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6de9cd9a DN |
1 | /* Dead code elimination pass for the GNU compiler. |
2 | Copyright (C) 2002, 2003, 2004 Free Software Foundation, Inc. | |
3 | Contributed by Ben Elliston <bje@redhat.com> | |
4 | and Andrew MacLeod <amacleod@redhat.com> | |
5 | Adapted to use control dependence by Steven Bosscher, SUSE Labs. | |
6 | ||
7 | This file is part of GCC. | |
8 | ||
9 | GCC is free software; you can redistribute it and/or modify it | |
10 | under the terms of the GNU General Public License as published by the | |
11 | Free Software Foundation; either version 2, or (at your option) any | |
12 | later version. | |
13 | ||
14 | GCC is distributed in the hope that it will be useful, but WITHOUT | |
15 | ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
16 | FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
17 | for more details. | |
18 | ||
19 | You should have received a copy of the GNU General Public License | |
20 | along with GCC; see the file COPYING. If not, write to the Free | |
21 | Software Foundation, 59 Temple Place - Suite 330, Boston, MA | |
22 | 02111-1307, USA. */ | |
23 | ||
24 | /* Dead code elimination. | |
25 | ||
26 | References: | |
27 | ||
28 | Building an Optimizing Compiler, | |
29 | Robert Morgan, Butterworth-Heinemann, 1998, Section 8.9. | |
30 | ||
31 | Advanced Compiler Design and Implementation, | |
32 | Steven Muchnick, Morgan Kaufmann, 1997, Section 18.10. | |
33 | ||
34 | Dead-code elimination is the removal of statements which have no | |
35 | impact on the program's output. "Dead statements" have no impact | |
36 | on the program's output, while "necessary statements" may have | |
37 | impact on the output. | |
38 | ||
39 | The algorithm consists of three phases: | |
40 | 1. Marking as necessary all statements known to be necessary, | |
41 | e.g. most function calls, writing a value to memory, etc; | |
42 | 2. Propagating necessary statements, e.g., the statements | |
43 | giving values to operands in necessary statements; and | |
44 | 3. Removing dead statements. */ | |
45 | ||
46 | #include "config.h" | |
47 | #include "system.h" | |
48 | #include "coretypes.h" | |
49 | #include "tm.h" | |
50 | #include "errors.h" | |
51 | #include "ggc.h" | |
52 | ||
53 | /* These RTL headers are needed for basic-block.h. */ | |
54 | #include "rtl.h" | |
55 | #include "tm_p.h" | |
56 | #include "hard-reg-set.h" | |
57 | #include "basic-block.h" | |
58 | ||
59 | #include "tree.h" | |
60 | #include "diagnostic.h" | |
61 | #include "tree-flow.h" | |
eadf906f | 62 | #include "tree-gimple.h" |
6de9cd9a DN |
63 | #include "tree-dump.h" |
64 | #include "tree-pass.h" | |
65 | #include "timevar.h" | |
66 | #include "flags.h" | |
67 | \f | |
68 | static struct stmt_stats | |
69 | { | |
70 | int total; | |
71 | int total_phis; | |
72 | int removed; | |
73 | int removed_phis; | |
74 | } stats; | |
75 | ||
76 | static varray_type worklist; | |
77 | ||
78 | /* Vector indicating an SSA name has already been processed and marked | |
79 | as necessary. */ | |
80 | static sbitmap processed; | |
81 | ||
82 | /* Vector indicating that last_stmt if a basic block has already been | |
83 | marked as necessary. */ | |
84 | static sbitmap last_stmt_necessary; | |
85 | ||
86 | /* Before we can determine whether a control branch is dead, we need to | |
87 | compute which blocks are control dependent on which edges. | |
88 | ||
89 | We expect each block to be control dependent on very few edges so we | |
90 | use a bitmap for each block recording its edges. An array holds the | |
91 | bitmap. The Ith bit in the bitmap is set if that block is dependent | |
92 | on the Ith edge. */ | |
93 | bitmap *control_dependence_map; | |
94 | ||
95 | /* Execute CODE for each edge (given number EDGE_NUMBER within the CODE) | |
96 | for which the block with index N is control dependent. */ | |
97 | #define EXECUTE_IF_CONTROL_DEPENDENT(N, EDGE_NUMBER, CODE) \ | |
98 | EXECUTE_IF_SET_IN_BITMAP (control_dependence_map[N], 0, EDGE_NUMBER, CODE) | |
99 | ||
100 | /* Local function prototypes. */ | |
101 | static inline void set_control_dependence_map_bit (basic_block, int); | |
102 | static inline void clear_control_dependence_bitmap (basic_block); | |
103 | static void find_all_control_dependences (struct edge_list *); | |
