gcc/:

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

/* Functions related to invoking methods and overloaded functions.
   Copyright (C) 1987, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
   1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009,
   2010, 2011, 2012
   Free Software Foundation, Inc.
   Contributed by Michael Tiemann (tiemann@cygnus.com) and
   modified by Brendan Kehoe (brendan@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/>.  */


/* High-level class interface.  */

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "tree.h"
#include "cp-tree.h"
#include "output.h"
#include "flags.h"
#include "toplev.h"
#include "diagnostic-core.h"
#include "intl.h"
#include "target.h"
#include "convert.h"
#include "langhooks.h"
#include "c-family/c-objc.h"
#include "timevar.h"

/* The various kinds of conversion.  */

typedef enum conversion_kind {
  ck_identity,
  ck_lvalue,
  ck_qual,
  ck_std,
  ck_ptr,
  ck_pmem,
  ck_base,
  ck_ref_bind,
  ck_user,
  ck_ambig,
  ck_list,
  ck_aggr,
  ck_rvalue
} conversion_kind;

/* The rank of the conversion.  Order of the enumerals matters; better
   conversions should come earlier in the list.  */

typedef enum conversion_rank {
  cr_identity,
  cr_exact,
  cr_promotion,
  cr_std,
  cr_pbool,
  cr_user,
  cr_ellipsis,
  cr_bad
} conversion_rank;

/* An implicit conversion sequence, in the sense of [over.best.ics].
   The first conversion to be performed is at the end of the chain.
   That conversion is always a cr_identity conversion.  */

typedef struct conversion conversion;
struct conversion {
  /* The kind of conversion represented by this step.  */
  conversion_kind kind;
  /* The rank of this conversion.  */
  conversion_rank rank;
  BOOL_BITFIELD user_conv_p : 1;
  BOOL_BITFIELD ellipsis_p : 1;
  BOOL_BITFIELD this_p : 1;
  /* True if this conversion would be permitted with a bending of
     language standards, e.g. disregarding pointer qualifiers or
     converting integers to pointers.  */
  BOOL_BITFIELD bad_p : 1;
  /* If KIND is ck_ref_bind ck_base_conv, true to indicate that a
     temporary should be created to hold the result of the
     conversion.  */
  BOOL_BITFIELD need_temporary_p : 1;
  /* If KIND is ck_ptr or ck_pmem, true to indicate that a conversion
     from a pointer-to-derived to pointer-to-base is being performed.  */
  BOOL_BITFIELD base_p : 1;
  /* If KIND is ck_ref_bind, true when either an lvalue reference is
     being bound to an lvalue expression or an rvalue reference is
     being bound to an rvalue expression.  If KIND is ck_rvalue,
     true when we should treat an lvalue as an rvalue (12.8p33).  If
     KIND is ck_base, always false.  */
  BOOL_BITFIELD rvaluedness_matches_p: 1;
  BOOL_BITFIELD check_narrowing: 1;
  /* The type of the expression resulting from the conversion.  */
  tree type;
  union {
    /* The next conversion in the chain.  Since the conversions are
       arranged from outermost to innermost, the NEXT conversion will
       actually be performed before this conversion.  This variant is
       used only when KIND is neither ck_identity, ck_ambig nor
       ck_list.  Please use the next_conversion function instead
       of using this field directly.  */
    conversion *next;
    /* The expression at the beginning of the conversion chain.  This
       variant is used only if KIND is ck_identity or ck_ambig.  */
    tree expr;
    /* The array of conversions for an initializer_list, so this
       variant is used only when KIN D is ck_list.  */
    conversion **list;
  } u;
  /* The function candidate corresponding to this conversion
     sequence.  This field is only used if KIND is ck_user.  */
  struct z_candidate *cand;
};

#define CONVERSION_RANK(NODE)                   \
  ((NODE)->bad_p ? cr_bad                       \
   : (NODE)->ellipsis_p ? cr_ellipsis           \
   : (NODE)->user_conv_p ? cr_user              \
   : (NODE)->rank)

#define BAD_CONVERSION_RANK(NODE)               \
  ((NODE)->ellipsis_p ? cr_ellipsis             \
   : (NODE)->user_conv_p ? cr_user              \
   : (NODE)->rank)

static struct obstack conversion_obstack;
static bool conversion_obstack_initialized;
struct rejection_reason;

static struct z_candidate * tourney (struct z_candidate *);
static int equal_functions (tree, tree);
static int joust (struct z_candidate *, struct z_candidate *, bool);
static int compare_ics (conversion *, conversion *);
static tree build_over_call (struct z_candidate *, int, tsubst_flags_t);
static tree build_java_interface_fn_ref (tree, tree);
#define convert_like(CONV, EXPR, COMPLAIN)                      \
  convert_like_real ((CONV), (EXPR), NULL_TREE, 0, 0,           \
                     /*issue_conversion_warnings=*/true,        \
                     /*c_cast_p=*/false, (COMPLAIN))
#define convert_like_with_context(CONV, EXPR, FN, ARGNO, COMPLAIN )     \
  convert_like_real ((CONV), (EXPR), (FN), (ARGNO), 0,                  \
                     /*issue_conversion_warnings=*/true,                \
                     /*c_cast_p=*/false, (COMPLAIN))
static tree convert_like_real (conversion *, tree, tree, int, int, bool,
                               bool, tsubst_flags_t);
static void op_error (enum tree_code, enum tree_code, tree, tree,
                      tree, bool);
static struct z_candidate *build_user_type_conversion_1 (tree, tree, int);
static void print_z_candidate (const char *, struct z_candidate *);
static void print_z_candidates (location_t, struct z_candidate *);
static tree build_this (tree);
static struct z_candidate *splice_viable (struct z_candidate *, bool, bool *);
static bool any_strictly_viable (struct z_candidate *);
static struct z_candidate *add_template_candidate
        (struct z_candidate **, tree, tree, tree, tree, const VEC(tree,gc) *,
         tree, tree, tree, int, unification_kind_t);
static struct z_candidate *add_template_candidate_real
        (struct z_candidate **, tree, tree, tree, tree, const VEC(tree,gc) *,
         tree, tree, tree, int, tree, unification_kind_t);
static struct z_candidate *add_template_conv_candidate
        (struct z_candidate **, tree, tree, tree, const VEC(tree,gc) *, tree,
         tree, tree);
static void add_builtin_candidates
        (struct z_candidate **, enum tree_code, enum tree_code,
         tree, tree *, int);
static void add_builtin_candidate
        (struct z_candidate **, enum tree_code, enum tree_code,
         tree, tree, tree, tree *, tree *, int);
static bool is_complete (tree);
static void build_builtin_candidate
        (struct z_candidate **, tree, tree, tree, tree *, tree *,
         int);
static struct z_candidate *add_conv_candidate
        (struct z_candidate **, tree, tree, tree, const VEC(tree,gc) *, tree,
         tree);
static struct z_candidate *add_function_candidate
        (struct z_candidate **, tree, tree, tree, const VEC(tree,gc) *, tree,
         tree, int);
static conversion *implicit_conversion (tree, tree, tree, bool, int);
static conversion *standard_conversion (tree, tree, tree, bool, int);
static conversion *reference_binding (tree, tree, tree, bool, int);
static conversion *build_conv (conversion_kind, tree, conversion *);
static conversion *build_list_conv (tree, tree, int);
static conversion *next_conversion (conversion *);
static bool is_subseq (conversion *, conversion *);
static conversion *maybe_handle_ref_bind (conversion **);
static void maybe_handle_implicit_object (conversion **);
static struct z_candidate *add_candidate
        (struct z_candidate **, tree, tree, const VEC(tree,gc) *, size_t,
         conversion **, tree, tree, int, struct rejection_reason *);
static tree source_type (conversion *);
static void add_warning (struct z_candidate *, struct z_candidate *);
static bool reference_compatible_p (tree, tree);
static conversion *direct_reference_binding (tree, conversion *);
static bool promoted_arithmetic_type_p (tree);
static conversion *conditional_conversion (tree, tree);
static char *name_as_c_string (tree, tree, bool *);
static tree prep_operand (tree);
static void add_candidates (tree, tree, const VEC(tree,gc) *, tree, tree, bool,
                            tree, tree, int, struct z_candidate **);
static conversion *merge_conversion_sequences (conversion *, conversion *);
static bool magic_varargs_p (tree);
static tree build_temp (tree, tree, int, diagnostic_t *, tsubst_flags_t);

/* Returns nonzero iff the destructor name specified in NAME matches BASETYPE.
   NAME can take many forms...  */

bool
check_dtor_name (tree basetype, tree name)
{
  /* Just accept something we've already complained about.  */
  if (name == error_mark_node)
    return true;

  if (TREE_CODE (name) == TYPE_DECL)
    name = TREE_TYPE (name);
  else if (TYPE_P (name))
    /* OK */;
  else if (TREE_CODE (name) == IDENTIFIER_NODE)
    {
      if ((MAYBE_CLASS_TYPE_P (basetype)
           && name == constructor_name (basetype))
          || (TREE_CODE (basetype) == ENUMERAL_TYPE
              && name == TYPE_IDENTIFIER (basetype)))
        return true;
      else
        name = get_type_value (name);
    }
  else
    {
      /* In the case of:

         template <class T> struct S { ~S(); };
         int i;
         i.~S();

         NAME will be a class template.  */
      gcc_assert (DECL_CLASS_TEMPLATE_P (name));
      return false;
    }

  if (!name || name == error_mark_node)
    return false;
  return same_type_p (TYPE_MAIN_VARIANT (basetype), TYPE_MAIN_VARIANT (name));
}

/* We want the address of a function or method.  We avoid creating a
   pointer-to-member function.  */

tree
build_addr_func (tree function)
{
  tree type = TREE_TYPE (function);

  /* We have to do these by hand to avoid real pointer to member
     functions.  */
  if (TREE_CODE (type) == METHOD_TYPE)
    {
      if (TREE_CODE (function) == OFFSET_REF)
        {
          tree object = build_address (TREE_OPERAND (function, 0));
          return get_member_function_from_ptrfunc (&object,
                                                   TREE_OPERAND (function, 1));
        }
      function = build_address (function);
    }
  else
    function = decay_conversion (function);

  return function;
}

/* Build a CALL_EXPR, we can handle FUNCTION_TYPEs, METHOD_TYPEs, or
   POINTER_TYPE to those.  Note, pointer to member function types
   (TYPE_PTRMEMFUNC_P) must be handled by our callers.  There are
   two variants.  build_call_a is the primitive taking an array of
   arguments, while build_call_n is a wrapper that handles varargs.  */

tree
build_call_n (tree function, int n, ...)
{
  if (n == 0)
    return build_call_a (function, 0, NULL);
  else
    {
      tree *argarray = XALLOCAVEC (tree, n);
      va_list ap;
      int i;

      va_start (ap, n);
      for (i = 0; i < n; i++)
        argarray[i] = va_arg (ap, tree);
      va_end (ap);
      return build_call_a (function, n, argarray);
    }
}

/* Update various flags in cfun and the call itself based on what is being
   called.  Split out of build_call_a so that bot_manip can use it too.  */

void
set_flags_from_callee (tree call)
{
  int nothrow;
  tree decl = get_callee_fndecl (call);

  /* We check both the decl and the type; a function may be known not to
     throw without being declared throw().  */
  nothrow = ((decl && TREE_NOTHROW (decl))
             || TYPE_NOTHROW_P (TREE_TYPE (TREE_TYPE (CALL_EXPR_FN (call)))));

  if (!nothrow && at_function_scope_p () && cfun && cp_function_chain)
    cp_function_chain->can_throw = 1;

  if (decl && TREE_THIS_VOLATILE (decl) && cfun && cp_function_chain)
    current_function_returns_abnormally = 1;

  TREE_NOTHROW (call) = nothrow;
}

tree
build_call_a (tree function, int n, tree *argarray)
{
  tree decl;
  tree result_type;
  tree fntype;
  int i;

  function = build_addr_func (function);

  gcc_assert (TYPE_PTR_P (TREE_TYPE (function)));
  fntype = TREE_TYPE (TREE_TYPE (function));
  gcc_assert (TREE_CODE (fntype) == FUNCTION_TYPE
              || TREE_CODE (fntype) == METHOD_TYPE);
  result_type = TREE_TYPE (fntype);
  /* An rvalue has no cv-qualifiers.  */
  if (SCALAR_TYPE_P (result_type) || VOID_TYPE_P (result_type))
    result_type = cv_unqualified (result_type);

  function = build_call_array_loc (input_location,
                                   result_type, function, n, argarray);
  set_flags_from_callee (function);

  decl = get_callee_fndecl (function);

  if (decl && !TREE_USED (decl))
    {
      /* We invoke build_call directly for several library
         functions.  These may have been declared normally if
         we're building libgcc, so we can't just check
         DECL_ARTIFICIAL.  */
      gcc_assert (DECL_ARTIFICIAL (decl)
                  || !strncmp (IDENTIFIER_POINTER (DECL_NAME (decl)),
                               "__", 2));
      mark_used (decl);
    }

  if (decl && TREE_DEPRECATED (decl))
    warn_deprecated_use (decl, NULL_TREE);
  require_complete_eh_spec_types (fntype, decl);

  TREE_HAS_CONSTRUCTOR (function) = (decl && DECL_CONSTRUCTOR_P (decl));

  /* Don't pass empty class objects by value.  This is useful
     for tags in STL, which are used to control overload resolution.
     We don't need to handle other cases of copying empty classes.  */
  if (! decl || ! DECL_BUILT_IN (decl))
    for (i = 0; i < n; i++)
      {
        tree arg = CALL_EXPR_ARG (function, i);
        if (is_empty_class (TREE_TYPE (arg))
            && ! TREE_ADDRESSABLE (TREE_TYPE (arg)))
          {
            tree t = build0 (EMPTY_CLASS_EXPR, TREE_TYPE (arg));
            arg = build2 (COMPOUND_EXPR, TREE_TYPE (t), arg, t);
            CALL_EXPR_ARG (function, i) = arg;
          }
      }

  return function;
}

/* Build something of the form ptr->method (args)
   or object.method (args).  This can also build
   calls to constructors, and find friends.

   Member functions always take their class variable
   as a pointer.

   INSTANCE is a class instance.

   NAME is the name of the method desired, usually an IDENTIFIER_NODE.

   PARMS help to figure out what that NAME really refers to.

   BASETYPE_PATH, if non-NULL, contains a chain from the type of INSTANCE
   down to the real instance type to use for access checking.  We need this
   information to get protected accesses correct.

   FLAGS is the logical disjunction of zero or more LOOKUP_
   flags.  See cp-tree.h for more info.

   If this is all OK, calls build_function_call with the resolved
   member function.

   This function must also handle being called to perform
   initialization, promotion/coercion of arguments, and
   instantiation of default parameters.

