src/compiler/glsl/opt_copy_propagation.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.cpp
  26  *
  27  * Moves usage of recently-copied variables to the previous copy of
  28  * the variable.
  29  *
  30  * This should reduce the number of MOV instructions in the generated
  31  * programs unless copy propagation is also done on the LIR, and may
  32  * help anyway by triggering other optimizations that live in the HIR.
  33  */
  34
  35 #include "ir.h"
  36 #include "ir_visitor.h"
  37 #include "ir_basic_block.h"
  38 #include "ir_optimization.h"
  39 #include "compiler/glsl_types.h"
  40 #include "util/hash_table.h"
  41
  42 namespace {
  43
  44 class kill_entry : public exec_node
  45 {
  46 public:
  47    /* override operator new from exec_node */
  48    DECLARE_LINEAR_ZALLOC_CXX_OPERATORS(kill_entry)
  49
  50    kill_entry(ir_variable *var)
  51    {
  52       assert(var);
  53       this->var = var;
  54    }
  55
  56    ir_variable *var;
  57 };
  58
  59 class ir_copy_propagation_visitor : public ir_hierarchical_visitor {
  60 public:
  61    ir_copy_propagation_visitor()
  62    {
  63       progress = false;
  64       mem_ctx = ralloc_context(0);
  65       lin_ctx = linear_alloc_parent(mem_ctx, 0);
  66       acp = _mesa_hash_table_create(mem_ctx, _mesa_hash_pointer,
  67                                     _mesa_key_pointer_equal);
  68       this->kills = new(mem_ctx) exec_list;
  69       killed_all = false;
  70    }
  71    ~ir_copy_propagation_visitor()
  72    {
  73       ralloc_free(mem_ctx);
  74    }
  75
  76    virtual ir_visitor_status visit(class ir_dereference_variable *);
  77    void handle_loop(class ir_loop *, bool keep_acp);
  78    virtual ir_visitor_status visit_enter(class ir_loop *);
  79    virtual ir_visitor_status visit_enter(class ir_function_signature *);
  80    virtual ir_visitor_status visit_enter(class ir_function *);
  81    virtual ir_visitor_status visit_leave(class ir_assignment *);
  82    virtual ir_visitor_status visit_enter(class ir_call *);
  83    virtual ir_visitor_status visit_enter(class ir_if *);
  84
  85    void add_copy(ir_assignment *ir);
  86    void kill(ir_variable *ir);
  87    void handle_if_block(exec_list *instructions);
  88
  89    /** Hash of lhs->rhs: The available copies to propagate */
  90    hash_table *acp;
  91    /**
  92     * List of kill_entry: The variables whose values were killed in this
  93     * block.
  94     */
  95    exec_list *kills;
  96
  97    bool progress;
  98
  99    bool killed_all;
 100
 101    void *mem_ctx;
 102    void *lin_ctx;
 103 };
 104
 105 } /* unnamed namespace */
 106
 107 ir_visitor_status
 108 ir_copy_propagation_visitor::visit_enter(ir_function_signature *ir)
 109 {
 110    /* Treat entry into a function signature as a completely separate
 111     * block.  Any instructions at global scope will be shuffled into
 112     * main() at link time, so they're irrelevant to us.
 113     */
 114    hash_table *orig_acp = this->acp;
 115    exec_list *orig_kills = this->kills;
 116    bool orig_killed_all = this->killed_all;
 117
 118    acp = _mesa_hash_table_create(NULL, _mesa_hash_pointer,
 119                                  _mesa_key_pointer_equal);
 120    this->kills = new(mem_ctx) exec_list;
 121    this->killed_all = false;
 122
 123    visit_list_elements(this, &ir->body);
 124
 125    _mesa_hash_table_destroy(acp, NULL);
 126    ralloc_free(this->kills);
 127
 128    this->kills = orig_kills;
 129    this->acp = orig_acp;
 130    this->killed_all = orig_killed_all;
 131
 132    return visit_continue_with_parent;
 133 }
 134
 135 ir_visitor_status
 136 ir_copy_propagation_visitor::visit_leave(ir_assignment *ir)
 137 {
 138    kill(ir->lhs->variable_referenced());
 139
 140    add_copy(ir);
 141
 142    return visit_continue;
 143 }
 144
 145 ir_visitor_status
 146 ir_copy_propagation_visitor::visit_enter(ir_function *ir)
 147 {
 148    (void) ir;
 149    return visit_continue;
 150 }
 151
 152 /**
 153  * Replaces dereferences of ACP RHS variables with ACP LHS variables.
