src/glsl/ir_constant_propagation.cpp

   1 /*
   2  * Constantright © 2010 Intel Corporation
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining a
   5  * constant 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, constant, 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 constantright 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 CONSTANTRIGHT 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 ir_constant_propagation.cpp
  26  *
  27  * Tracks assignments of constants to channels of variables, and
  28  * usage of those constant channels with direct usage of the constants.
  29  *
  30  * This can lead to constant folding and algebraic optimizations in
  31  * those later expressions, while causing no increase in instruction
  32  * count (due to constants being generally free to load from a
  33  * constant push buffer or as instruction immediate values) and
  34  * possibly reducing register pressure.
  35  */
  36
  37 #include "ir.h"
  38 #include "ir_visitor.h"
  39 #include "ir_basic_block.h"
  40 #include "ir_optimization.h"
  41 #include "glsl_types.h"
  42
  43 class acp_entry : public exec_node
  44 {
  45 public:
  46    acp_entry(ir_variable *var, unsigned write_mask, ir_constant *constant)
  47    {
  48       assert(var);
  49       assert(constant);
  50       this->var = var;
  51       this->write_mask = write_mask;
  52       this->constant = constant;
  53    }
  54
  55    ir_variable *var;
  56    ir_constant *constant;
  57    unsigned write_mask;
  58 };
  59
  60
  61 class kill_entry : public exec_node
  62 {
  63 public:
  64    kill_entry(ir_variable *var, unsigned write_mask)
  65    {
  66       assert(var);
  67       this->var = var;
  68       this->write_mask = write_mask;
  69    }
  70
  71    ir_variable *var;
  72    unsigned write_mask;
  73 };
  74
  75 class ir_constant_propagation_visitor : public ir_hierarchical_visitor {
  76 public:
  77    ir_constant_propagation_visitor()
  78    {
  79       progress = false;
  80       mem_ctx = talloc_new(0);
  81       this->acp = new(mem_ctx) exec_list;
  82       this->kills = new(mem_ctx) exec_list;
  83    }
  84    ~ir_constant_propagation_visitor()
  85    {
  86       talloc_free(mem_ctx);
  87    }
  88
  89    virtual ir_visitor_status visit_enter(class ir_loop *);
  90    virtual ir_visitor_status visit_enter(class ir_function_signature *);
  91    virtual ir_visitor_status visit_enter(class ir_function *);
  92    virtual ir_visitor_status visit_enter(class ir_assignment *);
  93    virtual ir_visitor_status visit_leave(class ir_assignment *);
  94    virtual ir_visitor_status visit_enter(class ir_expression *);
  95    virtual ir_visitor_status visit_enter(class ir_call *);
  96    virtual ir_visitor_status visit_enter(class ir_if *);
  97    virtual ir_visitor_status visit_enter(class ir_dereference_array *);
  98    virtual ir_visitor_status visit_enter(class ir_texture *);
  99
 100    void add_constant(ir_assignment *ir);
 101    void kill(ir_variable *ir, unsigned write_mask);
 102    void handle_if_block(exec_list *instructions);
 103    void handle_rvalue(ir_rvalue **rvalue);
 104
 105    /** List of acp_entry: The available constants to propagate */
 106    exec_list *acp;
 107
 108    /**
 109     * List of kill_entry: The masks of variables whose values were
 110     * killed in this block.
