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