1 @c Copyright (c) 1999, 2000, 2001 Free Software Foundation, Inc.
2 @c Free Software Foundation, Inc.
3 @c This is part of the GCC manual.
4 @c For copying conditions, see the file gcc.texi.
6 @c ---------------------------------------------------------------------
8 @c ---------------------------------------------------------------------
11 @chapter Trees: The intermediate representation used by the C and C++ front ends
13 @cindex C/C++ Internal Representation
15 This chapter documents the internal representation used by GCC and C++ to
16 represent C and C++ source programs. When presented with a C or C++
17 source program, GCC parses the program, performs semantic analysis
18 (including the generation of error messages), and then produces the
19 internal representation described here. This representation contains a
20 complete representation for the entire translation unit provided as
21 input to the front end. This representation is then typically processed
22 by a code-generator in order to produce machine code, but could also be
23 used in the creation of source browsers, intelligent editors, automatic
24 documentation generators, interpreters, and any other programs needing
25 the ability to process C or C++ code.
27 This chapter explains the internal representation. In particular, it
28 documents the internal representation for C and C++ source
29 constructs, and the macros, functions, and variables that can be used to
30 access these constructs. The C++ representation which is largely a superset
31 of the representation used in the C front end. There is only one
32 construct used in C that does not appear in the C++ front end and that
33 is the GNU ``nested function'' extension. Many of the macros documented
34 here do not apply in C because the corresponding language constructs do
37 If you are developing a ``back end'', be it is a code-generator or some
38 other tool, that uses this representation, you may occasionally find
39 that you need to ask questions not easily answered by the functions and
40 macros available here. If that situation occurs, it is quite likely
41 that GCC already supports the functionality you desire, but that the
42 interface is simply not documented here. In that case, you should ask
43 the GCC maintainers (via mail to @email{gcc@@gcc.gnu.org}) about
44 documenting the functionality you require. Similarly, if you find
45 yourself writing functions that do not deal directly with your back end,
46 but instead might be useful to other people using the GCC front end, you
47 should submit your patches for inclusion in GCC@.
50 * Deficiencies:: Topics net yet covered in this document.
51 * Tree overview:: All about @code{tree}s.
52 * Types:: Fundamental and aggregate types.
53 * Scopes:: Namespaces and classes.
54 * Functions:: Overloading, function bodies, and linkage.
55 * Declarations:: Type declarations and variables.
56 * Attributes:: Declaration and type attributes.
57 * Expression trees:: From @code{typeid} to @code{throw}.
60 @c ---------------------------------------------------------------------
62 @c ---------------------------------------------------------------------
67 There are many places in which this document is incomplet and incorrekt.
68 It is, as of yet, only @emph{preliminary} documentation.
70 @c ---------------------------------------------------------------------
72 @c ---------------------------------------------------------------------
79 The central data structure used by the internal representation is the
80 @code{tree}. These nodes, while all of the C type @code{tree}, are of
81 many varieties. A @code{tree} is a pointer type, but the object to
82 which it points may be of a variety of types. From this point forward,
83 we will refer to trees in ordinary type, rather than in @code{this
84 font}, except when talking about the actual C type @code{tree}.
86 You can tell what kind of node a particular tree is by using the
87 @code{TREE_CODE} macro. Many, many macros take a trees as input and
88 return trees as output. However, most macros require a certain kinds of
89 tree node as input. In other words, there is a type-system for trees,
90 but it is not reflected in the C type-system.
92 For safety, it is useful to configure GCC with @option{--enable-checking}.
93 Although this results in a significant performance penalty (since all
94 tree types are checked at run-time), and is therefore inappropriate in a
95 release version, it is extremely helpful during the development process.
97 Many macros behave as predicates. Many, although not all, of these
98 predicates end in @samp{_P}. Do not rely on the result type of these
99 macros being of any particular type. You may, however, rely on the fact
100 that the type can be compared to @code{0}, so that statements like
102 if (TEST_P (t) && !TEST_P (y))
108 int i = (TEST_P (t) != 0);
111 are legal. Macros that return @code{int} values now may be changed to
112 return @code{tree} values, or other pointers in the future. Even those
113 that continue to return @code{int} may return multiple nonzero codes
114 where previously they returned only zero and one. Therefore, you should
120 as this code is not guaranteed to work correctly in the future.
122 You should not take the address of values returned by the macros or
123 functions described here. In particular, no guarantee is given that the
126 In general, the names of macros are all in uppercase, while the names of
127 functions are entirely in lower case. There are rare exceptions to this
128 rule. You should assume that any macro or function whose name is made
129 up entirely of uppercase letters may evaluate its arguments more than
130 once. You may assume that a macro or function whose name is made up
131 entirely of lowercase letters will evaluate its arguments only once.
133 The @code{error_mark_node} is a special tree. Its tree code is
134 @code{ERROR_MARK}, but since there is only ever one node with that code,
135 the usual practice is to compare the tree against
136 @code{error_mark_node}. (This test is just a test for pointer
137 equality.) If an error has occurred during front-end processing the
138 flag @code{errorcount} will be set. If the front end has encountered
139 code it cannot handle, it will issue a message to the user and set
140 @code{sorrycount}. When these flags are set, any macro or function
141 which normally returns a tree of a particular kind may instead return
142 the @code{error_mark_node}. Thus, if you intend to do any processing of
143 erroneous code, you must be prepared to deal with the
144 @code{error_mark_node}.
146 Occasionally, a particular tree slot (like an operand to an expression,
147 or a particular field in a declaration) will be referred to as
148 ``reserved for the back end.'' These slots are used to store RTL when
149 the tree is converted to RTL for use by the GCC back end. However, if
150 that process is not taking place (e.g., if the front end is being hooked
151 up to an intelligent editor), then those slots may be used by the
152 back end presently in use.
154 If you encounter situations that do not match this documentation, such
155 as tree nodes of types not mentioned here, or macros documented to
156 return entities of a particular kind that instead return entities of
157 some different kind, you have found a bug, either in the front end or in
158 the documentation. Please report these bugs as you would any other
162 * Macros and Functions::Macros and functions that can be used with all trees.
163 * Identifiers:: The names of things.
164 * Containers:: Lists and vectors.
167 @c ---------------------------------------------------------------------
169 @c ---------------------------------------------------------------------
171 @node Macros and Functions
175 This section is not here yet.
177 @c ---------------------------------------------------------------------
179 @c ---------------------------------------------------------------------
182 @subsection Identifiers
185 @tindex IDENTIFIER_NODE
187 An @code{IDENTIFIER_NODE} represents a slightly more general concept
188 that the standard C or C++ concept of identifier. In particular, an
189 @code{IDENTIFIER_NODE} may contain a @samp{$}, or other extraordinary
192 There are never two distinct @code{IDENTIFIER_NODE}s representing the
193 same identifier. Therefore, you may use pointer equality to compare
194 @code{IDENTIFIER_NODE}s, rather than using a routine like @code{strcmp}.
196 You can use the following macros to access identifiers:
198 @item IDENTIFIER_POINTER
199 The string represented by the identifier, represented as a
200 @code{char*}. This string is always @code{NUL}-terminated, and contains
201 no embedded @code{NUL} characters.
203 @item IDENTIFIER_LENGTH
204 The length of the string returned by @code{IDENTIFIER_POINTER}, not
205 including the trailing @code{NUL}. This value of
206 @code{IDENTIFIER_LENGTH (x)} is always the same as @code{strlen
207 (IDENTIFIER_POINTER (x))}.
209 @item IDENTIFIER_OPNAME_P
210 This predicate holds if the identifier represents the name of an
211 overloaded operator. In this case, you should not depend on the
212 contents of either the @code{IDENTIFIER_POINTER} or the
213 @code{IDENTIFIER_LENGTH}.
215 @item IDENTIFIER_TYPENAME_P
216 This predicate holds if the identifier represents the name of a
217 user-defined conversion operator. In this case, the @code{TREE_TYPE} of
218 the @code{IDENTIFIER_NODE} holds the type to which the conversion
223 @c ---------------------------------------------------------------------
225 @c ---------------------------------------------------------------------
228 @subsection Containers
236 @findex TREE_VEC_LENGTH
239 Two common container data structures can be represented directly with
240 tree nodes. A @code{TREE_LIST} is a singly linked list containing two
241 trees per node. These are the @code{TREE_PURPOSE} and @code{TREE_VALUE}
242 of each node. (Often, the @code{TREE_PURPOSE} contains some kind of
243 tag, or additional information, while the @code{TREE_VALUE} contains the
244 majority of the payload. In other cases, the @code{TREE_PURPOSE} is
245 simply @code{NULL_TREE}, while in still others both the
246 @code{TREE_PURPOSE} and @code{TREE_VALUE} are of equal stature.) Given
247 one @code{TREE_LIST} node, the next node is found by following the
248 @code{TREE_CHAIN}. If the @code{TREE_CHAIN} is @code{NULL_TREE}, then
249 you have reached the end of the list.
251 A @code{TREE_VEC} is a simple vector. The @code{TREE_VEC_LENGTH} is an
252 integer (not a tree) giving the number of nodes in the vector. The
253 nodes themselves are accessed using the @code{TREE_VEC_ELT} macro, which
254 takes two arguments. The first is the @code{TREE_VEC} in question; the
255 second is an integer indicating which element in the vector is desired.
256 The elements are indexed from zero.
258 @c ---------------------------------------------------------------------
260 @c ---------------------------------------------------------------------
267 @cindex fundamental type
271 @tindex TYPE_MIN_VALUE
272 @tindex TYPE_MAX_VALUE
275 @tindex ENUMERAL_TYPE
278 @tindex REFERENCE_TYPE
279 @tindex FUNCTION_TYPE
286 @tindex TYPENAME_TYPE
288 @findex CP_TYPE_QUALS
289 @findex TYPE_UNQUALIFIED
290 @findex TYPE_QUAL_CONST
291 @findex TYPE_QUAL_VOLATILE
292 @findex TYPE_QUAL_RESTRICT
293 @findex TYPE_MAIN_VARIANT
294 @cindex qualified type
297 @findex TYPE_PRECISION
298 @findex TYPE_ARG_TYPES
299 @findex TYPE_METHOD_BASETYPE
300 @findex TYPE_PTRMEM_P
301 @findex TYPE_OFFSET_BASETYPE
305 @findex TYPENAME_TYPE_FULLNAME
307 @findex TYPE_PTROBV_P
309 All types have corresponding tree nodes. However, you should not assume
310 that there is exactly one tree node corresponding to each type. There
311 are often several nodes each of which correspond to the same type.
313 For the most part, different kinds of types have different tree codes.
314 (For example, pointer types use a @code{POINTER_TYPE} code while arrays
315 use an @code{ARRAY_TYPE} code.) However, pointers to member functions
316 use the @code{RECORD_TYPE} code. Therefore, when writing a
317 @code{switch} statement that depends on the code associated with a
318 particular type, you should take care to handle pointers to member
319 functions under the @code{RECORD_TYPE} case label.
