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       mem_ctx = ralloc_context(0);
  96       this->acp = new(mem_ctx) exec_list;
  97       this->kills = new(mem_ctx) exec_list;
  98    }
  99    ~ir_constant_propagation_visitor()
 100    {
 101       ralloc_free(mem_ctx);
 102    }
 103
 104    virtual ir_visitor_status visit_enter(class ir_loop *);
 105    virtual ir_visitor_status visit_enter(class ir_function_signature *);
 106    virtual ir_visitor_status visit_enter(class ir_function *);
 107    virtual ir_visitor_status visit_leave(class ir_assignment *);
 108    virtual ir_visitor_status visit_enter(class ir_call *);
 109    virtual ir_visitor_status visit_enter(class ir_if *);
 110
 111    void add_constant(ir_assignment *ir);
 112    void kill(ir_variable *ir, unsigned write_mask);
 113    void handle_if_block(exec_list *instructions);
 114    void handle_rvalue(ir_rvalue **rvalue);
 115
 116    /** List of acp_entry: The available constants to propagate */
 117    exec_list *acp;
 118
 119    /**
 120     * List of kill_entry: The masks of variables whose values were
 121     * killed in this block.
 122     */
 123    exec_list *kills;
 124
 125    bool progress;
 126
 127    bool killed_all;
 128
 129    void *mem_ctx;
 130 };
 131
 132
 133 void
 134 ir_constant_propagation_visitor::handle_rvalue(ir_rvalue **rvalue)
 135 {
 136    if (this->in_assignee || !*rvalue)
 137       return;
 138
 139    const glsl_type *type = (*rvalue)->type;
 140    if (!type->is_scalar() && !type->is_vector())
 141       return;
 142
 143    ir_swizzle *swiz = NULL;
 144    ir_dereference_variable *deref = (*rvalue)->as_dereference_variable();
 145    if (!deref) {
 146       swiz = (*rvalue)->as_swizzle();
 147       if (!swiz)
 148          return;
 149
 150       deref = swiz->val->as_dereference_variable();
 151       if (!deref)
 152          return;
 153    }
 154
 155    ir_constant_data data;
 156    memset(&data, 0, sizeof(data));
 157
 158    for (unsigned int i = 0; i < type->components(); i++) {
 159       int channel;
 160       acp_entry *found = NULL;
 161
 162       if (swiz) {
 163          switch (i) {
 164          case 0: channel = swiz->mask.x; break;
 165          case 1: channel = swiz->mask.y; break;
 166          case 2: channel = swiz->mask.z; break;
 167          case 3: channel = swiz->mask.w; break;
 168          default: assert(!"shouldn't be reached"); channel = 0; break;
 169          }
 170       } else {
 171          channel = i;
 172       }
 173
 174       foreach_iter(exec_list_iterator, iter, *this->acp) {
 175          acp_entry *entry = (acp_entry *)iter.get();
 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    exec_list_iterator sig_param_iter = ir->callee->parameters.iterator();
 284    foreach_iter(exec_list_iterator, iter, ir->actual_parameters) {
 285       ir_variable *sig_param = (ir_variable *)sig_param_iter.get();
 286       ir_rvalue *param = (ir_rvalue *)iter.get();
 287       if (sig_param->mode != ir_var_out && sig_param->mode != ir_var_inout) {
 288          ir_rvalue *new_param = param;
 289          handle_rvalue(&new_param);
 290          if (new_param != param)
 291             param->replace_with(new_param);
 292          else
 293             param->accept(this);
 294       }
 295       sig_param_iter.next();
 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_iter(exec_list_iterator, iter, *orig_acp) {
 320       acp_entry *a = (acp_entry *)iter.get();
 321       this->acp->push_tail(new(this->mem_ctx) acp_entry(a));
 322    }
 323
 324    visit_list_elements(this, instructions);
 325
 326    if (this->killed_all) {
 327       orig_acp->make_empty();
 328    }
 329
 330    exec_list *new_kills = this->kills;
 331    this->kills = orig_kills;
 332    this->acp = orig_acp;
 333    this->killed_all = this->killed_all || orig_killed_all;
 334
 335    foreach_iter(exec_list_iterator, iter, *new_kills) {
 336       kill_entry *k = (kill_entry *)iter.get();
 337       kill(k->var, k->write_mask);
 338    }
 339 }
 340
 341 ir_visitor_status
 342 ir_constant_propagation_visitor::visit_enter(ir_if *ir)
 343 {
 344    ir->condition->accept(this);
 345    handle_rvalue(&ir->condition);
 346
 347    handle_if_block(&ir->then_instructions);
 348    handle_if_block(&ir->else_instructions);
 349
 350    /* handle_if_block() already descended into the children. */
 351    return visit_continue_with_parent;
 352 }
 353
 354 ir_visitor_status
 355 ir_constant_propagation_visitor::visit_enter(ir_loop *ir)
 356 {
 357    exec_list *orig_acp = this->acp;
 358    exec_list *orig_kills = this->kills;
 359    bool orig_killed_all = this->killed_all;
 360
 361    /* FINISHME: For now, the initial acp for loops is totally empty.
