[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, 2007, 2008, 2009
   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 3, or (at your option)
any later version.

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

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */

/* 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 "intl.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"
#include "vecprim.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.  */
struct GTY (()) pending_template {
  struct pending_template *next;
  struct tinst_level *tinst;
};

static GTY(()) struct pending_template *pending_templates;
static GTY(()) struct pending_template *last_pending_template;

int processing_template_parmlist;
static int template_header_count;

static GTY(()) tree saved_trees;
static VEC(int,heap) *inline_parm_levels;

static GTY(()) struct tinst_level *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;

typedef struct GTY(()) spec_entry
{
  tree tmpl;
  tree args;
  tree spec;
} spec_entry;

static GTY ((param_is (spec_entry)))
  htab_t decl_specializations;

static GTY ((param_is (spec_entry)))
  htab_t type_specializations;

/* Contains canonical template parameter types. The vector is indexed by
   the TEMPLATE_TYPE_IDX of the template parameter. Each element is a
   TREE_LIST, whose TREE_VALUEs contain the canonical template
   parameters of various types and levels.  */
static GTY(()) VEC(tree,gc) *canonical_template_parms;

#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 bool 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 tree reopen_tinst_level (struct tinst_level *);
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,
                                   bool, bool);
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*,
                                             tree);
static int type_unification_real (tree, tree, tree, const tree *,
                                  unsigned int, 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*, bool);
static tree expand_template_argument_pack (tree);
static tree build_template_parm_index (int, int, int, tree, tree);
static bool 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 hashval_t hash_specialization (const void *p);
static tree reduce_template_parm_level (tree, tree, int, tree, tsubst_flags_t);
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 void template_parm_level_and_index (tree, int*, int*);
static int unify_pack_expansion (tree, tree, tree, tree, int, bool, bool);
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_class (tree, tree);
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 bool check_specialization_scope (void);
static tree process_partial_specialization (tree);
static void set_current_access_from_decl (tree);
static tree get_template_base (tree, 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 bool template_template_parm_bindings_ok_p (tree, tree);
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_template_arg_p (tree);
static bool any_template_arguments_need_structural_equality_p (tree);
static bool dependent_type_p_r (tree);
static tree tsubst_expr (tree, tree, tsubst_flags_t, tree, bool);
static tree tsubst_copy (tree, tree, tsubst_flags_t, tree);
static tree tsubst_pack_expansion (tree, tree, tsubst_flags_t, tree);
static tree tsubst_decl (tree, tree, tsubst_flags_t);
static void perform_typedefs_access_check (tree tmpl, tree targs);
static void append_type_to_template_for_access_check_1 (tree, tree, tree,
                                                        location_t);
static hashval_t iterative_hash_template_arg (tree arg, hashval_t val);
static tree listify (tree);
static tree listify_autos (tree, 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 (type == error_mark_node)
        return error_mark_node;
      if (MAYBE_CLASS_TYPE_P (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;
}

/* Create a template info node.  */

tree
build_template_info (tree template_decl, tree template_args)
{
  tree result = make_node (TEMPLATE_INFO);
  TI_TEMPLATE (result) = template_decl;
  TI_ARGS (result) = template_args;
  return result;
}

/* Return the template info node corresponding to T, whatever T is.  */

tree
get_template_info (const_tree t)
{
  tree tinfo = NULL_TREE;

  if (!t || t == error_mark_node)
    return NULL;

  if (DECL_P (t) && DECL_LANG_SPECIFIC (t))
    tinfo = DECL_TEMPLATE_INFO (t);

  if (!tinfo && DECL_IMPLICIT_TYPEDEF_P (t))
    t = TREE_TYPE (t);

  if (TAGGED_TYPE_P (t))
    tinfo = TYPE_TEMPLATE_INFO (t);
  else if (TREE_CODE (t) == BOUND_TEMPLATE_TEMPLATE_PARM)
    tinfo = TEMPLATE_TEMPLATE_PARM_TEMPLATE_INFO (t);

  return tinfo;
}

/* 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
   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.  */

int
template_class_depth (tree type)
{
  int depth;

  for (depth = 0;
       type && TREE_CODE (type) != NAMESPACE_DECL;
       type = (TREE_CODE (type) == FUNCTION_DECL)
         ? CP_DECL_CONTEXT (type) : TYPE_CONTEXT (type))
    {
      tree tinfo = get_template_info (type);

      if (tinfo && PRIMARY_TEMPLATE_P (TI_TEMPLATE (tinfo))
          && uses_template_parms (INNERMOST_TEMPLATE_ARGS (TI_ARGS (tinfo))))
        ++depth;
    }

  return depth;
}

/* Subroutine of maybe_begin_member_template_processing.
   Returns true if processing DECL needs us to push template parms.  */

static bool
inline_needs_template_parms (tree decl)
{
  if (! DECL_TEMPLATE_INFO (decl))
    return false;

  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));

      if (parm == error_mark_node)
        continue;

      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 (DECL_SOURCE_LOCATION (parm),
                                    CONST_DECL, DECL_NAME (parm),
                                    TREE_TYPE (parm));
            DECL_ARTIFICIAL (decl) = 1;
            TREE_CONSTANT (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.  */
  VEC_safe_push (int, heap, inline_parm_levels, levels);
}

/* Undo the effects of maybe_begin_member_template_processing.  */

void
maybe_end_member_template_processing (void)
{
  int i;
  int last;

  if (VEC_length (int, inline_parm_levels) == 0)
    return;

  last = VEC_pop (int, inline_parm_levels);
  for (i = 0; i < last; ++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;

  if (args == NULL_TREE)
    return extra_args;

  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;
}

/* The inverse of get_innermost_template_args: Return all but the innermost
   EXTRA_LEVELS levels of template arguments from the ARGS.  */

static tree
strip_innermost_template_args (tree args, int extra_levels)
{
  tree new_args;
  int n = TMPL_ARGS_DEPTH (args) - extra_levels;
  int i;

  gcc_assert (n >= 0);

  /* If N is 1, just return the outermost set of template arguments.  */
  if (n == 1)
    return TMPL_ARGS_LEVEL (args, 1);

  /* If we're not removing anything, just return the arguments we were
     given.  */
  gcc_assert (extra_levels >= 0);
  if (extra_levels == 0)
    return args;

  /* Make a new set of arguments, not containing the inner 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));

  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 and
   false is returned, otherwise this routine will return true.  */

static bool
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);
      return false;
    }

  /* [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");
      return false;
    }

  return true;
}

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

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

/* An 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 (current_scope() != DECL_CONTEXT (tmpl)
      && !at_namespace_scope_p ())
    {
      error ("specialization of %qD must appear at namespace scope", tmpl);
      return false;
    }
  if (is_associated_namespace (current_namespace, tpl_ns))
    /* Same or super-using namespace.  */
    return true;
  else
    {
      permerror (input_location, "specialization of %qD in different namespace", tmpl);
      permerror (input_location, "  from definition of %q+#D", tmpl);
      return false;
    }
}

/* SPEC is an explicit instantiation.  Check that it is valid to
   perform this explicit instantiation in the current namespace.  */

static void
check_explicit_instantiation_namespace (tree spec)
{
  tree ns;

  /* DR 275: An explicit instantiation shall appear in an enclosing
     namespace of its template.  */
  ns = decl_namespace_context (spec);
  if (!is_ancestor (current_namespace, ns))
    permerror (input_location, "explicit instantiation of %qD in namespace %qD "
               "(which does not enclose namespace %qD)",
               spec, current_namespace, ns);
}

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

tree
maybe_process_partial_specialization (tree type)
{
  tree context;

  if (type == error_mark_node)
    return error_mark_node;

  if (TREE_CODE (type) == BOUND_TEMPLATE_TEMPLATE_PARM)
    {
      error ("name of class shadows template template parameter %qD",
             TYPE_NAME (type));
      return error_mark_node;
    }

  context = TYPE_CONTEXT (type);

  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)
            {
              if (push_template_decl (TYPE_MAIN_DECL (type))
                  == error_mark_node)
                return error_mark_node;
            }
        }
      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;
          tree tmpl = CLASSTYPE_TI_TEMPLATE (type);

          if (current_namespace
              != decl_namespace_context (tmpl))
            {
              permerror (input_location, "specializing %q#T in different namespace", type);
              permerror (input_location, "  from definition of %q+#D", tmpl);
            }