321 In C++, an array type is not qualified; rather the type of the array
322 elements is qualified. This situation is reflected in the intermediate
323 representation. The macros described here will always examine the
324 qualification of the underlying element type when applied to an array
325 type. (If the element type is itself an array, then the recursion
326 continues until a non-array type is found, and the qualification of this
327 type is examined.) So, for example, @code{CP_TYPE_CONST_P} will hold of
328 the type @code{const int ()[7]}, denoting an array of seven @code{int}s.
330 The following functions and macros deal with cv-qualification of types:
333 This macro returns the set of type qualifiers applied to this type.
334 This value is @code{TYPE_UNQUALIFIED} if no qualifiers have been
335 applied. The @code{TYPE_QUAL_CONST} bit is set if the type is
336 @code{const}-qualified. The @code{TYPE_QUAL_VOLATILE} bit is set if the
337 type is @code{volatile}-qualified. The @code{TYPE_QUAL_RESTRICT} bit is
338 set if the type is @code{restrict}-qualified.
340 @item CP_TYPE_CONST_P
341 This macro holds if the type is @code{const}-qualified.
343 @item CP_TYPE_VOLATILE_P
344 This macro holds if the type is @code{volatile}-qualified.
346 @item CP_TYPE_RESTRICT_P
347 This macro holds if the type is @code{restrict}-qualified.
349 @item CP_TYPE_CONST_NON_VOLATILE_P
350 This predicate holds for a type that is @code{const}-qualified, but
351 @emph{not} @code{volatile}-qualified; other cv-qualifiers are ignored as
352 well: only the @code{const}-ness is tested.
354 @item TYPE_MAIN_VARIANT
355 This macro returns the unqualified version of a type. It may be applied
356 to an unqualified type, but it is not always the identity function in
360 A few other macros and functions are usable with all types:
363 The number of bits required to represent the type, represented as an
364 @code{INTEGER_CST}. For an incomplete type, @code{TYPE_SIZE} will be
368 The alignment of the type, in bits, represented as an @code{int}.
371 This macro returns a declaration (in the form of a @code{TYPE_DECL}) for
372 the type. (Note this macro does @emph{not} return a
373 @code{IDENTIFIER_NODE}, as you might expect, given its name!) You can
374 look at the @code{DECL_NAME} of the @code{TYPE_DECL} to obtain the
375 actual name of the type. The @code{TYPE_NAME} will be @code{NULL_TREE}
376 for a type that is not a built-in type, the result of a typedef, or a
379 @item CP_INTEGRAL_TYPE
380 This predicate holds if the type is an integral type. Notice that in
381 C++, enumerations are @emph{not} integral types.
383 @item ARITHMETIC_TYPE_P
384 This predicate holds if the type is an integral type (in the C++ sense)
385 or a floating point type.
388 This predicate holds for a class-type.
391 This predicate holds for a built-in type.
394 This predicate holds if the type is a pointer to data member.
397 This predicate holds if the type is a pointer type, and the pointee is
401 This predicate holds for a pointer to function type.
404 This predicate holds for a pointer to object type. Note however that it
405 does not hold for the generic pointer to object type @code{void *}. You
406 may use @code{TYPE_PTROBV_P} to test for a pointer to object type as
407 well as @code{void *}.
410 This predicate takes two types as input, and holds if they are the same
411 type. For example, if one type is a @code{typedef} for the other, or
412 both are @code{typedef}s for the same type. This predicate also holds if
413 the two trees given as input are simply copies of one another; i.e.,
414 there is no difference between them at the source level, but, for
415 whatever reason, a duplicate has been made in the representation. You
416 should never use @code{==} (pointer equality) to compare types; always
417 use @code{same_type_p} instead.
420 Detailed below are the various kinds of types, and the macros that can
421 be used to access them. Although other kinds of types are used
422 elsewhere in G++, the types described here are the only ones that you
423 will encounter while examining the intermediate representation.
427 Used to represent the @code{void} type.
430 Used to represent the various integral types, including @code{char},
431 @code{short}, @code{int}, @code{long}, and @code{long long}. This code
432 is not used for enumeration types, nor for the @code{bool} type. Note
433 that GCC's @code{CHAR_TYPE} node is @emph{not} used to represent
434 @code{char}. The @code{TYPE_PRECISION} is the number of bits used in
435 the representation, represented as an @code{unsigned int}. (Note that
436 in the general case this is not the same value as @code{TYPE_SIZE};
437 suppose that there were a 24-bit integer type, but that alignment
438 requirements for the ABI required 32-bit alignment. Then,
439 @code{TYPE_SIZE} would be an @code{INTEGER_CST} for 32, while
440 @code{TYPE_PRECISION} would be 24.) The integer type is unsigned if
441 @code{TREE_UNSIGNED} holds; otherwise, it is signed.
443 The @code{TYPE_MIN_VALUE} is an @code{INTEGER_CST} for the smallest
444 integer that may be represented by this type. Similarly, the
445 @code{TYPE_MAX_VALUE} is an @code{INTEGER_CST} for the largest integer
446 that may be represented by this type.
449 Used to represent the @code{float}, @code{double}, and @code{long
450 double} types. The number of bits in the floating-point representation
451 is given by @code{TYPE_PRECISION}, as in the @code{INTEGER_TYPE} case.
454 Used to represent GCC built-in @code{__complex__} data types. The
455 @code{TREE_TYPE} is the type of the real and imaginary parts.
458 Used to represent an enumeration type. The @code{TYPE_PRECISION} gives
459 (as an @code{int}), the number of bits used to represent the type. If
460 there are no negative enumeration constants, @code{TREE_UNSIGNED} will
461 hold. The minimum and maximum enumeration constants may be obtained
462 with @code{TYPE_MIN_VALUE} and @code{TYPE_MAX_VALUE}, respectively; each
463 of these macros returns an @code{INTEGER_CST}.
465 The actual enumeration constants themselves may be obtained by looking
466 at the @code{TYPE_VALUES}. This macro will return a @code{TREE_LIST},
467 containing the constants. The @code{TREE_PURPOSE} of each node will be
468 an @code{IDENTIFIER_NODE} giving the name of the constant; the
469 @code{TREE_VALUE} will be an @code{INTEGER_CST} giving the value
470 assigned to that constant. These constants will appear in the order in
471 which they were declared. The @code{TREE_TYPE} of each of these
472 constants will be the type of enumeration type itself.
475 Used to represent the @code{bool} type.
478 Used to represent pointer types, and pointer to data member types. The
479 @code{TREE_TYPE} gives the type to which this type points. If the type
480 is a pointer to data member type, then @code{TYPE_PTRMEM_P} will hold.
481 For a pointer to data member type of the form @samp{T X::*},
482 @code{TYPE_PTRMEM_CLASS_TYPE} will be the type @code{X}, while
483 @code{TYPE_PTRMEM_POINTED_TO_TYPE} will be the type @code{T}.
486 Used to represent reference types. The @code{TREE_TYPE} gives the type
487 to which this type refers.
490 Used to represent the type of non-member functions and of static member
491 functions. The @code{TREE_TYPE} gives the return type of the function.
492 The @code{TYPE_ARG_TYPES} are a @code{TREE_LIST} of the argument types.
493 The @code{TREE_VALUE} of each node in this list is the type of the
494 corresponding argument; the @code{TREE_PURPOSE} is an expression for the
495 default argument value, if any. If the last node in the list is
496 @code{void_list_node} (a @code{TREE_LIST} node whose @code{TREE_VALUE}
497 is the @code{void_type_node}), then functions of this type do not take
498 variable arguments. Otherwise, they do take a variable number of
501 Note that in C (but not in C++) a function declared like @code{void f()}
502 is an unprototyped function taking a variable number of arguments; the
503 @code{TYPE_ARG_TYPES} of such a function will be @code{NULL}.
506 Used to represent the type of a non-static member function. Like a
507 @code{FUNCTION_TYPE}, the return type is given by the @code{TREE_TYPE}.
508 The type of @code{*this}, i.e., the class of which functions of this
509 type are a member, is given by the @code{TYPE_METHOD_BASETYPE}. The
510 @code{TYPE_ARG_TYPES} is the parameter list, as for a
511 @code{FUNCTION_TYPE}, and includes the @code{this} argument.
514 Used to represent array types. The @code{TREE_TYPE} gives the type of
515 the elements in the array. If the array-bound is present in the type,
516 the @code{TYPE_DOMAIN} is an @code{INTEGER_TYPE} whose
517 @code{TYPE_MIN_VALUE} and @code{TYPE_MAX_VALUE} will be the lower and
518 upper bounds of the array, respectively. The @code{TYPE_MIN_VALUE} will
519 always be an @code{INTEGER_CST} for zero, while the
520 @code{TYPE_MAX_VALUE} will be one less than the number of elements in
521 the array, i.e., the highest value which may be used to index an element
525 Used to represent @code{struct} and @code{class} types, as well as
526 pointers to member functions and similar constructs in other languages.
527 @code{TYPE_FIELDS} contains the items contained in this type, each of
528 which can be a @code{FIELD_DECL}, @code{VAR_DECL}, @code{CONST_DECL}, or
529 @code{TYPE_DECL}. You may not make any assumptions about the ordering
530 of the fields in the type or whether one or more of them overlap. If
531 @code{TYPE_PTRMEMFUNC_P} holds, then this type is a pointer-to-member
532 type. In that case, the @code{TYPE_PTRMEMFUNC_FN_TYPE} is a
533 @code{POINTER_TYPE} pointing to a @code{METHOD_TYPE}. The
534 @code{METHOD_TYPE} is the type of a function pointed to by the
535 pointer-to-member function. If @code{TYPE_PTRMEMFUNC_P} does not hold,
536 this type is a class type. For more information, see @pxref{Classes}.
539 Used to represent @code{union} types. Similar to @code{RECORD_TYPE}
540 except that all @code{FIELD_DECL} nodes in @code{TYPE_FIELD} start at
543 @item QUAL_UNION_TYPE
544 Used to represent part of a variant record in Ada. Similar to
545 @code{UNION_TYPE} except that each @code{FIELD_DECL} has a
546 @code{DECL_QUALIFIER} field, which contains a boolean expression that
547 indicates whether the field is present in the object. The type will only
548 have one field, so each field's @code{DECL_QUALIFIER} is only evaluated
549 if none of the expressions in the previous fields in @code{TYPE_FIELDS}
550 are nonzero. Normally these expressions will reference a field in the
551 outer object using a @code{PLACEHOLDER_EXPR}.
554 This node is used to represent a type the knowledge of which is
555 insufficient for a sound processing.
558 This node is used to represent a data member; for example a
559 pointer-to-data-member is represented by a @code{POINTER_TYPE} whose
560 @code{TREE_TYPE} is an @code{OFFSET_TYPE}. For a data member @code{X::m}
561 the @code{TYPE_OFFSET_BASETYPE} is @code{X} and the @code{TREE_TYPE} is
562 the type of @code{m}.
