src/compiler/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 "compiler/glsl_types.h"
  40
  41 static bool debug = false;
  42
  43 namespace {
  44
  45 class assignment_entry : public exec_node
  46 {
  47 public:
  48    /* override operator new from exec_node */
  49    DECLARE_LINEAR_ZALLOC_CXX_OPERATORS(assignment_entry)
  50
  51    assignment_entry(ir_variable *lhs, ir_assignment *ir)
  52    {
  53       assert(lhs);
  54       assert(ir);
  55       this->lhs = lhs;
  56       this->ir = ir;
  57       this->unused = ir->write_mask;
  58    }
  59
  60    ir_variable *lhs;
  61    ir_assignment *ir;
  62
  63    /* bitmask of xyzw channels written that haven't been used so far. */
  64    int unused;
  65 };
  66
  67 class kill_for_derefs_visitor : public ir_hierarchical_visitor {
  68 public:
  69    kill_for_derefs_visitor(exec_list *assignments)
  70    {
  71       this->assignments = assignments;
  72    }
  73
  74    void use_channels(ir_variable *const var, int used)
  75    {
  76       foreach_in_list_safe(assignment_entry, entry, this->assignments) {
  77          if (entry->lhs == var) {
  78             if (var->type->is_scalar() || var->type->is_vector()) {
  79                if (debug)
  80                   printf("used %s (0x%01x - 0x%01x)\n", entry->lhs->name,
  81                          entry->unused, used & 0xf);
  82                entry->unused &= ~used;
  83                if (!entry->unused)
  84                   entry->remove();
  85             } else {
  86                if (debug)
  87                   printf("used %s\n", entry->lhs->name);
  88                entry->remove();
  89             }
  90          }
  91       }
  92    }
  93
  94    virtual ir_visitor_status visit(ir_dereference_variable *ir)
  95    {
  96       use_channels(ir->var, ~0);
  97
  98       return visit_continue;
  99    }
 100
 101    virtual ir_visitor_status visit(ir_swizzle *ir)
 102    {
 103       ir_dereference_variable *deref = ir->val->as_dereference_variable();
 104       if (!deref)
 105          return visit_continue;
 106
 107       int used = 0;
 108       used |= 1 << ir->mask.x;
 109       if (ir->mask.num_components > 1)
 110          used |= 1 << ir->mask.y;
 111       if (ir->mask.num_components > 2)
 112          used |= 1 << ir->mask.z;
 113       if (ir->mask.num_components > 3)
 114          used |= 1 << ir->mask.w;
 115
 116       use_channels(deref->var, used);
 117
 118       return visit_continue_with_parent;
 119    }
 120
 121    virtual ir_visitor_status visit_leave(ir_emit_vertex *)
 122    {
 123       /* For the purpose of dead code elimination, emitting a vertex counts as
 124        * "reading" all of the currently assigned output variables.
 125        */
 126       foreach_in_list_safe(assignment_entry, entry, this->assignments) {
 127          if (entry->lhs->data.mode == ir_var_shader_out) {
 128             if (debug)
 129                printf("kill %s\n", entry->lhs->name);
 130             entry->remove();
 131          }
 132       }
 133
 134       return visit_continue;
 135    }
 136
 137 private:
 138    exec_list *assignments;
 139 };
 140
 141 class array_index_visit : public ir_hierarchical_visitor {
 142 public:
 143    array_index_visit(ir_hierarchical_visitor *v)
 144    {
 145       this->visitor = v;
 146    }
 147
 148    virtual ir_visitor_status visit_enter(class ir_dereference_array *ir)
 149    {
 150       ir->array_index->accept(visitor);
 151       return visit_continue;
 152    }
 153
 154    static void run(ir_instruction *ir, ir_hierarchical_visitor *v)
 155    {
 156       array_index_visit top_visit(v);
 157       ir->accept(& top_visit);
 158    }
 159
 160    ir_hierarchical_visitor *visitor;
 161 };
 162
 163 } /* unnamed namespace */
 164
 165 /**
 166  * Adds an entry to the available copy list if it's a plain assignment
 167  * of a variable to a variable.
 168  */
 169 static bool
 170 process_assignment(void *lin_ctx, ir_assignment *ir, exec_list *assignments)
 171 {
 172    ir_variable *var = NULL;
 173    bool progress = false;
 174    kill_for_derefs_visitor v(assignments);
 175
 176    if (ir->condition == NULL) {
 177       /* If this is an assignment of the form "foo = foo;", remove the whole
 178        * instruction and be done with it.
 179        */
 180       const ir_variable *const lhs_var = ir->whole_variable_written();
 181       if (lhs_var != NULL && lhs_var == ir->rhs->whole_variable_referenced()) {
 182          ir->remove();
 183          return true;
 184       }
 185    }
 186
 187    /* Kill assignment entries for things used to produce this assignment. */
 188    ir->rhs->accept(&v);
 189    if (ir->condition) {
 190       ir->condition->accept(&v);
 191    }
 192
 193    /* Kill assignment enties used as array indices.
