Mercurial > hg > CbC > CbC_gcc
annotate gcc/tree-ssa-loop-prefetch.c @ 145:1830386684a0
gcc-9.2.0
| author | anatofuz |
|---|---|
| date | Thu, 13 Feb 2020 11:34:05 +0900 |
| parents | 84e7813d76e9 |
| children |
| rev | line source |
|---|---|
| 0 | 1 /* Array prefetching. |
| 145 | 2 Copyright (C) 2005-2020 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" | |
| 111 | 23 #include "backend.h" |
| 24 #include "target.h" | |
| 25 #include "rtl.h" | |
| 0 | 26 #include "tree.h" |
| 111 | 27 #include "gimple.h" |
| 28 #include "predict.h" | |
| 29 #include "tree-pass.h" | |
| 30 #include "gimple-ssa.h" | |
| 31 #include "optabs-query.h" | |
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32 #include "tree-pretty-print.h" |
| 111 | 33 #include "fold-const.h" |
| 34 #include "stor-layout.h" | |
| 35 #include "gimplify.h" | |
| 36 #include "gimple-iterator.h" | |
| 37 #include "gimplify-me.h" | |
| 38 #include "tree-ssa-loop-ivopts.h" | |
| 39 #include "tree-ssa-loop-manip.h" | |
| 40 #include "tree-ssa-loop-niter.h" | |
| 41 #include "tree-ssa-loop.h" | |
| 42 #include "ssa.h" | |
| 43 #include "tree-into-ssa.h" | |
| 0 | 44 #include "cfgloop.h" |
| 45 #include "tree-scalar-evolution.h" | |
| 46 #include "langhooks.h" | |
| 47 #include "tree-inline.h" | |
| 48 #include "tree-data-ref.h" | |
| 111 | 49 #include "diagnostic-core.h" |
| 50 #include "dbgcnt.h" | |
| 0 | 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 | |
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83 the cache line accessed by (5) is the same with probability only |
| 0 | 84 7/32. |
| 85 (5) has PREFETCH_MOD 1 as well. | |
| 86 | |
| 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 | |
| 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). | |
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103 |
| 0 | 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. | |
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108 |
| 0 | 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 | |
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113 A cost model is implemented to determine whether or not prefetching is |
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114 profitable for a given loop. The cost model has three heuristics: |
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115 |
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116 1. Function trip_count_to_ahead_ratio_too_small_p implements a |
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117 heuristic that determines whether or not the loop has too few |
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118 iterations (compared to ahead). Prefetching is not likely to be |
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119 beneficial if the trip count to ahead ratio is below a certain |
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120 minimum. |
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121 |
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122 2. Function mem_ref_count_reasonable_p implements a heuristic that |
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123 determines whether the given loop has enough CPU ops that can be |
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124 overlapped with cache missing memory ops. If not, the loop |
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125 won't benefit from prefetching. In the implementation, |
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126 prefetching is not considered beneficial if the ratio between |
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127 the instruction count and the mem ref count is below a certain |
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128 minimum. |
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129 |
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130 3. Function insn_to_prefetch_ratio_too_small_p implements a |
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131 heuristic that disables prefetching in a loop if the prefetching |
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132 cost is above a certain limit. The relative prefetching cost is |
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133 estimated by taking the ratio between the prefetch count and the |
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134 total intruction count (this models the I-cache cost). |
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135 |
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136 The limits used in these heuristics are defined as parameters with |
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137 reasonable default values. Machine-specific default values will be |
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138 added later. |
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139 |
| 0 | 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 | |
| 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 | |
| 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). */ | |
| 167 | |
| 168 #ifndef PREFETCH_BLOCK | |
| 145 | 169 #define PREFETCH_BLOCK param_l1_cache_line_size |
| 0 | 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 | |
| 187 is less then (1000 - ACCEPTABLE_MISS_RATE) per thousand. */ | |
| 188 | |
| 189 #ifndef ACCEPTABLE_MISS_RATE | |
| 190 #define ACCEPTABLE_MISS_RATE 50 | |
| 191 #endif | |
| 192 | |
| 145 | 193 #define L1_CACHE_SIZE_BYTES ((unsigned) (param_l1_cache_size * 1024)) |
| 194 #define L2_CACHE_SIZE_BYTES ((unsigned) (param_l2_cache_size * 1024)) | |
| 0 | 195 |
| 196 /* We consider a memory access nontemporal if it is not reused sooner than | |
| 197 after L2_CACHE_SIZE_BYTES of memory are accessed. However, we ignore | |
| 198 accesses closer than L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION, | |
| 199 so that we use nontemporal prefetches e.g. if single memory location | |
| 200 is accessed several times in a single iteration of the loop. */ | |
| 201 #define NONTEMPORAL_FRACTION 16 | |
| 202 | |
| 203 /* In case we have to emit a memory fence instruction after the loop that | |
| 204 uses nontemporal stores, this defines the builtin to use. */ | |
| 205 | |
| 206 #ifndef FENCE_FOLLOWING_MOVNT | |
| 207 #define FENCE_FOLLOWING_MOVNT NULL_TREE | |
| 208 #endif | |
| 209 | |
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210 /* It is not profitable to prefetch when the trip count is not at |
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211 least TRIP_COUNT_TO_AHEAD_RATIO times the prefetch ahead distance. |
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212 For example, in a loop with a prefetch ahead distance of 10, |
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213 supposing that TRIP_COUNT_TO_AHEAD_RATIO is equal to 4, it is |
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214 profitable to prefetch when the trip count is greater or equal to |
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215 40. In that case, 30 out of the 40 iterations will benefit from |
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216 prefetching. */ |
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217 |
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218 #ifndef TRIP_COUNT_TO_AHEAD_RATIO |
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219 #define TRIP_COUNT_TO_AHEAD_RATIO 4 |
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220 #endif |
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221 |
| 0 | 222 /* The group of references between that reuse may occur. */ |
| 223 | |
| 224 struct mem_ref_group | |
| 225 { | |
| 226 tree base; /* Base of the reference. */ | |
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227 tree step; /* Step of the reference. */ |
| 0 | 228 struct mem_ref *refs; /* References in the group. */ |
| 229 struct mem_ref_group *next; /* Next group of references. */ | |
| 111 | 230 unsigned int uid; /* Group UID, used only for debugging. */ |
| 0 | 231 }; |
| 232 | |
| 233 /* Assigned to PREFETCH_BEFORE when all iterations are to be prefetched. */ | |
| 234 | |
| 111 | 235 #define PREFETCH_ALL HOST_WIDE_INT_M1U |
| 0 | 236 |