565 Used to represent a construct of the form @code{typename T::A}. The
566 @code{TYPE_CONTEXT} is @code{T}; the @code{TYPE_NAME} is an
567 @code{IDENTIFIER_NODE} for @code{A}. If the type is specified via a
568 template-id, then @code{TYPENAME_TYPE_FULLNAME} yields a
569 @code{TEMPLATE_ID_EXPR}. The @code{TREE_TYPE} is non-@code{NULL} if the
570 node is implicitly generated in support for the implicit typename
571 extension; in which case the @code{TREE_TYPE} is a type node for the
575 Used to represent the @code{__typeof__} extension. The
576 @code{TYPE_FIELDS} is the expression the type of which is being
580 There are variables whose values represent some of the basic types.
584 A node for @code{void}.
586 @item integer_type_node
587 A node for @code{int}.
589 @item unsigned_type_node.
590 A node for @code{unsigned int}.
592 @item char_type_node.
593 A node for @code{char}.
596 It may sometimes be useful to compare one of these variables with a type
597 in hand, using @code{same_type_p}.
599 @c ---------------------------------------------------------------------
601 @c ---------------------------------------------------------------------
605 @cindex namespace, class, scope
607 The root of the entire intermediate representation is the variable
608 @code{global_namespace}. This is the namespace specified with @code{::}
609 in C++ source code. All other namespaces, types, variables, functions,
610 and so forth can be found starting with this namespace.
612 Besides namespaces, the other high-level scoping construct in C++ is the
613 class. (Throughout this manual the term @dfn{class} is used to mean the
614 types referred to in the ANSI/ISO C++ Standard as classes; these include
615 types defined with the @code{class}, @code{struct}, and @code{union}
619 * Namespaces:: Member functions, types, etc.
620 * Classes:: Members, bases, friends, etc.
623 @c ---------------------------------------------------------------------
625 @c ---------------------------------------------------------------------
628 @subsection Namespaces
630 @tindex NAMESPACE_DECL
632 A namespace is represented by a @code{NAMESPACE_DECL} node.
634 However, except for the fact that it is distinguished as the root of the
635 representation, the global namespace is no different from any other
636 namespace. Thus, in what follows, we describe namespaces generally,
637 rather than the global namespace in particular.
639 The following macros and functions can be used on a @code{NAMESPACE_DECL}:
643 This macro is used to obtain the @code{IDENTIFIER_NODE} corresponding to
644 the unqualified name of the name of the namespace (@pxref{Identifiers}).
645 The name of the global namespace is @samp{::}, even though in C++ the
646 global namespace is unnamed. However, you should use comparison with
647 @code{global_namespace}, rather than @code{DECL_NAME} to determine
648 whether or not a namespaces is the global one. An unnamed namespace
649 will have a @code{DECL_NAME} equal to @code{anonymous_namespace_name}.
650 Within a single translation unit, all unnamed namespaces will have the
654 This macro returns the enclosing namespace. The @code{DECL_CONTEXT} for
655 the @code{global_namespace} is @code{NULL_TREE}.
657 @item DECL_NAMESPACE_ALIAS
658 If this declaration is for a namespace alias, then
659 @code{DECL_NAMESPACE_ALIAS} is the namespace for which this one is an
662 Do not attempt to use @code{cp_namespace_decls} for a namespace which is
663 an alias. Instead, follow @code{DECL_NAMESPACE_ALIAS} links until you
664 reach an ordinary, non-alias, namespace, and call
665 @code{cp_namespace_decls} there.
667 @item DECL_NAMESPACE_STD_P
668 This predicate holds if the namespace is the special @code{::std}
671 @item cp_namespace_decls
672 This function will return the declarations contained in the namespace,
673 including types, overloaded functions, other namespaces, and so forth.
674 If there are no declarations, this function will return
675 @code{NULL_TREE}. The declarations are connected through their
676 @code{TREE_CHAIN} fields.
678 Although most entries on this list will be declarations,
679 @code{TREE_LIST} nodes may also appear. In this case, the
680 @code{TREE_VALUE} will be an @code{OVERLOAD}. The value of the
681 @code{TREE_PURPOSE} is unspecified; back ends should ignore this value.
682 As with the other kinds of declarations returned by
683 @code{cp_namespace_decls}, the @code{TREE_CHAIN} will point to the next
684 declaration in this list.
686 For more information on the kinds of declarations that can occur on this
687 list, @xref{Declarations}. Some declarations will not appear on this
688 list. In particular, no @code{FIELD_DECL}, @code{LABEL_DECL}, or
689 @code{PARM_DECL} nodes will appear here.
691 This function cannot be used with namespaces that have
692 @code{DECL_NAMESPACE_ALIAS} set.
696 @c ---------------------------------------------------------------------
698 @c ---------------------------------------------------------------------
705 @findex CLASSTYPE_DECLARED_CLASS
708 @findex TREE_VIA_PUBLIC
709 @findex TREE_VIA_PROTECTED
710 @findex TREE_VIA_PRIVATE
715 A class type is represented by either a @code{RECORD_TYPE} or a
716 @code{UNION_TYPE}. A class declared with the @code{union} tag is
717 represented by a @code{UNION_TYPE}, while classes declared with either
718 the @code{struct} or the @code{class} tag are represented by
719 @code{RECORD_TYPE}s. You can use the @code{CLASSTYPE_DECLARED_CLASS}
720 macro to discern whether or not a particular type is a @code{class} as
721 opposed to a @code{struct}. This macro will be true only for classes
722 declared with the @code{class} tag.
724 Almost all non-function members are available on the @code{TYPE_FIELDS}
725 list. Given one member, the next can be found by following the
726 @code{TREE_CHAIN}. You should not depend in any way on the order in
727 which fields appear on this list. All nodes on this list will be
728 @samp{DECL} nodes. A @code{FIELD_DECL} is used to represent a non-static
729 data member, a @code{VAR_DECL} is used to represent a static data
730 member, and a @code{TYPE_DECL} is used to represent a type. Note that
731 the @code{CONST_DECL} for an enumeration constant will appear on this
732 list, if the enumeration type was declared in the class. (Of course,
733 the @code{TYPE_DECL} for the enumeration type will appear here as well.)
734 There are no entries for base classes on this list. In particular,
735 there is no @code{FIELD_DECL} for the ``base-class portion'' of an
738 The @code{TYPE_VFIELD} is a compiler-generated field used to point to
739 virtual function tables. It may or may not appear on the
740 @code{TYPE_FIELDS} list. However, back ends should handle the
741 @code{TYPE_VFIELD} just like all the entries on the @code{TYPE_FIELDS}
744 The function members are available on the @code{TYPE_METHODS} list.
745 Again, subsequent members are found by following the @code{TREE_CHAIN}
746 field. If a function is overloaded, each of the overloaded functions
747 appears; no @code{OVERLOAD} nodes appear on the @code{TYPE_METHODS}
748 list. Implicitly declared functions (including default constructors,
749 copy constructors, assignment operators, and destructors) will appear on
752 Every class has an associated @dfn{binfo}, which can be obtained with
753 @code{TYPE_BINFO}. Binfos are used to represent base-classes. The
754 binfo given by @code{TYPE_BINFO} is the degenerate case, whereby every
755 class is considered to be its own base-class. The base classes for a
756 particular binfo can be obtained with @code{BINFO_BASETYPES}. These
757 base-classes are themselves binfos. The class type associated with a
758 binfo is given by @code{BINFO_TYPE}. It is always the case that
759 @code{BINFO_TYPE (TYPE_BINFO (x))} is the same type as @code{x}, up to
760 qualifiers. However, it is not always the case that @code{TYPE_BINFO
761 (BINFO_TYPE (y))} is always the same binfo as @code{y}. The reason is
762 that if @code{y} is a binfo representing a base-class @code{B} of a
763 derived class @code{D}, then @code{BINFO_TYPE (y)} will be @code{B}, and
764 @code{TYPE_INFO (BINFO_TYPE (y))} will be @code{B} as its own
765 base-class, rather than as a base-class of @code{D}.
767 The @code{BINFO_BASETYPES} is a @code{TREE_VEC} (@pxref{Containers}).
768 Base types appear in left-to-right order in this vector. You can tell
769 whether or @code{public}, @code{protected}, or @code{private}
770 inheritance was used by using the @code{TREE_VIA_PUBLIC},
771 @code{TREE_VIA_PROTECTED}, and @code{TREE_VIA_PRIVATE} macros. Each of
772 these macros takes a @code{BINFO} and is true if and only if the
773 indicated kind of inheritance was used. If @code{TREE_VIA_VIRTUAL}
774 holds of a binfo, then its @code{BINFO_TYPE} was inherited from
777 The following macros can be used on a tree node representing a class-type.
781 This predicate holds if the class is local class @emph{i.e.} declared
782 inside a function body.
784 @item TYPE_POLYMORPHIC_P
785 This predicate holds if the class has at least one virtual function
786 (declared or inherited).
788 @item TYPE_HAS_DEFAULT_CONSTRUCTOR
789 This predicate holds whenever its argument represents a class-type with
792 @item CLASSTYPE_HAS_MUTABLE
793 @item TYPE_HAS_MUTABLE_P
794 These predicates hold for a class-type having a mutable data member.
796 @item CLASSTYPE_NON_POD_P
797 This predicate holds only for class-types that are not PODs.
799 @item TYPE_HAS_NEW_OPERATOR
800 This predicate holds for a class-type that defines
803 @item TYPE_HAS_ARRAY_NEW_OPERATOR
804 This predicate holds for a class-type for which
805 @code{operator new[]} is defined.
807 @item TYPE_OVERLOADS_CALL_EXPR
808 This predicate holds for class-type for which the function call
809 @code{operator()} is overloaded.
811 @item TYPE_OVERLOADS_ARRAY_REF
812 This predicate holds for a class-type that overloads
815 @item TYPE_OVERLOADS_ARROW
816 This predicate holds for a class-type for which @code{operator->} is
821 @c ---------------------------------------------------------------------
823 @c ---------------------------------------------------------------------
826 @section Declarations
829 @cindex type declaration
836 @tindex NAMESPACE_DECL
838 @tindex TEMPLATE_DECL
845 @findex DECL_EXTERNAL
847 This section covers the various kinds of declarations that appear in the
848 internal representation, except for declarations of functions
849 (represented by @code{FUNCTION_DECL} nodes), which are described in
852 Some macros can be used with any kind of declaration. These include:
855 This macro returns an @code{IDENTIFIER_NODE} giving the name of the
859 This macro returns the type of the entity declared.
861 @item DECL_SOURCE_FILE
862 This macro returns the name of the file in which the entity was
863 declared, as a @code{char*}. For an entity declared implicitly by the
864 compiler (like @code{__builtin_memcpy}), this will be the string
867 @item DECL_SOURCE_LINE
868 This macro returns the line number at which the entity was declared, as
871 @item DECL_ARTIFICIAL
872 This predicate holds if the declaration was implicitly generated by the
873 compiler. For example, this predicate will hold of an implicitly
874 declared member function, or of the @code{TYPE_DECL} implicitly
875 generated for a class type. Recall that in C++ code like:
880 is roughly equivalent to C code like:
885 The implicitly generated @code{typedef} declaration is represented by a
886 @code{TYPE_DECL} for which @code{DECL_ARTIFICIAL} holds.
