tree.def   [plain text]

/* This file contains the definitions and documentation for the
   tree codes used in the GNU C compiler.
   Copyright (C) 1987, 1988, 1993, 1995, 1997, 1998, 2000, 2001
   Free Software Foundation, Inc.

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 2, or (at your option) any later

GCC is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING.  If not, write to the Free
Software Foundation, 59 Temple Place - Suite 330, Boston, MA
02111-1307, USA.  */

/* The third argument can be:
   'x' for an exceptional code (fits no category).
   't' for a type object code.
   'b' for a lexical block.
   'c' for codes for constants.
   'd' for codes for declarations (also serving as variable refs).
   'r' for codes for references to storage.
   '<' for codes for comparison expressions.
   '1' for codes for unary arithmetic expressions.
   '2' for codes for binary arithmetic expressions.
   's' for codes for expressions with inherent side effects.
   'e' for codes for other kinds of expressions.  */

/* For `r', `e', `<', `1', `2', `s' and `x' nodes,
   the 4th element is the number of argument slots to allocate.
   This determines the size of the tree node object.  */

/* Any erroneous construct is parsed into a node of this type.
   This type of node is accepted without complaint in all contexts
   by later parsing activities, to avoid multiple error messages
   for one error.
   No fields in these nodes are used except the TREE_CODE.  */
DEFTREECODE (ERROR_MARK, "error_mark", 'x', 0)

/* Used to represent a name (such as, in the DECL_NAME of a decl node).
   Internally it looks like a STRING_CST node.
   There is only one IDENTIFIER_NODE ever made for any particular name.
   Use `get_identifier' to get it (or create it, the first time).  */
DEFTREECODE (IDENTIFIER_NODE, "identifier_node", 'x', ((LANG_HOOKS_IDENTIFIER_SIZE - sizeof (struct tree_common) + sizeof (tree) - 1) / sizeof (tree)))

/* Has the TREE_VALUE and TREE_PURPOSE fields.  */
/* These nodes are made into lists by chaining through the
   TREE_CHAIN field.  The elements of the list live in the
   TREE_VALUE fields, while TREE_PURPOSE fields are occasionally
   used as well to get the effect of Lisp association lists.  */
DEFTREECODE (TREE_LIST, "tree_list", 'x', 2)

/* These nodes contain an array of tree nodes.  */
DEFTREECODE (TREE_VEC, "tree_vec", 'x', 2)

/* A symbol binding block.  These are arranged in a tree,
   where the BLOCK_SUBBLOCKS field contains a chain of subblocks
   chained through the BLOCK_CHAIN field.
   BLOCK_SUPERCONTEXT points to the parent block.
     For a block which represents the outermost scope of a function, it
     points to the FUNCTION_DECL node.
   BLOCK_VARS points to a chain of decl nodes.
   BLOCK_TYPE_TAGS points to a chain of types which have their own names.
   BLOCK_CHAIN points to the next BLOCK at the same level.
   BLOCK_ABSTRACT_ORIGIN points to the original (abstract) tree node which
   this block is an instance of, or else is NULL to indicate that this
   block is not an instance of anything else.  When non-NULL, the value
   could either point to another BLOCK node or it could point to a
   FUNCTION_DECL node (e.g. in the case of a block representing the
   outermost scope of a particular inlining of a function).
   BLOCK_ABSTRACT is nonzero if the block represents an abstract
   instance of a block (i.e. one which is nested within an abstract
   instance of an inline function). 
   TREE_ASM_WRITTEN is nonzero if the block was actually referenced
   in the generated assembly.  */
DEFTREECODE (BLOCK, "block", 'b', 0)
/* Each data type is represented by a tree node whose code is one of
   the following:  */
/* Each node that represents a data type has a component TYPE_SIZE
   containing a tree that is an expression for the size in bits.
   The TYPE_MODE contains the machine mode for values of this type.
   The TYPE_POINTER_TO field contains a type for a pointer to this type,
     or zero if no such has been created yet.
   The TYPE_NEXT_VARIANT field is used to chain together types
     that are variants made by type modifiers such as "const" and "volatile".
   The TYPE_MAIN_VARIANT field, in any member of such a chain,
     points to the start of the chain.
   The TYPE_NONCOPIED_PARTS field is a list specifying which parts
     of an object of this type should *not* be copied by assignment.
     The TREE_VALUE of each is a FIELD_DECL that should not be
     copied.  The TREE_PURPOSE is an initial value for that field when
     an object of this type is initialized via an INIT_EXPR.  It may
     be NULL if no special value is required.  Even the things in this
     list are copied if the right-hand side of an assignment is known
     to be a complete object (rather than being, perhaps, a subobject
     of some other object.)  The determination of what constitutes a
     complete object is done by fixed_type_p.
   The TYPE_NAME field contains info on the name used in the program
     for this type (for GDB symbol table output).  It is either a
     TYPE_DECL node, for types that are typedefs, or an IDENTIFIER_NODE
     in the case of structs, unions or enums that are known with a tag,
     or zero for types that have no special name.
   The TYPE_CONTEXT for any sort of type which could have a name or
    which could have named members (e.g. tagged types in C/C++) will
    point to the node which represents the scope of the given type, or
    will be NULL_TREE if the type has "file scope".  For most types, this
    will point to a BLOCK node or a FUNCTION_DECL node, but it could also
    point to a FUNCTION_TYPE node (for types whose scope is limited to the
    formal parameter list of some function type specification) or it
    could point to a RECORD_TYPE, UNION_TYPE or QUAL_UNION_TYPE node
    (for C++ "member" types).
    For non-tagged-types, TYPE_CONTEXT need not be set to anything in
    particular, since any type which is of some type category  (e.g.
    an array type or a function type) which cannot either have a name
    itself or have named members doesn't really have a "scope" per se.
  The TREE_CHAIN field is used as a forward-references to names for
    see below.  */

