src/compiler/nir/nir_opt_find_array_copies.c

   1 /*
   2  * Copyright © 2018 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 DEALINGS
  21  * IN THE SOFTWARE.
  22  */
  23
  24 #include "nir.h"
  25 #include "nir_builder.h"
  26 #include "nir_deref.h"
  27
  28 static bool
  29 index_ssa_def_cb(nir_ssa_def *def, void *state)
  30 {
  31    unsigned *index = (unsigned *) state;
  32    def->index = (*index)++;
  33
  34    return true;
  35 }
  36
  37 static nir_deref_instr *
  38 get_deref_for_load_src(nir_src src, unsigned first_valid_load)
  39 {
  40    nir_intrinsic_instr *load = nir_src_as_intrinsic(src);
  41    if (load == NULL || load->intrinsic != nir_intrinsic_load_deref)
  42       return NULL;
  43
  44    if (load->dest.ssa.index < first_valid_load)
  45       return NULL;
  46
  47    return nir_src_as_deref(load->src[0]);
  48 }
  49
  50 struct match_state {
  51    /* Index into the array of the last copy or -1 for no ongoing copy. */
  52    unsigned next_array_idx;
  53
  54    /* Length of the array we're copying */
  55    unsigned array_len;
  56
  57    /* Index into the deref path to the array we think is being copied */
  58    int src_deref_array_idx;
  59    int dst_deref_array_idx;
  60
  61    /* Deref paths of the first load/store pair or copy */
  62    nir_deref_path first_src_path;
  63    nir_deref_path first_dst_path;
  64 };
  65
  66 static void
  67 match_state_init(struct match_state *state)
  68 {
  69    state->next_array_idx = 0;
  70    state->array_len = 0;
  71    state->src_deref_array_idx = -1;
  72    state->dst_deref_array_idx = -1;
  73 }
  74
  75 static void
  76 match_state_finish(struct match_state *state)
  77 {
  78    if (state->next_array_idx > 0) {
  79       nir_deref_path_finish(&state->first_src_path);
  80       nir_deref_path_finish(&state->first_dst_path);
  81    }
  82 }
  83
  84 static void
  85 match_state_reset(struct match_state *state)
  86 {
  87    match_state_finish(state);
  88    match_state_init(state);
  89 }
  90
  91 static bool
  92 try_match_deref(nir_deref_path *base_path, int *path_array_idx,
  93                 nir_deref_instr *deref, int arr_idx, void *mem_ctx)
  94 {
  95    nir_deref_path deref_path;
  96    nir_deref_path_init(&deref_path, deref, mem_ctx);
  97
  98    bool found = false;
  99    for (int i = 0; ; i++) {
 100       nir_deref_instr *b = base_path->path[i];
 101       nir_deref_instr *d = deref_path.path[i];
 102       /* They have to be the same length */
 103       if ((b == NULL) != (d == NULL))
 104          goto fail;
 105
 106       if (b == NULL)
 107          break;
 108
 109       /* This can happen if one is a deref_array and the other a wildcard */
 110       if (b->deref_type != d->deref_type)
 111          goto fail;
 112
 113       switch (b->deref_type) {
 114       case nir_deref_type_var:
 115          if (b->var != d->var)
 116             goto fail;
 117          continue;
 118
 119       case nir_deref_type_array:
 120          assert(b->arr.index.is_ssa && d->arr.index.is_ssa);
 121          const bool const_b_idx = nir_src_is_const(b->arr.index);
 122          const bool const_d_idx = nir_src_is_const(d->arr.index);
 123          const unsigned b_idx = const_b_idx ? nir_src_as_uint(b->arr.index) : 0;
 124          const unsigned d_idx = const_d_idx ? nir_src_as_uint(d->arr.index) : 0;
 125
 126          /* If we don't have an index into the path yet or if this entry in
 127           * the path is at the array index, see if this is a candidate.  We're
 128           * looking for an index which is zero in the base deref and arr_idx
 129           * in the search deref.
 130           */
 131          if ((*path_array_idx < 0 || *path_array_idx == i) &&
 132              const_b_idx && b_idx == 0 &&
 133              const_d_idx && d_idx == arr_idx) {
 134             *path_array_idx = i;
 135             continue;
 136          }
 137
 138          /* We're at the array index but not a candidate */
 139          if (*path_array_idx == i)
 140             goto fail;
 141
 142          /* If we're not the path array index, we must match exactly.  We
 143           * could probably just compare SSA values and trust in copy
 144           * propagation but doing it ourselves means this pass can run a bit
 145           * earlier.
