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6de9cd9a | 1 | /* Dead code elimination pass for the GNU compiler. |
ad616de1 | 2 | Copyright (C) 2002, 2003, 2004, 2005 Free Software Foundation, Inc. |
6de9cd9a DN |
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 | |
366ccddb KC |
21 | Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA |
22 | 02110-1301, USA. */ | |
6de9cd9a DN |
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" | |
6de9cd9a DN |
50 | #include "ggc.h" |
51 | ||
52 | /* These RTL headers are needed for basic-block.h. */ | |
53 | #include "rtl.h" | |
54 | #include "tm_p.h" | |
55 | #include "hard-reg-set.h" | |
7932a3db | 56 | #include "obstack.h" |
6de9cd9a DN |
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" | |
49896738 | 67 | #include "cfgloop.h" |
a4176272 | 68 | #include "tree-scalar-evolution.h" |
6de9cd9a DN |
69 | \f |
70 | static struct stmt_stats | |
71 | { | |
72 | int total; | |
73 | int total_phis; | |
74 | int removed; | |
75 | int removed_phis; | |
76 | } stats; | |
77 | ||
906532aa | 78 | static VEC(tree,heap) *worklist; |
6de9cd9a DN |
79 | |
80 | /* Vector indicating an SSA name has already been processed and marked | |
81 | as necessary. */ | |
82 | static sbitmap processed; | |
83 | ||
84 | /* Vector indicating that last_stmt if a basic block has already been | |
85 | marked as necessary. */ | |
86 | static sbitmap last_stmt_necessary; | |
87 | ||
88 | /* Before we can determine whether a control branch is dead, we need to | |
89 | compute which blocks are control dependent on which edges. | |
90 | ||
91 | We expect each block to be control dependent on very few edges so we | |
92 | use a bitmap for each block recording its edges. An array holds the | |
93 | bitmap. The Ith bit in the bitmap is set if that block is dependent | |
94 | on the Ith edge. */ | |
8c80c4aa | 95 | static bitmap *control_dependence_map; |
6de9cd9a | 96 | |
a28fee03 SB |
97 | /* Vector indicating that a basic block has already had all the edges |
98 | processed that it is control dependent on. */ | |
8c80c4aa | 99 | static sbitmap visited_control_parents; |
a28fee03 | 100 | |
9da4058c JL |
101 | /* TRUE if this pass alters the CFG (by removing control statements). |
102 | FALSE otherwise. | |
103 | ||
104 | If this pass alters the CFG, then it will arrange for the dominators | |
105 | to be recomputed. */ | |
106 | static bool cfg_altered; | |
107 | ||
db490c39 KH |
108 | /* Execute code that follows the macro for each edge (given number |
109 | EDGE_NUMBER within the CODE) for which the block with index N is | |
110 | control dependent. */ | |
111 | #define EXECUTE_IF_CONTROL_DEPENDENT(BI, N, EDGE_NUMBER) \ | |
112 | EXECUTE_IF_SET_IN_BITMAP (control_dependence_map[(N)], 0, \ | |
113 | (EDGE_NUMBER), (BI)) | |
6de9cd9a DN |
114 | |
115 | /* Local function prototypes. */ | |
116 | static inline void set_control_dependence_map_bit (basic_block, int); | |
117 | static inline void clear_control_dependence_bitmap (basic_block); | |
118 | static void find_all_control_dependences (struct edge_list *); | |
119 | static void find_control_dependence (struct edge_list *, int); | |
120 | static inline basic_block find_pdom (basic_block); | |
121 | ||
122 | static inline void mark_stmt_necessary (tree, bool); | |
52328bf6 | 123 | static inline void mark_operand_necessary (tree, bool); |
6de9cd9a | 124 | |
6de9cd9a DN |
125 | static void mark_stmt_if_obviously_necessary (tree, bool); |
126 | static void find_obviously_necessary_stmts (struct edge_list *); | |
127 | ||
128 | static void mark_control_dependent_edges_necessary (basic_block, struct edge_list *); | |
129 | static void propagate_necessity (struct edge_list *); | |
130 | ||
131 | static void eliminate_unnecessary_stmts (void); | |
132 | static void remove_dead_phis (basic_block); | |
133 | static void remove_dead_stmt (block_stmt_iterator *, basic_block); | |
134 | ||
135 | static void print_stats (void); | |
136 | static void tree_dce_init (bool); | |
137 | static void tree_dce_done (bool); | |
138 | \f | |
139 | /* Indicate block BB is control dependent on an edge with index EDGE_INDEX. */ | |
140 | static inline void | |
141 | set_control_dependence_map_bit (basic_block bb, int edge_index) | |
142 | { | |
143 | if (bb == ENTRY_BLOCK_PTR) | |
144 | return; | |
1e128c5f | 145 | gcc_assert (bb != EXIT_BLOCK_PTR); |
6de9cd9a DN |
146 | bitmap_set_bit (control_dependence_map[bb->index], edge_index); |
147 | } | |
148 | ||
