ir_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 ir_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 <stdio.h>
  37 #include "ir.h"
  38 #include "ir_print_visitor.h"
  39 #include "ir_basic_block.h"
  40 #include "ir_optimization.h"
  41 #include "glsl_types.h"
  42
  43 static bool debug = false;
  44
  45 class assignment_entry : public exec_node
  46 {
  47 public:
  48    assignment_entry(ir_variable *lhs, ir_instruction *ir)
  49    {
  50       assert(lhs);
  51       assert(ir);
  52       this->lhs = lhs;
  53       this->ir = ir;
  54    }
  55
  56    ir_variable *lhs;
  57    ir_instruction *ir;
  58 };
  59
  60 class kill_for_derefs_visitor : public ir_hierarchical_visitor {
  61 public:
  62    kill_for_derefs_visitor(exec_list *assignments)
  63    {
  64       this->assignments = assignments;
  65    }
  66
  67    virtual ir_visitor_status visit(ir_dereference_variable *ir)
  68    {
  69       ir_variable *const var = ir->variable_referenced();
  70
  71       foreach_iter(exec_list_iterator, iter, *this->assignments) {
  72          assignment_entry *entry = (assignment_entry *)iter.get();
  73
  74          if (entry->lhs == var) {
  75             if (debug)
  76                printf("kill %s\n", entry->lhs->name);
  77             entry->remove();
  78          }
  79       }
  80
  81       return visit_continue;
  82    }
  83
  84 private:
  85    exec_list *assignments;
  86 };
  87
  88 class array_index_visit : public ir_hierarchical_visitor {
  89 public:
  90    array_index_visit(ir_hierarchical_visitor *v)
  91    {
  92       this->visitor = v;
  93    }
  94
  95    virtual ir_visitor_status visit_enter(class ir_dereference_array *ir)
  96    {
  97       ir->array_index->accept(visitor);
  98       return visit_continue;
  99    }
 100
 101    static void run(ir_instruction *ir, ir_hierarchical_visitor *v)
 102    {
 103       array_index_visit top_visit(v);
 104       ir->accept(& top_visit);
 105    }
 106
 107    ir_hierarchical_visitor *visitor;
 108 };
 109
 110
 111 /**
 112  * Adds an entry to the available copy list if it's a plain assignment
 113  * of a variable to a variable.
 114  */
 115 static bool
 116 process_assignment(ir_assignment *ir, exec_list *assignments)
 117 {
 118    ir_variable *var = NULL;
 119    bool progress = false;
 120    kill_for_derefs_visitor v(assignments);
 121
 122    /* Kill assignment entries for things used to produce this assignment. */
 123    ir->rhs->accept(&v);
 124    if (ir->condition) {
 125       ir->condition->accept(&v);
 126    }
 127
 128    /* Kill assignment enties used as array indices.
 129     */
 130    array_index_visit::run(ir->lhs, &v);
 131    var = ir->lhs->variable_referenced();
 132    assert(var);
 133
 134    bool always_assign = true;
 135    if (ir->condition) {
 136       ir_constant *condition = ir->condition->as_constant();
 137       if (!condition || !condition->value.b[0])
 138          always_assign = false;
 139    }
 140
 141    /* Now, check if we did a whole-variable assignment. */
 142    if (always_assign && (ir->lhs->whole_variable_referenced() != NULL)) {
 143       /* We did a whole-variable assignment.  So, any instruction in
 144        * the assignment list with the same LHS is dead.
 145        */
 146       if (debug)
 147          printf("looking for %s to remove\n", var->name);
 148       foreach_iter(exec_list_iterator, iter, *assignments) {
 149          assignment_entry *entry = (assignment_entry *)iter.get();
 150
 151          if (entry->lhs == var) {
 152             if (debug)
 153                printf("removing %s\n", var->name);
 154             entry->ir->remove();
 155             entry->remove();
 156             progress = true;
 157          }
 158       }
 159    }
 160
 161    /* Add this instruction to the assignment list. */
 162    assignment_entry *entry = new assignment_entry(var, ir);
 163    assignments->push_tail(entry);
 164
 165    if (debug) {
 166       printf("add %s\n", var->name);
 167
 168       printf("current entries\n");
 169       foreach_iter(exec_list_iterator, iter, *assignments) {
 170          assignment_entry *entry = (assignment_entry *)iter.get();
 171
 172          printf("    %s\n", entry->lhs->name);
 173       }
 174    }
 175
 176    return progress;
 177 }
 178
 179 static void
 180 dead_code_local_basic_block(ir_instruction *first,
 181                              ir_instruction *last,
 182                              void *data)
 183 {
 184    ir_instruction *ir, *ir_next;
 185    /* List of avaialble_copy */
 186    exec_list assignments;
 187    bool *out_progress = (bool *)data;
 188    bool progress = false;
 189
 190    /* Safe looping, since process_assignment */
 191    for (ir = first, ir_next = (ir_instruction *)first->next;;
 192         ir = ir_next, ir_next = (ir_instruction *)ir->next) {
 193       ir_assignment *ir_assign = ir->as_assignment();
 194
 195       if (debug) {
 196          ir_print_visitor v;
 197          ir->accept(&v);
 198          printf("\n");
 199       }
 200
 201       if (ir_assign) {
 202          progress = process_assignment(ir_assign, &assignments) || progress;
 203       } else {
 204          kill_for_derefs_visitor kill(&assignments);
 205          ir->accept(&kill);
 206       }
 207
 208       if (ir == last)
 209          break;
 210    }
 211    *out_progress = progress;
 212 }
 213
 214 /**
 215  * Does a copy propagation pass on the code present in the instruction stream.
 216  */
 217 bool
 218 do_dead_code_local(exec_list *instructions)
 219 {
 220    bool progress = false;
 221
 222    call_for_basic_blocks(instructions, dead_code_local_basic_block, &progress);
 223
 224    return progress;
 225 }