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_in_list(acp_entry, entry, this->acp) {
 176          if (entry->var == deref->var && entry->write_mask & (1 << channel)) {
 177             found = entry;
 178             break;
 179          }
 180       }
 181
 182       if (!found)
 183          return;
 184
 185       int rhs_channel = 0;
 186       for (int j = 0; j < 4; j++) {
 187          if (j == channel)
 188             break;
 189          if (found->initial_values & (1 << j))
 190             rhs_channel++;
 191       }
 192
 193       switch (type->base_type) {
 194       case GLSL_TYPE_FLOAT:
 195          data.f[i] = found->constant->value.f[rhs_channel];
 196          break;
 197       case GLSL_TYPE_INT:
 198          data.i[i] = found->constant->value.i[rhs_channel];
 199          break;
 200       case GLSL_TYPE_UINT:
 201          data.u[i] = found->constant->value.u[rhs_channel];
 202          break;
 203       case GLSL_TYPE_BOOL:
 204          data.b[i] = found->constant->value.b[rhs_channel];
 205          break;
 206       default:
 207          assert(!"not reached");
 208          break;
 209       }
 210    }
 211
 212    *rvalue = new(ralloc_parent(deref)) ir_constant(type, &data);
 213    this->progress = true;
 214 }
 215
 216 ir_visitor_status
 217 ir_constant_propagation_visitor::visit_enter(ir_function_signature *ir)
 218 {
 219    /* Treat entry into a function signature as a completely separate
 220     * block.  Any instructions at global scope will be shuffled into
 221     * main() at link time, so they're irrelevant to us.
 222     */
 223    exec_list *orig_acp = this->acp;
 224    exec_list *orig_kills = this->kills;
 225    bool orig_killed_all = this->killed_all;
 226
 227    this->acp = new(mem_ctx) exec_list;
 228    this->kills = new(mem_ctx) exec_list;
 229    this->killed_all = false;
 230
 231    visit_list_elements(this, &ir->body);
 232
 233    this->kills = orig_kills;
 234    this->acp = orig_acp;
 235    this->killed_all = orig_killed_all;
 236
 237    return visit_continue_with_parent;
 238 }
 239
 240 ir_visitor_status
 241 ir_constant_propagation_visitor::visit_leave(ir_assignment *ir)
 242 {
 243    if (this->in_assignee)
 244       return visit_continue;
 245
 246    unsigned kill_mask = ir->write_mask;
 247    if (ir->lhs->as_dereference_array()) {
 248       /* The LHS of the assignment uses an array indexing operator (e.g. v[i]
 249        * = ...;).  Since we only try to constant propagate vectors and
 250        * scalars, this means that either (a) array indexing is being used to
 251        * select a vector component, or (b) the variable in question is neither
 252        * a scalar or a vector, so we don't care about it.  In the former case,
 253        * we want to kill the whole vector, since in general we can't predict
 254        * which vector component will be selected by array indexing.  In the
 255        * latter case, it doesn't matter what we do, so go ahead and kill the
 256        * whole variable anyway.
 257        *
 258        * Note that if the array index is constant (e.g. v[2] = ...;), we could
 259        * in principle be smarter, but we don't need to, because a future
 260        * optimization pass will convert it to a simple assignment with the
 261        * correct mask.
 262        */
 263       kill_mask = ~0;
 264    }
 265    kill(ir->lhs->variable_referenced(), kill_mask);
 266
 267    add_constant(ir);
 268
 269    return visit_continue;
 270 }
 271
 272 ir_visitor_status
 273 ir_constant_propagation_visitor::visit_enter(ir_function *ir)
 274 {
 275    (void) ir;
 276    return visit_continue;
 277 }
 278
 279 ir_visitor_status
 280 ir_constant_propagation_visitor::visit_enter(ir_call *ir)
 281 {
 282    /* Do constant propagation on call parameters, but skip any out params */
 283    foreach_two_lists(formal_node, &ir->callee->parameters,
 284                      actual_node, &ir->actual_parameters) {
 285       ir_variable *sig_param = (ir_variable *) formal_node;
 286       ir_rvalue *param = (ir_rvalue *) actual_node;
 287       if (sig_param->data.mode != ir_var_function_out
 288           && sig_param->data.mode != ir_var_function_inout) {
 289          ir_rvalue *new_param = param;
 290          handle_rvalue(&new_param);
 291          if (new_param != param)
 292             param->replace_with(new_param);
 293          else
 294             param->accept(this);
 295       }
 296    }
 297
 298    /* Since we're unlinked, we don't (necssarily) know the side effects of
 299     * this call.  So kill all copies.
