gcc/tree.def

   1 /* This file contains the definitions and documentation for the
   2    tree codes used in the GNU C compiler.
   3    Copyright (C) 1987, 1988, 1993 Free Software Foundation, Inc.
   4
   5 This file is part of GNU CC.
   6
   7 GNU CC is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 2, or (at your option)
  10 any later version.
  11
  12 GNU CC is distributed in the hope that it will be useful,
  13 but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 GNU General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GNU CC; see the file COPYING.  If not, write to
  19 the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */
  20
  21
  22 /* The third argument can be:
  23    "x" for an exceptional code (fits no category).
  24    "t" for a type object code.
  25    "b" for a lexical block.
  26    "c" for codes for constants.
  27    "d" for codes for declarations (also serving as variable refs).
  28    "r" for codes for references to storage.
  29    "<" for codes for comparison expressions.
  30    "1" for codes for unary arithmetic expressions.
  31    "2" for codes for binary arithmetic expressions.
  32    "s" for codes for expressions with inherent side effects.
  33    "e" for codes for other kinds of expressions.  */
  34
  35 /* For `r', `e', `<', `1', `2', `s' and `x' nodes,
  36    the 4th element is the number of argument slots to allocate.
  37    This determines the size of the tree node object.  */
  38
  39 /* Any erroneous construct is parsed into a node of this type.
  40    This type of node is accepted without complaint in all contexts
  41    by later parsing activities, to avoid multiple error messages
  42    for one error.
  43    No fields in these nodes are used except the TREE_CODE.  */
  44 DEFTREECODE (ERROR_MARK, "error_mark", "x", 0)
  45
  46 /* Used to represent a name (such as, in the DECL_NAME of a decl node).
  47    Internally it looks like a STRING_CST node.
  48    There is only one IDENTIFIER_NODE ever made for any particular name.
  49    Use `get_identifier' to get it (or create it, the first time).  */
  50 DEFTREECODE (IDENTIFIER_NODE, "identifier_node", "x", -1)
  51
  52 /* Used to hold information to identify an operator (or combination
  53    of two operators) considered as a `noun' rather than a `verb'.
  54    The first operand is encoded in the TREE_TYPE field.  */
  55 DEFTREECODE (OP_IDENTIFIER, "op_identifier", "x", 2)
  56
  57 /* Has the TREE_VALUE and TREE_PURPOSE fields.  */
  58 /* These nodes are made into lists by chaining through the
  59    TREE_CHAIN field.  The elements of the list live in the
  60    TREE_VALUE fields, while TREE_PURPOSE fields are occasionally
  61    used as well to get the effect of Lisp association lists.  */
  62 DEFTREECODE (TREE_LIST, "tree_list", "x", 2)
  63
  64 /* These nodes contain an array of tree nodes.  */
  65 DEFTREECODE (TREE_VEC, "tree_vec", "x", 2)
  66
  67 /* A symbol binding block.  These are arranged in a tree,
  68    where the BLOCK_SUBBLOCKS field contains a chain of subblocks
  69    chained through the BLOCK_CHAIN field.
  70    BLOCK_SUPERCONTEXT points to the parent block.
  71      For a block which represents the outermost scope of a function, it
  72      points to the FUNCTION_DECL node.
  73    BLOCK_VARS points to a chain of decl nodes.
  74    BLOCK_TYPE_TAGS points to a chain of types which have their own names.
  75    BLOCK_CHAIN points to the next BLOCK at the same level.
  76    BLOCK_ABSTRACT_ORIGIN points to the original (abstract) tree node which
  77    this block is an instance of, or else is NULL to indicate that this
  78    block is not an instance of anything else.  When non-NULL, the value
  79    could either point to another BLOCK node or it could point to a
  80    FUNCTION_DECL node (e.g. in the case of a block representing the
  81    outermost scope of a particular inlining of a function).
  82    BLOCK_ABSTRACT is non-zero if the block represents an abstract
  83    instance of a block (i.e. one which is nested within an abstract
  84    instance of a inline function. */
  85 DEFTREECODE (BLOCK, "block", "b", 0)
  86 \f
  87 /* Each data type is represented by a tree node whose code is one of
  88    the following:  */
  89 /* Each node that represents a data type has a component TYPE_SIZE
  90    containing a tree that is an expression for the size in bits.
  91    The TYPE_MODE contains the machine mode for values of this type.
  92    The TYPE_POINTER_TO field contains a type for a pointer to this type,
  93      or zero if no such has been created yet.
  94    The TYPE_NEXT_VARIANT field is used to chain together types
  95      that are variants made by type modifiers such as "const" and "volatile".
  96    The TYPE_MAIN_VARIANT field, in any member of such a chain,
  97      points to the start of the chain.
  98    The TYPE_NONCOPIED_PARTS field is a list specifying which parts
  99      of an object of this type should *not* be copied by assignment.
 100      The TREE_PURPOSE of each element is the offset of the part
 101      and the TREE_VALUE is the size in bits of the part.
