Mercurial > hg > CbC > CbC_gcc
annotate gcc/tree-ssa-uncprop.c @ 86:12b3180c7d07
modify calls.c.
author | Nobuyasu Oshiro <dimolto@cr.ie.u-ryukyu.ac.jp> |
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date | Thu, 15 Dec 2011 02:37:13 +0900 |
parents | f6334be47118 |
children | 04ced10e8804 |
rev | line source |
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0 | 1 /* Routines for discovering and unpropagating edge equivalences. |
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2 Copyright (C) 2005, 2007, 2008, 2010 |
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3 Free Software Foundation, Inc. |
0 | 4 |
5 This file is part of GCC. | |
6 | |
7 GCC is free software; you can redistribute it and/or modify | |
8 it under the terms of the GNU General Public License as published by | |
9 the Free Software Foundation; either version 3, or (at your option) | |
10 any later version. | |
11 | |
12 GCC is distributed in the hope that it will be useful, | |
13 but WITHOUT ANY WARRANTY; without even the implied warranty of | |
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
15 GNU General Public License for more details. | |
16 | |
17 You should have received a copy of the GNU General Public License | |
18 along with GCC; see the file COPYING3. If not see | |
19 <http://www.gnu.org/licenses/>. */ | |
20 | |
21 #include "config.h" | |
22 #include "system.h" | |
23 #include "coretypes.h" | |
24 #include "tm.h" | |
25 #include "tree.h" | |
26 #include "flags.h" | |
27 #include "tm_p.h" | |
28 #include "basic-block.h" | |
29 #include "output.h" | |
30 #include "function.h" | |
31 #include "timevar.h" | |
32 #include "tree-dump.h" | |
33 #include "tree-flow.h" | |
34 #include "domwalk.h" | |
35 #include "tree-pass.h" | |
36 #include "tree-ssa-propagate.h" | |
37 #include "langhooks.h" | |
38 | |
39 /* The basic structure describing an equivalency created by traversing | |
40 an edge. Traversing the edge effectively means that we can assume | |
41 that we've seen an assignment LHS = RHS. */ | |
42 struct edge_equivalency | |
43 { | |
44 tree rhs; | |
45 tree lhs; | |
46 }; | |
47 | |
48 /* This routine finds and records edge equivalences for every edge | |
49 in the CFG. | |
50 | |
51 When complete, each edge that creates an equivalency will have an | |
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52 EDGE_EQUIVALENCY structure hanging off the edge's AUX field. |
0 | 53 The caller is responsible for freeing the AUX fields. */ |
54 | |
55 static void | |
56 associate_equivalences_with_edges (void) | |
57 { | |
58 basic_block bb; | |
59 | |
60 /* Walk over each block. If the block ends with a control statement, | |
61 then it might create a useful equivalence. */ | |
62 FOR_EACH_BB (bb) | |
63 { | |
64 gimple_stmt_iterator gsi = gsi_last_bb (bb); | |
65 gimple stmt; | |
66 | |
67 /* If the block does not end with a COND_EXPR or SWITCH_EXPR | |
68 then there is nothing to do. */ | |
69 if (gsi_end_p (gsi)) | |
70 continue; | |
71 | |
72 stmt = gsi_stmt (gsi); | |
73 | |
74 if (!stmt) | |
75 continue; | |
76 | |
77 /* A COND_EXPR may create an equivalency in a variety of different | |
78 ways. */ | |
79 if (gimple_code (stmt) == GIMPLE_COND) | |
80 { | |
81 edge true_edge; | |
82 edge false_edge; | |
83 struct edge_equivalency *equivalency; | |
84 enum tree_code code = gimple_cond_code (stmt); | |
85 | |
86 extract_true_false_edges_from_block (bb, &true_edge, &false_edge); | |
87 | |
88 /* Equality tests may create one or two equivalences. */ | |
89 if (code == EQ_EXPR || code == NE_EXPR) | |
90 { | |
91 tree op0 = gimple_cond_lhs (stmt); | |
92 tree op1 = gimple_cond_rhs (stmt); | |
93 | |
94 /* Special case comparing booleans against a constant as we | |