 300     */
 301    acp->make_empty();
 302    this->killed_all = true;
 303
 304    return visit_continue_with_parent;
 305 }
 306
 307 void
 308 ir_constant_propagation_visitor::handle_if_block(exec_list *instructions)
 309 {
 310    exec_list *orig_acp = this->acp;
 311    exec_list *orig_kills = this->kills;
 312    bool orig_killed_all = this->killed_all;
 313
 314    this->acp = new(mem_ctx) exec_list;
 315    this->kills = new(mem_ctx) exec_list;
 316    this->killed_all = false;
 317
 318    /* Populate the initial acp with a constant of the original */
 319    foreach_in_list(acp_entry, a, orig_acp) {
 320       this->acp->push_tail(new(this->mem_ctx) acp_entry(a));
 321    }
 322
 323    visit_list_elements(this, instructions);
 324
 325    if (this->killed_all) {
 326       orig_acp->make_empty();
 327    }
 328
 329    exec_list *new_kills = this->kills;
 330    this->kills = orig_kills;
 331    this->acp = orig_acp;
 332    this->killed_all = this->killed_all || orig_killed_all;
 333
 334    foreach_in_list(kill_entry, k, new_kills) {
 335       kill(k->var, k->write_mask);
 336    }
 337 }
 338
 339 ir_visitor_status
 340 ir_constant_propagation_visitor::visit_enter(ir_if *ir)
 341 {
 342    ir->condition->accept(this);
 343    handle_rvalue(&ir->condition);
 344
 345    handle_if_block(&ir->then_instructions);
 346    handle_if_block(&ir->else_instructions);
 347
 348    /* handle_if_block() already descended into the children. */
 349    return visit_continue_with_parent;
 350 }
 351
 352 ir_visitor_status
 353 ir_constant_propagation_visitor::visit_enter(ir_loop *ir)
 354 {
 355    exec_list *orig_acp = this->acp;
 356    exec_list *orig_kills = this->kills;
 357    bool orig_killed_all = this->killed_all;
 358
 359    /* FINISHME: For now, the initial acp for loops is totally empty.
 360     * We could go through once, then go through again with the acp
 361     * cloned minus the killed entries after the first run through.
 362     */
 363    this->acp = new(mem_ctx) exec_list;
 364    this->kills = new(mem_ctx) exec_list;
 365    this->killed_all = false;
 366
 367    visit_list_elements(this, &ir->body_instructions);
 368
 369    if (this->killed_all) {
 370       orig_acp->make_empty();
 371    }
 372
 373    exec_list *new_kills = this->kills;
 374    this->kills = orig_kills;
 375    this->acp = orig_acp;
 376    this->killed_all = this->killed_all || orig_killed_all;
 377
 378    foreach_in_list(kill_entry, k, new_kills) {
 379       kill(k->var, k->write_mask);
 380    }
 381
 382    /* already descended into the children. */
 383    return visit_continue_with_parent;
 384 }
 385
 386 void
 387 ir_constant_propagation_visitor::kill(ir_variable *var, unsigned write_mask)
 388 {
 389    assert(var != NULL);
 390
 391    /* We don't track non-vectors. */
 392    if (!var->type->is_vector() && !var->type->is_scalar())
 393       return;
 394
 395    /* Remove any entries currently in the ACP for this kill. */
 396    foreach_list_safe(n, this->acp) {
 397       acp_entry *entry = (acp_entry *) n;
 398
 399       if (entry->var == var) {
 400          entry->write_mask &= ~write_mask;
 401          if (entry->write_mask == 0)
 402             entry->remove();
 403       }
 404    }
 405
 406    /* Add this writemask of the variable to the list of killed
 407     * variables in this block.
 408     */
 409    foreach_in_list(kill_entry, entry, this->kills) {
 410       if (entry->var == var) {
 411          entry->write_mask |= write_mask;
 412          return;
 413       }
 414    }
 415    /* Not already in the list.  Make new entry. */
 416    this->kills->push_tail(new(this->mem_ctx) kill_entry(var, write_mask));
 417 }
 418
 419 /**
 420  * Adds an entry to the available constant list if it's a plain assignment
 421  * of a variable to a variable.
 422  */
 423 void
 424 ir_constant_propagation_visitor::add_constant(ir_assignment *ir)
 425 {
 426    acp_entry *entry;
 427
 428    if (ir->condition)
 429       return;
 430
 431    if (!ir->write_mask)
 432       return;
 433
 434    ir_dereference_variable *deref = ir->lhs->as_dereference_variable();
 435    ir_constant *constant = ir->rhs->as_constant();
 436
 437    if (!deref || !constant)
 438       return;
 439
 440    /* Only do constant propagation on vectors.  Constant matrices,
 441     * arrays, or structures would require more work elsewhere.
 442     */
 443    if (!deref->var->type->is_vector() && !deref->var->type->is_scalar())
 444       return;
 445
 446    entry = new(this->mem_ctx) acp_entry(deref->var, ir->write_mask, constant);
 447    this->acp->push_tail(entry);
 448 }
 449
 450 } /* unnamed namespace */
 451
 452 /**
 453  * Does a constant propagation pass on the code present in the instruction stream.
 454  */
 455 bool
 456 do_constant_propagation(exec_list *instructions)
 457 {
 458    ir_constant_propagation_visitor v;
 459
 460    visit_list_elements(&v, instructions);
 461
 462    return v.progress;
 463 }