DEFTREECODE (VOID_TYPE, "void_type", 't', 0)	/* The void type in C */

/* Integer types in all languages, including char in C.
   Also used for sub-ranges of other discrete types.
   Has components TYPE_MIN_VALUE, TYPE_MAX_VALUE (expressions, inclusive)
   and TYPE_PRECISION (number of bits used by this type).
   In the case of a subrange type in Pascal, the TREE_TYPE
   of this will point at the supertype (another INTEGER_TYPE,
   Otherwise, the TREE_TYPE is zero.  */
DEFTREECODE (INTEGER_TYPE, "integer_type", 't', 0)

/* C's float and double.  Different floating types are distinguished
   by machine mode and by the TYPE_SIZE and the TYPE_PRECISION.  */
DEFTREECODE (REAL_TYPE, "real_type", 't', 0)

/* Complex number types.  The TREE_TYPE field is the data type
   of the real and imaginary parts.  */
DEFTREECODE (COMPLEX_TYPE, "complex_type", 't', 0)

/* Vector types.  The TREE_TYPE field is the data type of the vector
   elements.  */
DEFTREECODE (VECTOR_TYPE, "vector_type", 't', 0)

/* C enums.  The type node looks just like an INTEGER_TYPE node.
   The symbols for the values of the enum type are defined by
   CONST_DECL nodes, but the type does not point to them;
   however, the TYPE_VALUES is a list in which each element's TREE_PURPOSE
   is a name and the TREE_VALUE is the value (an INTEGER_CST node).  */
/* A forward reference `enum foo' when no enum named foo is defined yet
   has zero (a null pointer) in its TYPE_SIZE.  The tag name is in
   the TYPE_NAME field.  If the type is later defined, the normal
   fields are filled in.
   RECORD_TYPE, UNION_TYPE, and QUAL_UNION_TYPE forward refs are
   treated similarly.  */
DEFTREECODE (ENUMERAL_TYPE, "enumeral_type", 't', 0)

/* Pascal's boolean type (true or false are the only values);
   no special fields needed.  */
DEFTREECODE (BOOLEAN_TYPE, "boolean_type", 't', 0)

/* CHAR in Pascal; not used in C.
   No special fields needed.  */
DEFTREECODE (CHAR_TYPE, "char_type", 't', 0)

/* All pointer-to-x types have code POINTER_TYPE.
   The TREE_TYPE points to the node for the type pointed to.  */
DEFTREECODE (POINTER_TYPE, "pointer_type", 't', 0)

/* An offset is a pointer relative to an object.
   The TREE_TYPE field is the type of the object at the offset.
   The TYPE_OFFSET_BASETYPE points to the node for the type of object
   that the offset is relative to.  */
DEFTREECODE (OFFSET_TYPE, "offset_type", 't', 0)

/* A reference is like a pointer except that it is coerced
   automatically to the value it points to.  Used in C++.  */
DEFTREECODE (REFERENCE_TYPE, "reference_type", 't', 0)

/* METHOD_TYPE is the type of a function which takes an extra first
   argument for "self", which is not present in the declared argument list.
   The TREE_TYPE is the return type of the method.  The TYPE_METHOD_BASETYPE
   is the type of "self".  TYPE_ARG_TYPES is the real argument list, which
   includes the hidden argument for "self".  */
DEFTREECODE (METHOD_TYPE, "method_type", 't', 0)

/* Used for Pascal; details not determined right now.  */
DEFTREECODE (FILE_TYPE, "file_type", 't', 0)

/* Types of arrays.  Special fields:
   TREE_TYPE		  Type of an array element.
   TYPE_DOMAIN		  Type to index by.
			    Its range of values specifies the array length.
 The field TYPE_POINTER_TO (TREE_TYPE (array_type)) is always nonzero
 and holds the type to coerce a value of that array type to in C.
 TYPE_STRING_FLAG indicates a string (in contrast to an array of chars)
 in languages (such as Chill) that make a distinction.  */
/* Array types in C or Pascal */
DEFTREECODE (ARRAY_TYPE, "array_type", 't', 0)

/* Types of sets for Pascal.  Special fields are the same as
   in an array type.  The target type is always a boolean type.
   Used for both bitstrings and powersets in Chill;
   TYPE_STRING_FLAG indicates a bitstring.  */
DEFTREECODE (SET_TYPE, "set_type", 't', 0)

/* Struct in C, or record in Pascal.  */
/* Special fields:
   TYPE_FIELDS  chain of FIELD_DECLs for the fields of the struct,
     and VAR_DECLs, TYPE_DECLs and CONST_DECLs for record-scope variables,
     types and enumerators.
   A few may need to be added for Pascal.  */
/* See the comment above, before ENUMERAL_TYPE, for how
   forward references to struct tags are handled in C.  */
DEFTREECODE (RECORD_TYPE, "record_type", 't', 0)