95 know the value of OP0 on both arms of the branch. i.e., we | |
96 can record an equivalence for OP0 rather than COND. */ | |
97 if (TREE_CODE (op0) == SSA_NAME | |
98 && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (op0) | |
99 && TREE_CODE (TREE_TYPE (op0)) == BOOLEAN_TYPE | |
100 && is_gimple_min_invariant (op1)) | |
101 { | |
102 if (code == EQ_EXPR) | |
103 { | |
104 equivalency = XNEW (struct edge_equivalency); | |
105 equivalency->lhs = op0; | |
106 equivalency->rhs = (integer_zerop (op1) | |
107 ? boolean_false_node | |
108 : boolean_true_node); | |
109 true_edge->aux = equivalency; | |
110 | |
111 equivalency = XNEW (struct edge_equivalency); | |
112 equivalency->lhs = op0; | |
113 equivalency->rhs = (integer_zerop (op1) | |
114 ? boolean_true_node | |
115 : boolean_false_node); | |
116 false_edge->aux = equivalency; | |
117 } | |
118 else | |
119 { | |
120 equivalency = XNEW (struct edge_equivalency); | |
121 equivalency->lhs = op0; | |
122 equivalency->rhs = (integer_zerop (op1) | |
123 ? boolean_true_node | |
124 : boolean_false_node); | |
125 true_edge->aux = equivalency; | |
126 | |
127 equivalency = XNEW (struct edge_equivalency); | |
128 equivalency->lhs = op0; | |
129 equivalency->rhs = (integer_zerop (op1) | |
130 ? boolean_false_node | |
131 : boolean_true_node); | |
132 false_edge->aux = equivalency; | |
133 } | |
134 } | |
135 | |
136 else if (TREE_CODE (op0) == SSA_NAME | |
137 && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (op0) | |
138 && (is_gimple_min_invariant (op1) | |
139 || (TREE_CODE (op1) == SSA_NAME | |
140 && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (op1)))) | |
141 { | |
142 /* For IEEE, -0.0 == 0.0, so we don't necessarily know | |
143 the sign of a variable compared against zero. If | |
144 we're honoring signed zeros, then we cannot record | |
145 this value unless we know that the value is nonzero. */ | |
146 if (HONOR_SIGNED_ZEROS (TYPE_MODE (TREE_TYPE (op0))) | |
147 && (TREE_CODE (op1) != REAL_CST | |
148 || REAL_VALUES_EQUAL (dconst0, TREE_REAL_CST (op1)))) | |
149 continue; | |
150 | |
151 equivalency = XNEW (struct edge_equivalency); | |
152 equivalency->lhs = op0; | |
153 equivalency->rhs = op1; | |
154 if (code == EQ_EXPR) | |
155 true_edge->aux = equivalency; | |
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156 else |
0 | 157 false_edge->aux = equivalency; |
158 | |
159 } | |
160 } | |
161 | |
162 /* ??? TRUTH_NOT_EXPR can create an equivalence too. */ | |
163 } | |
164 | |
165 /* For a SWITCH_EXPR, a case label which represents a single | |
166 value and which is the only case label which reaches the | |
167 target block creates an equivalence. */ | |
168 else if (gimple_code (stmt) == GIMPLE_SWITCH) | |
169 { | |
170 tree cond = gimple_switch_index (stmt); | |
171 | |
172 if (TREE_CODE (cond) == SSA_NAME | |
173 && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (cond)) | |
174 { | |
175 int i, n_labels = gimple_switch_num_labels (stmt); | |
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176 tree *info = XCNEWVEC (tree, last_basic_block); |
0 | 177 |
178 /* Walk over the case label vector. Record blocks | |
179 which are reached by a single case label which represents | |
180 a single value. */ | |
181 for (i = 0; i < n_labels; i++) | |
182 { | |
183 tree label = gimple_switch_label (stmt, i); | |
184 basic_block bb = label_to_block (CASE_LABEL (label)); | |
185 | |
186 if (CASE_HIGH (label) | |
187 || !CASE_LOW (label) | |
188 || info[bb->index]) | |
189 info[bb->index] = error_mark_node; | |
190 else | |
191 info[bb->index] = label; | |
192 } | |
193 | |
194 /* Now walk over the blocks to determine which ones were | |
195 marked as being reached by a useful case label. */ | |
