Mercurial > hg > CbC > CbC_gcc
annotate gcc/tree-ssa-loop-prefetch.c @ 55:77e2b8dfacca gcc-4.4.5
update it from 4.4.3 to 4.5.0
| author | ryoma <e075725@ie.u-ryukyu.ac.jp> |
|---|---|
| date | Fri, 12 Feb 2010 23:39:51 +0900 |
| parents | a06113de4d67 |
| children | b7f97abdc517 |
| rev | line source |
|---|---|
| 0 | 1 /* Array prefetching. |
| 2 Copyright (C) 2005, 2007, 2008 Free Software Foundation, Inc. | |
|
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3 |
| 0 | 4 This file is part of GCC. |
|
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5 |
| 0 | 6 GCC is free software; you can redistribute it and/or modify it |
| 7 under the terms of the GNU General Public License as published by the | |
| 8 Free Software Foundation; either version 3, or (at your option) any | |
| 9 later version. | |
|
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10 |
| 0 | 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. | |
|
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15 |
| 0 | 16 You should have received a copy of the GNU General Public License |
| 17 along with GCC; see the file COPYING3. If not see | |
| 18 <http://www.gnu.org/licenses/>. */ | |
| 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" | |
| 35 #include "varray.h" | |
| 36 #include "expr.h" | |
| 37 #include "tree-pass.h" | |
| 38 #include "ggc.h" | |
| 39 #include "insn-config.h" | |
| 40 #include "recog.h" | |
| 41 #include "hashtab.h" | |
| 42 #include "tree-chrec.h" | |
| 43 #include "tree-scalar-evolution.h" | |
| 44 #include "toplev.h" | |
| 45 #include "params.h" | |
| 46 #include "langhooks.h" | |
| 47 #include "tree-inline.h" | |
| 48 #include "tree-data-ref.h" | |
| 49 #include "optabs.h" | |
| 50 | |
| 51 /* This pass inserts prefetch instructions to optimize cache usage during | |
| 52 accesses to arrays in loops. It processes loops sequentially and: | |
| 53 | |
| 54 1) Gathers all memory references in the single loop. | |
| 55 2) For each of the references it decides when it is profitable to prefetch | |
| 56 it. To do it, we evaluate the reuse among the accesses, and determines | |
| 57 two values: PREFETCH_BEFORE (meaning that it only makes sense to do | |
| 58 prefetching in the first PREFETCH_BEFORE iterations of the loop) and | |
| 59 PREFETCH_MOD (meaning that it only makes sense to prefetch in the | |
| 60 iterations of the loop that are zero modulo PREFETCH_MOD). For example | |
| 61 (assuming cache line size is 64 bytes, char has size 1 byte and there | |
| 62 is no hardware sequential prefetch): | |
| 63 | |
| 64 char *a; | |
| 65 for (i = 0; i < max; i++) | |
| 66 { | |
| 67 a[255] = ...; (0) | |
| 68 a[i] = ...; (1) | |
| 69 a[i + 64] = ...; (2) | |
| 70 a[16*i] = ...; (3) | |
| 71 a[187*i] = ...; (4) | |
| 72 a[187*i + 50] = ...; (5) | |
| 73 } | |
| 74 | |
| 75 (0) obviously has PREFETCH_BEFORE 1 | |
| 76 (1) has PREFETCH_BEFORE 64, since (2) accesses the same memory | |
| 77 location 64 iterations before it, and PREFETCH_MOD 64 (since | |
| 78 it hits the same cache line otherwise). | |
| 79 (2) has PREFETCH_MOD 64 | |
| 80 (3) has PREFETCH_MOD 4 | |
| 81 (4) has PREFETCH_MOD 1. We do not set PREFETCH_BEFORE here, since | |
| 82 the cache line accessed by (4) is the same with probability only | |
| 83 7/32. | |
| 84 (5) has PREFETCH_MOD 1 as well. | |
| 85 | |
| 86 Additionally, we use data dependence analysis to determine for each | |
| 87 reference the distance till the first reuse; this information is used | |
| 88 to determine the temporality of the issued prefetch instruction. | |
| 89 | |
| 90 3) We determine how much ahead we need to prefetch. The number of | |
| 91 iterations needed is time to fetch / time spent in one iteration of | |
| 92 the loop. The problem is that we do not know either of these values, | |
| 93 so we just make a heuristic guess based on a magic (possibly) | |
| 94 target-specific constant and size of the loop. | |
| 95 | |
| 96 4) Determine which of the references we prefetch. We take into account | |
| 97 that there is a maximum number of simultaneous prefetches (provided | |
| 98 by machine description). We prefetch as many prefetches as possible | |
| 99 while still within this bound (starting with those with lowest | |
| 100 prefetch_mod, since they are responsible for most of the cache | |
| 101 misses). | |
|
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102 |
| 0 | 103 5) We unroll and peel loops so that we are able to satisfy PREFETCH_MOD |
| 104 and PREFETCH_BEFORE requirements (within some bounds), and to avoid | |
| 105 prefetching nonaccessed memory. | |
| 106 TODO -- actually implement peeling. | |
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107 |
| 0 | 108 6) We actually emit the prefetch instructions. ??? Perhaps emit the |
| 109 prefetch instructions with guards in cases where 5) was not sufficient | |
| 110 to satisfy the constraints? | |
| 111 | |
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112 The function is_loop_prefetching_profitable() implements a cost model |
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113 to determine if prefetching is profitable for a given loop. The cost |
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114 model has two heuristcs: |
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115 1. A heuristic that determines whether the given loop has enough CPU |
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116 ops that can be overlapped with cache missing memory ops. |
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117 If not, the loop won't benefit from prefetching. This is implemented |
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118 by requirung the ratio between the instruction count and the mem ref |
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119 count to be above a certain minimum. |
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120 2. A heuristic that disables prefetching in a loop with an unknown trip |
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121 count if the prefetching cost is above a certain limit. The relative |
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122 prefetching cost is estimated by taking the ratio between the |
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123 prefetch count and the total intruction count (this models the I-cache |
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124 cost). |
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125 The limits used in these heuristics are defined as parameters with |
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126 reasonable default values. Machine-specific default values will be |
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127 added later. |
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128 |
| 0 | 129 Some other TODO: |
| 130 -- write and use more general reuse analysis (that could be also used | |
| 131 in other cache aimed loop optimizations) | |
| 132 -- make it behave sanely together with the prefetches given by user | |
| 133 (now we just ignore them; at the very least we should avoid | |
| 134 optimizing loops in that user put his own prefetches) | |
| 135 -- we assume cache line size alignment of arrays; this could be | |
| 136 improved. */ | |
| 137 | |
| 138 /* Magic constants follow. These should be replaced by machine specific | |
| 139 numbers. */ | |
| 140 | |
| 141 /* True if write can be prefetched by a read prefetch. */ | |
| 142 | |
| 143 #ifndef WRITE_CAN_USE_READ_PREFETCH | |
| 144 #define WRITE_CAN_USE_READ_PREFETCH 1 | |
| 145 #endif | |
| 146 | |
| 147 /* True if read can be prefetched by a write prefetch. */ | |
| 148 | |
| 149 #ifndef READ_CAN_USE_WRITE_PREFETCH | |
| 150 #define READ_CAN_USE_WRITE_PREFETCH 0 | |
| 151 #endif | |
| 152 | |
| 153 /* The size of the block loaded by a single prefetch. Usually, this is | |
| 154 the same as cache line size (at the moment, we only consider one level | |
| 155 of cache hierarchy). */ | |
| 156 | |
| 157 #ifndef PREFETCH_BLOCK | |
| 158 #define PREFETCH_BLOCK L1_CACHE_LINE_SIZE | |
| 159 #endif | |
| 160 | |
| 161 /* Do we have a forward hardware sequential prefetching? */ | |
| 162 | |
| 163 #ifndef HAVE_FORWARD_PREFETCH | |
| 164 #define HAVE_FORWARD_PREFETCH 0 | |
| 165 #endif | |
| 166 | |
| 167 /* Do we have a backward hardware sequential prefetching? */ | |
| 168 | |
| 169 #ifndef HAVE_BACKWARD_PREFETCH | |
| 170 #define HAVE_BACKWARD_PREFETCH 0 | |
| 171 #endif | |
| 172 | |
| 173 /* In some cases we are only able to determine that there is a certain | |
| 174 probability that the two accesses hit the same cache line. In this | |
| 175 case, we issue the prefetches for both of them if this probability | |
| 176 is less then (1000 - ACCEPTABLE_MISS_RATE) per thousand. */ | |
| 177 | |
| 178 #ifndef ACCEPTABLE_MISS_RATE | |
| 179 #define ACCEPTABLE_MISS_RATE 50 | |
| 180 #endif | |
| 181 | |
| 182 #ifndef HAVE_prefetch | |
| 183 #define HAVE_prefetch 0 | |
| 184 #endif | |
| 185 | |
| 186 #define L1_CACHE_SIZE_BYTES ((unsigned) (L1_CACHE_SIZE * 1024)) | |
| 187 #define L2_CACHE_SIZE_BYTES ((unsigned) (L2_CACHE_SIZE * 1024)) | |
| 188 | |
| 189 /* We consider a memory access nontemporal if it is not reused sooner than | |
| 190 after L2_CACHE_SIZE_BYTES of memory are accessed. However, we ignore | |
| 191 accesses closer than L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION, | |
| 192 so that we use nontemporal prefetches e.g. if single memory location | |
| 193 is accessed several times in a single iteration of the loop. */ | |
| 194 #define NONTEMPORAL_FRACTION 16 | |
