c++: Directly fixup deferred eh-specs

eh-specifiers in a class definition are complete-definition contexts,
and we sometimes need to deferr their parsing.  We create a deferred
eh specifier, which can end up persisting in the type system due to
variants being created before the deferred parse.  This causes
problems in modules handling.

This patch adds fixup_deferred_exception_variants, which directly
modifies the variants of such an eh spec once parsed.  As commented,
the general case is quite hard, so it doesn't deal with everything.
But I do catch the cases I encountered (from the std library).

	gcc/cp/
	* cp-tree.h (fixup_deferred_exception_variants): Declare.
	* parser.c (cp_parser_class_specifier_1): Call it when
	completing deferred parses rather than creating a variant.
	(cp_parser_member_declaration): Move comment from ...
	(cp_parser_noexcept_specification_opt): ... here.  Refactor the
	deferred parse.
	* tree.c (fixup_deferred_exception_variants): New.

gcc/cp/cp-tree.h

@@ -7360,6 +7360,7 @@ extern const char *cxx_printable_name_translate	(tree, int);
 extern tree canonical_eh_spec			(tree);
 extern tree build_cp_fntype_variant		(tree, cp_ref_qualifier, tree, bool);
 extern tree build_exception_variant		(tree, tree);
+extern void fixup_deferred_exception_variants   (tree, tree);
 extern tree bind_template_template_parm		(tree, tree);
 extern tree array_type_nelts_total		(tree);
 extern tree array_type_nelts_top		(tree);

gcc/cp/parser.c

@@ -24334,8 +24334,12 @@ cp_parser_class_specifier_1 (cp_parser* parser)
 	  /* Now we can parse the noexcept-specifier.  */
 	  spec = cp_parser_late_noexcept_specifier (parser, spec);
 
-	  if (spec != error_mark_node)
-	    TREE_TYPE (decl) = build_exception_variant (TREE_TYPE (decl), spec);
+	  if (spec == error_mark_node)
+	    spec = NULL_TREE;
+
+	  /* Update the fn's type directly -- it might have escaped
+	     beyond this decl :(  */
+	  fixup_deferred_exception_variants (TREE_TYPE (decl), spec);
 
 	  /* Restore the state of local_variables_forbidden_p.  */
 	  parser->local_variables_forbidden_p = local_variables_forbidden_p;
@@ -25371,6 +25375,9 @@ cp_parser_member_declaration (cp_parser* parser)
 	      int ctor_dtor_or_conv_p;
 	      bool static_p = (decl_specifiers.storage_class == sc_static);
 	      cp_parser_flags flags = CP_PARSER_FLAGS_TYPENAME_OPTIONAL;
+	      /* We can't delay parsing for friends,
+		 alias-declarations, and typedefs, even though the
+		 standard seems to require it.  */
 	      if (!friend_p
 		  && !decl_spec_seq_has_spec_p (&decl_specifiers, ds_typedef))
 		flags |= CP_PARSER_FLAGS_DELAY_NOEXCEPT;
@@ -26059,19 +26066,14 @@ cp_parser_noexcept_specification_opt (cp_parser* parser,
 	 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.  */
-      const bool literal_p
-	= ((cp_lexer_nth_token_is (parser->lexer, 3, CPP_NUMBER)
-	    || cp_lexer_nth_token_is (parser->lexer, 3, CPP_KEYWORD))
-	   && cp_lexer_nth_token_is (parser->lexer, 4, CPP_CLOSE_PAREN));
 
-      if (cp_lexer_nth_token_is (parser->lexer, 2, CPP_OPEN_PAREN)
+      if ((flags & CP_PARSER_FLAGS_DELAY_NOEXCEPT)
+	  && cp_lexer_nth_token_is (parser->lexer, 2, CPP_OPEN_PAREN)
 	  /* No need to delay parsing for a number literal or true/false.  */
-	  && !literal_p
+	  && !((cp_lexer_nth_token_is (parser->lexer, 3, CPP_NUMBER)
+		|| cp_lexer_nth_token_is (parser->lexer, 3, CPP_KEYWORD))
+	       && cp_lexer_nth_token_is (parser->lexer, 4, CPP_CLOSE_PAREN))
 	  && at_class_scope_p ()
-	  /* We don't delay parsing for friend member functions,
-	     alias-declarations, and typedefs, even though the standard seems
-	     to require it.  */
-	  && (flags & CP_PARSER_FLAGS_DELAY_NOEXCEPT)
 	  && TYPE_BEING_DEFINED (current_class_type)
 	  && !LAMBDA_TYPE_P (current_class_type))
 	return cp_parser_save_noexcept (parser);

gcc/cp/tree.c

@@ -2676,6 +2676,52 @@ build_cp_fntype_variant (tree type, cp_ref_qualifier rqual,
   return v;
 }
 
+/* TYPE is a function or method type with a deferred exception
+   specification that has been parsed to RAISES.  Fixup all the type
+   variants that are affected in place.  Via decltype &| noexcept
+   tricks, the unparsed spec could have escaped into the type system.
+   The general case is hard to fixup canonical types for.  */
+
+void
+fixup_deferred_exception_variants (tree type, tree raises)
+{
+  tree original = TYPE_RAISES_EXCEPTIONS (type);
+  tree cr = flag_noexcept_type ? canonical_eh_spec (raises) : NULL_TREE;
+
+  gcc_checking_assert (TREE_CODE (TREE_PURPOSE (original))
+		       == DEFERRED_PARSE);
+
+  /* Though sucky, this walk will process the canonical variants
+     first.  */
+  for (tree variant = TYPE_MAIN_VARIANT (type);
+       variant; variant = TYPE_NEXT_VARIANT (variant))
+    if (TYPE_RAISES_EXCEPTIONS (variant) == original)
+      {
+	gcc_checking_assert (variant != TYPE_MAIN_VARIANT (type));
+
+	if (!TYPE_STRUCTURAL_EQUALITY_P (variant))
+	  {
+	    cp_cv_quals var_quals = TYPE_QUALS (variant);
+	    cp_ref_qualifier rqual = type_memfn_rqual (variant);
+
+	    tree v = TYPE_MAIN_VARIANT (type);
+	    for (; v; v = TYPE_NEXT_VARIANT (v))
+	      if (TYPE_CANONICAL (v) == v
+		  && cp_check_qualified_type (v, variant, var_quals,
+					      rqual, cr, false))
+		break;
+	    TYPE_RAISES_EXCEPTIONS (variant) = raises;
+
+	    if (!v)
+	      v = build_cp_fntype_variant (TYPE_CANONICAL (variant),
+					   rqual, cr, false);
+	    TYPE_CANONICAL (variant) = v;
+	  }
+	else
+	  TYPE_RAISES_EXCEPTIONS (variant) = raises;
+      }
+}
+
 /* Build the FUNCTION_TYPE or METHOD_TYPE which may throw exceptions
    listed in RAISES.  */