src/glsl/opt_constant_variable.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 opt_constant_variable.cpp
  26  *
  27  * Marks variables assigned a single constant value over the course
  28  * of the program as constant.
  29  *
  30  * The goal here is to trigger further constant folding and then dead
  31  * code elimination.  This is common with vector/matrix constructors
  32  * and calls to builtin functions.
  33  */
  34
  35 #include "ir.h"
  36 #include "ir_visitor.h"
  37 #include "ir_optimization.h"
  38 #include "glsl_types.h"
  39
  40 namespace {
  41
  42 struct assignment_entry {
  43    exec_node link;
  44    int assignment_count;
  45    ir_variable *var;
  46    ir_constant *constval;
  47    bool our_scope;
  48 };
  49
  50 class ir_constant_variable_visitor : public ir_hierarchical_visitor {
  51 public:
  52    virtual ir_visitor_status visit_enter(ir_dereference_variable *);
  53    virtual ir_visitor_status visit(ir_variable *);
  54    virtual ir_visitor_status visit_enter(ir_assignment *);
  55    virtual ir_visitor_status visit_enter(ir_call *);
  56
  57    exec_list list;
  58 };
  59
  60 } /* unnamed namespace */
  61
  62 static struct assignment_entry *
  63 get_assignment_entry(ir_variable *var, exec_list *list)
  64 {
  65    struct assignment_entry *entry;
  66
  67    foreach_list_typed(struct assignment_entry, entry, link, list) {
  68       if (entry->var == var)
  69          return entry;
  70    }
  71
  72    entry = (struct assignment_entry *)calloc(1, sizeof(*entry));
  73    entry->var = var;
  74    list->push_head(&entry->link);
  75    return entry;
  76 }
  77
  78 ir_visitor_status
  79 ir_constant_variable_visitor::visit(ir_variable *ir)
  80 {
  81    struct assignment_entry *entry = get_assignment_entry(ir, &this->list);
  82    entry->our_scope = true;
  83    return visit_continue;
  84 }
  85
  86 /* Skip derefs of variables so that we can detect declarations. */
  87 ir_visitor_status
  88 ir_constant_variable_visitor::visit_enter(ir_dereference_variable *ir)
  89 {
  90    (void)ir;
  91    return visit_continue_with_parent;
  92 }
  93
  94 ir_visitor_status
  95 ir_constant_variable_visitor::visit_enter(ir_assignment *ir)
  96 {
  97    ir_constant *constval;
  98    struct assignment_entry *entry;
  99
 100    entry = get_assignment_entry(ir->lhs->variable_referenced(), &this->list);
 101    assert(entry);
 102    entry->assignment_count++;
 103
 104    /* If it's already constant, don't do the work. */
 105    if (entry->var->constant_value)
 106       return visit_continue;
 107
 108    /* OK, now find if we actually have all the right conditions for
 109     * this to be a constant value assigned to the var.
 110     */
 111    if (ir->condition)
 112       return visit_continue;
 113
 114    ir_variable *var = ir->whole_variable_written();
 115    if (!var)
 116       return visit_continue;
 117
 118    constval = ir->rhs->constant_expression_value();
 119    if (!constval)
 120       return visit_continue;
 121
 122    /* Mark this entry as having a constant assignment (if the
 123     * assignment count doesn't go >1).  do_constant_variable will fix
 124     * up the variable with the constant value later.
 125     */
 126    entry->constval = constval;
 127
 128    return visit_continue;
 129 }
 130
 131 ir_visitor_status
 132 ir_constant_variable_visitor::visit_enter(ir_call *ir)
 133 {
 134    /* Mark any out parameters as assigned to */
 135    exec_list_iterator sig_iter = ir->callee->parameters.iterator();
 136    foreach_iter(exec_list_iterator, iter, *ir) {
 137       ir_rvalue *param_rval = (ir_rvalue *)iter.get();
 138       ir_variable *param = (ir_variable *)sig_iter.get();
 139
 140       if (param->mode == ir_var_function_out ||
 141           param->mode == ir_var_function_inout) {
 142          ir_variable *var = param_rval->variable_referenced();
 143          struct assignment_entry *entry;
 144
 145          assert(var);
 146          entry = get_assignment_entry(var, &this->list);
 147          entry->assignment_count++;
 148       }
 149       sig_iter.next();
 150    }
 151
 152    /* Mark the return storage as having been assigned to */
 153    if (ir->return_deref != NULL) {
 154       ir_variable *var = ir->return_deref->variable_referenced();
 155       struct assignment_entry *entry;
 156
 157       assert(var);
 158       entry = get_assignment_entry(var, &this->list);
 159       entry->assignment_count++;
 160    }
 161
 162    return visit_continue;
 163 }
 164
 165 /**
 166  * Does a copy propagation pass on the code present in the instruction stream.
 167  */
 168 bool
 169 do_constant_variable(exec_list *instructions)
 170 {
 171    bool progress = false;
 172    ir_constant_variable_visitor v;
 173
 174    v.run(instructions);
 175
 176    while (!v.list.is_empty()) {
 177
 178       struct assignment_entry *entry;
 179       entry = exec_node_data(struct assignment_entry, v.list.head, link);
 180
 181       if (entry->assignment_count == 1 && entry->constval && entry->our_scope) {
 182          entry->var->constant_value = entry->constval;
 183          progress = true;
 184       }
 185       entry->link.remove();
 186       free(entry);
 187    }
 188
 189    return progress;
 190 }
 191
 192 bool
 193 do_constant_variable_unlinked(exec_list *instructions)
 194 {
 195    bool progress = false;
 196
 197    foreach_iter(exec_list_iterator, iter, *instructions) {
 198       ir_instruction *ir = (ir_instruction *)iter.get();
 199       ir_function *f = ir->as_function();
 200       if (f) {
 201          foreach_iter(exec_list_iterator, sigiter, *f) {
 202             ir_function_signature *sig =
 203                (ir_function_signature *) sigiter.get();
 204             if (do_constant_variable(&sig->body))
 205                progress = true;
 206          }
 207       }
 208    }
 209
 210    return progress;
 211 }