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b076a3fd | 1 | /* Array prefetching. |
9f813990 PC |
2 | Copyright (C) 2005, 2007, 2008, 2009, 2010, 2011 |
3 | Free Software Foundation, Inc. | |
b8698a0f | 4 | |
b076a3fd | 5 | This file is part of GCC. |
b8698a0f | 6 | |
b076a3fd ZD |
7 | GCC is free software; you can redistribute it and/or modify it |
8 | under the terms of the GNU General Public License as published by the | |
9dcd6f09 | 9 | Free Software Foundation; either version 3, or (at your option) any |
b076a3fd | 10 | later version. |
b8698a0f | 11 | |
b076a3fd ZD |
12 | GCC is distributed in the hope that it will be useful, but WITHOUT |
13 | ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
14 | FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
15 | for more details. | |
b8698a0f | 16 | |
b076a3fd | 17 | You should have received a copy of the GNU General Public License |
9dcd6f09 NC |
18 | along with GCC; see the file COPYING3. If not see |
19 | <http://www.gnu.org/licenses/>. */ | |
b076a3fd ZD |
20 | |
21 | #include "config.h" | |
22 | #include "system.h" | |
23 | #include "coretypes.h" | |
24 | #include "tm.h" | |
25 | #include "tree.h" | |
b076a3fd | 26 | #include "tm_p.h" |
b076a3fd ZD |
27 | #include "basic-block.h" |
28 | #include "output.h" | |
cf835838 | 29 | #include "tree-pretty-print.h" |
b076a3fd ZD |
30 | #include "tree-flow.h" |
31 | #include "tree-dump.h" | |
32 | #include "timevar.h" | |
33 | #include "cfgloop.h" | |
b076a3fd | 34 | #include "tree-pass.h" |
b076a3fd ZD |
35 | #include "insn-config.h" |
36 | #include "recog.h" | |
37 | #include "hashtab.h" | |
38 | #include "tree-chrec.h" | |
39 | #include "tree-scalar-evolution.h" | |
718f9c0f | 40 | #include "diagnostic-core.h" |
b076a3fd ZD |
41 | #include "params.h" |
42 | #include "langhooks.h" | |
7f9bc51b | 43 | #include "tree-inline.h" |
5417e022 | 44 | #include "tree-data-ref.h" |
2eb79bbb SB |
45 | |
46 | ||
47 | /* FIXME: Needed for optabs, but this should all be moved to a TBD interface | |
48 | between the GIMPLE and RTL worlds. */ | |
49 | #include "expr.h" | |
79f5e442 | 50 | #include "optabs.h" |
b076a3fd ZD |
51 | |
52 | /* This pass inserts prefetch instructions to optimize cache usage during | |
53 | accesses to arrays in loops. It processes loops sequentially and: | |
54 | ||
55 | 1) Gathers all memory references in the single loop. | |
56 | 2) For each of the references it decides when it is profitable to prefetch | |
57 | it. To do it, we evaluate the reuse among the accesses, and determines | |
58 | two values: PREFETCH_BEFORE (meaning that it only makes sense to do | |
59 | prefetching in the first PREFETCH_BEFORE iterations of the loop) and | |
60 | PREFETCH_MOD (meaning that it only makes sense to prefetch in the | |
61 | iterations of the loop that are zero modulo PREFETCH_MOD). For example | |
62 | (assuming cache line size is 64 bytes, char has size 1 byte and there | |
63 | is no hardware sequential prefetch): | |
64 | ||
65 | char *a; | |
66 | for (i = 0; i < max; i++) | |
67 | { | |
68 | a[255] = ...; (0) | |
69 | a[i] = ...; (1) | |
70 | a[i + 64] = ...; (2) | |
71 | a[16*i] = ...; (3) | |
72 | a[187*i] = ...; (4) | |
73 | a[187*i + 50] = ...; (5) | |
74 | } | |
75 | ||
76 | (0) obviously has PREFETCH_BEFORE 1 | |
77 | (1) has PREFETCH_BEFORE 64, since (2) accesses the same memory | |
78 | location 64 iterations before it, and PREFETCH_MOD 64 (since | |
79 | it hits the same cache line otherwise). | |
80 | (2) has PREFETCH_MOD 64 | |
81 | (3) has PREFETCH_MOD 4 | |
82 | (4) has PREFETCH_MOD 1. We do not set PREFETCH_BEFORE here, since | |
bae077dc | 83 | the cache line accessed by (5) is the same with probability only |
b076a3fd ZD |
84 | 7/32. |
85 | (5) has PREFETCH_MOD 1 as well. | |
86 | ||
5417e022 ZD |
87 | Additionally, we use data dependence analysis to determine for each |
88 | reference the distance till the first reuse; this information is used | |
89 | to determine the temporality of the issued prefetch instruction. | |
90 | ||
b076a3fd ZD |
91 | 3) We determine how much ahead we need to prefetch. The number of |
92 | iterations needed is time to fetch / time spent in one iteration of | |
93 | the loop. The problem is that we do not know either of these values, | |
94 | so we just make a heuristic guess based on a magic (possibly) | |
95 | target-specific constant and size of the loop. | |
96 | ||
97 | 4) Determine which of the references we prefetch. We take into account | |
98 | that there is a maximum number of simultaneous prefetches (provided | |
99 | by machine description). We prefetch as many prefetches as possible | |
100 | while still within this bound (starting with those with lowest | |
101 | prefetch_mod, since they are responsible for most of the cache | |
102 | misses). | |
b8698a0f | 103 | |
b076a3fd ZD |
104 | 5) We unroll and peel loops so that we are able to satisfy PREFETCH_MOD |
105 | and PREFETCH_BEFORE requirements (within some bounds), and to avoid | |
106 | prefetching nonaccessed memory. | |
107 | TODO -- actually implement peeling. | |
b8698a0f | 108 | |
b076a3fd ZD |
109 | 6) We actually emit the prefetch instructions. ??? Perhaps emit the |
110 | prefetch instructions with guards in cases where 5) was not sufficient | |
111 | to satisfy the constraints? | |
112 | ||
0bbe50f6 CF |
113 | A cost model is implemented to determine whether or not prefetching is |
114 | profitable for a given loop. The cost model has three heuristics: | |
115 | ||
116 | 1. Function trip_count_to_ahead_ratio_too_small_p implements a | |
117 | heuristic that determines whether or not the loop has too few | |
118 | iterations (compared to ahead). Prefetching is not likely to be | |
119 | beneficial if the trip count to ahead ratio is below a certain | |
120 | minimum. | |
121 | ||
122 | 2. Function mem_ref_count_reasonable_p implements a heuristic that | |
123 | determines whether the given loop has enough CPU ops that can be | |
124 | overlapped with cache missing memory ops. If not, the loop | |
125 | won't benefit from prefetching. In the implementation, | |
126 | prefetching is not considered beneficial if the ratio between | |
127 | the instruction count and the mem ref count is below a certain | |
128 | minimum. | |
129 | ||
130 | 3. Function insn_to_prefetch_ratio_too_small_p implements a | |
131 | heuristic that disables prefetching in a loop if the prefetching | |
132 | cost is above a certain limit. The relative prefetching cost is | |
133 | estimated by taking the ratio between the prefetch count and the | |
134 | total intruction count (this models the I-cache cost). | |
135 | ||
db34470d | 136 | The limits used in these heuristics are defined as parameters with |
b8698a0f | 137 | reasonable default values. Machine-specific default values will be |
db34470d | 138 | added later. |
b8698a0f | 139 | |
b076a3fd ZD |
140 | Some other TODO: |
141 | -- write and use more general reuse analysis (that could be also used | |
142 | in other cache aimed loop optimizations) | |
143 | -- make it behave sanely together with the prefetches given by user | |
144 | (now we just ignore them; at the very least we should avoid | |
145 | optimizing loops in that user put his own prefetches) | |
146 | -- we assume cache line size alignment of arrays; this could be | |
147 | improved. */ | |
148 | ||
149 | /* Magic constants follow. These should be replaced by machine specific | |
150 | numbers. */ | |
151 | ||
b076a3fd ZD |
152 | /* True if write can be prefetched by a read prefetch. */ |
153 | ||
154 | #ifndef WRITE_CAN_USE_READ_PREFETCH | |
155 | #define WRITE_CAN_USE_READ_PREFETCH 1 | |
156 | #endif | |
157 | ||
158 | /* True if read can be prefetched by a write prefetch. */ | |
159 | ||
160 | #ifndef READ_CAN_USE_WRITE_PREFETCH | |
161 | #define READ_CAN_USE_WRITE_PREFETCH 0 | |
162 | #endif | |
163 | ||
47eb5b32 ZD |
164 | /* The size of the block loaded by a single prefetch. Usually, this is |
165 | the same as cache line size (at the moment, we only consider one level | |
166 | of cache hierarchy). */ | |
b076a3fd ZD |
167 | |
168 | #ifndef PREFETCH_BLOCK | |
47eb5b32 | 169 | #define PREFETCH_BLOCK L1_CACHE_LINE_SIZE |
b076a3fd ZD |
170 | #endif |
171 | ||
172 | /* Do we have a forward hardware sequential prefetching? */ | |
173 | ||
174 | #ifndef HAVE_FORWARD_PREFETCH | |
175 | #define HAVE_FORWARD_PREFETCH 0 | |
176 | #endif | |
177 | ||
178 | /* Do we have a backward hardware sequential prefetching? */ | |
179 | ||
180 | #ifndef HAVE_BACKWARD_PREFETCH | |
181 | #define HAVE_BACKWARD_PREFETCH 0 | |
182 | #endif | |
183 | ||
184 | /* In some cases we are only able to determine that there is a certain | |
185 | probability that the two accesses hit the same cache line. In this | |
186 | case, we issue the prefetches for both of them if this probability | |
fa10beec | 187 | is less then (1000 - ACCEPTABLE_MISS_RATE) per thousand. */ |
b076a3fd ZD |
188 | |
189 | #ifndef ACCEPTABLE_MISS_RATE | |
190 | #define ACCEPTABLE_MISS_RATE 50 | |
191 | #endif | |
192 | ||
193 | #ifndef HAVE_prefetch | |
194 | #define HAVE_prefetch 0 | |
195 | #endif | |
196 | ||
46cb0441 ZD |
197 | #define L1_CACHE_SIZE_BYTES ((unsigned) (L1_CACHE_SIZE * 1024)) |
198 | #define L2_CACHE_SIZE_BYTES ((unsigned) (L2_CACHE_SIZE * 1024)) | |
5417e022 ZD |
199 | |
200 | /* We consider a memory access nontemporal if it is not reused sooner than | |
201 | after L2_CACHE_SIZE_BYTES of memory are accessed. However, we ignore | |
202 | accesses closer than L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION, | |
203 | so that we use nontemporal prefetches e.g. if single memory location | |
204 | is accessed several times in a single iteration of the loop. */ | |
205 | #define NONTEMPORAL_FRACTION 16 | |
206 | ||
79f5e442 ZD |
207 | /* In case we have to emit a memory fence instruction after the loop that |
208 | uses nontemporal stores, this defines the builtin to use. */ | |
209 | ||
210 | #ifndef FENCE_FOLLOWING_MOVNT | |
