1 /* Dummy data flow analysis for GNU compiler in nonoptimizing mode.
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. */
21 /* This file performs stupid register allocation, which is used
22 when cc1 gets the -noreg switch (which is when cc does not get -O).
24 Stupid register allocation goes in place of the the flow_analysis,
25 local_alloc and global_alloc passes. combine_instructions cannot
26 be done with stupid allocation because the data flow info that it needs
29 In stupid allocation, the only user-defined variables that can
30 go in registers are those declared "register". They are assumed
31 to have a life span equal to their scope. Other user variables
32 are given stack slots in the rtl-generation pass and are not
33 represented as pseudo regs. A compiler-generated temporary
34 is assumed to live from its first mention to its last mention.
36 Since each pseudo-reg's life span is just an interval, it can be
37 represented as a pair of numbers, each of which identifies an insn by
38 its position in the function (number of insns before it). The first
39 thing done for stupid allocation is to compute such a number for each
40 insn. It is called the suid. Then the life-interval of each
41 pseudo reg is computed. Then the pseudo regs are ordered by priority
42 and assigned hard regs in priority order. */
47 #include "hard-reg-set.h"
51 /* Vector mapping INSN_UIDs to suids.
52 The suids are like uids but increase monotonically always.
53 We use them to see whether a subroutine call came
54 between a variable's birth and its death. */
58 /* Get the suid of an insn. */
60 #define INSN_SUID(INSN) (uid_suid[INSN_UID (INSN)])
62 /* Record the suid of the last CALL_INSN
63 so we can tell whether a pseudo reg crosses any calls. */
65 static int last_call_suid;
67 /* Record the suid of the last JUMP_INSN
68 so we can tell whether a pseudo reg crosses any jumps. */
70 static int last_jump_suid;
72 /* Record the suid of the last CODE_LABEL
73 so we can tell whether a pseudo reg crosses any labels. */
75 static int last_label_suid;
77 /* Element N is suid of insn where life span of pseudo reg N ends.
78 Element is 0 if register N has not been seen yet on backward scan. */
80 static int *reg_where_dead;
82 /* Element N is suid of insn where life span of pseudo reg N begins. */
84 static int *reg_where_born;
86 /* Element N is 1 if pseudo reg N lives across labels or jumps. */
88 static char *reg_crosses_blocks;
90 /* Numbers of pseudo-regs to be allocated, highest priority first. */
92 static int *reg_order;
94 /* Indexed by reg number (hard or pseudo), nonzero if register is live
95 at the current point in the instruction stream. */
97 static char *regs_live;
99 /* Indexed by insn's suid, the set of hard regs live after that insn. */
101 static HARD_REG_SET *after_insn_hard_regs;
103 /* Record that hard reg REGNO is live after insn INSN. */
105 #define MARK_LIVE_AFTER(INSN,REGNO) \
106 SET_HARD_REG_BIT (after_insn_hard_regs[INSN_SUID (INSN)], (REGNO))
108 static void stupid_mark_refs ();
109 static int stupid_reg_compare ();
110 static int stupid_find_reg ();
112 /* Stupid life analysis is for the case where only variables declared
113 `register' go in registers. For this case, we mark all
114 pseudo-registers that belong to register variables as
115 dying in the last instruction of the function, and all other
116 pseudo registers as dying in the last place they are referenced.
117 Hard registers are marked as dying in the last reference before
118 the end or before each store into them. */
121 stupid_life_analysis (f, nregs, file)
127 register rtx last, insn;
130 bzero (regs_ever_live, sizeof regs_ever_live);
132 regs_live = (char *) alloca (nregs);
134 /* First find the last real insn, and count the number of insns,
135 and assign insns their suids. */
137 for (insn = f, i = 0; insn; insn = NEXT_INSN (insn))
138 if (INSN_UID (insn) > i)
142 uid_suid = (int *) alloca ((i + 1) * sizeof (int));
144 /* Compute the mapping from uids to suids.
