1 /* 2 * Copyright 2016 Intel Corporation 3 * 4 * Permission is hereby granted, free of charge, to any person obtaining a 5 * copy of this software and associated documentation files (the "Software"), 6 * to deal in the Software without restriction, including without limitation 7 * the rights to use, copy, modify, merge, publish, distribute, sublicense, 8 * and/or sell copies of the Software, and to permit persons to whom the 9 * Software is furnished to do so, subject to the following conditions: 10 * 11 * The above copyright notice and this permission notice (including the next 12 * paragraph) shall be included in all copies or substantial portions of the 13 * Software. 14 * 15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 16 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 17 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL 18 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 19 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING 20 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER 21 * DEALINGS IN THE SOFTWARE. 22 */ 23 24 #include "nir.h" 25 #include "nir_builder.h" 26 #include "nir_control_flow.h" 27 #include "nir_loop_analyze.h" 28 29 /* Prepare this loop for unrolling by first converting to lcssa and then 30 * converting the phis from the loops first block and the block that follows 31 * the loop into regs. Partially converting out of SSA allows us to unroll 32 * the loop without having to keep track of and update phis along the way 33 * which gets tricky and doesn't add much value over conveting to regs. 34 * 35 * The loop may have a continue instruction at the end of the loop which does 36 * nothing. Once we're out of SSA, we can safely delete it so we don't have 37 * to deal with it later. 38 */ 39 static void 40 loop_prepare_for_unroll(nir_loop *loop) 41 { 42 nir_convert_loop_to_lcssa(loop); 43 44 nir_lower_phis_to_regs_block(nir_loop_first_block(loop)); 45 46 nir_block *block_after_loop = 47 nir_cf_node_as_block(nir_cf_node_next(&loop->cf_node)); 48 49 nir_lower_phis_to_regs_block(block_after_loop); 50 51 nir_instr *last_instr = nir_block_last_instr(nir_loop_last_block(loop)); 52 if (last_instr && last_instr->type == nir_instr_type_jump) { 53 assert(nir_instr_as_jump(last_instr)->type == nir_jump_continue); 54 nir_instr_remove(last_instr); 55 } 56 } 57 58 static void 59 get_first_blocks_in_terminator(nir_loop_terminator *term, 60 nir_block **first_break_block, 61 nir_block **first_continue_block) 62 { 63 if (term->continue_from_then) { 64 *first_continue_block = nir_if_first_then_block(term->nif); 65 *first_break_block = nir_if_first_else_block(term->nif); 66 } else { 67 *first_continue_block = nir_if_first_else_block(term->nif); 68 *first_break_block = nir_if_first_then_block(term->nif); 69 } 70 } 71 72 /** 73 * Unroll a loop where we know exactly how many iterations there are and there 74 * is only a single exit point. Note here we can unroll loops with multiple 75 * theoretical exits that only have a single terminating exit that we always 76 * know is the "real" exit. 77 * 78 * loop { 79 * ...instrs... 80 * } 81 * 82 * And the iteration count is 3, the output will be: 83 * 84 * ...instrs... ...instrs... ...instrs... 85 */ 86 static void 87 simple_unroll(nir_loop *loop) 88 { 89 nir_loop_terminator *limiting_term = loop->info->limiting_terminator; 90 assert(nir_is_trivial_loop_if(limiting_term->nif, 91 limiting_term->break_block)); 92 93 loop_prepare_for_unroll(loop); 94 95 /* Skip over loop terminator and get the loop body. */ 96 list_for_each_entry(nir_loop_terminator, terminator, 97 &loop->info->loop_terminator_list, 98 loop_terminator_link) { 99 100 /* Remove all but the limiting terminator as we know the other exit 101 * conditions can never be met. Note we need to extract any instructions 102 * in the