ir_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"),
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   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
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  20  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
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  22  */
  23
  24 /**
  25  * \file ir_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 <stdio.h>
  36 #include <stdlib.h>
  37 #include "ir.h"
  38 #include "ir_print_visitor.h"
  39 #include "ir_visitor.h"
  40 #include "ir_optimization.h"
  41 #include "glsl_types.h"
  42
  43 struct assignment_entry {
  44    exec_node link;
  45    int assignment_count;
  46    ir_variable *var;
  47    ir_constant *constval;
  48 };
  49
  50 class ir_constant_variable_visitor : public ir_hierarchical_visitor {
  51 public:
  52    virtual ir_visitor_status visit_enter(ir_assignment *);
  53
  54    exec_list list;
  55 };
  56
  57 static struct assignment_entry *
  58 get_assignment_entry(ir_variable *var, exec_list *list)
  59 {
  60    struct assignment_entry *entry;
  61
  62    foreach_list_typed(struct assignment_entry, entry, link, list) {
  63       if (entry->var == var)
  64          return entry;
  65    }
  66
  67    entry = (struct assignment_entry *)calloc(1, sizeof(*entry));
  68    entry->var = var;
  69    list->push_head(&entry->link);
  70    return entry;
  71 }
  72
  73 ir_visitor_status
  74 ir_constant_variable_visitor::visit_enter(ir_assignment *ir)
  75 {
  76    ir_constant *constval;
  77    struct assignment_entry *entry;
  78
  79    entry = get_assignment_entry(ir->lhs->variable_referenced(), &this->list);
  80    assert(entry);
  81    entry->assignment_count++;
  82
  83    /* If it's already constant, don't do the work. */
  84    if (entry->var->constant_value)
  85       return visit_continue;
  86
  87    /* OK, now find if we actually have all the right conditions for
  88     * this to be a constant value assigned to the var.
  89     */
  90    if (ir->condition) {
  91       constval = ir->condition->constant_expression_value();
  92       if (!constval || !constval->value.b[0])
  93          return visit_continue;
  94    }
  95
  96    ir_variable *var = ir->lhs->whole_variable_referenced();
  97    if (!var)
  98       return visit_continue;
  99
 100    constval = ir->rhs->constant_expression_value();
 101    if (!constval)
 102       return visit_continue;
 103
 104    /* Mark this entry as having a constant assignment (if the
 105     * assignment count doesn't go >1).  do_constant_variable will fix
 106     * up the variable with the constant value later.
 107     */
 108    entry->constval = constval;
 109
 110    return visit_continue;
 111 }
 112
 113 /**
 114  * Does a copy propagation pass on the code present in the instruction stream.
 115  */
 116 bool
 117 do_constant_variable(exec_list *instructions)
 118 {
 119    bool progress = false;
 120    ir_constant_variable_visitor v;
 121
 122    v.run(instructions);
 123
 124    while (!v.list.is_empty()) {
 125
 126       struct assignment_entry *entry;
 127       entry = exec_node_data(struct assignment_entry, v.list.head, link);
 128
 129       if (entry->assignment_count == 1 && entry->constval) {
 130          entry->var->constant_value = entry->constval;
 131          progress = true;
 132       }
 133       entry->link.remove();
 134       free(entry);
 135    }
 136
 137    return progress;
 138 }
 139
 140 bool
 141 do_constant_variable_unlinked(exec_list *instructions)
 142 {
 143    bool progress = false;
 144
 145    foreach_iter(exec_list_iterator, iter, *instructions) {
 146       ir_instruction *ir = (ir_instruction *)iter.get();
 147       ir_function *f = ir->as_function();
 148       if (f) {
 149          foreach_iter(exec_list_iterator, sigiter, *f) {
 150             ir_function_signature *sig =
 151                (ir_function_signature *) sigiter.get();
 152             if (do_constant_variable(&sig->body))
 153                progress = true;
 154          }
 155       }
 156    }
 157
 158    return progress;
 159 }