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
35static 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 */
44bool
45do_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 */
129bool
130do_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