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b076a3fd ZD |
1 | /* Array prefetching. |
2 | Copyright (C) 2005 Free Software Foundation, Inc. | |
3 | ||
4 | This file is part of GCC. | |
5 | ||
6 | GCC is free software; you can redistribute it and/or modify it | |
7 | under the terms of the GNU General Public License as published by the | |
8 | Free Software Foundation; either version 2, or (at your option) any | |
9 | later version. | |
10 | ||
11 | GCC is distributed in the hope that it will be useful, but WITHOUT | |
12 | ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
13 | FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
14 | for more details. | |
15 | ||
16 | You should have received a copy of the GNU General Public License | |
17 | along with GCC; see the file COPYING. If not, write to the Free | |
18 | Software Foundation, 59 Temple Place - Suite 330, Boston, MA | |
19 | 02111-1307, USA. */ | |
20 | ||
21 | #include "config.h" | |
22 | #include "system.h" | |
23 | #include "coretypes.h" | |
24 | #include "tm.h" | |
25 | #include "tree.h" | |
26 | #include "rtl.h" | |
27 | #include "tm_p.h" | |
28 | #include "hard-reg-set.h" | |
29 | #include "basic-block.h" | |
30 | #include "output.h" | |
31 | #include "diagnostic.h" | |
32 | #include "tree-flow.h" | |
33 | #include "tree-dump.h" | |
34 | #include "timevar.h" | |
35 | #include "cfgloop.h" | |
36 | #include "varray.h" | |
37 | #include "expr.h" | |
38 | #include "tree-pass.h" | |
39 | #include "ggc.h" | |
40 | #include "insn-config.h" | |
41 | #include "recog.h" | |
42 | #include "hashtab.h" | |
43 | #include "tree-chrec.h" | |
44 | #include "tree-scalar-evolution.h" | |
45 | #include "toplev.h" | |
46 | #include "params.h" | |
47 | #include "langhooks.h" | |
48 | ||
49 | /* This pass inserts prefetch instructions to optimize cache usage during | |
50 | accesses to arrays in loops. It processes loops sequentially and: | |
51 | ||
52 | 1) Gathers all memory references in the single loop. | |
53 | 2) For each of the references it decides when it is profitable to prefetch | |
54 | it. To do it, we evaluate the reuse among the accesses, and determines | |
55 | two values: PREFETCH_BEFORE (meaning that it only makes sense to do | |
56 | prefetching in the first PREFETCH_BEFORE iterations of the loop) and | |
57 | PREFETCH_MOD (meaning that it only makes sense to prefetch in the | |
58 | iterations of the loop that are zero modulo PREFETCH_MOD). For example | |
59 | (assuming cache line size is 64 bytes, char has size 1 byte and there | |
60 | is no hardware sequential prefetch): | |
61 | ||
62 | char *a; | |
63 | for (i = 0; i < max; i++) | |
64 | { | |
65 | a[255] = ...; (0) | |
66 | a[i] = ...; (1) | |
67 | a[i + 64] = ...; (2) | |
68 | a[16*i] = ...; (3) | |
69 | a[187*i] = ...; (4) | |
70 | a[187*i + 50] = ...; (5) | |
71 | } | |
72 | ||
73 | (0) obviously has PREFETCH_BEFORE 1 | |
74 | (1) has PREFETCH_BEFORE 64, since (2) accesses the same memory | |
75 | location 64 iterations before it, and PREFETCH_MOD 64 (since | |
76 | it hits the same cache line otherwise). | |
77 | (2) has PREFETCH_MOD 64 | |
78 | (3) has PREFETCH_MOD 4 | |
79 | (4) has PREFETCH_MOD 1. We do not set PREFETCH_BEFORE here, since | |
80 | the cache line accessed by (4) is the same with probability only | |
81 | 7/32. | |
82 | (5) has PREFETCH_MOD 1 as well. | |
83 | ||
84 | 3) We determine how much ahead we need to prefetch. The number of | |
85 | iterations needed is time to fetch / time spent in one iteration of | |
86 | the loop. The problem is that we do not know either of these values, | |
87 | so we just make a heuristic guess based on a magic (possibly) | |
88 | target-specific constant and size of the loop. | |
89 | ||
90 | 4) Determine which of the references we prefetch. We take into account | |
91 | that there is a maximum number of simultaneous prefetches (provided | |
92 | by machine description). We prefetch as many prefetches as possible | |
93 | while still within this bound (starting with those with lowest | |
94 | prefetch_mod, since they are responsible for most of the cache | |
95 | misses). | |
96 | ||
97 | 5) We unroll and peel loops so that we are able to satisfy PREFETCH_MOD | |
98 | and PREFETCH_BEFORE requirements (within some bounds), and to avoid | |
99 | prefetching nonaccessed memory. | |
100 | TODO -- actually implement peeling. | |
101 | ||
102 | 6) We actually emit the prefetch instructions. ??? Perhaps emit the | |
103 | prefetch instructions with guards in cases where 5) was not sufficient | |
104 | to satisfy the constraints? | |
105 | ||
106 | Some other TODO: | |
107 | -- write and use more general reuse analysis (that could be also used | |
108 | in other cache aimed loop optimizations) | |
109 | -- make it behave sanely together with the prefetches given by user | |
