1 /* Definitions for code generation pass of GNU compiler.
2 Copyright (C) 1987, 1991 Free Software Foundation, Inc.
4 This file is part of GNU CC.
6 GNU CC is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 2, or (at your option)
11 GNU CC is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with GNU CC; see the file COPYING. If not, write to
18 the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */
27 /* The default branch cost is 1. */
32 /* Macros to access the slots of a QUEUED rtx.
33 Here rather than in rtl.h because only the expansion pass
34 should ever encounter a QUEUED. */
36 /* The variable for which an increment is queued. */
37 #define QUEUED_VAR(P) XEXP (P, 0)
38 /* If the increment has been emitted, this is the insn
39 that does the increment. It is zero before the increment is emitted. */
40 #define QUEUED_INSN(P) XEXP (P, 1)
41 /* If a pre-increment copy has been generated, this is the copy
42 (it is a temporary reg). Zero if no copy made yet. */
43 #define QUEUED_COPY(P) XEXP (P, 2)
44 /* This is the body to use for the insn to do the increment.
45 It is used to emit the increment. */
46 #define QUEUED_BODY(P) XEXP (P, 3)
47 /* Next QUEUED in the queue. */
48 #define QUEUED_NEXT(P) XEXP (P, 4)
50 /* This is the 4th arg to `expand_expr'.
51 EXPAND_SUM means it is ok to return a PLUS rtx or MULT rtx.
52 EXPAND_INITIALIZER is similar but also record any labels on forced_labels.
53 EXPAND_CONST_ADDRESS means it is ok to return a MEM whose address
54 is a constant that is not a legitimate address. */
55 enum expand_modifier {EXPAND_NORMAL, EXPAND_SUM,
56 EXPAND_CONST_ADDRESS, EXPAND_INITIALIZER};
58 /* List of labels that must never be deleted. */
59 extern rtx forced_labels;
61 /* List (chain of EXPR_LISTs) of pseudo-regs of SAVE_EXPRs.
62 So we can mark them all live at the end of the function, if stupid. */
63 extern rtx save_expr_regs;
65 extern int current_function_calls_alloca;
66 extern int current_function_outgoing_args_size;
68 /* This is the offset from the arg pointer to the place where the first
69 anonymous arg can be found, if there is one. */
70 extern rtx current_function_arg_offset_rtx;
72 /* This is nonzero if the current function uses the constant pool. */
73 extern int current_function_uses_const_pool;
75 /* This is nonzero if the current function uses pic_offset_table_rtx. */
76 extern int current_function_uses_pic_offset_table;
78 /* The arg pointer hard register, or the pseudo into which it was copied. */
79 extern rtx current_function_internal_arg_pointer;
81 /* Nonzero means stack pops must not be deferred, and deferred stack
82 pops must not be output. It is nonzero inside a function call,
83 inside a conditional expression, inside a statement expression,
84 and in other cases as well. */
85 extern int inhibit_defer_pop;
87 /* Number of function calls seen so far in current function. */
89 extern int function_call_count;
91 /* RTX for stack slot that holds the current handler for nonlocal gotos.
92 Zero when function does not have nonlocal labels. */
94 extern rtx nonlocal_goto_handler_slot;
96 /* RTX for stack slot that holds the stack pointer value to restore
98 Zero when function does not have nonlocal labels. */
100 extern rtx nonlocal_goto_stack_level;
102 /* List (chain of TREE_LIST) of LABEL_DECLs for all nonlocal labels
103 (labels to which there can be nonlocal gotos from nested functions)
106 #ifdef TREE_CODE /* Don't lose if tree.h not included. */
107 extern tree nonlocal_labels;
110 #define NO_DEFER_POP (inhibit_defer_pop += 1)
111 #define OK_DEFER_POP (inhibit_defer_pop -= 1)
113 /* Number of units that we should eventually pop off the stack.
