Re: C++ PATCH to implement deferred parsing of noexcept-specifiers (c++/86476, c++/52869)

[Marek Polacek <polacek@redhat.com>]

Ping.

On Fri, May 10, 2019 at 03:21:33PM -0400, Marek Polacek wrote:
> Coming back to this.  I didn't think this was suitable for GCC 9.
> 
> On Mon, Jan 07, 2019 at 10:44:37AM -0500, Jason Merrill wrote:
> > On 12/19/18 3:27 PM, Marek Polacek wrote:
> > > Prompted by Jon's observation in 52869, I noticed that we don't treat
> > > a noexcept-specifier as a complete-class context of a class ([class.mem]/6).
> > > As with member function bodies, default arguments, and NSDMIs, names used in
> > > a noexcept-specifier of a member-function can be declared later in the class
> > > body, so we need to wait and parse them at the end of the class.
> > > For that, I've made use of DEFAULT_ARG (now best to be renamed to UNPARSED_ARG).
> > 
> > Or DEFERRED_PARSE, yes.
> 
> I didn't change the name but I'm happy to do it as a follow up.
> 
> > > +  /* We can't compare unparsed noexcept-specifiers.  Save the old decl
> > > +     and check this again after we've parsed the noexcept-specifiers
> > > +     for real.  */
> > > +  if (UNPARSED_NOEXCEPT_SPEC_P (new_exceptions))
> > > +    {
> > > +      vec_safe_push (DEFARG_INSTANTIATIONS (TREE_PURPOSE (new_exceptions)),
> > > +		     copy_decl (old_decl));
> > > +      return;
> > > +    }
> > 
> > Why copy_decl?
> 
> This is so that we don't lose the diagnostic in noexcept46.C.  If I don't use
> copy_decl then the tree is shared and subsequent changes to it make us not
> detect discrepancies like noexcept(false) vs. noexcept(true) on the same decl.
> 
> > It seems wasteful to allocate a vec to hold this single decl; let's make the
> > last field of tree_default_arg a union instead.  And add a new macro for the
> > single decl case.
> 
> Done.  But that required also adding GTY markers *and* a new BOOL_BITFIELD for
> the sake of GTY((desc)).
> 
> > I notice that default_arg currently uses tree_common for some reason, and we
> > ought to be able to save two words by switching to tree_base
> 
> Done.
> 
> > > @@ -1245,6 +1245,7 @@ nothrow_spec_p (const_tree spec)
> > >   	      || TREE_VALUE (spec)
> > >   	      || spec == noexcept_false_spec
> > >   	      || TREE_PURPOSE (spec) == error_mark_node
> > > +	      || TREE_CODE (TREE_PURPOSE (spec)) == DEFAULT_ARG
> > 
> > Maybe use UNPARSED_NOEXCEPT_SPEC_P here?
>  
> Done.
> 
> > > +/* Make sure that any member-function parameters are in scope.
> > > +   For instance, a function's noexcept-specifier can use the function's
> > > +   parameters:
> > > +
> > > +   struct S {
> > > +     void fn (int p) noexcept(noexcept(p));
> > > +   };
> > > +
> > > +   so we need to make sure name lookup can find them.  This is used
> > > +   when we delay parsing of the noexcept-specifier.  */
> > > +
> > > +static void
> > > +maybe_begin_member_function_processing (tree decl)
> > 
> > This name is pretty misleading.  How about inject_parm_decls, to go with
> > inject_this_parameter?
> 
> Done.
> 
> > > +/* Undo the effects of maybe_begin_member_function_processing.  */
> > > +
> > > +static void
> > > +maybe_end_member_function_processing (void)
> > 
> > And then perhaps pop_injected_parms.
> 
> Done.
> 
> > > +/* Check throw specifier of OVERRIDER is at least as strict as
> > > +   the one of BASEFN.  */
> > > +
> > > +bool
> > > +maybe_check_throw_specifier (tree overrider, tree basefn)
> > > +{
> > > +  maybe_instantiate_noexcept (basefn);
> > > +  maybe_instantiate_noexcept (overrider);
> > > +  tree base_throw = TYPE_RAISES_EXCEPTIONS (TREE_TYPE (basefn));
> > > +  tree over_throw = TYPE_RAISES_EXCEPTIONS (TREE_TYPE (overrider));
> > > +
> > > +  if (DECL_INVALID_OVERRIDER_P (overrider))
> > > +    return true;
> > > +
> > > +  /* Can't check this yet.  Pretend this is fine and let
> > > +     noexcept_override_late_checks check this later.  */
> > > +  if (UNPARSED_NOEXCEPT_SPEC_P (base_throw)
> > > +      || UNPARSED_NOEXCEPT_SPEC_P (over_throw))
> > > +    return true;
> > > +
> > > +  if (!comp_except_specs (base_throw, over_throw, ce_derived))
> > > +    {
> > > +      auto_diagnostic_group d;
> > > +      error ("looser throw specifier for %q+#F", overrider);
> > 
> > Since we're touching this diagnostic, let's correct it now to "exception
> > specification".  And add "on overriding virtual function".
> 
> Ok, changed to the more up-to-date term.
> 
> Two further changes were required since my changes to detecting 'this' for
> static member functions:
> 1) use THIS_FORBIDDEN if needed when parsing the delayed noexcept,
> 2) careful about friend member functions -- its DECL_CONTEXT is not the
>   containing class, need to use DECL_FRIEND_CONTEXT.
> 
> Both of these points are tested in g++.dg/cpp0x/this1.C.
> 
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
> 
> 2019-05-10  Marek Polacek  <polacek@redhat.com>
> 
> 	PR c++/86476 - noexcept-specifier is a complete-class context.
