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. If @code{TYPE_PTRMEMFUNC_P} holds, then
527 this type is a pointer-to-member type. In that case, the
528 @code{TYPE_PTRMEMFUNC_FN_TYPE} is a @code{POINTER_TYPE} pointing to a
529 @code{METHOD_TYPE}. The @code{METHOD_TYPE} is the type of a function
530 pointed to by the pointer-to-member function. If
531 @code{TYPE_PTRMEMFUNC_P} does not hold, this type is a class type. For
532 more information, see @pxref{Classes}.
535 This node is used to represent a type the knowledge of which is
536 insufficient for a sound processing.
539 This node is used to represent a data member; for example a
540 pointer-to-data-member is represented by a @code{POINTER_TYPE} whose
541 @code{TREE_TYPE} is an @code{OFFSET_TYPE}. For a data member @code{X::m}
542 the @code{TYPE_OFFSET_BASETYPE} is @code{X} and the @code{TREE_TYPE} is
543 the type of @code{m}.
546 Used to represent a construct of the form @code{typename T::A}. The
547 @code{TYPE_CONTEXT} is @code{T}; the @code{TYPE_NAME} is an
548 @code{IDENTIFIER_NODE} for @code{A}. If the type is specified via a
549 template-id, then @code{TYPENAME_TYPE_FULLNAME} yields a
550 @code{TEMPLATE_ID_EXPR}. The @code{TREE_TYPE} is non-@code{NULL} if the
551 node is implicitly generated in support for the implicit typename
552 extension; in which case the @code{TREE_TYPE} is a type node for the
556 Used to represent the @code{__typeof__} extension. The
557 @code{TYPE_FIELDS} is the expression the type of which is being
561 Used to represent @code{union} types. For more information, @pxref{Classes}.
564 There are variables whose values represent some of the basic types.
568 A node for @code{void}.
570 @item integer_type_node
571 A node for @code{int}.
573 @item unsigned_type_node.
574 A node for @code{unsigned int}.
576 @item char_type_node.
577 A node for @code{char}.
580 It may sometimes be useful to compare one of these variables with a type
581 in hand, using @code{same_type_p}.
583 @c ---------------------------------------------------------------------
585 @c ---------------------------------------------------------------------
589 @cindex namespace, class, scope
591 The root of the entire intermediate representation is the variable
592 @code{global_namespace}. This is the namespace specified with @code{::}
593 in C++ source code. All other namespaces, types, variables, functions,
594 and so forth can be found starting with this namespace.
596 Besides namespaces, the other high-level scoping construct in C++ is the
597 class. (Throughout this manual the term @dfn{class} is used to mean the
598 types referred to in the ANSI/ISO C++ Standard as classes; these include
599 types defined with the @code{class}, @code{struct}, and @code{union}
603 * Namespaces:: Member functions, types, etc.
604 * Classes:: Members, bases, friends, etc.
607 @c ---------------------------------------------------------------------
609 @c ---------------------------------------------------------------------
612 @subsection Namespaces
614 @tindex NAMESPACE_DECL
616 A namespace is represented by a @code{NAMESPACE_DECL} node.
618 However, except for the fact that it is distinguished as the root of the
619 representation, the global namespace is no different from any other
620 namespace. Thus, in what follows, we describe namespaces generally,
621 rather than the global namespace in particular.
623 The following macros and functions can be used on a @code{NAMESPACE_DECL}:
627 This macro is used to obtain the @code{IDENTIFIER_NODE} corresponding to
628 the unqualified name of the name of the namespace (@pxref{Identifiers}).
629 The name of the global namespace is @samp{::}, even though in C++ the
630 global namespace is unnamed. However, you should use comparison with
631 @code{global_namespace}, rather than @code{DECL_NAME} to determine
632 whether or not a namespaces is the global one. An unnamed namespace
633 will have a @code{DECL_NAME} equal to @code{anonymous_namespace_name}.
634 Within a single translation unit, all unnamed namespaces will have the
638 This macro returns the enclosing namespace. The @code{DECL_CONTEXT} for
639 the @code{global_namespace} is @code{NULL_TREE}.
641 @item DECL_NAMESPACE_ALIAS
642 If this declaration is for a namespace alias, then
643 @code{DECL_NAMESPACE_ALIAS} is the namespace for which this one is an
646 Do not attempt to use @code{cp_namespace_decls} for a namespace which is
647 an alias. Instead, follow @code{DECL_NAMESPACE_ALIAS} links until you
648 reach an ordinary, non-alias, namespace, and call
649 @code{cp_namespace_decls} there.
651 @item DECL_NAMESPACE_STD_P
652 This predicate holds if the namespace is the special @code{::std}
655 @item cp_namespace_decls
656 This function will return the declarations contained in the namespace,
657 including types, overloaded functions, other namespaces, and so forth.
658 If there are no declarations, this function will return
659 @code{NULL_TREE}. The declarations are connected through their
660 @code{TREE_CHAIN} fields.
662 Although most entries on this list will be declarations,
663 @code{TREE_LIST} nodes may also appear. In this case, the
664 @code{TREE_VALUE} will be an @code{OVERLOAD}. The value of the
665 @code{TREE_PURPOSE} is unspecified; back ends should ignore this value.
666 As with the other kinds of declarations returned by
667 @code{cp_namespace_decls}, the @code{TREE_CHAIN} will point to the next
668 declaration in this list.
670 For more information on the kinds of declarations that can occur on this
671 list, @xref{Declarations}. Some declarations will not appear on this
672 list. In particular, no @code{FIELD_DECL}, @code{LABEL_DECL}, or
673 @code{PARM_DECL} nodes will appear here.
675 This function cannot be used with namespaces that have
676 @code{DECL_NAMESPACE_ALIAS} set.
680 @c ---------------------------------------------------------------------
682 @c ---------------------------------------------------------------------
689 @findex CLASSTYPE_DECLARED_CLASS
692 @findex TREE_VIA_PUBLIC
693 @findex TREE_VIA_PROTECTED
694 @findex TREE_VIA_PRIVATE
699 A class type is represented by either a @code{RECORD_TYPE} or a
700 @code{UNION_TYPE}. A class declared with the @code{union} tag is
701 represented by a @code{UNION_TYPE}, while classes declared with either
702 the @code{struct} or the @code{class} tag are represented by
703 @code{RECORD_TYPE}s. You can use the @code{CLASSTYPE_DECLARED_CLASS}
704 macro to discern whether or not a particular type is a @code{class} as
705 opposed to a @code{struct}. This macro will be true only for classes
706 declared with the @code{class} tag.
708 Almost all non-function members are available on the @code{TYPE_FIELDS}
709 list. Given one member, the next can be found by following the
710 @code{TREE_CHAIN}. You should not depend in any way on the order in
711 which fields appear on this list. All nodes on this list will be
712 @samp{DECL} nodes. A @code{FIELD_DECL} is used to represent a non-static
713 data member, a @code{VAR_DECL} is used to represent a static data
714 member, and a @code{TYPE_DECL} is used to represent a type. Note that
715 the @code{CONST_DECL} for an enumeration constant will appear on this
716 list, if the enumeration type was declared in the class. (Of course,
717 the @code{TYPE_DECL} for the enumeration type will appear here as well.)
718 There are no entries for base classes on this list. In particular,
719 there is no @code{FIELD_DECL} for the ``base-class portion'' of an
722 The @code{TYPE_VFIELD} is a compiler-generated field used to point to
723 virtual function tables. It may or may not appear on the
724 @code{TYPE_FIELDS} list. However, back ends should handle the
725 @code{TYPE_VFIELD} just like all the entries on the @code{TYPE_FIELDS}
728 The function members are available on the @code{TYPE_METHODS} list.
729 Again, subsequent members are found by following the @code{TREE_CHAIN}
730 field. If a function is overloaded, each of the overloaded functions
731 appears; no @code{OVERLOAD} nodes appear on the @code{TYPE_METHODS}
732 list. Implicitly declared functions (including default constructors,
733 copy constructors, assignment operators, and destructors) will appear on
736 Every class has an associated @dfn{binfo}, which can be obtained with
737 @code{TYPE_BINFO}. Binfos are used to represent base-classes. The
738 binfo given by @code{TYPE_BINFO} is the degenerate case, whereby every
739 class is considered to be its own base-class. The base classes for a
740 particular binfo can be obtained with @code{BINFO_BASETYPES}. These
741 base-classes are themselves binfos. The class type associated with a
742 binfo is given by @code{BINFO_TYPE}. It is always the case that
743 @code{BINFO_TYPE (TYPE_BINFO (x))} is the same type as @code{x}, up to
744 qualifiers. However, it is not always the case that @code{TYPE_BINFO
745 (BINFO_TYPE (y))} is always the same binfo as @code{y}. The reason is
746 that if @code{y} is a binfo representing a base-class @code{B} of a
747 derived class @code{D}, then @code{BINFO_TYPE (y)} will be @code{B}, and
748 @code{TYPE_INFO (BINFO_TYPE (y))} will be @code{B} as its own
749 base-class, rather than as a base-class of @code{D}.
