src/glsl/opt_copy_propagation_elements.cpp

   1 /*
   2  * Copyright © 2010 Intel Corporation
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining a
   5  * copy 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, copy, 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 copyright 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 COPYRIGHT 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_copy_propagation_elements.cpp
  26  *
  27  * Replaces usage of recently-copied components of variables with the
  28  * previous copy of the variable.
  29  *
  30  * This pass can be compared with opt_copy_propagation, which operands
  31  * on arbitrary whole-variable copies.  However, in order to handle
  32  * the copy propagation of swizzled variables or writemasked writes,
  33  * we want to track things on a channel-wise basis.  I found that
  34  * trying to mix the swizzled/writemasked support here with the
  35  * whole-variable stuff in opt_copy_propagation.cpp just made a mess,
  36  * so this is separate despite the ACP handling being somewhat
  37  * similar.
  38  *
  39  * This should reduce the number of MOV instructions in the generated
  40  * programs unless copy propagation is also done on the LIR, and may
  41  * help anyway by triggering other optimizations that live in the HIR.
  42  */
  43
  44 #include "ir.h"
  45 #include "ir_rvalue_visitor.h"
  46 #include "ir_basic_block.h"
  47 #include "ir_optimization.h"
  48 #include "compiler/glsl_types.h"
  49
  50 static bool debug = false;
  51
  52 namespace {
  53
  54 class acp_entry : public exec_node
  55 {
  56 public:
  57    acp_entry(ir_variable *lhs, ir_variable *rhs, int write_mask, int swizzle[4])
  58    {
  59       this->lhs = lhs;
  60       this->rhs = rhs;
  61       this->write_mask = write_mask;
  62       memcpy(this->swizzle, swizzle, sizeof(this->swizzle));
  63    }
  64
  65    acp_entry(acp_entry *a)
  66    {
  67       this->lhs = a->lhs;
  68       this->rhs = a->rhs;
  69       this->write_mask = a->write_mask;
  70       memcpy(this->swizzle, a->swizzle, sizeof(this->swizzle));
  71    }
  72
  73    ir_variable *lhs;
  74    ir_variable *rhs;
  75    unsigned int write_mask;
  76    int swizzle[4];
  77 };
  78
  79
  80 class kill_entry : public exec_node
  81 {
  82 public:
  83    kill_entry(ir_variable *var, int write_mask)
  84    {
  85       this->var = var;
  86       this->write_mask = write_mask;
  87    }
  88
  89    ir_variable *var;
  90    unsigned int write_mask;
  91 };
  92
  93 class ir_copy_propagation_elements_visitor : public ir_rvalue_visitor {
  94 public:
  95    ir_copy_propagation_elements_visitor()
  96    {
  97       this->progress = false;
  98       this->killed_all = false;
  99       this->mem_ctx = ralloc_context(NULL);
 100       this->shader_mem_ctx = NULL;
 101       this->acp = new(mem_ctx) exec_list;
 102       this->kills = new(mem_ctx) exec_list;
 103    }
 104    ~ir_copy_propagation_elements_visitor()
 105    {
 106       ralloc_free(mem_ctx);
 107    }
 108
 109    virtual ir_visitor_status visit_enter(class ir_loop *);
 110    virtual ir_visitor_status visit_enter(class ir_function_signature *);
 111    virtual ir_visitor_status visit_leave(class ir_assignment *);
 112    virtual ir_visitor_status visit_enter(class ir_call *);
 113    virtual ir_visitor_status visit_enter(class ir_if *);
 114    virtual ir_visitor_status visit_leave(class ir_swizzle *);
 115
 116    void handle_rvalue(ir_rvalue **rvalue);
 117
 118    void add_copy(ir_assignment *ir);
 119    void kill(kill_entry *k);
 120    void handle_if_block(exec_list *instructions);
 121
 122    /** List of acp_entry: The available copies to propagate */
 123    exec_list *acp;
 124    /**
 125     * List of kill_entry: The variables whose values were killed in this
 126     * block.