   Note that NAME may refer to an instance variable name.  If
   `operator()()' is defined for the type of that field, then we return
   that result.  */

/* New overloading code.  */

typedef struct z_candidate z_candidate;

typedef struct candidate_warning candidate_warning;
struct candidate_warning {
  z_candidate *loser;
  candidate_warning *next;
};

/* Information for providing diagnostics about why overloading failed.  */

enum rejection_reason_code {
  rr_none,
  rr_arity,
  rr_explicit_conversion,
  rr_template_conversion,
  rr_arg_conversion,
  rr_bad_arg_conversion,
  rr_template_unification,
  rr_template_instantiation,
  rr_invalid_copy
};

struct conversion_info {
  /* The index of the argument, 0-based.  */
  int n_arg;
  /* The type of the actual argument.  */
  tree from_type;
  /* The type of the formal argument.  */
  tree to_type;
};
  
struct rejection_reason {
  enum rejection_reason_code code;
  union {
    /* Information about an arity mismatch.  */
    struct {
      /* The expected number of arguments.  */
      int expected;
      /* The actual number of arguments in the call.  */
      int actual;
      /* Whether the call was a varargs call.  */
      bool call_varargs_p;
    } arity;
    /* Information about an argument conversion mismatch.  */
    struct conversion_info conversion;
    /* Same, but for bad argument conversions.  */
    struct conversion_info bad_conversion;
    /* Information about template unification failures.  These are the
       parameters passed to fn_type_unification.  */
    struct {
      tree tmpl;
      tree explicit_targs;
      tree targs;
      const tree *args;
      unsigned int nargs;
      tree return_type;
      unification_kind_t strict;
      int flags;
    } template_unification;
    /* Information about template instantiation failures.  These are the
       parameters passed to instantiate_template.  */
    struct {
      tree tmpl;
      tree targs;
    } template_instantiation;
  } u;
};

struct z_candidate {
  /* The FUNCTION_DECL that will be called if this candidate is
     selected by overload resolution.  */
  tree fn;
  /* If not NULL_TREE, the first argument to use when calling this
     function.  */
  tree first_arg;
  /* The rest of the arguments to use when calling this function.  If
     there are no further arguments this may be NULL or it may be an
     empty vector.  */
  const VEC(tree,gc) *args;
  /* The implicit conversion sequences for each of the arguments to
     FN.  */
  conversion **convs;
  /* The number of implicit conversion sequences.  */
  size_t num_convs;
  /* If FN is a user-defined conversion, the standard conversion
     sequence from the type returned by FN to the desired destination
     type.  */
  conversion *second_conv;
  int viable;
  struct rejection_reason *reason;
  /* If FN is a member function, the binfo indicating the path used to
     qualify the name of FN at the call site.  This path is used to
     determine whether or not FN is accessible if it is selected by
     overload resolution.  The DECL_CONTEXT of FN will always be a
     (possibly improper) base of this binfo.  */
  tree access_path;
  /* If FN is a non-static member function, the binfo indicating the
     subobject to which the `this' pointer should be converted if FN
     is selected by overload resolution.  The type pointed to by
     the `this' pointer must correspond to the most derived class
     indicated by the CONVERSION_PATH.  */
  tree conversion_path;
  tree template_decl;
  tree explicit_targs;
  candidate_warning *warnings;
  z_candidate *next;
};

/* Returns true iff T is a null pointer constant in the sense of
   [conv.ptr].  */

bool
null_ptr_cst_p (tree t)
{
  /* [conv.ptr]

     A null pointer constant is an integral constant expression
     (_expr.const_) rvalue of integer type that evaluates to zero or
     an rvalue of type std::nullptr_t. */
  if (NULLPTR_TYPE_P (TREE_TYPE (t)))
    return true;
  if (CP_INTEGRAL_TYPE_P (TREE_TYPE (t)))
    {
      /* Core issue 903 says only literal 0 is a null pointer constant.  */
      if (cxx_dialect < cxx0x)
        t = integral_constant_value (t);
      STRIP_NOPS (t);
      if (integer_zerop (t) && !TREE_OVERFLOW (t))
        return true;
    }
  return false;
}

/* Returns true iff T is a null member pointer value (4.11).  */

bool
null_member_pointer_value_p (tree t)
{
  tree type = TREE_TYPE (t);
  if (!type)
    return false;
  else if (TYPE_PTRMEMFUNC_P (type))
    return (TREE_CODE (t) == CONSTRUCTOR
            && integer_zerop (CONSTRUCTOR_ELT (t, 0)->value));
  else if (TYPE_PTRMEM_P (type))
    return integer_all_onesp (t);
  else
    return false;
}

/* Returns nonzero if PARMLIST consists of only default parms,
   ellipsis, and/or undeduced parameter packs.  */

bool
sufficient_parms_p (const_tree parmlist)
{
  for (; parmlist && parmlist != void_list_node;
       parmlist = TREE_CHAIN (parmlist))
    if (!TREE_PURPOSE (parmlist)
        && !PACK_EXPANSION_P (TREE_VALUE (parmlist)))
      return false;
  return true;
}

/* Allocate N bytes of memory from the conversion obstack.  The memory
   is zeroed before being returned.  */

static void *
conversion_obstack_alloc (size_t n)
{
  void *p;
  if (!conversion_obstack_initialized)
    {
      gcc_obstack_init (&conversion_obstack);
      conversion_obstack_initialized = true;
    }
  p = obstack_alloc (&conversion_obstack, n);
  memset (p, 0, n);
  return p;
}

/* Allocate rejection reasons.  */

static struct rejection_reason *
alloc_rejection (enum rejection_reason_code code)
{
  struct rejection_reason *p;
  p = (struct rejection_reason *) conversion_obstack_alloc (sizeof *p);
  p->code = code;
  return p;
}

static struct rejection_reason *
arity_rejection (tree first_arg, int expected, int actual)
{
  struct rejection_reason *r = alloc_rejection (rr_arity);
  int adjust = first_arg != NULL_TREE;
  r->u.arity.expected = expected - adjust;
  r->u.arity.actual = actual - adjust;
  return r;
}

static struct rejection_reason *
arg_conversion_rejection (tree first_arg, int n_arg, tree from, tree to)
{
  struct rejection_reason *r = alloc_rejection (rr_arg_conversion);
  int adjust = first_arg != NULL_TREE;
  r->u.conversion.n_arg = n_arg - adjust;
  r->u.conversion.from_type = from;
  r->u.conversion.to_type = to;
  return r;
}

static struct rejection_reason *
bad_arg_conversion_rejection (tree first_arg, int n_arg, tree from, tree to)
{
  struct rejection_reason *r = alloc_rejection (rr_bad_arg_conversion);
  int adjust = first_arg != NULL_TREE;
  r->u.bad_conversion.n_arg = n_arg - adjust;
  r->u.bad_conversion.from_type = from;
  r->u.bad_conversion.to_type = to;
  return r;
}

static struct rejection_reason *
explicit_conversion_rejection (tree from, tree to)
{
  struct rejection_reason *r = alloc_rejection (rr_explicit_conversion);
  r->u.conversion.n_arg = 0;
  r->u.conversion.from_type = from;
  r->u.conversion.to_type = to;
  return r;
}

static struct rejection_reason *
template_conversion_rejection (tree from, tree to)
{
  struct rejection_reason *r = alloc_rejection (rr_template_conversion);
  r->u.conversion.n_arg = 0;
  r->u.conversion.from_type = from;
  r->u.conversion.to_type = to;
  return r;
}

static struct rejection_reason *
template_unification_rejection (tree tmpl, tree explicit_targs, tree targs,
                                const tree *args, unsigned int nargs,
                                tree return_type, unification_kind_t strict,
                                int flags)
{
  size_t args_n_bytes = sizeof (*args) * nargs;
  tree *args1 = (tree *) conversion_obstack_alloc (args_n_bytes);
  struct rejection_reason *r = alloc_rejection (rr_template_unification);
  r->u.template_unification.tmpl = tmpl;
  r->u.template_unification.explicit_targs = explicit_targs;
  r->u.template_unification.targs = targs;
  /* Copy args to our own storage.  */
  memcpy (args1, args, args_n_bytes);
  r->u.template_unification.args = args1;
  r->u.template_unification.nargs = nargs;
  r->u.template_unification.return_type = return_type;
  r->u.template_unification.strict = strict;
  r->u.template_unification.flags = flags;
  return r;
}

static struct rejection_reason *
template_unification_error_rejection (void)
{
  return alloc_rejection (rr_template_unification);
}

static struct rejection_reason *
template_instantiation_rejection (tree tmpl, tree targs)
{
  struct rejection_reason *r = alloc_rejection (rr_template_instantiation);
  r->u.template_instantiation.tmpl = tmpl;
  r->u.template_instantiation.targs = targs;
  return r;
}

static struct rejection_reason *
invalid_copy_with_fn_template_rejection (void)
{
  struct rejection_reason *r = alloc_rejection (rr_invalid_copy);
  return r;
}

/* Dynamically allocate a conversion.  */

static conversion *
alloc_conversion (conversion_kind kind)
{
  conversion *c;
  c = (conversion *) conversion_obstack_alloc (sizeof (conversion));
  c->kind = kind;
  return c;
}

#ifdef ENABLE_CHECKING

/* Make sure that all memory on the conversion obstack has been
   freed.  */

void
validate_conversion_obstack (void)
{
  if (conversion_obstack_initialized)
    gcc_assert ((obstack_next_free (&conversion_obstack)
                 == obstack_base (&conversion_obstack)));
}

#endif /* ENABLE_CHECKING */

/* Dynamically allocate an array of N conversions.  */

static conversion **
alloc_conversions (size_t n)
{
  return (conversion **) conversion_obstack_alloc (n * sizeof (conversion *));
}

static conversion *
build_conv (conversion_kind code, tree type, conversion *from)
{
  conversion *t;
  conversion_rank rank = CONVERSION_RANK (from);

  /* Note that the caller is responsible for filling in t->cand for
     user-defined conversions.  */
  t = alloc_conversion (code);
  t->type = type;
  t->u.next = from;

  switch (code)
    {
    case ck_ptr:
    case ck_pmem:
    case ck_base:
    case ck_std:
      if (rank < cr_std)
        rank = cr_std;
      break;

    case ck_qual:
      if (rank < cr_exact)
        rank = cr_exact;
      break;

    default:
      break;
    }
  t->rank = rank;
  t->user_conv_p = (code == ck_user || from->user_conv_p);
  t->bad_p = from->bad_p;
  t->base_p = false;
  return t;
}

/* Represent a conversion from CTOR, a braced-init-list, to TYPE, a
   specialization of std::initializer_list<T>, if such a conversion is
   possible.  */

static conversion *
build_list_conv (tree type, tree ctor, int flags)
{
  tree elttype = TREE_VEC_ELT (CLASSTYPE_TI_ARGS (type), 0);
  unsigned len = CONSTRUCTOR_NELTS (ctor);
  conversion **subconvs = alloc_conversions (len);
  conversion *t;
  unsigned i;
  tree val;

  /* Within a list-initialization we can have more user-defined
     conversions.  */
  flags &= ~LOOKUP_NO_CONVERSION;
  /* But no narrowing conversions.  */
  flags |= LOOKUP_NO_NARROWING;

  FOR_EACH_CONSTRUCTOR_VALUE (CONSTRUCTOR_ELTS (ctor), i, val)
    {
      conversion *sub
        = implicit_conversion (elttype, TREE_TYPE (val), val,
                               false, flags);
      if (sub == NULL)
        return NULL;

      subconvs[i] = sub;
    }

  t = alloc_conversion (ck_list);
  t->type = type;
  t->u.list = subconvs;
  t->rank = cr_exact;

  for (i = 0; i < len; ++i)
    {
      conversion *sub = subconvs[i];
      if (sub->rank > t->rank)
        t->rank = sub->rank;
      if (sub->user_conv_p)
        t->user_conv_p = true;
      if (sub->bad_p)
        t->bad_p = true;
    }

  return t;
}

/* Return the next conversion of the conversion chain (if applicable),
   or NULL otherwise.  Please use this function instead of directly
   accessing fields of struct conversion.  */

static conversion *
next_conversion (conversion *conv)
{
  if (conv == NULL
      || conv->kind == ck_identity
      || conv->kind == ck_ambig
      || conv->kind == ck_list)
    return NULL;
  return conv->u.next;
}

/* Subroutine of build_aggr_conv: check whether CTOR, a braced-init-list,
   is a valid aggregate initializer for array type ATYPE.  */

static bool
can_convert_array (tree atype, tree ctor, int flags)
{
  unsigned i;
  tree elttype = TREE_TYPE (atype);
  for (i = 0; i < CONSTRUCTOR_NELTS (ctor); ++i)
    {
      tree val = CONSTRUCTOR_ELT (ctor, i)->value;
      bool ok;
      if (TREE_CODE (elttype) == ARRAY_TYPE
          && TREE_CODE (val) == CONSTRUCTOR)
        ok = can_convert_array (elttype, val, flags);
      else
        ok = can_convert_arg (elttype, TREE_TYPE (val), val, flags);
      if (!ok)
        return false;
    }
  return true;
}

/* Represent a conversion from CTOR, a braced-init-list, to TYPE, an
   aggregate class, if such a conversion is possible.  */

static conversion *
build_aggr_conv (tree type, tree ctor, int flags)
{
  unsigned HOST_WIDE_INT i = 0;
  conversion *c;
  tree field = next_initializable_field (TYPE_FIELDS (type));
  tree empty_ctor = NULL_TREE;

  for (; field; field = next_initializable_field (DECL_CHAIN (field)))
    {
      tree ftype = TREE_TYPE (field);
      tree val;
      bool ok;

      if (i < CONSTRUCTOR_NELTS (ctor))
        val = CONSTRUCTOR_ELT (ctor, i)->value;
      else
        {
          if (empty_ctor == NULL_TREE)
            empty_ctor = build_constructor (init_list_type_node, NULL);
          val = empty_ctor;
        }
      ++i;

      if (TREE_CODE (ftype) == ARRAY_TYPE
          && TREE_CODE (val) == CONSTRUCTOR)
        ok = can_convert_array (ftype, val, flags);
      else
        ok = can_convert_arg (ftype, TREE_TYPE (val), val, flags);

      if (!ok)
        return NULL;

      if (TREE_CODE (type) == UNION_TYPE)
        break;
    }

  if (i < CONSTRUCTOR_NELTS (ctor))
    return NULL;

  c = alloc_conversion (ck_aggr);
  c->type = type;
  c->rank = cr_exact;
  c->user_conv_p = true;
  c->u.next = NULL;
  return c;
}

/* Represent a conversion from CTOR, a braced-init-list, to TYPE, an
   array type, if such a conversion is possible.  */

static conversion *
build_array_conv (tree type, tree ctor, int flags)
{
  conversion *c;
  unsigned HOST_WIDE_INT len = CONSTRUCTOR_NELTS (ctor);
  tree elttype = TREE_TYPE (type);
  unsigned i;
  tree val;
  bool bad = false;
  bool user = false;
  enum conversion_rank rank = cr_exact;

  if (TYPE_DOMAIN (type))
    {
      unsigned HOST_WIDE_INT alen = tree_low_cst (array_type_nelts_top (type), 1);
      if (alen < len)
        return NULL;
    }