104 | static void find_control_dependence (struct edge_list *, int); | |
105 | static inline basic_block find_pdom (basic_block); | |
106 | ||
107 | static inline void mark_stmt_necessary (tree, bool); | |
108 | static inline void mark_operand_necessary (tree); | |
109 | ||
6de9cd9a DN |
110 | static void mark_stmt_if_obviously_necessary (tree, bool); |
111 | static void find_obviously_necessary_stmts (struct edge_list *); | |
112 | ||
113 | static void mark_control_dependent_edges_necessary (basic_block, struct edge_list *); | |
114 | static void propagate_necessity (struct edge_list *); | |
115 | ||
116 | static void eliminate_unnecessary_stmts (void); | |
117 | static void remove_dead_phis (basic_block); | |
118 | static void remove_dead_stmt (block_stmt_iterator *, basic_block); | |
119 | ||
120 | static void print_stats (void); | |
121 | static void tree_dce_init (bool); | |
122 | static void tree_dce_done (bool); | |
123 | \f | |
124 | /* Indicate block BB is control dependent on an edge with index EDGE_INDEX. */ | |
125 | static inline void | |
126 | set_control_dependence_map_bit (basic_block bb, int edge_index) | |
127 | { | |
128 | if (bb == ENTRY_BLOCK_PTR) | |
129 | return; | |
130 | if (bb == EXIT_BLOCK_PTR) | |
131 | abort (); | |
132 | bitmap_set_bit (control_dependence_map[bb->index], edge_index); | |
133 | } | |
134 | ||
135 | /* Clear all control dependences for block BB. */ | |
136 | static inline | |
137 | void clear_control_dependence_bitmap (basic_block bb) | |
138 | { | |
139 | bitmap_clear (control_dependence_map[bb->index]); | |
140 | } | |
141 | ||
142 | /* Record all blocks' control dependences on all edges in the edge | |
143 | list EL, ala Morgan, Section 3.6. */ | |
144 | ||
145 | static void | |
146 | find_all_control_dependences (struct edge_list *el) | |
147 | { | |
148 | int i; | |
149 | ||
150 | for (i = 0; i < NUM_EDGES (el); ++i) | |
151 | find_control_dependence (el, i); | |
152 | } | |
153 | ||
154 | /* Determine all blocks' control dependences on the given edge with edge_list | |
155 | EL index EDGE_INDEX, ala Morgan, Section 3.6. */ | |
156 | ||
157 | static void | |
158 | find_control_dependence (struct edge_list *el, int edge_index) | |
159 | { | |
160 | basic_block current_block; | |
161 | basic_block ending_block; | |
162 | ||
163 | #ifdef ENABLE_CHECKING | |
164 | if (INDEX_EDGE_PRED_BB (el, edge_index) == EXIT_BLOCK_PTR) | |
165 | abort (); | |
166 | #endif | |
167 | ||
168 | if (INDEX_EDGE_PRED_BB (el, edge_index) == ENTRY_BLOCK_PTR) | |
169 | ending_block = ENTRY_BLOCK_PTR->next_bb; | |
170 | else | |
171 | ending_block = find_pdom (INDEX_EDGE_PRED_BB (el, edge_index)); | |
172 | ||
173 | for (current_block = INDEX_EDGE_SUCC_BB (el, edge_index); | |
174 | current_block != ending_block && current_block != EXIT_BLOCK_PTR; | |
175 | current_block = find_pdom (current_block)) | |
176 | { | |
177 | edge e = INDEX_EDGE (el, edge_index); | |
178 | ||
179 | /* For abnormal edges, we don't make current_block control | |
180 | dependent because instructions that throw are always necessary | |
181 | anyway. */ | |
182 | if (e->flags & EDGE_ABNORMAL) | |
183 | continue; | |
184 | ||
185 | set_control_dependence_map_bit (current_block, edge_index); | |
186 | } | |
187 | } | |
188 | ||
189 | /* Find the immediate postdominator PDOM of the specified basic block BLOCK. | |
190 | This function is necessary because some blocks have negative numbers. */ | |
191 | ||
192 | static inline basic_block | |
193 | find_pdom (basic_block block) | |
194 | { | |
195 | if (block == ENTRY_BLOCK_PTR) | |
196 | abort (); | |
197 | else if (block == EXIT_BLOCK_PTR) | |
198 | return EXIT_BLOCK_PTR; | |
199 | else | |
200 | { | |
201 | basic_block bb = get_immediate_dominator (CDI_POST_DOMINATORS, block); | |
202 | if (! bb) | |
203 | return EXIT_BLOCK_PTR; | |
204 | return bb; | |
205 | } | |
206 | } | |
207 | \f | |
208 | #define NECESSARY(stmt) stmt->common.asm_written_flag | |
209 | ||
210 | /* If STMT is not already marked necessary, mark it, and add it to the | |
211 | worklist if ADD_TO_WORKLIST is true. */ | |
212 | static inline void | |
213 | mark_stmt_necessary (tree stmt, bool add_to_worklist) | |
214 | { | |
215 | #ifdef ENABLE_CHECKING | |
216 | if (stmt == NULL | |