196 for (i = 0; i < n_basic_blocks; i++) | |
197 { | |
198 tree node = info[i]; | |
199 | |
200 if (node != NULL | |
201 && node != error_mark_node) | |
202 { | |
203 tree x = fold_convert (TREE_TYPE (cond), CASE_LOW (node)); | |
204 struct edge_equivalency *equivalency; | |
205 | |
206 /* Record an equivalency on the edge from BB to basic | |
207 block I. */ | |
208 equivalency = XNEW (struct edge_equivalency); | |
209 equivalency->rhs = x; | |
210 equivalency->lhs = cond; | |
211 find_edge (bb, BASIC_BLOCK (i))->aux = equivalency; | |
212 } | |
213 } | |
214 free (info); | |
215 } | |
216 } | |
217 | |
218 } | |
219 } | |
220 | |
221 | |
222 /* Translating out of SSA sometimes requires inserting copies and | |
223 constant initializations on edges to eliminate PHI nodes. | |
224 | |
225 In some cases those copies and constant initializations are | |
226 redundant because the target already has the value on the | |
227 RHS of the assignment. | |
228 | |
229 We previously tried to catch these cases after translating | |
230 out of SSA form. However, that code often missed cases. Worse | |
231 yet, the cases it missed were also often missed by the RTL | |
232 optimizers. Thus the resulting code had redundant instructions. | |
233 | |
234 This pass attempts to detect these situations before translating | |
235 out of SSA form. | |
236 | |
237 The key concept that this pass is built upon is that these | |
238 redundant copies and constant initializations often occur | |
239 due to constant/copy propagating equivalences resulting from | |
240 COND_EXPRs and SWITCH_EXPRs. | |
241 | |
242 We want to do those propagations as they can sometimes allow | |
243 the SSA optimizers to do a better job. However, in the cases | |
244 where such propagations do not result in further optimization, | |
245 we would like to "undo" the propagation to avoid the redundant | |
246 copies and constant initializations. | |
247 | |
248 This pass works by first associating equivalences with edges in | |
249 the CFG. For example, the edge leading from a SWITCH_EXPR to | |
250 its associated CASE_LABEL will have an equivalency between | |
251 SWITCH_COND and the value in the case label. | |
252 | |
253 Once we have found the edge equivalences, we proceed to walk | |
254 the CFG in dominator order. As we traverse edges we record | |
255 equivalences associated with those edges we traverse. | |
256 | |
257 When we encounter a PHI node, we walk its arguments to see if we | |
258 have an equivalence for the PHI argument. If so, then we replace | |
259 the argument. | |
260 | |
261 Equivalences are looked up based on their value (think of it as | |
262 the RHS of an assignment). A value may be an SSA_NAME or an | |
263 invariant. We may have several SSA_NAMEs with the same value, | |
264 so with each value we have a list of SSA_NAMEs that have the | |
265 same value. */ | |
266 | |
267 /* As we enter each block we record the value for any edge equivalency | |
268 leading to this block. If no such edge equivalency exists, then we | |
269 record NULL. These equivalences are live until we leave the dominator | |
270 subtree rooted at the block where we record the equivalency. */ | |
271 static VEC(tree,heap) *equiv_stack; | |
272 | |
273 /* Global hash table implementing a mapping from invariant values | |
274 to a list of SSA_NAMEs which have the same value. We might be | |
275 able to reuse tree-vn for this code. */ | |
276 static htab_t equiv; | |
277 | |
278 /* Main structure for recording equivalences into our hash table. */ | |
279 struct equiv_hash_elt | |
280 { | |
281 /* The value/key of this entry. */ | |
282 tree value; | |
283 | |
284 /* List of SSA_NAMEs which have the same value/key. */ | |
285 VEC(tree,heap) *equivalences; | |
