src/compiler/nir/nir_loop_analyze.c

   1 /*
   2  * Copyright © 2015 Thomas Helland
   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 DEALINGS
  21  * IN THE SOFTWARE.
  22  */
  23
  24 #include "nir.h"
  25 #include "nir_constant_expressions.h"
  26 #include "nir_loop_analyze.h"
  27
  28 typedef enum {
  29    undefined,
  30    invariant,
  31    not_invariant,
  32    basic_induction
  33 } nir_loop_variable_type;
  34
  35 struct nir_basic_induction_var;
  36
  37 typedef struct {
  38    /* A link for the work list */
  39    struct list_head process_link;
  40
  41    bool in_loop;
  42
  43    /* The ssa_def associated with this info */
  44    nir_ssa_def *def;
  45
  46    /* The type of this ssa_def */
  47    nir_loop_variable_type type;
  48
  49    /* If this is of type basic_induction */
  50    struct nir_basic_induction_var *ind;
  51
  52    /* True if variable is in an if branch or a nested loop */
  53    bool in_control_flow;
  54
  55 } nir_loop_variable;
  56
  57 typedef struct nir_basic_induction_var {
  58    nir_op alu_op;                           /* The type of alu-operation    */
  59    nir_loop_variable *alu_def;              /* The def of the alu-operation */
  60    nir_loop_variable *invariant;            /* The invariant alu-operand    */
  61    nir_loop_variable *def_outside_loop;     /* The phi-src outside the loop */
  62 } nir_basic_induction_var;
  63
  64 typedef struct {
  65    /* The loop we store information for */
  66    nir_loop *loop;
  67
  68    /* Loop_variable for all ssa_defs in function */
  69    nir_loop_variable *loop_vars;
  70
  71    /* A list of the loop_vars to analyze */
  72    struct list_head process_list;
  73
  74    nir_variable_mode indirect_mask;
  75
  76 } loop_info_state;
  77
  78 static nir_loop_variable *
  79 get_loop_var(nir_ssa_def *value, loop_info_state *state)
  80 {
  81    return &(state->loop_vars[value->index]);
  82 }
  83
  84 typedef struct {
  85    loop_info_state *state;
  86    bool in_control_flow;
  87 } init_loop_state;
  88
  89 static bool
  90 init_loop_def(nir_ssa_def *def, void *void_init_loop_state)
  91 {
  92    init_loop_state *loop_init_state = void_init_loop_state;
  93    nir_loop_variable *var = get_loop_var(def, loop_init_state->state);
  94
  95    if (loop_init_state->in_control_flow) {
  96       var->in_control_flow = true;
  97    } else {
  98       /* Add to the tail of the list. That way we start at the beginning of
  99        * the defs in the loop instead of the end when walking the list. This
 100        * means less recursive calls. Only add defs that are not in nested
 101        * loops or conditional blocks.
 102        */
 103       list_addtail(&var->process_link, &loop_init_state->state->process_list);
 104    }
 105
 106    var->in_loop = true;
 107
 108    return true;
 109 }
 110
 111 static bool
 112 init_loop_block(nir_block *block, loop_info_state *state,
 113                 bool in_control_flow)
 114 {
 115    init_loop_state init_state = {.in_control_flow = in_control_flow,
 116                                  .state = state };
 117
 118    nir_foreach_instr(instr, block) {
 119       if (instr->type == nir_instr_type_intrinsic ||
 120           instr->type == nir_instr_type_alu ||
 121           instr->type == nir_instr_type_tex) {
 122          state->loop->info->num_instructions++;
 123       }
 124
 125       nir_foreach_ssa_def(instr, init_loop_def, &init_state);
 126    }
 127
 128    return true;
 129 }
 130
 131 static inline bool
 132 is_var_alu(nir_loop_variable *var)
 133 {
 134    return var->def->parent_instr->type == nir_instr_type_alu;
 135 }
 136
 137 static inline bool
 138 is_var_constant(nir_loop_variable *var)
 139 {
 140    return var->def->parent_instr->type == nir_instr_type_load_const;
 141 }
 142
 143 static inline bool
 144 is_var_phi(nir_loop_variable *var)
 145 {
 146    return var->def->parent_instr->type == nir_instr_type_phi;
 147 }
 148
 149 static inline bool
 150 mark_invariant(nir_ssa_def *def, loop_info_state *state)
 151 {
 152    nir_loop_variable *var = get_loop_var(def, state);
 153
 154    if (var->type == invariant)
 155       return true;
 156
 157    if (!var->in_loop) {
 158       var->type = invariant;
 159       return true;
 160    }
 161
 162    if (var->type == not_invariant)
 163       return false;
 164
 165    if (is_var_alu(var)) {
 166       nir_alu_instr *alu = nir_instr_as_alu(def->parent_instr);
 167
 168       for (unsigned i = 0; i < nir_op_infos[alu->op].num_inputs; i++) {
 169          if (!mark_invariant(alu->src[i].src.ssa, state)) {
 170             var->type = not_invariant;
 171             return false;
 172          }
 173       }
 174       var->type = invariant;
 175       return true;
 176    }
 177
 178    /* Phis shouldn't be invariant except if one operand is invariant, and the
 179     * other is the phi itself. These should be removed by opt_remove_phis.