 102    The TYPE_NAME field contains info on the name used in the program
 103      for this type (for GDB symbol table output).  It is either a
 104      TYPE_DECL node, for types that are typedefs, or an IDENTIFIER_NODE
 105      in the case of structs, unions or enums that are known with a tag,
 106      or zero for types that have no special name.
 107    The TYPE_CONTEXT for any sort of type which could have a name or
 108     which could have named members (e.g. tagged types in C/C++) will
 109     point to the node which represents the scope of the given type, or
 110     will be NULL_TREE if the type has "file scope".  For most types, this
 111     will point to a BLOCK node or a FUNCTION_DECL node, but it could also
 112     point to a FUNCTION_TYPE node (for types whose scope is limited to the
 113     formal parameter list of some function type specification) or it
 114     could point to a RECORD_TYPE, UNION_TYPE or QUAL_UNION_TYPE node
 115     (for C++ "member" types).
 116     For non-tagged-types, TYPE_CONTEXT need not be set to anything in
 117     particular, since any type which is of some type category  (e.g.
 118     an array type or a function type) which cannot either have a name
 119     itself or have named members doesn't really have a "scope" per se.
 120   The TREE_CHAIN field is used as a forward-references to names for
 121     ENUMERAL_TYPE, RECORD_TYPE, UNION_TYPE, and QUAL_UNION_TYPE nodes;
 122     see below.  */
 123
 124 DEFTREECODE (VOID_TYPE, "void_type", "t", 0)    /* The void type in C */
 125
 126 /* Integer types in all languages, including char in C.
 127    Also used for sub-ranges of other discrete types.
 128    Has components TYPE_MIN_VALUE, TYPE_MAX_VALUE (expressions, inclusive)
 129    and TYPE_PRECISION (number of bits used by this type).
 130    In the case of a subrange type in Pascal, the TREE_TYPE
 131    of this will point at the supertype (another INTEGER_TYPE,
 132    or an ENUMERAL_TYPE, CHAR_TYPE, or BOOLEAN_TYPE).
 133    Otherwise, the TREE_TYPE is zero.  */
 134 DEFTREECODE (INTEGER_TYPE, "integer_type", "t", 0)
 135
 136 /* C's float and double.  Different floating types are distinguished
 137    by machine mode and by the TYPE_SIZE and the TYPE_PRECISION.  */
 138 DEFTREECODE (REAL_TYPE, "real_type", "t", 0)
 139
 140 /* Complex number types.  The TREE_TYPE field is the data type
 141    of the real and imaginary parts.  */
 142 DEFTREECODE (COMPLEX_TYPE, "complex_type", "t", 0)
 143
 144 /* C enums.  The type node looks just like an INTEGER_TYPE node.
 145    The symbols for the values of the enum type are defined by
 146    CONST_DECL nodes, but the type does not point to them;
 147    however, the TYPE_VALUES is a list in which each element's TREE_PURPOSE
 148    is a name and the TREE_VALUE is the value (an INTEGER_CST node).  */
 149 /* A forward reference `enum foo' when no enum named foo is defined yet
 150    has zero (a null pointer) in its TYPE_SIZE.  The tag name is in
 151    the TYPE_NAME field.  If the type is later defined, the normal
 152    fields are filled in.
 153    RECORD_TYPE, UNION_TYPE, and QUAL_UNION_TYPE forward refs are
 154    treated similarly.  */
 155 DEFTREECODE (ENUMERAL_TYPE, "enumeral_type", "t", 0)
 156
 157 /* Pascal's boolean type (true or false are the only values);
 158    no special fields needed.  */
 159 DEFTREECODE (BOOLEAN_TYPE, "boolean_type", "t", 0)
 160
 161 /* CHAR in Pascal; not used in C.
 162    No special fields needed.  */
 163 DEFTREECODE (CHAR_TYPE, "char_type", "t", 0)
 164
 165 /* All pointer-to-x types have code POINTER_TYPE.
 166    The TREE_TYPE points to the node for the type pointed to.  */
 167 DEFTREECODE (POINTER_TYPE, "pointer_type", "t", 0)
 168
 169 /* An offset is a pointer relative to an object.
 170    The TREE_TYPE field is the type of the object at the offset.
 171    The TYPE_OFFSET_BASETYPE points to the node for the type of object
 172    that the offset is relative to.  */
 173 DEFTREECODE (OFFSET_TYPE, "offset_type", "t", 0)
 174
 175 /* A reference is like a pointer except that it is coerced
 176    automatically to the value it points to.  Used in C++.  */
 177 DEFTREECODE (REFERENCE_TYPE, "reference_type", "t", 0)
 178
 179 /* METHOD_TYPE is the type of a function which takes an extra first
 180    argument for "self", which is not present in the declared argument list.