145 Suids are numbers assigned to insns, like uids,
146 except that suids increase monotonically through the code. */
148 last = 0; /* In case of empty function body */
149 for (insn = f, i = 0; insn; insn = NEXT_INSN (insn))
151 if (GET_CODE (insn) == INSN || GET_CODE (insn) == CALL_INSN
152 || GET_CODE (insn) == JUMP_INSN)
154 INSN_SUID (insn) = ++i;
157 last_call_suid = i + 1;
158 last_jump_suid = i + 1;
159 last_label_suid = i + 1;
163 /* Allocate tables to record info about regs. */
165 reg_where_dead = (int *) alloca (nregs * sizeof (int));
166 bzero (reg_where_dead, nregs * sizeof (int));
168 reg_where_born = (int *) alloca (nregs * sizeof (int));
169 bzero (reg_where_born, nregs * sizeof (int));
171 reg_crosses_blocks = (char *) alloca (nregs);
172 bzero (reg_crosses_blocks, nregs);
174 reg_order = (int *) alloca (nregs * sizeof (int));
175 bzero (reg_order, nregs * sizeof (int));
177 reg_renumber = (short *) oballoc (nregs * sizeof (short));
178 for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
181 for (i = FIRST_VIRTUAL_REGISTER; i <= LAST_VIRTUAL_REGISTER; i++)
182 reg_renumber[i] = -1;
184 after_insn_hard_regs = (HARD_REG_SET *) alloca (max_uid * sizeof (HARD_REG_SET));
185 bzero (after_insn_hard_regs, max_uid * sizeof (HARD_REG_SET));
187 /* Allocate and zero out many data structures
188 that will record the data from lifetime analysis. */
190 allocate_for_life_analysis ();
192 for (i = 0; i < max_regno; i++)
197 bzero (regs_live, nregs);
199 /* Find where each pseudo register is born and dies,
200 by scanning all insns from the end to the start
201 and noting all mentions of the registers.
203 Also find where each hard register is live
204 and record that info in after_insn_hard_regs.
205 regs_live[I] is 1 if hard reg I is live
206 at the current point in the scan. */
208 for (insn = last; insn; insn = PREV_INSN (insn))
210 register HARD_REG_SET *p = after_insn_hard_regs + INSN_SUID (insn);
212 /* Copy the info in regs_live
213 into the element of after_insn_hard_regs
214 for the current position in the rtl code. */
216 for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
218 SET_HARD_REG_BIT (*p, i);
220 /* Mark all call-clobbered regs as live after each call insn
221 so that a pseudo whose life span includes this insn
222 will not go in one of them.
223 Then mark those regs as all dead for the continuing scan
224 of the insns before the call. */
226 if (GET_CODE (insn) == CALL_INSN)
228 last_call_suid = INSN_SUID (insn);
229 IOR_HARD_REG_SET (after_insn_hard_regs[last_call_suid],
231 for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
232 if (call_used_regs[i])
236 if (GET_CODE (insn) == JUMP_INSN)
237 last_jump_suid = INSN_SUID (insn);
239 if (GET_CODE (insn) == CODE_LABEL)
240 last_label_suid = INSN_SUID (insn);
242 /* Update which hard regs are currently live
243 and also the birth and death suids of pseudo regs
244 based on the pattern of this insn. */
246 if (GET_CODE (insn) == INSN
247 || GET_CODE (insn) == CALL_INSN
248 || GET_CODE (insn) == JUMP_INSN)
250 stupid_mark_refs (PATTERN (insn), insn);
254 /* Now decide the order in which to allocate the pseudo registers. */
256 for (i = LAST_VIRTUAL_REGISTER + 1; i < max_regno; i++)
259 qsort (®_order[LAST_VIRTUAL_REGISTER + 1],
260 max_regno - LAST_VIRTUAL_REGISTER - 1, sizeof (int),
263 /* Now, in that order, try to find hard registers for those pseudo regs. */
265 for (i = LAST_VIRTUAL_REGISTER + 1; i < max_regno; i++)
267 register int r = reg_order[i];
268 enum reg_class class;
270 /* Some regnos disappear from the rtl. Ignore them to avoid crash. */
271 if (regno_reg_rtx[r] == 0)
274 /* Now find the best hard-register class for this pseudo register */
275 if (N_REG_CLASSES > 1)
277 class = reg_preferred_class (r);
279 reg_renumber[r] = stupid_find_reg (reg_n_calls_crossed[r], class,
280 PSEUDO_REGNO_MODE (r),
283 reg_crosses_blocks[r]);
286 reg_renumber[r] = -1;
288 /* If no reg available in that class,
290 if (reg_renumber[r] == -1)
291 reg_renumber[r] = stupid_find_reg (reg_n_calls_crossed[r],
293 PSEUDO_REGNO_MODE (r),
296 reg_crosses_blocks[r]);
300 dump_flow_info (file);
303 /* Comparison function for qsort.