888 @item DECL_NAMESPACE_SCOPE_P
889 This predicate holds if the entity was declared at a namespace scope.
891 @item DECL_CLASS_SCOPE_P
892 This predicate holds if the entity was declared at a class scope.
894 @item DECL_FUNCTION_SCOPE_P
895 This predicate holds if the entity was declared inside a function
900 The various kinds of declarations include:
903 These nodes are used to represent labels in function bodies. For more
904 information, see @ref{Functions}. These nodes only appear in block
908 These nodes are used to represent enumeration constants. The value of
909 the constant is given by @code{DECL_INITIAL} which will be an
910 @code{INTEGER_CST} with the same type as the @code{TREE_TYPE} of the
911 @code{CONST_DECL}, i.e., an @code{ENUMERAL_TYPE}.
914 These nodes represent the value returned by a function. When a value is
915 assigned to a @code{RESULT_DECL}, that indicates that the value should
916 be returned, via bitwise copy, by the function. You can use
917 @code{DECL_SIZE} and @code{DECL_ALIGN} on a @code{RESULT_DECL}, just as
918 with a @code{VAR_DECL}.
921 These nodes represent @code{typedef} declarations. The @code{TREE_TYPE}
922 is the type declared to have the name given by @code{DECL_NAME}. In
923 some cases, there is no associated name.
926 These nodes represent variables with namespace or block scope, as well
927 as static data members. The @code{DECL_SIZE} and @code{DECL_ALIGN} are
928 analogous to @code{TYPE_SIZE} and @code{TYPE_ALIGN}. For a declaration,
929 you should always use the @code{DECL_SIZE} and @code{DECL_ALIGN} rather
930 than the @code{TYPE_SIZE} and @code{TYPE_ALIGN} given by the
931 @code{TREE_TYPE}, since special attributes may have been applied to the
932 variable to give it a particular size and alignment. You may use the
933 predicates @code{DECL_THIS_STATIC} or @code{DECL_THIS_EXTERN} to test
934 whether the storage class specifiers @code{static} or @code{extern} were
935 used to declare a variable.
937 If this variable is initialized (but does not require a constructor),
938 the @code{DECL_INITIAL} will be an expression for the initializer. The
939 initializer should be evaluated, and a bitwise copy into the variable
940 performed. If the @code{DECL_INITIAL} is the @code{error_mark_node},
941 there is an initializer, but it is given by an explicit statement later
942 in the code; no bitwise copy is required.
944 GCC provides an extension that allows either automatic variables, or
945 global variables, to be placed in particular registers. This extension
946 is being used for a particular @code{VAR_DECL} if @code{DECL_REGISTER}
947 holds for the @code{VAR_DECL}, and if @code{DECL_ASSEMBLER_NAME} is not
948 equal to @code{DECL_NAME}. In that case, @code{DECL_ASSEMBLER_NAME} is
949 the name of the register into which the variable will be placed.
952 Used to represent a parameter to a function. Treat these nodes
953 similarly to @code{VAR_DECL} nodes. These nodes only appear in the
954 @code{DECL_ARGUMENTS} for a @code{FUNCTION_DECL}.
956 The @code{DECL_ARG_TYPE} for a @code{PARM_DECL} is the type that will
957 actually be used when a value is passed to this function. It may be a
958 wider type than the @code{TREE_TYPE} of the parameter; for example, the
959 ordinary type might be @code{short} while the @code{DECL_ARG_TYPE} is
963 These nodes represent non-static data members. The @code{DECL_SIZE} and
964 @code{DECL_ALIGN} behave as for @code{VAR_DECL} nodes. The
965 @code{DECL_FIELD_BITPOS} gives the first bit used for this field, as an
966 @code{INTEGER_CST}. These values are indexed from zero, where zero
967 indicates the first bit in the object.
969 If @code{DECL_C_BIT_FIELD} holds, this field is a bit-field.
976 These nodes are used to represent class, function, and variable (static
977 data member) templates. The @code{DECL_TEMPLATE_SPECIALIZATIONS} are a
978 @code{TREE_LIST}. The @code{TREE_VALUE} of each node in the list is a
979 @code{TEMPLATE_DECL}s or @code{FUNCTION_DECL}s representing
980 specializations (including instantiations) of this template. Back ends
981 can safely ignore @code{TEMPLATE_DECL}s, but should examine
982 @code{FUNCTION_DECL} nodes on the specializations list just as they
983 would ordinary @code{FUNCTION_DECL} nodes.
985 For a class template, the @code{DECL_TEMPLATE_INSTANTIATIONS} list
986 contains the instantiations. The @code{TREE_VALUE} of each node is an
987 instantiation of the class. The @code{DECL_TEMPLATE_SPECIALIZATIONS}
988 contains partial specializations of the class.
992 Back ends can safely ignore these nodes.
996 @c ---------------------------------------------------------------------
998 @c ---------------------------------------------------------------------
1003 @tindex FUNCTION_DECL
1008 A function is represented by a @code{FUNCTION_DECL} node. A set of
1009 overloaded functions is sometimes represented by a @code{OVERLOAD} node.
1011 An @code{OVERLOAD} node is not a declaration, so none of the
1012 @samp{DECL_} macros should be used on an @code{OVERLOAD}. An
1013 @code{OVERLOAD} node is similar to a @code{TREE_LIST}. Use
1014 @code{OVL_CURRENT} to get the function associated with an
1015 @code{OVERLOAD} node; use @code{OVL_NEXT} to get the next
1016 @code{OVERLOAD} node in the list of overloaded functions. The macros
1017 @code{OVL_CURRENT} and @code{OVL_NEXT} are actually polymorphic; you can
1018 use them to work with @code{FUNCTION_DECL} nodes as well as with
1019 overloads. In the case of a @code{FUNCTION_DECL}, @code{OVL_CURRENT}
1020 will always return the function itself, and @code{OVL_NEXT} will always
1021 be @code{NULL_TREE}.
1023 To determine the scope of a function, you can use the
1024 @code{DECL_REAL_CONTEXT} macro. This macro will return the class
1025 (either a @code{RECORD_TYPE} or a @code{UNION_TYPE}) or namespace (a
1026 @code{NAMESPACE_DECL}) of which the function is a member. For a virtual
1027 function, this macro returns the class in which the function was
1028 actually defined, not the base class in which the virtual declaration
1029 occurred. If a friend function is defined in a class scope, the
1030 @code{DECL_CLASS_CONTEXT} macro can be used to determine the class in
1031 which it was defined. For example, in
1033 class C @{ friend void f() @{@} @};
1035 the @code{DECL_REAL_CONTEXT} for @code{f} will be the
1036 @code{global_namespace}, but the @code{DECL_CLASS_CONTEXT} will be the
1037 @code{RECORD_TYPE} for @code{C}.
1039 The @code{DECL_REAL_CONTEXT} and @code{DECL_CLASS_CONTEXT} are not
1040 available in C; instead you should simply use @code{DECL_CONTEXT}. In C,
1041 the @code{DECL_CONTEXT} for a function maybe another function. This
1042 representation indicates that the GNU nested function extension is in
1043 use. For details on the semantics of nested functions, see the GCC
1044 Manual. The nested function can refer to local variables in its
1045 containing function. Such references are not explicitly marked in the
1046 tree structure; back ends must look at the @code{DECL_CONTEXT} for the
1047 referenced @code{VAR_DECL}. If the @code{DECL_CONTEXT} for the
1048 referenced @code{VAR_DECL} is not the same as the function currently
1049 being processed, and neither @code{DECL_EXTERNAL} nor @code{DECL_STATIC}
1050 hold, then the reference is to a local variable in a containing
1051 function, and the back end must take appropriate action.
1054 * Function Basics:: Function names, linkage, and so forth.
1055 * Function Bodies:: The statements that make up a function body.
1058 @c ---------------------------------------------------------------------
1060 @c ---------------------------------------------------------------------
1062 @node Function Basics
1063 @subsection Function Basics
1066 @cindex copy constructor
1067 @cindex assignment operator
1070 @findex DECL_ASSEMBLER_NAME
1072 @findex DECL_LINKONCE_P
1073 @findex DECL_FUNCTION_MEMBER_P
1074 @findex DECL_CONSTRUCTOR_P
1075 @findex DECL_DESTRUCTOR_P
1076 @findex DECL_OVERLOADED_OPERATOR_P
1077 @findex DECL_CONV_FN_P
1078 @findex DECL_ARTIFICIAL
1079 @findex DECL_GLOBAL_CTOR_P
1080 @findex DECL_GLOBAL_DTOR_P
1081 @findex GLOBAL_INIT_PRIORITY
1083 The following macros and functions can be used on a @code{FUNCTION_DECL}:
1086 This predicate holds for a function that is the program entry point
1090 This macro returns the unqualified name of the function, as an
1091 @code{IDENTIFIER_NODE}. For an instantiation of a function template,
1092 the @code{DECL_NAME} is the unqualified name of the template, not
1093 something like @code{f<int>}. The value of @code{DECL_NAME} is
1094 undefined when used on a constructor, destructor, overloaded operator,
1095 or type-conversion operator, or any function that is implicitly
1096 generated by the compiler. See below for macros that can be used to
1097 distinguish these cases.
1099 @item DECL_ASSEMBLER_NAME
1100 This macro returns the mangled name of the function, also an
1101 @code{IDENTIFIER_NODE}. This name does not contain leading underscores
1102 on systems that prefix all identifiers with underscores. The mangled
1103 name is computed in the same way on all platforms; if special processing
1104 is required to deal with the object file format used on a particular
1105 platform, it is the responsibility of the back end to perform those
1106 modifications. (Of course, the back end should not modify
1107 @code{DECL_ASSEMBLER_NAME} itself.)
1110 This predicate holds if the function is undefined.
1113 This predicate holds if the function has external linkage.
1115 @item DECL_LOCAL_FUNCTION_P
1116 This predicate holds if the function was declared at block scope, even
1117 though it has a global scope.
1119 @item DECL_ANTICIPATED
1120 This predicate holds if the function is a built-in function but its
1121 prototype is not yet explicitly declared.
1123 @item DECL_EXTERN_C_FUNCTION_P
1124 This predicate holds if the function is declared as an
1125 `@code{extern "C"}' function.
1127 @item DECL_LINKONCE_P
1128 This macro holds if multiple copies of this function may be emitted in
1129 various translation units. It is the responsibility of the linker to
1130 merge the various copies. Template instantiations are the most common
1131 example of functions for which @code{DECL_LINKONCE_P} holds; G++
1132 instantiates needed templates in all translation units which require them,
1133 and then relies on the linker to remove duplicate instantiations.
