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_DOUBLE:
 198          data.d[i] = found->constant->value.d[rhs_channel];
 199          break;
 200       case GLSL_TYPE_INT:
 201          data.i[i] = found->constant->value.i[rhs_channel];
 202          break;
 203       case GLSL_TYPE_UINT:
 204          data.u[i] = found->constant->value.u[rhs_channel];
 205          break;
 206       case GLSL_TYPE_BOOL:
 207          data.b[i] = found->constant->value.b[rhs_channel];
 208          break;
 209       default:
 210          assert(!"not reached");
 211          break;
 212       }
 213    }
 214
 215    *rvalue = new(ralloc_parent(deref)) ir_constant(type, &data);
 216    this->progress = true;
 217 }
 218
 219 ir_visitor_status
 220 ir_constant_propagation_visitor::visit_enter(ir_function_signature *ir)
 221 {
 222    /* Treat entry into a function signature as a completely separate
 223     * block.  Any instructions at global scope will be shuffled into
 224     * main() at link time, so they're irrelevant to us.
 225     */
 226    exec_list *orig_acp = this->acp;
 227    exec_list *orig_kills = this->kills;
 228    bool orig_killed_all = this->killed_all;
 229
 230    this->acp = new(mem_ctx) exec_list;
 231    this->kills = new(mem_ctx) exec_list;
 232    this->killed_all = false;
 233
 234    visit_list_elements(this, &ir->body);
 235
 236    this->kills = orig_kills;
 237    this->acp = orig_acp;
 238    this->killed_all = orig_killed_all;
 239
 240    return visit_continue_with_parent;
 241 }
 242
 243 ir_visitor_status
 244 ir_constant_propagation_visitor::visit_leave(ir_assignment *ir)
 245 {
 246    if (this->in_assignee)
 247       return visit_continue;
 248
 249    unsigned kill_mask = ir->write_mask;
 250    if (ir->lhs->as_dereference_array()) {
 251       /* The LHS of the assignment uses an array indexing operator (e.g. v[i]
 252        * = ...;).  Since we only try to constant propagate vectors and
 253        * scalars, this means that either (a) array indexing is being used to
 254        * select a vector component, or (b) the variable in question is neither
 255        * a scalar or a vector, so we don't care about it.  In the former case,
 256        * we want to kill the whole vector, since in general we can't predict
 257        * which vector component will be selected by array indexing.  In the
 258        * latter case, it doesn't matter what we do, so go ahead and kill the
 259        * whole variable anyway.
 260        *
 261        * Note that if the array index is constant (e.g. v[2] = ...;), we could
 262        * in principle be smarter, but we don't need to, because a future
 263        * optimization pass will convert it to a simple assignment with the
 264        * correct mask.
 265        */
 266       kill_mask = ~0;
 267    }
 268    kill(ir->lhs->variable_referenced(), kill_mask);
 269
 270    add_constant(ir);
 271
 272    return visit_continue;
 273 }
 274
 275 ir_visitor_status
 276 ir_constant_propagation_visitor::visit_enter(ir_function *ir)
 277 {
 278    (void) ir;
 279    return visit_continue;
 280 }
 281
 282 ir_visitor_status
 283 ir_constant_propagation_visitor::visit_enter(ir_call *ir)
 284 {
 285    /* Do constant propagation on call parameters, but skip any out params */
 286    foreach_two_lists(formal_node, &ir->callee->parameters,
 287                      actual_node, &ir->actual_parameters) {
 288       ir_variable *sig_param = (ir_variable *) formal_node;
 289       ir_rvalue *param = (ir_rvalue *) actual_node;
 290       if (sig_param->data.mode != ir_var_function_out
 291           && sig_param->data.mode != ir_var_function_inout) {
 292          ir_rvalue *new_param = param;
 293          handle_rvalue(&new_param);
 294          if (new_param != param)
 295             param->replace_with(new_param);
 296          else
 297             param->accept(this);
 298       }
 299    }
 300
 301    /* Since we're unlinked, we don't (necssarily) know the side effects of
 302     * this call.  So kill all copies.
 303     */
 304    acp->make_empty();
 305    this->killed_all = true;
 306
 307    return visit_continue_with_parent;
 308 }
 309
 310 void
 311 ir_constant_propagation_visitor::handle_if_block(exec_list *instructions)
 312 {
 313    exec_list *orig_acp = this->acp;
 314    exec_list *orig_kills = this->kills;
 315    bool orig_killed_all = this->killed_all;
 316
 317    this->acp = new(mem_ctx) exec_list;
 318    this->kills = new(mem_ctx) exec_list;
 319    this->killed_all = false;
 320
 321    /* Populate the initial acp with a constant of the original */
 322    foreach_in_list(acp_entry, a, orig_acp) {
 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_in_list(kill_entry, k, new_kills) {
 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_in_list(kill_entry, k, new_kills) {
 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_in_list_safe(acp_entry, entry, this->acp) {
 400       if (entry->var == var) {
 401          entry->write_mask &= ~write_mask;
 402          if (entry->write_mask == 0)
 403             entry->remove();
 404       }
 405    }
 406
 407    /* Add this writemask of the variable to the list of killed
 408     * variables in this block.
 409     */
 410    foreach_in_list(kill_entry, entry, this->kills) {
 411       if (entry->var == var) {
 412          entry->write_mask |= write_mask;
 413          return;
 414       }
 415    }
 416    /* Not already in the list.  Make new entry. */
 417    this->kills->push_tail(new(this->mem_ctx) kill_entry(var, write_mask));
 418 }
 419
 420 /**
 421  * Adds an entry to the available constant list if it's a plain assignment
 422  * of a variable to a variable.
 423  */
 424 void
 425 ir_constant_propagation_visitor::add_constant(ir_assignment *ir)
 426 {
 427    acp_entry *entry;
 428
 429    if (ir->condition)
 430       return;
 431
 432    if (!ir->write_mask)
 433       return;
 434
 435    ir_dereference_variable *deref = ir->lhs->as_dereference_variable();
 436    ir_constant *constant = ir->rhs->as_constant();
 437
 438    if (!deref || !constant)
 439       return;
 440
 441    /* Only do constant propagation on vectors.  Constant matrices,
 442     * arrays, or structures would require more work elsewhere.
 443     */
 444    if (!deref->var->type->is_vector() && !deref->var->type->is_scalar())
 445       return;
 446
 447    /* We can't do copy propagation on buffer variables, since the underlying
 448     * memory storage is shared across multiple threads we can't be sure that
 449     * the variable value isn't modified between this assignment and the next
 450     * instruction where its value is read.
 451     */
 452    if (deref->var->data.mode == ir_var_shader_storage)
 453       return;
 454
 455    entry = new(this->mem_ctx) acp_entry(deref->var, ir->write_mask, constant);
 456    this->acp->push_tail(entry);
 457 }
 458
 459 } /* unnamed namespace */
 460
 461 /**
 462  * Does a constant propagation pass on the code present in the instruction stream.
 463  */
 464 bool
 465 do_constant_propagation(exec_list *instructions)
 466 {
 467    ir_constant_propagation_visitor v;
 468
 469    visit_list_elements(&v, instructions);
 470
 471    return v.progress;
 472 }