751 The @code{BINFO_BASETYPES} is a @code{TREE_VEC} (@pxref{Containers}).
752 Base types appear in left-to-right order in this vector. You can tell
753 whether or @code{public}, @code{protected}, or @code{private}
754 inheritance was used by using the @code{TREE_VIA_PUBLIC},
755 @code{TREE_VIA_PROTECTED}, and @code{TREE_VIA_PRIVATE} macros. Each of
756 these macros takes a @code{BINFO} and is true if and only if the
757 indicated kind of inheritance was used. If @code{TREE_VIA_VIRTUAL}
758 holds of a binfo, then its @code{BINFO_TYPE} was inherited from
761 The following macros can be used on a tree node representing a class-type.
765 This predicate holds if the class is local class @emph{i.e.} declared
766 inside a function body.
768 @item TYPE_POLYMORPHIC_P
769 This predicate holds if the class has at least one virtual function
770 (declared or inherited).
772 @item TYPE_HAS_DEFAULT_CONSTRUCTOR
773 This predicate holds whenever its argument represents a class-type with
776 @item CLASSTYPE_HAS_MUTABLE
777 @item TYPE_HAS_MUTABLE_P
778 These predicates hold for a class-type having a mutable data member.
780 @item CLASSTYPE_NON_POD_P
781 This predicate holds only for class-types that are not PODs.
783 @item TYPE_HAS_NEW_OPERATOR
784 This predicate holds for a class-type that defines
787 @item TYPE_HAS_ARRAY_NEW_OPERATOR
788 This predicate holds for a class-type for which
789 @code{operator new[]} is defined.
791 @item TYPE_OVERLOADS_CALL_EXPR
792 This predicate holds for class-type for which the function call
793 @code{operator()} is overloaded.
795 @item TYPE_OVERLOADS_ARRAY_REF
796 This predicate holds for a class-type that overloads
799 @item TYPE_OVERLOADS_ARROW
800 This predicate holds for a class-type for which @code{operator->} is
805 @c ---------------------------------------------------------------------
807 @c ---------------------------------------------------------------------
810 @section Declarations
813 @cindex type declaration
820 @tindex NAMESPACE_DECL
822 @tindex TEMPLATE_DECL
829 @findex DECL_EXTERNAL
831 This section covers the various kinds of declarations that appear in the
832 internal representation, except for declarations of functions
833 (represented by @code{FUNCTION_DECL} nodes), which are described in
836 Some macros can be used with any kind of declaration. These include:
839 This macro returns an @code{IDENTIFIER_NODE} giving the name of the
843 This macro returns the type of the entity declared.
845 @item DECL_SOURCE_FILE
846 This macro returns the name of the file in which the entity was
847 declared, as a @code{char*}. For an entity declared implicitly by the
848 compiler (like @code{__builtin_memcpy}), this will be the string
851 @item DECL_SOURCE_LINE
852 This macro returns the line number at which the entity was declared, as
855 @item DECL_ARTIFICIAL
856 This predicate holds if the declaration was implicitly generated by the
857 compiler. For example, this predicate will hold of an implicitly
858 declared member function, or of the @code{TYPE_DECL} implicitly
859 generated for a class type. Recall that in C++ code like:
864 is roughly equivalent to C code like:
869 The implicitly generated @code{typedef} declaration is represented by a
870 @code{TYPE_DECL} for which @code{DECL_ARTIFICIAL} holds.
872 @item DECL_NAMESPACE_SCOPE_P
873 This predicate holds if the entity was declared at a namespace scope.
875 @item DECL_CLASS_SCOPE_P
876 This predicate holds if the entity was declared at a class scope.
878 @item DECL_FUNCTION_SCOPE_P
879 This predicate holds if the entity was declared inside a function
884 The various kinds of declarations include:
887 These nodes are used to represent labels in function bodies. For more
888 information, see @ref{Functions}. These nodes only appear in block
892 These nodes are used to represent enumeration constants. The value of
893 the constant is given by @code{DECL_INITIAL} which will be an
894 @code{INTEGER_CST} with the same type as the @code{TREE_TYPE} of the
895 @code{CONST_DECL}, i.e., an @code{ENUMERAL_TYPE}.
898 These nodes represent the value returned by a function. When a value is
899 assigned to a @code{RESULT_DECL}, that indicates that the value should
900 be returned, via bitwise copy, by the function. You can use
901 @code{DECL_SIZE} and @code{DECL_ALIGN} on a @code{RESULT_DECL}, just as
902 with a @code{VAR_DECL}.
905 These nodes represent @code{typedef} declarations. The @code{TREE_TYPE}
906 is the type declared to have the name given by @code{DECL_NAME}. In
907 some cases, there is no associated name.
910 These nodes represent variables with namespace or block scope, as well
911 as static data members. The @code{DECL_SIZE} and @code{DECL_ALIGN} are
912 analogous to @code{TYPE_SIZE} and @code{TYPE_ALIGN}. For a declaration,
913 you should always use the @code{DECL_SIZE} and @code{DECL_ALIGN} rather
914 than the @code{TYPE_SIZE} and @code{TYPE_ALIGN} given by the
915 @code{TREE_TYPE}, since special attributes may have been applied to the
916 variable to give it a particular size and alignment. You may use the
917 predicates @code{DECL_THIS_STATIC} or @code{DECL_THIS_EXTERN} to test
918 whether the storage class specifiers @code{static} or @code{extern} were
919 used to declare a variable.
921 If this variable is initialized (but does not require a constructor),
922 the @code{DECL_INITIAL} will be an expression for the initializer. The
923 initializer should be evaluated, and a bitwise copy into the variable
924 performed. If the @code{DECL_INITIAL} is the @code{error_mark_node},
925 there is an initializer, but it is given by an explicit statement later
926 in the code; no bitwise copy is required.
928 GCC provides an extension that allows either automatic variables, or
929 global variables, to be placed in particular registers. This extension
930 is being used for a particular @code{VAR_DECL} if @code{DECL_REGISTER}
931 holds for the @code{VAR_DECL}, and if @code{DECL_ASSEMBLER_NAME} is not
932 equal to @code{DECL_NAME}. In that case, @code{DECL_ASSEMBLER_NAME} is
933 the name of the register into which the variable will be placed.
936 Used to represent a parameter to a function. Treat these nodes
937 similarly to @code{VAR_DECL} nodes. These nodes only appear in the
938 @code{DECL_ARGUMENTS} for a @code{FUNCTION_DECL}.
940 The @code{DECL_ARG_TYPE} for a @code{PARM_DECL} is the type that will
941 actually be used when a value is passed to this function. It may be a
942 wider type than the @code{TREE_TYPE} of the parameter; for example, the
943 ordinary type might be @code{short} while the @code{DECL_ARG_TYPE} is
947 These nodes represent non-static data members. The @code{DECL_SIZE} and
948 @code{DECL_ALIGN} behave as for @code{VAR_DECL} nodes. The
949 @code{DECL_FIELD_BITPOS} gives the first bit used for this field, as an
950 @code{INTEGER_CST}. These values are indexed from zero, where zero
951 indicates the first bit in the object.
953 If @code{DECL_C_BIT_FIELD} holds, this field is a bit-field.
960 These nodes are used to represent class, function, and variable (static
961 data member) templates. The @code{DECL_TEMPLATE_SPECIALIZATIONS} are a
962 @code{TREE_LIST}. The @code{TREE_VALUE} of each node in the list is a
963 @code{TEMPLATE_DECL}s or @code{FUNCTION_DECL}s representing
964 specializations (including instantiations) of this template. Back ends
965 can safely ignore @code{TEMPLATE_DECL}s, but should examine
966 @code{FUNCTION_DECL} nodes on the specializations list just as they
967 would ordinary @code{FUNCTION_DECL} nodes.