114 These are the arguments to function calls that have already returned. */
115 extern int pending_stack_adjust;
117 /* A list of all cleanups which belong to the arguments of
118 function calls being expanded by expand_call. */
119 #ifdef TREE_CODE /* Don't lose if tree.h not included. */
120 extern tree cleanups_this_call;
123 #ifdef TREE_CODE /* Don't lose if tree.h not included. */
124 /* Structure to record the size of a sequence of arguments
125 as the sum of a tree-expression and a constant. */
134 /* Add the value of the tree INC to the `struct args_size' TO. */
136 #define ADD_PARM_SIZE(TO, INC) \
137 { tree inc = (INC); \
138 if (TREE_CODE (inc) == INTEGER_CST) \
139 (TO).constant += TREE_INT_CST_LOW (inc); \
140 else if ((TO).var == 0) \
143 (TO).var = size_binop (PLUS_EXPR, (TO).var, inc); }
145 #define SUB_PARM_SIZE(TO, DEC) \
146 { tree dec = (DEC); \
147 if (TREE_CODE (dec) == INTEGER_CST) \
148 (TO).constant -= TREE_INT_CST_LOW (dec); \
149 else if ((TO).var == 0) \
150 (TO).var = size_binop (MINUS_EXPR, integer_zero_node, dec); \
152 (TO).var = size_binop (MINUS_EXPR, (TO).var, dec); }
154 /* Convert the implicit sum in a `struct args_size' into an rtx. */
155 #define ARGS_SIZE_RTX(SIZE) \
156 ((SIZE).var == 0 ? GEN_INT ((SIZE).constant) \
157 : expand_expr (size_binop (PLUS_EXPR, (SIZE).var, \
158 size_int ((SIZE).constant)), \
159 NULL_RTX, VOIDmode, 0))
161 /* Convert the implicit sum in a `struct args_size' into a tree. */
162 #define ARGS_SIZE_TREE(SIZE) \
163 ((SIZE).var == 0 ? size_int ((SIZE).constant) \
164 : size_binop (PLUS_EXPR, (SIZE).var, size_int ((SIZE).constant)))
166 /* Supply a default definition for FUNCTION_ARG_PADDING:
167 usually pad upward, but pad short, non-BLKmode args downward on
168 big-endian machines. */
170 enum direction {none, upward, downward}; /* Value has this type. */
172 #ifndef FUNCTION_ARG_PADDING
174 #define FUNCTION_ARG_PADDING(MODE, TYPE) \
175 (((MODE) == BLKmode \
176 ? ((TYPE) && TREE_CODE (TYPE_SIZE (TYPE)) == INTEGER_CST \
177 && int_size_in_bytes (TYPE) < PARM_BOUNDARY / BITS_PER_UNIT) \
178 : GET_MODE_BITSIZE (MODE) < PARM_BOUNDARY) \
181 #define FUNCTION_ARG_PADDING(MODE, TYPE) upward
185 /* Supply a default definition for FUNCTION_ARG_BOUNDARY. Normally, we let
186 FUNCTION_ARG_PADDING, which also pads the length, handle any needed
189 #ifndef FUNCTION_ARG_BOUNDARY
190 #define FUNCTION_ARG_BOUNDARY(MODE, TYPE) PARM_BOUNDARY
193 /* Nonzero if we do not know how to pass TYPE solely in registers.
194 We cannot do so in the following cases:
196 - if the type has variable size
197 - if the type is marked as addressable (it is required to be constructed
199 - if the padding and mode of the type is such that a copy into a register
200 would put it into the wrong part of the register
201 - when STRICT_ALIGNMENT and the type is BLKmode and is is not
202 aligned to a boundary corresponding to what can be loaded into a
205 #define MUST_PASS_IN_STACK_BAD_ALIGN(MODE,TYPE) \
206 (STRICT_ALIGNMENT && MODE == BLKmode \
207 && TYPE_ALIGN (TYPE) < (BIGGEST_ALIGNMENT < BITS_PER_WORD \
208 ? BIGGEST_ALIGNMENT : BITS_PER_WORD))
210 /* Which padding can't be supported depends on the byte endianness. */
212 /* A value in a register is implicitly padded at the most significant end.