149 | /* Clear all control dependences for block BB. */ | |
150 | static inline | |
151 | void clear_control_dependence_bitmap (basic_block bb) | |
152 | { | |
153 | bitmap_clear (control_dependence_map[bb->index]); | |
154 | } | |
155 | ||
156 | /* Record all blocks' control dependences on all edges in the edge | |
157 | list EL, ala Morgan, Section 3.6. */ | |
158 | ||
159 | static void | |
160 | find_all_control_dependences (struct edge_list *el) | |
161 | { | |
162 | int i; | |
163 | ||
164 | for (i = 0; i < NUM_EDGES (el); ++i) | |
165 | find_control_dependence (el, i); | |
166 | } | |
167 | ||
168 | /* Determine all blocks' control dependences on the given edge with edge_list | |
169 | EL index EDGE_INDEX, ala Morgan, Section 3.6. */ | |
170 | ||
171 | static void | |
172 | find_control_dependence (struct edge_list *el, int edge_index) | |
173 | { | |
174 | basic_block current_block; | |
175 | basic_block ending_block; | |
176 | ||
1e128c5f | 177 | gcc_assert (INDEX_EDGE_PRED_BB (el, edge_index) != EXIT_BLOCK_PTR); |
6de9cd9a DN |
178 | |
179 | if (INDEX_EDGE_PRED_BB (el, edge_index) == ENTRY_BLOCK_PTR) | |
953ff289 | 180 | ending_block = single_succ (ENTRY_BLOCK_PTR); |
6de9cd9a DN |
181 | else |
182 | ending_block = find_pdom (INDEX_EDGE_PRED_BB (el, edge_index)); | |
183 | ||
184 | for (current_block = INDEX_EDGE_SUCC_BB (el, edge_index); | |
185 | current_block != ending_block && current_block != EXIT_BLOCK_PTR; | |
186 | current_block = find_pdom (current_block)) | |
187 | { | |
188 | edge e = INDEX_EDGE (el, edge_index); | |
189 | ||
190 | /* For abnormal edges, we don't make current_block control | |
191 | dependent because instructions that throw are always necessary | |
192 | anyway. */ | |
193 | if (e->flags & EDGE_ABNORMAL) | |
194 | continue; | |
195 | ||
196 | set_control_dependence_map_bit (current_block, edge_index); | |
197 | } | |
198 | } | |
199 | ||
200 | /* Find the immediate postdominator PDOM of the specified basic block BLOCK. | |
201 | This function is necessary because some blocks have negative numbers. */ | |
202 | ||
203 | static inline basic_block | |
204 | find_pdom (basic_block block) | |
205 | { | |
1e128c5f GB |
206 | gcc_assert (block != ENTRY_BLOCK_PTR); |
207 | ||
208 | if (block == EXIT_BLOCK_PTR) | |
6de9cd9a DN |
209 | return EXIT_BLOCK_PTR; |
210 | else | |
211 | { | |
212 | basic_block bb = get_immediate_dominator (CDI_POST_DOMINATORS, block); | |
213 | if (! bb) | |
214 | return EXIT_BLOCK_PTR; | |
215 | return bb; | |
216 | } | |
217 | } | |
218 | \f | |
219 | #define NECESSARY(stmt) stmt->common.asm_written_flag | |
220 | ||
221 | /* If STMT is not already marked necessary, mark it, and add it to the | |
222 | worklist if ADD_TO_WORKLIST is true. */ | |
223 | static inline void | |
224 | mark_stmt_necessary (tree stmt, bool add_to_worklist) | |
225 | { | |
1e128c5f | 226 | gcc_assert (stmt); |
1e128c5f | 227 | gcc_assert (!DECL_P (stmt)); |
6de9cd9a DN |
228 | |
229 | if (NECESSARY (stmt)) | |
230 | return; | |
231 | ||
232 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
233 | { | |
234 | fprintf (dump_file, "Marking useful stmt: "); | |
235 | print_generic_stmt (dump_file, stmt, TDF_SLIM); | |
236 | fprintf (dump_file, "\n"); | |
237 | } | |
238 | ||
239 | NECESSARY (stmt) = 1; | |
240 | if (add_to_worklist) | |
906532aa | 241 | VEC_safe_push (tree, heap, worklist, stmt); |
6de9cd9a DN |
242 | } |
243 | ||
52328bf6 DB |
244 | /* Mark the statement defining operand OP as necessary. PHIONLY is true |
245 | if we should only mark it necessary if it is a phi node. */ | |
6de9cd9a DN |
246 | |
247 | static inline void | |
52328bf6 | 248 | mark_operand_necessary (tree op, bool phionly) |
6de9cd9a DN |
249 | { |
250 | tree stmt; | |
251 | int ver; | |
252 | ||
1e128c5f | 253 | gcc_assert (op); |
6de9cd9a DN |
254 | |
255 | ver = SSA_NAME_VERSION (op); | |
256 | if (TEST_BIT (processed, ver)) | |
257 | return; | |
258 | SET_BIT (processed, ver); | |
259 | ||
260 | stmt = SSA_NAME_DEF_STMT (op); | |
1e128c5f | 261 | gcc_assert (stmt); |
6de9cd9a DN |
262 | |
263 | if (NECESSARY (stmt) | |
52328bf6 DB |
264 | || IS_EMPTY_STMT (stmt) |
265 | || (phionly && TREE_CODE (stmt) != PHI_NODE)) | |
6de9cd9a DN |
266 | return; |
267 | ||
268 | NECESSARY (stmt) = 1; | |
906532aa | 269 | VEC_safe_push (tree, heap, worklist, stmt); |
6de9cd9a DN |
270 | } |
271 | \f | |
6de9cd9a | 272 | |
adb35797 | 273 | /* Mark STMT as necessary if it obviously is. Add it to the worklist if |
6de9cd9a DN |