969 For a class template, the @code{DECL_TEMPLATE_INSTANTIATIONS} list
970 contains the instantiations. The @code{TREE_VALUE} of each node is an
971 instantiation of the class. The @code{DECL_TEMPLATE_SPECIALIZATIONS}
972 contains partial specializations of the class.
976 Back ends can safely ignore these nodes.
980 @c ---------------------------------------------------------------------
982 @c ---------------------------------------------------------------------
987 @tindex FUNCTION_DECL
992 A function is represented by a @code{FUNCTION_DECL} node. A set of
993 overloaded functions is sometimes represented by a @code{OVERLOAD} node.
995 An @code{OVERLOAD} node is not a declaration, so none of the
996 @samp{DECL_} macros should be used on an @code{OVERLOAD}. An
997 @code{OVERLOAD} node is similar to a @code{TREE_LIST}. Use
998 @code{OVL_CURRENT} to get the function associated with an
999 @code{OVERLOAD} node; use @code{OVL_NEXT} to get the next
1000 @code{OVERLOAD} node in the list of overloaded functions. The macros
1001 @code{OVL_CURRENT} and @code{OVL_NEXT} are actually polymorphic; you can
1002 use them to work with @code{FUNCTION_DECL} nodes as well as with
1003 overloads. In the case of a @code{FUNCTION_DECL}, @code{OVL_CURRENT}
1004 will always return the function itself, and @code{OVL_NEXT} will always
1005 be @code{NULL_TREE}.
1007 To determine the scope of a function, you can use the
1008 @code{DECL_REAL_CONTEXT} macro. This macro will return the class
1009 (either a @code{RECORD_TYPE} or a @code{UNION_TYPE}) or namespace (a
1010 @code{NAMESPACE_DECL}) of which the function is a member. For a virtual
1011 function, this macro returns the class in which the function was
1012 actually defined, not the base class in which the virtual declaration
1013 occurred. If a friend function is defined in a class scope, the
1014 @code{DECL_CLASS_CONTEXT} macro can be used to determine the class in
1015 which it was defined. For example, in
1017 class C @{ friend void f() @{@} @};
1019 the @code{DECL_REAL_CONTEXT} for @code{f} will be the
1020 @code{global_namespace}, but the @code{DECL_CLASS_CONTEXT} will be the
1021 @code{RECORD_TYPE} for @code{C}.
1023 The @code{DECL_REAL_CONTEXT} and @code{DECL_CLASS_CONTEXT} are not
1024 available in C; instead you should simply use @code{DECL_CONTEXT}. In C,
1025 the @code{DECL_CONTEXT} for a function maybe another function. This
1026 representation indicates that the GNU nested function extension is in
1027 use. For details on the semantics of nested functions, see the GCC
1028 Manual. The nested function can refer to local variables in its
1029 containing function. Such references are not explicitly marked in the
1030 tree structure; back ends must look at the @code{DECL_CONTEXT} for the
1031 referenced @code{VAR_DECL}. If the @code{DECL_CONTEXT} for the
1032 referenced @code{VAR_DECL} is not the same as the function currently
1033 being processed, and neither @code{DECL_EXTERNAL} nor @code{DECL_STATIC}
1034 hold, then the reference is to a local variable in a containing
1035 function, and the back end must take appropriate action.
1038 * Function Basics:: Function names, linkage, and so forth.
1039 * Function Bodies:: The statements that make up a function body.
1042 @c ---------------------------------------------------------------------
1044 @c ---------------------------------------------------------------------
1046 @node Function Basics
1047 @subsection Function Basics
1050 @cindex copy constructor
1051 @cindex assignment operator
1054 @findex DECL_ASSEMBLER_NAME
1056 @findex DECL_LINKONCE_P
1057 @findex DECL_FUNCTION_MEMBER_P
1058 @findex DECL_CONSTRUCTOR_P
1059 @findex DECL_DESTRUCTOR_P
1060 @findex DECL_OVERLOADED_OPERATOR_P
1061 @findex DECL_CONV_FN_P
1062 @findex DECL_ARTIFICIAL
1063 @findex DECL_GLOBAL_CTOR_P
1064 @findex DECL_GLOBAL_DTOR_P
1065 @findex GLOBAL_INIT_PRIORITY
1067 The following macros and functions can be used on a @code{FUNCTION_DECL}:
1070 This predicate holds for a function that is the program entry point
1074 This macro returns the unqualified name of the function, as an
1075 @code{IDENTIFIER_NODE}. For an instantiation of a function template,
1076 the @code{DECL_NAME} is the unqualified name of the template, not
1077 something like @code{f<int>}. The value of @code{DECL_NAME} is
1078 undefined when used on a constructor, destructor, overloaded operator,
1079 or type-conversion operator, or any function that is implicitly
1080 generated by the compiler. See below for macros that can be used to
1081 distinguish these cases.
1083 @item DECL_ASSEMBLER_NAME
1084 This macro returns the mangled name of the function, also an
1085 @code{IDENTIFIER_NODE}. This name does not contain leading underscores
1086 on systems that prefix all identifiers with underscores. The mangled
1087 name is computed in the same way on all platforms; if special processing
1088 is required to deal with the object file format used on a particular
1089 platform, it is the responsibility of the back end to perform those
1090 modifications. (Of course, the back end should not modify
1091 @code{DECL_ASSEMBLER_NAME} itself.)
1094 This predicate holds if the function is undefined.
1097 This predicate holds if the function has external linkage.
1099 @item DECL_LOCAL_FUNCTION_P
1100 This predicate holds if the function was declared at block scope, even
1101 though it has a global scope.
1103 @item DECL_ANTICIPATED
1104 This predicate holds if the function is a built-in function but its
1105 prototype is not yet explicitly declared.
1107 @item DECL_EXTERN_C_FUNCTION_P
1108 This predicate holds if the function is declared as an
1109 `@code{extern "C"}' function.
1111 @item DECL_LINKONCE_P
1112 This macro holds if multiple copies of this function may be emitted in
1113 various translation units. It is the responsibility of the linker to
1114 merge the various copies. Template instantiations are the most common
1115 example of functions for which @code{DECL_LINKONCE_P} holds; G++
1116 instantiates needed templates in all translation units which require them,
1117 and then relies on the linker to remove duplicate instantiations.
1119 FIXME: This macro is not yet implemented.
1121 @item DECL_FUNCTION_MEMBER_P
1122 This macro holds if the function is a member of a class, rather than a
1123 member of a namespace.
1125 @item DECL_STATIC_FUNCTION_P
1126 This predicate holds if the function a static member function.
1128 @item DECL_NONSTATIC_MEMBER_FUNCTION_P
1129 This macro holds for a non-static member function.
1131 @item DECL_CONST_MEMFUNC_P
1132 This predicate holds for a @code{const}-member function.
1134 @item DECL_VOLATILE_MEMFUNC_P
1135 This predicate holds for a @code{volatile}-member function.
1137 @item DECL_CONSTRUCTOR_P
1138 This macro holds if the function is a constructor.
1140 @item DECL_NONCONVERTING_P
1141 This predicate holds if the constructor is a non-converting constructor.
1143 @item DECL_COMPLETE_CONSTRUCTOR_P
1144 This predicate holds for a function which is a constructor for an object
1147 @item DECL_BASE_CONSTRUCTOR_P
1148 This predicate holds for a function which is a constructor for a base
1151 @item DECL_COPY_CONSTRUCTOR_P
1152 This predicate holds for a function which is a copy-constructor.
1154 @item DECL_DESTRUCTOR_P
1155 This macro holds if the function is a destructor.
1157 @item DECL_COMPLETE_DESTRUCTOR_P
1158 This predicate holds if the function is the destructor for an object a
1161 @item DECL_OVERLOADED_OPERATOR_P
1162 This macro holds if the function is an overloaded operator.
1164 @item DECL_CONV_FN_P
1165 This macro holds if the function is a type-conversion operator.
1167 @item DECL_GLOBAL_CTOR_P
1168 This predicate holds if the function is a file-scope initialization
1171 @item DECL_GLOBAL_DTOR_P
1172 This predicate holds if the function is a file-scope finalization
1176 This predicate holds if the function is a thunk.
1178 These functions represent stub code that adjusts the @code{this} pointer
1179 and then jumps to another function. When the jumped-to function
1180 returns, control is transferred directly to the caller, without
1181 returning to the thunk. The first parameter to the thunk is always the
1182 @code{this} pointer; the thunk should add @code{THUNK_DELTA} to this
1183 value. (The @code{THUNK_DELTA} is an @code{int}, not an
1184 @code{INTEGER_CST}.)