          /* 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 (tmpl);
               t; t = TREE_CHAIN (t))
            {
              tree inst = TREE_VALUE (t);
              if (CLASSTYPE_TEMPLATE_SPECIALIZATION (inst))
                {
                  /* We already have a full specialization of this partial
                     instantiation.  Reassign it to the new member
                     specialization template.  */
                  spec_entry elt;
                  spec_entry **slot;

                  elt.tmpl = most_general_template (tmpl);
                  elt.args = CLASSTYPE_TI_ARGS (inst);
                  elt.spec = inst;

                  htab_remove_elt (type_specializations, &elt);

                  elt.tmpl = tmpl;
                  elt.args = INNERMOST_TEMPLATE_ARGS (elt.args);

                  slot = (spec_entry **)
                    htab_find_slot (type_specializations, &elt, INSERT);
                  *slot = GGC_NEW (spec_entry);
                  **slot = elt;
                }
              else if (COMPLETE_TYPE_P (inst) || TYPE_BEING_DEFINED (inst))
                /* But if we've had an implicit instantiation, that's a
                   problem ([temp.expl.spec]/6).  */
                error ("specialization %qT after instantiation %qT",
                       type, inst);
            }

          /* 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);
      return error_mark_node;
    }

  return 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, hashval_t hash)
{
  if (args == error_mark_node)
    return NULL_TREE;

  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, 0);
      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
              /* using-declarations can add base methods to the method vec,
                 and we don't want those here.  */
              && DECL_CONTEXT (fn) == class_specialization)
            return fn;
        }
      return NULL_TREE;
    }
  else
    {
      spec_entry *found;
      spec_entry elt;
      htab_t specializations;

      elt.tmpl = tmpl;
      elt.args = args;
      elt.spec = NULL_TREE;

      if (DECL_CLASS_TEMPLATE_P (tmpl))
        specializations = type_specializations;
      else
        specializations = decl_specializations;

      if (hash == 0)
        hash = hash_specialization (&elt);
      found = (spec_entry *) htab_find_with_hash (specializations, &elt, hash);
      if (found)
        return found->spec;
    }

  return NULL_TREE;
}

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

static tree
retrieve_local_specialization (tree tmpl)
{
  tree spec;

  if (local_specializations == NULL)
    return NULL_TREE;

  spec = (tree) 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_DECL according to [temp.friend].  */

bool
is_specialization_of_friend (tree decl, tree friend_decl)
{
  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_DECL is an ordinary member function
     of a template class, we want to check if DECL is a specialization
     if this.  */
  if (TREE_CODE (friend_decl) == FUNCTION_DECL
      && DECL_TEMPLATE_INFO (friend_decl)
      && !DECL_USE_TEMPLATE (friend_decl))
    {
      /* We want a TEMPLATE_DECL for `is_specialization_of'.  */
      friend_decl = DECL_TI_TEMPLATE (friend_decl);
      need_template = false;
    }
  else if (TREE_CODE (friend_decl) == TEMPLATE_DECL
           && !PRIMARY_TEMPLATE_P (friend_decl))
    need_template = false;

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

  if (is_specialization_of (decl, friend_decl))
    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_decl));
  if (template_depth
      && DECL_CLASS_SCOPE_P (decl)
      && is_specialization_of (TYPE_NAME (DECL_CONTEXT (decl)),
                               CLASSTYPE_TI_TEMPLATE (DECL_CONTEXT (friend_decl))))
    {
      /* Next, we check the members themselves.  In order to handle
         a few tricky cases, such as when FRIEND_DECL'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_DECL 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_decl),
                                         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_decl), 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_decl))
            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_DECL 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_decl))
                return false;

              /* Now check template parameter list.  */
              friend_parms
                = tsubst_template_parms (DECL_TEMPLATE_PARMS (friend_decl),
                                         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_decl));
        }
    }
  return false;
}

/* Register the specialization SPEC as a specialization of TMPL with
   the indicated ARGS.  IS_FRIEND indicates whether the specialization
   is actually just a friend declaration.  Returns SPEC, or an
   equivalent prior declaration, if available.  */

static tree
register_specialization (tree spec, tree tmpl, tree args, bool is_friend,
                         hashval_t hash)
{
  tree fn;
  spec_entry **slot = NULL;
  spec_entry elt;

  gcc_assert (TREE_CODE (tmpl) == TEMPLATE_DECL && DECL_P (spec));

  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;

  if (optimize_specialization_lookup_p (tmpl))
    /* We don't put these specializations in the hash table, but we might
       want to give an error about a mismatch.  */
    fn = retrieve_specialization (tmpl, args, 0);
  else
    {
      elt.tmpl = tmpl;
      elt.args = args;
      elt.spec = spec;

      if (hash == 0)
        hash = hash_specialization (&elt);

      slot = (spec_entry **)
        htab_find_slot_with_hash (decl_specializations, &elt, hash, INSERT);
      if (*slot)
        fn = (*slot)->spec;
      else
        fn = NULL_TREE;
    }

  /* 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 (DECL_ODR_USED (fn)
              || DECL_EXPLICIT_INSTANTIATION (fn))
            {
              error ("specialization of %qD after instantiation",
                     fn);
              return error_mark_node;
            }
          else
            {
              tree clone;
              /* 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, is_friend);
              /* The call to duplicate_decls will have applied
                 [temp.expl.spec]:

                   An explicit specialization of a function template
                   is inline only if it is explicitly declared to be,
                   and independently of whether its function template
                   is.

                to the primary function; now copy the inline bits to
                the various clones.  */
              FOR_EACH_CLONE (clone, fn)
                {
                  DECL_DECLARED_INLINE_P (clone)
                    = DECL_DECLARED_INLINE_P (fn);
                  DECL_SOURCE_LOCATION (clone)
                    = DECL_SOURCE_LOCATION (fn);
                }
              check_specialization_namespace (fn);

              return fn;
            }
        }
      else if (DECL_TEMPLATE_SPECIALIZATION (fn))
        {
          if (!duplicate_decls (spec, fn, is_friend) && 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;
        }
    }
  else if (fn)
    return duplicate_decls (spec, fn, is_friend);

  /* 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_CONTEXT (tmpl);

  if (!optimize_specialization_lookup_p (tmpl))
    {
      gcc_assert (tmpl && args && spec);
      *slot = GGC_NEW (spec_entry);
      **slot = elt;
      if (TREE_CODE (spec) == FUNCTION_DECL && DECL_NAMESPACE_SCOPE_P (spec)
          && PRIMARY_TEMPLATE_P (tmpl)
          && DECL_SAVED_TREE (DECL_TEMPLATE_RESULT (tmpl)) == NULL_TREE)
        /* TMPL is a forward declaration of a template function; keep a list
           of all specializations in case we need to reassign them to a friend
           template later in tsubst_friend_function.  */
        DECL_TEMPLATE_INSTANTIATIONS (tmpl)
          = tree_cons (args, spec, DECL_TEMPLATE_INSTANTIATIONS (tmpl));
    }

  return spec;
}

/* Returns true iff two spec_entry nodes are equivalent.  Only compares the
   TMPL and ARGS members, ignores SPEC.  */

static int
eq_specializations (const void *p1, const void *p2)
{
  const spec_entry *e1 = (const spec_entry *)p1;
  const spec_entry *e2 = (const spec_entry *)p2;

  return (e1->tmpl == e2->tmpl
          && comp_template_args (e1->args, e2->args));
}

/* Returns a hash for a template TMPL and template arguments ARGS.  */

static hashval_t
hash_tmpl_and_args (tree tmpl, tree args)
{
  hashval_t val = DECL_UID (tmpl);
  return iterative_hash_template_arg (args, val);
}

/* Returns a hash for a spec_entry node based on the TMPL and ARGS members,
   ignoring SPEC.  */

static hashval_t
hash_specialization (const void *p)
{
  const spec_entry *e = (const spec_entry *)p;
  return hash_tmpl_and_args (e->tmpl, e->args);
}

