1 /*
2 * Copyright © 2016 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 propagate_invariance.cpp
26 * Propagate the "invariant" and "precise" qualifiers to variables used to
27 * compute invariant or precise values.
28 *
29 * The GLSL spec (depending on what version you read) says, among the
30 * conditions for getting bit-for-bit the same values on an invariant output:
31 *
32 * "All operations in the consuming expressions and any intermediate
33 * expressions must be the same, with the same order of operands and same
34 * associativity, to give the same order of evaluation."
35 *
36 * This effectively means that if a variable is used to compute an invariant
37 * value then that variable becomes invariant. The same should apply to the
38 * "precise" qualifier.
39 */
40
41 #include "ir.h"
42 #include "ir_visitor.h"
43 #include "ir_rvalue_visitor.h"
44 #include "ir_optimization.h"
45 #include "compiler/glsl_types.h"
46
47 namespace {
48
49 class ir_invariance_propagation_visitor : public ir_hierarchical_visitor {
50 public:
ir_invariance_propagation_visitor()51 ir_invariance_propagation_visitor()
52 {
53 this->progress = false;
54 this->dst_var = NULL;
55 }
56
~ir_invariance_propagation_visitor()57 virtual ~ir_invariance_propagation_visitor()
58 {
59 /* empty */
60 }
61
62 virtual ir_visitor_status visit_enter(ir_assignment *ir);
63 virtual ir_visitor_status visit_leave(ir_assignment *ir);
64 virtual ir_visitor_status visit(ir_dereference_variable *ir);
65
66 ir_variable *dst_var;
67 bool progress;
68 };
69
70 } /* unnamed namespace */
71
72 ir_visitor_status
visit_enter(ir_assignment * ir)73 ir_invariance_propagation_visitor::visit_enter(ir_assignment *ir)
74 {
75 assert(this->dst_var == NULL);
76 ir_variable *var = ir->lhs->variable_referenced();
77 if (var->data.invariant || var->data.precise) {
78 this->dst_var = var;
79 return visit_continue;
80 } else {
81 return visit_continue_with_parent;
82 }
83 }
84
85 ir_visitor_status
visit_leave(ir_assignment *)86 ir_invariance_propagation_visitor::visit_leave(ir_assignment *)
87 {
88 this->dst_var = NULL;
89
90 return visit_continue;
91 }
92
93 ir_visitor_status
visit(ir_dereference_variable * ir)94 ir_invariance_propagation_visitor::visit(ir_dereference_variable *ir)
95 {
96 if (this->dst_var == NULL)
97 return visit_continue;
98
99 if (this->dst_var->data.invariant) {
100 if (!ir->var->data.invariant)
101 this->progress = true;
102
103 ir->var->data.invariant = true;
104 }
105
106 if (this->dst_var->data.precise) {
107 if (!ir->var->data.precise)
108 this->progress = true;
109
110 ir->var->data.precise = true;
111 }
112
113 return visit_continue;
114 }
115
116 bool
propagate_invariance(exec_list * instructions)117 propagate_invariance(exec_list *instructions)
118 {
119 ir_invariance_propagation_visitor visitor;
120 bool progress = false;
121
122 do {
123 visitor.progress = false;
124 visit_list_elements(&visitor, instructions);
125 progress = progress || visitor.progress;
126 } while (visitor.progress);
127
128 return progress;
129 }
130