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_dead_code.cpp
26 *
27 * Eliminates dead assignments and variable declarations from the code.
28 */
29
30 #include "ir.h"
31 #include "ir_visitor.h"
32 #include "ir_variable_refcount.h"
33 #include "glsl_types.h"
34
35 static bool debug = false;
36
37 /**
38 * Do a dead code pass over instructions and everything that instructions
39 * references.
40 *
41 * Note that this will remove assignments to globals, so it is not suitable
42 * for usage on an unlinked instruction stream.
43 */
44 bool
do_dead_code(exec_list * instructions)45 do_dead_code(exec_list *instructions)
46 {
47 ir_variable_refcount_visitor v;
48 bool progress = false;
49
50 v.run(instructions);
51
52 foreach_iter(exec_list_iterator, iter, v.variable_list) {
53 variable_entry *entry = (variable_entry *)iter.get();
54
55 /* Since each assignment is a reference, the refereneced count must be
56 * greater than or equal to the assignment count. If they are equal,
57 * then all of the references are assignments, and the variable is
58 * dead.
59 *
60 * Note that if the variable is neither assigned nor referenced, both
61 * counts will be zero and will be caught by the equality test.
62 */
63 assert(entry->referenced_count >= entry->assigned_count);
64
65 if (debug) {
66 printf("%s@%p: %d refs, %d assigns, %sdeclared in our scope\n",
67 entry->var->name, (void *) entry->var,
68 entry->referenced_count, entry->assigned_count,
69 entry->declaration ? "" : "not ");
70 }
71
72 if ((entry->referenced_count > entry->assigned_count)
73 || !entry->declaration)
74 continue;
75
76 if (entry->assign) {
77 /* Remove a single dead assignment to the variable we found.
78 * Don't do so if it's a shader output, though.
79 */
80 if (entry->var->mode != ir_var_out &&
81 entry->var->mode != ir_var_inout &&
82 !ir_has_call(entry->assign)) {
83 entry->assign->remove();
84 progress = true;
85
86 if (debug) {
87 printf("Removed assignment to %s@%p\n",
88 entry->var->name, (void *) entry->var);
89 }
90 }
91 } else {
92 /* If there are no assignments or references to the variable left,
93 * then we can remove its declaration.
94 */
95
96 /* uniform initializers are precious, and could get used by another
97 * stage.
98 */
99 if (entry->var->mode == ir_var_uniform &&
100 entry->var->constant_value)
101 continue;
102
103 entry->var->remove();
104 progress = true;
105
106 if (debug) {
107 printf("Removed declaration of %s@%p\n",
108 entry->var->name, (void *) entry->var);
109 }
110 }
111 }
112
113 return progress;
114 }
115
116 /**
117 * Does a dead code pass on the functions present in the instruction stream.
118 *
119 * This is suitable for use while the program is not linked, as it will
120 * ignore variable declarations (and the assignments to them) for variables
121 * with global scope.
122 */
123 bool
do_dead_code_unlinked(exec_list * instructions)124 do_dead_code_unlinked(exec_list *instructions)
125 {
126 bool progress = false;
127
128 foreach_iter(exec_list_iterator, iter, *instructions) {
129 ir_instruction *ir = (ir_instruction *)iter.get();
130 ir_function *f = ir->as_function();
131 if (f) {
132 foreach_iter(exec_list_iterator, sigiter, *f) {
133 ir_function_signature *sig =
134 (ir_function_signature *) sigiter.get();
135 if (do_dead_code(&sig->body))
136 progress = true;
137 }
138 }
139 }
140
141 return progress;
142 }
143