1 @c Copyright (c) 1999, 2000, 2001, 2002, 2003 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 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 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 trees as input and
88 return trees as output. However, most macros require a certain kind 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 namespace 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},
764 and @code{TYPE_BINFO (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_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
1031 If a friend function is defined in a class scope, the
1032 @code{DECL_FRIEND_CONTEXT} macro can be used to determine the class in
1033 which it was defined. For example, in
1035 class C @{ friend void f() @{@} @};
1038 the @code{DECL_CONTEXT} for @code{f} will be the
1039 @code{global_namespace}, but the @code{DECL_FRIEND_CONTEXT} will be the
1040 @code{RECORD_TYPE} for @code{C}.
1042 In C, the @code{DECL_CONTEXT} for a function maybe another function.
1043 This representation indicates that the GNU nested function extension
1044 is in use. For details on the semantics of nested functions, see the
1045 GCC Manual. The nested function can refer to local variables in its
1046 containing function. Such references are not explicitly marked in the
1047 tree structure; back ends must look at the @code{DECL_CONTEXT} for the
1048 referenced @code{VAR_DECL}. If the @code{DECL_CONTEXT} for the
1049 referenced @code{VAR_DECL} is not the same as the function currently
1050 being processed, and neither @code{DECL_EXTERNAL} nor
1051 @code{DECL_STATIC} hold, then the reference is to a local variable in
1052 a containing function, and the back end must take appropriate action.
1055 * Function Basics:: Function names, linkage, and so forth.
1056 * Function Bodies:: The statements that make up a function body.
1059 @c ---------------------------------------------------------------------
1061 @c ---------------------------------------------------------------------
1063 @node Function Basics
1064 @subsection Function Basics
1067 @cindex copy constructor
1068 @cindex assignment operator
1071 @findex DECL_ASSEMBLER_NAME
1073 @findex DECL_LINKONCE_P
1074 @findex DECL_FUNCTION_MEMBER_P
1075 @findex DECL_CONSTRUCTOR_P
1076 @findex DECL_DESTRUCTOR_P
1077 @findex DECL_OVERLOADED_OPERATOR_P
1078 @findex DECL_CONV_FN_P
1079 @findex DECL_ARTIFICIAL
1080 @findex DECL_GLOBAL_CTOR_P
1081 @findex DECL_GLOBAL_DTOR_P
1082 @findex GLOBAL_INIT_PRIORITY
1084 The following macros and functions can be used on a @code{FUNCTION_DECL}:
1087 This predicate holds for a function that is the program entry point
1091 This macro returns the unqualified name of the function, as an
1092 @code{IDENTIFIER_NODE}. For an instantiation of a function template,
1093 the @code{DECL_NAME} is the unqualified name of the template, not
1094 something like @code{f<int>}. The value of @code{DECL_NAME} is
1095 undefined when used on a constructor, destructor, overloaded operator,
1096 or type-conversion operator, or any function that is implicitly
1097 generated by the compiler. See below for macros that can be used to
1098 distinguish these cases.
1100 @item DECL_ASSEMBLER_NAME
1101 This macro returns the mangled name of the function, also an
1102 @code{IDENTIFIER_NODE}. This name does not contain leading underscores
1103 on systems that prefix all identifiers with underscores. The mangled
1104 name is computed in the same way on all platforms; if special processing
1105 is required to deal with the object file format used on a particular
1106 platform, it is the responsibility of the back end to perform those
1107 modifications. (Of course, the back end should not modify
1108 @code{DECL_ASSEMBLER_NAME} itself.)
1111 This predicate holds if the function is undefined.
1114 This predicate holds if the function has external linkage.
1116 @item DECL_LOCAL_FUNCTION_P
1117 This predicate holds if the function was declared at block scope, even
1118 though it has a global scope.
1120 @item DECL_ANTICIPATED
1121 This predicate holds if the function is a built-in function but its
1122 prototype is not yet explicitly declared.
1124 @item DECL_EXTERN_C_FUNCTION_P
1125 This predicate holds if the function is declared as an
1126 `@code{extern "C"}' function.
1128 @item DECL_LINKONCE_P
1129 This macro holds if multiple copies of this function may be emitted in
1130 various translation units. It is the responsibility of the linker to
1131 merge the various copies. Template instantiations are the most common
1132 example of functions for which @code{DECL_LINKONCE_P} holds; G++
1133 instantiates needed templates in all translation units which require them,
1134 and then relies on the linker to remove duplicate instantiations.
1136 FIXME: This macro is not yet implemented.
1138 @item DECL_FUNCTION_MEMBER_P
1139 This macro holds if the function is a member of a class, rather than a
1140 member of a namespace.
1142 @item DECL_STATIC_FUNCTION_P
1143 This predicate holds if the function a static member function.
1145 @item DECL_NONSTATIC_MEMBER_FUNCTION_P
1146 This macro holds for a non-static member function.
1148 @item DECL_CONST_MEMFUNC_P
1149 This predicate holds for a @code{const}-member function.
1151 @item DECL_VOLATILE_MEMFUNC_P
1152 This predicate holds for a @code{volatile}-member function.
1154 @item DECL_CONSTRUCTOR_P
1155 This macro holds if the function is a constructor.
1157 @item DECL_NONCONVERTING_P
1158 This predicate holds if the constructor is a non-converting constructor.
1160 @item DECL_COMPLETE_CONSTRUCTOR_P
1161 This predicate holds for a function which is a constructor for an object
1164 @item DECL_BASE_CONSTRUCTOR_P
1165 This predicate holds for a function which is a constructor for a base
1168 @item DECL_COPY_CONSTRUCTOR_P
1169 This predicate holds for a function which is a copy-constructor.
1171 @item DECL_DESTRUCTOR_P
1172 This macro holds if the function is a destructor.
1174 @item DECL_COMPLETE_DESTRUCTOR_P
1175 This predicate holds if the function is the destructor for an object a
1178 @item DECL_OVERLOADED_OPERATOR_P
1179 This macro holds if the function is an overloaded operator.
1181 @item DECL_CONV_FN_P
1182 This macro holds if the function is a type-conversion operator.
1184 @item DECL_GLOBAL_CTOR_P
1185 This predicate holds if the function is a file-scope initialization
1188 @item DECL_GLOBAL_DTOR_P
1189 This predicate holds if the function is a file-scope finalization
1193 This predicate holds if the function is a thunk.
1195 These functions represent stub code that adjusts the @code{this} pointer
1196 and then jumps to another function. When the jumped-to function
1197 returns, control is transferred directly to the caller, without
1198 returning to the thunk. The first parameter to the thunk is always the
1199 @code{this} pointer; the thunk should add @code{THUNK_DELTA} to this
1200 value. (The @code{THUNK_DELTA} is an @code{int}, not an
1201 @code{INTEGER_CST}.)
