src/compiler/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 "compiler/glsl_types.h"
  39 #include "util/hash_table.h"
  40
  41 namespace {
  42
  43 struct assignment_entry {
  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    struct hash_table *ht;
  58 };
  59
  60 } /* unnamed namespace */
  61
  62 static struct assignment_entry *
  63 get_assignment_entry(ir_variable *var, struct hash_table *ht)
  64 {
  65    struct hash_entry *hte = _mesa_hash_table_search(ht, var);
  66    struct assignment_entry *entry;
  67
  68    if (hte) {
  69       entry = (struct assignment_entry *) hte->data;
  70    } else {
  71       entry = (struct assignment_entry *) calloc(1, sizeof(*entry));
  72       entry->var = var;
  73       _mesa_hash_table_insert(ht, var, entry);
  74    }
  75
  76    return entry;
  77 }
  78
  79 ir_visitor_status
  80 ir_constant_variable_visitor::visit(ir_variable *ir)
  81 {
  82    struct assignment_entry *entry = get_assignment_entry(ir, this->ht);
  83    entry->our_scope = true;
  84    return visit_continue;
  85 }
  86
  87 /* Skip derefs of variables so that we can detect declarations. */
  88 ir_visitor_status
  89 ir_constant_variable_visitor::visit_enter(ir_dereference_variable *ir)
  90 {
  91    (void)ir;
  92    return visit_continue_with_parent;
  93 }
  94
  95 ir_visitor_status
  96 ir_constant_variable_visitor::visit_enter(ir_assignment *ir)
  97 {
  98    ir_constant *constval;
  99    struct assignment_entry *entry;
 100
 101    entry = get_assignment_entry(ir->lhs->variable_referenced(), this->ht);
 102    assert(entry);
 103    entry->assignment_count++;
 104
 105    /* If there's more than one assignment, don't bother - we won't do anything
 106     * with this variable anyway, and continuing just wastes memory cloning
 107     * constant expressions.
 108     */
 109    if (entry->assignment_count > 1)
 110       return visit_continue;
 111
 112    /* If it's already constant, don't do the work. */
 113    if (entry->var->constant_value)
 114       return visit_continue;
 115
 116    /* OK, now find if we actually have all the right conditions for
 117     * this to be a constant value assigned to the var.
 118     */
 119    if (ir->condition)
 120       return visit_continue;
 121
 122    ir_variable *var = ir->whole_variable_written();
 123    if (!var)
 124       return visit_continue;
 125
 126    /* Ignore buffer variables, since the underlying storage is shared
 127     * and we can't be sure that this variable won't be written by another
 128     * thread.
 129     */
 130    if (var->data.mode == ir_var_shader_storage ||
 131        var->data.mode == ir_var_shader_shared)
 132       return visit_continue;
 133
 134    constval = ir->rhs->constant_expression_value();
 135    if (!constval)
 136       return visit_continue;
 137
 138    /* Mark this entry as having a constant assignment (if the
 139     * assignment count doesn't go >1).  do_constant_variable will fix
 140     * up the variable with the constant value later.
 141     */
 142    entry->constval = constval;
 143
 144    return visit_continue;
 145 }
 146
 147 ir_visitor_status
 148 ir_constant_variable_visitor::visit_enter(ir_call *ir)
 149 {
 150    /* Mark any out parameters as assigned to */
 151    foreach_two_lists(formal_node, &ir->callee->parameters,
 152                      actual_node, &ir->actual_parameters) {
 153       ir_rvalue *param_rval = (ir_rvalue *) actual_node;
 154       ir_variable *param = (ir_variable *) formal_node;
 155
 156       if (param->data.mode == ir_var_function_out ||
 157           param->data.mode == ir_var_function_inout) {
 158          ir_variable *var = param_rval->variable_referenced();
 159          struct assignment_entry *entry;
 160
 161          assert(var);
 162          entry = get_assignment_entry(var, this->ht);
 163          entry->assignment_count++;
 164       }
 165    }
 166
 167    /* Mark the return storage as having been assigned to */
 168    if (ir->return_deref != NULL) {
 169       ir_variable *var = ir->return_deref->variable_referenced();
 170       struct assignment_entry *entry;
 171
 172       assert(var);
 173       entry = get_assignment_entry(var, this->ht);
 174       entry->assignment_count++;
 175    }
 176
 177    return visit_continue;
 178 }
 179
 180 /**
 181  * Does a copy propagation pass on the code present in the instruction stream.
 182  */
 183 bool
 184 do_constant_variable(exec_list *instructions)
 185 {
 186    bool progress = false;
 187    ir_constant_variable_visitor v;
 188
 189    v.ht = _mesa_hash_table_create(NULL, _mesa_hash_pointer,
 190                                   _mesa_key_pointer_equal);
 191    v.run(instructions);
 192
 193    struct hash_entry *hte;
 194    hash_table_foreach(v.ht, hte) {
 195       struct assignment_entry *entry = (struct assignment_entry *) hte->data;
 196
 197       if (entry->assignment_count == 1 && entry->constval && entry->our_scope) {
 198          entry->var->constant_value = entry->constval;
 199          progress = true;
 200       }
 201       hte->data = NULL;
 202       free(entry);
 203    }
 204    _mesa_hash_table_destroy(v.ht, NULL);
 205
 206    return progress;
 207 }
 208
 209 bool
 210 do_constant_variable_unlinked(exec_list *instructions)
 211 {
 212    bool progress = false;
 213
 214    foreach_in_list(ir_instruction, ir, instructions) {
 215       ir_function *f = ir->as_function();
 216       if (f) {
 217          foreach_in_list(ir_function_signature, sig, &f->signatures) {
 218             if (do_constant_variable(&sig->body))
 219                progress = true;
 220          }
 221       }
 222    }
 223
 224    return progress;
 225 }