110 | (now we just ignore them; at the very least we should avoid | |
111 | optimizing loops in that user put his own prefetches) | |
112 | -- we assume cache line size alignment of arrays; this could be | |
113 | improved. */ | |
114 | ||
115 | /* Magic constants follow. These should be replaced by machine specific | |
116 | numbers. */ | |
117 | ||
c0220ea4 | 118 | /* A number that should roughly correspond to the number of instructions |
b076a3fd ZD |
119 | executed before the prefetch is completed. */ |
120 | ||
121 | #ifndef PREFETCH_LATENCY | |
122 | #define PREFETCH_LATENCY 200 | |
123 | #endif | |
124 | ||
125 | /* Number of prefetches that can run at the same time. */ | |
126 | ||
127 | #ifndef SIMULTANEOUS_PREFETCHES | |
128 | #define SIMULTANEOUS_PREFETCHES 3 | |
129 | #endif | |
130 | ||
131 | /* True if write can be prefetched by a read prefetch. */ | |
132 | ||
133 | #ifndef WRITE_CAN_USE_READ_PREFETCH | |
134 | #define WRITE_CAN_USE_READ_PREFETCH 1 | |
135 | #endif | |
136 | ||
137 | /* True if read can be prefetched by a write prefetch. */ | |
138 | ||
139 | #ifndef READ_CAN_USE_WRITE_PREFETCH | |
140 | #define READ_CAN_USE_WRITE_PREFETCH 0 | |
141 | #endif | |
142 | ||
143 | /* Cache line size. Assumed to be a power of two. */ | |
144 | ||
145 | #ifndef PREFETCH_BLOCK | |
146 | #define PREFETCH_BLOCK 32 | |
147 | #endif | |
148 | ||
149 | /* Do we have a forward hardware sequential prefetching? */ | |
150 | ||
151 | #ifndef HAVE_FORWARD_PREFETCH | |
152 | #define HAVE_FORWARD_PREFETCH 0 | |
153 | #endif | |
154 | ||
155 | /* Do we have a backward hardware sequential prefetching? */ | |
156 | ||
157 | #ifndef HAVE_BACKWARD_PREFETCH | |
158 | #define HAVE_BACKWARD_PREFETCH 0 | |
159 | #endif | |
160 | ||
161 | /* In some cases we are only able to determine that there is a certain | |
162 | probability that the two accesses hit the same cache line. In this | |
163 | case, we issue the prefetches for both of them if this probability | |
164 | is less then (1000 - ACCEPTABLE_MISS_RATE) promile. */ | |
165 | ||
166 | #ifndef ACCEPTABLE_MISS_RATE | |
167 | #define ACCEPTABLE_MISS_RATE 50 | |
168 | #endif | |
169 | ||
170 | #ifndef HAVE_prefetch | |
171 | #define HAVE_prefetch 0 | |
172 | #endif | |
173 | ||
174 | /* The group of references between that reuse may occur. */ | |
175 | ||
176 | struct mem_ref_group | |
177 | { | |
178 | tree base; /* Base of the reference. */ | |
179 | HOST_WIDE_INT step; /* Step of the reference. */ | |
180 | struct mem_ref *refs; /* References in the group. */ | |
181 | struct mem_ref_group *next; /* Next group of references. */ | |
182 | }; | |
183 | ||
184 | /* Assigned to PREFETCH_BEFORE when all iterations are to be prefetched. */ | |
185 | ||
186 | #define PREFETCH_ALL (~(unsigned HOST_WIDE_INT) 0) | |
187 | ||
188 | /* The memory reference. */ | |
189 | ||
190 | struct mem_ref | |
191 | { | |
192 | tree stmt; /* Statement in that the reference appears. */ | |
193 | tree mem; /* The reference. */ | |
194 | HOST_WIDE_INT delta; /* Constant offset of the reference. */ | |
195 | bool write_p; /* Is it a write? */ | |
196 | struct mem_ref_group *group; /* The group of references it belongs to. */ | |
197 | unsigned HOST_WIDE_INT prefetch_mod; | |
198 | /* Prefetch only each PREFETCH_MOD-th | |
199 | iteration. */ | |
200 | unsigned HOST_WIDE_INT prefetch_before; | |
201 | /* Prefetch only first PREFETCH_BEFORE | |
202 | iterations. */ | |
203 | bool issue_prefetch_p; /* Should we really issue the prefetch? */ | |
204 | struct mem_ref *next; /* The next reference in the group. */ | |
205 | }; | |
206 | ||
75c40d56 | 207 | /* Dumps information about reference REF to FILE. */ |
b076a3fd ZD |
208 | |
209 | static void | |
210 | dump_mem_ref (FILE *file, struct mem_ref *ref) | |
211 | { | |
212 | fprintf (file, "Reference %p:\n", (void *) ref); | |
213 | ||
214 | fprintf (file, " group %p (base ", (void *) ref->group); | |
215 | print_generic_expr (file, ref->group->base, TDF_SLIM); | |
216 | fprintf (file, ", step "); | |
217 | fprintf (file, HOST_WIDE_INT_PRINT_DEC, ref->group->step); | |
218 | fprintf (file, ")\n"); | |
219 | ||
220 | fprintf (dump_file, " delta "); | |
221 | fprintf (file, HOST_WIDE_INT_PRINT_DEC, ref->delta); | |
222 | fprintf (file, "\n"); | |
223 | ||
224 | fprintf (file, " %s\n", ref->write_p ? "write" : "read"); | |
225 | ||
226 | fprintf (file, "\n"); | |
227 | } | |
228 | ||
229 | /* Finds a group with BASE and STEP in GROUPS, or creates one if it does not | |
230 | exist. */ | |
231 | ||
232 | static struct mem_ref_group * | |
233 | find_or_create_group (struct mem_ref_group **groups, tree base, | |
234 | HOST_WIDE_INT step) | |
235 | { | |
236 | struct mem_ref_group *group; | |
237 | ||
238 | for (; *groups; groups = &(*groups)->next) | |
239 | { | |
240 | if ((*groups)->step == step | |