213 On a big-endian machine, that is the lower end in memory.
214 So a value padded in memory at the upper end can't go in a register.
215 For a little-endian machine, the reverse is true. */
218 #define MUST_PASS_IN_STACK_BAD_PADDING upward
220 #define MUST_PASS_IN_STACK_BAD_PADDING downward
223 #define MUST_PASS_IN_STACK(MODE,TYPE) \
225 && (TREE_CODE (TYPE_SIZE (TYPE)) != INTEGER_CST \
226 || TREE_ADDRESSABLE (TYPE) \
227 || ((MODE) == BLKmode \
228 && (FUNCTION_ARG_PADDING (MODE, TYPE) \
229 == MUST_PASS_IN_STACK_BAD_PADDING)) \
230 || MUST_PASS_IN_STACK_BAD_ALIGN (MODE, TYPE)))
232 /* Nonzero if type TYPE should be returned in memory
233 (even though its mode is not BLKmode).
234 Most machines can use the following default definition. */
236 #ifndef RETURN_IN_MEMORY
237 #define RETURN_IN_MEMORY(TYPE) 0
240 /* Optabs are tables saying how to generate insn bodies
241 for various machine modes and numbers of operands.
242 Each optab applies to one operation.
243 For example, add_optab applies to addition.
245 The insn_code slot is the enum insn_code that says how to
246 generate an insn for this operation on a particular machine mode.
247 It is CODE_FOR_nothing if there is no such insn on the target machine.
249 The `lib_call' slot is the name of the library function that
250 can be used to perform the operation.
252 A few optabs, such as move_optab and cmp_optab, are used
255 /* Everything that uses expr.h needs to define enum insn_code
256 but we don't list it in the Makefile dependencies just for that. */
257 #include "insn-codes.h"
263 enum insn_code insn_code;
265 } handlers [NUM_MACHINE_MODES];
268 /* Given an enum insn_code, access the function to construct
269 the body of that kind of insn. */
270 #ifdef FUNCTION_CONVERSION_BUG
271 /* Some compilers fail to convert a function properly to a
272 pointer-to-function when used as an argument.
273 So produce the pointer-to-function directly.
274 Luckily, these compilers seem to work properly when you
275 call the pointer-to-function. */
276 #define GEN_FCN(CODE) (insn_gen_function[(int) (CODE)])
278 #define GEN_FCN(CODE) (*insn_gen_function[(int) (CODE)])
281 extern rtx (*const insn_gen_function[]) ();
283 extern optab add_optab;
284 extern optab sub_optab;
285 extern optab smul_optab; /* Signed and floating-point multiply */
286 extern optab smul_widen_optab; /* Signed multiply with result
287 one machine mode wider than args */
288 extern optab umul_widen_optab;
289 extern optab sdiv_optab; /* Signed divide */
290 extern optab sdivmod_optab; /* Signed divide-and-remainder in one */
291 extern optab udiv_optab;
292 extern optab udivmod_optab;
293 extern optab smod_optab; /* Signed remainder */
294 extern optab umod_optab;
295 extern optab flodiv_optab; /* Optab for floating divide. */
296 extern optab ftrunc_optab; /* Convert float to integer in float fmt */
297 extern optab and_optab; /* Logical and */
298 extern optab ior_optab; /* Logical or */
299 extern optab xor_optab; /* Logical xor */
300 extern optab ashl_optab; /* Arithmetic shift left */
301 extern optab ashr_optab; /* Arithmetic shift right */
302 extern optab lshl_optab; /* Logical shift left */
303 extern optab lshr_optab; /* Logical shift right */
304 extern optab rotl_optab; /* Rotate left */
305 extern optab rotr_optab; /* Rotate right */
306 extern optab smin_optab; /* Signed and floating-point minimum value */
307 extern optab smax_optab; /* Signed and floating-point maximum value */
308 extern optab umin_optab; /* Unsigned minimum value */
309 extern optab umax_optab; /* Unsigned maximum value */
311 extern optab mov_optab; /* Move instruction. */
312 extern optab movstrict_optab; /* Move, preserving high part of register. */
314 extern optab cmp_optab; /* Compare insn; two operands. */
315 extern optab tst_optab; /* tst insn; compare one operand against 0 */
317 /* Unary operations */
318 extern optab neg_optab; /* Negation */
319 extern optab abs_optab; /* Abs value */
320 extern optab one_cmpl_optab; /* Bitwise not */
321 extern optab ffs_optab; /* Find first bit set */
322 extern optab sqrt_optab; /* Square root */
323 extern optab strlen_optab; /* String length */
325 /* Passed to expand_binop and expand_unop to say which options to try to use
326 if the requested operation can't be open-coded on the requisite mode.
