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    ir_visitor_status s;
 100
 101    /* Inline the rest of ir_assignment::accept(ir_hv *v), wrapping the
 102     * LHS part with setting in_lhs so that we can avoid copy
 103     * propagating into the LHS.
 104     *
 105     * Note that this means we won't copy propagate into the derefs of
 106     * an array index.  Oh well.
 107     */
 108    this->in_lhs = true;
 109    s = ir->lhs->accept(this);
 110    this->in_lhs = false;
 111    if (s != visit_continue)
 112       return (s == visit_continue_with_parent) ? visit_continue : s;
 113
 114    s = ir->rhs->accept(this);
 115    if (s != visit_continue)
 116       return (s == visit_continue_with_parent) ? visit_continue : s;
 117
 118    if (ir->condition)
 119       s = ir->condition->accept(this);
 120
 121    return (s == visit_stop) ? s : visit_continue_with_parent;
 122 }
 123
 124 ir_visitor_status
 125 ir_copy_propagation_visitor::visit_enter(ir_function *ir)
 126 {
 127    (void) ir;
 128    return visit_continue_with_parent;
 129 }
 130
 131 /**
 132  * Replaces dereferences of ACP RHS variables with ACP LHS variables.
 133  *
 134  * This is where the actual copy propagation occurs.  Note that the
 135  * rewriting of ir_dereference means that the ir_dereference instance
 136  * must not be shared by multiple IR operations!
 137  */
 138 ir_visitor_status
 139 ir_copy_propagation_visitor::visit(ir_dereference_variable *ir)
 140 {
 141    /* Ignores the LHS.  Don't want to rewrite the LHS to point at some
 142     * other storage!
 143     */
 144    if (this->in_lhs) {
 145       return visit_continue;
 146    }
 147
 148    ir_variable *var = ir->variable_referenced();
 149
 150    foreach_iter(exec_list_iterator, iter, *this->acp) {
 151       acp_entry *entry = (acp_entry *)iter.get();
 152
 153       if (var == entry->lhs) {
 154          ir->var = entry->rhs;
 155          this->progress = true;
 156          break;
 157       }
 158    }
 159
 160    return visit_continue;
 161 }
 162
 163
 164 ir_visitor_status
 165 ir_copy_propagation_visitor::visit_enter(ir_call *ir)
 166 {
 167    (void)ir;
 168
 169    /* Note, if we were to do copy propagation to parameters of calls, we'd
 170     * have to be careful about out params.
 171     */
 172    return visit_continue_with_parent;
 173 }
 174
 175
 176 ir_visitor_status
 177 ir_copy_propagation_visitor::visit_enter(ir_if *ir)
 178 {
 179    ir->condition->accept(this);
 180
 181    /* Do not traverse into the body of the if-statement since that is a
 182     * different basic block.
 183     */
 184    return visit_continue_with_parent;
 185 }
 186
 187 static bool
 188 propagate_copies(ir_instruction *ir, exec_list *acp)
 189 {
 190    ir_copy_propagation_visitor v(acp);
 191
 192    ir->accept(&v);
 193
 194    return v.progress;
 195 }
 196
 197 static void
 198 kill_invalidated_copies(ir_assignment *ir, exec_list *acp)
 199 {
 200    ir_variable *var = ir->lhs->variable_referenced();
 201    assert(var != NULL);
 202
 203    foreach_iter(exec_list_iterator, iter, *acp) {
 204       acp_entry *entry = (acp_entry *)iter.get();
 205
 206       if (entry->lhs == var || entry->rhs == var) {
 207          entry->remove();
 208       }
 209    }
 210 }
 211
 212 /**
 213  * Adds an entry to the available copy list if it's a plain assignment
 214  * of a variable to a variable.
 215  */
 216 static bool
 217 add_copy(void *ctx, ir_assignment *ir, exec_list *acp)
 218 {
 219    acp_entry *entry;
 220
 221    if (ir->condition) {
 222       ir_constant *condition = ir->condition->as_constant();
 223       if (!condition || !condition->value.b[0])
 224          return false;
 225    }
 226
 227    ir_variable *lhs_var = ir->whole_variable_written();
 228    ir_variable *rhs_var = ir->rhs->whole_variable_referenced();
 229
 230    if ((lhs_var != NULL) && (rhs_var != NULL)) {
 231       if (lhs_var == rhs_var) {
 232          /* This is a dumb assignment, but we've conveniently noticed
 233           * it here.  Removing it now would mess up the loop iteration
 234           * calling us.  Just flag it to not execute, and someone else
 235           * will clean up the mess.
 236           */
 237          ir->condition = new(talloc_parent(ir)) ir_constant(false);
 238          return true;
 239       } else {
 240          entry = new(ctx) acp_entry(lhs_var, rhs_var);
 241          acp->push_tail(entry);
 242       }
 243    }
 244
 245    return false;
 246 }
 247
 248 static void
 249 copy_propagation_basic_block(ir_instruction *first,
 250                              ir_instruction *last,
 251                              void *data)
 252 {
 253    ir_instruction *ir;
 254    /* List of avaialble_copy */
 255    exec_list acp;
 256    bool *out_progress = (bool *)data;
 257    bool progress = false;
 258
 259    void *ctx = talloc_new(NULL);
 260    for (ir = first;; ir = (ir_instruction *)ir->next) {
 261       ir_assignment *ir_assign = ir->as_assignment();
 262
 263       progress = propagate_copies(ir, &acp) || progress;
 264
 265       if (ir_assign) {
 266          kill_invalidated_copies(ir_assign, &acp);
 267
 268          progress = add_copy(ctx, ir_assign, &acp) || progress;
 269       }
 270       if (ir == last)
 271          break;
 272    }
 273    *out_progress = progress;
 274    talloc_free(ctx);
 275 }
 276
 277 /**
 278  * Does a copy propagation pass on the code present in the instruction stream.
 279  */
 280 bool
 281 do_copy_propagation(exec_list *instructions)
 282 {
 283    bool progress = false;
 284
 285    call_for_basic_blocks(instructions, copy_propagation_basic_block, &progress);
 286
 287    return progress;
 288 }