/* Union in C.  Like a struct, except that the offsets of the fields
   will all be zero.  */
/* See the comment above, before ENUMERAL_TYPE, for how
   forward references to union tags are handled in C.  */
DEFTREECODE (UNION_TYPE, "union_type", 't', 0)	/* C union type */

/* Similar to UNION_TYPE, except that the expressions in DECL_QUALIFIER
   in each FIELD_DECL determine what the union contains.  The first
   field whose DECL_QUALIFIER expression is true is deemed to occupy
   the union.  */
DEFTREECODE (QUAL_UNION_TYPE, "qual_union_type", 't', 0)

/* Type of functions.  Special fields:
   TREE_TYPE		    type of value returned.
   TYPE_ARG_TYPES      list of types of arguments expected.
	this list is made of TREE_LIST nodes.
   Types of "Procedures" in languages where they are different from functions
   have code FUNCTION_TYPE also, but then TREE_TYPE is zero or void type.  */
DEFTREECODE (FUNCTION_TYPE, "function_type", 't', 0)

/* This is a language-specific kind of type.
   Its meaning is defined by the language front end.
   layout_type does not know how to lay this out,
   so the front-end must do so manually.  */
DEFTREECODE (LANG_TYPE, "lang_type", 't', 0)
/* Expressions */

/* First, the constants.  */

/* Contents are in TREE_INT_CST_LOW and TREE_INT_CST_HIGH fields,
   32 bits each, giving us a 64 bit constant capability.
   Note: constants of type char in Pascal are INTEGER_CST,
   and so are pointer constants such as nil in Pascal or NULL in C.
   `(int *) 1' in C also results in an INTEGER_CST.  */
DEFTREECODE (INTEGER_CST, "integer_cst", 'c', 2)

/* Contents are in TREE_REAL_CST field.  Also there is TREE_CST_RTL.  */
DEFTREECODE (REAL_CST, "real_cst", 'c', 3)

/* Contents are in TREE_REALPART and TREE_IMAGPART fields,
   whose contents are other constant nodes.
   Also there is TREE_CST_RTL.  */
DEFTREECODE (COMPLEX_CST, "complex_cst", 'c', 3)

/* Contents are in TREE_VECTOR_CST_ELTS field.  */
DEFTREECODE (VECTOR_CST, "vector_cst", 'c', 3)     

   Also there is TREE_CST_RTL.  */
DEFTREECODE (STRING_CST, "string_cst", 'c', 3)

/* Declarations.  All references to names are represented as ..._DECL
   nodes.  The decls in one binding context are chained through the
   TREE_CHAIN field.  Each DECL has a DECL_NAME field which contains
   an IDENTIFIER_NODE.  (Some decls, most often labels, may have zero
   as the DECL_NAME).  DECL_CONTEXT points to the node representing
   the context in which this declaration has its scope.  For
   QUAL_UNION_TYPE node that the field is a member of.  For VAR_DECL,
   points to either the FUNCTION_DECL for the containing function, the
   RECORD_TYPE or UNION_TYPE for the containing type, or NULL_TREE or
   a TRANSLATION_UNIT_DECL if the given decl has "file scope".
   DECL_ABSTRACT_ORIGIN, if non-NULL, points to the original (abstract)
    ..._DECL node of which this decl is an (inlined or template expanded)
   The TREE_TYPE field holds the data type of the object, when relevant.
    LABEL_DECLs have no data type.  For TYPE_DECL, the TREE_TYPE field
    contents are the type whose name is being declared.
    and DECL_MODE fields exist in decl nodes just as in type nodes.
    They are unused in LABEL_DECL, TYPE_DECL and CONST_DECL nodes.

   DECL_FIELD_BIT_OFFSET holds an integer number of bits offset for
   the location.  DECL_VOFFSET holds an expression for a variable
   offset; it is to be multiplied by DECL_VOFFSET_UNIT (an integer).
   These fields are relevant only in FIELD_DECLs and PARM_DECLs.

   DECL_INITIAL holds the value to initialize a variable to,
   or the value of a constant.  For a function, it holds the body
   (a node of type BLOCK representing the function's binding contour
   and whose body contains the function's statements.)  For a LABEL_DECL
   in C, it is a flag, nonzero if the label's definition has been seen.

   PARM_DECLs use a special field:
   DECL_ARG_TYPE is the type in which the argument is actually
    passed, which may be different from its type within the function.

   FUNCTION_DECLs use four special fields:
   DECL_ARGUMENTS holds a chain of PARM_DECL nodes for the arguments.
   DECL_RESULT holds a RESULT_DECL node for the value of a function,
    or it is 0 for a function that returns no value.
    (C functions returning void have zero here.)
    The TREE_TYPE field is the type in which the result is actually
    returned.  This is usually the same as the return type of the
    FUNCTION_DECL, but it may be a wider integer type because of
   DECL_FUNCTION_CODE is a code number that is nonzero for
    built-in functions.  Its value is an enum built_in_function
    that says which built-in function it is.

   DECL_SOURCE_FILE holds a filename string and DECL_SOURCE_LINE
   holds a line number.  In some cases these can be the location of
   a reference, if no definition has been seen.