 146           */
 147          if (b->arr.index.ssa == d->arr.index.ssa ||
 148              (const_b_idx && const_d_idx && b_idx == d_idx))
 149             continue;
 150
 151          goto fail;
 152
 153       case nir_deref_type_array_wildcard:
 154          continue;
 155
 156       case nir_deref_type_struct:
 157          if (b->strct.index != d->strct.index)
 158             goto fail;
 159          continue;
 160
 161       default:
 162          unreachable("Invalid deref type in a path");
 163       }
 164    }
 165
 166    /* If we got here without failing, we've matched.  However, it isn't an
 167     * array match unless we found an altered array index.
 168     */
 169    found = *path_array_idx > 0;
 170
 171 fail:
 172    nir_deref_path_finish(&deref_path);
 173    return found;
 174 }
 175
 176 static nir_deref_instr *
 177 build_wildcard_deref(nir_builder *b, nir_deref_path *path,
 178                      unsigned wildcard_idx)
 179 {
 180    assert(path->path[wildcard_idx]->deref_type == nir_deref_type_array);
 181
 182    nir_deref_instr *tail =
 183       nir_build_deref_array_wildcard(b, path->path[wildcard_idx - 1]);
 184
 185    for (unsigned i = wildcard_idx + 1; path->path[i]; i++)
 186       tail = nir_build_deref_follower(b, tail, path->path[i]);
 187
 188    return tail;
 189 }
 190
 191 static bool
 192 opt_find_array_copies_block(nir_builder *b, nir_block *block,
 193                             unsigned *num_ssa_defs, void *mem_ctx)
 194 {
 195    bool progress = false;
 196
 197    struct match_state s;
 198    match_state_init(&s);
 199
 200    nir_variable *dst_var = NULL;
 201    unsigned prev_dst_var_last_write = *num_ssa_defs;
 202    unsigned dst_var_last_write = *num_ssa_defs;
 203
 204    nir_foreach_instr(instr, block) {
 205       /* Index the SSA defs before we do anything else. */
 206       nir_foreach_ssa_def(instr, index_ssa_def_cb, num_ssa_defs);
 207
 208       if (instr->type != nir_instr_type_intrinsic)
 209          continue;
 210
 211       nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
 212       if (intrin->intrinsic != nir_intrinsic_copy_deref &&
 213           intrin->intrinsic != nir_intrinsic_store_deref)
 214          continue;
 215
 216       nir_deref_instr *dst_deref = nir_src_as_deref(intrin->src[0]);
 217
 218       /* The destination must be local.  If we see a non-local store, we
 219        * continue on because it won't affect local stores or read-only
 220        * variables.
 221        */
 222       if (dst_deref->mode != nir_var_function_temp)
 223          continue;
 224
 225       /* We keep track of the SSA indices where the two last-written
 226        * variables are written.  The prev_dst_var_last_write tells us when
 227        * the last store_deref to something other than dst happened.  If the
 228        * SSA def index from a load is greater than or equal to this number
 229        * then we know it happened afterwards and no writes to anything other
 230        * than dst occur between the load and the current instruction.
 231        */
 232       if (nir_deref_instr_get_variable(dst_deref) != dst_var) {
 233          prev_dst_var_last_write = dst_var_last_write;
 234          dst_var = nir_deref_instr_get_variable(dst_deref);
 235       }
 236       dst_var_last_write = *num_ssa_defs;
 237
 238       /* If it's a full variable store or copy, reset.  This will trigger
 239        * eventually because we'll fail to match an array element.  However,
 240        * it's a cheap early-exit.
 241        */
 242       if (dst_deref->deref_type == nir_deref_type_var)
 243          goto reset;
 244
 245       nir_deref_instr *src_deref;
 246       if (intrin->intrinsic == nir_intrinsic_copy_deref) {
 247          src_deref = nir_src_as_deref(intrin->src[1]);
 248       } else {
 249          assert(intrin->intrinsic == nir_intrinsic_store_deref);
 250          src_deref = get_deref_for_load_src(intrin->src[1],
 251                                             prev_dst_var_last_write);
 252
 253          /* We can only handle full writes */
 254          if (nir_intrinsic_write_mask(intrin) !=
 255              (1 << glsl_get_components(dst_deref->type)) - 1)
 256             goto reset;
 257       }
 258
 259       /* If we didn't find a valid src, then we have an unknown store and it
 260        * could mess things up.
 261        */
 262       if (src_deref == NULL)
 263          goto reset;
 264
 265       /* The source must be either local or something that's guaranteed to be
 266        * read-only.
 267        */
 268       const nir_variable_mode read_only_modes =
 269          nir_var_shader_in | nir_var_uniform | nir_var_system_value;
 270       if (!(src_deref->mode & (nir_var_function_temp | read_only_modes)))
 271          goto reset;
 272
 273       /* If we don't yet have an active copy, then make this instruction the
 274        * active copy.
 275        */
 276       if (s.next_array_idx == 0) {
 277          /* We can't combine a copy if there is any chance the source and
 278           * destination will end up aliasing.  Just bail if they're the same
 279           * variable.