continue from branch and insert then into the loop body before 103 * removing it. 104 */ 105 if (terminator->nif != limiting_term->nif) { 106 nir_block *first_break_block; 107 nir_block *first_continue_block; 108 get_first_blocks_in_terminator(terminator, &first_break_block, 109 &first_continue_block); 110 111 assert(nir_is_trivial_loop_if(terminator->nif, 112 terminator->break_block)); 113 114 nir_cf_list continue_from_lst; 115 nir_cf_extract(&continue_from_lst, 116 nir_before_block(first_continue_block), 117 nir_after_block(terminator->continue_from_block)); 118 nir_cf_reinsert(&continue_from_lst, 119 nir_after_cf_node(&terminator->nif->cf_node)); 120 121 nir_cf_node_remove(&terminator->nif->cf_node); 122 } 123 } 124 125 nir_block *first_break_block; 126 nir_block *first_continue_block; 127 get_first_blocks_in_terminator(limiting_term, &first_break_block, 128 &first_continue_block); 129 130 /* Pluck out the loop header */ 131 nir_block *header_blk = nir_loop_first_block(loop); 132 nir_cf_list lp_header; 133 nir_cf_extract(&lp_header, nir_before_block(header_blk), 134 nir_before_cf_node(&limiting_term->nif->cf_node)); 135 136 /* Add the continue from block of the limiting terminator to the loop body 137 */ 138 nir_cf_list continue_from_lst; 139 nir_cf_extract(&continue_from_lst, nir_before_block(first_continue_block), 140 nir_after_block(limiting_term->continue_from_block)); 141 nir_cf_reinsert(&continue_from_lst, 142 nir_after_cf_node(&limiting_term->nif->cf_node)); 143 144 /* Pluck out the loop body */ 145 nir_cf_list loop_body; 146 nir_cf_extract(&loop_body, nir_after_cf_node(&limiting_term->nif->cf_node), 147 nir_after_block(nir_loop_last_block(loop))); 148 149 struct hash_table *remap_table = 150 _mesa_hash_table_create(NULL, _mesa_hash_pointer, 151 _mesa_key_pointer_equal); 152 153 /* Clone the loop header */ 154 nir_cf_list cloned_header; 155 nir_cf_list_clone(&cloned_header, &lp_header, loop->cf_node.parent, 156 remap_table); 157 158 /* Insert cloned loop header before the loop */ 159 nir_cf_reinsert(&cloned_header, nir_before_cf_node(&loop->cf_node)); 160 161 /* Temp list to store the cloned loop body as we unroll */ 162 nir_cf_list unrolled_lp_body; 163 164 /* Clone loop header and append to the loop body */ 165 for (unsigned i = 0; i < loop->info->trip_count; i++) { 166 /* Clone loop body */ 167 nir_cf_list_clone(&unrolled_lp_body, &loop_body, loop->cf_node.parent, 168 remap_table); 169 170 /* Insert unrolled loop body before the loop */ 171 nir_cf_reinsert(&unrolled_lp_body, nir_before_cf_node(&loop->cf_node)); 172 173 /* Clone loop header */ 174 nir_cf_list_clone(&cloned_header, &lp_header, loop->cf_node.parent, 175 remap_table); 176 177 /* Insert loop header after loop body */ 178 nir_cf_reinsert(&cloned_header, nir_before_cf_node(&loop->cf_node)); 179 } 180 181 /* Remove the break from the loop terminator and add instructions from 182 * the break block after the unrolled loop. 183 */ 184 nir_instr *break_instr = nir_block_last_instr(limiting_term->break_block); 185 nir_instr_remove(break_instr); 186 nir_cf_list break_list; 187 nir_cf_extract(&break_list, nir_before_block(first_break_block), 188 nir_after_block(limiting_term->break_block)); 189 190 /* Clone so things get properly remapped */ 191 nir_cf_list cloned_break_list; 192 nir_cf_list_clone(&cloned_break_list, &break_list, loop->cf_node.parent, 193 remap_table); 194 195 nir_cf_reinsert(&cloned_break_list, nir_before_cf_node(&loop->cf_node)); 196 197 /* Remove the loop */ 198 nir_cf_node_remove(&loop->cf_node); 199 200 /* Delete the original loop body, break block & header */ 201 nir_cf_delete(&lp_header); 202 nir_cf_delete(&loop_body); 203 nir_cf_delete(&break_list); 204 205 _mesa_hash_table_destroy(remap_table, NULL); 206 } 207 208 static void 209 move_cf_list_into_loop_term(nir_cf_list *lst, nir_loop_terminator *term) 210 { 211 /* Move the rest of the loop inside the continue-from-block */ 212 nir_cf_reinsert(lst, nir_after_block(term->continue_from_block)); 213 214 /* Remove the break */ 215 nir_instr_remove(nir_block_last_instr(term->break_block)); 216 } 217 218 static nir_cursor 219 get_complex_unroll_insert_location(nir_cf_node *node, bool continue_from_then) 220 { 221 if (node->type == nir_cf_node_loop) { 222 return nir_before_cf_node(node); 223 } else { 224 nir_if *if_stmt = nir_cf_node_as_if(node); 225 if (continue_from_then) { 226 return nir_after_block(nir_if_last_then_block(if_stmt)); 227 } else { 228 return nir_after_block(nir_if_last_else_block(if_stmt)); 229 } 230 } 231 } 232 233 /** 234 * Unroll a loop with two exists when the trip count of one of the exits is 235 * unknown. If continue_from_then is true, the loop is repeated only when the 236 * "then" branch of the if is taken; otherwise it is repeated only 237 * when the "else" branch of the if is taken. 238 * 239 * For example, if the input is: 240 * 241 * loop { 242 * ...phis/condition... 243 * if condition { 244 * ...then instructions... 245 * } else { 246 * ...continue instructions... 247 * break 248 * } 249 * ...body... 250 * } 251 * 252 * And the iteration count is 3, and unlimit_term->continue_from_then is true, 253 * then the output will be: 254 * 255 * ...condition... 256 * if condition { 257 * ...then instructions... 258 * ...body... 259 * if condition { 260 * ...then instructions... 261 * ...body... 262 * if condition { 263 * ...then instructions... 264 * ...body... 265 * } else { 266 * ...continue instructions... 267 * } 268 * } else { 269 * ...continue instructions... 270 * } 271 * } else { 272 * ...continue instructions... 273 * } 274 */ 275 static void 276 complex_unroll(nir_loop *loop, nir_loop_terminator *unlimit_term, 277 bool limiting_term_second) 278 { 279 assert(nir_is_trivial_loop_if(unlimit_term->nif, 280 unlimit_term->break_block)); 281 282 nir_loop_terminator *limiting_term = loop->info->limiting_terminator; 283 assert(nir_is_trivial_loop_if(limiting_term->nif, 284 limiting_term->break_block)); 285 286 loop_prepare_for_unroll(loop); 287 288 nir_block *header_blk = nir_loop_first_block(loop); 289 290 nir_cf_list lp_header; 291 nir_cf_list limit_break_list; 292 unsigned num_times_to_clone; 293 if (limiting_term_second) { 294 /* Pluck out the loop header */ 295 nir_cf_extract(&lp_header, nir_before_block(header_blk), 296 nir_before_cf_node(&unlimit_term->nif->cf_node)); 297 298 /* We need some special handling when its the second terminator causing 299 * us to exit the loop for example: 300 * 301 * for (int i = 0; i < uniform_lp_count; i++) { 302 * colour = vec4(0.0, 1.0, 0.0, 1.0); 303 * 304 * if (i == 1) { 305 * break; 306 * } 307 * ... any further code is unreachable after i == 1 ... 308 * } 309 */ 310 nir_cf_list after_lt; 311 nir_if *limit_if = limiting_term->nif; 312 nir_cf_extract(&after_lt, nir_after_cf_node(&limit_if->cf_node), 313 nir_after_block(nir_loop_last_block(loop))); 314 move_cf_list_into_loop_term(&after_lt, limiting_term); 315 316 /* Because the trip count is the number of times we pass over the entire 317 * loop before hitting a break when the second terminator is the 318 * limiting terminator we can actually execute code inside the loop when 319 * trip count == 0 e.g. the code above the break. So we need to bump 320 * the trip_count in order for the code below to clone anything. When 321 * trip count == 1 we execute the code above the break twice and the 322 * code below it once so we need clone things twice and so on. 323 */ 324 num_times_to_clone = loop->info->trip_count + 1; 325 } else { 326 /* Pluck out the loop header */ 327 nir_cf_extract(&lp_header, nir_before_block(header_blk), 328 nir_before_cf_node(&limiting_term->nif->cf_node)); 