@c Copyright (c) 1999, 2000, 2001 Free Software Foundation, Inc. @c Free Software Foundation, Inc. @c This is part of the GCC manual. @c For copying conditions, see the file gcc.texi. @c --------------------------------------------------------------------- @c Trees @c --------------------------------------------------------------------- @node Trees @chapter Trees: The intermediate representation used by the C and C++ front ends @cindex Trees @cindex C/C++ Internal Representation This chapter documents the internal representation used by GCC to represent C and C++ source programs. When presented with a C or C++ source program, GCC parses the program, performs semantic analysis (including the generation of error messages), and then produces the internal representation described here. This representation contains a complete representation for the entire translation unit provided as input to the front end. This representation is then typically processed by a code-generator in order to produce machine code, but could also be used in the creation of source browsers, intelligent editors, automatic documentation generators, interpreters, and any other programs needing the ability to process C or C++ code. This chapter explains the internal representation. In particular, it documents the internal representation for C and C++ source constructs, and the macros, functions, and variables that can be used to access these constructs. The C++ representation is largely a superset of the representation used in the C front end. There is only one construct used in C that does not appear in the C++ front end and that is the GNU ``nested function'' extension. Many of the macros documented here do not apply in C because the corresponding language constructs do not appear in C@. If you are developing a ``back end'', be it is a code-generator or some other tool, that uses this representation, you may occasionally find that you need to ask questions not easily answered by the functions and macros available here. If that situation occurs, it is quite likely that GCC already supports the functionality you desire, but that the interface is simply not documented here. In that case, you should ask the GCC maintainers (via mail to @email{gcc@@gcc.gnu.org}) about documenting the functionality you require. Similarly, if you find yourself writing functions that do not deal directly with your back end, but instead might be useful to other people using the GCC front end, you should submit your patches for inclusion in GCC@. @menu * Deficiencies:: Topics net yet covered in this document. * Tree overview:: All about @code{tree}s. * Types:: Fundamental and aggregate types. * Scopes:: Namespaces and classes. * Functions:: Overloading, function bodies, and linkage. * Declarations:: Type declarations and variables. * Attributes:: Declaration and type attributes. * Expression trees:: From @code{typeid} to @code{throw}. @end menu @c --------------------------------------------------------------------- @c Deficiencies @c --------------------------------------------------------------------- @node Deficiencies @section Deficiencies There are many places in which this document is incomplet and incorrekt. It is, as of yet, only @emph{preliminary} documentation. @c --------------------------------------------------------------------- @c Overview @c --------------------------------------------------------------------- @node Tree overview @section Overview @cindex tree @findex TREE_CODE The central data structure used by the internal representation is the @code{tree}. These nodes, while all of the C type @code{tree}, are of many varieties. A @code{tree} is a pointer type, but the object to which it points may be of a variety of types. From this point forward, we will refer to trees in ordinary type, rather than in @code{this font}, except when talking about the actual C type @code{tree}. You can tell what kind of node a particular tree is by using the @code{TREE_CODE} macro. Many, many macros take trees as input and return trees as output. However, most macros require a certain kind of tree node as input. In other words, there is a type-system for trees, but it is not reflected in the C type-system. For safety, it is useful to configure GCC with @option{--enable-checking}. Although this results in a significant performance penalty (since all tree types are checked at run-time), and is therefore inappropriate in a release version, it is extremely helpful during the development process. Many macros behave as predicates. Many, although not all, of these predicates end in @samp{_P}. Do not rely on the result type of these macros being of any particular type. You may, however, rely on the fact that the type can be compared to @code{0}, so that statements like @example if (TEST_P (t) && !TEST_P (y)) x = 1; @end example @noindent and @example int i = (TEST_P (t) != 0); @end example @noindent are legal. Macros that return @code{int} values now may be changed to return @code{tree} values, or other pointers in the future. Even those that continue to return @code{int} may return multiple nonzero codes where previously they returned only zero and one. Therefore, you should not write code like @example if (TEST_P (t) == 1) @end example @noindent as this code is not guaranteed to work correctly in the future. You should not take the address of values returned by the macros or functions described here. In particular, no guarantee is given that the values are lvalues. In general, the names of macros are all in uppercase, while the names of functions are entirely in lower case. There are rare exceptions to this rule. You should assume that any macro or function whose name is made up entirely of uppercase letters may evaluate its arguments more than once. You may assume that a macro or function whose name is made up entirely of lowercase letters will evaluate its arguments only once. The @code{error_mark_node} is a special tree. Its tree code is @code{ERROR_MARK}, but since there is only ever one node with that code, the usual practice is to compare the tree against @code{error_mark_node}. (This test is just a test for pointer equality.) If an error has occurred during front-end processing the flag @code{errorcount} will be set. If the front end has encountered code it cannot handle, it will issue a message to the user and set @code{sorrycount}. When these flags are set, any macro or function which normally returns a tree of a particular kind may instead return the @code{error_mark_node}. Thus, if you intend to do any processing of erroneous code, you must be prepared to deal with the @code{error_mark_node}. Occasionally, a particular tree slot (like an operand to an expression, or a particular field in a declaration) will be referred to as ``reserved for the back end.'' These slots are used to store RTL when the tree is converted to RTL for use by the GCC back end. However, if that process is not taking place (e.g., if the front end is being hooked up to an intelligent editor), then those slots may be used by the back end presently in use. If you encounter situations that do not match this documentation, such as tree nodes of types not mentioned here, or macros documented to return entities of a particular kind that instead return entities of some different kind, you have found a bug, either in the front end or in the documentation. Please report these bugs as you would any other bug. @menu * Macros and Functions::Macros and functions that can be used with all trees. * Identifiers:: The names of things. * Containers:: Lists and vectors. @end menu @c --------------------------------------------------------------------- @c Trees @c --------------------------------------------------------------------- @node Macros and Functions @subsection Trees @cindex tree This section is not here yet. @c --------------------------------------------------------------------- @c Identifiers @c --------------------------------------------------------------------- @node Identifiers @subsection Identifiers @cindex identifier @cindex name @tindex IDENTIFIER_NODE An @code{IDENTIFIER_NODE} represents a slightly more general concept that the standard C or C++ concept of identifier. In particular, an @code{IDENTIFIER_NODE} may contain a @samp{$}, or other extraordinary characters. There are never two distinct @code{IDENTIFIER_NODE}s representing the same identifier. Therefore, you may use pointer equality to compare @code{IDENTIFIER_NODE}s, rather than using a routine like @code{strcmp}. You can use the following macros to access identifiers: @ftable @code @item IDENTIFIER_POINTER The string represented by the identifier, represented as a @code{char*}. This string is always @code{NUL}-terminated, and contains no embedded @code{NUL} characters. @item IDENTIFIER_LENGTH The length of the string returned by @code{IDENTIFIER_POINTER}, not including the trailing @code{NUL}. This value of @code{IDENTIFIER_LENGTH (x)} is always the same as @code{strlen (IDENTIFIER_POINTER (x))}. @item IDENTIFIER_OPNAME_P This predicate holds if the identifier represents the name of an overloaded operator. In this case, you should not depend on the contents of either the @code{IDENTIFIER_POINTER} or the @code{IDENTIFIER_LENGTH}. @item IDENTIFIER_TYPENAME_P This predicate holds if the identifier represents the name of a user-defined conversion operator. In this case, the @code{TREE_TYPE} of the @code{IDENTIFIER_NODE} holds the type to which the conversion operator converts. @end ftable @c --------------------------------------------------------------------- @c Containers @c --------------------------------------------------------------------- @node Containers @subsection Containers @cindex container @cindex list @cindex vector @tindex TREE_LIST @tindex TREE_VEC @findex TREE_PURPOSE @findex TREE_VALUE @findex TREE_VEC_LENGTH @findex TREE_VEC_ELT Two common container data structures can be represented directly with tree nodes. A @code{TREE_LIST} is a singly linked list containing two trees per node. These are the @code{TREE_PURPOSE} and @code{TREE_VALUE} of each node. (Often, the @code{TREE_PURPOSE} contains some kind of tag, or additional information, while the @code{TREE_VALUE} contains the majority of the payload. In other cases, the @code{TREE_PURPOSE} is simply @code{NULL_TREE}, while in still others both the @code{TREE_PURPOSE} and @code{TREE_VALUE} are of equal stature.) Given one @code{TREE_LIST} node, the next node is found by following the @code{TREE_CHAIN}. If the @code{TREE_CHAIN} is @code{NULL_TREE}, then you have reached the end of the list. A @code{TREE_VEC} is a simple vector. The @code{TREE_VEC_LENGTH} is an integer (not a tree) giving the number of nodes in the vector. The nodes themselves are accessed using the @code{TREE_VEC_ELT} macro, which takes two arguments. The first is the @code{TREE_VEC} in question; the second is an integer indicating which element in the vector is desired. The elements are indexed from zero. @c --------------------------------------------------------------------- @c Types @c --------------------------------------------------------------------- @node Types @section Types @cindex type @cindex pointer @cindex reference @cindex fundamental type @cindex array @tindex VOID_TYPE @tindex INTEGER_TYPE @tindex TYPE_MIN_VALUE @tindex TYPE_MAX_VALUE @tindex REAL_TYPE @tindex COMPLEX_TYPE @tindex ENUMERAL_TYPE @tindex BOOLEAN_TYPE @tindex POINTER_TYPE @tindex REFERENCE_TYPE @tindex FUNCTION_TYPE @tindex METHOD_TYPE @tindex ARRAY_TYPE @tindex RECORD_TYPE @tindex UNION_TYPE @tindex UNKNOWN_TYPE @tindex OFFSET_TYPE @tindex TYPENAME_TYPE @tindex TYPEOF_TYPE @findex CP_TYPE_QUALS @findex TYPE_UNQUALIFIED @findex TYPE_QUAL_CONST @findex TYPE_QUAL_VOLATILE @findex TYPE_QUAL_RESTRICT @findex TYPE_MAIN_VARIANT @cindex qualified type @findex TYPE_SIZE @findex TYPE_ALIGN @findex TYPE_PRECISION @findex TYPE_ARG_TYPES @findex TYPE_METHOD_BASETYPE @findex TYPE_PTRMEM_P @findex TYPE_OFFSET_BASETYPE @findex TREE_TYPE @findex TYPE_CONTEXT @findex TYPE_NAME @findex TYPENAME_TYPE_FULLNAME @findex TYPE_FIELDS @findex TYPE_PTROBV_P All types have corresponding tree nodes. However, you should not assume that there is exactly one tree node corresponding to each type. There are often several nodes each of which correspond to the same type. For the most part, different kinds of types have different tree codes. (For example, pointer types use a @code{POINTER_TYPE} code while arrays use an @code{ARRAY_TYPE} code.) However, pointers to member functions use the @code{RECORD_TYPE} code. Therefore, when writing a @code{switch} statement that depends on the code associated with a particular type, you should take care to handle pointers to member functions under the @code{RECORD_TYPE} case label. In C++, an array type is not qualified; rather the type of the array elements is qualified. This situation is reflected in the intermediate representation. The macros described here will always examine the qualification of the underlying element type when applied to an array type. (If the element type is itself an array, then the recursion continues until a non-array type is found, and the qualification of this type is examined.) So, for example, @code{CP_TYPE_CONST_P} will hold of the type @code{const int ()[7]}, denoting an array of seven @code{int}s. The following functions and macros deal with cv-qualification of types: @ftable @code @item CP_TYPE_QUALS This macro returns the set of type qualifiers applied to this type. This value is @code{TYPE_UNQUALIFIED} if no qualifiers have been applied. The @code{TYPE_QUAL_CONST} bit is set if the type is @code{const}-qualified. The @code{TYPE_QUAL_VOLATILE} bit is set if the type is @code{volatile}-qualified. The @code{TYPE_QUAL_RESTRICT} bit is set if the type is @code{restrict}-qualified. @item CP_TYPE_CONST_P This macro holds if the type is @code{const}-qualified. @item CP_TYPE_VOLATILE_P This macro holds if the type is @code{volatile}-qualified. @item CP_TYPE_RESTRICT_P This macro holds if the type is @code{restrict}-qualified. @item CP_TYPE_CONST_NON_VOLATILE_P This predicate holds for a type that is @code{const}-qualified, but @emph{not} @code{volatile}-qualified; other cv-qualifiers are ignored as well: only the @code{const}-ness is tested. @item TYPE_MAIN_VARIANT This macro returns the unqualified version of a type. It may be applied to an unqualified type, but it is not always the identity function in that case. @end ftable A few other macros and functions are usable with all types: @ftable @code @item TYPE_SIZE The number of bits required to represent the type, represented as an @code{INTEGER_CST}. For an incomplete type, @code{TYPE_SIZE} will be @code{NULL_TREE}. @item TYPE_ALIGN The alignment of the type, in bits, represented as an @code{int}. @item TYPE_NAME This macro returns a declaration (in the form of a @code{TYPE_DECL}) for the type. (Note this macro does @emph{not} return a @code{IDENTIFIER_NODE}, as you might expect, given its name!) You can look at the @code{DECL_NAME} of the @code{TYPE_DECL} to obtain the actual name of the type. The @code{TYPE_NAME} will be @code{NULL_TREE} for a type that is not a built-in type, the result of a typedef, or a named class type. @item CP_INTEGRAL_TYPE This predicate holds if the type is an integral type. Notice that in C++, enumerations are @emph{not} integral types. @item ARITHMETIC_TYPE_P This predicate holds if the type is an integral type (in the C++ sense) or a floating point type. @item CLASS_TYPE_P This predicate holds for a class-type. @item TYPE_BUILT_IN This predicate holds for a built-in type. @item TYPE_PTRMEM_P This predicate holds if the type is a pointer to data member. @item TYPE_PTR_P This predicate holds if the type is a pointer type, and the pointee is not a data member. @item TYPE_PTRFN_P This predicate holds for a pointer to function type. @item TYPE_PTROB_P This predicate holds for a pointer to object type. Note however that it does not hold for the generic pointer to object type @code{void *}. You may use @code{TYPE_PTROBV_P} to test for a pointer to object type as well as @code{void *}. @item same_type_p This predicate takes two types as input, and holds if they are the same type. For example, if one type is a @code{typedef} for the other, or both are @code{typedef}s for the same type. This predicate also holds if the two trees given as input are simply copies of one another; i.e., there is no difference between them at the source level, but, for whatever reason, a duplicate has been made in the representation. You should never use @code{==} (pointer equality) to compare types; always use @code{same_type_p} instead. @end ftable Detailed below are the various kinds of types, and the macros that can be used to access them. Although other kinds of types are used elsewhere in G++, the types described here are the only ones that you will encounter while examining the intermediate representation. @table @code @item VOID_TYPE Used to represent the @code{void} type. @item INTEGER_TYPE Used to represent the various integral types, including @code{char}, @code{short}, @code{int}, @code{long}, and @code{long long}. This code is not used for enumeration types, nor for the @code{bool} type. Note that GCC's @code{CHAR_TYPE} node is @emph{not} used to represent @code{char}. The @code{TYPE_PRECISION} is the number of bits used in the representation, represented as an @code{unsigned int}. (Note that in the general case this is not the same value as @code{TYPE_SIZE}; suppose that there were a 24-bit integer type, but that alignment requirements for the ABI required 32-bit alignment. Then, @code{TYPE_SIZE} would be an @code{INTEGER_CST} for 32, while @code{TYPE_PRECISION} would be 24.) The integer type is unsigned if @code{TREE_UNSIGNED} holds; otherwise, it is signed. The @code{TYPE_MIN_VALUE} is an @code{INTEGER_CST} for the smallest integer that may be represented by this type. Similarly, the @code{TYPE_MAX_VALUE} is an @code{INTEGER_CST} for the largest integer that may be represented by this type. @item REAL_TYPE Used to represent the @code{float}, @code{double}, and @code{long double} types. The number of bits in the floating-point representation is given by @code{TYPE_PRECISION}, as in the @code{INTEGER_TYPE} case. @item COMPLEX_TYPE Used to represent GCC built-in @code{__complex__} data types. The @code{TREE_TYPE} is the type of the real and imaginary parts. @item ENUMERAL_TYPE Used to represent an enumeration type. The @code{TYPE_PRECISION} gives (as an @code{int}), the number of bits used to represent the type. If there are no negative enumeration constants, @code{TREE_UNSIGNED} will hold. The minimum and maximum enumeration constants may be obtained with @code{TYPE_MIN_VALUE} and @code{TYPE_MAX_VALUE}, respectively; each of these macros returns an @code{INTEGER_CST}. The actual enumeration constants themselves may be obtained by looking at the @code{TYPE_VALUES}. This macro will return a @code{TREE_LIST}, containing the constants. The @code{TREE_PURPOSE} of each node will be an @code{IDENTIFIER_NODE} giving the name of the constant; the @code{TREE_VALUE} will be an @code{INTEGER_CST} giving the value assigned to that constant. These constants will appear in the order in which they were declared. The @code{TREE_TYPE} of each of these constants will be the type of enumeration type itself. @item BOOLEAN_TYPE Used to represent the @code{bool} type. @item POINTER_TYPE Used to represent pointer types, and pointer to data member types. The @code{TREE_TYPE} gives the type to which this type points. If the type is a pointer to data member type, then @code{TYPE_PTRMEM_P} will hold. For a pointer to data member type of the form @samp{T X::*}, @code{TYPE_PTRMEM_CLASS_TYPE} will be the type @code{X}, while @code{TYPE_PTRMEM_POINTED_TO_TYPE} will be the type @code{T}. @item REFERENCE_TYPE Used to represent reference types. The @code{TREE_TYPE} gives the type to which this type refers. @item FUNCTION_TYPE Used to represent the type of non-member functions and of static member functions. The @code{TREE_TYPE} gives the return type of the function. The @code{TYPE_ARG_TYPES} are a @code{TREE_LIST} of the argument types. The @code{TREE_VALUE} of each node in this list is the type of the corresponding argument; the @code{TREE_PURPOSE} is an expression for the default argument value, if any. If the last node in the list is @code{void_list_node} (a @code{TREE_LIST} node whose @code{TREE_VALUE} is the @code{void_type_node}), then functions of this type do not take variable arguments. Otherwise, they do take a variable number of arguments. Note that in C (but not in C++) a function declared like @code{void f()} is an unprototyped function taking a variable number of arguments; the @code{TYPE_ARG_TYPES} of such a function will be @code{NULL}. @item METHOD_TYPE Used to represent the type of a non-static member function. Like a @code{FUNCTION_TYPE}, the return type is given by the @code{TREE_TYPE}. The type of @code{*this}, i.e., the class of which functions of this type are a member, is given by the @code{TYPE_METHOD_BASETYPE}. The @code{TYPE_ARG_TYPES} is the parameter list, as for a @code{FUNCTION_TYPE}, and includes the @code{this} argument. @item ARRAY_TYPE Used to represent array types. The @code{TREE_TYPE} gives the type of the elements in the array. If the array-bound is present in the type, the @code{TYPE_DOMAIN} is an @code{INTEGER_TYPE} whose @code{TYPE_MIN_VALUE} and @code{TYPE_MAX_VALUE} will be the lower and upper bounds of the array, respectively. The @code{TYPE_MIN_VALUE} will always be an @code{INTEGER_CST} for zero, while the @code{TYPE_MAX_VALUE} will be one less than the number of elements in the array, i.e., the highest value which may be used to index an element in the array. @item RECORD_TYPE Used to represent @code{struct} and @code{class} types, as well as pointers to member functions and similar constructs in other languages. @code{TYPE_FIELDS} contains the items contained in this type, each of which can be a @code{FIELD_DECL}, @code{VAR_DECL}, @code{CONST_DECL}, or @code{TYPE_DECL}. You may not make any assumptions about the ordering of the fields in the type or whether one or more of them overlap. If @code{TYPE_PTRMEMFUNC_P} holds, then this type is a pointer-to-member type. In that case, the @code{TYPE_PTRMEMFUNC_FN_TYPE} is a @code{POINTER_TYPE} pointing to a @code{METHOD_TYPE}. The @code{METHOD_TYPE} is the type of a function pointed to by the pointer-to-member function. If @code{TYPE_PTRMEMFUNC_P} does not hold, this type is a class type. For more information, see @pxref{Classes}. @item UNION_TYPE Used to represent @code{union} types. Similar to @code{RECORD_TYPE} except that all @code{FIELD_DECL} nodes in @code{TYPE_FIELD} start at bit position zero. @item QUAL_UNION_TYPE Used to represent part of a variant record in Ada. Similar to @code{UNION_TYPE} except that each @code{FIELD_DECL} has a @code{DECL_QUALIFIER} field, which contains a boolean expression that indicates whether the field is present in the object. The type will only have one field, so each field's @code{DECL_QUALIFIER} is only evaluated if none of the expressions in the previous fields in @code{TYPE_FIELDS} are nonzero. Normally these expressions will reference a field in the outer object using a @code{PLACEHOLDER_EXPR}. @item UNKNOWN_TYPE This node is used to represent a type the knowledge of which is insufficient for a sound processing. @item OFFSET_TYPE This node is used to represent a data member; for example a pointer-to-data-member is represented by a @code{POINTER_TYPE} whose @code{TREE_TYPE} is an @code{OFFSET_TYPE}. For a data member @code{X::m} the @code{TYPE_OFFSET_BASETYPE} is @code{X} and the @code{TREE_TYPE} is the type of @code{m}. @item TYPENAME_TYPE Used to represent a construct of the form @code{typename T::A}. The @code{TYPE_CONTEXT} is @code{T}; the @code{TYPE_NAME} is an @code{IDENTIFIER_NODE} for @code{A}. If the type is specified via a template-id, then @code{TYPENAME_TYPE_FULLNAME} yields a @code{TEMPLATE_ID_EXPR}. The @code{TREE_TYPE} is non-@code{NULL} if the node is implicitly generated in support for the implicit typename extension; in which case the @code{TREE_TYPE} is a type node for the base-class. @item TYPEOF_TYPE Used to represent the @code{__typeof__} extension. The @code{TYPE_FIELDS} is the expression the type of which is being represented. @end table There are variables whose values represent some of the basic types. These include: @table @code @item void_type_node A node for @code{void}. @item integer_type_node A node for @code{int}. @item unsigned_type_node. A node for @code{unsigned int}. @item char_type_node. A node for @code{char}. @end table @noindent It may sometimes be useful to compare one of these variables with a type in hand, using @code{same_type_p}. @c --------------------------------------------------------------------- @c Scopes @c --------------------------------------------------------------------- @node Scopes @section Scopes @cindex namespace, class, scope The root of the entire intermediate representation is the variable @code{global_namespace}. This is the namespace specified with @code{::} in C++ source code. All other namespaces, types, variables, functions, and so forth can be found starting with this namespace. Besides namespaces, the other high-level scoping construct in C++ is the class. (Throughout this manual the term @dfn{class} is used to mean the types referred to in the ANSI/ISO C++ Standard as classes; these include types defined with the @code{class}, @code{struct}, and @code{union} keywords.) @menu * Namespaces:: Member functions, types, etc. * Classes:: Members, bases, friends, etc. @end menu @c --------------------------------------------------------------------- @c Namespaces @c --------------------------------------------------------------------- @node Namespaces @subsection Namespaces @cindex namespace @tindex NAMESPACE_DECL A namespace is represented by a @code{NAMESPACE_DECL} node. However, except for the fact that it is distinguished as the root of the representation, the global namespace is no different from any other namespace. Thus, in what follows, we describe namespaces generally, rather than the global namespace in particular. The following macros and functions can be used on a @code{NAMESPACE_DECL}: @ftable @code @item DECL_NAME This macro is used to obtain the @code{IDENTIFIER_NODE} corresponding to the unqualified name of the name of the namespace (@pxref{Identifiers}). The name of the global namespace is @samp{::}, even though in C++ the global namespace is unnamed. However, you should use comparison with @code{global_namespace}, rather than @code{DECL_NAME} to determine whether or not a namespaces is the global one. An unnamed namespace will have a @code{DECL_NAME} equal to @code{anonymous_namespace_name}. Within a single translation unit, all unnamed namespaces will have the same name. @item DECL_CONTEXT This macro returns the enclosing namespace. The @code{DECL_CONTEXT} for the @code{global_namespace} is @code{NULL_TREE}. @item DECL_NAMESPACE_ALIAS If this declaration is for a namespace alias, then @code{DECL_NAMESPACE_ALIAS} is the namespace for which this one is an alias. Do not attempt to use @code{cp_namespace_decls} for a namespace which is an alias. Instead, follow @code{DECL_NAMESPACE_ALIAS} links until you reach an ordinary, non-alias, namespace, and call @code{cp_namespace_decls} there. @item DECL_NAMESPACE_STD_P This predicate holds if the namespace is the special @code{::std} namespace. @item cp_namespace_decls This function will return the declarations contained in the namespace, including types, overloaded functions, other namespaces, and so forth. If there are no declarations, this function will return @code{NULL_TREE}. The declarations are connected through their @code{TREE_CHAIN} fields. Although most entries on this list will be declarations, @code{TREE_LIST} nodes may also appear. In this case, the @code{TREE_VALUE} will be an @code{OVERLOAD}. The value of the @code{TREE_PURPOSE} is unspecified; back ends should ignore this value. As with the other kinds of declarations returned by @code{cp_namespace_decls}, the @code{TREE_CHAIN} will point to the next declaration in this list. For more information on the kinds of declarations that can occur on this list, @xref{Declarations}. Some declarations will not appear on this list. In particular, no @code{FIELD_DECL}, @code{LABEL_DECL}, or @code{PARM_DECL} nodes will appear here. This function cannot be used with namespaces that have @code{DECL_NAMESPACE_ALIAS} set. @end ftable @c --------------------------------------------------------------------- @c Classes @c --------------------------------------------------------------------- @node Classes @subsection Classes @cindex class @tindex RECORD_TYPE @tindex UNION_TYPE @findex CLASSTYPE_DECLARED_CLASS @findex TYPE_BINFO @findex BINFO_TYPE @findex TREE_VIA_PUBLIC @findex TREE_VIA_PROTECTED @findex TREE_VIA_PRIVATE @findex TYPE_FIELDS @findex TYPE_VFIELD @findex TYPE_METHODS A class type is represented by either a @code{RECORD_TYPE} or a @code{UNION_TYPE}. A class declared with the @code{union} tag is represented by a @code{UNION_TYPE}, while classes declared with either the @code{struct} or the @code{class} tag are represented by @code{RECORD_TYPE}s. You can use the @code{CLASSTYPE_DECLARED_CLASS} macro to discern whether or not a particular type is a @code{class} as opposed to a @code{struct}. This macro will be true only for classes declared with the @code{class} tag. Almost all non-function members are available on the @code{TYPE_FIELDS} list. Given one member, the next can be found by following the @code{TREE_CHAIN}. You should not depend in any way on the order in which fields appear on this list. All nodes on this list will be @samp{DECL} nodes. A @code{FIELD_DECL} is used to represent a non-static data member, a @code{VAR_DECL} is used to represent a static data member, and a @code{TYPE_DECL} is used to represent a type. Note that the @code{CONST_DECL} for an enumeration constant will appear on this list, if the enumeration type was declared in the class. (Of course, the @code{TYPE_DECL} for the enumeration type will appear here as well.) There are no entries for base classes on this list. In particular, there is no @code{FIELD_DECL} for the ``base-class portion'' of an object. The @code{TYPE_VFIELD} is a compiler-generated field used to point to virtual function tables. It may or may not appear on the @code{TYPE_FIELDS} list. However, back ends should handle the @code{TYPE_VFIELD} just like all the entries on the @code{TYPE_FIELDS} list. The function members are available on the @code{TYPE_METHODS} list. Again, subsequent members are found by following the @code{TREE_CHAIN} field. If a function is overloaded, each of the overloaded functions appears; no @code{OVERLOAD} nodes appear on the @code{TYPE_METHODS} list. Implicitly declared functions (including default constructors, copy constructors, assignment operators, and destructors) will appear on this list as well. Every class has an associated @dfn{binfo}, which can be obtained with @code{TYPE_BINFO}. Binfos are used to represent base-classes. The binfo given by @code{TYPE_BINFO} is the degenerate case, whereby every class is considered to be its own base-class. The base classes for a particular binfo can be obtained with @code{BINFO_BASETYPES}. These base-classes are themselves binfos. The class type associated with a binfo is given by @code{BINFO_TYPE}. It is always the case that @code{BINFO_TYPE (TYPE_BINFO (x))} is the same type as @code{x}, up to qualifiers. However, it is not always the case that @code{TYPE_BINFO (BINFO_TYPE (y))} is always the same binfo as @code{y}. The reason is that if @code{y} is a binfo representing a base-class @code{B} of a derived class @code{D}, then @code{BINFO_TYPE (y)} will be @code{B}, and @code{TYPE_BINFO (BINFO_TYPE (y))} will be @code{B} as its own base-class, rather than as a base-class of @code{D}. The @code{BINFO_BASETYPES} is a @code{TREE_VEC} (@pxref{Containers}). Base types appear in left-to-right order in this vector. You can tell whether or @code{public}, @code{protected}, or @code{private} inheritance was used by using the @code{TREE_VIA_PUBLIC}, @code{TREE_VIA_PROTECTED}, and @code{TREE_VIA_PRIVATE} macros. Each of these macros takes a @code{BINFO} and is true if and only if the indicated kind of inheritance was used. If @code{TREE_VIA_VIRTUAL} holds of a binfo, then its @code{BINFO_TYPE} was inherited from virtually. The following macros can be used on a tree node representing a class-type. @ftable @code @item LOCAL_CLASS_P This predicate holds if the class is local class @emph{i.e.} declared inside a function body. @item TYPE_POLYMORPHIC_P This predicate holds if the class has at least one virtual function (declared or inherited). @item TYPE_HAS_DEFAULT_CONSTRUCTOR This predicate holds whenever its argument represents a class-type with default constructor. @item CLASSTYPE_HAS_MUTABLE @item TYPE_HAS_MUTABLE_P These predicates hold for a class-type having a mutable data member. @item CLASSTYPE_NON_POD_P This predicate holds only for class-types that are not PODs. @item TYPE_HAS_NEW_OPERATOR This predicate holds for a class-type that defines @code{operator new}. @item TYPE_HAS_ARRAY_NEW_OPERATOR This predicate holds for a class-type for which @code{operator new[]} is defined. @item TYPE_OVERLOADS_CALL_EXPR This predicate holds for class-type for which the function call @code{operator()} is overloaded. @item TYPE_OVERLOADS_ARRAY_REF This predicate holds for a class-type that overloads @code{operator[]} @item TYPE_OVERLOADS_ARROW This predicate holds for a class-type for which @code{operator->} is overloaded. @end ftable @c --------------------------------------------------------------------- @c Declarations @c --------------------------------------------------------------------- @node Declarations @section Declarations @cindex declaration @cindex variable @cindex type declaration @tindex LABEL_DECL @tindex CONST_DECL @tindex TYPE_DECL @tindex VAR_DECL @tindex PARM_DECL @tindex FIELD_DECL @tindex NAMESPACE_DECL @tindex RESULT_DECL @tindex TEMPLATE_DECL @tindex THUNK_DECL @tindex USING_DECL @findex THUNK_DELTA @findex DECL_INITIAL @findex DECL_SIZE @findex DECL_ALIGN @findex DECL_EXTERNAL This section covers the various kinds of declarations that appear in the internal representation, except for declarations of functions (represented by @code{FUNCTION_DECL} nodes), which are described in @ref{Functions}. Some macros can be used with any kind of declaration. These include: @ftable @code @item DECL_NAME This macro returns an @code{IDENTIFIER_NODE} giving the name of the entity. @item TREE_TYPE This macro returns the type of the entity declared. @item DECL_SOURCE_FILE This macro returns the name of the file in which the entity was declared, as a @code{char*}. For an entity declared implicitly by the compiler (like @code{__builtin_memcpy}), this will be the string @code{""}. @item DECL_SOURCE_LINE This macro returns the line number at which the entity was declared, as an @code{int}. @item DECL_ARTIFICIAL This predicate holds if the declaration was implicitly generated by the compiler. For example, this predicate will hold of an implicitly declared member function, or of the @code{TYPE_DECL} implicitly generated for a class type. Recall that in C++ code like: @example struct S @{@}; @end example @noindent is roughly equivalent to C code like: @example struct S @{@}; typedef struct S S; @end example The implicitly generated @code{typedef} declaration is represented by a @code{TYPE_DECL} for which @code{DECL_ARTIFICIAL} holds. @item DECL_NAMESPACE_SCOPE_P This predicate holds if the entity was declared at a namespace scope. @item DECL_CLASS_SCOPE_P This predicate holds if the entity was declared at a class scope. @item DECL_FUNCTION_SCOPE_P This predicate holds if the entity was declared inside a function body. @end ftable The various kinds of declarations include: @table @code @item LABEL_DECL These nodes are used to represent labels in function bodies. For more information, see @ref{Functions}. These nodes only appear in block scopes. @item CONST_DECL These nodes are used to represent enumeration constants. The value of the constant is given by @code{DECL_INITIAL} which will be an @code{INTEGER_CST} with the same type as the @code{TREE_TYPE} of the @code{CONST_DECL}, i.e., an @code{ENUMERAL_TYPE}. @item RESULT_DECL These nodes represent the value returned by a function. When a value is assigned to a @code{RESULT_DECL}, that indicates that the value should be returned, via bitwise copy, by the function. You can use @code{DECL_SIZE} and @code{DECL_ALIGN} on a @code{RESULT_DECL}, just as with a @code{VAR_DECL}. @item TYPE_DECL These nodes represent @code{typedef} declarations. The @code{TREE_TYPE} is the type declared to have the name given by @code{DECL_NAME}. In some cases, there is no associated name. @item VAR_DECL These nodes represent variables with namespace or block scope, as well as static data members. The @code{DECL_SIZE} and @code{DECL_ALIGN} are analogous to @code{TYPE_SIZE} and @code{TYPE_ALIGN}. For a declaration, you should always use the @code{DECL_SIZE} and @code{DECL_ALIGN} rather than the @code{TYPE_SIZE} and @code{TYPE_ALIGN} given by the @code{TREE_TYPE}, since special attributes may have been applied to the variable to give it a particular size and alignment. You may use the predicates @code{DECL_THIS_STATIC} or @code{DECL_THIS_EXTERN} to test whether the storage class specifiers @code{static} or @code{extern} were used to declare a variable. If this variable is initialized (but does not require a constructor), the @code{DECL_INITIAL} will be an expression for the initializer. The initializer should be evaluated, and a bitwise copy into the variable performed. If the @code{DECL_INITIAL} is the @code{error_mark_node}, there is an initializer, but it is given by an explicit statement later in the code; no bitwise copy is required. GCC provides an extension that allows either automatic variables, or global variables, to be placed in particular registers. This extension is being used for a particular @code{VAR_DECL} if @code{DECL_REGISTER} holds for the @code{VAR_DECL}, and if @code{DECL_ASSEMBLER_NAME} is not equal to @code{DECL_NAME}. In that case, @code{DECL_ASSEMBLER_NAME} is the name of the register into which the variable will be placed. @item PARM_DECL Used to represent a parameter to a function. Treat these nodes similarly to @code{VAR_DECL} nodes. These nodes only appear in the @code{DECL_ARGUMENTS} for a @code{FUNCTION_DECL}. The @code{DECL_ARG_TYPE} for a @code{PARM_DECL} is the type that will actually be used when a value is passed to this function. It may be a wider type than the @code{TREE_TYPE} of the parameter; for example, the ordinary type might be @code{short} while the @code{DECL_ARG_TYPE} is @code{int}. @item FIELD_DECL These nodes represent non-static data members. The @code{DECL_SIZE} and @code{DECL_ALIGN} behave as for @code{VAR_DECL} nodes. The @code{DECL_FIELD_BITPOS} gives the first bit used for this field, as an @code{INTEGER_CST}. These values are indexed from zero, where zero indicates the first bit in the object. If @code{DECL_C_BIT_FIELD} holds, this field is a bit-field. @item NAMESPACE_DECL @xref{Namespaces}. @item TEMPLATE_DECL These nodes are used to represent class, function, and variable (static data member) templates. The @code{DECL_TEMPLATE_SPECIALIZATIONS} are a @code{TREE_LIST}. The @code{TREE_VALUE} of each node in the list is a @code{TEMPLATE_DECL}s or @code{FUNCTION_DECL}s representing specializations (including instantiations) of this template. Back ends can safely ignore @code{TEMPLATE_DECL}s, but should examine @code{FUNCTION_DECL} nodes on the specializations list just as they would ordinary @code{FUNCTION_DECL} nodes. For a class template, the @code{DECL_TEMPLATE_INSTANTIATIONS} list contains the instantiations. The @code{TREE_VALUE} of each node is an instantiation of the class. The @code{DECL_TEMPLATE_SPECIALIZATIONS} contains partial specializations of the class. @item USING_DECL Back ends can safely ignore these nodes. @end table @c --------------------------------------------------------------------- @c Functions @c --------------------------------------------------------------------- @node Functions @section Functions @cindex function @tindex FUNCTION_DECL @tindex OVERLOAD @findex OVL_CURRENT @findex OVL_NEXT A function is represented by a @code{FUNCTION_DECL} node. A set of overloaded functions is sometimes represented by a @code{OVERLOAD} node. An @code{OVERLOAD} node is not a declaration, so none of the @samp{DECL_} macros should be used on an @code{OVERLOAD}. An @code{OVERLOAD} node is similar to a @code{TREE_LIST}. Use @code{OVL_CURRENT} to get the function associated with an @code{OVERLOAD} node; use @code{OVL_NEXT} to get the next @code{OVERLOAD} node in the list of overloaded functions. The macros @code{OVL_CURRENT} and @code{OVL_NEXT} are actually polymorphic; you can use them to work with @code{FUNCTION_DECL} nodes as well as with overloads. In the case of a @code{FUNCTION_DECL}, @code{OVL_CURRENT} will always return the function itself, and @code{OVL_NEXT} will always be @code{NULL_TREE}. To determine the scope of a function, you can use the @code{DECL_REAL_CONTEXT} macro. This macro will return the class (either a @code{RECORD_TYPE} or a @code{UNION_TYPE}) or namespace (a @code{NAMESPACE_DECL}) of which the function is a member. For a virtual function, this macro returns the class in which the function was actually defined, not the base class in which the virtual declaration occurred. If a friend function is defined in a class scope, the @code{DECL_CLASS_CONTEXT} macro can be used to determine the class in which it was defined. For example, in @example class C @{ friend void f() @{@} @}; @end example the @code{DECL_REAL_CONTEXT} for @code{f} will be the @code{global_namespace}, but the @code{DECL_CLASS_CONTEXT} will be the @code{RECORD_TYPE} for @code{C}. The @code{DECL_REAL_CONTEXT} and @code{DECL_CLASS_CONTEXT} are not available in C; instead you should simply use @code{DECL_CONTEXT}. In C, the @code{DECL_CONTEXT} for a function maybe another function. This representation indicates that the GNU nested function extension is in use. For details on the semantics of nested functions, see the GCC Manual. The nested function can refer to local variables in its containing function. Such references are not explicitly marked in the tree structure; back ends must look at the @code{DECL_CONTEXT} for the referenced @code{VAR_DECL}. If the @code{DECL_CONTEXT} for the referenced @code{VAR_DECL} is not the same as the function currently being processed, and neither @code{DECL_EXTERNAL} nor @code{DECL_STATIC} hold, then the reference is to a local variable in a containing function, and the back end must take appropriate action. @menu * Function Basics:: Function names, linkage, and so forth. * Function Bodies:: The statements that make up a function body. @end menu @c --------------------------------------------------------------------- @c Function Basics @c --------------------------------------------------------------------- @node Function Basics @subsection Function Basics @cindex constructor @cindex destructor @cindex copy constructor @cindex assignment operator @cindex linkage @findex DECL_NAME @findex DECL_ASSEMBLER_NAME @findex TREE_PUBLIC @findex DECL_LINKONCE_P @findex DECL_FUNCTION_MEMBER_P @findex DECL_CONSTRUCTOR_P @findex DECL_DESTRUCTOR_P @findex DECL_OVERLOADED_OPERATOR_P @findex DECL_CONV_FN_P @findex DECL_ARTIFICIAL @findex DECL_GLOBAL_CTOR_P @findex DECL_GLOBAL_DTOR_P @findex GLOBAL_INIT_PRIORITY The following macros and functions can be used on a @code{FUNCTION_DECL}: @ftable @code @item DECL_MAIN_P This predicate holds for a function that is the program entry point @code{::code}. @item DECL_NAME This macro returns the unqualified name of the function, as an @code{IDENTIFIER_NODE}. For an instantiation of a function template, the @code{DECL_NAME} is the unqualified name of the template, not something like @code{f}. The value of @code{DECL_NAME} is undefined when used on a constructor, destructor, overloaded operator, or type-conversion operator, or any function that is implicitly generated by the compiler. See below for macros that can be used to distinguish these cases. @item DECL_ASSEMBLER_NAME This macro returns the mangled name of the function, also an @code{IDENTIFIER_NODE}. This name does not contain leading underscores on systems that prefix all identifiers with underscores. The mangled name is computed in the same way on all platforms; if special processing is required to deal with the object file format used on a particular platform, it is the responsibility of the back end to perform those modifications. (Of course, the back end should not modify @code{DECL_ASSEMBLER_NAME} itself.) @item DECL_EXTERNAL This predicate holds if the function is undefined. @item TREE_PUBLIC This predicate holds if the function has external linkage. @item DECL_LOCAL_FUNCTION_P This predicate holds if the function was declared at block scope, even though it has a global scope. @item DECL_ANTICIPATED This predicate holds if the function is a built-in function but its prototype is not yet explicitly declared. @item DECL_EXTERN_C_FUNCTION_P This predicate holds if the function is declared as an `@code{extern "C"}' function. @item DECL_LINKONCE_P This macro holds if multiple copies of this function may be emitted in various translation units. It is the responsibility of the linker to merge the various copies. Template instantiations are the most common example of functions for which @code{DECL_LINKONCE_P} holds; G++ instantiates needed templates in all translation units which require them, and then relies on the linker to remove duplicate instantiations. FIXME: This macro is not yet implemented. @item DECL_FUNCTION_MEMBER_P This macro holds if the function is a member of a class, rather than a member of a namespace. @item DECL_STATIC_FUNCTION_P This predicate holds if the function a static member