| 195 | |
| 196 /* In case we have to emit a memory fence instruction after the loop that | |
| 197 uses nontemporal stores, this defines the builtin to use. */ | |
| 198 | |
| 199 #ifndef FENCE_FOLLOWING_MOVNT | |
| 200 #define FENCE_FOLLOWING_MOVNT NULL_TREE | |
| 201 #endif | |
| 202 | |
| 203 /* The group of references between that reuse may occur. */ | |
| 204 | |
| 205 struct mem_ref_group | |
| 206 { | |
| 207 tree base; /* Base of the reference. */ | |
| 208 HOST_WIDE_INT step; /* Step of the reference. */ | |
| 209 struct mem_ref *refs; /* References in the group. */ | |
| 210 struct mem_ref_group *next; /* Next group of references. */ | |
| 211 }; | |
| 212 | |
| 213 /* Assigned to PREFETCH_BEFORE when all iterations are to be prefetched. */ | |
| 214 | |
| 215 #define PREFETCH_ALL (~(unsigned HOST_WIDE_INT) 0) | |
| 216 | |
| 217 /* The memory reference. */ | |
| 218 | |
| 219 struct mem_ref | |
| 220 { | |
| 221 gimple stmt; /* Statement in that the reference appears. */ | |
| 222 tree mem; /* The reference. */ | |
| 223 HOST_WIDE_INT delta; /* Constant offset of the reference. */ | |
| 224 struct mem_ref_group *group; /* The group of references it belongs to. */ | |
| 225 unsigned HOST_WIDE_INT prefetch_mod; | |
| 226 /* Prefetch only each PREFETCH_MOD-th | |
| 227 iteration. */ | |
| 228 unsigned HOST_WIDE_INT prefetch_before; | |
| 229 /* Prefetch only first PREFETCH_BEFORE | |
| 230 iterations. */ | |
| 231 unsigned reuse_distance; /* The amount of data accessed before the first | |
| 232 reuse of this value. */ | |
| 233 struct mem_ref *next; /* The next reference in the group. */ | |
| 234 unsigned write_p : 1; /* Is it a write? */ | |
| 235 unsigned independent_p : 1; /* True if the reference is independent on | |
| 236 all other references inside the loop. */ | |
| 237 unsigned issue_prefetch_p : 1; /* Should we really issue the prefetch? */ | |
| 238 unsigned storent_p : 1; /* True if we changed the store to a | |
| 239 nontemporal one. */ | |
| 240 }; | |
| 241 | |
| 242 /* Dumps information about reference REF to FILE. */ | |
| 243 | |
| 244 static void | |
| 245 dump_mem_ref (FILE *file, struct mem_ref *ref) | |
| 246 { | |
| 247 fprintf (file, "Reference %p:\n", (void *) ref); | |
| 248 | |
| 249 fprintf (file, " group %p (base ", (void *) ref->group); | |
| 250 print_generic_expr (file, ref->group->base, TDF_SLIM); | |
| 251 fprintf (file, ", step "); | |
| 252 fprintf (file, HOST_WIDE_INT_PRINT_DEC, ref->group->step); | |
| 253 fprintf (file, ")\n"); | |
| 254 | |
| 255 fprintf (file, " delta "); | |
| 256 fprintf (file, HOST_WIDE_INT_PRINT_DEC, ref->delta); | |
| 257 fprintf (file, "\n"); | |
| 258 | |
| 259 fprintf (file, " %s\n", ref->write_p ? "write" : "read"); | |
| 260 | |
| 261 fprintf (file, "\n"); | |
| 262 } | |
| 263 | |
| 264 /* Finds a group with BASE and STEP in GROUPS, or creates one if it does not | |
| 265 exist. */ | |
| 266 | |
| 267 static struct mem_ref_group * | |
| 268 find_or_create_group (struct mem_ref_group **groups, tree base, | |
| 269 HOST_WIDE_INT step) | |
| 270 { | |
| 271 struct mem_ref_group *group; | |
| 272 | |
| 273 for (; *groups; groups = &(*groups)->next) | |
| 274 { | |
| 275 if ((*groups)->step == step | |
| 276 && operand_equal_p ((*groups)->base, base, 0)) | |
| 277 return *groups; | |
| 278 | |
| 279 /* Keep the list of groups sorted by decreasing step. */ | |
| 280 if ((*groups)->step < step) | |
| 281 break; | |
| 282 } | |
| 283 | |
| 284 group = XNEW (struct mem_ref_group); | |
| 285 group->base = base; | |
| 286 group->step = step; | |
| 287 group->refs = NULL; | |
| 288 group->next = *groups; | |
| 289 *groups = group; | |
| 290 | |
| 291 return group; | |
| 292 } | |
| 293 | |
| 294 /* Records a memory reference MEM in GROUP with offset DELTA and write status | |
| 295 WRITE_P. The reference occurs in statement STMT. */ | |
| 296 | |
| 297 static void | |
| 298 record_ref (struct mem_ref_group *group, gimple stmt, tree mem, | |
| 299 HOST_WIDE_INT delta, bool write_p) | |
| 300 { | |
| 301 struct mem_ref **aref; | |
| 302 | |
| 303 /* Do not record the same address twice. */ | |
| 304 for (aref = &group->refs; *aref; aref = &(*aref)->next) | |
| 305 { | |
| 306 /* It does not have to be possible for write reference to reuse the read | |
| 307 prefetch, or vice versa. */ | |
| 308 if (!WRITE_CAN_USE_READ_PREFETCH | |
| 309 && write_p | |
| 310 && !(*aref)->write_p) | |
| 311 continue; | |
| 312 if (!READ_CAN_USE_WRITE_PREFETCH | |
| 313 && !write_p | |
| 314 && (*aref)->write_p) | |
| 315 continue; | |
| 316 | |
| 317 if ((*aref)->delta == delta) | |
| 318 return; | |
| 319 } | |
| 320 | |
| 321 (*aref) = XNEW (struct mem_ref); | |
| 322 (*aref)->stmt = stmt; | |
| 323 (*aref)->mem = mem; | |
| 324 (*aref)->delta = delta; | |
| 325 (*aref)->write_p = write_p; | |
| 326 (*aref)->prefetch_before = PREFETCH_ALL; | |
| 327 (*aref)->prefetch_mod = 1; | |
| 328 (*aref)->reuse_distance = 0; | |
| 329 (*aref)->issue_prefetch_p = false; | |
| 330 (*aref)->group = group; | |
| 331 (*aref)->next = NULL; | |
| 332 (*aref)->independent_p = false; | |
| 333 (*aref)->storent_p = false; | |
| 334 | |
| 335 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 336 dump_mem_ref (dump_file, *aref); | |
| 337 } | |
| 338 | |
| 339 /* Release memory references in GROUPS. */ | |
| 340 | |
| 341 static void | |
| 342 release_mem_refs (struct mem_ref_group *groups) | |
| 343 { | |
| 344 struct mem_ref_group *next_g; | |
| 345 struct mem_ref *ref, *next_r; | |
| 346 | |
| 347 for (; groups; groups = next_g) | |
| 348 { | |
| 349 next_g = groups->next; | |
| 350 for (ref = groups->refs; ref; ref = next_r) | |
| 351 { | |
| 352 next_r = ref->next; | |
| 353 free (ref); | |
| 354 } | |
| 355 free (groups); | |
| 356 } | |
| 357 } | |
| 358 | |
| 359 /* A structure used to pass arguments to idx_analyze_ref. */ | |
| 360 | |
| 361 struct ar_data | |
| 362 { | |
| 363 struct loop *loop; /* Loop of the reference. */ | |
| 364 gimple stmt; /* Statement of the reference. */ | |
| 365 HOST_WIDE_INT *step; /* Step of the memory reference. */ | |
| 366 HOST_WIDE_INT *delta; /* Offset of the memory reference. */ | |
| 367 }; | |
| 368 | |
| 369 /* Analyzes a single INDEX of a memory reference to obtain information | |
| 370 described at analyze_ref. Callback for for_each_index. */ | |
| 371 | |
| 372 static bool | |
| 373 idx_analyze_ref (tree base, tree *index, void *data) | |
| 374 { | |
| 375 struct ar_data *ar_data = (struct ar_data *) data; | |
| 376 tree ibase, step, stepsize; | |
| 377 HOST_WIDE_INT istep, idelta = 0, imult = 1; | |
| 378 affine_iv iv; | |
| 379 | |
| 380 if (TREE_CODE (base) == MISALIGNED_INDIRECT_REF | |
| 381 || TREE_CODE (base) == ALIGN_INDIRECT_REF) | |
| 382 return false; | |
| 383 | |
| 384 if (!simple_iv (ar_data->loop, loop_containing_stmt (ar_data->stmt), | |
| 385 *index, &iv, false)) | |
| 386 return false; | |
| 387 ibase = iv.base; | |
| 388 step = iv.step; | |
| 389 | |
| 390 if (!cst_and_fits_in_hwi (step)) | |
| 391 return false; | |
| 392 istep = int_cst_value (step); | |
| 393 | |
| 394 if (TREE_CODE (ibase) == POINTER_PLUS_EXPR | |
| 395 && cst_and_fits_in_hwi (TREE_OPERAND (ibase, 1))) | |
| 396 { | |
| 397 idelta = int_cst_value (TREE_OPERAND (ibase, 1)); | |
| 398 ibase = TREE_OPERAND (ibase, 0); | |
| 399 } | |
| 400 if (cst_and_fits_in_hwi (ibase)) | |
| 401 { | |
| 402 idelta += int_cst_value (ibase); | |
| 403 ibase = build_int_cst (TREE_TYPE (ibase), 0); | |
| 404 } | |
| 405 | |
| 406 if (TREE_CODE (base) == ARRAY_REF) | |
| 407 { | |
| 408 stepsize = array_ref_element_size (base); | |
| 409 if (!cst_and_fits_in_hwi (stepsize)) | |
| 410 return false; | |
| 411 imult = int_cst_value (stepsize); | |
| 412 | |
| 413 istep *= imult; | |
| 414 idelta *= imult; | |
| 415 } | |
| 416 | |
| 417 *ar_data->step += istep; | |
| 418 *ar_data->delta += idelta; | |
| 419 *index = ibase; | |
| 420 | |
| 421 return true; | |
| 422 } | |
| 423 | |
| 424 /* Tries to express REF_P in shape &BASE + STEP * iter + DELTA, where DELTA and | |
| 425 STEP are integer constants and iter is number of iterations of LOOP. The | |
| 426 reference occurs in statement STMT. Strips nonaddressable component | |
| 427 references from REF_P. */ | |
| 428 | |
| 429 static bool | |
| 430 analyze_ref (struct loop *loop, tree *ref_p, tree *base, | |
| 431 HOST_WIDE_INT *step, HOST_WIDE_INT *delta, | |
| 432 gimple stmt) | |
| 433 { | |
| 434 struct ar_data ar_data; | |
| 435 tree off; | |
| 436 HOST_WIDE_INT bit_offset; | |
| 437 tree ref = *ref_p; | |
| 438 | |
| 439 *step = 0; | |
| 440 *delta = 0; | |
| 441 | |
| 442 /* First strip off the component references. Ignore bitfields. */ | |
| 443 if (TREE_CODE (ref) == COMPONENT_REF | |
| 444 && DECL_NONADDRESSABLE_P (TREE_OPERAND (ref, 1))) | |
| 445 ref = TREE_OPERAND (ref, 0); | |
| 446 | |
| 447 *ref_p = ref; | |
| 448 | |
| 449 for (; TREE_CODE (ref) == COMPONENT_REF; ref = TREE_OPERAND (ref, 0)) | |
| 450 { | |
| 451 off = DECL_FIELD_BIT_OFFSET (TREE_OPERAND (ref, 1)); | |
| 452 bit_offset = TREE_INT_CST_LOW (off); | |
| 453 gcc_assert (bit_offset % BITS_PER_UNIT == 0); | |
|
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454 |
| 0 | 455 *delta += bit_offset / BITS_PER_UNIT; |
| 456 } | |
| 457 | |
| 458 *base = unshare_expr (ref); | |
| 459 ar_data.loop = loop; | |
| 460 ar_data.stmt = stmt; | |
| 461 ar_data.step = step; | |
| 462 ar_data.delta = delta; | |
| 463 return for_each_index (base, idx_analyze_ref, &ar_data); | |
| 464 } | |
| 465 | |
| 466 /* Record a memory reference REF to the list REFS. The reference occurs in | |