1186 Then, if @code{THUNK_VCALL_OFFSET} (an @code{INTEGER_CST}) is nonzero
1187 the adjusted @code{this} pointer must be adjusted again. The complete
1188 calculation is given by the following pseudo-code:
1192 if (THUNK_VCALL_OFFSET)
1193 this += (*((ptrdiff_t **) this))[THUNK_VCALL_OFFSET]
1196 Finally, the thunk should jump to the location given
1197 by @code{DECL_INITIAL}; this will always be an expression for the
1198 address of a function.
1200 @item DECL_NON_THUNK_FUNCTION_P
1201 This predicate holds if the function is @emph{not} a thunk function.
1203 @item GLOBAL_INIT_PRIORITY
1204 If either @code{DECL_GLOBAL_CTOR_P} or @code{DECL_GLOBAL_DTOR_P} holds,
1205 then this gives the initialization priority for the function. The
1206 linker will arrange that all functions for which
1207 @code{DECL_GLOBAL_CTOR_P} holds are run in increasing order of priority
1208 before @code{main} is called. When the program exits, all functions for
1209 which @code{DECL_GLOBAL_DTOR_P} holds are run in the reverse order.
1211 @item DECL_ARTIFICIAL
1212 This macro holds if the function was implicitly generated by the
1213 compiler, rather than explicitly declared. In addition to implicitly
1214 generated class member functions, this macro holds for the special
1215 functions created to implement static initialization and destruction, to
1216 compute run-time type information, and so forth.
1218 @item DECL_ARGUMENTS
1219 This macro returns the @code{PARM_DECL} for the first argument to the
1220 function. Subsequent @code{PARM_DECL} nodes can be obtained by
1221 following the @code{TREE_CHAIN} links.
1224 This macro returns the @code{RESULT_DECL} for the function.
1227 This macro returns the @code{FUNCTION_TYPE} or @code{METHOD_TYPE} for
1230 @item TYPE_RAISES_EXCEPTIONS
1231 This macro returns the list of exceptions that a (member-)function can
1232 raise. The returned list, if non @code{NULL}, is comprised of nodes
1233 whose @code{TREE_VALUE} represents a type.
1235 @item TYPE_NOTHROW_P
1236 This predicate holds when the exception-specification of its arguments
1237 if of the form `@code{()}'.
1239 @item DECL_ARRAY_DELETE_OPERATOR_P
1240 This predicate holds if the function an overloaded
1241 @code{operator delete[]}.
1245 @c ---------------------------------------------------------------------
1247 @c ---------------------------------------------------------------------
1249 @node Function Bodies
1250 @subsection Function Bodies
1251 @cindex function body
1258 @findex ASM_CLOBBERS
1260 @tindex CLEANUP_STMT
1261 @findex CLEANUP_DECL
1262 @findex CLEANUP_EXPR
1263 @tindex COMPOUND_STMT
1264 @findex COMPOUND_BODY
1265 @tindex CONTINUE_STMT
1267 @findex DECL_STMT_DECL
1271 @tindex EMPTY_CLASS_EXPR
1273 @findex EXPR_STMT_EXPR
1275 @findex FOR_INIT_STMT
1280 @findex GOTO_DESTINATION
1288 @tindex LABEL_STMT_LABEL
1293 @findex SCOPE_BEGIN_P
1295 @findex SCOPE_NULLIFIED_P
1297 @findex SUBOBJECT_CLEANUP
1303 @findex TRY_HANDLERS
1304 @findex HANDLER_PARMS
1305 @findex HANDLER_BODY
1311 A function that has a definition in the current translation unit will
1312 have a non-@code{NULL} @code{DECL_INITIAL}. However, back ends should not make
1313 use of the particular value given by @code{DECL_INITIAL}.
1315 The @code{DECL_SAVED_TREE} macro will give the complete body of the
1316 function. This node will usually be a @code{COMPOUND_STMT} representing
1317 the outermost block of the function, but it may also be a
1318 @code{TRY_BLOCK}, a @code{RETURN_INIT}, or any other valid statement.
1320 @subsubsection Statements
1322 There are tree nodes corresponding to all of the source-level statement
1323 constructs. These are enumerated here, together with a list of the
1324 various macros that can be used to obtain information about them. There
1325 are a few macros that can be used with all statements:
1329 This macro returns the line number for the statement. If the statement
1330 spans multiple lines, this value will be the number of the first line on
1331 which the statement occurs. Although we mention @code{CASE_LABEL} below
1332 as if it were a statement, they do not allow the use of
1333 @code{STMT_LINENO}. There is no way to obtain the line number for a
1336 Statements do not contain information about
1337 the file from which they came; that information is implicit in the
1338 @code{FUNCTION_DECL} from which the statements originate.
1340 @item STMT_IS_FULL_EXPR_P
1341 In C++, statements normally constitute ``full expressions''; temporaries
1342 created during a statement are destroyed when the statement is complete.
1343 However, G++ sometimes represents expressions by statements; these
1344 statements will not have @code{STMT_IS_FULL_EXPR_P} set. Temporaries
1345 created during such statements should be destroyed when the innermost
1346 enclosing statement with @code{STMT_IS_FULL_EXPR_P} set is exited.
1350 Here is the list of the various statement nodes, and the macros used to
1351 access them. This documentation describes the use of these nodes in
1352 non-template functions (including instantiations of template functions).
1353 In template functions, the same nodes are used, but sometimes in
1354 slightly different ways.
1356 Many of the statements have substatements. For example, a @code{while}
1357 loop will have a body, which is itself a statement. If the substatement
1358 is @code{NULL_TREE}, it is considered equivalent to a statement
1359 consisting of a single @code{;}, i.e., an expression statement in which
1360 the expression has been omitted. A substatement may in fact be a list
1361 of statements, connected via their @code{TREE_CHAIN}s. So, you should
1362 always process the statement tree by looping over substatements, like
1365 void process_stmt (stmt)
1370 switch (TREE_CODE (stmt))
1373 process_stmt (THEN_CLAUSE (stmt));
1374 /* More processing here. */
1380 stmt = TREE_CHAIN (stmt);
1384 In other words, while the @code{then} clause of an @code{if} statement
1385 in C++ can be only one statement (although that one statement may be a
1386 compound statement), the intermediate representation will sometimes use
1387 several statements chained together.
1392 Used to represent an inline assembly statement. For an inline assembly
1397 The @code{ASM_STRING} macro will return a @code{STRING_CST} node for
1398 @code{"mov x, y"}. If the original statement made use of the
1399 extended-assembly syntax, then @code{ASM_OUTPUTS},
1400 @code{ASM_INPUTS}, and @code{ASM_CLOBBERS} will be the outputs, inputs,
1401 and clobbers for the statement, represented as @code{STRING_CST} nodes.
1402 The extended-assembly syntax looks like:
1404 asm ("fsinx %1,%0" : "=f" (result) : "f" (angle));
1406 The first string is the @code{ASM_STRING}, containing the instruction
1407 template. The next two strings are the output and inputs, respectively;
1408 this statement has no clobbers. As this example indicates, ``plain''
1409 assembly statements are merely a special case of extended assembly
1410 statements; they have no cv-qualifiers, outputs, inputs, or clobbers.
1411 All of the strings will be @code{NUL}-terminated, and will contain no
1412 embedded @code{NUL}-characters.
1414 If the assembly statement is declared @code{volatile}, or if the
1415 statement was not an extended assembly statement, and is therefore
1416 implicitly volatile, then the predicate @code{ASM_VOLATILE_P} will hold
1417 of the @code{ASM_STMT}.
1421 Used to represent a @code{break} statement. There are no additional
1426 Use to represent a @code{case} label, range of @code{case} labels, or a
1427 @code{default} label. If @code{CASE_LOW} is @code{NULL_TREE}, then this is a
1428 @code{default} label. Otherwise, if @code{CASE_HIGH} is @code{NULL_TREE}, then
1429 this is an ordinary @code{case} label. In this case, @code{CASE_LOW} is
1430 an expression giving the value of the label. Both @code{CASE_LOW} and
1431 @code{CASE_HIGH} are @code{INTEGER_CST} nodes. These values will have
1432 the same type as the condition expression in the switch statement.
