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, 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 */
176bool
177do_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