GCC-3.4.6源代码学习笔记（113）

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5.12.3.2.1.2.2. 闭合类定义

自expand_or_defer_fn à cp_parser_late_parsing_for_member à cp_parser_late_parsing_for_memberà cp_parser_class_specifier à cp_parser_type_specifierà cp_parser_decl_specifier_seq返回至cp_parser_single_declaration，将执行下面的代码。

cp_parser_single_declaration (continue)

14549 /*Check for the declaration of a template class. */

14550 if (declares_class_or_enum)

14551 {

14552 if (cp_parser_declares_only_class_p(parser))

14553 {

14554 decl = shadow_tag (decl_specifiers);

14555 if (decl)

14556 decl = TYPE_NAME(decl);

14557 else

14558 decl = error_mark_node;

14559 }

14560 }

14561 /*If it's not a template class, try for a template function. If

14562 thenext token is a `;', then this declaration does not declare

14563 anything. But, if there were errors in the decl-specifiers, then

14564 theerror might well have come from an attempted class-specifier.

14565 Inthat case, there's no need to warn about a missing declarator. */

14566 if (!decl

14567 &&(cp_lexer_next_token_is_not (parser->lexer, CPP_SEMICOLON)

14568 || !value_member (error_mark_node,decl_specifiers)))

14569 decl = cp_parser_init_declarator (parser,

14570 decl_specifiers,

14571 attributes,

14572 /*function_definition_allowed_p=*/true,

14573 member_p,

14574 declares_class_or_enum,

14575 &function_definition_p);

14576

14577 pop_deferring_access_checks ();

14578

14579 /*Clear any current qualification; whatever comes next is the start

14580 ofsomething new. */

14581 parser->scope =NULL_TREE;

14582 parser->qualifying_scope= NULL_TREE;

14583 parser->object_scope =NULL_TREE;

14584 /*Look for a trailing `;' after the declaration. */

14585 if (!function_definition_p

14586 && (decl ==error_mark_node

14587 ||!cp_parser_require (parser, CPP_SEMICOLON, "`;'")))

14588 cp_parser_skip_to_end_of_block_or_statement (parser);

14589

14590 returndecl;

14591 }

我们已经看过，declares_class_or_enum可被设置为以下标记的按位与的结果：

1: 该decl-specifiers之一是一个elaborated-type-specifier（即一个类型声明）

2: 该decl-specifiers之一是一个enum-specifier或class-specifier（即一个类型定义）

因此如果declares_class_or_enum不是0，需要进一步看这是否为类定义。如果是，将执行一些安全检查，这些检查与前面章节中对嵌套类所执行的检查相仿。

因为现在只是完成了“decl-specifier-seq[opt]init-declarator [opt];”中decl-specifier-seq部分，函数cp_parser_declares_only_class_p用于确认是否出现声明符。

15029 static bool

15030 cp_parser_declares_only_class_p (cp_parser *parser) in parser.c

15031 {

15032 /*If the next token is a `;' or a `,' then there is no

15033 declarator. */

15034 return(cp_lexer_next_token_is (parser->lexer, CPP_SEMICOLON)

15035 || cp_lexer_next_token_is (parser->lexer,CPP_COMMA));

15036 }

如果没有声明符，这只能是类型声明。这需要确认。

3608 tree

3609 shadow_tag (tree declspecs) in decl.c

3610 {

3611 tree t = check_tag_decl (declspecs);

3612

3613 if (!t)

3614 returnNULL_TREE;

3615

3616 maybe_process_partial_specialization (t);

3617

3618 /*This is where the variables in an anonymous union are

3619 declared. An anonymous union declaration looks like:

3620 union{ ... } ;

3621 because there is no declarator after the union, the parser

3622 sendsthat declaration here. */

3623 if (ANON_AGGR_TYPE_P (t))

3624 {

3625 fixup_anonymous_aggr (t);

3626

3627 if (TYPE_FIELDS (t))

3628 {

3629 tree decl =grokdeclarator (NULL_TREE, declspecs, NORMAL,0,

3630 NULL);

3631 finish_anon_union(decl);

