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b076a3fd | 1 | /* Array prefetching. |
fa10beec | 2 | Copyright (C) 2005, 2007, 2008 Free Software Foundation, Inc. |
b8698a0f | 3 | |
b076a3fd | 4 | This file is part of GCC. |
b8698a0f | 5 | |
b076a3fd ZD |
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 | |
9dcd6f09 | 8 | Free Software Foundation; either version 3, or (at your option) any |
b076a3fd | 9 | later version. |
b8698a0f | 10 | |
b076a3fd ZD |
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. | |
b8698a0f | 15 | |
b076a3fd | 16 | You should have received a copy of the GNU General Public License |
9dcd6f09 NC |
17 | along with GCC; see the file COPYING3. If not see |
18 | <http://www.gnu.org/licenses/>. */ | |
b076a3fd ZD |
19 | |
20 | #include "config.h" | |
21 | #include "system.h" | |
22 | #include "coretypes.h" | |
23 | #include "tm.h" | |
24 | #include "tree.h" | |
25 | #include "rtl.h" | |
26 | #include "tm_p.h" | |
27 | #include "hard-reg-set.h" | |
28 | #include "basic-block.h" | |
29 | #include "output.h" | |
30 | #include "diagnostic.h" | |
31 | #include "tree-flow.h" | |
32 | #include "tree-dump.h" | |
33 | #include "timevar.h" | |
34 | #include "cfgloop.h" | |
b076a3fd ZD |
35 | #include "expr.h" |
36 | #include "tree-pass.h" | |
37 | #include "ggc.h" | |
38 | #include "insn-config.h" | |
39 | #include "recog.h" | |
40 | #include "hashtab.h" | |
41 | #include "tree-chrec.h" | |
42 | #include "tree-scalar-evolution.h" | |
43 | #include "toplev.h" | |
44 | #include "params.h" | |
45 | #include "langhooks.h" | |
7f9bc51b | 46 | #include "tree-inline.h" |
5417e022 | 47 | #include "tree-data-ref.h" |
79f5e442 | 48 | #include "optabs.h" |
b076a3fd ZD |
49 | |
50 | /* This pass inserts prefetch instructions to optimize cache usage during | |
51 | accesses to arrays in loops. It processes loops sequentially and: | |
52 | ||
53 | 1) Gathers all memory references in the single loop. | |
54 | 2) For each of the references it decides when it is profitable to prefetch | |
55 | it. To do it, we evaluate the reuse among the accesses, and determines | |
56 | two values: PREFETCH_BEFORE (meaning that it only makes sense to do | |
57 | prefetching in the first PREFETCH_BEFORE iterations of the loop) and | |
58 | PREFETCH_MOD (meaning that it only makes sense to prefetch in the | |
59 | iterations of the loop that are zero modulo PREFETCH_MOD). For example | |
60 | (assuming cache line size is 64 bytes, char has size 1 byte and there | |
61 | is no hardware sequential prefetch): | |
62 | ||
63 | char *a; | |
64 | for (i = 0; i < max; i++) | |
65 | { | |
66 | a[255] = ...; (0) | |
67 | a[i] = ...; (1) | |
68 | a[i + 64] = ...; (2) | |
69 | a[16*i] = ...; (3) | |
70 | a[187*i] = ...; (4) | |
71 | a[187*i + 50] = ...; (5) | |
72 | } | |
73 | ||
74 | (0) obviously has PREFETCH_BEFORE 1 | |
75 | (1) has PREFETCH_BEFORE 64, since (2) accesses the same memory | |
76 | location 64 iterations before it, and PREFETCH_MOD 64 (since | |
77 | it hits the same cache line otherwise). | |
78 | (2) has PREFETCH_MOD 64 | |
79 | (3) has PREFETCH_MOD 4 | |
80 | (4) has PREFETCH_MOD 1. We do not set PREFETCH_BEFORE here, since | |
81 | the cache line accessed by (4) is the same with probability only | |
82 | 7/32. | |
83 | (5) has PREFETCH_MOD 1 as well. | |
84 | ||
5417e022 ZD |
85 | Additionally, we use data dependence analysis to determine for each |
86 | reference the distance till the first reuse; this information is used | |
87 | to determine the temporality of the issued prefetch instruction. | |
88 | ||
b076a3fd ZD |
89 | 3) We determine how much ahead we need to prefetch. The number of |
90 | iterations needed is time to fetch / time spent in one iteration of | |
91 | the loop. The problem is that we do not know either of these values, | |
92 | so we just make a heuristic guess based on a magic (possibly) | |
93 | target-specific constant and size of the loop. | |
94 | ||
95 | 4) Determine which of the references we prefetch. We take into account | |
96 | that there is a maximum number of simultaneous prefetches (provided | |
97 | by machine description). We prefetch as many prefetches as possible | |
98 | while still within this bound (starting with those with lowest | |
99 | prefetch_mod, since they are responsible for most of the cache | |
100 | misses). | |
b8698a0f | 101 | |
b076a3fd ZD |
102 | 5) We unroll and peel loops so that we are able to satisfy PREFETCH_MOD |
103 | and PREFETCH_BEFORE requirements (within some bounds), and to avoid | |
104 | prefetching nonaccessed memory. | |
105 | TODO -- actually implement peeling. | |
b8698a0f | 106 | |
b076a3fd ZD |
107 | 6) We actually emit the prefetch instructions. ??? Perhaps emit the |
108 | prefetch instructions with guards in cases where 5) was not sufficient | |
109 | to satisfy the constraints? | |
110 | ||
db34470d GS |
111 | The function is_loop_prefetching_profitable() implements a cost model |
112 | to determine if prefetching is profitable for a given loop. The cost | |
113 | model has two heuristcs: | |
114 | 1. A heuristic that determines whether the given loop has enough CPU | |
115 | ops that can be overlapped with cache missing memory ops. | |
b8698a0f L |
116 | If not, the loop won't benefit from prefetching. This is implemented |
117 | by requirung the ratio between the instruction count and the mem ref | |
db34470d GS |
118 | count to be above a certain minimum. |
119 | 2. A heuristic that disables prefetching in a loop with an unknown trip | |
b8698a0f | 120 | count if the prefetching cost is above a certain limit. The relative |
db34470d GS |
121 | prefetching cost is estimated by taking the ratio between the |
122 | prefetch count and the total intruction count (this models the I-cache | |
123 | cost). | |
124 | The limits used in these heuristics are defined as parameters with | |
b8698a0f | 125 | reasonable default values. Machine-specific default values will be |
db34470d | 126 | added later. |
b8698a0f | 127 | |
b076a3fd ZD |
128 | Some other TODO: |
129 | -- write and use more general reuse analysis (that could be also used | |
130 | in other cache aimed loop optimizations) | |
131 | -- make it behave sanely together with the prefetches given by user | |
132 | (now we just ignore them; at the very least we should avoid | |
133 | optimizing loops in that user put his own prefetches) | |
134 | -- we assume cache line size alignment of arrays; this could be | |
135 | improved. */ | |
136 | ||
137 | /* Magic constants follow. These should be replaced by machine specific | |
138 | numbers. */ | |
139 | ||
b076a3fd ZD |
140 | /* True if write can be prefetched by a read prefetch. */ |
141 | ||
142 | #ifndef WRITE_CAN_USE_READ_PREFETCH | |
143 | #define WRITE_CAN_USE_READ_PREFETCH 1 | |
144 | #endif | |
145 | ||
146 | /* True if read can be prefetched by a write prefetch. */ | |
147 | ||
148 | #ifndef READ_CAN_USE_WRITE_PREFETCH | |
149 | #define READ_CAN_USE_WRITE_PREFETCH 0 | |
150 | #endif | |
151 | ||
47eb5b32 ZD |
152 | /* The size of the block loaded by a single prefetch. Usually, this is |
153 | the same as cache line size (at the moment, we only consider one level | |
154 | of cache hierarchy). */ | |
b076a3fd ZD |
155 | |
156 | #ifndef PREFETCH_BLOCK | |
47eb5b32 | 157 | #define PREFETCH_BLOCK L1_CACHE_LINE_SIZE |
b076a3fd ZD |
158 | #endif |
159 | ||
160 | /* Do we have a forward hardware sequential prefetching? */ | |
161 | ||
162 | #ifndef HAVE_FORWARD_PREFETCH | |
163 | #define HAVE_FORWARD_PREFETCH 0 | |
164 | #endif | |
165 | ||
166 | /* Do we have a backward hardware sequential prefetching? */ | |
167 | ||
168 | #ifndef HAVE_BACKWARD_PREFETCH | |
169 | #define HAVE_BACKWARD_PREFETCH 0 | |
170 | #endif | |
171 | ||
172 | /* In some cases we are only able to determine that there is a certain | |
173 | probability that the two accesses hit the same cache line. In this | |
174 | case, we issue the prefetches for both of them if this probability | |
fa10beec | 175 | is less then (1000 - ACCEPTABLE_MISS_RATE) per thousand. */ |
b076a3fd ZD |
176 | |
177 | #ifndef ACCEPTABLE_MISS_RATE | |
178 | #define ACCEPTABLE_MISS_RATE 50 | |
179 | #endif | |
180 | ||
181 | #ifndef HAVE_prefetch | |
182 | #define HAVE_prefetch 0 | |
183 | #endif | |
184 | ||
46cb0441 ZD |
185 | #define L1_CACHE_SIZE_BYTES ((unsigned) (L1_CACHE_SIZE * 1024)) |
186 | #define L2_CACHE_SIZE_BYTES ((unsigned) (L2_CACHE_SIZE * 1024)) | |
5417e022 ZD |
187 | |
188 | /* We consider a memory access nontemporal if it is not reused sooner than | |
189 | after L2_CACHE_SIZE_BYTES of memory are accessed. However, we ignore | |
190 | accesses closer than L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION, | |
191 | so that we use nontemporal prefetches e.g. if single memory location | |
192 | is accessed several times in a single iteration of the loop. */ | |
193 | #define NONTEMPORAL_FRACTION 16 | |
