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