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,bool uniform_locations_assigned)45 do_dead_code(exec_list *instructions, bool uniform_locations_assigned)
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 ir_variable_refcount_entry *entry = (ir_variable_refcount_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 entry->assign->remove();
83 progress = true;
84
85 if (debug) {
86 printf("Removed assignment to %s@%p\n",
87 entry->var->name, (void *) entry->var);
88 }
89 }
90 } else {
91 /* If there are no assignments or references to the variable left,
92 * then we can remove its declaration.
93 */
94
95 /* uniform initializers are precious, and could get used by another
96 * stage. Also, once uniform locations have been assigned, the
97 * declaration cannot be deleted.
98 *
99 * Also, GL_ARB_uniform_buffer_object says that std140
100 * uniforms will not be eliminated. Since we always do
101 * std140, just don't eliminate uniforms in UBOs.
102 */
103 if (entry->var->mode == ir_var_uniform &&
104 (uniform_locations_assigned ||
105 entry->var->constant_value ||
106 entry->var->uniform_block != -1))
107 continue;
108
109 entry->var->remove();
110 progress = true;
111
112 if (debug) {
113 printf("Removed declaration of %s@%p\n",
114 entry->var->name, (void *) entry->var);
115 }
116 }
117 }
118
119 return progress;
120 }
121
122 /**
123 * Does a dead code pass on the functions present in the instruction stream.
124 *
125 * This is suitable for use while the program is not linked, as it will
126 * ignore variable declarations (and the assignments to them) for variables
127 * with global scope.
128 */
129 bool
do_dead_code_unlinked(exec_list * instructions)130 do_dead_code_unlinked(exec_list *instructions)
131 {
132 bool progress = false;
133
134 foreach_iter(exec_list_iterator, iter, *instructions) {
135 ir_instruction *ir = (ir_instruction *)iter.get();
136 ir_function *f = ir->as_function();
137 if (f) {
138 foreach_iter(exec_list_iterator, sigiter, *f) {
139 ir_function_signature *sig =
140 (ir_function_signature *) sigiter.get();
141 /* The setting of the uniform_locations_assigned flag here is
142 * irrelevent. If there is a uniform declaration encountered
143 * inside the body of the function, something has already gone
144 * terribly, terribly wrong.
145 */
146 if (do_dead_code(&sig->body, false))
147 progress = true;
148 }
149 }
150 }
151
152 return progress;
153 }
154