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1 /* Generic routines for manipulating PHIs
2 Copyright (C) 2003-2014 Free Software Foundation, Inc.
3
4 This file is part of GCC.
5
6 GCC is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 3, or (at your option)
9 any later version.
10
11 GCC is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
15
16 You should have received a copy of the GNU General Public License
17 along with GCC; see the file COPYING3. If not see
18 <http://www.gnu.org/licenses/>. */
19
20 #include "config.h"
21 #include "system.h"
22 #include "coretypes.h"
23 #include "tm.h"
24 #include "tree.h"
25 #include "basic-block.h"
26 #include "tree-ssa-alias.h"
27 #include "internal-fn.h"
28 #include "gimple-expr.h"
29 #include "is-a.h"
30 #include "gimple.h"
31 #include "gimple-iterator.h"
32 #include "gimple-ssa.h"
33 #include "tree-phinodes.h"
34 #include "ssa-iterators.h"
35 #include "stringpool.h"
36 #include "tree-ssanames.h"
37 #include "tree-ssa.h"
38 #include "diagnostic-core.h"
39
40 /* Rewriting a function into SSA form can create a huge number of PHIs
41 many of which may be thrown away shortly after their creation if jumps
42 were threaded through PHI nodes.
43
44 While our garbage collection mechanisms will handle this situation, it
45 is extremely wasteful to create nodes and throw them away, especially
46 when the nodes can be reused.
47
48 For PR 8361, we can significantly reduce the number of nodes allocated
49 and thus the total amount of memory allocated by managing PHIs a
50 little. This additionally helps reduce the amount of work done by the
51 garbage collector. Similar results have been seen on a wider variety
52 of tests (such as the compiler itself).
53
54 PHI nodes have different sizes, so we can't have a single list of all
55 the PHI nodes as it would be too expensive to walk down that list to
56 find a PHI of a suitable size.
57
58 Instead we have an array of lists of free PHI nodes. The array is
59 indexed by the number of PHI alternatives that PHI node can hold.
60 Except for the last array member, which holds all remaining PHI
61 nodes.
62
63 So to find a free PHI node, we compute its index into the free PHI
64 node array and see if there are any elements with an exact match.
65 If so, then we are done. Otherwise, we test the next larger size
66 up and continue until we are in the last array element.
67
68 We do not actually walk members of the last array element. While it
69 might allow us to pick up a few reusable PHI nodes, it could potentially
70 be very expensive if the program has released a bunch of large PHI nodes,
71 but keeps asking for even larger PHI nodes. Experiments have shown that
72 walking the elements of the last array entry would result in finding less
73 than .1% additional reusable PHI nodes.
74
75 Note that we can never have less than two PHI argument slots. Thus,
76 the -2 on all the calculations below. */
77
78 #define NUM_BUCKETS 10
79 static GTY ((deletable (""))) vec<gimple, va_gc> *free_phinodes[NUM_BUCKETS - 2];
80 static unsigned long free_phinode_count;
81
82 static int ideal_phi_node_len (int);
83
84 unsigned int phi_nodes_reused;
85 unsigned int phi_nodes_created;
86
87 /* Dump some simple statistics regarding the re-use of PHI nodes. */
88
89 void
90 phinodes_print_statistics (void)
91 {
92 fprintf (stderr, "PHI nodes allocated: %u\n", phi_nodes_created);
93 fprintf (stderr, "PHI nodes reused: %u\n", phi_nodes_reused);
94 }
95
96 /* Allocate a PHI node with at least LEN arguments. If the free list
97 happens to contain a PHI node with LEN arguments or more, return
98 that one. */
99
100 static inline gimple_statement_phi *
101 allocate_phi_node (size_t len)
102 {
103 gimple_statement_phi *phi;
104 size_t bucket = NUM_BUCKETS - 2;
105 size_t size = sizeof (struct gimple_statement_phi)
106 + (len - 1) * sizeof (struct phi_arg_d);
107
108 if (free_phinode_count)
109 for (bucket = len - 2; bucket < NUM_BUCKETS - 2; bucket++)
110 if (free_phinodes[bucket])
111 break;
112
113 /* If our free list has an element, then use it. */
114 if (bucket < NUM_BUCKETS - 2
115 && gimple_phi_capacity ((*free_phinodes[bucket])[0]) >= len)
116 {
117 free_phinode_count--;
118 phi = as_a <gimple_statement_phi *> (free_phinodes[bucket]->pop ());
119 if (free_phinodes[bucket]->is_empty ())
120 vec_free (free_phinodes[bucket]);
121 if (GATHER_STATISTICS)
122 phi_nodes_reused++;
123 }
124 else
125 {
126 phi = static_cast <gimple_statement_phi *> (
127 ggc_internal_alloc_stat (size MEM_STAT_INFO));
128 if (GATHER_STATISTICS)
129 {
130 enum gimple_alloc_kind kind = gimple_alloc_kind (GIMPLE_PHI);
131 phi_nodes_created++;
132 gimple_alloc_counts[(int) kind]++;
133 gimple_alloc_sizes[(int) kind] += size;
134 }
135 }
136
137 return phi;
138 }
139
140 /* Given LEN, the original number of requested PHI arguments, return
141 a new, "ideal" length for the PHI node. The "ideal" length rounds
142 the total size of the PHI node up to the next power of two bytes.