 154  *
 155  * This is where the actual copy propagation occurs.  Note that the
 156  * rewriting of ir_dereference means that the ir_dereference instance
 157  * must not be shared by multiple IR operations!
 158  */
 159 ir_visitor_status
 160 ir_copy_propagation_visitor::visit(ir_dereference_variable *ir)
 161 {
 162    if (this->in_assignee)
 163       return visit_continue;
 164
 165    struct hash_entry *entry = _mesa_hash_table_search(acp, ir->var);
 166    if (entry) {
 167       ir->var = (ir_variable *) entry->data;
 168       progress = true;
 169    }
 170
 171    return visit_continue;
 172 }
 173
 174
 175 ir_visitor_status
 176 ir_copy_propagation_visitor::visit_enter(ir_call *ir)
 177 {
 178    /* Do copy propagation on call parameters, but skip any out params */
 179    foreach_two_lists(formal_node, &ir->callee->parameters,
 180                      actual_node, &ir->actual_parameters) {
 181       ir_variable *sig_param = (ir_variable *) formal_node;
 182       ir_rvalue *ir = (ir_rvalue *) actual_node;
 183       if (sig_param->data.mode != ir_var_function_out
 184           && sig_param->data.mode != ir_var_function_inout) {
 185          ir->accept(this);
 186       }
 187    }
 188
 189    /* Since this pass can run when unlinked, we don't (necessarily) know
 190     * the side effects of calls.  (When linked, most calls are inlined
 191     * anyway, so it doesn't matter much.)
 192     *
 193     * One place where this does matter is IR intrinsics.  They're never
 194     * inlined.  We also know what they do - while some have side effects
 195     * (such as image writes), none edit random global variables.  So we
 196     * can assume they're side-effect free (other than the return value
 197     * and out parameters).
 198     */
 199    if (!ir->callee->is_intrinsic()) {
 200       _mesa_hash_table_clear(acp, NULL);
 201       this->killed_all = true;
 202    } else {
 203       if (ir->return_deref)
 204          kill(ir->return_deref->var);
 205
 206       foreach_two_lists(formal_node, &ir->callee->parameters,
 207                         actual_node, &ir->actual_parameters) {
 208          ir_variable *sig_param = (ir_variable *) formal_node;
 209          if (sig_param->data.mode == ir_var_function_out ||
 210              sig_param->data.mode == ir_var_function_inout) {
 211             ir_rvalue *ir = (ir_rvalue *) actual_node;
 212             ir_variable *var = ir->variable_referenced();
 213             kill(var);
 214          }
 215       }
 216    }
 217
 218    return visit_continue_with_parent;
 219 }
 220
 221 void
 222 ir_copy_propagation_visitor::handle_if_block(exec_list *instructions)
 223 {
 224    hash_table *orig_acp = this->acp;
 225    exec_list *orig_kills = this->kills;
 226    bool orig_killed_all = this->killed_all;
 227
 228    acp = _mesa_hash_table_create(NULL, _mesa_hash_pointer,
 229                                  _mesa_key_pointer_equal);
 230    this->kills = new(mem_ctx) exec_list;
 231    this->killed_all = false;
 232
 233    /* Populate the initial acp with a copy of the original */
 234    struct hash_entry *entry;
 235    hash_table_foreach(orig_acp, entry) {
 236       _mesa_hash_table_insert(acp, entry->key, entry->data);
 237    }
 238
 239    visit_list_elements(this, instructions);
 240
 241    if (this->killed_all) {
 242       _mesa_hash_table_clear(orig_acp, NULL);
 243    }
 244
 245    exec_list *new_kills = this->kills;
 246    this->kills = orig_kills;
 247    _mesa_hash_table_destroy(acp, NULL);
 248    this->acp = orig_acp;
 249    this->killed_all = this->killed_all || orig_killed_all;
 250
 251    foreach_in_list(kill_entry, k, new_kills) {
 252       kill(k->var);
 253    }
 254
 255    ralloc_free(new_kills);
 256 }
 257
 258 ir_visitor_status
 259 ir_copy_propagation_visitor::visit_enter(ir_if *ir)
 260 {
 261    ir->condition->accept(this);
 262
 263    handle_if_block(&ir->then_instructions);
 264    handle_if_block(&ir->else_instructions);
 265
 266    /* handle_if_block() already descended into the children. */