 127     */
 128    exec_list *kills;
 129
 130    bool progress;
 131
 132    bool killed_all;
 133
 134    /* Context for our local data structures. */
 135    void *mem_ctx;
 136    /* Context for allocating new shader nodes. */
 137    void *shader_mem_ctx;
 138 };
 139
 140 } /* unnamed namespace */
 141
 142 ir_visitor_status
 143 ir_copy_propagation_elements_visitor::visit_enter(ir_function_signature *ir)
 144 {
 145    /* Treat entry into a function signature as a completely separate
 146     * block.  Any instructions at global scope will be shuffled into
 147     * main() at link time, so they're irrelevant to us.
 148     */
 149    exec_list *orig_acp = this->acp;
 150    exec_list *orig_kills = this->kills;
 151    bool orig_killed_all = this->killed_all;
 152
 153    this->acp = new(mem_ctx) exec_list;
 154    this->kills = new(mem_ctx) exec_list;
 155    this->killed_all = false;
 156
 157    visit_list_elements(this, &ir->body);
 158
 159    ralloc_free(this->acp);
 160    ralloc_free(this->kills);
 161
 162    this->kills = orig_kills;
 163    this->acp = orig_acp;
 164    this->killed_all = orig_killed_all;
 165
 166    return visit_continue_with_parent;
 167 }
 168
 169 ir_visitor_status
 170 ir_copy_propagation_elements_visitor::visit_leave(ir_assignment *ir)
 171 {
 172    ir_dereference_variable *lhs = ir->lhs->as_dereference_variable();
 173    ir_variable *var = ir->lhs->variable_referenced();
 174
 175    if (var->type->is_scalar() || var->type->is_vector()) {
 176       kill_entry *k;
 177
 178       if (lhs)
 179          k = new(this->kills) kill_entry(var, ir->write_mask);
 180       else
 181          k = new(this->kills) kill_entry(var, ~0);
 182
 183       kill(k);
 184    }
 185
 186    add_copy(ir);
 187
 188    return visit_continue;
 189 }
 190
 191 ir_visitor_status
 192 ir_copy_propagation_elements_visitor::visit_leave(ir_swizzle *)
 193 {
 194    /* Don't visit the values of swizzles since they are handled while
 195     * visiting the swizzle itself.
 196     */
 197    return visit_continue;
 198 }
 199
 200 /**
 201  * Replaces dereferences of ACP RHS variables with ACP LHS variables.
 202  *
 203  * This is where the actual copy propagation occurs.  Note that the
 204  * rewriting of ir_dereference means that the ir_dereference instance
 205  * must not be shared by multiple IR operations!
 206  */
 207 void
 208 ir_copy_propagation_elements_visitor::handle_rvalue(ir_rvalue **ir)
 209 {
 210    int swizzle_chan[4];
 211    ir_dereference_variable *deref_var;
 212    ir_variable *source[4] = {NULL, NULL, NULL, NULL};
 213    int source_chan[4] = {0, 0, 0, 0};
 214    int chans;
 215    bool noop_swizzle = true;
 216
 217    if (!*ir)
 218       return;
 219
 220    ir_swizzle *swizzle = (*ir)->as_swizzle();
 221    if (swizzle) {
 222       deref_var = swizzle->val->as_dereference_variable();
 223       if (!deref_var)
 224          return;
 225
 226       swizzle_chan[0] = swizzle->mask.x;
 227       swizzle_chan[1] = swizzle->mask.y;
 228       swizzle_chan[2] = swizzle->mask.z;
 229       swizzle_chan[3] = swizzle->mask.w;
 230       chans = swizzle->type->vector_elements;
 231    } else {
 232       deref_var = (*ir)->as_dereference_variable();
 233       if (!deref_var)
 234          return;
 235
 236       swizzle_chan[0] = 0;
 237       swizzle_chan[1] = 1;
 238       swizzle_chan[2] = 2;
 239       swizzle_chan[3] = 3;
 240       chans = deref_var->type->vector_elements;
 241    }
 242
 243    if (this->in_assignee)
 244       return;
 245
 246    ir_variable *var = deref_var->var;
 247
 248    /* Try to find ACP entries covering swizzle_chan[], hoping they're
 249     * the same source variable.