241 | && operand_equal_p ((*groups)->base, base, 0)) | |
242 | return *groups; | |
243 | ||
244 | /* Keep the list of groups sorted by decreasing step. */ | |
245 | if ((*groups)->step < step) | |
246 | break; | |
247 | } | |
248 | ||
249 | group = xcalloc (1, sizeof (struct mem_ref_group)); | |
250 | group->base = base; | |
251 | group->step = step; | |
252 | group->refs = NULL; | |
253 | group->next = *groups; | |
254 | *groups = group; | |
255 | ||
256 | return group; | |
257 | } | |
258 | ||
259 | /* Records a memory reference MEM in GROUP with offset DELTA and write status | |
260 | WRITE_P. The reference occurs in statement STMT. */ | |
261 | ||
262 | static void | |
263 | record_ref (struct mem_ref_group *group, tree stmt, tree mem, | |
264 | HOST_WIDE_INT delta, bool write_p) | |
265 | { | |
266 | struct mem_ref **aref; | |
267 | ||
268 | /* Do not record the same address twice. */ | |
269 | for (aref = &group->refs; *aref; aref = &(*aref)->next) | |
270 | { | |
271 | /* It does not have to be possible for write reference to reuse the read | |
272 | prefetch, or vice versa. */ | |
273 | if (!WRITE_CAN_USE_READ_PREFETCH | |
274 | && write_p | |
275 | && !(*aref)->write_p) | |
276 | continue; | |
277 | if (!READ_CAN_USE_WRITE_PREFETCH | |
278 | && !write_p | |
279 | && (*aref)->write_p) | |
280 | continue; | |
281 | ||
282 | if ((*aref)->delta == delta) | |
283 | return; | |
284 | } | |
285 | ||
286 | (*aref) = xcalloc (1, sizeof (struct mem_ref)); | |
287 | (*aref)->stmt = stmt; | |
288 | (*aref)->mem = mem; | |
289 | (*aref)->delta = delta; | |
290 | (*aref)->write_p = write_p; | |
291 | (*aref)->prefetch_before = PREFETCH_ALL; | |
292 | (*aref)->prefetch_mod = 1; | |
293 | (*aref)->issue_prefetch_p = false; | |
294 | (*aref)->group = group; | |
295 | (*aref)->next = NULL; | |
296 | ||
297 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
298 | dump_mem_ref (dump_file, *aref); | |
299 | } | |
300 | ||
301 | /* Release memory references in GROUPS. */ | |
302 | ||
303 | static void | |
304 | release_mem_refs (struct mem_ref_group *groups) | |
305 | { | |
306 | struct mem_ref_group *next_g; | |
307 | struct mem_ref *ref, *next_r; | |
308 | ||
309 | for (; groups; groups = next_g) | |
310 | { | |
311 | next_g = groups->next; | |
312 | for (ref = groups->refs; ref; ref = next_r) | |
313 | { | |
314 | next_r = ref->next; | |
315 | free (ref); | |
316 | } | |
317 | free (groups); | |
318 | } | |
319 | } | |
320 | ||
321 | /* A structure used to pass arguments to idx_analyze_ref. */ | |
322 | ||
323 | struct ar_data | |
324 | { | |
325 | struct loop *loop; /* Loop of the reference. */ | |
326 | tree stmt; /* Statement of the reference. */ | |
327 | HOST_WIDE_INT *step; /* Step of the memory reference. */ | |
328 | HOST_WIDE_INT *delta; /* Offset of the memory reference. */ | |
329 | }; | |
330 | ||
331 | /* Analyzes a single INDEX of a memory reference to obtain information | |
332 | described at analyze_ref. Callback for for_each_index. */ | |
333 | ||
334 | static bool | |
335 | idx_analyze_ref (tree base, tree *index, void *data) | |
336 | { | |
337 | struct ar_data *ar_data = data; | |
338 | tree ibase, step, stepsize; | |
339 | HOST_WIDE_INT istep, idelta = 0, imult = 1; | |
340 | affine_iv iv; | |
341 | ||
342 | if (TREE_CODE (base) == MISALIGNED_INDIRECT_REF | |
343 | || TREE_CODE (base) == ALIGN_INDIRECT_REF) | |
344 | return false; | |
345 | ||
346 | if (!simple_iv (ar_data->loop, ar_data->stmt, *index, &iv, false)) | |
347 | return false; | |
348 | ibase = iv.base; | |
349 | step = iv.step; | |
350 | ||
351 | if (zero_p (step)) | |
352 | istep = 0; | |
353 | else | |
354 | { | |
355 | if (!cst_and_fits_in_hwi (step)) | |
356 | return false; | |
357 | istep = int_cst_value (step); | |
358 | } | |
359 | ||
360 | if (TREE_CODE (ibase) == PLUS_EXPR | |
361 | && cst_and_fits_in_hwi (TREE_OPERAND (ibase, 1))) | |
362 | { | |
363 | idelta = int_cst_value (TREE_OPERAND (ibase, 1)); | |
364 | ibase = TREE_OPERAND (ibase, 0); | |
365 | } | |
366 | if (cst_and_fits_in_hwi (ibase)) | |
367 | { | |
368 | idelta += int_cst_value (ibase); | |
ff5e9a94 | 369 | ibase = build_int_cst (TREE_TYPE (ibase), 0); |
b076a3fd ZD |
370 | } |
371 | ||
372 | if (TREE_CODE (base) == ARRAY_REF) | |
373 | { | |
374 | stepsize = array_ref_element_size (base); | |
375 | if (!cst_and_fits_in_hwi (stepsize)) | |
376 | return false; | |
377 | imult = int_cst_value (stepsize); | |
378 | ||
379 | istep *= imult; | |
380 | idelta *= imult; | |
381 | } | |
382 | ||
383 | *ar_data->step += istep; | |
384 | *ar_data->delta += idelta; | |
385 | *index = ibase; | |
386 | ||
387 | return true; | |
388 | } | |
389 | ||
aac8b8ed | 390 | /* Tries to express REF_P in shape &BASE + STEP * iter + DELTA, where DELTA and |
b076a3fd | 391 | STEP are integer constants and iter is number of iterations of LOOP. The |