194 | ||
79f5e442 ZD |
195 | /* In case we have to emit a memory fence instruction after the loop that |
196 | uses nontemporal stores, this defines the builtin to use. */ | |
197 | ||
198 | #ifndef FENCE_FOLLOWING_MOVNT | |
199 | #define FENCE_FOLLOWING_MOVNT NULL_TREE | |
200 | #endif | |
201 | ||
9bf4598b CF |
202 | /* It is not profitable to prefetch when the trip count is not at |
203 | least TRIP_COUNT_TO_AHEAD_RATIO times the prefetch ahead distance. | |
204 | For example, in a loop with a prefetch ahead distance of 10, | |
205 | supposing that TRIP_COUNT_TO_AHEAD_RATIO is equal to 4, it is | |
206 | profitable to prefetch when the trip count is greater or equal to | |
207 | 40. In that case, 30 out of the 40 iterations will benefit from | |
208 | prefetching. */ | |
209 | ||
210 | #ifndef TRIP_COUNT_TO_AHEAD_RATIO | |
211 | #define TRIP_COUNT_TO_AHEAD_RATIO 4 | |
212 | #endif | |
213 | ||
b076a3fd ZD |
214 | /* The group of references between that reuse may occur. */ |
215 | ||
216 | struct mem_ref_group | |
217 | { | |
218 | tree base; /* Base of the reference. */ | |
219 | HOST_WIDE_INT step; /* Step of the reference. */ | |
220 | struct mem_ref *refs; /* References in the group. */ | |
221 | struct mem_ref_group *next; /* Next group of references. */ | |
222 | }; | |
223 | ||
224 | /* Assigned to PREFETCH_BEFORE when all iterations are to be prefetched. */ | |
225 | ||
226 | #define PREFETCH_ALL (~(unsigned HOST_WIDE_INT) 0) | |
227 | ||
228 | /* The memory reference. */ | |
229 | ||
230 | struct mem_ref | |
231 | { | |
726a989a | 232 | gimple stmt; /* Statement in that the reference appears. */ |
b076a3fd ZD |
233 | tree mem; /* The reference. */ |
234 | HOST_WIDE_INT delta; /* Constant offset of the reference. */ | |
b076a3fd ZD |
235 | struct mem_ref_group *group; /* The group of references it belongs to. */ |
236 | unsigned HOST_WIDE_INT prefetch_mod; | |
237 | /* Prefetch only each PREFETCH_MOD-th | |
238 | iteration. */ | |
239 | unsigned HOST_WIDE_INT prefetch_before; | |
240 | /* Prefetch only first PREFETCH_BEFORE | |
241 | iterations. */ | |
5417e022 ZD |
242 | unsigned reuse_distance; /* The amount of data accessed before the first |
243 | reuse of this value. */ | |
b076a3fd | 244 | struct mem_ref *next; /* The next reference in the group. */ |
79f5e442 ZD |
245 | unsigned write_p : 1; /* Is it a write? */ |
246 | unsigned independent_p : 1; /* True if the reference is independent on | |
247 | all other references inside the loop. */ | |
248 | unsigned issue_prefetch_p : 1; /* Should we really issue the prefetch? */ | |
249 | unsigned storent_p : 1; /* True if we changed the store to a | |
250 | nontemporal one. */ | |
b076a3fd ZD |
251 | }; |
252 | ||
75c40d56 | 253 | /* Dumps information about reference REF to FILE. */ |
b076a3fd ZD |
254 | |
255 | static void | |
256 | dump_mem_ref (FILE *file, struct mem_ref *ref) | |
257 | { | |
258 | fprintf (file, "Reference %p:\n", (void *) ref); | |
259 | ||
260 | fprintf (file, " group %p (base ", (void *) ref->group); | |
261 | print_generic_expr (file, ref->group->base, TDF_SLIM); | |
262 | fprintf (file, ", step "); | |
263 | fprintf (file, HOST_WIDE_INT_PRINT_DEC, ref->group->step); | |
264 | fprintf (file, ")\n"); | |
265 | ||
e324a72f | 266 | fprintf (file, " delta "); |
b076a3fd ZD |
267 | fprintf (file, HOST_WIDE_INT_PRINT_DEC, ref->delta); |
268 | fprintf (file, "\n"); | |
269 | ||
270 | fprintf (file, " %s\n", ref->write_p ? "write" : "read"); | |
271 | ||
272 | fprintf (file, "\n"); | |
273 | } | |
274 | ||
275 | /* Finds a group with BASE and STEP in GROUPS, or creates one if it does not | |
276 | exist. */ | |
277 | ||
278 | static struct mem_ref_group * | |
279 | find_or_create_group (struct mem_ref_group **groups, tree base, | |
280 | HOST_WIDE_INT step) | |
281 | { | |
282 | struct mem_ref_group *group; | |
283 | ||
284 | for (; *groups; groups = &(*groups)->next) | |
285 | { | |
286 | if ((*groups)->step == step | |
287 | && operand_equal_p ((*groups)->base, base, 0)) | |
288 | return *groups; | |
289 | ||
290 | /* Keep the list of groups sorted by decreasing step. */ | |
291 | if ((*groups)->step < step) | |
292 | break; | |
293 | } | |
294 | ||
5417e022 | 295 | group = XNEW (struct mem_ref_group); |
b076a3fd ZD |
296 | group->base = base; |
297 | group->step = step; | |
298 | group->refs = NULL; | |
299 | group->next = *groups; | |
300 | *groups = group; | |
301 | ||
302 | return group; | |
303 | } | |
304 | ||
305 | /* Records a memory reference MEM in GROUP with offset DELTA and write status | |
306 | WRITE_P. The reference occurs in statement STMT. */ | |
307 | ||
308 | static void | |
726a989a | 309 | record_ref (struct mem_ref_group *group, gimple stmt, tree mem, |
b076a3fd ZD |
310 | HOST_WIDE_INT delta, bool write_p) |
311 | { | |
312 | struct mem_ref **aref; | |
313 | ||
314 | /* Do not record the same address twice. */ | |
315 | for (aref = &group->refs; *aref; aref = &(*aref)->next) | |
316 | { | |
317 | /* It does not have to be possible for write reference to reuse the read | |
318 | prefetch, or vice versa. */ | |
319 | if (!WRITE_CAN_USE_READ_PREFETCH | |
320 | && write_p | |
321 | && !(*aref)->write_p) | |
322 | continue; | |
323 | if (!READ_CAN_USE_WRITE_PREFETCH | |
324 | && !write_p | |
325 | && (*aref)->write_p) | |
326 | continue; | |
327 | ||
328 | if ((*aref)->delta == delta) | |
329 | return; | |
330 | } | |
331 | ||
5417e022 | 332 | (*aref) = XNEW (struct mem_ref); |
b076a3fd ZD |
333 | (*aref)->stmt = stmt; |
334 | (*aref)->mem = mem; | |
335 | (*aref)->delta = delta; | |
336 | (*aref)->write_p = write_p; | |
337 | (*aref)->prefetch_before = PREFETCH_ALL; | |
338 | (*aref)->prefetch_mod = 1; | |
5417e022 | 339 | (*aref)->reuse_distance = 0; |
b076a3fd ZD |
340 | (*aref)->issue_prefetch_p = false; |
341 | (*aref)->group = group; | |
342 | (*aref)->next = NULL; | |
79f5e442 ZD |
343 | (*aref)->independent_p = false; |
344 | (*aref)->storent_p = false; | |
b076a3fd ZD |
345 | |
346 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
347 | dump_mem_ref (dump_file, *aref); | |
348 | } | |
349 | ||
350 | /* Release memory references in GROUPS. */ | |
351 | ||
352 | static void | |
353 | release_mem_refs (struct mem_ref_group *groups) | |
354 | { | |
355 | struct mem_ref_group *next_g; | |
356 | struct mem_ref *ref, *next_r; | |
357 | ||
358 | for (; groups; groups = next_g) | |
359 | { | |
360 | next_g = groups->next; | |
361 | for (ref = groups->refs; ref; ref = next_r) | |
362 | { | |
363 | next_r = ref->next; | |
364 | free (ref); | |
365 | } | |
366 | free (groups); | |
367 | } | |
368 | } | |
369 | ||
370 | /* A structure used to pass arguments to idx_analyze_ref. */ | |
371 | ||
372 | struct ar_data | |
373 | { | |
374 | struct loop *loop; /* Loop of the reference. */ | |
726a989a | 375 | gimple stmt; /* Statement of the reference. */ |
b076a3fd ZD |
376 | HOST_WIDE_INT *step; /* Step of the memory reference. */ |
377 | HOST_WIDE_INT *delta; /* Offset of the memory reference. */ | |
378 | }; | |
379 | ||
380 | /* Analyzes a single INDEX of a memory reference to obtain information | |
381 | described at analyze_ref. Callback for for_each_index. */ | |
382 | ||
383 | static bool | |
384 | idx_analyze_ref (tree base, tree *index, void *data) | |
385 | { | |
c22940cd | 386 | struct ar_data *ar_data = (struct ar_data *) data; |
b076a3fd ZD |
387 | tree ibase, step, stepsize; |
388 | HOST_WIDE_INT istep, idelta = 0, imult = 1; | |
389 | affine_iv iv; | |
390 | ||
391 | if (TREE_CODE (base) == MISALIGNED_INDIRECT_REF | |
392 | || TREE_CODE (base) == ALIGN_INDIRECT_REF) | |
393 | return false; | |
394 | ||
f017bf5e ZD |
395 | if (!simple_iv (ar_data->loop, loop_containing_stmt (ar_data->stmt), |
396 | *index, &iv, false)) | |
b076a3fd ZD |
397 | return false; |
398 | ibase = iv.base; | |
399 | step = iv.step; | |
400 | ||
6e42ce54 ZD |
401 | if (!cst_and_fits_in_hwi (step)) |
402 | return false; | |
403 | istep = int_cst_value (step); | |
b076a3fd | 404 | |
5be014d5 | 405 | if (TREE_CODE (ibase) == POINTER_PLUS_EXPR |
b076a3fd ZD |
406 | && cst_and_fits_in_hwi (TREE_OPERAND (ibase, 1))) |
407 | { | |
408 | idelta = int_cst_value (TREE_OPERAND (ibase, 1)); | |
409 | ibase = TREE_OPERAND (ibase, 0); | |
410 | } | |
411 | if (cst_and_fits_in_hwi (ibase)) | |
412 | { | |
413 | idelta += int_cst_value (ibase); | |
ff5e9a94 | 414 | ibase = build_int_cst (TREE_TYPE (ibase), 0); |
b076a3fd ZD |
415 | } |
416 | ||
417 | if (TREE_CODE (base) == ARRAY_REF) | |
418 | { | |
419 | stepsize = array_ref_element_size (base); | |
420 | if (!cst_and_fits_in_hwi (stepsize)) | |
421 | return false; | |
422 | imult = int_cst_value (stepsize); | |
423 | ||
424 | istep *= imult; | |
425 | idelta *= imult; | |
426 | } | |
427 | ||
428 | *ar_data->step += istep; | |
429 | *ar_data->delta += idelta; | |
430 | *index = ibase; | |
431 | ||
432 | return true; | |