function. @item DECL_NONSTATIC_MEMBER_FUNCTION_P This macro holds for a non-static member function. @item DECL_CONST_MEMFUNC_P This predicate holds for a @code{const}-member function. @item DECL_VOLATILE_MEMFUNC_P This predicate holds for a @code{volatile}-member function. @item DECL_CONSTRUCTOR_P This macro holds if the function is a constructor. @item DECL_NONCONVERTING_P This predicate holds if the constructor is a non-converting constructor. @item DECL_COMPLETE_CONSTRUCTOR_P This predicate holds for a function which is a constructor for an object of a complete type. @item DECL_BASE_CONSTRUCTOR_P This predicate holds for a function which is a constructor for a base class sub-object. @item DECL_COPY_CONSTRUCTOR_P This predicate holds for a function which is a copy-constructor. @item DECL_DESTRUCTOR_P This macro holds if the function is a destructor. @item DECL_COMPLETE_DESTRUCTOR_P This predicate holds if the function is the destructor for an object a complete type. @item DECL_OVERLOADED_OPERATOR_P This macro holds if the function is an overloaded operator. @item DECL_CONV_FN_P This macro holds if the function is a type-conversion operator. @item DECL_GLOBAL_CTOR_P This predicate holds if the function is a file-scope initialization function. @item DECL_GLOBAL_DTOR_P This predicate holds if the function is a file-scope finalization function. @item DECL_THUNK_P This predicate holds if the function is a thunk. These functions represent stub code that adjusts the @code{this} pointer and then jumps to another function. When the jumped-to function returns, control is transferred directly to the caller, without returning to the thunk. The first parameter to the thunk is always the @code{this} pointer; the thunk should add @code{THUNK_DELTA} to this value. (The @code{THUNK_DELTA} is an @code{int}, not an @code{INTEGER_CST}.) Then, if @code{THUNK_VCALL_OFFSET} (an @code{INTEGER_CST}) is nonzero the adjusted @code{this} pointer must be adjusted again. The complete calculation is given by the following pseudo-code: @smallexample this += THUNK_DELTA if (THUNK_VCALL_OFFSET) this += (*((ptrdiff_t **) this))[THUNK_VCALL_OFFSET] @end smallexample Finally, the thunk should jump to the location given by @code{DECL_INITIAL}; this will always be an expression for the address of a function. @item DECL_NON_THUNK_FUNCTION_P This predicate holds if the function is @emph{not} a thunk function. @item GLOBAL_INIT_PRIORITY If either @code{DECL_GLOBAL_CTOR_P} or @code{DECL_GLOBAL_DTOR_P} holds, then this gives the initialization priority for the function. The linker will arrange that all functions for which @code{DECL_GLOBAL_CTOR_P} holds are run in increasing order of priority before @code{main} is called. When the program exits, all functions for which @code{DECL_GLOBAL_DTOR_P} holds are run in the reverse order. @item DECL_ARTIFICIAL This macro holds if the function was implicitly generated by the compiler, rather than explicitly declared. In addition to implicitly generated class member functions, this macro holds for the special functions created to implement static initialization and destruction, to compute run-time type information, and so forth. @item DECL_ARGUMENTS This macro returns the @code{PARM_DECL} for the first argument to the function. Subsequent @code{PARM_DECL} nodes can be obtained by following the @code{TREE_CHAIN} links. @item DECL_RESULT This macro returns the @code{RESULT_DECL} for the function. @item TREE_TYPE This macro returns the @code{FUNCTION_TYPE} or @code{METHOD_TYPE} for the function. @item TYPE_RAISES_EXCEPTIONS This macro returns the list of exceptions that a (member-)function can raise. The returned list, if non @code{NULL}, is comprised of nodes whose @code{TREE_VALUE} represents a type. @item TYPE_NOTHROW_P This predicate holds when the exception-specification of its arguments if of the form `@code{()}'. @item DECL_ARRAY_DELETE_OPERATOR_P This predicate holds if the function an overloaded @code{operator delete[]}. @end ftable @c --------------------------------------------------------------------- @c Function Bodies @c --------------------------------------------------------------------- @node Function Bodies @subsection Function Bodies @cindex function body @cindex statements @tindex ASM_STMT @findex ASM_STRING @findex ASM_CV_QUAL @findex ASM_INPUTS @findex ASM_OUTPUTS @findex ASM_CLOBBERS @tindex BREAK_STMT @tindex CLEANUP_STMT @findex CLEANUP_DECL @findex CLEANUP_EXPR @tindex COMPOUND_STMT @findex COMPOUND_BODY @tindex CONTINUE_STMT @tindex DECL_STMT @findex DECL_STMT_DECL @tindex DO_STMT @findex DO_BODY @findex DO_COND @tindex EMPTY_CLASS_EXPR @tindex EXPR_STMT @findex EXPR_STMT_EXPR @tindex FOR_STMT @findex FOR_INIT_STMT @findex FOR_COND @findex FOR_EXPR @findex FOR_BODY @tindex FILE_STMT @findex FILE_STMT_FILENAME @tindex GOTO_STMT @findex GOTO_DESTINATION @findex GOTO_FAKE_P @tindex HANDLER @tindex IF_STMT @findex IF_COND @findex THEN_CLAUSE @findex ELSE_CLAUSE @tindex LABEL_STMT @tindex LABEL_STMT_LABEL @tindex RETURN_INIT @tindex RETURN_STMT @findex RETURN_EXPR @tindex SCOPE_STMT @findex SCOPE_BEGIN_P @findex SCOPE_END_P @findex SCOPE_NULLIFIED_P @tindex SUBOBJECT @findex SUBOBJECT_CLEANUP @tindex SWITCH_STMT @findex SWITCH_COND @findex SWITCH_BODY @tindex TRY_BLOCK @findex TRY_STMTS @findex TRY_HANDLERS @findex HANDLER_PARMS @findex HANDLER_BODY @findex USING_STMT @tindex WHILE_STMT @findex WHILE_BODY @findex WHILE_COND A function that has a definition in the current translation unit will have a non-@code{NULL} @code{DECL_INITIAL}. However, back ends should not make use of the particular value given by @code{DECL_INITIAL}. The @code{DECL_SAVED_TREE} macro will give the complete body of the function. This node will usually be a @code{COMPOUND_STMT} representing the outermost block of the function, but it may also be a @code{TRY_BLOCK}, a @code{RETURN_INIT}, or any other valid statement. @subsubsection Statements There are tree nodes corresponding to all of the source-level statement constructs. These are enumerated here, together with a list of the various macros that can be used to obtain information about them. There are a few macros that can be used with all statements: @ftable @code @item STMT_LINENO This macro returns the line number for the statement. If the statement spans multiple lines, this value will be the number of the first line on which the statement occurs. Although we mention @code{CASE_LABEL} below as if it were a statement, they do not allow the use of @code{STMT_LINENO}. There is no way to obtain the line number for a @code{CASE_LABEL}. Statements do not contain information about the file from which they came; that information is implicit in the @code{FUNCTION_DECL} from which the statements originate. @item STMT_IS_FULL_EXPR_P In C++, statements normally constitute ``full expressions''; temporaries created during a statement are destroyed when the statement is complete. However, G++ sometimes represents expressions by statements; these statements will not have @code{STMT_IS_FULL_EXPR_P} set. Temporaries created during such statements should be destroyed when the innermost enclosing statement with @code{STMT_IS_FULL_EXPR_P} set is exited. @end ftable Here is the list of the various statement nodes, and the macros used to access them. This documentation describes the use of these nodes in non-template functions (including instantiations of template functions). In template functions, the same nodes are used, but sometimes in slightly different ways. Many of the statements have substatements. For example, a @code{while} loop will have a body, which is itself a statement. If the substatement is @code{NULL_TREE}, it is considered equivalent to a statement consisting of a single @code{;}, i.e., an expression statement in which the expression has been omitted. A substatement may in fact be a list of statements, connected via their @code{TREE_CHAIN}s. So, you should always process the statement tree by looping over substatements, like this: @example void process_stmt (stmt) tree stmt; @{ while (stmt) @{ switch (TREE_CODE (stmt)) @{ case IF_STMT: process_stmt (THEN_CLAUSE (stmt)); /* More processing here. */ break; @dots{} @} stmt = TREE_CHAIN (stmt); @} @} @end example In other words, while the @code{then} clause of an @code{if} statement in C++ can be only one statement (although that one statement may be a compound statement), the intermediate representation will sometimes use several statements chained together. @table @code @item ASM_STMT Used to represent an inline assembly statement. For an inline assembly statement like: @example asm ("mov x, y"); @end example The @code{ASM_STRING} macro will return a @code{STRING_CST} node for @code{"mov x, y"}. If the original statement made use of the extended-assembly syntax, then @code{ASM_OUTPUTS}, @code{ASM_INPUTS}, and @code{ASM_CLOBBERS} will be the outputs, inputs, and clobbers for the statement, represented as @code{STRING_CST} nodes. The extended-assembly syntax looks like: @example asm ("fsinx %1,%0" : "=f" (result) : "f" (angle)); @end example The first string is the @code{ASM_STRING}, containing the instruction template. The next two strings are the output and inputs, respectively; this statement has no clobbers. As this example indicates, ``plain'' assembly statements are merely a special case of extended assembly statements; they have no cv-qualifiers, outputs, inputs, or clobbers. All of the strings will be @code{NUL}-terminated, and will contain no embedded @code{NUL}-characters. If the assembly statement is declared @code{volatile}, or if the statement was not an extended assembly statement, and is therefore implicitly volatile, then the predicate @code{ASM_VOLATILE_P} will hold of the @code{ASM_STMT}. @item BREAK_STMT Used to represent a @code{break} statement. There are no additional fields. @item CASE_LABEL Use to represent a @code{case} label, range of @code{case} labels, or a @code{default} label. If @code{CASE_LOW} is @code{NULL_TREE}, then this is a @code{default} label. Otherwise, if @code{CASE_HIGH} is @code{NULL_TREE}, then this is an ordinary @code{case} label. In this case, @code{CASE_LOW} is an expression giving the value of the label. Both @code{CASE_LOW} and @code{CASE_HIGH} are @code{INTEGER_CST} nodes. These values will have the same type as the condition expression in the switch statement. Otherwise, if both @code{CASE_LOW} and @code{CASE_HIGH} are defined, the statement is a range of case labels. Such statements originate with the extension that allows users to write things of the form: @example case 2 ... 