| 467 LOOP in statement STMT and it is write if WRITE_P. Returns true if the | |
| 468 reference was recorded, false otherwise. */ | |
| 469 | |
| 470 static bool | |
| 471 gather_memory_references_ref (struct loop *loop, struct mem_ref_group **refs, | |
| 472 tree ref, bool write_p, gimple stmt) | |
| 473 { | |
| 474 tree base; | |
| 475 HOST_WIDE_INT step, delta; | |
| 476 struct mem_ref_group *agrp; | |
| 477 | |
| 478 if (get_base_address (ref) == NULL) | |
| 479 return false; | |
| 480 | |
| 481 if (!analyze_ref (loop, &ref, &base, &step, &delta, stmt)) | |
| 482 return false; | |
| 483 | |
| 484 /* Now we know that REF = &BASE + STEP * iter + DELTA, where DELTA and STEP | |
| 485 are integer constants. */ | |
| 486 agrp = find_or_create_group (refs, base, step); | |
| 487 record_ref (agrp, stmt, ref, delta, write_p); | |
| 488 | |
| 489 return true; | |
| 490 } | |
| 491 | |
| 492 /* Record the suitable memory references in LOOP. NO_OTHER_REFS is set to | |
| 493 true if there are no other memory references inside the loop. */ | |
| 494 | |
| 495 static struct mem_ref_group * | |
|
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496 gather_memory_references (struct loop *loop, bool *no_other_refs, unsigned *ref_count) |
| 0 | 497 { |
| 498 basic_block *body = get_loop_body_in_dom_order (loop); | |
| 499 basic_block bb; | |
| 500 unsigned i; | |
| 501 gimple_stmt_iterator bsi; | |
| 502 gimple stmt; | |
| 503 tree lhs, rhs; | |
| 504 struct mem_ref_group *refs = NULL; | |
| 505 | |
| 506 *no_other_refs = true; | |
|
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507 *ref_count = 0; |
| 0 | 508 |
| 509 /* Scan the loop body in order, so that the former references precede the | |
| 510 later ones. */ | |
| 511 for (i = 0; i < loop->num_nodes; i++) | |
| 512 { | |
| 513 bb = body[i]; | |
| 514 if (bb->loop_father != loop) | |
| 515 continue; | |
| 516 | |
| 517 for (bsi = gsi_start_bb (bb); !gsi_end_p (bsi); gsi_next (&bsi)) | |
| 518 { | |
| 519 stmt = gsi_stmt (bsi); | |
| 520 | |
| 521 if (gimple_code (stmt) != GIMPLE_ASSIGN) | |
| 522 { | |
|
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523 if (gimple_vuse (stmt) |
| 0 | 524 || (is_gimple_call (stmt) |
| 525 && !(gimple_call_flags (stmt) & ECF_CONST))) | |
| 526 *no_other_refs = false; | |
| 527 continue; | |
| 528 } | |
| 529 | |
| 530 lhs = gimple_assign_lhs (stmt); | |
| 531 rhs = gimple_assign_rhs1 (stmt); | |
| 532 | |
| 533 if (REFERENCE_CLASS_P (rhs)) | |
|
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534 { |
| 0 | 535 *no_other_refs &= gather_memory_references_ref (loop, &refs, |
| 536 rhs, false, stmt); | |
|
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537 *ref_count += 1; |
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538 } |
| 0 | 539 if (REFERENCE_CLASS_P (lhs)) |
|
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540 { |
| 0 | 541 *no_other_refs &= gather_memory_references_ref (loop, &refs, |
| 542 lhs, true, stmt); | |
|
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543 *ref_count += 1; |
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544 } |
| 0 | 545 } |
| 546 } | |
| 547 free (body); | |
| 548 | |
| 549 return refs; | |
| 550 } | |
| 551 | |
| 552 /* Prune the prefetch candidate REF using the self-reuse. */ | |
| 553 | |
| 554 static void | |
| 555 prune_ref_by_self_reuse (struct mem_ref *ref) | |
| 556 { | |
| 557 HOST_WIDE_INT step = ref->group->step; | |
| 558 bool backward = step < 0; | |
| 559 | |
| 560 if (step == 0) | |
| 561 { | |
| 562 /* Prefetch references to invariant address just once. */ | |
| 563 ref->prefetch_before = 1; | |
| 564 return; | |
| 565 } | |
| 566 | |
| 567 if (backward) | |
| 568 step = -step; | |
| 569 | |
| 570 if (step > PREFETCH_BLOCK) | |
| 571 return; | |
| 572 | |
| 573 if ((backward && HAVE_BACKWARD_PREFETCH) | |
| 574 || (!backward && HAVE_FORWARD_PREFETCH)) | |
| 575 { | |
| 576 ref->prefetch_before = 1; | |
| 577 return; | |
| 578 } | |
| 579 | |
| 580 ref->prefetch_mod = PREFETCH_BLOCK / step; | |
| 581 } | |
| 582 | |
| 583 /* Divides X by BY, rounding down. */ | |
| 584 | |
| 585 static HOST_WIDE_INT | |
| 586 ddown (HOST_WIDE_INT x, unsigned HOST_WIDE_INT by) | |
| 587 { | |
| 588 gcc_assert (by > 0); | |
| 589 | |
| 590 if (x >= 0) | |
| 591 return x / by; | |
| 592 else | |
| 593 return (x + by - 1) / by; | |
| 594 } | |
| 595 | |
|
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596 /* Given a CACHE_LINE_SIZE and two inductive memory references |
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597 with a common STEP greater than CACHE_LINE_SIZE and an address |
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598 difference DELTA, compute the probability that they will fall |
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599 in different cache lines. DISTINCT_ITERS is the number of |
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600 distinct iterations after which the pattern repeats itself. |
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601 ALIGN_UNIT is the unit of alignment in bytes. */ |
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602 |
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603 static int |
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604 compute_miss_rate (unsigned HOST_WIDE_INT cache_line_size, |
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605 HOST_WIDE_INT step, HOST_WIDE_INT delta, |
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606 unsigned HOST_WIDE_INT distinct_iters, |
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607 int align_unit) |
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608 { |
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609 unsigned align, iter; |
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610 int total_positions, miss_positions, miss_rate; |
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611 int address1, address2, cache_line1, cache_line2; |
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612 |
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613 total_positions = 0; |
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614 miss_positions = 0; |
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615 |
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616 /* Iterate through all possible alignments of the first |
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617 memory reference within its cache line. */ |
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618 for (align = 0; align < cache_line_size; align += align_unit) |
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619 |
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620 /* Iterate through all distinct iterations. */ |
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621 for (iter = 0; iter < distinct_iters; iter++) |
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622 { |
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623 address1 = align + step * iter; |
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624 address2 = address1 + delta; |
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625 cache_line1 = address1 / cache_line_size; |
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626 cache_line2 = address2 / cache_line_size; |
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627 total_positions += 1; |
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628 if (cache_line1 != cache_line2) |
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629 miss_positions += 1; |
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630 } |
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631 miss_rate = 1000 * miss_positions / total_positions; |
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632 return miss_rate; |
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633 } |
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634 |
| 0 | 635 /* Prune the prefetch candidate REF using the reuse with BY. |
| 636 If BY_IS_BEFORE is true, BY is before REF in the loop. */ | |
| 637 | |
| 638 static void | |
| 639 prune_ref_by_group_reuse (struct mem_ref *ref, struct mem_ref *by, | |
| 640 bool by_is_before) | |
| 641 { | |
| 642 HOST_WIDE_INT step = ref->group->step; | |
| 643 bool backward = step < 0; | |
| 644 HOST_WIDE_INT delta_r = ref->delta, delta_b = by->delta; | |
| 645 HOST_WIDE_INT delta = delta_b - delta_r; | |
| 646 HOST_WIDE_INT hit_from; | |
| 647 unsigned HOST_WIDE_INT prefetch_before, prefetch_block; | |
|
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648 int miss_rate; |
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649 HOST_WIDE_INT reduced_step; |
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650 unsigned HOST_WIDE_INT reduced_prefetch_block; |
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651 tree ref_type; |
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652 int align_unit; |
| 0 | 653 |
| 654 if (delta == 0) | |
| 655 { | |
| 656 /* If the references has the same address, only prefetch the | |
| 657 former. */ | |
| 658 if (by_is_before) | |
| 659 ref->prefetch_before = 0; | |
|
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660 |
| 0 | 661 return; |
| 662 } | |
| 663 | |
| 664 if (!step) | |
| 665 { | |
| 666 /* If the reference addresses are invariant and fall into the | |
| 667 same cache line, prefetch just the first one. */ | |
| 668 if (!by_is_before) | |
| 669 return; | |
| 670 | |
| 671 if (ddown (ref->delta, PREFETCH_BLOCK) | |
| 672 != ddown (by->delta, PREFETCH_BLOCK)) | |