1135 FIXME: This macro is not yet implemented.
1137 @item DECL_FUNCTION_MEMBER_P
1138 This macro holds if the function is a member of a class, rather than a
1139 member of a namespace.
1141 @item DECL_STATIC_FUNCTION_P
1142 This predicate holds if the function a static member function.
1144 @item DECL_NONSTATIC_MEMBER_FUNCTION_P
1145 This macro holds for a non-static member function.
1147 @item DECL_CONST_MEMFUNC_P
1148 This predicate holds for a @code{const}-member function.
1150 @item DECL_VOLATILE_MEMFUNC_P
1151 This predicate holds for a @code{volatile}-member function.
1153 @item DECL_CONSTRUCTOR_P
1154 This macro holds if the function is a constructor.
1156 @item DECL_NONCONVERTING_P
1157 This predicate holds if the constructor is a non-converting constructor.
1159 @item DECL_COMPLETE_CONSTRUCTOR_P
1160 This predicate holds for a function which is a constructor for an object
1163 @item DECL_BASE_CONSTRUCTOR_P
1164 This predicate holds for a function which is a constructor for a base
1167 @item DECL_COPY_CONSTRUCTOR_P
1168 This predicate holds for a function which is a copy-constructor.
1170 @item DECL_DESTRUCTOR_P
1171 This macro holds if the function is a destructor.
1173 @item DECL_COMPLETE_DESTRUCTOR_P
1174 This predicate holds if the function is the destructor for an object a
1177 @item DECL_OVERLOADED_OPERATOR_P
1178 This macro holds if the function is an overloaded operator.
1180 @item DECL_CONV_FN_P
1181 This macro holds if the function is a type-conversion operator.
1183 @item DECL_GLOBAL_CTOR_P
1184 This predicate holds if the function is a file-scope initialization
1187 @item DECL_GLOBAL_DTOR_P
1188 This predicate holds if the function is a file-scope finalization
1192 This predicate holds if the function is a thunk.
1194 These functions represent stub code that adjusts the @code{this} pointer
1195 and then jumps to another function. When the jumped-to function
1196 returns, control is transferred directly to the caller, without
1197 returning to the thunk. The first parameter to the thunk is always the
1198 @code{this} pointer; the thunk should add @code{THUNK_DELTA} to this
1199 value. (The @code{THUNK_DELTA} is an @code{int}, not an
1200 @code{INTEGER_CST}.)
1202 Then, if @code{THUNK_VCALL_OFFSET} (an @code{INTEGER_CST}) is nonzero
1203 the adjusted @code{this} pointer must be adjusted again. The complete
1204 calculation is given by the following pseudo-code:
1208 if (THUNK_VCALL_OFFSET)
1209 this += (*((ptrdiff_t **) this))[THUNK_VCALL_OFFSET]
1212 Finally, the thunk should jump to the location given
1213 by @code{DECL_INITIAL}; this will always be an expression for the
1214 address of a function.
1216 @item DECL_NON_THUNK_FUNCTION_P
1217 This predicate holds if the function is @emph{not} a thunk function.
1219 @item GLOBAL_INIT_PRIORITY
1220 If either @code{DECL_GLOBAL_CTOR_P} or @code{DECL_GLOBAL_DTOR_P} holds,
1221 then this gives the initialization priority for the function. The
1222 linker will arrange that all functions for which
1223 @code{DECL_GLOBAL_CTOR_P} holds are run in increasing order of priority
1224 before @code{main} is called. When the program exits, all functions for
1225 which @code{DECL_GLOBAL_DTOR_P} holds are run in the reverse order.
1227 @item DECL_ARTIFICIAL
1228 This macro holds if the function was implicitly generated by the
1229 compiler, rather than explicitly declared. In addition to implicitly
1230 generated class member functions, this macro holds for the special
1231 functions created to implement static initialization and destruction, to
1232 compute run-time type information, and so forth.
1234 @item DECL_ARGUMENTS
1235 This macro returns the @code{PARM_DECL} for the first argument to the
1236 function. Subsequent @code{PARM_DECL} nodes can be obtained by
1237 following the @code{TREE_CHAIN} links.
1240 This macro returns the @code{RESULT_DECL} for the function.
1243 This macro returns the @code{FUNCTION_TYPE} or @code{METHOD_TYPE} for
1246 @item TYPE_RAISES_EXCEPTIONS
1247 This macro returns the list of exceptions that a (member-)function can
1248 raise. The returned list, if non @code{NULL}, is comprised of nodes
1249 whose @code{TREE_VALUE} represents a type.
1251 @item TYPE_NOTHROW_P
1252 This predicate holds when the exception-specification of its arguments
1253 if of the form `@code{()}'.
1255 @item DECL_ARRAY_DELETE_OPERATOR_P
1256 This predicate holds if the function an overloaded
1257 @code{operator delete[]}.
1261 @c ---------------------------------------------------------------------
1263 @c ---------------------------------------------------------------------
1265 @node Function Bodies
1266 @subsection Function Bodies
1267 @cindex function body
1274 @findex ASM_CLOBBERS
1276 @tindex CLEANUP_STMT
1277 @findex CLEANUP_DECL
1278 @findex CLEANUP_EXPR
1279 @tindex COMPOUND_STMT
1280 @findex COMPOUND_BODY
1281 @tindex CONTINUE_STMT
1283 @findex DECL_STMT_DECL
1287 @tindex EMPTY_CLASS_EXPR
1289 @findex EXPR_STMT_EXPR
1291 @findex FOR_INIT_STMT
1296 @findex GOTO_DESTINATION
1304 @tindex LABEL_STMT_LABEL
1309 @findex SCOPE_BEGIN_P
1311 @findex SCOPE_NULLIFIED_P
1313 @findex SUBOBJECT_CLEANUP
1319 @findex TRY_HANDLERS
1320 @findex HANDLER_PARMS
1321 @findex HANDLER_BODY
1327 A function that has a definition in the current translation unit will
1328 have a non-@code{NULL} @code{DECL_INITIAL}. However, back ends should not make
1329 use of the particular value given by @code{DECL_INITIAL}.
1331 The @code{DECL_SAVED_TREE} macro will give the complete body of the
1332 function. This node will usually be a @code{COMPOUND_STMT} representing
1333 the outermost block of the function, but it may also be a
1334 @code{TRY_BLOCK}, a @code{RETURN_INIT}, or any other valid statement.
1336 @subsubsection Statements
1338 There are tree nodes corresponding to all of the source-level statement
1339 constructs. These are enumerated here, together with a list of the
1340 various macros that can be used to obtain information about them. There
1341 are a few macros that can be used with all statements:
1345 This macro returns the line number for the statement. If the statement
1346 spans multiple lines, this value will be the number of the first line on
1347 which the statement occurs. Although we mention @code{CASE_LABEL} below
1348 as if it were a statement, they do not allow the use of
1349 @code{STMT_LINENO}. There is no way to obtain the line number for a
1352 Statements do not contain information about
1353 the file from which they came; that information is implicit in the
1354 @code{FUNCTION_DECL} from which the statements originate.
1356 @item STMT_IS_FULL_EXPR_P
1357 In C++, statements normally constitute ``full expressions''; temporaries
1358 created during a statement are destroyed when the statement is complete.
1359 However, G++ sometimes represents expressions by statements; these
1360 statements will not have @code{STMT_IS_FULL_EXPR_P} set. Temporaries
1361 created during such statements should be destroyed when the innermost
1362 enclosing statement with @code{STMT_IS_FULL_EXPR_P} set is exited.
1366 Here is the list of the various statement nodes, and the macros used to
1367 access them. This documentation describes the use of these nodes in
1368 non-template functions (including instantiations of template functions).
1369 In template functions, the same nodes are used, but sometimes in
1370 slightly different ways.
1372 Many of the statements have substatements. For example, a @code{while}
1373 loop will have a body, which is itself a statement. If the substatement
1374 is @code{NULL_TREE}, it is considered equivalent to a statement
1375 consisting of a single @code{;}, i.e., an expression statement in which
1376 the expression has been omitted. A substatement may in fact be a list
1377 of statements, connected via their @code{TREE_CHAIN}s. So, you should
1378 always process the statement tree by looping over substatements, like
1381 void process_stmt (stmt)
1386 switch (TREE_CODE (stmt))
1389 process_stmt (THEN_CLAUSE (stmt));
1390 /* More processing here. */
1396 stmt = TREE_CHAIN (stmt);
1400 In other words, while the @code{then} clause of an @code{if} statement
1401 in C++ can be only one statement (although that one statement may be a
1402 compound statement), the intermediate representation will sometimes use
1403 several statements chained together.
1408 Used to represent an inline assembly statement. For an inline assembly
1413 The @code{ASM_STRING} macro will return a @code{STRING_CST} node for
1414 @code{"mov x, y"}. If the original statement made use of the
1415 extended-assembly syntax, then @code{ASM_OUTPUTS},
1416 @code{ASM_INPUTS}, and @code{ASM_CLOBBERS} will be the outputs, inputs,
1417 and clobbers for the statement, represented as @code{STRING_CST} nodes.
1418 The extended-assembly syntax looks like:
1420 asm ("fsinx %1,%0" : "=f" (result) : "f" (angle));
1422 The first string is the @code{ASM_STRING}, containing the instruction
1423 template. The next two strings are the output and inputs, respectively;
1424 this statement has no clobbers. As this example indicates, ``plain''
1425 assembly statements are merely a special case of extended assembly
1426 statements; they have no cv-qualifiers, outputs, inputs, or clobbers.
1427 All of the strings will be @code{NUL}-terminated, and will contain no
1428 embedded @code{NUL}-characters.
1430 If the assembly statement is declared @code{volatile}, or if the
1431 statement was not an extended assembly statement, and is therefore
1432 implicitly volatile, then the predicate @code{ASM_VOLATILE_P} will hold
1433 of the @code{ASM_STMT}.
1437 Used to represent a @code{break} statement. There are no additional
1442 Use to represent a @code{case} label, range of @code{case} labels, or a
1443 @code{default} label. If @code{CASE_LOW} is @code{NULL_TREE}, then this is a
1444 @code{default} label. Otherwise, if @code{CASE_HIGH} is @code{NULL_TREE}, then
1445 this is an ordinary @code{case} label. In this case, @code{CASE_LOW} is
1446 an expression giving the value of the label. Both @code{CASE_LOW} and
1447 @code{CASE_HIGH} are @code{INTEGER_CST} nodes. These values will have
1448 the same type as the condition expression in the switch statement.
