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    foreach_two_lists(formal_node, &ir->callee->parameters,
 285                      actual_node, &ir->actual_parameters) {
 286       ir_variable *sig_param = (ir_variable *) formal_node;
 287       ir_rvalue *param = (ir_rvalue *) actual_node;
 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    }
 298
 299    /* Since we're unlinked, we don't (necssarily) know the side effects of
 300     * this call.  So kill all copies.
 301     */
 302    acp->make_empty();
 303    this->killed_all = true;
 304
 305    return visit_continue_with_parent;
 306 }
 307
 308 void
 309 ir_constant_propagation_visitor::handle_if_block(exec_list *instructions)
 310 {
 311    exec_list *orig_acp = this->acp;
 312    exec_list *orig_kills = this->kills;
 313    bool orig_killed_all = this->killed_all;
 314
 315    this->acp = new(mem_ctx) exec_list;
 316    this->kills = new(mem_ctx) exec_list;
 317    this->killed_all = false;
 318
 319    /* Populate the initial acp with a constant of the original */
 320    foreach_list(n, orig_acp) {
 321       acp_entry *a = (acp_entry *) n;
 322       this->acp->push_tail(new(this->mem_ctx) acp_entry(a));
 323    }
 324
 325    visit_list_elements(this, instructions);
 326
 327    if (this->killed_all) {
 328       orig_acp->make_empty();
 329    }
 330
 331    exec_list *new_kills = this->kills;
 332    this->kills = orig_kills;
 333    this->acp = orig_acp;
 334    this->killed_all = this->killed_all || orig_killed_all;
 335
 336    foreach_list(n, new_kills) {
 337       kill_entry *k = (kill_entry *) n;
 338       kill(k->var, k->write_mask);
 339    }
 340 }
 341
 342 ir_visitor_status
 343 ir_constant_propagation_visitor::visit_enter(ir_if *ir)
 344 {
 345    ir->condition->accept(this);
 346    handle_rvalue(&ir->condition);
 347
 348    handle_if_block(&ir->then_instructions);
 349    handle_if_block(&ir->else_instructions);
 350
 351    /* handle_if_block() already descended into the children. */
 352    return visit_continue_with_parent;
 353 }
 354
 355 ir_visitor_status
 356 ir_constant_propagation_visitor::visit_enter(ir_loop *ir)
 357 {
 358    exec_list *orig_acp = this->acp;
 359    exec_list *orig_kills = this->kills;
 360    bool orig_killed_all = this->killed_all;
 361
 362    /* FINISHME: For now, the initial acp for loops is totally empty.
 363     * We could go through once, then go through again with the acp
 364     * cloned minus the killed entries after the first run through.
 365     */
 366    this->acp = new(mem_ctx) exec_list;
 367    this->kills = new(mem_ctx) exec_list;
 368    this->killed_all = false;
 369
 370    visit_list_elements(this, &ir->body_instructions);
 371
 372    if (this->killed_all) {
 373       orig_acp->make_empty();
 374    }
 375
 376    exec_list *new_kills = this->kills;
 377    this->kills = orig_kills;
 378    this->acp = orig_acp;
 379    this->killed_all = this->killed_all || orig_killed_all;
 380
 381    foreach_list(n, new_kills) {
 382       kill_entry *k = (kill_entry *) n;
 383       kill(k->var, k->write_mask);
 384    }
 385
 386    /* already descended into the children. */
 387    return visit_continue_with_parent;
 388 }
 389
 390 void
 391 ir_constant_propagation_visitor::kill(ir_variable *var, unsigned write_mask)
 392 {
 393    assert(var != NULL);
 394
 395    /* We don't track non-vectors. */
 396    if (!var->type->is_vector() && !var->type->is_scalar())
 397       return;
 398
 399    /* Remove any entries currently in the ACP for this kill. */
 400    foreach_list_safe(n, this->acp) {
 401       acp_entry *entry = (acp_entry *) n;
 402
 403       if (entry->var == var) {
 404          entry->write_mask &= ~write_mask;
 405          if (entry->write_mask == 0)
 406             entry->remove();
 407       }
 408    }
 409
 410    /* Add this writemask of the variable to the list of killed
 411     * variables in this block.
 412     */
 413    foreach_list(n, this->kills) {
 414       kill_entry *entry = (kill_entry *) n;
 415
 416       if (entry->var == var) {
 417          entry->write_mask |= write_mask;
 418          return;
 419       }
 420    }
 421    /* Not already in the list.  Make new entry. */
 422    this->kills->push_tail(new(this->mem_ctx) kill_entry(var, write_mask));
 423 }
 424
 425 /**
 426  * Adds an entry to the available constant list if it's a plain assignment
 427  * of a variable to a variable.
 428  */
 429 void
 430 ir_constant_propagation_visitor::add_constant(ir_assignment *ir)
 431 {
 432    acp_entry *entry;
 433
 434    if (ir->condition)
 435       return;
 436
 437    if (!ir->write_mask)
 438       return;
 439
 440    ir_dereference_variable *deref = ir->lhs->as_dereference_variable();
 441    ir_constant *constant = ir->rhs->as_constant();
 442
 443    if (!deref || !constant)
 444       return;
 445
 446    /* Only do constant propagation on vectors.  Constant matrices,
 447     * arrays, or structures would require more work elsewhere.
 448     */
 449    if (!deref->var->type->is_vector() && !deref->var->type->is_scalar())
 450       return;
 451
 452    entry = new(this->mem_ctx) acp_entry(deref->var, ir->write_mask, constant);
 453    this->acp->push_tail(entry);
 454 }
 455
 456 } /* unnamed namespace */
 457
 458 /**
 459  * Does a constant propagation pass on the code present in the instruction stream.
 460  */
 461 bool
 462 do_constant_propagation(exec_list *instructions)
 463 {
 464    ir_constant_propagation_visitor v;
 465
 466    visit_list_elements(&v, instructions);
 467
 468    return v.progress;
 469 }