217 | || stmt == error_mark_node | |
218 | || (stmt && DECL_P (stmt))) | |
219 | abort (); | |
220 | #endif | |
221 | ||
222 | if (NECESSARY (stmt)) | |
223 | return; | |
224 | ||
225 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
226 | { | |
227 | fprintf (dump_file, "Marking useful stmt: "); | |
228 | print_generic_stmt (dump_file, stmt, TDF_SLIM); | |
229 | fprintf (dump_file, "\n"); | |
230 | } | |
231 | ||
232 | NECESSARY (stmt) = 1; | |
233 | if (add_to_worklist) | |
234 | VARRAY_PUSH_TREE (worklist, stmt); | |
235 | } | |
236 | ||
237 | /* Mark the statement defining operand OP as necessary. */ | |
238 | ||
239 | static inline void | |
240 | mark_operand_necessary (tree op) | |
241 | { | |
242 | tree stmt; | |
243 | int ver; | |
244 | ||
245 | #ifdef ENABLE_CHECKING | |
246 | if (op == NULL) | |
247 | abort (); | |
248 | #endif | |
249 | ||
250 | ver = SSA_NAME_VERSION (op); | |
251 | if (TEST_BIT (processed, ver)) | |
252 | return; | |
253 | SET_BIT (processed, ver); | |
254 | ||
255 | stmt = SSA_NAME_DEF_STMT (op); | |
256 | #ifdef ENABLE_CHECKING | |
257 | if (stmt == NULL) | |
258 | abort (); | |
259 | #endif | |
260 | ||
261 | if (NECESSARY (stmt) | |
262 | || IS_EMPTY_STMT (stmt)) | |
263 | return; | |
264 | ||
265 | NECESSARY (stmt) = 1; | |
266 | VARRAY_PUSH_TREE (worklist, stmt); | |
267 | } | |
268 | \f | |
6de9cd9a DN |
269 | |
270 | /* Mark STMT as necessary if it is obviously is. Add it to the worklist if | |
271 | it can make other statements necessary. | |
272 | ||
273 | If AGGRESSIVE is false, control statements are conservatively marked as | |
274 | necessary. */ | |
275 | ||
276 | static void | |
277 | mark_stmt_if_obviously_necessary (tree stmt, bool aggressive) | |
278 | { | |
279 | def_optype defs; | |
a32b97a2 BB |
280 | v_may_def_optype v_may_defs; |
281 | v_must_def_optype v_must_defs; | |
6de9cd9a DN |
282 | stmt_ann_t ann; |
283 | size_t i; | |
cd709752 | 284 | tree op; |
6de9cd9a DN |
285 | |
286 | /* Statements that are implicitly live. Most function calls, asm and return | |
287 | statements are required. Labels and BIND_EXPR nodes are kept because | |
288 | they are control flow, and we have no way of knowing whether they can be | |
289 | removed. DCE can eliminate all the other statements in a block, and CFG | |
290 | can then remove the block and labels. */ | |
291 | switch (TREE_CODE (stmt)) | |
292 | { | |
293 | case BIND_EXPR: | |
294 | case LABEL_EXPR: | |
295 | case CASE_LABEL_EXPR: | |
296 | mark_stmt_necessary (stmt, false); | |
297 | return; | |
298 | ||
299 | case ASM_EXPR: | |
300 | case RESX_EXPR: | |
301 | case RETURN_EXPR: | |
302 | mark_stmt_necessary (stmt, true); | |
303 | return; | |
304 | ||
305 | case CALL_EXPR: | |
306 | /* Most, but not all function calls are required. Function calls that | |
307 | produce no result and have no side effects (i.e. const pure | |
308 | functions) are unnecessary. */ | |
309 | if (TREE_SIDE_EFFECTS (stmt)) | |
310 | mark_stmt_necessary (stmt, true); | |
311 | return; | |
312 | ||
313 | case MODIFY_EXPR: | |
cd709752 RH |
314 | op = get_call_expr_in (stmt); |
315 | if (op && TREE_SIDE_EFFECTS (op)) | |
6de9cd9a DN |
316 | { |
317 | mark_stmt_necessary (stmt, true); | |
318 | return; | |
319 | } | |
320 | ||
321 | /* These values are mildly magic bits of the EH runtime. We can't | |
322 | see the entire lifetime of these values until landing pads are | |
323 | generated. */ | |
324 | if (TREE_CODE (TREE_OPERAND (stmt, 0)) == EXC_PTR_EXPR | |
325 | || TREE_CODE (TREE_OPERAND (stmt, 0)) == FILTER_EXPR) | |
326 | { | |
327 | mark_stmt_necessary (stmt, true); | |
328 | return; | |
329 | } | |
330 | break; | |
331 | ||
332 | case GOTO_EXPR: | |
333 | if (! simple_goto_p (stmt)) | |
334 | mark_stmt_necessary (stmt, true); | |
335 | return; | |
336 | ||
337 | case COND_EXPR: | |
338 | if (GOTO_DESTINATION (COND_EXPR_THEN (stmt)) | |
339 | == GOTO_DESTINATION (COND_EXPR_ELSE (stmt))) | |
340 | { | |
341 | /* A COND_EXPR is obviously dead if the target labels are the same. | |
342 | We cannot kill the statement at this point, so to prevent the | |
343 | statement from being marked necessary, we replace the condition | |
344 | with a constant. The stmt is killed later on in cfg_cleanup. */ | |
345 | COND_EXPR_COND (stmt) = integer_zero_node; | |