 111     */
 112    exec_list *kills;
 113
 114    bool progress;
 115
 116    bool killed_all;
 117
 118    void *mem_ctx;
 119 };
 120
 121
 122 void
 123 ir_constant_propagation_visitor::handle_rvalue(ir_rvalue **rvalue)
 124 {
 125    if (!*rvalue)
 126       return;
 127
 128    const glsl_type *type = (*rvalue)->type;
 129    if (!type->is_scalar() && !type->is_vector())
 130       return;
 131
 132    ir_swizzle *swiz = NULL;
 133    ir_dereference_variable *deref = (*rvalue)->as_dereference_variable();
 134    if (!deref) {
 135       swiz = (*rvalue)->as_swizzle();
 136       if (!swiz)
 137          return;
 138
 139       deref = swiz->val->as_dereference_variable();
 140       if (!deref)
 141          return;
 142    }
 143
 144    ir_constant_data data;
 145    memset(&data, 0, sizeof(data));
 146
 147    for (unsigned int i = 0; i < type->components(); i++) {
 148       int channel;
 149       acp_entry *found = NULL;
 150
 151       if (swiz) {
 152          switch (i) {
 153          case 0: channel = swiz->mask.x; break;
 154          case 1: channel = swiz->mask.y; break;
 155          case 2: channel = swiz->mask.z; break;
 156          case 3: channel = swiz->mask.w; break;
 157          default: assert(!"shouldn't be reached"); channel = 0; break;
 158          }
 159       } else {
 160          channel = i;
 161       }
 162
 163       foreach_iter(exec_list_iterator, iter, *this->acp) {
 164          acp_entry *entry = (acp_entry *)iter.get();
 165          if (entry->var == deref->var && entry->write_mask & (1 << channel)) {
 166             found = entry;
 167             break;
 168          }
 169       }
 170
 171       if (!found)
 172          return;
 173
 174       switch (type->base_type) {
 175       case GLSL_TYPE_FLOAT:
 176          data.f[i] = found->constant->value.f[channel];
 177          break;
 178       case GLSL_TYPE_INT:
 179          data.i[i] = found->constant->value.i[channel];
 180          break;
 181       case GLSL_TYPE_UINT:
 182          data.u[i] = found->constant->value.u[channel];
 183          break;
 184       case GLSL_TYPE_BOOL:
 185          data.b[i] = found->constant->value.b[channel];
 186          break;
 187       default:
 188          assert(!"not reached");
 189          break;
 190       }
 191    }
 192
 193    *rvalue = new(talloc_parent(deref)) ir_constant(type, &data);
 194    this->progress = true;
 195 }
 196
 197 ir_visitor_status
 198 ir_constant_propagation_visitor::visit_enter(ir_function_signature *ir)
 199 {
 200    /* Treat entry into a function signature as a completely separate
 201     * block.  Any instructions at global scope will be shuffled into
 202     * main() at link time, so they're irrelevant to us.
 203     */
 204    exec_list *orig_acp = this->acp;
 205    exec_list *orig_kills = this->kills;
 206    bool orig_killed_all = this->killed_all;
 207
 208    this->acp = new(mem_ctx) exec_list;
 209    this->kills = new(mem_ctx) exec_list;
 210    this->killed_all = false;
 211
 212    visit_list_elements(this, &ir->body);
 213
 214    this->kills = orig_kills;
 215    this->acp = orig_acp;
 216    this->killed_all = orig_killed_all;
 217
 218    return visit_continue_with_parent;
 219 }
 220
 221 ir_visitor_status
 222 ir_constant_propagation_visitor::visit_enter(ir_assignment *ir)
 223 {
 224    handle_rvalue(&ir->condition);
 225    handle_rvalue(&ir->rhs);
 226
 227    return visit_continue;
 228 }
 229
 230 ir_visitor_status
 231 ir_constant_propagation_visitor::visit_leave(ir_assignment *ir)
 232 {
 233    kill(ir->lhs->variable_referenced(), ir->write_mask);
 234
 235    add_constant(ir);
 236
 237    return visit_continue;
 238 }
 239
 240 ir_visitor_status
 241 ir_constant_propagation_visitor::visit_enter(ir_expression *ir)
 242 {
 243    for (unsigned int i = 0; i < ir->get_num_operands(); i++) {
 244       handle_rvalue(&ir->operands[i]);
 245    }
 246
 247    return visit_continue;
 248 }
 249
 250 ir_visitor_status
 251 ir_constant_propagation_visitor::visit_enter(ir_function *ir)
 252 {
 253    (void) ir;
 254    return visit_continue;
 255 }
 256
 257 ir_visitor_status
 258 ir_constant_propagation_visitor::visit_enter(ir_call *ir)
 259 {
 260    /* Do constant propagation on call parameters, but skip any out params */
 261    exec_list_iterator sig_param_iter = ir->get_callee()->parameters.iterator();
 262    foreach_iter(exec_list_iterator, iter, ir->actual_parameters) {
 263       ir_variable *sig_param = (ir_variable *)sig_param_iter.get();
 264       ir_rvalue *param = (ir_rvalue *)iter.get();
 265       if (sig_param->mode != ir_var_out && sig_param->mode != ir_var_inout) {
 266          ir_rvalue *new_param = param;
 267          handle_rvalue(&new_param);
 268          if (new_param != param)
 269             param->replace_with(new_param);
 270          else
 271             param->accept(this);
 272       }
 273       sig_param_iter.next();
 274    }
 275
 276    /* Since we're unlinked, we don't (necssarily) know the side effects of
 277     * this call.  So kill all copies.