211 | #define FENCE_FOLLOWING_MOVNT NULL_TREE | |
212 | #endif | |
213 | ||
9bf4598b CF |
214 | /* It is not profitable to prefetch when the trip count is not at |
215 | least TRIP_COUNT_TO_AHEAD_RATIO times the prefetch ahead distance. | |
216 | For example, in a loop with a prefetch ahead distance of 10, | |
217 | supposing that TRIP_COUNT_TO_AHEAD_RATIO is equal to 4, it is | |
218 | profitable to prefetch when the trip count is greater or equal to | |
219 | 40. In that case, 30 out of the 40 iterations will benefit from | |
220 | prefetching. */ | |
221 | ||
222 | #ifndef TRIP_COUNT_TO_AHEAD_RATIO | |
223 | #define TRIP_COUNT_TO_AHEAD_RATIO 4 | |
224 | #endif | |
225 | ||
b076a3fd ZD |
226 | /* The group of references between that reuse may occur. */ |
227 | ||
228 | struct mem_ref_group | |
229 | { | |
230 | tree base; /* Base of the reference. */ | |
81f32326 | 231 | tree step; /* Step of the reference. */ |
b076a3fd ZD |
232 | struct mem_ref *refs; /* References in the group. */ |
233 | struct mem_ref_group *next; /* Next group of references. */ | |
234 | }; | |
235 | ||
236 | /* Assigned to PREFETCH_BEFORE when all iterations are to be prefetched. */ | |
237 | ||
238 | #define PREFETCH_ALL (~(unsigned HOST_WIDE_INT) 0) | |
239 | ||
8532678c CF |
240 | /* Do not generate a prefetch if the unroll factor is significantly less |
241 | than what is required by the prefetch. This is to avoid redundant | |
f7963a7c CF |
242 | prefetches. For example, when prefetch_mod is 16 and unroll_factor is |
243 | 2, prefetching requires unrolling the loop 16 times, but | |
244 | the loop is actually unrolled twice. In this case (ratio = 8), | |
8532678c CF |
245 | prefetching is not likely to be beneficial. */ |
246 | ||
247 | #ifndef PREFETCH_MOD_TO_UNROLL_FACTOR_RATIO | |
f7963a7c | 248 | #define PREFETCH_MOD_TO_UNROLL_FACTOR_RATIO 4 |
8532678c CF |
249 | #endif |
250 | ||
0bbe50f6 CF |
251 | /* Some of the prefetch computations have quadratic complexity. We want to |
252 | avoid huge compile times and, therefore, want to limit the amount of | |
253 | memory references per loop where we consider prefetching. */ | |
254 | ||
255 | #ifndef PREFETCH_MAX_MEM_REFS_PER_LOOP | |
256 | #define PREFETCH_MAX_MEM_REFS_PER_LOOP 200 | |
257 | #endif | |
258 | ||
b076a3fd ZD |
259 | /* The memory reference. */ |
260 | ||
261 | struct mem_ref | |
262 | { | |
726a989a | 263 | gimple stmt; /* Statement in that the reference appears. */ |
b076a3fd ZD |
264 | tree mem; /* The reference. */ |
265 | HOST_WIDE_INT delta; /* Constant offset of the reference. */ | |
b076a3fd ZD |
266 | struct mem_ref_group *group; /* The group of references it belongs to. */ |
267 | unsigned HOST_WIDE_INT prefetch_mod; | |
268 | /* Prefetch only each PREFETCH_MOD-th | |
269 | iteration. */ | |
270 | unsigned HOST_WIDE_INT prefetch_before; | |
271 | /* Prefetch only first PREFETCH_BEFORE | |
272 | iterations. */ | |
5417e022 ZD |
273 | unsigned reuse_distance; /* The amount of data accessed before the first |
274 | reuse of this value. */ | |
b076a3fd | 275 | struct mem_ref *next; /* The next reference in the group. */ |
79f5e442 ZD |
276 | unsigned write_p : 1; /* Is it a write? */ |
277 | unsigned independent_p : 1; /* True if the reference is independent on | |
278 | all other references inside the loop. */ | |
279 | unsigned issue_prefetch_p : 1; /* Should we really issue the prefetch? */ | |
280 | unsigned storent_p : 1; /* True if we changed the store to a | |
281 | nontemporal one. */ | |
b076a3fd ZD |
282 | }; |
283 | ||
75c40d56 | 284 | /* Dumps information about reference REF to FILE. */ |
b076a3fd ZD |
285 | |
286 | static void | |
287 | dump_mem_ref (FILE *file, struct mem_ref *ref) | |
288 | { | |
289 | fprintf (file, "Reference %p:\n", (void *) ref); | |
290 | ||
291 | fprintf (file, " group %p (base ", (void *) ref->group); | |
292 | print_generic_expr (file, ref->group->base, TDF_SLIM); | |
293 | fprintf (file, ", step "); | |
81f32326 CB |
294 | if (cst_and_fits_in_hwi (ref->group->step)) |
295 | fprintf (file, HOST_WIDE_INT_PRINT_DEC, int_cst_value (ref->group->step)); | |
296 | else | |
297 | print_generic_expr (file, ref->group->step, TDF_TREE); | |
b076a3fd ZD |
298 | fprintf (file, ")\n"); |
299 | ||
e324a72f | 300 | fprintf (file, " delta "); |
b076a3fd ZD |
301 | fprintf (file, HOST_WIDE_INT_PRINT_DEC, ref->delta); |
302 | fprintf (file, "\n"); | |
303 | ||
304 | fprintf (file, " %s\n", ref->write_p ? "write" : "read"); | |
305 | ||
306 | fprintf (file, "\n"); | |
307 | } | |
308 | ||
309 | /* Finds a group with BASE and STEP in GROUPS, or creates one if it does not | |
310 | exist. */ | |
311 | ||
312 | static struct mem_ref_group * | |
81f32326 | 313 | find_or_create_group (struct mem_ref_group **groups, tree base, tree step) |
b076a3fd ZD |
314 | { |
315 | struct mem_ref_group *group; | |
316 | ||
317 | for (; *groups; groups = &(*groups)->next) | |
318 | { | |
81f32326 | 319 | if (operand_equal_p ((*groups)->step, step, 0) |
b076a3fd ZD |
320 | && operand_equal_p ((*groups)->base, base, 0)) |
321 | return *groups; | |
322 | ||
81f32326 CB |
323 | /* If step is an integer constant, keep the list of groups sorted |
324 | by decreasing step. */ | |
325 | if (cst_and_fits_in_hwi ((*groups)->step) && cst_and_fits_in_hwi (step) | |
326 | && int_cst_value ((*groups)->step) < int_cst_value (step)) | |
b076a3fd ZD |
327 | break; |
328 | } | |
329 | ||
5417e022 | 330 | group = XNEW (struct mem_ref_group); |
b076a3fd ZD |
331 | group->base = base; |
332 | group->step = step; | |
333 | group->refs = NULL; | |
334 | group->next = *groups; | |
335 | *groups = group; | |
336 | ||
337 | return group; | |
338 | } | |
339 | ||
340 | /* Records a memory reference MEM in GROUP with offset DELTA and write status | |
341 | WRITE_P. The reference occurs in statement STMT. */ | |
342 | ||
343 | static void | |
726a989a | 344 | record_ref (struct mem_ref_group *group, gimple stmt, tree mem, |
b076a3fd ZD |
345 | HOST_WIDE_INT delta, bool write_p) |
346 | { | |
347 | struct mem_ref **aref; | |
348 | ||
349 | /* Do not record the same address twice. */ | |
350 | for (aref = &group->refs; *aref; aref = &(*aref)->next) | |
351 | { | |
352 | /* It does not have to be possible for write reference to reuse the read | |
353 | prefetch, or vice versa. */ | |
354 | if (!WRITE_CAN_USE_READ_PREFETCH | |
355 | && write_p | |
356 | && !(*aref)->write_p) | |
357 | continue; | |
358 | if (!READ_CAN_USE_WRITE_PREFETCH | |
359 | && !write_p | |
360 | && (*aref)->write_p) | |
361 | continue; | |
362 | ||
363 | if ((*aref)->delta == delta) | |
364 | return; | |
365 | } | |
366 | ||
5417e022 | 367 | (*aref) = XNEW (struct mem_ref); |
b076a3fd ZD |
368 | (*aref)->stmt = stmt; |
369 | (*aref)->mem = mem; | |
370 | (*aref)->delta = delta; | |
371 | (*aref)->write_p = write_p; | |
372 | (*aref)->prefetch_before = PREFETCH_ALL; | |
373 | (*aref)->prefetch_mod = 1; | |
5417e022 | 374 | (*aref)->reuse_distance = 0; |
b076a3fd ZD |
375 | (*aref)->issue_prefetch_p = false; |
376 | (*aref)->group = group; | |
377 | (*aref)->next = NULL; | |
79f5e442 ZD |
378 | (*aref)->independent_p = false; |
379 | (*aref)->storent_p = false; | |
b076a3fd ZD |
380 | |
381 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
382 | dump_mem_ref (dump_file, *aref); | |
383 | } | |
384 | ||
385 | /* Release memory references in GROUPS. */ | |
386 | ||
387 | static void | |
388 | release_mem_refs (struct mem_ref_group *groups) | |
389 | { | |
390 | struct mem_ref_group *next_g; | |
391 | struct mem_ref *ref, *next_r; | |
392 | ||
393 | for (; groups; groups = next_g) | |
394 | { | |
395 | next_g = groups->next; | |
396 | for (ref = groups->refs; ref; ref = next_r) | |
397 | { | |
398 | next_r = ref->next; | |
399 | free (ref); | |
400 | } | |
401 | free (groups); | |
402 | } | |
403 | } | |
404 | ||
405 | /* A structure used to pass arguments to idx_analyze_ref. */ | |
406 | ||
407 | struct ar_data | |
408 | { | |
409 | struct loop *loop; /* Loop of the reference. */ | |
726a989a | 410 | gimple stmt; /* Statement of the reference. */ |
81f32326 | 411 | tree *step; /* Step of the memory reference. */ |
b076a3fd ZD |
412 | HOST_WIDE_INT *delta; /* Offset of the memory reference. */ |
413 | }; | |
414 | ||
415 | /* Analyzes a single INDEX of a memory reference to obtain information | |
416 | described at analyze_ref. Callback for for_each_index. */ | |
417 | ||
418 | static bool | |
419 | idx_analyze_ref (tree base, tree *index, void *data) | |
420 | { | |
c22940cd | 421 | struct ar_data *ar_data = (struct ar_data *) data; |
b076a3fd | 422 | tree ibase, step, stepsize; |
81f32326 | 423 | HOST_WIDE_INT idelta = 0, imult = 1; |
b076a3fd ZD |
424 | affine_iv iv; |
425 | ||
f017bf5e | 426 | if (!simple_iv (ar_data->loop, loop_containing_stmt (ar_data->stmt), |
81f32326 | 427 | *index, &iv, true)) |
b076a3fd ZD |
428 | return false; |
429 | ibase = iv.base; | |
430 | step = iv.step; | |
431 | ||
5be014d5 | 432 | if (TREE_CODE (ibase) == POINTER_PLUS_EXPR |
b076a3fd ZD |
433 | && cst_and_fits_in_hwi (TREE_OPERAND (ibase, 1))) |
434 | { | |
435 | idelta = int_cst_value (TREE_OPERAND (ibase, 1)); | |
436 | ibase = TREE_OPERAND (ibase, 0); | |
437 | } | |
438 | if (cst_and_fits_in_hwi (ibase)) | |
439 | { | |
440 | idelta += int_cst_value (ibase); | |
ff5e9a94 | 441 | ibase = build_int_cst (TREE_TYPE (ibase), 0); |
b076a3fd ZD |
442 | } |
443 | ||
444 | if (TREE_CODE (base) == ARRAY_REF) | |
445 | { | |
446 | stepsize = array_ref_element_size (base); | |
447 | if (!cst_and_fits_in_hwi (stepsize)) | |
448 | return false; | |
449 | imult = int_cst_value (stepsize); | |
8fde8b40 CB |
450 | step = fold_build2 (MULT_EXPR, sizetype, |
451 | fold_convert (sizetype, step), | |
452 | fold_convert (sizetype, stepsize)); | |
b076a3fd ZD |
453 | idelta *= imult; |
454 | } | |
455 | ||
8fde8b40 CB |
456 | if (*ar_data->step == NULL_TREE) |
457 | *ar_data->step = step; | |
458 | else | |
459 | *ar_data->step = fold_build2 (PLUS_EXPR, sizetype, | |
