_parms (DECL_TI_ARGS (type))))
            ++depth;
        }
    }

  return depth;
}

/* Returns the template nesting level of the indicated class TYPE.
   Like template_class_depth_real, but instantiations do not count in
   the depth.  */

int 
template_class_depth (tree type)
{
  return template_class_depth_real (type, /*count_specializations=*/0);
}

/* Returns 1 if processing DECL as part of do_pending_inlines
   needs us to push template parms.  */

static int
inline_needs_template_parms (tree decl)
{
  if (! DECL_TEMPLATE_INFO (decl))
    return 0;

  return (TMPL_PARMS_DEPTH (DECL_TEMPLATE_PARMS (most_general_template (decl)))
          > (processing_template_decl + DECL_TEMPLATE_SPECIALIZATION (decl)));
}

/* Subroutine of maybe_begin_member_template_processing.
   Push the template parms in PARMS, starting from LEVELS steps into the
   chain, and ending at the beginning, since template parms are listed
   innermost first.  */

static void
push_inline_template_parms_recursive (tree parmlist, int levels)
{
  tree parms = TREE_VALUE (parmlist);
  int i;

  if (levels > 1)
    push_inline_template_parms_recursive (TREE_CHAIN (parmlist), levels - 1);

  ++processing_template_decl;
  current_template_parms
    = tree_cons (size_int (processing_template_decl),
                 parms, current_template_parms);
  TEMPLATE_PARMS_FOR_INLINE (current_template_parms) = 1;

  begin_scope (TREE_VEC_LENGTH (parms) ? sk_template_parms : sk_template_spec,
               NULL);
  for (i = 0; i < TREE_VEC_LENGTH (parms); ++i) 
    {
      tree parm = TREE_VALUE (TREE_VEC_ELT (parms, i));
      gcc_assert (DECL_P (parm));

      switch (TREE_CODE (parm))
        {
        case TYPE_DECL:
        case TEMPLATE_DECL:
          pushdecl (parm);
          break;

        case PARM_DECL:
          {
            /* Make a CONST_DECL as is done in process_template_parm.
               It is ugly that we recreate this here; the original
               version built in process_template_parm is no longer
               available.  */
            tree decl = build_decl (CONST_DECL, DECL_NAME (parm),
                                    TREE_TYPE (parm));
            DECL_ARTIFICIAL (decl) = 1;
            TREE_CONSTANT (decl) = 1;
            TREE_INVARIANT (decl) = 1;
            TREE_READONLY (decl) = 1;
            DECL_INITIAL (decl) = DECL_INITIAL (parm);
            SET_DECL_TEMPLATE_PARM_P (decl);
            pushdecl (decl);
          }
          break;

        default:
          gcc_unreachable ();
        }
    }
}

/* Restore the template parameter context for a member template or
   a friend template defined in a class definition.  */

void
maybe_begin_member_template_processing (tree decl)
{
  tree parms;
  int levels = 0;

  if (inline_needs_template_parms (decl))
    {
      parms = DECL_TEMPLATE_PARMS (most_general_template (decl));
      levels = TMPL_PARMS_DEPTH (parms) - processing_template_decl;

      if (DECL_TEMPLATE_SPECIALIZATION (decl))
        {
          --levels;
          parms = TREE_CHAIN (parms);
        }

      push_inline_template_parms_recursive (parms, levels);
    }

  /* Remember how many levels of template parameters we pushed so that
     we can pop them later.  */
  if (!inline_parm_levels)
    VARRAY_INT_INIT (inline_parm_levels, 4, "inline_parm_levels");
  if (inline_parm_levels_used == inline_parm_levels->num_elements)
    VARRAY_GROW (inline_parm_levels, 2 * inline_parm_levels_used);
  VARRAY_INT (inline_parm_levels, inline_parm_levels_used) = levels;
  ++inline_parm_levels_used;
}

/* Undo the effects of maybe_begin_member_template_processing.  */

void 
maybe_end_member_template_processing (void)
{
  int i;

  if (!inline_parm_levels_used)
    return;

  --inline_parm_levels_used;
  for (i = 0; 
       i < VARRAY_INT (inline_parm_levels, inline_parm_levels_used);
       ++i) 
    {
      --processing_template_decl;
      current_template_parms = TREE_CHAIN (current_template_parms);
      poplevel (0, 0, 0);
    }
}

/* Return a new template argument vector which contains all of ARGS,
   but has as its innermost set of arguments the EXTRA_ARGS.  */

static tree
add_to_template_args (tree args, tree extra_args)
{
  tree new_args;
  int extra_depth;
  int i;
  int j;

  extra_depth = TMPL_ARGS_DEPTH (extra_args);
  new_args = make_tree_vec (TMPL_ARGS_DEPTH (args) + extra_depth);

  for (i = 1; i <= TMPL_ARGS_DEPTH (args); ++i)
    SET_TMPL_ARGS_LEVEL (new_args, i, TMPL_ARGS_LEVEL (args, i));

  for (j = 1; j <= extra_depth; ++j, ++i)
    SET_TMPL_ARGS_LEVEL (new_args, i, TMPL_ARGS_LEVEL (extra_args, j));
    
  return new_args;
}

/* Like add_to_template_args, but only the outermost ARGS are added to
   the EXTRA_ARGS.  In particular, all but TMPL_ARGS_DEPTH
   (EXTRA_ARGS) levels are added.  This function is used to combine
   the template arguments from a partial instantiation with the
   template arguments used to attain the full instantiation from the
   partial instantiation.  */

static tree
add_outermost_template_args (tree args, tree extra_args)
{
  tree new_args;

  /* If there are more levels of EXTRA_ARGS than there are ARGS,
     something very fishy is going on.  */
  gcc_assert (TMPL_ARGS_DEPTH (args) >= TMPL_ARGS_DEPTH (extra_args));

  /* If *all* the new arguments will be the EXTRA_ARGS, just return
     them.  */
  if (TMPL_ARGS_DEPTH (args) == TMPL_ARGS_DEPTH (extra_args))
    return extra_args;

  /* For the moment, we make ARGS look like it contains fewer levels.  */
  TREE_VEC_LENGTH (args) -= TMPL_ARGS_DEPTH (extra_args);
  
  new_args = add_to_template_args (args, extra_args);

  /* Now, we restore ARGS to its full dimensions.  */
  TREE_VEC_LENGTH (args) += TMPL_ARGS_DEPTH (extra_args);

  return new_args;
}

/* Return the N levels of innermost template arguments from the ARGS.  */

tree
get_innermost_template_args (tree args, int n)
{
  tree new_args;
  int extra_levels;
  int i;

  gcc_assert (n >= 0);

  /* If N is 1, just return the innermost set of template arguments.  */
  if (n == 1)
    return TMPL_ARGS_LEVEL (args, TMPL_ARGS_DEPTH (args));
  
  /* If we're not removing anything, just return the arguments we were
     given.  */
  extra_levels = TMPL_ARGS_DEPTH (args) - n;
  gcc_assert (extra_levels >= 0);
  if (extra_levels == 0)
    return args;

  /* Make a new set of arguments, not containing the outer arguments.  */
  new_args = make_tree_vec (n);
  for (i = 1; i <= n; ++i)
    SET_TMPL_ARGS_LEVEL (new_args, i, 
                         TMPL_ARGS_LEVEL (args, i + extra_levels));

  return new_args;
}

/* We've got a template header coming up; push to a new level for storing
   the parms.  */

void
begin_template_parm_list (void)
{
  /* We use a non-tag-transparent scope here, which causes pushtag to
     put tags in this scope, rather than in the enclosing class or
     namespace scope.  This is the right thing, since we want
     TEMPLATE_DECLS, and not TYPE_DECLS for template classes.  For a
     global template class, push_template_decl handles putting the
     TEMPLATE_DECL into top-level scope.  For a nested template class,
     e.g.:

       template <class T> struct S1 {
         template <class T> struct S2 {}; 
       };

     pushtag contains special code to call pushdecl_with_scope on the
     TEMPLATE_DECL for S2.  */
  begin_scope (sk_template_parms, NULL);
  ++processing_template_decl;
  ++processing_template_parmlist;
  note_template_header (0);
}

/* This routine is called when a specialization is declared.  If it is
   invalid to declare a specialization here, an error is reported.  */

static void
check_specialization_scope (void)
{
  tree scope = current_scope ();

  /* [temp.expl.spec] 
     
     An explicit specialization shall be declared in the namespace of
     which the template is a member, or, for member templates, in the
     namespace of which the enclosing class or enclosing class
     template is a member.  An explicit specialization of a member
     function, member class or static data member of a class template
     shall be declared in the namespace of which the class template
     is a member.  */
  if (scope && TREE_CODE (scope) != NAMESPACE_DECL)
    error ("explicit specialization in non-namespace scope %qD", scope);

  /* [temp.expl.spec] 

     In an explicit specialization declaration for a member of a class
     template or a member template that appears in namespace scope,
     the member template and some of its enclosing class templates may
     remain unspecialized, except that the declaration shall not
     explicitly specialize a class member template if its enclosing
     class templates are not explicitly specialized as well.  */
  if (current_template_parms) 
    error ("enclosing class templates are not explicitly specialized");
}

/* We've just seen template <>.  */

void
begin_specialization (void)
{
  begin_scope (sk_template_spec, NULL);
  note_template_header (1);
  check_specialization_scope ();
}

/* Called at then end of processing a declaration preceded by
   template<>.  */

void 
end_specialization (void)
{
  finish_scope ();
  reset_specialization ();
}

/* Any template <>'s that we have seen thus far are not referring to a
   function specialization.  */

void
reset_specialization (void)
{
  processing_specialization = 0;
  template_header_count = 0;
}

/* We've just seen a template header.  If SPECIALIZATION is nonzero,
   it was of the form template <>.  */

static void 
note_template_header (int specialization)
{
  processing_specialization = specialization;
  template_header_count++;
}

/* We're beginning an explicit instantiation.  */

void
begin_explicit_instantiation (void)
{
  gcc_assert (!processing_explicit_instantiation);
  processing_explicit_instantiation = true;
}


void
end_explicit_instantiation (void)
{
  gcc_assert (processing_explicit_instantiation);
  processing_explicit_instantiation = false;
}

/* A explicit specialization or partial specialization TMPL is being
   declared.  Check that the namespace in which the specialization is
   occurring is permissible.  Returns false iff it is invalid to
   specialize TMPL in the current namespace.  */
   
static bool
check_specialization_namespace (tree tmpl)
{
  tree tpl_ns = decl_namespace_context (tmpl);

  /* [tmpl.expl.spec]
     
     An explicit specialization shall be declared in the namespace of
     which the template is a member, or, for member templates, in the
     namespace of which the enclosing class or enclosing class
     template is a member.  An explicit specialization of a member
     function, member class or static data member of a class template
     shall be declared in the namespace of which the class template is
     a member.  */
  if (is_associated_namespace (current_namespace, tpl_ns))
    /* Same or super-using namespace.  */
    return true;
  else
    {
      pedwarn ("specialization of %qD in different namespace", tmpl);
      cp_pedwarn_at ("  from definition of %q#D", tmpl);
      return false;
    }
}

/* The TYPE is being declared.  If it is a template type, that means it
   is a partial specialization.  Do appropriate error-checking.  */

void 
maybe_process_partial_specialization (tree type)
{
  /* TYPE maybe an ERROR_MARK_NODE.  */
  tree context = TYPE_P (type) ? TYPE_CONTEXT (type) : NULL_TREE;

  if (CLASS_TYPE_P (type) && CLASSTYPE_USE_TEMPLATE (type))
    {
      /* This is for ordinary explicit specialization and partial
         specialization of a template class such as:

           template <> class C<int>;

         or:

           template <class T> class C<T*>;

         Make sure that `C<int>' and `C<T*>' are implicit instantiations.  */

      if (CLASSTYPE_IMPLICIT_INSTANTIATION (type)
          && !COMPLETE_TYPE_P (type))
        {
          check_specialization_namespace (CLASSTYPE_TI_TEMPLATE (type));
          SET_CLASSTYPE_TEMPLATE_SPECIALIZATION (type);
          if (processing_template_decl)
            push_template_decl (TYPE_MAIN_DECL (type));
        }
      else if (CLASSTYPE_TEMPLATE_INSTANTIATION (type))
        error ("specialization of %qT after instantiation", type);
    }
  else if (CLASS_TYPE_P (type)
           && !CLASSTYPE_USE_TEMPLATE (type)
           && CLASSTYPE_TEMPLATE_INFO (type)
           && context && CLASS_TYPE_P (context)
           && CLASSTYPE_TEMPLATE_INFO (context))
    {
      /* This is for an explicit specialization of member class
         template according to [temp.expl.spec/18]:

           template <> template <class U> class C<int>::D;

         The context `C<int>' must be an implicit instantiation.
         Otherwise this is just a member class template declared
         earlier like:

           template <> class C<int> { template <class U> class D; };
           template <> template <class U> class C<int>::D;

         In the first case, `C<int>::D' is a specialization of `C<T>::D'
         while in the second case, `C<int>::D' is a primary template
         and `C<T>::D' may not exist.  */

      if (CLASSTYPE_IMPLICIT_INSTANTIATION (context)
          && !COMPLETE_TYPE_P (type))
        {
          tree t;

          if (current_namespace
              != decl_namespace_context (CLASSTYPE_TI_TEMPLATE (type)))
            {
              pedwarn ("specializing %q#T in different namespace", type);
              cp_pedwarn_at ("  from definition of %q#D",
                             CLASSTYPE_TI_TEMPLATE (type));
            }

          /* Check for invalid specialization after instantiation:

               template <> template <> class C<int>::D<int>;
               template <> template <class U> class C<int>::D;  */

          for (t = DECL_TEMPLATE_INSTANTIATIONS
                 (most_general_template (CLASSTYPE_TI_TEMPLATE (type)));
               t; t = TREE_CHAIN (t))
            if (TREE_VALUE (t) != type
                && TYPE_CONTEXT (TREE_VALUE (t)) == context)
              error ("specialization %qT after instantiation %qT",
                     type, TREE_VALUE (t));

          /* Mark TYPE as a specialization.  And as a result, we only
             have one level of template argument for the innermost
             class template.  */
          SET_CLASSTYPE_TEMPLATE_SPECIALIZATION (type);
          CLASSTYPE_TI_ARGS (type)
            = INNERMOST_TEMPLATE_ARGS (CLASSTYPE_TI_ARGS (type));
        }
    }
  else if (processing_specialization)
    error ("explicit specialization of non-template %qT", type);
}

/* Returns nonzero if we can optimize the retrieval of specializations
   for TMPL, a TEMPLATE_DECL.  In particular, for such a template, we
   do not use DECL_TEMPLATE_SPECIALIZATIONS at all.  */

static inline bool 
optimize_specialization_lookup_p (tree tmpl)
{
  return (DECL_FUNCTION_TEMPLATE_P (tmpl)
          && DECL_CLASS_SCOPE_P (tmpl)
          /* DECL_CLASS_SCOPE_P holds of T::f even if T is a template
             parameter.  */
          && CLASS_TYPE_P (DECL_CONTEXT (tmpl))
          /* The optimized lookup depends on the fact that the
             template arguments for the member function template apply
             purely to the containing class, which is not true if the
             containing class is an explicit or partial
             specialization.  */
          && !CLASSTYPE_TEMPLATE_SPECIALIZATION (DECL_CONTEXT (tmpl))
          && !DECL_MEMBER_TEMPLATE_P (tmpl)
          && !DECL_CONV_FN_P (tmpl)
          /* It is possible to have a template that is not a member
             template and is not a member of a template class:
             
             template <typename T> 
             struct S { friend A::f(); };
             
             Here, the friend function is a template, but the context does
             not have template information.  The optimized lookup relies
             on having ARGS be the template arguments for both the class
             and the function template.  */
          && !DECL_FRIEND_P (DECL_TEMPLATE_RESULT (tmpl)));
}

/* Retrieve the specialization (in the sense of [temp.spec] - a
   specialization is either an instantiation or an explicit
   specialization) of TMPL for the given template ARGS.  If there is
   no such specialization, return NULL_TREE.  The ARGS are a vector of
   arguments, or a vector of vectors of arguments, in the case of
   templates with more than one level of parameters.  