 180     * load_consts are already set to invariant and constant during init,
 181     * and so should return earlier. Remaining op_codes are set undefined.
 182     */
 183    var->type = not_invariant;
 184    return false;
 185 }
 186
 187 static void
 188 compute_invariance_information(loop_info_state *state)
 189 {
 190    /* An expression is invariant in a loop L if:
 191     *  (base cases)
 192     *    – it’s a constant
 193     *    – it’s a variable use, all of whose single defs are outside of L
 194     *  (inductive cases)
 195     *    – it’s a pure computation all of whose args are loop invariant
 196     *    – it’s a variable use whose single reaching def, and the
 197     *      rhs of that def is loop-invariant
 198     */
 199    list_for_each_entry_safe(nir_loop_variable, var, &state->process_list,
 200                             process_link) {
 201       assert(!var->in_control_flow);
 202
 203       if (mark_invariant(var->def, state))
 204          list_del(&var->process_link);
 205    }
 206 }
 207
 208 static bool
 209 compute_induction_information(loop_info_state *state)
 210 {
 211    bool found_induction_var = false;
 212    list_for_each_entry_safe(nir_loop_variable, var, &state->process_list,
 213                             process_link) {
 214
 215       /* It can't be an induction variable if it is invariant. Invariants and
 216        * things in nested loops or conditionals should have been removed from
 217        * the list by compute_invariance_information().
 218        */
 219       assert(!var->in_control_flow && var->type != invariant);
 220
 221       /* We are only interested in checking phis for the basic induction
 222        * variable case as its simple to detect. All basic induction variables
 223        * have a phi node
 224        */
 225       if (!is_var_phi(var))
 226          continue;
 227
 228       nir_phi_instr *phi = nir_instr_as_phi(var->def->parent_instr);
 229       nir_basic_induction_var *biv = rzalloc(state, nir_basic_induction_var);
 230
 231       nir_foreach_phi_src(src, phi) {
 232          nir_loop_variable *src_var = get_loop_var(src->src.ssa, state);
 233
 234          /* If one of the sources is in a conditional or nested block then
 235           * panic.