460 | fold_convert (sizetype, *ar_data->step), | |
461 | fold_convert (sizetype, step)); | |
b076a3fd ZD |
462 | *ar_data->delta += idelta; |
463 | *index = ibase; | |
464 | ||
465 | return true; | |
466 | } | |
467 | ||
aac8b8ed | 468 | /* Tries to express REF_P in shape &BASE + STEP * iter + DELTA, where DELTA and |
b076a3fd | 469 | STEP are integer constants and iter is number of iterations of LOOP. The |
aac8b8ed RS |
470 | reference occurs in statement STMT. Strips nonaddressable component |
471 | references from REF_P. */ | |
b076a3fd ZD |
472 | |
473 | static bool | |
aac8b8ed | 474 | analyze_ref (struct loop *loop, tree *ref_p, tree *base, |
81f32326 | 475 | tree *step, HOST_WIDE_INT *delta, |
726a989a | 476 | gimple stmt) |
b076a3fd ZD |
477 | { |
478 | struct ar_data ar_data; | |
479 | tree off; | |
480 | HOST_WIDE_INT bit_offset; | |
aac8b8ed | 481 | tree ref = *ref_p; |
b076a3fd | 482 | |
81f32326 | 483 | *step = NULL_TREE; |
b076a3fd ZD |
484 | *delta = 0; |
485 | ||
7c6dafac CF |
486 | /* First strip off the component references. Ignore bitfields. |
487 | Also strip off the real and imagine parts of a complex, so that | |
488 | they can have the same base. */ | |
489 | if (TREE_CODE (ref) == REALPART_EXPR | |
490 | || TREE_CODE (ref) == IMAGPART_EXPR | |
491 | || (TREE_CODE (ref) == COMPONENT_REF | |
492 | && DECL_NONADDRESSABLE_P (TREE_OPERAND (ref, 1)))) | |
493 | { | |
494 | if (TREE_CODE (ref) == IMAGPART_EXPR) | |
495 | *delta += int_size_in_bytes (TREE_TYPE (ref)); | |
496 | ref = TREE_OPERAND (ref, 0); | |
497 | } | |
b076a3fd | 498 | |
aac8b8ed RS |
499 | *ref_p = ref; |
500 | ||
b076a3fd ZD |
501 | for (; TREE_CODE (ref) == COMPONENT_REF; ref = TREE_OPERAND (ref, 0)) |
502 | { | |
503 | off = DECL_FIELD_BIT_OFFSET (TREE_OPERAND (ref, 1)); | |
504 | bit_offset = TREE_INT_CST_LOW (off); | |
505 | gcc_assert (bit_offset % BITS_PER_UNIT == 0); | |
b8698a0f | 506 | |
b076a3fd ZD |
507 | *delta += bit_offset / BITS_PER_UNIT; |
508 | } | |
509 | ||
510 | *base = unshare_expr (ref); | |
511 | ar_data.loop = loop; | |
512 | ar_data.stmt = stmt; | |
513 | ar_data.step = step; | |
514 | ar_data.delta = delta; | |
515 | return for_each_index (base, idx_analyze_ref, &ar_data); | |
516 | } | |
517 | ||
518 | /* Record a memory reference REF to the list REFS. The reference occurs in | |
79f5e442 ZD |
519 | LOOP in statement STMT and it is write if WRITE_P. Returns true if the |
520 | reference was recorded, false otherwise. */ | |
b076a3fd | 521 | |
79f5e442 | 522 | static bool |
b076a3fd | 523 | gather_memory_references_ref (struct loop *loop, struct mem_ref_group **refs, |
726a989a | 524 | tree ref, bool write_p, gimple stmt) |
b076a3fd | 525 | { |
81f32326 CB |
526 | tree base, step; |
527 | HOST_WIDE_INT delta; | |
b076a3fd ZD |
528 | struct mem_ref_group *agrp; |
529 | ||
a80a2701 JJ |
530 | if (get_base_address (ref) == NULL) |
531 | return false; | |
532 | ||
aac8b8ed | 533 | if (!analyze_ref (loop, &ref, &base, &step, &delta, stmt)) |
79f5e442 | 534 | return false; |
81f32326 CB |
535 | /* If analyze_ref fails the default is a NULL_TREE. We can stop here. */ |
536 | if (step == NULL_TREE) | |
537 | return false; | |
b076a3fd | 538 | |
756f50ce | 539 | /* Stop if the address of BASE could not be taken. */ |
bc068a23 CF |
540 | if (may_be_nonaddressable_p (base)) |
541 | return false; | |
542 | ||
50814135 CF |
543 | /* Limit non-constant step prefetching only to the innermost loops. */ |
544 | if (!cst_and_fits_in_hwi (step) && loop->inner != NULL) | |
545 | return false; | |
546 | ||
b076a3fd ZD |
547 | /* Now we know that REF = &BASE + STEP * iter + DELTA, where DELTA and STEP |
548 | are integer constants. */ | |
549 | agrp = find_or_create_group (refs, base, step); | |
550 | record_ref (agrp, stmt, ref, delta, write_p); | |
79f5e442 ZD |
551 | |
552 | return true; | |
b076a3fd ZD |
553 | } |
554 | ||
79f5e442 ZD |
555 | /* Record the suitable memory references in LOOP. NO_OTHER_REFS is set to |
556 | true if there are no other memory references inside the loop. */ | |
b076a3fd ZD |
557 | |
558 | static struct mem_ref_group * | |
db34470d | 559 | gather_memory_references (struct loop *loop, bool *no_other_refs, unsigned *ref_count) |
b076a3fd ZD |
560 | { |
561 | basic_block *body = get_loop_body_in_dom_order (loop); | |
562 | basic_block bb; | |
563 | unsigned i; | |
726a989a RB |
564 | gimple_stmt_iterator bsi; |
565 | gimple stmt; | |
566 | tree lhs, rhs; | |
b076a3fd ZD |
567 | struct mem_ref_group *refs = NULL; |
568 | ||
79f5e442 | 569 | *no_other_refs = true; |
db34470d | 570 | *ref_count = 0; |
79f5e442 | 571 | |
b076a3fd ZD |
572 | /* Scan the loop body in order, so that the former references precede the |
573 | later ones. */ | |
574 | for (i = 0; i < loop->num_nodes; i++) | |
575 | { | |
576 | bb = body[i]; | |
577 | if (bb->loop_father != loop) | |
578 | continue; | |
579 | ||
726a989a | 580 | for (bsi = gsi_start_bb (bb); !gsi_end_p (bsi); gsi_next (&bsi)) |
b076a3fd | 581 | { |
726a989a | 582 | stmt = gsi_stmt (bsi); |
79f5e442 | 583 | |
726a989a | 584 | if (gimple_code (stmt) != GIMPLE_ASSIGN) |
79f5e442 | 585 | { |
5006671f | 586 | if (gimple_vuse (stmt) |
726a989a RB |
587 | || (is_gimple_call (stmt) |
588 | && !(gimple_call_flags (stmt) & ECF_CONST))) | |
79f5e442 ZD |
589 | *no_other_refs = false; |
590 | continue; | |
591 | } | |
b076a3fd | 592 | |
726a989a RB |
593 | lhs = gimple_assign_lhs (stmt); |
594 | rhs = gimple_assign_rhs1 (stmt); | |
b076a3fd ZD |
595 | |
596 | if (REFERENCE_CLASS_P (rhs)) | |
db34470d | 597 | { |
79f5e442 ZD |
598 | *no_other_refs &= gather_memory_references_ref (loop, &refs, |
599 | rhs, false, stmt); | |
db34470d GS |
600 | *ref_count += 1; |
601 | } | |
b076a3fd | 602 | if (REFERENCE_CLASS_P (lhs)) |
db34470d | 603 | { |
79f5e442 ZD |
604 | *no_other_refs &= gather_memory_references_ref (loop, &refs, |
605 | lhs, true, stmt); | |
db34470d GS |
606 | *ref_count += 1; |
607 | } | |
b076a3fd ZD |
608 | } |
609 | } | |
610 | free (body); | |
611 | ||
612 | return refs; | |
613 | } | |
614 | ||
615 | /* Prune the prefetch candidate REF using the self-reuse. */ | |
616 | ||
617 | static void | |
618 | prune_ref_by_self_reuse (struct mem_ref *ref) | |
619 | { | |
81f32326 CB |
620 | HOST_WIDE_INT step; |
621 | bool backward; | |
622 | ||
623 | /* If the step size is non constant, we cannot calculate prefetch_mod. */ | |
624 | if (!cst_and_fits_in_hwi (ref->group->step)) | |
625 | return; | |
626 | ||
627 | step = int_cst_value (ref->group->step); | |
628 | ||
629 | backward = step < 0; | |
b076a3fd ZD |
630 | |
631 | if (step == 0) | |
632 | { | |
633 | /* Prefetch references to invariant address just once. */ | |
634 | ref->prefetch_before = 1; | |
635 | return; | |
636 | } | |
637 | ||
638 | if (backward) | |
639 | step = -step; | |
640 | ||
641 | if (step > PREFETCH_BLOCK) | |
642 | return; | |
643 | ||
644 | if ((backward && HAVE_BACKWARD_PREFETCH) | |
645 | || (!backward && HAVE_FORWARD_PREFETCH)) | |
646 | { | |
647 | ref->prefetch_before = 1; | |
648 | return; | |
649 | } | |
650 | ||
651 | ref->prefetch_mod = PREFETCH_BLOCK / step; | |
652 | } | |
653 | ||
654 | /* Divides X by BY, rounding down. */ | |
655 | ||
656 | static HOST_WIDE_INT | |
657 | ddown (HOST_WIDE_INT x, unsigned HOST_WIDE_INT by) | |
658 | { | |
659 | gcc_assert (by > 0); | |
660 | ||
661 | if (x >= 0) | |
662 | return x / by; | |
663 | else | |
664 | return (x + by - 1) / by; | |
665 | } | |
666 | ||
b8698a0f L |
667 | /* Given a CACHE_LINE_SIZE and two inductive memory references |
668 | with a common STEP greater than CACHE_LINE_SIZE and an address | |
669 | difference DELTA, compute the probability that they will fall | |
14e444c3 CF |
670 | in different cache lines. Return true if the computed miss rate |
671 | is not greater than the ACCEPTABLE_MISS_RATE. DISTINCT_ITERS is the | |
672 | number of distinct iterations after which the pattern repeats itself. | |
2c6dd136 GS |
673 | ALIGN_UNIT is the unit of alignment in bytes. */ |
674 | ||
14e444c3 CF |
675 | static bool |
676 | is_miss_rate_acceptable (unsigned HOST_WIDE_INT cache_line_size, | |
2c6dd136 GS |
677 | HOST_WIDE_INT step, HOST_WIDE_INT delta, |
678 | unsigned HOST_WIDE_INT distinct_iters, | |
679 | int align_unit) | |
680 | { | |
681 | unsigned align, iter; | |
14e444c3 | 682 | int total_positions, miss_positions, max_allowed_miss_positions; |
2c6dd136 GS |
683 | int address1, address2, cache_line1, cache_line2; |
684 | ||
a245c04b CF |
685 | /* It always misses if delta is greater than or equal to the cache |
686 | line size. */ | |
14e444c3 CF |
687 | if (delta >= (HOST_WIDE_INT) cache_line_size) |
688 | return false; | |
a245c04b | 689 | |
2c6dd136 | 690 | miss_positions = 0; |
14e444c3 CF |
691 | total_positions = (cache_line_size / align_unit) * distinct_iters; |
692 | max_allowed_miss_positions = (ACCEPTABLE_MISS_RATE * total_positions) / 1000; | |
b8698a0f | 693 | |
2c6dd136 GS |
694 | /* Iterate through all possible alignments of the first |
695 | memory reference within its cache line. */ | |
696 | for (align = 0; align < cache_line_size; align += align_unit) | |
697 | ||
698 | /* Iterate through all distinct iterations. */ | |
699 | for (iter = 0; iter < distinct_iters; iter++) | |
700 | { | |
701 | address1 = align + step * iter; | |
702 | address2 = address1 + delta; | |
703 | cache_line1 = address1 / cache_line_size; | |
704 | cache_line2 = address2 / cache_line_size; | |
2c6dd136 | 705 | if (cache_line1 != cache_line2) |
14e444c3 CF |
706 | { |
707 | miss_positions += 1; | |
708 | if (miss_positions > max_allowed_miss_positions) | |
709 | return false; | |
710 | } | |
2c6dd136 | 711 | } |
14e444c3 | 712 | return true; |
2c6dd136 GS |
713 | } |
714 | ||
b076a3fd ZD |
715 | /* Prune the prefetch candidate REF using the reuse with BY. |
716 | If BY_IS_BEFORE is true, BY is before REF in the loop. */ | |
717 | ||
718 | static void | |
719 | prune_ref_by_group_reuse (struct mem_ref *ref, struct mem_ref *by, | |
720 | bool by_is_before) | |