274 | it can make other statements necessary. |
275 | ||
276 | If AGGRESSIVE is false, control statements are conservatively marked as | |
277 | necessary. */ | |
278 | ||
279 | static void | |
280 | mark_stmt_if_obviously_necessary (tree stmt, bool aggressive) | |
281 | { | |
6de9cd9a | 282 | stmt_ann_t ann; |
b729952b | 283 | tree op; |
6de9cd9a | 284 | |
75b80166 SB |
285 | /* With non-call exceptions, we have to assume that all statements could |
286 | throw. If a statement may throw, it is inherently necessary. */ | |
287 | if (flag_non_call_exceptions | |
288 | && tree_could_throw_p (stmt)) | |
289 | { | |
290 | mark_stmt_necessary (stmt, true); | |
291 | return; | |
292 | } | |
293 | ||
6de9cd9a DN |
294 | /* Statements that are implicitly live. Most function calls, asm and return |
295 | statements are required. Labels and BIND_EXPR nodes are kept because | |
296 | they are control flow, and we have no way of knowing whether they can be | |
297 | removed. DCE can eliminate all the other statements in a block, and CFG | |
298 | can then remove the block and labels. */ | |
299 | switch (TREE_CODE (stmt)) | |
300 | { | |
301 | case BIND_EXPR: | |
302 | case LABEL_EXPR: | |
303 | case CASE_LABEL_EXPR: | |
304 | mark_stmt_necessary (stmt, false); | |
305 | return; | |
306 | ||
307 | case ASM_EXPR: | |
308 | case RESX_EXPR: | |
309 | case RETURN_EXPR: | |
310 | mark_stmt_necessary (stmt, true); | |
311 | return; | |
312 | ||
313 | case CALL_EXPR: | |
314 | /* Most, but not all function calls are required. Function calls that | |
315 | produce no result and have no side effects (i.e. const pure | |
316 | functions) are unnecessary. */ | |
317 | if (TREE_SIDE_EFFECTS (stmt)) | |
318 | mark_stmt_necessary (stmt, true); | |
319 | return; | |
320 | ||
321 | case MODIFY_EXPR: | |
cd709752 RH |
322 | op = get_call_expr_in (stmt); |
323 | if (op && TREE_SIDE_EFFECTS (op)) | |
6de9cd9a DN |
324 | { |
325 | mark_stmt_necessary (stmt, true); | |
326 | return; | |
327 | } | |
328 | ||
329 | /* These values are mildly magic bits of the EH runtime. We can't | |
330 | see the entire lifetime of these values until landing pads are | |
331 | generated. */ | |
332 | if (TREE_CODE (TREE_OPERAND (stmt, 0)) == EXC_PTR_EXPR | |
333 | || TREE_CODE (TREE_OPERAND (stmt, 0)) == FILTER_EXPR) | |
334 | { | |
335 | mark_stmt_necessary (stmt, true); | |
336 | return; | |
337 | } | |
338 | break; | |
339 | ||
340 | case GOTO_EXPR: | |
7f604986 KH |
341 | gcc_assert (!simple_goto_p (stmt)); |
342 | mark_stmt_necessary (stmt, true); | |
6de9cd9a DN |
343 | return; |
344 | ||
345 | case COND_EXPR: | |
269da1e9 | 346 | gcc_assert (EDGE_COUNT (bb_for_stmt (stmt)->succs) == 2); |
6de9cd9a DN |
347 | /* Fall through. */ |
348 | ||
349 | case SWITCH_EXPR: | |
350 | if (! aggressive) | |
351 | mark_stmt_necessary (stmt, true); | |
352 | break; | |
353 | ||
354 | default: | |
355 | break; | |
356 | } | |
357 | ||
358 | ann = stmt_ann (stmt); | |
c597ef4e DN |
359 | |
360 | /* If the statement has volatile operands, it needs to be preserved. | |
361 | Same for statements that can alter control flow in unpredictable | |
362 | ways. */ | |
363 | if (ann->has_volatile_ops || is_ctrl_altering_stmt (stmt)) | |
6de9cd9a DN |
364 | { |
365 | mark_stmt_necessary (stmt, true); | |
366 | return; | |
367 | } | |
368 | ||
fa555252 | 369 | if (is_hidden_global_store (stmt)) |
a32b97a2 | 370 | { |
fa555252 DB |
371 | mark_stmt_necessary (stmt, true); |
372 | return; | |
6de9cd9a DN |
373 | } |
374 | ||
375 | return; | |
376 | } | |
377 | \f | |
378 | /* Find obviously necessary statements. These are things like most function | |
379 | calls, and stores to file level variables. | |
380 | ||
381 | If EL is NULL, control statements are conservatively marked as | |
382 | necessary. Otherwise it contains the list of edges used by control | |
383 | dependence analysis. */ | |
384 | ||
385 | static void | |
386 | find_obviously_necessary_stmts (struct edge_list *el) | |
387 | { | |
388 | basic_block bb; | |
389 | block_stmt_iterator i; | |
390 | edge e; | |
391 | ||
392 | FOR_EACH_BB (bb) | |
393 | { | |
394 | tree phi; | |
395 | ||
396 | /* Check any PHI nodes in the block. */ | |
17192884 | 397 | for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi)) |
6de9cd9a DN |
398 | { |
399 | NECESSARY (phi) = 0; | |
400 | ||
401 | /* PHIs for virtual variables do not directly affect code | |
402 | generation and need not be considered inherently necessary | |
