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    using ir_hierarchical_visitor::visit;
  70
  71    kill_for_derefs_visitor(exec_list *assignments)
  72    {
  73       this->assignments = assignments;
  74    }
  75
  76    void use_channels(ir_variable *const var, int used)
  77    {
  78       foreach_in_list_safe(assignment_entry, entry, this->assignments) {
  79          if (entry->lhs == var) {
  80             if (var->type->is_scalar() || var->type->is_vector()) {
  81                if (debug)
  82                   printf("used %s (0x%01x - 0x%01x)\n", entry->lhs->name,
  83                          entry->unused, used & 0xf);
  84                entry->unused &= ~used;
  85                if (!entry->unused)
  86                   entry->remove();
  87             } else {
  88                if (debug)
  89                   printf("used %s\n", entry->lhs->name);
  90                entry->remove();
  91             }
  92          }
  93       }
  94    }
  95
  96    virtual ir_visitor_status visit(ir_dereference_variable *ir)
  97    {
  98       use_channels(ir->var, ~0);
  99
 100       return visit_continue;
 101    }
 102
 103    virtual ir_visitor_status visit(ir_swizzle *ir)
 104    {
 105       ir_dereference_variable *deref = ir->val->as_dereference_variable();
 106       if (!deref)
 107          return visit_continue;
 108
 109       int used = 0;
 110       used |= 1 << ir->mask.x;
 111       if (ir->mask.num_components > 1)
 112          used |= 1 << ir->mask.y;
 113       if (ir->mask.num_components > 2)
 114          used |= 1 << ir->mask.z;
 115       if (ir->mask.num_components > 3)
 116          used |= 1 << ir->mask.w;
 117
 118       use_channels(deref->var, used);
 119
 120       return visit_continue_with_parent;
 121    }
 122
 123    virtual ir_visitor_status visit_leave(ir_emit_vertex *)
 124    {
 125       /* For the purpose of dead code elimination, emitting a vertex counts as
 126        * "reading" all of the currently assigned output variables.
 127        */
 128       foreach_in_list_safe(assignment_entry, entry, this->assignments) {
 129          if (entry->lhs->data.mode == ir_var_shader_out) {
 130             if (debug)
 131                printf("kill %s\n", entry->lhs->name);
 132             entry->remove();
 133          }
 134       }
 135
 136       return visit_continue;
 137    }
 138
 139 private:
 140    exec_list *assignments;
 141 };
 142
 143 class array_index_visit : public ir_hierarchical_visitor {
 144 public:
 145    array_index_visit(ir_hierarchical_visitor *v)
 146    {
 147       this->visitor = v;
 148    }
 149
 150    virtual ir_visitor_status visit_enter(class ir_dereference_array *ir)
 151    {
 152       ir->array_index->accept(visitor);
 153       return visit_continue;
 154    }
 155
 156    static void run(ir_instruction *ir, ir_hierarchical_visitor *v)
 157    {
 158       array_index_visit top_visit(v);
 159       ir->accept(& top_visit);
 160    }
 161
 162    ir_hierarchical_visitor *visitor;
 163 };
 164
 165 } /* unnamed namespace */
 166
 167 /**
 168  * Adds an entry to the available copy list if it's a plain assignment
 169  * of a variable to a variable.
 170  */
 171 static bool
 172 process_assignment(void *lin_ctx, ir_assignment *ir, exec_list *assignments)
 173 {
 174    ir_variable *var = NULL;
 175    bool progress = false;
 176    kill_for_derefs_visitor v(assignments);
 177
 178    if (ir->condition == NULL) {
 179       /* If this is an assignment of the form "foo = foo;", remove the whole
 180        * instruction and be done with it.
 181        */
 182       const ir_variable *const lhs_var = ir->whole_variable_written();
 183       if (lhs_var != NULL && lhs_var == ir->rhs->whole_variable_referenced()) {
 184          ir->remove();
 185          return true;
 186       }
 187    }
 188
 189    /* Kill assignment entries for things used to produce this assignment. */
 190    ir->rhs->accept(&v);
 191    if (ir->condition) {
 192       ir->condition->accept(&v);
 193    }
 194
 195    /* Kill assignment enties used as array indices.
 196     */
 197    array_index_visit::run(ir->lhs, &v);
 198    var = ir->lhs->variable_referenced();
 199    assert(var);
 200
 201    /* Now, check if we did a whole-variable assignment. */
 202    if (!ir->condition) {
 203       ir_dereference_variable *deref_var = ir->lhs->as_dereference_variable();
 204
 205       /* If it's a vector type, we can do per-channel elimination of
 206        * use of the RHS.