 280           */
 281          if (nir_deref_instr_get_variable(src_deref) == dst_var)
 282             goto reset;
 283
 284          /* The load/store pair is enough to guarantee the same bit size and
 285           * number of components but a copy_var requires the actual types to
 286           * match.
 287           */
 288          if (dst_deref->type != src_deref->type)
 289             continue;
 290
 291          /* The first time we see a store, we don't know which array in the
 292           * deref path is the one being copied so we just record the paths
 293           * as-is and continue.  On the next iteration, it will try to match
 294           * based on which array index changed.
 295           */
 296          nir_deref_path_init(&s.first_dst_path, dst_deref, mem_ctx);
 297          nir_deref_path_init(&s.first_src_path, src_deref, mem_ctx);
 298          s.next_array_idx = 1;
 299          continue;
 300       }
 301
 302       if (!try_match_deref(&s.first_dst_path, &s.dst_deref_array_idx,
 303                            dst_deref, s.next_array_idx, mem_ctx) ||
 304           !try_match_deref(&s.first_src_path, &s.src_deref_array_idx,
 305                            src_deref, s.next_array_idx, mem_ctx))
 306          goto reset;
 307
 308       if (s.next_array_idx == 1) {
 309          /* This is our first non-trivial match.  We now have indices into
 310           * the search paths so we can do a couple more checks.
 311           */
 312          assert(s.dst_deref_array_idx > 0 && s.src_deref_array_idx > 0);
 313          const struct glsl_type *dst_arr_type =
 314             s.first_dst_path.path[s.dst_deref_array_idx - 1]->type;
 315          const struct glsl_type *src_arr_type =
 316             s.first_src_path.path[s.src_deref_array_idx - 1]->type;
 317
 318          assert(glsl_type_is_array(dst_arr_type) ||
 319                 glsl_type_is_matrix(dst_arr_type));
 320          assert(glsl_type_is_array(src_arr_type) ||
 321                 glsl_type_is_matrix(src_arr_type));
 322
 323          /* They must be the same length */
 324          s.array_len = glsl_get_length(dst_arr_type);
 325          if (s.array_len != glsl_get_length(src_arr_type))
 326             goto reset;
 327       }
 328
 329       s.next_array_idx++;
 330
 331       if (s.next_array_idx == s.array_len) {
 332          /* Hooray, We found a copy! */
 333          b->cursor = nir_after_instr(instr);
 334          nir_copy_deref(b, build_wildcard_deref(b, &s.first_dst_path,
 335                                                 s.dst_deref_array_idx),
 336                            build_wildcard_deref(b, &s.first_src_path,
 337                                                 s.src_deref_array_idx));
 338          match_state_reset(&s);
 339          progress = true;
 340       }
 341
 342       continue;
 343
 344    reset:
 345       match_state_reset(&s);
 346    }
 347
 348    return progress;
 349 }
 350
 351 static bool
 352 opt_find_array_copies_impl(nir_function_impl *impl)
 353 {
 354    nir_builder b;
 355    nir_builder_init(&b, impl);
 356
 357    bool progress = false;
 358
 359    void *mem_ctx = ralloc_context(NULL);
 360
 361    /* We re-index the SSA defs as we go; it makes it easier to handle
 362     * resetting the state machine.
 363     */
 364    unsigned num_ssa_defs = 0;
 365
 366    nir_foreach_block(block, impl) {
 367       if (opt_find_array_copies_block(&b, block, &num_ssa_defs, mem_ctx))
 368          progress = true;
 369    }
 370
 371    impl->ssa_alloc = num_ssa_defs;
 372
 373    ralloc_free(mem_ctx);
 374
 375    if (progress) {
 376       nir_metadata_preserve(impl, nir_metadata_block_index |
 377                                   nir_metadata_dominance);
 378    }
 379
 380    return progress;
 381 }
 382
 383 /**
 384  * This peephole optimization looks for a series of load/store_deref or
 385  * copy_deref instructions that copy an array from one variable to another and
 386  * turns it into a copy_deref that copies the entire array.  The pattern it
 387  * looks for is extremely specific but it's good enough to pick up on the
 388  * input array copies in DXVK and should also be able to pick up the sequence
 389  * generated by spirv_to_nir for a OpLoad of a large composite followed by
 390  * OpStore.
 391  *
 392  * TODO: Use a hash table approach to support out-of-order and interleaved
 393  * copies.
 394  */
 395 bool
 396 nir_opt_find_array_copies(nir_shader *shader)
 397 {
 398    bool progress = false;
 399
 400    nir_foreach_function(function, shader) {
 401       if (function->impl && opt_find_array_copies_impl(function->impl))
 402          progress = true;
 403    }
 404
 405    return progress;
 406 }