1203 Then, if @code{THUNK_VCALL_OFFSET} (an @code{INTEGER_CST}) is nonzero
1204 the adjusted @code{this} pointer must be adjusted again. The complete
1205 calculation is given by the following pseudo-code:
1209 if (THUNK_VCALL_OFFSET)
1210 this += (*((ptrdiff_t **) this))[THUNK_VCALL_OFFSET]
1213 Finally, the thunk should jump to the location given
1214 by @code{DECL_INITIAL}; this will always be an expression for the
1215 address of a function.
1217 @item DECL_NON_THUNK_FUNCTION_P
1218 This predicate holds if the function is @emph{not} a thunk function.
1220 @item GLOBAL_INIT_PRIORITY
1221 If either @code{DECL_GLOBAL_CTOR_P} or @code{DECL_GLOBAL_DTOR_P} holds,
1222 then this gives the initialization priority for the function. The
1223 linker will arrange that all functions for which
1224 @code{DECL_GLOBAL_CTOR_P} holds are run in increasing order of priority
1225 before @code{main} is called. When the program exits, all functions for
1226 which @code{DECL_GLOBAL_DTOR_P} holds are run in the reverse order.
1228 @item DECL_ARTIFICIAL
1229 This macro holds if the function was implicitly generated by the
1230 compiler, rather than explicitly declared. In addition to implicitly
1231 generated class member functions, this macro holds for the special
1232 functions created to implement static initialization and destruction, to
1233 compute run-time type information, and so forth.
1235 @item DECL_ARGUMENTS
1236 This macro returns the @code{PARM_DECL} for the first argument to the
1237 function. Subsequent @code{PARM_DECL} nodes can be obtained by
1238 following the @code{TREE_CHAIN} links.
1241 This macro returns the @code{RESULT_DECL} for the function.
1244 This macro returns the @code{FUNCTION_TYPE} or @code{METHOD_TYPE} for
1247 @item TYPE_RAISES_EXCEPTIONS
1248 This macro returns the list of exceptions that a (member-)function can
1249 raise. The returned list, if non @code{NULL}, is comprised of nodes
1250 whose @code{TREE_VALUE} represents a type.
1252 @item TYPE_NOTHROW_P
1253 This predicate holds when the exception-specification of its arguments
1254 if of the form `@code{()}'.
1256 @item DECL_ARRAY_DELETE_OPERATOR_P
1257 This predicate holds if the function an overloaded
1258 @code{operator delete[]}.
1262 @c ---------------------------------------------------------------------
1264 @c ---------------------------------------------------------------------
1266 @node Function Bodies
1267 @subsection Function Bodies
1268 @cindex function body
1275 @findex ASM_CLOBBERS
1277 @tindex CLEANUP_STMT
1278 @findex CLEANUP_DECL
1279 @findex CLEANUP_EXPR
1280 @tindex COMPOUND_STMT
1281 @findex COMPOUND_BODY
1282 @tindex CONTINUE_STMT
1284 @findex DECL_STMT_DECL
1288 @tindex EMPTY_CLASS_EXPR
1290 @findex EXPR_STMT_EXPR
1292 @findex FOR_INIT_STMT
1297 @findex FILE_STMT_FILENAME
1299 @findex GOTO_DESTINATION
1307 @tindex LABEL_STMT_LABEL
1312 @findex SCOPE_BEGIN_P
1314 @findex SCOPE_NULLIFIED_P
1316 @findex SUBOBJECT_CLEANUP
1322 @findex TRY_HANDLERS
1323 @findex HANDLER_PARMS
1324 @findex HANDLER_BODY
1330 A function that has a definition in the current translation unit will
1331 have a non-@code{NULL} @code{DECL_INITIAL}. However, back ends should not make
1332 use of the particular value given by @code{DECL_INITIAL}.
1334 The @code{DECL_SAVED_TREE} macro will give the complete body of the
1335 function. This node will usually be a @code{COMPOUND_STMT} representing
1336 the outermost block of the function, but it may also be a
1337 @code{TRY_BLOCK}, a @code{RETURN_INIT}, or any other valid statement.
1339 @subsubsection Statements
1341 There are tree nodes corresponding to all of the source-level statement
1342 constructs. These are enumerated here, together with a list of the
1343 various macros that can be used to obtain information about them. There
1344 are a few macros that can be used with all statements:
1348 This macro returns the line number for the statement. If the statement
1349 spans multiple lines, this value will be the number of the first line on
1350 which the statement occurs. Although we mention @code{CASE_LABEL} below
1351 as if it were a statement, they do not allow the use of
1352 @code{STMT_LINENO}. There is no way to obtain the line number for a
1355 Statements do not contain information about
1356 the file from which they came; that information is implicit in the
1357 @code{FUNCTION_DECL} from which the statements originate.
1359 @item STMT_IS_FULL_EXPR_P
1360 In C++, statements normally constitute ``full expressions''; temporaries
1361 created during a statement are destroyed when the statement is complete.
1362 However, G++ sometimes represents expressions by statements; these
1363 statements will not have @code{STMT_IS_FULL_EXPR_P} set. Temporaries
1364 created during such statements should be destroyed when the innermost
1365 enclosing statement with @code{STMT_IS_FULL_EXPR_P} set is exited.
1369 Here is the list of the various statement nodes, and the macros used to
1370 access them. This documentation describes the use of these nodes in
1371 non-template functions (including instantiations of template functions).
1372 In template functions, the same nodes are used, but sometimes in
1373 slightly different ways.