1450 Otherwise, if both @code{CASE_LOW} and @code{CASE_HIGH} are defined, the
1451 statement is a range of case labels. Such statements originate with the
1452 extension that allows users to write things of the form:
1456 The first value will be @code{CASE_LOW}, while the second will be
1461 Used to represent an action that should take place upon exit from the
1462 enclosing scope. Typically, these actions are calls to destructors for
1463 local objects, but back ends cannot rely on this fact. If these nodes
1464 are in fact representing such destructors, @code{CLEANUP_DECL} will be
1465 the @code{VAR_DECL} destroyed. Otherwise, @code{CLEANUP_DECL} will be
1466 @code{NULL_TREE}. In any case, the @code{CLEANUP_EXPR} is the
1467 expression to execute. The cleanups executed on exit from a scope
1468 should be run in the reverse order of the order in which the associated
1469 @code{CLEANUP_STMT}s were encountered.
1473 Used to represent a brace-enclosed block. The first substatement is
1474 given by @code{COMPOUND_BODY}. Subsequent substatements are found by
1475 following the @code{TREE_CHAIN} link from one substatement to the next.
1476 The @code{COMPOUND_BODY} will be @code{NULL_TREE} if there are no
1481 Used to represent a @code{continue} statement. There are no additional
1486 Used to mark the beginning (if @code{CTOR_BEGIN_P} holds) or end (if
1487 @code{CTOR_END_P} holds of the main body of a constructor. See also
1488 @code{SUBOBJECT} for more information on how to use these nodes.
1492 Used to represent a local declaration. The @code{DECL_STMT_DECL} macro
1493 can be used to obtain the entity declared. This declaration may be a
1494 @code{LABEL_DECL}, indicating that the label declared is a local label.
1495 (As an extension, GCC allows the declaration of labels with scope.) In
1496 C, this declaration may be a @code{FUNCTION_DECL}, indicating the
1497 use of the GCC nested function extension. For more information,
1502 Used to represent a @code{do} loop. The body of the loop is given by
1503 @code{DO_BODY} while the termination condition for the loop is given by
1504 @code{DO_COND}. The condition for a @code{do}-statement is always an
1507 @item EMPTY_CLASS_EXPR
1509 Used to represent a temporary object of a class with no data whose
1510 address is never taken. (All such objects are interchangeable.) The
1511 @code{TREE_TYPE} represents the type of the object.
1515 Used to represent an expression statement. Use @code{EXPR_STMT_EXPR} to
1516 obtain the expression.
1520 Used to represent a @code{for} statement. The @code{FOR_INIT_STMT} is
1521 the initialization statement for the loop. The @code{FOR_COND} is the
1522 termination condition. The @code{FOR_EXPR} is the expression executed
1523 right before the @code{FOR_COND} on each loop iteration; often, this
1524 expression increments a counter. The body of the loop is given by
1525 @code{FOR_BODY}. Note that @code{FOR_INIT_STMT} and @code{FOR_BODY}
1526 return statements, while @code{FOR_COND} and @code{FOR_EXPR} return
1531 Used to represent a @code{goto} statement. The @code{GOTO_DESTINATION} will
1532 usually be a @code{LABEL_DECL}. However, if the ``computed goto'' extension
1533 has been used, the @code{GOTO_DESTINATION} will be an arbitrary expression
1534 indicating the destination. This expression will always have pointer type.
1535 Additionally the @code{GOTO_FAKE_P} flag is set whenever the goto statement
1536 does not come from source code, but it is generated implicitly by the compiler.
1537 This is used for branch prediction.
1541 Used to represent a C++ @code{catch} block. The @code{HANDLER_TYPE}
1542 is the type of exception that will be caught by this handler; it is
1543 equal (by pointer equality) to @code{CATCH_ALL_TYPE} if this handler
1544 is for all types. @code{HANDLER_PARMS} is the @code{DECL_STMT} for
1545 the catch parameter, and @code{HANDLER_BODY} is the
1546 @code{COMPOUND_STMT} for the block itself.
1550 Used to represent an @code{if} statement. The @code{IF_COND} is the
1553 If the condition is a @code{TREE_LIST}, then the @code{TREE_PURPOSE} is
1554 a statement (usually a @code{DECL_STMT}). Each time the condition is
1555 evaluated, the statement should be executed. Then, the
1556 @code{TREE_VALUE} should be used as the conditional expression itself.
1557 This representation is used to handle C++ code like this:
1560 if (int i = 7) @dots{}
1563 where there is a new local variable (or variables) declared within the
1566 The @code{THEN_CLAUSE} represents the statement given by the @code{then}
1567 condition, while the @code{ELSE_CLAUSE} represents the statement given
1568 by the @code{else} condition.
1572 Used to represent a label. The @code{LABEL_DECL} declared by this
1573 statement can be obtained with the @code{LABEL_STMT_LABEL} macro. The
1574 @code{IDENTIFIER_NODE} giving the name of the label can be obtained from
1575 the @code{LABEL_DECL} with @code{DECL_NAME}.
1579 If the function uses the G++ ``named return value'' extension, meaning
1580 that the function has been defined like:
1582 S f(int) return s @{@dots{}@}
1584 then there will be a @code{RETURN_INIT}. There is never a named
1585 returned value for a constructor. The first argument to the
1586 @code{RETURN_INIT} is the name of the object returned; the second
1587 argument is the initializer for the object. The object is initialized
1588 when the @code{RETURN_INIT} is encountered. The object referred to is
1589 the actual object returned; this extension is a manual way of doing the
1590 ``return-value optimization.'' Therefore, the object must actually be
1591 constructed in the place where the object will be returned.
1595 Used to represent a @code{return} statement. The @code{RETURN_EXPR} is
1596 the expression returned; it will be @code{NULL_TREE} if the statement
1604 A scope-statement represents the beginning or end of a scope. If
1605 @code{SCOPE_BEGIN_P} holds, this statement represents the beginning of a
1606 scope; if @code{SCOPE_END_P} holds this statement represents the end of
1607 a scope. On exit from a scope, all cleanups from @code{CLEANUP_STMT}s
1608 occurring in the scope must be run, in reverse order to the order in
1609 which they were encountered. If @code{SCOPE_NULLIFIED_P} or
1610 @code{SCOPE_NO_CLEANUPS_P} holds of the scope, back ends should behave
1611 as if the @code{SCOPE_STMT} were not present at all.
1615 In a constructor, these nodes are used to mark the point at which a
1616 subobject of @code{this} is fully constructed. If, after this point, an
1617 exception is thrown before a @code{CTOR_STMT} with @code{CTOR_END_P} set
1618 is encountered, the @code{SUBOBJECT_CLEANUP} must be executed. The
1619 cleanups must be executed in the reverse order in which they appear.
1623 Used to represent a @code{switch} statement. The @code{SWITCH_COND} is
1624 the expression on which the switch is occurring. See the documentation
1625 for an @code{IF_STMT} for more information on the representation used
1626 for the condition. The @code{SWITCH_BODY} is the body of the switch
1630 Used to represent a @code{try} block. The body of the try block is
1631 given by @code{TRY_STMTS}. Each of the catch blocks is a @code{HANDLER}
1632 node. The first handler is given by @code{TRY_HANDLERS}. Subsequent
1633 handlers are obtained by following the @code{TREE_CHAIN} link from one
1634 handler to the next. The body of the handler is given by
1635 @code{HANDLER_BODY}.
1637 If @code{CLEANUP_P} holds of the @code{TRY_BLOCK}, then the
1638 @code{TRY_HANDLERS} will not be a @code{HANDLER} node. Instead, it will
1639 be an expression that should be executed if an exception is thrown in
1640 the try block. It must rethrow the exception after executing that code.
1641 And, if an exception is thrown while the expression is executing,
1642 @code{terminate} must be called.
1645 Used to represent a @code{using} directive. The namespace is given by
1646 @code{USING_STMT_NAMESPACE}, which will be a NAMESPACE_DECL@. This node
1647 is needed inside template functions, to implement using directives
1648 during instantiation.
1652 Used to represent a @code{while} loop. The @code{WHILE_COND} is the
1653 termination condition for the loop. See the documentation for an
1654 @code{IF_STMT} for more information on the representation used for the
1657 The @code{WHILE_BODY} is the body of the loop.
1661 @c ---------------------------------------------------------------------
1663 @c ---------------------------------------------------------------------
1665 @section Attributes in trees
1668 Attributes, as specified using the @code{__attribute__} keyword, are
1669 represented internally as a @code{TREE_LIST}. The @code{TREE_PURPOSE}
1670 is the name of the attribute, as an @code{IDENTIFIER_NODE}. The
1671 @code{TREE_VALUE} is a @code{TREE_LIST} of the arguments of the
1672 attribute, if any, or @code{NULL_TREE} if there are no arguments; the
1673 arguments are stored as the @code{TREE_VALUE} of successive entries in
1674 the list, and may be identifiers or expressions. The @code{TREE_CHAIN}
1675 of the attribute is the next attribute in a list of attributes applying
1676 to the same declaration or type, or @code{NULL_TREE} if there are no
1677 further attributes in the list.
1679 Attributes may be attached to declarations and to types; these
1680 attributes may be accessed with the following macros. All attributes
1681 are stored in this way, and many also cause other changes to the
1682 declaration or type or to other internal compiler data structures.
1684 @deftypefn {Tree Macro} tree DECL_ATTRIBUTES (tree @var{decl})
1685 This macro returns the attributes on the declaration @var{decl}.
1688 @deftypefn {Tree Macro} tree TYPE_ATTRIBUTES (tree @var{type})
1689 This macro returns the attributes on the type @var{type}.
1692 @c ---------------------------------------------------------------------
1694 @c ---------------------------------------------------------------------
1696 @node Expression trees
1697 @section Expressions
1699 @findex TREE_OPERAND
1701 @findex TREE_INT_CST_HIGH
1702 @findex TREE_INT_CST_LOW
1703 @findex tree_int_cst_lt
1704 @findex tree_int_cst_equal
1708 @findex TREE_STRING_LENGTH
1709 @findex TREE_STRING_POINTER
1711 @findex PTRMEM_CST_CLASS
1712 @findex PTRMEM_CST_MEMBER
1715 @tindex BIT_NOT_EXPR
1716 @tindex TRUTH_NOT_EXPR
1718 @tindex INDIRECT_REF
1719 @tindex FIX_TRUNC_EXPR
1721 @tindex COMPLEX_EXPR
1723 @tindex REALPART_EXPR
1724 @tindex IMAGPART_EXPR
1726 @tindex CONVERT_EXPR
1730 @tindex BIT_IOR_EXPR
1731 @tindex BIT_XOR_EXPR
1732 @tindex BIT_AND_EXPR
1733 @tindex TRUTH_ANDIF_EXPR
1734 @tindex TRUTH_ORIF_EXPR
1735 @tindex TRUTH_AND_EXPR
1736 @tindex TRUTH_OR_EXPR
1737 @tindex TRUTH_XOR_EXPR
1741 @tindex TRUNC_DIV_EXPR
1742 @tindex TRUNC_MOD_EXPR
1752 @tindex COMPONENT_REF
1753 @tindex COMPOUND_EXPR
1757 @tindex COMPOUND_LITERAL_EXPR
1762 @tindex CLEANUP_POINT_EXPR
1766 The internal representation for expressions is for the most part quite
1767 straightforward. However, there are a few facts that one must bear in
1768 mind. In particular, the expression ``tree'' is actually a directed
1769 acyclic graph. (For example there may be many references to the integer
1770 constant zero throughout the source program; many of these will be
1771 represented by the same expression node.) You should not rely on
1772 certain kinds of node being shared, nor should rely on certain kinds of
1773 nodes being unshared.