 207        */
 208       if (deref_var && (deref_var->var->type->is_scalar() ||
 209                         deref_var->var->type->is_vector())) {
 210
 211          if (debug)
 212             printf("looking for %s.0x%01x to remove\n", var->name,
 213                    ir->write_mask);
 214
 215          foreach_in_list_safe(assignment_entry, entry, assignments) {
 216             if (entry->lhs != var)
 217                continue;
 218
 219             /* Skip if the assignment we're trying to eliminate isn't a plain
 220              * variable deref. */
 221             if (entry->ir->lhs->ir_type != ir_type_dereference_variable)
 222                continue;
 223
 224             int remove = entry->unused & ir->write_mask;
 225             if (debug) {
 226                printf("%s 0x%01x - 0x%01x = 0x%01x\n",
 227                       var->name,
 228                       entry->ir->write_mask,
 229                       remove, entry->ir->write_mask & ~remove);
 230             }
 231             if (remove) {
 232                progress = true;
 233
 234                if (debug) {
 235                   printf("rewriting:\n  ");
 236                   entry->ir->print();
 237                   printf("\n");
 238                }
 239
 240                entry->ir->write_mask &= ~remove;
 241                entry->unused &= ~remove;
 242                if (entry->ir->write_mask == 0) {
 243                   /* Delete the dead assignment. */
 244                   entry->ir->remove();
 245                   entry->remove();
 246                } else {
 247                   void *mem_ctx = ralloc_parent(entry->ir);
 248                   /* Reswizzle the RHS arguments according to the new
 249                    * write_mask.
 250                    */
 251                   unsigned components[4];
 252                   unsigned channels = 0;
 253                   unsigned next = 0;
 254
 255                   for (int i = 0; i < 4; i++) {
 256                      if ((entry->ir->write_mask | remove) & (1 << i)) {
 257                         if (!(remove & (1 << i)))
 258                            components[channels++] = next;
 259                         next++;
 260                      }
 261                   }
 262
 263                   entry->ir->rhs = new(mem_ctx) ir_swizzle(entry->ir->rhs,
 264                                                            components,
 265                                                            channels);
 266                   if (debug) {
 267                      printf("to:\n  ");
 268                      entry->ir->print();
 269                      printf("\n");
 270                   }
 271                }
 272             }
 273          }
 274       } else if (ir->whole_variable_written() != NULL) {
 275          /* We did a whole-variable assignment.  So, any instruction in
 276           * the assignment list with the same LHS is dead.
 277           */
 278          if (debug)
 279             printf("looking for %s to remove\n", var->name);
 280          foreach_in_list_safe(assignment_entry, entry, assignments) {
 281             if (entry->lhs == var) {
 282                if (debug)
 283                   printf("removing %s\n", var->name);
 284                entry->ir->remove();
 285                entry->remove();
 286                progress = true;
 287             }
 288          }
 289       }
 290    }
 291
 292    /* Add this instruction to the assignment list available to be removed. */
 293    assignment_entry *entry = new(lin_ctx) assignment_entry(var, ir);
 294    assignments->push_tail(entry);
 295
 296    if (debug) {
 297       printf("add %s\n", var->name);
 298
 299       printf("current entries\n");
 300       foreach_in_list(assignment_entry, entry, assignments) {
 301          printf("    %s (0x%01x)\n", entry->lhs->name, entry->unused);
 302       }
 303    }
 304
 305    return progress;
 306 }
 307
 308 static void
 309 dead_code_local_basic_block(ir_instruction *first,
 310                              ir_instruction *last,
 311                              void *data)
 312 {
 313    ir_instruction *ir, *ir_next;
 314    /* List of avaialble_copy */
 315    exec_list assignments;
 316    bool *out_progress = (bool *)data;
 317    bool progress = false;
 318
 319    void *ctx = ralloc_context(NULL);
 320    void *lin_ctx = linear_alloc_parent(ctx, 0);
 321
 322    /* Safe looping, since process_assignment */
 323    for (ir = first, ir_next = (ir_instruction *)first->next;;
 324         ir = ir_next, ir_next = (ir_instruction *)ir->next) {
 325       ir_assignment *ir_assign = ir->as_assignment();
 326
 327       if (debug) {
 328          ir->print();
 329          printf("\n");
 330       }
 331
 332       if (ir_assign) {
 333          progress = process_assignment(lin_ctx, ir_assign, &assignments) ||
 334                     progress;
 335       } else {
 336          kill_for_derefs_visitor kill(&assignments);
 337          ir->accept(&kill);
 338       }
 339
 340       if (ir == last)
 341          break;
 342    }
 343    *out_progress = progress;
 344    ralloc_free(ctx);
 345 }
 346
 347 /**
 348  * Does a copy propagation pass on the code present in the instruction stream.
 349  */
 350 bool
 351 do_dead_code_local(exec_list *instructions)
 352 {
 353    bool progress = false;
 354
 355    call_for_basic_blocks(instructions, dead_code_local_basic_block, &progress);
 356
 357    return progress;
 358 }