   DECL_ABSTRACT is nonzero if the decl represents an abstract instance
   of a decl (i.e. one which is nested within an abstract instance of a
   inline function.  */

DEFTREECODE (FUNCTION_DECL, "function_decl", 'd', 0)
DEFTREECODE (LABEL_DECL, "label_decl", 'd', 0)
DEFTREECODE (CONST_DECL, "const_decl", 'd', 0)
DEFTREECODE (TYPE_DECL, "type_decl", 'd', 0)
DEFTREECODE (VAR_DECL, "var_decl", 'd', 0)
DEFTREECODE (PARM_DECL, "parm_decl", 'd', 0)
DEFTREECODE (RESULT_DECL, "result_decl", 'd', 0)
DEFTREECODE (FIELD_DECL, "field_decl", 'd', 0)

/* A namespace declaration.  Namespaces appear in DECL_CONTEXT of other
   _DECLs, providing a hierarchy of names.  */
DEFTREECODE (NAMESPACE_DECL, "namespace_decl", 'd', 0)

/* A translation unit.  This is not technically a declaration, since it
   can't be looked up, but it's close enough.  */
DEFTREECODE (TRANSLATION_UNIT_DECL, "translation_unit_decl", 'd', 0)
/* References to storage.  */

/* Value is structure or union component.
   Operand 0 is the structure or union (an expression);
   operand 1 is the field (a node of type FIELD_DECL).  */
DEFTREECODE (COMPONENT_REF, "component_ref", 'r', 2)

/* Reference to a group of bits within an object.  Similar to COMPONENT_REF
   except the position is given explicitly rather than via a FIELD_DECL.
   Operand 0 is the structure or union expression;
   operand 1 is a tree giving the number of bits being referenced;
   operand 2 is a tree giving the position of the first referenced bit.
   The field can be either a signed or unsigned field;
   TREE_UNSIGNED says which.  */
DEFTREECODE (BIT_FIELD_REF, "bit_field_ref", 'r', 3)
/* C unary `*' or Pascal `^'.  One operand, an expression for a pointer.  */
DEFTREECODE (INDIRECT_REF, "indirect_ref", 'r', 1)

/* Pascal `^` on a file.  One operand, an expression for the file.  */
DEFTREECODE (BUFFER_REF, "buffer_ref", 'r', 1)

/* Array indexing.
   Operand 0 is the array; operand 1 is a (single) array index.  */
DEFTREECODE (ARRAY_REF, "array_ref", 'r', 2)

/* Likewise, except that the result is a range ("slice") of the array.  The
   starting index of the resulting array is taken from operand 1 and the size
   of the range is taken from the type of the expression.  */
DEFTREECODE (ARRAY_RANGE_REF, "array_range_ref", 'r', 2)

/* Vtable indexing.  Carries data useful for emitting information
   for vtable garbage collection.
   Operand 0: an array_ref (or equivalent expression)
   Operand 1: the vtable base (must be a var_decl)
   Operand 2: index into vtable (must be an integer_cst).  */
DEFTREECODE (VTABLE_REF, "vtable_ref", 'r', 3)

/* Constructor: return an aggregate value made from specified components.
   In C, this is used only for structure and array initializers.
   Also used for SET_TYPE in Chill (and potentially Pascal).
   The first "operand" is really a pointer to the RTL,
   for constant constructors only.
   The second operand is a list of component values
   made out of a chain of TREE_LIST nodes.

   The TREE_PURPOSE of each node is the corresponding index.
   If the TREE_PURPOSE is a RANGE_EXPR, it is a short-hand for many nodes,
   one for each index in the range.  (If the corresponding TREE_VALUE
   has side-effects, they are evaluated once for each element.  Wrap the
   value in a SAVE_EXPR if you want to evaluate side effects only once.)

   The TREE_PURPOSE of each node is a FIELD_DECL.

   For SET_TYPE:
   The TREE_VALUE specifies a value (index) in the set that is true.
   If TREE_PURPOSE is non-NULL, it specifies the lower limit of a
   range of true values.  Elements not listed are false (not in the set).  */
DEFTREECODE (CONSTRUCTOR, "constructor", 'e', 2)

/* The expression types are mostly straightforward, with the fourth argument
   of DEFTREECODE saying how many operands there are.
   Unless otherwise specified, the operands are expressions and the
   types of all the operands and the expression must all be the same.  */

/* Contains two expressions to compute, one followed by the other.
   the first value is ignored.  The second one's value is used.  The
   type of the first expression need not agree with the other types.  */
DEFTREECODE (COMPOUND_EXPR, "compound_expr", 'e', 2)

/* Assignment expression.  Operand 0 is the what to set; 1, the new value.  */
DEFTREECODE (MODIFY_EXPR, "modify_expr", 'e', 2)

/* Initialization expression.  Operand 0 is the variable to initialize;
   Operand 1 is the initializer.  */
DEFTREECODE (INIT_EXPR, "init_expr", 'e', 2)

/* For TARGET_EXPR, operand 0 is the target of an initialization,
   operand 1 is the initializer for the target,
   and operand 2 is the cleanup for this node, if any.
   and operand 3 is the saved initializer after this node has been
   expanded once, this is so we can re-expand the tree later.  */
DEFTREECODE (TARGET_EXPR, "target_expr", 'e', 4)

/* Conditional expression ( ... ? ... : ...  in C).
   Operand 0 is the condition.
   Operand 1 is the then-value.
   Operand 2 is the else-value.
   Operand 0 may be of any type.
   Operand 1 must have the same type as the entire expression, unless
   it unconditionally throws an exception, in which case it should
   have VOID_TYPE.  The same constraints apply to operand 2.  */
DEFTREECODE (COND_EXPR, "cond_expr", 'e', 3)

/* Declare local variables, including making RTL and allocating space.
   Operand 0 is a chain of VAR_DECL nodes for the variables.
   Operand 1 is the body, the expression to be computed using 
   the variables.  The value of operand 1 becomes that of the BIND_EXPR.
   Operand 2 is the BLOCK that corresponds to these bindings
   for debugging purposes.  If this BIND_EXPR is actually expanded,
   that sets the TREE_USED flag in the BLOCK.

