src/glsl/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 "ir.h"
  36 #include "ir_visitor.h"
  37 #include "ir_basic_block.h"
  38 #include "ir_optimization.h"
  39 #include "glsl_types.h"
  40
  41 class acp_entry : public exec_node
  42 {
  43 public:
  44    acp_entry(ir_variable *lhs, ir_variable *rhs)
  45    {
  46       assert(lhs);
  47       assert(rhs);
  48       this->lhs = lhs;
  49       this->rhs = rhs;
  50    }
  51
  52    ir_variable *lhs;
  53    ir_variable *rhs;
  54 };
  55
  56 class ir_copy_propagation_visitor : public ir_hierarchical_visitor {
  57 public:
  58    ir_copy_propagation_visitor(exec_list *acp)
  59    {
  60       progress = false;
  61       in_lhs = false;
  62       this->acp = acp;
  63    }
  64
  65    virtual ir_visitor_status visit(class ir_dereference_variable *);
  66    virtual ir_visitor_status visit_enter(class ir_loop *);
  67    virtual ir_visitor_status visit_enter(class ir_function_signature *);
  68    virtual ir_visitor_status visit_enter(class ir_function *);
  69    virtual ir_visitor_status visit_enter(class ir_assignment *);
  70    virtual ir_visitor_status visit_enter(class ir_call *);
  71    virtual ir_visitor_status visit_enter(class ir_if *);
  72
  73    /** List of acp_entry */
  74    exec_list *acp;
  75    bool progress;
  76
  77    /** Currently in the LHS of an assignment? */
  78    bool in_lhs;
  79 };
  80
  81
  82 ir_visitor_status
  83 ir_copy_propagation_visitor::visit_enter(ir_loop *ir)
  84 {
  85    (void)ir;
  86    return visit_continue_with_parent;
  87 }
  88
  89 ir_visitor_status
  90 ir_copy_propagation_visitor::visit_enter(ir_function_signature *ir)
  91 {
  92    (void)ir;
  93    return visit_continue_with_parent;
  94 }
  95
  96 ir_visitor_status
  97 ir_copy_propagation_visitor::visit_enter(ir_assignment *ir)
  98 {
  99    (void) ir;
 100    this->in_lhs = true;
 101    return visit_continue;
 102 }
 103
 104 ir_visitor_status
 105 ir_copy_propagation_visitor::visit_enter(ir_function *ir)
 106 {
 107    (void) ir;
 108    return visit_continue_with_parent;
 109 }
 110
 111 /**
 112  * Replaces dereferences of ACP RHS variables with ACP LHS variables.
 113  *
 114  * This is where the actual copy propagation occurs.  Note that the
 115  * rewriting of ir_dereference means that the ir_dereference instance
 116  * must not be shared by multiple IR operations!
 117  */
 118 ir_visitor_status
 119 ir_copy_propagation_visitor::visit(ir_dereference_variable *ir)
 120 {
 121    /* Ignores the LHS.  Don't want to rewrite the LHS to point at some
 122     * other storage!
 123     */
 124    if (this->in_lhs) {
 125       this->in_lhs = false;
 126       return visit_continue;
 127    }
 128
 129    ir_variable *var = ir->variable_referenced();
 130
 131    foreach_iter(exec_list_iterator, iter, *this->acp) {
 132       acp_entry *entry = (acp_entry *)iter.get();
 133
 134       if (var == entry->lhs) {
 135          ir->var = entry->rhs;
 136          this->progress = true;
 137          break;
 138       }
 139    }
 140
 141    return visit_continue;
 142 }
 143
 144
 145 ir_visitor_status
 146 ir_copy_propagation_visitor::visit_enter(ir_call *ir)
 147 {
 148    (void)ir;
 149
 150    /* Note, if we were to do copy propagation to parameters of calls, we'd
 151     * have to be careful about out params.
 152     */
 153    return visit_continue_with_parent;
 154 }
 155
 156
 157 ir_visitor_status
 158 ir_copy_propagation_visitor::visit_enter(ir_if *ir)
 159 {
 160    ir->condition->accept(this);
 161
 162    /* Do not traverse into the body of the if-statement since that is a
 163     * different basic block.
 164     */
 165    return visit_continue_with_parent;
 166 }
 167
 168 static bool
 169 propagate_copies(ir_instruction *ir, exec_list *acp)
 170 {
 171    ir_copy_propagation_visitor v(acp);
 172
 173    ir->accept(&v);
 174
 175    return v.progress;
 176 }
 177
 178 static void
 179 kill_invalidated_copies(ir_assignment *ir, exec_list *acp)
 180 {
 181    ir_variable *var = ir->lhs->variable_referenced();
 182    assert(var != NULL);
 183
 184    foreach_iter(exec_list_iterator, iter, *acp) {
 185       acp_entry *entry = (acp_entry *)iter.get();
 186
 187       if (entry->lhs == var || entry->rhs == var) {
 188          entry->remove();
 189       }
 190    }
 191 }
 192
 193 /**
 194  * Adds an entry to the available copy list if it's a plain assignment
 195  * of a variable to a variable.
 196  */
 197 static void
 198 add_copy(void *ctx, ir_assignment *ir, exec_list *acp)
 199 {
 200    acp_entry *entry;
 201
 202    if (ir->condition) {
 203       ir_constant *condition = ir->condition->as_constant();
 204       if (!condition || !condition->value.b[0])
 205          return;
 206    }
 207
 208    ir_variable *lhs_var = ir->lhs->whole_variable_referenced();
 209    ir_variable *rhs_var = ir->rhs->whole_variable_referenced();
 210
 211    if ((lhs_var != NULL) && (rhs_var != NULL)) {
 212       entry = new(ctx) acp_entry(lhs_var, rhs_var);
 213       acp->push_tail(entry);
 214    }
 215 }
 216
 217 static void
 218 copy_propagation_basic_block(ir_instruction *first,
 219                              ir_instruction *last,
 220                              void *data)
 221 {
 222    ir_instruction *ir;
 223    /* List of avaialble_copy */
 224    exec_list acp;
 225    bool *out_progress = (bool *)data;
 226    bool progress = false;
 227
 228    void *ctx = talloc_new(NULL);
 229    for (ir = first;; ir = (ir_instruction *)ir->next) {
 230       ir_assignment *ir_assign = ir->as_assignment();
 231
 232       progress = propagate_copies(ir, &acp) || progress;
 233
 234       if (ir_assign) {
 235          kill_invalidated_copies(ir_assign, &acp);
 236
 237          add_copy(ctx, ir_assign, &acp);
 238       }
 239       if (ir == last)
 240          break;
 241    }
 242    *out_progress = progress;
 243    talloc_free(ctx);
 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 }