> 	PR c++/52869
> 	* cp-tree.def (DEFAULT_ARG): Update commentary.
> 	* cp-tree.h (DEFARG_DECL, DEFARG_NOEXCEPT_P, UNPARSED_NOEXCEPT_SPEC_P):
> 	New macros.
> 	(tree_default_arg): Add a tree field, make the last two fields into a
> 	union.  Add GTY markers.
> 	(check_redeclaration_exception_specification): Declare.
> 	(maybe_check_throw_specifier): Declare.
> 	* decl.c (check_redeclaration_exception_specification): No longer
> 	static.  Handle UNPARSED_NOEXCEPT_SPEC_P.
> 	* except.c (nothrow_spec_p): Accept DEFAULT_ARG in the assert.
> 	* parser.c (cp_parser_noexcept_specification_opt,
> 	cp_parser_late_noexcept_specifier, noexcept_override_late_checks):
> 	Forward-declare.
> 	(unparsed_noexcepts): New macro.
> 	(push_unparsed_function_queues): Update initializer.
> 	(cp_parser_init_declarator): Maybe save the noexcept-specifier to
> 	post process.
> 	(inject_parm_decls): New.
> 	(pop_injected_parms): New.
> 	(cp_parser_class_specifier_1): Implement delayed parsing of
> 	noexcept-specifiers.
> 	(cp_parser_member_declaration): Maybe save the noexcept-specifier to
> 	post process.
> 	(cp_parser_save_noexcept): New.
> 	(cp_parser_late_noexcept_specifier): New.
> 	(noexcept_override_late_checks): New.
> 	(cp_parser_noexcept_specification_opt): Call cp_parser_save_noexcept
> 	instead of the normal processing if needed.
> 	(cp_parser_save_member_function_body): Maybe save the
> 	noexcept-specifier to post process.
> 	* parser.h (cp_unparsed_functions_entry): Add new field to carry
> 	a noexcept-specifier.
> 	* pt.c (dependent_type_p_r): Handle unparsed noexcept expression.
> 	* search.c (maybe_check_throw_specifier): New function, broken out
> 	of...
> 	(check_final_overrider): ...here.  Call maybe_check_throw_specifier.
> 	* tree.c (canonical_eh_spec): Handle UNPARSED_NOEXCEPT_SPEC_P.
> 	(cp_tree_equal): Handle DEFAULT_ARG.
> 	* typeck2.c (merge_exception_specifiers): If an unparsed noexcept
> 	expression has been passed, return it instead of merging it.
> 
> 	* g++.dg/cpp0x/noexcept41.C: New test.
> 	* g++.dg/cpp0x/noexcept42.C: New test.
> 	* g++.dg/cpp0x/noexcept43.C: New test.
> 	* g++.dg/cpp0x/noexcept44.C: New test.
> 	* g++.dg/cpp0x/noexcept45.C: New test.
> 	* g++.dg/cpp0x/noexcept46.C: New test.
> 	* g++.dg/eh/shadow1.C: Adjust dg-error.
> 
> diff --git gcc/cp/cp-tree.def gcc/cp/cp-tree.def
> index 03c105b5c4c..33eb5d25efe 100644
> --- gcc/cp/cp-tree.def
> +++ gcc/cp/cp-tree.def
> @@ -209,7 +209,9 @@ DEFTREECODE (USING_STMT, "using_stmt", tcc_statement, 1)
>  
>  /* An un-parsed default argument.  Holds a vector of input tokens and
>     a vector of places where the argument was instantiated before
> -   parsing had occurred.  */
> +   parsing had occurred.  This is also used for delayed NSDMIs and
> +   noexcept-specifier parsing.  For a noexcept-specifier, we use a tree
> +   holding a function declaration used for late checking.  */
>  DEFTREECODE (DEFAULT_ARG, "default_arg", tcc_exceptional, 0)
>  
>  /* An uninstantiated/unevaluated noexcept-specification.  For the
> diff --git gcc/cp/cp-tree.h gcc/cp/cp-tree.h
> index f253857b02a..ef14a011293 100644
> --- gcc/cp/cp-tree.h
> +++ gcc/cp/cp-tree.h
> @@ -1178,12 +1178,20 @@ enum cp_identifier_kind {
>  #define DEFARG_TOKENS(NODE) \
>    (((struct tree_default_arg *)DEFAULT_ARG_CHECK (NODE))->tokens)
>  #define DEFARG_INSTANTIATIONS(NODE) \
> -  (((struct tree_default_arg *)DEFAULT_ARG_CHECK (NODE))->instantiations)
> +  (((struct tree_default_arg *)DEFAULT_ARG_CHECK (NODE))->u.instantiations)
> +#define DEFARG_DECL(NODE) \
> +  (((struct tree_default_arg *)DEFAULT_ARG_CHECK (NODE))->u.decl)
> +#define DEFARG_NOEXCEPT_P(NODE) \
> +  (((struct tree_default_arg *)DEFAULT_ARG_CHECK (NODE))->noexcept_p)
>  
>  struct GTY (()) tree_default_arg {
> -  struct tree_common common;
> +  struct tree_base base;
>    struct cp_token_cache *tokens;
> -  vec<tree, va_gc> *instantiations;
> +  BOOL_BITFIELD noexcept_p : 1;
> +  union {
> +    vec<tree, va_gc>* GTY((tag ("0"))) instantiations;
> +    tree GTY((tag ("1"))) decl;
> +  } GTY((desc ("%1.noexcept_p"))) u;
>  };
>  
>  
> @@ -1197,6 +1205,9 @@ struct GTY (()) tree_default_arg {
>  #define UNEVALUATED_NOEXCEPT_SPEC_P(NODE)				\
>    (DEFERRED_NOEXCEPT_SPEC_P (NODE)					\
>     && DEFERRED_NOEXCEPT_PATTERN (TREE_PURPOSE (NODE)) == NULL_TREE)
> +#define UNPARSED_NOEXCEPT_SPEC_P(NODE) \