   If TMPL is a type template and CLASS_SPECIALIZATIONS_P is true,
   then we search for a partial specialization matching ARGS.  This
   parameter is ignored if TMPL is not a class template.  */
   
static tree
retrieve_specialization (tree tmpl, tree args, 
                         bool class_specializations_p)
{
  gcc_assert (TREE_CODE (tmpl) == TEMPLATE_DECL);

  /* There should be as many levels of arguments as there are
     levels of parameters.  */
  gcc_assert (TMPL_ARGS_DEPTH (args) 
              == TMPL_PARMS_DEPTH (DECL_TEMPLATE_PARMS (tmpl)));
                
  if (optimize_specialization_lookup_p (tmpl))
    {
      tree class_template;
      tree class_specialization;
      VEC(tree,gc) *methods;
      tree fns;
      int idx;

      /* The template arguments actually apply to the containing
         class.  Find the class specialization with those
         arguments.  */
      class_template = CLASSTYPE_TI_TEMPLATE (DECL_CONTEXT (tmpl));
      class_specialization 
        = retrieve_specialization (class_template, args,
                                   /*class_specializations_p=*/false);
      if (!class_specialization)
        return NULL_TREE;
      /* Now, find the appropriate entry in the CLASSTYPE_METHOD_VEC
         for the specialization.  */
      idx = class_method_index_for_fn (class_specialization, tmpl);
      if (idx == -1)
        return NULL_TREE;
      /* Iterate through the methods with the indicated name, looking
         for the one that has an instance of TMPL.  */
      methods = CLASSTYPE_METHOD_VEC (class_specialization);
      for (fns = VEC_index (tree, methods, idx); fns; fns = OVL_NEXT (fns))
        {
          tree fn = OVL_CURRENT (fns);
          if (DECL_TEMPLATE_INFO (fn) && DECL_TI_TEMPLATE (fn) == tmpl)
            return fn;
        }
      return NULL_TREE;
    }
  else
    {
      tree *sp;
      tree *head;

      /* Class templates store their instantiations on the
         DECL_TEMPLATE_INSTANTIATIONS list; other templates use the
         DECL_TEMPLATE_SPECIALIZATIONS list.  */
      if (!class_specializations_p
          && TREE_CODE (DECL_TEMPLATE_RESULT (tmpl)) == TYPE_DECL)
        sp = &DECL_TEMPLATE_INSTANTIATIONS (tmpl);
      else
        sp = &DECL_TEMPLATE_SPECIALIZATIONS (tmpl);
      head = sp;
      /* Iterate through the list until we find a matching template.  */
      while (*sp != NULL_TREE)
        {
          tree spec = *sp;
              
          if (comp_template_args (TREE_PURPOSE (spec), args))
            {
              /* Use the move-to-front heuristic to speed up future
                 searches.  */ 
              if (spec != *head)
                {
                  *sp = TREE_CHAIN (*sp);
                  TREE_CHAIN (spec) = *head;
                  *head = spec;
                }
              return TREE_VALUE (spec);
            }
          sp = &TREE_CHAIN (spec);
        }
    }

  return NULL_TREE;
}

/* Like retrieve_specialization, but for local declarations.  */

static tree
retrieve_local_specialization (tree tmpl)
{
  tree spec = htab_find_with_hash (local_specializations, tmpl,
                                   htab_hash_pointer (tmpl));
  return spec ? TREE_PURPOSE (spec) : NULL_TREE;
}

/* Returns nonzero iff DECL is a specialization of TMPL.  */

int
is_specialization_of (tree decl, tree tmpl)
{
  tree t;

  if (TREE_CODE (decl) == FUNCTION_DECL)
    {
      for (t = decl; 
           t != NULL_TREE;
           t = DECL_TEMPLATE_INFO (t) ? DECL_TI_TEMPLATE (t) : NULL_TREE)
        if (t == tmpl)
          return 1;
    }
  else 
    {
      gcc_assert (TREE_CODE (decl) == TYPE_DECL);

      for (t = TREE_TYPE (decl);
           t != NULL_TREE;
           t = CLASSTYPE_USE_TEMPLATE (t)
             ? TREE_TYPE (CLASSTYPE_TI_TEMPLATE (t)) : NULL_TREE)
        if (same_type_ignoring_top_level_qualifiers_p (t, TREE_TYPE (tmpl)))
          return 1;
    }  

  return 0;
}

/* Returns nonzero iff DECL is a specialization of friend declaration
   FRIEND according to [temp.friend].  */

bool
is_specialization_of_friend (tree decl, tree friend)
{
  bool need_template = true;
  int template_depth;

  gcc_assert (TREE_CODE (decl) == FUNCTION_DECL
              || TREE_CODE (decl) == TYPE_DECL);

  /* For [temp.friend/6] when FRIEND is an ordinary member function
     of a template class, we want to check if DECL is a specialization
     if this.  */
  if (TREE_CODE (friend) == FUNCTION_DECL
      && DECL_TEMPLATE_INFO (friend)
      && !DECL_USE_TEMPLATE (friend))
    {
      /* We want a TEMPLATE_DECL for `is_specialization_of'.  */
      friend = DECL_TI_TEMPLATE (friend);
      need_template = false;
    }
  else if (TREE_CODE (friend) == TEMPLATE_DECL
           && !PRIMARY_TEMPLATE_P (friend))
    need_template = false;

  /* There is nothing to do if this is not a template friend.  */
  if (TREE_CODE (friend) != TEMPLATE_DECL)
    return false;

  if (is_specialization_of (decl, friend))
    return true;

  /* [temp.friend/6]
     A member of a class template may be declared to be a friend of a
     non-template class.  In this case, the corresponding member of
     every specialization of the class template is a friend of the
     class granting friendship.
     
     For example, given a template friend declaration

       template <class T> friend void A<T>::f();

     the member function below is considered a friend

       template <> struct A<int> {
         void f();
       };

     For this type of template friend, TEMPLATE_DEPTH below will be
     nonzero.  To determine if DECL is a friend of FRIEND, we first
     check if the enclosing class is a specialization of another.  */

  template_depth = template_class_depth (DECL_CONTEXT (friend));
  if (template_depth
      && DECL_CLASS_SCOPE_P (decl)
      && is_specialization_of (TYPE_NAME (DECL_CONTEXT (decl)), 
                               CLASSTYPE_TI_TEMPLATE (DECL_CONTEXT (friend))))
    {
      /* Next, we check the members themselves.  In order to handle
         a few tricky cases, such as when FRIEND's are

           template <class T> friend void A<T>::g(T t);
           template <class T> template <T t> friend void A<T>::h();

         and DECL's are

           void A<int>::g(int);
           template <int> void A<int>::h();

         we need to figure out ARGS, the template arguments from
         the context of DECL.  This is required for template substitution
         of `T' in the function parameter of `g' and template parameter
         of `h' in the above examples.  Here ARGS corresponds to `int'.  */

      tree context = DECL_CONTEXT (decl);
      tree args = NULL_TREE;
      int current_depth = 0;

      while (current_depth < template_depth)
        {
          if (CLASSTYPE_TEMPLATE_INFO (context))
            {
              if (current_depth == 0)
                args = TYPE_TI_ARGS (context);
              else
                args = add_to_template_args (TYPE_TI_ARGS (context), args);
              current_depth++;
            }
          context = TYPE_CONTEXT (context);
        }

      if (TREE_CODE (decl) == FUNCTION_DECL)
        {
          bool is_template;
          tree friend_type;
          tree decl_type;
          tree friend_args_type;
          tree decl_args_type;

          /* Make sure that both DECL and FRIEND are templates or
             non-templates.  */
          is_template = DECL_TEMPLATE_INFO (decl)
                        && PRIMARY_TEMPLATE_P (DECL_TI_TEMPLATE (decl));
          if (need_template ^ is_template)
            return false;
          else if (is_template)
            {
              /* If both are templates, check template parameter list.  */
              tree friend_parms
                = tsubst_template_parms (DECL_TEMPLATE_PARMS (friend),
                                         args, tf_none);
              if (!comp_template_parms
                     (DECL_TEMPLATE_PARMS (DECL_TI_TEMPLATE (decl)),
                      friend_parms))
                return false;

              decl_type = TREE_TYPE (DECL_TI_TEMPLATE (decl));
            }
          else
            decl_type = TREE_TYPE (decl);

          friend_type = tsubst_function_type (TREE_TYPE (friend), args,
                                              tf_none, NULL_TREE);
          if (friend_type == error_mark_node)
            return false;

          /* Check if return types match.  */
          if (!same_type_p (TREE_TYPE (decl_type), TREE_TYPE (friend_type)))
            return false;

          /* Check if function parameter types match, ignoring the
             `this' parameter.  */
          friend_args_type = TYPE_ARG_TYPES (friend_type);
          decl_args_type = TYPE_ARG_TYPES (decl_type);
          if (DECL_NONSTATIC_MEMBER_FUNCTION_P (friend))
            friend_args_type = TREE_CHAIN (friend_args_type);
          if (DECL_NONSTATIC_MEMBER_FUNCTION_P (decl))
            decl_args_type = TREE_CHAIN (decl_args_type);

          return compparms (decl_args_type, friend_args_type);
        }
      else
        {
          /* DECL is a TYPE_DECL */
          bool is_template;
          tree decl_type = TREE_TYPE (decl);

          /* Make sure that both DECL and FRIEND are templates or
             non-templates.  */
          is_template
            = CLASSTYPE_TEMPLATE_INFO (decl_type)
              && PRIMARY_TEMPLATE_P (CLASSTYPE_TI_TEMPLATE (decl_type));

          if (need_template ^ is_template)
            return false;
          else if (is_template)
            {
              tree friend_parms;
              /* If both are templates, check the name of the two
                 TEMPLATE_DECL's first because is_friend didn't.  */
              if (DECL_NAME (CLASSTYPE_TI_TEMPLATE (decl_type))
                  != DECL_NAME (friend))
                return false;

              /* Now check template parameter list.  */
              friend_parms
                = tsubst_template_parms (DECL_TEMPLATE_PARMS (friend),
                                         args, tf_none);
              return comp_template_parms
                (DECL_TEMPLATE_PARMS (CLASSTYPE_TI_TEMPLATE (decl_type)),
                 friend_parms);
            }
          else
            return (DECL_NAME (decl)
                    == DECL_NAME (friend));
        }
    }
  return false;
}

/* Register the specialization SPEC as a specialization of TMPL with
   the indicated ARGS.  Returns SPEC, or an equivalent prior
   declaration, if available.  */

static tree
register_specialization (tree spec, tree tmpl, tree args)
{
  tree fn;

  gcc_assert (TREE_CODE (tmpl) == TEMPLATE_DECL);

  if (TREE_CODE (spec) == FUNCTION_DECL 
      && uses_template_parms (DECL_TI_ARGS (spec)))
    /* This is the FUNCTION_DECL for a partial instantiation.  Don't
       register it; we want the corresponding TEMPLATE_DECL instead.
       We use `uses_template_parms (DECL_TI_ARGS (spec))' rather than
       the more obvious `uses_template_parms (spec)' to avoid problems
       with default function arguments.  In particular, given
       something like this:

          template <class T> void f(T t1, T t = T())

       the default argument expression is not substituted for in an
       instantiation unless and until it is actually needed.  */
    return spec;

  /* There should be as many levels of arguments as there are
     levels of parameters.  */
  gcc_assert (TMPL_ARGS_DEPTH (args) 
              == TMPL_PARMS_DEPTH (DECL_TEMPLATE_PARMS (tmpl)));

  fn = retrieve_specialization (tmpl, args, 
                                /*class_specializations_p=*/false);
  /* We can sometimes try to re-register a specialization that we've
     already got.  In particular, regenerate_decl_from_template calls
     duplicate_decls which will update the specialization list.  But,
     we'll still get called again here anyhow.  It's more convenient
     to simply allow this than to try to prevent it.  */
  if (fn == spec)
    return spec;
  else if (fn && DECL_TEMPLATE_SPECIALIZATION (spec))
    {
      if (DECL_TEMPLATE_INSTANTIATION (fn))
        {
          if (TREE_USED (fn) 
              || DECL_EXPLICIT_INSTANTIATION (fn))
            {
              error ("specialization of %qD after instantiation",
                     fn);
              return spec;
            }
          else
            {
              /* This situation should occur only if the first
                 specialization is an implicit instantiation, the
                 second is an explicit specialization, and the
                 implicit instantiation has not yet been used.  That
                 situation can occur if we have implicitly
                 instantiated a member function and then specialized
                 it later.
                 
                 We can also wind up here if a friend declaration that
                 looked like an instantiation turns out to be a
                 specialization:
                 
                   template <class T> void foo(T);
                   class S { friend void foo<>(int) };
                   template <> void foo(int);  
                 
                 We transform the existing DECL in place so that any
                 pointers to it become pointers to the updated
                 declaration.

                 If there was a definition for the template, but not
                 for the specialization, we want this to look as if
                 there were no definition, and vice versa.  */
              DECL_INITIAL (fn) = NULL_TREE;
              duplicate_decls (spec, fn);
              
              return fn;
            }
        }
      else if (DECL_TEMPLATE_SPECIALIZATION (fn))
        {
          if (!duplicate_decls (spec, fn) && DECL_INITIAL (spec))
            /* Dup decl failed, but this is a new definition. Set the
               line number so any errors match this new
               definition.  */
            DECL_SOURCE_LOCATION (fn) = DECL_SOURCE_LOCATION (spec);
          
          return fn;
        }
    }

  /* A specialization must be declared in the same namespace as the
     template it is specializing.  */
  if (DECL_TEMPLATE_SPECIALIZATION (spec)
      && !check_specialization_namespace (tmpl))
    DECL_CONTEXT (spec) = decl_namespace_context (tmpl);

  if (!optimize_specialization_lookup_p (tmpl))
    DECL_TEMPLATE_SPECIALIZATIONS (tmpl)
      = tree_cons (args, spec, DECL_TEMPLATE_SPECIALIZATIONS (tmpl));

  return spec;
}

/* Unregister the specialization SPEC as a specialization of TMPL.
   Replace it with NEW_SPEC, if NEW_SPEC is non-NULL.  Returns true
   if the SPEC was listed as a specialization of TMPL.  */

bool
reregister_specialization (tree spec, tree tmpl, tree new_spec)
{
  tree* s;

  for (s = &DECL_TEMPLATE_SPECIALIZATIONS (tmpl);
       *s != NULL_TREE;
       s = &TREE_CHAIN (*s))
    if (TREE_VALUE (*s) == spec)
      {
        if (!new_spec)
          *s = TREE_CHAIN (*s);
        else
          TREE_VALUE (*s) = new_spec;
        return 1;
      }

  return 0;
}

/* Compare an entry in the local specializations hash table P1 (which
   is really a pointer to a TREE_LIST) with P2 (which is really a
   DECL).  */

static int
eq_local_specializations (const void *p1, const void *p2)
{
  return TREE_VALUE ((tree) p1) == (tree) p2;
}

/* Hash P1, an entry in the local specializations table.  */

static hashval_t
hash_local_specialization (const void* p1)
{
  return htab_hash_pointer (TREE_VALUE ((tree) p1));
}

/* Like register_specialization, but for local declarations.  We are
   registering SPEC, an instantiation of TMPL.  */

static void
register_local_specialization (tree spec, tree tmpl)
{
  void **slot;

  slot = htab_find_slot_with_hash (local_specializations, tmpl, 
                                   htab_hash_pointer (tmpl), INSERT);
  *slot = build_tree_list (spec, tmpl);
}

/* Print the list of candidate FNS in an error message.  */

void
print_candidates (tree fns)
{
  tree fn;

  const char *str = "candidates are:";

  for (fn = fns; fn != NULL_TREE; fn = TREE_CHAIN (fn))
    {
      tree f;

      for (f = TREE_VALUE (fn); f; f = OVL_NEXT (f))
        cp_error_at ("%s %+#D", str, OVL_CURRENT (f));
      str = "               ";
    }
}

/* Returns the template (one of the functions given by TEMPLATE_ID)
   which can be specialized to match the indicated DECL with the
   explicit template args given in TEMPLATE_ID.  The DECL may be
   NULL_TREE if none is available.  In that case, the functions in
   TEMPLATE_ID are non-members.