  FOR_EACH_CONSTRUCTOR_VALUE (CONSTRUCTOR_ELTS (ctor), i, val)
    {
      conversion *sub
        = implicit_conversion (elttype, TREE_TYPE (val), val,
                               false, flags);
      if (sub == NULL)
        return NULL;

      if (sub->rank > rank)
        rank = sub->rank;
      if (sub->user_conv_p)
        user = true;
      if (sub->bad_p)
        bad = true;
    }

  c = alloc_conversion (ck_aggr);
  c->type = type;
  c->rank = rank;
  c->user_conv_p = user;
  c->bad_p = bad;
  c->u.next = NULL;
  return c;
}

/* Represent a conversion from CTOR, a braced-init-list, to TYPE, a
   complex type, if such a conversion is possible.  */

static conversion *
build_complex_conv (tree type, tree ctor, int flags)
{
  conversion *c;
  unsigned HOST_WIDE_INT len = CONSTRUCTOR_NELTS (ctor);
  tree elttype = TREE_TYPE (type);
  unsigned i;
  tree val;
  bool bad = false;
  bool user = false;
  enum conversion_rank rank = cr_exact;

  if (len != 2)
    return NULL;

  FOR_EACH_CONSTRUCTOR_VALUE (CONSTRUCTOR_ELTS (ctor), i, val)
    {
      conversion *sub
        = implicit_conversion (elttype, TREE_TYPE (val), val,
                               false, flags);
      if (sub == NULL)
        return NULL;

      if (sub->rank > rank)
        rank = sub->rank;
      if (sub->user_conv_p)
        user = true;
      if (sub->bad_p)
        bad = true;
    }

  c = alloc_conversion (ck_aggr);
  c->type = type;
  c->rank = rank;
  c->user_conv_p = user;
  c->bad_p = bad;
  c->u.next = NULL;
  return c;
}

/* Build a representation of the identity conversion from EXPR to
   itself.  The TYPE should match the type of EXPR, if EXPR is non-NULL.  */

static conversion *
build_identity_conv (tree type, tree expr)
{
  conversion *c;

  c = alloc_conversion (ck_identity);
  c->type = type;
  c->u.expr = expr;

  return c;
}

/* Converting from EXPR to TYPE was ambiguous in the sense that there
   were multiple user-defined conversions to accomplish the job.
   Build a conversion that indicates that ambiguity.  */

static conversion *
build_ambiguous_conv (tree type, tree expr)
{
  conversion *c;

  c = alloc_conversion (ck_ambig);
  c->type = type;
  c->u.expr = expr;

  return c;
}

tree
strip_top_quals (tree t)
{
  if (TREE_CODE (t) == ARRAY_TYPE)
    return t;
  return cp_build_qualified_type (t, 0);
}

/* Returns the standard conversion path (see [conv]) from type FROM to type
   TO, if any.  For proper handling of null pointer constants, you must
   also pass the expression EXPR to convert from.  If C_CAST_P is true,
   this conversion is coming from a C-style cast.  */

static conversion *
standard_conversion (tree to, tree from, tree expr, bool c_cast_p,
                     int flags)
{
  enum tree_code fcode, tcode;
  conversion *conv;
  bool fromref = false;
  tree qualified_to;

  to = non_reference (to);
  if (TREE_CODE (from) == REFERENCE_TYPE)
    {
      fromref = true;
      from = TREE_TYPE (from);
    }
  qualified_to = to;
  to = strip_top_quals (to);
  from = strip_top_quals (from);

  if ((TYPE_PTRFN_P (to) || TYPE_PTRMEMFUNC_P (to))
      && expr && type_unknown_p (expr))
    {
      tsubst_flags_t tflags = tf_conv;
      if (!(flags & LOOKUP_PROTECT))
        tflags |= tf_no_access_control;
      expr = instantiate_type (to, expr, tflags);
      if (expr == error_mark_node)
        return NULL;
      from = TREE_TYPE (expr);
    }

  fcode = TREE_CODE (from);
  tcode = TREE_CODE (to);

  conv = build_identity_conv (from, expr);
  if (fcode == FUNCTION_TYPE || fcode == ARRAY_TYPE)
    {
      from = type_decays_to (from);
      fcode = TREE_CODE (from);
      conv = build_conv (ck_lvalue, from, conv);
    }
  else if (fromref || (expr && lvalue_p (expr)))
    {
      if (expr)
        {
          tree bitfield_type;
          bitfield_type = is_bitfield_expr_with_lowered_type (expr);
          if (bitfield_type)
            {
              from = strip_top_quals (bitfield_type);
              fcode = TREE_CODE (from);
            }
        }
      conv = build_conv (ck_rvalue, from, conv);
      if (flags & LOOKUP_PREFER_RVALUE)
        conv->rvaluedness_matches_p = true;
    }

   /* Allow conversion between `__complex__' data types.  */
  if (tcode == COMPLEX_TYPE && fcode == COMPLEX_TYPE)
    {
      /* The standard conversion sequence to convert FROM to TO is
         the standard conversion sequence to perform componentwise
         conversion.  */
      conversion *part_conv = standard_conversion
        (TREE_TYPE (to), TREE_TYPE (from), NULL_TREE, c_cast_p, flags);

      if (part_conv)
        {
          conv = build_conv (part_conv->kind, to, conv);
          conv->rank = part_conv->rank;
        }
      else
        conv = NULL;

      return conv;
    }

  if (same_type_p (from, to))
    {
      if (CLASS_TYPE_P (to) && conv->kind == ck_rvalue)
        conv->type = qualified_to;
      return conv;
    }

  /* [conv.ptr]
     A null pointer constant can be converted to a pointer type; ... A
     null pointer constant of integral type can be converted to an
     rvalue of type std::nullptr_t. */
  if ((tcode == POINTER_TYPE || TYPE_PTR_TO_MEMBER_P (to)
       || NULLPTR_TYPE_P (to))
      && expr && null_ptr_cst_p (expr))
    conv = build_conv (ck_std, to, conv);
  else if ((tcode == INTEGER_TYPE && fcode == POINTER_TYPE)
           || (tcode == POINTER_TYPE && fcode == INTEGER_TYPE))
    {
      /* For backwards brain damage compatibility, allow interconversion of
         pointers and integers with a pedwarn.  */
      conv = build_conv (ck_std, to, conv);
      conv->bad_p = true;
    }
  else if (UNSCOPED_ENUM_P (to) && fcode == INTEGER_TYPE)
    {
      /* For backwards brain damage compatibility, allow interconversion of
         enums and integers with a pedwarn.  */
      conv = build_conv (ck_std, to, conv);
      conv->bad_p = true;
    }
  else if ((tcode == POINTER_TYPE && fcode == POINTER_TYPE)
           || (TYPE_PTRMEM_P (to) && TYPE_PTRMEM_P (from)))
    {
      tree to_pointee;
      tree from_pointee;

      if (tcode == POINTER_TYPE
          && same_type_ignoring_top_level_qualifiers_p (TREE_TYPE (from),
                                                        TREE_TYPE (to)))
        ;
      else if (VOID_TYPE_P (TREE_TYPE (to))
               && !TYPE_PTRMEM_P (from)
               && TREE_CODE (TREE_TYPE (from)) != FUNCTION_TYPE)
        {
          tree nfrom = TREE_TYPE (from);
          from = build_pointer_type
            (cp_build_qualified_type (void_type_node, 
                                      cp_type_quals (nfrom)));
          conv = build_conv (ck_ptr, from, conv);
        }
      else if (TYPE_PTRMEM_P (from))
        {
          tree fbase = TYPE_PTRMEM_CLASS_TYPE (from);
          tree tbase = TYPE_PTRMEM_CLASS_TYPE (to);

          if (DERIVED_FROM_P (fbase, tbase)
              && (same_type_ignoring_top_level_qualifiers_p
                  (TYPE_PTRMEM_POINTED_TO_TYPE (from),
                   TYPE_PTRMEM_POINTED_TO_TYPE (to))))
            {
              from = build_ptrmem_type (tbase,
                                        TYPE_PTRMEM_POINTED_TO_TYPE (from));
              conv = build_conv (ck_pmem, from, conv);
            }
          else if (!same_type_p (fbase, tbase))
            return NULL;
        }
      else if (CLASS_TYPE_P (TREE_TYPE (from))
               && CLASS_TYPE_P (TREE_TYPE (to))
               /* [conv.ptr]

                  An rvalue of type "pointer to cv D," where D is a
                  class type, can be converted to an rvalue of type
                  "pointer to cv B," where B is a base class (clause
                  _class.derived_) of D.  If B is an inaccessible
                  (clause _class.access_) or ambiguous
                  (_class.member.lookup_) base class of D, a program
                  that necessitates this conversion is ill-formed.
                  Therefore, we use DERIVED_FROM_P, and do not check
                  access or uniqueness.  */
               && DERIVED_FROM_P (TREE_TYPE (to), TREE_TYPE (from)))
        {
          from =
            cp_build_qualified_type (TREE_TYPE (to),
                                     cp_type_quals (TREE_TYPE (from)));
          from = build_pointer_type (from);
          conv = build_conv (ck_ptr, from, conv);
          conv->base_p = true;
        }

      if (tcode == POINTER_TYPE)
        {
          to_pointee = TREE_TYPE (to);
          from_pointee = TREE_TYPE (from);
        }
      else
        {
          to_pointee = TYPE_PTRMEM_POINTED_TO_TYPE (to);
          from_pointee = TYPE_PTRMEM_POINTED_TO_TYPE (from);
        }

      if (same_type_p (from, to))
        /* OK */;
      else if (c_cast_p && comp_ptr_ttypes_const (to, from))
        /* In a C-style cast, we ignore CV-qualification because we
           are allowed to perform a static_cast followed by a
           const_cast.  */
        conv = build_conv (ck_qual, to, conv);
      else if (!c_cast_p && comp_ptr_ttypes (to_pointee, from_pointee))
        conv = build_conv (ck_qual, to, conv);
      else if (expr && string_conv_p (to, expr, 0))
        /* converting from string constant to char *.  */
        conv = build_conv (ck_qual, to, conv);
      /* Allow conversions among compatible ObjC pointer types (base
         conversions have been already handled above).  */
      else if (c_dialect_objc ()
               && objc_compare_types (to, from, -4, NULL_TREE))
        conv = build_conv (ck_ptr, to, conv);
      else if (ptr_reasonably_similar (to_pointee, from_pointee))
        {
          conv = build_conv (ck_ptr, to, conv);
          conv->bad_p = true;
        }
      else
        return NULL;

      from = to;
    }
  else if (TYPE_PTRMEMFUNC_P (to) && TYPE_PTRMEMFUNC_P (from))
    {
      tree fromfn = TREE_TYPE (TYPE_PTRMEMFUNC_FN_TYPE (from));
      tree tofn = TREE_TYPE (TYPE_PTRMEMFUNC_FN_TYPE (to));
      tree fbase = class_of_this_parm (fromfn);
      tree tbase = class_of_this_parm (tofn);

      if (!DERIVED_FROM_P (fbase, tbase)
          || !same_type_p (static_fn_type (fromfn),
                           static_fn_type (tofn)))
        return NULL;

      from = build_memfn_type (fromfn, tbase, cp_type_quals (tbase));
      from = build_ptrmemfunc_type (build_pointer_type (from));
      conv = build_conv (ck_pmem, from, conv);
      conv->base_p = true;
    }
  else if (tcode == BOOLEAN_TYPE)
    {
      /* [conv.bool]

          An rvalue of arithmetic, unscoped enumeration, pointer, or
          pointer to member type can be converted to an rvalue of type
          bool. ... An rvalue of type std::nullptr_t can be converted
          to an rvalue of type bool;  */
      if (ARITHMETIC_TYPE_P (from)
          || UNSCOPED_ENUM_P (from)
          || fcode == POINTER_TYPE
          || TYPE_PTR_TO_MEMBER_P (from)
          || NULLPTR_TYPE_P (from))
        {
          conv = build_conv (ck_std, to, conv);
          if (fcode == POINTER_TYPE
              || TYPE_PTRMEM_P (from)
              || (TYPE_PTRMEMFUNC_P (from)
                  && conv->rank < cr_pbool)
              || NULLPTR_TYPE_P (from))
            conv->rank = cr_pbool;
          return conv;
        }

      return NULL;
    }
  /* We don't check for ENUMERAL_TYPE here because there are no standard
     conversions to enum type.  */
  /* As an extension, allow conversion to complex type.  */
  else if (ARITHMETIC_TYPE_P (to))
    {
      if (! (INTEGRAL_CODE_P (fcode) || fcode == REAL_TYPE)
          || SCOPED_ENUM_P (from))
        return NULL;
      conv = build_conv (ck_std, to, conv);

      /* Give this a better rank if it's a promotion.  */
      if (same_type_p (to, type_promotes_to (from))
          && conv->u.next->rank <= cr_promotion)
        conv->rank = cr_promotion;
    }
  else if (fcode == VECTOR_TYPE && tcode == VECTOR_TYPE
           && vector_types_convertible_p (from, to, false))
    return build_conv (ck_std, to, conv);
  else if (MAYBE_CLASS_TYPE_P (to) && MAYBE_CLASS_TYPE_P (from)
           && is_properly_derived_from (from, to))
    {
      if (conv->kind == ck_rvalue)
        conv = conv->u.next;
      conv = build_conv (ck_base, to, conv);
      /* The derived-to-base conversion indicates the initialization
         of a parameter with base type from an object of a derived
         type.  A temporary object is created to hold the result of
         the conversion unless we're binding directly to a reference.  */
      conv->need_temporary_p = !(flags & LOOKUP_NO_TEMP_BIND);
    }
  else
    return NULL;

  if (flags & LOOKUP_NO_NARROWING)
    conv->check_narrowing = true;

  return conv;
}

/* Returns nonzero if T1 is reference-related to T2.  */

bool
reference_related_p (tree t1, tree t2)
{
  if (t1 == error_mark_node || t2 == error_mark_node)
    return false;

  t1 = TYPE_MAIN_VARIANT (t1);
  t2 = TYPE_MAIN_VARIANT (t2);

  /* [dcl.init.ref]

     Given types "cv1 T1" and "cv2 T2," "cv1 T1" is reference-related
     to "cv2 T2" if T1 is the same type as T2, or T1 is a base class
     of T2.  */
  return (same_type_p (t1, t2)
          || (CLASS_TYPE_P (t1) && CLASS_TYPE_P (t2)
              && DERIVED_FROM_P (t1, t2)));
}

/* Returns nonzero if T1 is reference-compatible with T2.  */

static bool
reference_compatible_p (tree t1, tree t2)
{
  /* [dcl.init.ref]

     "cv1 T1" is reference compatible with "cv2 T2" if T1 is
     reference-related to T2 and cv1 is the same cv-qualification as,
     or greater cv-qualification than, cv2.  */
  return (reference_related_p (t1, t2)
          && at_least_as_qualified_p (t1, t2));
}

/* A reference of the indicated TYPE is being bound directly to the
   expression represented by the implicit conversion sequence CONV.
   Return a conversion sequence for this binding.  */

static conversion *
direct_reference_binding (tree type, conversion *conv)
{
  tree t;

  gcc_assert (TREE_CODE (type) == REFERENCE_TYPE);
  gcc_assert (TREE_CODE (conv->type) != REFERENCE_TYPE);

  t = TREE_TYPE (type);

  /* [over.ics.rank]

     When a parameter of reference type binds directly
     (_dcl.init.ref_) to an argument expression, the implicit
     conversion sequence is the identity conversion, unless the
     argument expression has a type that is a derived class of the
     parameter type, in which case the implicit conversion sequence is
     a derived-to-base Conversion.