/* Recursively calculate a hash value for a template argument ARG, for use
   in the hash tables of template specializations.  */

static hashval_t
iterative_hash_template_arg (tree arg, hashval_t val)
{
  unsigned HOST_WIDE_INT i;
  enum tree_code code;
  char tclass;

  if (arg == NULL_TREE)
    return iterative_hash_object (arg, val);

  if (!TYPE_P (arg))
    STRIP_NOPS (arg);

  if (TREE_CODE (arg) == ARGUMENT_PACK_SELECT)
    /* We can get one of these when re-hashing a previous entry in the middle
       of substituting into a pack expansion.  Just look through it.  */
    arg = ARGUMENT_PACK_SELECT_FROM_PACK (arg);

  code = TREE_CODE (arg);
  tclass = TREE_CODE_CLASS (code);

  val = iterative_hash_object (code, val);

  switch (code)
    {
    case ERROR_MARK:
      return val;

    case IDENTIFIER_NODE:
      return iterative_hash_object (IDENTIFIER_HASH_VALUE (arg), val);

    case TREE_VEC:
      {
        int i, len = TREE_VEC_LENGTH (arg);
        for (i = 0; i < len; ++i)
          val = iterative_hash_template_arg (TREE_VEC_ELT (arg, i), val);
        return val;
      }

    case TYPE_PACK_EXPANSION:
    case EXPR_PACK_EXPANSION:
      return iterative_hash_template_arg (PACK_EXPANSION_PATTERN (arg), val);

    case TYPE_ARGUMENT_PACK:
    case NONTYPE_ARGUMENT_PACK:
      return iterative_hash_template_arg (ARGUMENT_PACK_ARGS (arg), val);

    case TREE_LIST:
      for (; arg; arg = TREE_CHAIN (arg))
        val = iterative_hash_template_arg (TREE_VALUE (arg), val);
      return val;

    case OVERLOAD:
      for (; arg; arg = OVL_CHAIN (arg))
        val = iterative_hash_template_arg (OVL_FUNCTION (arg), val);
      return val;

    case CONSTRUCTOR:
      {
        tree field, value;
        FOR_EACH_CONSTRUCTOR_ELT (CONSTRUCTOR_ELTS (arg), i, field, value)
          {
            val = iterative_hash_template_arg (field, val);
            val = iterative_hash_template_arg (value, val);
          }
        return val;
      }

    case PARM_DECL:
      if (!DECL_ARTIFICIAL (arg))
        val = iterative_hash_object (DECL_PARM_INDEX (arg), val);
      return iterative_hash_template_arg (TREE_TYPE (arg), val);

    case TARGET_EXPR:
      return iterative_hash_template_arg (TARGET_EXPR_INITIAL (arg), val);

    case PTRMEM_CST:
      val = iterative_hash_template_arg (PTRMEM_CST_CLASS (arg), val);
      return iterative_hash_template_arg (PTRMEM_CST_MEMBER (arg), val);

    case TEMPLATE_PARM_INDEX:
      val = iterative_hash_template_arg
        (TREE_TYPE (TEMPLATE_PARM_DECL (arg)), val);
      val = iterative_hash_object (TEMPLATE_PARM_LEVEL (arg), val);
      return iterative_hash_object (TEMPLATE_PARM_IDX (arg), val);

    case TRAIT_EXPR:
      val = iterative_hash_object (TRAIT_EXPR_KIND (arg), val);
      val = iterative_hash_template_arg (TRAIT_EXPR_TYPE1 (arg), val);
      return iterative_hash_template_arg (TRAIT_EXPR_TYPE2 (arg), val);

    case BASELINK:
      val = iterative_hash_template_arg (BINFO_TYPE (BASELINK_BINFO (arg)),
                                         val);
      return iterative_hash_template_arg (DECL_NAME (get_first_fn (arg)),
                                          val);

    case MODOP_EXPR:
      val = iterative_hash_template_arg (TREE_OPERAND (arg, 0), val);
      code = TREE_CODE (TREE_OPERAND (arg, 1));
      val = iterative_hash_object (code, val);
      return iterative_hash_template_arg (TREE_OPERAND (arg, 2), val);

    case ARRAY_TYPE:
      /* layout_type sets structural equality for arrays of
         incomplete type, so we can't rely on the canonical type
         for hashing.  */
      val = iterative_hash_template_arg (TREE_TYPE (arg), val);
      return iterative_hash_template_arg (TYPE_DOMAIN (arg), val);

    default:
      switch (tclass)
        {
        case tcc_type:
          if (TYPE_CANONICAL (arg))
            return iterative_hash_object (TYPE_HASH (TYPE_CANONICAL (arg)),
                                          val);
          else if (TREE_CODE (arg) == DECLTYPE_TYPE)
            return iterative_hash_template_arg (DECLTYPE_TYPE_EXPR (arg), val);
          /* Otherwise just compare the types during lookup.  */
          return val;

        case tcc_declaration:
        case tcc_constant:
          return iterative_hash_expr (arg, val);

        default:
          gcc_assert (IS_EXPR_CODE_CLASS (tclass));
          {
            unsigned n = TREE_OPERAND_LENGTH (arg);
            for (i = 0; i < n; ++i)
              val = iterative_hash_template_arg (TREE_OPERAND (arg, i), val);
            return val;
          }
        }
    }
  gcc_unreachable ();
  return 0;
}

/* 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.

   Note that SPEC has been ggc_freed, so we can't look inside it.  */

bool
reregister_specialization (tree spec, tree tinfo, tree new_spec)
{
  spec_entry **slot;
  spec_entry elt;

  elt.tmpl = most_general_template (TI_TEMPLATE (tinfo));
  elt.args = TI_ARGS (tinfo);
  elt.spec = NULL_TREE;

  slot = (spec_entry **) htab_find_slot (decl_specializations, &elt, INSERT);
  if (*slot)
    {
      gcc_assert ((*slot)->spec == spec || (*slot)->spec == new_spec);
      gcc_assert (new_spec != NULL_TREE);
      (*slot)->spec = 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 ((const_tree) p1) == (const_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 ((const_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);
}

/* TYPE is a class type.  Returns true if TYPE is an explicitly
   specialized class.  */

bool
explicit_class_specialization_p (tree type)
{
  if (!CLASSTYPE_TEMPLATE_SPECIALIZATION (type))
    return false;
  return !uses_template_parms (CLASSTYPE_TI_ARGS (type));
}

/* Print the list of functions at FNS, going through all the overloads
   for each element of the list.  Alternatively, FNS can not be a
   TREE_LIST, in which case it will be printed together with all the
   overloads.

   MORE and *STR should respectively be FALSE and NULL when the function
   is called from the outside.  They are used internally on recursive
   calls.  print_candidates manages the two parameters and leaves NULL
   in *STR when it ends.  */

static void
print_candidates_1 (tree fns, bool more, const char **str)
{
  tree fn, fn2;
  char *spaces = NULL;

  for (fn = fns; fn; fn = OVL_NEXT (fn))
    if (TREE_CODE (fn) == TREE_LIST)
      {
        gcc_assert (!OVL_NEXT (fn) && !is_overloaded_fn (fn));
        for (fn2 = fn; fn2 != NULL_TREE; fn2 = TREE_CHAIN (fn2))
          print_candidates_1 (TREE_VALUE (fn2),
                              TREE_CHAIN (fn2) || more, str);
      }
    else
      {
        if (!*str)
          {
            /* Pick the prefix string.  */
            if (!more && !OVL_NEXT (fns))
              {
                error ("candidate is: %+#D", OVL_CURRENT (fn));
                continue;
              }

            *str = _("candidates are:");
            spaces = get_spaces (*str);
          }
        error ("%s %+#D", *str, OVL_CURRENT (fn));
        *str = spaces ? spaces : *str;
      }

  if (!more)
    {
      free (spaces);
      *str = NULL;
    }
}

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

void
print_candidates (tree fns)
{
  const char *str = NULL;
  print_candidates_1 (fns, false, &str);
  gcc_assert (str == NULL);
}

/* 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.

   TSK indicates what kind of template declaration (if any) is being
   declared.  TSK_TEMPLATE indicates that the declaration given by
   DECL, though a FUNCTION_DECL, has template parameters, and is
   therefore a template function.