   If NEED_MEMBER_TEMPLATE is nonzero the function is known to be a
   specialization of a member template.

   The TEMPLATE_COUNT is the number of references to qualifying
   template classes that appeared in the name of the function. See
   check_explicit_specialization for a more accurate description.

   The template args (those explicitly specified and those deduced)
   are output in a newly created vector *TARGS_OUT.

   If it is impossible to determine the result, an error message is
   issued.  The error_mark_node is returned to indicate failure.  */

static tree
determine_specialization (tree template_id, 
                          tree decl, 
                          tree* targs_out, 
                          int need_member_template,
                          int template_count)
{
  tree fns;
  tree targs;
  tree explicit_targs;
  tree candidates = NULL_TREE;
  tree templates = NULL_TREE;
  int header_count;
  struct cp_binding_level *b;

  *targs_out = NULL_TREE;

  if (template_id == error_mark_node)
    return error_mark_node;

  fns = TREE_OPERAND (template_id, 0);
  explicit_targs = TREE_OPERAND (template_id, 1);

  if (fns == error_mark_node)
    return error_mark_node;

  /* Check for baselinks.  */
  if (BASELINK_P (fns))
    fns = BASELINK_FUNCTIONS (fns);

  if (!is_overloaded_fn (fns))
    {
      error ("%qD is not a function template", fns);
      return error_mark_node;
    }

  /* Count the number of template headers specified for this
     specialization.  */
  header_count = 0;
  for (b = current_binding_level; 
       b->kind == sk_template_parms;
       b = b->level_chain)
    ++header_count;

  for (; fns; fns = OVL_NEXT (fns))
    {
      tree fn = OVL_CURRENT (fns);

      if (TREE_CODE (fn) == TEMPLATE_DECL)
        {
          tree decl_arg_types;
          tree fn_arg_types;

          /* DECL might be a specialization of FN.  */

          /* Adjust the type of DECL in case FN is a static member.  */
          decl_arg_types = TYPE_ARG_TYPES (TREE_TYPE (decl));
          if (DECL_STATIC_FUNCTION_P (fn) 
              && DECL_NONSTATIC_MEMBER_FUNCTION_P (decl))
            decl_arg_types = TREE_CHAIN (decl_arg_types);

          /* Check that the number of function parameters matches.
             For example,
               template <class T> void f(int i = 0);
               template <> void f<int>();
             The specialization f<int> is invalid but is not caught
             by get_bindings below.  */

          fn_arg_types = TYPE_ARG_TYPES (TREE_TYPE (fn));
          if (list_length (fn_arg_types) != list_length (decl_arg_types))
            continue;

          /* For a non-static member function, we need to make sure that
             the const qualification is the same. This can be done by
             checking the 'this' in the argument list.  */
          if (DECL_NONSTATIC_MEMBER_FUNCTION_P (fn)
              && !same_type_p (TREE_VALUE (fn_arg_types), 
                               TREE_VALUE (decl_arg_types)))
            continue;

          /* In case of explicit specialization, we need to check if
             the number of template headers appearing in the specialization
             is correct. This is usually done in check_explicit_specialization,
             but the check done there cannot be exhaustive when specializing
             member functions. Consider the following code:

             template <> void A<int>::f(int);
             template <> template <> void A<int>::f(int);

             Assuming that A<int> is not itself an explicit specialization
             already, the first line specializes "f" which is a non-template
             member function, whilst the second line specializes "f" which
             is a template member function. So both lines are syntactically
             correct, and check_explicit_specialization does not reject
             them.
             
             Here, we can do better, as we are matching the specialization
             against the declarations. We count the number of template
             headers, and we check if they match TEMPLATE_COUNT + 1
             (TEMPLATE_COUNT is the number of qualifying template classes,
             plus there must be another header for the member template
             itself).
             
             Notice that if header_count is zero, this is not a
             specialization but rather a template instantiation, so there
             is no check we can perform here.  */
          if (header_count && header_count != template_count + 1)
            continue;

          /* Check that the number of template arguments at the
             innermost level for DECL is the same as for FN.  */
          if (current_binding_level->kind == sk_template_parms
              && !current_binding_level->explicit_spec_p
              && (TREE_VEC_LENGTH (DECL_INNERMOST_TEMPLATE_PARMS (fn))
                  != TREE_VEC_LENGTH (TREE_VALUE (current_template_parms))))
            continue;
 
          /* See whether this function might be a specialization of this
             template.  */
          targs = get_bindings (fn, decl, explicit_targs, /*check_ret=*/true);

          if (!targs)
            /* We cannot deduce template arguments that when used to
               specialize TMPL will produce DECL.  */
            continue;

          /* Save this template, and the arguments deduced.  */
          templates = tree_cons (targs, fn, templates);
        }
      else if (need_member_template)
        /* FN is an ordinary member function, and we need a
           specialization of a member template.  */
        ;
      else if (TREE_CODE (fn) != FUNCTION_DECL)
        /* We can get IDENTIFIER_NODEs here in certain erroneous
           cases.  */
        ;
      else if (!DECL_FUNCTION_MEMBER_P (fn))
        /* This is just an ordinary non-member function.  Nothing can
           be a specialization of that.  */
        ;
      else if (DECL_ARTIFICIAL (fn))
        /* Cannot specialize functions that are created implicitly.  */
        ;
      else
        {
          tree decl_arg_types;

          /* This is an ordinary member function.  However, since
             we're here, we can assume it's enclosing class is a
             template class.  For example,
             
               template <typename T> struct S { void f(); };
               template <> void S<int>::f() {}

             Here, S<int>::f is a non-template, but S<int> is a
             template class.  If FN has the same type as DECL, we
             might be in business.  */

          if (!DECL_TEMPLATE_INFO (fn))
            /* Its enclosing class is an explicit specialization
               of a template class.  This is not a candidate.  */
            continue;

          if (!same_type_p (TREE_TYPE (TREE_TYPE (decl)),
                            TREE_TYPE (TREE_TYPE (fn))))
            /* The return types differ.  */
            continue;

          /* Adjust the type of DECL in case FN is a static member.  */
          decl_arg_types = TYPE_ARG_TYPES (TREE_TYPE (decl));
          if (DECL_STATIC_FUNCTION_P (fn) 
              && DECL_NONSTATIC_MEMBER_FUNCTION_P (decl))
            decl_arg_types = TREE_CHAIN (decl_arg_types);

          if (compparms (TYPE_ARG_TYPES (TREE_TYPE (fn)), 
                         decl_arg_types))
            /* They match!  */
            candidates = tree_cons (NULL_TREE, fn, candidates);
        }
    }

  if (templates && TREE_CHAIN (templates))
    {
      /* We have:
         
           [temp.expl.spec]

           It is possible for a specialization with a given function
           signature to be instantiated from more than one function
           template.  In such cases, explicit specification of the
           template arguments must be used to uniquely identify the
           function template specialization being specialized.

         Note that here, there's no suggestion that we're supposed to
         determine which of the candidate templates is most
         specialized.  However, we, also have:

           [temp.func.order]

           Partial ordering of overloaded function template
           declarations is used in the following contexts to select
           the function template to which a function template
           specialization refers: 

           -- when an explicit specialization refers to a function
              template. 

         So, we do use the partial ordering rules, at least for now.
         This extension can only serve to make invalid programs valid,
         so it's safe.  And, there is strong anecdotal evidence that
         the committee intended the partial ordering rules to apply;
         the EDG front-end has that behavior, and John Spicer claims
         that the committee simply forgot to delete the wording in
         [temp.expl.spec].  */
     tree tmpl = most_specialized (templates, decl, explicit_targs);
     if (tmpl && tmpl != error_mark_node)
       {
         targs = get_bindings (tmpl, decl, explicit_targs, /*check_ret=*/true);
         templates = tree_cons (targs, tmpl, NULL_TREE);
       }
    }

  if (templates == NULL_TREE && candidates == NULL_TREE)
    {
      cp_error_at ("template-id %qD for %q+D does not match any template "
                   "declaration",
                   template_id, decl);
      return error_mark_node;
    }
  else if ((templates && TREE_CHAIN (templates))
           || (candidates && TREE_CHAIN (candidates))
           || (templates && candidates))
    {
      cp_error_at ("ambiguous template specialization %qD for %q+D",
                   template_id, decl);
      chainon (candidates, templates);
      print_candidates (candidates);
      return error_mark_node;
    }

  /* We have one, and exactly one, match.  */
  if (candidates)
    {
      /* It was a specialization of an ordinary member function in a
         template class.  */
      *targs_out = copy_node (DECL_TI_ARGS (TREE_VALUE (candidates)));
      return DECL_TI_TEMPLATE (TREE_VALUE (candidates));
    }

  /* It was a specialization of a template.  */
  targs = DECL_TI_ARGS (DECL_TEMPLATE_RESULT (TREE_VALUE (templates)));
  if (TMPL_ARGS_HAVE_MULTIPLE_LEVELS (targs))
    {
      *targs_out = copy_node (targs);
      SET_TMPL_ARGS_LEVEL (*targs_out, 
                           TMPL_ARGS_DEPTH (*targs_out),
                           TREE_PURPOSE (templates));
    }
  else
    *targs_out = TREE_PURPOSE (templates);
  return TREE_VALUE (templates);
}

/* Returns a chain of parameter types, exactly like the SPEC_TYPES,
   but with the default argument values filled in from those in the
   TMPL_TYPES.  */
      
static tree
copy_default_args_to_explicit_spec_1 (tree spec_types,
                                      tree tmpl_types)
{
  tree new_spec_types;

  if (!spec_types)
    return NULL_TREE;

  if (spec_types == void_list_node)
    return void_list_node;

  /* Substitute into the rest of the list.  */
  new_spec_types =
    copy_default_args_to_explicit_spec_1 (TREE_CHAIN (spec_types),
                                          TREE_CHAIN (tmpl_types));
  
  /* Add the default argument for this parameter.  */
  return hash_tree_cons (TREE_PURPOSE (tmpl_types),
                         TREE_VALUE (spec_types),
                         new_spec_types);
}

/* DECL is an explicit specialization.  Replicate default arguments
   from the template it specializes.  (That way, code like:

     template <class T> void f(T = 3);
     template <> void f(double);
     void g () { f (); } 

   works, as required.)  An alternative approach would be to look up
   the correct default arguments at the call-site, but this approach
   is consistent with how implicit instantiations are handled.  */

static void
copy_default_args_to_explicit_spec (tree decl)
{
  tree tmpl;
  tree spec_types;
  tree tmpl_types;
  tree new_spec_types;
  tree old_type;
  tree new_type;
  tree t;
  tree object_type = NULL_TREE;
  tree in_charge = NULL_TREE;
  tree vtt = NULL_TREE;

  /* See if there's anything we need to do.  */
  tmpl = DECL_TI_TEMPLATE (decl);
  tmpl_types = TYPE_ARG_TYPES (TREE_TYPE (DECL_TEMPLATE_RESULT (tmpl)));
  for (t = tmpl_types; t; t = TREE_CHAIN (t))
    if (TREE_PURPOSE (t))
      break;
  if (!t)
    return;

  old_type = TREE_TYPE (decl);
  spec_types = TYPE_ARG_TYPES (old_type);
  
  if (DECL_NONSTATIC_MEMBER_FUNCTION_P (decl))
    {
      /* Remove the this pointer, but remember the object's type for
         CV quals.  */
      object_type = TREE_TYPE (TREE_VALUE (spec_types));
      spec_types = TREE_CHAIN (spec_types);
      tmpl_types = TREE_CHAIN (tmpl_types);
      
      if (DECL_HAS_IN_CHARGE_PARM_P (decl))
        {
          /* DECL may contain more parameters than TMPL due to the extra
             in-charge parameter in constructors and destructors.  */
          in_charge = spec_types;
          spec_types = TREE_CHAIN (spec_types);
        }
      if (DECL_HAS_VTT_PARM_P (decl))
        {
          vtt = spec_types;
          spec_types = TREE_CHAIN (spec_types);
        }
    }

  /* Compute the merged default arguments.  */
  new_spec_types = 
    copy_default_args_to_explicit_spec_1 (spec_types, tmpl_types);

  /* Compute the new FUNCTION_TYPE.  */
  if (object_type)
    {
      if (vtt)
        new_spec_types = hash_tree_cons (TREE_PURPOSE (vtt),
                                         TREE_VALUE (vtt),
                                         new_spec_types);

      if (in_charge)
        /* Put the in-charge parameter back.  */
        new_spec_types = hash_tree_cons (TREE_PURPOSE (in_charge),
                                         TREE_VALUE (in_charge),
                                         new_spec_types);

      new_type = build_method_type_directly (object_type,
                                             TREE_TYPE (old_type),
                                             new_spec_types);
    }
  else
    new_type = build_function_type (TREE_TYPE (old_type),
                                    new_spec_types);
  new_type = cp_build_type_attribute_variant (new_type,
                                              TYPE_ATTRIBUTES (old_type));
  new_type = build_exception_variant (new_type,
                                      TYPE_RAISES_EXCEPTIONS (old_type));
  TREE_TYPE (decl) = new_type;
}

/* Check to see if the function just declared, as indicated in
   DECLARATOR, and in DECL, is a specialization of a function
   template.  We may also discover that the declaration is an explicit
   instantiation at this point.

   Returns DECL, or an equivalent declaration that should be used
   instead if all goes well.  Issues an error message if something is
   amiss.  Returns error_mark_node if the error is not easily
   recoverable.
   
   FLAGS is a bitmask consisting of the following flags: 

   2: The function has a definition.
   4: The function is a friend.

   The TEMPLATE_COUNT is the number of references to qualifying
   template classes that appeared in the name of the function.  For
   example, in

     template <class T> struct S { void f(); };
     void S<int>::f();
     
   the TEMPLATE_COUNT would be 1.  However, explicitly specialized
   classes are not counted in the TEMPLATE_COUNT, so that in

     template <class T> struct S {};
     template <> struct S<int> { void f(); }
     template <> void S<int>::f();

   the TEMPLATE_COUNT would be 0.  (Note that this declaration is
   invalid; there should be no template <>.)