329 330 nir_block *first_break_block; 331 nir_block *first_continue_block; 332 get_first_blocks_in_terminator(limiting_term, &first_break_block, 333 &first_continue_block); 334 335 /* Remove the break then extract instructions from the break block so we 336 * can insert them in the innermost else of the unrolled loop. 337 */ 338 nir_instr *break_instr = nir_block_last_instr(limiting_term->break_block); 339 nir_instr_remove(break_instr); 340 nir_cf_extract(&limit_break_list, nir_before_block(first_break_block), 341 nir_after_block(limiting_term->break_block)); 342 343 nir_cf_list continue_list; 344 nir_cf_extract(&continue_list, nir_before_block(first_continue_block), 345 nir_after_block(limiting_term->continue_from_block)); 346 347 nir_cf_reinsert(&continue_list, 348 nir_after_cf_node(&limiting_term->nif->cf_node)); 349 350 nir_cf_node_remove(&limiting_term->nif->cf_node); 351 352 num_times_to_clone = loop->info->trip_count; 353 } 354 355 /* In the terminator that we have no trip count for move everything after 356 * the terminator into the continue from branch. 357 */ 358 nir_cf_list loop_end; 359 nir_cf_extract(&loop_end, nir_after_cf_node(&unlimit_term->nif->cf_node), 360 nir_after_block(nir_loop_last_block(loop))); 361 move_cf_list_into_loop_term(&loop_end, unlimit_term); 362 363 /* Pluck out the loop body. */ 364 nir_cf_list loop_body; 365 nir_cf_extract(&loop_body, nir_before_block(nir_loop_first_block(loop)), 366 nir_after_block(nir_loop_last_block(loop))); 367 368 struct hash_table *remap_table = 369 _mesa_hash_table_create(NULL, _mesa_hash_pointer, 370 _mesa_key_pointer_equal); 371 372 /* Set unroll_loc to the loop as we will insert the unrolled loop before it 373 */ 374 nir_cf_node *unroll_loc = &loop->cf_node; 375 376 /* Temp lists to store the cloned loop as we unroll */ 377 nir_cf_list unrolled_lp_body; 378 nir_cf_list cloned_header; 379 380 for (unsigned i = 0; i < num_times_to_clone; i++) { 381 /* Clone loop header */ 382 nir_cf_list_clone(&cloned_header, &lp_header, loop->cf_node.parent, 383 remap_table); 384 385 nir_cursor cursor = 386 get_complex_unroll_insert_location(unroll_loc, 387 unlimit_term->continue_from_then); 388 389 /* Insert cloned loop header */ 390 nir_cf_reinsert(&cloned_header, cursor); 391 392 cursor = 393 get_complex_unroll_insert_location(unroll_loc, 394 unlimit_term->continue_from_then); 395 396 /* Clone loop body */ 397 nir_cf_list_clone(&unrolled_lp_body, &loop_body, loop->cf_node.parent, 398 remap_table); 399 400 unroll_loc = exec_node_data(nir_cf_node, 401 exec_list_get_tail(&unrolled_lp_body.list), 402 node); 403 assert(unroll_loc->type == nir_cf_node_block && 404 exec_list_is_empty(&nir_cf_node_as_block(unroll_loc)->instr_list)); 405 406 /* Get the unrolled if node */ 407 unroll_loc = nir_cf_node_prev(unroll_loc); 408 409 /* Insert unrolled loop body */ 410 nir_cf_reinsert(&unrolled_lp_body, cursor); 411 } 412 413 if (!limiting_term_second) { 414 assert(unroll_loc->type == nir_cf_node_if); 415 416 nir_cf_list_clone(&cloned_header, &lp_header, loop->cf_node.parent, 417 remap_table); 418 419 nir_cursor cursor = 420 get_complex_unroll_insert_location(unroll_loc, 421 unlimit_term->continue_from_then); 422 423 /* Insert cloned loop header */ 424 nir_cf_reinsert(&cloned_header, cursor); 425 426 /* Clone so things get properly remapped, and insert break block from 427 * the limiting terminator. 