   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,
                          tmpl_spec_kind tsk)
{
  tree fns;
  tree targs;
  tree explicit_targs;
  tree candidates = NULL_TREE;
  /* A TREE_LIST of templates of which DECL may be a specialization.
     The TREE_VALUE of each node is a TEMPLATE_DECL.  The
     corresponding TREE_PURPOSE is the set of template arguments that,
     when used to instantiate the template, would produce a function
     with the signature of DECL.  */
  tree templates = NULL_TREE;
  int header_count;
  struct cp_binding_level *b;

  *targs_out = NULL_TREE;

  if (template_id == error_mark_node || decl == 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;

          /* 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 (INNERMOST_TEMPLATE_PARMS
                                      (current_template_parms))))
            continue;

          /* DECL might be a specialization of FN.  */
          decl_arg_types = TYPE_ARG_TYPES (TREE_TYPE (decl));
          fn_arg_types = TYPE_ARG_TYPES (TREE_TYPE (fn));

          /* For a non-static member function, we need to make sure
             that the const qualification is the same.  Since
             get_bindings does not try to merge the "this" parameter,
             we must do the comparison explicitly.  */
          if (DECL_NONSTATIC_MEMBER_FUNCTION_P (fn)
              && !same_type_p (TREE_VALUE (fn_arg_types),
                               TREE_VALUE (decl_arg_types)))
            continue;

          /* Skip the "this" parameter and, for constructors of
             classes with virtual bases, the VTT parameter.  A
             full specialization of a constructor will have a VTT
             parameter, but a template never will.  */ 
          decl_arg_types 
            = skip_artificial_parms_for (decl, decl_arg_types);
          fn_arg_types 
            = skip_artificial_parms_for (fn, fn_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.  */
          if (list_length (fn_arg_types) != list_length (decl_arg_types))
            continue;

          /* Function templates cannot be specializations; there are
             no partial specializations of functions.  Therefore, if
             the type of DECL does not match FN, there is no
             match.  */
          if (tsk == tsk_template)
            {
              if (compparms (fn_arg_types, decl_arg_types))
                candidates = tree_cons (NULL_TREE, fn, candidates);
              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_instantiation (templates);
      if (tmpl != error_mark_node)
        {
          templates = tmpl;
          TREE_CHAIN (templates) = NULL_TREE;
        }
    }

  if (templates == NULL_TREE && candidates == NULL_TREE)
    {
      error ("template-id %qD for %q+D does not match any template "
             "declaration", template_id, decl);
      if (header_count && header_count != template_count + 1)
        inform (input_location, "saw %d %<template<>%>, need %d for "
                "specializing a member function template",
                header_count, template_count + 1);
      return error_mark_node;
    }
  else if ((templates && TREE_CHAIN (templates))
           || (candidates && TREE_CHAIN (candidates))
           || (templates && candidates))
    {
      error ("ambiguous template specialization %qD for %q+D",
             template_id, decl);
      candidates = chainon (candidates, templates);
      print_candidates (candidates);
      return error_mark_node;
    }

  /* We have one, and exactly one, match.  */
  if (candidates)
    {
      tree fn = TREE_VALUE (candidates);
      *targs_out = copy_node (DECL_TI_ARGS (fn));
      /* DECL is a re-declaration or partial instantiation of a template
         function.  */
      if (TREE_CODE (fn) == TEMPLATE_DECL)
        return fn;
      /* It was a specialization of an ordinary member function in a
         template class.  */
      return DECL_TI_TEMPLATE (fn);
    }

  /* 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))
          {
            permerror (input_location, 
                       "default argument specified in explicit specialization");
            break;
          }
    }

  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 = lookup_qualified_name (CP_DECL_CONTEXT (decl), dname,
                                           false, true);
              if (fns == error_mark_node || !is_overloaded_fn (fns))
                {
                  error ("%qD is not a template function", dname);
                  fns = error_mark_node;
                }
              else
                {
                  tree fn = OVL_CURRENT (fns);
                  if (!is_associated_namespace (CP_DECL_CONTEXT (decl),
                                                CP_DECL_CONTEXT (fn)))
                    error ("%qD is not declared in %qD",
                           decl, current_namespace);
                }
            }

          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_USER_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,
                                       tsk);

      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, we want to return the TEMPLATE_DECL, not
             the specialization of it.  */
          if (tsk == tsk_template)
            {
              tree result = DECL_TEMPLATE_RESULT (tmpl);
              SET_DECL_TEMPLATE_SPECIALIZATION (tmpl);
              DECL_INITIAL (result) = NULL_TREE;
              if (have_def)
                {
                  tree parm;
                  DECL_SOURCE_LOCATION (tmpl) = DECL_SOURCE_LOCATION (decl);
                  DECL_SOURCE_LOCATION (result)
                    = DECL_SOURCE_LOCATION (decl);
                  /* We want to use the argument list specified in the
                     definition, not in the original declaration.  */
                  DECL_ARGUMENTS (result) = DECL_ARGUMENTS (decl);
                  for (parm = DECL_ARGUMENTS (result); parm;
                       parm = TREE_CHAIN (parm))
                    DECL_CONTEXT (parm) = result;
                }
              return register_specialization (tmpl, gen_tmpl, targs,
                                              is_friend, 0);
            }

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

          /* 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);

          /* 7.1.1-1 [dcl.stc]

             A storage-class-specifier shall not be specified in an
             explicit specialization...

             The parser rejects these, so unless action is taken here,
             explicit function specializations will always appear with
             global linkage.

             The action recommended by the C++ CWG in response to C++
             defect report 605 is to make the storage class and linkage
             of the explicit specialization match the templated function:

             http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#605
           */
          if (tsk == tsk_expl_spec && DECL_FUNCTION_TEMPLATE_P (gen_tmpl))
            {
              tree tmpl_func = DECL_TEMPLATE_RESULT (gen_tmpl);
              gcc_assert (TREE_CODE (tmpl_func) == FUNCTION_DECL);

              /* This specialization has the same linkage and visibility as
                 the function template it specializes.  */
              TREE_PUBLIC (decl) = TREE_PUBLIC (tmpl_func);
              if (! TREE_PUBLIC (decl))
                {
                  DECL_INTERFACE_KNOWN (decl) = 1;
                  DECL_NOT_REALLY_EXTERN (decl) = 1;
                }
              DECL_THIS_STATIC (decl) = DECL_THIS_STATIC (tmpl_func);
              if (DECL_VISIBILITY_SPECIFIED (tmpl_func))
                {
                  DECL_VISIBILITY_SPECIFIED (decl) = 1;
                  DECL_VISIBILITY (decl) = DECL_VISIBILITY (tmpl_func);
                }
            }

          /* If DECL is a friend declaration, declared using an
             unqualified name, the namespace associated with DECL may
             have been set incorrectly.  For example, in:

               template <typename T> void f(T);
               namespace N {
                 struct S { friend void f<int>(int); }
               }

             we will have set the DECL_CONTEXT for the friend
             declaration to N, rather than to the global namespace.  */
          if (DECL_NAMESPACE_SCOPE_P (decl))
            DECL_CONTEXT (decl) = DECL_CONTEXT (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, is_friend, 0);
        }
    }

  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 (const_tree parms1, const_tree parms2)
{
  const_tree p1;
  const_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 either of the template parameters are invalid, assume
             they match for the sake of error recovery. */
          if (parm1 == error_mark_node || parm2 == error_mark_node)
            return 1;

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

          if (TREE_CODE (parm1) == TEMPLATE_TYPE_PARM
              && (TEMPLATE_TYPE_PARAMETER_PACK (parm1)
                  == TEMPLATE_TYPE_PARAMETER_PACK (parm2)))
            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;
}

/* Determine whether PARM is a parameter pack.  */

bool 
template_parameter_pack_p (const_tree parm)
{
  /* Determine if we have a non-type template parameter pack.  */
  if (TREE_CODE (parm) == PARM_DECL)
    return (DECL_TEMPLATE_PARM_P (parm) 
            && TEMPLATE_PARM_PARAMETER_PACK (DECL_INITIAL (parm)));

  /* If this is a list of template parameters, we could get a
     TYPE_DECL or a TEMPLATE_DECL.  */ 
  if (TREE_CODE (parm) == TYPE_DECL || TREE_CODE (parm) == TEMPLATE_DECL)
    parm = TREE_TYPE (parm);

  return ((TREE_CODE (parm) == TEMPLATE_TYPE_PARM
           || TREE_CODE (parm) == TEMPLATE_TEMPLATE_PARM)
          && TEMPLATE_TYPE_PARAMETER_PACK (parm));
}

/* Determine if T is a function parameter pack.  */

bool
function_parameter_pack_p (const_tree t)
{
  if (t && TREE_CODE (t) == PARM_DECL)
    return FUNCTION_PARAMETER_PACK_P (t);
  return false;
}