 181    The TREE_TYPE is the return type of the method.  The TYPE_METHOD_BASETYPE
 182    is the type of "self".  TYPE_ARG_TYPES is the real argument list, which
 183    includes the hidden argument for "self".  */
 184 DEFTREECODE (METHOD_TYPE, "method_type", "t", 0)
 185
 186 /* Used for Pascal; details not determined right now.  */
 187 DEFTREECODE (FILE_TYPE, "file_type", "t", 0)
 188
 189 /* Types of arrays.  Special fields:
 190    TREE_TYPE              Type of an array element.
 191    TYPE_DOMAIN            Type to index by.
 192                             Its range of values specifies the array length.
 193    TYPE_SEP               Expression for units from one elt to the next.
 194    TYPE_SEP_UNIT          Number of bits in a unit for previous.
 195  The field TYPE_POINTER_TO (TREE_TYPE (array_type)) is always nonzero
 196  and holds the type to coerce a value of that array type to in C.
 197  TYPE_STRING_FLAG indicates a string (in contrast to an array of chars)
 198  in languages (such as Chill) that make a distinction. */
 199 /* Array types in C or Pascal */
 200 DEFTREECODE (ARRAY_TYPE, "array_type", "t", 0)
 201
 202 /* Types of sets for Pascal.  Special fields are the same as
 203    in an array type.  The target type is always a boolean type.
 204    Used for both bitstrings and powersets in Chill;
 205    TYPE_STRING_FLAG indicates a bitstring. */
 206 DEFTREECODE (SET_TYPE, "set_type", "t", 0)
 207
 208 /* Struct in C, or record in Pascal.  */
 209 /* Special fields:
 210    TYPE_FIELDS  chain of FIELD_DECLs for the fields of the struct.
 211    A few may need to be added for Pascal.  */
 212 /* See the comment above, before ENUMERAL_TYPE, for how
 213    forward references to struct tags are handled in C.  */
 214 DEFTREECODE (RECORD_TYPE, "record_type", "t", 0)
 215
 216 /* Union in C.  Like a struct, except that the offsets of the fields
 217    will all be zero.  */
 218 /* See the comment above, before ENUMERAL_TYPE, for how
 219    forward references to union tags are handled in C.  */
 220 DEFTREECODE (UNION_TYPE, "union_type", "t", 0)  /* C union type */
 221
 222 /* Similar to UNION_TYPE, except that the expressions in DECL_QUALIFIER
 223    in each FIELD_DECL determine what the union contains.  The first
 224    field whose DECL_QUALIFIER expression is true is deemed to occupy
 225    the union.  */
 226 DEFTREECODE (QUAL_UNION_TYPE, "qual_union_type", "t", 0)
 227
 228 /* Type of functions.  Special fields:
 229    TREE_TYPE                type of value returned.
 230    TYPE_ARG_TYPES      list of types of arguments expected.
 231         this list is made of TREE_LIST nodes.
 232    Types of "Procedures" in languages where they are different from functions
 233    have code FUNCTION_TYPE also, but then TREE_TYPE is zero or void type.  */
 234 DEFTREECODE (FUNCTION_TYPE, "function_type", "t", 0)
 235
 236 /* This is a language-specific kind of type.
 237    Its meaning is defined by the language front end.
 238    layout_type does not know how to lay this out,
 239    so the front-end must do so manually.  */
 240 DEFTREECODE (LANG_TYPE, "lang_type", "t", 0)
 241 \f
 242 /* Expressions */
 243
 244 /* First, the constants.  */
 245
 246 /* Contents are in TREE_INT_CST_LOW and TREE_INT_CST_HIGH fields,
 247    32 bits each, giving us a 64 bit constant capability.
 248    Note: constants of type char in Pascal are INTEGER_CST,
 249    and so are pointer constants such as nil in Pascal or NULL in C.
 250    `(int *) 1' in C also results in an INTEGER_CST.  */
 251 DEFTREECODE (INTEGER_CST, "integer_cst", "c", 2)
 252
 253 /* Contents are in TREE_REAL_CST field.  Also there is TREE_CST_RTL.  */
 254 DEFTREECODE (REAL_CST, "real_cst", "c", 3)
 255
 256 /* Contents are in TREE_REALPART and TREE_IMAGPART fields,
 257    whose contents are other constant nodes.
 258    Also there is TREE_CST_RTL.  */
 259 DEFTREECODE (COMPLEX_CST, "complex_cst", "c", 3)
 260
 261 /* Contents are TREE_STRING_LENGTH and TREE_STRING_POINTER fields.
 262    Also there is TREE_CST_RTL.  */
 263 DEFTREECODE (STRING_CST, "string_cst", "c", 3)
 264
 265 /* Declarations.  All references to names are represented as ..._DECL nodes.
 266    The decls in one binding context are chained through the TREE_CHAIN field.
 267    Each DECL has a DECL_NAME field which contains an IDENTIFIER_NODE.
 268     (Some decls, most often labels, may have zero as the DECL_NAME).
