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