/* Return the function template declaration of PRIMARY_FUNC_TMPL_INST.
   PRIMARY_FUNC_TMPL_INST is a primary function template instantiation.  */

tree
get_function_template_decl (const_tree primary_func_tmpl_inst)
{
  if (! primary_func_tmpl_inst
      || TREE_CODE (primary_func_tmpl_inst) != FUNCTION_DECL
      || ! primary_template_instantiation_p (primary_func_tmpl_inst))
    return NULL;

  return DECL_TEMPLATE_RESULT (DECL_TI_TEMPLATE (primary_func_tmpl_inst));
}

/* Return true iff the function parameter PARAM_DECL was expanded
   from the function parameter pack PACK.  */

bool
function_parameter_expanded_from_pack_p (tree param_decl, tree pack)
{
  if (DECL_ARTIFICIAL (param_decl)
      || !function_parameter_pack_p (pack))
    return false;

  /* The parameter pack and its pack arguments have the same
     DECL_PARM_INDEX.  */
  return DECL_PARM_INDEX (pack) == DECL_PARM_INDEX (param_decl);
}

/* Determine whether ARGS describes a variadic template args list,
   i.e., one that is terminated by a template argument pack.  */

static bool 
template_args_variadic_p (tree args)
{
  int nargs;
  tree last_parm;

  if (args == NULL_TREE)
    return false;

  args = INNERMOST_TEMPLATE_ARGS (args);
  nargs = TREE_VEC_LENGTH (args);

  if (nargs == 0)
    return false;

  last_parm = TREE_VEC_ELT (args, nargs - 1);

  return ARGUMENT_PACK_P (last_parm);
}

/* Generate a new name for the parameter pack name NAME (an
   IDENTIFIER_NODE) that incorporates its */

static tree
make_ith_pack_parameter_name (tree name, int i)
{
  /* Munge the name to include the parameter index.  */
#define NUMBUF_LEN 128
  char numbuf[NUMBUF_LEN];
  char* newname;
  int newname_len;

  snprintf (numbuf, NUMBUF_LEN, "%i", i);
  newname_len = IDENTIFIER_LENGTH (name)
                + strlen (numbuf) + 2;
  newname = (char*)alloca (newname_len);
  snprintf (newname, newname_len,
            "%s#%i", IDENTIFIER_POINTER (name), i);
  return get_identifier (newname);
}

/* Return true if T is a primary function
   or class template instantiation.  */

bool
primary_template_instantiation_p (const_tree t)
{
  if (!t)
    return false;

  if (TREE_CODE (t) == FUNCTION_DECL)
    return DECL_LANG_SPECIFIC (t)
           && DECL_TEMPLATE_INSTANTIATION (t)
           && PRIMARY_TEMPLATE_P (DECL_TI_TEMPLATE (t));
  else if (CLASS_TYPE_P (t))
    return CLASSTYPE_TEMPLATE_INSTANTIATION (t)
           && PRIMARY_TEMPLATE_P (CLASSTYPE_TI_TEMPLATE (t));
  return false;
}

/* Return true if PARM is a template template parameter.  */

bool
template_template_parameter_p (const_tree parm)
{
  return DECL_TEMPLATE_TEMPLATE_PARM_P (parm);
}

/* Return the template parameters of T if T is a
   primary template instantiation, NULL otherwise.  */

tree
get_primary_template_innermost_parameters (const_tree t)
{
  tree parms = NULL, template_info = NULL;

  if ((template_info = get_template_info (t))
      && primary_template_instantiation_p (t))
    parms = INNERMOST_TEMPLATE_PARMS
        (DECL_TEMPLATE_PARMS (TI_TEMPLATE (template_info)));

  return parms;
}

/* Return the template parameters of the LEVELth level from the full list
   of template parameters PARMS.  */

tree
get_template_parms_at_level (tree parms, int level)
{
  tree p;
  if (!parms
      || TREE_CODE (parms) != TREE_LIST
      || level > TMPL_PARMS_DEPTH (parms))
    return NULL_TREE;

  for (p = parms; p; p = TREE_CHAIN (p))
    if (TMPL_PARMS_DEPTH (p) == level)
      return p;

  return NULL_TREE;
}

/* Returns the template arguments of T if T is a template instantiation,
   NULL otherwise.  */

tree
get_template_innermost_arguments (const_tree t)
{
  tree args = NULL, template_info = NULL;

  if ((template_info = get_template_info (t))
      && TI_ARGS (template_info))
    args = INNERMOST_TEMPLATE_ARGS (TI_ARGS (template_info));

  return args;
}

/* Return the argument pack elements of T if T is a template argument pack,
   NULL otherwise.  */

tree
get_template_argument_pack_elems (const_tree t)
{
  if (TREE_CODE (t) != TYPE_ARGUMENT_PACK
      && TREE_CODE (t) != NONTYPE_ARGUMENT_PACK)
    return NULL;

  return ARGUMENT_PACK_ARGS (t);
}

/* Structure used to track the progress of find_parameter_packs_r.  */
struct find_parameter_pack_data 
{
  /* TREE_LIST that will contain all of the parameter packs found by
     the traversal.  */
  tree* parameter_packs;

  /* Set of AST nodes that have been visited by the traversal.  */
  struct pointer_set_t *visited;
};

/* Identifies all of the argument packs that occur in a template
   argument and appends them to the TREE_LIST inside DATA, which is a
   find_parameter_pack_data structure. This is a subroutine of
   make_pack_expansion and uses_parameter_packs.  */
static tree
find_parameter_packs_r (tree *tp, int *walk_subtrees, void* data)
{
  tree t = *tp;
  struct find_parameter_pack_data* ppd = 
    (struct find_parameter_pack_data*)data;
  bool parameter_pack_p = false;

  /* Identify whether this is a parameter pack or not.  */
  switch (TREE_CODE (t))
    {
    case TEMPLATE_PARM_INDEX:
      if (TEMPLATE_PARM_PARAMETER_PACK (t))
        parameter_pack_p = true;
      break;

    case TEMPLATE_TYPE_PARM:
    case TEMPLATE_TEMPLATE_PARM:
      if (TEMPLATE_TYPE_PARAMETER_PACK (t))
        parameter_pack_p = true;
      break;

    case PARM_DECL:
      if (FUNCTION_PARAMETER_PACK_P (t))
        {
          /* We don't want to walk into the type of a PARM_DECL,
             because we don't want to see the type parameter pack.  */
          *walk_subtrees = 0;
          parameter_pack_p = true;
        }
      break;

    default:
      /* Not a parameter pack.  */
      break;
    }

  if (parameter_pack_p)
    {
      /* Add this parameter pack to the list.  */
      *ppd->parameter_packs = tree_cons (NULL_TREE, t, *ppd->parameter_packs);
    }

  if (TYPE_P (t))
    cp_walk_tree (&TYPE_CONTEXT (t), 
                  &find_parameter_packs_r, ppd, ppd->visited);

  /* This switch statement will return immediately if we don't find a
     parameter pack.  */
  switch (TREE_CODE (t)) 
    {
    case TEMPLATE_PARM_INDEX:
      return NULL_TREE;

    case BOUND_TEMPLATE_TEMPLATE_PARM:
      /* Check the template itself.  */
      cp_walk_tree (&TREE_TYPE (TYPE_TI_TEMPLATE (t)), 
                    &find_parameter_packs_r, ppd, ppd->visited);
      /* Check the template arguments.  */
      cp_walk_tree (&TYPE_TI_ARGS (t), &find_parameter_packs_r, ppd, 
                    ppd->visited);
      *walk_subtrees = 0;
      return NULL_TREE;

    case TEMPLATE_TYPE_PARM:
    case TEMPLATE_TEMPLATE_PARM:
      return NULL_TREE;

    case PARM_DECL:
      return NULL_TREE;

    case RECORD_TYPE:
      if (TYPE_PTRMEMFUNC_P (t))
        return NULL_TREE;
      /* Fall through.  */

    case UNION_TYPE:
    case ENUMERAL_TYPE:
      if (TYPE_TEMPLATE_INFO (t))
        cp_walk_tree (&TI_ARGS (TYPE_TEMPLATE_INFO (t)),
                      &find_parameter_packs_r, ppd, ppd->visited);