   The BIND_EXPR is not responsible for informing parsers
   about these variables.  If the body is coming from the input file,
   then the code that creates the BIND_EXPR is also responsible for 
   informing the parser of the variables.

   If the BIND_EXPR is ever expanded, its TREE_USED flag is set.
   This tells the code for debugging symbol tables not to ignore the BIND_EXPR.
   If the BIND_EXPR should be output for debugging but will not be expanded, 
   set the TREE_USED flag by hand.

   In order for the BIND_EXPR to be known at all, the code that creates it
   must also install it as a subblock in the tree of BLOCK
   nodes for the function.  */
DEFTREECODE (BIND_EXPR, "bind_expr", 'e', 3)

/* Function call.  Operand 0 is the function.
   Operand 1 is the argument list, a list of expressions
   made out of a chain of TREE_LIST nodes.  */
DEFTREECODE (CALL_EXPR, "call_expr", 'e', 2)

/* Call a method.  Operand 0 is the method, whose type is a METHOD_TYPE.
   Operand 1 is the expression for "self".
   Operand 2 is the list of explicit arguments.  */
DEFTREECODE (METHOD_CALL_EXPR, "method_call_expr", 'e', 4)

/* Specify a value to compute along with its corresponding cleanup.
   Operand 0 argument is an expression whose value needs a cleanup.
   Operand 1 is the cleanup expression for the object.
   Operand 2 is an RTL_EXPR which will eventually represent that value.
     The RTL_EXPR is used in this expression, which is how the expression
     manages to act on the proper value.
   The cleanup is executed by the first enclosing CLEANUP_POINT_EXPR, if
   it exists, otherwise it is the responsibility of the caller to manually
   call expand_start_target_temps/expand_end_target_temps, as needed.

   This differs from TRY_CATCH_EXPR in that operand 2 is always
   evaluated when an exception isn't thrown when cleanups are run.  */
DEFTREECODE (WITH_CLEANUP_EXPR, "with_cleanup_expr", 'e', 3)

/* Specify a cleanup point.
   Operand 0 is an expression that may have cleanups.  If it does, those
   cleanups are executed after the expression is expanded.

   Note that if the expression is a reference to storage, it is forced out
   of memory before the cleanups are run.  This is necessary to handle
   cases where the cleanups modify the storage referenced; in the
   expression 't.i', if 't' is a struct with an integer member 'i' and a
   cleanup which modifies 'i', the value of the expression depends on
   whether the cleanup is run before or after 't.i' is evaluated.  When
   expand_expr is run on 't.i', it returns a MEM.  This is not good enough;
   the value of 't.i' must be forced out of memory.

   As a consequence, the operand of a CLEANUP_POINT_EXPR must not have
   BLKmode, because it will not be forced out of memory.  */
DEFTREECODE (CLEANUP_POINT_EXPR, "cleanup_point_expr", 'e', 1)

/* The following two codes are used in languages that have types where
   some field in an object of the type contains a value that is used in
   the computation of another field's offset or size and/or the size of
   the type.  The positions and/or sizes of fields can vary from object
   to object of the same type.

   Record types with discriminants in Ada or schema types in Pascal are
   examples of such types.  This mechanism is also used to create "fat
   pointers" for unconstrained array types in Ada; the fat pointer is a
   structure one of whose fields is a pointer to the actual array type
   and the other field is a pointer to a template, which is a structure
   containing the bounds of the array.  The bounds in the type pointed
   to by the first field in the fat pointer refer to the values in the

   When you wish to construct such a type you need "self-references"
   that allow you to reference the object having this type from the
   TYPE node, i.e. without having a variable instantiating this type.

   Such a "self-references" is done using a PLACEHOLDER_EXPR.  This is
   a node that will later be replaced with the object being referenced.
   Its type is that of the object and selects which object to use from
   a chain of references (see below).  No other slots are used in the

   For example, if your type FOO is a RECORD_TYPE with a field BAR,
   and you need the value of <variable>.BAR to calculate TYPE_SIZE
   (FOO), just substitute <variable> above with a PLACEHOLDER_EXPR
   what contains both the expression we wish to
   evaluate and an expression within which the object may be found.
   The latter expression is the object itself in the simple case of an
   Ada record with discriminant, but it can be the array in the case of
   an unconstrained array.

   In the latter case, we need the fat pointer, because the bounds of
   the array can only be accessed from it.  However, we rely here on the
   fact that the expression for the array contains the dereference of
   the fat pointer that obtained the array pointer.

