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_local.cpp
26 *
27 * Eliminates local dead assignments from the code.
28 *
29 * This operates on basic blocks, tracking assignments and finding if
30 * they're used before the variable is completely reassigned.
31 *
32 * Compare this to ir_dead_code.cpp, which operates globally looking
33 * for assignments to variables that are never read.
34 */
35
36 #include "ir.h"
37 #include "ir_basic_block.h"
38 #include "ir_optimization.h"
39 #include "glsl_types.h"
40
41 static bool debug = false;
42
43 namespace {
44
45 class assignment_entry : public exec_node
46 {
47 public:
assignment_entry(ir_variable * lhs,ir_assignment * ir)48 assignment_entry(ir_variable *lhs, ir_assignment *ir)
49 {
50 assert(lhs);
51 assert(ir);
52 this->lhs = lhs;
53 this->ir = ir;
54 this->available = ir->write_mask;
55 }
56
57 ir_variable *lhs;
58 ir_assignment *ir;
59
60 /* bitmask of xyzw channels written that haven't been used so far. */
61 int available;
62 };
63
64 class kill_for_derefs_visitor : public ir_hierarchical_visitor {
65 public:
kill_for_derefs_visitor(exec_list * assignments)66 kill_for_derefs_visitor(exec_list *assignments)
67 {
68 this->assignments = assignments;
69 }
70
kill_channels(ir_variable * const var,int used)71 void kill_channels(ir_variable *const var, int used)
72 {
73 foreach_iter(exec_list_iterator, iter, *this->assignments) {
74 assignment_entry *entry = (assignment_entry *)iter.get();
75
76 if (entry->lhs == var) {
77 if (var->type->is_scalar() || var->type->is_vector()) {
78 if (debug)
79 printf("kill %s (0x%01x - 0x%01x)\n", entry->lhs->name,
80 entry->available, used);
81 entry->available &= ~used;
82 if (!entry->available)
83 entry->remove();
84 } else {
85 if (debug)
86 printf("kill %s\n", entry->lhs->name);
87 entry->remove();
88 }
89 }
90 }
91 }
92
visit(ir_dereference_variable * ir)93 virtual ir_visitor_status visit(ir_dereference_variable *ir)
94 {
95 kill_channels(ir->var, ~0);
96
97 return visit_continue;
98 }
99
visit(ir_swizzle * ir)100 virtual ir_visitor_status visit(ir_swizzle *ir)
101 {
102 ir_dereference_variable *deref = ir->val->as_dereference_variable();
103 if (!deref)
104 return visit_continue;
105
106 int used = 0;
107 used |= 1 << ir->mask.x;
108 used |= 1 << ir->mask.y;
109 used |= 1 << ir->mask.z;
110 used |= 1 << ir->mask.w;
111
112 kill_channels(deref->var, used);
113
114 return visit_continue_with_parent;
115 }
116
117 private:
118 exec_list *assignments;
119 };
120
121 class array_index_visit : public ir_hierarchical_visitor {
122 public:
array_index_visit(ir_hierarchical_visitor * v)123 array_index_visit(ir_hierarchical_visitor *v)
124 {
125 this->visitor = v;
126 }
127
visit_enter(class ir_dereference_array * ir)128 virtual ir_visitor_status visit_enter(class ir_dereference_array *ir)
129 {
130 ir->array_index->accept(visitor);
131 return visit_continue;
132 }
133
run(ir_instruction * ir,ir_hierarchical_visitor * v)134 static void run(ir_instruction *ir, ir_hierarchical_visitor *v)
135 {
136 array_index_visit top_visit(v);
137 ir->accept(& top_visit);
138 }
139
140 ir_hierarchical_visitor *visitor;
141 };
142
143 } /* unnamed namespace */
144
145 /**
146 * Adds an entry to the available copy list if it's a plain assignment
147 * of a variable to a variable.
148 */
149 static bool
process_assignment(void * ctx,ir_assignment * ir,exec_list * assignments)150 process_assignment(void *ctx, ir_assignment *ir, exec_list *assignments)
151 {
152 ir_variable *var = NULL;
153 bool progress = false;
154 kill_for_derefs_visitor v(assignments);
155
156 /* Kill assignment entries for things used to produce this assignment. */
157 ir->rhs->accept(&v);
158 if (ir->condition) {
159 ir->condition->accept(&v);
160 }
161
162 /* Kill assignment enties used as array indices.
163 */
164 array_index_visit::run(ir->lhs, &v);
165 var = ir->lhs->variable_referenced();
166 assert(var);
167
168 /* Now, check if we did a whole-variable assignment. */
169 if (!ir->condition) {
170 ir_dereference_variable *deref_var = ir->lhs->as_dereference_variable();
171
172 /* If it's a vector type, we can do per-channel elimination of
173 * use of the RHS.