     If the parameter binds directly to the result of applying a
     conversion function to the argument expression, the implicit
     conversion sequence is a user-defined conversion sequence
     (_over.ics.user_), with the second standard conversion sequence
     either an identity conversion or, if the conversion function
     returns an entity of a type that is a derived class of the
     parameter type, a derived-to-base conversion.  */
  if (!same_type_ignoring_top_level_qualifiers_p (t, conv->type))
    {
      /* Represent the derived-to-base conversion.  */
      conv = build_conv (ck_base, t, conv);
      /* We will actually be binding to the base-class subobject in
         the derived class, so we mark this conversion appropriately.
         That way, convert_like knows not to generate a temporary.  */
      conv->need_temporary_p = false;
    }
  return build_conv (ck_ref_bind, type, conv);
}

/* Returns the conversion path from type FROM to reference type TO for
   purposes of reference binding.  For lvalue binding, either pass a
   reference type to FROM or an lvalue expression to EXPR.  If the
   reference will be bound to a temporary, NEED_TEMPORARY_P is set for
   the conversion returned.  If C_CAST_P is true, this
   conversion is coming from a C-style cast.  */

static conversion *
reference_binding (tree rto, tree rfrom, tree expr, bool c_cast_p, int flags)
{
  conversion *conv = NULL;
  tree to = TREE_TYPE (rto);
  tree from = rfrom;
  tree tfrom;
  bool related_p;
  bool compatible_p;
  cp_lvalue_kind gl_kind;
  bool is_lvalue;

  if (TREE_CODE (to) == FUNCTION_TYPE && expr && type_unknown_p (expr))
    {
      expr = instantiate_type (to, expr, tf_none);
      if (expr == error_mark_node)
        return NULL;
      from = TREE_TYPE (expr);
    }

  if (expr && BRACE_ENCLOSED_INITIALIZER_P (expr))
    {
      maybe_warn_cpp0x (CPP0X_INITIALIZER_LISTS);
      conv = implicit_conversion (to, from, expr, c_cast_p,
                                  flags);
      if (!CLASS_TYPE_P (to)
          && CONSTRUCTOR_NELTS (expr) == 1)
        {
          expr = CONSTRUCTOR_ELT (expr, 0)->value;
          if (error_operand_p (expr))
            return NULL;
          from = TREE_TYPE (expr);
        }
    }

  if (TREE_CODE (from) == REFERENCE_TYPE)
    {
      from = TREE_TYPE (from);
      if (!TYPE_REF_IS_RVALUE (rfrom)
          || TREE_CODE (from) == FUNCTION_TYPE)
        gl_kind = clk_ordinary;
      else
        gl_kind = clk_rvalueref;
    }
  else if (expr)
    {
      gl_kind = lvalue_kind (expr);
      if (gl_kind & clk_class)
        /* A class prvalue is not a glvalue.  */
        gl_kind = clk_none;
    }
  else
    gl_kind = clk_none;
  is_lvalue = gl_kind && !(gl_kind & clk_rvalueref);

  tfrom = from;
  if ((gl_kind & clk_bitfield) != 0)
    tfrom = unlowered_expr_type (expr);

  /* Figure out whether or not the types are reference-related and
     reference compatible.  We have do do this after stripping
     references from FROM.  */
  related_p = reference_related_p (to, tfrom);
  /* If this is a C cast, first convert to an appropriately qualified
     type, so that we can later do a const_cast to the desired type.  */
  if (related_p && c_cast_p
      && !at_least_as_qualified_p (to, tfrom))
    to = cp_build_qualified_type (to, cp_type_quals (tfrom));
  compatible_p = reference_compatible_p (to, tfrom);

  /* Directly bind reference when target expression's type is compatible with
     the reference and expression is an lvalue. In DR391, the wording in
     [8.5.3/5 dcl.init.ref] is changed to also require direct bindings for
     const and rvalue references to rvalues of compatible class type.
     We should also do direct bindings for non-class xvalues.  */
  if (compatible_p
      && (is_lvalue
          || (((CP_TYPE_CONST_NON_VOLATILE_P (to)
                && !(flags & LOOKUP_NO_RVAL_BIND))
               || TYPE_REF_IS_RVALUE (rto))
              && (gl_kind
                  || (!(flags & LOOKUP_NO_TEMP_BIND)
                      && (CLASS_TYPE_P (from)
                          || TREE_CODE (from) == ARRAY_TYPE))))))
    {
      /* [dcl.init.ref]

         If the initializer expression

         -- is an lvalue (but not an lvalue for a bit-field), and "cv1 T1"
            is reference-compatible with "cv2 T2,"

         the reference is bound directly to the initializer expression
         lvalue.

         [...]
         If the initializer expression is an rvalue, with T2 a class type,
         and "cv1 T1" is reference-compatible with "cv2 T2", the reference
         is bound to the object represented by the rvalue or to a sub-object
         within that object.  */

      conv = build_identity_conv (tfrom, expr);
      conv = direct_reference_binding (rto, conv);

      if (flags & LOOKUP_PREFER_RVALUE)
        /* The top-level caller requested that we pretend that the lvalue
           be treated as an rvalue.  */
        conv->rvaluedness_matches_p = TYPE_REF_IS_RVALUE (rto);
      else if (TREE_CODE (rfrom) == REFERENCE_TYPE)
        /* Handle rvalue reference to function properly.  */
        conv->rvaluedness_matches_p
          = (TYPE_REF_IS_RVALUE (rto) == TYPE_REF_IS_RVALUE (rfrom));
      else
        conv->rvaluedness_matches_p 
          = (TYPE_REF_IS_RVALUE (rto) == !is_lvalue);

      if ((gl_kind & clk_bitfield) != 0
          || ((gl_kind & clk_packed) != 0 && !TYPE_PACKED (to)))
        /* For the purposes of overload resolution, we ignore the fact
           this expression is a bitfield or packed field. (In particular,
           [over.ics.ref] says specifically that a function with a
           non-const reference parameter is viable even if the
           argument is a bitfield.)

           However, when we actually call the function we must create
           a temporary to which to bind the reference.  If the
           reference is volatile, or isn't const, then we cannot make
           a temporary, so we just issue an error when the conversion
           actually occurs.  */
        conv->need_temporary_p = true;

      /* Don't allow binding of lvalues (other than function lvalues) to
         rvalue references.  */
      if (is_lvalue && TYPE_REF_IS_RVALUE (rto)
          && TREE_CODE (to) != FUNCTION_TYPE
          && !(flags & LOOKUP_PREFER_RVALUE))
        conv->bad_p = true;

      return conv;
    }
  /* [class.conv.fct] A conversion function is never used to convert a
     (possibly cv-qualified) object to the (possibly cv-qualified) same
     object type (or a reference to it), to a (possibly cv-qualified) base
     class of that type (or a reference to it).... */
  else if (CLASS_TYPE_P (from) && !related_p
           && !(flags & LOOKUP_NO_CONVERSION))
    {
      /* [dcl.init.ref]

         If the initializer expression

         -- has a class type (i.e., T2 is a class type) can be
            implicitly converted to an lvalue of type "cv3 T3," where
            "cv1 T1" is reference-compatible with "cv3 T3".  (this
            conversion is selected by enumerating the applicable
            conversion functions (_over.match.ref_) and choosing the
            best one through overload resolution.  (_over.match_).

        the reference is bound to the lvalue result of the conversion
        in the second case.  */
      z_candidate *cand = build_user_type_conversion_1 (rto, expr, flags);
      if (cand)
        return cand->second_conv;
    }

  /* From this point on, we conceptually need temporaries, even if we
     elide them.  Only the cases above are "direct bindings".  */
  if (flags & LOOKUP_NO_TEMP_BIND)
    return NULL;

  /* [over.ics.rank]

     When a parameter of reference type is not bound directly to an
     argument expression, the conversion sequence is the one required
     to convert the argument expression to the underlying type of the
     reference according to _over.best.ics_.  Conceptually, this
     conversion sequence corresponds to copy-initializing a temporary
     of the underlying type with the argument expression.  Any
     difference in top-level cv-qualification is subsumed by the
     initialization itself and does not constitute a conversion.  */

  /* [dcl.init.ref]

     Otherwise, the reference shall be to a non-volatile const type.

     Under C++0x, [8.5.3/5 dcl.init.ref] it may also be an rvalue reference */
  if (!CP_TYPE_CONST_NON_VOLATILE_P (to) && !TYPE_REF_IS_RVALUE (rto))
    return NULL;

  /* [dcl.init.ref]

     Otherwise, a temporary of type "cv1 T1" is created and
     initialized from the initializer expression using the rules for a
     non-reference copy initialization.  If T1 is reference-related to
     T2, cv1 must be the same cv-qualification as, or greater
     cv-qualification than, cv2; otherwise, the program is ill-formed.  */
  if (related_p && !at_least_as_qualified_p (to, from))
    return NULL;

  /* We're generating a temporary now, but don't bind any more in the
     conversion (specifically, don't slice the temporary returned by a
     conversion operator).  */
  flags |= LOOKUP_NO_TEMP_BIND;

  /* Core issue 899: When [copy-]initializing a temporary to be bound
     to the first parameter of a copy constructor (12.8) called with
     a single argument in the context of direct-initialization,
     explicit conversion functions are also considered.

     So don't set LOOKUP_ONLYCONVERTING in that case.  */
  if (!(flags & LOOKUP_COPY_PARM))
    flags |= LOOKUP_ONLYCONVERTING;

  if (!conv)
    conv = implicit_conversion (to, from, expr, c_cast_p,
                                flags);
  if (!conv)
    return NULL;

  conv = build_conv (ck_ref_bind, rto, conv);
  /* This reference binding, unlike those above, requires the
     creation of a temporary.  */
  conv->need_temporary_p = true;
  conv->rvaluedness_matches_p = TYPE_REF_IS_RVALUE (rto);

  return conv;
}

/* Returns the implicit conversion sequence (see [over.ics]) from type
   FROM to type TO.  The optional expression EXPR may affect the
   conversion.  FLAGS are the usual overloading flags.  If C_CAST_P is
   true, this conversion is coming from a C-style cast.  */

static conversion *
implicit_conversion (tree to, tree from, tree expr, bool c_cast_p,
                     int flags)
{
  conversion *conv;

  if (from == error_mark_node || to == error_mark_node
      || expr == error_mark_node)
    return NULL;

  /* Other flags only apply to the primary function in overload
     resolution, or after we've chosen one.  */
  flags &= (LOOKUP_ONLYCONVERTING|LOOKUP_NO_CONVERSION|LOOKUP_COPY_PARM
            |LOOKUP_NO_TEMP_BIND|LOOKUP_NO_RVAL_BIND|LOOKUP_PREFER_RVALUE
            |LOOKUP_NO_NARROWING|LOOKUP_PROTECT);

  if (TREE_CODE (to) == REFERENCE_TYPE)
    conv = reference_binding (to, from, expr, c_cast_p, flags);
  else
    conv = standard_conversion (to, from, expr, c_cast_p, flags);

  if (conv)
    return conv;

  if (expr && BRACE_ENCLOSED_INITIALIZER_P (expr))
    {
      if (is_std_init_list (to))
        return build_list_conv (to, expr, flags);

      /* As an extension, allow list-initialization of _Complex.  */
      if (TREE_CODE (to) == COMPLEX_TYPE)
        {
          conv = build_complex_conv (to, expr, flags);
          if (conv)
            return conv;
        }

      /* Allow conversion from an initializer-list with one element to a
         scalar type.  */
      if (SCALAR_TYPE_P (to))
        {
          int nelts = CONSTRUCTOR_NELTS (expr);
          tree elt;

          if (nelts == 0)
            elt = build_value_init (to, tf_none);
          else if (nelts == 1)
            elt = CONSTRUCTOR_ELT (expr, 0)->value;
          else
            elt = error_mark_node;

          conv = implicit_conversion (to, TREE_TYPE (elt), elt,
                                      c_cast_p, flags);
          if (conv)
            {
              conv->check_narrowing = true;
              if (BRACE_ENCLOSED_INITIALIZER_P (elt))
                /* Too many levels of braces, i.e. '{{1}}'.  */
                conv->bad_p = true;
              return conv;
            }
        }
      else if (TREE_CODE (to) == ARRAY_TYPE)
        return build_array_conv (to, expr, flags);
    }

  if (expr != NULL_TREE
      && (MAYBE_CLASS_TYPE_P (from)
          || MAYBE_CLASS_TYPE_P (to))
      && (flags & LOOKUP_NO_CONVERSION) == 0)
    {
      struct z_candidate *cand;

      if (CLASS_TYPE_P (to)
          && BRACE_ENCLOSED_INITIALIZER_P (expr)
          && !CLASSTYPE_NON_AGGREGATE (complete_type (to)))
        return build_aggr_conv (to, expr, flags);

      cand = build_user_type_conversion_1 (to, expr, flags);
      if (cand)
        conv = cand->second_conv;

      /* We used to try to bind a reference to a temporary here, but that
         is now handled after the recursive call to this function at the end
         of reference_binding.  */
      return conv;
    }

  return NULL;
}

/* Add a new entry to the list of candidates.  Used by the add_*_candidate
   functions.  ARGS will not be changed until a single candidate is
   selected.  */

static struct z_candidate *
add_candidate (struct z_candidate **candidates,
               tree fn, tree first_arg, const VEC(tree,gc) *args,
               size_t num_convs, conversion **convs,
               tree access_path, tree conversion_path,
               int viable, struct rejection_reason *reason)
{
  struct z_candidate *cand = (struct z_candidate *)
    conversion_obstack_alloc (sizeof (struct z_candidate));

  cand->fn = fn;
  cand->first_arg = first_arg;
  cand->args = args;
  cand->convs = convs;
  cand->num_convs = num_convs;
  cand->access_path = access_path;
  cand->conversion_path = conversion_path;
  cand->viable = viable;
  cand->reason = reason;
  cand->next = *candidates;
  *candidates = cand;

  return cand;
}

/* Return the number of remaining arguments in the parameter list
   beginning with ARG.  */

static int
remaining_arguments (tree arg)
{
  int n;

  for (n = 0; arg != NULL_TREE && arg != void_list_node;
       arg = TREE_CHAIN (arg))
    n++;

  return n;
}

/* Create an overload candidate for the function or method FN called
   with the argument list FIRST_ARG/ARGS and add it to CANDIDATES.
   FLAGS is passed on to implicit_conversion.