aac8b8ed RS |
392 | reference occurs in statement STMT. Strips nonaddressable component |
393 | references from REF_P. */ | |
b076a3fd ZD |
394 | |
395 | static bool | |
aac8b8ed | 396 | analyze_ref (struct loop *loop, tree *ref_p, tree *base, |
b076a3fd ZD |
397 | HOST_WIDE_INT *step, HOST_WIDE_INT *delta, |
398 | tree stmt) | |
399 | { | |
400 | struct ar_data ar_data; | |
401 | tree off; | |
402 | HOST_WIDE_INT bit_offset; | |
aac8b8ed | 403 | tree ref = *ref_p; |
b076a3fd ZD |
404 | |
405 | *step = 0; | |
406 | *delta = 0; | |
407 | ||
408 | /* First strip off the component references. Ignore bitfields. */ | |
409 | if (TREE_CODE (ref) == COMPONENT_REF | |
410 | && DECL_NONADDRESSABLE_P (TREE_OPERAND (ref, 1))) | |
411 | ref = TREE_OPERAND (ref, 0); | |
412 | ||
aac8b8ed RS |
413 | *ref_p = ref; |
414 | ||
b076a3fd ZD |
415 | for (; TREE_CODE (ref) == COMPONENT_REF; ref = TREE_OPERAND (ref, 0)) |
416 | { | |
417 | off = DECL_FIELD_BIT_OFFSET (TREE_OPERAND (ref, 1)); | |
418 | bit_offset = TREE_INT_CST_LOW (off); | |
419 | gcc_assert (bit_offset % BITS_PER_UNIT == 0); | |
420 | ||
421 | *delta += bit_offset / BITS_PER_UNIT; | |
422 | } | |
423 | ||
424 | *base = unshare_expr (ref); | |
425 | ar_data.loop = loop; | |
426 | ar_data.stmt = stmt; | |
427 | ar_data.step = step; | |
428 | ar_data.delta = delta; | |
429 | return for_each_index (base, idx_analyze_ref, &ar_data); | |
430 | } | |
431 | ||
432 | /* Record a memory reference REF to the list REFS. The reference occurs in | |
433 | LOOP in statement STMT and it is write if WRITE_P. */ | |
434 | ||
435 | static void | |
436 | gather_memory_references_ref (struct loop *loop, struct mem_ref_group **refs, | |
437 | tree ref, bool write_p, tree stmt) | |
438 | { | |
439 | tree base; | |
440 | HOST_WIDE_INT step, delta; | |
441 | struct mem_ref_group *agrp; | |
442 | ||
aac8b8ed | 443 | if (!analyze_ref (loop, &ref, &base, &step, &delta, stmt)) |
b076a3fd ZD |
444 | return; |
445 | ||
446 | /* Now we know that REF = &BASE + STEP * iter + DELTA, where DELTA and STEP | |
447 | are integer constants. */ | |
448 | agrp = find_or_create_group (refs, base, step); | |
449 | record_ref (agrp, stmt, ref, delta, write_p); | |
450 | } | |
451 | ||
452 | /* Record the suitable memory references in LOOP. */ | |
453 | ||
454 | static struct mem_ref_group * | |
455 | gather_memory_references (struct loop *loop) | |
456 | { | |
457 | basic_block *body = get_loop_body_in_dom_order (loop); | |
458 | basic_block bb; | |
459 | unsigned i; | |
460 | block_stmt_iterator bsi; | |
461 | tree stmt, lhs, rhs; | |
462 | struct mem_ref_group *refs = NULL; | |
463 | ||
464 | /* Scan the loop body in order, so that the former references precede the | |
465 | later ones. */ | |
466 | for (i = 0; i < loop->num_nodes; i++) | |
467 | { | |
468 | bb = body[i]; | |
469 | if (bb->loop_father != loop) | |
470 | continue; | |
471 | ||
472 | for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi)) | |
473 | { | |
474 | stmt = bsi_stmt (bsi); | |
475 | if (TREE_CODE (stmt) != MODIFY_EXPR) | |
476 | continue; | |
477 | ||
478 | lhs = TREE_OPERAND (stmt, 0); | |
479 | rhs = TREE_OPERAND (stmt, 1); | |
480 | ||
481 | if (REFERENCE_CLASS_P (rhs)) | |
482 | gather_memory_references_ref (loop, &refs, rhs, false, stmt); | |
483 | if (REFERENCE_CLASS_P (lhs)) | |
484 | gather_memory_references_ref (loop, &refs, lhs, true, stmt); | |
485 | } | |
486 | } | |
487 | free (body); | |
488 | ||
489 | return refs; | |
490 | } | |
491 | ||
492 | /* Prune the prefetch candidate REF using the self-reuse. */ | |
493 | ||
494 | static void | |
495 | prune_ref_by_self_reuse (struct mem_ref *ref) | |
496 | { | |
497 | HOST_WIDE_INT step = ref->group->step; | |
498 | bool backward = step < 0; | |
499 | ||
500 | if (step == 0) | |
501 | { | |
502 | /* Prefetch references to invariant address just once. */ | |
503 | ref->prefetch_before = 1; | |
504 | return; | |
505 | } | |
506 | ||
507 | if (backward) | |
508 | step = -step; | |
509 | ||
510 | if (step > PREFETCH_BLOCK) | |
511 | return; | |
512 | ||
513 | if ((backward && HAVE_BACKWARD_PREFETCH) | |
514 | || (!backward && HAVE_FORWARD_PREFETCH)) | |
515 | { | |
516 | ref->prefetch_before = 1; | |
517 | return; | |
518 | } | |
519 | ||
520 | ref->prefetch_mod = PREFETCH_BLOCK / step; | |
521 | } | |
522 | ||
523 | /* Divides X by BY, rounding down. */ | |
524 | ||
525 | static HOST_WIDE_INT | |
526 | ddown (HOST_WIDE_INT x, unsigned HOST_WIDE_INT by) | |
527 | { | |
528 | gcc_assert (by > 0); | |
529 | ||
530 | if (x >= 0) | |
531 | return x / by; | |
532 | else | |
533 | return (x + by - 1) / by; | |
534 | } | |
535 | ||
536 | /* Prune the prefetch candidate REF using the reuse with BY. | |
537 | If BY_IS_BEFORE is true, BY is before REF in the loop. */ | |
538 | ||
539 | static void | |
