src/glsl/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_basic_block.h"
  38 #include "ir_optimization.h"
  39 #include "glsl_types.h"
  40
  41 static bool debug = false;
  42
  43 class assignment_entry : public exec_node
  44 {
  45 public:
  46    assignment_entry(ir_variable *lhs, ir_instruction *ir)
  47    {
  48       assert(lhs);
  49       assert(ir);
  50       this->lhs = lhs;
  51       this->ir = ir;
  52    }
  53
  54    ir_variable *lhs;
  55    ir_instruction *ir;
  56 };
  57
  58 class kill_for_derefs_visitor : public ir_hierarchical_visitor {
  59 public:
  60    kill_for_derefs_visitor(exec_list *assignments)
  61    {
  62       this->assignments = assignments;
  63    }
  64
  65    virtual ir_visitor_status visit(ir_dereference_variable *ir)
  66    {
  67       ir_variable *const var = ir->variable_referenced();
  68
  69       foreach_iter(exec_list_iterator, iter, *this->assignments) {
  70          assignment_entry *entry = (assignment_entry *)iter.get();
  71
  72          if (entry->lhs == var) {
  73             if (debug)
  74                printf("kill %s\n", entry->lhs->name);
  75             entry->remove();
  76          }
  77       }
  78
  79       return visit_continue;
  80    }
  81
  82 private:
  83    exec_list *assignments;
  84 };
  85
  86 class array_index_visit : public ir_hierarchical_visitor {
  87 public:
  88    array_index_visit(ir_hierarchical_visitor *v)
  89    {
  90       this->visitor = v;
  91    }
  92
  93    virtual ir_visitor_status visit_enter(class ir_dereference_array *ir)
  94    {
  95       ir->array_index->accept(visitor);
  96       return visit_continue;
  97    }
  98
  99    static void run(ir_instruction *ir, ir_hierarchical_visitor *v)
 100    {
 101       array_index_visit top_visit(v);
 102       ir->accept(& top_visit);
 103    }
 104
 105    ir_hierarchical_visitor *visitor;
 106 };
 107
 108
 109 /**
 110  * Adds an entry to the available copy list if it's a plain assignment
 111  * of a variable to a variable.
 112  */
 113 static bool
 114 process_assignment(void *ctx, ir_assignment *ir, exec_list *assignments)
 115 {
 116    ir_variable *var = NULL;
 117    bool progress = false;
 118    kill_for_derefs_visitor v(assignments);
 119
 120    /* Kill assignment entries for things used to produce this assignment. */
 121    ir->rhs->accept(&v);
 122    if (ir->condition) {
 123       ir->condition->accept(&v);
 124    }
 125
 126    /* Kill assignment enties used as array indices.
 127     */
 128    array_index_visit::run(ir->lhs, &v);
 129    var = ir->lhs->variable_referenced();
 130    assert(var);
 131
 132    bool always_assign = true;
 133    if (ir->condition) {
 134       ir_constant *condition = ir->condition->as_constant();
 135       if (!condition || !condition->value.b[0])
 136          always_assign = false;
 137    }
 138
 139    /* Now, check if we did a whole-variable assignment. */
 140    if (always_assign && (ir->whole_variable_written() != NULL)) {
 141       /* We did a whole-variable assignment.  So, any instruction in
 142        * the assignment list with the same LHS is dead.
 143        */
 144       if (debug)
 145          printf("looking for %s to remove\n", var->name);
 146       foreach_iter(exec_list_iterator, iter, *assignments) {
 147          assignment_entry *entry = (assignment_entry *)iter.get();
 148
 149          if (entry->lhs == var) {
 150             if (debug)
 151                printf("removing %s\n", var->name);
 152             entry->ir->remove();
 153             entry->remove();
 154             progress = true;
 155          }
 156       }
 157    }
 158
 159    /* Add this instruction to the assignment list available to be removed.
 160     * But not if the assignment has other side effects.
 161     */
 162    if (ir_has_call(ir))
 163       return progress;
 164
 165    assignment_entry *entry = new(ctx) assignment_entry(var, ir);
 166    assignments->push_tail(entry);
 167
 168    if (debug) {
 169       printf("add %s\n", var->name);
 170
 171       printf("current entries\n");
 172       foreach_iter(exec_list_iterator, iter, *assignments) {
 173          assignment_entry *entry = (assignment_entry *)iter.get();
 174
 175          printf("    %s\n", entry->lhs->name);
 176       }
 177    }
 178
 179    return progress;
 180 }
 181
 182 static void
 183 dead_code_local_basic_block(ir_instruction *first,
 184                              ir_instruction *last,
 185                              void *data)
 186 {
 187    ir_instruction *ir, *ir_next;
 188    /* List of avaialble_copy */
 189    exec_list assignments;
 190    bool *out_progress = (bool *)data;
 191    bool progress = false;
 192
 193    void *ctx = talloc_new(NULL);
 194    /* Safe looping, since process_assignment */
 195    for (ir = first, ir_next = (ir_instruction *)first->next;;
 196         ir = ir_next, ir_next = (ir_instruction *)ir->next) {
 197       ir_assignment *ir_assign = ir->as_assignment();
 198
 199       if (debug) {
 200          ir->print();
 201          printf("\n");
 202       }
 203
 204       if (ir_assign) {
 205          progress = process_assignment(ctx, ir_assign, &assignments) || progress;
 206       } else {
 207          kill_for_derefs_visitor kill(&assignments);
 208          ir->accept(&kill);
 209       }
 210
 211       if (ir == last)
 212          break;
 213    }
 214    *out_progress = progress;
 215    talloc_free(ctx);
 216 }
 217
 218 /**
 219  * Does a copy propagation pass on the code present in the instruction stream.
 220  */
 221 bool
 222 do_dead_code_local(exec_list *instructions)
 223 {
 224    bool progress = false;
 225
 226    call_for_basic_blocks(instructions, dead_code_local_basic_block, &progress);
 227
 228    return progress;
 229 }