   If the function is a specialization, it is marked as such via
   DECL_TEMPLATE_SPECIALIZATION.  Furthermore, its DECL_TEMPLATE_INFO
   is set up correctly, and it is added to the list of specializations 
   for that template.  */

tree
check_explicit_specialization (tree declarator, 
                               tree decl, 
                               int template_count, 
                               int flags)
{
  int have_def = flags & 2;
  int is_friend = flags & 4;
  int specialization = 0;
  int explicit_instantiation = 0;
  int member_specialization = 0;
  tree ctype = DECL_CLASS_CONTEXT (decl);
  tree dname = DECL_NAME (decl);
  tmpl_spec_kind tsk;

  if (is_friend)
    {
      if (!processing_specialization)
        tsk = tsk_none;
      else
        tsk = tsk_excessive_parms;
    }
  else
    tsk = current_tmpl_spec_kind (template_count);

  switch (tsk)
    {
    case tsk_none:
      if (processing_specialization) 
        {
          specialization = 1;
          SET_DECL_TEMPLATE_SPECIALIZATION (decl);
        }
      else if (TREE_CODE (declarator) == TEMPLATE_ID_EXPR)
        {
          if (is_friend)
            /* This could be something like:

               template <class T> void f(T);
               class S { friend void f<>(int); }  */
            specialization = 1;
          else
            {
              /* This case handles bogus declarations like template <>
                 template <class T> void f<int>(); */

              error ("template-id %qD in declaration of primary template",
                     declarator);
              return decl;
            }
        }
      break;

    case tsk_invalid_member_spec:
      /* The error has already been reported in
         check_specialization_scope.  */
      return error_mark_node;

    case tsk_invalid_expl_inst:
      error ("template parameter list used in explicit instantiation");

      /* Fall through.  */

    case tsk_expl_inst:
      if (have_def)
        error ("definition provided for explicit instantiation");
      
      explicit_instantiation = 1;
      break;

    case tsk_excessive_parms:
    case tsk_insufficient_parms:
      if (tsk == tsk_excessive_parms)
        error ("too many template parameter lists in declaration of %qD",
               decl);
      else if (template_header_count)
        error("too few template parameter lists in declaration of %qD", decl);
      else
        error("explicit specialization of %qD must be introduced by "
              "%<template <>%>", decl);

      /* Fall through.  */
    case tsk_expl_spec:
      SET_DECL_TEMPLATE_SPECIALIZATION (decl);
      if (ctype)
        member_specialization = 1;
      else
        specialization = 1;
      break;

    case tsk_template:
      if (TREE_CODE (declarator) == TEMPLATE_ID_EXPR)
        {
          /* This case handles bogus declarations like template <>
             template <class T> void f<int>(); */

          if (uses_template_parms (declarator))
            error ("function template partial specialization %qD "
                   "is not allowed", declarator);
          else
            error ("template-id %qD in declaration of primary template",
                   declarator);
          return decl;
        }

      if (ctype && CLASSTYPE_TEMPLATE_INSTANTIATION (ctype))
        /* This is a specialization of a member template, without
           specialization the containing class.  Something like:

             template <class T> struct S {
               template <class U> void f (U); 
             };
             template <> template <class U> void S<int>::f(U) {}
             
           That's a specialization -- but of the entire template.  */
        specialization = 1;
      break;

    default:
      gcc_unreachable ();
    }

  if (specialization || member_specialization)
    {
      tree t = TYPE_ARG_TYPES (TREE_TYPE (decl));
      for (; t; t = TREE_CHAIN (t))
        if (TREE_PURPOSE (t))
          {
            pedwarn
              ("default argument specified in explicit specialization");
            break;
          }
      if (current_lang_name == lang_name_c)
        error ("template specialization with C linkage");
    }

  if (specialization || member_specialization || explicit_instantiation)
    {
      tree tmpl = NULL_TREE;
      tree targs = NULL_TREE;

      /* Make sure that the declarator is a TEMPLATE_ID_EXPR.  */
      if (TREE_CODE (declarator) != TEMPLATE_ID_EXPR)
        {
          tree fns;

          gcc_assert (TREE_CODE (declarator) == IDENTIFIER_NODE);
          if (ctype)
            fns = dname;
          else
            {
              /* If there is no class context, the explicit instantiation
                 must be at namespace scope.  */
              gcc_assert (DECL_NAMESPACE_SCOPE_P (decl));

              /* Find the namespace binding, using the declaration
                 context.  */
              fns = namespace_binding (dname, CP_DECL_CONTEXT (decl));
              if (!fns || !is_overloaded_fn (fns))
                {
                  error ("%qD is not a template function", dname);
                  fns = error_mark_node;
                }
            }

          declarator = lookup_template_function (fns, NULL_TREE);
        }

      if (declarator == error_mark_node)
        return error_mark_node;

      if (ctype != NULL_TREE && TYPE_BEING_DEFINED (ctype))
        {
          if (!explicit_instantiation)
            /* A specialization in class scope.  This is invalid,
               but the error will already have been flagged by
               check_specialization_scope.  */
            return error_mark_node;
          else
            {
              /* It's not valid to write an explicit instantiation in
                 class scope, e.g.:

                   class C { template void f(); }

                   This case is caught by the parser.  However, on
                   something like:
               
                   template class C { void f(); };

                   (which is invalid) we can get here.  The error will be
                   issued later.  */
              ;
            }

          return decl;
        }
      else if (ctype != NULL_TREE 
               && (TREE_CODE (TREE_OPERAND (declarator, 0)) ==
                   IDENTIFIER_NODE))
        {
          /* Find the list of functions in ctype that have the same
             name as the declared function.  */
          tree name = TREE_OPERAND (declarator, 0);
          tree fns = NULL_TREE;
          int idx;

          if (constructor_name_p (name, ctype))
            {
              int is_constructor = DECL_CONSTRUCTOR_P (decl);
              
              if (is_constructor ? !TYPE_HAS_CONSTRUCTOR (ctype)
                  : !CLASSTYPE_DESTRUCTORS (ctype))
                {
                  /* From [temp.expl.spec]:
                       
                     If such an explicit specialization for the member
                     of a class template names an implicitly-declared
                     special member function (clause _special_), the
                     program is ill-formed.  

                     Similar language is found in [temp.explicit].  */
                  error ("specialization of implicitly-declared special member function");
                  return error_mark_node;
                }

              name = is_constructor ? ctor_identifier : dtor_identifier;
            }

          if (!DECL_CONV_FN_P (decl))
            {
              idx = lookup_fnfields_1 (ctype, name);
              if (idx >= 0)
                fns = VEC_index (tree, CLASSTYPE_METHOD_VEC (ctype), idx);
            }
          else
            {
              VEC(tree,gc) *methods;
              tree ovl;

              /* For a type-conversion operator, we cannot do a
                 name-based lookup.  We might be looking for `operator
                 int' which will be a specialization of `operator T'.
                 So, we find *all* the conversion operators, and then
                 select from them.  */
              fns = NULL_TREE;

              methods = CLASSTYPE_METHOD_VEC (ctype);
              if (methods)
                for (idx = CLASSTYPE_FIRST_CONVERSION_SLOT;
                     VEC_iterate (tree, methods, idx, ovl);
                     ++idx)
                  {
                    if (!DECL_CONV_FN_P (OVL_CURRENT (ovl)))
                      /* There are no more conversion functions.  */
                      break;

                    /* Glue all these conversion functions together
                       with those we already have.  */
                    for (; ovl; ovl = OVL_NEXT (ovl))
                      fns = ovl_cons (OVL_CURRENT (ovl), fns);
                  }
            }
              
          if (fns == NULL_TREE) 
            {
              error ("no member function %qD declared in %qT", name, ctype);
              return error_mark_node;
            }
          else
            TREE_OPERAND (declarator, 0) = fns;
        }
      
      /* Figure out what exactly is being specialized at this point.
         Note that for an explicit instantiation, even one for a
         member function, we cannot tell apriori whether the
         instantiation is for a member template, or just a member
         function of a template class.  Even if a member template is
         being instantiated, the member template arguments may be
         elided if they can be deduced from the rest of the
         declaration.  */
      tmpl = determine_specialization (declarator, decl,
                                       &targs, 
                                       member_specialization,
                                       template_count);
            
      if (!tmpl || tmpl == error_mark_node)
        /* We couldn't figure out what this declaration was
           specializing.  */
        return error_mark_node;
      else
        {
          tree gen_tmpl = most_general_template (tmpl);

          if (explicit_instantiation)
            {
              /* We don't set DECL_EXPLICIT_INSTANTIATION here; that
                 is done by do_decl_instantiation later.  */ 

              int arg_depth = TMPL_ARGS_DEPTH (targs);
              int parm_depth = TMPL_PARMS_DEPTH (DECL_TEMPLATE_PARMS (tmpl));

              if (arg_depth > parm_depth)
                {
                  /* If TMPL is not the most general template (for
                     example, if TMPL is a friend template that is
                     injected into namespace scope), then there will
                     be too many levels of TARGS.  Remove some of them
                     here.  */
                  int i;
                  tree new_targs;

                  new_targs = make_tree_vec (parm_depth);
                  for (i = arg_depth - parm_depth; i < arg_depth; ++i)
                    TREE_VEC_ELT (new_targs, i - (arg_depth - parm_depth))
                      = TREE_VEC_ELT (targs, i);
                  targs = new_targs;
                }
                  
              return instantiate_template (tmpl, targs, tf_error);
            }

          /* If we thought that the DECL was a member function, but it
             turns out to be specializing a static member function,
             make DECL a static member function as well.  */
          if (DECL_STATIC_FUNCTION_P (tmpl)
              && DECL_NONSTATIC_MEMBER_FUNCTION_P (decl))
            revert_static_member_fn (decl);

          /* If this is a specialization of a member template of a
             template class.  In we want to return the TEMPLATE_DECL,
             not the specialization of it.  */
          if (tsk == tsk_template)
            {
              SET_DECL_TEMPLATE_SPECIALIZATION (tmpl);
              DECL_INITIAL (DECL_TEMPLATE_RESULT (tmpl)) = NULL_TREE;
              if (have_def)
                {
                  DECL_SOURCE_LOCATION (tmpl) = DECL_SOURCE_LOCATION (decl);
                  DECL_SOURCE_LOCATION (DECL_TEMPLATE_RESULT (tmpl))
                    = DECL_SOURCE_LOCATION (decl);
                  /* We want to use the argument list specified in the
                     definition, not in the original declaration.  */
                  DECL_ARGUMENTS (DECL_TEMPLATE_RESULT (tmpl))
                    = DECL_ARGUMENTS (decl);
                }
              return tmpl;
            }

          /* Set up the DECL_TEMPLATE_INFO for DECL.  */
          DECL_TEMPLATE_INFO (decl) = tree_cons (tmpl, targs, NULL_TREE);

          /* Inherit default function arguments from the template
             DECL is specializing.  */
          copy_default_args_to_explicit_spec (decl);

          /* This specialization has the same protection as the
             template it specializes.  */
          TREE_PRIVATE (decl) = TREE_PRIVATE (gen_tmpl);
          TREE_PROTECTED (decl) = TREE_PROTECTED (gen_tmpl);

          if (is_friend && !have_def)
            /* This is not really a declaration of a specialization.
               It's just the name of an instantiation.  But, it's not
               a request for an instantiation, either.  */
            SET_DECL_IMPLICIT_INSTANTIATION (decl);
          else if (DECL_CONSTRUCTOR_P (decl) || DECL_DESTRUCTOR_P (decl))
            /* This is indeed a specialization.  In case of constructors
               and destructors, we need in-charge and not-in-charge
               versions in V3 ABI.  */
            clone_function_decl (decl, /*update_method_vec_p=*/0);

          /* Register this specialization so that we can find it
             again.  */
          decl = register_specialization (decl, gen_tmpl, targs);
        }
    }
  
  return decl;
}

/* Returns 1 iff PARMS1 and PARMS2 are identical sets of template
   parameters.  These are represented in the same format used for
   DECL_TEMPLATE_PARMS.  */

int
comp_template_parms (tree parms1, tree parms2)
{
  tree p1;
  tree p2;

  if (parms1 == parms2)
    return 1;

  for (p1 = parms1, p2 = parms2; 
       p1 != NULL_TREE && p2 != NULL_TREE;
       p1 = TREE_CHAIN (p1), p2 = TREE_CHAIN (p2))
    {
      tree t1 = TREE_VALUE (p1);
      tree t2 = TREE_VALUE (p2);
      int i;

      gcc_assert (TREE_CODE (t1) == TREE_VEC);
      gcc_assert (TREE_CODE (t2) == TREE_VEC);

      if (TREE_VEC_LENGTH (t1) != TREE_VEC_LENGTH (t2))
        return 0;

      for (i = 0; i < TREE_VEC_LENGTH (t2); ++i) 
        {
          tree parm1 = TREE_VALUE (TREE_VEC_ELT (t1, i));
          tree parm2 = TREE_VALUE (TREE_VEC_ELT (t2, i));

          if (TREE_CODE (parm1) != TREE_CODE (parm2))
            return 0;

          if (TREE_CODE (parm1) == TEMPLATE_TYPE_PARM)
            continue;
          else if (!same_type_p (TREE_TYPE (parm1), TREE_TYPE (parm2)))
            return 0;
        }
    }

  if ((p1 != NULL_TREE) != (p2 != NULL_TREE))
    /* One set of parameters has more parameters lists than the
       other.  */
    return 0;

  return 1;
}

/* Complain if DECL shadows a template parameter.

   [temp.local]: A template-parameter shall not be redeclared within its
   scope (including nested scopes).  */

void
check_template_shadow (tree decl)
{
  tree olddecl;

  /* If we're not in a template, we can't possibly shadow a template
     parameter.  */
  if (!current_template_parms)
    return;

  /* Figure out what we're shadowing.  */
  if (TREE_CODE (decl) == OVERLOAD)
    decl = OVL_CURRENT (decl);
  olddecl = innermost_non_namespace_value (DECL_NAME (decl));

  /* If there's no previous binding for this name, we're not shadowing
     anything, let alone a template parameter.  */
  if (!olddecl)
    return;

  /* If we're not shadowing a template parameter, we're done.  Note
     that OLDDECL might be an OVERLOAD (or perhaps even an
     ERROR_MARK), so we can't just blithely assume it to be a _DECL
     node.  */
  if (!DECL_P (olddecl) || !DECL_TEMPLATE_PARM_P (olddecl))
    return;

  /* We check for decl != olddecl to avoid bogus errors for using a
     name inside a class.  We check TPFI to avoid duplicate errors for
     inline member templates.  */
  if (decl == olddecl 
      || TEMPLATE_PARMS_FOR_INLINE (current_template_parms))
    return;

  cp_error_at ("declaration of %q#D", decl);
  cp_error_at (" shadows template parm %q#D", olddecl);
}

/* Return a new TEMPLATE_PARM_INDEX with the indicated INDEX, LEVEL,
   ORIG_LEVEL, DECL, and TYPE.  */

static tree
build_template_parm_index (int index, 
                           int level, 
                           int orig_level, 
                           tree decl, 
                           tree type)
{
  tree t = make_node (TEMPLATE_PARM_INDEX);
  TEMPLATE_PARM_IDX (t) = index;
  TEMPLATE_PARM_LEVEL (t) = level;
  TEMPLATE_PARM_ORIG_LEVEL (t) = orig_level;
  TEMPLATE_PARM_DECL (t) = decl;
  TREE_TYPE (t) = type;
  TREE_CONSTANT (t) = TREE_CONSTANT (decl);
  TREE_INVARIANT (t) = TREE_INVARIANT (decl);
  TREE_READONLY (t) = TREE_READONLY (decl);

  return t;
}

/* Return a TEMPLATE_PARM_INDEX, similar to INDEX, but whose
   TEMPLATE_PARM_LEVEL has been decreased by LEVELS.  If such a
   TEMPLATE_PARM_INDEX already exists, it is returned; otherwise, a
   new one is created.  */

static tree 
reduce_template_parm_level (tree index, tree type, int levels)
{
  if (TEMPLATE_PARM_DESCENDANTS (index) == NULL_TREE
      || (TEMPLATE_PARM_LEVEL (TEMPLATE_PARM_DESCENDANTS (index))
          != TEMPLATE_PARM_LEVEL (index) - levels))
    {
      tree orig_decl = TEMPLATE_PARM_DECL (index);
      tree decl, t;
      
      decl = build_decl (TREE_CODE (orig_decl), DECL_NAME (orig_decl), type);
      TREE_CONSTANT (decl) = TREE_CONSTANT (orig_decl);
      TREE_INVARIANT (decl) = TREE_INVARIANT (orig_decl);
      TREE_READONLY (decl) = TREE_READONLY (orig_decl);
      DECL_ARTIFICIAL (decl) = 1;
      SET_DECL_TEMPLATE_PARM_P (decl);
      
      t = build_template_parm_index (TEMPLATE_PARM_IDX (index),
                                     TEMPLATE_PARM_LEVEL (index) - levels,
                                     TEMPLATE_PARM_ORIG_LEVEL (index),
                                     decl, type);
      TEMPLATE_PARM_DESCENDANTS (index) = t;