| 673 return; | |
| 674 | |
| 675 ref->prefetch_before = 0; | |
| 676 return; | |
| 677 } | |
| 678 | |
| 679 /* Only prune the reference that is behind in the array. */ | |
| 680 if (backward) | |
| 681 { | |
| 682 if (delta > 0) | |
| 683 return; | |
| 684 | |
| 685 /* Transform the data so that we may assume that the accesses | |
| 686 are forward. */ | |
| 687 delta = - delta; | |
| 688 step = -step; | |
| 689 delta_r = PREFETCH_BLOCK - 1 - delta_r; | |
| 690 delta_b = PREFETCH_BLOCK - 1 - delta_b; | |
| 691 } | |
| 692 else | |
| 693 { | |
| 694 if (delta < 0) | |
| 695 return; | |
| 696 } | |
| 697 | |
| 698 /* Check whether the two references are likely to hit the same cache | |
| 699 line, and how distant the iterations in that it occurs are from | |
| 700 each other. */ | |
| 701 | |
| 702 if (step <= PREFETCH_BLOCK) | |
| 703 { | |
| 704 /* The accesses are sure to meet. Let us check when. */ | |
| 705 hit_from = ddown (delta_b, PREFETCH_BLOCK) * PREFETCH_BLOCK; | |
| 706 prefetch_before = (hit_from - delta_r + step - 1) / step; | |
| 707 | |
| 708 if (prefetch_before < ref->prefetch_before) | |
| 709 ref->prefetch_before = prefetch_before; | |
| 710 | |
| 711 return; | |
| 712 } | |
| 713 | |
|
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714 /* A more complicated case with step > prefetch_block. First reduce |
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715 the ratio between the step and the cache line size to its simplest |
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716 terms. The resulting denominator will then represent the number of |
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717 distinct iterations after which each address will go back to its |
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718 initial location within the cache line. This computation assumes |
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719 that PREFETCH_BLOCK is a power of two. */ |
| 0 | 720 prefetch_block = PREFETCH_BLOCK; |
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721 reduced_prefetch_block = prefetch_block; |
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722 reduced_step = step; |
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723 while ((reduced_step & 1) == 0 |
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724 && reduced_prefetch_block > 1) |
| 0 | 725 { |
|
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726 reduced_step >>= 1; |
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727 reduced_prefetch_block >>= 1; |
| 0 | 728 } |
| 729 | |
| 730 prefetch_before = delta / step; | |
| 731 delta %= step; | |
|
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732 ref_type = TREE_TYPE (ref->mem); |
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733 align_unit = TYPE_ALIGN (ref_type) / 8; |
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734 miss_rate = compute_miss_rate(prefetch_block, step, delta, |
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735 reduced_prefetch_block, align_unit); |
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736 if (miss_rate <= ACCEPTABLE_MISS_RATE) |
| 0 | 737 { |
| 738 if (prefetch_before < ref->prefetch_before) | |
| 739 ref->prefetch_before = prefetch_before; | |
| 740 | |
| 741 return; | |
| 742 } | |
| 743 | |
| 744 /* Try also the following iteration. */ | |
| 745 prefetch_before++; | |
| 746 delta = step - delta; | |
|
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747 miss_rate = compute_miss_rate(prefetch_block, step, delta, |
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748 reduced_prefetch_block, align_unit); |
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749 if (miss_rate <= ACCEPTABLE_MISS_RATE) |
| 0 | 750 { |
| 751 if (prefetch_before < ref->prefetch_before) | |
| 752 ref->prefetch_before = prefetch_before; | |
| 753 | |
| 754 return; | |
| 755 } | |
| 756 | |
| 757 /* The ref probably does not reuse by. */ | |
| 758 return; | |
| 759 } | |
| 760 | |
| 761 /* Prune the prefetch candidate REF using the reuses with other references | |
| 762 in REFS. */ | |
| 763 | |
| 764 static void | |
| 765 prune_ref_by_reuse (struct mem_ref *ref, struct mem_ref *refs) | |
| 766 { | |
| 767 struct mem_ref *prune_by; | |
| 768 bool before = true; | |
| 769 | |
| 770 prune_ref_by_self_reuse (ref); | |
| 771 | |
| 772 for (prune_by = refs; prune_by; prune_by = prune_by->next) | |
| 773 { | |
| 774 if (prune_by == ref) | |
| 775 { | |
| 776 before = false; | |
| 777 continue; | |
| 778 } | |
| 779 | |
| 780 if (!WRITE_CAN_USE_READ_PREFETCH | |
| 781 && ref->write_p | |
| 782 && !prune_by->write_p) | |
| 783 continue; | |
| 784 if (!READ_CAN_USE_WRITE_PREFETCH | |
| 785 && !ref->write_p | |
| 786 && prune_by->write_p) | |
| 787 continue; | |
| 788 | |
| 789 prune_ref_by_group_reuse (ref, prune_by, before); | |
| 790 } | |
| 791 } | |
| 792 | |
| 793 /* Prune the prefetch candidates in GROUP using the reuse analysis. */ | |
| 794 | |
| 795 static void | |
| 796 prune_group_by_reuse (struct mem_ref_group *group) | |
| 797 { | |
| 798 struct mem_ref *ref_pruned; | |
| 799 | |
| 800 for (ref_pruned = group->refs; ref_pruned; ref_pruned = ref_pruned->next) | |
| 801 { | |
| 802 prune_ref_by_reuse (ref_pruned, group->refs); | |
| 803 | |
| 804 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 805 { | |
| 806 fprintf (dump_file, "Reference %p:", (void *) ref_pruned); | |
| 807 | |
| 808 if (ref_pruned->prefetch_before == PREFETCH_ALL | |
| 809 && ref_pruned->prefetch_mod == 1) | |
| 810 fprintf (dump_file, " no restrictions"); | |
| 811 else if (ref_pruned->prefetch_before == 0) | |
| 812 fprintf (dump_file, " do not prefetch"); | |
| 813 else if (ref_pruned->prefetch_before <= ref_pruned->prefetch_mod) | |
| 814 fprintf (dump_file, " prefetch once"); | |
| 815 else | |
| 816 { | |
| 817 if (ref_pruned->prefetch_before != PREFETCH_ALL) | |
| 818 { | |
| 819 fprintf (dump_file, " prefetch before "); | |
| 820 fprintf (dump_file, HOST_WIDE_INT_PRINT_DEC, | |
| 821 ref_pruned->prefetch_before); | |
| 822 } | |
| 823 if (ref_pruned->prefetch_mod != 1) | |
| 824 { | |
| 825 fprintf (dump_file, " prefetch mod "); | |
| 826 fprintf (dump_file, HOST_WIDE_INT_PRINT_DEC, | |
| 827 ref_pruned->prefetch_mod); | |
| 828 } | |
| 829 } | |
| 830 fprintf (dump_file, "\n"); | |
| 831 } | |
| 832 } | |
| 833 } | |
| 834 | |
| 835 /* Prune the list of prefetch candidates GROUPS using the reuse analysis. */ | |
| 836 | |
| 837 static void | |
| 838 prune_by_reuse (struct mem_ref_group *groups) | |
| 839 { | |
| 840 for (; groups; groups = groups->next) | |
| 841 prune_group_by_reuse (groups); | |
| 842 } | |
| 843 | |
| 844 /* Returns true if we should issue prefetch for REF. */ | |
| 845 | |
| 846 static bool | |
| 847 should_issue_prefetch_p (struct mem_ref *ref) | |
| 848 { | |
| 849 /* For now do not issue prefetches for only first few of the | |
| 850 iterations. */ | |
| 851 if (ref->prefetch_before != PREFETCH_ALL) | |
| 852 return false; | |
| 853 | |
| 854 /* Do not prefetch nontemporal stores. */ | |
| 855 if (ref->storent_p) | |
| 856 return false; | |
| 857 | |
| 858 return true; | |
| 859 } | |
| 860 | |
| 861 /* Decide which of the prefetch candidates in GROUPS to prefetch. | |
| 862 AHEAD is the number of iterations to prefetch ahead (which corresponds | |
| 863 to the number of simultaneous instances of one prefetch running at a | |
| 864 time). UNROLL_FACTOR is the factor by that the loop is going to be | |
| 865 unrolled. Returns true if there is anything to prefetch. */ | |
| 866 | |
| 867 static bool | |
| 868 schedule_prefetches (struct mem_ref_group *groups, unsigned unroll_factor, | |
| 869 unsigned ahead) | |
| 870 { | |
| 871 unsigned remaining_prefetch_slots, n_prefetches, prefetch_slots; | |
| 872 unsigned slots_per_prefetch; | |
| 873 struct mem_ref *ref; | |
| 874 bool any = false; | |
| 875 | |
| 876 /* At most SIMULTANEOUS_PREFETCHES should be running at the same time. */ | |
| 877 remaining_prefetch_slots = SIMULTANEOUS_PREFETCHES; | |
| 878 | |
| 879 /* The prefetch will run for AHEAD iterations of the original loop, i.e., | |
| 880 AHEAD / UNROLL_FACTOR iterations of the unrolled loop. In each iteration, | |
| 881 it will need a prefetch slot. */ | |
| 882 slots_per_prefetch = (ahead + unroll_factor / 2) / unroll_factor; | |
| 883 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 884 fprintf (dump_file, "Each prefetch instruction takes %u prefetch slots.\n", | |
| 885 slots_per_prefetch); | |
| 886 | |
| 887 /* For now we just take memory references one by one and issue | |
| 888 prefetches for as many as possible. The groups are sorted | |
| 889 starting with the largest step, since the references with | |
| 890 large step are more likely to cause many cache misses. */ | |
| 891 | |
| 892 for (; groups; groups = groups->next) | |
| 893 for (ref = groups->refs; ref; ref = ref->next) | |
| 894 { | |
| 895 if (!should_issue_prefetch_p (ref)) | |
| 896 continue; | |
| 897 | |
| 898 /* If we need to prefetch the reference each PREFETCH_MOD iterations, | |
| 899 and we unroll the loop UNROLL_FACTOR times, we need to insert | |
| 900 ceil (UNROLL_FACTOR / PREFETCH_MOD) instructions in each | |
| 901 iteration. */ | |
| 902 n_prefetches = ((unroll_factor + ref->prefetch_mod - 1) | |
| 903 / ref->prefetch_mod); | |
| 904 prefetch_slots = n_prefetches * slots_per_prefetch; | |
| 905 | |
| 906 /* If more than half of the prefetches would be lost anyway, do not | |
| 907 issue the prefetch. */ | |
| 908 if (2 * remaining_prefetch_slots < prefetch_slots) | |
| 909 continue; | |