 236           */
 237          if (src_var->in_control_flow)
 238             break;
 239
 240          if (!src_var->in_loop) {
 241             biv->def_outside_loop = src_var;
 242          } else if (is_var_alu(src_var)) {
 243             nir_alu_instr *alu = nir_instr_as_alu(src_var->def->parent_instr);
 244
 245             if (nir_op_infos[alu->op].num_inputs == 2) {
 246                biv->alu_def = src_var;
 247                biv->alu_op = alu->op;
 248
 249                for (unsigned i = 0; i < 2; i++) {
 250                   /* Is one of the operands const, and the other the phi */
 251                   if (alu->src[i].src.ssa->parent_instr->type == nir_instr_type_load_const &&
 252                       alu->src[1-i].src.ssa == &phi->dest.ssa)
 253                      biv->invariant = get_loop_var(alu->src[i].src.ssa, state);
 254                }
 255             }
 256          }
 257       }
 258
 259       if (biv->alu_def && biv->def_outside_loop && biv->invariant &&
 260           is_var_constant(biv->def_outside_loop)) {
 261          assert(is_var_constant(biv->invariant));
 262          biv->alu_def->type = basic_induction;
 263          biv->alu_def->ind = biv;
 264          var->type = basic_induction;
 265          var->ind = biv;
 266
 267          found_induction_var = true;
 268       } else {
 269          ralloc_free(biv);
 270       }
 271    }
 272    return found_induction_var;
 273 }
 274
 275 static bool
 276 initialize_ssa_def(nir_ssa_def *def, void *void_state)
 277 {
 278    loop_info_state *state = void_state;
 279    nir_loop_variable *var = get_loop_var(def, state);
 280
 281    var->in_loop = false;
 282    var->def = def;
 283
 284    if (def->parent_instr->type == nir_instr_type_load_const) {
 285       var->type = invariant;
 286    } else {
 287       var->type = undefined;
 288    }
 289
 290    return true;
 291 }
 292
 293 static bool
 294 find_loop_terminators(loop_info_state *state)
 295 {
 296    bool success = false;
 297    foreach_list_typed_safe(nir_cf_node, node, node, &state->loop->body) {
 298       if (node->type == nir_cf_node_if) {
 299          nir_if *nif = nir_cf_node_as_if(node);
 300
 301          nir_block *break_blk = NULL;
 302          nir_block *continue_from_blk = NULL;
 303          bool continue_from_then = true;
 304
 305          nir_block *last_then = nir_if_last_then_block(nif);
 306          nir_block *last_else = nir_if_last_else_block(nif);
 307          if (nir_block_ends_in_break(last_then)) {
 308             break_blk = last_then;
 309             continue_from_blk = last_else;
 310             continue_from_then = false;
 311          } else if (nir_block_ends_in_break(last_else)) {
 312             break_blk = last_else;
 313             continue_from_blk = last_then;
 314          }
 315
 316          /* If there is a break then we should find a terminator. If we can
 317           * not find a loop terminator, but there is a break-statement then
 318           * we should return false so that we do not try to find trip-count
 319           */
 320          if (!nir_is_trivial_loop_if(nif, break_blk)) {
 321             state->loop->info->complex_loop = true;
 322             return false;
 323          }
 324
 325          /* Continue if the if contained no jumps at all */
 326          if (!break_blk)
 327             continue;
 328
 329          if (nif->condition.ssa->parent_instr->type == nir_instr_type_phi) {
 330             state->loop->info->complex_loop = true;
 331             return false;
 332          }
 333
 334          nir_loop_terminator *terminator =
 335             rzalloc(state->loop->info, nir_loop_terminator);
 336
 337          list_addtail(&terminator->loop_terminator_link,
 338                       &state->loop->info->loop_terminator_list);
 339
 340          terminator->nif = nif;
 341          terminator->break_block = break_blk;
 342          terminator->continue_from_block = continue_from_blk;
 343          terminator->continue_from_then = continue_from_then;
 344          terminator->conditional_instr = nif->condition.ssa->parent_instr;
 345
 346          success = true;
 347       }
 348    }
 349
 350    return success;
 351 }
 352
 353 static int32_t
 354 get_iteration(nir_op cond_op, nir_const_value *initial, nir_const_value *step,
 355               nir_const_value *limit)
 356 {
 357    int32_t iter;
 358
 359    switch (cond_op) {
 360    case nir_op_ige:
 361    case nir_op_ilt:
 362    case nir_op_ieq:
 363    case nir_op_ine: {
 364       int32_t initial_val = initial->i32[0];
 365       int32_t span = limit->i32[0] - initial_val;
 366       iter = span / step->i32[0];
 367       break;
 368    }
 369    case nir_op_uge:
 370    case nir_op_ult: {
 371       uint32_t initial_val = initial->u32[0];
 372       uint32_t span = limit->u32[0] - initial_val;
 373       iter = span / step->u32[0];
 374       break;
 375    }
 376    case nir_op_fge:
 377    case nir_op_flt:
 378    case nir_op_feq:
 379    case nir_op_fne: {
 380       float initial_val = initial->f32[0];
 381       float span = limit->f32[0] - initial_val;
 382       iter = span / step->f32[0];
 383       break;
 384    }
 385    default:
 386       return -1;
 387    }
 388
 389    return iter;
 390 }
 391
 392 static bool
 393 test_iterations(int32_t iter_int, nir_const_value *step,
 394                 nir_const_value *limit, nir_op cond_op, unsigned bit_size,
 395                 nir_alu_type induction_base_type,
 396                 nir_const_value *initial, bool limit_rhs, bool invert_cond)
 397 {
 398    assert(nir_op_infos[cond_op].num_inputs == 2);
 399
 400    nir_const_value iter_src = { {0, } };
 401    nir_op mul_op;
 402    nir_op add_op;
 403    switch (induction_base_type) {
 404    case nir_type_float:
 405       iter_src.f32[0] = (float) iter_int;
 406       mul_op = nir_op_fmul;
 407       add_op = nir_op_fadd;
 408       break;
 409    case nir_type_int:
 410    case nir_type_uint:
 411       iter_src.i32[0] = iter_int;
 412       mul_op = nir_op_imul;
 413       add_op = nir_op_iadd;
 414       break;
 415    default:
 416       unreachable("Unhandled induction variable base type!");
 417    }
 418
 419    /* Multiple the iteration count we are testing by the number of times we
 420     * step the induction variable each iteration.