1375 Many of the statements have substatements. For example, a @code{while}
1376 loop will have a body, which is itself a statement. If the substatement
1377 is @code{NULL_TREE}, it is considered equivalent to a statement
1378 consisting of a single @code{;}, i.e., an expression statement in which
1379 the expression has been omitted. A substatement may in fact be a list
1380 of statements, connected via their @code{TREE_CHAIN}s. So, you should
1381 always process the statement tree by looping over substatements, like
1384 void process_stmt (stmt)
1389 switch (TREE_CODE (stmt))
1392 process_stmt (THEN_CLAUSE (stmt));
1393 /* More processing here. */
1399 stmt = TREE_CHAIN (stmt);
1403 In other words, while the @code{then} clause of an @code{if} statement
1404 in C++ can be only one statement (although that one statement may be a
1405 compound statement), the intermediate representation will sometimes use
1406 several statements chained together.
1411 Used to represent an inline assembly statement. For an inline assembly
1416 The @code{ASM_STRING} macro will return a @code{STRING_CST} node for
1417 @code{"mov x, y"}. If the original statement made use of the
1418 extended-assembly syntax, then @code{ASM_OUTPUTS},
1419 @code{ASM_INPUTS}, and @code{ASM_CLOBBERS} will be the outputs, inputs,
1420 and clobbers for the statement, represented as @code{STRING_CST} nodes.
1421 The extended-assembly syntax looks like:
1423 asm ("fsinx %1,%0" : "=f" (result) : "f" (angle));
1425 The first string is the @code{ASM_STRING}, containing the instruction
1426 template. The next two strings are the output and inputs, respectively;
1427 this statement has no clobbers. As this example indicates, ``plain''
1428 assembly statements are merely a special case of extended assembly
1429 statements; they have no cv-qualifiers, outputs, inputs, or clobbers.
1430 All of the strings will be @code{NUL}-terminated, and will contain no
1431 embedded @code{NUL}-characters.
1433 If the assembly statement is declared @code{volatile}, or if the
1434 statement was not an extended assembly statement, and is therefore
1435 implicitly volatile, then the predicate @code{ASM_VOLATILE_P} will hold
1436 of the @code{ASM_STMT}.
1440 Used to represent a @code{break} statement. There are no additional
1445 Use to represent a @code{case} label, range of @code{case} labels, or a
1446 @code{default} label. If @code{CASE_LOW} is @code{NULL_TREE}, then this is a
1447 @code{default} label. Otherwise, if @code{CASE_HIGH} is @code{NULL_TREE}, then
1448 this is an ordinary @code{case} label. In this case, @code{CASE_LOW} is
1449 an expression giving the value of the label. Both @code{CASE_LOW} and
1450 @code{CASE_HIGH} are @code{INTEGER_CST} nodes. These values will have
1451 the same type as the condition expression in the switch statement.
1453 Otherwise, if both @code{CASE_LOW} and @code{CASE_HIGH} are defined, the
1454 statement is a range of case labels. Such statements originate with the
1455 extension that allows users to write things of the form:
1459 The first value will be @code{CASE_LOW}, while the second will be
1464 Used to represent an action that should take place upon exit from the
1465 enclosing scope. Typically, these actions are calls to destructors for
1466 local objects, but back ends cannot rely on this fact. If these nodes
1467 are in fact representing such destructors, @code{CLEANUP_DECL} will be
1468 the @code{VAR_DECL} destroyed. Otherwise, @code{CLEANUP_DECL} will be
1469 @code{NULL_TREE}. In any case, the @code{CLEANUP_EXPR} is the
1470 expression to execute. The cleanups executed on exit from a scope
1471 should be run in the reverse order of the order in which the associated
1472 @code{CLEANUP_STMT}s were encountered.
1476 Used to represent a brace-enclosed block. The first substatement is
1477 given by @code{COMPOUND_BODY}. Subsequent substatements are found by
1478 following the @code{TREE_CHAIN} link from one substatement to the next.
1479 The @code{COMPOUND_BODY} will be @code{NULL_TREE} if there are no
1484 Used to represent a @code{continue} statement. There are no additional
1489 Used to mark the beginning (if @code{CTOR_BEGIN_P} holds) or end (if
1490 @code{CTOR_END_P} holds of the main body of a constructor. See also
1491 @code{SUBOBJECT} for more information on how to use these nodes.
1495 Used to represent a local declaration. The @code{DECL_STMT_DECL} macro
1496 can be used to obtain the entity declared. This declaration may be a
1497 @code{LABEL_DECL}, indicating that the label declared is a local label.
1498 (As an extension, GCC allows the declaration of labels with scope.) In
1499 C, this declaration may be a @code{FUNCTION_DECL}, indicating the
1500 use of the GCC nested function extension. For more information,
1505 Used to represent a @code{do} loop. The body of the loop is given by
1506 @code{DO_BODY} while the termination condition for the loop is given by
1507 @code{DO_COND}. The condition for a @code{do}-statement is always an
1510 @item EMPTY_CLASS_EXPR
1512 Used to represent a temporary object of a class with no data whose
1513 address is never taken. (All such objects are interchangeable.) The
1514 @code{TREE_TYPE} represents the type of the object.
1518 Used to represent an expression statement. Use @code{EXPR_STMT_EXPR} to
1519 obtain the expression.
1523 Used to record a change in filename within the body of a function.
1524 Use @code{FILE_STMT_FILENAME} to obtain the new filename.
1528 Used to represent a @code{for} statement. The @code{FOR_INIT_STMT} is
1529 the initialization statement for the loop. The @code{FOR_COND} is the
1530 termination condition. The @code{FOR_EXPR} is the expression executed
1531 right before the @code{FOR_COND} on each loop iteration; often, this
1532 expression increments a counter. The body of the loop is given by
1533 @code{FOR_BODY}. Note that @code{FOR_INIT_STMT} and @code{FOR_BODY}
1534 return statements, while @code{FOR_COND} and @code{FOR_EXPR} return
1539 Used to represent a @code{goto} statement. The @code{GOTO_DESTINATION} will
1540 usually be a @code{LABEL_DECL}. However, if the ``computed goto'' extension
1541 has been used, the @code{GOTO_DESTINATION} will be an arbitrary expression
1542 indicating the destination. This expression will always have pointer type.
1543 Additionally the @code{GOTO_FAKE_P} flag is set whenever the goto statement
1544 does not come from source code, but it is generated implicitly by the compiler.