1434 Otherwise, if both @code{CASE_LOW} and @code{CASE_HIGH} are defined, the
1435 statement is a range of case labels. Such statements originate with the
1436 extension that allows users to write things of the form:
1440 The first value will be @code{CASE_LOW}, while the second will be
1445 Used to represent an action that should take place upon exit from the
1446 enclosing scope. Typically, these actions are calls to destructors for
1447 local objects, but back ends cannot rely on this fact. If these nodes
1448 are in fact representing such destructors, @code{CLEANUP_DECL} will be
1449 the @code{VAR_DECL} destroyed. Otherwise, @code{CLEANUP_DECL} will be
1450 @code{NULL_TREE}. In any case, the @code{CLEANUP_EXPR} is the
1451 expression to execute. The cleanups executed on exit from a scope
1452 should be run in the reverse order of the order in which the associated
1453 @code{CLEANUP_STMT}s were encountered.
1457 Used to represent a brace-enclosed block. The first substatement is
1458 given by @code{COMPOUND_BODY}. Subsequent substatements are found by
1459 following the @code{TREE_CHAIN} link from one substatement to the next.
1460 The @code{COMPOUND_BODY} will be @code{NULL_TREE} if there are no
1465 Used to represent a @code{continue} statement. There are no additional
1470 Used to mark the beginning (if @code{CTOR_BEGIN_P} holds) or end (if
1471 @code{CTOR_END_P} holds of the main body of a constructor. See also
1472 @code{SUBOBJECT} for more information on how to use these nodes.
1476 Used to represent a local declaration. The @code{DECL_STMT_DECL} macro
1477 can be used to obtain the entity declared. This declaration may be a
1478 @code{LABEL_DECL}, indicating that the label declared is a local label.
1479 (As an extension, GCC allows the declaration of labels with scope.) In
1480 C, this declaration may be a @code{FUNCTION_DECL}, indicating the
1481 use of the GCC nested function extension. For more information,
1486 Used to represent a @code{do} loop. The body of the loop is given by
1487 @code{DO_BODY} while the termination condition for the loop is given by
1488 @code{DO_COND}. The condition for a @code{do}-statement is always an
1491 @item EMPTY_CLASS_EXPR
1493 Used to represent a temporary object of a class with no data whose
1494 address is never taken. (All such objects are interchangeable.) The
1495 @code{TREE_TYPE} represents the type of the object.
1499 Used to represent an expression statement. Use @code{EXPR_STMT_EXPR} to
1500 obtain the expression.
1504 Used to represent a @code{for} statement. The @code{FOR_INIT_STMT} is
1505 the initialization statement for the loop. The @code{FOR_COND} is the
1506 termination condition. The @code{FOR_EXPR} is the expression executed
1507 right before the @code{FOR_COND} on each loop iteration; often, this
1508 expression increments a counter. The body of the loop is given by
1509 @code{FOR_BODY}. Note that @code{FOR_INIT_STMT} and @code{FOR_BODY}
1510 return statements, while @code{FOR_COND} and @code{FOR_EXPR} return
1515 Used to represent a @code{goto} statement. The @code{GOTO_DESTINATION} will
1516 usually be a @code{LABEL_DECL}. However, if the ``computed goto'' extension
1517 has been used, the @code{GOTO_DESTINATION} will be an arbitrary expression
1518 indicating the destination. This expression will always have pointer type.
1519 Additionally the @code{GOTO_FAKE_P} flag is set whenever the goto statement
1520 does not come from source code, but it is generated implicitly by the compiler.
1521 This is used for branch prediction.
1525 Used to represent a C++ @code{catch} block. The @code{HANDLER_TYPE}
1526 is the type of exception that will be caught by this handler; it is
1527 equal (by pointer equality) to @code{CATCH_ALL_TYPE} if this handler
1528 is for all types. @code{HANDLER_PARMS} is the @code{DECL_STMT} for
1529 the catch parameter, and @code{HANDLER_BODY} is the
1530 @code{COMPOUND_STMT} for the block itself.
1534 Used to represent an @code{if} statement. The @code{IF_COND} is the
1537 If the condition is a @code{TREE_LIST}, then the @code{TREE_PURPOSE} is
1538 a statement (usually a @code{DECL_STMT}). Each time the condition is
1539 evaluated, the statement should be executed. Then, the
1540 @code{TREE_VALUE} should be used as the conditional expression itself.
1541 This representation is used to handle C++ code like this:
1544 if (int i = 7) @dots{}
1547 where there is a new local variable (or variables) declared within the
1550 The @code{THEN_CLAUSE} represents the statement given by the @code{then}
1551 condition, while the @code{ELSE_CLAUSE} represents the statement given
1552 by the @code{else} condition.
1556 Used to represent a label. The @code{LABEL_DECL} declared by this
1557 statement can be obtained with the @code{LABEL_STMT_LABEL} macro. The
1558 @code{IDENTIFIER_NODE} giving the name of the label can be obtained from
1559 the @code{LABEL_DECL} with @code{DECL_NAME}.
1563 If the function uses the G++ ``named return value'' extension, meaning
1564 that the function has been defined like:
1566 S f(int) return s @{@dots{}@}
1568 then there will be a @code{RETURN_INIT}. There is never a named
1569 returned value for a constructor. The first argument to the
1570 @code{RETURN_INIT} is the name of the object returned; the second
1571 argument is the initializer for the object. The object is initialized
1572 when the @code{RETURN_INIT} is encountered. The object referred to is
1573 the actual object returned; this extension is a manual way of doing the
1574 ``return-value optimization.'' Therefore, the object must actually be
1575 constructed in the place where the object will be returned.
1579 Used to represent a @code{return} statement. The @code{RETURN_EXPR} is
1580 the expression returned; it will be @code{NULL_TREE} if the statement
1588 A scope-statement represents the beginning or end of a scope. If
1589 @code{SCOPE_BEGIN_P} holds, this statement represents the beginning of a
1590 scope; if @code{SCOPE_END_P} holds this statement represents the end of
1591 a scope. On exit from a scope, all cleanups from @code{CLEANUP_STMT}s
1592 occurring in the scope must be run, in reverse order to the order in
1593 which they were encountered. If @code{SCOPE_NULLIFIED_P} or
1594 @code{SCOPE_NO_CLEANUPS_P} holds of the scope, back ends should behave
1595 as if the @code{SCOPE_STMT} were not present at all.
1599 In a constructor, these nodes are used to mark the point at which a
1600 subobject of @code{this} is fully constructed. If, after this point, an
1601 exception is thrown before a @code{CTOR_STMT} with @code{CTOR_END_P} set
1602 is encountered, the @code{SUBOBJECT_CLEANUP} must be executed. The
1603 cleanups must be executed in the reverse order in which they appear.
1607 Used to represent a @code{switch} statement. The @code{SWITCH_COND} is
1608 the expression on which the switch is occurring. See the documentation
1609 for an @code{IF_STMT} for more information on the representation used
1610 for the condition. The @code{SWITCH_BODY} is the body of the switch
1614 Used to represent a @code{try} block. The body of the try block is
1615 given by @code{TRY_STMTS}. Each of the catch blocks is a @code{HANDLER}
1616 node. The first handler is given by @code{TRY_HANDLERS}. Subsequent
1617 handlers are obtained by following the @code{TREE_CHAIN} link from one
1618 handler to the next. The body of the handler is given by
1619 @code{HANDLER_BODY}.
1621 If @code{CLEANUP_P} holds of the @code{TRY_BLOCK}, then the
1622 @code{TRY_HANDLERS} will not be a @code{HANDLER} node. Instead, it will
1623 be an expression that should be executed if an exception is thrown in
1624 the try block. It must rethrow the exception after executing that code.
1625 And, if an exception is thrown while the expression is executing,
1626 @code{terminate} must be called.
1629 Used to represent a @code{using} directive. The namespace is given by
1630 @code{USING_STMT_NAMESPACE}, which will be a NAMESPACE_DECL@. This node
1631 is needed inside template functions, to implement using directives
1632 during instantiation.