 421     */
 422    nir_const_value mul_src[2] = { iter_src, *step };
 423    nir_const_value mul_result =
 424       nir_eval_const_opcode(mul_op, 1, bit_size, mul_src);
 425
 426    /* Add the initial value to the accumulated induction variable total */
 427    nir_const_value add_src[2] = { mul_result, *initial };
 428    nir_const_value add_result =
 429       nir_eval_const_opcode(add_op, 1, bit_size, add_src);
 430
 431    nir_const_value src[2] = { { {0, } }, { {0, } } };
 432    src[limit_rhs ? 0 : 1] = add_result;
 433    src[limit_rhs ? 1 : 0] = *limit;
 434
 435    /* Evaluate the loop exit condition */
 436    nir_const_value result = nir_eval_const_opcode(cond_op, 1, bit_size, src);
 437
 438    return invert_cond ? (result.u32[0] == 0) : (result.u32[0] != 0);
 439 }
 440
 441 static int
 442 calculate_iterations(nir_const_value *initial, nir_const_value *step,
 443                      nir_const_value *limit, nir_loop_variable *alu_def,
 444                      nir_alu_instr *cond_alu, bool limit_rhs, bool invert_cond)
 445 {
 446    assert(initial != NULL && step != NULL && limit != NULL);
 447
 448    nir_alu_instr *alu = nir_instr_as_alu(alu_def->def->parent_instr);
 449
 450    /* nir_op_isub should have been lowered away by this point */
 451    assert(alu->op != nir_op_isub);
 452
 453    /* Make sure the alu type for our induction variable is compatible with the
 454     * conditional alus input type. If its not something has gone really wrong.
 455     */
 456    nir_alu_type induction_base_type =
 457       nir_alu_type_get_base_type(nir_op_infos[alu->op].output_type);
 458    if (induction_base_type == nir_type_int || induction_base_type == nir_type_uint) {
 459       assert(nir_alu_type_get_base_type(nir_op_infos[cond_alu->op].input_types[1]) == nir_type_int ||
 460              nir_alu_type_get_base_type(nir_op_infos[cond_alu->op].input_types[1]) == nir_type_uint);
 461    } else {
 462       assert(nir_alu_type_get_base_type(nir_op_infos[cond_alu->op].input_types[0]) ==
 463              induction_base_type);
 464    }
 465
 466    /* Check for nsupported alu operations */
 467    if (alu->op != nir_op_iadd && alu->op != nir_op_fadd)
 468       return -1;
 469
 470    /* do-while loops can increment the starting value before the condition is
 471     * checked. e.g.
 472     *
 473     *    do {
 474     *        ndx++;
 475     *     } while (ndx < 3);
 476     *
 477     * Here we check if the induction variable is used directly by the loop
 478     * condition and if so we assume we need to step the initial value.
 479     */
 480    unsigned trip_offset = 0;
 481    if (cond_alu->src[0].src.ssa == alu_def->def ||
 482        cond_alu->src[1].src.ssa == alu_def->def) {
 483       trip_offset = 1;
 484    }
 485
 486    int iter_int = get_iteration(cond_alu->op, initial, step, limit);
 487
 488    /* If iter_int is negative the loop is ill-formed or is the conditional is
 489     * unsigned with a huge iteration count so don't bother going any further.