346 | modify_stmt (stmt); | |
347 | return; | |
348 | } | |
349 | /* Fall through. */ | |
350 | ||
351 | case SWITCH_EXPR: | |
352 | if (! aggressive) | |
353 | mark_stmt_necessary (stmt, true); | |
354 | break; | |
355 | ||
356 | default: | |
357 | break; | |
358 | } | |
359 | ||
360 | ann = stmt_ann (stmt); | |
c597ef4e DN |
361 | |
362 | /* If the statement has volatile operands, it needs to be preserved. | |
363 | Same for statements that can alter control flow in unpredictable | |
364 | ways. */ | |
365 | if (ann->has_volatile_ops || is_ctrl_altering_stmt (stmt)) | |
6de9cd9a DN |
366 | { |
367 | mark_stmt_necessary (stmt, true); | |
368 | return; | |
369 | } | |
370 | ||
371 | get_stmt_operands (stmt); | |
372 | ||
373 | defs = DEF_OPS (ann); | |
374 | for (i = 0; i < NUM_DEFS (defs); i++) | |
375 | { | |
376 | tree def = DEF_OP (defs, i); | |
c597ef4e | 377 | if (is_global_var (SSA_NAME_VAR (def))) |
6de9cd9a DN |
378 | { |
379 | mark_stmt_necessary (stmt, true); | |
380 | return; | |
381 | } | |
382 | } | |
383 | ||
c597ef4e DN |
384 | /* Check virtual definitions. If we get here, the only virtual |
385 | definitions we should see are those generated by assignment | |
386 | statements. */ | |
a32b97a2 | 387 | v_may_defs = V_MAY_DEF_OPS (ann); |
a32b97a2 | 388 | v_must_defs = V_MUST_DEF_OPS (ann); |
c597ef4e | 389 | if (NUM_V_MAY_DEFS (v_may_defs) > 0 || NUM_V_MUST_DEFS (v_must_defs) > 0) |
a32b97a2 | 390 | { |
c597ef4e DN |
391 | tree lhs; |
392 | ||
393 | #if defined ENABLE_CHECKING | |
394 | if (TREE_CODE (stmt) != MODIFY_EXPR) | |
395 | abort (); | |
396 | #endif | |
397 | ||
398 | /* Note that we must not check the individual virtual operands | |
399 | here. In particular, if this is an aliased store, we could | |
400 | end up with something like the following (SSA notation | |
401 | redacted for brevity): | |
402 | ||
403 | foo (int *p, int i) | |
404 | { | |
405 | int x; | |
406 | p_1 = (i_2 > 3) ? &x : p_1; | |
407 | ||
408 | # x_4 = V_MAY_DEF <x_3> | |
409 | *p_1 = 5; | |
410 | ||
411 | return 2; | |
412 | } | |
413 | ||
414 | Notice that the store to '*p_1' should be preserved, if we | |
415 | were to check the virtual definitions in that store, we would | |
416 | not mark it needed. This is because 'x' is not a global | |
417 | variable. | |
418 | ||
419 | Therefore, we check the base address of the LHS. If the | |
420 | address is a pointer, we check if its name tag or type tag is | |
421 | a global variable. Otherwise, we check if the base variable | |
422 | is a global. */ | |
423 | lhs = TREE_OPERAND (stmt, 0); | |
424 | if (TREE_CODE_CLASS (TREE_CODE (lhs)) == 'r') | |
425 | lhs = get_base_address (lhs); | |
426 | ||
427 | if (lhs == NULL_TREE) | |
6de9cd9a | 428 | { |
c597ef4e DN |
429 | /* If LHS is NULL, it means that we couldn't get the base |
430 | address of the reference. In which case, we should not | |
431 | remove this store. */ | |
6de9cd9a | 432 | mark_stmt_necessary (stmt, true); |
c597ef4e DN |
433 | } |
434 | else if (DECL_P (lhs)) | |
435 | { | |
436 | /* If the store is to a global symbol, we need to keep it. */ | |
437 | if (is_global_var (lhs)) | |
438 | mark_stmt_necessary (stmt, true); | |
439 | } | |
440 | else if (TREE_CODE (lhs) == INDIRECT_REF) | |
441 | { | |
442 | tree ptr = TREE_OPERAND (lhs, 0); | |
443 | struct ptr_info_def *pi = SSA_NAME_PTR_INFO (ptr); | |
444 | tree nmt = (pi) ? pi->name_mem_tag : NULL_TREE; | |
445 | tree tmt = var_ann (SSA_NAME_VAR (ptr))->type_mem_tag; | |
446 | ||
447 | /* If either the name tag or the type tag for PTR is a | |
448 | global variable, then the store is necessary. */ | |
449 | if ((nmt && is_global_var (nmt)) | |
450 | || (tmt && is_global_var (tmt))) | |
451 | { | |
452 | mark_stmt_necessary (stmt, true); | |
453 | return; | |
454 | } | |
455 | } | |
456 | else | |
457 | abort (); | |
6de9cd9a DN |
458 | } |
459 | ||
460 | return; | |
461 | } | |
462 | \f | |
463 | /* Find obviously necessary statements. These are things like most function | |
464 | calls, and stores to file level variables. | |
465 | ||
466 | If EL is NULL, control statements are conservatively marked as | |
467 | necessary. Otherwise it contains the list of edges used by control | |
468 | dependence analysis. */ | |
469 | ||
470 | static void | |