428 */ 429 nir_cf_list cloned_break_blk; 430 nir_cf_list_clone(&cloned_break_blk, &limit_break_list, 431 loop->cf_node.parent, remap_table); 432 433 cursor = 434 get_complex_unroll_insert_location(unroll_loc, 435 unlimit_term->continue_from_then); 436 437 nir_cf_reinsert(&cloned_break_blk, cursor); 438 nir_cf_delete(&limit_break_list); 439 } 440 441 /* The loop has been unrolled so remove it. */ 442 nir_cf_node_remove(&loop->cf_node); 443 444 /* Delete the original loop header and body */ 445 nir_cf_delete(&lp_header); 446 nir_cf_delete(&loop_body); 447 448 _mesa_hash_table_destroy(remap_table, NULL); 449 } 450 451 static bool 452 is_loop_small_enough_to_unroll(nir_shader *shader, nir_loop_info *li) 453 { 454 unsigned max_iter = shader->options->max_unroll_iterations; 455 456 if (li->trip_count > max_iter) 457 return false; 458 459 if (li->force_unroll) 460 return true; 461 462 bool loop_not_too_large = 463 li->num_instructions * li->trip_count <= max_iter * 25; 464 465 return loop_not_too_large; 466 } 467 468 static bool 469 process_loops(nir_shader *sh, nir_cf_node *cf_node, bool *innermost_loop) 470 { 471 bool progress = false; 472 nir_loop *loop; 473 474 switch (cf_node->type) { 475 case nir_cf_node_block: 476 return progress; 477 case nir_cf_node_if: { 478 nir_if *if_stmt = nir_cf_node_as_if(cf_node); 479 foreach_list_typed_safe(nir_cf_node, nested_node, node, &if_stmt->then_list) 480 progress |= process_loops(sh, nested_node, innermost_loop); 481 foreach_list_typed_safe(nir_cf_node, nested_node, node, &if_stmt->else_list) 482 progress |= process_loops(sh, nested_node, innermost_loop); 483 return progress; 484 } 485 case nir_cf_node_loop: { 486 loop = nir_cf_node_as_loop(cf_node); 487 foreach_list_typed_safe(nir_cf_node, nested_node, node, &loop->body) 488 progress |= process_loops(sh, nested_node, innermost_loop); 489 break; 490 } 491 default: 492 unreachable("unknown cf node type"); 493 } 494 495 if (*innermost_loop) { 496 /* Don't attempt to unroll outer loops or a second inner loop in 497 * this pass wait until the next pass as we have altered the cf. 498 */ 499 *innermost_loop = false; 500 501 if (loop->info->limiting_terminator == NULL) 502 return progress; 503 504 if (!is_loop_small_enough_to_unroll(sh, loop->info)) 505 return progress; 506 507 if (loop->info->is_trip_count_known) { 508 simple_unroll(loop); 509 progress = true; 510 } else { 511 /* Attempt to unroll loops with two terminators. */ 512 unsigned num_lt = list_length(&loop->info->loop_terminator_list); 513 if (num_lt == 2) { 514 bool limiting_term_second = true; 515 nir_loop_terminator *terminator = 516 list_last_entry(&loop->info->loop_terminator_list, 517 nir_loop_terminator, loop_terminator_link); 518 519 520 if (terminator->nif == loop->info->limiting_terminator->nif) { 521 limiting_term_second = false; 522 terminator = 523 list_first_entry(&loop->info->loop_terminator_list, 524 nir_loop_terminator, loop_terminator_link); 525 } 526 527 /* If the first terminator has a trip count of zero and is the 528 * limiting terminator just do a simple unroll as the second 529 * terminator can never be reached. 530 */ 531 if (loop->info->trip_count == 0 && !limiting_term_second) { 532 simple_unroll(loop); 533 } else { 534 complex_unroll(loop, terminator, limiting_term_second); 535 } 536 progress = true; 537 } 538 } 539 } 540 541 return progress; 542 } 543 544 static bool 545 nir_opt_loop_unroll_impl(nir_function_impl *impl, 546 nir_variable_mode indirect_mask) 547 { 548 bool progress = false; 549 nir_metadata_require(impl, nir_metadata_loop_analysis, indirect_mask); 550 nir_metadata_require(impl, nir_metadata_block_index); 551 552 foreach_list_typed_safe(nir_cf_node, node, node, &impl->body) { 553 bool innermost_loop = true; 554 progress |= process_loops(impl->function->shader, node, 555 &innermost_loop); 556 } 557 558 if (progress) 559 nir_lower_regs_to_ssa_impl(impl); 560 561 return progress; 562 } 563 564 bool 565 nir_opt_loop_unroll(nir_shader *shader, nir_variable_mode indirect_mask) 566 { 567 bool progress = false; 568 569 nir_foreach_function(function, shader) { 570 if (function->impl) { 571 progress |= nir_opt_loop_unroll_impl(function->impl, indirect_mask); 572 } 573 } 574 return progress; 575 } 576