 490     */
 491    if (iter_int < 0)
 492       return -1;
 493
 494    /* An explanation from the GLSL unrolling pass:
 495     *
 496     * Make sure that the calculated number of iterations satisfies the exit
 497     * condition.  This is needed to catch off-by-one errors and some types of
 498     * ill-formed loops.  For example, we need to detect that the following
 499     * loop does not have a maximum iteration count.
 500     *
 501     *    for (float x = 0.0; x != 0.9; x += 0.2);
 502     */
 503    assert(nir_src_bit_size(alu->src[0].src) ==
 504           nir_src_bit_size(alu->src[1].src));
 505    unsigned bit_size = nir_src_bit_size(alu->src[0].src);
 506    for (int bias = -1; bias <= 1; bias++) {
 507       const int iter_bias = iter_int + bias;
 508
 509       if (test_iterations(iter_bias, step, limit, cond_alu->op, bit_size,
 510                           induction_base_type, initial,
 511                           limit_rhs, invert_cond)) {
 512          return iter_bias > 0 ? iter_bias - trip_offset : iter_bias;
 513       }
 514    }
 515
 516    return -1;
 517 }
 518
 519 /* Run through each of the terminators of the loop and try to infer a possible
 520  * trip-count. We need to check them all, and set the lowest trip-count as the
 521  * trip-count of our loop. If one of the terminators has an undecidable
 522  * trip-count we can not safely assume anything about the duration of the
 523  * loop.
 524  */
 525 static void
 526 find_trip_count(loop_info_state *state)
 527 {
 528    bool trip_count_known = true;
 529    nir_loop_terminator *limiting_terminator = NULL;
 530    int min_trip_count = -1;
 531
 532    list_for_each_entry(nir_loop_terminator, terminator,
 533                        &state->loop->info->loop_terminator_list,
 534                        loop_terminator_link) {
 535
 536       if (terminator->conditional_instr->type != nir_instr_type_alu) {
 537          /* If we get here the loop is dead and will get cleaned up by the
 538           * nir_opt_dead_cf pass.
 539           */
 540          trip_count_known = false;
 541          continue;
 542       }
 543
 544       nir_alu_instr *alu = nir_instr_as_alu(terminator->conditional_instr);
 545       nir_loop_variable *basic_ind = NULL;
 546       nir_loop_variable *limit = NULL;
 547       bool limit_rhs = true;
 548
 549       switch (alu->op) {
 550       case nir_op_fge:      case nir_op_ige:      case nir_op_uge:
 551       case nir_op_flt:      case nir_op_ilt:      case nir_op_ult:
 552       case nir_op_feq:      case nir_op_ieq:
 553       case nir_op_fne:      case nir_op_ine:
 554
 555          /* We assume that the limit is the "right" operand */
 556          basic_ind = get_loop_var(alu->src[0].src.ssa, state);
 557          limit = get_loop_var(alu->src[1].src.ssa, state);
 558
 559          if (basic_ind->type != basic_induction) {
 560             /* We had it the wrong way, flip things around */
 561             basic_ind = get_loop_var(alu->src[1].src.ssa, state);
 562             limit = get_loop_var(alu->src[0].src.ssa, state);
 563             limit_rhs = false;
 564          }
 565
 566          /* The comparison has to have a basic induction variable
 567           * and a constant for us to be able to find trip counts
 568           */
 569          if (basic_ind->type != basic_induction || !is_var_constant(limit)) {
 570             trip_count_known = false;
 571             continue;
 572          }
 573
 574          /* We have determined that we have the following constants:
 575           * (With the typical int i = 0; i < x; i++; as an example)
 576           *    - Upper limit.