471 | find_obviously_necessary_stmts (struct edge_list *el) | |
472 | { | |
473 | basic_block bb; | |
474 | block_stmt_iterator i; | |
475 | edge e; | |
476 | ||
477 | FOR_EACH_BB (bb) | |
478 | { | |
479 | tree phi; | |
480 | ||
481 | /* Check any PHI nodes in the block. */ | |
17192884 | 482 | for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi)) |
6de9cd9a DN |
483 | { |
484 | NECESSARY (phi) = 0; | |
485 | ||
486 | /* PHIs for virtual variables do not directly affect code | |
487 | generation and need not be considered inherently necessary | |
488 | regardless of the bits set in their decl. | |
489 | ||
490 | Thus, we only need to mark PHIs for real variables which | |
491 | need their result preserved as being inherently necessary. */ | |
492 | if (is_gimple_reg (PHI_RESULT (phi)) | |
c597ef4e | 493 | && is_global_var (SSA_NAME_VAR (PHI_RESULT (phi)))) |
6de9cd9a DN |
494 | mark_stmt_necessary (phi, true); |
495 | } | |
496 | ||
497 | /* Check all statements in the block. */ | |
498 | for (i = bsi_start (bb); ! bsi_end_p (i); bsi_next (&i)) | |
499 | { | |
500 | tree stmt = bsi_stmt (i); | |
501 | NECESSARY (stmt) = 0; | |
502 | mark_stmt_if_obviously_necessary (stmt, el != NULL); | |
503 | } | |
504 | ||
505 | /* Mark this basic block as `not visited'. A block will be marked | |
506 | visited when the edges that it is control dependent on have been | |
507 | marked. */ | |
508 | bb->flags &= ~BB_VISITED; | |
509 | } | |
510 | ||
511 | if (el) | |
512 | { | |
513 | /* Prevent the loops from being removed. We must keep the infinite loops, | |
514 | and we currently do not have a means to recognize the finite ones. */ | |
515 | FOR_EACH_BB (bb) | |
516 | { | |
517 | for (e = bb->succ; e; e = e->succ_next) | |
518 | if (e->flags & EDGE_DFS_BACK) | |
519 | mark_control_dependent_edges_necessary (e->dest, el); | |
520 | } | |
521 | } | |
522 | } | |
523 | \f | |
524 | /* Make corresponding control dependent edges necessary. We only | |
525 | have to do this once for each basic block, so we clear the bitmap | |
526 | after we're done. */ | |
527 | static void | |
528 | mark_control_dependent_edges_necessary (basic_block bb, struct edge_list *el) | |
529 | { | |
530 | int edge_number; | |
531 | ||
7e6eb623 DB |
532 | #ifdef ENABLE_CHECKING |
533 | if (bb == EXIT_BLOCK_PTR) | |
534 | abort (); | |
535 | #endif | |
536 | ||
537 | if (bb == ENTRY_BLOCK_PTR) | |
538 | return; | |
539 | ||
6de9cd9a DN |
540 | EXECUTE_IF_CONTROL_DEPENDENT (bb->index, edge_number, |
541 | { | |
542 | tree t; | |
543 | basic_block cd_bb = INDEX_EDGE_PRED_BB (el, edge_number); | |
544 | ||
545 | if (TEST_BIT (last_stmt_necessary, cd_bb->index)) | |
546 | continue; | |
547 | SET_BIT (last_stmt_necessary, cd_bb->index); | |
548 | ||
549 | t = last_stmt (cd_bb); | |
1eaba2f2 | 550 | if (t && is_ctrl_stmt (t)) |
6de9cd9a DN |
551 | mark_stmt_necessary (t, true); |
552 | }); | |
553 | } | |
554 | \f | |
555 | /* Propagate necessity using the operands of necessary statements. Process | |
556 | the uses on each statement in the worklist, and add all feeding statements | |
557 | which contribute to the calculation of this value to the worklist. | |
558 | ||
559 | In conservative mode, EL is NULL. */ | |
560 | ||
561 | static void | |
562 | propagate_necessity (struct edge_list *el) | |
563 | { | |
564 | tree i; | |
565 | bool aggressive = (el ? true : false); | |
566 | ||
567 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
568 | fprintf (dump_file, "\nProcessing worklist:\n"); | |
569 | ||
570 | while (VARRAY_ACTIVE_SIZE (worklist) > 0) | |
571 | { | |
572 | /* Take `i' from worklist. */ | |
573 | i = VARRAY_TOP_TREE (worklist); | |
574 | VARRAY_POP (worklist); | |
575 | ||
576 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
577 | { | |
578 | fprintf (dump_file, "processing: "); | |
579 | print_generic_stmt (dump_file, i, TDF_SLIM); | |
580 | fprintf (dump_file, "\n"); | |
581 | } | |
582 | ||
583 | if (aggressive) | |
584 | { | |
585 | /* Mark the last statements of the basic blocks that the block | |
586 | containing `i' is control dependent on, but only if we haven't | |
587 | already done so. */ | |
588 | basic_block bb = bb_for_stmt (i); | |
589 | if (! (bb->flags & BB_VISITED)) | |
590 | { | |
591 | bb->flags |= BB_VISITED; | |