 278     */
 279    acp->make_empty();
 280    this->killed_all = true;
 281
 282    return visit_continue_with_parent;
 283 }
 284
 285 void
 286 ir_constant_propagation_visitor::handle_if_block(exec_list *instructions)
 287 {
 288    exec_list *orig_acp = this->acp;
 289    exec_list *orig_kills = this->kills;
 290    bool orig_killed_all = this->killed_all;
 291
 292    this->acp = new(mem_ctx) exec_list;
 293    this->kills = new(mem_ctx) exec_list;
 294    this->killed_all = false;
 295
 296    /* Populate the initial acp with a constant of the original */
 297    foreach_iter(exec_list_iterator, iter, *orig_acp) {
 298       acp_entry *a = (acp_entry *)iter.get();
 299       this->acp->push_tail(new(this->mem_ctx) acp_entry(a->var, a->write_mask,
 300                                                         a->constant));
 301    }
 302
 303    visit_list_elements(this, instructions);
 304
 305    if (this->killed_all) {
 306       orig_acp->make_empty();
 307    }
 308
 309    exec_list *new_kills = this->kills;
 310    this->kills = orig_kills;
 311    this->acp = orig_acp;
 312    this->killed_all = this->killed_all || orig_killed_all;
 313
 314    foreach_iter(exec_list_iterator, iter, *new_kills) {
 315       kill_entry *k = (kill_entry *)iter.get();
 316       kill(k->var, k->write_mask);
 317    }
 318 }
 319
 320 ir_visitor_status
 321 ir_constant_propagation_visitor::visit_enter(ir_if *ir)
 322 {
 323    ir->condition->accept(this);
 324    handle_rvalue(&ir->condition);
 325
 326    handle_if_block(&ir->then_instructions);
 327    handle_if_block(&ir->else_instructions);
 328
 329    /* handle_if_block() already descended into the children. */
 330    return visit_continue_with_parent;
 331 }
 332
 333 ir_visitor_status
 334 ir_constant_propagation_visitor::visit_enter(ir_dereference_array *ir)
 335 {
 336    handle_rvalue(&ir->array_index);
 337    return visit_continue;
 338 }
 339
 340 ir_visitor_status
 341 ir_constant_propagation_visitor::visit_enter(ir_texture *ir)
 342 {
 343    handle_rvalue(&ir->coordinate);
 344    handle_rvalue(&ir->projector);
 345    handle_rvalue(&ir->shadow_comparitor);
 346
 347    switch (ir->op) {
 348    case ir_tex:
 349       break;
 350    case ir_txb:
 351       handle_rvalue(&ir->lod_info.bias);
 352       break;
 353    case ir_txf:
 354    case ir_txl:
 355       handle_rvalue(&ir->lod_info.lod);
 356       break;
 357    case ir_txd:
 358       handle_rvalue(&ir->lod_info.grad.dPdx);
 359       handle_rvalue(&ir->lod_info.grad.dPdy);
 360       break;
 361    }
 362
 363    return visit_continue;
 364 }
 365
 366 ir_visitor_status
 367 ir_constant_propagation_visitor::visit_enter(ir_loop *ir)
 368 {
 369    exec_list *orig_acp = this->acp;
 370    exec_list *orig_kills = this->kills;
 371    bool orig_killed_all = this->killed_all;
 372
 373    /* FINISHME: For now, the initial acp for loops is totally empty.