> +  ((NODE) && (TREE_PURPOSE (NODE)) \
> +   && (TREE_CODE (TREE_PURPOSE (NODE)) == DEFAULT_ARG))
>  
>  struct GTY (()) tree_deferred_noexcept {
>    struct tree_base base;
> @@ -6464,6 +6475,8 @@ extern bool check_array_designated_initializer  (constructor_elt *,
>  						 unsigned HOST_WIDE_INT);
>  extern bool check_for_uninitialized_const_var   (tree, bool, tsubst_flags_t);
>  extern tree build_explicit_specifier		(tree, tsubst_flags_t);
> +extern void check_redeclaration_exception_specification
> +  (tree, tree);
>  
>  /* in decl2.c */
>  extern void record_mangling			(tree, bool);
> @@ -6929,6 +6942,7 @@ extern tree copied_binfo			(tree, tree);
>  extern tree original_binfo			(tree, tree);
>  extern int shared_member_p			(tree);
>  extern bool any_dependent_bases_p (tree = current_nonlambda_class_type ());
> +extern bool maybe_check_throw_specifier		(tree, tree);
>  
>  /* The representation of a deferred access check.  */
>  
> diff --git gcc/cp/decl.c gcc/cp/decl.c
> index 36014dc628e..a2effa13623 100644
> --- gcc/cp/decl.c
> +++ gcc/cp/decl.c
> @@ -1139,7 +1139,7 @@ warn_extern_redeclared_static (tree newdecl, tree olddecl)
>     function templates.  If their exception specifications do not
>     match, issue a diagnostic.  */
>  
> -static void
> +void
>  check_redeclaration_exception_specification (tree new_decl,
>  					     tree old_decl)
>  {
> @@ -1151,6 +1151,15 @@ check_redeclaration_exception_specification (tree new_decl,
>        && UNEVALUATED_NOEXCEPT_SPEC_P (old_exceptions))
>      return;
>  
> +  /* We can't compare unparsed noexcept-specifiers.  Save the old decl
> +     and check this again after we've parsed the noexcept-specifiers
> +     for real.  */
> +  if (UNPARSED_NOEXCEPT_SPEC_P (new_exceptions))
> +    {
> +      DEFARG_DECL (TREE_PURPOSE (new_exceptions)) = copy_decl (old_decl);
> +      return;
> +    }
> +
>    if (!type_dependent_expression_p (old_decl))
>      {
>        maybe_instantiate_noexcept (new_decl);
> diff --git gcc/cp/except.c gcc/cp/except.c
> index afc261073d7..208c9c1461d 100644
> --- gcc/cp/except.c
> +++ gcc/cp/except.c
> @@ -1248,6 +1248,7 @@ nothrow_spec_p (const_tree spec)
>  	      || TREE_VALUE (spec)
>  	      || spec == noexcept_false_spec
>  	      || TREE_PURPOSE (spec) == error_mark_node
> +	      || UNPARSED_NOEXCEPT_SPEC_P (spec)
>  	      || processing_template_decl);
>  
>    return false;
> diff --git gcc/cp/parser.c gcc/cp/parser.c
> index 12beadf5096..41197ab3486 100644
> --- gcc/cp/parser.c
> +++ gcc/cp/parser.c
> @@ -247,6 +247,12 @@ static void cp_lexer_stop_debugging
>  
>  static cp_token_cache *cp_token_cache_new
>    (cp_token *, cp_token *);
> +static tree cp_parser_noexcept_specification_opt
> +  (cp_parser *, bool, bool *, bool);
> +static tree cp_parser_late_noexcept_specifier
> +  (cp_parser *, tree);
> +static void noexcept_override_late_checks
> +  (tree, tree);
>  
>  static void cp_parser_initial_pragma
>    (cp_token *);
> @@ -1974,11 +1980,14 @@ cp_parser_context_new (cp_parser_context* next)
>    parser->unparsed_queues->last ().nsdmis
>  #define unparsed_classes \
>    parser->unparsed_queues->last ().classes
> +#define unparsed_noexcepts \
> +  parser->unparsed_queues->last ().noexcepts
>  
>  static void
>  push_unparsed_function_queues (cp_parser *parser)
>  {
> -  cp_unparsed_functions_entry e = {NULL, make_tree_vector (), NULL, NULL};
> +  cp_unparsed_functions_entry e = { NULL, make_tree_vector (), NULL, NULL,
> +				    NULL };
>    vec_safe_push (parser->unparsed_queues, e);
>  }
>  
> @@ -20515,7 +20524,13 @@ cp_parser_init_declarator (cp_parser* parser,
>  			/*asmspec=*/NULL_TREE,
>  			attr_chainon (attributes, prefix_attributes));
>        if (decl && TREE_CODE (decl) == FUNCTION_DECL)
> -	cp_parser_save_default_args (parser, decl);
> +	{
> +	  cp_parser_save_default_args (parser, decl);
> +	  /* Remember if there is a noexcept-specifier to post process.  */
> +	  tree spec = TYPE_RAISES_EXCEPTIONS (TREE_TYPE (decl));
> +	  if (UNPARSED_NOEXCEPT_SPEC_P (spec))
> +	    vec_safe_push (unparsed_noexcepts, decl);
> +	}
>        cp_finalize_omp_declare_simd (parser, decl);
>        cp_finalize_oacc_routine (parser, decl, false);
>      }
> @@ -23334,6 +23349,45 @@ cp_parser_class_name (cp_parser *parser,
>    return decl;
>  }
>  
> +/* Make sure that any member-function parameters are in scope.