403 | regardless of the bits set in their decl. | |
404 | ||
405 | Thus, we only need to mark PHIs for real variables which | |
406 | need their result preserved as being inherently necessary. */ | |
407 | if (is_gimple_reg (PHI_RESULT (phi)) | |
c597ef4e | 408 | && is_global_var (SSA_NAME_VAR (PHI_RESULT (phi)))) |
6de9cd9a DN |
409 | mark_stmt_necessary (phi, true); |
410 | } | |
411 | ||
412 | /* Check all statements in the block. */ | |
413 | for (i = bsi_start (bb); ! bsi_end_p (i); bsi_next (&i)) | |
414 | { | |
415 | tree stmt = bsi_stmt (i); | |
416 | NECESSARY (stmt) = 0; | |
417 | mark_stmt_if_obviously_necessary (stmt, el != NULL); | |
418 | } | |
6de9cd9a DN |
419 | } |
420 | ||
421 | if (el) | |
422 | { | |
423 | /* Prevent the loops from being removed. We must keep the infinite loops, | |
424 | and we currently do not have a means to recognize the finite ones. */ | |
425 | FOR_EACH_BB (bb) | |
426 | { | |
628f6a4e BE |
427 | edge_iterator ei; |
428 | FOR_EACH_EDGE (e, ei, bb->succs) | |
6de9cd9a DN |
429 | if (e->flags & EDGE_DFS_BACK) |
430 | mark_control_dependent_edges_necessary (e->dest, el); | |
431 | } | |
432 | } | |
433 | } | |
434 | \f | |
435 | /* Make corresponding control dependent edges necessary. We only | |
436 | have to do this once for each basic block, so we clear the bitmap | |
437 | after we're done. */ | |
438 | static void | |
439 | mark_control_dependent_edges_necessary (basic_block bb, struct edge_list *el) | |
440 | { | |
db490c39 | 441 | bitmap_iterator bi; |
3cd8c58a | 442 | unsigned edge_number; |
6de9cd9a | 443 | |
1e128c5f | 444 | gcc_assert (bb != EXIT_BLOCK_PTR); |
7e6eb623 DB |
445 | |
446 | if (bb == ENTRY_BLOCK_PTR) | |
447 | return; | |
448 | ||
db490c39 | 449 | EXECUTE_IF_CONTROL_DEPENDENT (bi, bb->index, edge_number) |
6de9cd9a DN |
450 | { |
451 | tree t; | |
452 | basic_block cd_bb = INDEX_EDGE_PRED_BB (el, edge_number); | |
453 | ||
454 | if (TEST_BIT (last_stmt_necessary, cd_bb->index)) | |
455 | continue; | |
456 | SET_BIT (last_stmt_necessary, cd_bb->index); | |
457 | ||
458 | t = last_stmt (cd_bb); | |
1eaba2f2 | 459 | if (t && is_ctrl_stmt (t)) |
6de9cd9a | 460 | mark_stmt_necessary (t, true); |
db490c39 | 461 | } |
6de9cd9a DN |
462 | } |
463 | \f | |
464 | /* Propagate necessity using the operands of necessary statements. Process | |
465 | the uses on each statement in the worklist, and add all feeding statements | |
466 | which contribute to the calculation of this value to the worklist. | |
467 | ||
468 | In conservative mode, EL is NULL. */ | |
469 | ||
470 | static void | |
471 | propagate_necessity (struct edge_list *el) | |
472 | { | |
473 | tree i; | |
474 | bool aggressive = (el ? true : false); | |
475 | ||
476 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
477 | fprintf (dump_file, "\nProcessing worklist:\n"); | |
478 | ||
906532aa | 479 | while (VEC_length (tree, worklist) > 0) |
6de9cd9a DN |
480 | { |
481 | /* Take `i' from worklist. */ | |
906532aa | 482 | i = VEC_pop (tree, worklist); |
6de9cd9a DN |
483 | |
484 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
485 | { | |
486 | fprintf (dump_file, "processing: "); | |
487 | print_generic_stmt (dump_file, i, TDF_SLIM); | |
488 | fprintf (dump_file, "\n"); | |
489 | } | |
490 | ||
491 | if (aggressive) | |
492 | { | |
493 | /* Mark the last statements of the basic blocks that the block | |
494 | containing `i' is control dependent on, but only if we haven't | |
495 | already done so. */ | |
496 | basic_block bb = bb_for_stmt (i); | |
a28fee03 SB |
497 | if (bb != ENTRY_BLOCK_PTR |
498 | && ! TEST_BIT (visited_control_parents, bb->index)) | |
6de9cd9a | 499 | { |
a28fee03 | 500 | SET_BIT (visited_control_parents, bb->index); |
6de9cd9a DN |
501 | mark_control_dependent_edges_necessary (bb, el); |
502 | } | |
503 | } | |
504 | ||
505 | if (TREE_CODE (i) == PHI_NODE) | |
506 | { | |
507 | /* PHI nodes are somewhat special in that each PHI alternative has | |
508 | data and control dependencies. All the statements feeding the | |
509 | PHI node's arguments are always necessary. In aggressive mode, | |
510 | we also consider the control dependent edges leading to the | |
511 | predecessor block associated with each PHI alternative as | |
512 | necessary. */ | |
513 | int k; | |
514 | for (k = 0; k < PHI_NUM_ARGS (i); k++) | |
515 | { | |
516 | tree arg = PHI_ARG_DEF (i, k); | |
517 | if (TREE_CODE (arg) == SSA_NAME) | |
52328bf6 | 518 | mark_operand_necessary (arg, false); |
6de9cd9a DN |