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237 /* Do not generate a prefetch if the unroll factor is significantly less |
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238 than what is required by the prefetch. This is to avoid redundant |
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239 prefetches. For example, when prefetch_mod is 16 and unroll_factor is |
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240 2, prefetching requires unrolling the loop 16 times, but |
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241 the loop is actually unrolled twice. In this case (ratio = 8), |
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242 prefetching is not likely to be beneficial. */ |
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243 |
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244 #ifndef PREFETCH_MOD_TO_UNROLL_FACTOR_RATIO |
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245 #define PREFETCH_MOD_TO_UNROLL_FACTOR_RATIO 4 |
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246 #endif |
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247 |
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248 /* Some of the prefetch computations have quadratic complexity. We want to |
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249 avoid huge compile times and, therefore, want to limit the amount of |
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250 memory references per loop where we consider prefetching. */ |
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251 |
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252 #ifndef PREFETCH_MAX_MEM_REFS_PER_LOOP |
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253 #define PREFETCH_MAX_MEM_REFS_PER_LOOP 200 |
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254 #endif |
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255 |
| 0 | 256 /* The memory reference. */ |
| 257 | |
| 258 struct mem_ref | |
| 259 { | |
| 111 | 260 gimple *stmt; /* Statement in that the reference appears. */ |
| 0 | 261 tree mem; /* The reference. */ |
| 262 HOST_WIDE_INT delta; /* Constant offset of the reference. */ | |
| 263 struct mem_ref_group *group; /* The group of references it belongs to. */ | |
| 264 unsigned HOST_WIDE_INT prefetch_mod; | |
| 265 /* Prefetch only each PREFETCH_MOD-th | |
| 266 iteration. */ | |
| 267 unsigned HOST_WIDE_INT prefetch_before; | |
| 268 /* Prefetch only first PREFETCH_BEFORE | |
| 269 iterations. */ | |
| 270 unsigned reuse_distance; /* The amount of data accessed before the first | |
| 271 reuse of this value. */ | |
| 272 struct mem_ref *next; /* The next reference in the group. */ | |
| 111 | 273 unsigned int uid; /* Ref UID, used only for debugging. */ |
| 0 | 274 unsigned write_p : 1; /* Is it a write? */ |
| 275 unsigned independent_p : 1; /* True if the reference is independent on | |
| 276 all other references inside the loop. */ | |
| 277 unsigned issue_prefetch_p : 1; /* Should we really issue the prefetch? */ | |
| 278 unsigned storent_p : 1; /* True if we changed the store to a | |
| 279 nontemporal one. */ | |
| 280 }; | |
| 281 | |
| 111 | 282 /* Dumps information about memory reference */ |
| 283 static void | |
| 284 dump_mem_details (FILE *file, tree base, tree step, | |
| 285 HOST_WIDE_INT delta, bool write_p) | |
| 286 { | |
| 287 fprintf (file, "(base "); | |
| 288 print_generic_expr (file, base, TDF_SLIM); | |
| 289 fprintf (file, ", step "); | |
| 290 if (cst_and_fits_in_hwi (step)) | |
| 291 fprintf (file, HOST_WIDE_INT_PRINT_DEC, int_cst_value (step)); | |
| 292 else | |
| 293 print_generic_expr (file, step, TDF_SLIM); | |
| 294 fprintf (file, ")\n"); | |
| 295 fprintf (file, " delta " HOST_WIDE_INT_PRINT_DEC "\n", delta); | |
| 296 fprintf (file, " %s\n\n", write_p ? "write" : "read"); | |
| 297 } | |
| 298 | |
| 0 | 299 /* Dumps information about reference REF to FILE. */ |
| 300 | |
| 301 static void | |
| 302 dump_mem_ref (FILE *file, struct mem_ref *ref) | |
| 303 { | |
| 111 | 304 fprintf (file, "reference %u:%u (", ref->group->uid, ref->uid); |
| 305 print_generic_expr (file, ref->mem, TDF_SLIM); | |
| 0 | 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 * | |
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313 find_or_create_group (struct mem_ref_group **groups, tree base, tree step) |
| 0 | 314 { |
| 111 | 315 /* Global count for setting struct mem_ref_group->uid. */ |
| 316 static unsigned int last_mem_ref_group_uid = 0; | |
| 317 | |
| 0 | 318 struct mem_ref_group *group; |
| 319 | |
| 320 for (; *groups; groups = &(*groups)->next) | |
| 321 { | |
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322 if (operand_equal_p ((*groups)->step, step, 0) |
| 0 | 323 && operand_equal_p ((*groups)->base, base, 0)) |
| 324 return *groups; | |
| 325 | |
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326 /* If step is an integer constant, keep the list of groups sorted |
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327 by decreasing step. */ |
| 111 | 328 if (cst_and_fits_in_hwi ((*groups)->step) && cst_and_fits_in_hwi (step) |
| 329 && int_cst_value ((*groups)->step) < int_cst_value (step)) | |
| 0 | 330 break; |
| 331 } | |
| 332 | |
| 333 group = XNEW (struct mem_ref_group); | |
| 334 group->base = base; | |
| 335 group->step = step; | |
| 336 group->refs = NULL; | |
| 111 | 337 group->uid = ++last_mem_ref_group_uid; |
| 0 | 338 group->next = *groups; |
| 339 *groups = group; | |
| 340 | |
| 341 return group; | |
| 342 } | |
| 343 | |
| 344 /* Records a memory reference MEM in GROUP with offset DELTA and write status | |
| 345 WRITE_P. The reference occurs in statement STMT. */ | |
| 346 | |
| 347 static void | |
| 111 | 348 record_ref (struct mem_ref_group *group, gimple *stmt, tree mem, |
| 0 | 349 HOST_WIDE_INT delta, bool write_p) |
| 350 { | |
| 111 | 351 unsigned int last_mem_ref_uid = 0; |
| 0 | 352 struct mem_ref **aref; |
| 353 | |
| 354 /* Do not record the same address twice. */ | |
| 355 for (aref = &group->refs; *aref; aref = &(*aref)->next) | |
| 356 { | |
| 111 | 357 last_mem_ref_uid = (*aref)->uid; |
| 358 | |
| 0 | 359 /* It does not have to be possible for write reference to reuse the read |
| 360 prefetch, or vice versa. */ | |
| 361 if (!WRITE_CAN_USE_READ_PREFETCH | |
| 362 && write_p | |
| 363 && !(*aref)->write_p) | |
| 364 continue; | |
| 365 if (!READ_CAN_USE_WRITE_PREFETCH | |
| 366 && !write_p | |
| 367 && (*aref)->write_p) | |
| 368 continue; | |
| 369 | |
| 370 if ((*aref)->delta == delta) | |
| 371 return; | |
| 372 } | |
| 373 | |
| 374 (*aref) = XNEW (struct mem_ref); | |
| 375 (*aref)->stmt = stmt; | |
| 376 (*aref)->mem = mem; | |
| 377 (*aref)->delta = delta; | |
| 378 (*aref)->write_p = write_p; | |
| 379 (*aref)->prefetch_before = PREFETCH_ALL; | |
| 380 (*aref)->prefetch_mod = 1; | |
| 381 (*aref)->reuse_distance = 0; | |
| 382 (*aref)->issue_prefetch_p = false; | |
| 383 (*aref)->group = group; | |
| 384 (*aref)->next = NULL; | |
| 385 (*aref)->independent_p = false; | |
| 386 (*aref)->storent_p = false; | |
| 111 | 387 (*aref)->uid = last_mem_ref_uid + 1; |
| 0 | 388 |
| 389 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 111 | 390 { |
| 391 dump_mem_ref (dump_file, *aref); | |
| 392 | |
| 393 fprintf (dump_file, " group %u ", group->uid); | |
| 394 dump_mem_details (dump_file, group->base, group->step, delta, | |
| 395 write_p); | |
| 396 } | |
| 0 | 397 } |
| 398 | |
| 399 /* Release memory references in GROUPS. */ | |
| 400 | |
| 401 static void | |
| 402 release_mem_refs (struct mem_ref_group *groups) | |
| 403 { | |
| 404 struct mem_ref_group *next_g; | |
| 405 struct mem_ref *ref, *next_r; | |
| 406 | |
| 407 for (; groups; groups = next_g) | |
| 408 { | |
| 409 next_g = groups->next; | |
| 410 for (ref = groups->refs; ref; ref = next_r) | |
| 411 { | |
| 412 next_r = ref->next; | |
| 413 free (ref); | |
| 414 } | |
| 415 free (groups); | |
| 416 } | |
| 417 } | |
| 418 | |
| 419 /* A structure used to pass arguments to idx_analyze_ref. */ | |
| 420 | |
| 421 struct ar_data | |
| 422 { | |
| 145 | 423 class loop *loop; /* Loop of the reference. */ |
| 111 | 424 gimple *stmt; /* Statement of the reference. */ |