5: @end example The first value will be @code{CASE_LOW}, while the second will be @code{CASE_HIGH}. @item CLEANUP_STMT Used to represent an action that should take place upon exit from the enclosing scope. Typically, these actions are calls to destructors for local objects, but back ends cannot rely on this fact. If these nodes are in fact representing such destructors, @code{CLEANUP_DECL} will be the @code{VAR_DECL} destroyed. Otherwise, @code{CLEANUP_DECL} will be @code{NULL_TREE}. In any case, the @code{CLEANUP_EXPR} is the expression to execute. The cleanups executed on exit from a scope should be run in the reverse order of the order in which the associated @code{CLEANUP_STMT}s were encountered. @item COMPOUND_STMT Used to represent a brace-enclosed block. The first substatement is given by @code{COMPOUND_BODY}. Subsequent substatements are found by following the @code{TREE_CHAIN} link from one substatement to the next. The @code{COMPOUND_BODY} will be @code{NULL_TREE} if there are no substatements. @item CONTINUE_STMT Used to represent a @code{continue} statement. There are no additional fields. @item CTOR_STMT Used to mark the beginning (if @code{CTOR_BEGIN_P} holds) or end (if @code{CTOR_END_P} holds of the main body of a constructor. See also @code{SUBOBJECT} for more information on how to use these nodes. @item DECL_STMT Used to represent a local declaration. The @code{DECL_STMT_DECL} macro can be used to obtain the entity declared. This declaration may be a @code{LABEL_DECL}, indicating that the label declared is a local label. (As an extension, GCC allows the declaration of labels with scope.) In C, this declaration may be a @code{FUNCTION_DECL}, indicating the use of the GCC nested function extension. For more information, @pxref{Functions}. @item DO_STMT Used to represent a @code{do} loop. The body of the loop is given by @code{DO_BODY} while the termination condition for the loop is given by @code{DO_COND}. The condition for a @code{do}-statement is always an expression. @item EMPTY_CLASS_EXPR Used to represent a temporary object of a class with no data whose address is never taken. (All such objects are interchangeable.) The @code{TREE_TYPE} represents the type of the object. @item EXPR_STMT Used to represent an expression statement. Use @code{EXPR_STMT_EXPR} to obtain the expression. @item FILE_STMT Used to record a change in filename within the body of a function. Use @code{FILE_STMT_FILENAME} to obtain the new filename. @item FOR_STMT Used to represent a @code{for} statement. The @code{FOR_INIT_STMT} is the initialization statement for the loop. The @code{FOR_COND} is the termination condition. The @code{FOR_EXPR} is the expression executed right before the @code{FOR_COND} on each loop iteration; often, this expression increments a counter. The body of the loop is given by @code{FOR_BODY}. Note that @code{FOR_INIT_STMT} and @code{FOR_BODY} return statements, while @code{FOR_COND} and @code{FOR_EXPR} return expressions. @item GOTO_STMT Used to represent a @code{goto} statement. The @code{GOTO_DESTINATION} will usually be a @code{LABEL_DECL}. However, if the ``computed goto'' extension has been used, the @code{GOTO_DESTINATION} will be an arbitrary expression indicating the destination. This expression will always have pointer type. Additionally the @code{GOTO_FAKE_P} flag is set whenever the goto statement does not come from source code, but it is generated implicitly by the compiler. This is used for branch prediction. @item HANDLER Used to represent a C++ @code{catch} block. The @code{HANDLER_TYPE} is the type of exception that will be caught by this handler; it is equal (by pointer equality) to @code{CATCH_ALL_TYPE} if this handler is for all types. @code{HANDLER_PARMS} is the @code{DECL_STMT} for the catch parameter, and @code{HANDLER_BODY} is the @code{COMPOUND_STMT} for the block itself. @item IF_STMT Used to represent an @code{if} statement. The @code{IF_COND} is the expression. If the condition is a @code{TREE_LIST}, then the @code{TREE_PURPOSE} is a statement (usually a @code{DECL_STMT}). Each time the condition is evaluated, the statement should be executed. Then, the @code{TREE_VALUE} should be used as the conditional expression itself. This representation is used to handle C++ code like this: @example if (int i = 7) @dots{} @end example where there is a new local variable (or variables) declared within the condition. The @code{THEN_CLAUSE} represents the statement given by the @code{then} condition, while the @code{ELSE_CLAUSE} represents the statement given by the @code{else} condition. @item LABEL_STMT Used to represent a label. The @code{LABEL_DECL} declared by this statement can be obtained with the @code{LABEL_STMT_LABEL} macro. The @code{IDENTIFIER_NODE} giving the name of the label can be obtained from the @code{LABEL_DECL} with @code{DECL_NAME}. @item RETURN_INIT If the function uses the G++ ``named return value'' extension, meaning that the function has been defined like: @example S f(int) return s @{@dots{}@} @end example then there will be a @code{RETURN_INIT}. There is never a named returned value for a constructor. The first argument to the @code{RETURN_INIT} is the name of the object returned; the second argument is the initializer for the object. The object is initialized when the @code{RETURN_INIT} is encountered. The object referred to is the actual object returned; this extension is a manual way of doing the ``return-value optimization.'' Therefore, the object must actually be constructed in the place where the object will be returned. @item RETURN_STMT Used to represent a @code{return} statement. The @code{RETURN_EXPR} is the expression returned; it will be @code{NULL_TREE} if the statement was just @example return; @end example @item SCOPE_STMT A scope-statement represents the beginning or end of a scope. If @code{SCOPE_BEGIN_P} holds, this statement represents the beginning of a scope; if @code{SCOPE_END_P} holds this statement represents the end of a scope. On exit from a scope, all cleanups from @code{CLEANUP_STMT}s occurring in the scope must be run, in reverse order to the order in which they were encountered. If @code{SCOPE_NULLIFIED_P} or @code{SCOPE_NO_CLEANUPS_P} holds of the scope, back ends should behave as if the @code{SCOPE_STMT} were not present at all. @item SUBOBJECT In a constructor, these nodes are used to mark the point at which a subobject of @code{this} is fully constructed. If, after this point, an exception is thrown before a @code{CTOR_STMT} with @code{CTOR_END_P} set is encountered, the @code{SUBOBJECT_CLEANUP} must be executed. The cleanups must be executed in the reverse order in which they appear. @item SWITCH_STMT Used to represent a @code{switch} statement. The @code{SWITCH_COND} is the expression on which the switch is occurring. See the documentation for an @code{IF_STMT} for more information on the representation used for the condition. The @code{SWITCH_BODY} is the body of the switch statement. The @code{SWITCH_TYPE} is the original type of switch expression as given in the source, before any compiler conversions. @item TRY_BLOCK Used to represent a @code{try} block. The body of the try block is given by @code{TRY_STMTS}. Each of the catch blocks is a @code{HANDLER} node. The first handler is given by @code{TRY_HANDLERS}. Subsequent handlers are obtained by following the @code{TREE_CHAIN} link from one handler to the next. The body of the handler is given by @code{HANDLER_BODY}. If @code{CLEANUP_P} holds of the @code{TRY_BLOCK}, then the @code{TRY_HANDLERS} will not be a @code{HANDLER} node. Instead, it will be an expression that should be executed if an exception is thrown in the try block. It must rethrow the exception after executing that code. And, if an exception is thrown while the expression is executing, @code{terminate} must be called. @item USING_STMT Used to represent a @code{using} directive. The namespace is given by @code{USING_STMT_NAMESPACE}, which will be a NAMESPACE_DECL@. This node is needed inside template functions, to implement using directives during instantiation. @item WHILE_STMT Used to represent a @code{while} loop. The @code{WHILE_COND} is the termination condition for the loop. See the documentation for an @code{IF_STMT} for more information on the representation used for the condition. The @code{WHILE_BODY} is the body of the loop. @end table @c --------------------------------------------------------------------- @c Attributes @c --------------------------------------------------------------------- @node Attributes @section Attributes in trees @cindex attributes Attributes, as specified using the @code{__attribute__} keyword, are represented internally as a @code{TREE_LIST}. The @code{TREE_PURPOSE} is the name of the attribute, as an @code{IDENTIFIER_NODE}. The @code{TREE_VALUE} is a @code{TREE_LIST} of the arguments of the attribute, if any, or @code{NULL_TREE} if there are no arguments; the arguments are stored as the @code{TREE_VALUE} of successive entries in the list, and may be identifiers or expressions. The @code{TREE_CHAIN} of the attribute is the next attribute in a list of attributes applying to the same declaration or type, or @code{NULL_TREE} if there are no further attributes in the list. Attributes may be attached to declarations and to types; these attributes may be accessed with the following macros. All attributes are stored in this way, and many also cause other changes to the declaration or type or to other internal compiler data structures. @deftypefn {Tree Macro} tree DECL_ATTRIBUTES (tree @var{decl}) This macro returns the attributes on the declaration @var{decl}. @end deftypefn @deftypefn {Tree Macro} tree TYPE_ATTRIBUTES (tree @var{type}) This macro returns the attributes on the type @var{type}. @end deftypefn @c --------------------------------------------------------------------- @c Expressions @c --------------------------------------------------------------------- @node Expression trees @section Expressions @cindex expression @findex TREE_OPERAND @tindex INTEGER_CST @findex TREE_INT_CST_HIGH @findex TREE_INT_CST_LOW @findex tree_int_cst_lt @findex tree_int_cst_equal @tindex REAL_CST @tindex COMPLEX_CST @tindex VECTOR_CST @tindex STRING_CST @findex TREE_STRING_LENGTH @findex TREE_STRING_POINTER @tindex PTRMEM_CST @findex PTRMEM_CST_CLASS @findex PTRMEM_CST_MEMBER @tindex VAR_DECL @tindex NEGATE_EXPR @tindex BIT_NOT_EXPR @tindex TRUTH_NOT_EXPR @tindex ADDR_EXPR @tindex INDIRECT_REF @tindex FIX_TRUNC_EXPR @tindex FLOAT_EXPR @tindex COMPLEX_EXPR @tindex CONJ_EXPR @tindex REALPART_EXPR @tindex IMAGPART_EXPR @tindex NOP_EXPR @tindex CONVERT_EXPR @tindex THROW_EXPR @tindex LSHIFT_EXPR @tindex RSHIFT_EXPR @tindex BIT_IOR_EXPR @tindex BIT_XOR_EXPR @tindex BIT_AND_EXPR @tindex TRUTH_ANDIF_EXPR @tindex TRUTH_ORIF_EXPR @tindex TRUTH_AND_EXPR @tindex TRUTH_OR_EXPR @tindex TRUTH_XOR_EXPR @tindex PLUS_EXPR @tindex MINUS_EXPR @tindex MULT_EXPR @tindex TRUNC_DIV_EXPR @tindex TRUNC_MOD_EXPR @tindex RDIV_EXPR @tindex LT_EXPR @tindex LE_EXPR @tindex GT_EXPR @tindex GE_EXPR @tindex EQ_EXPR @tindex NE_EXPR @tindex INIT_EXPR @tindex MODIFY_EXPR @tindex COMPONENT_REF @tindex COMPOUND_EXPR @tindex COND_EXPR @tindex CALL_EXPR @tindex CONSTRUCTOR @tindex COMPOUND_LITERAL_EXPR @tindex STMT_EXPR @tindex BIND_EXPR @tindex LOOP_EXPR @tindex EXIT_EXPR @tindex CLEANUP_POINT_EXPR @tindex ARRAY_REF @tindex VTABLE_REF @tindex VA_ARG_EXPR The internal representation for expressions is for the most part quite straightforward. However, there are a few facts that one must bear in mind. In particular, the expression ``tree'' is actually a directed acyclic graph. (For example there may be many references to the integer constant zero throughout the source program; many of these will be represented by the same expression node.) You should not rely on certain kinds of node being shared, nor should rely on certain kinds of nodes being unshared. The following macros can be used with all expression nodes: @ftable @code @item TREE_TYPE Returns the type of the expression. This value may not be precisely the same type that would be given the expression in the original program. @end ftable In what follows, some nodes that one might expect to always have type @code{bool} are documented to have either integral or boolean type. At some point in the future, the C front end may also make use of this same intermediate representation, and at this point these nodes will certainly have integral type. The previous sentence is not meant to imply that the C++ front end