 194     */
 195    array_index_visit::run(ir->lhs, &v);
 196    var = ir->lhs->variable_referenced();
 197    assert(var);
 198
 199    /* Now, check if we did a whole-variable assignment. */
 200    if (!ir->condition) {
 201       ir_dereference_variable *deref_var = ir->lhs->as_dereference_variable();
 202
 203       /* If it's a vector type, we can do per-channel elimination of
 204        * use of the RHS.
 205        */
 206       if (deref_var && (deref_var->var->type->is_scalar() ||
 207                         deref_var->var->type->is_vector())) {
 208
 209          if (debug)
 210             printf("looking for %s.0x%01x to remove\n", var->name,
 211                    ir->write_mask);
 212
 213          foreach_in_list_safe(assignment_entry, entry, assignments) {
 214             if (entry->lhs != var)
 215                continue;
 216
 217             /* Skip if the assignment we're trying to eliminate isn't a plain
 218              * variable deref. */
 219             if (entry->ir->lhs->ir_type != ir_type_dereference_variable)
 220                continue;
 221
 222             int remove = entry->unused & ir->write_mask;
 223             if (debug) {
 224                printf("%s 0x%01x - 0x%01x = 0x%01x\n",
 225                       var->name,
 226                       entry->ir->write_mask,
 227                       remove, entry->ir->write_mask & ~remove);
 228             }
 229             if (remove) {
 230                progress = true;
 231
 232                if (debug) {
 233                   printf("rewriting:\n  ");
 234                   entry->ir->print();
 235                   printf("\n");
 236                }
 237
 238                entry->ir->write_mask &= ~remove;
 239                entry->unused &= ~remove;
 240                if (entry->ir->write_mask == 0) {
 241                   /* Delete the dead assignment. */
 242                   entry->ir->remove();
 243                   entry->remove();
 244                } else {
 245                   void *mem_ctx = ralloc_parent(entry->ir);
 246                   /* Reswizzle the RHS arguments according to the new
 247                    * write_mask.
 248                    */
 249                   unsigned components[4];
 250                   unsigned channels = 0;
 251                   unsigned next = 0;
 252
 253                   for (int i = 0; i < 4; i++) {
 254                      if ((entry->ir->write_mask | remove) & (1 << i)) {
 255                         if (!(remove & (1 << i)))
 256                            components[channels++] = next;
 257                         next++;
 258                      }
 259                   }
 260
 261                   entry->ir->rhs = new(mem_ctx) ir_swizzle(entry->ir->rhs,
 262                                                            components,
 263                                                            channels);
 264                   if (debug) {
 265                      printf("to:\n  ");
 266                      entry->ir->print();
 267                      printf("\n");
 268                   }
 269                }
 270             }
 271          }
 272       } else if (ir->whole_variable_written() != NULL) {
 273          /* We did a whole-variable assignment.  So, any instruction in
 274           * the assignment list with the same LHS is dead.
 275           */
 276          if (debug)
 277             printf("looking for %s to remove\n", var->name);
 278          foreach_in_list_safe(assignment_entry, entry, assignments) {
 279             if (entry->lhs == var) {
 280                if (debug)
 281                   printf("removing %s\n", var->name);
 282                entry->ir->remove();
 283                entry->remove();
 284                progress = true;
 285             }
 286          }
 287       }
 288    }
 289
 290    /* Add this instruction to the assignment list available to be removed. */
 291    assignment_entry *entry = new(lin_ctx) assignment_entry(var, ir);
 292    assignments->push_tail(entry);
 293
 294    if (debug) {
 295       printf("add %s\n", var->name);
 296
 297       printf("current entries\n");
 298       foreach_in_list(assignment_entry, entry, assignments) {
 299          printf("    %s (0x%01x)\n", entry->lhs->name, entry->unused);
 300       }
 301    }
 302
 303    return progress;
 304 }
 305
 306 static void
 307 dead_code_local_basic_block(ir_instruction *first,
 308                              ir_instruction *last,
 309                              void *data)
 310 {
 311    ir_instruction *ir, *ir_next;
 312    /* List of avaialble_copy */
 313    exec_list assignments;
 314    bool *out_progress = (bool *)data;
 315    bool progress = false;
 316
 317    void *ctx = ralloc_context(NULL);
 318    void *lin_ctx = linear_alloc_parent(ctx, 0);
 319
 320    /* Safe looping, since process_assignment */
 321    for (ir = first, ir_next = (ir_instruction *)first->next;;
 322         ir = ir_next, ir_next = (ir_instruction *)ir->next) {
 323       ir_assignment *ir_assign = ir->as_assignment();
 324
 325       if (debug) {
 326          ir->print();
 327          printf("\n");
 328       }
 329
 330       if (ir_assign) {
 331          progress = process_assignment(lin_ctx, ir_assign, &assignments) ||
 332                     progress;
 333       } else {
 334          kill_for_derefs_visitor kill(&assignments);
 335          ir->accept(&kill);
 336       }
 337
 338       if (ir == last)
 339          break;
 340    }
 341    *out_progress = progress;
 342    ralloc_free(ctx);
 343 }
 344
 345 /**
 346  * Does a copy propagation pass on the code present in the instruction stream.
 347  */
 348 bool
 349 do_dead_code_local(exec_list *instructions)
 350 {
 351    bool progress = false;
 352
 353    call_for_basic_blocks(instructions, dead_code_local_basic_block, &progress);
 354
 355    return progress;
 356 }