src/glsl/opt_dead_code_local.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_dead_code_local.cpp
  26  *
  27  * Eliminates local dead assignments from the code.
  28  *
  29  * This operates on basic blocks, tracking assignments and finding if
  30  * they're used before the variable is completely reassigned.
  31  *
  32  * Compare this to ir_dead_code.cpp, which operates globally looking
  33  * for assignments to variables that are never read.
  34  */
  35
  36 #include "ir.h"
  37 #include "ir_basic_block.h"
  38 #include "ir_optimization.h"
  39 #include "glsl_types.h"
  40
  41 static bool debug = false;
  42
  43 namespace {
  44
  45 class assignment_entry : public exec_node
  46 {
  47 public:
  48    assignment_entry(ir_variable *lhs, ir_assignment *ir)
  49    {
  50       assert(lhs);
  51       assert(ir);
  52       this->lhs = lhs;
  53       this->ir = ir;
  54       this->available = ir->write_mask;
  55    }
  56
  57    ir_variable *lhs;
  58    ir_assignment *ir;
  59
  60    /* bitmask of xyzw channels written that haven't been used so far. */
  61    int available;
  62 };
  63
  64 class kill_for_derefs_visitor : public ir_hierarchical_visitor {
  65 public:
  66    kill_for_derefs_visitor(exec_list *assignments)
  67    {
  68       this->assignments = assignments;
  69    }
  70
  71    void kill_channels(ir_variable *const var, int used)
  72    {
  73       foreach_iter(exec_list_iterator, iter, *this->assignments) {
  74          assignment_entry *entry = (assignment_entry *)iter.get();
  75
  76          if (entry->lhs == var) {
  77             if (var->type->is_scalar() || var->type->is_vector()) {
  78                if (debug)
  79                   printf("kill %s (0x%01x - 0x%01x)\n", entry->lhs->name,
  80                          entry->available, used);
  81                entry->available &= ~used;
  82                if (!entry->available)
  83                   entry->remove();
  84             } else {
  85                if (debug)
  86                   printf("kill %s\n", entry->lhs->name);
  87                entry->remove();
  88             }
  89          }
  90       }
  91    }
  92
  93    virtual ir_visitor_status visit(ir_dereference_variable *ir)
  94    {
  95       kill_channels(ir->var, ~0);
  96
  97       return visit_continue;
  98    }
  99
 100    virtual ir_visitor_status visit(ir_swizzle *ir)
 101    {
 102       ir_dereference_variable *deref = ir->val->as_dereference_variable();
 103       if (!deref)
 104          return visit_continue;
 105
 106       int used = 0;
 107       used |= 1 << ir->mask.x;
 108       used |= 1 << ir->mask.y;
 109       used |= 1 << ir->mask.z;
 110       used |= 1 << ir->mask.w;
 111
 112       kill_channels(deref->var, used);
 113
 114       return visit_continue_with_parent;
 115    }
 116
 117 private:
 118    exec_list *assignments;
 119 };
 120
 121 class array_index_visit : public ir_hierarchical_visitor {
 122 public:
 123    array_index_visit(ir_hierarchical_visitor *v)
 124    {
 125       this->visitor = v;
 126    }
 127
 128    virtual ir_visitor_status visit_enter(class ir_dereference_array *ir)
 129    {
 130       ir->array_index->accept(visitor);
 131       return visit_continue;
 132    }
 133
 134    static void run(ir_instruction *ir, ir_hierarchical_visitor *v)
 135    {
 136       array_index_visit top_visit(v);
 137       ir->accept(& top_visit);
 138    }
 139
 140    ir_hierarchical_visitor *visitor;
 141 };
 142
 143 } /* unnamed namespace */
 144
 145 /**
 146  * Adds an entry to the available copy list if it's a plain assignment
 147  * of a variable to a variable.
 148  */
 149 static bool
 150 process_assignment(void *ctx, ir_assignment *ir, exec_list *assignments)
 151 {
 152    ir_variable *var = NULL;
 153    bool progress = false;
 154    kill_for_derefs_visitor v(assignments);
 155
 156    /* Kill assignment entries for things used to produce this assignment. */
 157    ir->rhs->accept(&v);
 158    if (ir->condition) {
 159       ir->condition->accept(&v);
 160    }
 161
 162    /* Kill assignment enties used as array indices.
 163     */
 164    array_index_visit::run(ir->lhs, &v);
 165    var = ir->lhs->variable_referenced();
 166    assert(var);
 167
 168    /* Now, check if we did a whole-variable assignment. */
 169    if (!ir->condition) {
 170       ir_dereference_variable *deref_var = ir->lhs->as_dereference_variable();
 171
 172       /* If it's a vector type, we can do per-channel elimination of
 173        * use of the RHS.
