src/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 "glsl_types.h"
  40
  41 class acp_entry : public exec_node
  42 {
  43 public:
  44    acp_entry(ir_variable *lhs, ir_variable *rhs)
  45    {
  46       assert(lhs);
  47       assert(rhs);
  48       this->lhs = lhs;
  49       this->rhs = rhs;
  50    }
  51
  52    ir_variable *lhs;
  53    ir_variable *rhs;
  54 };
  55
  56
  57 class kill_entry : public exec_node
  58 {
  59 public:
  60    kill_entry(ir_variable *var)
  61    {
  62       assert(var);
  63       this->var = var;
  64    }
  65
  66    ir_variable *var;
  67 };
  68
  69 class ir_copy_propagation_visitor : public ir_hierarchical_visitor {
  70 public:
  71    ir_copy_propagation_visitor()
  72    {
  73       progress = false;
  74       mem_ctx = talloc_new(0);
  75       this->acp = new(mem_ctx) exec_list;
  76       this->kills = new(mem_ctx) exec_list;
  77    }
  78    ~ir_copy_propagation_visitor()
  79    {
  80       talloc_free(mem_ctx);
  81    }
  82
  83    virtual ir_visitor_status visit(class ir_dereference_variable *);
  84    virtual ir_visitor_status visit_enter(class ir_loop *);
  85    virtual ir_visitor_status visit_enter(class ir_function_signature *);
  86    virtual ir_visitor_status visit_enter(class ir_function *);
  87    virtual ir_visitor_status visit_leave(class ir_assignment *);
  88    virtual ir_visitor_status visit_enter(class ir_call *);
  89    virtual ir_visitor_status visit_enter(class ir_if *);
  90
  91    void add_copy(ir_assignment *ir);
  92    void kill(ir_variable *ir);
  93    void handle_if_block(exec_list *instructions);
  94
  95    /** List of acp_entry: The available copies to propagate */
  96    exec_list *acp;
  97    /**
  98     * List of kill_entry: The variables whose values were killed in this
  99     * block.
 100     */
 101    exec_list *kills;
 102
 103    bool progress;
 104
 105    bool killed_all;
 106
 107    void *mem_ctx;
 108 };
 109
 110 ir_visitor_status
 111 ir_copy_propagation_visitor::visit_enter(ir_function_signature *ir)
 112 {
 113    /* Treat entry into a function signature as a completely separate
 114     * block.  Any instructions at global scope will be shuffled into
 115     * main() at link time, so they're irrelevant to us.
 116     */
 117    exec_list *orig_acp = this->acp;
 118    exec_list *orig_kills = this->kills;
 119    bool orig_killed_all = this->killed_all;
 120
 121    this->acp = new(mem_ctx) exec_list;
 122    this->kills = new(mem_ctx) exec_list;
 123    this->killed_all = false;
 124
 125    visit_list_elements(this, &ir->body);
 126
 127    this->kills = orig_kills;
 128    this->acp = orig_acp;
 129    this->killed_all = orig_killed_all;
 130
 131    return visit_continue_with_parent;
 132 }
 133
 134 ir_visitor_status
 135 ir_copy_propagation_visitor::visit_leave(ir_assignment *ir)
 136 {
 137    kill(ir->lhs->variable_referenced());
 138
 139    add_copy(ir);
 140
 141    return visit_continue;
 142 }
 143
 144 ir_visitor_status
 145 ir_copy_propagation_visitor::visit_enter(ir_function *ir)
 146 {
 147    (void) ir;
 148    return visit_continue;
 149 }
 150
 151 /**
 152  * Replaces dereferences of ACP RHS variables with ACP LHS variables.
 153  *
 154  * This is where the actual copy propagation occurs.  Note that the
 155  * rewriting of ir_dereference means that the ir_dereference instance
 156  * must not be shared by multiple IR operations!
 157  */
 158 ir_visitor_status
 159 ir_copy_propagation_visitor::visit(ir_dereference_variable *ir)
 160 {
 161    if (this->in_assignee)
 162       return visit_continue;
 163
 164    ir_variable *var = ir->var;
 165
 166    foreach_iter(exec_list_iterator, iter, *this->acp) {
 167       acp_entry *entry = (acp_entry *)iter.get();
 168
 169       if (var == entry->lhs) {
 170          ir->var = entry->rhs;
 171          this->progress = true;
 172          break;
 173       }
 174    }
 175
 176    return visit_continue;
 177 }
 178
 179
 180 ir_visitor_status
 181 ir_copy_propagation_visitor::visit_enter(ir_call *ir)
 182 {
 183    /* Do copy propagation on call parameters, but skip any out params */
 184    exec_list_iterator sig_param_iter = ir->get_callee()->parameters.iterator();
 185    foreach_iter(exec_list_iterator, iter, ir->actual_parameters) {
 186       ir_variable *sig_param = (ir_variable *)sig_param_iter.get();
 187       ir_instruction *ir = (ir_instruction *)iter.get();
 188       if (sig_param->mode != ir_var_out && sig_param->mode != ir_var_inout) {
 189          ir->accept(this);
 190       }
 191       sig_param_iter.next();
 192    }
 193
 194    /* Since we're unlinked, we don't (necssarily) know the side effects of
 195     * this call.  So kill all copies.
