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