433 | } | |
434 | ||
aac8b8ed | 435 | /* Tries to express REF_P in shape &BASE + STEP * iter + DELTA, where DELTA and |
b076a3fd | 436 | STEP are integer constants and iter is number of iterations of LOOP. The |
aac8b8ed RS |
437 | reference occurs in statement STMT. Strips nonaddressable component |
438 | references from REF_P. */ | |
b076a3fd ZD |
439 | |
440 | static bool | |
aac8b8ed | 441 | analyze_ref (struct loop *loop, tree *ref_p, tree *base, |
b076a3fd | 442 | HOST_WIDE_INT *step, HOST_WIDE_INT *delta, |
726a989a | 443 | gimple stmt) |
b076a3fd ZD |
444 | { |
445 | struct ar_data ar_data; | |
446 | tree off; | |
447 | HOST_WIDE_INT bit_offset; | |
aac8b8ed | 448 | tree ref = *ref_p; |
b076a3fd ZD |
449 | |
450 | *step = 0; | |
451 | *delta = 0; | |
452 | ||
453 | /* First strip off the component references. Ignore bitfields. */ | |
454 | if (TREE_CODE (ref) == COMPONENT_REF | |
455 | && DECL_NONADDRESSABLE_P (TREE_OPERAND (ref, 1))) | |
456 | ref = TREE_OPERAND (ref, 0); | |
457 | ||
aac8b8ed RS |
458 | *ref_p = ref; |
459 | ||
b076a3fd ZD |
460 | for (; TREE_CODE (ref) == COMPONENT_REF; ref = TREE_OPERAND (ref, 0)) |
461 | { | |
462 | off = DECL_FIELD_BIT_OFFSET (TREE_OPERAND (ref, 1)); | |
463 | bit_offset = TREE_INT_CST_LOW (off); | |
464 | gcc_assert (bit_offset % BITS_PER_UNIT == 0); | |
b8698a0f | 465 | |
b076a3fd ZD |
466 | *delta += bit_offset / BITS_PER_UNIT; |
467 | } | |
468 | ||
469 | *base = unshare_expr (ref); | |
470 | ar_data.loop = loop; | |
471 | ar_data.stmt = stmt; | |
472 | ar_data.step = step; | |
473 | ar_data.delta = delta; | |
474 | return for_each_index (base, idx_analyze_ref, &ar_data); | |
475 | } | |
476 | ||
477 | /* Record a memory reference REF to the list REFS. The reference occurs in | |
79f5e442 ZD |
478 | LOOP in statement STMT and it is write if WRITE_P. Returns true if the |
479 | reference was recorded, false otherwise. */ | |
b076a3fd | 480 | |
79f5e442 | 481 | static bool |
b076a3fd | 482 | gather_memory_references_ref (struct loop *loop, struct mem_ref_group **refs, |
726a989a | 483 | tree ref, bool write_p, gimple stmt) |
b076a3fd ZD |
484 | { |
485 | tree base; | |
486 | HOST_WIDE_INT step, delta; | |
487 | struct mem_ref_group *agrp; | |
488 | ||
a80a2701 JJ |
489 | if (get_base_address (ref) == NULL) |
490 | return false; | |
491 | ||
aac8b8ed | 492 | if (!analyze_ref (loop, &ref, &base, &step, &delta, stmt)) |
79f5e442 | 493 | return false; |
b076a3fd ZD |
494 | |
495 | /* Now we know that REF = &BASE + STEP * iter + DELTA, where DELTA and STEP | |
496 | are integer constants. */ | |
497 | agrp = find_or_create_group (refs, base, step); | |
498 | record_ref (agrp, stmt, ref, delta, write_p); | |
79f5e442 ZD |
499 | |
500 | return true; | |
b076a3fd ZD |
501 | } |
502 | ||
79f5e442 ZD |
503 | /* Record the suitable memory references in LOOP. NO_OTHER_REFS is set to |
504 | true if there are no other memory references inside the loop. */ | |
b076a3fd ZD |
505 | |
506 | static struct mem_ref_group * | |
db34470d | 507 | gather_memory_references (struct loop *loop, bool *no_other_refs, unsigned *ref_count) |
b076a3fd ZD |
508 | { |
509 | basic_block *body = get_loop_body_in_dom_order (loop); | |
510 | basic_block bb; | |
511 | unsigned i; | |
726a989a RB |
512 | gimple_stmt_iterator bsi; |
513 | gimple stmt; | |
514 | tree lhs, rhs; | |
b076a3fd ZD |
515 | struct mem_ref_group *refs = NULL; |
516 | ||
79f5e442 | 517 | *no_other_refs = true; |
db34470d | 518 | *ref_count = 0; |
79f5e442 | 519 | |
b076a3fd ZD |
520 | /* Scan the loop body in order, so that the former references precede the |
521 | later ones. */ | |
522 | for (i = 0; i < loop->num_nodes; i++) | |
523 | { | |
524 | bb = body[i]; | |
525 | if (bb->loop_father != loop) | |
526 | continue; | |
527 | ||
726a989a | 528 | for (bsi = gsi_start_bb (bb); !gsi_end_p (bsi); gsi_next (&bsi)) |
b076a3fd | 529 | { |
726a989a | 530 | stmt = gsi_stmt (bsi); |
79f5e442 | 531 | |
726a989a | 532 | if (gimple_code (stmt) != GIMPLE_ASSIGN) |
79f5e442 | 533 | { |
5006671f | 534 | if (gimple_vuse (stmt) |
726a989a RB |
535 | || (is_gimple_call (stmt) |
536 | && !(gimple_call_flags (stmt) & ECF_CONST))) | |
79f5e442 ZD |
537 | *no_other_refs = false; |
538 | continue; | |
539 | } | |
b076a3fd | 540 | |
726a989a RB |
541 | lhs = gimple_assign_lhs (stmt); |
542 | rhs = gimple_assign_rhs1 (stmt); | |
b076a3fd ZD |
543 | |
544 | if (REFERENCE_CLASS_P (rhs)) | |
db34470d | 545 | { |
79f5e442 ZD |
546 | *no_other_refs &= gather_memory_references_ref (loop, &refs, |
547 | rhs, false, stmt); | |
db34470d GS |
548 | *ref_count += 1; |
549 | } | |
b076a3fd | 550 | if (REFERENCE_CLASS_P (lhs)) |
db34470d | 551 | { |
79f5e442 ZD |
552 | *no_other_refs &= gather_memory_references_ref (loop, &refs, |
553 | lhs, true, stmt); | |
db34470d GS |
554 | *ref_count += 1; |
555 | } | |
b076a3fd ZD |
556 | } |
557 | } | |
558 | free (body); | |
559 | ||
560 | return refs; | |
561 | } | |
562 | ||
563 | /* Prune the prefetch candidate REF using the self-reuse. */ | |
564 | ||
565 | static void | |
566 | prune_ref_by_self_reuse (struct mem_ref *ref) | |
567 | { | |
568 | HOST_WIDE_INT step = ref->group->step; | |
569 | bool backward = step < 0; | |
570 | ||
571 | if (step == 0) | |
572 | { | |
573 | /* Prefetch references to invariant address just once. */ | |
574 | ref->prefetch_before = 1; | |
575 | return; | |
576 | } | |
577 | ||
578 | if (backward) | |
579 | step = -step; | |
580 | ||
581 | if (step > PREFETCH_BLOCK) | |
582 | return; | |
583 | ||
584 | if ((backward && HAVE_BACKWARD_PREFETCH) | |
585 | || (!backward && HAVE_FORWARD_PREFETCH)) | |
586 | { | |
587 | ref->prefetch_before = 1; | |
588 | return; | |
589 | } | |
590 | ||
591 | ref->prefetch_mod = PREFETCH_BLOCK / step; | |
592 | } | |
593 | ||
594 | /* Divides X by BY, rounding down. */ | |
595 | ||
596 | static HOST_WIDE_INT | |
597 | ddown (HOST_WIDE_INT x, unsigned HOST_WIDE_INT by) | |
598 | { | |
599 | gcc_assert (by > 0); | |
600 | ||
601 | if (x >= 0) | |
602 | return x / by; | |
603 | else | |
604 | return (x + by - 1) / by; | |
605 | } | |
606 | ||
b8698a0f L |
607 | /* Given a CACHE_LINE_SIZE and two inductive memory references |
608 | with a common STEP greater than CACHE_LINE_SIZE and an address | |
609 | difference DELTA, compute the probability that they will fall | |
610 | in different cache lines. DISTINCT_ITERS is the number of | |
611 | distinct iterations after which the pattern repeats itself. | |
2c6dd136 GS |
612 | ALIGN_UNIT is the unit of alignment in bytes. */ |
613 | ||
614 | static int | |
b8698a0f | 615 | compute_miss_rate (unsigned HOST_WIDE_INT cache_line_size, |
2c6dd136 GS |
616 | HOST_WIDE_INT step, HOST_WIDE_INT delta, |
617 | unsigned HOST_WIDE_INT distinct_iters, | |
618 | int align_unit) | |
619 | { | |
620 | unsigned align, iter; | |
621 | int total_positions, miss_positions, miss_rate; | |
622 | int address1, address2, cache_line1, cache_line2; | |
623 | ||
624 | total_positions = 0; | |
625 | miss_positions = 0; | |
b8698a0f | 626 | |
2c6dd136 GS |
627 | /* Iterate through all possible alignments of the first |
628 | memory reference within its cache line. */ | |
629 | for (align = 0; align < cache_line_size; align += align_unit) | |
630 | ||
631 | /* Iterate through all distinct iterations. */ | |
632 | for (iter = 0; iter < distinct_iters; iter++) | |
633 | { | |
634 | address1 = align + step * iter; | |
635 | address2 = address1 + delta; | |
636 | cache_line1 = address1 / cache_line_size; | |
637 | cache_line2 = address2 / cache_line_size; | |
638 | total_positions += 1; | |
639 | if (cache_line1 != cache_line2) | |
640 | miss_positions += 1; | |
641 | } | |
642 | miss_rate = 1000 * miss_positions / total_positions; | |
643 | return miss_rate; | |
644 | } | |
645 | ||
b076a3fd ZD |
646 | /* Prune the prefetch candidate REF using the reuse with BY. |
647 | If BY_IS_BEFORE is true, BY is before REF in the loop. */ | |
648 | ||
649 | static void | |
650 | prune_ref_by_group_reuse (struct mem_ref *ref, struct mem_ref *by, | |
651 | bool by_is_before) | |
652 | { | |
653 | HOST_WIDE_INT step = ref->group->step; | |
654 | bool backward = step < 0; | |
655 | HOST_WIDE_INT delta_r = ref->delta, delta_b = by->delta; | |
656 | HOST_WIDE_INT delta = delta_b - delta_r; | |
657 | HOST_WIDE_INT hit_from; | |
658 | unsigned HOST_WIDE_INT prefetch_before, prefetch_block; | |
2c6dd136 GS |
659 | int miss_rate; |
660 | HOST_WIDE_INT reduced_step; | |
661 | unsigned HOST_WIDE_INT reduced_prefetch_block; | |
662 | tree ref_type; | |
663 | int align_unit; | |
b076a3fd ZD |
664 | |
665 | if (delta == 0) | |
666 | { | |
667 | /* If the references has the same address, only prefetch the | |
668 | former. */ | |
669 | if (by_is_before) | |
670 | ref->prefetch_before = 0; | |
b8698a0f | 671 | |
b076a3fd ZD |
672 | return; |
673 | } | |
674 | ||
675 | if (!step) | |
676 | { | |