540 | prune_ref_by_group_reuse (struct mem_ref *ref, struct mem_ref *by, | |
541 | bool by_is_before) | |
542 | { | |
543 | HOST_WIDE_INT step = ref->group->step; | |
544 | bool backward = step < 0; | |
545 | HOST_WIDE_INT delta_r = ref->delta, delta_b = by->delta; | |
546 | HOST_WIDE_INT delta = delta_b - delta_r; | |
547 | HOST_WIDE_INT hit_from; | |
548 | unsigned HOST_WIDE_INT prefetch_before, prefetch_block; | |
549 | ||
550 | if (delta == 0) | |
551 | { | |
552 | /* If the references has the same address, only prefetch the | |
553 | former. */ | |
554 | if (by_is_before) | |
555 | ref->prefetch_before = 0; | |
556 | ||
557 | return; | |
558 | } | |
559 | ||
560 | if (!step) | |
561 | { | |
562 | /* If the reference addresses are invariant and fall into the | |
563 | same cache line, prefetch just the first one. */ | |
564 | if (!by_is_before) | |
565 | return; | |
566 | ||
567 | if (ddown (ref->delta, PREFETCH_BLOCK) | |
568 | != ddown (by->delta, PREFETCH_BLOCK)) | |
569 | return; | |
570 | ||
571 | ref->prefetch_before = 0; | |
572 | return; | |
573 | } | |
574 | ||
575 | /* Only prune the reference that is behind in the array. */ | |
576 | if (backward) | |
577 | { | |
578 | if (delta > 0) | |
579 | return; | |
580 | ||
581 | /* Transform the data so that we may assume that the accesses | |
582 | are forward. */ | |
583 | delta = - delta; | |
584 | step = -step; | |
585 | delta_r = PREFETCH_BLOCK - 1 - delta_r; | |
586 | delta_b = PREFETCH_BLOCK - 1 - delta_b; | |
587 | } | |
588 | else | |
589 | { | |
590 | if (delta < 0) | |
591 | return; | |
592 | } | |
593 | ||
594 | /* Check whether the two references are likely to hit the same cache | |
595 | line, and how distant the iterations in that it occurs are from | |
596 | each other. */ | |
597 | ||
598 | if (step <= PREFETCH_BLOCK) | |
599 | { | |
600 | /* The accesses are sure to meet. Let us check when. */ | |
601 | hit_from = ddown (delta_b, PREFETCH_BLOCK) * PREFETCH_BLOCK; | |
602 | prefetch_before = (hit_from - delta_r + step - 1) / step; | |
603 | ||
604 | if (prefetch_before < ref->prefetch_before) | |
605 | ref->prefetch_before = prefetch_before; | |
606 | ||
607 | return; | |
608 | } | |
609 | ||
610 | /* A more complicated case. First let us ensure that size of cache line | |
611 | and step are coprime (here we assume that PREFETCH_BLOCK is a power | |
612 | of two. */ | |
613 | prefetch_block = PREFETCH_BLOCK; | |
614 | while ((step & 1) == 0 | |
615 | && prefetch_block > 1) | |
616 | { | |
617 | step >>= 1; | |
618 | prefetch_block >>= 1; | |
619 | delta >>= 1; | |
620 | } | |
621 | ||
622 | /* Now step > prefetch_block, and step and prefetch_block are coprime. | |
623 | Determine the probability that the accesses hit the same cache line. */ | |
624 | ||
625 | prefetch_before = delta / step; | |
626 | delta %= step; | |
627 | if ((unsigned HOST_WIDE_INT) delta | |
628 | <= (prefetch_block * ACCEPTABLE_MISS_RATE / 1000)) | |
629 | { | |
630 | if (prefetch_before < ref->prefetch_before) | |
631 | ref->prefetch_before = prefetch_before; | |
632 | ||
633 | return; | |
634 | } | |
635 | ||
636 | /* Try also the following iteration. */ | |
637 | prefetch_before++; | |
638 | delta = step - delta; | |
639 | if ((unsigned HOST_WIDE_INT) delta | |
640 | <= (prefetch_block * ACCEPTABLE_MISS_RATE / 1000)) | |
641 | { | |
642 | if (prefetch_before < ref->prefetch_before) | |
643 | ref->prefetch_before = prefetch_before; | |
644 | ||
645 | return; | |
646 | } | |
647 | ||
648 | /* The ref probably does not reuse by. */ | |
649 | return; | |
650 | } | |
651 | ||
652 | /* Prune the prefetch candidate REF using the reuses with other references | |
653 | in REFS. */ | |
654 | ||
655 | static void | |
656 | prune_ref_by_reuse (struct mem_ref *ref, struct mem_ref *refs) | |
657 | { | |
658 | struct mem_ref *prune_by; | |
659 | bool before = true; | |
660 | ||
661 | prune_ref_by_self_reuse (ref); | |
662 | ||
663 | for (prune_by = refs; prune_by; prune_by = prune_by->next) | |
664 | { | |
665 | if (prune_by == ref) | |
666 | { | |
667 | before = false; | |
668 | continue; | |
669 | } | |
670 | ||
671 | if (!WRITE_CAN_USE_READ_PREFETCH | |
672 | && ref->write_p | |
673 | && !prune_by->write_p) | |
674 | continue; | |
675 | if (!READ_CAN_USE_WRITE_PREFETCH | |
676 | && !ref->write_p | |
677 | && prune_by->write_p) | |
678 | continue; | |
679 | ||
680 | prune_ref_by_group_reuse (ref, prune_by, before); | |
681 | } | |
682 | } | |
683 | ||
684 | /* Prune the prefetch candidates in GROUP using the reuse analysis. */ | |
685 | ||
686 | static void | |
687 | prune_group_by_reuse (struct mem_ref_group *group) | |
688 | { | |
689 | struct mem_ref *ref_pruned; | |
690 | ||
691 | for (ref_pruned = group->refs; ref_pruned; ref_pruned = ref_pruned->next) | |
692 | { | |
693 | prune_ref_by_reuse (ref_pruned, group->refs); | |