   Accordingly, when looking for the object to substitute in place of
   a PLACEHOLDER_EXPR, we look down the first operand of the expression
   passed as the second operand to WITH_RECORD_EXPR until we find
   something of the desired type or reach a constant.  */

/* Denotes a record to later be supplied with a WITH_RECORD_EXPR when
   evaluating this expression.  The type of this expression is used to
   find the record to replace it.  */
DEFTREECODE (PLACEHOLDER_EXPR, "placeholder_expr", 'x', 0)

/* Provide an expression that references a record to be used in place
   of a PLACEHOLDER_EXPR.  The record to be used is the record within
   operand 1 that has the same type as the PLACEHOLDER_EXPR in
   operand 0.  */
DEFTREECODE (WITH_RECORD_EXPR, "with_record_expr", 'e', 2)

/* Simple arithmetic.  */
DEFTREECODE (PLUS_EXPR, "plus_expr", '2', 2)
DEFTREECODE (MINUS_EXPR, "minus_expr", '2', 2)
DEFTREECODE (MULT_EXPR, "mult_expr", '2', 2)

/* Division for integer result that rounds the quotient toward zero.  */
DEFTREECODE (TRUNC_DIV_EXPR, "trunc_div_expr", '2', 2)

/* Division for integer result that rounds the quotient toward infinity.  */
DEFTREECODE (CEIL_DIV_EXPR, "ceil_div_expr", '2', 2)

/* Division for integer result that rounds toward minus infinity.  */
DEFTREECODE (FLOOR_DIV_EXPR, "floor_div_expr", '2', 2)

/* Division for integer result that rounds toward nearest integer.  */
DEFTREECODE (ROUND_DIV_EXPR, "round_div_expr", '2', 2)

/* Four kinds of remainder that go with the four kinds of division.  */
DEFTREECODE (TRUNC_MOD_EXPR, "trunc_mod_expr", '2', 2)
DEFTREECODE (CEIL_MOD_EXPR, "ceil_mod_expr", '2', 2)
DEFTREECODE (FLOOR_MOD_EXPR, "floor_mod_expr", '2', 2)
DEFTREECODE (ROUND_MOD_EXPR, "round_mod_expr", '2', 2)

/* Division for real result.  */
DEFTREECODE (RDIV_EXPR, "rdiv_expr", '2', 2)

/* Division which is not supposed to need rounding.
   Used for pointer subtraction in C.  */
DEFTREECODE (EXACT_DIV_EXPR, "exact_div_expr", '2', 2)

/* Conversion of real to fixed point: four ways to round,
   like the four ways to divide.
   CONVERT_EXPR can also be used to convert a real to an integer,
   and that is what is used in languages that do not have ways of
   specifying which of these is wanted.  Maybe these are not needed.  */
DEFTREECODE (FIX_TRUNC_EXPR, "fix_trunc_expr", '1', 1)
DEFTREECODE (FIX_CEIL_EXPR, "fix_ceil_expr", '1', 1)
DEFTREECODE (FIX_FLOOR_EXPR, "fix_floor_expr", '1', 1)
DEFTREECODE (FIX_ROUND_EXPR, "fix_round_expr", '1', 1)

/* Conversion of an integer to a real.  */
DEFTREECODE (FLOAT_EXPR, "float_expr", '1', 1)

/* Unary negation.  */
DEFTREECODE (NEGATE_EXPR, "negate_expr", '1', 1)

DEFTREECODE (MIN_EXPR, "min_expr", '2', 2)
DEFTREECODE (MAX_EXPR, "max_expr", '2', 2)

/* Represents the absolute value of the operand.

   An ABS_EXPR must have either an INTEGER_TYPE or a REAL_TYPE.  The
   operand of the ABS_EXPR must have the same type.  */
DEFTREECODE (ABS_EXPR, "abs_expr", '1', 1)

DEFTREECODE (FFS_EXPR, "ffs_expr", '1', 1)

/* Shift operations for shift and rotate.
   Shift means logical shift if done on an
   unsigned type, arithmetic shift if done on a signed type.
   The second operand is the number of bits to
   shift by; it need not be the same type as the first operand and result.
   Note that the result is undefined if the second operand is larger
   than the first operand's type size.  */
DEFTREECODE (LSHIFT_EXPR, "lshift_expr", '2', 2)
DEFTREECODE (RSHIFT_EXPR, "rshift_expr", '2', 2)
DEFTREECODE (LROTATE_EXPR, "lrotate_expr", '2', 2)
DEFTREECODE (RROTATE_EXPR, "rrotate_expr", '2', 2)

/* Bitwise operations.  Operands have same mode as result.  */
DEFTREECODE (BIT_IOR_EXPR, "bit_ior_expr", '2', 2)
DEFTREECODE (BIT_XOR_EXPR, "bit_xor_expr", '2', 2)
DEFTREECODE (BIT_AND_EXPR, "bit_and_expr", '2', 2)
DEFTREECODE (BIT_ANDTC_EXPR, "bit_andtc_expr", '2', 2)
DEFTREECODE (BIT_NOT_EXPR, "bit_not_expr", '1', 1)

/* ANDIF and ORIF allow the second operand not to be computed if the
   value of the expression is determined from the first operand.  AND,
   OR, and XOR always compute the second operand whether its value is
   needed or not (for side effects).  The operand may have
   BOOLEAN_TYPE or INTEGER_TYPE.  In either case, the argument will be
   either zero or one.  For example, a TRUTH_NOT_EXPR will never have
   an INTEGER_TYPE VAR_DECL as its argument; instead, a NE_EXPR will be
   used to compare the VAR_DECL to zero, thereby obtaining a node with
   value zero or one.  */
DEFTREECODE (TRUTH_ANDIF_EXPR, "truth_andif_expr", 'e', 2)
DEFTREECODE (TRUTH_ORIF_EXPR, "truth_orif_expr", 'e', 2)
DEFTREECODE (TRUTH_AND_EXPR, "truth_and_expr", 'e', 2)
DEFTREECODE (TRUTH_OR_EXPR, "truth_or_expr", 'e', 2)
DEFTREECODE (TRUTH_XOR_EXPR, "truth_xor_expr", 'e', 2)
DEFTREECODE (TRUTH_NOT_EXPR, "truth_not_expr", 'e', 1)