143
144 Rounding up will not result in wasting any memory since the size request
145 will be rounded up by the GC system anyway. [ Note this is not entirely
146 true since the original length might have fit on one of the special
147 GC pages. ] By rounding up, we may avoid the need to reallocate the
148 PHI node later if we increase the number of arguments for the PHI. */
149
150 static int
151 ideal_phi_node_len (int len)
152 {
153 size_t size, new_size;
154 int log2, new_len;
155
156 /* We do not support allocations of less than two PHI argument slots. */
157 if (len < 2)
158 len = 2;
159
160 /* Compute the number of bytes of the original request. */
161 size = sizeof (struct gimple_statement_phi)
162 + (len - 1) * sizeof (struct phi_arg_d);
163
164 /* Round it up to the next power of two. */
165 log2 = ceil_log2 (size);
166 new_size = 1 << log2;
167
168 /* Now compute and return the number of PHI argument slots given an
169 ideal size allocation. */
170 new_len = len + (new_size - size) / sizeof (struct phi_arg_d);
171 return new_len;
172 }
173
174 /* Return a PHI node with LEN argument slots for variable VAR. */
175
176 static gimple
177 make_phi_node (tree var, int len)
178 {
179 gimple_statement_phi *phi;
180 int capacity, i;
181
182 capacity = ideal_phi_node_len (len);
183
184 phi = allocate_phi_node (capacity);
185
186 /* We need to clear the entire PHI node, including the argument
187 portion, because we represent a "missing PHI argument" by placing
188 NULL_TREE in PHI_ARG_DEF. */
189 memset (phi, 0, (sizeof (struct gimple_statement_phi)
190 - sizeof (struct phi_arg_d)
191 + sizeof (struct phi_arg_d) * len));
192 phi->code = GIMPLE_PHI;
193 gimple_init_singleton (phi);
194 phi->nargs = len;
195 phi->capacity = capacity;
196 if (!var)
197 ;
198 else if (TREE_CODE (var) == SSA_NAME)
199 gimple_phi_set_result (phi, var);
200 else
201 gimple_phi_set_result (phi, make_ssa_name (var, phi));
202
203 for (i = 0; i < capacity; i++)
204 {
205 use_operand_p imm;
206
207 gimple_phi_arg_set_location (phi, i, UNKNOWN_LOCATION);
208 imm = gimple_phi_arg_imm_use_ptr (phi, i);
209 imm->use = gimple_phi_arg_def_ptr (phi, i);
210 imm->prev = NULL;
211 imm->next = NULL;
212 imm->loc.stmt = phi;
213 }
214
215 return phi;
216 }
217
218 /* We no longer need PHI, release it so that it may be reused. */
219
220 void
221 release_phi_node (gimple phi)
222 {
223 size_t bucket;
224 size_t len = gimple_phi_capacity (phi);
225 size_t x;
226
227 for (x = 0; x < gimple_phi_num_args (phi); x++)
228 {
229 use_operand_p imm;
230 imm = gimple_phi_arg_imm_use_ptr (phi, x);
231 delink_imm_use (imm);
232 }
233
234 bucket = len > NUM_BUCKETS - 1 ? NUM_BUCKETS - 1 : len;
235 bucket -= 2;
236 vec_safe_push (free_phinodes[bucket], phi);
237 free_phinode_count++;
238 }
239
240
241 /* Resize an existing PHI node. The only way is up. Return the
242 possibly relocated phi. */
243
244 static gimple_statement_phi *
245 resize_phi_node (gimple_statement_phi *phi, size_t len)
246 {
247 size_t old_size, i;
248 gimple_statement_phi *new_phi;
249
250 gcc_assert (len > gimple_phi_capacity (phi));
251
252 /* The garbage collector will not look at the PHI node beyond the
253 first PHI_NUM_ARGS elements. Therefore, all we have to copy is a