677 | /* If the reference addresses are invariant and fall into the | |
678 | same cache line, prefetch just the first one. */ | |
679 | if (!by_is_before) | |
680 | return; | |
681 | ||
682 | if (ddown (ref->delta, PREFETCH_BLOCK) | |
683 | != ddown (by->delta, PREFETCH_BLOCK)) | |
684 | return; | |
685 | ||
686 | ref->prefetch_before = 0; | |
687 | return; | |
688 | } | |
689 | ||
690 | /* Only prune the reference that is behind in the array. */ | |
691 | if (backward) | |
692 | { | |
693 | if (delta > 0) | |
694 | return; | |
695 | ||
696 | /* Transform the data so that we may assume that the accesses | |
697 | are forward. */ | |
698 | delta = - delta; | |
699 | step = -step; | |
700 | delta_r = PREFETCH_BLOCK - 1 - delta_r; | |
701 | delta_b = PREFETCH_BLOCK - 1 - delta_b; | |
702 | } | |
703 | else | |
704 | { | |
705 | if (delta < 0) | |
706 | return; | |
707 | } | |
708 | ||
709 | /* Check whether the two references are likely to hit the same cache | |
710 | line, and how distant the iterations in that it occurs are from | |
711 | each other. */ | |
712 | ||
713 | if (step <= PREFETCH_BLOCK) | |
714 | { | |
715 | /* The accesses are sure to meet. Let us check when. */ | |
716 | hit_from = ddown (delta_b, PREFETCH_BLOCK) * PREFETCH_BLOCK; | |
717 | prefetch_before = (hit_from - delta_r + step - 1) / step; | |
718 | ||
719 | if (prefetch_before < ref->prefetch_before) | |
720 | ref->prefetch_before = prefetch_before; | |
721 | ||
722 | return; | |
723 | } | |
724 | ||
b8698a0f | 725 | /* A more complicated case with step > prefetch_block. First reduce |
2c6dd136 | 726 | the ratio between the step and the cache line size to its simplest |
b8698a0f L |
727 | terms. The resulting denominator will then represent the number of |
728 | distinct iterations after which each address will go back to its | |
729 | initial location within the cache line. This computation assumes | |
2c6dd136 | 730 | that PREFETCH_BLOCK is a power of two. */ |
b076a3fd | 731 | prefetch_block = PREFETCH_BLOCK; |
2c6dd136 GS |
732 | reduced_prefetch_block = prefetch_block; |
733 | reduced_step = step; | |
734 | while ((reduced_step & 1) == 0 | |
735 | && reduced_prefetch_block > 1) | |
b076a3fd | 736 | { |
2c6dd136 GS |
737 | reduced_step >>= 1; |
738 | reduced_prefetch_block >>= 1; | |
b076a3fd ZD |
739 | } |
740 | ||
b076a3fd ZD |
741 | prefetch_before = delta / step; |
742 | delta %= step; | |
2c6dd136 GS |
743 | ref_type = TREE_TYPE (ref->mem); |
744 | align_unit = TYPE_ALIGN (ref_type) / 8; | |
b8698a0f | 745 | miss_rate = compute_miss_rate(prefetch_block, step, delta, |
2c6dd136 GS |
746 | reduced_prefetch_block, align_unit); |
747 | if (miss_rate <= ACCEPTABLE_MISS_RATE) | |
b076a3fd ZD |
748 | { |
749 | if (prefetch_before < ref->prefetch_before) | |
750 | ref->prefetch_before = prefetch_before; | |
751 | ||
752 | return; | |
753 | } | |
754 | ||
755 | /* Try also the following iteration. */ | |
756 | prefetch_before++; | |
757 | delta = step - delta; | |
b8698a0f | 758 | miss_rate = compute_miss_rate(prefetch_block, step, delta, |
2c6dd136 | 759 | reduced_prefetch_block, align_unit); |
b8698a0f | 760 | if (miss_rate <= ACCEPTABLE_MISS_RATE) |
b076a3fd ZD |
761 | { |
762 | if (prefetch_before < ref->prefetch_before) | |
763 | ref->prefetch_before = prefetch_before; | |
764 | ||
765 | return; | |
766 | } | |
767 | ||
768 | /* The ref probably does not reuse by. */ | |
769 | return; | |
770 | } | |
771 | ||
772 | /* Prune the prefetch candidate REF using the reuses with other references | |
773 | in REFS. */ | |
774 | ||
775 | static void | |
776 | prune_ref_by_reuse (struct mem_ref *ref, struct mem_ref *refs) | |
777 | { | |
778 | struct mem_ref *prune_by; | |
779 | bool before = true; | |
780 | ||
781 | prune_ref_by_self_reuse (ref); | |
782 | ||
783 | for (prune_by = refs; prune_by; prune_by = prune_by->next) | |
784 | { | |
785 | if (prune_by == ref) | |
786 | { | |
787 | before = false; | |
788 | continue; | |
789 | } | |
790 | ||
791 | if (!WRITE_CAN_USE_READ_PREFETCH | |
792 | && ref->write_p | |
793 | && !prune_by->write_p) | |
794 | continue; | |
795 | if (!READ_CAN_USE_WRITE_PREFETCH | |
796 | && !ref->write_p | |
797 | && prune_by->write_p) | |
798 | continue; | |
799 | ||
800 | prune_ref_by_group_reuse (ref, prune_by, before); | |
801 | } | |
802 | } | |
803 | ||
804 | /* Prune the prefetch candidates in GROUP using the reuse analysis. */ | |
805 | ||
806 | static void | |
807 | prune_group_by_reuse (struct mem_ref_group *group) | |
808 | { | |
809 | struct mem_ref *ref_pruned; | |
810 | ||
811 | for (ref_pruned = group->refs; ref_pruned; ref_pruned = ref_pruned->next) | |
812 | { | |
813 | prune_ref_by_reuse (ref_pruned, group->refs); | |
814 | ||
815 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
816 | { | |
817 | fprintf (dump_file, "Reference %p:", (void *) ref_pruned); | |
818 | ||
819 | if (ref_pruned->prefetch_before == PREFETCH_ALL | |
820 | && ref_pruned->prefetch_mod == 1) | |
821 | fprintf (dump_file, " no restrictions"); | |
822 | else if (ref_pruned->prefetch_before == 0) | |
823 | fprintf (dump_file, " do not prefetch"); | |
824 | else if (ref_pruned->prefetch_before <= ref_pruned->prefetch_mod) | |
825 | fprintf (dump_file, " prefetch once"); | |
826 | else | |
827 | { | |
828 | if (ref_pruned->prefetch_before != PREFETCH_ALL) | |
829 | { | |
830 | fprintf (dump_file, " prefetch before "); | |
831 | fprintf (dump_file, HOST_WIDE_INT_PRINT_DEC, | |
832 | ref_pruned->prefetch_before); | |
833 | } | |
834 | if (ref_pruned->prefetch_mod != 1) | |
835 | { | |
836 | fprintf (dump_file, " prefetch mod "); | |
837 | fprintf (dump_file, HOST_WIDE_INT_PRINT_DEC, | |
838 | ref_pruned->prefetch_mod); | |
839 | } | |
840 | } | |
841 | fprintf (dump_file, "\n"); | |
842 | } | |
843 | } | |
844 | } | |
845 | ||
846 | /* Prune the list of prefetch candidates GROUPS using the reuse analysis. */ | |
847 | ||
848 | static void | |
849 | prune_by_reuse (struct mem_ref_group *groups) | |
850 | { | |
851 | for (; groups; groups = groups->next) | |
852 | prune_group_by_reuse (groups); | |
853 | } | |
854 | ||
855 | /* Returns true if we should issue prefetch for REF. */ | |
856 | ||
857 | static bool | |
858 | should_issue_prefetch_p (struct mem_ref *ref) | |
859 | { | |
860 | /* For now do not issue prefetches for only first few of the | |
861 | iterations. */ | |
862 | if (ref->prefetch_before != PREFETCH_ALL) | |
863 | return false; | |
864 | ||
79f5e442 ZD |
865 | /* Do not prefetch nontemporal stores. */ |
866 | if (ref->storent_p) | |
867 | return false; | |
868 | ||
b076a3fd ZD |
869 | return true; |
870 | } | |
871 | ||
872 | /* Decide which of the prefetch candidates in GROUPS to prefetch. | |
873 | AHEAD is the number of iterations to prefetch ahead (which corresponds | |
874 | to the number of simultaneous instances of one prefetch running at a | |
875 | time). UNROLL_FACTOR is the factor by that the loop is going to be | |
876 | unrolled. Returns true if there is anything to prefetch. */ | |
877 | ||
878 | static bool | |
879 | schedule_prefetches (struct mem_ref_group *groups, unsigned unroll_factor, | |
880 | unsigned ahead) | |
881 | { | |
911b3fdb ZD |
882 | unsigned remaining_prefetch_slots, n_prefetches, prefetch_slots; |
883 | unsigned slots_per_prefetch; | |
b076a3fd ZD |
884 | struct mem_ref *ref; |
885 | bool any = false; | |
886 | ||
911b3fdb ZD |
887 | /* At most SIMULTANEOUS_PREFETCHES should be running at the same time. */ |
888 | remaining_prefetch_slots = SIMULTANEOUS_PREFETCHES; | |
b076a3fd | 889 | |
911b3fdb ZD |
890 | /* The prefetch will run for AHEAD iterations of the original loop, i.e., |
891 | AHEAD / UNROLL_FACTOR iterations of the unrolled loop. In each iteration, | |
892 | it will need a prefetch slot. */ | |
893 | slots_per_prefetch = (ahead + unroll_factor / 2) / unroll_factor; | |
b076a3fd | 894 | if (dump_file && (dump_flags & TDF_DETAILS)) |
911b3fdb ZD |
895 | fprintf (dump_file, "Each prefetch instruction takes %u prefetch slots.\n", |
896 | slots_per_prefetch); | |
b076a3fd ZD |
897 | |
898 | /* For now we just take memory references one by one and issue | |
899 | prefetches for as many as possible. The groups are sorted | |
900 | starting with the largest step, since the references with | |
c0220ea4 | 901 | large step are more likely to cause many cache misses. */ |
b076a3fd ZD |
902 | |
903 | for (; groups; groups = groups->next) | |
904 | for (ref = groups->refs; ref; ref = ref->next) | |
905 | { | |
906 | if (!should_issue_prefetch_p (ref)) | |
907 | continue; | |
908 | ||
911b3fdb ZD |
909 | /* If we need to prefetch the reference each PREFETCH_MOD iterations, |
910 | and we unroll the loop UNROLL_FACTOR times, we need to insert | |
911 | ceil (UNROLL_FACTOR / PREFETCH_MOD) instructions in each | |
912 | iteration. */ | |
b076a3fd ZD |
913 | n_prefetches = ((unroll_factor + ref->prefetch_mod - 1) |
914 | / ref->prefetch_mod); | |