      *walk_subtrees = 0;
      return NULL_TREE;

    case TEMPLATE_DECL:
      cp_walk_tree (&TREE_TYPE (t),
                    &find_parameter_packs_r, ppd, ppd->visited);
      return NULL_TREE;
 
    case TYPENAME_TYPE:
      cp_walk_tree (&TYPENAME_TYPE_FULLNAME (t), &find_parameter_packs_r,
                   ppd, ppd->visited);
      *walk_subtrees = 0;
      return NULL_TREE;
      
    case TYPE_PACK_EXPANSION:
    case EXPR_PACK_EXPANSION:
      *walk_subtrees = 0;
      return NULL_TREE;

    case INTEGER_TYPE:
      cp_walk_tree (&TYPE_MAX_VALUE (t), &find_parameter_packs_r, 
                    ppd, ppd->visited);
      *walk_subtrees = 0;
      return NULL_TREE;

    case IDENTIFIER_NODE:
      cp_walk_tree (&TREE_TYPE (t), &find_parameter_packs_r, ppd, 
                    ppd->visited);
      *walk_subtrees = 0;
      return NULL_TREE;

    default:
      return NULL_TREE;
    }

  return NULL_TREE;
}

/* Determines if the expression or type T uses any parameter packs.  */
bool
uses_parameter_packs (tree t)
{
  tree parameter_packs = NULL_TREE;
  struct find_parameter_pack_data ppd;
  ppd.parameter_packs = &parameter_packs;
  ppd.visited = pointer_set_create ();
  cp_walk_tree (&t, &find_parameter_packs_r, &ppd, ppd.visited);
  pointer_set_destroy (ppd.visited);
  return parameter_packs != NULL_TREE;
}

/* Turn ARG, which may be an expression, type, or a TREE_LIST
   representation a base-class initializer into a parameter pack
   expansion. If all goes well, the resulting node will be an
   EXPR_PACK_EXPANSION, TYPE_PACK_EXPANSION, or TREE_LIST,
   respectively.  */
tree 
make_pack_expansion (tree arg)
{
  tree result;
  tree parameter_packs = NULL_TREE;
  bool for_types = false;
  struct find_parameter_pack_data ppd;

  if (!arg || arg == error_mark_node)
    return arg;

  if (TREE_CODE (arg) == TREE_LIST)
    {
      /* The only time we will see a TREE_LIST here is for a base
         class initializer.  In this case, the TREE_PURPOSE will be a
         _TYPE node (representing the base class expansion we're
         initializing) and the TREE_VALUE will be a TREE_LIST
         containing the initialization arguments. 

         The resulting expansion looks somewhat different from most
         expansions. Rather than returning just one _EXPANSION, we
         return a TREE_LIST whose TREE_PURPOSE is a
         TYPE_PACK_EXPANSION containing the bases that will be
         initialized.  The TREE_VALUE will be identical to the
         original TREE_VALUE, which is a list of arguments that will
         be passed to each base.  We do not introduce any new pack
         expansion nodes into the TREE_VALUE (although it is possible
         that some already exist), because the TREE_PURPOSE and
         TREE_VALUE all need to be expanded together with the same
         _EXPANSION node.  Note that the TYPE_PACK_EXPANSION in the
         resulting TREE_PURPOSE will mention the parameter packs in
         both the bases and the arguments to the bases.  */
      tree purpose;
      tree value;
      tree parameter_packs = NULL_TREE;

      /* Determine which parameter packs will be used by the base
         class expansion.  */
      ppd.visited = pointer_set_create ();
      ppd.parameter_packs = &parameter_packs;
      cp_walk_tree (&TREE_PURPOSE (arg), &find_parameter_packs_r, 
                    &ppd, ppd.visited);

      if (parameter_packs == NULL_TREE)
        {
          error ("base initializer expansion %<%T%> contains no parameter packs", arg);
          pointer_set_destroy (ppd.visited);
          return error_mark_node;
        }

      if (TREE_VALUE (arg) != void_type_node)
        {
          /* Collect the sets of parameter packs used in each of the
             initialization arguments.  */
          for (value = TREE_VALUE (arg); value; value = TREE_CHAIN (value))
            {
              /* Determine which parameter packs will be expanded in this
                 argument.  */
              cp_walk_tree (&TREE_VALUE (value), &find_parameter_packs_r, 
                            &ppd, ppd.visited);
            }
        }

      pointer_set_destroy (ppd.visited);

      /* Create the pack expansion type for the base type.  */
      purpose = cxx_make_type (TYPE_PACK_EXPANSION);
      SET_PACK_EXPANSION_PATTERN (purpose, TREE_PURPOSE (arg));
      PACK_EXPANSION_PARAMETER_PACKS (purpose) = parameter_packs;

      /* Just use structural equality for these TYPE_PACK_EXPANSIONS;
         they will rarely be compared to anything.  */
      SET_TYPE_STRUCTURAL_EQUALITY (purpose);

      return tree_cons (purpose, TREE_VALUE (arg), NULL_TREE);
    }

  if (TYPE_P (arg) || TREE_CODE (arg) == TEMPLATE_DECL)
    for_types = true;

  /* Build the PACK_EXPANSION_* node.  */
  result = for_types
     ? cxx_make_type (TYPE_PACK_EXPANSION)
     : make_node (EXPR_PACK_EXPANSION);
  SET_PACK_EXPANSION_PATTERN (result, arg);
  if (TREE_CODE (result) == EXPR_PACK_EXPANSION)
    {
      /* Propagate type and const-expression information.  */
      TREE_TYPE (result) = TREE_TYPE (arg);
      TREE_CONSTANT (result) = TREE_CONSTANT (arg);
    }
  else
    /* Just use structural equality for these TYPE_PACK_EXPANSIONS;
       they will rarely be compared to anything.  */
    SET_TYPE_STRUCTURAL_EQUALITY (result);

  /* Determine which parameter packs will be expanded.  */
  ppd.parameter_packs = &parameter_packs;
  ppd.visited = pointer_set_create ();
  cp_walk_tree (&arg, &find_parameter_packs_r, &ppd, ppd.visited);
  pointer_set_destroy (ppd.visited);

  /* Make sure we found some parameter packs.  */
  if (parameter_packs == NULL_TREE)
    {
      if (TYPE_P (arg))
        error ("expansion pattern %<%T%> contains no argument packs", arg);
      else
        error ("expansion pattern %<%E%> contains no argument packs", arg);
      return error_mark_node;
    }
  PACK_EXPANSION_PARAMETER_PACKS (result) = parameter_packs;

  return result;
}

/* Checks T for any "bare" parameter packs, which have not yet been
   expanded, and issues an error if any are found. This operation can
   only be done on full expressions or types (e.g., an expression
   statement, "if" condition, etc.), because we could have expressions like:

     foo(f(g(h(args)))...)

   where "args" is a parameter pack. check_for_bare_parameter_packs
   should not be called for the subexpressions args, h(args),
   g(h(args)), or f(g(h(args))), because we would produce erroneous
   error messages. 

   Returns TRUE and emits an error if there were bare parameter packs,
   returns FALSE otherwise.  */
bool 
check_for_bare_parameter_packs (tree t)
{
  tree parameter_packs = NULL_TREE;
  struct find_parameter_pack_data ppd;

  if (!processing_template_decl || !t || t == error_mark_node)
    return false;

  if (TREE_CODE (t) == TYPE_DECL)
    t = TREE_TYPE (t);

  ppd.parameter_packs = &parameter_packs;
  ppd.visited = pointer_set_create ();
  cp_walk_tree (&t, &find_parameter_packs_r, &ppd, ppd.visited);
  pointer_set_destroy (ppd.visited);

  if (parameter_packs) 
    {
      error ("parameter packs not expanded with %<...%>:");
      while (parameter_packs)
        {
          tree pack = TREE_VALUE (parameter_packs);
          tree name = NULL_TREE;

          if (TREE_CODE (pack) == TEMPLATE_TYPE_PARM
              || TREE_CODE (pack) == TEMPLATE_TEMPLATE_PARM)
            name = TYPE_NAME (pack);
          else if (TREE_CODE (pack) == TEMPLATE_PARM_INDEX)
            name = DECL_NAME (TEMPLATE_PARM_DECL (pack));
          else
            name = DECL_NAME (pack);

          if (name)
            inform (input_location, "        %qD", name);
          else
            inform (input_location, "        <anonymous>");

          parameter_packs = TREE_CHAIN (parameter_packs);
        }

      return true;
    }

  return false;
}

/* Expand any parameter packs that occur in the template arguments in
   ARGS.  */
tree
expand_template_argument_pack (tree args)
{
  tree result_args = NULL_TREE;
  int in_arg, out_arg = 0, nargs = args ? TREE_VEC_LENGTH (args) : 0;
  int num_result_args = -1;
  int non_default_args_count = -1;

