src/compiler/glsl/opt_array_splitting.cpp

   1 /*
   2  * Copyright © 2010 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 /**
  25  * \file opt_array_splitting.cpp
  26  *
  27  * If an array is always dereferenced with a constant index, then
  28  * split it apart into its elements, making it more amenable to other
  29  * optimization passes.
  30  *
  31  * This skips uniform/varying arrays, which would need careful
  32  * handling due to their ir->location fields tying them to the GL API
  33  * and other shader stages.
  34  */
  35
  36 #include "ir.h"
  37 #include "ir_visitor.h"
  38 #include "ir_rvalue_visitor.h"
  39 #include "compiler/glsl_types.h"
  40
  41 static bool debug = false;
  42
  43 namespace {
  44
  45 namespace opt_array_splitting {
  46
  47 class variable_entry : public exec_node
  48 {
  49 public:
  50    variable_entry(ir_variable *var)
  51    {
  52       this->var = var;
  53       this->split = true;
  54       this->declaration = false;
  55       this->components = NULL;
  56       this->mem_ctx = NULL;
  57       if (var->type->is_array())
  58          this->size = var->type->length;
  59       else
  60          this->size = var->type->matrix_columns;
  61    }
  62
  63    ir_variable *var; /* The key: the variable's pointer. */
  64    unsigned size; /* array length or matrix columns */
  65
  66    /** Whether this array should be split or not. */
  67    bool split;
  68
  69    /* If the variable had a decl we can work with in the instruction
  70     * stream.  We can't do splitting on function arguments, which
  71     * don't get this variable set.
  72     */
  73    bool declaration;
  74
  75    ir_variable **components;
  76
  77    /** ralloc_parent(this->var) -- the shader's talloc context. */
  78    void *mem_ctx;
  79 };
  80
  81 } /* namespace */
  82
  83 using namespace opt_array_splitting;
  84
  85 /**
  86  * This class does a walk over the tree, coming up with the set of
  87  * variables that could be split by looking to see if they are arrays
  88  * that are only ever constant-index dereferenced.
  89  */
  90 class ir_array_reference_visitor : public ir_hierarchical_visitor {
  91 public:
  92    ir_array_reference_visitor(void)
  93    {
  94       this->mem_ctx = ralloc_context(NULL);
  95       this->variable_list.make_empty();
  96       this->in_whole_array_copy = false;
  97    }
  98
  99    ~ir_array_reference_visitor(void)
 100    {
 101       ralloc_free(mem_ctx);
 102    }
 103
 104    bool get_split_list(exec_list *instructions, bool linked);
 105
 106    virtual ir_visitor_status visit(ir_variable *);
 107    virtual ir_visitor_status visit(ir_dereference_variable *);
 108    virtual ir_visitor_status visit_enter(ir_assignment *);
 109    virtual ir_visitor_status visit_leave(ir_assignment *);
 110    virtual ir_visitor_status visit_enter(ir_dereference_array *);
 111    virtual ir_visitor_status visit_enter(ir_function_signature *);
 112
 113    variable_entry *get_variable_entry(ir_variable *var);
 114
 115    /* List of variable_entry */
 116    exec_list variable_list;
 117
 118    void *mem_ctx;
 119
 120    bool in_whole_array_copy;
 121 };
 122
 123 } /* namespace */
 124
 125 variable_entry *
 126 ir_array_reference_visitor::get_variable_entry(ir_variable *var)
 127 {
 128    assert(var);
 129
 130    if (var->data.mode != ir_var_auto &&
 131        var->data.mode != ir_var_temporary)
 132       return NULL;
 133
 134    if (!(var->type->is_array() || var->type->is_matrix()))
 135       return NULL;
 136
 137    /* If the array hasn't been sized yet, we can't split it.  After
 138     * linking, this should be resolved.
 139     */
 140    if (var->type->is_unsized_array())
 141       return NULL;
 142
 143    /* FIXME: arrays of arrays are not handled correctly by this pass so we
 144     * skip it for now. While the pass will create functioning code it actually
 145     * produces worse code.