911b3fdb ZD |
915 | prefetch_slots = n_prefetches * slots_per_prefetch; |
916 | ||
917 | /* If more than half of the prefetches would be lost anyway, do not | |
918 | issue the prefetch. */ | |
919 | if (2 * remaining_prefetch_slots < prefetch_slots) | |
920 | continue; | |
921 | ||
922 | ref->issue_prefetch_p = true; | |
b076a3fd | 923 | |
911b3fdb ZD |
924 | if (remaining_prefetch_slots <= prefetch_slots) |
925 | return true; | |
926 | remaining_prefetch_slots -= prefetch_slots; | |
b076a3fd ZD |
927 | any = true; |
928 | } | |
929 | ||
930 | return any; | |
931 | } | |
932 | ||
db34470d | 933 | /* Estimate the number of prefetches in the given GROUPS. */ |
b076a3fd | 934 | |
db34470d GS |
935 | static int |
936 | estimate_prefetch_count (struct mem_ref_group *groups) | |
b076a3fd ZD |
937 | { |
938 | struct mem_ref *ref; | |
db34470d | 939 | int prefetch_count = 0; |
b076a3fd ZD |
940 | |
941 | for (; groups; groups = groups->next) | |
942 | for (ref = groups->refs; ref; ref = ref->next) | |
943 | if (should_issue_prefetch_p (ref)) | |
db34470d | 944 | prefetch_count++; |
b076a3fd | 945 | |
db34470d | 946 | return prefetch_count; |
b076a3fd ZD |
947 | } |
948 | ||
949 | /* Issue prefetches for the reference REF into loop as decided before. | |
950 | HEAD is the number of iterations to prefetch ahead. UNROLL_FACTOR | |
917f1b7e | 951 | is the factor by which LOOP was unrolled. */ |
b076a3fd ZD |
952 | |
953 | static void | |
954 | issue_prefetch_ref (struct mem_ref *ref, unsigned unroll_factor, unsigned ahead) | |
955 | { | |
956 | HOST_WIDE_INT delta; | |
726a989a RB |
957 | tree addr, addr_base, write_p, local; |
958 | gimple prefetch; | |
959 | gimple_stmt_iterator bsi; | |
b076a3fd | 960 | unsigned n_prefetches, ap; |
5417e022 | 961 | bool nontemporal = ref->reuse_distance >= L2_CACHE_SIZE_BYTES; |
b076a3fd ZD |
962 | |
963 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
5417e022 ZD |
964 | fprintf (dump_file, "Issued%s prefetch for %p.\n", |
965 | nontemporal ? " nontemporal" : "", | |
966 | (void *) ref); | |
b076a3fd | 967 | |
726a989a | 968 | bsi = gsi_for_stmt (ref->stmt); |
b076a3fd ZD |
969 | |
970 | n_prefetches = ((unroll_factor + ref->prefetch_mod - 1) | |
971 | / ref->prefetch_mod); | |
972 | addr_base = build_fold_addr_expr_with_type (ref->mem, ptr_type_node); | |
726a989a RB |
973 | addr_base = force_gimple_operand_gsi (&bsi, unshare_expr (addr_base), |
974 | true, NULL, true, GSI_SAME_STMT); | |
911b3fdb | 975 | write_p = ref->write_p ? integer_one_node : integer_zero_node; |
5417e022 | 976 | local = build_int_cst (integer_type_node, nontemporal ? 0 : 3); |
b076a3fd ZD |
977 | |
978 | for (ap = 0; ap < n_prefetches; ap++) | |
979 | { | |
980 | /* Determine the address to prefetch. */ | |
981 | delta = (ahead + ap * ref->prefetch_mod) * ref->group->step; | |
5be014d5 AP |
982 | addr = fold_build2 (POINTER_PLUS_EXPR, ptr_type_node, |
983 | addr_base, size_int (delta)); | |
726a989a RB |
984 | addr = force_gimple_operand_gsi (&bsi, unshare_expr (addr), true, NULL, |
985 | true, GSI_SAME_STMT); | |
b076a3fd ZD |
986 | |
987 | /* Create the prefetch instruction. */ | |
726a989a RB |
988 | prefetch = gimple_build_call (built_in_decls[BUILT_IN_PREFETCH], |
989 | 3, addr, write_p, local); | |
990 | gsi_insert_before (&bsi, prefetch, GSI_SAME_STMT); | |
b076a3fd ZD |
991 | } |
992 | } | |
993 | ||
994 | /* Issue prefetches for the references in GROUPS into loop as decided before. | |
995 | HEAD is the number of iterations to prefetch ahead. UNROLL_FACTOR is the | |
996 | factor by that LOOP was unrolled. */ | |
997 | ||
998 | static void | |
999 | issue_prefetches (struct mem_ref_group *groups, | |
1000 | unsigned unroll_factor, unsigned ahead) | |
1001 | { | |
1002 | struct mem_ref *ref; | |
1003 | ||
1004 | for (; groups; groups = groups->next) | |
1005 | for (ref = groups->refs; ref; ref = ref->next) | |
1006 | if (ref->issue_prefetch_p) | |
1007 | issue_prefetch_ref (ref, unroll_factor, ahead); | |
1008 | } | |
1009 | ||
79f5e442 ZD |
1010 | /* Returns true if REF is a memory write for that a nontemporal store insn |
1011 | can be used. */ | |
1012 | ||
1013 | static bool | |
1014 | nontemporal_store_p (struct mem_ref *ref) | |
1015 | { | |
1016 | enum machine_mode mode; | |
1017 | enum insn_code code; | |
1018 | ||
1019 | /* REF must be a write that is not reused. We require it to be independent | |
1020 | on all other memory references in the loop, as the nontemporal stores may | |
1021 | be reordered with respect to other memory references. */ | |
1022 | if (!ref->write_p | |
1023 | || !ref->independent_p | |
1024 | || ref->reuse_distance < L2_CACHE_SIZE_BYTES) | |
1025 | return false; | |
1026 | ||
1027 | /* Check that we have the storent instruction for the mode. */ | |
1028 | mode = TYPE_MODE (TREE_TYPE (ref->mem)); | |
1029 | if (mode == BLKmode) | |
1030 | return false; | |
1031 | ||
166cdb08 | 1032 | code = optab_handler (storent_optab, mode)->insn_code; |
79f5e442 ZD |
1033 | return code != CODE_FOR_nothing; |
1034 | } | |
1035 | ||
1036 | /* If REF is a nontemporal store, we mark the corresponding modify statement | |
1037 | and return true. Otherwise, we return false. */ | |
1038 | ||
1039 | static bool | |
1040 | mark_nontemporal_store (struct mem_ref *ref) | |
1041 | { | |
1042 | if (!nontemporal_store_p (ref)) | |
1043 | return false; | |
1044 | ||
1045 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
1046 | fprintf (dump_file, "Marked reference %p as a nontemporal store.\n", | |
1047 | (void *) ref); | |
1048 | ||
726a989a | 1049 | gimple_assign_set_nontemporal_move (ref->stmt, true); |
79f5e442 ZD |
1050 | ref->storent_p = true; |
1051 | ||
1052 | return true; | |
1053 | } | |
1054 | ||
1055 | /* Issue a memory fence instruction after LOOP. */ | |
1056 | ||
1057 | static void | |
1058 | emit_mfence_after_loop (struct loop *loop) | |
1059 | { | |
1060 | VEC (edge, heap) *exits = get_loop_exit_edges (loop); | |
1061 | edge exit; | |
726a989a RB |
1062 | gimple call; |
1063 | gimple_stmt_iterator bsi; | |
79f5e442 ZD |
1064 | unsigned i; |
1065 | ||
1066 | for (i = 0; VEC_iterate (edge, exits, i, exit); i++) | |
1067 | { | |
726a989a | 1068 | call = gimple_build_call (FENCE_FOLLOWING_MOVNT, 0); |
79f5e442 ZD |
1069 | |
1070 | if (!single_pred_p (exit->dest) | |
1071 | /* If possible, we prefer not to insert the fence on other paths | |
1072 | in cfg. */ | |
1073 | && !(exit->flags & EDGE_ABNORMAL)) | |
1074 | split_loop_exit_edge (exit); | |
726a989a | 1075 | bsi = gsi_after_labels (exit->dest); |
79f5e442 | 1076 | |
726a989a | 1077 | gsi_insert_before (&bsi, call, GSI_NEW_STMT); |
79f5e442 ZD |
1078 | mark_virtual_ops_for_renaming (call); |
1079 | } | |
1080 | ||
1081 | VEC_free (edge, heap, exits); | |
1082 | update_ssa (TODO_update_ssa_only_virtuals); | |
1083 | } | |
1084 | ||
1085 | /* Returns true if we can use storent in loop, false otherwise. */ | |
1086 | ||
1087 | static bool | |
1088 | may_use_storent_in_loop_p (struct loop *loop) | |
1089 | { | |
1090 | bool ret = true; | |
1091 | ||
1092 | if (loop->inner != NULL) | |
1093 | return false; | |
1094 | ||
1095 | /* If we must issue a mfence insn after using storent, check that there | |
1096 | is a suitable place for it at each of the loop exits. */ | |
1097 | if (FENCE_FOLLOWING_MOVNT != NULL_TREE) | |
1098 | { | |
1099 | VEC (edge, heap) *exits = get_loop_exit_edges (loop); | |
1100 | unsigned i; | |
1101 | edge exit; | |
1102 | ||
1103 | for (i = 0; VEC_iterate (edge, exits, i, exit); i++) | |
1104 | if ((exit->flags & EDGE_ABNORMAL) | |
1105 | && exit->dest == EXIT_BLOCK_PTR) | |
1106 | ret = false; | |
1107 | ||
1108 | VEC_free (edge, heap, exits); | |
1109 | } | |
1110 | ||
1111 | return ret; | |
1112 | } | |
1113 | ||
1114 | /* Marks nontemporal stores in LOOP. GROUPS contains the description of memory | |
1115 | references in the loop. */ | |
1116 | ||
1117 | static void | |
1118 | mark_nontemporal_stores (struct loop *loop, struct mem_ref_group *groups) | |
1119 | { | |
1120 | struct mem_ref *ref; | |
1121 | bool any = false; | |
1122 | ||
1123 | if (!may_use_storent_in_loop_p (loop)) | |
1124 | return; | |
1125 | ||
1126 | for (; groups; groups = groups->next) | |
1127 | for (ref = groups->refs; ref; ref = ref->next) | |
1128 | any |= mark_nontemporal_store (ref); | |
1129 | ||
1130 | if (any && FENCE_FOLLOWING_MOVNT != NULL_TREE) | |
1131 | emit_mfence_after_loop (loop); | |
1132 | } | |
1133 | ||
b076a3fd ZD |
1134 | /* Determines whether we can profitably unroll LOOP FACTOR times, and if |
1135 | this is the case, fill in DESC by the description of number of | |
1136 | iterations. */ | |
1137 | ||
1138 | static bool | |
1139 | should_unroll_loop_p (struct loop *loop, struct tree_niter_desc *desc, | |
1140 | unsigned factor) | |
1141 | { | |
1142 | if (!can_unroll_loop_p (loop, factor, desc)) | |
1143 | return false; | |