      /* Template template parameters need this.  */
      DECL_TEMPLATE_PARMS (decl)
        = DECL_TEMPLATE_PARMS (TEMPLATE_PARM_DECL (index));
    }

  return TEMPLATE_PARM_DESCENDANTS (index);
}

/* Process information from new template parameter NEXT and append it to the
   LIST being built.  This new parameter is a non-type parameter iff
   IS_NON_TYPE is true.  */

tree
process_template_parm (tree list, tree next, bool is_non_type)
{
  tree parm;
  tree decl = 0;
  tree defval;
  int idx;

  parm = next;
  gcc_assert (TREE_CODE (parm) == TREE_LIST);
  defval = TREE_PURPOSE (parm);

  if (list)
    {
      tree p = TREE_VALUE (tree_last (list));

      if (TREE_CODE (p) == TYPE_DECL || TREE_CODE (p) == TEMPLATE_DECL)
        idx = TEMPLATE_TYPE_IDX (TREE_TYPE (p));
      else
        idx = TEMPLATE_PARM_IDX (DECL_INITIAL (p));
      ++idx;
    }
  else
    idx = 0;

  if (is_non_type)
    {
      parm = TREE_VALUE (parm);

      SET_DECL_TEMPLATE_PARM_P (parm);

      /* [temp.param]

         The top-level cv-qualifiers on the template-parameter are
         ignored when determining its type.  */
      TREE_TYPE (parm) = TYPE_MAIN_VARIANT (TREE_TYPE (parm));

      /* A template parameter is not modifiable.  */
      TREE_CONSTANT (parm) = 1;
      TREE_INVARIANT (parm) = 1;
      TREE_READONLY (parm) = 1;
      if (invalid_nontype_parm_type_p (TREE_TYPE (parm), 1))
        TREE_TYPE (parm) = void_type_node;
      decl = build_decl (CONST_DECL, DECL_NAME (parm), TREE_TYPE (parm));
      TREE_CONSTANT (decl) = 1;
      TREE_INVARIANT (decl) = 1;
      TREE_READONLY (decl) = 1;
      DECL_INITIAL (parm) = DECL_INITIAL (decl) 
        = build_template_parm_index (idx, processing_template_decl,
                                     processing_template_decl,
                                     decl, TREE_TYPE (parm));
    }
  else
    {
      tree t;
      parm = TREE_VALUE (TREE_VALUE (parm));
      
      if (parm && TREE_CODE (parm) == TEMPLATE_DECL)
        {
          t = make_aggr_type (TEMPLATE_TEMPLATE_PARM);
          /* This is for distinguishing between real templates and template 
             template parameters */
          TREE_TYPE (parm) = t;
          TREE_TYPE (DECL_TEMPLATE_RESULT (parm)) = t;
          decl = parm;
        }
      else
        {
          t = make_aggr_type (TEMPLATE_TYPE_PARM);
          /* parm is either IDENTIFIER_NODE or NULL_TREE.  */
          decl = build_decl (TYPE_DECL, parm, t);
        }
        
      TYPE_NAME (t) = decl;
      TYPE_STUB_DECL (t) = decl;
      parm = decl;
      TEMPLATE_TYPE_PARM_INDEX (t)
        = build_template_parm_index (idx, processing_template_decl, 
                                     processing_template_decl,
                                     decl, TREE_TYPE (parm));
    }
  DECL_ARTIFICIAL (decl) = 1;
  SET_DECL_TEMPLATE_PARM_P (decl);
  pushdecl (decl);
  parm = build_tree_list (defval, parm);
  return chainon (list, parm);
}

/* The end of a template parameter list has been reached.  Process the
   tree list into a parameter vector, converting each parameter into a more
   useful form.  Type parameters are saved as IDENTIFIER_NODEs, and others
   as PARM_DECLs.  */

tree
end_template_parm_list (tree parms)
{
  int nparms;
  tree parm, next;
  tree saved_parmlist = make_tree_vec (list_length (parms));

  current_template_parms
    = tree_cons (size_int (processing_template_decl),
                 saved_parmlist, current_template_parms);

  for (parm = parms, nparms = 0; parm; parm = next, nparms++)
    {
      next = TREE_CHAIN (parm);
      TREE_VEC_ELT (saved_parmlist, nparms) = parm;
      TREE_CHAIN (parm) = NULL_TREE;
    }

  --processing_template_parmlist;

  return saved_parmlist;
}

/* end_template_decl is called after a template declaration is seen.  */

void
end_template_decl (void)
{
  reset_specialization ();

  if (! processing_template_decl)
    return;

  /* This matches the pushlevel in begin_template_parm_list.  */
  finish_scope ();

  --processing_template_decl;
  current_template_parms = TREE_CHAIN (current_template_parms);
}

/* Given a template argument vector containing the template PARMS.
   The innermost PARMS are given first.  */

tree
current_template_args (void)
{
  tree header;
  tree args = NULL_TREE;
  int length = TMPL_PARMS_DEPTH (current_template_parms);
  int l = length;

  /* If there is only one level of template parameters, we do not
     create a TREE_VEC of TREE_VECs.  Instead, we return a single
     TREE_VEC containing the arguments.  */
  if (length > 1)
    args = make_tree_vec (length);

  for (header = current_template_parms; header; header = TREE_CHAIN (header))
    {
      tree a = copy_node (TREE_VALUE (header));
      int i;

      TREE_TYPE (a) = NULL_TREE;
      for (i = TREE_VEC_LENGTH (a) - 1; i >= 0; --i)
        {
          tree t = TREE_VEC_ELT (a, i);

          /* T will be a list if we are called from within a
             begin/end_template_parm_list pair, but a vector directly
             if within a begin/end_member_template_processing pair.  */
          if (TREE_CODE (t) == TREE_LIST) 
            {
              t = TREE_VALUE (t);
              
              if (TREE_CODE (t) == TYPE_DECL 
                  || TREE_CODE (t) == TEMPLATE_DECL)
                t = TREE_TYPE (t);
              else
                t = DECL_INITIAL (t);
              TREE_VEC_ELT (a, i) = t;
            }
        }

      if (length > 1)
        TREE_VEC_ELT (args, --l) = a;
      else
        args = a;
    }

  return args;
}

/* Return a TEMPLATE_DECL corresponding to DECL, using the indicated
   template PARMS.  If MEMBER_TEMPLATE_P is true, the new template is
   a member template.  Used by push_template_decl below.  */

static tree
build_template_decl (tree decl, tree parms, bool member_template_p)
{
  tree tmpl = build_lang_decl (TEMPLATE_DECL, DECL_NAME (decl), NULL_TREE);
  DECL_TEMPLATE_PARMS (tmpl) = parms;
  DECL_CONTEXT (tmpl) = DECL_CONTEXT (decl);
  DECL_MEMBER_TEMPLATE_P (tmpl) = member_template_p;
  if (DECL_LANG_SPECIFIC (decl))
    {
      DECL_STATIC_FUNCTION_P (tmpl) = DECL_STATIC_FUNCTION_P (decl);
      DECL_CONSTRUCTOR_P (tmpl) = DECL_CONSTRUCTOR_P (decl);
      DECL_DESTRUCTOR_P (tmpl) = DECL_DESTRUCTOR_P (decl);
      DECL_NONCONVERTING_P (tmpl) = DECL_NONCONVERTING_P (decl);
      DECL_ASSIGNMENT_OPERATOR_P (tmpl) = DECL_ASSIGNMENT_OPERATOR_P (decl);
      if (DECL_OVERLOADED_OPERATOR_P (decl))
        SET_OVERLOADED_OPERATOR_CODE (tmpl, 
                                      DECL_OVERLOADED_OPERATOR_P (decl));
    }

  return tmpl;
}

struct template_parm_data
{
  /* The level of the template parameters we are currently
     processing.  */
  int level;

  /* The index of the specialization argument we are currently
     processing.  */
  int current_arg;

  /* An array whose size is the number of template parameters.  The
     elements are nonzero if the parameter has been used in any one
     of the arguments processed so far.  */
  int* parms;

  /* An array whose size is the number of template arguments.  The
     elements are nonzero if the argument makes use of template
     parameters of this level.  */
  int* arg_uses_template_parms;
};

/* Subroutine of push_template_decl used to see if each template
   parameter in a partial specialization is used in the explicit
   argument list.  If T is of the LEVEL given in DATA (which is
   treated as a template_parm_data*), then DATA->PARMS is marked
   appropriately.  */

static int
mark_template_parm (tree t, void* data)
{
  int level;
  int idx;
  struct template_parm_data* tpd = (struct template_parm_data*) data;

  if (TREE_CODE (t) == TEMPLATE_PARM_INDEX)
    {
      level = TEMPLATE_PARM_LEVEL (t);
      idx = TEMPLATE_PARM_IDX (t);
    }
  else
    {
      level = TEMPLATE_TYPE_LEVEL (t);
      idx = TEMPLATE_TYPE_IDX (t);
    }

  if (level == tpd->level)
    {
      tpd->parms[idx] = 1;
      tpd->arg_uses_template_parms[tpd->current_arg] = 1;
    }

  /* Return zero so that for_each_template_parm will continue the
     traversal of the tree; we want to mark *every* template parm.  */
  return 0;
}

/* Process the partial specialization DECL.  */

static tree
process_partial_specialization (tree decl)
{
  tree type = TREE_TYPE (decl);
  tree maintmpl = CLASSTYPE_TI_TEMPLATE (type);
  tree specargs = CLASSTYPE_TI_ARGS (type);
  tree inner_args = INNERMOST_TEMPLATE_ARGS (specargs);
  tree inner_parms = INNERMOST_TEMPLATE_PARMS (current_template_parms);
  tree main_inner_parms = DECL_INNERMOST_TEMPLATE_PARMS (maintmpl);
  int nargs = TREE_VEC_LENGTH (inner_args);
  int ntparms = TREE_VEC_LENGTH (inner_parms);
  int  i;
  int did_error_intro = 0;
  struct template_parm_data tpd;
  struct template_parm_data tpd2;

  /* We check that each of the template parameters given in the
     partial specialization is used in the argument list to the
     specialization.  For example:

       template <class T> struct S;
       template <class T> struct S<T*>;

     The second declaration is OK because `T*' uses the template
     parameter T, whereas

       template <class T> struct S<int>;

     is no good.  Even trickier is:

       template <class T>
       struct S1
       {
          template <class U>
          struct S2;
          template <class U>
          struct S2<T>;
       };

     The S2<T> declaration is actually invalid; it is a
     full-specialization.  Of course, 

          template <class U>
          struct S2<T (*)(U)>;

     or some such would have been OK.  */
  tpd.level = TMPL_PARMS_DEPTH (current_template_parms);
  tpd.parms = alloca (sizeof (int) * ntparms);
  memset (tpd.parms, 0, sizeof (int) * ntparms);

  tpd.arg_uses_template_parms = alloca (sizeof (int) * nargs);
  memset (tpd.arg_uses_template_parms, 0, sizeof (int) * nargs);
  for (i = 0; i < nargs; ++i)
    {
      tpd.current_arg = i;
      for_each_template_parm (TREE_VEC_ELT (inner_args, i),
                              &mark_template_parm,
                              &tpd,
                              NULL);
    }
  for (i = 0; i < ntparms; ++i)
    if (tpd.parms[i] == 0)
      {
        /* One of the template parms was not used in the
           specialization.  */
        if (!did_error_intro)
          {
            error ("template parameters not used in partial specialization:");
            did_error_intro = 1;
          }

        error ("        %qD", TREE_VALUE (TREE_VEC_ELT (inner_parms, i)));
      }

  /* [temp.class.spec]

     The argument list of the specialization shall not be identical to
     the implicit argument list of the primary template.  */
  if (comp_template_args 
      (inner_args, 
       INNERMOST_TEMPLATE_ARGS (CLASSTYPE_TI_ARGS (TREE_TYPE
                                                   (maintmpl)))))
    error ("partial specialization %qT does not specialize any template arguments", type);

  /* [temp.class.spec]

     A partially specialized non-type argument expression shall not
     involve template parameters of the partial specialization except
     when the argument expression is a simple identifier.

     The type of a template parameter corresponding to a specialized
     non-type argument shall not be dependent on a parameter of the
     specialization.  */
  gcc_assert (nargs == DECL_NTPARMS (maintmpl));
  tpd2.parms = 0;
  for (i = 0; i < nargs; ++i)
    {
      tree arg = TREE_VEC_ELT (inner_args, i);
      if (/* These first two lines are the `non-type' bit.  */
          !TYPE_P (arg)
          && TREE_CODE (arg) != TEMPLATE_DECL
          /* This next line is the `argument expression is not just a
             simple identifier' condition and also the `specialized
             non-type argument' bit.  */
          && TREE_CODE (arg) != TEMPLATE_PARM_INDEX)
        {
          if (tpd.arg_uses_template_parms[i])
            error ("template argument %qE involves template parameter(s)", arg);
          else 
            {
              /* Look at the corresponding template parameter,
                 marking which template parameters its type depends
                 upon.  */
              tree type = 
                TREE_TYPE (TREE_VALUE (TREE_VEC_ELT (main_inner_parms, 
                                                     i)));

              if (!tpd2.parms)
                {
                  /* We haven't yet initialized TPD2.  Do so now.  */
                  tpd2.arg_uses_template_parms 
                    = alloca (sizeof (int) * nargs);
                  /* The number of parameters here is the number in the
                     main template, which, as checked in the assertion
                     above, is NARGS.  */
                  tpd2.parms = alloca (sizeof (int) * nargs);
                  tpd2.level = 
                    TMPL_PARMS_DEPTH (DECL_TEMPLATE_PARMS (maintmpl));
                }

              /* Mark the template parameters.  But this time, we're
                 looking for the template parameters of the main
                 template, not in the specialization.  */
              tpd2.current_arg = i;
              tpd2.arg_uses_template_parms[i] = 0;
              memset (tpd2.parms, 0, sizeof (int) * nargs);
              for_each_template_parm (type,
                                      &mark_template_parm,
                                      &tpd2,
                                      NULL);
                  
              if (tpd2.arg_uses_template_parms [i])
                {
                  /* The type depended on some template parameters.
                     If they are fully specialized in the
                     specialization, that's OK.  */
                  int j;
                  for (j = 0; j < nargs; ++j)
                    if (tpd2.parms[j] != 0
                        && tpd.arg_uses_template_parms [j])
                      {
                        error ("type %qT of template argument %qE depends "
                               "on template parameter(s)", 
                               type,
                               arg);
                        break;
                      }
                }
            }
        }
    }

  if (retrieve_specialization (maintmpl, specargs, 
                               /*class_specializations_p=*/true))
    /* We've already got this specialization.  */
    return decl;

  DECL_TEMPLATE_SPECIALIZATIONS (maintmpl)
    = tree_cons (inner_args, inner_parms,
                 DECL_TEMPLATE_SPECIALIZATIONS (maintmpl));
  TREE_TYPE (DECL_TEMPLATE_SPECIALIZATIONS (maintmpl)) = type;
  return decl;
}

/* Check that a template declaration's use of default arguments is not
   invalid.  Here, PARMS are the template parameters.  IS_PRIMARY is
   nonzero if DECL is the thing declared by a primary template.
   IS_PARTIAL is nonzero if DECL is a partial specialization.  */

static void
check_default_tmpl_args (tree decl, tree parms, int is_primary, int is_partial)
{
  const char *msg;
  int last_level_to_check;
  tree parm_level;

  /* [temp.param] 

     A default template-argument shall not be specified in a
     function template declaration or a function template definition, nor
     in the template-parameter-list of the definition of a member of a
     class template.  */

  if (TREE_CODE (CP_DECL_CONTEXT (decl)) == FUNCTION_DECL)
    /* You can't have a function template declaration in a local
       scope, nor you can you define a member of a class template in a
       local scope.  */
    return;

  if (current_class_type
      && !TYPE_BEING_DEFINED (current_class_type)
      && DECL_LANG_SPECIFIC (decl)
      /* If this is either a friend defined in the scope of the class
         or a member function.  */
      && (DECL_FUNCTION_MEMBER_P (decl)
          ? same_type_p (DECL_CONTEXT (decl), current_class_type)
          : DECL_FRIEND_CONTEXT (decl)
          ? same_type_p (DECL_FRIEND_CONTEXT (decl), current_class_type)
          : false)
      /* And, if it was a member function, it really was defined in
         the scope of the class.  */
      && (!DECL_FUNCTION_MEMBER_P (decl)
          || DECL_INITIALIZED_IN_CLASS_P (decl)))
    /* We already checked these parameters when the template was
       declared, so there's no need to do it again now.  This function
       was defined in class scope, but we're processing it's body now
       that the class is complete.  */
    return;

  /* [temp.param]
         
     If a template-parameter has a default template-argument, all
     subsequent template-parameters shall have a default
     template-argument supplied.  */
  for (parm_level = parms; parm_level; parm_level = TREE_CHAIN (parm_level))
    {
      tree inner_parms = TREE_VALUE (parm_level);
      int ntparms = TREE_VEC_LENGTH (inner_parms);
      int seen_def_arg_p = 0; 
      int i;

      for (i = 0; i < ntparms; ++i) 
        {
          tree parm = TREE_VEC_ELT (inner_parms, i);
          if (TREE_PURPOSE (parm))
            seen_def_arg_p = 1;
          else if (seen_def_arg_p)
            {
              error ("no default argument for %qD", TREE_VALUE (parm));
              /* For better subsequent error-recovery, we indicate that
                 there should have been a default argument.  */
              TREE_PURPOSE (parm) = error_mark_node;
            }
        }
    }

  if (TREE_CODE (decl) != TYPE_DECL || is_partial || !is_primary)
    /* For an ordinary class template, default template arguments are
       allowed at the innermost level, e.g.:
         template <class T = int>
         struct S {};
       but, in a partial specialization, they're not allowed even
       there, as we have in [temp.class.spec]:
     
         The template parameter list of a specialization shall not
         contain default template argument values.  

