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
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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    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.  Also, once uniform locations have been assigned, the
126 	  * declaration cannot be deleted.
127 	  */
128          if (entry->var->data.mode == ir_var_uniform ||
129              entry->var->data.mode == ir_var_shader_storage) {
130             if (uniform_locations_assigned || entry->var->constant_initializer)
131                continue;
132 
133             /* Section 2.11.6 (Uniform Variables) of the OpenGL ES 3.0.3 spec
134              * says:
135              *
136              *     "All members of a named uniform block declared with a
137              *     shared or std140 layout qualifier are considered active,
138              *     even if they are not referenced in any shader in the
139              *     program. The uniform block itself is also considered
140              *     active, even if no member of the block is referenced."
141              *
142              * If the variable is in a uniform block with one of those
143              * layouts, do not eliminate it.
144              */
145             if (entry->var->is_in_buffer_block()) {
146                if (entry->var->get_interface_type_packing() !=
147                    GLSL_INTERFACE_PACKING_PACKED) {
148                   /* Set used to false so it doesn't get set as referenced by
149                    * the shader in the program resource list. This will also
150                    * help avoid the state being unnecessarily flushed for the
151                    * shader stage.
152                    */
153                   entry->var->data.used = false;
154                   continue;
155                }
156             }
157 
158             if (entry->var->type->is_subroutine())
159                continue;
160          }
161 
162 	 entry->var->remove();
163 	 progress = true;
164 
165 	 if (debug) {
166 	    printf("Removed declaration of %s@%p\n",
167 		   entry->var->name, (void *) entry->var);
168 	 }
169       }
170    }
171 
172    return progress;
173 }
174 
175 /**
176  * Does a dead code pass on the functions present in the instruction stream.
177  *
178  * This is suitable for use while the program is not linked, as it will
179  * ignore variable declarations (and the assignments to them) for variables
180  * with global scope.
181  */
182 bool
do_dead_code_unlinked(exec_list * instructions)183 do_dead_code_unlinked(exec_list *instructions)
184 {
185    bool progress = false;
186 
187    foreach_in_list(ir_instruction, ir, instructions) {
188       ir_function *f = ir->as_function();
189       if (f) {
190 	 foreach_in_list(ir_function_signature, sig, &f->signatures) {
191 	    /* The setting of the uniform_locations_assigned flag here is
192 	     * irrelevent.  If there is a uniform declaration encountered
193 	     * inside the body of the function, something has already gone
194 	     * terribly, terribly wrong.
195 	     */
196 	    if (do_dead_code(&sig->body, false))
197 	       progress = true;
198 	 }
199       }
200    }
201 
202    return progress;
203 }
204