 250     */
 251    foreach_in_list(acp_entry, entry, this->acp) {
 252       if (var == entry->lhs) {
 253          for (int c = 0; c < chans; c++) {
 254             if (entry->write_mask & (1 << swizzle_chan[c])) {
 255                source[c] = entry->rhs;
 256                source_chan[c] = entry->swizzle[swizzle_chan[c]];
 257
 258                if (source_chan[c] != swizzle_chan[c])
 259                   noop_swizzle = false;
 260             }
 261          }
 262       }
 263    }
 264
 265    /* Make sure all channels are copying from the same source variable. */
 266    if (!source[0])
 267       return;
 268    for (int c = 1; c < chans; c++) {
 269       if (source[c] != source[0])
 270          return;
 271    }
 272
 273    if (!shader_mem_ctx)
 274       shader_mem_ctx = ralloc_parent(deref_var);
 275
 276    /* Don't pointlessly replace the rvalue with itself (or a noop swizzle
 277     * of itself, which would just be deleted by opt_noop_swizzle).
 278     */
 279    if (source[0] == var && noop_swizzle)
 280       return;
 281
 282    if (debug) {
 283       printf("Copy propagation from:\n");
 284       (*ir)->print();
 285    }
 286
 287    deref_var = new(shader_mem_ctx) ir_dereference_variable(source[0]);
 288    *ir = new(shader_mem_ctx) ir_swizzle(deref_var,
 289                                         source_chan[0],
 290                                         source_chan[1],
 291                                         source_chan[2],
 292                                         source_chan[3],
 293                                         chans);
 294    progress = true;
 295
 296    if (debug) {
 297       printf("to:\n");
 298       (*ir)->print();
 299       printf("\n");
 300    }
 301 }
 302
 303
 304 ir_visitor_status
 305 ir_copy_propagation_elements_visitor::visit_enter(ir_call *ir)
 306 {
 307    /* Do copy propagation on call parameters, but skip any out params */
 308    foreach_two_lists(formal_node, &ir->callee->parameters,
 309                      actual_node, &ir->actual_parameters) {
 310       ir_variable *sig_param = (ir_variable *) formal_node;
 311       ir_rvalue *ir = (ir_rvalue *) actual_node;
 312       if (sig_param->data.mode != ir_var_function_out
 313           && sig_param->data.mode != ir_var_function_inout) {
 314          ir->accept(this);
 315       }
 316    }
 317
 318    /* Since we're unlinked, we don't (necessarily) know the side effects of
 319     * this call.  So kill all copies.
 320     */
 321    acp->make_empty();
 322    this->killed_all = true;
 323
 324    return visit_continue_with_parent;
 325 }
 326
 327 void
 328 ir_copy_propagation_elements_visitor::handle_if_block(exec_list *instructions)
 329 {
 330    exec_list *orig_acp = this->acp;
 331    exec_list *orig_kills = this->kills;
 332    bool orig_killed_all = this->killed_all;
 333
 334    this->acp = new(mem_ctx) exec_list;
 335    this->kills = new(mem_ctx) exec_list;
 336    this->killed_all = false;
 337
 338    /* Populate the initial acp with a copy of the original */
 339    foreach_in_list(acp_entry, a, orig_acp) {
 340       this->acp->push_tail(new(this->acp) acp_entry(a));
 341    }
 342
 343    visit_list_elements(this, instructions);
 344
 345    if (this->killed_all) {
 346       orig_acp->make_empty();
 347    }
 348
 349    exec_list *new_kills = this->kills;
 350    this->kills = orig_kills;
 351    ralloc_free(this->acp);
 352    this->acp = orig_acp;
 353    this->killed_all = this->killed_all || orig_killed_all;
 354
 355    /* Move the new kills into the parent block's list, removing them
 356     * from the parent's ACP list in the process.
 357     */
 358    foreach_in_list_safe(kill_entry, k, new_kills) {
 359       kill(k);
 360    }
 361
 362    ralloc_free(new_kills);
 363 }
 364
 365 ir_visitor_status
 366 ir_copy_propagation_elements_visitor::visit_enter(ir_if *ir)
 367 {
 368    ir->condition->accept(this);
 369
 370    handle_if_block(&ir->then_instructions);
 371    handle_if_block(&ir->else_instructions);
 372
 373    /* handle_if_block() already descended into the children. */
 374    return visit_continue_with_parent;
 375 }
 376
 377 ir_visitor_status
 378 ir_copy_propagation_elements_visitor::visit_enter(ir_loop *ir)
 379 {
 380    exec_list *orig_acp = this->acp;
 381    exec_list *orig_kills = this->kills;
 382    bool orig_killed_all = this->killed_all;
 383
 384    /* FINISHME: For now, the initial acp for loops is totally empty.
