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 using std::calloc;
  41 using std::free;
  42
  43 struct assignment_entry {
  44    exec_node link;
  45    int assignment_count;
  46    ir_variable *var;
  47    ir_constant *constval;
  48    bool our_scope;
  49 };
  50
  51 class ir_constant_variable_visitor : public ir_hierarchical_visitor {
  52 public:
  53    virtual ir_visitor_status visit_enter(ir_dereference_variable *);
  54    virtual ir_visitor_status visit(ir_variable *);
  55    virtual ir_visitor_status visit_enter(ir_assignment *);
  56    virtual ir_visitor_status visit_enter(ir_call *);
  57
  58    exec_list list;
  59 };
  60
  61 static struct assignment_entry *
  62 get_assignment_entry(ir_variable *var, exec_list *list)
  63 {
  64    struct assignment_entry *entry;
  65
  66    foreach_list_typed(struct assignment_entry, entry, link, list) {
  67       if (entry->var == var)
  68          return entry;
  69    }
  70
  71    entry = (struct assignment_entry *)calloc(1, sizeof(*entry));
  72    entry->var = var;
  73    list->push_head(&entry->link);
  74    return entry;
  75 }
  76
  77 ir_visitor_status
  78 ir_constant_variable_visitor::visit(ir_variable *ir)
  79 {
  80    struct assignment_entry *entry = get_assignment_entry(ir, &this->list);
  81    entry->our_scope = true;
  82    return visit_continue;
  83 }
  84
  85 /* Skip derefs of variables so that we can detect declarations. */
  86 ir_visitor_status
  87 ir_constant_variable_visitor::visit_enter(ir_dereference_variable *ir)
  88 {
  89    (void)ir;
  90    return visit_continue_with_parent;
  91 }
  92
  93 ir_visitor_status
  94 ir_constant_variable_visitor::visit_enter(ir_assignment *ir)
  95 {
  96    ir_constant *constval;
  97    struct assignment_entry *entry;
  98
  99    entry = get_assignment_entry(ir->lhs->variable_referenced(), &this->list);
 100    assert(entry);
 101    entry->assignment_count++;
 102
 103    /* If it's already constant, don't do the work. */
 104    if (entry->var->constant_value)
 105       return visit_continue;
 106
 107    /* OK, now find if we actually have all the right conditions for
 108     * this to be a constant value assigned to the var.
 109     */
 110    if (ir->condition) {
 111       constval = ir->condition->constant_expression_value();
 112       if (!constval || !constval->value.b[0])
 113          return visit_continue;
 114    }
 115
 116    ir_variable *var = ir->whole_variable_written();
 117    if (!var)
 118       return visit_continue;
 119
 120    constval = ir->rhs->constant_expression_value();
 121    if (!constval)
 122       return visit_continue;
 123
 124    /* Mark this entry as having a constant assignment (if the
 125     * assignment count doesn't go >1).  do_constant_variable will fix
 126     * up the variable with the constant value later.
 127     */
 128    entry->constval = constval;
 129
 130    return visit_continue;
 131 }
 132
 133 ir_visitor_status
 134 ir_constant_variable_visitor::visit_enter(ir_call *ir)
 135 {
 136    exec_list_iterator sig_iter = ir->get_callee()->parameters.iterator();
 137    foreach_iter(exec_list_iterator, iter, *ir) {
 138       ir_rvalue *param_rval = (ir_rvalue *)iter.get();
 139       ir_variable *param = (ir_variable *)sig_iter.get();
 140
 141       if (param->mode == ir_var_out ||
 142           param->mode == ir_var_inout) {
 143          ir_variable *var = param_rval->variable_referenced();
 144          struct assignment_entry *entry;
 145
 146          assert(var);
 147          entry = get_assignment_entry(var, &this->list);
 148          entry->assignment_count++;
 149       }
 150       sig_iter.next();
 151    }
 152    return visit_continue;
 153 }
 154
 155 /**
 156  * Does a copy propagation pass on the code present in the instruction stream.
 157  */
 158 bool
 159 do_constant_variable(exec_list *instructions)
 160 {
 161    bool progress = false;
 162    ir_constant_variable_visitor v;
 163
 164    v.run(instructions);
 165
 166    while (!v.list.is_empty()) {
 167
 168       struct assignment_entry *entry;
 169       entry = exec_node_data(struct assignment_entry, v.list.head, link);
 170
 171       if (entry->assignment_count == 1 && entry->constval && entry->our_scope) {
 172          entry->var->constant_value = entry->constval;
 173          progress = true;
 174       }
 175       entry->link.remove();
 176       free(entry);
 177    }
 178
 179    return progress;
 180 }
 181
 182 bool
 183 do_constant_variable_unlinked(exec_list *instructions)
 184 {
 185    bool progress = false;
 186
 187    foreach_iter(exec_list_iterator, iter, *instructions) {
 188       ir_instruction *ir = (ir_instruction *)iter.get();
 189       ir_function *f = ir->as_function();
 190       if (f) {
 191          foreach_iter(exec_list_iterator, sigiter, *f) {
 192             ir_function_signature *sig =
 193                (ir_function_signature *) sigiter.get();
 194             if (do_constant_variable(&sig->body))
 195                progress = true;
 196          }
 197       }
 198    }
 199
 200    return progress;
 201 }