   This does not change ARGS.

   CTYPE, if non-NULL, is the type we want to pretend this function
   comes from for purposes of overload resolution.  */

static struct z_candidate *
add_function_candidate (struct z_candidate **candidates,
                        tree fn, tree ctype, tree first_arg,
                        const VEC(tree,gc) *args, tree access_path,
                        tree conversion_path, int flags)
{
  tree parmlist = TYPE_ARG_TYPES (TREE_TYPE (fn));
  int i, len;
  conversion **convs;
  tree parmnode;
  tree orig_first_arg = first_arg;
  int skip;
  int viable = 1;
  struct rejection_reason *reason = NULL;

  /* At this point we should not see any functions which haven't been
     explicitly declared, except for friend functions which will have
     been found using argument dependent lookup.  */
  gcc_assert (!DECL_ANTICIPATED (fn) || DECL_HIDDEN_FRIEND_P (fn));

  /* The `this', `in_chrg' and VTT arguments to constructors are not
     considered in overload resolution.  */
  if (DECL_CONSTRUCTOR_P (fn))
    {
      parmlist = skip_artificial_parms_for (fn, parmlist);
      skip = num_artificial_parms_for (fn);
      if (skip > 0 && first_arg != NULL_TREE)
        {
          --skip;
          first_arg = NULL_TREE;
        }
    }
  else
    skip = 0;

  len = VEC_length (tree, args) - skip + (first_arg != NULL_TREE ? 1 : 0);
  convs = alloc_conversions (len);

  /* 13.3.2 - Viable functions [over.match.viable]
     First, to be a viable function, a candidate function shall have enough
     parameters to agree in number with the arguments in the list.

     We need to check this first; otherwise, checking the ICSes might cause
     us to produce an ill-formed template instantiation.  */

  parmnode = parmlist;
  for (i = 0; i < len; ++i)
    {
      if (parmnode == NULL_TREE || parmnode == void_list_node)
        break;
      parmnode = TREE_CHAIN (parmnode);
    }

  if ((i < len && parmnode)
      || !sufficient_parms_p (parmnode))
    {
      int remaining = remaining_arguments (parmnode);
      viable = 0;
      reason = arity_rejection (first_arg, i + remaining, len);
    }
  /* When looking for a function from a subobject from an implicit
     copy/move constructor/operator=, don't consider anything that takes (a
     reference to) an unrelated type.  See c++/44909 and core 1092.  */
  else if (parmlist && (flags & LOOKUP_DEFAULTED))
    {
      if (DECL_CONSTRUCTOR_P (fn))
        i = 1;
      else if (DECL_ASSIGNMENT_OPERATOR_P (fn)
               && DECL_OVERLOADED_OPERATOR_P (fn) == NOP_EXPR)
        i = 2;
      else
        i = 0;
      if (i && len == i)
        {
          parmnode = chain_index (i-1, parmlist);
          if (!reference_related_p (non_reference (TREE_VALUE (parmnode)),
                                    ctype))
            viable = 0;
        }

      /* This only applies at the top level.  */
      flags &= ~LOOKUP_DEFAULTED;
    }

  if (! viable)
    goto out;

  /* Second, for F to be a viable function, there shall exist for each
     argument an implicit conversion sequence that converts that argument
     to the corresponding parameter of F.  */

  parmnode = parmlist;

  for (i = 0; i < len; ++i)
    {
      tree arg, argtype, to_type;
      conversion *t;
      int is_this;

      if (parmnode == void_list_node)
        break;

      if (i == 0 && first_arg != NULL_TREE)
        arg = first_arg;
      else
        arg = VEC_index (tree, args,
                         i + skip - (first_arg != NULL_TREE ? 1 : 0));
      argtype = lvalue_type (arg);

      is_this = (i == 0 && DECL_NONSTATIC_MEMBER_FUNCTION_P (fn)
                 && ! DECL_CONSTRUCTOR_P (fn));

      if (parmnode)
        {
          tree parmtype = TREE_VALUE (parmnode);
          int lflags = flags;

          parmnode = TREE_CHAIN (parmnode);

          /* The type of the implicit object parameter ('this') for
             overload resolution is not always the same as for the
             function itself; conversion functions are considered to
             be members of the class being converted, and functions
             introduced by a using-declaration are considered to be
             members of the class that uses them.

             Since build_over_call ignores the ICS for the `this'
             parameter, we can just change the parm type.  */
          if (ctype && is_this)
            {
              parmtype = cp_build_qualified_type
                (ctype, cp_type_quals (TREE_TYPE (parmtype)));
              parmtype = build_pointer_type (parmtype);
            }

          /* Core issue 899: When [copy-]initializing a temporary to be bound
             to the first parameter of a copy constructor (12.8) called with
             a single argument in the context of direct-initialization,
             explicit conversion functions are also considered.

             So set LOOKUP_COPY_PARM to let reference_binding know that
             it's being called in that context.  We generalize the above
             to handle move constructors and template constructors as well;
             the standardese should soon be updated similarly.  */
          if (ctype && i == 0 && (len-skip == 1)
              && DECL_CONSTRUCTOR_P (fn)
              && parmtype != error_mark_node
              && (same_type_ignoring_top_level_qualifiers_p
                  (non_reference (parmtype), ctype)))
            {
              if (!(flags & LOOKUP_ONLYCONVERTING))
                lflags |= LOOKUP_COPY_PARM;
              /* We allow user-defined conversions within init-lists, but
                 don't list-initialize the copy parm, as that would mean
                 using two levels of braces for the same type.  */
              if ((flags & LOOKUP_LIST_INIT_CTOR)
                  && BRACE_ENCLOSED_INITIALIZER_P (arg))
                lflags |= LOOKUP_NO_CONVERSION;
            }
          else
            lflags |= LOOKUP_ONLYCONVERTING;

          t = implicit_conversion (parmtype, argtype, arg,
                                   /*c_cast_p=*/false, lflags);
          to_type = parmtype;
        }
      else
        {
          t = build_identity_conv (argtype, arg);
          t->ellipsis_p = true;
          to_type = argtype;
        }

      if (t && is_this)
        t->this_p = true;

      convs[i] = t;
      if (! t)
        {
          viable = 0;
          reason = arg_conversion_rejection (first_arg, i, argtype, to_type);
          break;
        }

      if (t->bad_p)
        {
          viable = -1;
          reason = bad_arg_conversion_rejection (first_arg, i, argtype, to_type);
        }
    }

 out:
  return add_candidate (candidates, fn, orig_first_arg, args, len, convs,
                        access_path, conversion_path, viable, reason);
}

/* Create an overload candidate for the conversion function FN which will
   be invoked for expression OBJ, producing a pointer-to-function which
   will in turn be called with the argument list FIRST_ARG/ARGLIST,
   and add it to CANDIDATES.  This does not change ARGLIST.  FLAGS is
   passed on to implicit_conversion.

   Actually, we don't really care about FN; we care about the type it
   converts to.  There may be multiple conversion functions that will
   convert to that type, and we rely on build_user_type_conversion_1 to
   choose the best one; so when we create our candidate, we record the type
   instead of the function.  */

static struct z_candidate *
add_conv_candidate (struct z_candidate **candidates, tree fn, tree obj,
                    tree first_arg, const VEC(tree,gc) *arglist,
                    tree access_path, tree conversion_path)
{
  tree totype = TREE_TYPE (TREE_TYPE (fn));
  int i, len, viable, flags;
  tree parmlist, parmnode;
  conversion **convs;
  struct rejection_reason *reason;

  for (parmlist = totype; TREE_CODE (parmlist) != FUNCTION_TYPE; )
    parmlist = TREE_TYPE (parmlist);
  parmlist = TYPE_ARG_TYPES (parmlist);

  len = VEC_length (tree, arglist) + (first_arg != NULL_TREE ? 1 : 0) + 1;
  convs = alloc_conversions (len);
  parmnode = parmlist;
  viable = 1;
  flags = LOOKUP_IMPLICIT;
  reason = NULL;

  /* Don't bother looking up the same type twice.  */
  if (*candidates && (*candidates)->fn == totype)
    return NULL;

  for (i = 0; i < len; ++i)
    {
      tree arg, argtype, convert_type = NULL_TREE;
      conversion *t;

      if (i == 0)
        arg = obj;
      else if (i == 1 && first_arg != NULL_TREE)
        arg = first_arg;
      else
        arg = VEC_index (tree, arglist,
                         i - (first_arg != NULL_TREE ? 1 : 0) - 1);
      argtype = lvalue_type (arg);

      if (i == 0)
        {
          t = implicit_conversion (totype, argtype, arg, /*c_cast_p=*/false,
                                   flags);
          convert_type = totype;
        }
      else if (parmnode == void_list_node)
        break;
      else if (parmnode)
        {
          t = implicit_conversion (TREE_VALUE (parmnode), argtype, arg,
                                   /*c_cast_p=*/false, flags);
          convert_type = TREE_VALUE (parmnode);
        }
      else
        {
          t = build_identity_conv (argtype, arg);
          t->ellipsis_p = true;
          convert_type = argtype;
        }

      convs[i] = t;
      if (! t)
        break;

      if (t->bad_p)
        {
          viable = -1;
          reason = bad_arg_conversion_rejection (NULL_TREE, i, argtype, convert_type);
        }

      if (i == 0)
        continue;

      if (parmnode)
        parmnode = TREE_CHAIN (parmnode);
    }

  if (i < len
      || ! sufficient_parms_p (parmnode))
    {
      int remaining = remaining_arguments (parmnode);
      viable = 0;
      reason = arity_rejection (NULL_TREE, i + remaining, len);
    }

  return add_candidate (candidates, totype, first_arg, arglist, len, convs,
                        access_path, conversion_path, viable, reason);
}

static void
build_builtin_candidate (struct z_candidate **candidates, tree fnname,
                         tree type1, tree type2, tree *args, tree *argtypes,
                         int flags)
{
  conversion *t;
  conversion **convs;
  size_t num_convs;
  int viable = 1, i;
  tree types[2];
  struct rejection_reason *reason = NULL;

  types[0] = type1;
  types[1] = type2;

  num_convs =  args[2] ? 3 : (args[1] ? 2 : 1);
  convs = alloc_conversions (num_convs);

  /* TRUTH_*_EXPR do "contextual conversion to bool", which means explicit
     conversion ops are allowed.  We handle that here by just checking for
     boolean_type_node because other operators don't ask for it.  COND_EXPR
     also does contextual conversion to bool for the first operand, but we
     handle that in build_conditional_expr, and type1 here is operand 2.  */
  if (type1 != boolean_type_node)
    flags |= LOOKUP_ONLYCONVERTING;

  for (i = 0; i < 2; ++i)
    {
      if (! args[i])
        break;

      t = implicit_conversion (types[i], argtypes[i], args[i],
                               /*c_cast_p=*/false, flags);
      if (! t)
        {
          viable = 0;
          /* We need something for printing the candidate.  */
          t = build_identity_conv (types[i], NULL_TREE);
          reason = arg_conversion_rejection (NULL_TREE, i, argtypes[i], types[i]);
        }
      else if (t->bad_p)
        {
          viable = 0;
          reason = bad_arg_conversion_rejection (NULL_TREE, i, argtypes[i], types[i]);
        }
      convs[i] = t;
    }

  /* For COND_EXPR we rearranged the arguments; undo that now.  */
  if (args[2])
    {
      convs[2] = convs[1];
      convs[1] = convs[0];
      t = implicit_conversion (boolean_type_node, argtypes[2], args[2],
                               /*c_cast_p=*/false, flags);
      if (t)
        convs[0] = t;
      else
        {
          viable = 0;
          reason = arg_conversion_rejection (NULL_TREE, 0, argtypes[2],
                                             boolean_type_node);
        }
    }

  add_candidate (candidates, fnname, /*first_arg=*/NULL_TREE, /*args=*/NULL,
                 num_convs, convs,
                 /*access_path=*/NULL_TREE,
                 /*conversion_path=*/NULL_TREE,
                 viable, reason);
}

static bool
is_complete (tree t)
{
  return COMPLETE_TYPE_P (complete_type (t));
}

/* Returns nonzero if TYPE is a promoted arithmetic type.  */

static bool
promoted_arithmetic_type_p (tree type)
{
  /* [over.built]

     In this section, the term promoted integral type is used to refer
     to those integral types which are preserved by integral promotion
     (including e.g.  int and long but excluding e.g.  char).
     Similarly, the term promoted arithmetic type refers to promoted
     integral types plus floating types.  */
  return ((CP_INTEGRAL_TYPE_P (type)
           && same_type_p (type_promotes_to (type), type))
          || TREE_CODE (type) == REAL_TYPE);
}

/* Create any builtin operator overload candidates for the operator in
   question given the converted operand types TYPE1 and TYPE2.  The other
   args are passed through from add_builtin_candidates to
   build_builtin_candidate.