721 | { | |
81f32326 CB |
722 | HOST_WIDE_INT step; |
723 | bool backward; | |
b076a3fd ZD |
724 | HOST_WIDE_INT delta_r = ref->delta, delta_b = by->delta; |
725 | HOST_WIDE_INT delta = delta_b - delta_r; | |
726 | HOST_WIDE_INT hit_from; | |
727 | unsigned HOST_WIDE_INT prefetch_before, prefetch_block; | |
2c6dd136 GS |
728 | HOST_WIDE_INT reduced_step; |
729 | unsigned HOST_WIDE_INT reduced_prefetch_block; | |
730 | tree ref_type; | |
731 | int align_unit; | |
b076a3fd | 732 | |
81f32326 CB |
733 | /* If the step is non constant we cannot calculate prefetch_before. */ |
734 | if (!cst_and_fits_in_hwi (ref->group->step)) { | |
735 | return; | |
736 | } | |
737 | ||
738 | step = int_cst_value (ref->group->step); | |
739 | ||
740 | backward = step < 0; | |
741 | ||
742 | ||
b076a3fd ZD |
743 | if (delta == 0) |
744 | { | |
745 | /* If the references has the same address, only prefetch the | |
746 | former. */ | |
747 | if (by_is_before) | |
748 | ref->prefetch_before = 0; | |
b8698a0f | 749 | |
b076a3fd ZD |
750 | return; |
751 | } | |
752 | ||
753 | if (!step) | |
754 | { | |
755 | /* If the reference addresses are invariant and fall into the | |
756 | same cache line, prefetch just the first one. */ | |
757 | if (!by_is_before) | |
758 | return; | |
759 | ||
760 | if (ddown (ref->delta, PREFETCH_BLOCK) | |
761 | != ddown (by->delta, PREFETCH_BLOCK)) | |
762 | return; | |
763 | ||
764 | ref->prefetch_before = 0; | |
765 | return; | |
766 | } | |
767 | ||
768 | /* Only prune the reference that is behind in the array. */ | |
769 | if (backward) | |
770 | { | |
771 | if (delta > 0) | |
772 | return; | |
773 | ||
774 | /* Transform the data so that we may assume that the accesses | |
775 | are forward. */ | |
776 | delta = - delta; | |
777 | step = -step; | |
778 | delta_r = PREFETCH_BLOCK - 1 - delta_r; | |
779 | delta_b = PREFETCH_BLOCK - 1 - delta_b; | |
780 | } | |
781 | else | |
782 | { | |
783 | if (delta < 0) | |
784 | return; | |
785 | } | |
786 | ||
787 | /* Check whether the two references are likely to hit the same cache | |
788 | line, and how distant the iterations in that it occurs are from | |
789 | each other. */ | |
790 | ||
791 | if (step <= PREFETCH_BLOCK) | |
792 | { | |
793 | /* The accesses are sure to meet. Let us check when. */ | |
794 | hit_from = ddown (delta_b, PREFETCH_BLOCK) * PREFETCH_BLOCK; | |
795 | prefetch_before = (hit_from - delta_r + step - 1) / step; | |
796 | ||
57762e97 | 797 | /* Do not reduce prefetch_before if we meet beyond cache size. */ |
4c9cf7af | 798 | if (prefetch_before > absu_hwi (L2_CACHE_SIZE_BYTES / step)) |
57762e97 | 799 | prefetch_before = PREFETCH_ALL; |
b076a3fd ZD |
800 | if (prefetch_before < ref->prefetch_before) |
801 | ref->prefetch_before = prefetch_before; | |
802 | ||
803 | return; | |
804 | } | |
805 | ||
b8698a0f | 806 | /* A more complicated case with step > prefetch_block. First reduce |
2c6dd136 | 807 | the ratio between the step and the cache line size to its simplest |
b8698a0f L |
808 | terms. The resulting denominator will then represent the number of |
809 | distinct iterations after which each address will go back to its | |
810 | initial location within the cache line. This computation assumes | |
2c6dd136 | 811 | that PREFETCH_BLOCK is a power of two. */ |
b076a3fd | 812 | prefetch_block = PREFETCH_BLOCK; |
2c6dd136 GS |
813 | reduced_prefetch_block = prefetch_block; |
814 | reduced_step = step; | |
815 | while ((reduced_step & 1) == 0 | |
816 | && reduced_prefetch_block > 1) | |
b076a3fd | 817 | { |
2c6dd136 GS |
818 | reduced_step >>= 1; |
819 | reduced_prefetch_block >>= 1; | |
b076a3fd ZD |
820 | } |
821 | ||
b076a3fd ZD |
822 | prefetch_before = delta / step; |
823 | delta %= step; | |
2c6dd136 GS |
824 | ref_type = TREE_TYPE (ref->mem); |
825 | align_unit = TYPE_ALIGN (ref_type) / 8; | |
14e444c3 CF |
826 | if (is_miss_rate_acceptable (prefetch_block, step, delta, |
827 | reduced_prefetch_block, align_unit)) | |
b076a3fd | 828 | { |
57762e97 CB |
829 | /* Do not reduce prefetch_before if we meet beyond cache size. */ |
830 | if (prefetch_before > L2_CACHE_SIZE_BYTES / PREFETCH_BLOCK) | |
831 | prefetch_before = PREFETCH_ALL; | |
b076a3fd ZD |
832 | if (prefetch_before < ref->prefetch_before) |
833 | ref->prefetch_before = prefetch_before; | |
834 | ||
835 | return; | |
836 | } | |
837 | ||
838 | /* Try also the following iteration. */ | |
839 | prefetch_before++; | |
840 | delta = step - delta; | |
14e444c3 CF |
841 | if (is_miss_rate_acceptable (prefetch_block, step, delta, |
842 | reduced_prefetch_block, align_unit)) | |
b076a3fd ZD |
843 | { |
844 | if (prefetch_before < ref->prefetch_before) | |
845 | ref->prefetch_before = prefetch_before; | |
846 | ||
847 | return; | |
848 | } | |
849 | ||
850 | /* The ref probably does not reuse by. */ | |
851 | return; | |
852 | } | |
853 | ||
854 | /* Prune the prefetch candidate REF using the reuses with other references | |
855 | in REFS. */ | |
856 | ||
857 | static void | |
858 | prune_ref_by_reuse (struct mem_ref *ref, struct mem_ref *refs) | |
859 | { | |
860 | struct mem_ref *prune_by; | |
861 | bool before = true; | |
862 | ||
863 | prune_ref_by_self_reuse (ref); | |
864 | ||
865 | for (prune_by = refs; prune_by; prune_by = prune_by->next) | |
866 | { | |
867 | if (prune_by == ref) | |
868 | { | |
869 | before = false; | |
870 | continue; | |
871 | } | |
872 | ||
873 | if (!WRITE_CAN_USE_READ_PREFETCH | |
874 | && ref->write_p | |
875 | && !prune_by->write_p) | |
876 | continue; | |
877 | if (!READ_CAN_USE_WRITE_PREFETCH | |
878 | && !ref->write_p | |
879 | && prune_by->write_p) | |
880 | continue; | |
881 | ||
882 | prune_ref_by_group_reuse (ref, prune_by, before); | |
883 | } | |
884 | } | |
885 | ||
886 | /* Prune the prefetch candidates in GROUP using the reuse analysis. */ | |
887 | ||
888 | static void | |
889 | prune_group_by_reuse (struct mem_ref_group *group) | |
890 | { | |
891 | struct mem_ref *ref_pruned; | |
892 | ||
893 | for (ref_pruned = group->refs; ref_pruned; ref_pruned = ref_pruned->next) | |
894 | { | |
895 | prune_ref_by_reuse (ref_pruned, group->refs); | |
896 | ||
897 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
898 | { | |
899 | fprintf (dump_file, "Reference %p:", (void *) ref_pruned); | |
900 | ||
901 | if (ref_pruned->prefetch_before == PREFETCH_ALL | |
902 | && ref_pruned->prefetch_mod == 1) | |
903 | fprintf (dump_file, " no restrictions"); | |
904 | else if (ref_pruned->prefetch_before == 0) | |
905 | fprintf (dump_file, " do not prefetch"); | |
906 | else if (ref_pruned->prefetch_before <= ref_pruned->prefetch_mod) | |
907 | fprintf (dump_file, " prefetch once"); | |
908 | else | |
909 | { | |
910 | if (ref_pruned->prefetch_before != PREFETCH_ALL) | |
911 | { | |
912 | fprintf (dump_file, " prefetch before "); | |
913 | fprintf (dump_file, HOST_WIDE_INT_PRINT_DEC, | |
914 | ref_pruned->prefetch_before); | |
915 | } | |
916 | if (ref_pruned->prefetch_mod != 1) | |
917 | { | |
918 | fprintf (dump_file, " prefetch mod "); | |
919 | fprintf (dump_file, HOST_WIDE_INT_PRINT_DEC, | |
920 | ref_pruned->prefetch_mod); | |
921 | } | |
922 | } | |
923 | fprintf (dump_file, "\n"); | |
924 | } | |
925 | } | |
926 | } | |
927 | ||
928 | /* Prune the list of prefetch candidates GROUPS using the reuse analysis. */ | |
929 | ||
930 | static void | |
931 | prune_by_reuse (struct mem_ref_group *groups) | |
932 | { | |
933 | for (; groups; groups = groups->next) | |
934 | prune_group_by_reuse (groups); | |
935 | } | |
936 | ||
937 | /* Returns true if we should issue prefetch for REF. */ | |
938 | ||
939 | static bool | |
940 | should_issue_prefetch_p (struct mem_ref *ref) | |
941 | { | |
942 | /* For now do not issue prefetches for only first few of the | |
943 | iterations. */ | |
944 | if (ref->prefetch_before != PREFETCH_ALL) | |
a8beb3a7 CB |
945 | { |
946 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
947 | fprintf (dump_file, "Ignoring %p due to prefetch_before\n", | |
948 | (void *) ref); | |
949 | return false; | |
950 | } | |
b076a3fd | 951 | |
79f5e442 ZD |
952 | /* Do not prefetch nontemporal stores. */ |
953 | if (ref->storent_p) | |
a8beb3a7 CB |
954 | { |
955 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
956 | fprintf (dump_file, "Ignoring nontemporal store %p\n", (void *) ref); | |
957 | return false; | |
958 | } | |
79f5e442 | 959 | |
b076a3fd ZD |
960 | return true; |
961 | } | |
962 | ||
963 | /* Decide which of the prefetch candidates in GROUPS to prefetch. | |
964 | AHEAD is the number of iterations to prefetch ahead (which corresponds | |
965 | to the number of simultaneous instances of one prefetch running at a | |
966 | time). UNROLL_FACTOR is the factor by that the loop is going to be | |
967 | unrolled. Returns true if there is anything to prefetch. */ | |
968 | ||
969 | static bool | |
970 | schedule_prefetches (struct mem_ref_group *groups, unsigned unroll_factor, | |
971 | unsigned ahead) | |
972 | { | |
911b3fdb ZD |
973 | unsigned remaining_prefetch_slots, n_prefetches, prefetch_slots; |
974 | unsigned slots_per_prefetch; | |
b076a3fd ZD |
975 | struct mem_ref *ref; |
976 | bool any = false; | |
977 | ||
911b3fdb ZD |
978 | /* At most SIMULTANEOUS_PREFETCHES should be running at the same time. */ |
979 | remaining_prefetch_slots = SIMULTANEOUS_PREFETCHES; | |
b076a3fd | 980 | |
911b3fdb ZD |
981 | /* The prefetch will run for AHEAD iterations of the original loop, i.e., |
982 | AHEAD / UNROLL_FACTOR iterations of the unrolled loop. In each iteration, | |
983 | it will need a prefetch slot. */ | |
984 | slots_per_prefetch = (ahead + unroll_factor / 2) / unroll_factor; | |
b076a3fd | 985 | if (dump_file && (dump_flags & TDF_DETAILS)) |
911b3fdb ZD |
986 | fprintf (dump_file, "Each prefetch instruction takes %u prefetch slots.\n", |
987 | slots_per_prefetch); | |
b076a3fd ZD |
988 | |
989 | /* For now we just take memory references one by one and issue | |
990 | prefetches for as many as possible. The groups are sorted | |