254 portion of the PHI node currently in use. */
255 old_size = sizeof (struct gimple_statement_phi)
256 + (gimple_phi_num_args (phi) - 1) * sizeof (struct phi_arg_d);
257
258 new_phi = allocate_phi_node (len);
259
260 memcpy (new_phi, phi, old_size);
261
262 for (i = 0; i < gimple_phi_num_args (new_phi); i++)
263 {
264 use_operand_p imm, old_imm;
265 imm = gimple_phi_arg_imm_use_ptr (new_phi, i);
266 old_imm = gimple_phi_arg_imm_use_ptr (phi, i);
267 imm->use = gimple_phi_arg_def_ptr (new_phi, i);
268 relink_imm_use_stmt (imm, old_imm, new_phi);
269 }
270
271 new_phi->capacity = len;
272
273 for (i = gimple_phi_num_args (new_phi); i < len; i++)
274 {
275 use_operand_p imm;
276
277 gimple_phi_arg_set_location (new_phi, i, UNKNOWN_LOCATION);
278 imm = gimple_phi_arg_imm_use_ptr (new_phi, i);
279 imm->use = gimple_phi_arg_def_ptr (new_phi, i);
280 imm->prev = NULL;
281 imm->next = NULL;
282 imm->loc.stmt = new_phi;
283 }
284
285 return new_phi;
286 }
287
288 /* Reserve PHI arguments for a new edge to basic block BB. */
289
290 void
291 reserve_phi_args_for_new_edge (basic_block bb)
292 {
293 size_t len = EDGE_COUNT (bb->preds);
294 size_t cap = ideal_phi_node_len (len + 4);
295 gimple_stmt_iterator gsi;
296
297 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
298 {
299 gimple_statement_phi *stmt =
300 as_a <gimple_statement_phi *> (gsi_stmt (gsi));
301
302 if (len > gimple_phi_capacity (stmt))
303 {
304 gimple_statement_phi *new_phi = resize_phi_node (stmt, cap);
305
306 /* The result of the PHI is defined by this PHI node. */
307 SSA_NAME_DEF_STMT (gimple_phi_result (new_phi)) = new_phi;
308 gsi_set_stmt (&gsi, new_phi);
309
310 release_phi_node (stmt);
311 stmt = new_phi;
312 }
313
314 /* We represent a "missing PHI argument" by placing NULL_TREE in
315 the corresponding slot. If PHI arguments were added
316 immediately after an edge is created, this zeroing would not
317 be necessary, but unfortunately this is not the case. For
318 example, the loop optimizer duplicates several basic blocks,
319 redirects edges, and then fixes up PHI arguments later in
320 batch. */
321 SET_PHI_ARG_DEF (stmt, len - 1, NULL_TREE);
322 gimple_phi_arg_set_location (stmt, len - 1, UNKNOWN_LOCATION);
323
324 stmt->nargs++;
325 }
326 }
327
328 /* Adds PHI to BB. */
329
330 void
331 add_phi_node_to_bb (gimple phi, basic_block bb)
332 {
333 gimple_seq seq = phi_nodes (bb);
334 /* Add the new PHI node to the list of PHI nodes for block BB. */
335 if (seq == NULL)
336 set_phi_nodes (bb, gimple_seq_alloc_with_stmt (phi));
337 else
338 {
339 gimple_seq_add_stmt (&seq, phi);
340 gcc_assert (seq == phi_nodes (bb));
341 }
342
343 /* Associate BB to the PHI node. */
344 gimple_set_bb (phi, bb);
345
346 }
347
348 /* Create a new PHI node for variable VAR at basic block BB. */
349
350 gimple
351 create_phi_node (tree var, basic_block bb)
352 {
353 gimple phi = make_phi_node (var, EDGE_COUNT (bb->preds));
354
355 add_phi_node_to_bb (phi, bb);
356 return phi;
357 }
358
359
360 /* Add a new argument to PHI node PHI. DEF is the incoming reaching
361 definition and E is the edge through which DEF reaches PHI. The new
362 argument is added at the end of the argument list.