 577           *    - Starting value
 578           *    - Step / iteration size
 579           * Thats all thats needed to calculate the trip-count
 580           */
 581
 582          nir_const_value initial_val =
 583             nir_instr_as_load_const(basic_ind->ind->def_outside_loop->
 584                                        def->parent_instr)->value;
 585
 586          nir_const_value step_val =
 587             nir_instr_as_load_const(basic_ind->ind->invariant->def->
 588                                        parent_instr)->value;
 589
 590          nir_const_value limit_val =
 591             nir_instr_as_load_const(limit->def->parent_instr)->value;
 592
 593          int iterations = calculate_iterations(&initial_val, &step_val,
 594                                                &limit_val,
 595                                                basic_ind->ind->alu_def, alu,
 596                                                limit_rhs,
 597                                                terminator->continue_from_then);
 598
 599          /* Where we not able to calculate the iteration count */
 600          if (iterations == -1) {
 601             trip_count_known = false;
 602             continue;
 603          }
 604
 605          /* If this is the first run or we have found a smaller amount of
 606           * iterations than previously (we have identified a more limiting
 607           * terminator) set the trip count and limiting terminator.
 608           */
 609          if (min_trip_count == -1 || iterations < min_trip_count) {
 610             min_trip_count = iterations;
 611             limiting_terminator = terminator;
 612          }
 613          break;
 614
 615       default:
 616          trip_count_known = false;
 617       }
 618    }
 619
 620    state->loop->info->is_trip_count_known = trip_count_known;
 621    if (min_trip_count > -1)
 622       state->loop->info->trip_count = min_trip_count;
 623    state->loop->info->limiting_terminator = limiting_terminator;
 624 }
 625
 626 static bool
 627 force_unroll_array_access(loop_info_state *state, nir_shader *ns,
 628                           nir_deref_instr *deref)
 629 {
 630    for (nir_deref_instr *d = deref; d; d = nir_deref_instr_parent(d)) {
 631       if (d->deref_type != nir_deref_type_array)
 632          continue;
 633
 634       assert(d->arr.index.is_ssa);
 635       nir_loop_variable *array_index = get_loop_var(d->arr.index.ssa, state);
 636
 637       if (array_index->type != basic_induction)
 638          continue;
 639
 640       nir_deref_instr *parent = nir_deref_instr_parent(d);
 641       assert(glsl_type_is_array(parent->type) ||
 642              glsl_type_is_matrix(parent->type));
 643       if (glsl_get_length(parent->type) == state->loop->info->trip_count) {
 644          state->loop->info->force_unroll = true;
 645          return true;
 646       }
 647
 648       if (deref->mode & state->indirect_mask) {
 649          state->loop->info->force_unroll = true;
 650          return true;
 651       }
 652    }
 653
 654    return false;
 655 }
 656
 657 static bool
 658 force_unroll_heuristics(loop_info_state *state, nir_shader *ns,
 659                         nir_block *block)
 660 {
 661    nir_foreach_instr(instr, block) {
 662       if (instr->type != nir_instr_type_intrinsic)
 663          continue;
 664
 665       nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
 666
 667       /* Check for arrays variably-indexed by a loop induction variable.
 668        * Unrolling the loop may convert that access into constant-indexing.
 669        */
 670       if (intrin->intrinsic == nir_intrinsic_load_deref ||
 671           intrin->intrinsic == nir_intrinsic_store_deref ||
 672           intrin->intrinsic == nir_intrinsic_copy_deref) {
 673          if (force_unroll_array_access(state, ns,
 674                                        nir_src_as_deref(intrin->src[0])))
 675             return true;
 676
 677          if (intrin->intrinsic == nir_intrinsic_copy_deref &&
 678              force_unroll_array_access(state, ns,
 679                                        nir_src_as_deref(intrin->src[1])))
 680             return true;
 681       }
 682    }
 683
 684    return false;
 685 }
 686
 687 static void
 688 get_loop_info(loop_info_state *state, nir_function_impl *impl)
 689 {
 690    /* Initialize all variables to "outside_loop". This also marks defs
 691     * invariant and constant if they are nir_instr_type_load_consts
 692     */
 693    nir_foreach_block(block, impl) {
 694       nir_foreach_instr(instr, block)
 695          nir_foreach_ssa_def(instr, initialize_ssa_def, state);
 696    }
 697
 698    /* Add all entries in the outermost part of the loop to the processing list
 699     * Mark the entries in conditionals or in nested loops accordingly
 700     */
 701    foreach_list_typed_safe(nir_cf_node, node, node, &state->loop->body) {
 702       switch (node->type) {
 703
 704       case nir_cf_node_block:
 705          init_loop_block(nir_cf_node_as_block(node), state, false);
 706          break;
 707
 708       case nir_cf_node_if:
 709          nir_foreach_block_in_cf_node(block, node)
 710             init_loop_block(block, state, true);
 711          break;
 712
 713       case nir_cf_node_loop:
 714          nir_foreach_block_in_cf_node(block, node) {
 715             init_loop_block(block, state, true);
 716          }
 717          break;
 718
 719       case nir_cf_node_function:
 720          break;
 721       }
 722    }
 723
 724    /* Try to find all simple terminators of the loop. If we can't find any,
 725     * or we find possible terminators that have side effects then bail.