694 | ||
695 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
696 | { | |
697 | fprintf (dump_file, "Reference %p:", (void *) ref_pruned); | |
698 | ||
699 | if (ref_pruned->prefetch_before == PREFETCH_ALL | |
700 | && ref_pruned->prefetch_mod == 1) | |
701 | fprintf (dump_file, " no restrictions"); | |
702 | else if (ref_pruned->prefetch_before == 0) | |
703 | fprintf (dump_file, " do not prefetch"); | |
704 | else if (ref_pruned->prefetch_before <= ref_pruned->prefetch_mod) | |
705 | fprintf (dump_file, " prefetch once"); | |
706 | else | |
707 | { | |
708 | if (ref_pruned->prefetch_before != PREFETCH_ALL) | |
709 | { | |
710 | fprintf (dump_file, " prefetch before "); | |
711 | fprintf (dump_file, HOST_WIDE_INT_PRINT_DEC, | |
712 | ref_pruned->prefetch_before); | |
713 | } | |
714 | if (ref_pruned->prefetch_mod != 1) | |
715 | { | |
716 | fprintf (dump_file, " prefetch mod "); | |
717 | fprintf (dump_file, HOST_WIDE_INT_PRINT_DEC, | |
718 | ref_pruned->prefetch_mod); | |
719 | } | |
720 | } | |
721 | fprintf (dump_file, "\n"); | |
722 | } | |
723 | } | |
724 | } | |
725 | ||
726 | /* Prune the list of prefetch candidates GROUPS using the reuse analysis. */ | |
727 | ||
728 | static void | |
729 | prune_by_reuse (struct mem_ref_group *groups) | |
730 | { | |
731 | for (; groups; groups = groups->next) | |
732 | prune_group_by_reuse (groups); | |
733 | } | |
734 | ||
735 | /* Returns true if we should issue prefetch for REF. */ | |
736 | ||
737 | static bool | |
738 | should_issue_prefetch_p (struct mem_ref *ref) | |
739 | { | |
740 | /* For now do not issue prefetches for only first few of the | |
741 | iterations. */ | |
742 | if (ref->prefetch_before != PREFETCH_ALL) | |
743 | return false; | |
744 | ||
745 | return true; | |
746 | } | |
747 | ||
748 | /* Decide which of the prefetch candidates in GROUPS to prefetch. | |
749 | AHEAD is the number of iterations to prefetch ahead (which corresponds | |
750 | to the number of simultaneous instances of one prefetch running at a | |
751 | time). UNROLL_FACTOR is the factor by that the loop is going to be | |
752 | unrolled. Returns true if there is anything to prefetch. */ | |
753 | ||
754 | static bool | |
755 | schedule_prefetches (struct mem_ref_group *groups, unsigned unroll_factor, | |
756 | unsigned ahead) | |
757 | { | |
758 | unsigned max_prefetches, n_prefetches; | |
759 | struct mem_ref *ref; | |
760 | bool any = false; | |
761 | ||
762 | max_prefetches = (SIMULTANEOUS_PREFETCHES * unroll_factor) / ahead; | |
763 | if (max_prefetches > (unsigned) SIMULTANEOUS_PREFETCHES) | |
764 | max_prefetches = SIMULTANEOUS_PREFETCHES; | |
765 | ||
766 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
767 | fprintf (dump_file, "Max prefetches to issue: %d.\n", max_prefetches); | |
768 | ||
769 | if (!max_prefetches) | |
770 | return false; | |
771 | ||
772 | /* For now we just take memory references one by one and issue | |
773 | prefetches for as many as possible. The groups are sorted | |
774 | starting with the largest step, since the references with | |
c0220ea4 | 775 | large step are more likely to cause many cache misses. */ |
b076a3fd ZD |
776 | |
777 | for (; groups; groups = groups->next) | |
778 | for (ref = groups->refs; ref; ref = ref->next) | |
779 | { | |
780 | if (!should_issue_prefetch_p (ref)) | |
781 | continue; | |
782 | ||
783 | ref->issue_prefetch_p = true; | |
784 | ||
785 | /* If prefetch_mod is less then unroll_factor, we need to insert | |
786 | several prefetches for the reference. */ | |
787 | n_prefetches = ((unroll_factor + ref->prefetch_mod - 1) | |
788 | / ref->prefetch_mod); | |
789 | if (max_prefetches <= n_prefetches) | |
790 | return true; | |
791 | ||
792 | max_prefetches -= n_prefetches; | |
793 | any = true; | |
794 | } | |
795 | ||
796 | return any; | |
797 | } | |
798 | ||
799 | /* Determine whether there is any reference suitable for prefetching | |
800 | in GROUPS. */ | |
801 | ||
802 | static bool | |
803 | anything_to_prefetch_p (struct mem_ref_group *groups) | |
804 | { | |
805 | struct mem_ref *ref; | |
806 | ||
807 | for (; groups; groups = groups->next) | |
808 | for (ref = groups->refs; ref; ref = ref->next) | |
809 | if (should_issue_prefetch_p (ref)) | |
810 | return true; | |
811 | ||
812 | return false; | |
813 | } | |
814 | ||
815 | /* Issue prefetches for the reference REF into loop as decided before. | |
816 | HEAD is the number of iterations to prefetch ahead. UNROLL_FACTOR | |
917f1b7e | 817 | is the factor by which LOOP was unrolled. */ |
b076a3fd ZD |
818 | |
819 | static void | |
820 | issue_prefetch_ref (struct mem_ref *ref, unsigned unroll_factor, unsigned ahead) | |
821 | { | |
822 | HOST_WIDE_INT delta; | |
823 | tree addr, addr_base, prefetch, params, write_p; | |
824 | block_stmt_iterator bsi; | |
825 | unsigned n_prefetches, ap; | |