 385     * We could go through once, then go through again with the acp
 386     * cloned minus the killed entries after the first run through.
 387     */
 388    this->acp = new(mem_ctx) exec_list;
 389    this->kills = new(mem_ctx) exec_list;
 390    this->killed_all = false;
 391
 392    visit_list_elements(this, &ir->body_instructions);
 393
 394    if (this->killed_all) {
 395       orig_acp->make_empty();
 396    }
 397
 398    exec_list *new_kills = this->kills;
 399    this->kills = orig_kills;
 400    ralloc_free(this->acp);
 401    this->acp = orig_acp;
 402    this->killed_all = this->killed_all || orig_killed_all;
 403
 404    foreach_in_list_safe(kill_entry, k, new_kills) {
 405       kill(k);
 406    }
 407
 408    ralloc_free(new_kills);
 409
 410    /* already descended into the children. */
 411    return visit_continue_with_parent;
 412 }
 413
 414 /* Remove any entries currently in the ACP for this kill. */
 415 void
 416 ir_copy_propagation_elements_visitor::kill(kill_entry *k)
 417 {
 418    foreach_in_list_safe(acp_entry, entry, acp) {
 419       if (entry->lhs == k->var) {
 420          entry->write_mask = entry->write_mask & ~k->write_mask;
 421          if (entry->write_mask == 0) {
 422             entry->remove();
 423             continue;
 424          }
 425       }
 426       if (entry->rhs == k->var) {
 427          entry->remove();
 428       }
 429    }
 430
 431    /* If we were on a list, remove ourselves before inserting */
 432    if (k->next)
 433       k->remove();
 434
 435    ralloc_steal(this->kills, k);
 436    this->kills->push_tail(k);
 437 }
 438
 439 /**
 440  * Adds directly-copied channels between vector variables to the available
 441  * copy propagation list.
 442  */
 443 void
 444 ir_copy_propagation_elements_visitor::add_copy(ir_assignment *ir)
 445 {
 446    acp_entry *entry;
 447    int orig_swizzle[4] = {0, 1, 2, 3};
 448    int swizzle[4];
 449
 450    if (ir->condition)
 451       return;
 452
 453    ir_dereference_variable *lhs = ir->lhs->as_dereference_variable();
 454    if (!lhs || !(lhs->type->is_scalar() || lhs->type->is_vector()))
 455       return;
 456
 457    ir_dereference_variable *rhs = ir->rhs->as_dereference_variable();
 458    if (!rhs) {
 459       ir_swizzle *swiz = ir->rhs->as_swizzle();
 460       if (!swiz)
 461          return;
 462
 463       rhs = swiz->val->as_dereference_variable();
 464       if (!rhs)
 465          return;
 466
 467       orig_swizzle[0] = swiz->mask.x;
 468       orig_swizzle[1] = swiz->mask.y;
 469       orig_swizzle[2] = swiz->mask.z;
 470       orig_swizzle[3] = swiz->mask.w;
 471    }
 472
 473    /* Move the swizzle channels out to the positions they match in the
 474     * destination.  We don't want to have to rewrite the swizzle[]
 475     * array every time we clear a bit of the write_mask.
 476     */
 477    int j = 0;
 478    for (int i = 0; i < 4; i++) {
 479       if (ir->write_mask & (1 << i))
 480          swizzle[i] = orig_swizzle[j++];
 481    }
 482
 483    int write_mask = ir->write_mask;
 484    if (lhs->var == rhs->var) {
 485       /* If this is a copy from the variable to itself, then we need
 486        * to be sure not to include the updated channels from this
 487        * instruction in the set of new source channels to be
 488        * copy-propagated from.
 489        */
 490       for (int i = 0; i < 4; i++) {
 491          if (ir->write_mask & (1 << orig_swizzle[i]))
 492             write_mask &= ~(1 << i);
 493       }
 494    }
 495
 496    entry = new(this->mem_ctx) acp_entry(lhs->var, rhs->var, write_mask,
 497                                         swizzle);
 498    this->acp->push_tail(entry);
 499 }
 500
 501 bool
 502 do_copy_propagation_elements(exec_list *instructions)
 503 {
 504    ir_copy_propagation_elements_visitor v;
 505
 506    visit_list_elements(&v, instructions);
 507
 508    return v.progress;
 509 }