 269    DECL_CONTEXT points to the node representing the context in which
 270     this declaration has its scope.  For FIELD_DECLs, this is the
 271     RECORD_TYPE, UNION_TYPE, or QUAL_UNION_TYPE node that the field
 272     is a member of.  For VAR_DECL, PARM_DECL, FUNCTION_DECL, LABEL_DECL,
 273     and CONST_DECL nodes, this points to the FUNCTION_DECL for the
 274     containing function, or else yields NULL_TREE if the given decl
 275     has "file scope".
 276    DECL_ABSTRACT_ORIGIN, if non-NULL, points to the original (abstract)
 277     ..._DECL node of which this decl is an (inlined or template expanded)
 278     instance.
 279    The TREE_TYPE field holds the data type of the object, when relevant.
 280     LABEL_DECLs have no data type.  For TYPE_DECL, the TREE_TYPE field
 281     contents are the type whose name is being declared.
 282    The DECL_ALIGN, DECL_SIZE,
 283     and DECL_MODE fields exist in decl nodes just as in type nodes.
 284     They are unused in LABEL_DECL, TYPE_DECL and CONST_DECL nodes.
 285
 286    DECL_OFFSET holds an integer number of bits offset for the location.
 287    DECL_VOFFSET holds an expression for a variable offset; it is
 288    to be multiplied by DECL_VOFFSET_UNIT (an integer).
 289    These fields are relevant only in FIELD_DECLs and PARM_DECLs.
 290
 291    DECL_INITIAL holds the value to initialize a variable to,
 292    or the value of a constant.  For a function, it holds the body
 293    (a node of type BLOCK representing the function's binding contour
 294    and whose body contains the function's statements.)  For a LABEL_DECL
 295    in C, it is a flag, nonzero if the label's definition has been seen.
 296
 297    PARM_DECLs use a special field:
 298    DECL_ARG_TYPE is the type in which the argument is actually
 299     passed, which may be different from its type within the function.
 300
 301    FUNCTION_DECLs use four special fields:
 302    DECL_ARGUMENTS holds a chain of PARM_DECL nodes for the arguments.
 303    DECL_RESULT holds a RESULT_DECL node for the value of a function,
 304     or it is 0 for a function that returns no value.
 305     (C functions returning void have zero here.)
 306    DECL_RESULT_TYPE holds the type in which the result is actually
 307     returned.  This is usually the same as the type of DECL_RESULT,
 308     but (1) it may be a wider integer type and
 309     (2) it remains valid, for the sake of inlining, even after the
 310     function's compilation is done.
 311    DECL_FUNCTION_CODE is a code number that is nonzero for
 312     built-in functions.  Its value is an enum built_in_function
 313     that says which built-in function it is.
 314
 315    DECL_SOURCE_FILE holds a filename string and DECL_SOURCE_LINE
 316    holds a line number.  In some cases these can be the location of
 317    a reference, if no definition has been seen.
 318
 319    DECL_ABSTRACT is non-zero if the decl represents an abstract instance
 320    of a decl (i.e. one which is nested within an abstract instance of a
 321    inline function.  */
 322
 323 DEFTREECODE (FUNCTION_DECL, "function_decl", "d", 0)
 324 DEFTREECODE (LABEL_DECL, "label_decl", "d", 0)
 325 DEFTREECODE (CONST_DECL, "const_decl", "d", 0)
 326 DEFTREECODE (TYPE_DECL, "type_decl", "d", 0)
 327 DEFTREECODE (VAR_DECL, "var_decl", "d", 0)
 328 DEFTREECODE (PARM_DECL, "parm_decl", "d", 0)
 329 DEFTREECODE (RESULT_DECL, "result_decl", "d", 0)
 330 DEFTREECODE (FIELD_DECL, "field_decl", "d", 0)
 331 \f
 332 /* References to storage.  */
 333
 334 /* Value is structure or union component.
 335    Operand 0 is the structure or union (an expression);
 336    operand 1 is the field (a node of type FIELD_DECL).  */
 337 DEFTREECODE (COMPONENT_REF, "component_ref", "r", 2)
 338
 339 /* Reference to a group of bits within an object.  Similar to COMPONENT_REF
 340    except the position is given explicitly rather than via a FIELD_DECL.
 341    Operand 0 is the structure or union expression;
 342    operand 1 is a tree giving the number of bits being referenced;
 343    operand 2 is a tree giving the position of the first referenced bit.
 344    The field can be either a signed or unsigned field;
 345    TREE_UNSIGNED says which.  */
 346 DEFTREECODE (BIT_FIELD_REF, "bit_field_ref", "r", 3)
 347
 348 /* C unary `*' or Pascal `^'.  One operand, an expression for a pointer.  */
 349 DEFTREECODE (INDIRECT_REF, "indirect_ref", "r", 1)
 350
 351 /* Reference to the contents of an offset
 352    (a value whose type is an OFFSET_TYPE).