991 | starting with the largest step, since the references with | |
c0220ea4 | 992 | large step are more likely to cause many cache misses. */ |
b076a3fd ZD |
993 | |
994 | for (; groups; groups = groups->next) | |
995 | for (ref = groups->refs; ref; ref = ref->next) | |
996 | { | |
997 | if (!should_issue_prefetch_p (ref)) | |
998 | continue; | |
999 | ||
8532678c CF |
1000 | /* The loop is far from being sufficiently unrolled for this |
1001 | prefetch. Do not generate prefetch to avoid many redudant | |
1002 | prefetches. */ | |
1003 | if (ref->prefetch_mod / unroll_factor > PREFETCH_MOD_TO_UNROLL_FACTOR_RATIO) | |
1004 | continue; | |
1005 | ||
911b3fdb ZD |
1006 | /* If we need to prefetch the reference each PREFETCH_MOD iterations, |
1007 | and we unroll the loop UNROLL_FACTOR times, we need to insert | |
1008 | ceil (UNROLL_FACTOR / PREFETCH_MOD) instructions in each | |
1009 | iteration. */ | |
b076a3fd ZD |
1010 | n_prefetches = ((unroll_factor + ref->prefetch_mod - 1) |
1011 | / ref->prefetch_mod); | |
911b3fdb ZD |
1012 | prefetch_slots = n_prefetches * slots_per_prefetch; |
1013 | ||
1014 | /* If more than half of the prefetches would be lost anyway, do not | |
1015 | issue the prefetch. */ | |
1016 | if (2 * remaining_prefetch_slots < prefetch_slots) | |
1017 | continue; | |
1018 | ||
1019 | ref->issue_prefetch_p = true; | |
b076a3fd | 1020 | |
911b3fdb ZD |
1021 | if (remaining_prefetch_slots <= prefetch_slots) |
1022 | return true; | |
1023 | remaining_prefetch_slots -= prefetch_slots; | |
b076a3fd ZD |
1024 | any = true; |
1025 | } | |
1026 | ||
1027 | return any; | |
1028 | } | |
1029 | ||
d5058523 CF |
1030 | /* Return TRUE if no prefetch is going to be generated in the given |
1031 | GROUPS. */ | |
1032 | ||
1033 | static bool | |
1034 | nothing_to_prefetch_p (struct mem_ref_group *groups) | |
1035 | { | |
1036 | struct mem_ref *ref; | |
1037 | ||
1038 | for (; groups; groups = groups->next) | |
1039 | for (ref = groups->refs; ref; ref = ref->next) | |
1040 | if (should_issue_prefetch_p (ref)) | |
1041 | return false; | |
1042 | ||
1043 | return true; | |
1044 | } | |
1045 | ||
1046 | /* Estimate the number of prefetches in the given GROUPS. | |
1047 | UNROLL_FACTOR is the factor by which LOOP was unrolled. */ | |
b076a3fd | 1048 | |
db34470d | 1049 | static int |
d5058523 | 1050 | estimate_prefetch_count (struct mem_ref_group *groups, unsigned unroll_factor) |
b076a3fd ZD |
1051 | { |
1052 | struct mem_ref *ref; | |
d5058523 | 1053 | unsigned n_prefetches; |
db34470d | 1054 | int prefetch_count = 0; |
b076a3fd ZD |
1055 | |
1056 | for (; groups; groups = groups->next) | |
1057 | for (ref = groups->refs; ref; ref = ref->next) | |
1058 | if (should_issue_prefetch_p (ref)) | |
d5058523 CF |
1059 | { |
1060 | n_prefetches = ((unroll_factor + ref->prefetch_mod - 1) | |
1061 | / ref->prefetch_mod); | |
1062 | prefetch_count += n_prefetches; | |
1063 | } | |
b076a3fd | 1064 | |
db34470d | 1065 | return prefetch_count; |
b076a3fd ZD |
1066 | } |
1067 | ||
1068 | /* Issue prefetches for the reference REF into loop as decided before. | |
1069 | HEAD is the number of iterations to prefetch ahead. UNROLL_FACTOR | |
917f1b7e | 1070 | is the factor by which LOOP was unrolled. */ |
b076a3fd ZD |
1071 | |
1072 | static void | |
1073 | issue_prefetch_ref (struct mem_ref *ref, unsigned unroll_factor, unsigned ahead) | |
1074 | { | |
1075 | HOST_WIDE_INT delta; | |
81f32326 | 1076 | tree addr, addr_base, write_p, local, forward; |
726a989a RB |
1077 | gimple prefetch; |
1078 | gimple_stmt_iterator bsi; | |
b076a3fd | 1079 | unsigned n_prefetches, ap; |
5417e022 | 1080 | bool nontemporal = ref->reuse_distance >= L2_CACHE_SIZE_BYTES; |
b076a3fd ZD |
1081 | |
1082 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
5417e022 ZD |
1083 | fprintf (dump_file, "Issued%s prefetch for %p.\n", |
1084 | nontemporal ? " nontemporal" : "", | |
1085 | (void *) ref); | |
b076a3fd | 1086 | |
726a989a | 1087 | bsi = gsi_for_stmt (ref->stmt); |
b076a3fd ZD |
1088 | |
1089 | n_prefetches = ((unroll_factor + ref->prefetch_mod - 1) | |
1090 | / ref->prefetch_mod); | |
1091 | addr_base = build_fold_addr_expr_with_type (ref->mem, ptr_type_node); | |
726a989a RB |
1092 | addr_base = force_gimple_operand_gsi (&bsi, unshare_expr (addr_base), |
1093 | true, NULL, true, GSI_SAME_STMT); | |
911b3fdb | 1094 | write_p = ref->write_p ? integer_one_node : integer_zero_node; |
9a9d280e | 1095 | local = nontemporal ? integer_zero_node : integer_three_node; |
b076a3fd ZD |
1096 | |
1097 | for (ap = 0; ap < n_prefetches; ap++) | |
1098 | { | |
81f32326 CB |
1099 | if (cst_and_fits_in_hwi (ref->group->step)) |
1100 | { | |
1101 | /* Determine the address to prefetch. */ | |
1102 | delta = (ahead + ap * ref->prefetch_mod) * | |
1103 | int_cst_value (ref->group->step); | |
5d49b6a7 | 1104 | addr = fold_build_pointer_plus_hwi (addr_base, delta); |
81f32326 CB |
1105 | addr = force_gimple_operand_gsi (&bsi, unshare_expr (addr), true, NULL, |
1106 | true, GSI_SAME_STMT); | |
1107 | } | |
1108 | else | |
1109 | { | |
1110 | /* The step size is non-constant but loop-invariant. We use the | |
1111 | heuristic to simply prefetch ahead iterations ahead. */ | |
1112 | forward = fold_build2 (MULT_EXPR, sizetype, | |
1113 | fold_convert (sizetype, ref->group->step), | |
1114 | fold_convert (sizetype, size_int (ahead))); | |
5d49b6a7 | 1115 | addr = fold_build_pointer_plus (addr_base, forward); |
81f32326 CB |
1116 | addr = force_gimple_operand_gsi (&bsi, unshare_expr (addr), true, |
1117 | NULL, true, GSI_SAME_STMT); | |
1118 | } | |
b076a3fd | 1119 | /* Create the prefetch instruction. */ |
e79983f4 | 1120 | prefetch = gimple_build_call (builtin_decl_explicit (BUILT_IN_PREFETCH), |
726a989a RB |
1121 | 3, addr, write_p, local); |
1122 | gsi_insert_before (&bsi, prefetch, GSI_SAME_STMT); | |
b076a3fd ZD |
1123 | } |
1124 | } | |
1125 | ||
1126 | /* Issue prefetches for the references in GROUPS into loop as decided before. | |
1127 | HEAD is the number of iterations to prefetch ahead. UNROLL_FACTOR is the | |
1128 | factor by that LOOP was unrolled. */ | |
1129 | ||
1130 | static void | |
1131 | issue_prefetches (struct mem_ref_group *groups, | |
1132 | unsigned unroll_factor, unsigned ahead) | |
1133 | { | |
1134 | struct mem_ref *ref; | |
1135 | ||
1136 | for (; groups; groups = groups->next) | |
1137 | for (ref = groups->refs; ref; ref = ref->next) | |
1138 | if (ref->issue_prefetch_p) | |
1139 | issue_prefetch_ref (ref, unroll_factor, ahead); | |
1140 | } | |
1141 | ||
79f5e442 ZD |
1142 | /* Returns true if REF is a memory write for that a nontemporal store insn |
1143 | can be used. */ | |
1144 | ||
1145 | static bool | |
1146 | nontemporal_store_p (struct mem_ref *ref) | |
1147 | { | |
1148 | enum machine_mode mode; | |
1149 | enum insn_code code; | |
1150 | ||
1151 | /* REF must be a write that is not reused. We require it to be independent | |
1152 | on all other memory references in the loop, as the nontemporal stores may | |
1153 | be reordered with respect to other memory references. */ | |
1154 | if (!ref->write_p | |
1155 | || !ref->independent_p | |
1156 | || ref->reuse_distance < L2_CACHE_SIZE_BYTES) | |
1157 | return false; | |
1158 | ||
1159 | /* Check that we have the storent instruction for the mode. */ | |
1160 | mode = TYPE_MODE (TREE_TYPE (ref->mem)); | |
1161 | if (mode == BLKmode) | |
1162 | return false; | |
1163 | ||
947131ba | 1164 | code = optab_handler (storent_optab, mode); |
79f5e442 ZD |
1165 | return code != CODE_FOR_nothing; |
1166 | } | |
1167 | ||
1168 | /* If REF is a nontemporal store, we mark the corresponding modify statement | |
1169 | and return true. Otherwise, we return false. */ | |
1170 | ||
1171 | static bool | |
1172 | mark_nontemporal_store (struct mem_ref *ref) | |
1173 | { | |
1174 | if (!nontemporal_store_p (ref)) | |
1175 | return false; | |
1176 | ||
1177 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
1178 | fprintf (dump_file, "Marked reference %p as a nontemporal store.\n", | |
1179 | (void *) ref); | |
1180 | ||
726a989a | 1181 | gimple_assign_set_nontemporal_move (ref->stmt, true); |
79f5e442 ZD |
1182 | ref->storent_p = true; |
1183 | ||
1184 | return true; | |
1185 | } | |
1186 | ||
1187 | /* Issue a memory fence instruction after LOOP. */ | |
1188 | ||
1189 | static void | |
1190 | emit_mfence_after_loop (struct loop *loop) | |
1191 | { | |
1192 | VEC (edge, heap) *exits = get_loop_exit_edges (loop); | |
1193 | edge exit; | |
726a989a RB |
1194 | gimple call; |
1195 | gimple_stmt_iterator bsi; | |
79f5e442 ZD |
1196 | unsigned i; |
1197 | ||
ac47786e | 1198 | FOR_EACH_VEC_ELT (edge, exits, i, exit) |
79f5e442 | 1199 | { |
726a989a | 1200 | call = gimple_build_call (FENCE_FOLLOWING_MOVNT, 0); |
79f5e442 ZD |
1201 | |
1202 | if (!single_pred_p (exit->dest) | |
1203 | /* If possible, we prefer not to insert the fence on other paths | |
1204 | in cfg. */ | |
1205 | && !(exit->flags & EDGE_ABNORMAL)) | |
1206 | split_loop_exit_edge (exit); | |
726a989a | 1207 | bsi = gsi_after_labels (exit->dest); |
79f5e442 | 1208 | |
726a989a | 1209 | gsi_insert_before (&bsi, call, GSI_NEW_STMT); |
79f5e442 ZD |
1210 | mark_virtual_ops_for_renaming (call); |
1211 | } | |
1212 | ||
1213 | VEC_free (edge, heap, exits); | |
1214 | update_ssa (TODO_update_ssa_only_virtuals); | |
1215 | } | |
1216 | ||
1217 | /* Returns true if we can use storent in loop, false otherwise. */ | |
1218 | ||
1219 | static bool | |
1220 | may_use_storent_in_loop_p (struct loop *loop) | |
1221 | { | |
1222 | bool ret = true; | |
1223 | ||
1224 | if (loop->inner != NULL) | |
1225 | return false; | |
1226 | ||
1227 | /* If we must issue a mfence insn after using storent, check that there | |
1228 | is a suitable place for it at each of the loop exits. */ | |
1229 | if (FENCE_FOLLOWING_MOVNT != NULL_TREE) | |
1230 | { | |
1231 | VEC (edge, heap) *exits = get_loop_exit_edges (loop); | |
1232 | unsigned i; | |
1233 | edge exit; | |
1234 | ||
ac47786e | 1235 | FOR_EACH_VEC_ELT (edge, exits, i, exit) |
