ir_copy_propagation.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_copy_propagation.cpp
  26  *
  27  * Moves usage of recently-copied variables to the previous copy of
  28  * the variable within basic blocks.
  29  *
  30  * This should reduce the number of MOV instructions in the generated
  31  * programs unless copy propagation is also done on the LIR, and may
  32  * help anyway by triggering other optimizations that live in the HIR.
  33  */
  34
  35 #include <stdio.h>
  36 #include "ir.h"
  37 #include "ir_visitor.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 class acp_entry : public exec_node
  44 {
  45 public:
  46    acp_entry(ir_variable *lhs, ir_variable *rhs)
  47    {
  48       assert(lhs);
  49       assert(rhs);
  50       this->lhs = lhs;
  51       this->rhs = rhs;
  52    }
  53
  54    ir_variable *lhs;
  55    ir_variable *rhs;
  56 };
  57
  58 class ir_copy_propagation_visitor : public ir_hierarchical_visitor {
  59 public:
  60    ir_copy_propagation_visitor(exec_list *acp)
  61    {
  62       progress = false;
  63       in_lhs = false;
  64       this->acp = acp;
  65    }
  66
  67    virtual ir_visitor_status visit(class ir_dereference_variable *);
  68    virtual ir_visitor_status visit_enter(class ir_loop *);
  69    virtual ir_visitor_status visit_enter(class ir_function_signature *);
  70    virtual ir_visitor_status visit_enter(class ir_function *);
  71    virtual ir_visitor_status visit_enter(class ir_assignment *);
  72    virtual ir_visitor_status visit_enter(class ir_call *);
  73    virtual ir_visitor_status visit_enter(class ir_if *);
  74
  75    /** List of acp_entry */
  76    exec_list *acp;
  77    bool progress;
  78
  79    /** Currently in the LHS of an assignment? */
  80    bool in_lhs;
  81 };
  82
  83
  84 ir_visitor_status
  85 ir_copy_propagation_visitor::visit_enter(ir_loop *ir)
  86 {
  87    (void)ir;
  88    return visit_continue_with_parent;
  89 }
  90
  91 ir_visitor_status
  92 ir_copy_propagation_visitor::visit_enter(ir_function_signature *ir)
  93 {
  94    (void)ir;
  95    return visit_continue_with_parent;
  96 }
  97
  98 ir_visitor_status
  99 ir_copy_propagation_visitor::visit_enter(ir_assignment *ir)
 100 {
 101    (void) ir;
 102    this->in_lhs = true;
 103    return visit_continue;
 104 }
 105
 106 ir_visitor_status
 107 ir_copy_propagation_visitor::visit_enter(ir_function *ir)
 108 {
 109    (void) ir;
 110    return visit_continue_with_parent;
 111 }
 112
 113 /**
 114  * Replaces dereferences of ACP RHS variables with ACP LHS variables.
 115  *
 116  * This is where the actual copy propagation occurs.  Note that the
 117  * rewriting of ir_dereference means that the ir_dereference instance
 118  * must not be shared by multiple IR operations!
 119  */
 120 ir_visitor_status
 121 ir_copy_propagation_visitor::visit(ir_dereference_variable *ir)
 122 {
 123    /* Ignores the LHS.  Don't want to rewrite the LHS to point at some
 124     * other storage!
 125     */
 126    if (this->in_lhs) {
 127       this->in_lhs = false;
 128       return visit_continue;
 129    }
 130
 131    ir_variable *var = ir->variable_referenced();
 132
 133    foreach_iter(exec_list_iterator, iter, *this->acp) {
 134       acp_entry *entry = (acp_entry *)iter.get();
 135
 136       if (var == entry->lhs) {
 137          ir->var = entry->rhs;
 138          this->progress = true;
 139          break;
 140       }
 141    }
 142
 143    return visit_continue;
 144 }
 145
 146
 147 ir_visitor_status
 148 ir_copy_propagation_visitor::visit_enter(ir_call *ir)
 149 {
 150    (void)ir;
 151
 152    /* Note, if we were to do copy propagation to parameters of calls, we'd
 153     * have to be careful about out params.
 154     */
 155    return visit_continue_with_parent;
 156 }
 157
 158
 159 ir_visitor_status
 160 ir_copy_propagation_visitor::visit_enter(ir_if *ir)
 161 {
 162    ir->condition->accept(this);
 163
 164    /* Do not traverse into the body of the if-statement since that is a
 165     * different basic block.
 166     */
 167    return visit_continue_with_parent;
 168 }
 169
 170 static bool
 171 propagate_copies(ir_instruction *ir, exec_list *acp)
 172 {
 173    ir_copy_propagation_visitor v(acp);
 174
 175    ir->accept(&v);
 176
 177    return v.progress;
 178 }
 179
 180 static void
 181 kill_invalidated_copies(ir_assignment *ir, exec_list *acp)
 182 {
 183    ir_variable *var = ir->lhs->variable_referenced();
 184    assert(var != NULL);
 185
 186    foreach_iter(exec_list_iterator, iter, *acp) {
 187       acp_entry *entry = (acp_entry *)iter.get();
 188
 189       if (entry->lhs == var || entry->rhs == var) {
 190          entry->remove();
 191       }
 192    }
 193 }
 194
 195 /**
 196  * Adds an entry to the available copy list if it's a plain assignment
 197  * of a variable to a variable.
 198  */
 199 static void
 200 add_copy(ir_assignment *ir, exec_list *acp)
 201 {
 202    acp_entry *entry;
 203
 204    if (ir->condition) {
 205       ir_constant *condition = ir->condition->as_constant();
 206       if (!condition || !condition->value.b[0])
 207          return;
 208    }
 209
 210    ir_variable *lhs_var = ir->lhs->whole_variable_referenced();
 211    ir_variable *rhs_var = ir->rhs->whole_variable_referenced();
 212
 213    if ((lhs_var != NULL) && (rhs_var != NULL)) {
 214       entry = new acp_entry(lhs_var, rhs_var);
 215       acp->push_tail(entry);
 216    }
 217 }
 218
 219 static void
 220 copy_propagation_basic_block(ir_instruction *first,
 221                              ir_instruction *last,
 222                              void *data)
 223 {
 224    ir_instruction *ir;
 225    /* List of avaialble_copy */
 226    exec_list acp;
 227    bool *out_progress = (bool *)data;
 228    bool progress = false;
 229
 230    for (ir = first;; ir = (ir_instruction *)ir->next) {
 231       ir_assignment *ir_assign = ir->as_assignment();
 232
 233       progress = propagate_copies(ir, &acp) || progress;
 234
 235       if (ir_assign) {
 236          kill_invalidated_copies(ir_assign, &acp);
 237
 238          add_copy(ir_assign, &acp);
 239       }
 240       if (ir == last)
 241          break;
 242    }
 243    *out_progress = progress;
 244 }
 245
 246 /**
 247  * Does a copy propagation pass on the code present in the instruction stream.
 248  */
 249 bool
 250 do_copy_propagation(exec_list *instructions)
 251 {
 252    bool progress = false;
 253
 254    call_for_basic_blocks(instructions, copy_propagation_basic_block, &progress);
 255
 256    return progress;
 257 }