  /* First, determine if we need to expand anything, and the number of
     slots we'll need.  */
  for (in_arg = 0; in_arg < nargs; ++in_arg)
    {
      tree arg = TREE_VEC_ELT (args, in_arg);
      if (arg == NULL_TREE)
        return args;
      if (ARGUMENT_PACK_P (arg))
        {
          int num_packed = TREE_VEC_LENGTH (ARGUMENT_PACK_ARGS (arg));
          if (num_result_args < 0)
            num_result_args = in_arg + num_packed;
          else
            num_result_args += num_packed;
        }
      else
        {
          if (num_result_args >= 0)
            num_result_args++;
        }
    }

  /* If no expansion is necessary, we're done.  */
  if (num_result_args < 0)
    return args;

  /* Expand arguments.  */
  result_args = make_tree_vec (num_result_args);
  if (NON_DEFAULT_TEMPLATE_ARGS_COUNT (args))
    non_default_args_count =
      GET_NON_DEFAULT_TEMPLATE_ARGS_COUNT (args);
  for (in_arg = 0; in_arg < nargs; ++in_arg)
    {
      tree arg = TREE_VEC_ELT (args, in_arg);
      if (ARGUMENT_PACK_P (arg))
        {
          tree packed = ARGUMENT_PACK_ARGS (arg);
          int i, num_packed = TREE_VEC_LENGTH (packed);
          for (i = 0; i < num_packed; ++i, ++out_arg)
            TREE_VEC_ELT (result_args, out_arg) = TREE_VEC_ELT(packed, i);
          if (non_default_args_count > 0)
            non_default_args_count += num_packed;
        }
      else
        {
          TREE_VEC_ELT (result_args, out_arg) = arg;
          ++out_arg;
        }
    }
  if (non_default_args_count >= 0)
    SET_NON_DEFAULT_TEMPLATE_ARGS_COUNT (result_args, non_default_args_count);
  return result_args;
}

/* Checks if DECL shadows a template parameter.

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

   Emits an error and returns TRUE if the DECL shadows a parameter,
   returns FALSE otherwise.  */

bool
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 true;

  /* 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 true;

  /* 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 true;

  /* 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 true;

  error ("declaration of %q+#D", decl);
  error (" shadows template parm %q+#D", olddecl);
  return false;
}

/* 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_READONLY (t) = TREE_READONLY (decl);

  return t;
}

/* Find the canonical type parameter for the given template type
   parameter.  Returns the canonical type parameter, which may be TYPE
   if no such parameter existed.  */
static tree
canonical_type_parameter (tree type)
{
  tree list;
  int idx = TEMPLATE_TYPE_IDX (type);
  if (!canonical_template_parms)
    canonical_template_parms = VEC_alloc (tree, gc, idx+1);

  while (VEC_length (tree, canonical_template_parms) <= (unsigned)idx)
    VEC_safe_push (tree, gc, canonical_template_parms, NULL_TREE);

  list = VEC_index (tree, canonical_template_parms, idx);
  while (list && !comptypes (type, TREE_VALUE (list), COMPARE_STRUCTURAL))
    list = TREE_CHAIN (list);

  if (list)
    return TREE_VALUE (list);
  else
    {
      VEC_replace(tree, canonical_template_parms, idx,
                  tree_cons (NULL_TREE, type, 
                             VEC_index (tree, canonical_template_parms, idx)));
      return type;
    }
}

/* 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, tree args,
                            tsubst_flags_t complain)
{
  if (TEMPLATE_PARM_DESCENDANTS (index) == NULL_TREE
      || (TEMPLATE_PARM_LEVEL (TEMPLATE_PARM_DESCENDANTS (index))
          != TEMPLATE_PARM_LEVEL (index) - levels)
      || !same_type_p (type, TREE_TYPE (TEMPLATE_PARM_DESCENDANTS (index))))
    {
      tree orig_decl = TEMPLATE_PARM_DECL (index);
      tree decl, t;

      decl = build_decl (DECL_SOURCE_LOCATION (orig_decl),
                         TREE_CODE (orig_decl), DECL_NAME (orig_decl), type);
      TREE_CONSTANT (decl) = TREE_CONSTANT (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_PARM_PARAMETER_PACK (t) 
        = TEMPLATE_PARM_PARAMETER_PACK (index);

        /* Template template parameters need this.  */
      if (TREE_CODE (decl) == TEMPLATE_DECL)
        DECL_TEMPLATE_PARMS (decl) = tsubst_template_parms
          (DECL_TEMPLATE_PARMS (TEMPLATE_PARM_DECL (index)),
           args, complain);
    }

  return TEMPLATE_PARM_DESCENDANTS (index);
}

/* Process information from new template parameter PARM and append it to the
   LIST being built.  This new parameter is a non-type parameter iff
   IS_NON_TYPE is true. This new parameter is a parameter
   pack iff IS_PARAMETER_PACK is true.  The location of PARM is in 
   PARM_LOC.  */

tree
process_template_parm (tree list, location_t parm_loc, tree parm, bool is_non_type, 
                       bool is_parameter_pack)
{
  tree decl = 0;
  tree defval;
  tree err_parm_list;
  int idx = 0;

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

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

      if (p && TREE_VALUE (p) != error_mark_node)
        {
          p = TREE_VALUE (p);
          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);

      if (TREE_TYPE (parm) == error_mark_node)
        {
          err_parm_list = build_tree_list (defval, parm);
          TREE_VALUE (err_parm_list) = error_mark_node;
           return chainon (list, err_parm_list);
        }
      else
      {
        /* [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));
        if (invalid_nontype_parm_type_p (TREE_TYPE (parm), 1))
          {
            err_parm_list = build_tree_list (defval, parm);
            TREE_VALUE (err_parm_list) = error_mark_node;
             return chainon (list, err_parm_list);
          }

        if (uses_parameter_packs (TREE_TYPE (parm)) && !is_parameter_pack)
          {
            /* This template parameter is not a parameter pack, but it
               should be. Complain about "bare" parameter packs.  */
            check_for_bare_parameter_packs (TREE_TYPE (parm));
            
            /* Recover by calling this a parameter pack.  */
            is_parameter_pack = true;
          }
      }

      /* A template parameter is not modifiable.  */
      TREE_CONSTANT (parm) = 1;
      TREE_READONLY (parm) = 1;
      decl = build_decl (parm_loc,
                         CONST_DECL, DECL_NAME (parm), TREE_TYPE (parm));
      TREE_CONSTANT (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));

      TEMPLATE_PARM_PARAMETER_PACK (DECL_INITIAL (parm)) 
        = is_parameter_pack;
    }
  else
    {
      tree t;
      parm = TREE_VALUE (TREE_VALUE (parm));

      if (parm && TREE_CODE (parm) == TEMPLATE_DECL)
        {
          t = cxx_make_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 = cxx_make_type (TEMPLATE_TYPE_PARM);
          /* parm is either IDENTIFIER_NODE or NULL_TREE.  */
          decl = build_decl (parm_loc,
                             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));
      TEMPLATE_TYPE_PARAMETER_PACK (t) = is_parameter_pack;
      TYPE_CANONICAL (t) = canonical_type_parameter (t);
    }
  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;
      if (TREE_CODE (TREE_VALUE (parm)) == TYPE_DECL)
        TEMPLATE_TYPE_PARM_SIBLING_PARMS (TREE_TYPE (TREE_VALUE (parm))) =
              current_template_parms;
    }

  --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);
}

/* Within the declaration of a template, return all levels of template
   parameters that apply.  The template parameters are represented as
   a TREE_VEC, in the form documented in cp-tree.h for template
   arguments.  */

static 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 (!error_operand_p (t))
                {
                  if (TREE_CODE (t) == TYPE_DECL
                      || TREE_CODE (t) == TEMPLATE_DECL)
                    {
                      t = TREE_TYPE (t);
                      
                      if (TEMPLATE_TYPE_PARAMETER_PACK (t))
                        {
                          /* Turn this argument into a TYPE_ARGUMENT_PACK
                             with a single element, which expands T.  */
                          tree vec = make_tree_vec (1);
#ifdef ENABLE_CHECKING
                          SET_NON_DEFAULT_TEMPLATE_ARGS_COUNT
                                (vec, TREE_VEC_LENGTH (vec));
#endif
                          TREE_VEC_ELT (vec, 0) = make_pack_expansion (t);
                          