174 */
175 if (deref_var && (deref_var->var->type->is_scalar() ||
176 deref_var->var->type->is_vector())) {
177
178 if (debug)
179 printf("looking for %s.0x%01x to remove\n", var->name,
180 ir->write_mask);
181
182 foreach_iter(exec_list_iterator, iter, *assignments) {
183 assignment_entry *entry = (assignment_entry *)iter.get();
184
185 if (entry->lhs != var)
186 continue;
187
188 int remove = entry->available & ir->write_mask;
189 if (debug) {
190 printf("%s 0x%01x - 0x%01x = 0x%01x\n",
191 var->name,
192 entry->ir->write_mask,
193 remove, entry->ir->write_mask & ~remove);
194 }
195 if (remove) {
196 progress = true;
197
198 if (debug) {
199 printf("rewriting:\n ");
200 entry->ir->print();
201 printf("\n");
202 }
203
204 entry->ir->write_mask &= ~remove;
205 entry->available &= ~remove;
206 if (entry->ir->write_mask == 0) {
207 /* Delete the dead assignment. */
208 entry->ir->remove();
209 entry->remove();
210 } else {
211 void *mem_ctx = ralloc_parent(entry->ir);
212 /* Reswizzle the RHS arguments according to the new
213 * write_mask.
214 */
215 unsigned components[4];
216 unsigned channels = 0;
217 unsigned next = 0;
218
219 for (int i = 0; i < 4; i++) {
220 if ((entry->ir->write_mask | remove) & (1 << i)) {
221 if (!(remove & (1 << i)))
222 components[channels++] = next;
223 next++;
224 }
225 }
226
227 entry->ir->rhs = new(mem_ctx) ir_swizzle(entry->ir->rhs,
228 components,
229 channels);
230 if (debug) {
231 printf("to:\n ");
232 entry->ir->print();
233 printf("\n");
234 }
235 }
236 }
237 }
238 } else if (ir->whole_variable_written() != NULL) {
239 /* We did a whole-variable assignment. So, any instruction in
240 * the assignment list with the same LHS is dead.
241 */
242 if (debug)
243 printf("looking for %s to remove\n", var->name);
244 foreach_iter(exec_list_iterator, iter, *assignments) {
245 assignment_entry *entry = (assignment_entry *)iter.get();
246
247 if (entry->lhs == var) {
248 if (debug)
249 printf("removing %s\n", var->name);
250 entry->ir->remove();
251 entry->remove();
252 progress = true;
253 }
254 }
255 }
256 }
257
258 /* Add this instruction to the assignment list available to be removed. */
259 assignment_entry *entry = new(ctx) assignment_entry(var, ir);
260 assignments->push_tail(entry);
261
262 if (debug) {
263 printf("add %s\n", var->name);
264
265 printf("current entries\n");
266 foreach_iter(exec_list_iterator, iter, *assignments) {
267 assignment_entry *entry = (assignment_entry *)iter.get();
268
269 printf(" %s (0x%01x)\n", entry->lhs->name, entry->available);
270 }
271 }
272
273 return progress;
274 }
275
276 static void
dead_code_local_basic_block(ir_instruction * first,ir_instruction * last,void * data)277 dead_code_local_basic_block(ir_instruction *first,
278 ir_instruction *last,
279 void *data)
280 {
281 ir_instruction *ir, *ir_next;
282 /* List of avaialble_copy */
283 exec_list assignments;
284 bool *out_progress = (bool *)data;
285 bool progress = false;
286
287 void *ctx = ralloc_context(NULL);
288 /* Safe looping, since process_assignment */
289 for (ir = first, ir_next = (ir_instruction *)first->next;;
290 ir = ir_next, ir_next = (ir_instruction *)ir->next) {
291 ir_assignment *ir_assign = ir->as_assignment();
292
293 if (debug) {
294 ir->print();
295 printf("\n");
296 }
297
298 if (ir_assign) {
299 progress = process_assignment(ctx, ir_assign, &assignments) || progress;
300 } else {
301 kill_for_derefs_visitor kill(&assignments);
302 ir->accept(&kill);
303 }
304
305 if (ir == last)
306 break;
307 }
308 *out_progress = progress;
309 ralloc_free(ctx);
310 }
311
312 /**
313 * Does a copy propagation pass on the code present in the instruction stream.
314 */
315 bool
do_dead_code_local(exec_list * instructions)316 do_dead_code_local(exec_list *instructions)
317 {
318 bool progress = false;
319
320 call_for_basic_blocks(instructions, dead_code_local_basic_block, &progress);
321
322 return progress;
323 }
324