 726     */
 727    if (!find_loop_terminators(state)) {
 728       list_for_each_entry_safe(nir_loop_terminator, terminator,
 729                                &state->loop->info->loop_terminator_list,
 730                                loop_terminator_link) {
 731          list_del(&terminator->loop_terminator_link);
 732          ralloc_free(terminator);
 733       }
 734       return;
 735    }
 736
 737    /* Induction analysis needs invariance information so get that first */
 738    compute_invariance_information(state);
 739
 740    /* We have invariance information so try to find induction variables */
 741    if (!compute_induction_information(state))
 742       return;
 743
 744    /* Run through each of the terminators and try to compute a trip-count */
 745    find_trip_count(state);
 746
 747    nir_shader *ns = impl->function->shader;
 748    foreach_list_typed_safe(nir_cf_node, node, node, &state->loop->body) {
 749       if (node->type == nir_cf_node_block) {
 750          if (force_unroll_heuristics(state, ns, nir_cf_node_as_block(node)))
 751             break;
 752       } else {
 753          nir_foreach_block_in_cf_node(block, node) {
 754             if (force_unroll_heuristics(state, ns, block))
 755                break;
 756          }
 757       }
 758    }
 759 }
 760
 761 static loop_info_state *
 762 initialize_loop_info_state(nir_loop *loop, void *mem_ctx,
 763                            nir_function_impl *impl)
 764 {
 765    loop_info_state *state = rzalloc(mem_ctx, loop_info_state);
 766    state->loop_vars = rzalloc_array(mem_ctx, nir_loop_variable,
 767                                     impl->ssa_alloc);
 768    state->loop = loop;
 769
 770    list_inithead(&state->process_list);
 771
 772    if (loop->info)
 773      ralloc_free(loop->info);
 774
 775    loop->info = rzalloc(loop, nir_loop_info);
 776
 777    list_inithead(&loop->info->loop_terminator_list);
 778
 779    return state;
 780 }
 781
 782 static void
 783 process_loops(nir_cf_node *cf_node, nir_variable_mode indirect_mask)
 784 {
 785    switch (cf_node->type) {
 786    case nir_cf_node_block:
 787       return;
 788    case nir_cf_node_if: {
 789       nir_if *if_stmt = nir_cf_node_as_if(cf_node);
 790       foreach_list_typed(nir_cf_node, nested_node, node, &if_stmt->then_list)
 791          process_loops(nested_node, indirect_mask);
 792       foreach_list_typed(nir_cf_node, nested_node, node, &if_stmt->else_list)
 793          process_loops(nested_node, indirect_mask);
 794       return;
 795    }
 796    case nir_cf_node_loop: {
 797       nir_loop *loop = nir_cf_node_as_loop(cf_node);
 798       foreach_list_typed(nir_cf_node, nested_node, node, &loop->body)
 799          process_loops(nested_node, indirect_mask);
 800       break;
 801    }
 802    default:
 803       unreachable("unknown cf node type");
 804    }
 805
 806    nir_loop *loop = nir_cf_node_as_loop(cf_node);
 807    nir_function_impl *impl = nir_cf_node_get_function(cf_node);
 808    void *mem_ctx = ralloc_context(NULL);
 809
 810    loop_info_state *state = initialize_loop_info_state(loop, mem_ctx, impl);
 811    state->indirect_mask = indirect_mask;
 812
 813    get_loop_info(state, impl);
 814
 815    ralloc_free(mem_ctx);
 816 }
 817
 818 void
 819 nir_loop_analyze_impl(nir_function_impl *impl,
 820                       nir_variable_mode indirect_mask)
 821 {
 822    nir_index_ssa_defs(impl);
 823    foreach_list_typed(nir_cf_node, node, node, &impl->body)
 824       process_loops(node, indirect_mask);
 825 }