 353    Operand 0 is the object within which the offset is taken.
 354    Operand 1 is the offset.  */
 355 DEFTREECODE (OFFSET_REF, "offset_ref", "r", 2)
 356
 357 /* Pascal `^` on a file.  One operand, an expression for the file.  */
 358 DEFTREECODE (BUFFER_REF, "buffer_ref", "r", 1)
 359
 360 /* Array indexing in languages other than C.
 361    Operand 0 is the array; operand 1 is a list of indices
 362    stored as a chain of TREE_LIST nodes.  */
 363 DEFTREECODE (ARRAY_REF, "array_ref", "r", 2)
 364
 365 /* Constructor: return an aggregate value made from specified components.
 366    In C, this is used only for structure and array initializers.
 367    The first "operand" is really a pointer to the RTL,
 368    for constant constructors only.
 369    The second operand is a list of component values
 370    made out of a chain of TREE_LIST nodes.  */
 371 DEFTREECODE (CONSTRUCTOR, "constructor", "e", 2)
 372
 373 /* The expression types are mostly straightforward,
 374    with the fourth argument of DEFTREECODE saying
 375    how many operands there are.
 376    Unless otherwise specified, the operands are expressions.  */
 377
 378 /* Contains two expressions to compute, one followed by the other.
 379    the first value is ignored.  The second one's value is used.  */
 380 DEFTREECODE (COMPOUND_EXPR, "compound_expr", "e", 2)
 381
 382 /* Assignment expression.  Operand 0 is the what to set; 1, the new value.  */
 383 DEFTREECODE (MODIFY_EXPR, "modify_expr", "e", 2)
 384
 385 /* Initialization expression.  Operand 0 is the variable to initialize;
 386    Operand 1 is the initializer.  */
 387 DEFTREECODE (INIT_EXPR, "init_expr", "e", 2)
 388
 389 /* For TARGET_EXPR, operand 0 is the target of an initialization,
 390    operand 1 is the initializer for the target,
 391    and operand 2 is the cleanup for this node, if any.  */
 392 DEFTREECODE (TARGET_EXPR, "target_expr", "e", 3)
 393
 394 /* Conditional expression ( ... ? ... : ...  in C).
 395    Operand 0 is the condition.
 396    Operand 1 is the then-value.
 397    Operand 2 is the else-value.  */
 398 DEFTREECODE (COND_EXPR, "cond_expr", "e", 3)
 399
 400 /* Declare local variables, including making RTL and allocating space.
 401    Operand 0 is a chain of VAR_DECL nodes for the variables.
 402    Operand 1 is the body, the expression to be computed using
 403    the variables.  The value of operand 1 becomes that of the BIND_EXPR.
 404    Operand 2 is the BLOCK that corresponds to these bindings
 405    for debugging purposes.  If this BIND_EXPR is actually expanded,
 406    that sets the TREE_USED flag in the BLOCK.
 407
 408    The BIND_EXPR is not responsible for informing parsers
 409    about these variables.  If the body is coming from the input file,
 410    then the code that creates the BIND_EXPR is also responsible for
 411    informing the parser of the variables.
 412
 413    If the BIND_EXPR is ever expanded, its TREE_USED flag is set.
 414    This tells the code for debugging symbol tables not to ignore the BIND_EXPR.
 415    If the BIND_EXPR should be output for debugging but will not be expanded,
 416    set the TREE_USED flag by hand.
 417
 418    In order for the BIND_EXPR to be known at all, the code that creates it
 419    must also install it as a subblock in the tree of BLOCK
 420    nodes for the function.  */
 421 DEFTREECODE (BIND_EXPR, "bind_expr", "e", 3)
 422
 423 /* Function call.  Operand 0 is the function.
 424    Operand 1 is the argument list, a list of expressions
 425    made out of a chain of TREE_LIST nodes.
 426    There is no operand 2.  That slot is used for the
 427    CALL_EXPR_RTL macro (see preexpand_calls).  */
 428 DEFTREECODE (CALL_EXPR, "call_expr", "e", 3)
 429
 430 /* Call a method.  Operand 0 is the method, whose type is a METHOD_TYPE.
 431    Operand 1 is the expression for "self".
 432    Operand 2 is the list of explicit arguments.  */
 433 DEFTREECODE (METHOD_CALL_EXPR, "method_call_expr", "e", 4)
 434
 435 /* Specify a value to compute along with its corresponding cleanup.
 436    Operand 0 argument is an expression whose value needs a cleanup.
 437    Operand 1 is an RTL_EXPR which will eventually represent that value.
 438    Operand 2 is the cleanup expression for the object.
 439      The RTL_EXPR is used in this expression, which is how the expression
 440      manages to act on the proper value.
 441    The cleanup is executed by the first enclosing CLEANUP_POINT_EXPR, if
 442    it exists, otherwise it is the responsibility of the caller to manually
 443    call expand_cleanups_to, as needed.  */
 444 DEFTREECODE (WITH_CLEANUP_EXPR, "with_cleanup_expr", "e", 3)
 445
 446 /* Specify a cleanup point.