 374     * We could go through once, then go through again with the acp
 375     * cloned minus the killed entries after the first run through.
 376     */
 377    this->acp = new(mem_ctx) exec_list;
 378    this->kills = new(mem_ctx) exec_list;
 379    this->killed_all = false;
 380
 381    visit_list_elements(this, &ir->body_instructions);
 382
 383    if (this->killed_all) {
 384       orig_acp->make_empty();
 385    }
 386
 387    exec_list *new_kills = this->kills;
 388    this->kills = orig_kills;
 389    this->acp = orig_acp;
 390    this->killed_all = this->killed_all || orig_killed_all;
 391
 392    foreach_iter(exec_list_iterator, iter, *new_kills) {
 393       kill_entry *k = (kill_entry *)iter.get();
 394       kill(k->var, k->write_mask);
 395    }
 396
 397    /* already descended into the children. */
 398    return visit_continue_with_parent;
 399 }
 400
 401 void
 402 ir_constant_propagation_visitor::kill(ir_variable *var, unsigned write_mask)
 403 {
 404    assert(var != NULL);
 405
 406    /* We don't track non-vectors. */
 407    if (!var->type->is_vector() && !var->type->is_scalar())
 408       return;
 409
 410    /* Remove any entries currently in the ACP for this kill. */
 411    foreach_iter(exec_list_iterator, iter, *this->acp) {
 412       acp_entry *entry = (acp_entry *)iter.get();
 413
 414       if (entry->var == var) {
 415          entry->write_mask &= ~write_mask;
 416          if (entry->write_mask == 0)
 417             entry->remove();
 418       }
 419    }
 420
 421    /* Add this writemask of the variable to the list of killed
 422     * variables in this block.
 423     */
 424    foreach_iter(exec_list_iterator, iter, *this->kills) {
 425       kill_entry *entry = (kill_entry *)iter.get();
 426
 427       if (entry->var == var) {
 428          entry->write_mask |= write_mask;
 429          return;
 430       }
 431    }
 432    /* Not already in the list.  Make new entry. */
 433    this->kills->push_tail(new(this->mem_ctx) kill_entry(var, write_mask));
 434 }
 435
 436 /**
 437  * Adds an entry to the available constant list if it's a plain assignment
 438  * of a variable to a variable.
 439  */
 440 void
 441 ir_constant_propagation_visitor::add_constant(ir_assignment *ir)
 442 {
 443    acp_entry *entry;
 444
 445    if (ir->condition) {
 446       ir_constant *condition = ir->condition->as_constant();
 447       if (!condition || !condition->value.b[0])
 448          return;
 449    }
 450
 451    if (!ir->write_mask)
 452       return;
 453
 454    ir_dereference_variable *deref = ir->lhs->as_dereference_variable();
 455    ir_constant *constant = ir->rhs->as_constant();
 456
 457    if (!deref || !constant)
 458       return;
 459
 460    /* Only do constant propagation on vectors.  Constant matrices,
 461     * arrays, or structures would require more work elsewhere.
 462     */
 463    if (!deref->var->type->is_vector() && !deref->var->type->is_scalar())
 464       return;
 465
 466    entry = new(this->mem_ctx) acp_entry(deref->var, ir->write_mask, constant);
 467    this->acp->push_tail(entry);
 468 }
 469
 470 /**
 471  * Does a constant propagation pass on the code present in the instruction stream.
 472  */
 473 bool
 474 do_constant_propagation(exec_list *instructions)
 475 {
 476    ir_constant_propagation_visitor v;
 477
 478    visit_list_elements(&v, instructions);
 479
 480    return v.progress;
 481 }