 146     *
 147     * For example the array:
 148     *
 149     *    int[3][2] a;
 150     *
 151     * ends up being split up into:
 152     *
 153     *    int[3][2] a_0;
 154     *    int[3][2] a_1;
 155     *    int[3][2] a_2;
 156     *
 157     * And we end up referencing each of these new arrays for example:
 158     *
 159     *    a[0][1] will be turned into a_0[0][1]
 160     *    a[1][0] will be turned into a_1[1][0]
 161     *    a[2][0] will be turned into a_2[2][0]
 162     */
 163    if (var->type->is_array() && var->type->fields.array->is_array())
 164       return NULL;
 165
 166    foreach_in_list(variable_entry, entry, &this->variable_list) {
 167       if (entry->var == var)
 168          return entry;
 169    }
 170
 171    variable_entry *entry = new(mem_ctx) variable_entry(var);
 172    this->variable_list.push_tail(entry);
 173    return entry;
 174 }
 175
 176
 177 ir_visitor_status
 178 ir_array_reference_visitor::visit(ir_variable *ir)
 179 {
 180    variable_entry *entry = this->get_variable_entry(ir);
 181
 182    if (entry)
 183       entry->declaration = true;
 184
 185    return visit_continue;
 186 }
 187
 188 ir_visitor_status
 189 ir_array_reference_visitor::visit_enter(ir_assignment *ir)
 190 {
 191    in_whole_array_copy =
 192       ir->lhs->type->is_array() && ir->whole_variable_written();
 193
 194    return visit_continue;
 195 }
 196
 197 ir_visitor_status
 198 ir_array_reference_visitor::visit_leave(ir_assignment *)
 199 {
 200    in_whole_array_copy = false;
 201
 202    return visit_continue;
 203 }
 204
 205 ir_visitor_status
 206 ir_array_reference_visitor::visit(ir_dereference_variable *ir)
 207 {
 208    variable_entry *entry = this->get_variable_entry(ir->var);
 209
 210    /* Allow whole-array assignments on the LHS.  We can split those
 211     * by "unrolling" the assignment into component-wise assignments.
 212     */
 213    if (in_assignee && in_whole_array_copy)
 214       return visit_continue;
 215
 216    /* If we made it to here without seeing an ir_dereference_array,
 217     * then the dereference of this array didn't have a constant index
 218     * (see the visit_continue_with_parent below), so we can't split
 219     * the variable.
 220     */
 221    if (entry)
 222       entry->split = false;
 223
 224    return visit_continue;
 225 }
 226
 227 ir_visitor_status
 228 ir_array_reference_visitor::visit_enter(ir_dereference_array *ir)
 229 {
 230    ir_dereference_variable *deref = ir->array->as_dereference_variable();
 231    if (!deref)
 232       return visit_continue;
 233
 234    variable_entry *entry = this->get_variable_entry(deref->var);
 235
 236    /* If the access to the array has a variable index, we wouldn't
 237     * know which split variable this dereference should go to.
 238     */
 239    if (!ir->array_index->as_constant()) {
 240       if (entry)
 241          entry->split = false;
 242       /* This variable indexing could come from a different array dereference
 243        * that also has variable indexing, that is, something like a[b[a[b[0]]]].
 244        * If we return visit_continue_with_parent here for the first appearence
 245        * of a, then we can miss that b also has indirect indexing (if this is
 246        * the only place in the program where such indirect indexing into b
 247        * happens), so keep going.
 248        */
 249       return visit_continue;
 250    }
 251
 252    /* If the index is also array dereference, visit index. */
 253    if (ir->array_index->as_dereference_array())
 254       visit_enter(ir->array_index->as_dereference_array());
 255
 256    return visit_continue_with_parent;
 257 }
 258
 259 ir_visitor_status
 260 ir_array_reference_visitor::visit_enter(ir_function_signature *ir)
 261 {
 262    /* We don't have logic for array-splitting function arguments,
 263     * so just look at the body instructions and not the parameter
 264     * declarations.
 265     */
 266    visit_list_elements(this, &ir->body);
 267    return visit_continue_with_parent;
 268 }
 269
 270 bool
 271 ir_array_reference_visitor::get_split_list(exec_list *instructions,
 272                                            bool linked)
 273 {
 274    visit_list_elements(this, instructions);
 275
 276    /* If the shaders aren't linked yet, we can't mess with global
 277     * declarations, which need to be matched by name across shaders.