519 | } |
520 | ||
521 | if (aggressive) | |
522 | { | |
523 | for (k = 0; k < PHI_NUM_ARGS (i); k++) | |
524 | { | |
525 | basic_block arg_bb = PHI_ARG_EDGE (i, k)->src; | |
a28fee03 SB |
526 | if (arg_bb != ENTRY_BLOCK_PTR |
527 | && ! TEST_BIT (visited_control_parents, arg_bb->index)) | |
6de9cd9a | 528 | { |
a28fee03 | 529 | SET_BIT (visited_control_parents, arg_bb->index); |
6de9cd9a DN |
530 | mark_control_dependent_edges_necessary (arg_bb, el); |
531 | } | |
532 | } | |
533 | } | |
534 | } | |
535 | else | |
536 | { | |
537 | /* Propagate through the operands. Examine all the USE, VUSE and | |
a32b97a2 BB |
538 | V_MAY_DEF operands in this statement. Mark all the statements |
539 | which feed this statement's uses as necessary. */ | |
4c124b4c AM |
540 | ssa_op_iter iter; |
541 | tree use; | |
6de9cd9a | 542 | |
a32b97a2 | 543 | /* The operands of V_MAY_DEF expressions are also needed as they |
6de9cd9a | 544 | represent potential definitions that may reach this |
a32b97a2 BB |
545 | statement (V_MAY_DEF operands allow us to follow def-def |
546 | links). */ | |
4c124b4c AM |
547 | |
548 | FOR_EACH_SSA_TREE_OPERAND (use, i, iter, SSA_OP_ALL_USES) | |
52328bf6 | 549 | mark_operand_necessary (use, false); |
6de9cd9a DN |
550 | } |
551 | } | |
552 | } | |
52328bf6 DB |
553 | |
554 | ||
555 | /* Propagate necessity around virtual phi nodes used in kill operands. | |
556 | The reason this isn't done during propagate_necessity is because we don't | |
557 | want to keep phis around that are just there for must-defs, unless we | |
558 | absolutely have to. After we've rewritten the reaching definitions to be | |
559 | correct in the previous part of the fixup routine, we can simply propagate | |
560 | around the information about which of these virtual phi nodes are really | |
561 | used, and set the NECESSARY flag accordingly. | |
562 | Note that we do the minimum here to ensure that we keep alive the phis that | |
563 | are actually used in the corrected SSA form. In particular, some of these | |
564 | phis may now have all of the same operand, and will be deleted by some | |
565 | other pass. */ | |
566 | ||
567 | static void | |
568 | mark_really_necessary_kill_operand_phis (void) | |
569 | { | |
570 | basic_block bb; | |
571 | int i; | |
572 | ||
573 | /* Seed the worklist with the new virtual phi arguments and virtual | |
574 | uses */ | |
575 | FOR_EACH_BB (bb) | |
576 | { | |
577 | block_stmt_iterator bsi; | |
578 | tree phi; | |
579 | ||
580 | for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi)) | |
581 | { | |
582 | if (!is_gimple_reg (PHI_RESULT (phi)) && NECESSARY (phi)) | |
583 | { | |
584 | for (i = 0; i < PHI_NUM_ARGS (phi); i++) | |
585 | mark_operand_necessary (PHI_ARG_DEF (phi, i), true); | |
586 | } | |
587 | } | |
588 | ||
589 | for (bsi = bsi_last (bb); !bsi_end_p (bsi); bsi_prev (&bsi)) | |
590 | { | |
591 | tree stmt = bsi_stmt (bsi); | |
592 | ||
593 | if (NECESSARY (stmt)) | |
594 | { | |
595 | use_operand_p use_p; | |
596 | ssa_op_iter iter; | |
597 | FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, | |
598 | SSA_OP_VIRTUAL_USES | SSA_OP_VIRTUAL_KILLS) | |
599 | { | |
600 | tree use = USE_FROM_PTR (use_p); | |
601 | mark_operand_necessary (use, true); | |
602 | } | |
603 | } | |
604 | } | |
605 | } | |
606 | ||
607 | /* Mark all virtual phis still in use as necessary, and all of their | |
608 | arguments that are phis as necessary. */ | |
906532aa | 609 | while (VEC_length (tree, worklist) > 0) |
52328bf6 | 610 | { |
906532aa | 611 | tree use = VEC_pop (tree, worklist); |
52328bf6 DB |
612 | |
613 | for (i = 0; i < PHI_NUM_ARGS (use); i++) | |
614 | mark_operand_necessary (PHI_ARG_DEF (use, i), true); | |
615 | } | |
616 | } | |
617 | ||
618 | ||
6de9cd9a | 619 | \f |
52328bf6 | 620 | |
6de9cd9a DN |
621 | /* Eliminate unnecessary statements. Any instruction not marked as necessary |
622 | contributes nothing to the program, and can be deleted. */ | |
623 | ||
624 | static void | |
625 | eliminate_unnecessary_stmts (void) | |
626 | { | |
627 | basic_block bb; | |
628 | block_stmt_iterator i; | |
629 | ||
630 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
631 | fprintf (dump_file, "\nEliminating unnecessary statements:\n"); | |
52328bf6 | 632 | |
6de9cd9a DN |
633 | clear_special_calls (); |
634 | FOR_EACH_BB (bb) | |
635 | { | |
636 | /* Remove dead PHI nodes. */ | |
637 | remove_dead_phis (bb); | |
e18d4a19 | 638 | } |
6de9cd9a | 639 | |
e18d4a19 AO |
640 | FOR_EACH_BB (bb) |