286 }; | |
287 | |
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288 static void uncprop_enter_block (struct dom_walk_data *, basic_block); |
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289 static void uncprop_leave_block (struct dom_walk_data *, basic_block); |
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290 static void uncprop_into_successor_phis (basic_block); |
0 | 291 |
292 /* Hashing and equality routines for the hash table. */ | |
293 | |
294 static hashval_t | |
295 equiv_hash (const void *p) | |
296 { | |
297 tree const value = ((const struct equiv_hash_elt *)p)->value; | |
298 return iterative_hash_expr (value, 0); | |
299 } | |
300 | |
301 static int | |
302 equiv_eq (const void *p1, const void *p2) | |
303 { | |
304 tree value1 = ((const struct equiv_hash_elt *)p1)->value; | |
305 tree value2 = ((const struct equiv_hash_elt *)p2)->value; | |
306 | |
307 return operand_equal_p (value1, value2, 0); | |
308 } | |
309 | |
310 /* Free an instance of equiv_hash_elt. */ | |
311 | |
312 static void | |
313 equiv_free (void *p) | |
314 { | |
315 struct equiv_hash_elt *elt = (struct equiv_hash_elt *) p; | |
316 VEC_free (tree, heap, elt->equivalences); | |
317 free (elt); | |
318 } | |
319 | |
320 /* Remove the most recently recorded equivalency for VALUE. */ | |
321 | |
322 static void | |
323 remove_equivalence (tree value) | |
324 { | |
325 struct equiv_hash_elt equiv_hash_elt, *equiv_hash_elt_p; | |
326 void **slot; | |
327 | |
328 equiv_hash_elt.value = value; | |
329 equiv_hash_elt.equivalences = NULL; | |
330 | |
331 slot = htab_find_slot (equiv, &equiv_hash_elt, NO_INSERT); | |
332 | |
333 equiv_hash_elt_p = (struct equiv_hash_elt *) *slot; | |
334 VEC_pop (tree, equiv_hash_elt_p->equivalences); | |
335 } | |
336 | |
337 /* Record EQUIVALENCE = VALUE into our hash table. */ | |
338 | |
339 static void | |
340 record_equiv (tree value, tree equivalence) | |
341 { | |
342 struct equiv_hash_elt *equiv_hash_elt; | |
343 void **slot; | |
344 | |
345 equiv_hash_elt = XNEW (struct equiv_hash_elt); | |
346 equiv_hash_elt->value = value; | |
347 equiv_hash_elt->equivalences = NULL; | |
348 | |
349 slot = htab_find_slot (equiv, equiv_hash_elt, INSERT); | |
350 | |
351 if (*slot == NULL) | |
352 *slot = (void *) equiv_hash_elt; | |
353 else | |
354 free (equiv_hash_elt); | |
355 | |
356 equiv_hash_elt = (struct equiv_hash_elt *) *slot; | |
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357 |
0 | 358 VEC_safe_push (tree, heap, equiv_hash_elt->equivalences, equivalence); |
359 } | |
360 | |
361 /* Main driver for un-cprop. */ | |
362 | |
363 static unsigned int | |
364 tree_ssa_uncprop (void) | |
365 { | |
366 struct dom_walk_data walk_data; | |
367 basic_block bb; | |
368 | |
369 associate_equivalences_with_edges (); | |
370 | |
371 /* Create our global data structures. */ | |
372 equiv = htab_create (1024, equiv_hash, equiv_eq, equiv_free); | |
373 equiv_stack = VEC_alloc (tree, heap, 2); | |
374 | |
375 /* We're going to do a dominator walk, so ensure that we have | |
376 dominance information. */ | |
377 calculate_dominance_info (CDI_DOMINATORS); | |
378 | |
379 /* Setup callbacks for the generic dominator tree walker. */ | |
380 walk_data.dom_direction = CDI_DOMINATORS; | |
381 walk_data.initialize_block_local_data = NULL; | |
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382 walk_data.before_dom_children = uncprop_enter_block; |
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383 walk_data.after_dom_children = uncprop_leave_block; |
0 | 384 walk_data.global_data = NULL; |
385 walk_data.block_local_data_size = 0; | |
386 | |
387 /* Now initialize the dominator walker. */ | |
388 init_walk_dominator_tree (&walk_data); | |