 447    Operand 0 is the expression that has cleanups that we want ensure are
 448    cleaned up.  */
 449 DEFTREECODE (CLEANUP_POINT_EXPR, "cleanup_point_expr", "e", 1)
 450
 451 /* The following two codes are used in languages that have types where
 452    the position and/or sizes of fields vary from object to object of the
 453    same type, i.e., where some other field in the object contains a value
 454    that is used in the computation of another field's offset or size.
 455
 456    For example, a record type with a discriminant in Ada is such a type.
 457    This mechanism is also used to create "fat pointers" for unconstrained
 458    array types in Ada; the fat pointer is a structure one of whose fields is
 459    a pointer to the actual array type and the other field is a pointer to a
 460    template, which is a structure containing the bounds of the array.  The
 461    bounds in the type pointed to by the first field in the fat pointer refer
 462    to the values in the template.
 463
 464    These "self-references" are doing using a PLACEHOLDER_EXPR.  This is a
 465    node that will later be replaced with the object being referenced.  Its type
 466    is that of the object and selects which object to use from a chain of
 467    references (see below).
 468
 469    When we wish to evaluate a size or offset, we check it is contains a
 470    placeholder.  If it does, we construct a WITH_RECORD_EXPR that contains
 471    both the expression we wish to evaluate and an expression within which the
 472    object may be found.  The latter expression is the object itself in
 473    the simple case of an Ada record with discriminant, but it can be the
 474    array in the case of an unconstrained array.
 475
 476    In the latter case, we need the fat pointer, because the bounds of the
 477    array can only be accessed from it.  However, we rely here on the fact that
 478    the expression for the array contains the dereference of the fat pointer
 479    that obtained the array pointer.
 480
 481    Accordingly, when looking for the object to substitute in place of
 482    a PLACEHOLDER_EXPR, we look down the first operand of the expression
 483    passed as the second operand to WITH_RECORD_EXPR until we find something
 484    of the desired type or reach a constant.  */
 485
 486 /* Denotes a record to later be supplied with a WITH_RECORD_EXPR when
 487    evaluating this expression.  The type of this expression is used to
 488    find the record to replace it.  */
 489 DEFTREECODE (PLACEHOLDER_EXPR, "placeholder_expr", "x", 0)
 490
 491 /* Provide an expression that references a record to be used in place
 492    of a PLACEHOLDER_EXPR.  The record to be used is the record within
 493    operand 1 that has the same type as the PLACEHOLDER_EXPR in
 494    operand 0.  */
 495 DEFTREECODE (WITH_RECORD_EXPR, "with_record_expr", "e", 2)
 496
 497 /* Simple arithmetic.  Operands must have the same machine mode
 498    and the value shares that mode.  */
 499 DEFTREECODE (PLUS_EXPR, "plus_expr", "2", 2)
 500 DEFTREECODE (MINUS_EXPR, "minus_expr", "2", 2)
 501 DEFTREECODE (MULT_EXPR, "mult_expr", "2", 2)
 502
 503 /* Division for integer result that rounds the quotient toward zero.  */
 504 /* Operands must have the same machine mode.
 505    In principle they may be real, but that is not currently supported.
 506    The result is always fixed point, and it has the same type as the
 507    operands if they are fixed point.   */
 508 DEFTREECODE (TRUNC_DIV_EXPR, "trunc_div_expr", "2", 2)
 509
 510 /* Division for integer result that rounds the quotient toward infinity.  */
 511 DEFTREECODE (CEIL_DIV_EXPR, "ceil_div_expr", "2", 2)
 512
 513 /* Division for integer result that rounds toward minus infinity.  */
 514 DEFTREECODE (FLOOR_DIV_EXPR, "floor_div_expr", "2", 2)
 515
 516 /* Division for integer result that rounds toward nearest integer.  */
 517 DEFTREECODE (ROUND_DIV_EXPR, "round_div_expr", "2", 2)
 518
 519 /* Four kinds of remainder that go with the four kinds of division.  */
 520 DEFTREECODE (TRUNC_MOD_EXPR, "trunc_mod_expr", "2", 2)
 521 DEFTREECODE (CEIL_MOD_EXPR, "ceil_mod_expr", "2", 2)
 522 DEFTREECODE (FLOOR_MOD_EXPR, "floor_mod_expr", "2", 2)
 523 DEFTREECODE (ROUND_MOD_EXPR, "round_mod_expr", "2", 2)
 524
 525 /* Division for real result.  The two operands must have the same type.
 526    In principle they could be integers, but currently only real
 527    operands are supported.  The result must have the same type
 528    as the operands.  */
 529 DEFTREECODE (RDIV_EXPR, "rdiv_expr", "2", 2)
 530
 531 /* Division which is not supposed to need rounding.
 532    Used for pointer subtraction in C.  */
 533 DEFTREECODE (EXACT_DIV_EXPR, "exact_div_expr", "2", 2)
 534
 535 /* Conversion of real to fixed point: four ways to round,
 536    like the four ways to divide.