641 | { | |
6de9cd9a DN |
642 | /* Remove dead statements. */ |
643 | for (i = bsi_start (bb); ! bsi_end_p (i) ; ) | |
644 | { | |
52328bf6 DB |
645 | tree t = bsi_stmt (i); |
646 | ||
647 | stats.total++; | |
648 | ||
649 | /* If `i' is not necessary then remove it. */ | |
650 | if (! NECESSARY (t)) | |
651 | remove_dead_stmt (&i, bb); | |
652 | else | |
653 | { | |
654 | tree call = get_call_expr_in (t); | |
655 | if (call) | |
656 | notice_special_calls (call); | |
657 | bsi_next (&i); | |
658 | } | |
6de9cd9a DN |
659 | } |
660 | } | |
52328bf6 | 661 | } |
6de9cd9a DN |
662 | \f |
663 | /* Remove dead PHI nodes from block BB. */ | |
664 | ||
665 | static void | |
666 | remove_dead_phis (basic_block bb) | |
667 | { | |
668 | tree prev, phi; | |
669 | ||
670 | prev = NULL_TREE; | |
671 | phi = phi_nodes (bb); | |
672 | while (phi) | |
673 | { | |
674 | stats.total_phis++; | |
675 | ||
676 | if (! NECESSARY (phi)) | |
677 | { | |
17192884 | 678 | tree next = PHI_CHAIN (phi); |
6de9cd9a DN |
679 | |
680 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
681 | { | |
682 | fprintf (dump_file, "Deleting : "); | |
683 | print_generic_stmt (dump_file, phi, TDF_SLIM); | |
684 | fprintf (dump_file, "\n"); | |
685 | } | |
686 | ||
d19e3ef6 | 687 | remove_phi_node (phi, prev); |
6de9cd9a DN |
688 | stats.removed_phis++; |
689 | phi = next; | |
690 | } | |
691 | else | |
692 | { | |
693 | prev = phi; | |
17192884 | 694 | phi = PHI_CHAIN (phi); |
6de9cd9a DN |
695 | } |
696 | } | |
697 | } | |
698 | \f | |
206048bd | 699 | /* Remove dead statement pointed to by iterator I. Receives the basic block BB |
6de9cd9a DN |
700 | containing I so that we don't have to look it up. */ |
701 | ||
702 | static void | |
703 | remove_dead_stmt (block_stmt_iterator *i, basic_block bb) | |
704 | { | |
705 | tree t = bsi_stmt (*i); | |
52328bf6 DB |
706 | def_operand_p def_p; |
707 | ||
708 | ssa_op_iter iter; | |
6de9cd9a DN |
709 | |
710 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
711 | { | |
712 | fprintf (dump_file, "Deleting : "); | |
713 | print_generic_stmt (dump_file, t, TDF_SLIM); | |
714 | fprintf (dump_file, "\n"); | |
715 | } | |
716 | ||
717 | stats.removed++; | |
718 | ||
719 | /* If we have determined that a conditional branch statement contributes | |
720 | nothing to the program, then we not only remove it, but we also change | |
721 | the flow graph so that the current block will simply fall-thru to its | |
722 | immediate post-dominator. The blocks we are circumventing will be | |
32cd8777 | 723 | removed by cleaup_tree_cfg if this change in the flow graph makes them |
6de9cd9a DN |
724 | unreachable. */ |
725 | if (is_ctrl_stmt (t)) | |
726 | { | |
727 | basic_block post_dom_bb; | |
e18d4a19 | 728 | |
6de9cd9a | 729 | /* The post dominance info has to be up-to-date. */ |
1e128c5f | 730 | gcc_assert (dom_computed[CDI_POST_DOMINATORS] == DOM_OK); |
6de9cd9a DN |
731 | /* Get the immediate post dominator of bb. */ |
732 | post_dom_bb = get_immediate_dominator (CDI_POST_DOMINATORS, bb); | |
6de9cd9a | 733 | |
0a180c0e JL |
734 | /* There are three particularly problematical cases. |
735 | ||
736 | 1. Blocks that do not have an immediate post dominator. This | |
737 | can happen with infinite loops. | |
738 | ||
739 | 2. Blocks that are only post dominated by the exit block. These | |
740 | can also happen for infinite loops as we create fake edges | |
741 | in the dominator tree. | |
742 | ||
743 | 3. If the post dominator has PHI nodes we may be able to compute | |
744 | the right PHI args for them. | |
745 | ||
746 | ||
747 | In each of these cases we must remove the control statement | |
748 | as it may reference SSA_NAMEs which are going to be removed and | |
749 | we remove all but one outgoing edge from the block. */ | |
750 | if (! post_dom_bb | |
751 | || post_dom_bb == EXIT_BLOCK_PTR | |
752 | || phi_nodes (post_dom_bb)) | |
753 | ; | |
e18d4a19 AO |
754 | else |
755 | { | |
756 | /* Redirect the first edge out of BB to reach POST_DOM_BB. */ | |
757 | redirect_edge_and_branch (EDGE_SUCC (bb, 0), post_dom_bb); | |
758 | PENDING_STMT (EDGE_SUCC (bb, 0)) = NULL; | |
759 | } | |
628f6a4e BE |
760 | EDGE_SUCC (bb, 0)->probability = REG_BR_PROB_BASE; |
761 | EDGE_SUCC (bb, 0)->count = bb->count; | |
6de9cd9a DN |
762 | |
763 | /* The edge is no longer associated with a conditional, so it does | |
764 | not have TRUE/FALSE flags. */ | |
628f6a4e | 765 | EDGE_SUCC (bb, 0)->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE); |