 278     */
 279    if (!linked) {
 280       foreach_in_list(ir_instruction, node, instructions) {
 281          ir_variable *var = node->as_variable();
 282          if (var) {
 283             variable_entry *entry = get_variable_entry(var);
 284             if (entry)
 285                entry->remove();
 286          }
 287       }
 288    }
 289
 290    /* Trim out variables we found that we can't split. */
 291    foreach_in_list_safe(variable_entry, entry, &variable_list) {
 292       if (debug) {
 293          printf("array %s@%p: decl %d, split %d\n",
 294                 entry->var->name, (void *) entry->var, entry->declaration,
 295                 entry->split);
 296       }
 297
 298       if (!(entry->declaration && entry->split)) {
 299          entry->remove();
 300       }
 301    }
 302
 303    return !variable_list.is_empty();
 304 }
 305
 306 /**
 307  * This class rewrites the dereferences of arrays that have been split
 308  * to use the newly created ir_variables for each component.
 309  */
 310 class ir_array_splitting_visitor : public ir_rvalue_visitor {
 311 public:
 312    ir_array_splitting_visitor(exec_list *vars)
 313    {
 314       this->variable_list = vars;
 315    }
 316
 317    virtual ~ir_array_splitting_visitor()
 318    {
 319    }
 320
 321    virtual ir_visitor_status visit_leave(ir_assignment *);
 322
 323    void split_deref(ir_dereference **deref);
 324    void handle_rvalue(ir_rvalue **rvalue);
 325    variable_entry *get_splitting_entry(ir_variable *var);
 326
 327    exec_list *variable_list;
 328 };
 329
 330 variable_entry *
 331 ir_array_splitting_visitor::get_splitting_entry(ir_variable *var)
 332 {
 333    assert(var);
 334
 335    foreach_in_list(variable_entry, entry, this->variable_list) {
 336       if (entry->var == var) {
 337          return entry;
 338       }
 339    }
 340
 341    return NULL;
 342 }
 343
 344 void
 345 ir_array_splitting_visitor::split_deref(ir_dereference **deref)
 346 {
 347    ir_dereference_array *deref_array = (*deref)->as_dereference_array();
 348    if (!deref_array)
 349       return;
 350
 351    ir_dereference_variable *deref_var = deref_array->array->as_dereference_variable();
 352    if (!deref_var)
 353       return;
 354    ir_variable *var = deref_var->var;
 355
 356    variable_entry *entry = get_splitting_entry(var);
 357    if (!entry)
 358       return;
 359
 360    ir_constant *constant = deref_array->array_index->as_constant();
 361    assert(constant);
 362
 363    if (constant->value.i[0] >= 0 && constant->value.i[0] < (int)entry->size) {
 364       *deref = new(entry->mem_ctx)
 365                ir_dereference_variable(entry->components[constant->value.i[0]]);
 366    } else {
 367       /* There was a constant array access beyond the end of the
 368        * array.  This might have happened due to constant folding
 369        * after the initial parse.  This produces an undefined value,
 370        * but shouldn't crash.  Just give them an uninitialized
 371        * variable.
 372        */
 373       ir_variable *temp = new(entry->mem_ctx) ir_variable(deref_array->type,
 374                                                           "undef",
 375                                                           ir_var_temporary);
 376       entry->components[0]->insert_before(temp);
 377       *deref = new(entry->mem_ctx) ir_dereference_variable(temp);
 378    }
 379 }
 380
 381 void
 382 ir_array_splitting_visitor::handle_rvalue(ir_rvalue **rvalue)
 383 {
 384    if (!*rvalue)
 385       return;
 386
 387    ir_dereference *deref = (*rvalue)->as_dereference();
 388
 389    if (!deref)
 390       return;
 391
 392    split_deref(&deref);
 393    *rvalue = deref;
 394 }
 395
 396 ir_visitor_status
 397 ir_array_splitting_visitor::visit_leave(ir_assignment *ir)
 398 {
 399    /* The normal rvalue visitor skips the LHS of assignments, but we
 400     * need to process those just the same.