327 Either OPTAB_LIB or OPTAB_LIB_WIDEN says try using a library call.
328 Either OPTAB_WIDEN or OPTAB_LIB_WIDEN says try using a wider mode.
329 OPTAB_MUST_WIDEN says try widening and don't try anything else. */
340 /* SYMBOL_REF rtx's for the library functions that are called
341 implicitly and not via optabs. */
343 extern rtx extendsfdf2_libfunc;
344 extern rtx extendsfxf2_libfunc;
345 extern rtx extendsftf2_libfunc;
346 extern rtx extenddfxf2_libfunc;
347 extern rtx extenddftf2_libfunc;
349 extern rtx truncdfsf2_libfunc;
350 extern rtx truncxfsf2_libfunc;
351 extern rtx trunctfsf2_libfunc;
352 extern rtx truncxfdf2_libfunc;
353 extern rtx trunctfdf2_libfunc;
355 extern rtx memcpy_libfunc;
356 extern rtx bcopy_libfunc;
357 extern rtx memcmp_libfunc;
358 extern rtx bcmp_libfunc;
359 extern rtx memset_libfunc;
360 extern rtx bzero_libfunc;
362 extern rtx eqsf2_libfunc;
363 extern rtx nesf2_libfunc;
364 extern rtx gtsf2_libfunc;
365 extern rtx gesf2_libfunc;
366 extern rtx ltsf2_libfunc;
367 extern rtx lesf2_libfunc;
369 extern rtx eqdf2_libfunc;
370 extern rtx nedf2_libfunc;
371 extern rtx gtdf2_libfunc;
372 extern rtx gedf2_libfunc;
373 extern rtx ltdf2_libfunc;
374 extern rtx ledf2_libfunc;
376 extern rtx eqxf2_libfunc;
377 extern rtx nexf2_libfunc;
378 extern rtx gtxf2_libfunc;
379 extern rtx gexf2_libfunc;
380 extern rtx ltxf2_libfunc;
381 extern rtx lexf2_libfunc;
383 extern rtx eqtf2_libfunc;
384 extern rtx netf2_libfunc;
385 extern rtx gttf2_libfunc;
386 extern rtx getf2_libfunc;
387 extern rtx lttf2_libfunc;
388 extern rtx letf2_libfunc;
390 extern rtx floatsisf_libfunc;
391 extern rtx floatdisf_libfunc;
392 extern rtx floattisf_libfunc;
394 extern rtx floatsidf_libfunc;
395 extern rtx floatdidf_libfunc;
396 extern rtx floattidf_libfunc;
398 extern rtx floatsixf_libfunc;
399 extern rtx floatdixf_libfunc;
400 extern rtx floattixf_libfunc;
402 extern rtx floatsitf_libfunc;
403 extern rtx floatditf_libfunc;
404 extern rtx floattitf_libfunc;
406 extern rtx fixsfsi_libfunc;
407 extern rtx fixsfdi_libfunc;
408 extern rtx fixsfti_libfunc;
410 extern rtx fixdfsi_libfunc;
411 extern rtx fixdfdi_libfunc;
412 extern rtx fixdfti_libfunc;
414 extern rtx fixxfsi_libfunc;
415 extern rtx fixxfdi_libfunc;
416 extern rtx fixxfti_libfunc;
418 extern rtx fixtfsi_libfunc;
419 extern rtx fixtfdi_libfunc;
420 extern rtx fixtfti_libfunc;
422 extern rtx fixunssfsi_libfunc;
423 extern rtx fixunssfdi_libfunc;
424 extern rtx fixunssfti_libfunc;
426 extern rtx fixunsdfsi_libfunc;
427 extern rtx fixunsdfdi_libfunc;
428 extern rtx fixunsdfti_libfunc;
430 extern rtx fixunsxfsi_libfunc;
431 extern rtx fixunsxfdi_libfunc;
432 extern rtx fixunsxfti_libfunc;
434 extern rtx fixunstfsi_libfunc;
435 extern rtx fixunstfdi_libfunc;
436 extern rtx fixunstfti_libfunc;
438 typedef rtx (*rtxfun) ();
440 /* Indexed by the rtx-code for a conditional (eg. EQ, LT,...)