6de9cd9a | 766 | |
0a180c0e JL |
767 | /* The lone outgoing edge from BB will be a fallthru edge. */ |
768 | EDGE_SUCC (bb, 0)->flags |= EDGE_FALLTHRU; | |
6de9cd9a DN |
769 | |
770 | /* Remove the remaining the outgoing edges. */ | |
c5cbcccf | 771 | while (!single_succ_p (bb)) |
9da4058c JL |
772 | { |
773 | /* FIXME. When we remove the edge, we modify the CFG, which | |
774 | in turn modifies the dominator and post-dominator tree. | |
775 | Is it safe to postpone recomputing the dominator and | |
776 | post-dominator tree until the end of this pass given that | |
777 | the post-dominators are used above? */ | |
778 | cfg_altered = true; | |
779 | remove_edge (EDGE_SUCC (bb, 1)); | |
780 | } | |
6de9cd9a | 781 | } |
52328bf6 | 782 | |
66d3fe47 | 783 | FOR_EACH_SSA_DEF_OPERAND (def_p, t, iter, SSA_OP_VIRTUAL_DEFS) |
52328bf6 DB |
784 | { |
785 | tree def = DEF_FROM_PTR (def_p); | |
0bca51f0 | 786 | mark_sym_for_renaming (SSA_NAME_VAR (def)); |
52328bf6 | 787 | } |
736432ee | 788 | bsi_remove (i, true); |
52328bf6 | 789 | release_defs (t); |
6de9cd9a DN |
790 | } |
791 | \f | |
792 | /* Print out removed statement statistics. */ | |
793 | ||
794 | static void | |
795 | print_stats (void) | |
796 | { | |
797 | if (dump_file && (dump_flags & (TDF_STATS|TDF_DETAILS))) | |
798 | { | |
799 | float percg; | |
800 | ||
801 | percg = ((float) stats.removed / (float) stats.total) * 100; | |
802 | fprintf (dump_file, "Removed %d of %d statements (%d%%)\n", | |
803 | stats.removed, stats.total, (int) percg); | |
804 | ||
805 | if (stats.total_phis == 0) | |
806 | percg = 0; | |
807 | else | |
808 | percg = ((float) stats.removed_phis / (float) stats.total_phis) * 100; | |
809 | ||
810 | fprintf (dump_file, "Removed %d of %d PHI nodes (%d%%)\n", | |
811 | stats.removed_phis, stats.total_phis, (int) percg); | |
812 | } | |
813 | } | |
814 | \f | |
815 | /* Initialization for this pass. Set up the used data structures. */ | |
816 | ||
817 | static void | |
818 | tree_dce_init (bool aggressive) | |
819 | { | |
820 | memset ((void *) &stats, 0, sizeof (stats)); | |
821 | ||
822 | if (aggressive) | |
823 | { | |
824 | int i; | |
825 | ||
e1111e8e | 826 | control_dependence_map = XNEWVEC (bitmap, last_basic_block); |
6de9cd9a | 827 | for (i = 0; i < last_basic_block; ++i) |
8bdbfff5 | 828 | control_dependence_map[i] = BITMAP_ALLOC (NULL); |
6de9cd9a DN |
829 | |
830 | last_stmt_necessary = sbitmap_alloc (last_basic_block); | |
831 | sbitmap_zero (last_stmt_necessary); | |
832 | } | |
833 | ||
95a3742c | 834 | processed = sbitmap_alloc (num_ssa_names + 1); |
6de9cd9a DN |
835 | sbitmap_zero (processed); |
836 | ||
906532aa | 837 | worklist = VEC_alloc (tree, heap, 64); |
9da4058c | 838 | cfg_altered = false; |
6de9cd9a DN |
839 | } |
840 | ||
841 | /* Cleanup after this pass. */ | |
842 | ||
843 | static void | |
844 | tree_dce_done (bool aggressive) | |
845 | { | |
846 | if (aggressive) | |
847 | { | |
848 | int i; | |
849 | ||
850 | for (i = 0; i < last_basic_block; ++i) | |
8bdbfff5 | 851 | BITMAP_FREE (control_dependence_map[i]); |
6de9cd9a DN |
852 | free (control_dependence_map); |
853 | ||
a28fee03 | 854 | sbitmap_free (visited_control_parents); |
6de9cd9a DN |
855 | sbitmap_free (last_stmt_necessary); |
856 | } | |
857 | ||
858 | sbitmap_free (processed); | |
906532aa KH |
859 | |
860 | VEC_free (tree, heap, worklist); | |
6de9cd9a DN |
861 | } |
862 | \f | |
863 | /* Main routine to eliminate dead code. | |
864 | ||
865 | AGGRESSIVE controls the aggressiveness of the algorithm. | |
866 | In conservative mode, we ignore control dependence and simply declare | |
867 | all but the most trivially dead branches necessary. This mode is fast. | |
868 | In aggressive mode, control dependences are taken into account, which | |
869 | results in more dead code elimination, but at the cost of some time. | |
870 | ||
871 | FIXME: Aggressive mode before PRE doesn't work currently because | |
872 | the dominance info is not invalidated after DCE1. This is | |
873 | not an issue right now because we only run aggressive DCE | |
874 | as the last tree SSA pass, but keep this in mind when you | |
875 | start experimenting with pass ordering. */ | |
876 | ||
877 | static void | |
878 | perform_tree_ssa_dce (bool aggressive) | |
879 | { | |
880 | struct edge_list *el = NULL; | |
881 | ||
882 | tree_dce_init (aggressive); | |
883 | ||
884 | if (aggressive) | |
885 | { | |
886 | /* Compute control dependence. */ | |