389 | |
390 /* Recursively walk the dominator tree undoing unprofitable | |
391 constant/copy propagations. */ | |
392 walk_dominator_tree (&walk_data, ENTRY_BLOCK_PTR); | |
393 | |
394 /* Finalize and clean up. */ | |
395 fini_walk_dominator_tree (&walk_data); | |
396 | |
397 /* EQUIV_STACK should already be empty at this point, so we just | |
398 need to empty elements out of the hash table, free EQUIV_STACK, | |
399 and cleanup the AUX field on the edges. */ | |
400 htab_delete (equiv); | |
401 VEC_free (tree, heap, equiv_stack); | |
402 FOR_EACH_BB (bb) | |
403 { | |
404 edge e; | |
405 edge_iterator ei; | |
406 | |
407 FOR_EACH_EDGE (e, ei, bb->succs) | |
408 { | |
409 if (e->aux) | |
410 { | |
411 free (e->aux); | |
412 e->aux = NULL; | |
413 } | |
414 } | |
415 } | |
416 return 0; | |
417 } | |
418 | |
419 | |
420 /* We have finished processing the dominator children of BB, perform | |
421 any finalization actions in preparation for leaving this node in | |
422 the dominator tree. */ | |
423 | |
424 static void | |
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425 uncprop_leave_block (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED, |
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426 basic_block bb ATTRIBUTE_UNUSED) |
0 | 427 { |
428 /* Pop the topmost value off the equiv stack. */ | |
429 tree value = VEC_pop (tree, equiv_stack); | |
430 | |
431 /* If that value was non-null, then pop the topmost equivalency off | |
432 its equivalency stack. */ | |
433 if (value != NULL) | |
434 remove_equivalence (value); | |
435 } | |
436 | |
437 /* Unpropagate values from PHI nodes in successor blocks of BB. */ | |
438 | |
439 static void | |
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440 uncprop_into_successor_phis (basic_block bb) |
0 | 441 { |
442 edge e; | |
443 edge_iterator ei; | |
444 | |
445 /* For each successor edge, first temporarily record any equivalence | |
446 on that edge. Then unpropagate values in any PHI nodes at the | |
447 destination of the edge. Then remove the temporary equivalence. */ | |
448 FOR_EACH_EDGE (e, ei, bb->succs) | |
449 { | |
450 gimple_seq phis = phi_nodes (e->dest); | |
451 gimple_stmt_iterator gsi; | |
452 | |
453 /* If there are no PHI nodes in this destination, then there is | |
454 no sense in recording any equivalences. */ | |
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455 if (gimple_seq_empty_p (phis)) |
0 | 456 continue; |
457 | |
458 /* Record any equivalency associated with E. */ | |
459 if (e->aux) | |
460 { | |
461 struct edge_equivalency *equiv = (struct edge_equivalency *) e->aux; | |
462 record_equiv (equiv->rhs, equiv->lhs); | |
463 } | |
464 | |
465 /* Walk over the PHI nodes, unpropagating values. */ | |
466 for (gsi = gsi_start (phis) ; !gsi_end_p (gsi); gsi_next (&gsi)) | |
467 { | |
468 gimple phi = gsi_stmt (gsi); | |
469 tree arg = PHI_ARG_DEF (phi, e->dest_idx); | |
470 struct equiv_hash_elt equiv_hash_elt; | |
471 void **slot; | |
472 | |
473 /* If the argument is not an invariant, or refers to the same | |
474 underlying variable as the PHI result, then there's no | |
475 point in un-propagating the argument. */ | |
476 if (!is_gimple_min_invariant (arg) | |
477 && SSA_NAME_VAR (arg) != SSA_NAME_VAR (PHI_RESULT (phi))) | |
478 continue; | |
479 | |
480 /* Lookup this argument's value in the hash table. */ | |
481 equiv_hash_elt.value = arg; | |
482 equiv_hash_elt.equivalences = NULL; | |
483 slot = htab_find_slot (equiv, &equiv_hash_elt, NO_INSERT); | |
484 | |
485 if (slot) | |
486 { | |
487 struct equiv_hash_elt *elt = (struct equiv_hash_elt *) *slot; | |
488 int j; | |
489 | |
490 /* Walk every equivalence with the same value. If we find | |