| 910 | |
| 911 ref->issue_prefetch_p = true; | |
| 912 | |
| 913 if (remaining_prefetch_slots <= prefetch_slots) | |
| 914 return true; | |
| 915 remaining_prefetch_slots -= prefetch_slots; | |
| 916 any = true; | |
| 917 } | |
| 918 | |
| 919 return any; | |
| 920 } | |
| 921 | |
|
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922 /* Estimate the number of prefetches in the given GROUPS. */ |
| 0 | 923 |
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924 static int |
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925 estimate_prefetch_count (struct mem_ref_group *groups) |
| 0 | 926 { |
| 927 struct mem_ref *ref; | |
|
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928 int prefetch_count = 0; |
| 0 | 929 |
| 930 for (; groups; groups = groups->next) | |
| 931 for (ref = groups->refs; ref; ref = ref->next) | |
| 932 if (should_issue_prefetch_p (ref)) | |
|
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933 prefetch_count++; |
| 0 | 934 |
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935 return prefetch_count; |
| 0 | 936 } |
| 937 | |
| 938 /* Issue prefetches for the reference REF into loop as decided before. | |
| 939 HEAD is the number of iterations to prefetch ahead. UNROLL_FACTOR | |
| 940 is the factor by which LOOP was unrolled. */ | |
| 941 | |
| 942 static void | |
| 943 issue_prefetch_ref (struct mem_ref *ref, unsigned unroll_factor, unsigned ahead) | |
| 944 { | |
| 945 HOST_WIDE_INT delta; | |
| 946 tree addr, addr_base, write_p, local; | |
| 947 gimple prefetch; | |
| 948 gimple_stmt_iterator bsi; | |
| 949 unsigned n_prefetches, ap; | |
| 950 bool nontemporal = ref->reuse_distance >= L2_CACHE_SIZE_BYTES; | |
| 951 | |
| 952 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 953 fprintf (dump_file, "Issued%s prefetch for %p.\n", | |
| 954 nontemporal ? " nontemporal" : "", | |
| 955 (void *) ref); | |
| 956 | |
| 957 bsi = gsi_for_stmt (ref->stmt); | |
| 958 | |
| 959 n_prefetches = ((unroll_factor + ref->prefetch_mod - 1) | |
| 960 / ref->prefetch_mod); | |
| 961 addr_base = build_fold_addr_expr_with_type (ref->mem, ptr_type_node); | |
| 962 addr_base = force_gimple_operand_gsi (&bsi, unshare_expr (addr_base), | |
| 963 true, NULL, true, GSI_SAME_STMT); | |
| 964 write_p = ref->write_p ? integer_one_node : integer_zero_node; | |
| 965 local = build_int_cst (integer_type_node, nontemporal ? 0 : 3); | |
| 966 | |
| 967 for (ap = 0; ap < n_prefetches; ap++) | |
| 968 { | |
| 969 /* Determine the address to prefetch. */ | |
| 970 delta = (ahead + ap * ref->prefetch_mod) * ref->group->step; | |
| 971 addr = fold_build2 (POINTER_PLUS_EXPR, ptr_type_node, | |
| 972 addr_base, size_int (delta)); | |
| 973 addr = force_gimple_operand_gsi (&bsi, unshare_expr (addr), true, NULL, | |
| 974 true, GSI_SAME_STMT); | |
| 975 | |
| 976 /* Create the prefetch instruction. */ | |
| 977 prefetch = gimple_build_call (built_in_decls[BUILT_IN_PREFETCH], | |
| 978 3, addr, write_p, local); | |
| 979 gsi_insert_before (&bsi, prefetch, GSI_SAME_STMT); | |
| 980 } | |
| 981 } | |
| 982 | |
| 983 /* Issue prefetches for the references in GROUPS into loop as decided before. | |
| 984 HEAD is the number of iterations to prefetch ahead. UNROLL_FACTOR is the | |
| 985 factor by that LOOP was unrolled. */ | |
| 986 | |
| 987 static void | |
| 988 issue_prefetches (struct mem_ref_group *groups, | |
| 989 unsigned unroll_factor, unsigned ahead) | |
| 990 { | |
| 991 struct mem_ref *ref; | |
| 992 | |
| 993 for (; groups; groups = groups->next) | |
| 994 for (ref = groups->refs; ref; ref = ref->next) | |
| 995 if (ref->issue_prefetch_p) | |
| 996 issue_prefetch_ref (ref, unroll_factor, ahead); | |
| 997 } | |
| 998 | |
| 999 /* Returns true if REF is a memory write for that a nontemporal store insn | |
| 1000 can be used. */ | |
| 1001 | |
| 1002 static bool | |
| 1003 nontemporal_store_p (struct mem_ref *ref) | |
| 1004 { | |
| 1005 enum machine_mode mode; | |
| 1006 enum insn_code code; | |
| 1007 | |
| 1008 /* REF must be a write that is not reused. We require it to be independent | |
| 1009 on all other memory references in the loop, as the nontemporal stores may | |
| 1010 be reordered with respect to other memory references. */ | |
| 1011 if (!ref->write_p | |
| 1012 || !ref->independent_p | |
| 1013 || ref->reuse_distance < L2_CACHE_SIZE_BYTES) | |
| 1014 return false; | |
| 1015 | |
| 1016 /* Check that we have the storent instruction for the mode. */ | |
| 1017 mode = TYPE_MODE (TREE_TYPE (ref->mem)); | |
| 1018 if (mode == BLKmode) | |
| 1019 return false; | |
| 1020 | |
| 1021 code = optab_handler (storent_optab, mode)->insn_code; | |
| 1022 return code != CODE_FOR_nothing; | |
| 1023 } | |
| 1024 | |
| 1025 /* If REF is a nontemporal store, we mark the corresponding modify statement | |
| 1026 and return true. Otherwise, we return false. */ | |
| 1027 | |
| 1028 static bool | |
| 1029 mark_nontemporal_store (struct mem_ref *ref) | |
| 1030 { | |
| 1031 if (!nontemporal_store_p (ref)) | |
| 1032 return false; | |
| 1033 | |
| 1034 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 1035 fprintf (dump_file, "Marked reference %p as a nontemporal store.\n", | |
| 1036 (void *) ref); | |
| 1037 | |
| 1038 gimple_assign_set_nontemporal_move (ref->stmt, true); | |
| 1039 ref->storent_p = true; | |
| 1040 | |
| 1041 return true; | |
| 1042 } | |
| 1043 | |
| 1044 /* Issue a memory fence instruction after LOOP. */ | |
| 1045 | |
| 1046 static void | |
| 1047 emit_mfence_after_loop (struct loop *loop) | |
| 1048 { | |
| 1049 VEC (edge, heap) *exits = get_loop_exit_edges (loop); | |
| 1050 edge exit; | |
| 1051 gimple call; | |
| 1052 gimple_stmt_iterator bsi; | |
| 1053 unsigned i; | |
| 1054 | |
| 1055 for (i = 0; VEC_iterate (edge, exits, i, exit); i++) | |
| 1056 { | |
| 1057 call = gimple_build_call (FENCE_FOLLOWING_MOVNT, 0); | |
| 1058 | |
| 1059 if (!single_pred_p (exit->dest) | |
| 1060 /* If possible, we prefer not to insert the fence on other paths | |
| 1061 in cfg. */ | |
| 1062 && !(exit->flags & EDGE_ABNORMAL)) | |
| 1063 split_loop_exit_edge (exit); | |
| 1064 bsi = gsi_after_labels (exit->dest); | |
| 1065 | |
| 1066 gsi_insert_before (&bsi, call, GSI_NEW_STMT); | |
| 1067 mark_virtual_ops_for_renaming (call); | |
| 1068 } | |
| 1069 | |
| 1070 VEC_free (edge, heap, exits); | |
| 1071 update_ssa (TODO_update_ssa_only_virtuals); | |
| 1072 } | |
| 1073 | |
| 1074 /* Returns true if we can use storent in loop, false otherwise. */ | |
| 1075 | |
| 1076 static bool | |
| 1077 may_use_storent_in_loop_p (struct loop *loop) | |
| 1078 { | |
| 1079 bool ret = true; | |
| 1080 | |
| 1081 if (loop->inner != NULL) | |
| 1082 return false; | |
| 1083 | |
| 1084 /* If we must issue a mfence insn after using storent, check that there | |
| 1085 is a suitable place for it at each of the loop exits. */ | |
| 1086 if (FENCE_FOLLOWING_MOVNT != NULL_TREE) | |
| 1087 { | |
| 1088 VEC (edge, heap) *exits = get_loop_exit_edges (loop); | |
| 1089 unsigned i; | |
| 1090 edge exit; | |
| 1091 | |
| 1092 for (i = 0; VEC_iterate (edge, exits, i, exit); i++) | |
| 1093 if ((exit->flags & EDGE_ABNORMAL) | |
| 1094 && exit->dest == EXIT_BLOCK_PTR) | |
| 1095 ret = false; | |
| 1096 | |
| 1097 VEC_free (edge, heap, exits); | |
| 1098 } | |
| 1099 | |
| 1100 return ret; | |
| 1101 } | |
| 1102 | |
| 1103 /* Marks nontemporal stores in LOOP. GROUPS contains the description of memory | |
| 1104 references in the loop. */ | |
| 1105 | |
| 1106 static void | |
| 1107 mark_nontemporal_stores (struct loop *loop, struct mem_ref_group *groups) | |
| 1108 { | |
| 1109 struct mem_ref *ref; | |
| 1110 bool any = false; | |
| 1111 | |
| 1112 if (!may_use_storent_in_loop_p (loop)) | |
| 1113 return; | |
| 1114 | |
| 1115 for (; groups; groups = groups->next) | |
| 1116 for (ref = groups->refs; ref; ref = ref->next) | |
| 1117 any |= mark_nontemporal_store (ref); | |
| 1118 | |
| 1119 if (any && FENCE_FOLLOWING_MOVNT != NULL_TREE) | |
| 1120 emit_mfence_after_loop (loop); | |
| 1121 } | |
| 1122 | |
| 1123 /* Determines whether we can profitably unroll LOOP FACTOR times, and if | |
| 1124 this is the case, fill in DESC by the description of number of | |
| 1125 iterations. */ | |
| 1126 | |
| 1127 static bool | |
| 1128 should_unroll_loop_p (struct loop *loop, struct tree_niter_desc *desc, | |
| 1129 unsigned factor) | |
| 1130 { | |
| 1131 if (!can_unroll_loop_p (loop, factor, desc)) | |
| 1132 return false; | |
| 1133 | |
| 1134 /* We only consider loops without control flow for unrolling. This is not | |
| 1135 a hard restriction -- tree_unroll_loop works with arbitrary loops | |
| 1136 as well; but the unrolling/prefetching is usually more profitable for | |
| 1137 loops consisting of a single basic block, and we want to limit the | |
| 1138 code growth. */ | |
| 1139 if (loop->num_nodes > 2) | |
| 1140 return false; | |
| 1141 | |
| 1142 return true; | |
| 1143 } | |
| 1144 | |
| 1145 /* Determine the coefficient by that unroll LOOP, from the information | |
| 1146 contained in the list of memory references REFS. Description of | |
| 1147 umber of iterations of LOOP is stored to DESC. NINSNS is the number of | |
| 1148 insns of the LOOP. EST_NITER is the estimated number of iterations of | |
| 1149 the loop, or -1 if no estimate is available. */ | |
| 1150 | |
| 1151 static unsigned | |
| 1152 determine_unroll_factor (struct loop *loop, struct mem_ref_group *refs, | |
| 1153 unsigned ninsns, struct tree_niter_desc *desc, | |
| 1154 HOST_WIDE_INT est_niter) | |
| 1155 { | |
| 1156 unsigned upper_bound; | |