 174        */
 175       if (deref_var && (deref_var->var->type->is_scalar() ||
 176                         deref_var->var->type->is_vector())) {
 177
 178          if (debug)
 179             printf("looking for %s.0x%01x to remove\n", var->name,
 180                    ir->write_mask);
 181
 182          foreach_iter(exec_list_iterator, iter, *assignments) {
 183             assignment_entry *entry = (assignment_entry *)iter.get();
 184
 185             if (entry->lhs != var)
 186                continue;
 187
 188             int remove = entry->available & ir->write_mask;
 189             if (debug) {
 190                printf("%s 0x%01x - 0x%01x = 0x%01x\n",
 191                       var->name,
 192                       entry->ir->write_mask,
 193                       remove, entry->ir->write_mask & ~remove);
 194             }
 195             if (remove) {
 196                progress = true;
 197
 198                if (debug) {
 199                   printf("rewriting:\n  ");
 200                   entry->ir->print();
 201                   printf("\n");
 202                }
 203
 204                entry->ir->write_mask &= ~remove;
 205                entry->available &= ~remove;
 206                if (entry->ir->write_mask == 0) {
 207                   /* Delete the dead assignment. */
 208                   entry->ir->remove();
 209                   entry->remove();
 210                } else {
 211                   void *mem_ctx = ralloc_parent(entry->ir);
 212                   /* Reswizzle the RHS arguments according to the new
 213                    * write_mask.
 214                    */
 215                   unsigned components[4];
 216                   unsigned channels = 0;
 217                   unsigned next = 0;
 218
 219                   for (int i = 0; i < 4; i++) {
 220                      if ((entry->ir->write_mask | remove) & (1 << i)) {
 221                         if (!(remove & (1 << i)))
 222                            components[channels++] = next;
 223                         next++;
 224                      }
 225                   }
 226
 227                   entry->ir->rhs = new(mem_ctx) ir_swizzle(entry->ir->rhs,
 228                                                            components,
 229                                                            channels);
 230                   if (debug) {
 231                      printf("to:\n  ");
 232                      entry->ir->print();
 233                      printf("\n");
 234                   }
 235                }
 236             }
 237          }
 238       } else if (ir->whole_variable_written() != NULL) {
 239          /* We did a whole-variable assignment.  So, any instruction in
 240           * the assignment list with the same LHS is dead.
 241           */
 242          if (debug)
 243             printf("looking for %s to remove\n", var->name);
 244          foreach_iter(exec_list_iterator, iter, *assignments) {
 245             assignment_entry *entry = (assignment_entry *)iter.get();
 246
 247             if (entry->lhs == var) {
 248                if (debug)
 249                   printf("removing %s\n", var->name);
 250                entry->ir->remove();
 251                entry->remove();
 252                progress = true;
 253             }
 254          }
 255       }
 256    }
 257
 258    /* Add this instruction to the assignment list available to be removed. */
 259    assignment_entry *entry = new(ctx) assignment_entry(var, ir);
 260    assignments->push_tail(entry);
 261
 262    if (debug) {
 263       printf("add %s\n", var->name);
 264
 265       printf("current entries\n");
 266       foreach_iter(exec_list_iterator, iter, *assignments) {
 267          assignment_entry *entry = (assignment_entry *)iter.get();
 268
 269          printf("    %s (0x%01x)\n", entry->lhs->name, entry->available);
 270       }
 271    }
 272
 273    return progress;
 274 }
 275
 276 static void
 277 dead_code_local_basic_block(ir_instruction *first,
 278                              ir_instruction *last,
 279                              void *data)
 280 {
 281    ir_instruction *ir, *ir_next;
 282    /* List of avaialble_copy */
 283    exec_list assignments;
 284    bool *out_progress = (bool *)data;
 285    bool progress = false;
 286
 287    void *ctx = ralloc_context(NULL);
 288    /* Safe looping, since process_assignment */
 289    for (ir = first, ir_next = (ir_instruction *)first->next;;
 290         ir = ir_next, ir_next = (ir_instruction *)ir->next) {
 291       ir_assignment *ir_assign = ir->as_assignment();
 292
 293       if (debug) {
 294          ir->print();
 295          printf("\n");
 296       }
 297
 298       if (ir_assign) {
 299          progress = process_assignment(ctx, ir_assign, &assignments) || progress;
 300       } else {
 301          kill_for_derefs_visitor kill(&assignments);
 302          ir->accept(&kill);
 303       }
 304
 305       if (ir == last)
 306          break;
 307    }
 308    *out_progress = progress;
 309    ralloc_free(ctx);
 310 }
 311
 312 /**
 313  * Does a copy propagation pass on the code present in the instruction stream.
 314  */
 315 bool
 316 do_dead_code_local(exec_list *instructions)
 317 {
 318    bool progress = false;
 319
 320    call_for_basic_blocks(instructions, dead_code_local_basic_block, &progress);
 321
 322    return progress;
 323 }