3632 }

3633 }

3634

3635 returnt;

3636 }

上面的check_tag_decl返回了所声明的类型（*_TYPE类型的节点），或者NULL如果不是声明类型的话。这个值进而又被shadow_tag返回。那么在cp_parser_single_declaration的14556行，decl所指向的就是对应的TYPE_DECL节点。而在14566行，若decl是NULL，表明这不是类型声明，因为cp_parser_single_declaration只被cp_parser_explicit_specialization及cp_parser_template_declaration_after_export所调用（这里是后者），那么剩下的可能就是模板函数，由14569行的cp_parser_init_declarator来解析之。

从cp_parser_single_declaration回到cp_parser_template_declaration_after_export。

cp_parser_template_declaration_after_export(continue)

14461 else

14462 {

14463 decl = cp_parser_single_declaration (parser,

14464 member_p,

14465 &friend_p);

14466

14467 /*If this is a member template declaration, let the front

14468 endknow. */

14469 if (member_p &&!friend_p && decl)

14470 {

14471 if (TREE_CODE (decl) ==TYPE_DECL)

14472 cp_parser_check_access_in_redeclaration (decl);

14473

14474 decl =finish_member_template_decl (decl);

14475 }

14476 else if (friend_p&& decl && TREE_CODE (decl) == TYPE_DECL)

14477 make_friend_class (current_class_type,TREE_TYPE (decl),

14478 /*complain=*/true);

14479 }

14480 /*We are done with the current parameter list. */

14481 --parser->num_template_parameter_lists;

14482

14483 /*Finish up. */

14484 finish_template_decl (parameter_list);

14485

14486 /*Register member declarations. */

14487 if (member_p &&!friend_p && decl && !DECL_CLASS_TEMPLATE_P (decl))

14488 finish_member_declaration(decl);

14489

14490 /*If DECL is a function template, we must return to parse it later.

14491 (Eventhough there is no definition, there might be default

14492 arguments that need handling.) */

14493 if (member_p && decl

14494 && (TREE_CODE(decl) == FUNCTION_DECL

14495 ||DECL_FUNCTION_TEMPLATE_P (decl)))

14496 TREE_VALUE(parser->unparsed_functions_queues)

14497 = tree_cons (NULL_TREE, decl,

14498 TREE_VALUE (parser->unparsed_functions_queues));

14499 }

上面，对于我们作为例子的模板声明，它不是一个类成员，因此参数member_p是false。那么对于这个例子，仅有的操作由finish_template_decl完成。

2208 void

2209 finish_template_decl (tree parms) insemantics.c

2210 {

2211 if (parms)

2212 end_template_decl ();

2213 else

2214 end_specialization ();

2215 }

参数parms提取自“<…>”，因此如果它是NULL，它一定是一个特化。

2279 void

2280 end_template_decl (void) inpt.c

2281 {

2282 reset_specialization ();

2283

2284 if (!processing_template_decl)

2285 return;

2286

2287 /*This matches the pushlevel in begin_template_parm_list. */

2288 finish_scope();

2289

2290 --processing_template_decl;

2291 current_template_parms = TREE_CHAIN(current_template_parms);

2292 }

在完成目标声明解析时，意味着我们到达了其作用域的边界。这个作用域也是由finish_scope来关闭。并且要记住把正在处理模板声明的数目减一。参考图：嵌套模板参数的布局，上面在2291行，current_template_parms的域TREE_CHAIN指向封闭模板（containing template）的目标参数，如果存在的话。

354 void

355 finish_scope (void) indecl.c

356 {

357 poplevel (0, 0, 0);

358 }

为了方便起见，在下面我们重新显示poplevel的代码。因为我们正要退出类的作用域，因此参数functionbody是0；而keep是0，则使得没有BLOCK节点为该域中的声明而构建。

423 tree

424 poplevel (int keep, int reverse, int functionbody) indecl.c

425 {

426 tree link;

427 /*The chain of decls was accumulated in reverse order.