| 1157 unsigned nfactor, factor, mod_constraint; | |
| 1158 struct mem_ref_group *agp; | |
| 1159 struct mem_ref *ref; | |
| 1160 | |
| 1161 /* First check whether the loop is not too large to unroll. We ignore | |
| 1162 PARAM_MAX_UNROLL_TIMES, because for small loops, it prevented us | |
| 1163 from unrolling them enough to make exactly one cache line covered by each | |
| 1164 iteration. Also, the goal of PARAM_MAX_UNROLL_TIMES is to prevent | |
| 1165 us from unrolling the loops too many times in cases where we only expect | |
| 1166 gains from better scheduling and decreasing loop overhead, which is not | |
| 1167 the case here. */ | |
| 1168 upper_bound = PARAM_VALUE (PARAM_MAX_UNROLLED_INSNS) / ninsns; | |
| 1169 | |
| 1170 /* If we unrolled the loop more times than it iterates, the unrolled version | |
| 1171 of the loop would be never entered. */ | |
| 1172 if (est_niter >= 0 && est_niter < (HOST_WIDE_INT) upper_bound) | |
| 1173 upper_bound = est_niter; | |
| 1174 | |
| 1175 if (upper_bound <= 1) | |
| 1176 return 1; | |
| 1177 | |
| 1178 /* Choose the factor so that we may prefetch each cache just once, | |
| 1179 but bound the unrolling by UPPER_BOUND. */ | |
| 1180 factor = 1; | |
| 1181 for (agp = refs; agp; agp = agp->next) | |
| 1182 for (ref = agp->refs; ref; ref = ref->next) | |
| 1183 if (should_issue_prefetch_p (ref)) | |
| 1184 { | |
| 1185 mod_constraint = ref->prefetch_mod; | |
| 1186 nfactor = least_common_multiple (mod_constraint, factor); | |
| 1187 if (nfactor <= upper_bound) | |
| 1188 factor = nfactor; | |
| 1189 } | |
| 1190 | |
| 1191 if (!should_unroll_loop_p (loop, desc, factor)) | |
| 1192 return 1; | |
| 1193 | |
| 1194 return factor; | |
| 1195 } | |
| 1196 | |
| 1197 /* Returns the total volume of the memory references REFS, taking into account | |
| 1198 reuses in the innermost loop and cache line size. TODO -- we should also | |
| 1199 take into account reuses across the iterations of the loops in the loop | |
| 1200 nest. */ | |
| 1201 | |
| 1202 static unsigned | |
| 1203 volume_of_references (struct mem_ref_group *refs) | |
| 1204 { | |
| 1205 unsigned volume = 0; | |
| 1206 struct mem_ref_group *gr; | |
| 1207 struct mem_ref *ref; | |
| 1208 | |
| 1209 for (gr = refs; gr; gr = gr->next) | |
| 1210 for (ref = gr->refs; ref; ref = ref->next) | |
| 1211 { | |
| 1212 /* Almost always reuses another value? */ | |
| 1213 if (ref->prefetch_before != PREFETCH_ALL) | |
| 1214 continue; | |
| 1215 | |
| 1216 /* If several iterations access the same cache line, use the size of | |
| 1217 the line divided by this number. Otherwise, a cache line is | |
| 1218 accessed in each iteration. TODO -- in the latter case, we should | |
| 1219 take the size of the reference into account, rounding it up on cache | |
| 1220 line size multiple. */ | |
| 1221 volume += L1_CACHE_LINE_SIZE / ref->prefetch_mod; | |
| 1222 } | |
| 1223 return volume; | |
| 1224 } | |
| 1225 | |
| 1226 /* Returns the volume of memory references accessed across VEC iterations of | |
| 1227 loops, whose sizes are described in the LOOP_SIZES array. N is the number | |
| 1228 of the loops in the nest (length of VEC and LOOP_SIZES vectors). */ | |
| 1229 | |
| 1230 static unsigned | |
| 1231 volume_of_dist_vector (lambda_vector vec, unsigned *loop_sizes, unsigned n) | |
| 1232 { | |
| 1233 unsigned i; | |
| 1234 | |
| 1235 for (i = 0; i < n; i++) | |
| 1236 if (vec[i] != 0) | |
| 1237 break; | |
| 1238 | |
| 1239 if (i == n) | |
| 1240 return 0; | |
| 1241 | |
| 1242 gcc_assert (vec[i] > 0); | |
| 1243 | |
| 1244 /* We ignore the parts of the distance vector in subloops, since usually | |
| 1245 the numbers of iterations are much smaller. */ | |
| 1246 return loop_sizes[i] * vec[i]; | |
| 1247 } | |
| 1248 | |
| 1249 /* Add the steps of ACCESS_FN multiplied by STRIDE to the array STRIDE | |
| 1250 at the position corresponding to the loop of the step. N is the depth | |
| 1251 of the considered loop nest, and, LOOP is its innermost loop. */ | |
| 1252 | |
| 1253 static void | |
| 1254 add_subscript_strides (tree access_fn, unsigned stride, | |
| 1255 HOST_WIDE_INT *strides, unsigned n, struct loop *loop) | |
| 1256 { | |
| 1257 struct loop *aloop; | |
| 1258 tree step; | |
| 1259 HOST_WIDE_INT astep; | |
| 1260 unsigned min_depth = loop_depth (loop) - n; | |
| 1261 | |
| 1262 while (TREE_CODE (access_fn) == POLYNOMIAL_CHREC) | |
| 1263 { | |
| 1264 aloop = get_chrec_loop (access_fn); | |
| 1265 step = CHREC_RIGHT (access_fn); | |
| 1266 access_fn = CHREC_LEFT (access_fn); | |
| 1267 | |
| 1268 if ((unsigned) loop_depth (aloop) <= min_depth) | |
| 1269 continue; | |
| 1270 | |
| 1271 if (host_integerp (step, 0)) | |
| 1272 astep = tree_low_cst (step, 0); | |
| 1273 else | |
| 1274 astep = L1_CACHE_LINE_SIZE; | |
| 1275 | |
| 1276 strides[n - 1 - loop_depth (loop) + loop_depth (aloop)] += astep * stride; | |
| 1277 | |
| 1278 } | |
| 1279 } | |
| 1280 | |
| 1281 /* Returns the volume of memory references accessed between two consecutive | |
| 1282 self-reuses of the reference DR. We consider the subscripts of DR in N | |
| 1283 loops, and LOOP_SIZES contains the volumes of accesses in each of the | |
| 1284 loops. LOOP is the innermost loop of the current loop nest. */ | |
| 1285 | |
| 1286 static unsigned | |
| 1287 self_reuse_distance (data_reference_p dr, unsigned *loop_sizes, unsigned n, | |
| 1288 struct loop *loop) | |
| 1289 { | |
| 1290 tree stride, access_fn; | |
| 1291 HOST_WIDE_INT *strides, astride; | |
| 1292 VEC (tree, heap) *access_fns; | |
| 1293 tree ref = DR_REF (dr); | |
| 1294 unsigned i, ret = ~0u; | |
| 1295 | |
| 1296 /* In the following example: | |
| 1297 | |
| 1298 for (i = 0; i < N; i++) | |
| 1299 for (j = 0; j < N; j++) | |
| 1300 use (a[j][i]); | |
| 1301 the same cache line is accessed each N steps (except if the change from | |
| 1302 i to i + 1 crosses the boundary of the cache line). Thus, for self-reuse, | |
| 1303 we cannot rely purely on the results of the data dependence analysis. | |
| 1304 | |
| 1305 Instead, we compute the stride of the reference in each loop, and consider | |
| 1306 the innermost loop in that the stride is less than cache size. */ | |
| 1307 | |
| 1308 strides = XCNEWVEC (HOST_WIDE_INT, n); | |
| 1309 access_fns = DR_ACCESS_FNS (dr); | |
| 1310 | |
| 1311 for (i = 0; VEC_iterate (tree, access_fns, i, access_fn); i++) | |
| 1312 { | |
| 1313 /* Keep track of the reference corresponding to the subscript, so that we | |
| 1314 know its stride. */ | |
| 1315 while (handled_component_p (ref) && TREE_CODE (ref) != ARRAY_REF) | |
| 1316 ref = TREE_OPERAND (ref, 0); | |
|
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1317 |
| 0 | 1318 if (TREE_CODE (ref) == ARRAY_REF) |
| 1319 { | |
| 1320 stride = TYPE_SIZE_UNIT (TREE_TYPE (ref)); | |
| 1321 if (host_integerp (stride, 1)) | |
| 1322 astride = tree_low_cst (stride, 1); | |
| 1323 else | |
| 1324 astride = L1_CACHE_LINE_SIZE; | |
| 1325 | |
| 1326 ref = TREE_OPERAND (ref, 0); | |
| 1327 } | |
| 1328 else | |
| 1329 astride = 1; | |
| 1330 | |
| 1331 add_subscript_strides (access_fn, astride, strides, n, loop); | |
| 1332 } | |
| 1333 | |
| 1334 for (i = n; i-- > 0; ) | |
| 1335 { | |
| 1336 unsigned HOST_WIDE_INT s; | |
| 1337 | |
| 1338 s = strides[i] < 0 ? -strides[i] : strides[i]; | |
| 1339 | |
| 1340 if (s < (unsigned) L1_CACHE_LINE_SIZE | |
| 1341 && (loop_sizes[i] | |
| 1342 > (unsigned) (L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION))) | |
| 1343 { | |
| 1344 ret = loop_sizes[i]; | |
| 1345 break; | |
| 1346 } | |
| 1347 } | |
| 1348 | |
| 1349 free (strides); | |
| 1350 return ret; | |
| 1351 } | |
| 1352 | |
| 1353 /* Determines the distance till the first reuse of each reference in REFS | |
| 1354 in the loop nest of LOOP. NO_OTHER_REFS is true if there are no other | |
| 1355 memory references in the loop. */ | |
| 1356 | |
| 1357 static void | |
| 1358 determine_loop_nest_reuse (struct loop *loop, struct mem_ref_group *refs, | |
| 1359 bool no_other_refs) | |
| 1360 { | |
| 1361 struct loop *nest, *aloop; | |
| 1362 VEC (data_reference_p, heap) *datarefs = NULL; | |
| 1363 VEC (ddr_p, heap) *dependences = NULL; | |
| 1364 struct mem_ref_group *gr; | |
| 1365 struct mem_ref *ref, *refb; | |
| 1366 VEC (loop_p, heap) *vloops = NULL; | |
| 1367 unsigned *loop_data_size; | |
| 1368 unsigned i, j, n; | |
| 1369 unsigned volume, dist, adist; | |
| 1370 HOST_WIDE_INT vol; | |
| 1371 data_reference_p dr; | |
| 1372 ddr_p dep; | |
| 1373 | |
| 1374 if (loop->inner) | |
| 1375 return; | |
| 1376 | |
| 1377 /* Find the outermost loop of the loop nest of loop (we require that | |
| 1378 there are no sibling loops inside the nest). */ | |
| 1379 nest = loop; | |
| 1380 while (1) | |
| 1381 { | |
| 1382 aloop = loop_outer (nest); | |
| 1383 | |
| 1384 if (aloop == current_loops->tree_root | |
| 1385 || aloop->inner->next) | |
| 1386 break; | |
| 1387 | |
| 1388 nest = aloop; | |
| 1389 } | |
| 1390 | |
| 1391 /* For each loop, determine the amount of data accessed in each iteration. | |
| 1392 We use this to estimate whether the reference is evicted from the | |
| 1393 cache before its reuse. */ | |
| 1394 find_loop_nest (nest, &vloops); | |
| 1395 n = VEC_length (loop_p, vloops); | |
| 1396 loop_data_size = XNEWVEC (unsigned, n); | |
| 1397 volume = volume_of_references (refs); | |
| 1398 i = n; | |
| 1399 while (i-- != 0) | |
| 1400 { | |
| 1401 loop_data_size[i] = volume; | |
| 1402 /* Bound the volume by the L2 cache size, since above this bound, | |
| 1403 all dependence distances are equivalent. */ | |
| 1404 if (volume > L2_CACHE_SIZE_BYTES) | |