/* Relational operators.
   `EQ_EXPR' and `NE_EXPR' are allowed for any types.
   The others are allowed only for integer (or pointer or enumeral)
   or real types.
   In all cases the operands will have the same type,
   and the value is always the type used by the language for booleans.  */
DEFTREECODE (LT_EXPR, "lt_expr", '<', 2)
DEFTREECODE (LE_EXPR, "le_expr", '<', 2)
DEFTREECODE (GT_EXPR, "gt_expr", '<', 2)
DEFTREECODE (GE_EXPR, "ge_expr", '<', 2)
DEFTREECODE (EQ_EXPR, "eq_expr", '<', 2)
DEFTREECODE (NE_EXPR, "ne_expr", '<', 2)

/* Additional relational operators for floating point unordered.  */
DEFTREECODE (UNORDERED_EXPR, "unordered_expr", '<', 2)
DEFTREECODE (ORDERED_EXPR, "ordered_expr", '<', 2)

/* These are equivalent to unordered or ...  */
DEFTREECODE (UNLT_EXPR, "unlt_expr", '<', 2)
DEFTREECODE (UNLE_EXPR, "unle_expr", '<', 2)
DEFTREECODE (UNGT_EXPR, "ungt_expr", '<', 2)
DEFTREECODE (UNGE_EXPR, "unge_expr", '<', 2)
DEFTREECODE (UNEQ_EXPR, "uneq_expr", '<', 2)

/* Operations for Pascal sets.  Not used now.  */
DEFTREECODE (IN_EXPR, "in_expr", '2', 2)
DEFTREECODE (SET_LE_EXPR, "set_le_expr", '<', 2)
DEFTREECODE (CARD_EXPR, "card_expr", '1', 1)
DEFTREECODE (RANGE_EXPR, "range_expr", '2', 2)

/* Represents a conversion of type of a value.
   All conversions, including implicit ones, must be
   represented by CONVERT_EXPR or NOP_EXPR nodes.  */
DEFTREECODE (CONVERT_EXPR, "convert_expr", '1', 1)

/* Represents a conversion expected to require no code to be generated.  */
DEFTREECODE (NOP_EXPR, "nop_expr", '1', 1)

/* Value is same as argument, but guaranteed not an lvalue.  */
DEFTREECODE (NON_LVALUE_EXPR, "non_lvalue_expr", '1', 1)

/* Represents viewing something of one type as being of a second type.
   This corresponds to an "Unchecked Conversion" in Ada and roughly to
   the idiom *(type2 *)&X in C.  The only operand is the value to be
   viewed as being of another type.  It is undefined if the type of the
   input and of the expression have different sizes.

   This code may also be used within the LHS of a MODIFY_EXPR, in which
   case no actual data motion may occur.  TREE_ADDRESSABLE will be set in
   this case and GCC must abort if it could not do the operation without
   generating insns.  */
DEFTREECODE (VIEW_CONVERT_EXPR, "view_convert_expr", '1', 1)

/* Represents something we computed once and will use multiple times.
   First operand is that expression.  Second is the function decl
   in which the SAVE_EXPR was created.  The third operand is the RTL,
   nonzero only after the expression has been computed.  */
DEFTREECODE (SAVE_EXPR, "save_expr", 'e', 3)

/* For a UNSAVE_EXPR, operand 0 is the value to unsave.  By unsave, we
   mean that all _EXPRs such as TARGET_EXPRs, SAVE_EXPRs,
   CALL_EXPRs and RTL_EXPRs, that are protected
   from being evaluated more than once should be reset so that a new
   expand_expr call of this expr will cause those to be re-evaluated.
   This is useful when we want to reuse a tree in different places,
   but where we must re-expand.  */
DEFTREECODE (UNSAVE_EXPR, "unsave_expr", 'e', 1)

/* Represents something whose RTL has already been expanded as a
   sequence which should be emitted when this expression is expanded.
   The first operand is the RTL to emit.  It is the first of a chain
   of insns.  The second is the RTL expression for the result.  Any
   temporaries created during the building of the RTL_EXPR can be
   reused once the RTL_EXPR has been expanded, with the exception of
   the RTL_EXPR_RTL.  */
DEFTREECODE (RTL_EXPR, "rtl_expr", 'e', 2)

/* & in C.  Value is the address at which the operand's value resides.
   Operand may have any mode.  Result mode is Pmode.  */
DEFTREECODE (ADDR_EXPR, "addr_expr", 'e', 1)

/* Non-lvalue reference or pointer to an object.  */
DEFTREECODE (REFERENCE_EXPR, "reference_expr", 'e', 1)

/* Operand is a function constant; result is a function variable value
   of type EPmode.  Used only for languages that need static chains.  */
DEFTREECODE (ENTRY_VALUE_EXPR, "entry_value_expr", 'e', 1)

/* Operand0 is a function constant; result is part N of a function 
   descriptor of type ptr_mode.  */
DEFTREECODE (FDESC_EXPR, "fdesc_expr", 'e', 2)

/* Given two real or integer operands of the same type,
   returns a complex value of the corresponding complex type.  */
DEFTREECODE (COMPLEX_EXPR, "complex_expr", '2', 2)