1775 The following macros can be used with all expression nodes:
1779 Returns the type of the expression. This value may not be precisely the
1780 same type that would be given the expression in the original program.
1783 In what follows, some nodes that one might expect to always have type
1784 @code{bool} are documented to have either integral or boolean type. At
1785 some point in the future, the C front end may also make use of this same
1786 intermediate representation, and at this point these nodes will
1787 certainly have integral type. The previous sentence is not meant to
1788 imply that the C++ front end does not or will not give these nodes
1791 Below, we list the various kinds of expression nodes. Except where
1792 noted otherwise, the operands to an expression are accessed using the
1793 @code{TREE_OPERAND} macro. For example, to access the first operand to
1794 a binary plus expression @code{expr}, use:
1797 TREE_OPERAND (expr, 0)
1800 As this example indicates, the operands are zero-indexed.
1802 The table below begins with constants, moves on to unary expressions,
1803 then proceeds to binary expressions, and concludes with various other
1804 kinds of expressions:
1808 These nodes represent integer constants. Note that the type of these
1809 constants is obtained with @code{TREE_TYPE}; they are not always of type
1810 @code{int}. In particular, @code{char} constants are represented with
1811 @code{INTEGER_CST} nodes. The value of the integer constant @code{e} is
1813 ((TREE_INT_CST_HIGH (e) << HOST_BITS_PER_WIDE_INT)
1814 + TREE_INST_CST_LOW (e))
1817 HOST_BITS_PER_WIDE_INT is at least thirty-two on all platforms. Both
1818 @code{TREE_INT_CST_HIGH} and @code{TREE_INT_CST_LOW} return a
1819 @code{HOST_WIDE_INT}. The value of an @code{INTEGER_CST} is interpreted
1820 as a signed or unsigned quantity depending on the type of the constant.
1821 In general, the expression given above will overflow, so it should not
1822 be used to calculate the value of the constant.
1824 The variable @code{integer_zero_node} is an integer constant with value
1825 zero. Similarly, @code{integer_one_node} is an integer constant with
1826 value one. The @code{size_zero_node} and @code{size_one_node} variables
1827 are analogous, but have type @code{size_t} rather than @code{int}.
1829 The function @code{tree_int_cst_lt} is a predicate which holds if its
1830 first argument is less than its second. Both constants are assumed to
1831 have the same signedness (i.e., either both should be signed or both
1832 should be unsigned.) The full width of the constant is used when doing
1833 the comparison; the usual rules about promotions and conversions are
1834 ignored. Similarly, @code{tree_int_cst_equal} holds if the two
1835 constants are equal. The @code{tree_int_cst_sgn} function returns the
1836 sign of a constant. The value is @code{1}, @code{0}, or @code{-1}
1837 according on whether the constant is greater than, equal to, or less
1838 than zero. Again, the signedness of the constant's type is taken into
1839 account; an unsigned constant is never less than zero, no matter what
1844 FIXME: Talk about how to obtain representations of this constant, do
1845 comparisons, and so forth.
1848 These nodes are used to represent complex number constants, that is a
1849 @code{__complex__} whose parts are constant nodes. The
1850 @code{TREE_REALPART} and @code{TREE_IMAGPART} return the real and the
1851 imaginary parts respectively.
1854 These nodes represent string-constants. The @code{TREE_STRING_LENGTH}
1855 returns the length of the string, as an @code{int}. The
1856 @code{TREE_STRING_POINTER} is a @code{char*} containing the string
1857 itself. The string may not be @code{NUL}-terminated, and it may contain
1858 embedded @code{NUL} characters. Therefore, the
1859 @code{TREE_STRING_LENGTH} includes the trailing @code{NUL} if it is
1862 For wide string constants, the @code{TREE_STRING_LENGTH} is the number
1863 of bytes in the string, and the @code{TREE_STRING_POINTER}
1864 points to an array of the bytes of the string, as represented on the
1865 target system (that is, as integers in the target endianness). Wide and
1866 non-wide string constants are distinguished only by the @code{TREE_TYPE}
1867 of the @code{STRING_CST}.
1869 FIXME: The formats of string constants are not well-defined when the
1870 target system bytes are not the same width as host system bytes.
1873 These nodes are used to represent pointer-to-member constants. The
1874 @code{PTRMEM_CST_CLASS} is the class type (either a @code{RECORD_TYPE}
1875 or @code{UNION_TYPE} within which the pointer points), and the
1876 @code{PTRMEM_CST_MEMBER} is the declaration for the pointed to object.
1877 Note that the @code{DECL_CONTEXT} for the @code{PTRMEM_CST_MEMBER} is in
1878 general different from the @code{PTRMEM_CST_CLASS}. For example,
1881 struct B @{ int i; @};
1882 struct D : public B @{@};
1886 The @code{PTRMEM_CST_CLASS} for @code{&D::i} is @code{D}, even though
1887 the @code{DECL_CONTEXT} for the @code{PTRMEM_CST_MEMBER} is @code{B},
1888 since @code{B::i} is a member of @code{B}, not @code{D}.
1892 These nodes represent variables, including static data members. For
1893 more information, @pxref{Declarations}.
1896 These nodes represent unary negation of the single operand, for both
1897 integer and floating-point types. The type of negation can be
1898 determined by looking at the type of the expression.
1901 These nodes represent bitwise complement, and will always have integral
1902 type. The only operand is the value to be complemented.
1904 @item TRUTH_NOT_EXPR
1905 These nodes represent logical negation, and will always have integral
1906 (or boolean) type. The operand is the value being negated.
1908 @item PREDECREMENT_EXPR
1909 @itemx PREINCREMENT_EXPR
1910 @itemx POSTDECREMENT_EXPR
1911 @itemx POSTINCREMENT_EXPR
1912 These nodes represent increment and decrement expressions. The value of
1913 the single operand is computed, and the operand incremented or
1914 decremented. In the case of @code{PREDECREMENT_EXPR} and
1915 @code{PREINCREMENT_EXPR}, the value of the expression is the value
1916 resulting after the increment or decrement; in the case of
1917 @code{POSTDECREMENT_EXPR} and @code{POSTINCREMENT_EXPR} is the value
1918 before the increment or decrement occurs. The type of the operand, like
1919 that of the result, will be either integral, boolean, or floating-point.
1922 These nodes are used to represent the address of an object. (These
1923 expressions will always have pointer or reference type.) The operand may
1924 be another expression, or it may be a declaration.
1926 As an extension, GCC allows users to take the address of a label. In
1927 this case, the operand of the @code{ADDR_EXPR} will be a
1928 @code{LABEL_DECL}. The type of such an expression is @code{void*}.
1930 If the object addressed is not an lvalue, a temporary is created, and
1931 the address of the temporary is used.
1934 These nodes are used to represent the object pointed to by a pointer.
1935 The operand is the pointer being dereferenced; it will always have
1936 pointer or reference type.
1938 @item FIX_TRUNC_EXPR
1939 These nodes represent conversion of a floating-point value to an
1940 integer. The single operand will have a floating-point type, while the
1941 the complete expression will have an integral (or boolean) type. The
1942 operand is rounded towards zero.
1945 These nodes represent conversion of an integral (or boolean) value to a
1946 floating-point value. The single operand will have integral type, while
1947 the complete expression will have a floating-point type.
1949 FIXME: How is the operand supposed to be rounded? Is this dependent on
1953 These nodes are used to represent complex numbers constructed from two
1954 expressions of the same (integer or real) type. The first operand is the
1955 real part and the second operand is the imaginary part.
1958 These nodes represent the conjugate of their operand.
1962 These nodes represent respectively the real and the imaginary parts
1963 of complex numbers (their sole argument).
1965 @item NON_LVALUE_EXPR
1966 These nodes indicate that their one and only operand is not an lvalue.
1967 A back end can treat these identically to the single operand.
1970 These nodes are used to represent conversions that do not require any
1971 code-generation. For example, conversion of a @code{char*} to an
1972 @code{int*} does not require any code be generated; such a conversion is
1973 represented by a @code{NOP_EXPR}. The single operand is the expression
1974 to be converted. The conversion from a pointer to a reference is also
1975 represented with a @code{NOP_EXPR}.
1978 These nodes are similar to @code{NOP_EXPR}s, but are used in those
1979 situations where code may need to be generated. For example, if an
1980 @code{int*} is converted to an @code{int} code may need to be generated
1981 on some platforms. These nodes are never used for C++-specific
1982 conversions, like conversions between pointers to different classes in
1983 an inheritance hierarchy. Any adjustments that need to be made in such
1984 cases are always indicated explicitly. Similarly, a user-defined
1985 conversion is never represented by a @code{CONVERT_EXPR}; instead, the
1986 function calls are made explicit.
1989 These nodes represent @code{throw} expressions. The single operand is
1990 an expression for the code that should be executed to throw the
1991 exception. However, there is one implicit action not represented in
1992 that expression; namely the call to @code{__throw}. This function takes
1993 no arguments. If @code{setjmp}/@code{longjmp} exceptions are used, the
1994 function @code{__sjthrow} is called instead. The normal GCC back end
1995 uses the function @code{emit_throw} to generate this code; you can
1996 examine this function to see what needs to be done.
2000 These nodes represent left and right shifts, respectively. The first
2001 operand is the value to shift; it will always be of integral type. The
2002 second operand is an expression for the number of bits by which to
2003 shift. Right shift should be treated as arithmetic, i.e., the
2004 high-order bits should be zero-filled when the expression has unsigned
2005 type and filled with the sign bit when the expression has signed type.
2006 Note that the result is undefined if the second operand is larger
2007 than the first operand's type size.
2013 These nodes represent bitwise inclusive or, bitwise exclusive or, and
2014 bitwise and, respectively. Both operands will always have integral
2017 @item TRUTH_ANDIF_EXPR
2018 @itemx TRUTH_ORIF_EXPR
2019 These nodes represent logical and and logical or, respectively. These
2020 operators are not strict; i.e., the second operand is evaluated only if
2021 the value of the expression is not determined by evaluation of the first
2022 operand. The type of the operands, and the result type, is always of
2023 boolean or integral type.