 267    return visit_continue_with_parent;
 268 }
 269
 270 void
 271 ir_copy_propagation_visitor::handle_loop(ir_loop *ir, bool keep_acp)
 272 {
 273    hash_table *orig_acp = this->acp;
 274    exec_list *orig_kills = this->kills;
 275    bool orig_killed_all = this->killed_all;
 276
 277    acp = _mesa_hash_table_create(NULL, _mesa_hash_pointer,
 278                                  _mesa_key_pointer_equal);
 279    this->kills = new(mem_ctx) exec_list;
 280    this->killed_all = false;
 281
 282    if (keep_acp) {
 283       struct hash_entry *entry;
 284       hash_table_foreach(orig_acp, entry) {
 285          _mesa_hash_table_insert(acp, entry->key, entry->data);
 286       }
 287    }
 288
 289    visit_list_elements(this, &ir->body_instructions);
 290
 291    if (this->killed_all) {
 292       _mesa_hash_table_clear(orig_acp, NULL);
 293    }
 294
 295    exec_list *new_kills = this->kills;
 296    this->kills = orig_kills;
 297    _mesa_hash_table_destroy(acp, NULL);
 298    this->acp = orig_acp;
 299    this->killed_all = this->killed_all || orig_killed_all;
 300
 301    foreach_in_list(kill_entry, k, new_kills) {
 302       kill(k->var);
 303    }
 304
 305    ralloc_free(new_kills);
 306 }
 307
 308 ir_visitor_status
 309 ir_copy_propagation_visitor::visit_enter(ir_loop *ir)
 310 {
 311    /* Make a conservative first pass over the loop with an empty ACP set.
 312     * This also removes any killed entries from the original ACP set.
 313     */
 314    handle_loop(ir, false);
 315
 316    /* Then, run it again with the real ACP set, minus any killed entries.
 317     * This takes care of propagating values from before the loop into it.
 318     */
 319    handle_loop(ir, true);
 320
 321    /* already descended into the children. */
 322    return visit_continue_with_parent;
 323 }
 324
 325 void
 326 ir_copy_propagation_visitor::kill(ir_variable *var)
 327 {
 328    assert(var != NULL);
 329
 330    /* Remove any entries currently in the ACP for this kill. */
 331    struct hash_entry *entry = _mesa_hash_table_search(acp, var);
 332    if (entry) {
 333       _mesa_hash_table_remove(acp, entry);
 334    }
 335
 336    hash_table_foreach(acp, entry) {
 337       if (var == (ir_variable *) entry->data) {
 338          _mesa_hash_table_remove(acp, entry);
 339       }
 340    }
 341
 342    /* Add the LHS variable to the list of killed variables in this block.
 343     */
 344    this->kills->push_tail(new(this->lin_ctx) kill_entry(var));
 345 }
 346
 347 /**
 348  * Adds an entry to the available copy list if it's a plain assignment
 349  * of a variable to a variable.
 350  */
 351 void
 352 ir_copy_propagation_visitor::add_copy(ir_assignment *ir)
 353 {
 354    if (ir->condition)
 355       return;
 356
 357    ir_variable *lhs_var = ir->whole_variable_written();
 358    ir_variable *rhs_var = ir->rhs->whole_variable_referenced();
 359
 360    if ((lhs_var != NULL) && (rhs_var != NULL)) {
 361       if (lhs_var == rhs_var) {
 362          /* This is a dumb assignment, but we've conveniently noticed
 363           * it here.  Removing it now would mess up the loop iteration
 364           * calling us.  Just flag it to not execute, and someone else
 365           * will clean up the mess.
 366           */
 367          ir->condition = new(ralloc_parent(ir)) ir_constant(false);
 368          this->progress = true;
 369       } else if (lhs_var->data.mode != ir_var_shader_storage &&
 370                  lhs_var->data.mode != ir_var_shader_shared &&
 371                  lhs_var->data.precise == rhs_var->data.precise) {
 372          assert(lhs_var);
 373          assert(rhs_var);
 374          _mesa_hash_table_insert(acp, lhs_var, rhs_var);
 375       }
 376    }
 377 }
 378
 379 /**
 380  * Does a copy propagation pass on the code present in the instruction stream.
 381  */
 382 bool
 383 do_copy_propagation(exec_list *instructions)
 384 {
 385    ir_copy_propagation_visitor v;
 386
 387    visit_list_elements(&v, instructions);
 388
 389    return v.progress;
 390 }