826 | ||
827 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
828 | fprintf (dump_file, "Issued prefetch for %p.\n", (void *) ref); | |
829 | ||
830 | bsi = bsi_for_stmt (ref->stmt); | |
831 | ||
832 | n_prefetches = ((unroll_factor + ref->prefetch_mod - 1) | |
833 | / ref->prefetch_mod); | |
834 | addr_base = build_fold_addr_expr_with_type (ref->mem, ptr_type_node); | |
835 | addr_base = force_gimple_operand_bsi (&bsi, unshare_expr (addr_base), true, NULL); | |
836 | ||
837 | for (ap = 0; ap < n_prefetches; ap++) | |
838 | { | |
839 | /* Determine the address to prefetch. */ | |
840 | delta = (ahead + ap * ref->prefetch_mod) * ref->group->step; | |
841 | addr = fold_build2 (PLUS_EXPR, ptr_type_node, | |
842 | addr_base, build_int_cst (ptr_type_node, delta)); | |
843 | addr = force_gimple_operand_bsi (&bsi, unshare_expr (addr), true, NULL); | |
844 | ||
845 | /* Create the prefetch instruction. */ | |
846 | write_p = ref->write_p ? integer_one_node : integer_zero_node; | |
847 | params = tree_cons (NULL_TREE, addr, | |
848 | tree_cons (NULL_TREE, write_p, NULL_TREE)); | |
849 | ||
850 | prefetch = build_function_call_expr (built_in_decls[BUILT_IN_PREFETCH], | |
851 | params); | |
852 | bsi_insert_before (&bsi, prefetch, BSI_SAME_STMT); | |
853 | } | |
854 | } | |
855 | ||
856 | /* Issue prefetches for the references in GROUPS into loop as decided before. | |
857 | HEAD is the number of iterations to prefetch ahead. UNROLL_FACTOR is the | |
858 | factor by that LOOP was unrolled. */ | |
859 | ||
860 | static void | |
861 | issue_prefetches (struct mem_ref_group *groups, | |
862 | unsigned unroll_factor, unsigned ahead) | |
863 | { | |
864 | struct mem_ref *ref; | |
865 | ||
866 | for (; groups; groups = groups->next) | |
867 | for (ref = groups->refs; ref; ref = ref->next) | |
868 | if (ref->issue_prefetch_p) | |
869 | issue_prefetch_ref (ref, unroll_factor, ahead); | |
870 | } | |
871 | ||
872 | /* Determines whether we can profitably unroll LOOP FACTOR times, and if | |
873 | this is the case, fill in DESC by the description of number of | |
874 | iterations. */ | |
875 | ||
876 | static bool | |
877 | should_unroll_loop_p (struct loop *loop, struct tree_niter_desc *desc, | |
878 | unsigned factor) | |
879 | { | |
880 | if (!can_unroll_loop_p (loop, factor, desc)) | |
881 | return false; | |
882 | ||
883 | /* We only consider loops without control flow for unrolling. This is not | |
884 | a hard restriction -- tree_unroll_loop works with arbitrary loops | |
885 | as well; but the unrolling/prefetching is usually more profitable for | |
886 | loops consisting of a single basic block, and we want to limit the | |
887 | code growth. */ | |
888 | if (loop->num_nodes > 2) | |
889 | return false; | |
890 | ||
891 | return true; | |
892 | } | |
893 | ||
894 | /* Determine the coefficient by that unroll LOOP, from the information | |
895 | contained in the list of memory references REFS. Description of | |
896 | umber of iterations of LOOP is stored to DESC. AHEAD is the number | |
897 | of iterations ahead that we need to prefetch. NINSNS is number of | |
898 | insns of the LOOP. */ | |
899 | ||
900 | static unsigned | |
901 | determine_unroll_factor (struct loop *loop, struct mem_ref_group *refs, | |
902 | unsigned ahead, unsigned ninsns, | |
903 | struct tree_niter_desc *desc) | |
904 | { | |
905 | unsigned upper_bound, size_factor, constraint_factor; | |
906 | unsigned factor, max_mod_constraint, ahead_factor; | |
907 | struct mem_ref_group *agp; | |
908 | struct mem_ref *ref; | |
909 | ||
910 | upper_bound = PARAM_VALUE (PARAM_MAX_UNROLL_TIMES); | |
911 | ||
912 | /* First check whether the loop is not too large to unroll. */ | |
913 | size_factor = PARAM_VALUE (PARAM_MAX_UNROLLED_INSNS) / ninsns; | |
914 | if (size_factor <= 1) | |
915 | return 1; | |
916 | ||
917 | if (size_factor < upper_bound) | |
918 | upper_bound = size_factor; | |
919 | ||
920 | max_mod_constraint = 1; | |
921 | for (agp = refs; agp; agp = agp->next) | |
922 | for (ref = agp->refs; ref; ref = ref->next) | |
923 | if (should_issue_prefetch_p (ref) | |
924 | && ref->prefetch_mod > max_mod_constraint) | |
925 | max_mod_constraint = ref->prefetch_mod; | |
926 | ||
927 | /* Set constraint_factor as large as needed to be able to satisfy the | |
928 | largest modulo constraint. */ | |
929 | constraint_factor = max_mod_constraint; | |
930 | ||
931 | /* If ahead is too large in comparison with the number of available | |
932 | prefetches, unroll the loop as much as needed to be able to prefetch | |
933 | at least partially some of the references in the loop. */ | |
934 | ahead_factor = ((ahead + SIMULTANEOUS_PREFETCHES - 1) | |
935 | / SIMULTANEOUS_PREFETCHES); | |
936 | ||
937 | /* Unroll as much as useful, but bound the code size growth. */ | |