 196     */
 197    acp->make_empty();
 198    this->killed_all = true;
 199
 200    return visit_continue_with_parent;
 201 }
 202
 203 void
 204 ir_copy_propagation_visitor::handle_if_block(exec_list *instructions)
 205 {
 206    exec_list *orig_acp = this->acp;
 207    exec_list *orig_kills = this->kills;
 208    bool orig_killed_all = this->killed_all;
 209
 210    this->acp = new(mem_ctx) exec_list;
 211    this->kills = new(mem_ctx) exec_list;
 212    this->killed_all = false;
 213
 214    /* Populate the initial acp with a copy of the original */
 215    foreach_iter(exec_list_iterator, iter, *orig_acp) {
 216       acp_entry *a = (acp_entry *)iter.get();
 217       this->acp->push_tail(new(this->mem_ctx) acp_entry(a->lhs, a->rhs));
 218    }
 219
 220    visit_list_elements(this, instructions);
 221
 222    if (this->killed_all) {
 223       orig_acp->make_empty();
 224    }
 225
 226    exec_list *new_kills = this->kills;
 227    this->kills = orig_kills;
 228    this->acp = orig_acp;
 229    this->killed_all = this->killed_all || orig_killed_all;
 230
 231    foreach_iter(exec_list_iterator, iter, *new_kills) {
 232       kill_entry *k = (kill_entry *)iter.get();
 233       kill(k->var);
 234    }
 235 }
 236
 237 ir_visitor_status
 238 ir_copy_propagation_visitor::visit_enter(ir_if *ir)
 239 {
 240    ir->condition->accept(this);
 241
 242    handle_if_block(&ir->then_instructions);
 243    handle_if_block(&ir->else_instructions);
 244
 245    /* handle_if_block() already descended into the children. */
 246    return visit_continue_with_parent;
 247 }
 248
 249 ir_visitor_status
 250 ir_copy_propagation_visitor::visit_enter(ir_loop *ir)
 251 {
 252    exec_list *orig_acp = this->acp;
 253    exec_list *orig_kills = this->kills;
 254    bool orig_killed_all = this->killed_all;
 255
 256    /* FINISHME: For now, the initial acp for loops is totally empty.
 257     * We could go through once, then go through again with the acp
 258     * cloned minus the killed entries after the first run through.
 259     */
 260    this->acp = new(mem_ctx) exec_list;
 261    this->kills = new(mem_ctx) exec_list;
 262    this->killed_all = false;
 263
 264    visit_list_elements(this, &ir->body_instructions);
 265
 266    if (this->killed_all) {
 267       orig_acp->make_empty();
 268    }
 269
 270    exec_list *new_kills = this->kills;
 271    this->kills = orig_kills;
 272    this->acp = orig_acp;
 273    this->killed_all = this->killed_all || orig_killed_all;
 274
 275    foreach_iter(exec_list_iterator, iter, *new_kills) {
 276       kill_entry *k = (kill_entry *)iter.get();
 277       kill(k->var);
 278    }
 279
 280    /* already descended into the children. */
 281    return visit_continue_with_parent;
 282 }
 283
 284 void
 285 ir_copy_propagation_visitor::kill(ir_variable *var)
 286 {
 287    assert(var != NULL);
 288
 289    /* Remove any entries currently in the ACP for this kill. */
 290    foreach_iter(exec_list_iterator, iter, *acp) {
 291       acp_entry *entry = (acp_entry *)iter.get();
 292
 293       if (entry->lhs == var || entry->rhs == var) {
 294          entry->remove();
 295       }
 296    }
 297
 298    /* Add the LHS variable to the list of killed variables in this block.
 299     */
 300    this->kills->push_tail(new(this->mem_ctx) kill_entry(var));
 301 }
 302
 303 /**
 304  * Adds an entry to the available copy list if it's a plain assignment
 305  * of a variable to a variable.
 306  */
 307 void
 308 ir_copy_propagation_visitor::add_copy(ir_assignment *ir)
 309 {
 310    acp_entry *entry;
 311
 312    if (ir->condition) {
 313       ir_constant *condition = ir->condition->as_constant();
 314       if (!condition || !condition->value.b[0])
 315          return;
 316    }
 317
 318    ir_variable *lhs_var = ir->whole_variable_written();
 319    ir_variable *rhs_var = ir->rhs->whole_variable_referenced();
 320
 321    if ((lhs_var != NULL) && (rhs_var != NULL)) {
 322       if (lhs_var == rhs_var) {
 323          /* This is a dumb assignment, but we've conveniently noticed
 324           * it here.  Removing it now would mess up the loop iteration
 325           * calling us.  Just flag it to not execute, and someone else
 326           * will clean up the mess.
 327           */
 328          ir->condition = new(talloc_parent(ir)) ir_constant(false);
 329          this->progress = true;
 330       } else {
 331          entry = new(this->mem_ctx) acp_entry(lhs_var, rhs_var);
 332          this->acp->push_tail(entry);
 333       }
 334    }
 335 }
 336
 337 /**
 338  * Does a copy propagation pass on the code present in the instruction stream.
 339  */
 340 bool
 341 do_copy_propagation(exec_list *instructions)
 342 {
 343    ir_copy_propagation_visitor v;
 344
 345    visit_list_elements(&v, instructions);
 346
 347    return v.progress;
 348 }