1144 | ||
1145 | /* We only consider loops without control flow for unrolling. This is not | |
1146 | a hard restriction -- tree_unroll_loop works with arbitrary loops | |
1147 | as well; but the unrolling/prefetching is usually more profitable for | |
1148 | loops consisting of a single basic block, and we want to limit the | |
1149 | code growth. */ | |
1150 | if (loop->num_nodes > 2) | |
1151 | return false; | |
1152 | ||
1153 | return true; | |
1154 | } | |
1155 | ||
1156 | /* Determine the coefficient by that unroll LOOP, from the information | |
1157 | contained in the list of memory references REFS. Description of | |
2711355f ZD |
1158 | umber of iterations of LOOP is stored to DESC. NINSNS is the number of |
1159 | insns of the LOOP. EST_NITER is the estimated number of iterations of | |
1160 | the loop, or -1 if no estimate is available. */ | |
b076a3fd ZD |
1161 | |
1162 | static unsigned | |
1163 | determine_unroll_factor (struct loop *loop, struct mem_ref_group *refs, | |
2711355f ZD |
1164 | unsigned ninsns, struct tree_niter_desc *desc, |
1165 | HOST_WIDE_INT est_niter) | |
b076a3fd | 1166 | { |
911b3fdb ZD |
1167 | unsigned upper_bound; |
1168 | unsigned nfactor, factor, mod_constraint; | |
b076a3fd ZD |
1169 | struct mem_ref_group *agp; |
1170 | struct mem_ref *ref; | |
1171 | ||
911b3fdb ZD |
1172 | /* First check whether the loop is not too large to unroll. We ignore |
1173 | PARAM_MAX_UNROLL_TIMES, because for small loops, it prevented us | |
1174 | from unrolling them enough to make exactly one cache line covered by each | |
1175 | iteration. Also, the goal of PARAM_MAX_UNROLL_TIMES is to prevent | |
1176 | us from unrolling the loops too many times in cases where we only expect | |
1177 | gains from better scheduling and decreasing loop overhead, which is not | |
1178 | the case here. */ | |
1179 | upper_bound = PARAM_VALUE (PARAM_MAX_UNROLLED_INSNS) / ninsns; | |
2711355f ZD |
1180 | |
1181 | /* If we unrolled the loop more times than it iterates, the unrolled version | |
1182 | of the loop would be never entered. */ | |
1183 | if (est_niter >= 0 && est_niter < (HOST_WIDE_INT) upper_bound) | |
1184 | upper_bound = est_niter; | |
1185 | ||
911b3fdb | 1186 | if (upper_bound <= 1) |
b076a3fd ZD |
1187 | return 1; |
1188 | ||
911b3fdb ZD |
1189 | /* Choose the factor so that we may prefetch each cache just once, |
1190 | but bound the unrolling by UPPER_BOUND. */ | |
1191 | factor = 1; | |
b076a3fd ZD |
1192 | for (agp = refs; agp; agp = agp->next) |
1193 | for (ref = agp->refs; ref; ref = ref->next) | |
911b3fdb ZD |
1194 | if (should_issue_prefetch_p (ref)) |
1195 | { | |
1196 | mod_constraint = ref->prefetch_mod; | |
1197 | nfactor = least_common_multiple (mod_constraint, factor); | |
1198 | if (nfactor <= upper_bound) | |
1199 | factor = nfactor; | |
1200 | } | |
b076a3fd ZD |
1201 | |
1202 | if (!should_unroll_loop_p (loop, desc, factor)) | |
1203 | return 1; | |
1204 | ||
1205 | return factor; | |
1206 | } | |
1207 | ||
5417e022 ZD |
1208 | /* Returns the total volume of the memory references REFS, taking into account |
1209 | reuses in the innermost loop and cache line size. TODO -- we should also | |
1210 | take into account reuses across the iterations of the loops in the loop | |
1211 | nest. */ | |
1212 | ||
1213 | static unsigned | |
1214 | volume_of_references (struct mem_ref_group *refs) | |
1215 | { | |
1216 | unsigned volume = 0; | |
1217 | struct mem_ref_group *gr; | |
1218 | struct mem_ref *ref; | |
1219 | ||
1220 | for (gr = refs; gr; gr = gr->next) | |
1221 | for (ref = gr->refs; ref; ref = ref->next) | |
1222 | { | |
1223 | /* Almost always reuses another value? */ | |
1224 | if (ref->prefetch_before != PREFETCH_ALL) | |
1225 | continue; | |
1226 | ||
1227 | /* If several iterations access the same cache line, use the size of | |
1228 | the line divided by this number. Otherwise, a cache line is | |
1229 | accessed in each iteration. TODO -- in the latter case, we should | |
1230 | take the size of the reference into account, rounding it up on cache | |
1231 | line size multiple. */ | |
1232 | volume += L1_CACHE_LINE_SIZE / ref->prefetch_mod; | |
1233 | } | |
1234 | return volume; | |
1235 | } | |
1236 | ||
1237 | /* Returns the volume of memory references accessed across VEC iterations of | |
1238 | loops, whose sizes are described in the LOOP_SIZES array. N is the number | |
1239 | of the loops in the nest (length of VEC and LOOP_SIZES vectors). */ | |
1240 | ||
1241 | static unsigned | |
1242 | volume_of_dist_vector (lambda_vector vec, unsigned *loop_sizes, unsigned n) | |
1243 | { | |
1244 | unsigned i; | |
1245 | ||
1246 | for (i = 0; i < n; i++) | |
1247 | if (vec[i] != 0) | |
1248 | break; | |
1249 | ||
1250 | if (i == n) | |
1251 | return 0; | |
1252 | ||
1253 | gcc_assert (vec[i] > 0); | |
1254 | ||
1255 | /* We ignore the parts of the distance vector in subloops, since usually | |
1256 | the numbers of iterations are much smaller. */ | |
1257 | return loop_sizes[i] * vec[i]; | |
1258 | } | |
1259 | ||
1260 | /* Add the steps of ACCESS_FN multiplied by STRIDE to the array STRIDE | |
1261 | at the position corresponding to the loop of the step. N is the depth | |
1262 | of the considered loop nest, and, LOOP is its innermost loop. */ | |
1263 | ||
1264 | static void | |
1265 | add_subscript_strides (tree access_fn, unsigned stride, | |
1266 | HOST_WIDE_INT *strides, unsigned n, struct loop *loop) | |
1267 | { | |
1268 | struct loop *aloop; | |
1269 | tree step; | |
1270 | HOST_WIDE_INT astep; | |
1271 | unsigned min_depth = loop_depth (loop) - n; | |
1272 | ||
1273 | while (TREE_CODE (access_fn) == POLYNOMIAL_CHREC) | |
1274 | { | |
1275 | aloop = get_chrec_loop (access_fn); | |
1276 | step = CHREC_RIGHT (access_fn); | |
1277 | access_fn = CHREC_LEFT (access_fn); | |
1278 | ||
1279 | if ((unsigned) loop_depth (aloop) <= min_depth) | |
1280 | continue; | |
1281 | ||
1282 | if (host_integerp (step, 0)) | |
1283 | astep = tree_low_cst (step, 0); | |
1284 | else | |
1285 | astep = L1_CACHE_LINE_SIZE; | |
1286 | ||
1287 | strides[n - 1 - loop_depth (loop) + loop_depth (aloop)] += astep * stride; | |
1288 | ||
1289 | } | |
1290 | } | |
1291 | ||
1292 | /* Returns the volume of memory references accessed between two consecutive | |
1293 | self-reuses of the reference DR. We consider the subscripts of DR in N | |
1294 | loops, and LOOP_SIZES contains the volumes of accesses in each of the | |
1295 | loops. LOOP is the innermost loop of the current loop nest. */ | |
1296 | ||
1297 | static unsigned | |
1298 | self_reuse_distance (data_reference_p dr, unsigned *loop_sizes, unsigned n, | |
1299 | struct loop *loop) | |
1300 | { | |
1301 | tree stride, access_fn; | |
1302 | HOST_WIDE_INT *strides, astride; | |
1303 | VEC (tree, heap) *access_fns; | |
1304 | tree ref = DR_REF (dr); | |
1305 | unsigned i, ret = ~0u; | |
1306 | ||
1307 | /* In the following example: | |
1308 | ||
1309 | for (i = 0; i < N; i++) | |
1310 | for (j = 0; j < N; j++) | |
1311 | use (a[j][i]); | |
1312 | the same cache line is accessed each N steps (except if the change from | |
1313 | i to i + 1 crosses the boundary of the cache line). Thus, for self-reuse, | |
1314 | we cannot rely purely on the results of the data dependence analysis. | |
1315 | ||
1316 | Instead, we compute the stride of the reference in each loop, and consider | |
1317 | the innermost loop in that the stride is less than cache size. */ | |
1318 | ||
1319 | strides = XCNEWVEC (HOST_WIDE_INT, n); | |
1320 | access_fns = DR_ACCESS_FNS (dr); | |
1321 | ||
1322 | for (i = 0; VEC_iterate (tree, access_fns, i, access_fn); i++) | |
1323 | { | |
1324 | /* Keep track of the reference corresponding to the subscript, so that we | |
1325 | know its stride. */ | |
1326 | while (handled_component_p (ref) && TREE_CODE (ref) != ARRAY_REF) | |
1327 | ref = TREE_OPERAND (ref, 0); | |
b8698a0f | 1328 | |
5417e022 ZD |
1329 | if (TREE_CODE (ref) == ARRAY_REF) |
1330 | { | |
1331 | stride = TYPE_SIZE_UNIT (TREE_TYPE (ref)); | |
1332 | if (host_integerp (stride, 1)) | |
1333 | astride = tree_low_cst (stride, 1); | |
1334 | else | |
1335 | astride = L1_CACHE_LINE_SIZE; | |
1336 | ||
1337 | ref = TREE_OPERAND (ref, 0); | |
1338 | } | |
1339 | else | |
1340 | astride = 1; | |
1341 | ||
1342 | add_subscript_strides (access_fn, astride, strides, n, loop); | |
1343 | } | |
1344 | ||
1345 | for (i = n; i-- > 0; ) | |
1346 | { | |
1347 | unsigned HOST_WIDE_INT s; | |
1348 | ||
1349 | s = strides[i] < 0 ? -strides[i] : strides[i]; | |
1350 | ||
1351 | if (s < (unsigned) L1_CACHE_LINE_SIZE | |
1352 | && (loop_sizes[i] | |
1353 | > (unsigned) (L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION))) | |
1354 | { | |
1355 | ret = loop_sizes[i]; | |
1356 | break; | |
1357 | } | |
1358 | } | |
1359 | ||
1360 | free (strides); | |
1361 | return ret; | |
1362 | } | |
1363 | ||