       So, for a partial specialization, or for a function template,
       we look at all of them.  */
    ;
  else
    /* But, for a primary class template that is not a partial
       specialization we look at all template parameters except the
       innermost ones.  */
    parms = TREE_CHAIN (parms);

  /* Figure out what error message to issue.  */
  if (TREE_CODE (decl) == FUNCTION_DECL)
    msg = "default template arguments may not be used in function templates";
  else if (is_partial)
    msg = "default template arguments may not be used in partial specializations";
  else
    msg = "default argument for template parameter for class enclosing %qD";

  if (current_class_type && TYPE_BEING_DEFINED (current_class_type))
    /* If we're inside a class definition, there's no need to
       examine the parameters to the class itself.  On the one
       hand, they will be checked when the class is defined, and,
       on the other, default arguments are valid in things like:
         template <class T = double>
         struct S { template <class U> void f(U); };
       Here the default argument for `S' has no bearing on the
       declaration of `f'.  */
    last_level_to_check = template_class_depth (current_class_type) + 1;
  else
    /* Check everything.  */
    last_level_to_check = 0;

  for (parm_level = parms; 
       parm_level && TMPL_PARMS_DEPTH (parm_level) >= last_level_to_check; 
       parm_level = TREE_CHAIN (parm_level))
    {
      tree inner_parms = TREE_VALUE (parm_level);
      int i;
      int ntparms;

      ntparms = TREE_VEC_LENGTH (inner_parms);
      for (i = 0; i < ntparms; ++i) 
        if (TREE_PURPOSE (TREE_VEC_ELT (inner_parms, i)))
          {
            if (msg)
              {
                error (msg, decl);
                msg = 0;
              }

            /* Clear out the default argument so that we are not
               confused later.  */
            TREE_PURPOSE (TREE_VEC_ELT (inner_parms, i)) = NULL_TREE;
          }

      /* At this point, if we're still interested in issuing messages,
         they must apply to classes surrounding the object declared.  */
      if (msg)
        msg = "default argument for template parameter for class enclosing %qD"; 
    }
}

/* Worker for push_template_decl_real, called via
   for_each_template_parm.  DATA is really an int, indicating the
   level of the parameters we are interested in.  If T is a template
   parameter of that level, return nonzero.  */

static int
template_parm_this_level_p (tree t, void* data)
{
  int this_level = *(int *)data;
  int level;

  if (TREE_CODE (t) == TEMPLATE_PARM_INDEX)
    level = TEMPLATE_PARM_LEVEL (t);
  else
    level = TEMPLATE_TYPE_LEVEL (t);
  return level == this_level;
}

/* Creates a TEMPLATE_DECL for the indicated DECL using the template
   parameters given by current_template_args, or reuses a
   previously existing one, if appropriate.  Returns the DECL, or an
   equivalent one, if it is replaced via a call to duplicate_decls.  

   If IS_FRIEND is nonzero, DECL is a friend declaration.  */

tree
push_template_decl_real (tree decl, int is_friend)
{
  tree tmpl;
  tree args;
  tree info;
  tree ctx;
  int primary;
  int is_partial;
  int new_template_p = 0;
  /* True if the template is a member template, in the sense of
     [temp.mem].  */
  bool member_template_p = false;

  if (decl == error_mark_node)
    return decl;

  /* See if this is a partial specialization.  */
  is_partial = (DECL_IMPLICIT_TYPEDEF_P (decl)
                && TREE_CODE (TREE_TYPE (decl)) != ENUMERAL_TYPE
                && CLASSTYPE_TEMPLATE_SPECIALIZATION (TREE_TYPE (decl)));

  is_friend |= (TREE_CODE (decl) == FUNCTION_DECL && DECL_FRIEND_P (decl));

  if (is_friend)
    /* For a friend, we want the context of the friend function, not
       the type of which it is a friend.  */
    ctx = DECL_CONTEXT (decl);
  else if (CP_DECL_CONTEXT (decl)
           && TREE_CODE (CP_DECL_CONTEXT (decl)) != NAMESPACE_DECL)
    /* In the case of a virtual function, we want the class in which
       it is defined.  */
    ctx = CP_DECL_CONTEXT (decl);
  else
    /* Otherwise, if we're currently defining some class, the DECL
       is assumed to be a member of the class.  */
    ctx = current_scope ();

  if (ctx && TREE_CODE (ctx) == NAMESPACE_DECL)
    ctx = NULL_TREE;

  if (!DECL_CONTEXT (decl))
    DECL_CONTEXT (decl) = FROB_CONTEXT (current_namespace);

  /* See if this is a primary template.  */
  primary = template_parm_scope_p ();

  if (primary)
    {
      if (DECL_CLASS_SCOPE_P (decl))
        member_template_p = true;
      if (current_lang_name == lang_name_c)
        error ("template with C linkage");
      else if (TREE_CODE (decl) == TYPE_DECL 
               && ANON_AGGRNAME_P (DECL_NAME (decl))) 
        error ("template class without a name");
      else if (TREE_CODE (decl) == FUNCTION_DECL)
        {
          if (DECL_DESTRUCTOR_P (decl))
            {
              /* [temp.mem]
                 
                 A destructor shall not be a member template.  */
              error ("destructor %qD declared as member template", decl);
              return error_mark_node;
            }
          if (NEW_DELETE_OPNAME_P (DECL_NAME (decl))
              && (!TYPE_ARG_TYPES (TREE_TYPE (decl))
                  || TYPE_ARG_TYPES (TREE_TYPE (decl)) == void_list_node
                  || !TREE_CHAIN (TYPE_ARG_TYPES (TREE_TYPE (decl)))
                  || (TREE_CHAIN (TYPE_ARG_TYPES ((TREE_TYPE (decl))))
                      == void_list_node)))
            {
              /* [basic.stc.dynamic.allocation] 

                 An allocation function can be a function
                 template. ... Template allocation functions shall
                 have two or more parameters.  */
              error ("invalid template declaration of %qD", decl);
              return decl;
            }
        }
      else if ((DECL_IMPLICIT_TYPEDEF_P (decl)
                && CLASS_TYPE_P (TREE_TYPE (decl)))
               || (TREE_CODE (decl) == VAR_DECL && ctx && CLASS_TYPE_P (ctx)))
        /* OK */;
      else
        {
          error ("template declaration of %q#D", decl);
          return error_mark_node;
        }
    }

  /* Check to see that the rules regarding the use of default
     arguments are not being violated.  */
  check_default_tmpl_args (decl, current_template_parms, 
                           primary, is_partial);

  if (is_partial)
    return process_partial_specialization (decl);

  args = current_template_args ();

  if (!ctx 
      || TREE_CODE (ctx) == FUNCTION_DECL
      || (CLASS_TYPE_P (ctx) && TYPE_BEING_DEFINED (ctx))
      || (is_friend && !DECL_TEMPLATE_INFO (decl)))
    {
      if (DECL_LANG_SPECIFIC (decl)
          && DECL_TEMPLATE_INFO (decl)
          && DECL_TI_TEMPLATE (decl))
        tmpl = DECL_TI_TEMPLATE (decl);
      /* If DECL is a TYPE_DECL for a class-template, then there won't
         be DECL_LANG_SPECIFIC.  The information equivalent to
         DECL_TEMPLATE_INFO is found in TYPE_TEMPLATE_INFO instead.  */
      else if (DECL_IMPLICIT_TYPEDEF_P (decl) 
               && TYPE_TEMPLATE_INFO (TREE_TYPE (decl))
               && TYPE_TI_TEMPLATE (TREE_TYPE (decl)))
        {
          /* Since a template declaration already existed for this
             class-type, we must be redeclaring it here.  Make sure
             that the redeclaration is valid.  */
          redeclare_class_template (TREE_TYPE (decl),
                                    current_template_parms);
          /* We don't need to create a new TEMPLATE_DECL; just use the
             one we already had.  */
          tmpl = TYPE_TI_TEMPLATE (TREE_TYPE (decl));
        }
      else
        {
          tmpl = build_template_decl (decl, current_template_parms,
                                      member_template_p);
          new_template_p = 1;

          if (DECL_LANG_SPECIFIC (decl)
              && DECL_TEMPLATE_SPECIALIZATION (decl))
            {
              /* A specialization of a member template of a template
                 class.  */
              SET_DECL_TEMPLATE_SPECIALIZATION (tmpl);
              DECL_TEMPLATE_INFO (tmpl) = DECL_TEMPLATE_INFO (decl);
              DECL_TEMPLATE_INFO (decl) = NULL_TREE;
            }
        }
    }
  else
    {
      tree a, t, current, parms;
      int i;

      if (TREE_CODE (decl) == TYPE_DECL)
        {
          if ((IS_AGGR_TYPE_CODE (TREE_CODE (TREE_TYPE (decl)))
               || TREE_CODE (TREE_TYPE (decl)) == ENUMERAL_TYPE)
              && TYPE_TEMPLATE_INFO (TREE_TYPE (decl))
              && TYPE_TI_TEMPLATE (TREE_TYPE (decl)))
            tmpl = TYPE_TI_TEMPLATE (TREE_TYPE (decl));
          else
            {
              error ("%qD does not declare a template type", decl);
              return decl;
            }
        }
      else if (!DECL_LANG_SPECIFIC (decl) || !DECL_TEMPLATE_INFO (decl))
        {
          error ("template definition of non-template %q#D", decl);
          return decl;
        }
      else
        tmpl = DECL_TI_TEMPLATE (decl);
      
      if (DECL_FUNCTION_TEMPLATE_P (tmpl)
          && DECL_TEMPLATE_INFO (decl) && DECL_TI_ARGS (decl) 
          && DECL_TEMPLATE_SPECIALIZATION (decl)
          && DECL_MEMBER_TEMPLATE_P (tmpl))
        {
          tree new_tmpl;

          /* The declaration is a specialization of a member
             template, declared outside the class.  Therefore, the
             innermost template arguments will be NULL, so we
             replace them with the arguments determined by the
             earlier call to check_explicit_specialization.  */
          args = DECL_TI_ARGS (decl);

          new_tmpl 
            = build_template_decl (decl, current_template_parms,
                                   member_template_p);
          DECL_TEMPLATE_RESULT (new_tmpl) = decl;
          TREE_TYPE (new_tmpl) = TREE_TYPE (decl);
          DECL_TI_TEMPLATE (decl) = new_tmpl;
          SET_DECL_TEMPLATE_SPECIALIZATION (new_tmpl);
          DECL_TEMPLATE_INFO (new_tmpl) 
            = tree_cons (tmpl, args, NULL_TREE);

          register_specialization (new_tmpl, 
                                   most_general_template (tmpl), 
                                   args);
          return decl;
        }

      /* Make sure the template headers we got make sense.  */

      parms = DECL_TEMPLATE_PARMS (tmpl);
      i = TMPL_PARMS_DEPTH (parms);
      if (TMPL_ARGS_DEPTH (args) != i)
        {
          error ("expected %d levels of template parms for %q#D, got %d",
                 i, decl, TMPL_ARGS_DEPTH (args));
        }
      else
        for (current = decl; i > 0; --i, parms = TREE_CHAIN (parms))
          {
            a = TMPL_ARGS_LEVEL (args, i);
            t = INNERMOST_TEMPLATE_PARMS (parms);

            if (TREE_VEC_LENGTH (t) != TREE_VEC_LENGTH (a))
              {
                if (current == decl)
                  error ("got %d template parameters for %q#D",
                         TREE_VEC_LENGTH (a), decl);
                else
                  error ("got %d template parameters for %q#T",
                         TREE_VEC_LENGTH (a), current);
                error ("  but %d required", TREE_VEC_LENGTH (t));
              }

            /* Perhaps we should also check that the parms are used in the
               appropriate qualifying scopes in the declarator?  */

            if (current == decl)
              current = ctx;
            else
              current = TYPE_CONTEXT (current);
          }
    }

  DECL_TEMPLATE_RESULT (tmpl) = decl;
  TREE_TYPE (tmpl) = TREE_TYPE (decl);

  /* Push template declarations for global functions and types.  Note
     that we do not try to push a global template friend declared in a
     template class; such a thing may well depend on the template
     parameters of the class.  */
  if (new_template_p && !ctx 
      && !(is_friend && template_class_depth (current_class_type) > 0))
    {
      tmpl = pushdecl_namespace_level (tmpl);
      if (tmpl == error_mark_node)
        return error_mark_node;

      /* Hide template friend classes that haven't been declared yet.  */
      if (is_friend && TREE_CODE (decl) == TYPE_DECL)
        {
          DECL_ANTICIPATED (tmpl) = 1;
          DECL_FRIEND_P (tmpl) = 1;
        }
    }

  if (primary)
    {
      DECL_PRIMARY_TEMPLATE (tmpl) = tmpl;
      if (DECL_CONV_FN_P (tmpl))
        {
          int depth = TMPL_PARMS_DEPTH (DECL_TEMPLATE_PARMS (tmpl));

          /* It is a conversion operator. See if the type converted to
             depends on innermost template operands.  */
          
          if (uses_template_parms_level (TREE_TYPE (TREE_TYPE (tmpl)),
                                         depth))
            DECL_TEMPLATE_CONV_FN_P (tmpl) = 1;
        }
    }