1636 Used to represent a @code{while} loop. The @code{WHILE_COND} is the
1637 termination condition for the loop. See the documentation for an
1638 @code{IF_STMT} for more information on the representation used for the
1641 The @code{WHILE_BODY} is the body of the loop.
1645 @c ---------------------------------------------------------------------
1647 @c ---------------------------------------------------------------------
1649 @section Attributes in trees
1652 Attributes, as specified using the @code{__attribute__} keyword, are
1653 represented internally as a @code{TREE_LIST}. The @code{TREE_PURPOSE}
1654 is the name of the attribute, as an @code{IDENTIFIER_NODE}. The
1655 @code{TREE_VALUE} is a @code{TREE_LIST} of the arguments of the
1656 attribute, if any, or @code{NULL_TREE} if there are no arguments; the
1657 arguments are stored as the @code{TREE_VALUE} of successive entries in
1658 the list, and may be identifiers or expressions. The @code{TREE_CHAIN}
1659 of the attribute is the next attribute in a list of attributes applying
1660 to the same declaration or type, or @code{NULL_TREE} if there are no
1661 further attributes in the list.
1663 Attributes may be attached to declarations and to types; these
1664 attributes may be accessed with the following macros. All attributes
1665 are stored in this way, and many also cause other changes to the
1666 declaration or type or to other internal compiler data structures.
1668 @deftypefn {Tree Macro} tree DECL_ATTRIBUTES (tree @var{decl})
1669 This macro returns the attributes on the declaration @var{decl}.
1672 @deftypefn {Tree Macro} tree TYPE_ATTRIBUTES (tree @var{type})
1673 This macro returns the attributes on the type @var{type}.
1676 @c ---------------------------------------------------------------------
1678 @c ---------------------------------------------------------------------
1680 @node Expression trees
1681 @section Expressions
1683 @findex TREE_OPERAND
1685 @findex TREE_INT_CST_HIGH
1686 @findex TREE_INT_CST_LOW
1687 @findex tree_int_cst_lt
1688 @findex tree_int_cst_equal
1692 @findex TREE_STRING_LENGTH
1693 @findex TREE_STRING_POINTER
1695 @findex PTRMEM_CST_CLASS
1696 @findex PTRMEM_CST_MEMBER
1699 @tindex BIT_NOT_EXPR
1700 @tindex TRUTH_NOT_EXPR
1702 @tindex INDIRECT_REF
1703 @tindex FIX_TRUNC_EXPR
1705 @tindex COMPLEX_EXPR
1707 @tindex REALPART_EXPR
1708 @tindex IMAGPART_EXPR
1710 @tindex CONVERT_EXPR
1714 @tindex BIT_IOR_EXPR
1715 @tindex BIT_XOR_EXPR
1716 @tindex BIT_AND_EXPR
1717 @tindex TRUTH_ANDIF_EXPR
1718 @tindex TRUTH_ORIF_EXPR
1719 @tindex TRUTH_AND_EXPR
1720 @tindex TRUTH_OR_EXPR
1721 @tindex TRUTH_XOR_EXPR
1725 @tindex TRUNC_DIV_EXPR
1726 @tindex TRUNC_MOD_EXPR
1736 @tindex COMPONENT_REF
1737 @tindex COMPOUND_EXPR
1741 @tindex COMPOUND_LITERAL_EXPR
1746 @tindex CLEANUP_POINT_EXPR
1750 The internal representation for expressions is for the most part quite
1751 straightforward. However, there are a few facts that one must bear in
1752 mind. In particular, the expression ``tree'' is actually a directed
1753 acyclic graph. (For example there may be many references to the integer
1754 constant zero throughout the source program; many of these will be
1755 represented by the same expression node.) You should not rely on
1756 certain kinds of node being shared, nor should rely on certain kinds of
1757 nodes being unshared.
1759 The following macros can be used with all expression nodes:
1763 Returns the type of the expression. This value may not be precisely the
1764 same type that would be given the expression in the original program.
1767 In what follows, some nodes that one might expect to always have type
1768 @code{bool} are documented to have either integral or boolean type. At
1769 some point in the future, the C front end may also make use of this same
1770 intermediate representation, and at this point these nodes will
1771 certainly have integral type. The previous sentence is not meant to
1772 imply that the C++ front end does not or will not give these nodes
1775 Below, we list the various kinds of expression nodes. Except where
1776 noted otherwise, the operands to an expression are accessed using the
1777 @code{TREE_OPERAND} macro. For example, to access the first operand to
1778 a binary plus expression @code{expr}, use:
1781 TREE_OPERAND (expr, 0)
1784 As this example indicates, the operands are zero-indexed.
1786 The table below begins with constants, moves on to unary expressions,
1787 then proceeds to binary expressions, and concludes with various other
1788 kinds of expressions:
1792 These nodes represent integer constants. Note that the type of these
1793 constants is obtained with @code{TREE_TYPE}; they are not always of type
1794 @code{int}. In particular, @code{char} constants are represented with
1795 @code{INTEGER_CST} nodes. The value of the integer constant @code{e} is
1797 ((TREE_INT_CST_HIGH (e) << HOST_BITS_PER_WIDE_INT)
1798 + TREE_INST_CST_LOW (e))
1801 HOST_BITS_PER_WIDE_INT is at least thirty-two on all platforms. Both
1802 @code{TREE_INT_CST_HIGH} and @code{TREE_INT_CST_LOW} return a
1803 @code{HOST_WIDE_INT}. The value of an @code{INTEGER_CST} is interpreted
1804 as a signed or unsigned quantity depending on the type of the constant.
1805 In general, the expression given above will overflow, so it should not
1806 be used to calculate the value of the constant.
1808 The variable @code{integer_zero_node} is an integer constant with value
1809 zero. Similarly, @code{integer_one_node} is an integer constant with
1810 value one. The @code{size_zero_node} and @code{size_one_node} variables
1811 are analogous, but have type @code{size_t} rather than @code{int}.
1813 The function @code{tree_int_cst_lt} is a predicate which holds if its
1814 first argument is less than its second. Both constants are assumed to
1815 have the same signedness (i.e., either both should be signed or both
1816 should be unsigned.) The full width of the constant is used when doing
1817 the comparison; the usual rules about promotions and conversions are
1818 ignored. Similarly, @code{tree_int_cst_equal} holds if the two
1819 constants are equal. The @code{tree_int_cst_sgn} function returns the
1820 sign of a constant. The value is @code{1}, @code{0}, or @code{-1}
1821 according on whether the constant is greater than, equal to, or less
1822 than zero. Again, the signedness of the constant's type is taken into
1823 account; an unsigned constant is never less than zero, no matter what
1828 FIXME: Talk about how to obtain representations of this constant, do
1829 comparisons, and so forth.
1832 These nodes are used to represent complex number constants, that is a
1833 @code{__complex__} whose parts are constant nodes. The
1834 @code{TREE_REALPART} and @code{TREE_IMAGPART} return the real and the
1835 imaginary parts respectively.
1838 These nodes represent string-constants. The @code{TREE_STRING_LENGTH}
1839 returns the length of the string, as an @code{int}. The
1840 @code{TREE_STRING_POINTER} is a @code{char*} containing the string
1841 itself. The string may not be @code{NUL}-terminated, and it may contain
1842 embedded @code{NUL} characters. Therefore, the
1843 @code{TREE_STRING_LENGTH} includes the trailing @code{NUL} if it is
1846 For wide string constants, the @code{TREE_STRING_LENGTH} is the number
1847 of bytes in the string, and the @code{TREE_STRING_POINTER}
1848 points to an array of the bytes of the string, as represented on the
1849 target system (that is, as integers in the target endianness). Wide and
1850 non-wide string constants are distinguished only by the @code{TREE_TYPE}
1851 of the @code{STRING_CST}.
1853 FIXME: The formats of string constants are not well-defined when the
1854 target system bytes are not the same width as host system bytes.
1857 These nodes are used to represent pointer-to-member constants. The
1858 @code{PTRMEM_CST_CLASS} is the class type (either a @code{RECORD_TYPE}
1859 or @code{UNION_TYPE} within which the pointer points), and the
1860 @code{PTRMEM_CST_MEMBER} is the declaration for the pointed to object.
1861 Note that the @code{DECL_CONTEXT} for the @code{PTRMEM_CST_MEMBER} is in
1862 general different from the @code{PTRMEM_CST_CLASS}. For example,
1865 struct B @{ int i; @};
1866 struct D : public B @{@};
1870 The @code{PTRMEM_CST_CLASS} for @code{&D::i} is @code{D}, even though
1871 the @code{DECL_CONTEXT} for the @code{PTRMEM_CST_MEMBER} is @code{B},
1872 since @code{B::i} is a member of @code{B}, not @code{D}.