                          t = cxx_make_type (TYPE_ARGUMENT_PACK);
                          SET_ARGUMENT_PACK_ARGS (t, vec);
                        }
                    }
                  else
                    {
                      t = DECL_INITIAL (t);
                      
                      if (TEMPLATE_PARM_PARAMETER_PACK (t))
                        {
                          /* Turn this argument into a NONTYPE_ARGUMENT_PACK
                             with a single element, which expands T.  */
                          tree vec = make_tree_vec (1);
                          tree type = TREE_TYPE (TEMPLATE_PARM_DECL (t));
#ifdef ENABLE_CHECKING
                          SET_NON_DEFAULT_TEMPLATE_ARGS_COUNT
                                (vec, TREE_VEC_LENGTH (vec));
#endif
                          TREE_VEC_ELT (vec, 0) = make_pack_expansion (t);
                          
                          t  = make_node (NONTYPE_ARGUMENT_PACK);
                          SET_ARGUMENT_PACK_ARGS (t, vec);
                          TREE_TYPE (t) = type;
                        }
                    }
                  TREE_VEC_ELT (a, i) = t;
                }
            }
        }

#ifdef ENABLE_CHECKING
      SET_NON_DEFAULT_TEMPLATE_ARGS_COUNT (a, TREE_VEC_LENGTH (a));
#endif

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

  return args;
}

/* Update the declared TYPE by doing any lookups which were thought to be
   dependent, but are not now that we know the SCOPE of the declarator.  */

tree
maybe_update_decl_type (tree orig_type, tree scope)
{
  tree type = orig_type;

  if (type == NULL_TREE)
    return type;

  if (TREE_CODE (orig_type) == TYPE_DECL)
    type = TREE_TYPE (type);

  if (scope && TYPE_P (scope) && dependent_type_p (scope)
      && dependent_type_p (type)
      /* Don't bother building up the args in this case.  */
      && TREE_CODE (type) != TEMPLATE_TYPE_PARM)
    {
      /* tsubst in the args corresponding to the template parameters,
         including auto if present.  Most things will be unchanged, but
         make_typename_type and tsubst_qualified_id will resolve
         TYPENAME_TYPEs and SCOPE_REFs that were previously dependent.  */
      tree args = current_template_args ();
      tree auto_node = type_uses_auto (type);
      tree pushed;
      if (auto_node)
        {
          tree auto_vec = make_tree_vec (1);
          TREE_VEC_ELT (auto_vec, 0) = auto_node;
          args = add_to_template_args (args, auto_vec);
        }
      pushed = push_scope (scope);
      type = tsubst (type, args, tf_warning_or_error, NULL_TREE);
      if (pushed)
        pop_scope (scope);
    }

  if (type == error_mark_node)
    return orig_type;

  if (TREE_CODE (orig_type) == TYPE_DECL)
    {
      if (same_type_p (type, TREE_TYPE (orig_type)))
        type = orig_type;
      else
        type = TYPE_NAME (type);
    }
  return type;
}

/* 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;

  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 main_inner_parms = DECL_INNERMOST_TEMPLATE_PARMS (maintmpl);
  tree inner_parms;
  int nargs = TREE_VEC_LENGTH (inner_args);
  int ntparms;
  int  i;
  int did_error_intro = 0;
  struct template_parm_data tpd;
  struct template_parm_data tpd2;

  gcc_assert (current_template_parms);

  inner_parms = INNERMOST_TEMPLATE_PARMS (current_template_parms);
  ntparms = TREE_VEC_LENGTH (inner_parms);

  /* 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 = (int *) alloca (sizeof (int) * ntparms);
  memset (tpd.parms, 0, sizeof (int) * ntparms);

  tpd.arg_uses_template_parms = (int *) 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,
                              /*include_nondeduced_p=*/false);
    }
  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. 

     Also, we verify that pack expansions only occur at the
     end of the argument list.  */
  gcc_assert (nargs == DECL_NTPARMS (maintmpl));
  tpd2.parms = 0;
  for (i = 0; i < nargs; ++i)
    {
      tree parm = TREE_VALUE (TREE_VEC_ELT (main_inner_parms, i));
      tree arg = TREE_VEC_ELT (inner_args, i);
      tree packed_args = NULL_TREE;
      int j, len = 1;

      if (ARGUMENT_PACK_P (arg))
        {
          /* Extract the arguments from the argument pack. We'll be
             iterating over these in the following loop.  */
          packed_args = ARGUMENT_PACK_ARGS (arg);
          len = TREE_VEC_LENGTH (packed_args);
        }

      for (j = 0; j < len; j++)
        {
          if (packed_args)
            /* Get the Jth argument in the parameter pack.  */
            arg = TREE_VEC_ELT (packed_args, j);

          if (PACK_EXPANSION_P (arg))
            {
              /* Pack expansions must come at the end of the
                 argument list.  */
              if ((packed_args && j < len - 1)
                  || (!packed_args && i < nargs - 1))
                {
                  if (TREE_CODE (arg) == EXPR_PACK_EXPANSION)
                    error ("parameter pack argument %qE must be at the "
                           "end of the template argument list", arg);
                  else
                    error ("parameter pack argument %qT must be at the "
                           "end of the template argument list", arg);
                }
            }

          if (TREE_CODE (arg) == EXPR_PACK_EXPANSION)
            /* We only care about the pattern.  */
            arg = PACK_EXPANSION_PATTERN (arg);

          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 ((!packed_args && tpd.arg_uses_template_parms[i])
                  || (packed_args && uses_template_parms (arg)))
                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 (parm);

                  if (!tpd2.parms)
                    {
                      /* We haven't yet initialized TPD2.  Do so now.  */
                      tpd2.arg_uses_template_parms 
                        = (int *) 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 = (int *) 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,
                                          /*include_nondeduced_p=*/false);

                  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;
                      int count = 0;
                      for (j = 0; j < nargs; ++j)
                        if (tpd2.parms[j] != 0
                            && tpd.arg_uses_template_parms [j])
                          ++count;
                      if (count != 0)
                        error_n (input_location, count,
                                 "type %qT of template argument %qE depends "
                                 "on a template parameter",
                                 "type %qT of template argument %qE depends "
                                 "on template parameters",
                                 type,
                                 arg);
                    }
                }
            }
        }
    }

  /* We should only get here once.  */
  gcc_assert (!COMPLETE_TYPE_P (type));

  DECL_TEMPLATE_SPECIALIZATIONS (maintmpl)
    = tree_cons (specargs, 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 and
   parameter packs 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.
   

   IS_FRIEND_DECL is nonzero if DECL is a friend function template
   declaration (but not a definition); 1 indicates a declaration, 2
   indicates a redeclaration. When IS_FRIEND_DECL=2, no errors are
   emitted for extraneous default arguments.

   Returns TRUE if there were no errors found, FALSE otherwise. */

bool
check_default_tmpl_args (tree decl, tree parms, int is_primary, 
                         int is_partial, int is_friend_decl)
{
  const char *msg;
  int last_level_to_check;
  tree parm_level;
  bool no_errors = true;

  /* [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 true;

  if (current_class_type
      && !TYPE_BEING_DEFINED (current_class_type)
      && DECL_LANG_SPECIFIC (decl)
      && DECL_DECLARES_FUNCTION_P (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 true;

  /* Core issue 226 (C++0x only): the following only applies to class
     templates.  */
  if ((cxx_dialect == cxx98) || TREE_CODE (decl) != FUNCTION_DECL)
    {
      /* [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 (parm == error_mark_node)
                continue;

              if (TREE_PURPOSE (parm))
                seen_def_arg_p = 1;
              else if (seen_def_arg_p
                       && !template_parameter_pack_p (TREE_VALUE (parm)))
                {
                  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;
                  no_errors = false;
                }
              else if (is_primary
                       && !is_partial
                       && !is_friend_decl
                       /* Don't complain about an enclosing partial
                          specialization.  */
                       && parm_level == parms
                       && TREE_CODE (decl) == TYPE_DECL
                       && i < ntparms - 1
                       && template_parameter_pack_p (TREE_VALUE (parm)))
                {
                  /* A primary class template can only have one
                     parameter pack, at the end of the template
                     parameter list.  */

                  if (TREE_CODE (TREE_VALUE (parm)) == PARM_DECL)
                    error ("parameter pack %qE must be at the end of the"
                           " template parameter list", TREE_VALUE (parm));
                  else