src/glsl/opt_constant_propagation.cpp

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