1545 This is used for branch prediction.
1549 Used to represent a C++ @code{catch} block. The @code{HANDLER_TYPE}
1550 is the type of exception that will be caught by this handler; it is
1551 equal (by pointer equality) to @code{CATCH_ALL_TYPE} if this handler
1552 is for all types. @code{HANDLER_PARMS} is the @code{DECL_STMT} for
1553 the catch parameter, and @code{HANDLER_BODY} is the
1554 @code{COMPOUND_STMT} for the block itself.
1558 Used to represent an @code{if} statement. The @code{IF_COND} is the
1561 If the condition is a @code{TREE_LIST}, then the @code{TREE_PURPOSE} is
1562 a statement (usually a @code{DECL_STMT}). Each time the condition is
1563 evaluated, the statement should be executed. Then, the
1564 @code{TREE_VALUE} should be used as the conditional expression itself.
1565 This representation is used to handle C++ code like this:
1568 if (int i = 7) @dots{}
1571 where there is a new local variable (or variables) declared within the
1574 The @code{THEN_CLAUSE} represents the statement given by the @code{then}
1575 condition, while the @code{ELSE_CLAUSE} represents the statement given
1576 by the @code{else} condition.
1580 Used to represent a label. The @code{LABEL_DECL} declared by this
1581 statement can be obtained with the @code{LABEL_STMT_LABEL} macro. The
1582 @code{IDENTIFIER_NODE} giving the name of the label can be obtained from
1583 the @code{LABEL_DECL} with @code{DECL_NAME}.
1587 If the function uses the G++ ``named return value'' extension, meaning
1588 that the function has been defined like:
1590 S f(int) return s @{@dots{}@}
1592 then there will be a @code{RETURN_INIT}. There is never a named
1593 returned value for a constructor. The first argument to the
1594 @code{RETURN_INIT} is the name of the object returned; the second
1595 argument is the initializer for the object. The object is initialized
1596 when the @code{RETURN_INIT} is encountered. The object referred to is
1597 the actual object returned; this extension is a manual way of doing the
1598 ``return-value optimization.'' Therefore, the object must actually be
1599 constructed in the place where the object will be returned.
1603 Used to represent a @code{return} statement. The @code{RETURN_EXPR} is
1604 the expression returned; it will be @code{NULL_TREE} if the statement
1612 A scope-statement represents the beginning or end of a scope. If
1613 @code{SCOPE_BEGIN_P} holds, this statement represents the beginning of a
1614 scope; if @code{SCOPE_END_P} holds this statement represents the end of
1615 a scope. On exit from a scope, all cleanups from @code{CLEANUP_STMT}s
1616 occurring in the scope must be run, in reverse order to the order in
1617 which they were encountered. If @code{SCOPE_NULLIFIED_P} or
1618 @code{SCOPE_NO_CLEANUPS_P} holds of the scope, back ends should behave
1619 as if the @code{SCOPE_STMT} were not present at all.
1623 In a constructor, these nodes are used to mark the point at which a
1624 subobject of @code{this} is fully constructed. If, after this point, an
1625 exception is thrown before a @code{CTOR_STMT} with @code{CTOR_END_P} set
1626 is encountered, the @code{SUBOBJECT_CLEANUP} must be executed. The
1627 cleanups must be executed in the reverse order in which they appear.
1631 Used to represent a @code{switch} statement. The @code{SWITCH_COND} is
1632 the expression on which the switch is occurring. See the documentation
1633 for an @code{IF_STMT} for more information on the representation used
1634 for the condition. The @code{SWITCH_BODY} is the body of the switch
1635 statement. The @code{SWITCH_TYPE} is the original type of switch
1636 expression as given in the source, before any compiler conversions.
1639 Used to represent a @code{try} block. The body of the try block is
1640 given by @code{TRY_STMTS}. Each of the catch blocks is a @code{HANDLER}
1641 node. The first handler is given by @code{TRY_HANDLERS}. Subsequent
1642 handlers are obtained by following the @code{TREE_CHAIN} link from one
1643 handler to the next. The body of the handler is given by
1644 @code{HANDLER_BODY}.
1646 If @code{CLEANUP_P} holds of the @code{TRY_BLOCK}, then the
1647 @code{TRY_HANDLERS} will not be a @code{HANDLER} node. Instead, it will
1648 be an expression that should be executed if an exception is thrown in
1649 the try block. It must rethrow the exception after executing that code.
1650 And, if an exception is thrown while the expression is executing,
1651 @code{terminate} must be called.
1654 Used to represent a @code{using} directive. The namespace is given by
1655 @code{USING_STMT_NAMESPACE}, which will be a NAMESPACE_DECL@. This node
1656 is needed inside template functions, to implement using directives
1657 during instantiation.
1661 Used to represent a @code{while} loop. The @code{WHILE_COND} is the
1662 termination condition for the loop. See the documentation for an
1663 @code{IF_STMT} for more information on the representation used for the
1666 The @code{WHILE_BODY} is the body of the loop.
1670 @c ---------------------------------------------------------------------
1672 @c ---------------------------------------------------------------------
1674 @section Attributes in trees
1677 Attributes, as specified using the @code{__attribute__} keyword, are
1678 represented internally as a @code{TREE_LIST}. The @code{TREE_PURPOSE}
1679 is the name of the attribute, as an @code{IDENTIFIER_NODE}. The
1680 @code{TREE_VALUE} is a @code{TREE_LIST} of the arguments of the
1681 attribute, if any, or @code{NULL_TREE} if there are no arguments; the
1682 arguments are stored as the @code{TREE_VALUE} of successive entries in
1683 the list, and may be identifiers or expressions. The @code{TREE_CHAIN}
1684 of the attribute is the next attribute in a list of attributes applying
1685 to the same declaration or type, or @code{NULL_TREE} if there are no
1686 further attributes in the list.
1688 Attributes may be attached to declarations and to types; these
1689 attributes may be accessed with the following macros. All attributes
1690 are stored in this way, and many also cause other changes to the
1691 declaration or type or to other internal compiler data structures.