 362     * We could go through once, then go through again with the acp
 363     * cloned minus the killed entries after the first run through.
 364     */
 365    this->acp = new(mem_ctx) exec_list;
 366    this->kills = new(mem_ctx) exec_list;
 367    this->killed_all = false;
 368
 369    visit_list_elements(this, &ir->body_instructions);
 370
 371    if (this->killed_all) {
 372       orig_acp->make_empty();
 373    }
 374
 375    exec_list *new_kills = this->kills;
 376    this->kills = orig_kills;
 377    this->acp = orig_acp;
 378    this->killed_all = this->killed_all || orig_killed_all;
 379
 380    foreach_iter(exec_list_iterator, iter, *new_kills) {
 381       kill_entry *k = (kill_entry *)iter.get();
 382       kill(k->var, k->write_mask);
 383    }
 384
 385    /* already descended into the children. */
 386    return visit_continue_with_parent;
 387 }
 388
 389 void
 390 ir_constant_propagation_visitor::kill(ir_variable *var, unsigned write_mask)
 391 {
 392    assert(var != NULL);
 393
 394    /* We don't track non-vectors. */
 395    if (!var->type->is_vector() && !var->type->is_scalar())
 396       return;
 397
 398    /* Remove any entries currently in the ACP for this kill. */
 399    foreach_iter(exec_list_iterator, iter, *this->acp) {
 400       acp_entry *entry = (acp_entry *)iter.get();
 401
 402       if (entry->var == var) {
 403          entry->write_mask &= ~write_mask;
 404          if (entry->write_mask == 0)
 405             entry->remove();
 406       }
 407    }
 408
 409    /* Add this writemask of the variable to the list of killed
 410     * variables in this block.
 411     */
 412    foreach_iter(exec_list_iterator, iter, *this->kills) {
 413       kill_entry *entry = (kill_entry *)iter.get();
 414
 415       if (entry->var == var) {
 416          entry->write_mask |= write_mask;
 417          return;
 418       }
 419    }
 420    /* Not already in the list.  Make new entry. */
 421    this->kills->push_tail(new(this->mem_ctx) kill_entry(var, write_mask));
 422 }
 423
 424 /**
 425  * Adds an entry to the available constant list if it's a plain assignment
 426  * of a variable to a variable.
 427  */
 428 void
 429 ir_constant_propagation_visitor::add_constant(ir_assignment *ir)
 430 {
 431    acp_entry *entry;
 432
 433    if (ir->condition)
 434       return;
 435
 436    if (!ir->write_mask)
 437       return;
 438
 439    ir_dereference_variable *deref = ir->lhs->as_dereference_variable();
 440    ir_constant *constant = ir->rhs->as_constant();
 441
 442    if (!deref || !constant)
 443       return;
 444
 445    /* Only do constant propagation on vectors.  Constant matrices,
 446     * arrays, or structures would require more work elsewhere.
 447     */
 448    if (!deref->var->type->is_vector() && !deref->var->type->is_scalar())
 449       return;
 450
 451    entry = new(this->mem_ctx) acp_entry(deref->var, ir->write_mask, constant);
 452    this->acp->push_tail(entry);
 453 }
 454
 455 } /* unnamed namespace */
 456
 457 /**
 458  * Does a constant propagation pass on the code present in the instruction stream.
 459  */
 460 bool
 461 do_constant_propagation(exec_list *instructions)
 462 {
 463    ir_constant_propagation_visitor v;
 464
 465    visit_list_elements(&v, instructions);
 466
 467    return v.progress;
 468 }