does not or will not give these nodes integral type. Below, we list the various kinds of expression nodes. Except where noted otherwise, the operands to an expression are accessed using the @code{TREE_OPERAND} macro. For example, to access the first operand to a binary plus expression @code{expr}, use: @example TREE_OPERAND (expr, 0) @end example @noindent As this example indicates, the operands are zero-indexed. The table below begins with constants, moves on to unary expressions, then proceeds to binary expressions, and concludes with various other kinds of expressions: @table @code @item INTEGER_CST These nodes represent integer constants. Note that the type of these constants is obtained with @code{TREE_TYPE}; they are not always of type @code{int}. In particular, @code{char} constants are represented with @code{INTEGER_CST} nodes. The value of the integer constant @code{e} is given by @example ((TREE_INT_CST_HIGH (e) << HOST_BITS_PER_WIDE_INT) + TREE_INST_CST_LOW (e)) @end example @noindent HOST_BITS_PER_WIDE_INT is at least thirty-two on all platforms. Both @code{TREE_INT_CST_HIGH} and @code{TREE_INT_CST_LOW} return a @code{HOST_WIDE_INT}. The value of an @code{INTEGER_CST} is interpreted as a signed or unsigned quantity depending on the type of the constant. In general, the expression given above will overflow, so it should not be used to calculate the value of the constant. The variable @code{integer_zero_node} is an integer constant with value zero. Similarly, @code{integer_one_node} is an integer constant with value one. The @code{size_zero_node} and @code{size_one_node} variables are analogous, but have type @code{size_t} rather than @code{int}. The function @code{tree_int_cst_lt} is a predicate which holds if its first argument is less than its second. Both constants are assumed to have the same signedness (i.e., either both should be signed or both should be unsigned.) The full width of the constant is used when doing the comparison; the usual rules about promotions and conversions are ignored. Similarly, @code{tree_int_cst_equal} holds if the two constants are equal. The @code{tree_int_cst_sgn} function returns the sign of a constant. The value is @code{1}, @code{0}, or @code{-1} according on whether the constant is greater than, equal to, or less than zero. Again, the signedness of the constant's type is taken into account; an unsigned constant is never less than zero, no matter what its bit-pattern. @item REAL_CST FIXME: Talk about how to obtain representations of this constant, do comparisons, and so forth. @item COMPLEX_CST These nodes are used to represent complex number constants, that is a @code{__complex__} whose parts are constant nodes. The @code{TREE_REALPART} and @code{TREE_IMAGPART} return the real and the imaginary parts respectively. @item VECTOR_CST These nodes are used to represent vector constants, whose parts are constant nodes. Each individual constant node is either an integer or a double constant node. The first operand is a @code{TREE_LIST} of the constant nodes and is accessed through @code{TREE_VECTOR_CST_ELTS}. @item STRING_CST These nodes represent string-constants. The @code{TREE_STRING_LENGTH} returns the length of the string, as an @code{int}. The @code{TREE_STRING_POINTER} is a @code{char*} containing the string itself. The string may not be @code{NUL}-terminated, and it may contain embedded @code{NUL} characters. Therefore, the @code{TREE_STRING_LENGTH} includes the trailing @code{NUL} if it is present. For wide string constants, the @code{TREE_STRING_LENGTH} is the number of bytes in the string, and the @code{TREE_STRING_POINTER} points to an array of the bytes of the string, as represented on the target system (that is, as integers in the target endianness). Wide and non-wide string constants are distinguished only by the @code{TREE_TYPE} of the @code{STRING_CST}. FIXME: The formats of string constants are not well-defined when the target system bytes are not the same width as host system bytes. @item PTRMEM_CST These nodes are used to represent pointer-to-member constants. The @code{PTRMEM_CST_CLASS} is the class type (either a @code{RECORD_TYPE} or @code{UNION_TYPE} within which the pointer points), and the @code{PTRMEM_CST_MEMBER} is the declaration for the pointed to object. Note that the @code{DECL_CONTEXT} for the @code{PTRMEM_CST_MEMBER} is in general different from the @code{PTRMEM_CST_CLASS}. For example, given: @example struct B @{ int i; @}; struct D : public B @{@}; int D::*dp = &D::i; @end example @noindent The @code{PTRMEM_CST_CLASS} for @code{&D::i} is @code{D}, even though the @code{DECL_CONTEXT} for the @code{PTRMEM_CST_MEMBER} is @code{B}, since @code{B::i} is a member of @code{B}, not @code{D}. @item VAR_DECL These nodes represent variables, including static data members. For more information, @pxref{Declarations}. @item NEGATE_EXPR These nodes represent unary negation of the single operand, for both integer and floating-point types. The type of negation can be determined by looking at the type of the expression. @item BIT_NOT_EXPR These nodes represent bitwise complement, and will always have integral type. The only operand is the value to be complemented. @item TRUTH_NOT_EXPR These nodes represent logical negation, and will always have integral (or boolean) type. The operand is the value being negated. @item PREDECREMENT_EXPR @itemx PREINCREMENT_EXPR @itemx POSTDECREMENT_EXPR @itemx POSTINCREMENT_EXPR These nodes represent increment and decrement expressions. The value of the single operand is computed, and the operand incremented or decremented. In the case of @code{PREDECREMENT_EXPR} and @code{PREINCREMENT_EXPR}, the value of the expression is the value resulting after the increment or decrement; in the case of @code{POSTDECREMENT_EXPR} and @code{POSTINCREMENT_EXPR} is the value before the increment or decrement occurs. The type of the operand, like that of the result, will be either integral, boolean, or floating-point. @item ADDR_EXPR These nodes are used to represent the address of an object. (These expressions will always have pointer or reference type.) The operand may be another expression, or it may be a declaration. As an extension, GCC allows users to take the address of a label. In this case, the operand of the @code{ADDR_EXPR} will be a @code{LABEL_DECL}. The type of such an expression is @code{void*}. If the object addressed is not an lvalue, a temporary is created, and the address of the temporary is used. @item INDIRECT_REF These nodes are used to represent the object pointed to by a pointer. The operand is the pointer being dereferenced; it will always have pointer or reference type. @item FIX_TRUNC_EXPR These nodes represent conversion of a floating-point value to an integer. The single operand will have a floating-point type, while the the complete expression will have an integral (or boolean) type. The operand is rounded towards zero. @item FLOAT_EXPR These nodes represent conversion of an integral (or boolean) value to a floating-point value. The single operand will have integral type, while the complete expression will have a floating-point type. FIXME: How is the operand supposed to be rounded? Is this dependent on @option{-mieee}? @item COMPLEX_EXPR These nodes are used to represent complex numbers constructed from two expressions of the same (integer or real) type. The first operand is the real part and the second operand is the imaginary part. @item CONJ_EXPR These nodes represent the conjugate of their operand. @item REALPART_EXPR @item IMAGPART_EXPR These nodes represent respectively the real and the imaginary parts of complex numbers (their sole argument). @item NON_LVALUE_EXPR These nodes indicate that their one and only operand is not an lvalue. A back end can treat these identically to the single operand. @item NOP_EXPR These nodes are used to represent conversions that do not require any code-generation. For example, conversion of a @code{char*} to an @code{int*} does not require any code be generated; such a conversion is represented by a @code{NOP_EXPR}. The single operand is the expression to be converted. The conversion from a pointer to a reference is also represented with a @code{NOP_EXPR}. @item CONVERT_EXPR These nodes are similar to @code{NOP_EXPR}s, but are used in those situations where code may need to be generated. For example, if an @code{int*} is converted to an @code{int} code may need to be generated on some platforms. These nodes are never used for C++-specific conversions, like conversions between pointers to different classes in an inheritance hierarchy. Any adjustments that need to be made in such cases are always indicated explicitly. Similarly, a user-defined conversion is never represented by a @code{CONVERT_EXPR}; instead, the function calls are made explicit. @item THROW_EXPR These nodes represent @code{throw} expressions. The single operand is an expression for the code that should be executed to throw the exception. However, there is one implicit action not represented in that expression; namely the call to @code{__throw}. This function takes no arguments. If @code{setjmp}/@code{longjmp} exceptions are used, the function @code{__sjthrow} is called instead. The normal GCC back end uses the function @code{emit_throw} to generate this code; you can examine this function to see what needs to be done. @item LSHIFT_EXPR @itemx RSHIFT_EXPR These nodes represent left and right shifts, respectively. The first operand is the value to shift; it will always be of integral type. The second operand is an expression for the number of bits by which to shift. Right shift should be treated as arithmetic, i.e., the high-order bits should be zero-filled when the expression has unsigned type and filled with the sign bit when the expression has signed type. Note that the result is undefined if the second operand is larger than the first operand's type size. @item BIT_IOR_EXPR @itemx BIT_XOR_EXPR @itemx BIT_AND_EXPR These nodes represent bitwise inclusive or, bitwise exclusive or, and bitwise and, respectively. Both operands will always have integral type. @item TRUTH_ANDIF_EXPR @itemx TRUTH_ORIF_EXPR These nodes represent logical and and logical or, respectively. These operators are not strict; i.e., the second operand is evaluated only if the value of the expression is not determined by evaluation of the first operand. The type of the operands, and the result type, is always of boolean or integral type. @item TRUTH_AND_EXPR @itemx TRUTH_OR_EXPR @itemx TRUTH_XOR_EXPR These nodes represent logical and, logical or, and logical exclusive or. They are strict; both arguments are always evaluated. There are no corresponding operators in C or C++, but the front end will sometimes generate these expressions anyhow, if it can tell that strictness does not matter. @itemx PLUS_EXPR @itemx MINUS_EXPR @itemx MULT_EXPR @itemx TRUNC_DIV_EXPR @itemx TRUNC_MOD_EXPR @itemx RDIV_EXPR These nodes represent various binary arithmetic operations. Respectively, these operations are addition, subtraction (of the second operand from the first), multiplication, integer division, integer remainder, and floating-point division. The operands to the first three of these may have either integral or floating type, but there will never be case in which one operand is of floating type and the other is of integral type. The result of a @code{TRUNC_DIV_EXPR} is always rounded towards zero. The @code{TRUNC_MOD_EXPR} of two operands @code{a} and @code{b} is always @code{a - (a/b)*b} where the division is as if computed