79f5e442 ZD |
1236 | if ((exit->flags & EDGE_ABNORMAL) |
1237 | && exit->dest == EXIT_BLOCK_PTR) | |
1238 | ret = false; | |
1239 | ||
1240 | VEC_free (edge, heap, exits); | |
1241 | } | |
1242 | ||
1243 | return ret; | |
1244 | } | |
1245 | ||
1246 | /* Marks nontemporal stores in LOOP. GROUPS contains the description of memory | |
1247 | references in the loop. */ | |
1248 | ||
1249 | static void | |
1250 | mark_nontemporal_stores (struct loop *loop, struct mem_ref_group *groups) | |
1251 | { | |
1252 | struct mem_ref *ref; | |
1253 | bool any = false; | |
1254 | ||
1255 | if (!may_use_storent_in_loop_p (loop)) | |
1256 | return; | |
1257 | ||
1258 | for (; groups; groups = groups->next) | |
1259 | for (ref = groups->refs; ref; ref = ref->next) | |
1260 | any |= mark_nontemporal_store (ref); | |
1261 | ||
1262 | if (any && FENCE_FOLLOWING_MOVNT != NULL_TREE) | |
1263 | emit_mfence_after_loop (loop); | |
1264 | } | |
1265 | ||
b076a3fd ZD |
1266 | /* Determines whether we can profitably unroll LOOP FACTOR times, and if |
1267 | this is the case, fill in DESC by the description of number of | |
1268 | iterations. */ | |
1269 | ||
1270 | static bool | |
1271 | should_unroll_loop_p (struct loop *loop, struct tree_niter_desc *desc, | |
1272 | unsigned factor) | |
1273 | { | |
1274 | if (!can_unroll_loop_p (loop, factor, desc)) | |
1275 | return false; | |
1276 | ||
1277 | /* We only consider loops without control flow for unrolling. This is not | |
1278 | a hard restriction -- tree_unroll_loop works with arbitrary loops | |
1279 | as well; but the unrolling/prefetching is usually more profitable for | |
1280 | loops consisting of a single basic block, and we want to limit the | |
1281 | code growth. */ | |
1282 | if (loop->num_nodes > 2) | |
1283 | return false; | |
1284 | ||
1285 | return true; | |
1286 | } | |
1287 | ||
1288 | /* Determine the coefficient by that unroll LOOP, from the information | |
1289 | contained in the list of memory references REFS. Description of | |
2711355f ZD |
1290 | umber of iterations of LOOP is stored to DESC. NINSNS is the number of |
1291 | insns of the LOOP. EST_NITER is the estimated number of iterations of | |
1292 | the loop, or -1 if no estimate is available. */ | |
b076a3fd ZD |
1293 | |
1294 | static unsigned | |
1295 | determine_unroll_factor (struct loop *loop, struct mem_ref_group *refs, | |
2711355f ZD |
1296 | unsigned ninsns, struct tree_niter_desc *desc, |
1297 | HOST_WIDE_INT est_niter) | |
b076a3fd | 1298 | { |
911b3fdb ZD |
1299 | unsigned upper_bound; |
1300 | unsigned nfactor, factor, mod_constraint; | |
b076a3fd ZD |
1301 | struct mem_ref_group *agp; |
1302 | struct mem_ref *ref; | |
1303 | ||
911b3fdb ZD |
1304 | /* First check whether the loop is not too large to unroll. We ignore |
1305 | PARAM_MAX_UNROLL_TIMES, because for small loops, it prevented us | |
1306 | from unrolling them enough to make exactly one cache line covered by each | |
1307 | iteration. Also, the goal of PARAM_MAX_UNROLL_TIMES is to prevent | |
1308 | us from unrolling the loops too many times in cases where we only expect | |
1309 | gains from better scheduling and decreasing loop overhead, which is not | |
1310 | the case here. */ | |
1311 | upper_bound = PARAM_VALUE (PARAM_MAX_UNROLLED_INSNS) / ninsns; | |
2711355f ZD |
1312 | |
1313 | /* If we unrolled the loop more times than it iterates, the unrolled version | |
1314 | of the loop would be never entered. */ | |
1315 | if (est_niter >= 0 && est_niter < (HOST_WIDE_INT) upper_bound) | |
1316 | upper_bound = est_niter; | |
1317 | ||
911b3fdb | 1318 | if (upper_bound <= 1) |
b076a3fd ZD |
1319 | return 1; |
1320 | ||
911b3fdb ZD |
1321 | /* Choose the factor so that we may prefetch each cache just once, |
1322 | but bound the unrolling by UPPER_BOUND. */ | |
1323 | factor = 1; | |
b076a3fd ZD |
1324 | for (agp = refs; agp; agp = agp->next) |
1325 | for (ref = agp->refs; ref; ref = ref->next) | |
911b3fdb ZD |
1326 | if (should_issue_prefetch_p (ref)) |
1327 | { | |
1328 | mod_constraint = ref->prefetch_mod; | |
1329 | nfactor = least_common_multiple (mod_constraint, factor); | |
1330 | if (nfactor <= upper_bound) | |
1331 | factor = nfactor; | |
1332 | } | |
b076a3fd ZD |
1333 | |
1334 | if (!should_unroll_loop_p (loop, desc, factor)) | |
1335 | return 1; | |
1336 | ||
1337 | return factor; | |
1338 | } | |
1339 | ||
5417e022 ZD |
1340 | /* Returns the total volume of the memory references REFS, taking into account |
1341 | reuses in the innermost loop and cache line size. TODO -- we should also | |
1342 | take into account reuses across the iterations of the loops in the loop | |
1343 | nest. */ | |
1344 | ||
1345 | static unsigned | |
1346 | volume_of_references (struct mem_ref_group *refs) | |
1347 | { | |
1348 | unsigned volume = 0; | |
1349 | struct mem_ref_group *gr; | |
1350 | struct mem_ref *ref; | |
1351 | ||
1352 | for (gr = refs; gr; gr = gr->next) | |
1353 | for (ref = gr->refs; ref; ref = ref->next) | |
1354 | { | |
1355 | /* Almost always reuses another value? */ | |
1356 | if (ref->prefetch_before != PREFETCH_ALL) | |
1357 | continue; | |
1358 | ||
1359 | /* If several iterations access the same cache line, use the size of | |
1360 | the line divided by this number. Otherwise, a cache line is | |
1361 | accessed in each iteration. TODO -- in the latter case, we should | |
1362 | take the size of the reference into account, rounding it up on cache | |
1363 | line size multiple. */ | |
1364 | volume += L1_CACHE_LINE_SIZE / ref->prefetch_mod; | |
1365 | } | |
1366 | return volume; | |
1367 | } | |
1368 | ||
1369 | /* Returns the volume of memory references accessed across VEC iterations of | |
1370 | loops, whose sizes are described in the LOOP_SIZES array. N is the number | |
1371 | of the loops in the nest (length of VEC and LOOP_SIZES vectors). */ | |
1372 | ||
1373 | static unsigned | |
1374 | volume_of_dist_vector (lambda_vector vec, unsigned *loop_sizes, unsigned n) | |
1375 | { | |
1376 | unsigned i; | |
1377 | ||
1378 | for (i = 0; i < n; i++) | |
1379 | if (vec[i] != 0) | |
1380 | break; | |
1381 | ||
1382 | if (i == n) | |
1383 | return 0; | |
1384 | ||
1385 | gcc_assert (vec[i] > 0); | |
1386 | ||
1387 | /* We ignore the parts of the distance vector in subloops, since usually | |
1388 | the numbers of iterations are much smaller. */ | |
1389 | return loop_sizes[i] * vec[i]; | |
1390 | } | |
1391 | ||
1392 | /* Add the steps of ACCESS_FN multiplied by STRIDE to the array STRIDE | |
1393 | at the position corresponding to the loop of the step. N is the depth | |
1394 | of the considered loop nest, and, LOOP is its innermost loop. */ | |
1395 | ||
1396 | static void | |
1397 | add_subscript_strides (tree access_fn, unsigned stride, | |
1398 | HOST_WIDE_INT *strides, unsigned n, struct loop *loop) | |
1399 | { | |
1400 | struct loop *aloop; | |
1401 | tree step; | |
1402 | HOST_WIDE_INT astep; | |
1403 | unsigned min_depth = loop_depth (loop) - n; | |
1404 | ||
1405 | while (TREE_CODE (access_fn) == POLYNOMIAL_CHREC) | |
1406 | { | |
1407 | aloop = get_chrec_loop (access_fn); | |
1408 | step = CHREC_RIGHT (access_fn); | |
1409 | access_fn = CHREC_LEFT (access_fn); | |
1410 | ||
1411 | if ((unsigned) loop_depth (aloop) <= min_depth) | |
1412 | continue; | |
1413 | ||
1414 | if (host_integerp (step, 0)) | |
1415 | astep = tree_low_cst (step, 0); | |
1416 | else | |
1417 | astep = L1_CACHE_LINE_SIZE; | |
1418 | ||
1419 | strides[n - 1 - loop_depth (loop) + loop_depth (aloop)] += astep * stride; | |
1420 | ||
1421 | } | |
1422 | } | |
1423 | ||
1424 | /* Returns the volume of memory references accessed between two consecutive | |
1425 | self-reuses of the reference DR. We consider the subscripts of DR in N | |
1426 | loops, and LOOP_SIZES contains the volumes of accesses in each of the | |
1427 | loops. LOOP is the innermost loop of the current loop nest. */ | |
1428 | ||
1429 | static unsigned | |
1430 | self_reuse_distance (data_reference_p dr, unsigned *loop_sizes, unsigned n, | |
1431 | struct loop *loop) | |
1432 | { | |
1433 | tree stride, access_fn; | |
1434 | HOST_WIDE_INT *strides, astride; | |
1435 | VEC (tree, heap) *access_fns; | |
1436 | tree ref = DR_REF (dr); | |
1437 | unsigned i, ret = ~0u; | |
1438 | ||
1439 | /* In the following example: | |
1440 | ||
1441 | for (i = 0; i < N; i++) | |
1442 | for (j = 0; j < N; j++) | |
1443 | use (a[j][i]); | |
1444 | the same cache line is accessed each N steps (except if the change from | |
1445 | i to i + 1 crosses the boundary of the cache line). Thus, for self-reuse, | |
1446 | we cannot rely purely on the results of the data dependence analysis. | |
1447 | ||
1448 | Instead, we compute the stride of the reference in each loop, and consider | |
1449 | the innermost loop in that the stride is less than cache size. */ | |
1450 | ||
1451 | strides = XCNEWVEC (HOST_WIDE_INT, n); | |
1452 | access_fns = DR_ACCESS_FNS (dr); | |
1453 | ||
ac47786e | 1454 | FOR_EACH_VEC_ELT (tree, access_fns, i, access_fn) |
5417e022 ZD |
1455 | { |
1456 | /* Keep track of the reference corresponding to the subscript, so that we | |
1457 | know its stride. */ | |
1458 | while (handled_component_p (ref) && TREE_CODE (ref) != ARRAY_REF) | |
1459 | ref = TREE_OPERAND (ref, 0); | |
b8698a0f | 1460 | |
5417e022 ZD |
1461 | if (TREE_CODE (ref) == ARRAY_REF) |
1462 | { | |
1463 | stride = TYPE_SIZE_UNIT (TREE_TYPE (ref)); | |
1464 | if (host_integerp (stride, 1)) | |
1465 | astride = tree_low_cst (stride, 1); | |
1466 | else | |
1467 | astride = L1_CACHE_LINE_SIZE; | |
1468 | ||
1469 | ref = TREE_OPERAND (ref, 0); | |
1470 | } | |
1471 | else | |
1472 | astride = 1; | |
1473 | ||
1474 | add_subscript_strides (access_fn, astride, strides, n, loop); | |
1475 | } | |
1476 | ||
1477 | for (i = n; i-- > 0; ) | |
1478 | { | |
1479 | unsigned HOST_WIDE_INT s; | |
1480 | ||
1481 | s = strides[i] < 0 ? -strides[i] : strides[i]; | |
1482 | ||
1483 | if (s < (unsigned) L1_CACHE_LINE_SIZE | |