 537    CONVERT_EXPR can also be used to convert a real to an integer,
 538    and that is what is used in languages that do not have ways of
 539    specifying which of these is wanted.  Maybe these are not needed.  */
 540 DEFTREECODE (FIX_TRUNC_EXPR, "fix_trunc_expr", "1", 1)
 541 DEFTREECODE (FIX_CEIL_EXPR, "fix_ceil_expr", "1", 1)
 542 DEFTREECODE (FIX_FLOOR_EXPR, "fix_floor_expr", "1", 1)
 543 DEFTREECODE (FIX_ROUND_EXPR, "fix_round_expr", "1", 1)
 544
 545 /* Conversion of an integer to a real.  */
 546 DEFTREECODE (FLOAT_EXPR, "float_expr", "1", 1)
 547
 548 /* Exponentiation.  Operands may have any types;
 549    constraints on value type are not known yet.  */
 550 DEFTREECODE (EXPON_EXPR, "expon_expr", "2", 2)
 551
 552 /* Unary negation.  Value has same type as operand.  */
 553 DEFTREECODE (NEGATE_EXPR, "negate_expr", "1", 1)
 554
 555 DEFTREECODE (MIN_EXPR, "min_expr", "2", 2)
 556 DEFTREECODE (MAX_EXPR, "max_expr", "2", 2)
 557 DEFTREECODE (ABS_EXPR, "abs_expr", "1", 1)
 558 DEFTREECODE (FFS_EXPR, "ffs_expr", "1", 1)
 559
 560 /* Shift operations for shift and rotate.
 561    Shift is supposed to mean logical shift if done on an
 562    unsigned type, arithmetic shift on a signed type.
 563    The second operand is the number of bits to
 564    shift by, and must always have mode SImode.
 565    The result has the same mode as the first operand.  */
 566 DEFTREECODE (LSHIFT_EXPR, "alshift_expr", "2", 2)
 567 DEFTREECODE (RSHIFT_EXPR, "arshift_expr", "2", 2)
 568 DEFTREECODE (LROTATE_EXPR, "lrotate_expr", "2", 2)
 569 DEFTREECODE (RROTATE_EXPR, "rrotate_expr", "2", 2)
 570
 571 /* Bitwise operations.  Operands have same mode as result.  */
 572 DEFTREECODE (BIT_IOR_EXPR, "bit_ior_expr", "2", 2)
 573 DEFTREECODE (BIT_XOR_EXPR, "bit_xor_expr", "2", 2)
 574 DEFTREECODE (BIT_AND_EXPR, "bit_and_expr", "2", 2)
 575 DEFTREECODE (BIT_ANDTC_EXPR, "bit_andtc_expr", "2", 2)
 576 DEFTREECODE (BIT_NOT_EXPR, "bit_not_expr", "1", 1)
 577
 578 /* Combination of boolean values or of integers considered only
 579    as zero or nonzero.  ANDIF and ORIF allow the second operand
 580    not to be computed if the value of the expression is determined
 581    from the first operand.  AND, OR, and XOR always compute the second
 582    operand whether its value is needed or not (for side effects).  */
 583 DEFTREECODE (TRUTH_ANDIF_EXPR, "truth_andif_expr", "e", 2)
 584 DEFTREECODE (TRUTH_ORIF_EXPR, "truth_orif_expr", "e", 2)
 585 DEFTREECODE (TRUTH_AND_EXPR, "truth_and_expr", "e", 2)
 586 DEFTREECODE (TRUTH_OR_EXPR, "truth_or_expr", "e", 2)
 587 DEFTREECODE (TRUTH_XOR_EXPR, "truth_xor_expr", "e", 2)
 588 DEFTREECODE (TRUTH_NOT_EXPR, "truth_not_expr", "e", 1)
 589
 590 /* Relational operators.
 591    `EQ_EXPR' and `NE_EXPR' are allowed for any types.
 592    The others are allowed only for integer (or pointer or enumeral)
 593    or real types.
 594    In all cases the operands will have the same type,
 595    and the value is always the type used by the language for booleans.  */
 596 DEFTREECODE (LT_EXPR, "lt_expr", "<", 2)
 597 DEFTREECODE (LE_EXPR, "le_expr", "<", 2)
 598 DEFTREECODE (GT_EXPR, "gt_expr", "<", 2)
 599 DEFTREECODE (GE_EXPR, "ge_expr", "<", 2)
 600 DEFTREECODE (EQ_EXPR, "eq_expr", "<", 2)
 601 DEFTREECODE (NE_EXPR, "ne_expr", "<", 2)
 602
 603 /* Operations for Pascal sets.  Not used now.  */
 604 DEFTREECODE (IN_EXPR, "in_expr", "2", 2)
 605 DEFTREECODE (SET_LE_EXPR, "set_le_expr", "<", 2)
 606 DEFTREECODE (CARD_EXPR, "card_expr", "1", 1)
 607 DEFTREECODE (RANGE_EXPR, "range_expr", "2", 2)
 608
 609 /* Represents a conversion of type of a value.