> +   For instance, a function's noexcept-specifier can use the function's
> +   parameters:
> +
> +   struct S {
> +     void fn (int p) noexcept(noexcept(p));
> +   };
> +
> +   so we need to make sure name lookup can find them.  This is used
> +   when we delay parsing of the noexcept-specifier.  */
> +
> +static void
> +inject_parm_decls (tree decl)
> +{
> +  begin_scope (sk_function_parms, decl);
> +  tree args = DECL_ARGUMENTS (decl);
> +  args = nreverse (args);
> +
> +  tree next;
> +  for (tree parm = args; parm; parm = next)
> +    {
> +      next = DECL_CHAIN (parm);
> +      if (TREE_CODE (parm) == PARM_DECL)
> +	pushdecl (parm);
> +    }
> +  /* Get the decls in their original chain order and record in the
> +     function.  This is all and only the PARM_DECLs that were
> +     pushed into scope by the loop above.  */
> +  DECL_ARGUMENTS (decl) = get_local_decls ();
> +}
> +
> +/* Undo the effects of inject_parm_decls.  */
> +
> +static void
> +pop_injected_parms (void)
> +{
> +  pop_bindings_and_leave_scope ();
> +}
> +
>  /* Parse a class-specifier.
>  
>     class-specifier:
> @@ -23644,6 +23698,66 @@ cp_parser_class_specifier_1 (cp_parser* parser)
>        vec_safe_truncate (unparsed_classes, 0);
>        after_nsdmi_defaulted_late_checks (type);
>  
> +      /* If there are noexcept-specifiers that have not yet been processed,
> +	 take care of them now.  */
> +      class_type = NULL_TREE;
> +      pushed_scope = NULL_TREE;
> +      FOR_EACH_VEC_SAFE_ELT (unparsed_noexcepts, ix, decl)
> +	{
> +	  tree ctx = (DECL_FRIEND_P (decl) ? DECL_FRIEND_CONTEXT (decl)
> +		      : DECL_CONTEXT (decl));
> +	  if (class_type != ctx)
> +	    {
> +	      if (pushed_scope)
> +		pop_scope (pushed_scope);
> +	      class_type = ctx;
> +	      pushed_scope = push_scope (class_type);
> +	    }
> +
> +	  /* Make sure that any template parameters are in scope.  */
> +	  maybe_begin_member_template_processing (decl);
> +
> +	  /* Make sure that any member-function parameters are in scope.  */
> +	  inject_parm_decls (decl);
> +
> +	  tree spec = TYPE_RAISES_EXCEPTIONS (TREE_TYPE (decl));
> +	  spec = TREE_PURPOSE (spec);
> +	  tree old_decl = DEFARG_DECL (spec);
> +
> +	  /* 'this' is not allowed in static member functions.  */
> +	  unsigned char local_variables_forbidden_p
> +	    = parser->local_variables_forbidden_p;
> +	  if (DECL_THIS_STATIC (decl))
> +	    parser->local_variables_forbidden_p |= THIS_FORBIDDEN;
> +
> +	  /* Now we can parse the noexcept-specifier.  */
> +	  spec = cp_parser_late_noexcept_specifier (parser, spec);
> +
> +	  /* Restore the state of local_variables_forbidden_p.  */
> +	  parser->local_variables_forbidden_p = local_variables_forbidden_p;
> +	  if (spec != error_mark_node)
> +	    TREE_TYPE (decl) = build_exception_variant (TREE_TYPE (decl), spec);
> +
> +	  /* If we've stashed an old declaration, it means we need to
> +	     perform late redeclaration checking.  */
> +	  if (old_decl)
> +	    check_redeclaration_exception_specification (decl, old_decl);
> +
> +	  /* The finish_struct call above performed various override checking,
> +	     but it skipped unparsed noexcept-specifier operands.  Now that we
> +	     have resolved them, check again.  */
> +	  noexcept_override_late_checks (type, decl);
> +
> +	  /* Remove any member-function parameters from the symbol table.  */
> +	  pop_injected_parms ();
> +
> +	  /* Remove any template parameters from the symbol table.  */
> +	  maybe_end_member_template_processing ();
> +	}
> +      vec_safe_truncate (unparsed_noexcepts, 0);
> +      if (pushed_scope)
> +	pop_scope (pushed_scope);
> +
>        /* Now parse the body of the functions.  */
>        if (flag_openmp)
>  	{
> @@ -24817,6 +24931,12 @@ cp_parser_member_declaration (cp_parser* parser)
>  		  else
>  		    decl = finish_fully_implicit_template (parser, decl);
>  		}
> +	      if (decl && TREE_CODE (decl) == FUNCTION_DECL)
> +		{
> +		  tree spec = TYPE_RAISES_EXCEPTIONS (TREE_TYPE (decl));
> +		  if (UNPARSED_NOEXCEPT_SPEC_P (spec))
> +		    vec_safe_push (unparsed_noexcepts, decl);
> +		}
>  	    }
>  
>  	  cp_finalize_omp_declare_simd (parser, decl);
> @@ -25199,6 +25319,90 @@ cp_parser_base_specifier (cp_parser* parser)
>  
>  /* Exception handling [gram.exception] */
>  
> +/* Save the tokens that make up the noexcept-specifier for a member-function.
