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_visitor.h"
  39 #include "ir_print_visitor.h"
  40 #include "ir_basic_block.h"
  41 #include "ir_visit_tree.h"
  42 #include "ir_optimization.h"
  43 #include "glsl_types.h"
  44
  45 static bool debug = false;
  46
  47 class assignment_entry : public exec_node
  48 {
  49 public:
  50    assignment_entry(ir_variable *lhs, ir_instruction *ir)
  51    {
  52       assert(lhs);
  53       assert(ir);
  54       this->lhs = lhs;
  55       this->ir = ir;
  56    }
  57
  58    ir_variable *lhs;
  59    ir_instruction *ir;
  60 };
  61
  62 static void
  63 ir_kill_for_derefs_callback(ir_instruction *ir, void *data)
  64 {
  65    exec_list *assignments = (exec_list *)data;
  66    ir_variable *var = ir->as_variable();
  67
  68    if (!var)
  69       return;
  70
  71    foreach_iter(exec_list_iterator, iter, *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
  82 static void
  83 kill_for_derefs(ir_instruction *ir, exec_list *assignments)
  84 {
  85    ir_visit_tree(ir, ir_kill_for_derefs_callback, assignments);
  86 }
  87
  88 /**
  89  * Adds an entry to the available copy list if it's a plain assignment
  90  * of a variable to a variable.
  91  */
  92 static bool
  93 process_assignment(ir_assignment *ir, exec_list *assignments)
  94 {
  95    ir_variable *var = NULL;
  96    bool progress = false;
  97    ir_instruction *current;
  98
  99    /* Kill assignment entries for things used to produce this assignment. */
 100    kill_for_derefs(ir->rhs, assignments);
 101    if (ir->condition) {
 102       kill_for_derefs(ir->condition, assignments);
 103    }
 104
 105    /* Walk down the dereference chain to find the variable at the end
 106     * of it that we're actually modifying.  Kill assignment enties used as
 107     * array indices, too.
 108     */
 109    for (current = ir->lhs; current != NULL;) {
 110       ir_swizzle *swiz;
 111       ir_dereference *deref;
 112
 113       if ((swiz = current->as_swizzle())) {
 114          current = swiz->val;
 115       } else if ((deref = current->as_dereference())) {
 116          if (deref->mode == ir_dereference::ir_reference_array)
 117             kill_for_derefs(deref->selector.array_index, assignments);
 118          current = deref->var;
 119       } else {
 120          var = current->as_variable();
 121
 122          current = NULL;
 123          break;
 124       }
 125    }
 126
 127    assert(var);
 128
 129    bool always_assign = true;
 130    if (ir->condition) {
 131       ir_constant *condition = ir->condition->as_constant();
 132       if (!condition || !condition->value.b[0])
 133          always_assign = false;
 134    }
 135
 136    /* Now, check if we did a whole-variable assignment. */
 137    ir_dereference *lhs_deref = ir->lhs->as_dereference();
 138    if (always_assign &&
 139        lhs_deref &&
 140        lhs_deref->mode == ir_dereference::ir_reference_variable) {
 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. */
 160    assignment_entry *entry = new assignment_entry(var, ir);
 161    assignments->push_tail(entry);
 162
 163    if (debug) {
 164       printf("add %s\n", var->name);
 165
 166       printf("current entries\n");
 167       foreach_iter(exec_list_iterator, iter, *assignments) {
 168          assignment_entry *entry = (assignment_entry *)iter.get();
 169
 170          printf("    %s\n", entry->lhs->name);
 171       }
 172    }
 173
 174    return progress;
 175 }
 176
 177 static void
 178 dead_code_local_basic_block(ir_instruction *first,
 179                              ir_instruction *last,
 180                              void *data)
 181 {
 182    ir_instruction *ir, *ir_next;
 183    /* List of avaialble_copy */
 184    exec_list assignments;
 185    bool *out_progress = (bool *)data;
 186    bool progress = false;
 187
 188    /* Safe looping, since process_assignment */
 189    for (ir = first, ir_next = (ir_instruction *)first->next;;
 190         ir = ir_next, ir_next = (ir_instruction *)ir->next) {
 191       ir_assignment *ir_assign = ir->as_assignment();
 192
 193       if (debug) {
 194          ir_print_visitor v;
 195          ir->accept(&v);
 196          printf("\n");
 197       }
 198
 199       if (ir_assign) {
 200          progress = process_assignment(ir_assign, &assignments) || progress;
 201       } else {
 202          kill_for_derefs(ir, &assignments);
 203       }
 204
 205       if (ir == last)
 206          break;
 207    }
 208    *out_progress = progress;
 209 }
 210
 211 /**
 212  * Does a copy propagation pass on the code present in the instruction stream.
 213  */
 214 bool
 215 do_dead_code_local(exec_list *instructions)
 216 {
 217    bool progress = false;
 218
 219    call_for_basic_blocks(instructions, dead_code_local_basic_block, &progress);
 220
 221    return progress;
 222 }