441 gives the gen_function to make a branch to test that condition. */
443 extern rtxfun bcc_gen_fctn[NUM_RTX_CODE];
445 /* Indexed by the rtx-code for a conditional (eg. EQ, LT,...)
446 gives the insn code to make a store-condition insn
447 to test that condition. */
449 extern enum insn_code setcc_gen_code[NUM_RTX_CODE];
451 /* Expand a binary operation given optab and rtx operands. */
452 extern rtx expand_binop ();
454 /* Expand a binary operation with both signed and unsigned forms. */
455 extern rtx sign_expand_binop ();
457 /* Expand a unary arithmetic operation given optab rtx operand. */
458 extern rtx expand_unop ();
460 /* Arguments MODE, RTX: return an rtx for the negation of that value.
462 extern rtx negate_rtx ();
464 /* Expand a logical AND operation. */
465 extern rtx expand_and ();
467 /* Emit a store-flag operation. */
468 extern rtx emit_store_flag ();
470 /* Return the CODE_LABEL rtx for a LABEL_DECL, creating it if necessary. */
471 extern rtx label_rtx ();
473 /* Given a JUMP_INSN, return a description of the test being made. */
474 extern rtx get_condition ();
476 /* Return the INSN_CODE to use for an extend operation. */
477 extern enum insn_code can_extend_p ();
479 /* Initialize the tables that control conversion between fixed and
481 extern void init_fixtab ();
482 extern void init_floattab ();
484 /* Generate code for a FIX_EXPR. */
485 extern void expand_fix ();
487 /* Generate code for a FLOAT_EXPR. */
488 extern void expand_float ();
490 /* Create but don't emit one rtl instruction to add one rtx into another.
491 Modes must match; operands must meet the operation's predicates.
492 Likewise for subtraction and for just copying.
493 These do not call protect_from_queue; caller must do so. */
494 extern rtx gen_add2_insn ();
495 extern rtx gen_sub2_insn ();
496 extern rtx gen_move_insn ();
498 /* Emit one rtl instruction to store zero in specified rtx. */
499 extern void emit_clr_insn ();
501 /* Emit one rtl insn to store 1 in specified rtx assuming it contains 0. */
502 extern void emit_0_to_1_insn ();
504 /* Emit one rtl insn to compare two rtx's. */
505 extern void emit_cmp_insn ();
507 /* Generate rtl to compare two rtx's, will call emit_cmp_insn. */
508 extern rtx compare_from_rtx ();
510 /* Emit some rtl insns to move data between rtx's, converting machine modes.
511 Both modes must be floating or both fixed. */
512 extern void convert_move ();
514 /* Convert an rtx to specified machine mode and return the result. */
515 extern rtx convert_to_mode ();
517 /* Emit code to push some arguments and call a library routine,
518 storing the value in a specified place. Calling sequence is
520 extern void emit_library_call ();
522 /* Given an rtx that may include add and multiply operations,
523 generate them as insns and return a pseudo-reg containing the value.
524 Useful after calling expand_expr with 1 as sum_ok. */
525 extern rtx force_operand ();
527 /* Return an rtx for the size in bytes of the value of an expr. */
528 extern rtx expr_size ();
530 extern rtx lookup_static_chain ();
532 /* Return an rtx like arg but sans any constant terms.
533 Returns the original rtx if it has no constant terms.
534 The constant terms are added and stored via a second arg. */
535 extern rtx eliminate_constant_term ();
537 /* Convert arg to a valid memory address for specified machine mode,
538 by emitting insns to perform arithmetic if nec. */
539 extern rtx memory_address ();
541 /* Like `memory_address' but pretent `flag_force_addr' is 0. */
542 extern rtx memory_address_noforce ();
544 /* Return a memory reference like MEMREF, but with its mode changed
545 to MODE and its address changed to ADDR.
546 (VOIDmode means don't change the mode.