| 1405 continue; | |
| 1406 | |
| 1407 aloop = VEC_index (loop_p, vloops, i); | |
| 1408 vol = estimated_loop_iterations_int (aloop, false); | |
| 1409 if (vol < 0) | |
| 1410 vol = expected_loop_iterations (aloop); | |
| 1411 volume *= vol; | |
| 1412 } | |
| 1413 | |
| 1414 /* Prepare the references in the form suitable for data dependence | |
| 1415 analysis. We ignore unanalyzable data references (the results | |
| 1416 are used just as a heuristics to estimate temporality of the | |
| 1417 references, hence we do not need to worry about correctness). */ | |
| 1418 for (gr = refs; gr; gr = gr->next) | |
| 1419 for (ref = gr->refs; ref; ref = ref->next) | |
| 1420 { | |
| 1421 dr = create_data_ref (nest, ref->mem, ref->stmt, !ref->write_p); | |
| 1422 | |
| 1423 if (dr) | |
| 1424 { | |
| 1425 ref->reuse_distance = volume; | |
| 1426 dr->aux = ref; | |
| 1427 VEC_safe_push (data_reference_p, heap, datarefs, dr); | |
| 1428 } | |
| 1429 else | |
| 1430 no_other_refs = false; | |
| 1431 } | |
| 1432 | |
| 1433 for (i = 0; VEC_iterate (data_reference_p, datarefs, i, dr); i++) | |
| 1434 { | |
| 1435 dist = self_reuse_distance (dr, loop_data_size, n, loop); | |
| 1436 ref = (struct mem_ref *) dr->aux; | |
| 1437 if (ref->reuse_distance > dist) | |
| 1438 ref->reuse_distance = dist; | |
| 1439 | |
| 1440 if (no_other_refs) | |
| 1441 ref->independent_p = true; | |
| 1442 } | |
| 1443 | |
| 1444 compute_all_dependences (datarefs, &dependences, vloops, true); | |
| 1445 | |
| 1446 for (i = 0; VEC_iterate (ddr_p, dependences, i, dep); i++) | |
| 1447 { | |
| 1448 if (DDR_ARE_DEPENDENT (dep) == chrec_known) | |
| 1449 continue; | |
| 1450 | |
| 1451 ref = (struct mem_ref *) DDR_A (dep)->aux; | |
| 1452 refb = (struct mem_ref *) DDR_B (dep)->aux; | |
| 1453 | |
| 1454 if (DDR_ARE_DEPENDENT (dep) == chrec_dont_know | |
| 1455 || DDR_NUM_DIST_VECTS (dep) == 0) | |
| 1456 { | |
| 1457 /* If the dependence cannot be analyzed, assume that there might be | |
| 1458 a reuse. */ | |
| 1459 dist = 0; | |
|
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1460 |
| 0 | 1461 ref->independent_p = false; |
| 1462 refb->independent_p = false; | |
| 1463 } | |
| 1464 else | |
| 1465 { | |
| 1466 /* The distance vectors are normalized to be always lexicographically | |
| 1467 positive, hence we cannot tell just from them whether DDR_A comes | |
| 1468 before DDR_B or vice versa. However, it is not important, | |
| 1469 anyway -- if DDR_A is close to DDR_B, then it is either reused in | |
| 1470 DDR_B (and it is not nontemporal), or it reuses the value of DDR_B | |
| 1471 in cache (and marking it as nontemporal would not affect | |
| 1472 anything). */ | |
| 1473 | |
| 1474 dist = volume; | |
| 1475 for (j = 0; j < DDR_NUM_DIST_VECTS (dep); j++) | |
| 1476 { | |
| 1477 adist = volume_of_dist_vector (DDR_DIST_VECT (dep, j), | |
| 1478 loop_data_size, n); | |
| 1479 | |
| 1480 /* If this is a dependence in the innermost loop (i.e., the | |
| 1481 distances in all superloops are zero) and it is not | |
| 1482 the trivial self-dependence with distance zero, record that | |
| 1483 the references are not completely independent. */ | |
| 1484 if (lambda_vector_zerop (DDR_DIST_VECT (dep, j), n - 1) | |
| 1485 && (ref != refb | |
| 1486 || DDR_DIST_VECT (dep, j)[n-1] != 0)) | |
| 1487 { | |
| 1488 ref->independent_p = false; | |
| 1489 refb->independent_p = false; | |
| 1490 } | |
| 1491 | |
| 1492 /* Ignore accesses closer than | |
| 1493 L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION, | |
| 1494 so that we use nontemporal prefetches e.g. if single memory | |
| 1495 location is accessed several times in a single iteration of | |
| 1496 the loop. */ | |
| 1497 if (adist < L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION) | |
| 1498 continue; | |
| 1499 | |
| 1500 if (adist < dist) | |
| 1501 dist = adist; | |
| 1502 } | |
| 1503 } | |
| 1504 | |
| 1505 if (ref->reuse_distance > dist) | |
| 1506 ref->reuse_distance = dist; | |
| 1507 if (refb->reuse_distance > dist) | |
| 1508 refb->reuse_distance = dist; | |
| 1509 } | |
| 1510 | |
| 1511 free_dependence_relations (dependences); | |
| 1512 free_data_refs (datarefs); | |
| 1513 free (loop_data_size); | |
| 1514 | |
| 1515 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 1516 { | |
| 1517 fprintf (dump_file, "Reuse distances:\n"); | |
| 1518 for (gr = refs; gr; gr = gr->next) | |
| 1519 for (ref = gr->refs; ref; ref = ref->next) | |
| 1520 fprintf (dump_file, " ref %p distance %u\n", | |
| 1521 (void *) ref, ref->reuse_distance); | |
| 1522 } | |
| 1523 } | |
| 1524 | |
|
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1525 /* Do a cost-benefit analysis to determine if prefetching is profitable |
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1526 for the current loop given the following parameters: |
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1527 AHEAD: the iteration ahead distance, |
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1528 EST_NITER: the estimated trip count, |
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1529 NINSNS: estimated number of instructions in the loop, |
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1530 PREFETCH_COUNT: an estimate of the number of prefetches |
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1531 MEM_REF_COUNT: total number of memory references in the loop. */ |
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1532 |
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1533 static bool |
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1534 is_loop_prefetching_profitable (unsigned ahead, HOST_WIDE_INT est_niter, |
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1535 unsigned ninsns, unsigned prefetch_count, |
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1536 unsigned mem_ref_count) |
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1537 { |
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1538 int insn_to_mem_ratio, insn_to_prefetch_ratio; |
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1539 |
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1540 if (mem_ref_count == 0) |
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1541 return false; |
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1542 |
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1543 /* Prefetching improves performance by overlapping cache missing |
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1544 memory accesses with CPU operations. If the loop does not have |
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1545 enough CPU operations to overlap with memory operations, prefetching |
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1546 won't give a significant benefit. One approximate way of checking |
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1547 this is to require the ratio of instructions to memory references to |
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1548 be above a certain limit. This approximation works well in practice. |
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1549 TODO: Implement a more precise computation by estimating the time |
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1550 for each CPU or memory op in the loop. Time estimates for memory ops |
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1551 should account for cache misses. */ |
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1552 insn_to_mem_ratio = ninsns / mem_ref_count; |
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1553 |
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1554 if (insn_to_mem_ratio < PREFETCH_MIN_INSN_TO_MEM_RATIO) |
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1555 return false; |
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1556 |
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1557 /* Profitability of prefetching is highly dependent on the trip count. |
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1558 For a given AHEAD distance, the first AHEAD iterations do not benefit |
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diff
changeset
|
1559 from prefetching, and the last AHEAD iterations execute useless |
|
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diff
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|
1560 prefetches. So, if the trip count is not large enough relative to AHEAD, |
|
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|
1561 prefetching may cause serious performance degradation. To avoid this |
|
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diff
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|
1562 problem when the trip count is not known at compile time, we |
|
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diff
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|
1563 conservatively skip loops with high prefetching costs. For now, only |
|
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|
1564 the I-cache cost is considered. The relative I-cache cost is estimated |
|
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|
1565 by taking the ratio between the number of prefetches and the total |
|
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|
1566 number of instructions. Since we are using integer arithmetic, we |
|
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|
1567 compute the reciprocal of this ratio. |
|
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|
1568 TODO: Account for loop unrolling, which may reduce the costs of |
|
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|