592 | mark_control_dependent_edges_necessary (bb, el); | |
593 | } | |
594 | } | |
595 | ||
596 | if (TREE_CODE (i) == PHI_NODE) | |
597 | { | |
598 | /* PHI nodes are somewhat special in that each PHI alternative has | |
599 | data and control dependencies. All the statements feeding the | |
600 | PHI node's arguments are always necessary. In aggressive mode, | |
601 | we also consider the control dependent edges leading to the | |
602 | predecessor block associated with each PHI alternative as | |
603 | necessary. */ | |
604 | int k; | |
605 | for (k = 0; k < PHI_NUM_ARGS (i); k++) | |
606 | { | |
607 | tree arg = PHI_ARG_DEF (i, k); | |
608 | if (TREE_CODE (arg) == SSA_NAME) | |
609 | mark_operand_necessary (arg); | |
610 | } | |
611 | ||
612 | if (aggressive) | |
613 | { | |
614 | for (k = 0; k < PHI_NUM_ARGS (i); k++) | |
615 | { | |
616 | basic_block arg_bb = PHI_ARG_EDGE (i, k)->src; | |
617 | if (! (arg_bb->flags & BB_VISITED)) | |
618 | { | |
619 | arg_bb->flags |= BB_VISITED; | |
620 | mark_control_dependent_edges_necessary (arg_bb, el); | |
621 | } | |
622 | } | |
623 | } | |
624 | } | |
625 | else | |
626 | { | |
627 | /* Propagate through the operands. Examine all the USE, VUSE and | |
a32b97a2 BB |
628 | V_MAY_DEF operands in this statement. Mark all the statements |
629 | which feed this statement's uses as necessary. */ | |
6de9cd9a | 630 | vuse_optype vuses; |
a32b97a2 | 631 | v_may_def_optype v_may_defs; |
6de9cd9a DN |
632 | use_optype uses; |
633 | stmt_ann_t ann; | |
634 | size_t k; | |
635 | ||
636 | get_stmt_operands (i); | |
637 | ann = stmt_ann (i); | |
638 | ||
639 | uses = USE_OPS (ann); | |
640 | for (k = 0; k < NUM_USES (uses); k++) | |
641 | mark_operand_necessary (USE_OP (uses, k)); | |
642 | ||
643 | vuses = VUSE_OPS (ann); | |
644 | for (k = 0; k < NUM_VUSES (vuses); k++) | |
645 | mark_operand_necessary (VUSE_OP (vuses, k)); | |
646 | ||
a32b97a2 | 647 | /* The operands of V_MAY_DEF expressions are also needed as they |
6de9cd9a | 648 | represent potential definitions that may reach this |
a32b97a2 BB |
649 | statement (V_MAY_DEF operands allow us to follow def-def |
650 | links). */ | |
651 | v_may_defs = V_MAY_DEF_OPS (ann); | |
652 | for (k = 0; k < NUM_V_MAY_DEFS (v_may_defs); k++) | |
653 | mark_operand_necessary (V_MAY_DEF_OP (v_may_defs, k)); | |
6de9cd9a DN |
654 | } |
655 | } | |
656 | } | |
657 | \f | |
658 | /* Eliminate unnecessary statements. Any instruction not marked as necessary | |
659 | contributes nothing to the program, and can be deleted. */ | |
660 | ||
661 | static void | |
662 | eliminate_unnecessary_stmts (void) | |
663 | { | |
664 | basic_block bb; | |
665 | block_stmt_iterator i; | |
666 | ||
667 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
668 | fprintf (dump_file, "\nEliminating unnecessary statements:\n"); | |
669 | ||
670 | clear_special_calls (); | |
671 | FOR_EACH_BB (bb) | |
672 | { | |
673 | /* Remove dead PHI nodes. */ | |
674 | remove_dead_phis (bb); | |
675 | ||
676 | /* Remove dead statements. */ | |
677 | for (i = bsi_start (bb); ! bsi_end_p (i) ; ) | |
678 | { | |
679 | tree t = bsi_stmt (i); | |
680 | ||
681 | stats.total++; | |
682 | ||
683 | /* If `i' is not necessary then remove it. */ | |
684 | if (! NECESSARY (t)) | |
685 | remove_dead_stmt (&i, bb); | |
686 | else | |
687 | { | |
cd709752 RH |
688 | tree call = get_call_expr_in (t); |
689 | if (call) | |
690 | notice_special_calls (call); | |
6de9cd9a DN |
691 | bsi_next (&i); |
692 | } | |
693 | } | |
694 | } | |
695 | } | |
696 | \f | |
697 | /* Remove dead PHI nodes from block BB. */ | |
698 | ||
699 | static void | |
700 | remove_dead_phis (basic_block bb) | |
701 | { | |
702 | tree prev, phi; | |
703 | ||
704 | prev = NULL_TREE; | |
705 | phi = phi_nodes (bb); | |
706 | while (phi) | |
707 | { | |
708 | stats.total_phis++; | |
709 | ||
710 | if (! NECESSARY (phi)) | |
711 | { | |
17192884 | 712 | tree next = PHI_CHAIN (phi); |
6de9cd9a DN |
713 | |
714 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
715 | { | |
716 | fprintf (dump_file, "Deleting : "); | |
717 | print_generic_stmt (dump_file, phi, TDF_SLIM); | |
718 | fprintf (dump_file, "\n"); | |
719 | } | |
720 | ||
721 | remove_phi_node (phi, prev, bb); | |
722 | stats.removed_phis++; | |
723 | phi = next; | |