 610    All conversions, including implicit ones, must be
 611    represented by CONVERT_EXPR nodes.  */
 612 DEFTREECODE (CONVERT_EXPR, "convert_expr", "1", 1)
 613
 614 /* Represents a conversion expected to require no code to be generated.  */
 615 DEFTREECODE (NOP_EXPR, "nop_expr", "1", 1)
 616
 617 /* Value is same as argument, but guaranteed not an lvalue.  */
 618 DEFTREECODE (NON_LVALUE_EXPR, "non_lvalue_expr", "1", 1)
 619
 620 /* Represents something we computed once and will use multiple times.
 621    First operand is that expression.  Second is the function decl
 622    in which the SAVE_EXPR was created.  The third operand is the RTL,
 623    nonzero only after the expression has been computed.  */
 624 DEFTREECODE (SAVE_EXPR, "save_expr", "e", 3)
 625
 626 /* Represents something whose RTL has already been expanded
 627    as a sequence which should be emitted when this expression is expanded.
 628    The first operand is the RTL to emit.  It is the first of a chain of insns.
 629    The second is the RTL expression for the result.  */
 630 DEFTREECODE (RTL_EXPR, "rtl_expr", "e", 2)
 631
 632 /* & in C.  Value is the address at which the operand's value resides.
 633    Operand may have any mode.  Result mode is Pmode.  */
 634 DEFTREECODE (ADDR_EXPR, "addr_expr", "e", 1)
 635
 636 /* Non-lvalue reference or pointer to an object.  */
 637 DEFTREECODE (REFERENCE_EXPR, "reference_expr", "e", 1)
 638
 639 /* Operand is a function constant; result is a function variable value
 640    of typeEPmode.  Used only for languages that need static chains.  */
 641 DEFTREECODE (ENTRY_VALUE_EXPR, "entry_value_expr", "e", 1)
 642
 643 /* Given two real or integer operands of the same type,
 644    returns a complex value of the corresponding complex type.  */
 645 DEFTREECODE (COMPLEX_EXPR, "complex_expr", "2", 2)
 646
 647 /* Complex conjugate of operand.  Used only on complex types.
 648    The value has the same type as the operand.  */
 649 DEFTREECODE (CONJ_EXPR, "conj_expr", "1", 1)
 650
 651 /* Used only on an operand of complex type, these return
 652    a value of the corresponding component type.  */
 653 DEFTREECODE (REALPART_EXPR, "realpart_expr", "1", 1)
 654 DEFTREECODE (IMAGPART_EXPR, "imagpart_expr", "1", 1)
 655
 656 /* Nodes for ++ and -- in C.
 657    The second arg is how much to increment or decrement by.
 658    For a pointer, it would be the size of the object pointed to.  */
 659 DEFTREECODE (PREDECREMENT_EXPR, "predecrement_expr", "e", 2)
 660 DEFTREECODE (PREINCREMENT_EXPR, "preincrement_expr", "e", 2)
 661 DEFTREECODE (POSTDECREMENT_EXPR, "postdecrement_expr", "e", 2)
 662 DEFTREECODE (POSTINCREMENT_EXPR, "postincrement_expr", "e", 2)
 663 \f
 664 /* These types of expressions have no useful value,
 665    and always have side effects.  */
 666
 667 /* A label definition, encapsulated as a statement.
 668    Operand 0 is the LABEL_DECL node for the label that appears here.
 669    The type should be void and the value should be ignored.  */
 670 DEFTREECODE (LABEL_EXPR, "label_expr", "s", 1)
 671
 672 /* GOTO.  Operand 0 is a LABEL_DECL node.
 673    The type should be void and the value should be ignored.  */
 674 DEFTREECODE (GOTO_EXPR, "goto_expr", "s", 1)
 675
 676 /* RETURN.  Evaluates operand 0, then returns from the current function.
 677    Presumably that operand is an assignment that stores into the
 678    RESULT_DECL that hold the value to be returned.
 679    The operand may be null.
 680    The type should be void and the value should be ignored.  */
 681 DEFTREECODE (RETURN_EXPR, "return_expr", "s", 1)
 682
 683 /* Exit the inner most loop conditionally.  Operand 0 is the condition.
 684    The type should be void and the value should be ignored.  */
 685 DEFTREECODE (EXIT_EXPR, "exit_expr", "s", 1)
 686
 687 /* A loop.  Operand 0 is the body of the loop.
 688    It must contain an EXIT_EXPR or is an infinite loop.
 689    The type should be void and the value should be ignored.  */
 690 DEFTREECODE (LOOP_EXPR, "loop_expr", "s", 1)
 691
 692 /*
 693 Local variables:
 694 mode:c
 695 version-control: t
 696 End:
 697 */