304 Returns -1 (1) if register *R1P is higher priority than *R2P. */
307 stupid_reg_compare (r1p, r2p)
310 register int r1 = *r1p, r2 = *r2p;
311 register int len1 = reg_where_dead[r1] - reg_where_born[r1];
312 register int len2 = reg_where_dead[r2] - reg_where_born[r2];
316 if (tem != 0) return tem;
318 tem = reg_n_refs[r1] - reg_n_refs[r2];
319 if (tem != 0) return tem;
321 /* If regs are equally good, sort by regno,
322 so that the results of qsort leave nothing to chance. */
326 /* Find a block of SIZE words of hard registers in reg_class CLASS
327 that can hold a value of machine-mode MODE
328 (but actually we test only the first of the block for holding MODE)
329 currently free from after insn whose suid is BIRTH
330 through the insn whose suid is DEATH,
331 and return the number of the first of them.
332 Return -1 if such a block cannot be found.
334 If CALL_PRESERVED is nonzero, insist on registers preserved
335 over subroutine calls, and return -1 if cannot find such.
336 If CROSSES_BLOCKS is nonzero, reject registers for which
337 PRESERVE_DEATH_INFO_REGNO_P is true. */
340 stupid_find_reg (call_preserved, class, mode,
341 born_insn, dead_insn, crosses_blocks)
343 enum reg_class class;
344 enum machine_mode mode;
345 int born_insn, dead_insn;
350 register /* Declare them register if they are scalars. */
352 HARD_REG_SET used, this_reg;
353 #ifdef ELIMINABLE_REGS
354 static struct {int from, to; } eliminables[] = ELIMINABLE_REGS;
357 COPY_HARD_REG_SET (used,
358 call_preserved ? call_used_reg_set : fixed_reg_set);
360 #ifdef ELIMINABLE_REGS
361 for (i = 0; i < sizeof eliminables / sizeof eliminables[0]; i++)
362 SET_HARD_REG_BIT (used, eliminables[i].from);
363 #if HARD_FRAME_POINTER_REGNUM != FRAME_POINTER_REGNUM
364 SET_HARD_REG_BIT (used, HARD_FRAME_POINTER_REGNUM);
367 SET_HARD_REG_BIT (used, FRAME_POINTER_REGNUM);
370 for (ins = born_insn; ins < dead_insn; ins++)
371 IOR_HARD_REG_SET (used, after_insn_hard_regs[ins]);
373 IOR_COMPL_HARD_REG_SET (used, reg_class_contents[(int) class]);
375 for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
377 #ifdef REG_ALLOC_ORDER
378 int regno = reg_alloc_order[i];
383 /* If we need reasonable death info on this hard reg,
384 don't use it for anything whose life spans a label or a jump. */
385 #ifdef PRESERVE_DEATH_INFO_REGNO_P
386 if (PRESERVE_DEATH_INFO_REGNO_P (regno)
390 /* If a register has screwy overlap problems,
391 don't use it at all if not optimizing.