1876 These nodes represent variables, including static data members. For
1877 more information, @pxref{Declarations}.
1880 These nodes represent unary negation of the single operand, for both
1881 integer and floating-point types. The type of negation can be
1882 determined by looking at the type of the expression.
1885 These nodes represent bitwise complement, and will always have integral
1886 type. The only operand is the value to be complemented.
1888 @item TRUTH_NOT_EXPR
1889 These nodes represent logical negation, and will always have integral
1890 (or boolean) type. The operand is the value being negated.
1892 @item PREDECREMENT_EXPR
1893 @itemx PREINCREMENT_EXPR
1894 @itemx POSTDECREMENT_EXPR
1895 @itemx POSTINCREMENT_EXPR
1896 These nodes represent increment and decrement expressions. The value of
1897 the single operand is computed, and the operand incremented or
1898 decremented. In the case of @code{PREDECREMENT_EXPR} and
1899 @code{PREINCREMENT_EXPR}, the value of the expression is the value
1900 resulting after the increment or decrement; in the case of
1901 @code{POSTDECREMENT_EXPR} and @code{POSTINCREMENT_EXPR} is the value
1902 before the increment or decrement occurs. The type of the operand, like
1903 that of the result, will be either integral, boolean, or floating-point.
1906 These nodes are used to represent the address of an object. (These
1907 expressions will always have pointer or reference type.) The operand may
1908 be another expression, or it may be a declaration.
1910 As an extension, GCC allows users to take the address of a label. In
1911 this case, the operand of the @code{ADDR_EXPR} will be a
1912 @code{LABEL_DECL}. The type of such an expression is @code{void*}.
1914 If the object addressed is not an lvalue, a temporary is created, and
1915 the address of the temporary is used.
1918 These nodes are used to represent the object pointed to by a pointer.
1919 The operand is the pointer being dereferenced; it will always have
1920 pointer or reference type.
1922 @item FIX_TRUNC_EXPR
1923 These nodes represent conversion of a floating-point value to an
1924 integer. The single operand will have a floating-point type, while the
1925 the complete expression will have an integral (or boolean) type. The
1926 operand is rounded towards zero.
1929 These nodes represent conversion of an integral (or boolean) value to a
1930 floating-point value. The single operand will have integral type, while
1931 the complete expression will have a floating-point type.
1933 FIXME: How is the operand supposed to be rounded? Is this dependent on
1937 These nodes are used to represent complex numbers constructed from two
1938 expressions of the same (integer or real) type. The first operand is the
1939 real part and the second operand is the imaginary part.
1942 These nodes represent the conjugate of their operand.
1946 These nodes represent respectively the real and the imaginary parts
1947 of complex numbers (their sole argument).
1949 @item NON_LVALUE_EXPR
1950 These nodes indicate that their one and only operand is not an lvalue.
1951 A back end can treat these identically to the single operand.
1954 These nodes are used to represent conversions that do not require any
1955 code-generation. For example, conversion of a @code{char*} to an
1956 @code{int*} does not require any code be generated; such a conversion is
1957 represented by a @code{NOP_EXPR}. The single operand is the expression
1958 to be converted. The conversion from a pointer to a reference is also
1959 represented with a @code{NOP_EXPR}.
1962 These nodes are similar to @code{NOP_EXPR}s, but are used in those
1963 situations where code may need to be generated. For example, if an
1964 @code{int*} is converted to an @code{int} code may need to be generated
1965 on some platforms. These nodes are never used for C++-specific
1966 conversions, like conversions between pointers to different classes in
1967 an inheritance hierarchy. Any adjustments that need to be made in such
1968 cases are always indicated explicitly. Similarly, a user-defined
1969 conversion is never represented by a @code{CONVERT_EXPR}; instead, the
1970 function calls are made explicit.
1973 These nodes represent @code{throw} expressions. The single operand is
1974 an expression for the code that should be executed to throw the
1975 exception. However, there is one implicit action not represented in
1976 that expression; namely the call to @code{__throw}. This function takes
1977 no arguments. If @code{setjmp}/@code{longjmp} exceptions are used, the
1978 function @code{__sjthrow} is called instead. The normal GCC back end
1979 uses the function @code{emit_throw} to generate this code; you can
1980 examine this function to see what needs to be done.
1984 These nodes represent left and right shifts, respectively. The first
1985 operand is the value to shift; it will always be of integral type. The
1986 second operand is an expression for the number of bits by which to
1987 shift. Right shift should be treated as arithmetic, i.e., the
1988 high-order bits should be zero-filled when the expression has unsigned
1989 type and filled with the sign bit when the expression has signed type.
1990 Note that the result is undefined if the second operand is larger
1991 than the first operand's type size.
1997 These nodes represent bitwise inclusive or, bitwise exclusive or, and
1998 bitwise and, respectively. Both operands will always have integral
2001 @item TRUTH_ANDIF_EXPR
2002 @itemx TRUTH_ORIF_EXPR
2003 These nodes represent logical and and logical or, respectively. These
2004 operators are not strict; i.e., the second operand is evaluated only if
2005 the value of the expression is not determined by evaluation of the first
2006 operand. The type of the operands, and the result type, is always of
2007 boolean or integral type.
2009 @item TRUTH_AND_EXPR
2010 @itemx TRUTH_OR_EXPR
2011 @itemx TRUTH_XOR_EXPR
2012 These nodes represent logical and, logical or, and logical exclusive or.
2013 They are strict; both arguments are always evaluated. There are no
2014 corresponding operators in C or C++, but the front end will sometimes
2015 generate these expressions anyhow, if it can tell that strictness does
2021 @itemx TRUNC_DIV_EXPR
2022 @itemx TRUNC_MOD_EXPR
2024 These nodes represent various binary arithmetic operations.
2025 Respectively, these operations are addition, subtraction (of the second
2026 operand from the first), multiplication, integer division, integer
2027 remainder, and floating-point division. The operands to the first three
2028 of these may have either integral or floating type, but there will never
2029 be case in which one operand is of floating type and the other is of
2032 The result of a @code{TRUNC_DIV_EXPR} is always rounded towards zero.
2033 The @code{TRUNC_MOD_EXPR} of two operands @code{a} and @code{b} is
2034 always @code{a - a/b} where the division is as if computed by a
2035 @code{TRUNC_DIV_EXPR}.
2038 These nodes represent array accesses. The first operand is the array;
2039 the second is the index. To calculate the address of the memory
2040 accessed, you must scale the index by the size of the type of the array
2041 elements. The type of these expressions must be the type of a component of
2044 @item ARRAY_RANGE_REF
2045 These nodes represent access to a range (or ``slice'') of an array. The
2046 operands are the same as that for @code{ARRAY_REF} and have the same
2047 meanings. The type of these expressions must be an array whose component
2048 type is the same as that of the first operand. The range of that array
2049 type determines the amount of data these expressions access.
2051 @item EXACT_DIV_EXPR
2061 These nodes represent the less than, less than or equal to, greater
2062 than, greater than or equal to, equal, and not equal comparison
2063 operators. The first and second operand with either be both of integral
2064 type or both of floating type. The result type of these expressions
2065 will always be of integral or boolean type.
2068 These nodes represent assignment. The left-hand side is the first
2069 operand; the right-hand side is the second operand. The left-hand side
2070 will be a @code{VAR_DECL}, @code{INDIRECT_REF}, @code{COMPONENT_REF}, or
2073 These nodes are used to represent not only assignment with @samp{=} but
2074 also compound assignments (like @samp{+=}), by reduction to @samp{=}
2075 assignment. In other words, the representation for @samp{i += 3} looks
2076 just like that for @samp{i = i + 3}.
2079 These nodes are just like @code{MODIFY_EXPR}, but are used only when a
2080 variable is initialized, rather than assigned to subsequently.
2083 These nodes represent non-static data member accesses. The first
2084 operand is the object (rather than a pointer to it); the second operand
2085 is the @code{FIELD_DECL} for the data member.
2088 These nodes represent comma-expressions. The first operand is an
2089 expression whose value is computed and thrown away prior to the
2090 evaluation of the second operand. The value of the entire expression is
2091 the value of the second operand.