   TYPE1 and TYPE2 may not be permissible, and we must filter them.
   If CODE is requires candidates operands of the same type of the kind
   of which TYPE1 and TYPE2 are, we add both candidates
   CODE (TYPE1, TYPE1) and CODE (TYPE2, TYPE2).  */

static void
add_builtin_candidate (struct z_candidate **candidates, enum tree_code code,
                       enum tree_code code2, tree fnname, tree type1,
                       tree type2, tree *args, tree *argtypes, int flags)
{
  switch (code)
    {
    case POSTINCREMENT_EXPR:
    case POSTDECREMENT_EXPR:
      args[1] = integer_zero_node;
      type2 = integer_type_node;
      break;
    default:
      break;
    }

  switch (code)
    {

/* 4 For every pair T, VQ), where T is an arithmetic or  enumeration  type,
     and  VQ  is  either  volatile or empty, there exist candidate operator
     functions of the form
             VQ T&   operator++(VQ T&);
             T       operator++(VQ T&, int);
   5 For every pair T, VQ), where T is an enumeration type or an arithmetic
     type  other than bool, and VQ is either volatile or empty, there exist
     candidate operator functions of the form
             VQ T&   operator--(VQ T&);
             T       operator--(VQ T&, int);
   6 For every pair T, VQ), where T is  a  cv-qualified  or  cv-unqualified
     complete  object type, and VQ is either volatile or empty, there exist
     candidate operator functions of the form
             T*VQ&   operator++(T*VQ&);
             T*VQ&   operator--(T*VQ&);
             T*      operator++(T*VQ&, int);
             T*      operator--(T*VQ&, int);  */

    case POSTDECREMENT_EXPR:
    case PREDECREMENT_EXPR:
      if (TREE_CODE (type1) == BOOLEAN_TYPE)
        return;
    case POSTINCREMENT_EXPR:
    case PREINCREMENT_EXPR:
      if (ARITHMETIC_TYPE_P (type1) || TYPE_PTROB_P (type1))
        {
          type1 = build_reference_type (type1);
          break;
        }
      return;

/* 7 For every cv-qualified or cv-unqualified object type T, there
     exist candidate operator functions of the form

             T&      operator*(T*);

   8 For every function type T, there exist candidate operator functions of
     the form
             T&      operator*(T*);  */

    case INDIRECT_REF:
      if (TREE_CODE (type1) == POINTER_TYPE
          && !uses_template_parms (TREE_TYPE (type1))
          && (TYPE_PTROB_P (type1)
              || TREE_CODE (TREE_TYPE (type1)) == FUNCTION_TYPE))
        break;
      return;

/* 9 For every type T, there exist candidate operator functions of the form
             T*      operator+(T*);

   10For  every  promoted arithmetic type T, there exist candidate operator
     functions of the form
             T       operator+(T);
             T       operator-(T);  */

    case UNARY_PLUS_EXPR: /* unary + */
      if (TREE_CODE (type1) == POINTER_TYPE)
        break;
    case NEGATE_EXPR:
      if (ARITHMETIC_TYPE_P (type1))
        break;
      return;

/* 11For every promoted integral type T,  there  exist  candidate  operator
     functions of the form
             T       operator~(T);  */

    case BIT_NOT_EXPR:
      if (INTEGRAL_OR_UNSCOPED_ENUMERATION_TYPE_P (type1))
        break;
      return;

/* 12For every quintuple C1, C2, T, CV1, CV2), where C2 is a class type, C1
     is the same type as C2 or is a derived class of C2, T  is  a  complete
     object type or a function type, and CV1 and CV2 are cv-qualifier-seqs,
     there exist candidate operator functions of the form
             CV12 T& operator->*(CV1 C1*, CV2 T C2::*);
     where CV12 is the union of CV1 and CV2.  */

    case MEMBER_REF:
      if (TREE_CODE (type1) == POINTER_TYPE
          && TYPE_PTR_TO_MEMBER_P (type2))
        {
          tree c1 = TREE_TYPE (type1);
          tree c2 = TYPE_PTRMEM_CLASS_TYPE (type2);

          if (MAYBE_CLASS_TYPE_P (c1) && DERIVED_FROM_P (c2, c1)
              && (TYPE_PTRMEMFUNC_P (type2)
                  || is_complete (TYPE_PTRMEM_POINTED_TO_TYPE (type2))))
            break;
        }
      return;

/* 13For every pair of promoted arithmetic types L and R, there exist  can-
     didate operator functions of the form
             LR      operator*(L, R);
             LR      operator/(L, R);
             LR      operator+(L, R);
             LR      operator-(L, R);
             bool    operator<(L, R);
             bool    operator>(L, R);
             bool    operator<=(L, R);
             bool    operator>=(L, R);
             bool    operator==(L, R);
             bool    operator!=(L, R);
     where  LR  is  the  result of the usual arithmetic conversions between
     types L and R.

   14For every pair of types T and I, where T  is  a  cv-qualified  or  cv-
     unqualified  complete  object  type and I is a promoted integral type,
     there exist candidate operator functions of the form
             T*      operator+(T*, I);
             T&      operator[](T*, I);
             T*      operator-(T*, I);
             T*      operator+(I, T*);
             T&      operator[](I, T*);

   15For every T, where T is a pointer to complete object type, there exist
     candidate operator functions of the form112)
             ptrdiff_t operator-(T, T);

   16For every pointer or enumeration type T, there exist candidate operator
     functions of the form
             bool    operator<(T, T);
             bool    operator>(T, T);
             bool    operator<=(T, T);
             bool    operator>=(T, T);
             bool    operator==(T, T);
             bool    operator!=(T, T);

   17For every pointer to member type T,  there  exist  candidate  operator
     functions of the form
             bool    operator==(T, T);
             bool    operator!=(T, T);  */

    case MINUS_EXPR:
      if (TYPE_PTROB_P (type1) && TYPE_PTROB_P (type2))
        break;
      if (TYPE_PTROB_P (type1)
          && INTEGRAL_OR_UNSCOPED_ENUMERATION_TYPE_P (type2))
        {
          type2 = ptrdiff_type_node;
          break;
        }
    case MULT_EXPR:
    case TRUNC_DIV_EXPR:
      if (ARITHMETIC_TYPE_P (type1) && ARITHMETIC_TYPE_P (type2))
        break;
      return;

    case EQ_EXPR:
    case NE_EXPR:
      if ((TYPE_PTRMEMFUNC_P (type1) && TYPE_PTRMEMFUNC_P (type2))
          || (TYPE_PTRMEM_P (type1) && TYPE_PTRMEM_P (type2)))
        break;
      if (TYPE_PTR_TO_MEMBER_P (type1) && null_ptr_cst_p (args[1]))
        {
          type2 = type1;
          break;
        }
      if (TYPE_PTR_TO_MEMBER_P (type2) && null_ptr_cst_p (args[0]))
        {
          type1 = type2;
          break;
        }
      /* Fall through.  */
    case LT_EXPR:
    case GT_EXPR:
    case LE_EXPR:
    case GE_EXPR:
    case MAX_EXPR:
    case MIN_EXPR:
      if (ARITHMETIC_TYPE_P (type1) && ARITHMETIC_TYPE_P (type2))
        break;
      if (TYPE_PTR_P (type1) && TYPE_PTR_P (type2))
        break;
      if (TREE_CODE (type1) == ENUMERAL_TYPE 
          && TREE_CODE (type2) == ENUMERAL_TYPE)
        break;
      if (TYPE_PTR_P (type1) 
          && null_ptr_cst_p (args[1])
          && !uses_template_parms (type1))
        {
          type2 = type1;
          break;
        }
      if (null_ptr_cst_p (args[0]) 
          && TYPE_PTR_P (type2)
          && !uses_template_parms (type2))
        {
          type1 = type2;
          break;
        }
      return;

    case PLUS_EXPR:
      if (ARITHMETIC_TYPE_P (type1) && ARITHMETIC_TYPE_P (type2))
        break;
    case ARRAY_REF:
      if (INTEGRAL_OR_UNSCOPED_ENUMERATION_TYPE_P (type1) && TYPE_PTROB_P (type2))
        {
          type1 = ptrdiff_type_node;
          break;
        }
      if (TYPE_PTROB_P (type1) && INTEGRAL_OR_UNSCOPED_ENUMERATION_TYPE_P (type2))
        {
          type2 = ptrdiff_type_node;
          break;
        }
      return;

/* 18For  every pair of promoted integral types L and R, there exist candi-
     date operator functions of the form
             LR      operator%(L, R);
             LR      operator&(L, R);
             LR      operator^(L, R);
             LR      operator|(L, R);
             L       operator<<(L, R);
             L       operator>>(L, R);
     where LR is the result of the  usual  arithmetic  conversions  between
     types L and R.  */

    case TRUNC_MOD_EXPR:
    case BIT_AND_EXPR:
    case BIT_IOR_EXPR:
    case BIT_XOR_EXPR:
    case LSHIFT_EXPR:
    case RSHIFT_EXPR:
      if (INTEGRAL_OR_UNSCOPED_ENUMERATION_TYPE_P (type1) && INTEGRAL_OR_UNSCOPED_ENUMERATION_TYPE_P (type2))
        break;
      return;

/* 19For  every  triple  L, VQ, R), where L is an arithmetic or enumeration
     type, VQ is either volatile or empty, and R is a  promoted  arithmetic
     type, there exist candidate operator functions of the form
             VQ L&   operator=(VQ L&, R);
             VQ L&   operator*=(VQ L&, R);
             VQ L&   operator/=(VQ L&, R);
             VQ L&   operator+=(VQ L&, R);
             VQ L&   operator-=(VQ L&, R);

   20For  every  pair T, VQ), where T is any type and VQ is either volatile
     or empty, there exist candidate operator functions of the form
             T*VQ&   operator=(T*VQ&, T*);

   21For every pair T, VQ), where T is a pointer to member type and  VQ  is
     either  volatile or empty, there exist candidate operator functions of
     the form
             VQ T&   operator=(VQ T&, T);

   22For every triple  T,  VQ,  I),  where  T  is  a  cv-qualified  or  cv-
     unqualified  complete object type, VQ is either volatile or empty, and
     I is a promoted integral type, there exist  candidate  operator  func-
     tions of the form
             T*VQ&   operator+=(T*VQ&, I);
             T*VQ&   operator-=(T*VQ&, I);

   23For  every  triple  L,  VQ,  R), where L is an integral or enumeration
     type, VQ is either volatile or empty, and R  is  a  promoted  integral
     type, there exist candidate operator functions of the form

             VQ L&   operator%=(VQ L&, R);
             VQ L&   operator<<=(VQ L&, R);
             VQ L&   operator>>=(VQ L&, R);
             VQ L&   operator&=(VQ L&, R);
             VQ L&   operator^=(VQ L&, R);
             VQ L&   operator|=(VQ L&, R);  */

    case MODIFY_EXPR:
      switch (code2)
        {
        case PLUS_EXPR:
        case MINUS_EXPR:
          if (TYPE_PTROB_P (type1) && INTEGRAL_OR_UNSCOPED_ENUMERATION_TYPE_P (type2))
            {
              type2 = ptrdiff_type_node;
              break;
            }
        case MULT_EXPR:
        case TRUNC_DIV_EXPR:
          if (ARITHMETIC_TYPE_P (type1) && ARITHMETIC_TYPE_P (type2))
            break;
          return;

        case TRUNC_MOD_EXPR:
        case BIT_AND_EXPR:
        case BIT_IOR_EXPR:
        case BIT_XOR_EXPR:
        case LSHIFT_EXPR:
        case RSHIFT_EXPR:
          if (INTEGRAL_OR_UNSCOPED_ENUMERATION_TYPE_P (type1) && INTEGRAL_OR_UNSCOPED_ENUMERATION_TYPE_P (type2))
            break;
          return;

        case NOP_EXPR:
          if (ARITHMETIC_TYPE_P (type1) && ARITHMETIC_TYPE_P (type2))
            break;
          if ((TYPE_PTRMEMFUNC_P (type1) && TYPE_PTRMEMFUNC_P (type2))
              || (TYPE_PTR_P (type1) && TYPE_PTR_P (type2))
              || (TYPE_PTRMEM_P (type1) && TYPE_PTRMEM_P (type2))
              || ((TYPE_PTRMEMFUNC_P (type1)
                   || TREE_CODE (type1) == POINTER_TYPE)
                  && null_ptr_cst_p (args[1])))
            {
              type2 = type1;
              break;
            }
          return;

        default:
          gcc_unreachable ();
        }
      type1 = build_reference_type (type1);
      break;

    case COND_EXPR:
      /* [over.built]

         For every pair of promoted arithmetic types L and R, there
         exist candidate operator functions of the form

         LR operator?(bool, L, R);

         where LR is the result of the usual arithmetic conversions
         between types L and R.

         For every type T, where T is a pointer or pointer-to-member
         type, there exist candidate operator functions of the form T
         operator?(bool, T, T);  */

      if (promoted_arithmetic_type_p (type1)
          && promoted_arithmetic_type_p (type2))
        /* That's OK.  */
        break;

      /* Otherwise, the types should be pointers.  */
      if (!(TYPE_PTR_P (type1) || TYPE_PTR_TO_MEMBER_P (type1))
          || !(TYPE_PTR_P (type2) || TYPE_PTR_TO_MEMBER_P (type2)))
        return;

      /* We don't check that the two types are the same; the logic
         below will actually create two candidates; one in which both
         parameter types are TYPE1, and one in which both parameter
         types are TYPE2.  */
      break;

    case REALPART_EXPR:
    case IMAGPART_EXPR:
      if (ARITHMETIC_TYPE_P (type1))
        break;
      return;
 
    default:
      gcc_unreachable ();
    }

  /* If we're dealing with two pointer types or two enumeral types,
     we need candidates for both of them.  */
  if (type2 && !same_type_p (type1, type2)
      && TREE_CODE (type1) == TREE_CODE (type2)
      && (TREE_CODE (type1) == REFERENCE_TYPE
          || (TYPE_PTR_P (type1) && TYPE_PTR_P (type2))
          || (TYPE_PTRMEM_P (type1) && TYPE_PTRMEM_P (type2))
          || TYPE_PTRMEMFUNC_P (type1)
          || MAYBE_CLASS_TYPE_P (type1)
          || TREE_CODE (type1) == ENUMERAL_TYPE))
    {
      if (TYPE_PTR_P (type1) || TYPE_PTR_TO_MEMBER_P (type1))
        {
          tree cptype = composite_pointer_type (type1, type2,
                                                error_mark_node,
                                                error_mark_node,
                                                CPO_CONVERSION,
                                                tf_none);
          if (cptype != error_mark_node)
            {
              build_builtin_candidate
                (candidates, fnname, cptype, cptype, args, argtypes, flags);
              return;
            }
        }

      build_builtin_candidate
        (candidates, fnname, type1, type1, args, argtypes, flags);
      build_builtin_candidate
        (candidates, fnname, type2, type2, args, argtypes, flags);
      return;
    }

  build_builtin_candidate
    (candidates, fnname, type1, type2, args, argtypes, flags);
}

tree
type_decays_to (tree type)
{
  if (TREE_CODE (type) == ARRAY_TYPE)
    return build_pointer_type (TREE_TYPE (type));
  if (TREE_CODE (type) == FUNCTION_TYPE)
    return build_pointer_type (type);
  return type;
}

/* There are three conditions of builtin candidates:

   1) bool-taking candidates.  These are the same regardless of the input.
   2) pointer-pair taking candidates.  These are generated for each type
      one of the input types converts to.
   3) arithmetic candidates.  According to the standard, we should generate
      all of these, but I'm trying not to...