|
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425 tree *step; /* Step of the memory reference. */ |
| 0 | 426 HOST_WIDE_INT *delta; /* Offset of the memory reference. */ |
| 427 }; | |
| 428 | |
| 429 /* Analyzes a single INDEX of a memory reference to obtain information | |
| 430 described at analyze_ref. Callback for for_each_index. */ | |
| 431 | |
| 432 static bool | |
| 433 idx_analyze_ref (tree base, tree *index, void *data) | |
| 434 { | |
| 435 struct ar_data *ar_data = (struct ar_data *) data; | |
| 436 tree ibase, step, stepsize; | |
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437 HOST_WIDE_INT idelta = 0, imult = 1; |
| 0 | 438 affine_iv iv; |
| 439 | |
| 440 if (!simple_iv (ar_data->loop, loop_containing_stmt (ar_data->stmt), | |
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441 *index, &iv, true)) |
| 0 | 442 return false; |
| 443 ibase = iv.base; | |
| 444 step = iv.step; | |
| 445 | |
| 446 if (TREE_CODE (ibase) == POINTER_PLUS_EXPR | |
| 447 && cst_and_fits_in_hwi (TREE_OPERAND (ibase, 1))) | |
| 448 { | |
| 449 idelta = int_cst_value (TREE_OPERAND (ibase, 1)); | |
| 450 ibase = TREE_OPERAND (ibase, 0); | |
| 451 } | |
| 452 if (cst_and_fits_in_hwi (ibase)) | |
| 453 { | |
| 454 idelta += int_cst_value (ibase); | |
| 455 ibase = build_int_cst (TREE_TYPE (ibase), 0); | |
| 456 } | |
| 457 | |
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458 if (TREE_CODE (base) == ARRAY_REF) |
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459 { |
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460 stepsize = array_ref_element_size (base); |
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461 if (!cst_and_fits_in_hwi (stepsize)) |
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462 return false; |
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463 imult = int_cst_value (stepsize); |
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464 step = fold_build2 (MULT_EXPR, sizetype, |
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465 fold_convert (sizetype, step), |
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466 fold_convert (sizetype, stepsize)); |
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467 idelta *= imult; |
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468 } |
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469 |
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470 if (*ar_data->step == NULL_TREE) |
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471 *ar_data->step = step; |
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472 else |
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473 *ar_data->step = fold_build2 (PLUS_EXPR, sizetype, |
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474 fold_convert (sizetype, *ar_data->step), |
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475 fold_convert (sizetype, step)); |
| 0 | 476 *ar_data->delta += idelta; |
| 477 *index = ibase; | |
| 478 | |
| 479 return true; | |
| 480 } | |
| 481 | |
| 482 /* Tries to express REF_P in shape &BASE + STEP * iter + DELTA, where DELTA and | |
| 483 STEP are integer constants and iter is number of iterations of LOOP. The | |
| 484 reference occurs in statement STMT. Strips nonaddressable component | |
| 485 references from REF_P. */ | |
| 486 | |
| 487 static bool | |
| 145 | 488 analyze_ref (class loop *loop, tree *ref_p, tree *base, |
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489 tree *step, HOST_WIDE_INT *delta, |
| 111 | 490 gimple *stmt) |
| 0 | 491 { |
| 492 struct ar_data ar_data; | |
| 493 tree off; | |
| 494 HOST_WIDE_INT bit_offset; | |
| 495 tree ref = *ref_p; | |
| 496 | |
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497 *step = NULL_TREE; |
| 0 | 498 *delta = 0; |
| 499 | |
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500 /* First strip off the component references. Ignore bitfields. |
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501 Also strip off the real and imagine parts of a complex, so that |
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502 they can have the same base. */ |
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503 if (TREE_CODE (ref) == REALPART_EXPR |
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504 || TREE_CODE (ref) == IMAGPART_EXPR |
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505 || (TREE_CODE (ref) == COMPONENT_REF |
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506 && DECL_NONADDRESSABLE_P (TREE_OPERAND (ref, 1)))) |
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507 { |
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508 if (TREE_CODE (ref) == IMAGPART_EXPR) |
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509 *delta += int_size_in_bytes (TREE_TYPE (ref)); |
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510 ref = TREE_OPERAND (ref, 0); |
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511 } |
| 0 | 512 |
| 513 *ref_p = ref; | |
| 514 | |
| 515 for (; TREE_CODE (ref) == COMPONENT_REF; ref = TREE_OPERAND (ref, 0)) | |
| 516 { | |
| 517 off = DECL_FIELD_BIT_OFFSET (TREE_OPERAND (ref, 1)); | |
| 518 bit_offset = TREE_INT_CST_LOW (off); | |
| 519 gcc_assert (bit_offset % BITS_PER_UNIT == 0); | |
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520 |
| 0 | 521 *delta += bit_offset / BITS_PER_UNIT; |
| 522 } | |
| 523 | |
| 524 *base = unshare_expr (ref); | |
| 525 ar_data.loop = loop; | |
| 526 ar_data.stmt = stmt; | |
| 527 ar_data.step = step; | |
| 528 ar_data.delta = delta; | |
| 529 return for_each_index (base, idx_analyze_ref, &ar_data); | |
| 530 } | |
| 531 | |
| 532 /* Record a memory reference REF to the list REFS. The reference occurs in | |
| 533 LOOP in statement STMT and it is write if WRITE_P. Returns true if the | |
| 534 reference was recorded, false otherwise. */ | |
| 535 | |
| 536 static bool | |
| 145 | 537 gather_memory_references_ref (class loop *loop, struct mem_ref_group **refs, |
| 111 | 538 tree ref, bool write_p, gimple *stmt) |
| 0 | 539 { |
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540 tree base, step; |
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541 HOST_WIDE_INT delta; |
| 0 | 542 struct mem_ref_group *agrp; |
| 543 | |
| 544 if (get_base_address (ref) == NULL) | |
| 545 return false; | |
| 546 | |
| 547 if (!analyze_ref (loop, &ref, &base, &step, &delta, stmt)) | |
| 548 return false; | |
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549 /* If analyze_ref fails the default is a NULL_TREE. We can stop here. */ |
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550 if (step == NULL_TREE) |
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551 return false; |
| 0 | 552 |
|
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553 /* Stop if the address of BASE could not be taken. */ |
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554 if (may_be_nonaddressable_p (base)) |
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555 return false; |
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556 |
| 111 | 557 /* Limit non-constant step prefetching only to the innermost loops and |
| 558 only when the step is loop invariant in the entire loop nest. */ | |
| 559 if (!cst_and_fits_in_hwi (step)) | |
| 560 { | |
| 561 if (loop->inner != NULL) | |
| 562 { | |
| 563 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 564 { | |
| 565 fprintf (dump_file, "Memory expression %p\n",(void *) ref ); | |
| 566 print_generic_expr (dump_file, ref, TDF_SLIM); | |
| 567 fprintf (dump_file,":"); | |
| 568 dump_mem_details (dump_file, base, step, delta, write_p); | |
| 569 fprintf (dump_file, | |
| 570 "Ignoring %p, non-constant step prefetching is " | |
| 571 "limited to inner most loops \n", | |
| 572 (void *) ref); | |
| 573 } | |
| 574 return false; | |
| 575 } | |
| 576 else | |
| 577 { | |
| 578 if (!expr_invariant_in_loop_p (loop_outermost (loop), step)) | |
| 579 { | |
| 580 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 581 { | |
| 582 fprintf (dump_file, "Memory expression %p\n",(void *) ref ); | |
| 583 print_generic_expr (dump_file, ref, TDF_SLIM); | |
| 584 fprintf (dump_file,":"); | |
| 585 dump_mem_details (dump_file, base, step, delta, write_p); | |
| 586 fprintf (dump_file, | |
| 587 "Not prefetching, ignoring %p due to " | |
| 588 "loop variant step\n", | |
| 589 (void *) ref); | |
| 590 } | |
| 591 return false; | |
| 592 } | |
| 593 } | |
| 594 } | |
|
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595 |
| 0 | 596 /* Now we know that REF = &BASE + STEP * iter + DELTA, where DELTA and STEP |
| 597 are integer constants. */ | |
| 598 agrp = find_or_create_group (refs, base, step); | |
| 599 record_ref (agrp, stmt, ref, delta, write_p); | |
| 600 | |
| 601 return true; | |
| 602 } | |
| 603 | |
| 604 /* Record the suitable memory references in LOOP. NO_OTHER_REFS is set to | |
| 605 true if there are no other memory references inside the loop. */ | |
| 606 | |
| 607 static struct mem_ref_group * | |
| 145 | 608 gather_memory_references (class loop *loop, bool *no_other_refs, unsigned *ref_count) |
| 0 | 609 { |
| 610 basic_block *body = get_loop_body_in_dom_order (loop); | |
| 611 basic_block bb; | |
| 612 unsigned i; | |
| 613 gimple_stmt_iterator bsi; | |
| 111 | 614 gimple *stmt; |
| 0 | 615 tree lhs, rhs; |
| 616 struct mem_ref_group *refs = NULL; | |
| 617 | |
| 618 *no_other_refs = true; | |
|
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619 *ref_count = 0; |
| 0 | 620 |
| 621 /* Scan the loop body in order, so that the former references precede the | |
| 622 later ones. */ | |
| 623 for (i = 0; i < loop->num_nodes; i++) | |
| 624 { | |
| 625 bb = body[i]; | |
| 626 if (bb->loop_father != loop) | |
| 627 continue; | |
| 628 | |
| 629 for (bsi = gsi_start_bb (bb); !gsi_end_p (bsi); gsi_next (&bsi)) | |
| 630 { | |
| 631 stmt = gsi_stmt (bsi); | |
| 632 | |
| 633 if (gimple_code (stmt) != GIMPLE_ASSIGN) | |
| 634 { | |
|
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635 if (gimple_vuse (stmt) |
| 0 | 636 || (is_gimple_call (stmt) |
| 637 && !(gimple_call_flags (stmt) & ECF_CONST))) | |
| 638 *no_other_refs = false; | |
| 639 continue; | |
| 640 } | |
| 641 | |
| 111 | 642 if (! gimple_vuse (stmt)) |
| 643 continue; | |
| 644 | |
| 0 | 645 lhs = gimple_assign_lhs (stmt); |
| 646 rhs = gimple_assign_rhs1 (stmt); | |
| 647 | |
| 648 if (REFERENCE_CLASS_P (rhs)) | |
|
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649 { |
| 0 | 650 *no_other_refs &= gather_memory_references_ref (loop, &refs, |
| 651 rhs, false, stmt); | |
|
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652 *ref_count += 1; |
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653 } |
| 0 | 654 if (REFERENCE_CLASS_P (lhs)) |
|
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655 { |
| 0 | 656 *no_other_refs &= gather_memory_references_ref (loop, &refs, |
| 657 lhs, true, stmt); | |
|
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658 *ref_count += 1; |
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659 } |
| 0 | 660 } |
| 661 } | |
| 662 free (body); | |
| 663 | |
| 664 return refs; | |
| 665 } | |
| 666 | |
| 667 /* Prune the prefetch candidate REF using the self-reuse. */ | |
| 668 | |
| 669 static void | |
| 670 prune_ref_by_self_reuse (struct mem_ref *ref) | |
| 671 { | |
|
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672 HOST_WIDE_INT step; |
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673 bool backward; |
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674 |
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675 /* If the step size is non constant, we cannot calculate prefetch_mod. */ |
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676 if (!cst_and_fits_in_hwi (ref->group->step)) |
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677 return; |
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678 |
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679 step = int_cst_value (ref->group->step); |
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680 |
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681 backward = step < 0; |
| 0 | 682 |
| 683 if (step == 0) | |
| 684 { | |
| 685 /* Prefetch references to invariant address just once. */ | |
| 686 ref->prefetch_before = 1; | |
| 687 return; | |
| 688 } | |
| 689 | |
| 690 if (backward) | |
| 691 step = -step; | |
| 692 | |
| 693 if (step > PREFETCH_BLOCK) | |
| 694 return; | |
| 695 | |
| 696 if ((backward && HAVE_BACKWARD_PREFETCH) | |
| 697 || (!backward && HAVE_FORWARD_PREFETCH)) | |
| 698 { | |
| 699 ref->prefetch_before = 1; | |
| 700 return; | |
| 701 } | |
| 702 | |
| 703 ref->prefetch_mod = PREFETCH_BLOCK / step; | |
| 704 } | |
| 705 | |
| 706 /* Divides X by BY, rounding down. */ | |
| 707 | |
| 708 static HOST_WIDE_INT | |
| 709 ddown (HOST_WIDE_INT x, unsigned HOST_WIDE_INT by) | |
| 710 { | |
| 711 gcc_assert (by > 0); | |
| 712 | |
| 713 if (x >= 0) | |
| 111 | 714 return x / (HOST_WIDE_INT) by; |
| 0 | 715 else |
| 111 | 716 return (x + (HOST_WIDE_INT) by - 1) / (HOST_WIDE_INT) by; |
| 0 | 717 } |
| 718 | |
|
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719 /* Given a CACHE_LINE_SIZE and two inductive memory references |
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720 with a common STEP greater than CACHE_LINE_SIZE and an address |
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721 difference DELTA, compute the probability that they will fall |
|
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722 in different cache lines. Return true if the computed miss rate |
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723 is not greater than the ACCEPTABLE_MISS_RATE. DISTINCT_ITERS is the |
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724 number of distinct iterations after which the pattern repeats itself. |
|
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725 ALIGN_UNIT is the unit of alignment in bytes. */ |
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726 |
|
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727 static bool |
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728 is_miss_rate_acceptable (unsigned HOST_WIDE_INT cache_line_size, |
|
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729 HOST_WIDE_INT step, HOST_WIDE_INT delta, |
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730 unsigned HOST_WIDE_INT distinct_iters, |
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731 int align_unit) |
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732 { |
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733 unsigned align, iter; |
|
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734 int total_positions, miss_positions, max_allowed_miss_positions; |
|
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735 int address1, address2, cache_line1, cache_line2; |
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736 |
|
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737 /* It always misses if delta is greater than or equal to the cache |
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738 line size. */ |
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739 if (delta >= (HOST_WIDE_INT) cache_line_size) |
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740 return false; |
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741 |
|
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742 miss_positions = 0; |
|
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743 total_positions = (cache_line_size / align_unit) * distinct_iters; |
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744 max_allowed_miss_positions = (ACCEPTABLE_MISS_RATE * total_positions) / 1000; |
|
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745 |
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746 /* Iterate through all possible alignments of the first |
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747 memory reference within its cache line. */ |
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748 for (align = 0; align < cache_line_size; align += align_unit) |
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749 |
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750 /* Iterate through all distinct iterations. */ |
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751 for (iter = 0; iter < distinct_iters; iter++) |
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752 { |
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753 address1 = align + step * iter; |
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754 address2 = address1 + delta; |
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755 cache_line1 = address1 / cache_line_size; |
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756 cache_line2 = address2 / cache_line_size; |
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757 if (cache_line1 != cache_line2) |
|
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758 { |
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759 miss_positions += 1; |
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760 if (miss_positions > max_allowed_miss_positions) |
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761 return false; |
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762 } |
|
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763 } |
|
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764 return true; |
|
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765 } |
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766 |
| 0 | 767 /* Prune the prefetch candidate REF using the reuse with BY. |
| 768 If BY_IS_BEFORE is true, BY is before REF in the loop. */ | |
| 769 | |
| 770 static void | |
| 771 prune_ref_by_group_reuse (struct mem_ref *ref, struct mem_ref *by, | |
| 772 bool by_is_before) | |
| 773 { | |
|
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774 HOST_WIDE_INT step; |
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775 bool backward; |
| 0 | 776 HOST_WIDE_INT delta_r = ref->delta, delta_b = by->delta; |
| 777 HOST_WIDE_INT delta = delta_b - delta_r; | |
| 778 HOST_WIDE_INT hit_from; | |
| 779 unsigned HOST_WIDE_INT prefetch_before, prefetch_block; | |
|
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780 HOST_WIDE_INT reduced_step; |
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781 unsigned HOST_WIDE_INT reduced_prefetch_block; |
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782 tree ref_type; |
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783 int align_unit; |
| 0 | 784 |
|
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785 /* If the step is non constant we cannot calculate prefetch_before. */ |
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786 if (!cst_and_fits_in_hwi (ref->group->step)) { |
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787 return; |
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788 } |
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789 |
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790 step = int_cst_value (ref->group->step); |
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791 |
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792 backward = step < 0; |
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793 |
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794 |
| 0 | 795 if (delta == 0) |
| 796 { | |
| 797 /* If the references has the same address, only prefetch the | |
| 798 former. */ | |
| 799 if (by_is_before) | |
| 800 ref->prefetch_before = 0; | |
|
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801 |
| 0 | 802 return; |
| 803 } | |
| 804 | |
| 805 if (!step) | |
| 806 { | |
| 807 /* If the reference addresses are invariant and fall into the | |
| 808 same cache line, prefetch just the first one. */ | |
| 809 if (!by_is_before) | |
| 810 return; | |
| 811 | |
| 812 if (ddown (ref->delta, PREFETCH_BLOCK) | |
| 813 != ddown (by->delta, PREFETCH_BLOCK)) | |
| 814 return; | |
| 815 | |
| 816 ref->prefetch_before = 0; | |
| 817 return; | |
| 818 } | |
| 819 | |
| 820 /* Only prune the reference that is behind in the array. */ | |
| 821 if (backward) | |
| 822 { | |
| 823 if (delta > 0) | |
| 824 return; | |
| 825 | |
| 826 /* Transform the data so that we may assume that the accesses | |
| 827 are forward. */ | |
| 828 delta = - delta; | |
| 829 step = -step; | |
| 830 delta_r = PREFETCH_BLOCK - 1 - delta_r; | |
| 831 delta_b = PREFETCH_BLOCK - 1 - delta_b; | |
| 832 } | |
| 833 else | |
| 834 { | |
| 835 if (delta < 0) | |
| 836 return; | |
| 837 } | |
| 838 | |
| 839 /* Check whether the two references are likely to hit the same cache | |
| 840 line, and how distant the iterations in that it occurs are from | |
| 841 each other. */ | |
| 842 | |
| 843 if (step <= PREFETCH_BLOCK) | |
| 844 { | |
| 845 /* The accesses are sure to meet. Let us check when. */ | |
| 846 hit_from = ddown (delta_b, PREFETCH_BLOCK) * PREFETCH_BLOCK; | |
| 847 prefetch_before = (hit_from - delta_r + step - 1) / step; | |
| 848 | |
|
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849 /* Do not reduce prefetch_before if we meet beyond cache size. */ |
| 111 | 850 if (prefetch_before > absu_hwi (L2_CACHE_SIZE_BYTES / step)) |
|
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851 prefetch_before = PREFETCH_ALL; |
| 0 | 852 if (prefetch_before < ref->prefetch_before) |
| 853 ref->prefetch_before = prefetch_before; | |
| 854 | |
| 855 return; | |
| 856 } | |
| 857 | |
|
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858 /* A more complicated case with step > prefetch_block. First reduce |
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859 the ratio between the step and the cache line size to its simplest |
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860 terms. The resulting denominator will then represent the number of |
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861 distinct iterations after which each address will go back to its |
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862 initial location within the cache line. This computation assumes |
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863 that PREFETCH_BLOCK is a power of two. */ |
| 0 | 864 prefetch_block = PREFETCH_BLOCK; |
|
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865 reduced_prefetch_block = prefetch_block; |
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866 reduced_step = step; |
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867 while ((reduced_step & 1) == 0 |
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868 && reduced_prefetch_block > 1) |
| 0 | 869 { |
|
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870 reduced_step >>= 1; |
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871 reduced_prefetch_block >>= 1; |
| 0 | 872 } |
| 873 | |
| 874 prefetch_before = delta / step; | |
| 875 delta %= step; | |
|
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876 ref_type = TREE_TYPE (ref->mem); |
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877 align_unit = TYPE_ALIGN (ref_type) / 8; |
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878 if (is_miss_rate_acceptable (prefetch_block, step, delta, |
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879 reduced_prefetch_block, align_unit)) |
| 0 | 880 { |
|
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881 /* Do not reduce prefetch_before if we meet beyond cache size. */ |
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882 if (prefetch_before > L2_CACHE_SIZE_BYTES / PREFETCH_BLOCK) |
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883 prefetch_before = PREFETCH_ALL; |
| 0 | 884 if (prefetch_before < ref->prefetch_before) |
| 885 ref->prefetch_before = prefetch_before; | |
| 886 | |
| 887 return; | |
| 888 } | |
| 889 | |
| 890 /* Try also the following iteration. */ | |
| 891 prefetch_before++; | |
| 892 delta = step - delta; | |
|
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893 if (is_miss_rate_acceptable (prefetch_block, step, delta, |
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894 reduced_prefetch_block, align_unit)) |
| 0 | 895 { |
| 896 if (prefetch_before < ref->prefetch_before) | |
| 897 ref->prefetch_before = prefetch_before; | |
| 898 | |
| 899 return; | |
| 900 } | |
| 901 | |
| 902 /* The ref probably does not reuse by. */ | |
| 903 return; | |
| 904 } | |
| 905 | |
| 906 /* Prune the prefetch candidate REF using the reuses with other references | |
| 907 in REFS. */ | |
| 908 | |
| 909 static void | |
| 910 prune_ref_by_reuse (struct mem_ref *ref, struct mem_ref *refs) | |
| 911 { | |
| 912 struct mem_ref *prune_by; | |
| 913 bool before = true; | |
| 914 | |
| 915 prune_ref_by_self_reuse (ref); | |
| 916 | |
| 917 for (prune_by = refs; prune_by; prune_by = prune_by->next) | |
| 918 { | |
| 919 if (prune_by == ref) | |
| 920 { | |
| 921 before = false; | |
| 922 continue; | |
| 923 } | |
| 924 | |
| 925 if (!WRITE_CAN_USE_READ_PREFETCH | |
| 926 && ref->write_p | |
| 927 && !prune_by->write_p) | |
| 928 continue; | |
| 929 if (!READ_CAN_USE_WRITE_PREFETCH | |
| 930 && !ref->write_p | |
| 931 && prune_by->write_p) | |
| 932 continue; | |
| 933 | |
| 934 prune_ref_by_group_reuse (ref, prune_by, before); | |
| 935 } | |
| 936 } | |
| 937 | |
| 938 /* Prune the prefetch candidates in GROUP using the reuse analysis. */ | |
| 939 | |
| 940 static void | |
| 941 prune_group_by_reuse (struct mem_ref_group *group) | |
| 942 { | |
| 943 struct mem_ref *ref_pruned; | |
| 944 | |
| 945 for (ref_pruned = group->refs; ref_pruned; ref_pruned = ref_pruned->next) | |
| 946 { | |
| 947 prune_ref_by_reuse (ref_pruned, group->refs); | |
| 948 | |
| 949 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 950 { | |
| 111 | 951 dump_mem_ref (dump_file, ref_pruned); |
| 0 | 952 |
| 953 if (ref_pruned->prefetch_before == PREFETCH_ALL | |
| 954 && ref_pruned->prefetch_mod == 1) | |
| 955 fprintf (dump_file, " no restrictions"); | |
| 956 else if (ref_pruned->prefetch_before == 0) | |
| 957 fprintf (dump_file, " do not prefetch"); | |
| 958 else if (ref_pruned->prefetch_before <= ref_pruned->prefetch_mod) | |
| 959 fprintf (dump_file, " prefetch once"); | |
| 960 else | |
| 961 { | |
| 962 if (ref_pruned->prefetch_before != PREFETCH_ALL) | |
| 963 { | |
| 964 fprintf (dump_file, " prefetch before "); | |
| 965 fprintf (dump_file, HOST_WIDE_INT_PRINT_DEC, | |
| 966 ref_pruned->prefetch_before); | |
| 967 } | |
| 968 if (ref_pruned->prefetch_mod != 1) | |
| 969 { | |
| 970 fprintf (dump_file, " prefetch mod "); | |
| 971 fprintf (dump_file, HOST_WIDE_INT_PRINT_DEC, | |
| 972 ref_pruned->prefetch_mod); | |
| 973 } | |
| 974 } | |
| 975 fprintf (dump_file, "\n"); | |
| 976 } | |
| 977 } | |
| 978 } | |
| 979 | |
| 980 /* Prune the list of prefetch candidates GROUPS using the reuse analysis. */ | |
| 981 | |
| 982 static void | |
| 983 prune_by_reuse (struct mem_ref_group *groups) | |
| 984 { | |
| 985 for (; groups; groups = groups->next) | |
| 986 prune_group_by_reuse (groups); | |
| 987 } | |
| 988 | |
| 989 /* Returns true if we should issue prefetch for REF. */ | |
| 990 | |
| 991 static bool | |
| 992 should_issue_prefetch_p (struct mem_ref *ref) | |
| 993 { | |
| 131 | 994 /* Do we want to issue prefetches for non-constant strides? */ |
| 145 | 995 if (!cst_and_fits_in_hwi (ref->group->step) |
| 996 && param_prefetch_dynamic_strides == 0) | |
| 131 | 997 { |
| 998 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 999 fprintf (dump_file, | |
| 1000 "Skipping non-constant step for reference %u:%u\n", | |
| 1001 ref->group->uid, ref->uid); | |
| 1002 return false; | |
| 1003 } | |
| 1004 | |
| 1005 /* Some processors may have a hardware prefetcher that may conflict with | |
| 1006 prefetch hints for a range of strides. Make sure we don't issue | |
| 1007 prefetches for such cases if the stride is within this particular | |
| 1008 range. */ | |
| 1009 if (cst_and_fits_in_hwi (ref->group->step) | |
| 1010 && abs_hwi (int_cst_value (ref->group->step)) | |
| 145 | 1011 < (HOST_WIDE_INT) param_prefetch_minimum_stride) |
| 131 | 1012 { |
| 1013 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 1014 fprintf (dump_file, | |
| 1015 "Step for reference %u:%u (" HOST_WIDE_INT_PRINT_DEC | |
| 1016 ") is less than the mininum required stride of %d\n", | |
| 1017 ref->group->uid, ref->uid, int_cst_value (ref->group->step), | |
| 145 | 1018 param_prefetch_minimum_stride); |
| 131 | 1019 return false; |
| 1020 } | |
| 1021 | |
| 0 | 1022 /* For now do not issue prefetches for only first few of the |
| 1023 iterations. */ | |
| 1024 if (ref->prefetch_before != PREFETCH_ALL) | |
|
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1025 { |
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1026 if (dump_file && (dump_flags & TDF_DETAILS)) |
| 111 | 1027 fprintf (dump_file, "Ignoring reference %u:%u due to prefetch_before\n", |
| 1028 ref->group->uid, ref->uid); | |
|
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1029 return false; |
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1030 } |
| 0 | 1031 |
| 1032 /* Do not prefetch nontemporal stores. */ | |
| 1033 if (ref->storent_p) | |
|
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1034 { |
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1035 if (dump_file && (dump_flags & TDF_DETAILS)) |
| 111 | 1036 fprintf (dump_file, "Ignoring nontemporal store reference %u:%u\n", ref->group->uid, ref->uid); |
|
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1037 return false; |
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1038 } |
| 0 | 1039 |
| 1040 return true; | |
| 1041 } | |
| 1042 | |
| 1043 /* Decide which of the prefetch candidates in GROUPS to prefetch. | |
| 1044 AHEAD is the number of iterations to prefetch ahead (which corresponds | |
| 1045 to the number of simultaneous instances of one prefetch running at a | |
| 1046 time). UNROLL_FACTOR is the factor by that the loop is going to be | |
| 1047 unrolled. Returns true if there is anything to prefetch. */ | |
| 1048 | |
| 1049 static bool | |
| 1050 schedule_prefetches (struct mem_ref_group *groups, unsigned unroll_factor, | |
| 1051 unsigned ahead) | |
| 1052 { | |
| 1053 unsigned remaining_prefetch_slots, n_prefetches, prefetch_slots; | |
| 1054 unsigned slots_per_prefetch; | |
| 1055 struct mem_ref *ref; | |
| 1056 bool any = false; | |
| 1057 | |
| 145 | 1058 /* At most param_simultaneous_prefetches should be running |
| 1059 at the same time. */ | |
| 1060 remaining_prefetch_slots = param_simultaneous_prefetches; | |
| 0 | 1061 |
| 1062 /* The prefetch will run for AHEAD iterations of the original loop, i.e., | |
| 1063 AHEAD / UNROLL_FACTOR iterations of the unrolled loop. In each iteration, | |
| 1064 it will need a prefetch slot. */ | |
| 1065 slots_per_prefetch = (ahead + unroll_factor / 2) / unroll_factor; | |
| 1066 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 1067 fprintf (dump_file, "Each prefetch instruction takes %u prefetch slots.\n", | |
| 1068 slots_per_prefetch); | |
| 1069 | |
| 1070 /* For now we just take memory references one by one and issue | |
| 1071 prefetches for as many as possible. The groups are sorted | |
| 1072 starting with the largest step, since the references with | |
| 1073 large step are more likely to cause many cache misses. */ | |
| 1074 | |
| 1075 for (; groups; groups = groups->next) | |
| 1076 for (ref = groups->refs; ref; ref = ref->next) | |
| 1077 { | |
| 1078 if (!should_issue_prefetch_p (ref)) | |
| 1079 continue; | |
| 1080 | |
|
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1081 /* The loop is far from being sufficiently unrolled for this |
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1082 prefetch. Do not generate prefetch to avoid many redudant |
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1083 prefetches. */ |
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1084 if (ref->prefetch_mod / unroll_factor > PREFETCH_MOD_TO_UNROLL_FACTOR_RATIO) |
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1085 continue; |
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1086 |
| 0 | 1087 /* If we need to prefetch the reference each PREFETCH_MOD iterations, |
| 1088 and we unroll the loop UNROLL_FACTOR times, we need to insert | |
| 1089 ceil (UNROLL_FACTOR / PREFETCH_MOD) instructions in each | |
| 1090 iteration. */ | |
| 1091 n_prefetches = ((unroll_factor + ref->prefetch_mod - 1) | |
| 1092 / ref->prefetch_mod); | |
| 1093 prefetch_slots = n_prefetches * slots_per_prefetch; | |
| 1094 | |
| 1095 /* If more than half of the prefetches would be lost anyway, do not | |
| 1096 issue the prefetch. */ | |
| 1097 if (2 * remaining_prefetch_slots < prefetch_slots) | |
| 1098 continue; | |
| 1099 | |
| 111 | 1100 /* Stop prefetching if debug counter is activated. */ |
| 1101 if (!dbg_cnt (prefetch)) | |
| 1102 continue; | |
| 1103 | |
| 0 | 1104 ref->issue_prefetch_p = true; |
| 111 | 1105 if (dump_file && (dump_flags & TDF_DETAILS)) |
| 1106 fprintf (dump_file, "Decided to issue prefetch for reference %u:%u\n", | |
| 1107 ref->group->uid, ref->uid); | |
| 0 | 1108 |
| 1109 if (remaining_prefetch_slots <= prefetch_slots) | |
| 1110 return true; | |
| 1111 remaining_prefetch_slots -= prefetch_slots; | |
| 1112 any = true; | |
| 1113 } | |
| 1114 | |
| 1115 return any; | |
| 1116 } | |
| 1117 | |
|
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1118 /* Return TRUE if no prefetch is going to be generated in the given |
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1119 GROUPS. */ |
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1120 |
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1121 static bool |
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1122 nothing_to_prefetch_p (struct mem_ref_group *groups) |
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1123 { |
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1124 struct mem_ref *ref; |
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1125 |
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1126 for (; groups; groups = groups->next) |
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1127 for (ref = groups->refs; ref; ref = ref->next) |
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1128 if (should_issue_prefetch_p (ref)) |
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1129 return false; |
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1130 |
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1131 return true; |
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1132 } |
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1133 |
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1134 /* Estimate the number of prefetches in the given GROUPS. |
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1135 UNROLL_FACTOR is the factor by which LOOP was unrolled. */ |
| 0 | 1136 |
|
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1137 static int |
|
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1138 estimate_prefetch_count (struct mem_ref_group *groups, unsigned unroll_factor) |
| 0 | 1139 { |
| 1140 struct mem_ref *ref; | |
|
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1141 unsigned n_prefetches; |
|
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1142 int prefetch_count = 0; |
| 0 | 1143 |
| 1144 for (; groups; groups = groups->next) | |
| 1145 for (ref = groups->refs; ref; ref = ref->next) | |
| 1146 if (should_issue_prefetch_p (ref)) | |
|
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1147 { |
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1148 n_prefetches = ((unroll_factor + ref->prefetch_mod - 1) |
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1149 / ref->prefetch_mod); |
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1150 prefetch_count += n_prefetches; |
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1151 } |
| 0 | 1152 |
|
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1153 return prefetch_count; |
| 0 | 1154 } |
| 1155 | |
| 1156 /* Issue prefetches for the reference REF into loop as decided before. | |
| 1157 HEAD is the number of iterations to prefetch ahead. UNROLL_FACTOR | |
| 1158 is the factor by which LOOP was unrolled. */ | |
| 1159 | |
| 1160 static void | |
| 1161 issue_prefetch_ref (struct mem_ref *ref, unsigned unroll_factor, unsigned ahead) | |
| 1162 { | |
| 1163 HOST_WIDE_INT delta; | |
|
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1164 tree addr, addr_base, write_p, local, forward; |
| 111 | 1165 gcall *prefetch; |
| 0 | 1166 gimple_stmt_iterator bsi; |
| 1167 unsigned n_prefetches, ap; | |
| 1168 bool nontemporal = ref->reuse_distance >= L2_CACHE_SIZE_BYTES; | |
| 1169 | |
| 1170 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 111 | 1171 fprintf (dump_file, "Issued%s prefetch for reference %u:%u.\n", |
| 0 | 1172 nontemporal ? " nontemporal" : "", |
| 111 | 1173 ref->group->uid, ref->uid); |
| 0 | 1174 |
| 1175 bsi = gsi_for_stmt (ref->stmt); | |
| 1176 | |
| 1177 n_prefetches = ((unroll_factor + ref->prefetch_mod - 1) | |
| 1178 / ref->prefetch_mod); | |
| 1179 addr_base = build_fold_addr_expr_with_type (ref->mem, ptr_type_node); | |
| 1180 addr_base = force_gimple_operand_gsi (&bsi, unshare_expr (addr_base), | |
| 1181 true, NULL, true, GSI_SAME_STMT); | |
| 1182 write_p = ref->write_p ? integer_one_node : integer_zero_node; | |
|
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1183 local = nontemporal ? integer_zero_node : integer_three_node; |
| 0 | 1184 |
| 1185 for (ap = 0; ap < n_prefetches; ap++) | |
| 1186 { | |
|
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1187 if (cst_and_fits_in_hwi (ref->group->step)) |
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1188 { |
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1189 /* Determine the address to prefetch. */ |
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1190 delta = (ahead + ap * ref->prefetch_mod) * |
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1191 int_cst_value (ref->group->step); |
| 111 | 1192 addr = fold_build_pointer_plus_hwi (addr_base, delta); |
| 1193 addr = force_gimple_operand_gsi (&bsi, unshare_expr (addr), true, | |
| 1194 NULL, true, GSI_SAME_STMT); | |
|
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1195 } |
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1196 else |
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1197 { |
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1198 /* The step size is non-constant but loop-invariant. We use the |
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1199 heuristic to simply prefetch ahead iterations ahead. */ |
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1200 forward = fold_build2 (MULT_EXPR, sizetype, |
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1201 fold_convert (sizetype, ref->group->step), |
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1202 fold_convert (sizetype, size_int (ahead))); |
| 111 | 1203 addr = fold_build_pointer_plus (addr_base, forward); |
|
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1204 addr = force_gimple_operand_gsi (&bsi, unshare_expr (addr), true, |
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1205 NULL, true, GSI_SAME_STMT); |
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1206 } |
| 111 | 1207 |
| 1208 if (addr_base != addr | |
| 1209 && TREE_CODE (addr_base) == SSA_NAME | |
| 1210 && TREE_CODE (addr) == SSA_NAME) | |
| 1211 { | |
| 1212 duplicate_ssa_name_ptr_info (addr, SSA_NAME_PTR_INFO (addr_base)); | |
| 1213 /* As this isn't a plain copy we have to reset alignment | |
| 1214 information. */ | |
| 1215 if (SSA_NAME_PTR_INFO (addr)) | |
| 1216 mark_ptr_info_alignment_unknown (SSA_NAME_PTR_INFO (addr)); | |
| 1217 } | |
| 1218 | |
| 0 | 1219 /* Create the prefetch instruction. */ |
| 111 | 1220 prefetch = gimple_build_call (builtin_decl_explicit (BUILT_IN_PREFETCH), |
| 0 | 1221 3, addr, write_p, local); |
| 1222 gsi_insert_before (&bsi, prefetch, GSI_SAME_STMT); | |
| 1223 } | |
| 1224 } | |
| 1225 | |
| 1226 /* Issue prefetches for the references in GROUPS into loop as decided before. | |
| 1227 HEAD is the number of iterations to prefetch ahead. UNROLL_FACTOR is the | |
| 1228 factor by that LOOP was unrolled. */ | |
| 1229 | |
| 1230 static void | |
| 1231 issue_prefetches (struct mem_ref_group *groups, | |
| 1232 unsigned unroll_factor, unsigned ahead) | |
| 1233 { | |
| 1234 struct mem_ref *ref; | |
| 1235 | |
| 1236 for (; groups; groups = groups->next) | |
| 1237 for (ref = groups->refs; ref; ref = ref->next) | |
| 1238 if (ref->issue_prefetch_p) | |
| 1239 issue_prefetch_ref (ref, unroll_factor, ahead); | |
| 1240 } | |
| 1241 | |
| 1242 /* Returns true if REF is a memory write for that a nontemporal store insn | |
| 1243 can be used. */ | |
| 1244 | |
| 1245 static bool | |
| 1246 nontemporal_store_p (struct mem_ref *ref) | |
| 1247 { | |
| 111 | 1248 machine_mode mode; |
| 0 | 1249 enum insn_code code; |
| 1250 | |
| 1251 /* REF must be a write that is not reused. We require it to be independent | |
| 1252 on all other memory references in the loop, as the nontemporal stores may | |
| 1253 be reordered with respect to other memory references. */ | |
| 1254 if (!ref->write_p | |
| 1255 || !ref->independent_p | |
| 1256 || ref->reuse_distance < L2_CACHE_SIZE_BYTES) | |
| 1257 return false; | |
| 1258 | |
| 1259 /* Check that we have the storent instruction for the mode. */ | |
| 1260 mode = TYPE_MODE (TREE_TYPE (ref->mem)); | |
| 1261 if (mode == BLKmode) | |
| 1262 return false; | |
| 1263 | |
|
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1264 code = optab_handler (storent_optab, mode); |
| 0 | 1265 return code != CODE_FOR_nothing; |
| 1266 } | |
| 1267 | |
| 1268 /* If REF is a nontemporal store, we mark the corresponding modify statement | |
| 1269 and return true. Otherwise, we return false. */ | |
| 1270 | |
| 1271 static bool | |
| 1272 mark_nontemporal_store (struct mem_ref *ref) | |
| 1273 { | |
| 1274 if (!nontemporal_store_p (ref)) | |
| 1275 return false; | |
| 1276 | |
| 1277 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 111 | 1278 fprintf (dump_file, "Marked reference %u:%u as a nontemporal store.\n", |
| 1279 ref->group->uid, ref->uid); | |
| 0 | 1280 |
| 1281 gimple_assign_set_nontemporal_move (ref->stmt, true); | |
| 1282 ref->storent_p = true; | |
| 1283 | |
| 1284 return true; | |
| 1285 } | |
| 1286 | |
| 1287 /* Issue a memory fence instruction after LOOP. */ | |
| 1288 | |
| 1289 static void | |
| 145 | 1290 emit_mfence_after_loop (class loop *loop) |
| 0 | 1291 { |
| 111 | 1292 vec<edge> exits = get_loop_exit_edges (loop); |
| 0 | 1293 edge exit; |
| 111 | 1294 gcall *call; |
| 0 | 1295 gimple_stmt_iterator bsi; |
| 1296 unsigned i; | |
| 1297 | |
| 111 | 1298 FOR_EACH_VEC_ELT (exits, i, exit) |
| 0 | 1299 { |
| 1300 call = gimple_build_call (FENCE_FOLLOWING_MOVNT, 0); | |
| 1301 | |
| 1302 if (!single_pred_p (exit->dest) | |
| 1303 /* If possible, we prefer not to insert the fence on other paths | |
| 1304 in cfg. */ | |
| 1305 && !(exit->flags & EDGE_ABNORMAL)) | |
| 1306 split_loop_exit_edge (exit); | |
| 1307 bsi = gsi_after_labels (exit->dest); | |
| 1308 | |
| 1309 gsi_insert_before (&bsi, call, GSI_NEW_STMT); | |
| 1310 } | |
| 1311 | |
| 111 | 1312 exits.release (); |
| 0 | 1313 update_ssa (TODO_update_ssa_only_virtuals); |
| 1314 } | |
| 1315 | |
| 1316 /* Returns true if we can use storent in loop, false otherwise. */ | |
| 1317 | |
| 1318 static bool | |
| 145 | 1319 may_use_storent_in_loop_p (class loop *loop) |
| 0 | 1320 { |
| 1321 bool ret = true; | |
| 1322 | |
| 1323 if (loop->inner != NULL) | |
| 1324 return false; | |
| 1325 | |
| 1326 /* If we must issue a mfence insn after using storent, check that there | |
| 1327 is a suitable place for it at each of the loop exits. */ | |
| 1328 if (FENCE_FOLLOWING_MOVNT != NULL_TREE) | |
| 1329 { | |
| 111 | 1330 vec<edge> exits = get_loop_exit_edges (loop); |
| 0 | 1331 unsigned i; |
| 1332 edge exit; | |
| 1333 | |
| 111 | 1334 FOR_EACH_VEC_ELT (exits, i, exit) |
| 0 | 1335 if ((exit->flags & EDGE_ABNORMAL) |
| 111 | 1336 && exit->dest == EXIT_BLOCK_PTR_FOR_FN (cfun)) |
| 0 | 1337 ret = false; |
| 1338 | |
| 111 | 1339 exits.release (); |
| 0 | 1340 } |
| 1341 | |
| 1342 return ret; | |
| 1343 } | |
| 1344 | |
| 1345 /* Marks nontemporal stores in LOOP. GROUPS contains the description of memory | |
| 1346 references in the loop. */ | |
| 1347 | |
| 1348 static void | |
| 145 | 1349 mark_nontemporal_stores (class loop *loop, struct mem_ref_group *groups) |
| 0 | 1350 { |
| 1351 struct mem_ref *ref; | |
| 1352 bool any = false; | |
| 1353 | |
| 1354 if (!may_use_storent_in_loop_p (loop)) | |
| 1355 return; | |
| 1356 | |
| 1357 for (; groups; groups = groups->next) | |
| 1358 for (ref = groups->refs; ref; ref = ref->next) | |
| 1359 any |= mark_nontemporal_store (ref); | |
| 1360 | |
| 1361 if (any && FENCE_FOLLOWING_MOVNT != NULL_TREE) | |
| 1362 emit_mfence_after_loop (loop); | |
| 1363 } | |
| 1364 | |
| 1365 /* Determines whether we can profitably unroll LOOP FACTOR times, and if | |
| 1366 this is the case, fill in DESC by the description of number of | |
| 1367 iterations. */ | |
| 1368 | |
| 1369 static bool | |
| 145 | 1370 should_unroll_loop_p (class loop *loop, class tree_niter_desc *desc, |
| 0 | 1371 unsigned factor) |
| 1372 { | |
| 1373 if (!can_unroll_loop_p (loop, factor, desc)) | |
| 1374 return false; | |
| 1375 | |
| 1376 /* We only consider loops without control flow for unrolling. This is not | |
| 1377 a hard restriction -- tree_unroll_loop works with arbitrary loops | |
| 1378 as well; but the unrolling/prefetching is usually more profitable for | |
| 1379 loops consisting of a single basic block, and we want to limit the | |
| 1380 code growth. */ | |
| 1381 if (loop->num_nodes > 2) | |
| 1382 return false; | |
| 1383 | |
| 1384 return true; | |
| 1385 } | |
| 1386 | |
| 1387 /* Determine the coefficient by that unroll LOOP, from the information | |
| 1388 contained in the list of memory references REFS. Description of | |
| 111 | 1389 number of iterations of LOOP is stored to DESC. NINSNS is the number of |
| 0 | 1390 insns of the LOOP. EST_NITER is the estimated number of iterations of |
| 1391 the loop, or -1 if no estimate is available. */ | |
| 1392 | |
| 1393 static unsigned | |
| 145 | 1394 determine_unroll_factor (class loop *loop, struct mem_ref_group *refs, |
| 1395 unsigned ninsns, class tree_niter_desc *desc, | |
| 0 | 1396 HOST_WIDE_INT est_niter) |
| 1397 { | |
| 1398 unsigned upper_bound; | |
| 1399 unsigned nfactor, factor, mod_constraint; | |
| 1400 struct mem_ref_group *agp; | |
| 1401 struct mem_ref *ref; | |
| 1402 | |
| 1403 /* First check whether the loop is not too large to unroll. We ignore | |
| 1404 PARAM_MAX_UNROLL_TIMES, because for small loops, it prevented us | |
| 1405 from unrolling them enough to make exactly one cache line covered by each | |
| 1406 iteration. Also, the goal of PARAM_MAX_UNROLL_TIMES is to prevent | |
| 1407 us from unrolling the loops too many times in cases where we only expect | |
| 1408 gains from better scheduling and decreasing loop overhead, which is not | |
| 1409 the case here. */ | |
| 145 | 1410 upper_bound = param_max_unrolled_insns / ninsns; |
| 0 | 1411 |
| 1412 /* If we unrolled the loop more times than it iterates, the unrolled version | |
| 1413 of the loop would be never entered. */ | |
| 1414 if (est_niter >= 0 && est_niter < (HOST_WIDE_INT) upper_bound) | |
| 1415 upper_bound = est_niter; | |
| 1416 | |
| 1417 if (upper_bound <= 1) | |
| 1418 return 1; | |
| 1419 | |
| 1420 /* Choose the factor so that we may prefetch each cache just once, | |
| 1421 but bound the unrolling by UPPER_BOUND. */ | |
| 1422 factor = 1; | |
| 1423 for (agp = refs; agp; agp = agp->next) | |
| 1424 for (ref = agp->refs; ref; ref = ref->next) | |
| 1425 if (should_issue_prefetch_p (ref)) | |
| 1426 { | |
| 1427 mod_constraint = ref->prefetch_mod; | |
| 1428 nfactor = least_common_multiple (mod_constraint, factor); | |
| 1429 if (nfactor <= upper_bound) | |
| 1430 factor = nfactor; | |
| 1431 } | |
| 1432 | |
| 1433 if (!should_unroll_loop_p (loop, desc, factor)) | |
| 1434 return 1; | |
| 1435 | |
| 1436 return factor; | |
| 1437 } | |
| 1438 | |
| 1439 /* Returns the total volume of the memory references REFS, taking into account | |
| 1440 reuses in the innermost loop and cache line size. TODO -- we should also | |
| 1441 take into account reuses across the iterations of the loops in the loop | |
| 1442 nest. */ | |
| 1443 | |
| 1444 static unsigned | |
| 1445 volume_of_references (struct mem_ref_group *refs) | |
| 1446 { | |
| 1447 unsigned volume = 0; | |
| 1448 struct mem_ref_group *gr; | |
| 1449 struct mem_ref *ref; | |
| 1450 | |
| 1451 for (gr = refs; gr; gr = gr->next) | |
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