2094 These nodes represent @code{?:} expressions. The first operand
2095 is of boolean or integral type. If it evaluates to a nonzero value,
2096 the second operand should be evaluated, and returned as the value of the
2097 expression. Otherwise, the third operand is evaluated, and returned as
2098 the value of the expression. As a GNU extension, the middle operand of
2099 the @code{?:} operator may be omitted in the source, like this:
2105 which is equivalent to
2112 assuming that @code{x} is an expression without side-effects. However,
2113 in the case that the first operation causes side effects, the
2114 side-effects occur only once. Consumers of the internal representation
2115 do not need to worry about this oddity; the second operand will be
2116 always be present in the internal representation.
2119 These nodes are used to represent calls to functions, including
2120 non-static member functions. The first operand is a pointer to the
2121 function to call; it is always an expression whose type is a
2122 @code{POINTER_TYPE}. The second argument is a @code{TREE_LIST}. The
2123 arguments to the call appear left-to-right in the list. The
2124 @code{TREE_VALUE} of each list node contains the expression
2125 corresponding to that argument. (The value of @code{TREE_PURPOSE} for
2126 these nodes is unspecified, and should be ignored.) For non-static
2127 member functions, there will be an operand corresponding to the
2128 @code{this} pointer. There will always be expressions corresponding to
2129 all of the arguments, even if the function is declared with default
2130 arguments and some arguments are not explicitly provided at the call
2134 These nodes are used to represent GCC's statement-expression extension.
2135 The statement-expression extension allows code like this:
2137 int f() @{ return (@{ int j; j = 3; j + 7; @}); @}
2139 In other words, an sequence of statements may occur where a single
2140 expression would normally appear. The @code{STMT_EXPR} node represents
2141 such an expression. The @code{STMT_EXPR_STMT} gives the statement
2142 contained in the expression; this is always a @code{COMPOUND_STMT}. The
2143 value of the expression is the value of the last sub-statement in the
2144 @code{COMPOUND_STMT}. More precisely, the value is the value computed
2145 by the last @code{EXPR_STMT} in the outermost scope of the
2146 @code{COMPOUND_STMT}. For example, in:
2150 the value is @code{3} while in:
2152 (@{ if (x) @{ 3; @} @})
2154 (represented by a nested @code{COMPOUND_STMT}), there is no value. If
2155 the @code{STMT_EXPR} does not yield a value, it's type will be
2159 These nodes represent local blocks. The first operand is a list of
2160 temporary variables, connected via their @code{TREE_CHAIN} field. These
2161 will never require cleanups. The scope of these variables is just the
2162 body of the @code{BIND_EXPR}. The body of the @code{BIND_EXPR} is the
2166 These nodes represent ``infinite'' loops. The @code{LOOP_EXPR_BODY}
2167 represents the body of the loop. It should be executed forever, unless
2168 an @code{EXIT_EXPR} is encountered.
2171 These nodes represent conditional exits from the nearest enclosing
2172 @code{LOOP_EXPR}. The single operand is the condition; if it is
2173 nonzero, then the loop should be exited. An @code{EXIT_EXPR} will only
2174 appear within a @code{LOOP_EXPR}.
2176 @item CLEANUP_POINT_EXPR
2177 These nodes represent full-expressions. The single operand is an
2178 expression to evaluate. Any destructor calls engendered by the creation
2179 of temporaries during the evaluation of that expression should be
2180 performed immediately after the expression is evaluated.
2183 These nodes represent the brace-enclosed initializers for a structure or
2184 array. The first operand is reserved for use by the back end. The
2185 second operand is a @code{TREE_LIST}. If the @code{TREE_TYPE} of the
2186 @code{CONSTRUCTOR} is a @code{RECORD_TYPE} or @code{UNION_TYPE}, then
2187 the @code{TREE_PURPOSE} of each node in the @code{TREE_LIST} will be a
2188 @code{FIELD_DECL} and the @code{TREE_VALUE} of each node will be the
2189 expression used to initialize that field. You should not depend on the
2190 fields appearing in any particular order, nor should you assume that all
2191 fields will be represented. Unrepresented fields may be assigned any
2194 If the @code{TREE_TYPE} of the @code{CONSTRUCTOR} is an
2195 @code{ARRAY_TYPE}, then the @code{TREE_PURPOSE} of each element in the
2196 @code{TREE_LIST} will be an @code{INTEGER_CST}. This constant indicates
2197 which element of the array (indexed from zero) is being assigned to;
2198 again, the @code{TREE_VALUE} is the corresponding initializer. If the
2199 @code{TREE_PURPOSE} is @code{NULL_TREE}, then the initializer is for the
2200 next available array element.
2202 Conceptually, before any initialization is done, the entire area of
2203 storage is initialized to zero.
2205 @item COMPOUND_LITERAL_EXPR
2206 @findex COMPOUND_LITERAL_EXPR_DECL
2207 These nodes represent ISO C99 compound literals. The
2208 @code{COMPOUND_LITERAL_EXPR_DECL} is an anonymous @code{VAR_DECL} for
2209 the unnamed object represented by the compound literal; the
2210 @code{DECL_INITIAL} of that @code{VAR_DECL} is a @code{CONSTRUCTOR}
2211 representing the brace-enclosed list of initializers in the compound
2216 A @code{SAVE_EXPR} represents an expression (possibly involving
2217 side-effects) that is used more than once. The side-effects should
2218 occur only the first time the expression is evaluated. Subsequent uses
2219 should just reuse the computed value. The first operand to the
2220 @code{SAVE_EXPR} is the expression to evaluate. The side-effects should
2221 be executed where the @code{SAVE_EXPR} is first encountered in a
2222 depth-first preorder traversal of the expression tree.
2225 A @code{TARGET_EXPR} represents a temporary object. The first operand
2226 is a @code{VAR_DECL} for the temporary variable. The second operand is
2227 the initializer for the temporary. The initializer is evaluated, and
2228 copied (bitwise) into the temporary.
2230 Often, a @code{TARGET_EXPR} occurs on the right-hand side of an
2231 assignment, or as the second operand to a comma-expression which is
2232 itself the right-hand side of an assignment, etc. In this case, we say
2233 that the @code{TARGET_EXPR} is ``normal''; otherwise, we say it is
2234 ``orphaned''. For a normal @code{TARGET_EXPR} the temporary variable
2235 should be treated as an alias for the left-hand side of the assignment,
2236 rather than as a new temporary variable.
2238 The third operand to the @code{TARGET_EXPR}, if present, is a
2239 cleanup-expression (i.e., destructor call) for the temporary. If this
2240 expression is orphaned, then this expression must be executed when the
2241 statement containing this expression is complete. These cleanups must
2242 always be executed in the order opposite to that in which they were
2243 encountered. Note that if a temporary is created on one branch of a
2244 conditional operator (i.e., in the second or third operand to a
2245 @code{COND_EXPR}), the cleanup must be run only if that branch is
2248 See @code{STMT_IS_FULL_EXPR_P} for more information about running these
2251 @item AGGR_INIT_EXPR
2252 An @code{AGGR_INIT_EXPR} represents the initialization as the return
2253 value of a function call, or as the result of a constructor. An
2254 @code{AGGR_INIT_EXPR} will only appear as the second operand of a
2255 @code{TARGET_EXPR}. The first operand to the @code{AGGR_INIT_EXPR} is
2256 the address of a function to call, just as in a @code{CALL_EXPR}. The
2257 second operand are the arguments to pass that function, as a
2258 @code{TREE_LIST}, again in a manner similar to that of a
2259 @code{CALL_EXPR}. The value of the expression is that returned by the
2262 If @code{AGGR_INIT_VIA_CTOR_P} holds of the @code{AGGR_INIT_EXPR}, then
2263 the initialization is via a constructor call. The address of the third
2264 operand of the @code{AGGR_INIT_EXPR}, which is always a @code{VAR_DECL},
2265 is taken, and this value replaces the first argument in the argument
2266 list. In this case, the value of the expression is the @code{VAR_DECL}
2267 given by the third operand to the @code{AGGR_INIT_EXPR}; constructors do
2271 A @code{VTABLE_REF} indicates that the interior expression computes
2272 a value that is a vtable entry. It is used with @option{-fvtable-gc}
2273 to track the reference through to front end to the middle end, at
2274 which point we transform this to a @code{REG_VTABLE_REF} note, which
2275 survives the balance of code generation.
2277 The first operand is the expression that computes the vtable reference.
2278 The second operand is the @code{VAR_DECL} of the vtable. The third
2279 operand is an @code{INTEGER_CST} of the byte offset into the vtable.