491 one with the same underlying variable as the PHI result, | |
492 then replace the value in the argument with its equivalent | |
493 SSA_NAME. Use the most recent equivalence as hopefully | |
494 that results in shortest lifetimes. */ | |
495 for (j = VEC_length (tree, elt->equivalences) - 1; j >= 0; j--) | |
496 { | |
497 tree equiv = VEC_index (tree, elt->equivalences, j); | |
498 | |
499 if (SSA_NAME_VAR (equiv) == SSA_NAME_VAR (PHI_RESULT (phi))) | |
500 { | |
501 SET_PHI_ARG_DEF (phi, e->dest_idx, equiv); | |
502 break; | |
503 } | |
504 } | |
505 } | |
506 } | |
507 | |
508 /* If we had an equivalence associated with this edge, remove it. */ | |
509 if (e->aux) | |
510 { | |
511 struct edge_equivalency *equiv = (struct edge_equivalency *) e->aux; | |
512 remove_equivalence (equiv->rhs); | |
513 } | |
514 } | |
515 } | |
516 | |
517 /* Ignoring loop backedges, if BB has precisely one incoming edge then | |
518 return that edge. Otherwise return NULL. */ | |
519 static edge | |
520 single_incoming_edge_ignoring_loop_edges (basic_block bb) | |
521 { | |
522 edge retval = NULL; | |
523 edge e; | |
524 edge_iterator ei; | |
525 | |
526 FOR_EACH_EDGE (e, ei, bb->preds) | |
527 { | |
528 /* A loop back edge can be identified by the destination of | |
529 the edge dominating the source of the edge. */ | |
530 if (dominated_by_p (CDI_DOMINATORS, e->src, e->dest)) | |
531 continue; | |
532 | |
533 /* If we have already seen a non-loop edge, then we must have | |
534 multiple incoming non-loop edges and thus we return NULL. */ | |
535 if (retval) | |
536 return NULL; | |
537 | |
538 /* This is the first non-loop incoming edge we have found. Record | |
539 it. */ | |
540 retval = e; | |
541 } | |
542 | |
543 return retval; | |
544 } | |
545 | |
546 static void | |
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547 uncprop_enter_block (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED, |
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548 basic_block bb) |
0 | 549 { |
550 basic_block parent; | |
551 edge e; | |
552 bool recorded = false; | |
553 | |
554 /* If this block is dominated by a single incoming edge and that edge | |
555 has an equivalency, then record the equivalency and push the | |
556 VALUE onto EQUIV_STACK. Else push a NULL entry on EQUIV_STACK. */ | |
557 parent = get_immediate_dominator (CDI_DOMINATORS, bb); | |
558 if (parent) | |
559 { | |
560 e = single_incoming_edge_ignoring_loop_edges (bb); | |
561 | |
562 if (e && e->src == parent && e->aux) | |
563 { | |
564 struct edge_equivalency *equiv = (struct edge_equivalency *) e->aux; | |
565 | |
566 record_equiv (equiv->rhs, equiv->lhs); | |
567 VEC_safe_push (tree, heap, equiv_stack, equiv->rhs); | |
568 recorded = true; | |
569 } | |
570 } | |
571 | |
572 if (!recorded) | |
573 VEC_safe_push (tree, heap, equiv_stack, NULL_TREE); | |
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574 |
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575 uncprop_into_successor_phis (bb); |
0 | 576 } |
577 | |
578 static bool | |
579 gate_uncprop (void) | |
580 { | |
581 return flag_tree_dom != 0; | |
582 } | |
583 | |
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584 struct gimple_opt_pass pass_uncprop = |
0 | 585 { |
586 { | |
587 GIMPLE_PASS, | |
588 "uncprop", /* name */ | |
589 gate_uncprop, /* gate */ | |
590 tree_ssa_uncprop, /* execute */ | |
591 NULL, /* sub */ | |
592 NULL, /* next */ | |
593 0, /* static_pass_number */ | |
594 TV_TREE_SSA_UNCPROP, /* tv_id */ | |
595 PROP_cfg | PROP_ssa, /* properties_required */ | |
596 0, /* properties_provided */ | |
597 0, /* properties_destroyed */ | |
598 0, /* todo_flags_start */ | |
599 TODO_dump_func | TODO_verify_ssa /* todo_flags_finish */ | |
600 } | |
601 }; | |
602 |