> +   Returns a DEFAULT_ARG.  */
> +
> +static tree
> +cp_parser_save_noexcept (cp_parser *parser)
> +{
> +  cp_token *first = parser->lexer->next_token;
> +  /* We want everything up to, including, the final ')'.  */
> +  cp_parser_cache_group (parser, CPP_CLOSE_PAREN, /*depth=*/0);
> +  cp_token *last = parser->lexer->next_token;
> +
> +  /* As with default arguments and NSDMIs, make use of DEFAULT_ARG
> +     to carry the information we will need.  */
> +  tree expr = make_node (DEFAULT_ARG);
> +  /* Save away the noexcept-specifier; we will process it when the
> +     class is complete.  */
> +  DEFARG_TOKENS (expr) = cp_token_cache_new (first, last);
> +  DEFARG_DECL (expr) = NULL_TREE;
> +  DEFARG_NOEXCEPT_P (expr) = true;
> +  expr = build_tree_list (expr, NULL_TREE);
> +  return expr;
> +}
> +
> +/* Used for late processing of noexcept-specifiers of member-functions.
> +   DEFAULT_ARG is the unparsed operand of a noexcept-specifier which
> +   we saved for later; parse it now.  */
> +
> +static tree
> +cp_parser_late_noexcept_specifier (cp_parser *parser, tree default_arg)
> +{
> +  /* Make sure we've gotten something that hasn't been parsed yet.  */
> +  gcc_assert (TREE_CODE (default_arg) == DEFAULT_ARG);
> +
> +  push_unparsed_function_queues (parser);
> +
> +  /* Push the saved tokens for the noexcept-specifier onto the parser's
> +     lexer stack.  */
> +  cp_token_cache *tokens = DEFARG_TOKENS (default_arg);
> +  cp_parser_push_lexer_for_tokens (parser, tokens);
> +
> +  /* Parse the cached noexcept-specifier.  */
> +  tree parsed_arg
> +    = cp_parser_noexcept_specification_opt (parser,
> +					    /*require_constexpr=*/true,
> +					    NULL,
> +					    /*return_cond=*/false);
> +
> +  /* Revert to the main lexer.  */
> +  cp_parser_pop_lexer (parser);
> +
> +  /* Restore the queue.  */
> +  pop_unparsed_function_queues (parser);
> +
> +  /* And we're done.  */
> +  return parsed_arg;
> +}
> +
> +/* Perform late checking of overriding function with respect to their
> +   noexcept-specifiers.  TYPE is the class and FNDECL is the function
> +   that potentially overrides some virtual function with the same
> +   signature.  */
> +
> +static void
> +noexcept_override_late_checks (tree type, tree fndecl)
> +{
> +  tree binfo = TYPE_BINFO (type);
> +  tree base_binfo;
> +
> +  if (DECL_STATIC_FUNCTION_P (fndecl))
> +    return;
> +
> +  for (int i = 0; BINFO_BASE_ITERATE (binfo, i, base_binfo); ++i)
> +    {
> +      tree basetype = BINFO_TYPE (base_binfo);
> +
> +      if (!TYPE_POLYMORPHIC_P (basetype))
> +	continue;
> +
> +      tree fn = look_for_overrides_here (basetype, fndecl);
> +      if (fn)
> +	maybe_check_throw_specifier (fndecl, fn);
> +    }
> +}
> +
>  /* Parse an (optional) noexcept-specification.
>  
>     noexcept-specification:
> @@ -25227,6 +25431,18 @@ cp_parser_noexcept_specification_opt (cp_parser* parser,
>    if (cp_parser_is_keyword (token, RID_NOEXCEPT))
>      {
>        tree expr;
> +
> +      /* [class.mem]/6 says that a noexcept-specifer (within the
> +	 member-specification of the class) is a complete-class context of
> +	 a class.  So, if the noexcept-specifier has the optional expression,
> +	 just save the tokens, and reparse this after we're done with the
> +	 class.  */
> +      if (cp_lexer_peek_nth_token (parser->lexer, 2)->type == CPP_OPEN_PAREN
> +	  && at_class_scope_p ()
> +	  && TYPE_BEING_DEFINED (current_class_type)
> +	  && !LAMBDA_TYPE_P (current_class_type))
> +	return cp_parser_save_noexcept (parser);
> +
>        cp_lexer_consume_token (parser->lexer);
>  
>        if (cp_lexer_peek_token (parser->lexer)->type == CPP_OPEN_PAREN)
> @@ -28427,7 +28643,12 @@ cp_parser_save_member_function_body (cp_parser* parser,
>        return error_mark_node;
>      }
>  
> -  /* Remember it, if there default args to post process.  */
> +  /* Remember if there is a noexcept-specifier to post process.  */
> +  tree spec = TYPE_RAISES_EXCEPTIONS (TREE_TYPE (fn));
> +  if (UNPARSED_NOEXCEPT_SPEC_P (spec))
> +    vec_safe_push (unparsed_noexcepts, fn);
> +
> +  /* Remember it, if there are default args to post process.  */
>    cp_parser_save_default_args (parser, fn);
>  
>    /* Save away the tokens that make up the body of the
> diff --git gcc/cp/parser.h gcc/cp/parser.h
> index c03a9d87af5..2890788f489 100644
> --- gcc/cp/parser.h
> +++ gcc/cp/parser.h
> @@ -166,6 +166,9 @@ struct GTY(()) cp_unparsed_functions_entry {
>    /* Nested classes go in this vector, so that we can do some final