/* Complex conjugate of operand.  Used only on complex types.  */
DEFTREECODE (CONJ_EXPR, "conj_expr", '1', 1)

/* Used only on an operand of complex type, these return
   a value of the corresponding component type.  */
DEFTREECODE (REALPART_EXPR, "realpart_expr", '1', 1)
DEFTREECODE (IMAGPART_EXPR, "imagpart_expr", '1', 1)

/* Nodes for ++ and -- in C.
   The second arg is how much to increment or decrement by.
   For a pointer, it would be the size of the object pointed to.  */
DEFTREECODE (PREDECREMENT_EXPR, "predecrement_expr", 'e', 2)
DEFTREECODE (PREINCREMENT_EXPR, "preincrement_expr", 'e', 2)
DEFTREECODE (POSTDECREMENT_EXPR, "postdecrement_expr", 'e', 2)
DEFTREECODE (POSTINCREMENT_EXPR, "postincrement_expr", 'e', 2)

/* Used to implement `va_arg'.  */
DEFTREECODE (VA_ARG_EXPR, "va_arg_expr", 'e', 1)

/* Evaluate operand 1.  If and only if an exception is thrown during
   the evaluation of operand 1, evaluate operand 2.

   This differs from WITH_CLEANUP_EXPR, in that operand 2 is never
   evaluated unless an exception is throw.  */
DEFTREECODE (TRY_CATCH_EXPR, "try_catch_expr", 'e', 2)

/* Evaluate the first operand.
   The second operand is a cleanup expression which is evaluated
   before an exit (normal, exception, or jump out) from this expression.

   Like a CLEANUP_POINT_EXPR/WITH_CLEANUP_EXPR combination, but those
   always copy the cleanup expression where needed.  In contrast,
   TRY_FINALLY_EXPR generates a jump to a cleanup subroutine.
   (At least conceptually; the optimizer could inline the cleanup
   subroutine in the same way it could inline normal subroutines.)
   TRY_FINALLY_EXPR should be used when the cleanup is actual statements
   in the source of the current function (which people might want to
   set breakpoints in).  */
DEFTREECODE (TRY_FINALLY_EXPR, "try_finally", 'e', 2)

/* Used internally for cleanups in the implementation of TRY_FINALLY_EXPR.
   (Specifically, it is created by expand_expr, not front-ends.)
   Operand 0 is the rtx for the start of the subroutine we need to call.
   Operand 1 is the rtx for a variable in which to store the address
   of where the subroutine should return to.  */
DEFTREECODE (GOTO_SUBROUTINE_EXPR, "goto_subroutine", 'e', 2)
/* These types of expressions have no useful value,
   and always have side effects.  */

/* A label definition, encapsulated as a statement.
   Operand 0 is the LABEL_DECL node for the label that appears here.
   The type should be void and the value should be ignored.  */
DEFTREECODE (LABEL_EXPR, "label_expr", 's', 1)

/* GOTO.  Operand 0 is a LABEL_DECL node or an expression.
   The type should be void and the value should be ignored.  */
DEFTREECODE (GOTO_EXPR, "goto_expr", 's', 1)

/* RETURN.  Evaluates operand 0, then returns from the current function.
   Presumably that operand is an assignment that stores into the
   RESULT_DECL that hold the value to be returned.
   The operand may be null.
   The type should be void and the value should be ignored.  */
DEFTREECODE (RETURN_EXPR, "return_expr", 's', 1)

/* Exit the inner most loop conditionally.  Operand 0 is the condition.
   The type should be void and the value should be ignored.  */
DEFTREECODE (EXIT_EXPR, "exit_expr", 's', 1)

/* A loop.  Operand 0 is the body of the loop.
   It must contain an EXIT_EXPR or is an infinite loop.
   The type should be void and the value should be ignored.  */
DEFTREECODE (LOOP_EXPR, "loop_expr", 's', 1)

/* A labeled block. Operand 0 is the label that will be generated to
   mark the end of the block.
   Operand 1 is the labeled block body.  */
DEFTREECODE (LABELED_BLOCK_EXPR, "labeled_block_expr", 'e', 2)

/* Exit a labeled block, possibly returning a value.  Operand 0 is a
   LABELED_BLOCK_EXPR to exit.  Operand 1 is the value to return. It
   may be left null.  */
DEFTREECODE (EXIT_BLOCK_EXPR, "exit_block_expr", 'e', 2)

/* Annotates a tree node (usually an expression) with source location
   information: a file name (EXPR_WFL_FILENAME);  a line number
   (EXPR_WFL_LINENO); and column number (EXPR_WFL_COLNO).  It is
   expanded as the contained node (EXPR_WFL_NODE);  a line note should
   be emitted first if EXPR_WFL_EMIT_LINE_NOTE.  
   The third operand is only used in the Java front-end, and will
   eventually be removed.  */
DEFTREECODE (EXPR_WITH_FILE_LOCATION, "expr_with_file_location", 'e', 3)

/* Switch expression.
   Operand 0 is the expression used to perform the branch,
   Operand 1 contains the case values. The way they're organized is
   front-end implementation defined.  */
DEFTREECODE (SWITCH_EXPR, "switch_expr", 'e', 2)

/* The exception object from the runtime.  */
DEFTREECODE (EXC_PTR_EXPR, "exc_ptr_expr", 'e', 0)

Local variables: