Mercurial > hg > CbC > CbC_gcc
annotate gcc/tree-ssa-loop-prefetch.c @ 86:12b3180c7d07
modify calls.c.
| author | Nobuyasu Oshiro <dimolto@cr.ie.u-ryukyu.ac.jp> |
|---|---|
| date | Thu, 15 Dec 2011 02:37:13 +0900 |
| parents | f6334be47118 |
| children | 04ced10e8804 |
| rev | line source |
|---|---|
| 0 | 1 /* Array prefetching. |
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2 Copyright (C) 2005, 2007, 2008, 2009, 2010 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 "tm_p.h" | |
| 26 #include "basic-block.h" | |
| 27 #include "output.h" | |
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28 #include "tree-pretty-print.h" |
| 0 | 29 #include "tree-flow.h" |
| 30 #include "tree-dump.h" | |
| 31 #include "timevar.h" | |
| 32 #include "cfgloop.h" | |
| 33 #include "tree-pass.h" | |
| 34 #include "insn-config.h" | |
| 35 #include "recog.h" | |
| 36 #include "hashtab.h" | |
| 37 #include "tree-chrec.h" | |
| 38 #include "tree-scalar-evolution.h" | |
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39 #include "diagnostic-core.h" |
| 0 | 40 #include "params.h" |
| 41 #include "langhooks.h" | |
| 42 #include "tree-inline.h" | |
| 43 #include "tree-data-ref.h" | |
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44 |
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45 |
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46 /* FIXME: Needed for optabs, but this should all be moved to a TBD interface |
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47 between the GIMPLE and RTL worlds. */ |
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48 #include "expr.h" |
| 0 | 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 | |
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82 the cache line accessed by (5) is the same with probability only |
| 0 | 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 A cost model is implemented to determine whether or not prefetching is |
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113 profitable for a given loop. The cost model has three heuristics: |
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114 |
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115 1. Function trip_count_to_ahead_ratio_too_small_p implements a |
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116 heuristic that determines whether or not the loop has too few |
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117 iterations (compared to ahead). Prefetching is not likely to be |
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118 beneficial if the trip count to ahead ratio is below a certain |
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119 minimum. |
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120 |
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121 2. Function mem_ref_count_reasonable_p implements a heuristic that |
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122 determines whether the given loop has enough CPU ops that can be |
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123 overlapped with cache missing memory ops. If not, the loop |
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124 won't benefit from prefetching. In the implementation, |
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125 prefetching is not considered beneficial if the ratio between |
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126 the instruction count and the mem ref count is below a certain |
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127 minimum. |
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128 |
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129 3. Function insn_to_prefetch_ratio_too_small_p implements a |
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130 heuristic that disables prefetching in a loop if the prefetching |
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131 cost is above a certain limit. The relative prefetching cost is |
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132 estimated by taking the ratio between the prefetch count and the |
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133 total intruction count (this models the I-cache cost). |
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134 |
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135 The limits used in these heuristics are defined as parameters with |
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136 reasonable default values. Machine-specific default values will be |
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137 added later. |
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138 |
| 0 | 139 Some other TODO: |
| 140 -- write and use more general reuse analysis (that could be also used | |
| 141 in other cache aimed loop optimizations) | |
| 142 -- make it behave sanely together with the prefetches given by user | |
| 143 (now we just ignore them; at the very least we should avoid | |
| 144 optimizing loops in that user put his own prefetches) | |
| 145 -- we assume cache line size alignment of arrays; this could be | |
| 146 improved. */ | |
| 147 | |
| 148 /* Magic constants follow. These should be replaced by machine specific | |
| 149 numbers. */ | |
| 150 | |
| 151 /* True if write can be prefetched by a read prefetch. */ | |
| 152 | |
| 153 #ifndef WRITE_CAN_USE_READ_PREFETCH | |
| 154 #define WRITE_CAN_USE_READ_PREFETCH 1 | |
| 155 #endif | |
| 156 | |
| 157 /* True if read can be prefetched by a write prefetch. */ | |
| 158 | |
| 159 #ifndef READ_CAN_USE_WRITE_PREFETCH | |
| 160 #define READ_CAN_USE_WRITE_PREFETCH 0 | |
| 161 #endif | |
| 162 | |
| 163 /* The size of the block loaded by a single prefetch. Usually, this is | |
| 164 the same as cache line size (at the moment, we only consider one level | |
| 165 of cache hierarchy). */ | |
| 166 | |
| 167 #ifndef PREFETCH_BLOCK | |
| 168 #define PREFETCH_BLOCK L1_CACHE_LINE_SIZE | |
| 169 #endif | |
| 170 | |
| 171 /* Do we have a forward hardware sequential prefetching? */ | |
| 172 | |
| 173 #ifndef HAVE_FORWARD_PREFETCH | |
| 174 #define HAVE_FORWARD_PREFETCH 0 | |
| 175 #endif | |
| 176 | |
| 177 /* Do we have a backward hardware sequential prefetching? */ | |
| 178 | |
| 179 #ifndef HAVE_BACKWARD_PREFETCH | |
| 180 #define HAVE_BACKWARD_PREFETCH 0 | |
| 181 #endif | |
| 182 | |
| 183 /* In some cases we are only able to determine that there is a certain | |
| 184 probability that the two accesses hit the same cache line. In this | |
| 185 case, we issue the prefetches for both of them if this probability | |
| 186 is less then (1000 - ACCEPTABLE_MISS_RATE) per thousand. */ | |
| 187 | |
| 188 #ifndef ACCEPTABLE_MISS_RATE | |
| 189 #define ACCEPTABLE_MISS_RATE 50 | |
| 190 #endif | |
| 191 | |
| 192 #ifndef HAVE_prefetch | |
| 193 #define HAVE_prefetch 0 | |
| 194 #endif | |
| 195 | |
| 196 #define L1_CACHE_SIZE_BYTES ((unsigned) (L1_CACHE_SIZE * 1024)) | |
| 197 #define L2_CACHE_SIZE_BYTES ((unsigned) (L2_CACHE_SIZE * 1024)) | |
| 198 | |
| 199 /* We consider a memory access nontemporal if it is not reused sooner than | |
| 200 after L2_CACHE_SIZE_BYTES of memory are accessed. However, we ignore | |
| 201 accesses closer than L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION, | |
| 202 so that we use nontemporal prefetches e.g. if single memory location | |
| 203 is accessed several times in a single iteration of the loop. */ | |
| 204 #define NONTEMPORAL_FRACTION 16 | |
| 205 | |
| 206 /* In case we have to emit a memory fence instruction after the loop that | |
| 207 uses nontemporal stores, this defines the builtin to use. */ | |
| 208 | |
| 209 #ifndef FENCE_FOLLOWING_MOVNT | |
| 210 #define FENCE_FOLLOWING_MOVNT NULL_TREE | |
| 211 #endif | |
| 212 | |
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213 /* It is not profitable to prefetch when the trip count is not at |
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214 least TRIP_COUNT_TO_AHEAD_RATIO times the prefetch ahead distance. |
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215 For example, in a loop with a prefetch ahead distance of 10, |
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216 supposing that TRIP_COUNT_TO_AHEAD_RATIO is equal to 4, it is |
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217 profitable to prefetch when the trip count is greater or equal to |
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218 40. In that case, 30 out of the 40 iterations will benefit from |
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219 prefetching. */ |
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220 |
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221 #ifndef TRIP_COUNT_TO_AHEAD_RATIO |
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222 #define TRIP_COUNT_TO_AHEAD_RATIO 4 |
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223 #endif |
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224 |
| 0 | 225 /* The group of references between that reuse may occur. */ |
| 226 | |
| 227 struct mem_ref_group | |
| 228 { | |
| 229 tree base; /* Base of the reference. */ | |
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230 tree step; /* Step of the reference. */ |
| 0 | 231 struct mem_ref *refs; /* References in the group. */ |
| 232 struct mem_ref_group *next; /* Next group of references. */ | |
| 233 }; | |
| 234 | |
| 235 /* Assigned to PREFETCH_BEFORE when all iterations are to be prefetched. */ | |
| 236 | |
| 237 #define PREFETCH_ALL (~(unsigned HOST_WIDE_INT) 0) | |
| 238 | |
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239 /* Do not generate a prefetch if the unroll factor is significantly less |
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240 than what is required by the prefetch. This is to avoid redundant |
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241 prefetches. For example, when prefetch_mod is 16 and unroll_factor is |
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242 2, prefetching requires unrolling the loop 16 times, but |
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243 the loop is actually unrolled twice. In this case (ratio = 8), |
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244 prefetching is not likely to be beneficial. */ |
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245 |
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246 #ifndef PREFETCH_MOD_TO_UNROLL_FACTOR_RATIO |
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247 #define PREFETCH_MOD_TO_UNROLL_FACTOR_RATIO 4 |
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248 #endif |
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249 |
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250 /* Some of the prefetch computations have quadratic complexity. We want to |
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251 avoid huge compile times and, therefore, want to limit the amount of |
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252 memory references per loop where we consider prefetching. */ |
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253 |
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254 #ifndef PREFETCH_MAX_MEM_REFS_PER_LOOP |
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255 #define PREFETCH_MAX_MEM_REFS_PER_LOOP 200 |
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256 #endif |
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257 |
| 0 | 258 /* The memory reference. */ |
| 259 | |
| 260 struct mem_ref | |
| 261 { | |
| 262 gimple stmt; /* Statement in that the reference appears. */ | |
| 263 tree mem; /* The reference. */ | |
| 264 HOST_WIDE_INT delta; /* Constant offset of the reference. */ | |
| 265 struct mem_ref_group *group; /* The group of references it belongs to. */ | |
| 266 unsigned HOST_WIDE_INT prefetch_mod; | |
| 267 /* Prefetch only each PREFETCH_MOD-th | |
| 268 iteration. */ | |
| 269 unsigned HOST_WIDE_INT prefetch_before; | |
| 270 /* Prefetch only first PREFETCH_BEFORE | |
| 271 iterations. */ | |
| 272 unsigned reuse_distance; /* The amount of data accessed before the first | |
| 273 reuse of this value. */ | |
| 274 struct mem_ref *next; /* The next reference in the group. */ | |
| 275 unsigned write_p : 1; /* Is it a write? */ | |
| 276 unsigned independent_p : 1; /* True if the reference is independent on | |
| 277 all other references inside the loop. */ | |
| 278 unsigned issue_prefetch_p : 1; /* Should we really issue the prefetch? */ | |
| 279 unsigned storent_p : 1; /* True if we changed the store to a | |
| 280 nontemporal one. */ | |
| 281 }; | |
| 282 | |
| 283 /* Dumps information about reference REF to FILE. */ | |
| 284 | |
| 285 static void | |
| 286 dump_mem_ref (FILE *file, struct mem_ref *ref) | |
| 287 { | |
| 288 fprintf (file, "Reference %p:\n", (void *) ref); | |
| 289 | |
| 290 fprintf (file, " group %p (base ", (void *) ref->group); | |
| 291 print_generic_expr (file, ref->group->base, TDF_SLIM); | |
| 292 fprintf (file, ", step "); | |
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293 if (cst_and_fits_in_hwi (ref->group->step)) |
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294 fprintf (file, HOST_WIDE_INT_PRINT_DEC, int_cst_value (ref->group->step)); |
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295 else |
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296 print_generic_expr (file, ref->group->step, TDF_TREE); |
| 0 | 297 fprintf (file, ")\n"); |
| 298 | |
| 299 fprintf (file, " delta "); | |
| 300 fprintf (file, HOST_WIDE_INT_PRINT_DEC, ref->delta); | |
| 301 fprintf (file, "\n"); | |
| 302 | |
| 303 fprintf (file, " %s\n", ref->write_p ? "write" : "read"); | |
| 304 | |
| 305 fprintf (file, "\n"); | |
| 306 } | |
| 307 | |
| 308 /* Finds a group with BASE and STEP in GROUPS, or creates one if it does not | |
| 309 exist. */ | |
| 310 | |
| 311 static struct mem_ref_group * | |
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312 find_or_create_group (struct mem_ref_group **groups, tree base, tree step) |
| 0 | 313 { |
| 314 struct mem_ref_group *group; | |
| 315 | |
| 316 for (; *groups; groups = &(*groups)->next) | |
| 317 { | |
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318 if (operand_equal_p ((*groups)->step, step, 0) |
| 0 | 319 && operand_equal_p ((*groups)->base, base, 0)) |
| 320 return *groups; | |
| 321 | |
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322 /* If step is an integer constant, keep the list of groups sorted |
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323 by decreasing step. */ |
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324 if (cst_and_fits_in_hwi ((*groups)->step) && cst_and_fits_in_hwi (step) |
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325 && int_cst_value ((*groups)->step) < int_cst_value (step)) |
| 0 | 326 break; |
| 327 } | |
| 328 | |
| 329 group = XNEW (struct mem_ref_group); | |
| 330 group->base = base; | |
| 331 group->step = step; | |
| 332 group->refs = NULL; | |
| 333 group->next = *groups; | |
| 334 *groups = group; | |
| 335 | |
| 336 return group; | |
| 337 } | |
| 338 | |
| 339 /* Records a memory reference MEM in GROUP with offset DELTA and write status | |
| 340 WRITE_P. The reference occurs in statement STMT. */ | |
| 341 | |
| 342 static void | |
| 343 record_ref (struct mem_ref_group *group, gimple stmt, tree mem, | |
| 344 HOST_WIDE_INT delta, bool write_p) | |
| 345 { | |
| 346 struct mem_ref **aref; | |
| 347 | |
| 348 /* Do not record the same address twice. */ | |
| 349 for (aref = &group->refs; *aref; aref = &(*aref)->next) | |
| 350 { | |
| 351 /* It does not have to be possible for write reference to reuse the read | |
| 352 prefetch, or vice versa. */ | |
| 353 if (!WRITE_CAN_USE_READ_PREFETCH | |
| 354 && write_p | |
| 355 && !(*aref)->write_p) | |
| 356 continue; | |
| 357 if (!READ_CAN_USE_WRITE_PREFETCH | |
| 358 && !write_p | |
| 359 && (*aref)->write_p) | |
| 360 continue; | |
| 361 | |
| 362 if ((*aref)->delta == delta) | |
| 363 return; | |
| 364 } | |
| 365 | |
| 366 (*aref) = XNEW (struct mem_ref); | |
| 367 (*aref)->stmt = stmt; | |
| 368 (*aref)->mem = mem; | |
| 369 (*aref)->delta = delta; | |
| 370 (*aref)->write_p = write_p; | |
| 371 (*aref)->prefetch_before = PREFETCH_ALL; | |
| 372 (*aref)->prefetch_mod = 1; | |
| 373 (*aref)->reuse_distance = 0; | |
| 374 (*aref)->issue_prefetch_p = false; | |
| 375 (*aref)->group = group; | |
| 376 (*aref)->next = NULL; | |
| 377 (*aref)->independent_p = false; | |
| 378 (*aref)->storent_p = false; | |
| 379 | |
| 380 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 381 dump_mem_ref (dump_file, *aref); | |
| 382 } | |
| 383 | |
| 384 /* Release memory references in GROUPS. */ | |
| 385 | |
| 386 static void | |
| 387 release_mem_refs (struct mem_ref_group *groups) | |
| 388 { | |
| 389 struct mem_ref_group *next_g; | |
| 390 struct mem_ref *ref, *next_r; | |
| 391 | |
| 392 for (; groups; groups = next_g) | |
| 393 { | |
| 394 next_g = groups->next; | |
| 395 for (ref = groups->refs; ref; ref = next_r) | |
| 396 { | |
| 397 next_r = ref->next; | |
| 398 free (ref); | |
| 399 } | |
| 400 free (groups); | |
| 401 } | |
| 402 } | |
| 403 | |
| 404 /* A structure used to pass arguments to idx_analyze_ref. */ | |
| 405 | |
| 406 struct ar_data | |
| 407 { | |
| 408 struct loop *loop; /* Loop of the reference. */ | |
| 409 gimple stmt; /* Statement of the reference. */ | |
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410 tree *step; /* Step of the memory reference. */ |
| 0 | 411 HOST_WIDE_INT *delta; /* Offset of the memory reference. */ |
| 412 }; | |
| 413 | |
| 414 /* Analyzes a single INDEX of a memory reference to obtain information | |
| 415 described at analyze_ref. Callback for for_each_index. */ | |
| 416 | |
| 417 static bool | |
| 418 idx_analyze_ref (tree base, tree *index, void *data) | |
| 419 { | |
| 420 struct ar_data *ar_data = (struct ar_data *) data; | |
| 421 tree ibase, step, stepsize; | |
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422 HOST_WIDE_INT idelta = 0, imult = 1; |
| 0 | 423 affine_iv iv; |
| 424 | |
| 425 if (!simple_iv (ar_data->loop, loop_containing_stmt (ar_data->stmt), | |
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426 *index, &iv, true)) |
| 0 | 427 return false; |
| 428 ibase = iv.base; | |
| 429 step = iv.step; | |
| 430 | |
| 431 if (TREE_CODE (ibase) == POINTER_PLUS_EXPR | |
| 432 && cst_and_fits_in_hwi (TREE_OPERAND (ibase, 1))) | |
| 433 { | |
| 434 idelta = int_cst_value (TREE_OPERAND (ibase, 1)); | |
| 435 ibase = TREE_OPERAND (ibase, 0); | |
| 436 } | |
| 437 if (cst_and_fits_in_hwi (ibase)) | |
| 438 { | |
| 439 idelta += int_cst_value (ibase); | |
| 440 ibase = build_int_cst (TREE_TYPE (ibase), 0); | |
| 441 } | |
| 442 | |
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443 if (TREE_CODE (base) == ARRAY_REF) |
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444 { |
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445 stepsize = array_ref_element_size (base); |
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446 if (!cst_and_fits_in_hwi (stepsize)) |
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447 return false; |
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448 imult = int_cst_value (stepsize); |
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449 step = fold_build2 (MULT_EXPR, sizetype, |
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450 fold_convert (sizetype, step), |
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451 fold_convert (sizetype, stepsize)); |
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452 idelta *= imult; |
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453 } |
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454 |
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455 if (*ar_data->step == NULL_TREE) |
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456 *ar_data->step = step; |
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457 else |
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458 *ar_data->step = fold_build2 (PLUS_EXPR, sizetype, |
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459 fold_convert (sizetype, *ar_data->step), |
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460 fold_convert (sizetype, step)); |
| 0 | 461 *ar_data->delta += idelta; |
| 462 *index = ibase; | |
| 463 | |
| 464 return true; | |
| 465 } | |
| 466 | |
| 467 /* Tries to express REF_P in shape &BASE + STEP * iter + DELTA, where DELTA and | |
| 468 STEP are integer constants and iter is number of iterations of LOOP. The | |
| 469 reference occurs in statement STMT. Strips nonaddressable component | |
| 470 references from REF_P. */ | |
| 471 | |
| 472 static bool | |
| 473 analyze_ref (struct loop *loop, tree *ref_p, tree *base, | |
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474 tree *step, HOST_WIDE_INT *delta, |
| 0 | 475 gimple stmt) |
| 476 { | |
| 477 struct ar_data ar_data; | |
| 478 tree off; | |
| 479 HOST_WIDE_INT bit_offset; | |
| 480 tree ref = *ref_p; | |
| 481 | |
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482 *step = NULL_TREE; |
| 0 | 483 *delta = 0; |
| 484 | |
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485 /* First strip off the component references. Ignore bitfields. |
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486 Also strip off the real and imagine parts of a complex, so that |
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487 they can have the same base. */ |
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488 if (TREE_CODE (ref) == REALPART_EXPR |
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489 || TREE_CODE (ref) == IMAGPART_EXPR |
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490 || (TREE_CODE (ref) == COMPONENT_REF |
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491 && DECL_NONADDRESSABLE_P (TREE_OPERAND (ref, 1)))) |
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492 { |
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493 if (TREE_CODE (ref) == IMAGPART_EXPR) |
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494 *delta += int_size_in_bytes (TREE_TYPE (ref)); |
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495 ref = TREE_OPERAND (ref, 0); |
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496 } |
| 0 | 497 |
| 498 *ref_p = ref; | |
| 499 | |
| 500 for (; TREE_CODE (ref) == COMPONENT_REF; ref = TREE_OPERAND (ref, 0)) | |
| 501 { | |
| 502 off = DECL_FIELD_BIT_OFFSET (TREE_OPERAND (ref, 1)); | |
| 503 bit_offset = TREE_INT_CST_LOW (off); | |
| 504 gcc_assert (bit_offset % BITS_PER_UNIT == 0); | |
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505 |
| 0 | 506 *delta += bit_offset / BITS_PER_UNIT; |
| 507 } | |
| 508 | |
| 509 *base = unshare_expr (ref); | |
| 510 ar_data.loop = loop; | |
| 511 ar_data.stmt = stmt; | |
| 512 ar_data.step = step; | |
| 513 ar_data.delta = delta; | |
| 514 return for_each_index (base, idx_analyze_ref, &ar_data); | |
| 515 } | |
| 516 | |
| 517 /* Record a memory reference REF to the list REFS. The reference occurs in | |
| 518 LOOP in statement STMT and it is write if WRITE_P. Returns true if the | |
| 519 reference was recorded, false otherwise. */ | |
| 520 | |
| 521 static bool | |
| 522 gather_memory_references_ref (struct loop *loop, struct mem_ref_group **refs, | |
| 523 tree ref, bool write_p, gimple stmt) | |
| 524 { | |
|
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525 tree base, step; |
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526 HOST_WIDE_INT delta; |
| 0 | 527 struct mem_ref_group *agrp; |
| 528 | |
| 529 if (get_base_address (ref) == NULL) | |
| 530 return false; | |
| 531 | |
| 532 if (!analyze_ref (loop, &ref, &base, &step, &delta, stmt)) | |
| 533 return false; | |
|
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534 /* If analyze_ref fails the default is a NULL_TREE. We can stop here. */ |
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535 if (step == NULL_TREE) |
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536 return false; |
| 0 | 537 |
|
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538 /* Stop if the address of BASE could not be taken. */ |
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539 if (may_be_nonaddressable_p (base)) |
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540 return false; |
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541 |
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542 /* Limit non-constant step prefetching only to the innermost loops. */ |
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543 if (!cst_and_fits_in_hwi (step) && loop->inner != NULL) |
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544 return false; |
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545 |
| 0 | 546 /* Now we know that REF = &BASE + STEP * iter + DELTA, where DELTA and STEP |
| 547 are integer constants. */ | |
| 548 agrp = find_or_create_group (refs, base, step); | |
| 549 record_ref (agrp, stmt, ref, delta, write_p); | |
| 550 | |
| 551 return true; | |
| 552 } | |
| 553 | |
| 554 /* Record the suitable memory references in LOOP. NO_OTHER_REFS is set to | |
| 555 true if there are no other memory references inside the loop. */ | |
| 556 | |
| 557 static struct mem_ref_group * | |
|
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558 gather_memory_references (struct loop *loop, bool *no_other_refs, unsigned *ref_count) |
| 0 | 559 { |
| 560 basic_block *body = get_loop_body_in_dom_order (loop); | |
| 561 basic_block bb; | |
| 562 unsigned i; | |
| 563 gimple_stmt_iterator bsi; | |
| 564 gimple stmt; | |
| 565 tree lhs, rhs; | |
| 566 struct mem_ref_group *refs = NULL; | |
| 567 | |
| 568 *no_other_refs = true; | |
|
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569 *ref_count = 0; |
| 0 | 570 |
| 571 /* Scan the loop body in order, so that the former references precede the | |
| 572 later ones. */ | |
| 573 for (i = 0; i < loop->num_nodes; i++) | |
| 574 { | |
| 575 bb = body[i]; | |
| 576 if (bb->loop_father != loop) | |
| 577 continue; | |
| 578 | |
| 579 for (bsi = gsi_start_bb (bb); !gsi_end_p (bsi); gsi_next (&bsi)) | |
| 580 { | |
| 581 stmt = gsi_stmt (bsi); | |
| 582 | |
| 583 if (gimple_code (stmt) != GIMPLE_ASSIGN) | |
| 584 { | |
|
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585 if (gimple_vuse (stmt) |
| 0 | 586 || (is_gimple_call (stmt) |
| 587 && !(gimple_call_flags (stmt) & ECF_CONST))) | |
| 588 *no_other_refs = false; | |
| 589 continue; | |
| 590 } | |
| 591 | |
| 592 lhs = gimple_assign_lhs (stmt); | |
| 593 rhs = gimple_assign_rhs1 (stmt); | |
| 594 | |
| 595 if (REFERENCE_CLASS_P (rhs)) | |
|
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596 { |
| 0 | 597 *no_other_refs &= gather_memory_references_ref (loop, &refs, |
| 598 rhs, false, stmt); | |
|
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599 *ref_count += 1; |
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600 } |
| 0 | 601 if (REFERENCE_CLASS_P (lhs)) |
|
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602 { |
| 0 | 603 *no_other_refs &= gather_memory_references_ref (loop, &refs, |
| 604 lhs, true, stmt); | |
|
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605 *ref_count += 1; |
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606 } |
| 0 | 607 } |
| 608 } | |
| 609 free (body); | |
| 610 | |
| 611 return refs; | |
| 612 } | |
| 613 | |
| 614 /* Prune the prefetch candidate REF using the self-reuse. */ | |
| 615 | |
| 616 static void | |
| 617 prune_ref_by_self_reuse (struct mem_ref *ref) | |
| 618 { | |
|
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619 HOST_WIDE_INT step; |
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620 bool backward; |
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621 |
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622 /* If the step size is non constant, we cannot calculate prefetch_mod. */ |
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623 if (!cst_and_fits_in_hwi (ref->group->step)) |
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624 return; |
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625 |
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626 step = int_cst_value (ref->group->step); |
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627 |
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628 backward = step < 0; |
| 0 | 629 |
| 630 if (step == 0) | |
| 631 { | |
| 632 /* Prefetch references to invariant address just once. */ | |
| 633 ref->prefetch_before = 1; | |
| 634 return; | |
| 635 } | |
| 636 | |
| 637 if (backward) | |
| 638 step = -step; | |
| 639 | |
| 640 if (step > PREFETCH_BLOCK) | |
| 641 return; | |
| 642 | |
| 643 if ((backward && HAVE_BACKWARD_PREFETCH) | |
| 644 || (!backward && HAVE_FORWARD_PREFETCH)) | |
| 645 { | |
| 646 ref->prefetch_before = 1; | |
| 647 return; | |
| 648 } | |
| 649 | |
| 650 ref->prefetch_mod = PREFETCH_BLOCK / step; | |
| 651 } | |
| 652 | |
| 653 /* Divides X by BY, rounding down. */ | |
| 654 | |
| 655 static HOST_WIDE_INT | |
| 656 ddown (HOST_WIDE_INT x, unsigned HOST_WIDE_INT by) | |
| 657 { | |
| 658 gcc_assert (by > 0); | |
| 659 | |
| 660 if (x >= 0) | |
| 661 return x / by; | |
| 662 else | |
| 663 return (x + by - 1) / by; | |
| 664 } | |
| 665 | |
|
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666 /* Given a CACHE_LINE_SIZE and two inductive memory references |
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667 with a common STEP greater than CACHE_LINE_SIZE and an address |
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668 difference DELTA, compute the probability that they will fall |
|
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669 in different cache lines. Return true if the computed miss rate |
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670 is not greater than the ACCEPTABLE_MISS_RATE. DISTINCT_ITERS is the |
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671 number of distinct iterations after which the pattern repeats itself. |
|
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672 ALIGN_UNIT is the unit of alignment in bytes. */ |
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673 |
|
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674 static bool |
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675 is_miss_rate_acceptable (unsigned HOST_WIDE_INT cache_line_size, |
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676 HOST_WIDE_INT step, HOST_WIDE_INT delta, |
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677 unsigned HOST_WIDE_INT distinct_iters, |
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678 int align_unit) |
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679 { |
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680 unsigned align, iter; |
|
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681 int total_positions, miss_positions, max_allowed_miss_positions; |
|
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682 int address1, address2, cache_line1, cache_line2; |
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683 |
|
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684 /* It always misses if delta is greater than or equal to the cache |
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685 line size. */ |
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686 if (delta >= (HOST_WIDE_INT) cache_line_size) |
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687 return false; |
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688 |
|
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689 miss_positions = 0; |
|
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690 total_positions = (cache_line_size / align_unit) * distinct_iters; |
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691 max_allowed_miss_positions = (ACCEPTABLE_MISS_RATE * total_positions) / 1000; |
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692 |
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693 /* Iterate through all possible alignments of the first |
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694 memory reference within its cache line. */ |
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695 for (align = 0; align < cache_line_size; align += align_unit) |
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696 |
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697 /* Iterate through all distinct iterations. */ |
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698 for (iter = 0; iter < distinct_iters; iter++) |
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699 { |
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700 address1 = align + step * iter; |
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701 address2 = address1 + delta; |
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702 cache_line1 = address1 / cache_line_size; |
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703 cache_line2 = address2 / cache_line_size; |
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704 if (cache_line1 != cache_line2) |
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705 { |
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706 miss_positions += 1; |
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707 if (miss_positions > max_allowed_miss_positions) |
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708 return false; |
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709 } |
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710 } |
|
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711 return true; |
|
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712 } |
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713 |
| 0 | 714 /* Prune the prefetch candidate REF using the reuse with BY. |
| 715 If BY_IS_BEFORE is true, BY is before REF in the loop. */ | |
| 716 | |
| 717 static void | |
| 718 prune_ref_by_group_reuse (struct mem_ref *ref, struct mem_ref *by, | |
| 719 bool by_is_before) | |
| 720 { | |
|
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721 HOST_WIDE_INT step; |
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722 bool backward; |
| 0 | 723 HOST_WIDE_INT delta_r = ref->delta, delta_b = by->delta; |
| 724 HOST_WIDE_INT delta = delta_b - delta_r; | |
| 725 HOST_WIDE_INT hit_from; | |
| 726 unsigned HOST_WIDE_INT prefetch_before, prefetch_block; | |
|
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727 HOST_WIDE_INT reduced_step; |
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728 unsigned HOST_WIDE_INT reduced_prefetch_block; |
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729 tree ref_type; |
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730 int align_unit; |
| 0 | 731 |
|
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732 /* If the step is non constant we cannot calculate prefetch_before. */ |
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733 if (!cst_and_fits_in_hwi (ref->group->step)) { |
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734 return; |
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735 } |
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736 |
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737 step = int_cst_value (ref->group->step); |
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738 |
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739 backward = step < 0; |
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740 |
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741 |
| 0 | 742 if (delta == 0) |
| 743 { | |
| 744 /* If the references has the same address, only prefetch the | |
| 745 former. */ | |
| 746 if (by_is_before) | |
| 747 ref->prefetch_before = 0; | |
|
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748 |
| 0 | 749 return; |
| 750 } | |
| 751 | |
| 752 if (!step) | |
| 753 { | |
| 754 /* If the reference addresses are invariant and fall into the | |
| 755 same cache line, prefetch just the first one. */ | |
| 756 if (!by_is_before) | |
| 757 return; | |
| 758 | |
| 759 if (ddown (ref->delta, PREFETCH_BLOCK) | |
| 760 != ddown (by->delta, PREFETCH_BLOCK)) | |
| 761 return; | |
| 762 | |
| 763 ref->prefetch_before = 0; | |
| 764 return; | |
| 765 } | |
| 766 | |
| 767 /* Only prune the reference that is behind in the array. */ | |
| 768 if (backward) | |
| 769 { | |
| 770 if (delta > 0) | |
| 771 return; | |
| 772 | |
| 773 /* Transform the data so that we may assume that the accesses | |
| 774 are forward. */ | |
| 775 delta = - delta; | |
| 776 step = -step; | |
| 777 delta_r = PREFETCH_BLOCK - 1 - delta_r; | |
| 778 delta_b = PREFETCH_BLOCK - 1 - delta_b; | |
| 779 } | |
| 780 else | |
| 781 { | |
| 782 if (delta < 0) | |
| 783 return; | |
| 784 } | |
| 785 | |
| 786 /* Check whether the two references are likely to hit the same cache | |
| 787 line, and how distant the iterations in that it occurs are from | |
| 788 each other. */ | |
| 789 | |
| 790 if (step <= PREFETCH_BLOCK) | |
| 791 { | |
| 792 /* The accesses are sure to meet. Let us check when. */ | |
| 793 hit_from = ddown (delta_b, PREFETCH_BLOCK) * PREFETCH_BLOCK; | |
| 794 prefetch_before = (hit_from - delta_r + step - 1) / step; | |
| 795 | |
|
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796 /* Do not reduce prefetch_before if we meet beyond cache size. */ |
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797 if (prefetch_before > (unsigned) abs (L2_CACHE_SIZE_BYTES / step)) |
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798 prefetch_before = PREFETCH_ALL; |
| 0 | 799 if (prefetch_before < ref->prefetch_before) |
| 800 ref->prefetch_before = prefetch_before; | |
| 801 | |
| 802 return; | |
| 803 } | |
| 804 | |
|
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805 /* A more complicated case with step > prefetch_block. First reduce |
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806 the ratio between the step and the cache line size to its simplest |
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807 terms. The resulting denominator will then represent the number of |
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808 distinct iterations after which each address will go back to its |
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809 initial location within the cache line. This computation assumes |
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810 that PREFETCH_BLOCK is a power of two. */ |
| 0 | 811 prefetch_block = PREFETCH_BLOCK; |
|
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812 reduced_prefetch_block = prefetch_block; |
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813 reduced_step = step; |
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814 while ((reduced_step & 1) == 0 |
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815 && reduced_prefetch_block > 1) |
| 0 | 816 { |
|
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817 reduced_step >>= 1; |
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818 reduced_prefetch_block >>= 1; |
| 0 | 819 } |
| 820 | |
| 821 prefetch_before = delta / step; | |
| 822 delta %= step; | |
|
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823 ref_type = TREE_TYPE (ref->mem); |
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824 align_unit = TYPE_ALIGN (ref_type) / 8; |
|
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825 if (is_miss_rate_acceptable (prefetch_block, step, delta, |
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826 reduced_prefetch_block, align_unit)) |
| 0 | 827 { |
|
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828 /* Do not reduce prefetch_before if we meet beyond cache size. */ |
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829 if (prefetch_before > L2_CACHE_SIZE_BYTES / PREFETCH_BLOCK) |
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830 prefetch_before = PREFETCH_ALL; |
| 0 | 831 if (prefetch_before < ref->prefetch_before) |
| 832 ref->prefetch_before = prefetch_before; | |
| 833 | |
| 834 return; | |
| 835 } | |
| 836 | |
| 837 /* Try also the following iteration. */ | |
| 838 prefetch_before++; | |
| 839 delta = step - delta; | |
|
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840 if (is_miss_rate_acceptable (prefetch_block, step, delta, |
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841 reduced_prefetch_block, align_unit)) |
| 0 | 842 { |
| 843 if (prefetch_before < ref->prefetch_before) | |
| 844 ref->prefetch_before = prefetch_before; | |
| 845 | |
| 846 return; | |
| 847 } | |
| 848 | |
| 849 /* The ref probably does not reuse by. */ | |
| 850 return; | |
| 851 } | |
| 852 | |
| 853 /* Prune the prefetch candidate REF using the reuses with other references | |
| 854 in REFS. */ | |
| 855 | |
| 856 static void | |
| 857 prune_ref_by_reuse (struct mem_ref *ref, struct mem_ref *refs) | |
| 858 { | |
| 859 struct mem_ref *prune_by; | |
| 860 bool before = true; | |
| 861 | |
| 862 prune_ref_by_self_reuse (ref); | |
| 863 | |
| 864 for (prune_by = refs; prune_by; prune_by = prune_by->next) | |
| 865 { | |
| 866 if (prune_by == ref) | |
| 867 { | |
| 868 before = false; | |
| 869 continue; | |
| 870 } | |
| 871 | |
| 872 if (!WRITE_CAN_USE_READ_PREFETCH | |
| 873 && ref->write_p | |
| 874 && !prune_by->write_p) | |
| 875 continue; | |
| 876 if (!READ_CAN_USE_WRITE_PREFETCH | |
| 877 && !ref->write_p | |
| 878 && prune_by->write_p) | |
| 879 continue; | |
| 880 | |
| 881 prune_ref_by_group_reuse (ref, prune_by, before); | |
| 882 } | |
| 883 } | |
| 884 | |
| 885 /* Prune the prefetch candidates in GROUP using the reuse analysis. */ | |
| 886 | |
| 887 static void | |
| 888 prune_group_by_reuse (struct mem_ref_group *group) | |
| 889 { | |
| 890 struct mem_ref *ref_pruned; | |
| 891 | |
| 892 for (ref_pruned = group->refs; ref_pruned; ref_pruned = ref_pruned->next) | |
| 893 { | |
| 894 prune_ref_by_reuse (ref_pruned, group->refs); | |
| 895 | |
| 896 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 897 { | |
| 898 fprintf (dump_file, "Reference %p:", (void *) ref_pruned); | |
| 899 | |
| 900 if (ref_pruned->prefetch_before == PREFETCH_ALL | |
| 901 && ref_pruned->prefetch_mod == 1) | |
| 902 fprintf (dump_file, " no restrictions"); | |
| 903 else if (ref_pruned->prefetch_before == 0) | |
| 904 fprintf (dump_file, " do not prefetch"); | |
| 905 else if (ref_pruned->prefetch_before <= ref_pruned->prefetch_mod) | |
| 906 fprintf (dump_file, " prefetch once"); | |
| 907 else | |
| 908 { | |
| 909 if (ref_pruned->prefetch_before != PREFETCH_ALL) | |
| 910 { | |
| 911 fprintf (dump_file, " prefetch before "); | |
| 912 fprintf (dump_file, HOST_WIDE_INT_PRINT_DEC, | |
| 913 ref_pruned->prefetch_before); | |
| 914 } | |
| 915 if (ref_pruned->prefetch_mod != 1) | |
| 916 { | |
| 917 fprintf (dump_file, " prefetch mod "); | |
| 918 fprintf (dump_file, HOST_WIDE_INT_PRINT_DEC, | |
| 919 ref_pruned->prefetch_mod); | |
| 920 } | |
| 921 } | |
| 922 fprintf (dump_file, "\n"); | |
| 923 } | |
| 924 } | |
| 925 } | |
| 926 | |
| 927 /* Prune the list of prefetch candidates GROUPS using the reuse analysis. */ | |
| 928 | |
| 929 static void | |
| 930 prune_by_reuse (struct mem_ref_group *groups) | |
| 931 { | |
| 932 for (; groups; groups = groups->next) | |
| 933 prune_group_by_reuse (groups); | |
| 934 } | |
| 935 | |
| 936 /* Returns true if we should issue prefetch for REF. */ | |
| 937 | |
| 938 static bool | |
| 939 should_issue_prefetch_p (struct mem_ref *ref) | |
| 940 { | |
| 941 /* For now do not issue prefetches for only first few of the | |
| 942 iterations. */ | |
| 943 if (ref->prefetch_before != PREFETCH_ALL) | |
|
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944 { |
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945 if (dump_file && (dump_flags & TDF_DETAILS)) |
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946 fprintf (dump_file, "Ignoring %p due to prefetch_before\n", |
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947 (void *) ref); |
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948 return false; |
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949 } |
| 0 | 950 |
| 951 /* Do not prefetch nontemporal stores. */ | |
| 952 if (ref->storent_p) | |
|
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953 { |
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954 if (dump_file && (dump_flags & TDF_DETAILS)) |
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955 fprintf (dump_file, "Ignoring nontemporal store %p\n", (void *) ref); |
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956 return false; |
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957 } |
| 0 | 958 |
| 959 return true; | |
| 960 } | |
| 961 | |
| 962 /* Decide which of the prefetch candidates in GROUPS to prefetch. | |
| 963 AHEAD is the number of iterations to prefetch ahead (which corresponds | |
| 964 to the number of simultaneous instances of one prefetch running at a | |
| 965 time). UNROLL_FACTOR is the factor by that the loop is going to be | |
| 966 unrolled. Returns true if there is anything to prefetch. */ | |
| 967 | |
| 968 static bool | |
| 969 schedule_prefetches (struct mem_ref_group *groups, unsigned unroll_factor, | |
| 970 unsigned ahead) | |
| 971 { | |
| 972 unsigned remaining_prefetch_slots, n_prefetches, prefetch_slots; | |
| 973 unsigned slots_per_prefetch; | |
| 974 struct mem_ref *ref; | |
| 975 bool any = false; | |
| 976 | |
| 977 /* At most SIMULTANEOUS_PREFETCHES should be running at the same time. */ | |
| 978 remaining_prefetch_slots = SIMULTANEOUS_PREFETCHES; | |
| 979 | |
| 980 /* The prefetch will run for AHEAD iterations of the original loop, i.e., | |
| 981 AHEAD / UNROLL_FACTOR iterations of the unrolled loop. In each iteration, | |
| 982 it will need a prefetch slot. */ | |
| 983 slots_per_prefetch = (ahead + unroll_factor / 2) / unroll_factor; | |
| 984 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 985 fprintf (dump_file, "Each prefetch instruction takes %u prefetch slots.\n", | |
| 986 slots_per_prefetch); | |
| 987 | |
| 988 /* For now we just take memory references one by one and issue | |
| 989 prefetches for as many as possible. The groups are sorted | |
| 990 starting with the largest step, since the references with | |
| 991 large step are more likely to cause many cache misses. */ | |
| 992 | |
| 993 for (; groups; groups = groups->next) | |
| 994 for (ref = groups->refs; ref; ref = ref->next) | |
| 995 { | |
| 996 if (!should_issue_prefetch_p (ref)) | |
| 997 continue; | |
| 998 | |
|
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999 /* The loop is far from being sufficiently unrolled for this |
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1000 prefetch. Do not generate prefetch to avoid many redudant |
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1001 prefetches. */ |
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1002 if (ref->prefetch_mod / unroll_factor > PREFETCH_MOD_TO_UNROLL_FACTOR_RATIO) |
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1003 continue; |
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1004 |
| 0 | 1005 /* If we need to prefetch the reference each PREFETCH_MOD iterations, |
| 1006 and we unroll the loop UNROLL_FACTOR times, we need to insert | |
| 1007 ceil (UNROLL_FACTOR / PREFETCH_MOD) instructions in each | |
| 1008 iteration. */ | |
| 1009 n_prefetches = ((unroll_factor + ref->prefetch_mod - 1) | |
| 1010 / ref->prefetch_mod); | |
| 1011 prefetch_slots = n_prefetches * slots_per_prefetch; | |
| 1012 | |
| 1013 /* If more than half of the prefetches would be lost anyway, do not | |
| 1014 issue the prefetch. */ | |
| 1015 if (2 * remaining_prefetch_slots < prefetch_slots) | |
| 1016 continue; | |
| 1017 | |
| 1018 ref->issue_prefetch_p = true; | |
| 1019 | |
| 1020 if (remaining_prefetch_slots <= prefetch_slots) | |
| 1021 return true; | |
| 1022 remaining_prefetch_slots -= prefetch_slots; | |
| 1023 any = true; | |
| 1024 } | |
| 1025 | |
| 1026 return any; | |
| 1027 } | |
| 1028 | |
|
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1029 /* Return TRUE if no prefetch is going to be generated in the given |
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1030 GROUPS. */ |
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1031 |
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1032 static bool |
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1033 nothing_to_prefetch_p (struct mem_ref_group *groups) |
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1034 { |
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1035 struct mem_ref *ref; |
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1036 |
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1037 for (; groups; groups = groups->next) |
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1038 for (ref = groups->refs; ref; ref = ref->next) |
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1039 if (should_issue_prefetch_p (ref)) |
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1040 return false; |
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1041 |
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1042 return true; |
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1043 } |
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1044 |
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1045 /* Estimate the number of prefetches in the given GROUPS. |
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1046 UNROLL_FACTOR is the factor by which LOOP was unrolled. */ |
| 0 | 1047 |
|
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1048 static int |
|
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1049 estimate_prefetch_count (struct mem_ref_group *groups, unsigned unroll_factor) |
| 0 | 1050 { |
| 1051 struct mem_ref *ref; | |
|
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1052 unsigned n_prefetches; |
|
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1053 int prefetch_count = 0; |
| 0 | 1054 |
| 1055 for (; groups; groups = groups->next) | |
| 1056 for (ref = groups->refs; ref; ref = ref->next) | |
| 1057 if (should_issue_prefetch_p (ref)) | |
|
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1058 { |
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1059 n_prefetches = ((unroll_factor + ref->prefetch_mod - 1) |
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1060 / ref->prefetch_mod); |
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1061 prefetch_count += n_prefetches; |
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1062 } |
| 0 | 1063 |
|
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1064 return prefetch_count; |
| 0 | 1065 } |
| 1066 | |
| 1067 /* Issue prefetches for the reference REF into loop as decided before. | |
| 1068 HEAD is the number of iterations to prefetch ahead. UNROLL_FACTOR | |
| 1069 is the factor by which LOOP was unrolled. */ | |
| 1070 | |
| 1071 static void | |
| 1072 issue_prefetch_ref (struct mem_ref *ref, unsigned unroll_factor, unsigned ahead) | |
| 1073 { | |
| 1074 HOST_WIDE_INT delta; | |
|
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1075 tree addr, addr_base, write_p, local, forward; |
| 0 | 1076 gimple prefetch; |
| 1077 gimple_stmt_iterator bsi; | |
| 1078 unsigned n_prefetches, ap; | |
| 1079 bool nontemporal = ref->reuse_distance >= L2_CACHE_SIZE_BYTES; | |
| 1080 | |
| 1081 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 1082 fprintf (dump_file, "Issued%s prefetch for %p.\n", | |
| 1083 nontemporal ? " nontemporal" : "", | |
| 1084 (void *) ref); | |
| 1085 | |
| 1086 bsi = gsi_for_stmt (ref->stmt); | |
| 1087 | |
| 1088 n_prefetches = ((unroll_factor + ref->prefetch_mod - 1) | |
| 1089 / ref->prefetch_mod); | |
| 1090 addr_base = build_fold_addr_expr_with_type (ref->mem, ptr_type_node); | |
| 1091 addr_base = force_gimple_operand_gsi (&bsi, unshare_expr (addr_base), | |
| 1092 true, NULL, true, GSI_SAME_STMT); | |
| 1093 write_p = ref->write_p ? integer_one_node : integer_zero_node; | |
|
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1094 local = nontemporal ? integer_zero_node : integer_three_node; |
| 0 | 1095 |
| 1096 for (ap = 0; ap < n_prefetches; ap++) | |
| 1097 { | |
|
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1098 if (cst_and_fits_in_hwi (ref->group->step)) |
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1099 { |
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1100 /* Determine the address to prefetch. */ |
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1101 delta = (ahead + ap * ref->prefetch_mod) * |
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1102 int_cst_value (ref->group->step); |
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1103 addr = fold_build2 (POINTER_PLUS_EXPR, ptr_type_node, |
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1104 addr_base, size_int (delta)); |
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1105 addr = force_gimple_operand_gsi (&bsi, unshare_expr (addr), true, NULL, |
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1106 true, GSI_SAME_STMT); |
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1107 } |
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1108 else |
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1109 { |
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1110 /* The step size is non-constant but loop-invariant. We use the |
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1111 heuristic to simply prefetch ahead iterations ahead. */ |
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1112 forward = fold_build2 (MULT_EXPR, sizetype, |
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1113 fold_convert (sizetype, ref->group->step), |
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1114 fold_convert (sizetype, size_int (ahead))); |
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1115 addr = fold_build2 (POINTER_PLUS_EXPR, ptr_type_node, addr_base, |
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1116 forward); |
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1117 addr = force_gimple_operand_gsi (&bsi, unshare_expr (addr), true, |
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1118 NULL, true, GSI_SAME_STMT); |
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1119 } |
| 0 | 1120 /* Create the prefetch instruction. */ |
| 1121 prefetch = gimple_build_call (built_in_decls[BUILT_IN_PREFETCH], | |
| 1122 3, addr, write_p, local); | |
| 1123 gsi_insert_before (&bsi, prefetch, GSI_SAME_STMT); | |
| 1124 } | |
| 1125 } | |
| 1126 | |
| 1127 /* Issue prefetches for the references in GROUPS into loop as decided before. | |
| 1128 HEAD is the number of iterations to prefetch ahead. UNROLL_FACTOR is the | |
| 1129 factor by that LOOP was unrolled. */ | |
| 1130 | |
| 1131 static void | |
| 1132 issue_prefetches (struct mem_ref_group *groups, | |
| 1133 unsigned unroll_factor, unsigned ahead) | |
| 1134 { | |
| 1135 struct mem_ref *ref; | |
| 1136 | |
| 1137 for (; groups; groups = groups->next) | |
| 1138 for (ref = groups->refs; ref; ref = ref->next) | |
| 1139 if (ref->issue_prefetch_p) | |
| 1140 issue_prefetch_ref (ref, unroll_factor, ahead); | |
| 1141 } | |
| 1142 | |
| 1143 /* Returns true if REF is a memory write for that a nontemporal store insn | |
| 1144 can be used. */ | |
| 1145 | |
| 1146 static bool | |
| 1147 nontemporal_store_p (struct mem_ref *ref) | |
| 1148 { | |
| 1149 enum machine_mode mode; | |
| 1150 enum insn_code code; | |
| 1151 | |
| 1152 /* REF must be a write that is not reused. We require it to be independent | |
| 1153 on all other memory references in the loop, as the nontemporal stores may | |
| 1154 be reordered with respect to other memory references. */ | |
| 1155 if (!ref->write_p | |
| 1156 || !ref->independent_p | |
| 1157 || ref->reuse_distance < L2_CACHE_SIZE_BYTES) | |
| 1158 return false; | |
| 1159 | |
| 1160 /* Check that we have the storent instruction for the mode. */ | |
| 1161 mode = TYPE_MODE (TREE_TYPE (ref->mem)); | |
| 1162 if (mode == BLKmode) | |
| 1163 return false; | |
| 1164 | |
|
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1165 code = optab_handler (storent_optab, mode); |
| 0 | 1166 return code != CODE_FOR_nothing; |
| 1167 } | |
| 1168 | |
| 1169 /* If REF is a nontemporal store, we mark the corresponding modify statement | |
| 1170 and return true. Otherwise, we return false. */ | |
| 1171 | |
| 1172 static bool | |
| 1173 mark_nontemporal_store (struct mem_ref *ref) | |
| 1174 { | |
| 1175 if (!nontemporal_store_p (ref)) | |
| 1176 return false; | |
| 1177 | |
| 1178 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 1179 fprintf (dump_file, "Marked reference %p as a nontemporal store.\n", | |
| 1180 (void *) ref); | |
| 1181 | |
| 1182 gimple_assign_set_nontemporal_move (ref->stmt, true); | |
| 1183 ref->storent_p = true; | |
| 1184 | |
| 1185 return true; | |
| 1186 } | |
| 1187 | |
| 1188 /* Issue a memory fence instruction after LOOP. */ | |
| 1189 | |
| 1190 static void | |
| 1191 emit_mfence_after_loop (struct loop *loop) | |
| 1192 { | |
| 1193 VEC (edge, heap) *exits = get_loop_exit_edges (loop); | |
| 1194 edge exit; | |
| 1195 gimple call; | |
| 1196 gimple_stmt_iterator bsi; | |
| 1197 unsigned i; | |
| 1198 | |
|
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1199 FOR_EACH_VEC_ELT (edge, exits, i, exit) |
| 0 | 1200 { |
| 1201 call = gimple_build_call (FENCE_FOLLOWING_MOVNT, 0); | |
| 1202 | |
| 1203 if (!single_pred_p (exit->dest) | |
| 1204 /* If possible, we prefer not to insert the fence on other paths | |
| 1205 in cfg. */ | |
| 1206 && !(exit->flags & EDGE_ABNORMAL)) | |
| 1207 split_loop_exit_edge (exit); | |
| 1208 bsi = gsi_after_labels (exit->dest); | |
| 1209 | |
| 1210 gsi_insert_before (&bsi, call, GSI_NEW_STMT); | |
| 1211 mark_virtual_ops_for_renaming (call); | |
| 1212 } | |
| 1213 | |
| 1214 VEC_free (edge, heap, exits); | |
| 1215 update_ssa (TODO_update_ssa_only_virtuals); | |
| 1216 } | |
| 1217 | |
| 1218 /* Returns true if we can use storent in loop, false otherwise. */ | |
| 1219 | |
| 1220 static bool | |
| 1221 may_use_storent_in_loop_p (struct loop *loop) | |
| 1222 { | |
| 1223 bool ret = true; | |
| 1224 | |
| 1225 if (loop->inner != NULL) | |
| 1226 return false; | |
| 1227 | |
| 1228 /* If we must issue a mfence insn after using storent, check that there | |
| 1229 is a suitable place for it at each of the loop exits. */ | |
| 1230 if (FENCE_FOLLOWING_MOVNT != NULL_TREE) | |
| 1231 { | |
| 1232 VEC (edge, heap) *exits = get_loop_exit_edges (loop); | |
| 1233 unsigned i; | |
| 1234 edge exit; | |
| 1235 | |
|
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1236 FOR_EACH_VEC_ELT (edge, exits, i, exit) |
| 0 | 1237 if ((exit->flags & EDGE_ABNORMAL) |
| 1238 && exit->dest == EXIT_BLOCK_PTR) | |
| 1239 ret = false; | |
| 1240 | |
| 1241 VEC_free (edge, heap, exits); | |
| 1242 } | |
| 1243 | |
| 1244 return ret; | |
| 1245 } | |
| 1246 | |
| 1247 /* Marks nontemporal stores in LOOP. GROUPS contains the description of memory | |
| 1248 references in the loop. */ | |
| 1249 | |
| 1250 static void | |
| 1251 mark_nontemporal_stores (struct loop *loop, struct mem_ref_group *groups) | |
| 1252 { | |
| 1253 struct mem_ref *ref; | |
| 1254 bool any = false; | |
| 1255 | |
| 1256 if (!may_use_storent_in_loop_p (loop)) | |
| 1257 return; | |
| 1258 | |
| 1259 for (; groups; groups = groups->next) | |
| 1260 for (ref = groups->refs; ref; ref = ref->next) | |
| 1261 any |= mark_nontemporal_store (ref); | |
| 1262 | |
| 1263 if (any && FENCE_FOLLOWING_MOVNT != NULL_TREE) | |
| 1264 emit_mfence_after_loop (loop); | |
| 1265 } | |
| 1266 | |
| 1267 /* Determines whether we can profitably unroll LOOP FACTOR times, and if | |
| 1268 this is the case, fill in DESC by the description of number of | |
| 1269 iterations. */ | |
| 1270 | |
| 1271 static bool | |
| 1272 should_unroll_loop_p (struct loop *loop, struct tree_niter_desc *desc, | |
| 1273 unsigned factor) | |
| 1274 { | |
| 1275 if (!can_unroll_loop_p (loop, factor, desc)) | |
| 1276 return false; | |
| 1277 | |
| 1278 /* We only consider loops without control flow for unrolling. This is not | |
| 1279 a hard restriction -- tree_unroll_loop works with arbitrary loops | |
| 1280 as well; but the unrolling/prefetching is usually more profitable for | |
| 1281 loops consisting of a single basic block, and we want to limit the | |
| 1282 code growth. */ | |
| 1283 if (loop->num_nodes > 2) | |
| 1284 return false; | |
| 1285 | |
| 1286 return true; | |
| 1287 } | |
| 1288 | |
| 1289 /* Determine the coefficient by that unroll LOOP, from the information | |
| 1290 contained in the list of memory references REFS. Description of | |
| 1291 umber of iterations of LOOP is stored to DESC. NINSNS is the number of | |
| 1292 insns of the LOOP. EST_NITER is the estimated number of iterations of | |
| 1293 the loop, or -1 if no estimate is available. */ | |
| 1294 | |
| 1295 static unsigned | |
| 1296 determine_unroll_factor (struct loop *loop, struct mem_ref_group *refs, | |
| 1297 unsigned ninsns, struct tree_niter_desc *desc, | |
| 1298 HOST_WIDE_INT est_niter) | |
| 1299 { | |
| 1300 unsigned upper_bound; | |
| 1301 unsigned nfactor, factor, mod_constraint; | |
| 1302 struct mem_ref_group *agp; | |
| 1303 struct mem_ref *ref; | |
| 1304 | |
| 1305 /* First check whether the loop is not too large to unroll. We ignore | |
| 1306 PARAM_MAX_UNROLL_TIMES, because for small loops, it prevented us | |
| 1307 from unrolling them enough to make exactly one cache line covered by each | |
| 1308 iteration. Also, the goal of PARAM_MAX_UNROLL_TIMES is to prevent | |
| 1309 us from unrolling the loops too many times in cases where we only expect | |
| 1310 gains from better scheduling and decreasing loop overhead, which is not | |
| 1311 the case here. */ | |
| 1312 upper_bound = PARAM_VALUE (PARAM_MAX_UNROLLED_INSNS) / ninsns; | |
| 1313 | |
| 1314 /* If we unrolled the loop more times than it iterates, the unrolled version | |
| 1315 of the loop would be never entered. */ | |
| 1316 if (est_niter >= 0 && est_niter < (HOST_WIDE_INT) upper_bound) | |
| 1317 upper_bound = est_niter; | |
| 1318 | |
| 1319 if (upper_bound <= 1) | |
| 1320 return 1; | |
| 1321 | |
| 1322 /* Choose the factor so that we may prefetch each cache just once, | |
| 1323 but bound the unrolling by UPPER_BOUND. */ | |
| 1324 factor = 1; | |
| 1325 for (agp = refs; agp; agp = agp->next) | |
| 1326 for (ref = agp->refs; ref; ref = ref->next) | |
| 1327 if (should_issue_prefetch_p (ref)) | |
| 1328 { | |
| 1329 mod_constraint = ref->prefetch_mod; | |
| 1330 nfactor = least_common_multiple (mod_constraint, factor); | |
| 1331 if (nfactor <= upper_bound) | |
| 1332 factor = nfactor; | |
| 1333 } | |
| 1334 | |
| 1335 if (!should_unroll_loop_p (loop, desc, factor)) | |
| 1336 return 1; | |
| 1337 | |
| 1338 return factor; | |
| 1339 } | |
| 1340 | |
| 1341 /* Returns the total volume of the memory references REFS, taking into account | |
| 1342 reuses in the innermost loop and cache line size. TODO -- we should also | |
| 1343 take into account reuses across the iterations of the loops in the loop | |
| 1344 nest. */ | |
| 1345 | |
| 1346 static unsigned | |
| 1347 volume_of_references (struct mem_ref_group *refs) | |
| 1348 { | |
| 1349 unsigned volume = 0; | |
| 1350 struct mem_ref_group *gr; | |
| 1351 struct mem_ref *ref; | |
| 1352 | |
| 1353 for (gr = refs; gr; gr = gr->next) | |
| 1354 for (ref = gr->refs; ref; ref = ref->next) | |
| 1355 { | |
| 1356 /* Almost always reuses another value? */ | |
| 1357 if (ref->prefetch_before != PREFETCH_ALL) | |
| 1358 continue; | |
| 1359 | |
| 1360 /* If several iterations access the same cache line, use the size of | |
| 1361 the line divided by this number. Otherwise, a cache line is | |
| 1362 accessed in each iteration. TODO -- in the latter case, we should | |
| 1363 take the size of the reference into account, rounding it up on cache | |
| 1364 line size multiple. */ | |
| 1365 volume += L1_CACHE_LINE_SIZE / ref->prefetch_mod; | |
| 1366 } | |
| 1367 return volume; | |
| 1368 } | |
| 1369 | |
| 1370 /* Returns the volume of memory references accessed across VEC iterations of | |
| 1371 loops, whose sizes are described in the LOOP_SIZES array. N is the number | |
| 1372 of the loops in the nest (length of VEC and LOOP_SIZES vectors). */ | |
| 1373 | |
| 1374 static unsigned | |
| 1375 volume_of_dist_vector (lambda_vector vec, unsigned *loop_sizes, unsigned n) | |
| 1376 { | |
| 1377 unsigned i; | |
| 1378 | |
| 1379 for (i = 0; i < n; i++) | |
| 1380 if (vec[i] != 0) | |
| 1381 break; | |
| 1382 | |
| 1383 if (i == n) | |
| 1384 return 0; | |
| 1385 | |
| 1386 gcc_assert (vec[i] > 0); | |
| 1387 | |
| 1388 /* We ignore the parts of the distance vector in subloops, since usually | |
| 1389 the numbers of iterations are much smaller. */ | |
| 1390 return loop_sizes[i] * vec[i]; | |
| 1391 } | |
| 1392 | |
| 1393 /* Add the steps of ACCESS_FN multiplied by STRIDE to the array STRIDE | |
| 1394 at the position corresponding to the loop of the step. N is the depth | |
| 1395 of the considered loop nest, and, LOOP is its innermost loop. */ | |
| 1396 | |
| 1397 static void | |
| 1398 add_subscript_strides (tree access_fn, unsigned stride, | |
| 1399 HOST_WIDE_INT *strides, unsigned n, struct loop *loop) | |
| 1400 { | |
| 1401 struct loop *aloop; | |
| 1402 tree step; | |
| 1403 HOST_WIDE_INT astep; | |
| 1404 unsigned min_depth = loop_depth (loop) - n; | |
| 1405 | |
| 1406 while (TREE_CODE (access_fn) == POLYNOMIAL_CHREC) | |
| 1407 { | |
| 1408 aloop = get_chrec_loop (access_fn); | |
| 1409 step = CHREC_RIGHT (access_fn); | |
| 1410 access_fn = CHREC_LEFT (access_fn); | |
| 1411 | |
| 1412 if ((unsigned) loop_depth (aloop) <= min_depth) | |
| 1413 continue; | |
| 1414 | |
| 1415 if (host_integerp (step, 0)) | |
| 1416 astep = tree_low_cst (step, 0); | |
| 1417 else | |
| 1418 astep = L1_CACHE_LINE_SIZE; | |
| 1419 | |
| 1420 strides[n - 1 - loop_depth (loop) + loop_depth (aloop)] += astep * stride; | |
| 1421 | |
| 1422 } | |
| 1423 } | |
| 1424 | |
| 1425 /* Returns the volume of memory references accessed between two consecutive | |
| 1426 self-reuses of the reference DR. We consider the subscripts of DR in N | |
| 1427 loops, and LOOP_SIZES contains the volumes of accesses in each of the | |
| 1428 loops. LOOP is the innermost loop of the current loop nest. */ | |
| 1429 | |
| 1430 static unsigned | |
| 1431 self_reuse_distance (data_reference_p dr, unsigned *loop_sizes, unsigned n, | |
| 1432 struct loop *loop) | |
| 1433 { | |
| 1434 tree stride, access_fn; | |
| 1435 HOST_WIDE_INT *strides, astride; | |
| 1436 VEC (tree, heap) *access_fns; | |
| 1437 tree ref = DR_REF (dr); | |
| 1438 unsigned i, ret = ~0u; | |
| 1439 | |
| 1440 /* In the following example: | |
| 1441 | |
| 1442 for (i = 0; i < N; i++) | |
| 1443 for (j = 0; j < N; j++) | |
| 1444 use (a[j][i]); | |
| 1445 the same cache line is accessed each N steps (except if the change from | |
| 1446 i to i + 1 crosses the boundary of the cache line). Thus, for self-reuse, | |
| 1447 we cannot rely purely on the results of the data dependence analysis. | |
| 1448 | |
| 1449 Instead, we compute the stride of the reference in each loop, and consider | |
| 1450 the innermost loop in that the stride is less than cache size. */ | |
| 1451 | |
| 1452 strides = XCNEWVEC (HOST_WIDE_INT, n); | |
| 1453 access_fns = DR_ACCESS_FNS (dr); | |
| 1454 | |
|
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1455 FOR_EACH_VEC_ELT (tree, access_fns, i, access_fn) |
| 0 | 1456 { |
| 1457 /* Keep track of the reference corresponding to the subscript, so that we | |
| 1458 know its stride. */ | |
| 1459 while (handled_component_p (ref) && TREE_CODE (ref) != ARRAY_REF) | |
| 1460 ref = TREE_OPERAND (ref, 0); | |
|
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1461 |
| 0 | 1462 if (TREE_CODE (ref) == ARRAY_REF) |
| 1463 { | |
| 1464 stride = TYPE_SIZE_UNIT (TREE_TYPE (ref)); | |
| 1465 if (host_integerp (stride, 1)) | |
| 1466 astride = tree_low_cst (stride, 1); | |
| 1467 else | |
| 1468 astride = L1_CACHE_LINE_SIZE; | |
| 1469 | |
| 1470 ref = TREE_OPERAND (ref, 0); | |
| 1471 } | |
| 1472 else | |
| 1473 astride = 1; | |
| 1474 | |
| 1475 add_subscript_strides (access_fn, astride, strides, n, loop); | |
| 1476 } | |
| 1477 | |
| 1478 for (i = n; i-- > 0; ) | |
| 1479 { | |
| 1480 unsigned HOST_WIDE_INT s; | |
| 1481 | |
| 1482 s = strides[i] < 0 ? -strides[i] : strides[i]; | |
| 1483 | |
| 1484 if (s < (unsigned) L1_CACHE_LINE_SIZE | |
| 1485 && (loop_sizes[i] | |
| 1486 > (unsigned) (L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION))) | |
| 1487 { | |
| 1488 ret = loop_sizes[i]; | |
| 1489 break; | |
| 1490 } | |
| 1491 } | |
| 1492 | |
| 1493 free (strides); | |
| 1494 return ret; | |
| 1495 } | |
| 1496 | |
| 1497 /* Determines the distance till the first reuse of each reference in REFS | |
| 1498 in the loop nest of LOOP. NO_OTHER_REFS is true if there are no other | |
| 1499 memory references in the loop. */ | |
| 1500 | |
| 1501 static void | |
| 1502 determine_loop_nest_reuse (struct loop *loop, struct mem_ref_group *refs, | |
| 1503 bool no_other_refs) | |
| 1504 { | |
| 1505 struct loop *nest, *aloop; | |
| 1506 VEC (data_reference_p, heap) *datarefs = NULL; | |
| 1507 VEC (ddr_p, heap) *dependences = NULL; | |
| 1508 struct mem_ref_group *gr; | |
| 1509 struct mem_ref *ref, *refb; | |
| 1510 VEC (loop_p, heap) *vloops = NULL; | |
| 1511 unsigned *loop_data_size; | |
| 1512 unsigned i, j, n; | |
| 1513 unsigned volume, dist, adist; | |
| 1514 HOST_WIDE_INT vol; | |
| 1515 data_reference_p dr; | |
| 1516 ddr_p dep; | |
| 1517 | |
| 1518 if (loop->inner) | |
| 1519 return; | |
| 1520 | |
| 1521 /* Find the outermost loop of the loop nest of loop (we require that | |
| 1522 there are no sibling loops inside the nest). */ | |
| 1523 nest = loop; | |
| 1524 while (1) | |
| 1525 { | |
| 1526 aloop = loop_outer (nest); | |
| 1527 | |
| 1528 if (aloop == current_loops->tree_root | |
| 1529 || aloop->inner->next) | |
| 1530 break; | |
| 1531 | |
| 1532 nest = aloop; | |
| 1533 } | |
| 1534 | |
| 1535 /* For each loop, determine the amount of data accessed in each iteration. | |
| 1536 We use this to estimate whether the reference is evicted from the | |
| 1537 cache before its reuse. */ | |
| 1538 find_loop_nest (nest, &vloops); | |
| 1539 n = VEC_length (loop_p, vloops); | |
| 1540 loop_data_size = XNEWVEC (unsigned, n); | |
| 1541 volume = volume_of_references (refs); | |
| 1542 i = n; | |
| 1543 while (i-- != 0) | |
| 1544 { | |
| 1545 loop_data_size[i] = volume; | |
| 1546 /* Bound the volume by the L2 cache size, since above this bound, | |
| 1547 all dependence distances are equivalent. */ | |
| 1548 if (volume > L2_CACHE_SIZE_BYTES) | |
| 1549 continue; | |
| 1550 | |
| 1551 aloop = VEC_index (loop_p, vloops, i); | |
| 1552 vol = estimated_loop_iterations_int (aloop, false); | |
| 1553 if (vol < 0) | |
| 1554 vol = expected_loop_iterations (aloop); | |
| 1555 volume *= vol; | |
| 1556 } | |
| 1557 | |
| 1558 /* Prepare the references in the form suitable for data dependence | |
| 1559 analysis. We ignore unanalyzable data references (the results | |
| 1560 are used just as a heuristics to estimate temporality of the | |
| 1561 references, hence we do not need to worry about correctness). */ | |
| 1562 for (gr = refs; gr; gr = gr->next) | |
| 1563 for (ref = gr->refs; ref; ref = ref->next) | |
| 1564 { | |
|
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|
1565 dr = create_data_ref (nest, loop_containing_stmt (ref->stmt), |
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1566 ref->mem, ref->stmt, !ref->write_p); |
| 0 | 1567 |
| 1568 if (dr) | |
| 1569 { | |
| 1570 ref->reuse_distance = volume; | |
| 1571 dr->aux = ref; | |
| 1572 VEC_safe_push (data_reference_p, heap, datarefs, dr); | |
| 1573 } | |
| 1574 else | |
| 1575 no_other_refs = false; | |
| 1576 } | |
| 1577 | |
|
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1578 FOR_EACH_VEC_ELT (data_reference_p, datarefs, i, dr) |
| 0 | 1579 { |
| 1580 dist = self_reuse_distance (dr, loop_data_size, n, loop); | |
| 1581 ref = (struct mem_ref *) dr->aux; | |
| 1582 if (ref->reuse_distance > dist) | |
| 1583 ref->reuse_distance = dist; | |
| 1584 | |
| 1585 if (no_other_refs) | |
| 1586 ref->independent_p = true; | |
| 1587 } | |
| 1588 | |
| 1589 compute_all_dependences (datarefs, &dependences, vloops, true); | |
| 1590 | |
|
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1591 FOR_EACH_VEC_ELT (ddr_p, dependences, i, dep) |
| 0 | 1592 { |
| 1593 if (DDR_ARE_DEPENDENT (dep) == chrec_known) | |
| 1594 continue; | |
| 1595 | |
| 1596 ref = (struct mem_ref *) DDR_A (dep)->aux; | |
| 1597 refb = (struct mem_ref *) DDR_B (dep)->aux; | |
| 1598 | |
| 1599 if (DDR_ARE_DEPENDENT (dep) == chrec_dont_know | |
| 1600 || DDR_NUM_DIST_VECTS (dep) == 0) | |
| 1601 { | |
| 1602 /* If the dependence cannot be analyzed, assume that there might be | |
| 1603 a reuse. */ | |
| 1604 dist = 0; | |
|
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1605 |
| 0 | 1606 ref->independent_p = false; |
| 1607 refb->independent_p = false; | |
| 1608 } | |
| 1609 else | |
| 1610 { | |
| 1611 /* The distance vectors are normalized to be always lexicographically | |
| 1612 positive, hence we cannot tell just from them whether DDR_A comes | |
| 1613 before DDR_B or vice versa. However, it is not important, | |
| 1614 anyway -- if DDR_A is close to DDR_B, then it is either reused in | |
| 1615 DDR_B (and it is not nontemporal), or it reuses the value of DDR_B | |
| 1616 in cache (and marking it as nontemporal would not affect | |
| 1617 anything). */ | |
| 1618 | |
| 1619 dist = volume; | |
| 1620 for (j = 0; j < DDR_NUM_DIST_VECTS (dep); j++) | |
| 1621 { | |
| 1622 adist = volume_of_dist_vector (DDR_DIST_VECT (dep, j), | |
| 1623 loop_data_size, n); | |
| 1624 | |
| 1625 /* If this is a dependence in the innermost loop (i.e., the | |
| 1626 distances in all superloops are zero) and it is not | |
| 1627 the trivial self-dependence with distance zero, record that | |
| 1628 the references are not completely independent. */ | |
| 1629 if (lambda_vector_zerop (DDR_DIST_VECT (dep, j), n - 1) | |
| 1630 && (ref != refb | |
| 1631 || DDR_DIST_VECT (dep, j)[n-1] != 0)) | |
| 1632 { | |
| 1633 ref->independent_p = false; | |
| 1634 refb->independent_p = false; | |
| 1635 } | |
| 1636 | |
| 1637 /* Ignore accesses closer than | |
| 1638 L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION, | |
| 1639 so that we use nontemporal prefetches e.g. if single memory | |
| 1640 location is accessed several times in a single iteration of | |
| 1641 the loop. */ | |
| 1642 if (adist < L1_CACHE_SIZE_BYTES / NONTEMPORAL_FRACTION) | |
| 1643 continue; | |
| 1644 | |
| 1645 if (adist < dist) | |
| 1646 dist = adist; | |
| 1647 } | |
| 1648 } | |
| 1649 | |
| 1650 if (ref->reuse_distance > dist) | |
| 1651 ref->reuse_distance = dist; | |
| 1652 if (refb->reuse_distance > dist) | |
| 1653 refb->reuse_distance = dist; | |
| 1654 } | |
| 1655 | |
| 1656 free_dependence_relations (dependences); | |
| 1657 free_data_refs (datarefs); | |
| 1658 free (loop_data_size); | |
| 1659 | |
| 1660 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 1661 { | |
| 1662 fprintf (dump_file, "Reuse distances:\n"); | |
| 1663 for (gr = refs; gr; gr = gr->next) | |
| 1664 for (ref = gr->refs; ref; ref = ref->next) | |
| 1665 fprintf (dump_file, " ref %p distance %u\n", | |
| 1666 (void *) ref, ref->reuse_distance); | |
| 1667 } | |
| 1668 } | |
| 1669 | |
|
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1670 /* Determine whether or not the trip count to ahead ratio is too small based |
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1671 on prefitablility consideration. |
|
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1672 AHEAD: the iteration ahead distance, |
|
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1673 EST_NITER: the estimated trip count. */ |
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1674 |
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1675 static bool |
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1676 trip_count_to_ahead_ratio_too_small_p (unsigned ahead, HOST_WIDE_INT est_niter) |
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1677 { |
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1678 /* Assume trip count to ahead ratio is big enough if the trip count could not |
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1679 be estimated at compile time. */ |
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1680 if (est_niter < 0) |
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1681 return false; |
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1682 |
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|
1683 if (est_niter < (HOST_WIDE_INT) (TRIP_COUNT_TO_AHEAD_RATIO * ahead)) |
|
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1684 { |
|
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1685 if (dump_file && (dump_flags & TDF_DETAILS)) |
|
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|
1686 fprintf (dump_file, |
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|
1687 "Not prefetching -- loop estimated to roll only %d times\n", |
|
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|
1688 (int) est_niter); |
|
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|
1689 return true; |
|
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|
1690 } |
|
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|
1691 |
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|
1692 return false; |
|
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|
1693 } |
|
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|
1694 |
|
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|
1695 /* Determine whether or not the number of memory references in the loop is |
|
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|
1696 reasonable based on the profitablity and compilation time considerations. |
|
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parents:
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diff
changeset
|
1697 NINSNS: estimated number of instructions in the loop, |
|
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|
1698 MEM_REF_COUNT: total number of memory references in the loop. */ |
|
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|
1699 |
|
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|
1700 static bool |
|
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|
1701 mem_ref_count_reasonable_p (unsigned ninsns, unsigned mem_ref_count) |
|
55
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|
1702 { |
|
67
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|
1703 int insn_to_mem_ratio; |
|
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1704 |
|
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|
1705 if (mem_ref_count == 0) |
|
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|
1706 return false; |
|
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|
1707 |
|
67
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|
1708 /* Miss rate computation (is_miss_rate_acceptable) and dependence analysis |
|
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|
1709 (compute_all_dependences) have high costs based on quadratic complexity. |
|
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1710 To avoid huge compilation time, we give up prefetching if mem_ref_count |
|
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|
1711 is too large. */ |
|
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|
1712 if (mem_ref_count > PREFETCH_MAX_MEM_REFS_PER_LOOP) |
|
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|
1713 return false; |
|
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|
1714 |
|
55
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|
1715 /* Prefetching improves performance by overlapping cache missing |
|
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|
1716 memory accesses with CPU operations. If the loop does not have |
|
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|
1717 enough CPU operations to overlap with memory operations, prefetching |
|
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changeset
|
1718 won't give a significant benefit. One approximate way of checking |
|
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diff
changeset
|
1719 this is to require the ratio of instructions to memory references to |
|
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|
1720 be above a certain limit. This approximation works well in practice. |
|
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diff
changeset
|
1721 TODO: Implement a more precise computation by estimating the time |
|
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parents:
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diff
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|
1722 for each CPU or memory op in the loop. Time estimates for memory ops |
|
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parents:
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diff
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|
1723 should account for cache misses. */ |
|
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parents:
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|
1724 insn_to_mem_ratio = ninsns / mem_ref_count; |
|
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|
1725 |
|
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parents:
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diff
changeset
|
1726 if (insn_to_mem_ratio < PREFETCH_MIN_INSN_TO_MEM_RATIO) |
|
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|
1727 { |
|
63
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|
1728 if (dump_file && (dump_flags & TDF_DETAILS)) |
|
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|
1729 fprintf (dump_file, |
|
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|
1730 "Not prefetching -- instruction to memory reference ratio (%d) too small\n", |
|
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|
1731 insn_to_mem_ratio); |
|
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|
1732 return false; |
|
55
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parents:
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|
1733 } |
|
77e2b8dfacca
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|
1734 |
|
67
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|
1735 return true; |
|
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|
1736 } |
|
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|
1737 |
|
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|
1738 /* Determine whether or not the instruction to prefetch ratio in the loop is |
|
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|
1739 too small based on the profitablity consideration. |
|
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|
1740 NINSNS: estimated number of instructions in the loop, |
|
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|
1741 PREFETCH_COUNT: an estimate of the number of prefetches, |
|
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|
1742 UNROLL_FACTOR: the factor to unroll the loop if prefetching. */ |
|
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|
1743 |
|
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|
1744 static bool |
|
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|
1745 insn_to_prefetch_ratio_too_small_p (unsigned ninsns, unsigned prefetch_count, |
|
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|
1746 unsigned unroll_factor) |
|
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|
1747 { |
|
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|
1748 int insn_to_prefetch_ratio; |
|
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|
1749 |
|
63
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|
1750 /* Prefetching most likely causes performance degradation when the instruction |
|
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diff
changeset
|
1751 to prefetch ratio is too small. Too many prefetch instructions in a loop |
|
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|
1752 may reduce the I-cache performance. |
|
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diff
changeset
|
1753 (unroll_factor * ninsns) is used to estimate the number of instructions in |
|
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diff
changeset
|
1754 the unrolled loop. This implementation is a bit simplistic -- the number |
|
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diff
changeset
|
1755 of issued prefetch instructions is also affected by unrolling. So, |
|
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diff
changeset
|
1756 prefetch_mod and the unroll factor should be taken into account when |
|
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|
1757 determining prefetch_count. Also, the number of insns of the unrolled |
|
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diff
changeset
|
1758 loop will usually be significantly smaller than the number of insns of the |
|
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|
1759 original loop * unroll_factor (at least the induction variable increases |
|
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|
1760 and the exit branches will get eliminated), so it might be better to use |
|
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changeset
|
1761 tree_estimate_loop_size + estimated_unrolled_size. */ |
|
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changeset
|
1762 insn_to_prefetch_ratio = (unroll_factor * ninsns) / prefetch_count; |
|
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|
1763 if (insn_to_prefetch_ratio < MIN_INSN_TO_PREFETCH_RATIO) |
|
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changeset
|
1764 { |
|
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changeset
|
1765 if (dump_file && (dump_flags & TDF_DETAILS)) |
|
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changeset
|
1766 fprintf (dump_file, |
|
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changeset
|
1767 "Not prefetching -- instruction to prefetch ratio (%d) too small\n", |
|
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changeset
|
1768 insn_to_prefetch_ratio); |
|
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|
1769 return true; |
|
63
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changeset
|
1770 } |
|
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changeset
|
1771 |
|
67
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|
1772 return false; |
|
55
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diff
changeset
|
1773 } |
|
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diff
changeset
|
1774 |
|
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diff
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|
1775 |
| 0 | 1776 /* Issue prefetch instructions for array references in LOOP. Returns |
| 1777 true if the LOOP was unrolled. */ | |
| 1778 | |
| 1779 static bool | |
| 1780 loop_prefetch_arrays (struct loop *loop) | |
| 1781 { | |
| 1782 struct mem_ref_group *refs; | |
| 1783 unsigned ahead, ninsns, time, unroll_factor; | |
| 1784 HOST_WIDE_INT est_niter; | |
| 1785 struct tree_niter_desc desc; | |
| 1786 bool unrolled = false, no_other_refs; | |
|
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1787 unsigned prefetch_count; |
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1788 unsigned mem_ref_count; |
| 0 | 1789 |
| 1790 if (optimize_loop_nest_for_size_p (loop)) | |
| 1791 { | |
| 1792 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 1793 fprintf (dump_file, " ignored (cold area)\n"); | |
| 1794 return false; | |
| 1795 } | |
| 1796 | |
|
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1797 /* FIXME: the time should be weighted by the probabilities of the blocks in |
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1798 the loop body. */ |
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1799 time = tree_num_loop_insns (loop, &eni_time_weights); |
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1800 if (time == 0) |
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1801 return false; |
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1802 |
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1803 ahead = (PREFETCH_LATENCY + time - 1) / time; |
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1804 est_niter = estimated_loop_iterations_int (loop, false); |
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1805 |
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1806 /* Prefetching is not likely to be profitable if the trip count to ahead |
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1807 ratio is too small. */ |
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1808 if (trip_count_to_ahead_ratio_too_small_p (ahead, est_niter)) |
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1809 return false; |
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1810 |
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1811 ninsns = tree_num_loop_insns (loop, &eni_size_weights); |
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1812 |
| 0 | 1813 /* Step 1: gather the memory references. */ |
|
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1814 refs = gather_memory_references (loop, &no_other_refs, &mem_ref_count); |
| 0 | 1815 |
|
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1816 /* Give up prefetching if the number of memory references in the |
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1817 loop is not reasonable based on profitablity and compilation time |
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1818 considerations. */ |
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1819 if (!mem_ref_count_reasonable_p (ninsns, mem_ref_count)) |
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1820 goto fail; |
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1821 |
| 0 | 1822 /* Step 2: estimate the reuse effects. */ |
| 1823 prune_by_reuse (refs); | |
| 1824 | |
|
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1825 if (nothing_to_prefetch_p (refs)) |
| 0 | 1826 goto fail; |
| 1827 | |
| 1828 determine_loop_nest_reuse (loop, refs, no_other_refs); | |
| 1829 | |
|
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1830 /* Step 3: determine unroll factor. */ |
| 0 | 1831 unroll_factor = determine_unroll_factor (loop, refs, ninsns, &desc, |
| 1832 est_niter); | |
|
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1833 |
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1834 /* Estimate prefetch count for the unrolled loop. */ |
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1835 prefetch_count = estimate_prefetch_count (refs, unroll_factor); |
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1836 if (prefetch_count == 0) |
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1837 goto fail; |
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1838 |
| 0 | 1839 if (dump_file && (dump_flags & TDF_DETAILS)) |
|
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1840 fprintf (dump_file, "Ahead %d, unroll factor %d, trip count " |
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1841 HOST_WIDE_INT_PRINT_DEC "\n" |
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1842 "insn count %d, mem ref count %d, prefetch count %d\n", |
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1843 ahead, unroll_factor, est_niter, |
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1844 ninsns, mem_ref_count, prefetch_count); |
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1845 |
|
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1846 /* Prefetching is not likely to be profitable if the instruction to prefetch |
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1847 ratio is too small. */ |
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1848 if (insn_to_prefetch_ratio_too_small_p (ninsns, prefetch_count, |
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1849 unroll_factor)) |
|
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1850 goto fail; |
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1851 |
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1852 mark_nontemporal_stores (loop, refs); |
| 0 | 1853 |
| 1854 /* Step 4: what to prefetch? */ | |
| 1855 if (!schedule_prefetches (refs, unroll_factor, ahead)) | |
| 1856 goto fail; | |
| 1857 | |
| 1858 /* Step 5: unroll the loop. TODO -- peeling of first and last few | |
| 1859 iterations so that we do not issue superfluous prefetches. */ | |
| 1860 if (unroll_factor != 1) | |
| 1861 { | |
| 1862 tree_unroll_loop (loop, unroll_factor, | |
| 1863 single_dom_exit (loop), &desc); | |
| 1864 unrolled = true; | |
| 1865 } | |
| 1866 | |
| 1867 /* Step 6: issue the prefetches. */ | |
| 1868 issue_prefetches (refs, unroll_factor, ahead); | |
| 1869 | |
| 1870 fail: | |
| 1871 release_mem_refs (refs); | |
| 1872 return unrolled; | |
| 1873 } | |
| 1874 | |
| 1875 /* Issue prefetch instructions for array references in loops. */ | |
| 1876 | |
| 1877 unsigned int | |
| 1878 tree_ssa_prefetch_arrays (void) | |
| 1879 { | |
| 1880 loop_iterator li; | |
| 1881 struct loop *loop; | |
| 1882 bool unrolled = false; | |
| 1883 int todo_flags = 0; | |
| 1884 | |
| 1885 if (!HAVE_prefetch | |
| 1886 /* It is possible to ask compiler for say -mtune=i486 -march=pentium4. | |
| 1887 -mtune=i486 causes us having PREFETCH_BLOCK 0, since this is part | |
| 1888 of processor costs and i486 does not have prefetch, but | |
| 1889 -march=pentium4 causes HAVE_prefetch to be true. Ugh. */ | |
| 1890 || PREFETCH_BLOCK == 0) | |
| 1891 return 0; | |
| 1892 | |
| 1893 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 1894 { | |
| 1895 fprintf (dump_file, "Prefetching parameters:\n"); | |
| 1896 fprintf (dump_file, " simultaneous prefetches: %d\n", | |
| 1897 SIMULTANEOUS_PREFETCHES); | |
| 1898 fprintf (dump_file, " prefetch latency: %d\n", PREFETCH_LATENCY); | |
| 1899 fprintf (dump_file, " prefetch block size: %d\n", PREFETCH_BLOCK); | |
| 1900 fprintf (dump_file, " L1 cache size: %d lines, %d kB\n", | |
| 1901 L1_CACHE_SIZE_BYTES / L1_CACHE_LINE_SIZE, L1_CACHE_SIZE); | |
| 1902 fprintf (dump_file, " L1 cache line size: %d\n", L1_CACHE_LINE_SIZE); | |
| 1903 fprintf (dump_file, " L2 cache size: %d kB\n", L2_CACHE_SIZE); | |
|
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1904 fprintf (dump_file, " min insn-to-prefetch ratio: %d \n", |
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1905 MIN_INSN_TO_PREFETCH_RATIO); |
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1906 fprintf (dump_file, " min insn-to-mem ratio: %d \n", |
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1907 PREFETCH_MIN_INSN_TO_MEM_RATIO); |
| 0 | 1908 fprintf (dump_file, "\n"); |
| 1909 } | |
| 1910 | |
| 1911 initialize_original_copy_tables (); | |
| 1912 | |
| 1913 if (!built_in_decls[BUILT_IN_PREFETCH]) | |
| 1914 { | |
|
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1915 tree type = build_function_type_list (void_type_node, |
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1916 const_ptr_type_node, NULL_TREE); |
| 0 | 1917 tree decl = add_builtin_function ("__builtin_prefetch", type, |
| 1918 BUILT_IN_PREFETCH, BUILT_IN_NORMAL, | |
| 1919 NULL, NULL_TREE); | |
| 1920 DECL_IS_NOVOPS (decl) = true; | |
| 1921 built_in_decls[BUILT_IN_PREFETCH] = decl; | |
| 1922 } | |
| 1923 | |
| 1924 /* We assume that size of cache line is a power of two, so verify this | |
| 1925 here. */ | |
| 1926 gcc_assert ((PREFETCH_BLOCK & (PREFETCH_BLOCK - 1)) == 0); | |
| 1927 | |
| 1928 FOR_EACH_LOOP (li, loop, LI_FROM_INNERMOST) | |
| 1929 { | |
| 1930 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 1931 fprintf (dump_file, "Processing loop %d:\n", loop->num); | |
| 1932 | |
| 1933 unrolled |= loop_prefetch_arrays (loop); | |
| 1934 | |
| 1935 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 1936 fprintf (dump_file, "\n\n"); | |
| 1937 } | |
| 1938 | |
| 1939 if (unrolled) | |
| 1940 { | |
| 1941 scev_reset (); | |
| 1942 todo_flags |= TODO_cleanup_cfg; | |
| 1943 } | |
| 1944 | |
| 1945 free_original_copy_tables (); | |
| 1946 return todo_flags; | |
| 1947 } |