363 If PHI has reached its maximum capacity, add a few slots. In this case,
364 PHI points to the reallocated phi node when we return. */
365
366 void
367 add_phi_arg (gimple phi, tree def, edge e, source_location locus)
368 {
369 basic_block bb = e->dest;
370
371 gcc_assert (bb == gimple_bb (phi));
372
373 /* We resize PHI nodes upon edge creation. We should always have
374 enough room at this point. */
375 gcc_assert (gimple_phi_num_args (phi) <= gimple_phi_capacity (phi));
376
377 /* We resize PHI nodes upon edge creation. We should always have
378 enough room at this point. */
379 gcc_assert (e->dest_idx < gimple_phi_num_args (phi));
380
381 /* Copy propagation needs to know what object occur in abnormal
382 PHI nodes. This is a convenient place to record such information. */
383 if (e->flags & EDGE_ABNORMAL)
384 {
385 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (def) = 1;
386 SSA_NAME_OCCURS_IN_ABNORMAL_PHI (PHI_RESULT (phi)) = 1;
387 }
388
389 SET_PHI_ARG_DEF (phi, e->dest_idx, def);
390 gimple_phi_arg_set_location (phi, e->dest_idx, locus);
391 }
392
393
394 /* Remove the Ith argument from PHI's argument list. This routine
395 implements removal by swapping the last alternative with the
396 alternative we want to delete and then shrinking the vector, which
397 is consistent with how we remove an edge from the edge vector. */
398
399 static void
400 remove_phi_arg_num (gimple_statement_phi *phi, int i)
401 {
402 int num_elem = gimple_phi_num_args (phi);
403
404 gcc_assert (i < num_elem);
405
406 /* Delink the item which is being removed. */
407 delink_imm_use (gimple_phi_arg_imm_use_ptr (phi, i));
408
409 /* If it is not the last element, move the last element
410 to the element we want to delete, resetting all the links. */
411 if (i != num_elem - 1)
412 {
413 use_operand_p old_p, new_p;
414 old_p = gimple_phi_arg_imm_use_ptr (phi, num_elem - 1);
415 new_p = gimple_phi_arg_imm_use_ptr (phi, i);
416 /* Set use on new node, and link into last element's place. */
417 *(new_p->use) = *(old_p->use);
418 relink_imm_use (new_p, old_p);
419 /* Move the location as well. */
420 gimple_phi_arg_set_location (phi, i,
421 gimple_phi_arg_location (phi, num_elem - 1));
422 }
423
424 /* Shrink the vector and return. Note that we do not have to clear
425 PHI_ARG_DEF because the garbage collector will not look at those
426 elements beyond the first PHI_NUM_ARGS elements of the array. */
427 phi->nargs--;
428 }
429
430
431 /* Remove all PHI arguments associated with edge E. */
432
433 void
434 remove_phi_args (edge e)
435 {
436 gimple_stmt_iterator gsi;
437
438 for (gsi = gsi_start_phis (e->dest); !gsi_end_p (gsi); gsi_next (&gsi))
439 remove_phi_arg_num (as_a <gimple_statement_phi *> (gsi_stmt (gsi)),
440 e->dest_idx);
441 }
442
443
444 /* Remove the PHI node pointed-to by iterator GSI from basic block BB. After
445 removal, iterator GSI is updated to point to the next PHI node in the
446 sequence. If RELEASE_LHS_P is true, the LHS of this PHI node is released
447 into the free pool of SSA names. */
448
449 void
450 remove_phi_node (gimple_stmt_iterator *gsi, bool release_lhs_p)
451 {
452 gimple phi = gsi_stmt (*gsi);
453
454 if (release_lhs_p)
455 insert_debug_temps_for_defs (gsi);
456
457 gsi_remove (gsi, false);
458
459 /* If we are deleting the PHI node, then we should release the
460 SSA_NAME node so that it can be reused. */
461 release_phi_node (phi);
462 if (release_lhs_p)
463 release_ssa_name (gimple_phi_result (phi));
464 }
465
466 /* Remove all the phi nodes from BB. */
467
468 void
469 remove_phi_nodes (basic_block bb)
470 {
471 gimple_stmt_iterator gsi;
472
473 for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); )
474 remove_phi_node (&gsi, true);
475
476 set_phi_nodes (bb, NULL);
477 }
478
479 /* Given PHI, return its RHS if the PHI is a degenerate, otherwise return
480 NULL. */
481
482 tree
483 degenerate_phi_result (gimple phi)
484 {
485 tree lhs = gimple_phi_result (phi);
486 tree val = NULL;
487 size_t i;
488
489 /* Ignoring arguments which are the same as LHS, if all the remaining
490 arguments are the same, then the PHI is a degenerate and has the
491 value of that common argument. */
492 for (i = 0; i < gimple_phi_num_args (phi); i++)
493 {
494 tree arg = gimple_phi_arg_def (phi, i);
495
496 if (arg == lhs)
497 continue;
498 else if (!arg)
499 break;
500 else if (!val)
501 val = arg;
502 else if (arg == val)
503 continue;
504 /* We bring in some of operand_equal_p not only to speed things
505 up, but also to avoid crashing when dereferencing the type of
506 a released SSA name. */
507 else if (TREE_CODE (val) != TREE_CODE (arg)
508 || TREE_CODE (val) == SSA_NAME
509 || !operand_equal_p (arg, val, 0))
510 break;
511 }
512 return (i == gimple_phi_num_args (phi) ? val : NULL);
513 }
514
515 /* Set PHI nodes of a basic block BB to SEQ. */
516
517 void
518 set_phi_nodes (basic_block bb, gimple_seq seq)
519 {
520 gimple_stmt_iterator i;
521
522 gcc_checking_assert (!(bb->flags & BB_RTL));
523 bb->il.gimple.phi_nodes = seq;
524 if (seq)
525 for (i = gsi_start (seq); !gsi_end_p (i); gsi_next (&i))
526 gimple_set_bb (gsi_stmt (i), bb);
527 }
528
529 #include "gt-tree-phinodes.h"