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    using ir_hierarchical_visitor::visit;
  53    using ir_hierarchical_visitor::visit_enter;
  54
  55    virtual ir_visitor_status visit_enter(ir_dereference_variable *);
  56    virtual ir_visitor_status visit(ir_variable *);
  57    virtual ir_visitor_status visit_enter(ir_assignment *);
  58    virtual ir_visitor_status visit_enter(ir_call *);
  59
  60    struct hash_table *ht;
  61 };
  62
  63 } /* unnamed namespace */
  64
  65 static struct assignment_entry *
  66 get_assignment_entry(ir_variable *var, struct hash_table *ht)
  67 {
  68    struct hash_entry *hte = _mesa_hash_table_search(ht, var);
  69    struct assignment_entry *entry;
  70
  71    if (hte) {
  72       entry = (struct assignment_entry *) hte->data;
  73    } else {
  74       entry = (struct assignment_entry *) calloc(1, sizeof(*entry));
  75       entry->var = var;
  76       _mesa_hash_table_insert(ht, var, entry);
  77    }
  78
  79    return entry;
  80 }
  81
  82 ir_visitor_status
  83 ir_constant_variable_visitor::visit(ir_variable *ir)
  84 {
  85    struct assignment_entry *entry = get_assignment_entry(ir, this->ht);
  86    entry->our_scope = true;
  87    return visit_continue;
  88 }
  89
  90 /* Skip derefs of variables so that we can detect declarations. */
  91 ir_visitor_status
  92 ir_constant_variable_visitor::visit_enter(ir_dereference_variable *ir)
  93 {
  94    (void)ir;
  95    return visit_continue_with_parent;
  96 }
  97
  98 ir_visitor_status
  99 ir_constant_variable_visitor::visit_enter(ir_assignment *ir)
 100 {
 101    ir_constant *constval;
 102    struct assignment_entry *entry;
 103
 104    entry = get_assignment_entry(ir->lhs->variable_referenced(), this->ht);
 105    assert(entry);
 106    entry->assignment_count++;
 107
 108    /* If there's more than one assignment, don't bother - we won't do anything
 109     * with this variable anyway, and continuing just wastes memory cloning
 110     * constant expressions.
 111     */
 112    if (entry->assignment_count > 1)
 113       return visit_continue;
 114
 115    /* If it's already constant, don't do the work. */
 116    if (entry->var->constant_value)
 117       return visit_continue;
 118
 119    /* OK, now find if we actually have all the right conditions for
 120     * this to be a constant value assigned to the var.
 121     */
 122    if (ir->condition)
 123       return visit_continue;
 124
 125    ir_variable *var = ir->whole_variable_written();
 126    if (!var)
 127       return visit_continue;
 128
 129    /* Ignore buffer variables, since the underlying storage is shared
 130     * and we can't be sure that this variable won't be written by another
 131     * thread.
 132     */
 133    if (var->data.mode == ir_var_shader_storage ||
 134        var->data.mode == ir_var_shader_shared)
 135       return visit_continue;
 136
 137    constval = ir->rhs->constant_expression_value(ralloc_parent(ir));
 138    if (!constval)
 139       return visit_continue;
 140
 141    /* Mark this entry as having a constant assignment (if the
 142     * assignment count doesn't go >1).  do_constant_variable will fix
 143     * up the variable with the constant value later.
 144     */
 145    entry->constval = constval;
 146
 147    return visit_continue;
 148 }
 149
 150 ir_visitor_status
 151 ir_constant_variable_visitor::visit_enter(ir_call *ir)
 152 {
 153    /* Mark any out parameters as assigned to */
 154    foreach_two_lists(formal_node, &ir->callee->parameters,
 155                      actual_node, &ir->actual_parameters) {
 156       ir_rvalue *param_rval = (ir_rvalue *) actual_node;
 157       ir_variable *param = (ir_variable *) formal_node;
 158
 159       if (param->data.mode == ir_var_function_out ||
 160           param->data.mode == ir_var_function_inout) {
 161          ir_variable *var = param_rval->variable_referenced();
 162          struct assignment_entry *entry;
 163
 164          assert(var);
 165          entry = get_assignment_entry(var, this->ht);
 166          entry->assignment_count++;
 167       }
 168
 169       /* We don't know if the variable passed to this function has been
 170        * assigned a value or if it is undefined, so for now we always assume
 171        * it has been assigned a value. Once functions have been inlined any
 172        * further potential optimisations will be taken care of.
 173        */
 174       struct assignment_entry *entry;
 175       entry = get_assignment_entry(param, this->ht);
 176       entry->assignment_count++;
 177    }
 178
 179    /* Mark the return storage as having been assigned to */
 180    if (ir->return_deref != NULL) {
 181       ir_variable *var = ir->return_deref->variable_referenced();
 182       struct assignment_entry *entry;
 183
 184       assert(var);
 185       entry = get_assignment_entry(var, this->ht);
 186       entry->assignment_count++;
 187    }
 188
 189    return visit_continue;
 190 }
 191
 192 /**
 193  * Does a copy propagation pass on the code present in the instruction stream.
 194  */
 195 bool
 196 do_constant_variable(exec_list *instructions)
 197 {
 198    bool progress = false;
 199    ir_constant_variable_visitor v;
 200
 201    v.ht = _mesa_pointer_hash_table_create(NULL);
 202    v.run(instructions);
 203
 204    hash_table_foreach(v.ht, hte) {
 205       struct assignment_entry *entry = (struct assignment_entry *) hte->data;
 206
 207       if (entry->assignment_count == 1 && entry->constval && entry->our_scope) {
 208          entry->var->constant_value = entry->constval;
 209          progress = true;
 210       }
 211       hte->data = NULL;
 212       free(entry);
 213    }
 214    _mesa_hash_table_destroy(v.ht, NULL);
 215
 216    return progress;
 217 }
 218
 219 bool
 220 do_constant_variable_unlinked(exec_list *instructions)
 221 {
 222    bool progress = false;
 223
 224    foreach_in_list(ir_instruction, ir, instructions) {
 225       ir_function *f = ir->as_function();
 226       if (f) {
 227          foreach_in_list(ir_function_signature, sig, &f->signatures) {
 228             if (do_constant_variable(&sig->body))
 229                progress = true;
 230          }
 231       }
 232    }
 233
 234    return progress;
 235 }