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
36static 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 */
45bool
46do_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 */
181bool
182do_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