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 "compiler/glsl_types.h"
34 #include "util/hash_table.h"
35
36 static bool debug = false;
37
38 /**
39 * Do a dead code pass over instructions and everything that instructions
40 * references.
41 *
42 * Note that this will remove assignments to globals, so it is not suitable
43 * for usage on an unlinked instruction stream.
44 */
45 bool
do_dead_code(exec_list * instructions)46 do_dead_code(exec_list *instructions)
47 {
48 ir_variable_refcount_visitor v;
49 bool progress = false;
50
51 v.run(instructions);
52
53 hash_table_foreach(v.ht, e) {
54 ir_variable_refcount_entry *entry = (ir_variable_refcount_entry *)e->data;
55
56 /* Since each assignment is a reference, the refereneced count must be
57 * greater than or equal to the assignment count. If they are equal,
58 * then all of the references are assignments, and the variable is
59 * dead.
60 *
61 * Note that if the variable is neither assigned nor referenced, both
62 * counts will be zero and will be caught by the equality test.
63 */
64 assert(entry->referenced_count >= entry->assigned_count);
65
66 if (debug) {
67 printf("%s@%p: %d refs, %d assigns, %sdeclared in our scope\n",
68 entry->var->name, (void *) entry->var,
69 entry->referenced_count, entry->assigned_count,
70 entry->declaration ? "" : "not ");
71 }
72
73 if ((entry->referenced_count > entry->assigned_count)
74 || !entry->declaration)
75 continue;
76
77 /* Section 7.4.1 (Shader Interface Matching) of the OpenGL 4.5
78 * (Core Profile) spec says:
79 *
80 * "With separable program objects, interfaces between shader
81 * stages may involve the outputs from one program object and the
82 * inputs from a second program object. For such interfaces, it is
83 * not possible to detect mismatches at link time, because the
84 * programs are linked separately. When each such program is
85 * linked, all inputs or outputs interfacing with another program
86 * stage are treated as active."
87 */
88 if (entry->var->data.always_active_io)
89 continue;
90
91 if (!entry->assign_list.is_empty()) {
92 /* Remove all the dead assignments to the variable we found.
93 * Don't do so if it's a shader or function output, though.
94 */
95 if (entry->var->data.mode != ir_var_function_out &&
96 entry->var->data.mode != ir_var_function_inout &&
97 entry->var->data.mode != ir_var_shader_out &&
98 entry->var->data.mode != ir_var_shader_storage) {
99
100 while (!entry->assign_list.is_empty()) {
101 struct assignment_entry *assignment_entry =
102 exec_node_data(struct assignment_entry,
103 entry->assign_list.get_head_raw(), link);
104
105 assignment_entry->assign->remove();
106
107 if (debug) {
108 printf("Removed assignment to %s@%p\n",
109 entry->var->name, (void *) entry->var);
110 }
111
112 assignment_entry->link.remove();
113 free(assignment_entry);
114 }
115 progress = true;
116 }
117 }
118
119 if (entry->assign_list.is_empty()) {
120 /* If there are no assignments or references to the variable left,
121 * then we can remove its declaration.
122 */
123
124 /* uniform initializers are precious, and could get used by another
125 * stage.
126 */
127 if (entry->var->data.mode == ir_var_uniform ||
128 entry->var->data.mode == ir_var_shader_storage) {
129 if (entry->var->constant_initializer)
130 continue;
131
132 /* Section 2.11.6 (Uniform Variables) of the OpenGL ES 3.0.3 spec
133 * says:
134 *
135 * "All members of a named uniform block declared with a
136 * shared or std140 layout qualifier are considered active,
137 * even if they are not referenced in any shader in the
138 * program. The uniform block itself is also considered
139 * active, even if no member of the block is referenced."
140 *
141 * If the variable is in a uniform block with one of those
142 * layouts, do not eliminate it.
143 */
144 if (entry->var->is_in_buffer_block()) {
145 if (entry->var->get_interface_type_packing() !=
146 GLSL_INTERFACE_PACKING_PACKED) {
147 /* Set used to false so it doesn't get set as referenced by
148 * the shader in the program resource list. This will also
149 * help avoid the state being unnecessarily flushed for the
150 * shader stage.
151 */
152 entry->var->data.used = false;
153 continue;
154 }
155 }
156
157 if (entry->var->type->is_subroutine())
158 continue;
159 }
160
161 entry->var->remove();
162 progress = true;
163
164 if (debug) {
165 printf("Removed declaration of %s@%p\n",
166 entry->var->name, (void *) entry->var);
167 }
168 }
169 }
170
171 return progress;
172 }
173
174 /**
175 * Does a dead code pass on the functions present in the instruction stream.
176 *
177 * This is suitable for use while the program is not linked, as it will
178 * ignore variable declarations (and the assignments to them) for variables
179 * with global scope.
180 */
181 bool
do_dead_code_unlinked(exec_list * instructions)182 do_dead_code_unlinked(exec_list *instructions)
183 {
184 bool progress = false;
185
186 foreach_in_list(ir_instruction, ir, instructions) {
187 ir_function *f = ir->as_function();
188 if (f) {
189 foreach_in_list(ir_function_signature, sig, &f->signatures) {
190 if (do_dead_code(&sig->body))
191 progress = true;
192 }
193 }
194 }
195
196 return progress;
197 }
198