by a @code{TRUNC_DIV_EXPR}. @item ARRAY_REF These nodes represent array accesses. The first operand is the array; the second is the index. To calculate the address of the memory accessed, you must scale the index by the size of the type of the array elements. The type of these expressions must be the type of a component of the array. @item ARRAY_RANGE_REF These nodes represent access to a range (or ``slice'') of an array. The operands are the same as that for @code{ARRAY_REF} and have the same meanings. The type of these expressions must be an array whose component type is the same as that of the first operand. The range of that array type determines the amount of data these expressions access. @item EXACT_DIV_EXPR Document. @item LT_EXPR @itemx LE_EXPR @itemx GT_EXPR @itemx GE_EXPR @itemx EQ_EXPR @itemx NE_EXPR These nodes represent the less than, less than or equal to, greater than, greater than or equal to, equal, and not equal comparison operators. The first and second operand with either be both of integral type or both of floating type. The result type of these expressions will always be of integral or boolean type. @item MODIFY_EXPR These nodes represent assignment. The left-hand side is the first operand; the right-hand side is the second operand. The left-hand side will be a @code{VAR_DECL}, @code{INDIRECT_REF}, @code{COMPONENT_REF}, or other lvalue. These nodes are used to represent not only assignment with @samp{=} but also compound assignments (like @samp{+=}), by reduction to @samp{=} assignment. In other words, the representation for @samp{i += 3} looks just like that for @samp{i = i + 3}. @item INIT_EXPR These nodes are just like @code{MODIFY_EXPR}, but are used only when a variable is initialized, rather than assigned to subsequently. @item COMPONENT_REF These nodes represent non-static data member accesses. The first operand is the object (rather than a pointer to it); the second operand is the @code{FIELD_DECL} for the data member. @item COMPOUND_EXPR These nodes represent comma-expressions. The first operand is an expression whose value is computed and thrown away prior to the evaluation of the second operand. The value of the entire expression is the value of the second operand. @item COND_EXPR These nodes represent @code{?:} expressions. The first operand is of boolean or integral type. If it evaluates to a nonzero value, the second operand should be evaluated, and returned as the value of the expression. Otherwise, the third operand is evaluated, and returned as the value of the expression. The second operand must have the same type as the entire expression, unless it unconditionally throws an exception or calls a noreturn function, in which case it should have void type. The same constraints apply to the third operand. This allows array bounds checks to be represented conveniently as @code{(i >= 0 && i < 10) ? i : abort()}. As a GNU extension, the C language front-ends allow the second operand of the @code{?:} operator may be omitted in the source. For example, @code{x ? : 3} is equivalent to @code{x ? x : 3}, assuming that @code{x} is an expression without side-effects. In the tree representation, however, the second operand is always present, possibly protected by @code{SAVE_EXPR} if the first argument does cause side-effects. @item CALL_EXPR These nodes are used to represent calls to functions, including non-static member functions. The first operand is a pointer to the function to call; it is always an expression whose type is a @code{POINTER_TYPE}. The second argument is a @code{TREE_LIST}. The arguments to the call appear left-to-right in the list. The @code{TREE_VALUE} of each list node contains the expression corresponding to that argument. (The value of @code{TREE_PURPOSE} for these nodes is unspecified, and should be ignored.) For non-static member functions, there will be an operand corresponding to the @code{this} pointer. There will always be expressions corresponding to all of the arguments, even if the function is declared with default arguments and some arguments are not explicitly provided at the call sites. @item STMT_EXPR These nodes are used to represent GCC's statement-expression extension. The statement-expression extension allows code like this: @example int f() @{ return (@{ int j; j = 3; j + 7; @}); @} @end example In other words, an sequence of statements may occur where a single expression would normally appear. The @code{STMT_EXPR} node represents such an expression. The @code{STMT_EXPR_STMT} gives the statement contained in the expression; this is always a @code{COMPOUND_STMT}. The value of the expression is the value of the last sub-statement in the @code{COMPOUND_STMT}. More precisely, the value is the value computed by the last @code{EXPR_STMT} in the outermost scope of the @code{COMPOUND_STMT}. For example, in: @example (@{ 3; @}) @end example the value is @code{3} while in: @example (@{ if (x) @{ 3; @} @}) @end example (represented by a nested @code{COMPOUND_STMT}), there is no value. If the @code{STMT_EXPR} does not yield a value, it's type will be @code{void}. @item BIND_EXPR These nodes represent local blocks. The first operand is a list of temporary variables, connected via their @code{TREE_CHAIN} field. These will never require cleanups. The scope of these variables is just the body of the @code{BIND_EXPR}. The body of the @code{BIND_EXPR} is the second operand. @item LOOP_EXPR These nodes represent ``infinite'' loops. The @code{LOOP_EXPR_BODY} represents the body of the loop. It should be executed forever, unless an @code{EXIT_EXPR} is encountered. @item EXIT_EXPR These nodes represent conditional exits from the nearest enclosing @code{LOOP_EXPR}. The single operand is the condition; if it is nonzero, then the loop should be exited. An @code{EXIT_EXPR} will only appear within a @code{LOOP_EXPR}. @item CLEANUP_POINT_EXPR These nodes represent full-expressions. The single operand is an expression to evaluate. Any destructor calls engendered by the creation of temporaries during the evaluation of that expression should be performed immediately after the expression is evaluated. @item CONSTRUCTOR These nodes represent the brace-enclosed initializers for a structure or array. The first operand is reserved for use by the back end. The second operand is a @code{TREE_LIST}. If the @code{TREE_TYPE} of the @code{CONSTRUCTOR} is a @code{RECORD_TYPE} or @code{UNION_TYPE}, then the @code{TREE_PURPOSE} of each node in the @code{TREE_LIST} will be a @code{FIELD_DECL} and the @code{TREE_VALUE} of each node will be the expression used to initialize that field. You should not depend on the fields appearing in any particular order, nor should you assume that all fields will be represented. Unrepresented fields may be assigned any value. If the @code{TREE_TYPE} of the @code{CONSTRUCTOR} is an @code{ARRAY_TYPE}, then the @code{TREE_PURPOSE} of each element in the @code{TREE_LIST} will be an @code{INTEGER_CST}. This constant indicates which element of the array (indexed from zero) is being assigned to; again, the @code{TREE_VALUE} is the corresponding initializer. If the @code{TREE_PURPOSE} is @code{NULL_TREE}, then the initializer is for the next available array element. Conceptually, before any initialization is done, the entire area of storage is initialized to zero. @item COMPOUND_LITERAL_EXPR @findex COMPOUND_LITERAL_EXPR_DECL_STMT @findex COMPOUND_LITERAL_EXPR_DECL These nodes represent ISO C99 compound literals. The @code{COMPOUND_LITERAL_EXPR_DECL_STMT} is a @code{DECL_STMT} containing an anonymous @code{VAR_DECL} for the unnamed object represented by the compound literal; the @code{DECL_INITIAL} of that @code{VAR_DECL} is a @code{CONSTRUCTOR} representing the brace-enclosed list of initializers in the compound literal. That anonymous @code{VAR_DECL} can also be accessed directly by the @code{COMPOUND_LITERAL_EXPR_DECL} macro. @item SAVE_EXPR A @code{SAVE_EXPR} represents an expression (possibly involving side-effects) that is used more than once. The side-effects should occur only the first time the expression is evaluated. Subsequent uses should just reuse the computed value. The first operand to the @code{SAVE_EXPR} is the expression to evaluate. The side-effects should be executed where the @code{SAVE_EXPR} is first encountered in a depth-first preorder traversal of the expression tree. @item TARGET_EXPR A @code{TARGET_EXPR} represents a temporary object. The first operand is a @code{VAR_DECL} for the temporary variable. The second operand is the initializer for the temporary. The initializer is evaluated, and copied (bitwise) into the temporary. Often, a @code{TARGET_EXPR} occurs on the right-hand side of an assignment, or as the second operand to a comma-expression which is itself the right-hand side of an assignment, etc. In this case, we say that the @code{TARGET_EXPR} is ``normal''; otherwise, we say it is ``orphaned''. For a normal @code{TARGET_EXPR} the temporary variable should be treated as an alias for the left-hand side of the assignment, rather than as a new temporary variable. The third operand to the @code{TARGET_EXPR}, if present, is a cleanup-expression (i.e., destructor call) for the temporary. If this expression is orphaned, then this expression must be executed when the statement containing this expression is complete. These cleanups must always be executed in the order opposite to that in which they were encountered. Note that if a temporary is created on one branch of a conditional operator (i.e., in the second or third operand to a @code{COND_EXPR}), the cleanup must be run only if that branch is actually executed. See @code{STMT_IS_FULL_EXPR_P} for more information about running these cleanups. @item AGGR_INIT_EXPR An @code{AGGR_INIT_EXPR} represents the initialization as the return value of a function call, or as the result of a constructor. An @code{AGGR_INIT_EXPR} will only appear as the second operand of a @code{TARGET_EXPR}. The first operand to the @code{AGGR_INIT_EXPR} is the address of a function to call, just as in a @code{CALL_EXPR}. The second operand are the arguments to pass that function, as a @code{TREE_LIST}, again in a manner similar to that of a @code{CALL_EXPR}. The value of the expression is that returned by the function. If @code{AGGR_INIT_VIA_CTOR_P} holds of the @code{AGGR_INIT_EXPR}, then the initialization is via a constructor call. The address of the third operand of the @code{AGGR_INIT_EXPR}, which is always a @code{VAR_DECL}, is taken, and this value replaces the first argument in the argument list. In this case, the value of the expression is the @code{VAR_DECL} given by the third operand to the @code{AGGR_INIT_EXPR}; constructors do not return a value. @item VTABLE_REF A @code{VTABLE_REF} indicates that the interior expression computes a value that is a vtable entry. It is used with @option{-fvtable-gc} to track the reference through to front end to the middle end, at which point we transform this to a @code{REG_VTABLE_REF} note, which survives the balance of code generation. The first operand is the expression that computes the vtable reference. The second operand is the @code{VAR_DECL} of the vtable. The third operand is an @code{INTEGER_CST} of the byte offset into the vtable. @item VA_ARG_EXPR This node is used to implement support for the C/C++ variable argument-list mechanism. It represents expressions like @code{va_arg (ap, type)}. Its @code{TREE_TYPE} yields the tree representation for @code{type} and its sole argument yields the representation for @code{ap}. @end table