724 | } | |
725 | else | |
726 | { | |
727 | prev = phi; | |
17192884 | 728 | phi = PHI_CHAIN (phi); |
6de9cd9a DN |
729 | } |
730 | } | |
731 | } | |
732 | \f | |
733 | /* Remove dead statement pointed by iterator I. Receives the basic block BB | |
734 | containing I so that we don't have to look it up. */ | |
735 | ||
736 | static void | |
737 | remove_dead_stmt (block_stmt_iterator *i, basic_block bb) | |
738 | { | |
739 | tree t = bsi_stmt (*i); | |
740 | ||
741 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
742 | { | |
743 | fprintf (dump_file, "Deleting : "); | |
744 | print_generic_stmt (dump_file, t, TDF_SLIM); | |
745 | fprintf (dump_file, "\n"); | |
746 | } | |
747 | ||
748 | stats.removed++; | |
749 | ||
750 | /* If we have determined that a conditional branch statement contributes | |
751 | nothing to the program, then we not only remove it, but we also change | |
752 | the flow graph so that the current block will simply fall-thru to its | |
753 | immediate post-dominator. The blocks we are circumventing will be | |
754 | removed by cleaup_cfg if this change in the flow graph makes them | |
755 | unreachable. */ | |
756 | if (is_ctrl_stmt (t)) | |
757 | { | |
758 | basic_block post_dom_bb; | |
759 | edge e; | |
760 | #ifdef ENABLE_CHECKING | |
761 | /* The post dominance info has to be up-to-date. */ | |
762 | if (dom_computed[CDI_POST_DOMINATORS] != DOM_OK) | |
763 | abort (); | |
764 | #endif | |
765 | /* Get the immediate post dominator of bb. */ | |
766 | post_dom_bb = get_immediate_dominator (CDI_POST_DOMINATORS, bb); | |
767 | /* Some blocks don't have an immediate post dominator. This can happen | |
768 | for example with infinite loops. Removing an infinite loop is an | |
769 | inappropriate transformation anyway... */ | |
770 | if (! post_dom_bb) | |
771 | { | |
772 | bsi_next (i); | |
773 | return; | |
774 | } | |
775 | ||
776 | /* Redirect the first edge out of BB to reach POST_DOM_BB. */ | |
777 | redirect_edge_and_branch (bb->succ, post_dom_bb); | |
778 | PENDING_STMT (bb->succ) = NULL; | |
779 | ||
780 | /* The edge is no longer associated with a conditional, so it does | |
781 | not have TRUE/FALSE flags. */ | |
782 | bb->succ->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE); | |
783 | ||
784 | /* If the edge reaches any block other than the exit, then it is a | |
785 | fallthru edge; if it reaches the exit, then it is not a fallthru | |
786 | edge. */ | |
787 | if (post_dom_bb != EXIT_BLOCK_PTR) | |
788 | bb->succ->flags |= EDGE_FALLTHRU; | |
789 | else | |
790 | bb->succ->flags &= ~EDGE_FALLTHRU; | |
791 | ||
792 | /* Remove the remaining the outgoing edges. */ | |
793 | for (e = bb->succ->succ_next; e != NULL;) | |
794 | { | |
795 | edge tmp = e; | |
796 | e = e->succ_next; | |
797 | remove_edge (tmp); | |
798 | } | |
799 | } | |
800 | ||
801 | bsi_remove (i); | |
53b4bf74 | 802 | release_defs (t); |
6de9cd9a DN |
803 | } |
804 | \f | |
805 | /* Print out removed statement statistics. */ | |
806 | ||
807 | static void | |
808 | print_stats (void) | |
809 | { | |
810 | if (dump_file && (dump_flags & (TDF_STATS|TDF_DETAILS))) | |
811 | { | |
812 | float percg; | |
813 | ||
814 | percg = ((float) stats.removed / (float) stats.total) * 100; | |
815 | fprintf (dump_file, "Removed %d of %d statements (%d%%)\n", | |
816 | stats.removed, stats.total, (int) percg); | |
817 | ||
818 | if (stats.total_phis == 0) | |
819 | percg = 0; | |
820 | else | |
821 | percg = ((float) stats.removed_phis / (float) stats.total_phis) * 100; | |
822 | ||
823 | fprintf (dump_file, "Removed %d of %d PHI nodes (%d%%)\n", | |
824 | stats.removed_phis, stats.total_phis, (int) percg); | |
825 | } | |
826 | } | |
827 | \f | |
828 | /* Initialization for this pass. Set up the used data structures. */ | |
829 | ||
830 | static void | |
831 | tree_dce_init (bool aggressive) | |
832 | { | |
833 | memset ((void *) &stats, 0, sizeof (stats)); | |
834 | ||
835 | if (aggressive) | |
836 | { | |
837 | int i; | |
838 | ||
839 | control_dependence_map | |
840 | = xmalloc (last_basic_block * sizeof (bitmap)); | |
841 | for (i = 0; i < last_basic_block; ++i) | |
842 | control_dependence_map[i] = BITMAP_XMALLOC (); | |
843 | ||
844 | last_stmt_necessary = sbitmap_alloc (last_basic_block); | |
845 | sbitmap_zero (last_stmt_necessary); | |
