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 "compiler/glsl_types.h"
40
41 static bool debug = false;
42
43 namespace {
44
45 class assignment_entry : public exec_node
46 {
47 public:
48 /* override operator new from exec_node */
49 DECLARE_LINEAR_ZALLOC_CXX_OPERATORS(assignment_entry)
50
assignment_entry(ir_variable * lhs,ir_assignment * ir)51 assignment_entry(ir_variable *lhs, ir_assignment *ir)
52 {
53 assert(lhs);
54 assert(ir);
55 this->lhs = lhs;
56 this->ir = ir;
57 this->unused = ir->write_mask;
58 }
59
60 ir_variable *lhs;
61 ir_assignment *ir;
62
63 /* bitmask of xyzw channels written that haven't been used so far. */
64 int unused;
65 };
66
67 class kill_for_derefs_visitor : public ir_hierarchical_visitor {
68 public:
69 using ir_hierarchical_visitor::visit;
70
kill_for_derefs_visitor(exec_list * assignments)71 kill_for_derefs_visitor(exec_list *assignments)
72 {
73 this->assignments = assignments;
74 }
75
use_channels(ir_variable * const var,int used)76 void use_channels(ir_variable *const var, int used)
77 {
78 foreach_in_list_safe(assignment_entry, entry, this->assignments) {
79 if (entry->lhs == var) {
80 if (var->type->is_scalar() || var->type->is_vector()) {
81 if (debug)
82 printf("used %s (0x%01x - 0x%01x)\n", entry->lhs->name,
83 entry->unused, used & 0xf);
84 entry->unused &= ~used;
85 if (!entry->unused)
86 entry->remove();
87 } else {
88 if (debug)
89 printf("used %s\n", entry->lhs->name);
90 entry->remove();
91 }
92 }
93 }
94 }
95
visit(ir_dereference_variable * ir)96 virtual ir_visitor_status visit(ir_dereference_variable *ir)
97 {
98 use_channels(ir->var, ~0);
99
100 return visit_continue;
101 }
102
visit(ir_swizzle * ir)103 virtual ir_visitor_status visit(ir_swizzle *ir)
104 {
105 ir_dereference_variable *deref = ir->val->as_dereference_variable();
106 if (!deref)
107 return visit_continue;
108
109 int used = 0;
110 used |= 1 << ir->mask.x;
111 if (ir->mask.num_components > 1)
112 used |= 1 << ir->mask.y;
113 if (ir->mask.num_components > 2)
114 used |= 1 << ir->mask.z;
115 if (ir->mask.num_components > 3)
116 used |= 1 << ir->mask.w;
117
118 use_channels(deref->var, used);
119
120 return visit_continue_with_parent;
121 }
122
visit_leave(ir_emit_vertex *)123 virtual ir_visitor_status visit_leave(ir_emit_vertex *)
124 {
125 /* For the purpose of dead code elimination, emitting a vertex counts as
126 * "reading" all of the currently assigned output variables.
127 */
128 foreach_in_list_safe(assignment_entry, entry, this->assignments) {
129 if (entry->lhs->data.mode == ir_var_shader_out) {
130 if (debug)
131 printf("kill %s\n", entry->lhs->name);
132 entry->remove();
133 }
134 }
135
136 return visit_continue;
137 }
138
139 private:
140 exec_list *assignments;
141 };
142
143 class array_index_visit : public ir_hierarchical_visitor {
144 public:
array_index_visit(ir_hierarchical_visitor * v)145 array_index_visit(ir_hierarchical_visitor *v)
146 {
147 this->visitor = v;
148 }
149
visit_enter(class ir_dereference_array * ir)150 virtual ir_visitor_status visit_enter(class ir_dereference_array *ir)
151 {
152 ir->array_index->accept(visitor);
153 return visit_continue;
154 }
155
run(ir_instruction * ir,ir_hierarchical_visitor * v)156 static void run(ir_instruction *ir, ir_hierarchical_visitor *v)
157 {
158 array_index_visit top_visit(v);
159 ir->accept(& top_visit);
160 }
161
162 ir_hierarchical_visitor *visitor;
163 };
164
165 } /* unnamed namespace */
166
167 /**
168 * Adds an entry to the available copy list if it's a plain assignment
169 * of a variable to a variable.
170 */
171 static bool
process_assignment(void * lin_ctx,ir_assignment * ir,exec_list * assignments)172 process_assignment(void *lin_ctx, ir_assignment *ir, exec_list *assignments)
173 {
174 ir_variable *var = NULL;
175 bool progress = false;
176 kill_for_derefs_visitor v(assignments);
177
178 if (ir->condition == NULL) {
179 /* If this is an assignment of the form "foo = foo;", remove the whole
180 * instruction and be done with it.
181 */
182 const ir_variable *const lhs_var = ir->whole_variable_written();
183 if (lhs_var != NULL && lhs_var == ir->rhs->whole_variable_referenced()) {
184 ir->remove();
185 return true;
186 }
187 }
188
189 /* Kill assignment entries for things used to produce this assignment. */
190 ir->rhs->accept(&v);
191 if (ir->condition) {
192 ir->condition->accept(&v);
193 }
194
195 /* Kill assignment enties used as array indices.