1364 | /* Determines the distance till the first reuse of each reference in REFS | |
79f5e442 ZD |
1365 | in the loop nest of LOOP. NO_OTHER_REFS is true if there are no other |
1366 | memory references in the loop. */ | |
5417e022 ZD |
1367 | |
1368 | static void | |
79f5e442 ZD |
1369 | determine_loop_nest_reuse (struct loop *loop, struct mem_ref_group *refs, |
1370 | bool no_other_refs) | |
5417e022 ZD |
1371 | { |
1372 | struct loop *nest, *aloop; | |
1373 | VEC (data_reference_p, heap) *datarefs = NULL; | |
1374 | VEC (ddr_p, heap) *dependences = NULL; | |
1375 | struct mem_ref_group *gr; | |
79f5e442 | 1376 | struct mem_ref *ref, *refb; |
5417e022 ZD |
1377 | VEC (loop_p, heap) *vloops = NULL; |
1378 | unsigned *loop_data_size; | |
1379 | unsigned i, j, n; | |
1380 | unsigned volume, dist, adist; | |
1381 | HOST_WIDE_INT vol; | |
1382 | data_reference_p dr; | |
1383 | ddr_p dep; | |
1384 | ||
1385 | if (loop->inner) | |
1386 | return; | |
1387 | ||
1388 | /* Find the outermost loop of the loop nest of loop (we require that | |
1389 | there are no sibling loops inside the nest). */ | |
1390 | nest = loop; | |
1391 | while (1) | |
1392 | { | |
1393 | aloop = loop_outer (nest); | |
1394 | ||
1395 | if (aloop == current_loops->tree_root | |
1396 | || aloop->inner->next) | |
1397 | break; | |
1398 | ||
1399 | nest = aloop; | |
1400 | } | |
1401 | ||
1402 | /* For each loop, determine the amount of data accessed in each iteration. | |
1403 | We use this to estimate whether the reference is evicted from the | |
1404 | cache before its reuse. */ | |
1405 | find_loop_nest (nest, &vloops); | |
1406 | n = VEC_length (loop_p, vloops); | |
1407 | loop_data_size = XNEWVEC (unsigned, n); | |
1408 | volume = volume_of_references (refs); | |
1409 | i = n; | |
1410 | while (i-- != 0) | |
1411 | { | |
1412 | loop_data_size[i] = volume; | |
1413 | /* Bound the volume by the L2 cache size, since above this bound, | |
1414 | all dependence distances are equivalent. */ | |
1415 | if (volume > L2_CACHE_SIZE_BYTES) | |
1416 | continue; | |
1417 | ||
1418 | aloop = VEC_index (loop_p, vloops, i); | |
1419 | vol = estimated_loop_iterations_int (aloop, false); | |
1420 | if (vol < 0) | |
1421 | vol = expected_loop_iterations (aloop); | |
1422 | volume *= vol; | |
1423 | } | |
1424 | ||
1425 | /* Prepare the references in the form suitable for data dependence | |
0d52bcc1 | 1426 | analysis. We ignore unanalyzable data references (the results |
5417e022 ZD |
1427 | are used just as a heuristics to estimate temporality of the |
1428 | references, hence we do not need to worry about correctness). */ | |
1429 | for (gr = refs; gr; gr = gr->next) | |
1430 | for (ref = gr->refs; ref; ref = ref->next) | |
1431 | { | |
1432 | dr = create_data_ref (nest, ref->mem, ref->stmt, !ref->write_p); | |
1433 | ||
1434 | if (dr) | |
1435 | { | |
1436 | ref->reuse_distance = volume; | |
1437 | dr->aux = ref; | |
1438 | VEC_safe_push (data_reference_p, heap, datarefs, dr); | |
1439 | } | |
79f5e442 ZD |
1440 | else |
1441 | no_other_refs = false; | |
5417e022 ZD |
1442 | } |
1443 | ||
1444 | for (i = 0; VEC_iterate (data_reference_p, datarefs, i, dr); i++) | |
1445 | { | |
1446 | dist = self_reuse_distance (dr, loop_data_size, n, loop); | |
3d9a9f94 | 1447 | ref = (struct mem_ref *) dr->aux; |
5417e022 ZD |
1448 | if (ref->reuse_distance > dist) |
1449 | ref->reuse_distance = dist; | |
79f5e442 ZD |
1450 | |
1451 | if (no_other_refs) | |
1452 | ref->independent_p = true; | |
5417e022 ZD |
1453 | } |
1454 | ||
1455 | compute_all_dependences (datarefs, &dependences, vloops, true); | |
1456 | ||
1457 | for (i = 0; VEC_iterate (ddr_p, dependences, i, dep); i++) | |
1458 | { | |
1459 | if (DDR_ARE_DEPENDENT (dep) == chrec_known) | |
1460 | continue; | |
1461 | ||
3d9a9f94 KG |
1462 | ref = (struct mem_ref *) DDR_A (dep)->aux; |
1463 | refb = (struct mem_ref *) DDR_B (dep)->aux; | |
79f5e442 | 1464 | |
5417e022 ZD |
1465 | if (DDR_ARE_DEPENDENT (dep) == chrec_dont_know |
1466 | || DDR_NUM_DIST_VECTS (dep) == 0) | |
1467 | { | |
0d52bcc1 | 1468 | /* If the dependence cannot be analyzed, assume that there might be |
5417e022 ZD |
1469 | a reuse. */ |
1470 | dist = 0; | |
b8698a0f | 1471 | |
79f5e442 ZD |
1472 | ref->independent_p = false; |
1473 | refb->independent_p = false; | |
5417e022 ZD |
1474 | } |
1475 | else | |
1476 | { | |
0d52bcc1 | 1477 | /* The distance vectors are normalized to be always lexicographically |
5417e022 ZD |
1478 | positive, hence we cannot tell just from them whether DDR_A comes |
1479 | before DDR_B or vice versa. However, it is not important, | |
1480 | anyway -- if DDR_A is close to DDR_B, then it is either reused in | |
1481 | DDR_B (and it is not nontemporal), or it reuses the value of DDR_B | |
1482 | in cache (and marking it as nontemporal would not affect | |
1483 | anything). */ | |
1484 | ||
1485 | dist = volume; | |
1486 | for (j = 0; j < DDR_NUM_DIST_VECTS (dep); j++) | |
1487 | { | |
1488 | adist = volume_of_dist_vector (DDR_DIST_VECT (dep, j), | |
1489 | loop_data_size, n); | |
1490 | ||
79f5e442 ZD |
1491 | /* If this is a dependence in the innermost loop (i.e., the |
1492 | distances in all superloops are zero) and it is not | |
1493 | the trivial self-dependence with distance zero, record that | |
1494 | the references are not completely independent. */ | |
1495 | if (lambda_vector_zerop (DDR_DIST_VECT (dep, j), n - 1) | |
1496 | && (ref != refb | |
1497 | || DDR_DIST_VECT (dep, j)[n-1] != 0)) | |
1498 | { | |
1499 | ref->independent_p = false; | |
1500 | refb->independent_p = false; | |
1501 | } | |
1502 | ||
5417e022 ZD |
1503 | /* Ignore accesses closer than |
1504 | L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION, | |
1505 | so that we use nontemporal prefetches e.g. if single memory | |
1506 | location is accessed several times in a single iteration of | |
1507 | the loop. */ | |
1508 | if (adist < L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION) | |
1509 | continue; | |
1510 | ||
1511 | if (adist < dist) | |
1512 | dist = adist; | |
1513 | } | |
1514 | } | |
1515 | ||
5417e022 ZD |
1516 | if (ref->reuse_distance > dist) |
1517 | ref->reuse_distance = dist; | |
79f5e442 ZD |
1518 | if (refb->reuse_distance > dist) |
1519 | refb->reuse_distance = dist; | |
5417e022 ZD |
1520 | } |
1521 | ||
1522 | free_dependence_relations (dependences); | |
1523 | free_data_refs (datarefs); | |
1524 | free (loop_data_size); | |
1525 | ||
1526 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
1527 | { | |
1528 | fprintf (dump_file, "Reuse distances:\n"); | |
1529 | for (gr = refs; gr; gr = gr->next) | |
1530 | for (ref = gr->refs; ref; ref = ref->next) | |
1531 | fprintf (dump_file, " ref %p distance %u\n", | |
1532 | (void *) ref, ref->reuse_distance); | |
1533 | } | |
1534 | } | |
1535 | ||
db34470d GS |
1536 | /* Do a cost-benefit analysis to determine if prefetching is profitable |
1537 | for the current loop given the following parameters: | |
1538 | AHEAD: the iteration ahead distance, | |
b8698a0f | 1539 | EST_NITER: the estimated trip count, |
db34470d GS |
1540 | NINSNS: estimated number of instructions in the loop, |
1541 | PREFETCH_COUNT: an estimate of the number of prefetches | |
1542 | MEM_REF_COUNT: total number of memory references in the loop. */ | |
1543 | ||
b8698a0f L |
1544 | static bool |
1545 | is_loop_prefetching_profitable (unsigned ahead, HOST_WIDE_INT est_niter, | |
1546 | unsigned ninsns, unsigned prefetch_count, | |
ccacf0e1 | 1547 | unsigned mem_ref_count, unsigned unroll_factor) |
db34470d GS |
1548 | { |
1549 | int insn_to_mem_ratio, insn_to_prefetch_ratio; | |
1550 | ||
1551 | if (mem_ref_count == 0) | |
1552 | return false; | |
1553 | ||
b8698a0f L |
1554 | /* Prefetching improves performance by overlapping cache missing |
1555 | memory accesses with CPU operations. If the loop does not have | |
1556 | enough CPU operations to overlap with memory operations, prefetching | |
1557 | won't give a significant benefit. One approximate way of checking | |
1558 | this is to require the ratio of instructions to memory references to | |
db34470d GS |
1559 | be above a certain limit. This approximation works well in practice. |
1560 | TODO: Implement a more precise computation by estimating the time | |
1561 | for each CPU or memory op in the loop. Time estimates for memory ops | |
1562 | should account for cache misses. */ | |
b8698a0f | 1563 | insn_to_mem_ratio = ninsns / mem_ref_count; |
db34470d GS |
1564 | |
1565 | if (insn_to_mem_ratio < PREFETCH_MIN_INSN_TO_MEM_RATIO) | |
55e5a2eb CF |
1566 | { |
1567 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
1568 | fprintf (dump_file, | |
1569 | "Not prefetching -- instruction to memory reference ratio (%d) too small\n", | |
1570 | insn_to_mem_ratio); | |
1571 | return false; | |
1572 | } | |
db34470d GS |
1573 | |
1574 | /* Profitability of prefetching is highly dependent on the trip count. | |