392 Actually this is only for the 387 stack register,
393 and it's because subsequent code won't work. */
394 #ifdef OVERLAPPING_REGNO_P
395 if (OVERLAPPING_REGNO_P (regno))
399 if (! TEST_HARD_REG_BIT (used, regno)
400 && HARD_REGNO_MODE_OK (regno, mode))
403 register int size1 = HARD_REGNO_NREGS (regno, mode);
404 for (j = 1; j < size1 && ! TEST_HARD_REG_BIT (used, regno + j); j++);
407 CLEAR_HARD_REG_SET (this_reg);
409 SET_HARD_REG_BIT (this_reg, regno + j);
410 for (ins = born_insn; ins < dead_insn; ins++)
412 IOR_HARD_REG_SET (after_insn_hard_regs[ins], this_reg);
416 #ifndef REG_ALLOC_ORDER
417 i += j; /* Skip starting points we know will lose */
424 /* Walk X, noting all assignments and references to registers
425 and recording what they imply about life spans.
426 INSN is the current insn, supplied so we can find its suid. */
429 stupid_mark_refs (x, insn)
432 register RTX_CODE code = GET_CODE (x);
434 register int regno, i;
436 if (code == SET || code == CLOBBER)
438 if (SET_DEST (x) != 0 && GET_CODE (SET_DEST (x)) == REG)
440 /* Register is being assigned. */
441 regno = REGNO (SET_DEST (x));
443 /* For hard regs, update the where-live info. */
444 if (regno < FIRST_PSEUDO_REGISTER)
447 = HARD_REGNO_NREGS (regno, GET_MODE (SET_DEST (x)));
450 regs_ever_live[regno+j] = 1;
451 regs_live[regno+j] = 0;
452 /* The following line is for unused outputs;
453 they do get stored even though never used again. */
454 MARK_LIVE_AFTER (insn, regno);
455 /* When a hard reg is clobbered, mark it in use
456 just before this insn, so it is live all through. */
457 if (code == CLOBBER && INSN_SUID (insn) > 0)
458 SET_HARD_REG_BIT (after_insn_hard_regs[INSN_SUID (insn) - 1],
462 /* For pseudo regs, record where born, where dead, number of
463 times used, and whether live across a call. */
466 /* Update the life-interval bounds of this pseudo reg. */
468 /* When a pseudo-reg is CLOBBERed, it is born just before
469 the clobbering insn. When setting, just after. */
470 int where_born = INSN_SUID (insn) - (code == CLOBBER);
472 reg_where_born[regno] = where_born;
473 /* The reg must live at least one insn even
474 in it is never again used--because it has to go
475 in SOME hard reg. Mark it as dying after the current
476 insn so that it will conflict with any other outputs of
478 if (reg_where_dead[regno] < where_born + 2)
479 reg_where_dead[regno] = where_born + 2;
481 /* Count the refs of this reg. */
484 if (last_call_suid < reg_where_dead[regno])
485 reg_n_calls_crossed[regno] += 1;
486 if (last_jump_suid < reg_where_dead[regno]
487 || last_label_suid < reg_where_dead[regno])
488 reg_crosses_blocks[regno] = 1;
491 /* Record references from the value being set,
492 or from addresses in the place being set if that's not a reg.
493 If setting a SUBREG, we treat the entire reg as *used*. */
496 stupid_mark_refs (SET_SRC (x), insn);
497 if (GET_CODE (SET_DEST (x)) != REG)
498 stupid_mark_refs (SET_DEST (x), insn);
503 /* Register value being used, not set. */
508 if (regno < FIRST_PSEUDO_REGISTER)
510 /* Hard reg: mark it live for continuing scan of previous insns. */
511 register int j = HARD_REGNO_NREGS (regno, GET_MODE (x));
514 regs_ever_live[regno+j] = 1;
515 regs_live[regno+j] = 1;
520 /* Pseudo reg: record first use, last use and number of uses. */
522 reg_where_born[regno] = INSN_SUID (insn);
524 if (regs_live[regno] == 0)
526 regs_live[regno] = 1;
527 reg_where_dead[regno] = INSN_SUID (insn);
533 /* Recursive scan of all other rtx's. */
535 fmt = GET_RTX_FORMAT (code);
536 for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
539 stupid_mark_refs (XEXP (x, i), insn);
543 for (j = XVECLEN (x, i) - 1; j >= 0; j--)
544 stupid_mark_refs (XVECEXP (x, i, j), insn);