938 | if (constraint_factor < ahead_factor) | |
939 | factor = ahead_factor; | |
940 | else | |
941 | factor = constraint_factor; | |
942 | if (factor > upper_bound) | |
943 | factor = upper_bound; | |
944 | ||
945 | if (!should_unroll_loop_p (loop, desc, factor)) | |
946 | return 1; | |
947 | ||
948 | return factor; | |
949 | } | |
950 | ||
951 | /* Issue prefetch instructions for array references in LOOP. Returns | |
952 | true if the LOOP was unrolled. LOOPS is the array containing all | |
953 | loops. */ | |
954 | ||
955 | static bool | |
956 | loop_prefetch_arrays (struct loops *loops, struct loop *loop) | |
957 | { | |
958 | struct mem_ref_group *refs; | |
959 | unsigned ahead, ninsns, unroll_factor; | |
960 | struct tree_niter_desc desc; | |
961 | bool unrolled = false; | |
962 | ||
963 | /* Step 1: gather the memory references. */ | |
964 | refs = gather_memory_references (loop); | |
965 | ||
966 | /* Step 2: estimate the reuse effects. */ | |
967 | prune_by_reuse (refs); | |
968 | ||
969 | if (!anything_to_prefetch_p (refs)) | |
970 | goto fail; | |
971 | ||
972 | /* Step 3: determine the ahead and unroll factor. */ | |
973 | ||
974 | /* FIXME: We should use not size of the loop, but the average number of | |
975 | instructions executed per iteration of the loop. */ | |
976 | ninsns = tree_num_loop_insns (loop); | |
977 | ahead = (PREFETCH_LATENCY + ninsns - 1) / ninsns; | |
978 | unroll_factor = determine_unroll_factor (loop, refs, ahead, ninsns, | |
979 | &desc); | |
980 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
981 | fprintf (dump_file, "Ahead %d, unroll factor %d\n", ahead, unroll_factor); | |
982 | ||
983 | /* If the loop rolls less than the required unroll factor, prefetching | |
984 | is useless. */ | |
985 | if (unroll_factor > 1 | |
986 | && cst_and_fits_in_hwi (desc.niter) | |
987 | && (unsigned HOST_WIDE_INT) int_cst_value (desc.niter) < unroll_factor) | |
988 | goto fail; | |
989 | ||
990 | /* Step 4: what to prefetch? */ | |
991 | if (!schedule_prefetches (refs, unroll_factor, ahead)) | |
992 | goto fail; | |
993 | ||
994 | /* Step 5: unroll the loop. TODO -- peeling of first and last few | |
995 | iterations so that we do not issue superfluous prefetches. */ | |
996 | if (unroll_factor != 1) | |
997 | { | |
998 | tree_unroll_loop (loops, loop, unroll_factor, | |
999 | single_dom_exit (loop), &desc); | |
1000 | unrolled = true; | |
1001 | } | |
1002 | ||
1003 | /* Step 6: issue the prefetches. */ | |
1004 | issue_prefetches (refs, unroll_factor, ahead); | |
1005 | ||
1006 | fail: | |
1007 | release_mem_refs (refs); | |
1008 | return unrolled; | |
1009 | } | |
1010 | ||
1011 | /* Issue prefetch instructions for array references in LOOPS. */ | |
1012 | ||
c7f965b6 | 1013 | unsigned int |
b076a3fd ZD |
1014 | tree_ssa_prefetch_arrays (struct loops *loops) |
1015 | { | |
1016 | unsigned i; | |
1017 | struct loop *loop; | |
1018 | bool unrolled = false; | |
c7f965b6 | 1019 | int todo_flags = 0; |
b076a3fd ZD |
1020 | |
1021 | if (!HAVE_prefetch | |
1022 | /* It is possible to ask compiler for say -mtune=i486 -march=pentium4. | |
1023 | -mtune=i486 causes us having PREFETCH_BLOCK 0, since this is part | |
1024 | of processor costs and i486 does not have prefetch, but | |
1025 | -march=pentium4 causes HAVE_prefetch to be true. Ugh. */ | |
1026 | || PREFETCH_BLOCK == 0) | |
c7f965b6 | 1027 | return 0; |
b076a3fd ZD |
1028 | |
1029 | initialize_original_copy_tables (); | |
1030 | ||
1031 | if (!built_in_decls[BUILT_IN_PREFETCH]) | |
1032 | { | |
1033 | tree type = build_function_type (void_type_node, | |
1034 | tree_cons (NULL_TREE, | |
1035 | const_ptr_type_node, | |
1036 | NULL_TREE)); | |
c79efc4d RÁE |
1037 | tree decl = add_builtin_function ("__builtin_prefetch", type, |
1038 | BUILT_IN_PREFETCH, BUILT_IN_NORMAL, | |
1039 | NULL, NULL_TREE); | |
b076a3fd ZD |
1040 | DECL_IS_NOVOPS (decl) = true; |
1041 | built_in_decls[BUILT_IN_PREFETCH] = decl; | |
1042 | } | |
1043 | ||
1044 | /* We assume that size of cache line is a power of two, so verify this | |
1045 | here. */ | |
1046 | gcc_assert ((PREFETCH_BLOCK & (PREFETCH_BLOCK - 1)) == 0); | |
1047 | ||
1048 | for (i = loops->num - 1; i > 0; i--) | |
1049 | { | |
1050 | loop = loops->parray[i]; | |
1051 | ||
1052 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
1053 | fprintf (dump_file, "Processing loop %d:\n", loop->num); | |
1054 | ||
1055 | if (loop) | |
1056 | unrolled |= loop_prefetch_arrays (loops, loop); | |
1057 | ||
1058 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
1059 | fprintf (dump_file, "\n\n"); | |
1060 | } | |
1061 | ||
1062 | if (unrolled) | |
1063 | { | |
1064 | scev_reset (); | |
c7f965b6 | 1065 | todo_flags |= TODO_cleanup_cfg; |
b076a3fd ZD |
1066 | } |
1067 | ||
1068 | free_original_copy_tables (); | |
c7f965b6 | 1069 | return todo_flags; |
b076a3fd | 1070 | } |