>       processing after parsing any NSDMIs.  */
>    vec<tree, va_gc> *classes;
> +
> +  /* Functions with noexcept-specifiers that require post-processing.  */
> +  vec<tree, va_gc> *noexcepts;
>  };
>  
>  
> diff --git gcc/cp/pt.c gcc/cp/pt.c
> index d6976e08690..c00d14fd954 100644
> --- gcc/cp/pt.c
> +++ gcc/cp/pt.c
> @@ -25308,8 +25308,9 @@ dependent_type_p_r (tree type)
>  	  if (tree noex = TREE_PURPOSE (spec))
>  	    /* Treat DEFERRED_NOEXCEPT as non-dependent, since it doesn't
>  	       affect overload resolution and treating it as dependent breaks
> -	       things.  */
> +	       things.  Same for an unparsed noexcept expression.  */
>  	    if (TREE_CODE (noex) != DEFERRED_NOEXCEPT
> +		&& TREE_CODE (noex) != DEFAULT_ARG
>  		&& value_dependent_expression_p (noex))
>  	      return true;
>        return false;
> diff --git gcc/cp/search.c gcc/cp/search.c
> index 4c3fffda717..5a3a0cf2824 100644
> --- gcc/cp/search.c
> +++ gcc/cp/search.c
> @@ -1863,6 +1863,39 @@ locate_field_accessor (tree basetype_path, tree field_decl, bool const_p)
>  				   NULL, &lfd);
>  }
>  
> +/* Check throw specifier of OVERRIDER is at least as strict as
> +   the one of BASEFN.  */
> +
> +bool
> +maybe_check_throw_specifier (tree overrider, tree basefn)
> +{
> +  maybe_instantiate_noexcept (basefn);
> +  maybe_instantiate_noexcept (overrider);
> +  tree base_throw = TYPE_RAISES_EXCEPTIONS (TREE_TYPE (basefn));
> +  tree over_throw = TYPE_RAISES_EXCEPTIONS (TREE_TYPE (overrider));
> +
> +  if (DECL_INVALID_OVERRIDER_P (overrider))
> +    return true;
> +
> +  /* Can't check this yet.  Pretend this is fine and let
> +     noexcept_override_late_checks check this later.  */
> +  if (UNPARSED_NOEXCEPT_SPEC_P (base_throw)
> +      || UNPARSED_NOEXCEPT_SPEC_P (over_throw))
> +    return true;
> +
> +  if (!comp_except_specs (base_throw, over_throw, ce_derived))
> +    {
> +      auto_diagnostic_group d;
> +      error ("looser exception specification on overriding virtual function "
> +	     "%q+#F", overrider);
> +      inform (DECL_SOURCE_LOCATION (basefn),
> +	      "overridden function is %q#F", basefn);
> +      DECL_INVALID_OVERRIDER_P (overrider) = 1;
> +      return false;
> +    }
> +  return true;
> +}
> +
>  /* Check that virtual overrider OVERRIDER is acceptable for base function
>     BASEFN. Issue diagnostic, and return zero, if unacceptable.  */
>  
> @@ -1873,7 +1906,6 @@ check_final_overrider (tree overrider, tree basefn)
>    tree base_type = TREE_TYPE (basefn);
>    tree over_return = fndecl_declared_return_type (overrider);
>    tree base_return = fndecl_declared_return_type (basefn);
> -  tree over_throw, base_throw;
>  
>    int fail = 0;
>  
> @@ -1957,21 +1989,8 @@ check_final_overrider (tree overrider, tree basefn)
>        return 0;
>      }
>  
> -  /* Check throw specifier is at least as strict.  */
> -  maybe_instantiate_noexcept (basefn);
> -  maybe_instantiate_noexcept (overrider);
> -  base_throw = TYPE_RAISES_EXCEPTIONS (TREE_TYPE (basefn));
> -  over_throw = TYPE_RAISES_EXCEPTIONS (TREE_TYPE (overrider));
> -
> -  if (!comp_except_specs (base_throw, over_throw, ce_derived))
> -    {
> -      auto_diagnostic_group d;
> -      error ("looser throw specifier for %q+#F", overrider);
> -      inform (DECL_SOURCE_LOCATION (basefn),
> -	      "overridden function is %q#F", basefn);
> -      DECL_INVALID_OVERRIDER_P (overrider) = 1;
> -      return 0;
> -    }
> +  if (!maybe_check_throw_specifier (overrider, basefn))
> +    return 0;
>  
>    /* Check for conflicting type attributes.  But leave transaction_safe for
>       set_one_vmethod_tm_attributes.  */
> diff --git gcc/cp/tree.c gcc/cp/tree.c
> index 718eed349c6..bc0080d6720 100644
> --- gcc/cp/tree.c
> +++ gcc/cp/tree.c
> @@ -2550,6 +2550,7 @@ canonical_eh_spec (tree raises)
>    if (raises == NULL_TREE)
>      return raises;
>    else if (DEFERRED_NOEXCEPT_SPEC_P (raises)
> +	   || UNPARSED_NOEXCEPT_SPEC_P (raises)
>  	   || uses_template_parms (raises)
>  	   || uses_template_parms (TREE_PURPOSE (raises)))
>      /* Keep a dependent or deferred exception specification.  */
> @@ -3662,6 +3663,7 @@ cp_tree_equal (tree t1, tree t2)
>      case IDENTIFIER_NODE:
>      case SSA_NAME:
>      case USING_DECL:
> +    case DEFAULT_ARG:
>        return false;
>  
>      case BASELINK:
> diff --git gcc/cp/typeck2.c gcc/cp/typeck2.c
> index df002a1664c..8cbc48fb44f 100644
> --- gcc/cp/typeck2.c
> +++ gcc/cp/typeck2.c