887 | timevar_push (TV_CONTROL_DEPENDENCES); | |
888 | calculate_dominance_info (CDI_POST_DOMINATORS); | |
889 | el = create_edge_list (); | |
890 | find_all_control_dependences (el); | |
891 | timevar_pop (TV_CONTROL_DEPENDENCES); | |
892 | ||
a28fee03 SB |
893 | visited_control_parents = sbitmap_alloc (last_basic_block); |
894 | sbitmap_zero (visited_control_parents); | |
895 | ||
6de9cd9a DN |
896 | mark_dfs_back_edges (); |
897 | } | |
898 | ||
899 | find_obviously_necessary_stmts (el); | |
900 | ||
901 | propagate_necessity (el); | |
902 | ||
52328bf6 | 903 | mark_really_necessary_kill_operand_phis (); |
6de9cd9a DN |
904 | eliminate_unnecessary_stmts (); |
905 | ||
906 | if (aggressive) | |
907 | free_dominance_info (CDI_POST_DOMINATORS); | |
908 | ||
9da4058c JL |
909 | /* If we removed paths in the CFG, then we need to update |
910 | dominators as well. I haven't investigated the possibility | |
911 | of incrementally updating dominators. */ | |
912 | if (cfg_altered) | |
913 | free_dominance_info (CDI_DOMINATORS); | |
914 | ||
6de9cd9a DN |
915 | /* Debugging dumps. */ |
916 | if (dump_file) | |
88a40e67 | 917 | print_stats (); |
6de9cd9a DN |
918 | |
919 | tree_dce_done (aggressive); | |
960076d9 AP |
920 | |
921 | free_edge_list (el); | |
6de9cd9a DN |
922 | } |
923 | ||
924 | /* Pass entry points. */ | |
c2924966 | 925 | static unsigned int |
6de9cd9a DN |
926 | tree_ssa_dce (void) |
927 | { | |
928 | perform_tree_ssa_dce (/*aggressive=*/false); | |
c2924966 | 929 | return 0; |
6de9cd9a DN |
930 | } |
931 | ||
c2924966 | 932 | static unsigned int |
49896738 RH |
933 | tree_ssa_dce_loop (void) |
934 | { | |
935 | perform_tree_ssa_dce (/*aggressive=*/false); | |
936 | free_numbers_of_iterations_estimates (current_loops); | |
a4176272 | 937 | scev_reset (); |
c2924966 | 938 | return 0; |
49896738 RH |
939 | } |
940 | ||
c2924966 | 941 | static unsigned int |
6de9cd9a DN |
942 | tree_ssa_cd_dce (void) |
943 | { | |
944 | perform_tree_ssa_dce (/*aggressive=*/optimize >= 2); | |
c2924966 | 945 | return 0; |
6de9cd9a DN |
946 | } |
947 | ||
948 | static bool | |
949 | gate_dce (void) | |
950 | { | |
951 | return flag_tree_dce != 0; | |
952 | } | |
953 | ||
954 | struct tree_opt_pass pass_dce = | |
955 | { | |
956 | "dce", /* name */ | |
957 | gate_dce, /* gate */ | |
958 | tree_ssa_dce, /* execute */ | |
959 | NULL, /* sub */ | |
960 | NULL, /* next */ | |
961 | 0, /* static_pass_number */ | |
962 | TV_TREE_DCE, /* tv_id */ | |
c1b763fa | 963 | PROP_cfg | PROP_ssa | PROP_alias, /* properties_required */ |
6de9cd9a DN |
964 | 0, /* properties_provided */ |
965 | 0, /* properties_destroyed */ | |
966 | 0, /* todo_flags_start */ | |
0bca51f0 | 967 | TODO_dump_func |
8b1062b2 | 968 | | TODO_update_ssa |
0bca51f0 DN |
969 | | TODO_cleanup_cfg |
970 | | TODO_ggc_collect | |
3f519b35 RG |
971 | | TODO_verify_ssa |
972 | | TODO_remove_unused_locals, /* todo_flags_finish */ | |
9f8628ba | 973 | 0 /* letter */ |
6de9cd9a DN |
974 | }; |
975 | ||
49896738 RH |
976 | struct tree_opt_pass pass_dce_loop = |
977 | { | |
978 | "dceloop", /* name */ | |
979 | gate_dce, /* gate */ | |
980 | tree_ssa_dce_loop, /* execute */ | |
981 | NULL, /* sub */ | |
982 | NULL, /* next */ | |
983 | 0, /* static_pass_number */ | |
984 | TV_TREE_DCE, /* tv_id */ | |
985 | PROP_cfg | PROP_ssa | PROP_alias, /* properties_required */ | |
986 | 0, /* properties_provided */ | |
987 | 0, /* properties_destroyed */ | |
988 | 0, /* todo_flags_start */ | |
989 | TODO_dump_func | |
8b1062b2 | 990 | | TODO_update_ssa |
49896738 RH |
991 | | TODO_cleanup_cfg |
992 | | TODO_verify_ssa, /* todo_flags_finish */ | |
993 | 0 /* letter */ | |
994 | }; | |
995 | ||
6de9cd9a DN |
996 | struct tree_opt_pass pass_cd_dce = |
997 | { | |
998 | "cddce", /* name */ | |
999 | gate_dce, /* gate */ | |
1000 | tree_ssa_cd_dce, /* execute */ | |
1001 | NULL, /* sub */ | |
1002 | NULL, /* next */ | |
1003 | 0, /* static_pass_number */ | |
1004 | TV_TREE_CD_DCE, /* tv_id */ | |
c1b763fa | 1005 | PROP_cfg | PROP_ssa | PROP_alias, /* properties_required */ |
6de9cd9a DN |
1006 | 0, /* properties_provided */ |
1007 | 0, /* properties_destroyed */ | |
1008 | 0, /* todo_flags_start */ | |
0bca51f0 | 1009 | TODO_dump_func |
8b1062b2 | 1010 | | TODO_update_ssa |
0bca51f0 DN |
1011 | | TODO_cleanup_cfg |
1012 | | TODO_ggc_collect | |
1013 | | TODO_verify_ssa | |
1014 | | TODO_verify_flow, /* todo_flags_finish */ | |
9f8628ba | 1015 | 0 /* letter */ |
6de9cd9a | 1016 | }; |