   Here we generate a superset of the possible candidates for this particular
   case.  That is a subset of the full set the standard defines, plus some
   other cases which the standard disallows. add_builtin_candidate will
   filter out the invalid set.  */

static void
add_builtin_candidates (struct z_candidate **candidates, enum tree_code code,
                        enum tree_code code2, tree fnname, tree *args,
                        int flags)
{
  int ref1, i;
  int enum_p = 0;
  tree type, argtypes[3], t;
  /* TYPES[i] is the set of possible builtin-operator parameter types
     we will consider for the Ith argument.  */
  VEC(tree,gc) *types[2];
  unsigned ix;

  for (i = 0; i < 3; ++i)
    {
      if (args[i])
        argtypes[i] = unlowered_expr_type (args[i]);
      else
        argtypes[i] = NULL_TREE;
    }

  switch (code)
    {
/* 4 For every pair T, VQ), where T is an arithmetic or  enumeration  type,
     and  VQ  is  either  volatile or empty, there exist candidate operator
     functions of the form
                 VQ T&   operator++(VQ T&);  */

    case POSTINCREMENT_EXPR:
    case PREINCREMENT_EXPR:
    case POSTDECREMENT_EXPR:
    case PREDECREMENT_EXPR:
    case MODIFY_EXPR:
      ref1 = 1;
      break;

/* 24There also exist candidate operator functions of the form
             bool    operator!(bool);
             bool    operator&&(bool, bool);
             bool    operator||(bool, bool);  */

    case TRUTH_NOT_EXPR:
      build_builtin_candidate
        (candidates, fnname, boolean_type_node,
         NULL_TREE, args, argtypes, flags);
      return;

    case TRUTH_ORIF_EXPR:
    case TRUTH_ANDIF_EXPR:
      build_builtin_candidate
        (candidates, fnname, boolean_type_node,
         boolean_type_node, args, argtypes, flags);
      return;

    case ADDR_EXPR:
    case COMPOUND_EXPR:
    case COMPONENT_REF:
      return;

    case COND_EXPR:
    case EQ_EXPR:
    case NE_EXPR:
    case LT_EXPR:
    case LE_EXPR:
    case GT_EXPR:
    case GE_EXPR:
      enum_p = 1;
      /* Fall through.  */

    default:
      ref1 = 0;
    }

  types[0] = make_tree_vector ();
  types[1] = make_tree_vector ();

  for (i = 0; i < 2; ++i)
    {
      if (! args[i])
        ;
      else if (MAYBE_CLASS_TYPE_P (argtypes[i]))
        {
          tree convs;

          if (i == 0 && code == MODIFY_EXPR && code2 == NOP_EXPR)
            return;

          convs = lookup_conversions (argtypes[i]);

          if (code == COND_EXPR)
            {
              if (real_lvalue_p (args[i]))
                VEC_safe_push (tree, gc, types[i],
                               build_reference_type (argtypes[i]));

              VEC_safe_push (tree, gc, types[i],
                             TYPE_MAIN_VARIANT (argtypes[i]));
            }

          else if (! convs)
            return;

          for (; convs; convs = TREE_CHAIN (convs))
            {
              type = TREE_TYPE (convs);

              if (i == 0 && ref1
                  && (TREE_CODE (type) != REFERENCE_TYPE
                      || CP_TYPE_CONST_P (TREE_TYPE (type))))
                continue;

              if (code == COND_EXPR && TREE_CODE (type) == REFERENCE_TYPE)
                VEC_safe_push (tree, gc, types[i], type);

              type = non_reference (type);
              if (i != 0 || ! ref1)
                {
                  type = cv_unqualified (type_decays_to (type));
                  if (enum_p && TREE_CODE (type) == ENUMERAL_TYPE)
                    VEC_safe_push (tree, gc, types[i], type);
                  if (INTEGRAL_OR_UNSCOPED_ENUMERATION_TYPE_P (type))
                    type = type_promotes_to (type);
                }

              if (! vec_member (type, types[i]))
                VEC_safe_push (tree, gc, types[i], type);
            }
        }
      else
        {
          if (code == COND_EXPR && real_lvalue_p (args[i]))
            VEC_safe_push (tree, gc, types[i],
                           build_reference_type (argtypes[i]));
          type = non_reference (argtypes[i]);
          if (i != 0 || ! ref1)
            {
              type = cv_unqualified (type_decays_to (type));
              if (enum_p && UNSCOPED_ENUM_P (type))
                VEC_safe_push (tree, gc, types[i], type);
              if (INTEGRAL_OR_UNSCOPED_ENUMERATION_TYPE_P (type))
                type = type_promotes_to (type);
            }
          VEC_safe_push (tree, gc, types[i], type);
        }
    }

  /* Run through the possible parameter types of both arguments,
     creating candidates with those parameter types.  */
  FOR_EACH_VEC_ELT_REVERSE (tree, types[0], ix, t)
    {
      unsigned jx;
      tree u;

      if (!VEC_empty (tree, types[1]))
        FOR_EACH_VEC_ELT_REVERSE (tree, types[1], jx, u)
          add_builtin_candidate
            (candidates, code, code2, fnname, t,
             u, args, argtypes, flags);
      else
        add_builtin_candidate
          (candidates, code, code2, fnname, t,
           NULL_TREE, args, argtypes, flags);
    }

  release_tree_vector (types[0]);
  release_tree_vector (types[1]);
}


/* If TMPL can be successfully instantiated as indicated by
   EXPLICIT_TARGS and ARGLIST, adds the instantiation to CANDIDATES.

   TMPL is the template.  EXPLICIT_TARGS are any explicit template
   arguments.  ARGLIST is the arguments provided at the call-site.
   This does not change ARGLIST.  The RETURN_TYPE is the desired type
   for conversion operators.  If OBJ is NULL_TREE, FLAGS and CTYPE are
   as for add_function_candidate.  If an OBJ is supplied, FLAGS and
   CTYPE are ignored, and OBJ is as for add_conv_candidate.  */

static struct z_candidate*
add_template_candidate_real (struct z_candidate **candidates, tree tmpl,
                             tree ctype, tree explicit_targs, tree first_arg,
                             const VEC(tree,gc) *arglist, tree return_type,
                             tree access_path, tree conversion_path,
                             int flags, tree obj, unification_kind_t strict)
{
  int ntparms = DECL_NTPARMS (tmpl);
  tree targs = make_tree_vec (ntparms);
  unsigned int len = VEC_length (tree, arglist);
  unsigned int nargs = (first_arg == NULL_TREE ? 0 : 1) + len;
  unsigned int skip_without_in_chrg = 0;
  tree first_arg_without_in_chrg = first_arg;
  tree *args_without_in_chrg;
  unsigned int nargs_without_in_chrg;
  unsigned int ia, ix;
  tree arg;
  struct z_candidate *cand;
  int i;
  tree fn;
  struct rejection_reason *reason = NULL;
  int errs;

  /* We don't do deduction on the in-charge parameter, the VTT
     parameter or 'this'.  */
  if (DECL_NONSTATIC_MEMBER_FUNCTION_P (tmpl))
    {
      if (first_arg_without_in_chrg != NULL_TREE)
        first_arg_without_in_chrg = NULL_TREE;
      else
        ++skip_without_in_chrg;
    }

  if ((DECL_MAYBE_IN_CHARGE_CONSTRUCTOR_P (tmpl)
       || DECL_BASE_CONSTRUCTOR_P (tmpl))
      && CLASSTYPE_VBASECLASSES (DECL_CONTEXT (tmpl)))
    {
      if (first_arg_without_in_chrg != NULL_TREE)
        first_arg_without_in_chrg = NULL_TREE;
      else
        ++skip_without_in_chrg;
    }

  if (len < skip_without_in_chrg)
    return NULL;

  nargs_without_in_chrg = ((first_arg_without_in_chrg != NULL_TREE ? 1 : 0)
                           + (len - skip_without_in_chrg));
  args_without_in_chrg = XALLOCAVEC (tree, nargs_without_in_chrg);
  ia = 0;
  if (first_arg_without_in_chrg != NULL_TREE)
    {
      args_without_in_chrg[ia] = first_arg_without_in_chrg;
      ++ia;
    }
  for (ix = skip_without_in_chrg;
       VEC_iterate (tree, arglist, ix, arg);
       ++ix)
    {
      args_without_in_chrg[ia] = arg;
      ++ia;
    }
  gcc_assert (ia == nargs_without_in_chrg);

  errs = errorcount+sorrycount;
  i = fn_type_unification (tmpl, explicit_targs, targs,
                           args_without_in_chrg,
                           nargs_without_in_chrg,
                           return_type, strict, flags, false);

  if (i != 0)
    {
      /* Don't repeat unification later if it already resulted in errors.  */
      if (errorcount+sorrycount == errs)
        reason = template_unification_rejection (tmpl, explicit_targs,
                                                 targs, args_without_in_chrg,
                                                 nargs_without_in_chrg,
                                                 return_type, strict, flags);
      else
        reason = template_unification_error_rejection ();
      goto fail;
    }

  fn = instantiate_template (tmpl, targs, tf_none);
  if (fn == error_mark_node)
    {
      reason = template_instantiation_rejection (tmpl, targs);
      goto fail;
    }

  /* In [class.copy]:

       A member function template is never instantiated to perform the
       copy of a class object to an object of its class type.

     It's a little unclear what this means; the standard explicitly
     does allow a template to be used to copy a class.  For example,
     in:

       struct A {
         A(A&);
         template <class T> A(const T&);
       };
       const A f ();
       void g () { A a (f ()); }

     the member template will be used to make the copy.  The section
     quoted above appears in the paragraph that forbids constructors
     whose only parameter is (a possibly cv-qualified variant of) the
     class type, and a logical interpretation is that the intent was
     to forbid the instantiation of member templates which would then
     have that form.  */
  if (DECL_CONSTRUCTOR_P (fn) && nargs == 2)
    {
      tree arg_types = FUNCTION_FIRST_USER_PARMTYPE (fn);
      if (arg_types && same_type_p (TYPE_MAIN_VARIANT (TREE_VALUE (arg_types)),
                                    ctype))
        {
          reason = invalid_copy_with_fn_template_rejection ();
          goto fail;
        }
    }

  if (obj != NULL_TREE)
    /* Aha, this is a conversion function.  */
    cand = add_conv_candidate (candidates, fn, obj, first_arg, arglist,
                               access_path, conversion_path);
  else
    cand = add_function_candidate (candidates, fn, ctype,
                                   first_arg, arglist, access_path,
                                   conversion_path, flags);
  if (DECL_TI_TEMPLATE (fn) != tmpl)
    /* This situation can occur if a member template of a template
       class is specialized.  Then, instantiate_template might return
       an instantiation of the specialization, in which case the
       DECL_TI_TEMPLATE field will point at the original
       specialization.  For example:

         template <class T> struct S { template <class U> void f(U);
                                       template <> void f(int) {}; };
         S<double> sd;
         sd.f(3);

       Here, TMPL will be template <class U> S<double>::f(U).
       And, instantiate template will give us the specialization
       template <> S<double>::f(int).  But, the DECL_TI_TEMPLATE field
       for this will point at template <class T> template <> S<T>::f(int),
       so that we can find the definition.  For the purposes of
       overload resolution, however, we want the original TMPL.  */
    cand->template_decl = build_template_info (tmpl, targs);
  else
    cand->template_decl = DECL_TEMPLATE_INFO (fn);
  cand->explicit_targs = explicit_targs;

  return cand;
 fail:
  return add_candidate (candidates, tmpl, first_arg, arglist, nargs, NULL,
                        access_path, conversion_path, 0, reason);
}


static struct z_candidate *
add_template_candidate (struct z_candidate **candidates, tree tmpl, tree ctype,
                        tree explicit_targs, tree first_arg,
                        const VEC(tree,gc) *arglist, tree return_type,
                        tree access_path, tree conversion_path, int flags,
                        unification_kind_t strict)
{
  return
    add_template_candidate_real (candidates, tmpl, ctype,
                                 explicit_targs, first_arg, arglist,
                                 return_type, access_path, conversion_path,
                                 flags, NULL_TREE, strict);
}


static struct z_candidate *
add_template_conv_candidate (struct z_candidate **candidates, tree tmpl,
                             tree obj, tree first_arg,
                             const VEC(tree,gc) *arglist,
                             tree return_type, tree access_path,
                             tree conversion_path)
{
  return
    add_template_candidate_real (candidates, tmpl, NULL_TREE, NULL_TREE,
                                 first_arg, arglist, return_type, access_path,
                                 conversion_path, 0, obj, DEDUCE_CONV);
}

/* The CANDS are the set of candidates that were considered for
   overload resolution.  Return the set of viable candidates, or CANDS
   if none are viable.  If any of the candidates were viable, set
   *ANY_VIABLE_P to true.  STRICT_P is true if a candidate should be
   considered viable only if it is strictly viable.  */

static struct z_candidate*
splice_viable (struct z_candidate *cands,
               bool strict_p,
               bool *any_viable_p)
{
  struct z_candidate *viable;
  struct z_candidate **last_viable;
  struct z_candidate **cand;

  /* Be strict inside templates, since build_over_call won't actually
     do the conversions to get pedwarns.  */
  if (processing_template_decl)
    strict_p = true;

  viable = NULL;
  last_viable = &viable;
  *any_viable_p = false;

  cand = &cands;
  while (*cand)
    {
      struct z_candidate *c = *cand;
      if (strict_p ? c->viable == 1 : c->viable)
        {
          *last_viable = c;
          *cand = c->next;
          c->next = NULL;
          last_viable = &c->next;
          *any_viable_p = true;
        }
      else
        cand = &c->next;
    }

  return viable ? viable : cands;
}

static bool
any_strictly_viable (struct z_candidate *cands)
{
  for (; cands; cands = cands->next)
    if (cands->viable == 1)
      return true;
  return false;
}

/* OBJ is being used in an expression like "OBJ.f (...)".  In other
   words, it is about to become the "this" pointer for a member
   function call.  Take the address of the object.  */

static tree
build_this (tree obj)
{
  /* In a template, we are only concerned about the type of the
     expression, so we can take a shortcut.  */
  if (processing_template_decl)
    return build_address (obj);

  return cp_build_addr_expr (obj, tf_warning_or_error);
}

/* Returns true iff functions are equivalent. Equivalent functions are
   not '==' only if one is a function-local extern function or if
   both are extern "C".  */

static inline int
equal_functions (tree fn1, tree fn2)
{
  if (TREE_CODE (fn1) != TREE_CODE (fn2))
    return 0;
  if (TREE_CODE (fn1) == TEMPLATE_DECL)
    return fn1 == fn2;
  if (DECL_LOCAL_FUNCTION_P (fn1) || DECL_LOCAL_FUNCTION_P (fn2)
      || DECL_EXTERN_C_FUNCTION_P (fn1))
    return decls_match (fn1, fn2);
  return fn1 == fn2;
}

/* Print information about a candidate being rejected due to INFO.  */

static void
print_conversion_rejection (location_t loc, struct conversion_info *info)
{
  if (info->n_arg == -1)
    /* Conversion of implicit `this' argument failed.  */
    inform (loc, "  no known conversion for implicit "
            "%<this%> parameter from %qT to %qT",
            info->from_type, info->to_type);
  else
    inform (loc, "  no known conversion for argument %d from %qT to %qT",
            info->n_arg+1, info->from_type, info->to_type);
}

/* Print information about a candidate with WANT parameters and we found
   HAVE.  */

static void
print_arity_information (location_t loc, unsigned int have, unsigned int want)
{
  inform_n (loc, want,
            "  candidate expects %d argument, %d provided",
            "  candidate expects %d arguments, %d provided",
            want, have);
}

/* Print information about one overload candidate CANDIDATE.  MSGSTR
   is the text to print before the candidate itself.