1693 @deftypefn {Tree Macro} tree DECL_ATTRIBUTES (tree @var{decl})
1694 This macro returns the attributes on the declaration @var{decl}.
1697 @deftypefn {Tree Macro} tree TYPE_ATTRIBUTES (tree @var{type})
1698 This macro returns the attributes on the type @var{type}.
1701 @c ---------------------------------------------------------------------
1703 @c ---------------------------------------------------------------------
1705 @node Expression trees
1706 @section Expressions
1708 @findex TREE_OPERAND
1710 @findex TREE_INT_CST_HIGH
1711 @findex TREE_INT_CST_LOW
1712 @findex tree_int_cst_lt
1713 @findex tree_int_cst_equal
1718 @findex TREE_STRING_LENGTH
1719 @findex TREE_STRING_POINTER
1721 @findex PTRMEM_CST_CLASS
1722 @findex PTRMEM_CST_MEMBER
1725 @tindex BIT_NOT_EXPR
1726 @tindex TRUTH_NOT_EXPR
1728 @tindex INDIRECT_REF
1729 @tindex FIX_TRUNC_EXPR
1731 @tindex COMPLEX_EXPR
1733 @tindex REALPART_EXPR
1734 @tindex IMAGPART_EXPR
1736 @tindex CONVERT_EXPR
1740 @tindex BIT_IOR_EXPR
1741 @tindex BIT_XOR_EXPR
1742 @tindex BIT_AND_EXPR
1743 @tindex TRUTH_ANDIF_EXPR
1744 @tindex TRUTH_ORIF_EXPR
1745 @tindex TRUTH_AND_EXPR
1746 @tindex TRUTH_OR_EXPR
1747 @tindex TRUTH_XOR_EXPR
1751 @tindex TRUNC_DIV_EXPR
1752 @tindex TRUNC_MOD_EXPR
1762 @tindex COMPONENT_REF
1763 @tindex COMPOUND_EXPR
1767 @tindex COMPOUND_LITERAL_EXPR
1772 @tindex CLEANUP_POINT_EXPR
1777 The internal representation for expressions is for the most part quite
1778 straightforward. However, there are a few facts that one must bear in
1779 mind. In particular, the expression ``tree'' is actually a directed
1780 acyclic graph. (For example there may be many references to the integer
1781 constant zero throughout the source program; many of these will be
1782 represented by the same expression node.) You should not rely on
1783 certain kinds of node being shared, nor should rely on certain kinds of
1784 nodes being unshared.
1786 The following macros can be used with all expression nodes:
1790 Returns the type of the expression. This value may not be precisely the
1791 same type that would be given the expression in the original program.
1794 In what follows, some nodes that one might expect to always have type
1795 @code{bool} are documented to have either integral or boolean type. At
1796 some point in the future, the C front end may also make use of this same
1797 intermediate representation, and at this point these nodes will
1798 certainly have integral type. The previous sentence is not meant to
1799 imply that the C++ front end does not or will not give these nodes
1802 Below, we list the various kinds of expression nodes. Except where
1803 noted otherwise, the operands to an expression are accessed using the
1804 @code{TREE_OPERAND} macro. For example, to access the first operand to
1805 a binary plus expression @code{expr}, use:
1808 TREE_OPERAND (expr, 0)
1811 As this example indicates, the operands are zero-indexed.
1813 The table below begins with constants, moves on to unary expressions,
1814 then proceeds to binary expressions, and concludes with various other
1815 kinds of expressions:
1819 These nodes represent integer constants. Note that the type of these
1820 constants is obtained with @code{TREE_TYPE}; they are not always of type
1821 @code{int}. In particular, @code{char} constants are represented with
1822 @code{INTEGER_CST} nodes. The value of the integer constant @code{e} is
1824 ((TREE_INT_CST_HIGH (e) << HOST_BITS_PER_WIDE_INT)
1825 + TREE_INST_CST_LOW (e))
1828 HOST_BITS_PER_WIDE_INT is at least thirty-two on all platforms. Both
1829 @code{TREE_INT_CST_HIGH} and @code{TREE_INT_CST_LOW} return a
1830 @code{HOST_WIDE_INT}. The value of an @code{INTEGER_CST} is interpreted
1831 as a signed or unsigned quantity depending on the type of the constant.
1832 In general, the expression given above will overflow, so it should not
1833 be used to calculate the value of the constant.
1835 The variable @code{integer_zero_node} is an integer constant with value
1836 zero. Similarly, @code{integer_one_node} is an integer constant with
1837 value one. The @code{size_zero_node} and @code{size_one_node} variables
1838 are analogous, but have type @code{size_t} rather than @code{int}.
1840 The function @code{tree_int_cst_lt} is a predicate which holds if its
1841 first argument is less than its second. Both constants are assumed to
1842 have the same signedness (i.e., either both should be signed or both
1843 should be unsigned.) The full width of the constant is used when doing
1844 the comparison; the usual rules about promotions and conversions are
1845 ignored. Similarly, @code{tree_int_cst_equal} holds if the two
1846 constants are equal. The @code{tree_int_cst_sgn} function returns the
1847 sign of a constant. The value is @code{1}, @code{0}, or @code{-1}
1848 according on whether the constant is greater than, equal to, or less
1849 than zero. Again, the signedness of the constant's type is taken into
1850 account; an unsigned constant is never less than zero, no matter what
1855 FIXME: Talk about how to obtain representations of this constant, do
1856 comparisons, and so forth.
1859 These nodes are used to represent complex number constants, that is a
1860 @code{__complex__} whose parts are constant nodes. The
1861 @code{TREE_REALPART} and @code{TREE_IMAGPART} return the real and the
1862 imaginary parts respectively.
1865 These nodes are used to represent vector constants, whose parts are
1866 constant nodes. Each individual constant node is either an integer or a
1867 double constant node. The first operand is a @code{TREE_LIST} of the
1868 constant nodes and is accessed through @code{TREE_VECTOR_CST_ELTS}.
1871 These nodes represent string-constants. The @code{TREE_STRING_LENGTH}
1872 returns the length of the string, as an @code{int}. The
1873 @code{TREE_STRING_POINTER} is a @code{char*} containing the string
1874 itself. The string may not be @code{NUL}-terminated, and it may contain
1875 embedded @code{NUL} characters. Therefore, the
1876 @code{TREE_STRING_LENGTH} includes the trailing @code{NUL} if it is
1879 For wide string constants, the @code{TREE_STRING_LENGTH} is the number
1880 of bytes in the string, and the @code{TREE_STRING_POINTER}
1881 points to an array of the bytes of the string, as represented on the
1882 target system (that is, as integers in the target endianness). Wide and
1883 non-wide string constants are distinguished only by the @code{TREE_TYPE}
1884 of the @code{STRING_CST}.