> @@ -2393,6 +2393,12 @@ merge_exception_specifiers (tree list, tree add)
>    if (list == error_mark_node || add == error_mark_node)
>      return error_mark_node;
>  
> +  /* We don't want to lose the unparsed operand lest we miss diagnostics.  */
> +  if (UNPARSED_NOEXCEPT_SPEC_P (list))
> +    return list;
> +  else if (UNPARSED_NOEXCEPT_SPEC_P (add))
> +    return add;
> +
>    /* No exception-specifier or noexcept(false) are less strict than
>       anything else.  Prefer the newer variant (LIST).  */
>    if (!list || list == noexcept_false_spec)
> diff --git gcc/testsuite/g++.dg/cpp0x/noexcept41.C gcc/testsuite/g++.dg/cpp0x/noexcept41.C
> new file mode 100644
> index 00000000000..43b38c2446f
> --- /dev/null
> +++ gcc/testsuite/g++.dg/cpp0x/noexcept41.C
> @@ -0,0 +1,147 @@
> +// PR c++/86476 - noexcept-specifier is a complete-class context
> +// { dg-do compile { target c++11 } }
> +
> +#define SA(X) static_assert(X, #X)
> +
> +struct S {
> +  void f1() noexcept(noexcept(i)) { }
> +  void f2() noexcept(noexcept(fn())) { }
> +  void f3() noexcept(noexcept(fnx())) { }
> +  void f4() noexcept(noexcept(i));
> +  void f5() noexcept(noexcept(fn()));
> +  void f6() noexcept(noexcept(fnx()));
> +
> +  void f7() noexcept(1);
> +  void f8() noexcept(0);
> +  void f9() noexcept(b);
> +  void f10() noexcept(!b);
> +
> +  int i;
> +  static constexpr auto b = true;
> +  void fny() noexcept(noexcept(fn()));
> +  void fn();
> +  void fnx() noexcept;
> +};
> +
> +S s;
> +SA(noexcept(s.f1()));
> +SA(!noexcept(s.f2()));
> +SA(noexcept(s.f3()));
> +SA(noexcept(s.f4()));
> +SA(!noexcept(s.f5()));
> +SA(noexcept(s.f6()));
> +SA(noexcept(s.f7()));
> +SA(!noexcept(s.f8()));
> +SA(noexcept(s.f9()));
> +SA(!noexcept(s.f10()));
> +
> +struct S2 {
> +  struct V {
> +    void f1() noexcept(noexcept(fn()));
> +    void f2() noexcept(noexcept(fnx()));
> +    void f3() noexcept(noexcept(fn())) { }
> +    void f4() noexcept(noexcept(fnx())) { }
> +    void fn();
> +    void fnx() noexcept;
> +  } v;
> +  void fn();
> +  void fnx();
> +};
> +
> +S2 s2;
> +SA(!noexcept(s2.v.f1()));
> +SA(noexcept(s2.v.f2()));
> +SA(!noexcept(s2.v.f3()));
> +SA(noexcept(s2.v.f4()));
> +
> +struct S3 {
> +  void f1() noexcept(noexcept(fn()));
> +  void f2() noexcept(noexcept(fnx()));
> +  void fn();
> +  void fnx() noexcept;
> +};
> +
> +void
> +S3::f1() noexcept(noexcept(fn()))
> +{
> +}
> +
> +void
> +S3::f2() noexcept(noexcept(fnx()))
> +{
> +}
> +
> +struct S4 {
> +  int f1 (int p) noexcept(noexcept(p)) { return p; }
> +  int f2 (int p) noexcept(noexcept(p));
> +  int f3 (int p = 10) noexcept(noexcept(p));
> +  int f4 () noexcept(noexcept(S4{}));
> +};
> +
> +S4 s4;
> +SA(noexcept(s4.f1(1)));
> +SA(noexcept(s4.f2(1)));
> +SA(noexcept(s4.f3()));
> +SA(noexcept(s4.f4()));
> +
> +template<typename T>
> +struct S5 {
> +  void f1() noexcept(noexcept(i)) { }
> +  void f2() noexcept(noexcept(fn())) { }
> +  void f3() noexcept(noexcept(fnx())) { }
> +  void f4() noexcept(noexcept(i));
> +  void f5() noexcept(noexcept(fn()));
> +  void f6() noexcept(noexcept(fnx()));
> +    
> +  int i;
> +  void fny() noexcept(noexcept(fn()));
> +  void fn();
> +  void fnx() noexcept;
> +};
> +
> +S5<int> s5;
> +SA(noexcept(s5.f1()));
> +SA(!noexcept(s5.f2()));
> +SA(noexcept(s5.f3()));
> +SA(noexcept(s5.f4()));
> +SA(!noexcept(s5.f5()));
> +SA(noexcept(s5.f6()));
> +
> +template<typename T>
> +struct S6 {
> +  void f1() noexcept(noexcept(x));
> +  T x;
> +};
> +
> +struct S7 {
> +  template<typename U>
> +  void f1 () noexcept(noexcept(U(1))) { }
> +
> +  template<int N>
> +  void f2() noexcept(noexcept(N));
> +
> +  template <typename _Up>
> +  void f3(_Up __p) noexcept(noexcept(__p));
> +};
> +
> +void glob();
> +void globx() noexcept;
> +struct S8 {
> +  void f1 () noexcept(noexcept(glob()));
> +  void f2 () noexcept(noexcept(globx()));
> +};
> +
> +S8 s8;
> +SA(!noexcept(s8.f1()));
> +SA(noexcept(s8.f2()));
> +
> +struct W {
> +  constexpr operator bool();
> +};
> +
> +template<typename T>
> +struct S9 {
> +  S9() noexcept(noexcept(w)) { }
> +  S9 &operator=(S9 &&) noexcept(T::X);
> +  W w;
> +};
> diff --git gcc/testsuite/g++.dg/cpp0x/noexcept42.C gcc/testsuite/g++.dg/cpp0x/noexcept42.C
> new file mode 100644
> index 00000000000..b3859de9ebc
> --- /dev/null
> +++ gcc/testsuite/g++.dg/cpp0x/noexcept42.C
> @@ -0,0 +1,26 @@
> +// PR c++/86476 - noexcept-specifier is a complete-class context
> +// { dg-do compile { target c++11 } }
> +
> +struct S {
> +  void f1() noexcept(noexcept(fn()));
> +  void f2() noexcept(noexcept(fnx()));