846 | } | |
847 | ||
95a3742c | 848 | processed = sbitmap_alloc (num_ssa_names + 1); |
6de9cd9a DN |
849 | sbitmap_zero (processed); |
850 | ||
851 | VARRAY_TREE_INIT (worklist, 64, "work list"); | |
852 | } | |
853 | ||
854 | /* Cleanup after this pass. */ | |
855 | ||
856 | static void | |
857 | tree_dce_done (bool aggressive) | |
858 | { | |
859 | if (aggressive) | |
860 | { | |
861 | int i; | |
862 | ||
863 | for (i = 0; i < last_basic_block; ++i) | |
864 | BITMAP_XFREE (control_dependence_map[i]); | |
865 | free (control_dependence_map); | |
866 | ||
867 | sbitmap_free (last_stmt_necessary); | |
868 | } | |
869 | ||
870 | sbitmap_free (processed); | |
871 | } | |
872 | \f | |
873 | /* Main routine to eliminate dead code. | |
874 | ||
875 | AGGRESSIVE controls the aggressiveness of the algorithm. | |
876 | In conservative mode, we ignore control dependence and simply declare | |
877 | all but the most trivially dead branches necessary. This mode is fast. | |
878 | In aggressive mode, control dependences are taken into account, which | |
879 | results in more dead code elimination, but at the cost of some time. | |
880 | ||
881 | FIXME: Aggressive mode before PRE doesn't work currently because | |
882 | the dominance info is not invalidated after DCE1. This is | |
883 | not an issue right now because we only run aggressive DCE | |
884 | as the last tree SSA pass, but keep this in mind when you | |
885 | start experimenting with pass ordering. */ | |
886 | ||
887 | static void | |
888 | perform_tree_ssa_dce (bool aggressive) | |
889 | { | |
890 | struct edge_list *el = NULL; | |
891 | ||
892 | tree_dce_init (aggressive); | |
893 | ||
894 | if (aggressive) | |
895 | { | |
896 | /* Compute control dependence. */ | |
897 | timevar_push (TV_CONTROL_DEPENDENCES); | |
898 | calculate_dominance_info (CDI_POST_DOMINATORS); | |
899 | el = create_edge_list (); | |
900 | find_all_control_dependences (el); | |
901 | timevar_pop (TV_CONTROL_DEPENDENCES); | |
902 | ||
903 | mark_dfs_back_edges (); | |
904 | } | |
905 | ||
906 | find_obviously_necessary_stmts (el); | |
907 | ||
908 | propagate_necessity (el); | |
909 | ||
910 | eliminate_unnecessary_stmts (); | |
911 | ||
912 | if (aggressive) | |
913 | free_dominance_info (CDI_POST_DOMINATORS); | |
914 | ||
915 | cleanup_tree_cfg (); | |
916 | ||
917 | /* Debugging dumps. */ | |
918 | if (dump_file) | |
919 | { | |
920 | dump_function_to_file (current_function_decl, dump_file, dump_flags); | |
921 | print_stats (); | |
922 | } | |
923 | ||
924 | tree_dce_done (aggressive); | |
960076d9 AP |
925 | |
926 | free_edge_list (el); | |
6de9cd9a DN |
927 | } |
928 | ||
929 | /* Pass entry points. */ | |
930 | static void | |
931 | tree_ssa_dce (void) | |
932 | { | |
933 | perform_tree_ssa_dce (/*aggressive=*/false); | |
934 | } | |
935 | ||
936 | static void | |
937 | tree_ssa_cd_dce (void) | |
938 | { | |
939 | perform_tree_ssa_dce (/*aggressive=*/optimize >= 2); | |
940 | } | |
941 | ||
942 | static bool | |
943 | gate_dce (void) | |
944 | { | |
945 | return flag_tree_dce != 0; | |
946 | } | |
947 | ||
948 | struct tree_opt_pass pass_dce = | |
949 | { | |
950 | "dce", /* name */ | |
951 | gate_dce, /* gate */ | |
952 | tree_ssa_dce, /* execute */ | |
953 | NULL, /* sub */ | |
954 | NULL, /* next */ | |
955 | 0, /* static_pass_number */ | |
956 | TV_TREE_DCE, /* tv_id */ | |
c1b763fa | 957 | PROP_cfg | PROP_ssa | PROP_alias, /* properties_required */ |
6de9cd9a DN |
958 | 0, /* properties_provided */ |
959 | 0, /* properties_destroyed */ | |
960 | 0, /* todo_flags_start */ | |
961 | TODO_ggc_collect | TODO_verify_ssa /* todo_flags_finish */ | |
962 | }; | |
963 | ||
964 | struct tree_opt_pass pass_cd_dce = | |
965 | { | |
966 | "cddce", /* name */ | |
967 | gate_dce, /* gate */ | |
968 | tree_ssa_cd_dce, /* execute */ | |
969 | NULL, /* sub */ | |
970 | NULL, /* next */ | |
971 | 0, /* static_pass_number */ | |
972 | TV_TREE_CD_DCE, /* tv_id */ | |
c1b763fa | 973 | PROP_cfg | PROP_ssa | PROP_alias, /* properties_required */ |
6de9cd9a DN |
974 | 0, /* properties_provided */ |
975 | 0, /* properties_destroyed */ | |
976 | 0, /* todo_flags_start */ | |
977 | TODO_ggc_collect | TODO_verify_ssa | TODO_verify_flow | |
978 | /* todo_flags_finish */ | |
979 | }; | |
980 |