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