1886 FIXME: The formats of string constants are not well-defined when the
1887 target system bytes are not the same width as host system bytes.
1890 These nodes are used to represent pointer-to-member constants. The
1891 @code{PTRMEM_CST_CLASS} is the class type (either a @code{RECORD_TYPE}
1892 or @code{UNION_TYPE} within which the pointer points), and the
1893 @code{PTRMEM_CST_MEMBER} is the declaration for the pointed to object.
1894 Note that the @code{DECL_CONTEXT} for the @code{PTRMEM_CST_MEMBER} is in
1895 general different from the @code{PTRMEM_CST_CLASS}. For example,
1898 struct B @{ int i; @};
1899 struct D : public B @{@};
1903 The @code{PTRMEM_CST_CLASS} for @code{&D::i} is @code{D}, even though
1904 the @code{DECL_CONTEXT} for the @code{PTRMEM_CST_MEMBER} is @code{B},
1905 since @code{B::i} is a member of @code{B}, not @code{D}.
1909 These nodes represent variables, including static data members. For
1910 more information, @pxref{Declarations}.
1913 These nodes represent unary negation of the single operand, for both
1914 integer and floating-point types. The type of negation can be
1915 determined by looking at the type of the expression.
1918 These nodes represent bitwise complement, and will always have integral
1919 type. The only operand is the value to be complemented.
1921 @item TRUTH_NOT_EXPR
1922 These nodes represent logical negation, and will always have integral
1923 (or boolean) type. The operand is the value being negated.
1925 @item PREDECREMENT_EXPR
1926 @itemx PREINCREMENT_EXPR
1927 @itemx POSTDECREMENT_EXPR
1928 @itemx POSTINCREMENT_EXPR
1929 These nodes represent increment and decrement expressions. The value of
1930 the single operand is computed, and the operand incremented or
1931 decremented. In the case of @code{PREDECREMENT_EXPR} and
1932 @code{PREINCREMENT_EXPR}, the value of the expression is the value
1933 resulting after the increment or decrement; in the case of
1934 @code{POSTDECREMENT_EXPR} and @code{POSTINCREMENT_EXPR} is the value
1935 before the increment or decrement occurs. The type of the operand, like
1936 that of the result, will be either integral, boolean, or floating-point.
1939 These nodes are used to represent the address of an object. (These
1940 expressions will always have pointer or reference type.) The operand may
1941 be another expression, or it may be a declaration.
1943 As an extension, GCC allows users to take the address of a label. In
1944 this case, the operand of the @code{ADDR_EXPR} will be a
1945 @code{LABEL_DECL}. The type of such an expression is @code{void*}.
1947 If the object addressed is not an lvalue, a temporary is created, and
1948 the address of the temporary is used.
1951 These nodes are used to represent the object pointed to by a pointer.
1952 The operand is the pointer being dereferenced; it will always have
1953 pointer or reference type.
1955 @item FIX_TRUNC_EXPR
1956 These nodes represent conversion of a floating-point value to an
1957 integer. The single operand will have a floating-point type, while the
1958 the complete expression will have an integral (or boolean) type. The
1959 operand is rounded towards zero.
1962 These nodes represent conversion of an integral (or boolean) value to a
1963 floating-point value. The single operand will have integral type, while
1964 the complete expression will have a floating-point type.
1966 FIXME: How is the operand supposed to be rounded? Is this dependent on
1970 These nodes are used to represent complex numbers constructed from two
1971 expressions of the same (integer or real) type. The first operand is the
1972 real part and the second operand is the imaginary part.
1975 These nodes represent the conjugate of their operand.
1979 These nodes represent respectively the real and the imaginary parts
1980 of complex numbers (their sole argument).
1982 @item NON_LVALUE_EXPR
1983 These nodes indicate that their one and only operand is not an lvalue.
1984 A back end can treat these identically to the single operand.
1987 These nodes are used to represent conversions that do not require any
1988 code-generation. For example, conversion of a @code{char*} to an
1989 @code{int*} does not require any code be generated; such a conversion is
1990 represented by a @code{NOP_EXPR}. The single operand is the expression
1991 to be converted. The conversion from a pointer to a reference is also
1992 represented with a @code{NOP_EXPR}.
1995 These nodes are similar to @code{NOP_EXPR}s, but are used in those
1996 situations where code may need to be generated. For example, if an
1997 @code{int*} is converted to an @code{int} code may need to be generated
1998 on some platforms. These nodes are never used for C++-specific
1999 conversions, like conversions between pointers to different classes in
2000 an inheritance hierarchy. Any adjustments that need to be made in such
2001 cases are always indicated explicitly. Similarly, a user-defined
2002 conversion is never represented by a @code{CONVERT_EXPR}; instead, the
2003 function calls are made explicit.
2006 These nodes represent @code{throw} expressions. The single operand is
2007 an expression for the code that should be executed to throw the
2008 exception. However, there is one implicit action not represented in
2009 that expression; namely the call to @code{__throw}. This function takes
2010 no arguments. If @code{setjmp}/@code{longjmp} exceptions are used, the
2011 function @code{__sjthrow} is called instead. The normal GCC back end
2012 uses the function @code{emit_throw} to generate this code; you can
2013 examine this function to see what needs to be done.
2017 These nodes represent left and right shifts, respectively. The first
2018 operand is the value to shift; it will always be of integral type. The
2019 second operand is an expression for the number of bits by which to
2020 shift. Right shift should be treated as arithmetic, i.e., the
2021 high-order bits should be zero-filled when the expression has unsigned
2022 type and filled with the sign bit when the expression has signed type.
2023 Note that the result is undefined if the second operand is larger
2024 than the first operand's type size.
2030 These nodes represent bitwise inclusive or, bitwise exclusive or, and
2031 bitwise and, respectively. Both operands will always have integral
2034 @item TRUTH_ANDIF_EXPR
2035 @itemx TRUTH_ORIF_EXPR
2036 These nodes represent logical and and logical or, respectively. These
2037 operators are not strict; i.e., the second operand is evaluated only if
2038 the value of the expression is not determined by evaluation of the first
2039 operand. The type of the operands, and the result type, is always of
2040 boolean or integral type.