1484 | && (loop_sizes[i] | |
1485 | > (unsigned) (L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION))) | |
1486 | { | |
1487 | ret = loop_sizes[i]; | |
1488 | break; | |
1489 | } | |
1490 | } | |
1491 | ||
1492 | free (strides); | |
1493 | return ret; | |
1494 | } | |
1495 | ||
1496 | /* Determines the distance till the first reuse of each reference in REFS | |
79f5e442 ZD |
1497 | in the loop nest of LOOP. NO_OTHER_REFS is true if there are no other |
1498 | memory references in the loop. */ | |
5417e022 ZD |
1499 | |
1500 | static void | |
79f5e442 ZD |
1501 | determine_loop_nest_reuse (struct loop *loop, struct mem_ref_group *refs, |
1502 | bool no_other_refs) | |
5417e022 ZD |
1503 | { |
1504 | struct loop *nest, *aloop; | |
1505 | VEC (data_reference_p, heap) *datarefs = NULL; | |
1506 | VEC (ddr_p, heap) *dependences = NULL; | |
1507 | struct mem_ref_group *gr; | |
79f5e442 | 1508 | struct mem_ref *ref, *refb; |
5417e022 ZD |
1509 | VEC (loop_p, heap) *vloops = NULL; |
1510 | unsigned *loop_data_size; | |
1511 | unsigned i, j, n; | |
1512 | unsigned volume, dist, adist; | |
1513 | HOST_WIDE_INT vol; | |
1514 | data_reference_p dr; | |
1515 | ddr_p dep; | |
1516 | ||
1517 | if (loop->inner) | |
1518 | return; | |
1519 | ||
1520 | /* Find the outermost loop of the loop nest of loop (we require that | |
1521 | there are no sibling loops inside the nest). */ | |
1522 | nest = loop; | |
1523 | while (1) | |
1524 | { | |
1525 | aloop = loop_outer (nest); | |
1526 | ||
1527 | if (aloop == current_loops->tree_root | |
1528 | || aloop->inner->next) | |
1529 | break; | |
1530 | ||
1531 | nest = aloop; | |
1532 | } | |
1533 | ||
1534 | /* For each loop, determine the amount of data accessed in each iteration. | |
1535 | We use this to estimate whether the reference is evicted from the | |
1536 | cache before its reuse. */ | |
1537 | find_loop_nest (nest, &vloops); | |
1538 | n = VEC_length (loop_p, vloops); | |
1539 | loop_data_size = XNEWVEC (unsigned, n); | |
1540 | volume = volume_of_references (refs); | |
1541 | i = n; | |
1542 | while (i-- != 0) | |
1543 | { | |
1544 | loop_data_size[i] = volume; | |
1545 | /* Bound the volume by the L2 cache size, since above this bound, | |
1546 | all dependence distances are equivalent. */ | |
1547 | if (volume > L2_CACHE_SIZE_BYTES) | |
1548 | continue; | |
1549 | ||
1550 | aloop = VEC_index (loop_p, vloops, i); | |
b4a9343c | 1551 | vol = max_stmt_executions_int (aloop, false); |
5417e022 ZD |
1552 | if (vol < 0) |
1553 | vol = expected_loop_iterations (aloop); | |
1554 | volume *= vol; | |
1555 | } | |
1556 | ||
1557 | /* Prepare the references in the form suitable for data dependence | |
0d52bcc1 | 1558 | analysis. We ignore unanalyzable data references (the results |
5417e022 ZD |
1559 | are used just as a heuristics to estimate temporality of the |
1560 | references, hence we do not need to worry about correctness). */ | |
1561 | for (gr = refs; gr; gr = gr->next) | |
1562 | for (ref = gr->refs; ref; ref = ref->next) | |
1563 | { | |
5c640e29 SP |
1564 | dr = create_data_ref (nest, loop_containing_stmt (ref->stmt), |
1565 | ref->mem, ref->stmt, !ref->write_p); | |
5417e022 ZD |
1566 | |
1567 | if (dr) | |
1568 | { | |
1569 | ref->reuse_distance = volume; | |
1570 | dr->aux = ref; | |
1571 | VEC_safe_push (data_reference_p, heap, datarefs, dr); | |
1572 | } | |
79f5e442 ZD |
1573 | else |
1574 | no_other_refs = false; | |
5417e022 ZD |
1575 | } |
1576 | ||
ac47786e | 1577 | FOR_EACH_VEC_ELT (data_reference_p, datarefs, i, dr) |
5417e022 ZD |
1578 | { |
1579 | dist = self_reuse_distance (dr, loop_data_size, n, loop); | |
3d9a9f94 | 1580 | ref = (struct mem_ref *) dr->aux; |
5417e022 ZD |
1581 | if (ref->reuse_distance > dist) |
1582 | ref->reuse_distance = dist; | |
79f5e442 ZD |
1583 | |
1584 | if (no_other_refs) | |
1585 | ref->independent_p = true; | |
5417e022 ZD |
1586 | } |
1587 | ||
1588 | compute_all_dependences (datarefs, &dependences, vloops, true); | |
1589 | ||
ac47786e | 1590 | FOR_EACH_VEC_ELT (ddr_p, dependences, i, dep) |
5417e022 ZD |
1591 | { |
1592 | if (DDR_ARE_DEPENDENT (dep) == chrec_known) | |
1593 | continue; | |
1594 | ||
3d9a9f94 KG |
1595 | ref = (struct mem_ref *) DDR_A (dep)->aux; |
1596 | refb = (struct mem_ref *) DDR_B (dep)->aux; | |
79f5e442 | 1597 | |
5417e022 ZD |
1598 | if (DDR_ARE_DEPENDENT (dep) == chrec_dont_know |
1599 | || DDR_NUM_DIST_VECTS (dep) == 0) | |
1600 | { | |
0d52bcc1 | 1601 | /* If the dependence cannot be analyzed, assume that there might be |
5417e022 ZD |
1602 | a reuse. */ |
1603 | dist = 0; | |
b8698a0f | 1604 | |
79f5e442 ZD |
1605 | ref->independent_p = false; |
1606 | refb->independent_p = false; | |
5417e022 ZD |
1607 | } |
1608 | else | |
1609 | { | |
0d52bcc1 | 1610 | /* The distance vectors are normalized to be always lexicographically |
5417e022 ZD |
1611 | positive, hence we cannot tell just from them whether DDR_A comes |
1612 | before DDR_B or vice versa. However, it is not important, | |
1613 | anyway -- if DDR_A is close to DDR_B, then it is either reused in | |
1614 | DDR_B (and it is not nontemporal), or it reuses the value of DDR_B | |
1615 | in cache (and marking it as nontemporal would not affect | |
1616 | anything). */ | |
1617 | ||
1618 | dist = volume; | |
1619 | for (j = 0; j < DDR_NUM_DIST_VECTS (dep); j++) | |
1620 | { | |
1621 | adist = volume_of_dist_vector (DDR_DIST_VECT (dep, j), | |
1622 | loop_data_size, n); | |
1623 | ||
79f5e442 ZD |
1624 | /* If this is a dependence in the innermost loop (i.e., the |
1625 | distances in all superloops are zero) and it is not | |
1626 | the trivial self-dependence with distance zero, record that | |
1627 | the references are not completely independent. */ | |
1628 | if (lambda_vector_zerop (DDR_DIST_VECT (dep, j), n - 1) | |
1629 | && (ref != refb | |
1630 | || DDR_DIST_VECT (dep, j)[n-1] != 0)) | |
1631 | { | |
1632 | ref->independent_p = false; | |
1633 | refb->independent_p = false; | |
1634 | } | |
1635 | ||
5417e022 ZD |
1636 | /* Ignore accesses closer than |
1637 | L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION, | |
1638 | so that we use nontemporal prefetches e.g. if single memory | |
1639 | location is accessed several times in a single iteration of | |
1640 | the loop. */ | |
1641 | if (adist < L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION) | |
1642 | continue; | |
1643 | ||
1644 | if (adist < dist) | |
1645 | dist = adist; | |
1646 | } | |
1647 | } | |
1648 | ||
5417e022 ZD |
1649 | if (ref->reuse_distance > dist) |
1650 | ref->reuse_distance = dist; | |
79f5e442 ZD |
1651 | if (refb->reuse_distance > dist) |
1652 | refb->reuse_distance = dist; | |
5417e022 ZD |
1653 | } |
1654 | ||
1655 | free_dependence_relations (dependences); | |
1656 | free_data_refs (datarefs); | |
1657 | free (loop_data_size); | |
1658 | ||
1659 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
1660 | { | |
1661 | fprintf (dump_file, "Reuse distances:\n"); | |
1662 | for (gr = refs; gr; gr = gr->next) | |
1663 | for (ref = gr->refs; ref; ref = ref->next) | |
1664 | fprintf (dump_file, " ref %p distance %u\n", | |
1665 | (void *) ref, ref->reuse_distance); | |
1666 | } | |
1667 | } | |
1668 | ||
0bbe50f6 CF |
1669 | /* Determine whether or not the trip count to ahead ratio is too small based |
1670 | on prefitablility consideration. | |
db34470d | 1671 | AHEAD: the iteration ahead distance, |
0bbe50f6 CF |
1672 | EST_NITER: the estimated trip count. */ |
1673 | ||
1674 | static bool | |
1675 | trip_count_to_ahead_ratio_too_small_p (unsigned ahead, HOST_WIDE_INT est_niter) | |
1676 | { | |
1677 | /* Assume trip count to ahead ratio is big enough if the trip count could not | |
1678 | be estimated at compile time. */ | |
1679 | if (est_niter < 0) | |
1680 | return false; | |
1681 | ||
1682 | if (est_niter < (HOST_WIDE_INT) (TRIP_COUNT_TO_AHEAD_RATIO * ahead)) | |
1683 | { | |
1684 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
1685 | fprintf (dump_file, | |
1686 | "Not prefetching -- loop estimated to roll only %d times\n", | |
1687 | (int) est_niter); | |
1688 | return true; | |
1689 | } | |
1690 | ||
1691 | return false; | |
1692 | } | |
1693 | ||
1694 | /* Determine whether or not the number of memory references in the loop is | |
1695 | reasonable based on the profitablity and compilation time considerations. | |
db34470d | 1696 | NINSNS: estimated number of instructions in the loop, |
db34470d GS |
1697 | MEM_REF_COUNT: total number of memory references in the loop. */ |
1698 | ||
b8698a0f | 1699 | static bool |
0bbe50f6 | 1700 | mem_ref_count_reasonable_p (unsigned ninsns, unsigned mem_ref_count) |
db34470d | 1701 | { |
0bbe50f6 | 1702 | int insn_to_mem_ratio; |
db34470d GS |
1703 | |
1704 | if (mem_ref_count == 0) | |
1705 | return false; | |
1706 | ||
0bbe50f6 CF |
1707 | /* Miss rate computation (is_miss_rate_acceptable) and dependence analysis |
1708 | (compute_all_dependences) have high costs based on quadratic complexity. | |
1709 | To avoid huge compilation time, we give up prefetching if mem_ref_count | |
1710 | is too large. */ | |
1711 | if (mem_ref_count > PREFETCH_MAX_MEM_REFS_PER_LOOP) | |
1712 | return false; | |
1713 | ||
b8698a0f L |
1714 | /* Prefetching improves performance by overlapping cache missing |
1715 | memory accesses with CPU operations. If the loop does not have | |
1716 | enough CPU operations to overlap with memory operations, prefetching | |
1717 | won't give a significant benefit. One approximate way of checking | |
1718 | this is to require the ratio of instructions to memory references to | |
db34470d GS |
1719 | be above a certain limit. This approximation works well in practice. |
1720 | TODO: Implement a more precise computation by estimating the time | |
1721 | for each CPU or memory op in the loop. Time estimates for memory ops | |
1722 | should account for cache misses. */ | |
b8698a0f | 1723 | insn_to_mem_ratio = ninsns / mem_ref_count; |
db34470d GS |
1724 | |
1725 | if (insn_to_mem_ratio < PREFETCH_MIN_INSN_TO_MEM_RATIO) | |