  /* The DECL_TI_ARGS of DECL contains full set of arguments referring
     back to its most general template.  If TMPL is a specialization,
     ARGS may only have the innermost set of arguments.  Add the missing
     argument levels if necessary.  */
  if (DECL_TEMPLATE_INFO (tmpl))
    args = add_outermost_template_args (DECL_TI_ARGS (tmpl), args);

  info = tree_cons (tmpl, args, NULL_TREE);

  if (DECL_IMPLICIT_TYPEDEF_P (decl))
    {
      SET_TYPE_TEMPLATE_INFO (TREE_TYPE (tmpl), info);
      if ((!ctx || TREE_CODE (ctx) != FUNCTION_DECL)
          && TREE_CODE (TREE_TYPE (decl)) != ENUMERAL_TYPE
          /* Don't change the name if we've already set it up.  */
          && !IDENTIFIER_TEMPLATE (DECL_NAME (decl)))
        DECL_NAME (decl) = classtype_mangled_name (TREE_TYPE (decl));
    }
  else if (DECL_LANG_SPECIFIC (decl))
    DECL_TEMPLATE_INFO (decl) = info;

  return DECL_TEMPLATE_RESULT (tmpl);
}

tree
push_template_decl (tree decl)
{
  return push_template_decl_real (decl, 0);
}

/* Called when a class template TYPE is redeclared with the indicated
   template PARMS, e.g.:

     template <class T> struct S;
     template <class T> struct S {};  */

void 
redeclare_class_template (tree type, tree parms)
{
  tree tmpl;
  tree tmpl_parms;
  int i;

  if (!TYPE_TEMPLATE_INFO (type))
    {
      error ("%qT is not a template type", type);
      return;
    }

  tmpl = TYPE_TI_TEMPLATE (type);
  if (!PRIMARY_TEMPLATE_P (tmpl))
    /* The type is nested in some template class.  Nothing to worry
       about here; there are no new template parameters for the nested
       type.  */
    return;

  if (!parms)
    {
      error ("template specifiers not specified in declaration of %qD",
             tmpl);
      return;
    }

  parms = INNERMOST_TEMPLATE_PARMS (parms);
  tmpl_parms = DECL_INNERMOST_TEMPLATE_PARMS (tmpl);

  if (TREE_VEC_LENGTH (parms) != TREE_VEC_LENGTH (tmpl_parms))
    {
      cp_error_at ("previous declaration %qD", tmpl);
      error ("used %d template parameter%s instead of %d",
                TREE_VEC_LENGTH (tmpl_parms), 
                TREE_VEC_LENGTH (tmpl_parms) == 1 ? "" : "s",
                TREE_VEC_LENGTH (parms));
      return;
    }

  for (i = 0; i < TREE_VEC_LENGTH (tmpl_parms); ++i)
    {
      tree tmpl_parm = TREE_VALUE (TREE_VEC_ELT (tmpl_parms, i));
      tree parm = TREE_VALUE (TREE_VEC_ELT (parms, i));
      tree tmpl_default = TREE_PURPOSE (TREE_VEC_ELT (tmpl_parms, i));
      tree parm_default = TREE_PURPOSE (TREE_VEC_ELT (parms, i));

      /* TMPL_PARM and PARM can be either TYPE_DECL, PARM_DECL, or
         TEMPLATE_DECL.  */
      if (TREE_CODE (tmpl_parm) != TREE_CODE (parm)
          || (TREE_CODE (tmpl_parm) != TYPE_DECL
              && !same_type_p (TREE_TYPE (tmpl_parm), TREE_TYPE (parm))))
        {
          cp_error_at ("template parameter %q#D", tmpl_parm);
          error ("redeclared here as %q#D", parm);
          return;
        }

      if (tmpl_default != NULL_TREE && parm_default != NULL_TREE)
        {
          /* We have in [temp.param]:

             A template-parameter may not be given default arguments
             by two different declarations in the same scope.  */
          error ("redefinition of default argument for %q#D", parm);
          error ("%J  original definition appeared here", tmpl_parm);
          return;
        }

      if (parm_default != NULL_TREE)
        /* Update the previous template parameters (which are the ones
           that will really count) with the new default value.  */
        TREE_PURPOSE (TREE_VEC_ELT (tmpl_parms, i)) = parm_default;
      else if (tmpl_default != NULL_TREE)
        /* Update the new parameters, too; they'll be used as the
           parameters for any members.  */
        TREE_PURPOSE (TREE_VEC_ELT (parms, i)) = tmpl_default;
    }
}

/* Simplify EXPR if it is a non-dependent expression.  Returns the
   (possibly simplified) expression.  */

tree
fold_non_dependent_expr (tree expr)
{
  /* If we're in a template, but EXPR isn't value dependent, simplify
     it.  We're supposed to treat:
     
       template <typename T> void f(T[1 + 1]);
       template <typename T> void f(T[2]);
                   
     as two declarations of the same function, for example.  */
  if (processing_template_decl
      && !type_dependent_expression_p (expr)
      && !value_dependent_expression_p (expr))
    {
      HOST_WIDE_INT saved_processing_template_decl;

      saved_processing_template_decl = processing_template_decl;
      processing_template_decl = 0;
      expr = tsubst_copy_and_build (expr,
                                    /*args=*/NULL_TREE,
                                    tf_error,
                                    /*in_decl=*/NULL_TREE,
                                    /*function_p=*/false);
      processing_template_decl = saved_processing_template_decl;
    }
  return expr;
}

/* EXPR is an expression which is used in a constant-expression context.
   For instance, it could be a VAR_DECL with a constant initializer.
   Extract the innest constant expression.
   
   This is basically a more powerful version of
   integral_constant_value, which can be used also in templates where
   initializers can maintain a syntactic rather than semantic form
   (even if they are non-dependent, for access-checking purposes).  */

tree
fold_decl_constant_value (tree expr)
{
  tree const_expr = expr;
  do
    {
      expr = fold_non_dependent_expr (const_expr);
      const_expr = integral_constant_value (expr);
    }
  while (expr != const_expr);

  return expr;
}

/* Subroutine of convert_nontype_argument. Converts EXPR to TYPE, which
   must be a function or a pointer-to-function type, as specified
   in [temp.arg.nontype]: disambiguate EXPR if it is an overload set,
   and check that the resulting function has external linkage.  */

static tree
convert_nontype_argument_function (tree type, tree expr)
{
  tree fns = expr;
  tree fn, fn_no_ptr;

  fn = instantiate_type (type, fns, tf_none);
  if (fn == error_mark_node)
    return error_mark_node;

  fn_no_ptr = fn;
  if (TREE_CODE (fn_no_ptr) == ADDR_EXPR)
    fn_no_ptr = TREE_OPERAND (fn_no_ptr, 0);

  /* [temp.arg.nontype]/1

     A template-argument for a non-type, non-template template-parameter
     shall be one of:
     [...]
     -- the address of an object or function with external linkage.  */
  if (!DECL_EXTERNAL_LINKAGE_P (fn_no_ptr))
    {
      error ("%qE is not a valid template argument for type %qT "
             "because function %qD has not external linkage",
             expr, type, fn_no_ptr);
      return NULL_TREE;
    }

  return fn;
}

/* Attempt to convert the non-type template parameter EXPR to the
   indicated TYPE.  If the conversion is successful, return the
   converted value.  If the conversion is unsuccessful, return
   NULL_TREE if we issued an error message, or error_mark_node if we
   did not.  We issue error messages for out-and-out bad template
   parameters, but not simply because the conversion failed, since we
   might be just trying to do argument deduction.  Both TYPE and EXPR
   must be non-dependent.

   The conversion follows the special rules described in
   [temp.arg.nontype], and it is much more strict than an implicit
   conversion.

   This function is called twice for each template argument (see
   lookup_template_class for a more accurate description of this
   problem). This means that we need to handle expressions which
   are not valid in a C++ source, but can be created from the
   first call (for instance, casts to perform conversions). These
   hacks can go away after we fix the double coercion problem.  */

static tree
convert_nontype_argument (tree type, tree expr)
{
  tree expr_type;

  /* Detect immediately string literals as invalid non-type argument.
     This special-case is not needed for correctness (we would easily
     catch this later), but only to provide better diagnostic for this
     common user mistake. As suggested by DR 100, we do not mention
     linkage issues in the diagnostic as this is not the point.  */
  if (TREE_CODE (expr) == STRING_CST)
    {
      error ("%qE is not a valid template argument for type %qT "
             "because string literals can never be used in this context",
             expr, type);
      return NULL_TREE;
    }

  /* If we are in a template, EXPR may be non-dependent, but still
     have a syntactic, rather than semantic, form.  For example, EXPR
     might be a SCOPE_REF, rather than the VAR_DECL to which the
     SCOPE_REF refers.  Preserving the qualifying scope is necessary
     so that access checking can be performed when the template is
     instantiated -- but here we need the resolved form so that we can
     convert the argument.  */
  expr = fold_non_dependent_expr (expr);
  expr_type = TREE_TYPE (expr);

  /* HACK: Due to double coercion, we can get a
     NOP_EXPR<REFERENCE_TYPE>(ADDR_EXPR<POINTER_TYPE> (arg)) here,
     which is the tree that we built on the first call (see
     below when coercing to reference to object or to reference to
     function). We just strip everything and get to the arg.
     See g++.old-deja/g++.oliva/template4.C and g++.dg/template/nontype9.C
     for examples.  */
  if (TREE_CODE (expr) == NOP_EXPR)
    {
      if (TYPE_REF_OBJ_P (type) || TYPE_REFFN_P (type))
        {
          /* ??? Maybe we could use convert_from_reference here, but we
             would need to relax its constraints because the NOP_EXPR
             could actually change the type to something more cv-qualified,
             and this is not folded by convert_from_reference.  */
          tree addr = TREE_OPERAND (expr, 0);
          gcc_assert (TREE_CODE (expr_type) == REFERENCE_TYPE);
          gcc_assert (TREE_CODE (addr) == ADDR_EXPR);
          gcc_assert (TREE_CODE (TREE_TYPE (addr)) == POINTER_TYPE);
          gcc_assert (same_type_ignoring_top_level_qualifiers_p
                      (TREE_TYPE (expr_type),
                       TREE_TYPE (TREE_TYPE (addr))));

          expr = TREE_OPERAND (addr, 0);
          expr_type = TREE_TYPE (expr);
        }

      /* We could also generate a NOP_EXPR(ADDR_EXPR()) when the
         parameter is a pointer to object, through decay and
         qualification conversion. Let's strip everything.  */
      else if (TYPE_PTROBV_P (type))
        {
          STRIP_NOPS (expr);
          gcc_assert (TREE_CODE (expr) == ADDR_EXPR);
          gcc_assert (TREE_CODE (TREE_TYPE (expr)) == POINTER_TYPE);
          /* Skip the ADDR_EXPR only if it is part of the decay for
             an array. Otherwise, it is part of the original argument
             in the source code.  */
          if (TREE_CODE (TREE_TYPE (TREE_OPERAND (expr, 0))) == ARRAY_TYPE)
            expr = TREE_OPERAND (expr, 0);
          expr_type = TREE_TYPE (expr);
        }
    }

  /* [temp.arg.nontype]/5, bullet 1

     For a non-type template-parameter of integral or enumeration type,
     integral promotions (_conv.prom_) and integral conversions
     (_conv.integral_) are applied.  */
  if (INTEGRAL_TYPE_P (type))
    {
      if (!INTEGRAL_TYPE_P (expr_type))
        return error_mark_node;

      expr = fold_decl_constant_value (expr);
      /* Notice that there are constant expressions like '4 % 0' which
         do not fold into integer constants.  */
      if (TREE_CODE (expr) != INTEGER_CST)
        {
          error ("%qE is not a valid template argument for type %qT "
                 "because it is a non-constant expression", expr, type);
          return NULL_TREE;
        }

      /* At this point, an implicit conversion does what we want,
         because we already know that the expression is of integral
         type.  */
      expr = ocp_convert (type, expr, CONV_IMPLICIT, LOOKUP_PROTECT);
      if (expr == error_mark_node)
        return error_mark_node;

      /* Conversion was allowed: fold it to a bare integer constant.  */
      expr = fold (expr);
    }
  /* [temp.arg.nontype]/5, bullet 2

     For a non-type template-parameter of type pointer to object,
     qualification conversions (_conv.qual_) and the array-to-pointer
     conversion (_conv.array_) are applied.  */
  else if (TYPE_PTROBV_P (type))
    {
      /* [temp.arg.nontype]/1  (TC1 version, DR 49):

         A template-argument for a non-type, non-template template-parameter
         shall be one of: [...]

         -- the name of a non-type template-parameter;
         -- the address of an object or function with external linkage, [...]
            expressed as "& id-expression" where the & is optional if the name
            refers to a function or array, or if the corresponding
            template-parameter is a reference.
            
        Here, we do not care about functions, as they are invalid anyway
        for a parameter of type pointer-to-object.  */
      bool constant_address_p =
        (TREE_CODE (expr) == ADDR_EXPR
         || TREE_CODE (expr_type) == ARRAY_TYPE
         || (DECL_P (expr) && DECL_TEMPLATE_PARM_P (expr)));

      expr = decay_conversion (expr);
      if (expr == error_mark_node)
        return error_mark_node;

      expr = perform_qualification_conversions (type, expr);
      if (expr == error_mark_node)
        return error_mark_node;

      if (!constant_address_p)
        {
            error ("%qE is not a valid template argument for type %qT "
                  "because it is not a constant pointer", expr, type);
            return NULL_TREE;
        }
    }
  /* [temp.arg.nontype]/5, bullet 3

     For a non-type template-parameter of type reference to object, no
     conversions apply. The type referred to by the reference may be more
     cv-qualified than the (otherwise identical) type of the
     template-argument. The template-parameter is bound directly to the
     template-argument, which must be an lvalue.  */
  else if (TYPE_REF_OBJ_P (type))
    {
      if (!same_type_ignoring_top_level_qualifiers_p (TREE_TYPE (type),
                                                      expr_type))
        return error_mark_node;

      if (!at_least_as_qualified_p (TREE_TYPE (type), expr_type))
        {
          error ("%qE is not a valid template argument for type %qT "
                 "because of conflicts in cv-qualification", expr, type);
          return NULL_TREE;
        }
        
      if (!real_lvalue_p (expr))
        {
          error ("%qE is not a valid template argument for type %qT "
                 "because it is not a lvalue", expr, type);
          return NULL_TREE;
        }

      /* [temp.arg.nontype]/1

         A template-argument for a non-type, non-template template-parameter
         shall be one of: [...]

         -- the address of an object or function with external linkage.  */
      if (!DECL_EXTERNAL_LINKAGE_P (expr))
        {
          error ("%qE is not a valid template argument for type %qT "
                 "because object %qD has not external linkage",
                 expr, type, expr);
          return NULL_TREE;
        }

      expr = build_nop (type, build_address (expr));
    }
  /* [temp.arg.nontype]/5, bullet 4

     For a non-type template-parameter of type pointer to function, only
     the function-to-pointer conversion (_conv.func_) is applied. If the
     template-argument represents a set of overloaded functions (or a
     pointer to such), the matching function is selected from the set
     (_over.over_).  */
  else if (TYPE_PTRFN_P (type))
    {
      /* If the argument is a template-id, we might not have enough
         context information to decay the pointer.
         ??? Why static5.C requires decay and subst1.C works fine
         even without it?  */
      if (!type_unknown_p (expr_type))
        {
          expr = decay_conversion (expr);
          if (expr == error_mark_node)
            return error_mark_node;
        }

      expr = convert_nontype_argument_function (type, expr);
      if (!expr || expr == error_mark_node)
        return expr;
    }
  /* [temp.arg.nontype]/5, bullet 5

     For a non-type template-parameter of type reference to function, no
     conversions apply. If the template-argument represents a set of
     overloaded functions, the matching function is selected from the set
     (_over.over_).  */
  else if (TYPE_REFFN_P (type))
    {
      if (TREE_CODE (expr) == ADDR_EXPR)
        {
          error ("%qE is not a valid template argument for type %qT "
                 "because it is a pointer", expr, type);
          inform ("try using %qE instead", TREE_OPERAND (expr, 0));
          return NULL_TREE;
        }

      expr = convert_nontype_argument_function (TREE_TYPE (type), expr);
      if (!expr || expr == error_mark_node)
        return expr;

      expr = build_nop (type, build_address (expr));
    }
  /* [temp.arg.nontype]/5, bullet 6

     For a non-type template-parameter of type pointer to member function,
     no conversions apply. If the template-argument represents a set of
     overloaded member functions, the matching member function is selected
     from the set (_over.over_).  */
  else if (TYPE_PTRMEMFUNC_P (type))
    {
      expr = instantiate_type (type, expr, tf_none);
      if (expr == error_mark_node)
        return error_mark_node;

      /* There is no way to disable standard conversions in
         resolve_address_of_overloaded_function (called by
         instantiate_type). It is possible that the call succeeded by
         converting &B::I to &D::I (where B is a base of D), so we need
         to reject this conversion here.