2042 @item TRUTH_AND_EXPR
2043 @itemx TRUTH_OR_EXPR
2044 @itemx TRUTH_XOR_EXPR
2045 These nodes represent logical and, logical or, and logical exclusive or.
2046 They are strict; both arguments are always evaluated. There are no
2047 corresponding operators in C or C++, but the front end will sometimes
2048 generate these expressions anyhow, if it can tell that strictness does
2054 @itemx TRUNC_DIV_EXPR
2055 @itemx TRUNC_MOD_EXPR
2057 These nodes represent various binary arithmetic operations.
2058 Respectively, these operations are addition, subtraction (of the second
2059 operand from the first), multiplication, integer division, integer
2060 remainder, and floating-point division. The operands to the first three
2061 of these may have either integral or floating type, but there will never
2062 be case in which one operand is of floating type and the other is of
2065 The result of a @code{TRUNC_DIV_EXPR} is always rounded towards zero.
2066 The @code{TRUNC_MOD_EXPR} of two operands @code{a} and @code{b} is
2067 always @code{a - (a/b)*b} where the division is as if computed by a
2068 @code{TRUNC_DIV_EXPR}.
2071 These nodes represent array accesses. The first operand is the array;
2072 the second is the index. To calculate the address of the memory
2073 accessed, you must scale the index by the size of the type of the array
2074 elements. The type of these expressions must be the type of a component of
2077 @item ARRAY_RANGE_REF
2078 These nodes represent access to a range (or ``slice'') of an array. The
2079 operands are the same as that for @code{ARRAY_REF} and have the same
2080 meanings. The type of these expressions must be an array whose component
2081 type is the same as that of the first operand. The range of that array
2082 type determines the amount of data these expressions access.
2084 @item EXACT_DIV_EXPR
2094 These nodes represent the less than, less than or equal to, greater
2095 than, greater than or equal to, equal, and not equal comparison
2096 operators. The first and second operand with either be both of integral
2097 type or both of floating type. The result type of these expressions
2098 will always be of integral or boolean type.
2101 These nodes represent assignment. The left-hand side is the first
2102 operand; the right-hand side is the second operand. The left-hand side
2103 will be a @code{VAR_DECL}, @code{INDIRECT_REF}, @code{COMPONENT_REF}, or
2106 These nodes are used to represent not only assignment with @samp{=} but
2107 also compound assignments (like @samp{+=}), by reduction to @samp{=}
2108 assignment. In other words, the representation for @samp{i += 3} looks
2109 just like that for @samp{i = i + 3}.
2112 These nodes are just like @code{MODIFY_EXPR}, but are used only when a
2113 variable is initialized, rather than assigned to subsequently.
2116 These nodes represent non-static data member accesses. The first
2117 operand is the object (rather than a pointer to it); the second operand
2118 is the @code{FIELD_DECL} for the data member.
2121 These nodes represent comma-expressions. The first operand is an
2122 expression whose value is computed and thrown away prior to the
2123 evaluation of the second operand. The value of the entire expression is
2124 the value of the second operand.
2127 These nodes represent @code{?:} expressions. The first operand
2128 is of boolean or integral type. If it evaluates to a nonzero value,
2129 the second operand should be evaluated, and returned as the value of the
2130 expression. Otherwise, the third operand is evaluated, and returned as
2131 the value of the expression.
2133 The second operand must have the same type as the entire expression,
2134 unless it unconditionally throws an exception or calls a noreturn
2135 function, in which case it should have void type. The same constraints
2136 apply to the third operand. This allows array bounds checks to be
2137 represented conveniently as @code{(i >= 0 && i < 10) ? i : abort()}.
2139 As a GNU extension, the C language front-ends allow the second
2140 operand of the @code{?:} operator may be omitted in the source.
2141 For example, @code{x ? : 3} is equivalent to @code{x ? x : 3},
2142 assuming that @code{x} is an expression without side-effects.
2143 In the tree representation, however, the second operand is always
2144 present, possibly protected by @code{SAVE_EXPR} if the first
2145 argument does cause side-effects.
2148 These nodes are used to represent calls to functions, including
2149 non-static member functions. The first operand is a pointer to the
2150 function to call; it is always an expression whose type is a
2151 @code{POINTER_TYPE}. The second argument is a @code{TREE_LIST}. The
2152 arguments to the call appear left-to-right in the list. The
2153 @code{TREE_VALUE} of each list node contains the expression
2154 corresponding to that argument. (The value of @code{TREE_PURPOSE} for
2155 these nodes is unspecified, and should be ignored.) For non-static
2156 member functions, there will be an operand corresponding to the
2157 @code{this} pointer. There will always be expressions corresponding to
2158 all of the arguments, even if the function is declared with default
2159 arguments and some arguments are not explicitly provided at the call
2163 These nodes are used to represent GCC's statement-expression extension.
2164 The statement-expression extension allows code like this:
2166 int f() @{ return (@{ int j; j = 3; j + 7; @}); @}
2168 In other words, an sequence of statements may occur where a single
2169 expression would normally appear. The @code{STMT_EXPR} node represents
2170 such an expression. The @code{STMT_EXPR_STMT} gives the statement
2171 contained in the expression; this is always a @code{COMPOUND_STMT}. The
2172 value of the expression is the value of the last sub-statement in the
2173 @code{COMPOUND_STMT}. More precisely, the value is the value computed
2174 by the last @code{EXPR_STMT} in the outermost scope of the
2175 @code{COMPOUND_STMT}. For example, in:
2179 the value is @code{3} while in:
2181 (@{ if (x) @{ 3; @} @})
2183 (represented by a nested @code{COMPOUND_STMT}), there is no value. If
2184 the @code{STMT_EXPR} does not yield a value, it's type will be
2188 These nodes represent local blocks. The first operand is a list of
2189 temporary variables, connected via their @code{TREE_CHAIN} field. These
2190 will never require cleanups. The scope of these variables is just the
2191 body of the @code{BIND_EXPR}. The body of the @code{BIND_EXPR} is the
2195 These nodes represent ``infinite'' loops. The @code{LOOP_EXPR_BODY}
2196 represents the body of the loop. It should be executed forever, unless
2197 an @code{EXIT_EXPR} is encountered.