 401     */
 402    ir_rvalue *lhs = ir->lhs;
 403
 404    /* "Unroll" any whole array assignments, creating assignments for
 405     * each array element.  Then, do splitting on each new assignment.
 406     */
 407    if (lhs->type->is_array() && ir->whole_variable_written() &&
 408        get_splitting_entry(ir->whole_variable_written())) {
 409       void *mem_ctx = ralloc_parent(ir);
 410
 411       for (unsigned i = 0; i < lhs->type->length; i++) {
 412          ir_rvalue *lhs_i =
 413             new(mem_ctx) ir_dereference_array(ir->lhs->clone(mem_ctx, NULL),
 414                                               new(mem_ctx) ir_constant(i));
 415          ir_rvalue *rhs_i =
 416             new(mem_ctx) ir_dereference_array(ir->rhs->clone(mem_ctx, NULL),
 417                                               new(mem_ctx) ir_constant(i));
 418          ir_rvalue *condition_i =
 419             ir->condition ? ir->condition->clone(mem_ctx, NULL) : NULL;
 420
 421          ir_assignment *assign_i =
 422             new(mem_ctx) ir_assignment(lhs_i, rhs_i, condition_i);
 423
 424          ir->insert_before(assign_i);
 425          assign_i->accept(this);
 426       }
 427       ir->remove();
 428       return visit_continue;
 429    }
 430
 431    handle_rvalue(&lhs);
 432    ir->lhs = lhs->as_dereference();
 433
 434    ir->lhs->accept(this);
 435
 436    handle_rvalue(&ir->rhs);
 437    ir->rhs->accept(this);
 438
 439    if (ir->condition) {
 440       handle_rvalue(&ir->condition);
 441       ir->condition->accept(this);
 442    }
 443
 444    return visit_continue;
 445 }
 446
 447 bool
 448 optimize_split_arrays(exec_list *instructions, bool linked)
 449 {
 450    ir_array_reference_visitor refs;
 451    if (!refs.get_split_list(instructions, linked))
 452       return false;
 453
 454    void *mem_ctx = ralloc_context(NULL);
 455
 456    /* Replace the decls of the arrays to be split with their split
 457     * components.
 458     */
 459    foreach_in_list(variable_entry, entry, &refs.variable_list) {
 460       const struct glsl_type *type = entry->var->type;
 461       const struct glsl_type *subtype;
 462
 463       if (type->is_matrix())
 464          subtype = type->column_type();
 465       else
 466          subtype = type->fields.array;
 467
 468       entry->mem_ctx = ralloc_parent(entry->var);
 469
 470       entry->components = ralloc_array(mem_ctx, ir_variable *, entry->size);
 471
 472       for (unsigned int i = 0; i < entry->size; i++) {
 473          const char *name = ralloc_asprintf(mem_ctx, "%s_%d",
 474                                             entry->var->name, i);
 475          ir_variable *new_var =
 476             new(entry->mem_ctx) ir_variable(subtype, name, ir_var_temporary);
 477
 478          /* Do not lose memory/format qualifiers when arrays of images are
 479           * split.
 480           */
 481          new_var->data.memory_read_only = entry->var->data.memory_read_only;
 482          new_var->data.memory_write_only = entry->var->data.memory_write_only;
 483          new_var->data.memory_coherent = entry->var->data.memory_coherent;
 484          new_var->data.memory_volatile = entry->var->data.memory_volatile;
 485          new_var->data.memory_restrict = entry->var->data.memory_restrict;
 486          new_var->data.image_format = entry->var->data.image_format;
 487
 488          entry->components[i] = new_var;
 489          entry->var->insert_before(entry->components[i]);
 490       }
 491
 492       entry->var->remove();
 493    }
 494
 495    ir_array_splitting_visitor split(&refs.variable_list);
 496    visit_list_elements(&split, instructions);
 497
 498    if (debug)
 499       _mesa_print_ir(stdout, instructions, NULL);
 500
 501    ralloc_free(mem_ctx);
 502
 503    return true;
 504
 505 }