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    /* Kill assignment entries for things used to produce this assignment. */
 177    ir->rhs->accept(&v);
 178    if (ir->condition) {
 179       ir->condition->accept(&v);
 180    }
 181
 182    /* Kill assignment enties used as array indices.
 183     */
 184    array_index_visit::run(ir->lhs, &v);
 185    var = ir->lhs->variable_referenced();
 186    assert(var);
 187
 188    /* Now, check if we did a whole-variable assignment. */
 189    if (!ir->condition) {
 190       ir_dereference_variable *deref_var = ir->lhs->as_dereference_variable();
 191
 192       /* If it's a vector type, we can do per-channel elimination of
 193        * use of the RHS.
 194        */
 195       if (deref_var && (deref_var->var->type->is_scalar() ||
 196                         deref_var->var->type->is_vector())) {
 197
 198          if (debug)
 199             printf("looking for %s.0x%01x to remove\n", var->name,
 200                    ir->write_mask);
 201
 202          foreach_in_list_safe(assignment_entry, entry, assignments) {
 203             if (entry->lhs != var)
 204                continue;
 205
 206             /* Skip if the assignment we're trying to eliminate isn't a plain
 207              * variable deref. */
 208             if (entry->ir->lhs->ir_type != ir_type_dereference_variable)
 209                continue;
 210
 211             int remove = entry->unused & ir->write_mask;
 212             if (debug) {
 213                printf("%s 0x%01x - 0x%01x = 0x%01x\n",
 214                       var->name,
 215                       entry->ir->write_mask,
 216                       remove, entry->ir->write_mask & ~remove);
 217             }
 218             if (remove) {
 219                progress = true;
 220
 221                if (debug) {
 222                   printf("rewriting:\n  ");
 223                   entry->ir->print();
 224                   printf("\n");
 225                }
 226
 227                entry->ir->write_mask &= ~remove;
 228                entry->unused &= ~remove;
 229                if (entry->ir->write_mask == 0) {
 230                   /* Delete the dead assignment. */
 231                   entry->ir->remove();
 232                   entry->remove();
 233                } else {
 234                   void *mem_ctx = ralloc_parent(entry->ir);
 235                   /* Reswizzle the RHS arguments according to the new
 236                    * write_mask.
 237                    */
 238                   unsigned components[4];
 239                   unsigned channels = 0;
 240                   unsigned next = 0;
 241
 242                   for (int i = 0; i < 4; i++) {
 243                      if ((entry->ir->write_mask | remove) & (1 << i)) {
 244                         if (!(remove & (1 << i)))
 245                            components[channels++] = next;
 246                         next++;
 247                      }
 248                   }
 249
 250                   entry->ir->rhs = new(mem_ctx) ir_swizzle(entry->ir->rhs,
 251                                                            components,
 252                                                            channels);
 253                   if (debug) {
 254                      printf("to:\n  ");
 255                      entry->ir->print();
 256                      printf("\n");
 257                   }
 258                }
 259             }
 260          }
 261       } else if (ir->whole_variable_written() != NULL) {
 262          /* We did a whole-variable assignment.  So, any instruction in
 263           * the assignment list with the same LHS is dead.
 264           */
 265          if (debug)
 266             printf("looking for %s to remove\n", var->name);
 267          foreach_in_list_safe(assignment_entry, entry, assignments) {
 268             if (entry->lhs == var) {
 269                if (debug)
 270                   printf("removing %s\n", var->name);
 271                entry->ir->remove();
 272                entry->remove();
 273                progress = true;
 274             }
 275          }
 276       }
 277    }
 278
 279    /* Add this instruction to the assignment list available to be removed. */
 280    assignment_entry *entry = new(lin_ctx) assignment_entry(var, ir);
 281    assignments->push_tail(entry);
 282
 283    if (debug) {
 284       printf("add %s\n", var->name);
 285
 286       printf("current entries\n");
 287       foreach_in_list(assignment_entry, entry, assignments) {
 288          printf("    %s (0x%01x)\n", entry->lhs->name, entry->unused);
 289       }
 290    }
 291
 292    return progress;
 293 }
 294
 295 static void
 296 dead_code_local_basic_block(ir_instruction *first,
 297                              ir_instruction *last,
 298                              void *data)
 299 {
 300    ir_instruction *ir, *ir_next;
 301    /* List of avaialble_copy */
 302    exec_list assignments;
 303    bool *out_progress = (bool *)data;
 304    bool progress = false;
 305
 306    void *ctx = ralloc_context(NULL);
 307    void *lin_ctx = linear_alloc_parent(ctx, 0);
 308
 309    /* Safe looping, since process_assignment */
 310    for (ir = first, ir_next = (ir_instruction *)first->next;;
 311         ir = ir_next, ir_next = (ir_instruction *)ir->next) {
 312       ir_assignment *ir_assign = ir->as_assignment();
 313
 314       if (debug) {
 315          ir->print();
 316          printf("\n");
 317       }
 318
 319       if (ir_assign) {
 320          progress = process_assignment(lin_ctx, ir_assign, &assignments) ||
 321                     progress;
 322       } else {
 323          kill_for_derefs_visitor kill(&assignments);
 324          ir->accept(&kill);
 325       }
 326
 327       if (ir == last)
 328          break;
 329    }
 330    *out_progress = progress;
 331    ralloc_free(ctx);
 332 }
 333
 334 /**
 335  * Does a copy propagation pass on the code present in the instruction stream.
 336  */
 337 bool
 338 do_dead_code_local(exec_list *instructions)
 339 {
 340    bool progress = false;
 341
 342    call_for_basic_blocks(instructions, dead_code_local_basic_block, &progress);
 343
 344    return progress;
 345 }