428 Put itinto forward order, just for cleanliness. */

429 tree decls;

430 int tmp = functionbody;

431 int real_functionbody;

432 tree subblocks;

433 tree block = NULL_TREE;

434 tree decl;

435 int leaving_for_scope;

436 scope_kind kind;

…

454 if (current_binding_level->keep)

455 keep = 1;

…

493 /*Get the decls in the order they were written.

494 Usually current_binding_level->names is in reverse order.

495 Butparameter decls were previously put in forward order. */

496

497 if (reverse)

498 current_binding_level->names

499 = decls = nreverse(current_binding_level->names);

500 else

501 decls =current_binding_level->names;

502

503 /*Output any nested inline functions within this block

504 ifthey weren't already output. */

505 for(decl = decls; decl; decl = TREE_CHAIN (decl))

506 if (TREE_CODE (decl) ==FUNCTION_DECL

507 && !TREE_ASM_WRITTEN (decl)

508 && DECL_INITIAL(decl) != NULL_TREE

509 &&TREE_ADDRESSABLE (decl)

510 &&decl_function_context (decl) == current_function_decl)

511 {

…

523 }

524

525 /*When not in function-at-a-time mode, expand_end_bindings will

526 warnabout unused variables. But, in function-at-a-time mode

527 expand_end_bindings is not passed the list of variables in the

528 current scope, and therefore no warning is emitted. So, we

529 explicitly warn here. */

530 if (!processing_template_decl)

531 warn_about_unused_variables (getdecls ());

532

533 /*If there were any declarations or structure tags in that level,

534 or ifthis level is a function body,

535 createa BLOCK to record them for the life of this function. */

536 block = NULL_TREE;

…

550 /*We still support the old for-scope rules, whereby the variables

551 in afor-init statement were in scope after the for-statement

552 ended.We only use the new rules if flag_new_for_scope is

553 nonzero. */

554 leaving_for_scope

555 =current_binding_level->kind == sk_for && flag_new_for_scope == 1;

556

557 /*Remove declarations for all the DECLs in this level. */

558 for(link = decls; link; link = TREE_CHAIN (link))

559 {

560 if (leaving_for_scope&& TREE_CODE (link) == VAR_DECL

561 && DECL_NAME(link))

562 {

…

619 }

620 else

621 {

622 /*Remove the binding. */

623 decl = link;

624 if (TREE_CODE (decl) ==TREE_LIST)

625 decl = TREE_VALUE(decl);

626 if (DECL_P (decl))

627 pop_binding(DECL_NAME (decl), decl);

628 else if (TREE_CODE(decl) == OVERLOAD)

629 pop_binding(DECL_NAME (OVL_FUNCTION (decl)), decl);

630 else

631 abort ();

632 }

633 }

634

635 /*Remove declarations for any `for' variables from inner scopes

636 thatwe kept around. */

637 for(link = current_binding_level->dead_vars_from_for;

638 link; link = TREE_CHAIN(link))

639 pop_binding(DECL_NAME (TREE_VALUE (link)), TREE_VALUE (link));

640

641 /*Restore the IDENTIFIER_TYPE_VALUEs. */

642 for(link = current_binding_level->type_shadowed;

643 link; link = TREE_CHAIN(link))

644 SET_IDENTIFIER_TYPE_VALUE(TREE_PURPOSE (link), TREE_VALUE (link));

645

646 /*Restore the IDENTIFIER_LABEL_VALUEs for local labels. */

647 for(link = current_binding_level->shadowed_labels;

648 link;

649 link = TREE_CHAIN(link))

650 pop_label (TREE_VALUE(link), TREE_PURPOSE (link));

…

682 kind =current_binding_level->kind;

683

684 leave_scope();

…

722 POP_TIMEVAR_AND_RETURN(TV_NAME_LOOKUP, block);

723 }

因为对应于作用域的cxx_scope对象的names域记录了在其中的所有声明，并且对应的IDENTIFIER_NODE的bindings域绑定了该名字与该作用域中的声明。在退出该作用域时，毫无疑问需要移除这些绑定。这样才可以安全地撤到上一级作用域。