         Actually, even if there was a way to disable standard conversions,
         it would still be better to reject them here so that we can
         provide a superior diagnostic.  */
      if (!same_type_p (TREE_TYPE (expr), type))
        {
          /* Make sure we are just one standard conversion off.  */
          gcc_assert (can_convert (type, TREE_TYPE (expr)));
          error ("%qE is not a valid template argument for type %qT "
                 "because it is of type %qT", expr, type,
                 TREE_TYPE (expr));
          inform ("standard conversions are not allowed in this context");
          return NULL_TREE;
        }
    }
  /* [temp.arg.nontype]/5, bullet 7

     For a non-type template-parameter of type pointer to data member,
     qualification conversions (_conv.qual_) are applied.  */
  else if (TYPE_PTRMEM_P (type))
    {
      expr = perform_qualification_conversions (type, expr);
      if (expr == error_mark_node)
        return expr;
    }
  /* A template non-type parameter must be one of the above.  */
  else
    gcc_unreachable ();

  /* Sanity check: did we actually convert the argument to the
     right type?  */
  gcc_assert (same_type_p (type, TREE_TYPE (expr)));
  return expr;
}


/* Return 1 if PARM_PARMS and ARG_PARMS matches using rule for 
   template template parameters.  Both PARM_PARMS and ARG_PARMS are 
   vectors of TREE_LIST nodes containing TYPE_DECL, TEMPLATE_DECL 
   or PARM_DECL.
   
   ARG_PARMS may contain more parameters than PARM_PARMS.  If this is 
   the case, then extra parameters must have default arguments.

   Consider the example:
     template <class T, class Allocator = allocator> class vector;
     template<template <class U> class TT> class C;

   C<vector> is a valid instantiation.  PARM_PARMS for the above code 
   contains a TYPE_DECL (for U),  ARG_PARMS contains two TYPE_DECLs (for 
   T and Allocator) and OUTER_ARGS contains the argument that is used to 
   substitute the TT parameter.  */

static int
coerce_template_template_parms (tree parm_parms, 
                                tree arg_parms, 
                                tsubst_flags_t complain, 
                                tree in_decl,
                                tree outer_args)
{
  int nparms, nargs, i;
  tree parm, arg;

  gcc_assert (TREE_CODE (parm_parms) == TREE_VEC);
  gcc_assert (TREE_CODE (arg_parms) == TREE_VEC);

  nparms = TREE_VEC_LENGTH (parm_parms);
  nargs = TREE_VEC_LENGTH (arg_parms);

  /* The rule here is opposite of coerce_template_parms.  */
  if (nargs < nparms
      || (nargs > nparms
          && TREE_PURPOSE (TREE_VEC_ELT (arg_parms, nparms)) == NULL_TREE))
    return 0;

  for (i = 0; i < nparms; ++i)
    {
      parm = TREE_VALUE (TREE_VEC_ELT (parm_parms, i));
      arg = TREE_VALUE (TREE_VEC_ELT (arg_parms, i));

      if (arg == NULL_TREE || arg == error_mark_node
          || parm == NULL_TREE || parm == error_mark_node)
        return 0;

      if (TREE_CODE (arg) != TREE_CODE (parm))
        return 0;

      switch (TREE_CODE (parm))
        {
        case TYPE_DECL:
          break;

        case TEMPLATE_DECL:
          /* We encounter instantiations of templates like
               template <template <template <class> class> class TT>
               class C;  */
          {
            tree parmparm = DECL_INNERMOST_TEMPLATE_PARMS (parm);
            tree argparm = DECL_INNERMOST_TEMPLATE_PARMS (arg);

            if (!coerce_template_template_parms
                (parmparm, argparm, complain, in_decl, outer_args))
              return 0;
          }
          break;

        case PARM_DECL:
          /* The tsubst call is used to handle cases such as

               template <int> class C {};
               template <class T, template <T> class TT> class D {};
               D<int, C> d;

             i.e. the parameter list of TT depends on earlier parameters.  */
          if (!dependent_type_p (TREE_TYPE (arg))
              && !same_type_p
                    (tsubst (TREE_TYPE (parm), outer_args, complain, in_decl),
                             TREE_TYPE (arg)))
            return 0;
          break;
          
        default:
          gcc_unreachable ();
        }
    }
  return 1;
}

/* Convert the indicated template ARG as necessary to match the
   indicated template PARM.  Returns the converted ARG, or
   error_mark_node if the conversion was unsuccessful.  Error and
   warning messages are issued under control of COMPLAIN.  This
   conversion is for the Ith parameter in the parameter list.  ARGS is
   the full set of template arguments deduced so far.  */

static tree
convert_template_argument (tree parm, 
                           tree arg, 
                           tree args, 
                           tsubst_flags_t complain, 
                           int i, 
                           tree in_decl)
{
  tree val;
  tree inner_args;
  int is_type, requires_type, is_tmpl_type, requires_tmpl_type;
  
  inner_args = INNERMOST_TEMPLATE_ARGS (args);

  if (TREE_CODE (arg) == TREE_LIST 
      && TREE_CODE (TREE_VALUE (arg)) == OFFSET_REF)
    {  
      /* The template argument was the name of some
         member function.  That's usually
         invalid, but static members are OK.  In any
         case, grab the underlying fields/functions
         and issue an error later if required.  */
      arg = TREE_VALUE (arg);
      TREE_TYPE (arg) = unknown_type_node;
    }

  requires_tmpl_type = TREE_CODE (parm) == TEMPLATE_DECL;
  requires_type = (TREE_CODE (parm) == TYPE_DECL
                   || requires_tmpl_type);

  is_tmpl_type = ((TREE_CODE (arg) == TEMPLATE_DECL
                   && TREE_CODE (DECL_TEMPLATE_RESULT (arg)) == TYPE_DECL)
                  || TREE_CODE (arg) == TEMPLATE_TEMPLATE_PARM
                  || TREE_CODE (arg) == UNBOUND_CLASS_TEMPLATE);
  
  if (is_tmpl_type
      && (TREE_CODE (arg) == TEMPLATE_TEMPLATE_PARM
          || TREE_CODE (arg) == UNBOUND_CLASS_TEMPLATE))
    arg = TYPE_STUB_DECL (arg);

  is_type = TYPE_P (arg) || is_tmpl_type;

  if (requires_type && ! is_type && TREE_CODE (arg) == SCOPE_REF
      && TREE_CODE (TREE_OPERAND (arg, 0)) == TEMPLATE_TYPE_PARM)
    {
      pedwarn ("to refer to a type member of a template parameter, "
               "use %<typename %E%>", arg);
      
      arg = make_typename_type (TREE_OPERAND (arg, 0),
                                TREE_OPERAND (arg, 1),
                                typename_type,
                                complain & tf_error);
      is_type = 1;
    }
  if (is_type != requires_type)
    {
      if (in_decl)
        {
          if (complain & tf_error)
            {
              error ("type/value mismatch at argument %d in template "
                     "parameter list for %qD",
                     i + 1, in_decl);
              if (is_type)
                error ("  expected a constant of type %qT, got %qT",
                       TREE_TYPE (parm),
                       (is_tmpl_type ? DECL_NAME (arg) : arg));
              else if (requires_tmpl_type)
                error ("  expected a class template, got %qE", arg);
              else
                error ("  expected a type, got %qE", arg);
            }
        }
      return error_mark_node;
    }
  if (is_tmpl_type ^ requires_tmpl_type)
    {
      if (in_decl && (complain & tf_error))
        {
          error ("type/value mismatch at argument %d in template "
                 "parameter list for %qD",
                 i + 1, in_decl);
          if (is_tmpl_type)
            error ("  expected a type, got %qT", DECL_NAME (arg));
          else
            error ("  expected a class template, got %qT", arg);
        }
      return error_mark_node;
    }
      
  if (is_type)
    {
      if (requires_tmpl_type)
        {
          if (TREE_CODE (TREE_TYPE (arg)) == UNBOUND_CLASS_TEMPLATE)
            /* The number of argument required is not known yet.
               Just accept it for now.  */
            val = TREE_TYPE (arg);
          else
            {
              tree parmparm = DECL_INNERMOST_TEMPLATE_PARMS (parm);
              tree argparm = DECL_INNERMOST_TEMPLATE_PARMS (arg);

              if (coerce_template_template_parms (parmparm, argparm,
                                                  complain, in_decl,
                                                  inner_args))
                {
                  val = arg;
                  
                  /* TEMPLATE_TEMPLATE_PARM node is preferred over 
                     TEMPLATE_DECL.  */
                  if (val != error_mark_node 
                      && DECL_TEMPLATE_TEMPLATE_PARM_P (val))
                    val = TREE_TYPE (val);
                }
              else
                {
                  if (in_decl && (complain & tf_error))
                    {
                      error ("type/value mismatch at argument %d in "
                             "template parameter list for %qD",
                             i + 1, in_decl);
                      error ("  expected a template of type %qD, got %qD",
                             parm, arg);
                    }
                  
                  val = error_mark_node;
                }
            }
        }
      else
        val = arg;
    }
  else
    {
      tree t = tsubst (TREE_TYPE (parm), args, complain, in_decl);

      if (invalid_nontype_parm_type_p (t, complain))
        return error_mark_node;
      
      if (!uses_template_parms (arg) && !uses_template_parms (t))
        /* We used to call digest_init here.  However, digest_init
           will report errors, which we don't want when complain
           is zero.  More importantly, digest_init will try too
           hard to convert things: for example, `0' should not be
           converted to pointer type at this point according to
           the standard.  Accepting this is not merely an
           extension, since deciding whether or not these
           conversions can occur is part of determining which
           function template to call, or whether a given explicit
           argument specification is valid.  */
        val = convert_nontype_argument (t, arg);
      else
        val = arg;

      if (val == NULL_TREE)
        val = error_mark_node;
      else if (val == error_mark_node && (complain & tf_error))
        error ("could not convert template argument %qE to %qT",  arg, t);
    }

  return val;
}

/* Convert all template arguments to their appropriate types, and
   return a vector containing the innermost resulting template
   arguments.  If any error occurs, return error_mark_node. Error and
   warning messages are issued under control of COMPLAIN.

   If REQUIRE_ALL_ARGUMENTS is nonzero, all arguments must be
   provided in ARGLIST, or else trailing parameters must have default
   values.  If REQUIRE_ALL_ARGUMENTS is zero, we will attempt argument
   deduction for any unspecified trailing arguments.  */
   
static tree
coerce_template_parms (tree parms, 
                       tree args, 
                       tree in_decl,
                       tsubst_flags_t complain,
                       int require_all_arguments)
{
  int nparms, nargs, i, lost = 0;
  tree inner_args;
  tree new_args;
  tree new_inner_args;

  inner_args = INNERMOST_TEMPLATE_ARGS (args);
  nargs = inner_args ? NUM_TMPL_ARGS (inner_args) : 0;
  nparms = TREE_VEC_LENGTH (parms);

  if (nargs > nparms
      || (nargs < nparms
          && require_all_arguments
          && TREE_PURPOSE (TREE_VEC_ELT (parms, nargs)) == NULL_TREE))
    {
      if (complain & tf_error) 
        {
          error ("wrong number of template arguments (%d, should be %d)",
                 nargs, nparms);
          
          if (in_decl)
            cp_error_at ("provided for %qD", in_decl);
        }

      return error_mark_node;
    }

  new_inner_args = make_tree_vec (nparms);
  new_args = add_outermost_template_args (args, new_inner_args);
  for (i = 0; i < nparms; i++)
    {
      tree arg;
      tree parm;

      /* Get the Ith template parameter.  */
      parm = TREE_VEC_ELT (parms, i);

      /* Calculate the Ith argument.  */
      if (i < nargs)
        arg = TREE_VEC_ELT (inner_args, i);
      else if (require_all_arguments)
        /* There must be a default arg in this case.  */
        arg = tsubst_template_arg (TREE_PURPOSE (parm), new_args,
                                   complain, in_decl);
      else
        break;
      
      gcc_assert (arg);
      if (arg == error_mark_node)
        {
          if (complain & tf_error)
            error ("template argument %d is invalid", i + 1);
        }
      else 
        arg = convert_template_argument (TREE_VALUE (parm), 
                                         arg, new_args, complain, i,
                                         in_decl); 
      
      if (arg == error_mark_node)
        lost++;
      TREE_VEC_ELT (new_inner_args, i) = arg;
    }

  if (lost)
    return error_mark_node;

  return new_inner_args;
}

/* Returns 1 if template args OT and NT are equivalent.  */

static int
template_args_equal (tree ot, tree nt)
{
  if (nt == ot)
    return 1;

  if (TREE_CODE (nt) == TREE_VEC)
    /* For member templates */
    return TREE_CODE (ot) == TREE_VEC && comp_template_args (ot, nt);
  else if (TYPE_P (nt))
    {
      int c1, c2;

      if (!TYPE_P (ot))
        return 0;

      /* We must handle ObjC types specially because they may differ
         only in protocol qualifications (e.g., 'NSObject *' vs.
         'NSObject <Foo> *') that must be taken into account here.
         See also cp/typeck.c:build_c_cast(), where a similar problem
         arises.  We must call objc_comptypes() twice, since its
         comparisons are _not_ symmetric.  */
      if ((c1 = objc_comptypes (ot, nt, 0)) >= 0
          && (c2 = objc_comptypes (nt, ot, 0)) >= 0)
        return (c1 && c2);

      return same_type_p (ot, nt);
    }
  else if (TREE_CODE (ot) == TREE_VEC || TYPE_P (ot))
    return 0;
  else
    return cp_tree_equal (ot, nt);
}

/* Returns 1 iff the OLDARGS and NEWARGS are in fact identical sets
   of template arguments.  Returns 0 otherwise.  */

int
comp_template_args (tree oldargs, tree newargs)
{
  int i;

  if (TREE_VEC_LENGTH (oldargs) != TREE_VEC_LENGTH (newargs))
    return 0;

  for (i = 0; i < TREE_VEC_LENGTH (oldargs); ++i)
    {
      tree nt = TREE_VEC_ELT (newargs, i);
      tree ot = TREE_VEC_ELT (oldargs, i);

      if (! template_args_equal (ot, nt))
        return 0;
    }
  return 1;
}

/* Given class template name and parameter list, produce a user-friendly name
   for the instantiation.  */

static char *
mangle_class_name_for_template (const char* name, tree parms, tree arglist)
{
  static struct obstack scratch_obstack;
  static char *scratch_firstobj;
  int i, nparms;

  if (!scratch_firstobj)
    gcc_obstack_init (&scratch_obstack);
  else
    obstack_free (&scratch_obstack, scratch_firstobj);
  scratch_firstobj = obstack_alloc (&scratch_obstack, 1);

#define ccat(C) obstack_1grow (&scratch_obstack, (C));
#define cat(S)  obstack_grow (&scratch_obstack, (S), strlen (S))

  cat (name);
  ccat ('<');
  nparms = TREE_VEC_LENGTH (parms);
  arglist = INNERMOST_TEMPLATE_ARGS (arglist);
  gcc_assert (nparms == TREE_VEC_LENGTH (arglist));
  for (i = 0; i < nparms; i++)