547 NULL for ADDR means don't change the address.) */
548 extern rtx change_address ();
550 /* Return a memory reference like MEMREF, but which is known to have a
553 extern rtx validize_mem ();
555 /* Convert a stack slot address ADDR valid in function FNDECL
556 into an address valid in this function (using a static chain). */
557 extern rtx fix_lexical_addr ();
559 /* Return the address of the trampoline for entering nested fn FUNCTION. */
560 extern rtx trampoline_address ();
562 /* Assemble the static constant template for function entry trampolines. */
563 extern rtx assemble_trampoline_template ();
565 /* Return 1 if two rtx's are equivalent in structure and elements. */
566 extern int rtx_equal_p ();
568 /* Given rtx, return new rtx whose address won't be affected by
569 any side effects. It has been copied to a new temporary reg. */
570 extern rtx stabilize ();
572 /* Given an rtx, copy all regs it refers to into new temps
573 and return a modified copy that refers to the new temps. */
574 extern rtx copy_all_regs ();
576 /* Copy given rtx to a new temp reg and return that. */
577 extern rtx copy_to_reg ();
579 /* Like copy_to_reg but always make the reg Pmode. */
580 extern rtx copy_addr_to_reg ();
582 /* Like copy_to_reg but always make the reg the specified mode MODE. */
583 extern rtx copy_to_mode_reg ();
585 /* Copy given rtx to given temp reg and return that. */
586 extern rtx copy_to_suggested_reg ();
588 /* Copy a value to a register if it isn't already a register.
589 Args are mode (in case value is a constant) and the value. */
590 extern rtx force_reg ();
592 /* Return given rtx, copied into a new temp reg if it was in memory. */
593 extern rtx force_not_mem ();
595 /* Remove some bytes from the stack. An rtx says how many. */
596 extern void adjust_stack ();
598 /* Add some bytes to the stack. An rtx says how many. */
599 extern void anti_adjust_stack ();
601 /* This enum is used for the following two functions. */
602 enum save_level {SAVE_BLOCK, SAVE_FUNCTION, SAVE_NONLOCAL};
604 /* Save the stack pointer at the specified level. */
605 extern void emit_stack_save ();
607 /* Restore the stack pointer from a save area of the specified level. */
608 extern void emit_stack_restore ();
610 /* Allocate some space on the stack dynamically and return its address. An rtx
611 says how many bytes. */
612 extern rtx allocate_dynamic_stack_space ();
614 /* Emit code to copy function value to a new temp reg and return that reg. */
615 extern rtx function_value ();
617 /* Return an rtx that refers to the value returned by a function
618 in its original home. This becomes invalid if any more code is emitted. */
619 extern rtx hard_function_value ();
621 /* Return an rtx that refers to the value returned by a library call
622 in its original home. This becomes invalid if any more code is emitted. */
623 extern rtx hard_libcall_value ();
625 /* Emit code to copy function value to a specified place. */
626 extern void copy_function_value ();
628 /* Given an rtx, return an rtx for a value rounded up to a multiple
629 of STACK_BOUNDARY / BITS_PER_UNIT. */
630 extern rtx round_push ();
632 /* Push a block of length SIZE (perhaps variable)
633 and return an rtx to address the beginning of the block. */
634 extern rtx push_block ();
636 /* Generate code for computing expression EXP,
637 and storing the value into TARGET.
638 If SUGGEST_REG is nonzero, copy the value through a register
639 and return that register, if that is possible. */
640 extern rtx store_expr ();
642 extern rtx prepare_call_address ();
643 extern rtx expand_call ();
644 extern void emit_call_1 ();
646 extern void emit_block_move ();
647 extern void emit_push_insn ();
648 extern void use_regs ();
649 extern void move_block_to_reg ();
651 extern rtx store_bit_field ();
652 extern rtx extract_bit_field ();
653 extern rtx expand_shift ();
654 extern rtx expand_mult ();
655 extern rtx expand_divmod ();
656 extern rtx expand_mult_add ();
657 extern rtx expand_stmt_expr ();
658 extern rtx emit_no_conflict_block ();
659 extern void emit_libcall_block ();
661 extern void jumpifnot ();
662 extern void jumpif ();
663 extern void do_jump ();
665 extern rtx assemble_static_space ();
667 extern void locate_and_pad_parm ();
669 extern rtx expand_inline_function ();
671 /* Hook called by expand_expr for language-specific tree codes.
672 It is up to the language front end to install a hook
673 if it has any such codes that expand_expr needs to know about. */
674 extern rtx (*lang_expand_expr) ();