1569 shorter stride prefetches. Note that not accounting for loop |
|
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|
1570 unrolling over-estimates the cost and hence gives more conservative |
|
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|
1571 results. */ |
|
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|
1572 if (est_niter < 0) |
|
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|
1573 { |
|
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|
1574 insn_to_prefetch_ratio = ninsns / prefetch_count; |
|
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|
1575 return insn_to_prefetch_ratio >= MIN_INSN_TO_PREFETCH_RATIO; |
|
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|
1576 } |
|
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|
1577 |
|
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|
1578 if (est_niter <= (HOST_WIDE_INT) ahead) |
|
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|
1579 { |
|
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|
1580 if (dump_file && (dump_flags & TDF_DETAILS)) |
|
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|
1581 fprintf (dump_file, |
|
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|
1582 "Not prefetching -- loop estimated to roll only %d times\n", |
|
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|
1583 (int) est_niter); |
|
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|
1584 return false; |
|
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diff
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|
1585 } |
|
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|
1586 return true; |
|
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|
1587 } |
|
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|
1588 |
|
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|
1589 |
| 0 | 1590 /* Issue prefetch instructions for array references in LOOP. Returns |
| 1591 true if the LOOP was unrolled. */ | |
| 1592 | |
| 1593 static bool | |
| 1594 loop_prefetch_arrays (struct loop *loop) | |
| 1595 { | |
| 1596 struct mem_ref_group *refs; | |
| 1597 unsigned ahead, ninsns, time, unroll_factor; | |
| 1598 HOST_WIDE_INT est_niter; | |
| 1599 struct tree_niter_desc desc; | |
| 1600 bool unrolled = false, no_other_refs; | |
|
55
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|
1601 unsigned prefetch_count; |
|
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|
1602 unsigned mem_ref_count; |
| 0 | 1603 |
| 1604 if (optimize_loop_nest_for_size_p (loop)) | |
| 1605 { | |
| 1606 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 1607 fprintf (dump_file, " ignored (cold area)\n"); | |
| 1608 return false; | |
| 1609 } | |
| 1610 | |
| 1611 /* Step 1: gather the memory references. */ | |
|
55
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|
1612 refs = gather_memory_references (loop, &no_other_refs, &mem_ref_count); |
| 0 | 1613 |
| 1614 /* Step 2: estimate the reuse effects. */ | |
| 1615 prune_by_reuse (refs); | |
| 1616 | |
|
55
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diff
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|
1617 prefetch_count = estimate_prefetch_count (refs); |
|
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diff
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|
1618 if (prefetch_count == 0) |
| 0 | 1619 goto fail; |
| 1620 | |
| 1621 determine_loop_nest_reuse (loop, refs, no_other_refs); | |
| 1622 | |
| 1623 /* Step 3: determine the ahead and unroll factor. */ | |
| 1624 | |
| 1625 /* FIXME: the time should be weighted by the probabilities of the blocks in | |
| 1626 the loop body. */ | |
| 1627 time = tree_num_loop_insns (loop, &eni_time_weights); | |
| 1628 ahead = (PREFETCH_LATENCY + time - 1) / time; | |
| 1629 est_niter = estimated_loop_iterations_int (loop, false); | |
| 1630 | |
| 1631 ninsns = tree_num_loop_insns (loop, &eni_size_weights); | |
| 1632 unroll_factor = determine_unroll_factor (loop, refs, ninsns, &desc, | |
| 1633 est_niter); | |
| 1634 if (dump_file && (dump_flags & TDF_DETAILS)) | |
|
55
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diff
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|
1635 fprintf (dump_file, "Ahead %d, unroll factor %d, trip count " |
|
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diff
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|
1636 HOST_WIDE_INT_PRINT_DEC "\n" |
|
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diff
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|
1637 "insn count %d, mem ref count %d, prefetch count %d\n", |
|
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diff
changeset
|
1638 ahead, unroll_factor, est_niter, |
|
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diff
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|
1639 ninsns, mem_ref_count, prefetch_count); |
|
77e2b8dfacca
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diff
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|
1640 |
|
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diff
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|
1641 if (!is_loop_prefetching_profitable (ahead, est_niter, ninsns, |
|
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diff
changeset
|
1642 prefetch_count, mem_ref_count)) |
|
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|
1643 goto fail; |
|
77e2b8dfacca
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0
diff
changeset
|
1644 |
|
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diff
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|
1645 mark_nontemporal_stores (loop, refs); |
| 0 | 1646 |
| 1647 /* Step 4: what to prefetch? */ | |
| 1648 if (!schedule_prefetches (refs, unroll_factor, ahead)) | |
| 1649 goto fail; | |
| 1650 | |
| 1651 /* Step 5: unroll the loop. TODO -- peeling of first and last few | |
| 1652 iterations so that we do not issue superfluous prefetches. */ | |
| 1653 if (unroll_factor != 1) | |
| 1654 { | |
| 1655 tree_unroll_loop (loop, unroll_factor, | |
| 1656 single_dom_exit (loop), &desc); | |
| 1657 unrolled = true; | |
| 1658 } | |
| 1659 | |
| 1660 /* Step 6: issue the prefetches. */ | |
| 1661 issue_prefetches (refs, unroll_factor, ahead); | |
| 1662 | |
| 1663 fail: | |
| 1664 release_mem_refs (refs); | |
| 1665 return unrolled; | |
| 1666 } | |
| 1667 | |
| 1668 /* Issue prefetch instructions for array references in loops. */ | |
| 1669 | |
| 1670 unsigned int | |
| 1671 tree_ssa_prefetch_arrays (void) | |
| 1672 { | |
| 1673 loop_iterator li; | |
| 1674 struct loop *loop; | |
| 1675 bool unrolled = false; | |
| 1676 int todo_flags = 0; | |
| 1677 | |
| 1678 if (!HAVE_prefetch | |
| 1679 /* It is possible to ask compiler for say -mtune=i486 -march=pentium4. | |
| 1680 -mtune=i486 causes us having PREFETCH_BLOCK 0, since this is part | |
| 1681 of processor costs and i486 does not have prefetch, but | |
| 1682 -march=pentium4 causes HAVE_prefetch to be true. Ugh. */ | |
| 1683 || PREFETCH_BLOCK == 0) | |
| 1684 return 0; | |
| 1685 | |
| 1686 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 1687 { | |
| 1688 fprintf (dump_file, "Prefetching parameters:\n"); | |
| 1689 fprintf (dump_file, " simultaneous prefetches: %d\n", | |
| 1690 SIMULTANEOUS_PREFETCHES); | |
| 1691 fprintf (dump_file, " prefetch latency: %d\n", PREFETCH_LATENCY); | |
| 1692 fprintf (dump_file, " prefetch block size: %d\n", PREFETCH_BLOCK); | |
| 1693 fprintf (dump_file, " L1 cache size: %d lines, %d kB\n", | |
| 1694 L1_CACHE_SIZE_BYTES / L1_CACHE_LINE_SIZE, L1_CACHE_SIZE); | |
| 1695 fprintf (dump_file, " L1 cache line size: %d\n", L1_CACHE_LINE_SIZE); | |
| 1696 fprintf (dump_file, " L2 cache size: %d kB\n", L2_CACHE_SIZE); | |
|
55
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0
diff
changeset
|
1697 fprintf (dump_file, " min insn-to-prefetch ratio: %d \n", |
|
77e2b8dfacca
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0
diff
changeset
|
1698 MIN_INSN_TO_PREFETCH_RATIO); |
|
77e2b8dfacca
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0
diff
changeset
|
1699 fprintf (dump_file, " min insn-to-mem ratio: %d \n", |
|
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|
1700 PREFETCH_MIN_INSN_TO_MEM_RATIO); |
| 0 | 1701 fprintf (dump_file, "\n"); |
| 1702 } | |
| 1703 | |
| 1704 initialize_original_copy_tables (); | |
| 1705 | |
| 1706 if (!built_in_decls[BUILT_IN_PREFETCH]) | |
| 1707 { | |
| 1708 tree type = build_function_type (void_type_node, | |
| 1709 tree_cons (NULL_TREE, | |
| 1710 const_ptr_type_node, | |
| 1711 NULL_TREE)); | |
| 1712 tree decl = add_builtin_function ("__builtin_prefetch", type, | |
| 1713 BUILT_IN_PREFETCH, BUILT_IN_NORMAL, | |
| 1714 NULL, NULL_TREE); | |
| 1715 DECL_IS_NOVOPS (decl) = true; | |
| 1716 built_in_decls[BUILT_IN_PREFETCH] = decl; | |
| 1717 } | |
| 1718 | |
| 1719 /* We assume that size of cache line is a power of two, so verify this | |
| 1720 here. */ | |
| 1721 gcc_assert ((PREFETCH_BLOCK & (PREFETCH_BLOCK - 1)) == 0); | |
| 1722 | |
| 1723 FOR_EACH_LOOP (li, loop, LI_FROM_INNERMOST) | |
| 1724 { | |
| 1725 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 1726 fprintf (dump_file, "Processing loop %d:\n", loop->num); | |
| 1727 | |
| 1728 unrolled |= loop_prefetch_arrays (loop); | |
| 1729 | |
| 1730 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 1731 fprintf (dump_file, "\n\n"); | |
| 1732 } | |
| 1733 | |
| 1734 if (unrolled) | |
| 1735 { | |
| 1736 scev_reset (); | |
| 1737 todo_flags |= TODO_cleanup_cfg; | |
| 1738 } | |
| 1739 | |
| 1740 free_original_copy_tables (); | |
| 1741 return todo_flags; | |
| 1742 } |