b8698a0f L |
1575 | For a given AHEAD distance, the first AHEAD iterations do not benefit |
1576 | from prefetching, and the last AHEAD iterations execute useless | |
db34470d GS |
1577 | prefetches. So, if the trip count is not large enough relative to AHEAD, |
1578 | prefetching may cause serious performance degradation. To avoid this | |
b8698a0f | 1579 | problem when the trip count is not known at compile time, we |
db34470d | 1580 | conservatively skip loops with high prefetching costs. For now, only |
b8698a0f | 1581 | the I-cache cost is considered. The relative I-cache cost is estimated |
db34470d GS |
1582 | by taking the ratio between the number of prefetches and the total |
1583 | number of instructions. Since we are using integer arithmetic, we | |
b8698a0f | 1584 | compute the reciprocal of this ratio. |
ccacf0e1 CF |
1585 | (unroll_factor * ninsns) is used to estimate the number of instructions in |
1586 | the unrolled loop. This implementation is a bit simplistic -- the number | |
1587 | of issued prefetch instructions is also affected by unrolling. So, | |
1588 | prefetch_mod and the unroll factor should be taken into account when | |
1589 | determining prefetch_count. Also, the number of insns of the unrolled | |
1590 | loop will usually be significantly smaller than the number of insns of the | |
1591 | original loop * unroll_factor (at least the induction variable increases | |
1592 | and the exit branches will get eliminated), so it might be better to use | |
1593 | tree_estimate_loop_size + estimated_unrolled_size. */ | |
db34470d GS |
1594 | if (est_niter < 0) |
1595 | { | |
ccacf0e1 | 1596 | insn_to_prefetch_ratio = (unroll_factor * ninsns) / prefetch_count; |
db34470d GS |
1597 | return insn_to_prefetch_ratio >= MIN_INSN_TO_PREFETCH_RATIO; |
1598 | } | |
b8698a0f | 1599 | |
9bf4598b | 1600 | if (est_niter < (HOST_WIDE_INT) (TRIP_COUNT_TO_AHEAD_RATIO * ahead)) |
db34470d GS |
1601 | { |
1602 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
1603 | fprintf (dump_file, | |
1604 | "Not prefetching -- loop estimated to roll only %d times\n", | |
1605 | (int) est_niter); | |
1606 | return false; | |
1607 | } | |
1608 | return true; | |
1609 | } | |
1610 | ||
1611 | ||
b076a3fd | 1612 | /* Issue prefetch instructions for array references in LOOP. Returns |
d73be268 | 1613 | true if the LOOP was unrolled. */ |
b076a3fd ZD |
1614 | |
1615 | static bool | |
d73be268 | 1616 | loop_prefetch_arrays (struct loop *loop) |
b076a3fd ZD |
1617 | { |
1618 | struct mem_ref_group *refs; | |
2711355f ZD |
1619 | unsigned ahead, ninsns, time, unroll_factor; |
1620 | HOST_WIDE_INT est_niter; | |
b076a3fd | 1621 | struct tree_niter_desc desc; |
79f5e442 | 1622 | bool unrolled = false, no_other_refs; |
db34470d GS |
1623 | unsigned prefetch_count; |
1624 | unsigned mem_ref_count; | |
b076a3fd | 1625 | |
efd8f750 | 1626 | if (optimize_loop_nest_for_size_p (loop)) |
2732d767 ZD |
1627 | { |
1628 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
1629 | fprintf (dump_file, " ignored (cold area)\n"); | |
1630 | return false; | |
1631 | } | |
1632 | ||
b076a3fd | 1633 | /* Step 1: gather the memory references. */ |
db34470d | 1634 | refs = gather_memory_references (loop, &no_other_refs, &mem_ref_count); |
b076a3fd ZD |
1635 | |
1636 | /* Step 2: estimate the reuse effects. */ | |
1637 | prune_by_reuse (refs); | |
1638 | ||
db34470d GS |
1639 | prefetch_count = estimate_prefetch_count (refs); |
1640 | if (prefetch_count == 0) | |
b076a3fd ZD |
1641 | goto fail; |
1642 | ||
79f5e442 | 1643 | determine_loop_nest_reuse (loop, refs, no_other_refs); |
5417e022 | 1644 | |
b076a3fd ZD |
1645 | /* Step 3: determine the ahead and unroll factor. */ |
1646 | ||
2711355f ZD |
1647 | /* FIXME: the time should be weighted by the probabilities of the blocks in |
1648 | the loop body. */ | |
1649 | time = tree_num_loop_insns (loop, &eni_time_weights); | |
1650 | ahead = (PREFETCH_LATENCY + time - 1) / time; | |
b8698a0f | 1651 | est_niter = estimated_loop_iterations_int (loop, false); |
79f5e442 | 1652 | |
2711355f ZD |
1653 | ninsns = tree_num_loop_insns (loop, &eni_size_weights); |
1654 | unroll_factor = determine_unroll_factor (loop, refs, ninsns, &desc, | |
1655 | est_niter); | |
1656 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
b8698a0f | 1657 | fprintf (dump_file, "Ahead %d, unroll factor %d, trip count " |
d81f5387 | 1658 | HOST_WIDE_INT_PRINT_DEC "\n" |
b8698a0f L |
1659 | "insn count %d, mem ref count %d, prefetch count %d\n", |
1660 | ahead, unroll_factor, est_niter, | |
1661 | ninsns, mem_ref_count, prefetch_count); | |
db34470d | 1662 | |
ccacf0e1 CF |
1663 | if (!is_loop_prefetching_profitable (ahead, est_niter, ninsns, prefetch_count, |
1664 | mem_ref_count, unroll_factor)) | |
db34470d GS |
1665 | goto fail; |
1666 | ||
1667 | mark_nontemporal_stores (loop, refs); | |
2711355f | 1668 | |
b076a3fd ZD |
1669 | /* Step 4: what to prefetch? */ |
1670 | if (!schedule_prefetches (refs, unroll_factor, ahead)) | |
1671 | goto fail; | |
1672 | ||
1673 | /* Step 5: unroll the loop. TODO -- peeling of first and last few | |
1674 | iterations so that we do not issue superfluous prefetches. */ | |
1675 | if (unroll_factor != 1) | |
1676 | { | |
d73be268 | 1677 | tree_unroll_loop (loop, unroll_factor, |
b076a3fd ZD |
1678 | single_dom_exit (loop), &desc); |
1679 | unrolled = true; | |
1680 | } | |
1681 | ||
1682 | /* Step 6: issue the prefetches. */ | |
1683 | issue_prefetches (refs, unroll_factor, ahead); | |
1684 | ||
1685 | fail: | |
1686 | release_mem_refs (refs); | |
1687 | return unrolled; | |
1688 | } | |
1689 | ||
d73be268 | 1690 | /* Issue prefetch instructions for array references in loops. */ |
b076a3fd | 1691 | |
c7f965b6 | 1692 | unsigned int |
d73be268 | 1693 | tree_ssa_prefetch_arrays (void) |
b076a3fd | 1694 | { |
42fd6772 | 1695 | loop_iterator li; |
b076a3fd ZD |
1696 | struct loop *loop; |
1697 | bool unrolled = false; | |
c7f965b6 | 1698 | int todo_flags = 0; |
b076a3fd ZD |
1699 | |
1700 | if (!HAVE_prefetch | |
1701 | /* It is possible to ask compiler for say -mtune=i486 -march=pentium4. | |
1702 | -mtune=i486 causes us having PREFETCH_BLOCK 0, since this is part | |
1703 | of processor costs and i486 does not have prefetch, but | |
1704 | -march=pentium4 causes HAVE_prefetch to be true. Ugh. */ | |
1705 | || PREFETCH_BLOCK == 0) | |
c7f965b6 | 1706 | return 0; |
b076a3fd | 1707 | |
47eb5b32 ZD |
1708 | if (dump_file && (dump_flags & TDF_DETAILS)) |
1709 | { | |
1710 | fprintf (dump_file, "Prefetching parameters:\n"); | |
1711 | fprintf (dump_file, " simultaneous prefetches: %d\n", | |
1712 | SIMULTANEOUS_PREFETCHES); | |
1713 | fprintf (dump_file, " prefetch latency: %d\n", PREFETCH_LATENCY); | |
47eb5b32 | 1714 | fprintf (dump_file, " prefetch block size: %d\n", PREFETCH_BLOCK); |
46cb0441 ZD |
1715 | fprintf (dump_file, " L1 cache size: %d lines, %d kB\n", |
1716 | L1_CACHE_SIZE_BYTES / L1_CACHE_LINE_SIZE, L1_CACHE_SIZE); | |
5417e022 | 1717 | fprintf (dump_file, " L1 cache line size: %d\n", L1_CACHE_LINE_SIZE); |
b8698a0f L |
1718 | fprintf (dump_file, " L2 cache size: %d kB\n", L2_CACHE_SIZE); |
1719 | fprintf (dump_file, " min insn-to-prefetch ratio: %d \n", | |
db34470d | 1720 | MIN_INSN_TO_PREFETCH_RATIO); |
b8698a0f | 1721 | fprintf (dump_file, " min insn-to-mem ratio: %d \n", |
db34470d | 1722 | PREFETCH_MIN_INSN_TO_MEM_RATIO); |
47eb5b32 ZD |
1723 | fprintf (dump_file, "\n"); |
1724 | } | |
1725 | ||
b076a3fd ZD |
1726 | initialize_original_copy_tables (); |
1727 | ||
1728 | if (!built_in_decls[BUILT_IN_PREFETCH]) | |
1729 | { | |
1730 | tree type = build_function_type (void_type_node, | |
1731 | tree_cons (NULL_TREE, | |
1732 | const_ptr_type_node, | |
1733 | NULL_TREE)); | |
c79efc4d RÁE |
1734 | tree decl = add_builtin_function ("__builtin_prefetch", type, |
1735 | BUILT_IN_PREFETCH, BUILT_IN_NORMAL, | |
1736 | NULL, NULL_TREE); | |
b076a3fd ZD |
1737 | DECL_IS_NOVOPS (decl) = true; |
1738 | built_in_decls[BUILT_IN_PREFETCH] = decl; | |
1739 | } | |
1740 | ||
1741 | /* We assume that size of cache line is a power of two, so verify this | |
1742 | here. */ | |
1743 | gcc_assert ((PREFETCH_BLOCK & (PREFETCH_BLOCK - 1)) == 0); | |
1744 | ||
42fd6772 | 1745 | FOR_EACH_LOOP (li, loop, LI_FROM_INNERMOST) |
b076a3fd | 1746 | { |
b076a3fd ZD |
1747 | if (dump_file && (dump_flags & TDF_DETAILS)) |
1748 | fprintf (dump_file, "Processing loop %d:\n", loop->num); | |
1749 | ||
d73be268 | 1750 | unrolled |= loop_prefetch_arrays (loop); |
b076a3fd ZD |
1751 | |
1752 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
1753 | fprintf (dump_file, "\n\n"); | |
1754 | } | |
1755 | ||
1756 | if (unrolled) | |
1757 | { | |
1758 | scev_reset (); | |
c7f965b6 | 1759 | todo_flags |= TODO_cleanup_cfg; |
b076a3fd ZD |
1760 | } |
1761 | ||
1762 | free_original_copy_tables (); | |
c7f965b6 | 1763 | return todo_flags; |
b076a3fd | 1764 | } |