> +  void fn();
> +  void fnx() noexcept;
> +};
> +
> +void
> +S::f1() noexcept // { dg-error "different exception specifier" }
> +{
> +}
> +
> +void
> +S::f2() // { dg-error "different exception specifier" }
> +{
> +}
> +
> +struct S2 {
> +  void f1() noexcept(noexcept(nosuchfn())); // { dg-error "not declared in this scope" }
> +  void f2() noexcept(noexcept(nothere)); // { dg-error "not declared in this scope" }
> +  void f3() noexcept(noexcept(nosuchfn())) { } // { dg-error "not declared in this scope" }
> +  void f4() noexcept(noexcept(nothere)) { } // { dg-error "not declared in this scope" }
> +};
> diff --git gcc/testsuite/g++.dg/cpp0x/noexcept43.C gcc/testsuite/g++.dg/cpp0x/noexcept43.C
> new file mode 100644
> index 00000000000..12c6d364099
> --- /dev/null
> +++ gcc/testsuite/g++.dg/cpp0x/noexcept43.C
> @@ -0,0 +1,9 @@
> +// PR c++/86476 - noexcept-specifier is a complete-class context
> +// { dg-do compile { target c++11 } }
> +
> +template <typename _Alloc> class A {
> +  typedef _Alloc _Alloc_traits;
> +  A &operator=(A &&) noexcept(_Alloc_traits::_S_nothrow_move);
> +  A &m_fn1(A &&) noexcept(_Alloc_traits::_S_nothrow_move);
> +  void m_fn2(A<char>) {}
> +};
> diff --git gcc/testsuite/g++.dg/cpp0x/noexcept44.C gcc/testsuite/g++.dg/cpp0x/noexcept44.C
> new file mode 100644
> index 00000000000..a81032f28e9
> --- /dev/null
> +++ gcc/testsuite/g++.dg/cpp0x/noexcept44.C
> @@ -0,0 +1,14 @@
> +// PR c++/86476 - noexcept-specifier is a complete-class context
> +// { dg-do compile { target c++11 } }
> +
> +void fn1(void());
> +template <typename> class A {
> +  void _M_local_data();
> +  A() noexcept(_M_local_data);
> +};
> +
> +class B {
> +  void _S_initialize();
> +  static void _S_initialize_once();
> +};
> +void B::_S_initialize() { fn1(_S_initialize_once); }
> diff --git gcc/testsuite/g++.dg/cpp0x/noexcept45.C gcc/testsuite/g++.dg/cpp0x/noexcept45.C
> new file mode 100644
> index 00000000000..39df4a6571e
> --- /dev/null
> +++ gcc/testsuite/g++.dg/cpp0x/noexcept45.C
> @@ -0,0 +1,23 @@
> +// PR c++/86476 - noexcept-specifier is a complete-class context
> +// { dg-do compile { target c++11 } }
> +
> +struct A
> +{
> +  virtual void f();
> +  virtual void g() noexcept;
> +  virtual void h() noexcept(false);
> +};
> +
> +struct B : A
> +{
> +  void f() noexcept(true);
> +  void g() noexcept(true);
> +  void h() noexcept(true);
> +};
> +
> +struct D : A
> +{
> +  void f() noexcept(false);
> +  void g() noexcept(false); // { dg-error "looser exception specification" }
> +  void h() noexcept(false);
> +};
> diff --git gcc/testsuite/g++.dg/cpp0x/noexcept46.C gcc/testsuite/g++.dg/cpp0x/noexcept46.C
> new file mode 100644
> index 00000000000..da7490d651c
> --- /dev/null
> +++ gcc/testsuite/g++.dg/cpp0x/noexcept46.C
> @@ -0,0 +1,28 @@
> +// PR c++/86476 - noexcept-specifier is a complete-class context
> +// { dg-do compile { target c++11 } }
> +
> +void f() noexcept(false);
> +void g() noexcept(true);
> +void h() noexcept;
> +
> +struct B {
> +  friend void f() noexcept(false);
> +  friend void g() noexcept(false); // { dg-error "different exception specifier" }
> +  friend void h() noexcept(false); // { dg-error "different exception specifier" }
> +};
> +
> +struct C {
> +  friend void f() noexcept(true); // { dg-error "different exception specifier" }
> +  friend void g() noexcept(true); // { dg-error "different exception specifier" }
> +  friend void h() noexcept(true); // { dg-error "different exception specifier" }
> +};
> +
> +void o() noexcept(false);
> +void p() noexcept(true);
> +void q() noexcept;
> +
> +struct D {
> +  friend void o() noexcept(true); // { dg-error "different exception specifier" }
> +  friend void p() noexcept(true);
> +  friend void q() noexcept(true);
> +};
> diff --git gcc/testsuite/g++.dg/eh/shadow1.C gcc/testsuite/g++.dg/eh/shadow1.C
> index 0ba6145ef0c..6bccc704d49 100644
> --- gcc/testsuite/g++.dg/eh/shadow1.C
> +++ gcc/testsuite/g++.dg/eh/shadow1.C
> @@ -18,7 +18,7 @@ struct D : private B
>  				// { dg-warning "deprecated" "" { target { c++11 && { ! c++17 } } } .-2 }
>  struct E : public D
>  {
> -  virtual void V () throw (D); // { dg-error "looser throw" "" { target { ! c++17 } } }
> +  virtual void V () throw (D); // { dg-error "looser exception" "" { target { ! c++17 } } }
>  };			       // { dg-error "dynamic exception specification" "" { target c++17 } .-1 }
>  			       // { dg-warning "deprecated" "" { target { c++11 && { ! c++17 } } } .-2 }
>  B* foo (D *);

Marek