2025 @item TRUTH_AND_EXPR
2026 @itemx TRUTH_OR_EXPR
2027 @itemx TRUTH_XOR_EXPR
2028 These nodes represent logical and, logical or, and logical exclusive or.
2029 They are strict; both arguments are always evaluated. There are no
2030 corresponding operators in C or C++, but the front end will sometimes
2031 generate these expressions anyhow, if it can tell that strictness does
2037 @itemx TRUNC_DIV_EXPR
2038 @itemx TRUNC_MOD_EXPR
2040 These nodes represent various binary arithmetic operations.
2041 Respectively, these operations are addition, subtraction (of the second
2042 operand from the first), multiplication, integer division, integer
2043 remainder, and floating-point division. The operands to the first three
2044 of these may have either integral or floating type, but there will never
2045 be case in which one operand is of floating type and the other is of
2048 The result of a @code{TRUNC_DIV_EXPR} is always rounded towards zero.
2049 The @code{TRUNC_MOD_EXPR} of two operands @code{a} and @code{b} is
2050 always @code{a - a/b} where the division is as if computed by a
2051 @code{TRUNC_DIV_EXPR}.
2054 These nodes represent array accesses. The first operand is the array;
2055 the second is the index. To calculate the address of the memory
2056 accessed, you must scale the index by the size of the type of the array
2057 elements. The type of these expressions must be the type of a component of
2060 @item ARRAY_RANGE_REF
2061 These nodes represent access to a range (or ``slice'') of an array. The
2062 operands are the same as that for @code{ARRAY_REF} and have the same
2063 meanings. The type of these expressions must be an array whose component
2064 type is the same as that of the first operand. The range of that array
2065 type determines the amount of data these expressions access.
2067 @item EXACT_DIV_EXPR
2077 These nodes represent the less than, less than or equal to, greater
2078 than, greater than or equal to, equal, and not equal comparison
2079 operators. The first and second operand with either be both of integral
2080 type or both of floating type. The result type of these expressions
2081 will always be of integral or boolean type.
2084 These nodes represent assignment. The left-hand side is the first
2085 operand; the right-hand side is the second operand. The left-hand side
2086 will be a @code{VAR_DECL}, @code{INDIRECT_REF}, @code{COMPONENT_REF}, or
2089 These nodes are used to represent not only assignment with @samp{=} but
2090 also compound assignments (like @samp{+=}), by reduction to @samp{=}
2091 assignment. In other words, the representation for @samp{i += 3} looks
2092 just like that for @samp{i = i + 3}.
2095 These nodes are just like @code{MODIFY_EXPR}, but are used only when a
2096 variable is initialized, rather than assigned to subsequently.
2099 These nodes represent non-static data member accesses. The first
2100 operand is the object (rather than a pointer to it); the second operand
2101 is the @code{FIELD_DECL} for the data member.
2104 These nodes represent comma-expressions. The first operand is an
2105 expression whose value is computed and thrown away prior to the
2106 evaluation of the second operand. The value of the entire expression is
2107 the value of the second operand.
2110 These nodes represent @code{?:} expressions. The first operand
2111 is of boolean or integral type. If it evaluates to a nonzero value,
2112 the second operand should be evaluated, and returned as the value of the
2113 expression. Otherwise, the third operand is evaluated, and returned as
2114 the value of the expression. As a GNU extension, the middle operand of
2115 the @code{?:} operator may be omitted in the source, like this:
2121 which is equivalent to
2128 assuming that @code{x} is an expression without side-effects. However,
2129 in the case that the first operation causes side effects, the
2130 side-effects occur only once. Consumers of the internal representation
2131 do not need to worry about this oddity; the second operand will be
2132 always be present in the internal representation.
2135 These nodes are used to represent calls to functions, including
2136 non-static member functions. The first operand is a pointer to the
2137 function to call; it is always an expression whose type is a
2138 @code{POINTER_TYPE}. The second argument is a @code{TREE_LIST}. The
2139 arguments to the call appear left-to-right in the list. The
2140 @code{TREE_VALUE} of each list node contains the expression
2141 corresponding to that argument. (The value of @code{TREE_PURPOSE} for
2142 these nodes is unspecified, and should be ignored.) For non-static
2143 member functions, there will be an operand corresponding to the
2144 @code{this} pointer. There will always be expressions corresponding to
2145 all of the arguments, even if the function is declared with default
2146 arguments and some arguments are not explicitly provided at the call
2150 These nodes are used to represent GCC's statement-expression extension.
2151 The statement-expression extension allows code like this:
2153 int f() @{ return (@{ int j; j = 3; j + 7; @}); @}
2155 In other words, an sequence of statements may occur where a single
2156 expression would normally appear. The @code{STMT_EXPR} node represents
2157 such an expression. The @code{STMT_EXPR_STMT} gives the statement
2158 contained in the expression; this is always a @code{COMPOUND_STMT}. The
2159 value of the expression is the value of the last sub-statement in the
2160 @code{COMPOUND_STMT}. More precisely, the value is the value computed
2161 by the last @code{EXPR_STMT} in the outermost scope of the
2162 @code{COMPOUND_STMT}. For example, in:
2166 the value is @code{3} while in:
2168 (@{ if (x) @{ 3; @} @})
2170 (represented by a nested @code{COMPOUND_STMT}), there is no value. If
2171 the @code{STMT_EXPR} does not yield a value, it's type will be
2175 These nodes represent local blocks. The first operand is a list of
2176 temporary variables, connected via their @code{TREE_CHAIN} field. These
2177 will never require cleanups. The scope of these variables is just the
2178 body of the @code{BIND_EXPR}. The body of the @code{BIND_EXPR} is the
2182 These nodes represent ``infinite'' loops. The @code{LOOP_EXPR_BODY}
2183 represents the body of the loop. It should be executed forever, unless
2184 an @code{EXIT_EXPR} is encountered.
2187 These nodes represent conditional exits from the nearest enclosing
2188 @code{LOOP_EXPR}. The single operand is the condition; if it is
2189 nonzero, then the loop should be exited. An @code{EXIT_EXPR} will only
2190 appear within a @code{LOOP_EXPR}.
2192 @item CLEANUP_POINT_EXPR
2193 These nodes represent full-expressions. The single operand is an
2194 expression to evaluate. Any destructor calls engendered by the creation
2195 of temporaries during the evaluation of that expression should be
2196 performed immediately after the expression is evaluated.
2199 These nodes represent the brace-enclosed initializers for a structure or
2200 array. The first operand is reserved for use by the back end. The
2201 second operand is a @code{TREE_LIST}. If the @code{TREE_TYPE} of the
2202 @code{CONSTRUCTOR} is a @code{RECORD_TYPE} or @code{UNION_TYPE}, then
2203 the @code{TREE_PURPOSE} of each node in the @code{TREE_LIST} will be a
2204 @code{FIELD_DECL} and the @code{TREE_VALUE} of each node will be the
2205 expression used to initialize that field. You should not depend on the
2206 fields appearing in any particular order, nor should you assume that all
2207 fields will be represented. Unrepresented fields may be assigned any
2210 If the @code{TREE_TYPE} of the @code{CONSTRUCTOR} is an
2211 @code{ARRAY_TYPE}, then the @code{TREE_PURPOSE} of each element in the
2212 @code{TREE_LIST} will be an @code{INTEGER_CST}. This constant indicates
2213 which element of the array (indexed from zero) is being assigned to;
2214 again, the @code{TREE_VALUE} is the corresponding initializer. If the
2215 @code{TREE_PURPOSE} is @code{NULL_TREE}, then the initializer is for the
2216 next available array element.
2218 Conceptually, before any initialization is done, the entire area of
2219 storage is initialized to zero.
2221 @item COMPOUND_LITERAL_EXPR
2222 @findex COMPOUND_LITERAL_EXPR_DECL
2223 These nodes represent ISO C99 compound literals. The
2224 @code{COMPOUND_LITERAL_EXPR_DECL} is an anonymous @code{VAR_DECL} for
2225 the unnamed object represented by the compound literal; the
2226 @code{DECL_INITIAL} of that @code{VAR_DECL} is a @code{CONSTRUCTOR}
2227 representing the brace-enclosed list of initializers in the compound
2232 A @code{SAVE_EXPR} represents an expression (possibly involving
2233 side-effects) that is used more than once. The side-effects should
2234 occur only the first time the expression is evaluated. Subsequent uses
2235 should just reuse the computed value. The first operand to the
2236 @code{SAVE_EXPR} is the expression to evaluate. The side-effects should
2237 be executed where the @code{SAVE_EXPR} is first encountered in a
2238 depth-first preorder traversal of the expression tree.
2241 A @code{TARGET_EXPR} represents a temporary object. The first operand
2242 is a @code{VAR_DECL} for the temporary variable. The second operand is
2243 the initializer for the temporary. The initializer is evaluated, and
2244 copied (bitwise) into the temporary.
2246 Often, a @code{TARGET_EXPR} occurs on the right-hand side of an
2247 assignment, or as the second operand to a comma-expression which is
2248 itself the right-hand side of an assignment, etc. In this case, we say
2249 that the @code{TARGET_EXPR} is ``normal''; otherwise, we say it is
2250 ``orphaned''. For a normal @code{TARGET_EXPR} the temporary variable
2251 should be treated as an alias for the left-hand side of the assignment,
2252 rather than as a new temporary variable.
2254 The third operand to the @code{TARGET_EXPR}, if present, is a
2255 cleanup-expression (i.e., destructor call) for the temporary. If this
2256 expression is orphaned, then this expression must be executed when the
2257 statement containing this expression is complete. These cleanups must
2258 always be executed in the order opposite to that in which they were
2259 encountered. Note that if a temporary is created on one branch of a
2260 conditional operator (i.e., in the second or third operand to a
2261 @code{COND_EXPR}), the cleanup must be run only if that branch is
2264 See @code{STMT_IS_FULL_EXPR_P} for more information about running these
2267 @item AGGR_INIT_EXPR
2268 An @code{AGGR_INIT_EXPR} represents the initialization as the return
2269 value of a function call, or as the result of a constructor. An
2270 @code{AGGR_INIT_EXPR} will only appear as the second operand of a
2271 @code{TARGET_EXPR}. The first operand to the @code{AGGR_INIT_EXPR} is
2272 the address of a function to call, just as in a @code{CALL_EXPR}. The
2273 second operand are the arguments to pass that function, as a
2274 @code{TREE_LIST}, again in a manner similar to that of a
2275 @code{CALL_EXPR}. The value of the expression is that returned by the
2278 If @code{AGGR_INIT_VIA_CTOR_P} holds of the @code{AGGR_INIT_EXPR}, then
2279 the initialization is via a constructor call. The address of the third
2280 operand of the @code{AGGR_INIT_EXPR}, which is always a @code{VAR_DECL},
2281 is taken, and this value replaces the first argument in the argument
2282 list. In this case, the value of the expression is the @code{VAR_DECL}
2283 given by the third operand to the @code{AGGR_INIT_EXPR}; constructors do
2287 A @code{VTABLE_REF} indicates that the interior expression computes
2288 a value that is a vtable entry. It is used with @option{-fvtable-gc}
2289 to track the reference through to front end to the middle end, at
2290 which point we transform this to a @code{REG_VTABLE_REF} note, which
2291 survives the balance of code generation.
2293 The first operand is the expression that computes the vtable reference.
2294 The second operand is the @code{VAR_DECL} of the vtable. The third
2295 operand is an @code{INTEGER_CST} of the byte offset into the vtable.