196 */
197 array_index_visit::run(ir->lhs, &v);
198 var = ir->lhs->variable_referenced();
199 assert(var);
200
201 /* Now, check if we did a whole-variable assignment. */
202 if (!ir->condition) {
203 ir_dereference_variable *deref_var = ir->lhs->as_dereference_variable();
204
205 /* If it's a vector type, we can do per-channel elimination of
206 * use of the RHS.
207 */
208 if (deref_var && (deref_var->var->type->is_scalar() ||
209 deref_var->var->type->is_vector())) {
210
211 if (debug)
212 printf("looking for %s.0x%01x to remove\n", var->name,
213 ir->write_mask);
214
215 foreach_in_list_safe(assignment_entry, entry, assignments) {
216 if (entry->lhs != var)
217 continue;
218
219 /* Skip if the assignment we're trying to eliminate isn't a plain
220 * variable deref. */
221 if (entry->ir->lhs->ir_type != ir_type_dereference_variable)
222 continue;
223
224 int remove = entry->unused & ir->write_mask;
225 if (debug) {
226 printf("%s 0x%01x - 0x%01x = 0x%01x\n",
227 var->name,
228 entry->ir->write_mask,
229 remove, entry->ir->write_mask & ~remove);
230 }
231 if (remove) {
232 progress = true;
233
234 if (debug) {
235 printf("rewriting:\n ");
236 entry->ir->print();
237 printf("\n");
238 }
239
240 entry->ir->write_mask &= ~remove;
241 entry->unused &= ~remove;
242 if (entry->ir->write_mask == 0) {
243 /* Delete the dead assignment. */
244 entry->ir->remove();
245 entry->remove();
246 } else {
247 void *mem_ctx = ralloc_parent(entry->ir);
248 /* Reswizzle the RHS arguments according to the new
249 * write_mask.
250 */
251 unsigned components[4];
252 unsigned channels = 0;
253 unsigned next = 0;
254
255 for (int i = 0; i < 4; i++) {
256 if ((entry->ir->write_mask | remove) & (1 << i)) {
257 if (!(remove & (1 << i)))
258 components[channels++] = next;
259 next++;
260 }
261 }
262
263 entry->ir->rhs = new(mem_ctx) ir_swizzle(entry->ir->rhs,
264 components,
265 channels);
266 if (debug) {
267 printf("to:\n ");
268 entry->ir->print();
269 printf("\n");
270 }
271 }
272 }
273 }
274 } else if (ir->whole_variable_written() != NULL) {
275 /* We did a whole-variable assignment. So, any instruction in
276 * the assignment list with the same LHS is dead.
277 */
278 if (debug)
279 printf("looking for %s to remove\n", var->name);
280 foreach_in_list_safe(assignment_entry, entry, assignments) {
281 if (entry->lhs == var) {
282 if (debug)
283 printf("removing %s\n", var->name);
284 entry->ir->remove();
285 entry->remove();
286 progress = true;
287 }
288 }
289 }
290 }
291
292 /* Add this instruction to the assignment list available to be removed. */
293 assignment_entry *entry = new(lin_ctx) assignment_entry(var, ir);
294 assignments->push_tail(entry);
295
296 if (debug) {
297 printf("add %s\n", var->name);
298
299 printf("current entries\n");
300 foreach_in_list(assignment_entry, entry, assignments) {
301 printf(" %s (0x%01x)\n", entry->lhs->name, entry->unused);
302 }
303 }
304
305 return progress;
306 }
307
308 static void
dead_code_local_basic_block(ir_instruction * first,ir_instruction * last,void * data)309 dead_code_local_basic_block(ir_instruction *first,
310 ir_instruction *last,
311 void *data)
312 {
313 ir_instruction *ir, *ir_next;
314 /* List of avaialble_copy */
315 exec_list assignments;
316 bool *out_progress = (bool *)data;
317 bool progress = false;
318
319 void *ctx = ralloc_context(NULL);
320 void *lin_ctx = linear_alloc_parent(ctx, 0);
321
322 /* Safe looping, since process_assignment */
323 for (ir = first, ir_next = (ir_instruction *)first->next;;
324 ir = ir_next, ir_next = (ir_instruction *)ir->next) {
325 ir_assignment *ir_assign = ir->as_assignment();
326
327 if (debug) {
328 ir->print();
329 printf("\n");
330 }
331
332 if (ir_assign) {
333 progress = process_assignment(lin_ctx, ir_assign, &assignments) ||
334 progress;
335 } else {
336 kill_for_derefs_visitor kill(&assignments);
337 ir->accept(&kill);
338 }
339
340 if (ir == last)
341 break;
342 }
343 *out_progress = progress;
344 ralloc_free(ctx);
345 }
346
347 /**
348 * Does a copy propagation pass on the code present in the instruction stream.
349 */
350 bool
do_dead_code_local(exec_list * instructions)351 do_dead_code_local(exec_list *instructions)
352 {
353 bool progress = false;
354
355 call_for_basic_blocks(instructions, dead_code_local_basic_block, &progress);
356
357 return progress;
358 }
359