55e5a2eb CF |
1726 | { |
1727 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
1728 | fprintf (dump_file, | |
1729 | "Not prefetching -- instruction to memory reference ratio (%d) too small\n", | |
1730 | insn_to_mem_ratio); | |
1731 | return false; | |
1732 | } | |
db34470d | 1733 | |
0bbe50f6 CF |
1734 | return true; |
1735 | } | |
1736 | ||
1737 | /* Determine whether or not the instruction to prefetch ratio in the loop is | |
1738 | too small based on the profitablity consideration. | |
1739 | NINSNS: estimated number of instructions in the loop, | |
1740 | PREFETCH_COUNT: an estimate of the number of prefetches, | |
1741 | UNROLL_FACTOR: the factor to unroll the loop if prefetching. */ | |
1742 | ||
1743 | static bool | |
1744 | insn_to_prefetch_ratio_too_small_p (unsigned ninsns, unsigned prefetch_count, | |
1745 | unsigned unroll_factor) | |
1746 | { | |
1747 | int insn_to_prefetch_ratio; | |
1748 | ||
d3a9b459 CF |
1749 | /* Prefetching most likely causes performance degradation when the instruction |
1750 | to prefetch ratio is too small. Too many prefetch instructions in a loop | |
1751 | may reduce the I-cache performance. | |
ccacf0e1 CF |
1752 | (unroll_factor * ninsns) is used to estimate the number of instructions in |
1753 | the unrolled loop. This implementation is a bit simplistic -- the number | |
1754 | of issued prefetch instructions is also affected by unrolling. So, | |
1755 | prefetch_mod and the unroll factor should be taken into account when | |
1756 | determining prefetch_count. Also, the number of insns of the unrolled | |
1757 | loop will usually be significantly smaller than the number of insns of the | |
1758 | original loop * unroll_factor (at least the induction variable increases | |
1759 | and the exit branches will get eliminated), so it might be better to use | |
1760 | tree_estimate_loop_size + estimated_unrolled_size. */ | |
d3a9b459 CF |
1761 | insn_to_prefetch_ratio = (unroll_factor * ninsns) / prefetch_count; |
1762 | if (insn_to_prefetch_ratio < MIN_INSN_TO_PREFETCH_RATIO) | |
db34470d | 1763 | { |
d3a9b459 CF |
1764 | if (dump_file && (dump_flags & TDF_DETAILS)) |
1765 | fprintf (dump_file, | |
1766 | "Not prefetching -- instruction to prefetch ratio (%d) too small\n", | |
1767 | insn_to_prefetch_ratio); | |
0bbe50f6 | 1768 | return true; |
db34470d | 1769 | } |
b8698a0f | 1770 | |
0bbe50f6 | 1771 | return false; |
db34470d GS |
1772 | } |
1773 | ||
1774 | ||
b076a3fd | 1775 | /* Issue prefetch instructions for array references in LOOP. Returns |
d73be268 | 1776 | true if the LOOP was unrolled. */ |
b076a3fd ZD |
1777 | |
1778 | static bool | |
d73be268 | 1779 | loop_prefetch_arrays (struct loop *loop) |
b076a3fd ZD |
1780 | { |
1781 | struct mem_ref_group *refs; | |
2711355f ZD |
1782 | unsigned ahead, ninsns, time, unroll_factor; |
1783 | HOST_WIDE_INT est_niter; | |
b076a3fd | 1784 | struct tree_niter_desc desc; |
79f5e442 | 1785 | bool unrolled = false, no_other_refs; |
db34470d GS |
1786 | unsigned prefetch_count; |
1787 | unsigned mem_ref_count; | |
b076a3fd | 1788 | |
efd8f750 | 1789 | if (optimize_loop_nest_for_size_p (loop)) |
2732d767 ZD |
1790 | { |
1791 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
1792 | fprintf (dump_file, " ignored (cold area)\n"); | |
1793 | return false; | |
1794 | } | |
1795 | ||
0bbe50f6 CF |
1796 | /* FIXME: the time should be weighted by the probabilities of the blocks in |
1797 | the loop body. */ | |
1798 | time = tree_num_loop_insns (loop, &eni_time_weights); | |
1799 | if (time == 0) | |
1800 | return false; | |
1801 | ||
1802 | ahead = (PREFETCH_LATENCY + time - 1) / time; | |
b4a9343c | 1803 | est_niter = max_stmt_executions_int (loop, false); |
0bbe50f6 CF |
1804 | |
1805 | /* Prefetching is not likely to be profitable if the trip count to ahead | |
1806 | ratio is too small. */ | |
1807 | if (trip_count_to_ahead_ratio_too_small_p (ahead, est_niter)) | |
1808 | return false; | |
1809 | ||
1810 | ninsns = tree_num_loop_insns (loop, &eni_size_weights); | |
1811 | ||
b076a3fd | 1812 | /* Step 1: gather the memory references. */ |
db34470d | 1813 | refs = gather_memory_references (loop, &no_other_refs, &mem_ref_count); |
b076a3fd | 1814 | |
0bbe50f6 CF |
1815 | /* Give up prefetching if the number of memory references in the |
1816 | loop is not reasonable based on profitablity and compilation time | |
1817 | considerations. */ | |
1818 | if (!mem_ref_count_reasonable_p (ninsns, mem_ref_count)) | |
1819 | goto fail; | |
1820 | ||
b076a3fd ZD |
1821 | /* Step 2: estimate the reuse effects. */ |
1822 | prune_by_reuse (refs); | |
1823 | ||
d5058523 | 1824 | if (nothing_to_prefetch_p (refs)) |
b076a3fd ZD |
1825 | goto fail; |
1826 | ||
79f5e442 | 1827 | determine_loop_nest_reuse (loop, refs, no_other_refs); |
5417e022 | 1828 | |
0bbe50f6 | 1829 | /* Step 3: determine unroll factor. */ |
2711355f ZD |
1830 | unroll_factor = determine_unroll_factor (loop, refs, ninsns, &desc, |
1831 | est_niter); | |
d5058523 CF |
1832 | |
1833 | /* Estimate prefetch count for the unrolled loop. */ | |
1834 | prefetch_count = estimate_prefetch_count (refs, unroll_factor); | |
1835 | if (prefetch_count == 0) | |
1836 | goto fail; | |
1837 | ||
2711355f | 1838 | if (dump_file && (dump_flags & TDF_DETAILS)) |
b8698a0f | 1839 | fprintf (dump_file, "Ahead %d, unroll factor %d, trip count " |
d81f5387 | 1840 | HOST_WIDE_INT_PRINT_DEC "\n" |
b8698a0f L |
1841 | "insn count %d, mem ref count %d, prefetch count %d\n", |
1842 | ahead, unroll_factor, est_niter, | |
1843 | ninsns, mem_ref_count, prefetch_count); | |
db34470d | 1844 | |
0bbe50f6 CF |
1845 | /* Prefetching is not likely to be profitable if the instruction to prefetch |
1846 | ratio is too small. */ | |
1847 | if (insn_to_prefetch_ratio_too_small_p (ninsns, prefetch_count, | |
1848 | unroll_factor)) | |
db34470d GS |
1849 | goto fail; |
1850 | ||
1851 | mark_nontemporal_stores (loop, refs); | |
2711355f | 1852 | |
b076a3fd ZD |
1853 | /* Step 4: what to prefetch? */ |
1854 | if (!schedule_prefetches (refs, unroll_factor, ahead)) | |
1855 | goto fail; | |
1856 | ||
1857 | /* Step 5: unroll the loop. TODO -- peeling of first and last few | |
1858 | iterations so that we do not issue superfluous prefetches. */ | |
1859 | if (unroll_factor != 1) | |
1860 | { | |
d73be268 | 1861 | tree_unroll_loop (loop, unroll_factor, |
b076a3fd ZD |
1862 | single_dom_exit (loop), &desc); |
1863 | unrolled = true; | |
1864 | } | |
1865 | ||
1866 | /* Step 6: issue the prefetches. */ | |
1867 | issue_prefetches (refs, unroll_factor, ahead); | |
1868 | ||
1869 | fail: | |
1870 | release_mem_refs (refs); | |
1871 | return unrolled; | |
1872 | } | |
1873 | ||
d73be268 | 1874 | /* Issue prefetch instructions for array references in loops. */ |
b076a3fd | 1875 | |
c7f965b6 | 1876 | unsigned int |
d73be268 | 1877 | tree_ssa_prefetch_arrays (void) |
b076a3fd | 1878 | { |
42fd6772 | 1879 | loop_iterator li; |
b076a3fd ZD |
1880 | struct loop *loop; |
1881 | bool unrolled = false; | |
c7f965b6 | 1882 | int todo_flags = 0; |
b076a3fd ZD |
1883 | |
1884 | if (!HAVE_prefetch | |
1885 | /* It is possible to ask compiler for say -mtune=i486 -march=pentium4. | |
1886 | -mtune=i486 causes us having PREFETCH_BLOCK 0, since this is part | |
1887 | of processor costs and i486 does not have prefetch, but | |
1888 | -march=pentium4 causes HAVE_prefetch to be true. Ugh. */ | |
1889 | || PREFETCH_BLOCK == 0) | |
c7f965b6 | 1890 | return 0; |
b076a3fd | 1891 | |
47eb5b32 ZD |
1892 | if (dump_file && (dump_flags & TDF_DETAILS)) |
1893 | { | |
1894 | fprintf (dump_file, "Prefetching parameters:\n"); | |
1895 | fprintf (dump_file, " simultaneous prefetches: %d\n", | |
1896 | SIMULTANEOUS_PREFETCHES); | |
1897 | fprintf (dump_file, " prefetch latency: %d\n", PREFETCH_LATENCY); | |
47eb5b32 | 1898 | fprintf (dump_file, " prefetch block size: %d\n", PREFETCH_BLOCK); |
46cb0441 ZD |
1899 | fprintf (dump_file, " L1 cache size: %d lines, %d kB\n", |
1900 | L1_CACHE_SIZE_BYTES / L1_CACHE_LINE_SIZE, L1_CACHE_SIZE); | |
5417e022 | 1901 | fprintf (dump_file, " L1 cache line size: %d\n", L1_CACHE_LINE_SIZE); |
b8698a0f L |
1902 | fprintf (dump_file, " L2 cache size: %d kB\n", L2_CACHE_SIZE); |
1903 | fprintf (dump_file, " min insn-to-prefetch ratio: %d \n", | |
db34470d | 1904 | MIN_INSN_TO_PREFETCH_RATIO); |
b8698a0f | 1905 | fprintf (dump_file, " min insn-to-mem ratio: %d \n", |
db34470d | 1906 | PREFETCH_MIN_INSN_TO_MEM_RATIO); |
47eb5b32 ZD |
1907 | fprintf (dump_file, "\n"); |
1908 | } | |
1909 | ||
b076a3fd ZD |
1910 | initialize_original_copy_tables (); |
1911 | ||
e79983f4 | 1912 | if (!builtin_decl_explicit_p (BUILT_IN_PREFETCH)) |
b076a3fd | 1913 | { |
6a4825bd NF |
1914 | tree type = build_function_type_list (void_type_node, |
1915 | const_ptr_type_node, NULL_TREE); | |
c79efc4d RÁE |
1916 | tree decl = add_builtin_function ("__builtin_prefetch", type, |
1917 | BUILT_IN_PREFETCH, BUILT_IN_NORMAL, | |
1918 | NULL, NULL_TREE); | |
b076a3fd | 1919 | DECL_IS_NOVOPS (decl) = true; |
e79983f4 | 1920 | set_builtin_decl (BUILT_IN_PREFETCH, decl, false); |
b076a3fd ZD |
1921 | } |
1922 | ||
1923 | /* We assume that size of cache line is a power of two, so verify this | |
1924 | here. */ | |
1925 | gcc_assert ((PREFETCH_BLOCK & (PREFETCH_BLOCK - 1)) == 0); | |
1926 | ||
42fd6772 | 1927 | FOR_EACH_LOOP (li, loop, LI_FROM_INNERMOST) |
b076a3fd | 1928 | { |
b076a3fd ZD |
1929 | if (dump_file && (dump_flags & TDF_DETAILS)) |
1930 | fprintf (dump_file, "Processing loop %d:\n", loop->num); | |
1931 | ||
d73be268 | 1932 | unrolled |= loop_prefetch_arrays (loop); |
b076a3fd ZD |
1933 | |
1934 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
1935 | fprintf (dump_file, "\n\n"); | |
1936 | } | |
1937 | ||
1938 | if (unrolled) | |
1939 | { | |
1940 | scev_reset (); | |
c7f965b6 | 1941 | todo_flags |= TODO_cleanup_cfg; |
b076a3fd ZD |
1942 | } |
1943 | ||
1944 | free_original_copy_tables (); | |
c7f965b6 | 1945 | return todo_flags; |
b076a3fd | 1946 | } |