   NOTE: Unlike most diagnostic functions in GCC, MSGSTR is expected
   to have been run through gettext by the caller.  This wart makes
   life simpler in print_z_candidates and for the translators.  */

static void
print_z_candidate (const char *msgstr, struct z_candidate *candidate)
{
  const char *msg = (msgstr == NULL
                     ? ""
                     : ACONCAT ((msgstr, " ", NULL)));
  location_t loc = location_of (candidate->fn);

  if (TREE_CODE (candidate->fn) == IDENTIFIER_NODE)
    {
      if (candidate->num_convs == 3)
        inform (input_location, "%s%D(%T, %T, %T) <built-in>", msg, candidate->fn,
                candidate->convs[0]->type,
                candidate->convs[1]->type,
                candidate->convs[2]->type);
      else if (candidate->num_convs == 2)
        inform (input_location, "%s%D(%T, %T) <built-in>", msg, candidate->fn,
                candidate->convs[0]->type,
                candidate->convs[1]->type);
      else
        inform (input_location, "%s%D(%T) <built-in>", msg, candidate->fn,
                candidate->convs[0]->type);
    }
  else if (TYPE_P (candidate->fn))
    inform (input_location, "%s%T <conversion>", msg, candidate->fn);
  else if (candidate->viable == -1)
    inform (loc, "%s%#D <near match>", msg, candidate->fn);
  else if (DECL_DELETED_FN (STRIP_TEMPLATE (candidate->fn)))
    inform (loc, "%s%#D <deleted>", msg, candidate->fn);
  else
    inform (loc, "%s%#D", msg, candidate->fn);
  /* Give the user some information about why this candidate failed.  */
  if (candidate->reason != NULL)
    {
      struct rejection_reason *r = candidate->reason;

      switch (r->code)
        {
        case rr_arity:
          print_arity_information (loc, r->u.arity.actual,
                                   r->u.arity.expected);
          break;
        case rr_arg_conversion:
          print_conversion_rejection (loc, &r->u.conversion);
          break;
        case rr_bad_arg_conversion:
          print_conversion_rejection (loc, &r->u.bad_conversion);
          break;
        case rr_explicit_conversion:
          inform (loc, "  return type %qT of explicit conversion function "
                  "cannot be converted to %qT with a qualification "
                  "conversion", r->u.conversion.from_type,
                  r->u.conversion.to_type);
          break;
        case rr_template_conversion:
          inform (loc, "  conversion from return type %qT of template "
                  "conversion function specialization to %qT is not an "
                  "exact match", r->u.conversion.from_type,
                  r->u.conversion.to_type);
          break;
        case rr_template_unification:
          /* We use template_unification_error_rejection if unification caused
             actual non-SFINAE errors, in which case we don't need to repeat
             them here.  */
          if (r->u.template_unification.tmpl == NULL_TREE)
            {
              inform (loc, "  substitution of deduced template arguments "
                      "resulted in errors seen above");
              break;
            }
          /* Re-run template unification with diagnostics.  */
          inform (loc, "  template argument deduction/substitution failed:");
          fn_type_unification (r->u.template_unification.tmpl,
                               r->u.template_unification.explicit_targs,
                               r->u.template_unification.targs,
                               r->u.template_unification.args,
                               r->u.template_unification.nargs,
                               r->u.template_unification.return_type,
                               r->u.template_unification.strict,
                               r->u.template_unification.flags,
                               true);
          break;
        case rr_template_instantiation:
          /* Re-run template instantiation with diagnostics.  */
          instantiate_template (r->u.template_instantiation.tmpl,
                                r->u.template_instantiation.targs,
                                tf_warning_or_error);
          break;
        case rr_invalid_copy:
          inform (loc,
                  "  a constructor taking a single argument of its own "
                  "class type is invalid");
          break;
        case rr_none:
        default:
          /* This candidate didn't have any issues or we failed to
             handle a particular code.  Either way...  */
          gcc_unreachable ();
        }
    }
}

static void
print_z_candidates (location_t loc, struct z_candidate *candidates)
{
  struct z_candidate *cand1;
  struct z_candidate **cand2;
  int n_candidates;

  if (!candidates)
    return;

  /* Remove non-viable deleted candidates.  */
  cand1 = candidates;
  for (cand2 = &cand1; *cand2; )
    {
      if (TREE_CODE ((*cand2)->fn) == FUNCTION_DECL
          && !(*cand2)->viable
          && DECL_DELETED_FN ((*cand2)->fn))
        *cand2 = (*cand2)->next;
      else
        cand2 = &(*cand2)->next;
    }
  /* ...if there are any non-deleted ones.  */
  if (cand1)
    candidates = cand1;

  /* There may be duplicates in the set of candidates.  We put off
     checking this condition as long as possible, since we have no way
     to eliminate duplicates from a set of functions in less than n^2
     time.  Now we are about to emit an error message, so it is more
     permissible to go slowly.  */
  for (cand1 = candidates; cand1; cand1 = cand1->next)
    {
      tree fn = cand1->fn;
      /* Skip builtin candidates and conversion functions.  */
      if (!DECL_P (fn))
        continue;
      cand2 = &cand1->next;
      while (*cand2)
        {
          if (DECL_P ((*cand2)->fn)
              && equal_functions (fn, (*cand2)->fn))
            *cand2 = (*cand2)->next;
          else
            cand2 = &(*cand2)->next;
        }
    }

  for (n_candidates = 0, cand1 = candidates; cand1; cand1 = cand1->next)
    n_candidates++;

  inform_n (loc, n_candidates, "candidate is:", "candidates are:");
  for (; candidates; candidates = candidates->next)
    print_z_candidate (NULL, candidates);
}

/* USER_SEQ is a user-defined conversion sequence, beginning with a
   USER_CONV.  STD_SEQ is the standard conversion sequence applied to
   the result of the conversion function to convert it to the final
   desired type.  Merge the two sequences into a single sequence,
   and return the merged sequence.  */

static conversion *
merge_conversion_sequences (conversion *user_seq, conversion *std_seq)
{
  conversion **t;
  bool bad = user_seq->bad_p;

  gcc_assert (user_seq->kind == ck_user);

  /* Find the end of the second conversion sequence.  */
  for (t = &std_seq; (*t)->kind != ck_identity; t = &((*t)->u.next))
    {
      /* The entire sequence is a user-conversion sequence.  */
      (*t)->user_conv_p = true;
      if (bad)
        (*t)->bad_p = true;
    }

  /* Replace the identity conversion with the user conversion
     sequence.  */
  *t = user_seq;

  return std_seq;
}

/* Handle overload resolution for initializing an object of class type from
   an initializer list.  First we look for a suitable constructor that
   takes a std::initializer_list; if we don't find one, we then look for a
   non-list constructor.

   Parameters are as for add_candidates, except that the arguments are in
   the form of a CONSTRUCTOR (the initializer list) rather than a VEC, and
   the RETURN_TYPE parameter is replaced by TOTYPE, the desired type.  */

static void
add_list_candidates (tree fns, tree first_arg,
                     tree init_list, tree totype,
                     tree explicit_targs, bool template_only,
                     tree conversion_path, tree access_path,
                     int flags,
                     struct z_candidate **candidates)
{
  VEC(tree,gc) *args;

  gcc_assert (*candidates == NULL);

  /* We're looking for a ctor for list-initialization.  */
  flags |= LOOKUP_LIST_INIT_CTOR;
  /* And we don't allow narrowing conversions.  We also use this flag to
     avoid the copy constructor call for copy-list-initialization.  */
  flags |= LOOKUP_NO_NARROWING;

  /* Always use the default constructor if the list is empty (DR 990).  */
  if (CONSTRUCTOR_NELTS (init_list) == 0
      && TYPE_HAS_DEFAULT_CONSTRUCTOR (totype))
    ;
  /* If the class has a list ctor, try passing the list as a single
     argument first, but only consider list ctors.  */
  else if (TYPE_HAS_LIST_CTOR (totype))
    {
      flags |= LOOKUP_LIST_ONLY;
      args = make_tree_vector_single (init_list);
      add_candidates (fns, first_arg, args, NULL_TREE,
                      explicit_targs, template_only, conversion_path,
                      access_path, flags, candidates);
      if (any_strictly_viable (*candidates))
        return;
    }

  args = ctor_to_vec (init_list);

  /* We aren't looking for list-ctors anymore.  */
  flags &= ~LOOKUP_LIST_ONLY;
  /* We allow more user-defined conversions within an init-list.  */
  flags &= ~LOOKUP_NO_CONVERSION;

  add_candidates (fns, first_arg, args, NULL_TREE,
                  explicit_targs, template_only, conversion_path,
                  access_path, flags, candidates);
}

/* Returns the best overload candidate to perform the requested
   conversion.  This function is used for three the overloading situations
   described in [over.match.copy], [over.match.conv], and [over.match.ref].
   If TOTYPE is a REFERENCE_TYPE, we're trying to find a direct binding as
   per [dcl.init.ref], so we ignore temporary bindings.  */

static struct z_candidate *
build_user_type_conversion_1 (tree totype, tree expr, int flags)
{
  struct z_candidate *candidates, *cand;
  tree fromtype;
  tree ctors = NULL_TREE;
  tree conv_fns = NULL_TREE;
  conversion *conv = NULL;
  tree first_arg = NULL_TREE;
  VEC(tree,gc) *args = NULL;
  bool any_viable_p;
  int convflags;

  if (!expr)
    return NULL;

  fromtype = TREE_TYPE (expr);

  /* We represent conversion within a hierarchy using RVALUE_CONV and
     BASE_CONV, as specified by [over.best.ics]; these become plain
     constructor calls, as specified in [dcl.init].  */
  gcc_assert (!MAYBE_CLASS_TYPE_P (fromtype) || !MAYBE_CLASS_TYPE_P (totype)
              || !DERIVED_FROM_P (totype, fromtype));

  if (MAYBE_CLASS_TYPE_P (totype))
    /* Use lookup_fnfields_slot instead of lookup_fnfields to avoid
       creating a garbage BASELINK; constructors can't be inherited.  */
    ctors = lookup_fnfields_slot (totype, complete_ctor_identifier);

  if (MAYBE_CLASS_TYPE_P (fromtype))
    {
      tree to_nonref = non_reference (totype);
      if (same_type_ignoring_top_level_qualifiers_p (to_nonref, fromtype) ||
          (CLASS_TYPE_P (to_nonref) && CLASS_TYPE_P (fromtype)
           && DERIVED_FROM_P (to_nonref, fromtype)))
        {
          /* [class.conv.fct] A conversion function is never used to
             convert a (possibly cv-qualified) object to the (possibly
             cv-qualified) same object type (or a reference to it), to a
             (possibly cv-qualified) base class of that type (or a
             reference to it)...  */
        }
      else
        conv_fns = lookup_conversions (fromtype);
    }

  candidates = 0;
  flags |= LOOKUP_NO_CONVERSION;
  if (BRACE_ENCLOSED_INITIALIZER_P (expr))
    flags |= LOOKUP_NO_NARROWING;

  /* It's OK to bind a temporary for converting constructor arguments, but
     not in converting the return value of a conversion operator.  */
  convflags = ((flags & LOOKUP_NO_TEMP_BIND) | LOOKUP_NO_CONVERSION);
  flags &= ~LOOKUP_NO_TEMP_BIND;

  if (ctors)
    {
      int ctorflags = flags;

      first_arg = build_int_cst (build_pointer_type (totype), 0);

      /* We should never try to call the abstract or base constructor
         from here.  */
      gcc_assert (!DECL_HAS_IN_CHARGE_PARM_P (OVL_CURRENT (ctors))
                  && !DECL_HAS_VTT_PARM_P (OVL_CURRENT (ctors)));

      if (BRACE_ENCLOSED_INITIALIZER_P (expr))
        {
          /* List-initialization.  */
          add_list_candidates (ctors, first_arg, expr, totype, NULL_TREE,
                               false, TYPE_BINFO (totype), TYPE_BINFO (totype),
                               ctorflags, &candidates);
        }
      else
        {
          args = make_tree_vector_single (expr);
          add_candidates (ctors, first_arg, args, NULL_TREE, NULL_TREE, false,
                          TYPE_BINFO (totype), TYPE_BINFO (totype),
                          ctorflags, &candidates);
        }

      for (cand = candidates; cand; cand = cand->next)
        {
          cand->second_conv = build_identity_conv (totype, NULL_TREE);

          /* If totype isn't a reference, and LOOKUP_NO_TEMP_BIND isn't
             set, then this is copy-initialization.  In that case, "The
             result of the call is then used to direct-initialize the
             object that is the destination of the copy-initialization."
             [dcl.init]

             We represent this in the conversion sequence with an
             rvalue conversion, which means a constructor call.  */
          if (TREE_CODE (totype) != REFERENCE_TYPE
              && !(convflags & LOOKUP_NO_TEMP_BIND))
            cand->second_conv
              = build_conv (ck_rvalue, totype, cand->second_conv);
        }
    }

  if (conv_fns)
    first_arg = build_this (expr);

  for (; conv_fns; conv_fns = TREE_CHAIN (conv_fns))
    {
      tree conversion_path = TREE_PURPOSE (conv_fns);
      struct z_candidate *old_candidates;

      /* If we are called to convert to a reference type, we are trying to
         find a direct binding, so don't even consider temporaries.  If
         we don't find a direct binding, the caller will try again to
         look for a temporary binding.  */
      if (TREE_CODE (totype) == REFERENCE_TYPE)
        convflags |= LOOKUP_NO_TEMP_BIND;

      old_candidates = candidates;
      add_candidates (TREE_VALUE (conv_fns), first_arg, NULL, totype,
                      NULL_TREE, false,
                      conversion_path, TYPE_BINFO (fromtype),
                      flags, &candidates);

      for (cand = candidates; cand != old_candidates; cand = cand->next)
        {
          tree rettype = TREE_TYPE (TREE_TYPE (cand->fn));
          conversion *ics
            = implicit_conversion (totype,
                                   rettype,
                                   0,
                                   /*c_cast_p=*/false, convflags);

          /* If LOOKUP_NO_TEMP_BIND isn't set, then this is
             copy-initialization.  In that case, "The result of the
             call is then used to direct-initialize the object that is
             the destination of the copy-initialization."  [dcl.init]

             We represent this in the conversion sequence with an
             rvalue conversion, which means a constructor call.  But
             don't add a second rvalue conversion if there's already
             one there.  Which there really shouldn't be, but it's
             harmless since we'd add it here anyway. */
          if (ics && MAYBE_CLASS_TYPE_P (totype) && ics->kind != ck_rvalue
              && !(convflags & LOOKUP_NO_TEMP_BIND))
            ics = build_conv (ck_rvalue, totype, ics);

          cand->second_conv = ics;

          if (!ics)
            {
              cand->viable = 0;
              cand->reason = arg_conversion_rejection (NULL_TREE, -1,
                                                       rettype, totype);