2200 These nodes represent conditional exits from the nearest enclosing
2201 @code{LOOP_EXPR}. The single operand is the condition; if it is
2202 nonzero, then the loop should be exited. An @code{EXIT_EXPR} will only
2203 appear within a @code{LOOP_EXPR}.
2205 @item CLEANUP_POINT_EXPR
2206 These nodes represent full-expressions. The single operand is an
2207 expression to evaluate. Any destructor calls engendered by the creation
2208 of temporaries during the evaluation of that expression should be
2209 performed immediately after the expression is evaluated.
2212 These nodes represent the brace-enclosed initializers for a structure or
2213 array. The first operand is reserved for use by the back end. The
2214 second operand is a @code{TREE_LIST}. If the @code{TREE_TYPE} of the
2215 @code{CONSTRUCTOR} is a @code{RECORD_TYPE} or @code{UNION_TYPE}, then
2216 the @code{TREE_PURPOSE} of each node in the @code{TREE_LIST} will be a
2217 @code{FIELD_DECL} and the @code{TREE_VALUE} of each node will be the
2218 expression used to initialize that field. You should not depend on the
2219 fields appearing in any particular order, nor should you assume that all
2220 fields will be represented. Unrepresented fields may be assigned any
2223 If the @code{TREE_TYPE} of the @code{CONSTRUCTOR} is an
2224 @code{ARRAY_TYPE}, then the @code{TREE_PURPOSE} of each element in the
2225 @code{TREE_LIST} will be an @code{INTEGER_CST}. This constant indicates
2226 which element of the array (indexed from zero) is being assigned to;
2227 again, the @code{TREE_VALUE} is the corresponding initializer. If the
2228 @code{TREE_PURPOSE} is @code{NULL_TREE}, then the initializer is for the
2229 next available array element.
2231 Conceptually, before any initialization is done, the entire area of
2232 storage is initialized to zero.
2234 @item COMPOUND_LITERAL_EXPR
2235 @findex COMPOUND_LITERAL_EXPR_DECL_STMT
2236 @findex COMPOUND_LITERAL_EXPR_DECL
2237 These nodes represent ISO C99 compound literals. The
2238 @code{COMPOUND_LITERAL_EXPR_DECL_STMT} is a @code{DECL_STMT}
2239 containing an anonymous @code{VAR_DECL} for
2240 the unnamed object represented by the compound literal; the
2241 @code{DECL_INITIAL} of that @code{VAR_DECL} is a @code{CONSTRUCTOR}
2242 representing the brace-enclosed list of initializers in the compound
2243 literal. That anonymous @code{VAR_DECL} can also be accessed directly
2244 by the @code{COMPOUND_LITERAL_EXPR_DECL} macro.
2248 A @code{SAVE_EXPR} represents an expression (possibly involving
2249 side-effects) that is used more than once. The side-effects should
2250 occur only the first time the expression is evaluated. Subsequent uses
2251 should just reuse the computed value. The first operand to the
2252 @code{SAVE_EXPR} is the expression to evaluate. The side-effects should
2253 be executed where the @code{SAVE_EXPR} is first encountered in a
2254 depth-first preorder traversal of the expression tree.
2257 A @code{TARGET_EXPR} represents a temporary object. The first operand
2258 is a @code{VAR_DECL} for the temporary variable. The second operand is
2259 the initializer for the temporary. The initializer is evaluated, and
2260 copied (bitwise) into the temporary.
2262 Often, a @code{TARGET_EXPR} occurs on the right-hand side of an
2263 assignment, or as the second operand to a comma-expression which is
2264 itself the right-hand side of an assignment, etc. In this case, we say
2265 that the @code{TARGET_EXPR} is ``normal''; otherwise, we say it is
2266 ``orphaned''. For a normal @code{TARGET_EXPR} the temporary variable
2267 should be treated as an alias for the left-hand side of the assignment,
2268 rather than as a new temporary variable.
2270 The third operand to the @code{TARGET_EXPR}, if present, is a
2271 cleanup-expression (i.e., destructor call) for the temporary. If this
2272 expression is orphaned, then this expression must be executed when the
2273 statement containing this expression is complete. These cleanups must
2274 always be executed in the order opposite to that in which they were
2275 encountered. Note that if a temporary is created on one branch of a
2276 conditional operator (i.e., in the second or third operand to a
2277 @code{COND_EXPR}), the cleanup must be run only if that branch is
2280 See @code{STMT_IS_FULL_EXPR_P} for more information about running these
2283 @item AGGR_INIT_EXPR
2284 An @code{AGGR_INIT_EXPR} represents the initialization as the return
2285 value of a function call, or as the result of a constructor. An
2286 @code{AGGR_INIT_EXPR} will only appear as the second operand of a
2287 @code{TARGET_EXPR}. The first operand to the @code{AGGR_INIT_EXPR} is
2288 the address of a function to call, just as in a @code{CALL_EXPR}. The
2289 second operand are the arguments to pass that function, as a
2290 @code{TREE_LIST}, again in a manner similar to that of a
2291 @code{CALL_EXPR}. The value of the expression is that returned by the
2294 If @code{AGGR_INIT_VIA_CTOR_P} holds of the @code{AGGR_INIT_EXPR}, then
2295 the initialization is via a constructor call. The address of the third
2296 operand of the @code{AGGR_INIT_EXPR}, which is always a @code{VAR_DECL},
2297 is taken, and this value replaces the first argument in the argument
2298 list. In this case, the value of the expression is the @code{VAR_DECL}
2299 given by the third operand to the @code{AGGR_INIT_EXPR}; constructors do
2303 A @code{VTABLE_REF} indicates that the interior expression computes
2304 a value that is a vtable entry. It is used with @option{-fvtable-gc}
2305 to track the reference through to front end to the middle end, at
2306 which point we transform this to a @code{REG_VTABLE_REF} note, which
2307 survives the balance of code generation.
2309 The first operand is the expression that computes the vtable reference.
2310 The second operand is the @code{VAR_DECL} of the vtable. The third
2311 operand is an @code{INTEGER_CST} of the byte offset into the vtable.
2314 This node is used to implement support for the C/C++ variable argument-list
2315 mechanism. It represents expressions like @code{va_arg (ap, type)}.
2316 Its @code{TREE_TYPE} yields the tree representation for @code{type} and
2317 its sole argument yields the representation for @code{ap}.