1 | /* Calculate (post)dominators in slightly super-linear time. |
2 | Copyright (C) 2000-2023 Free Software Foundation, Inc. |
3 | Contributed by Michael Matz (matz@ifh.de). |
4 | |
5 | This file is part of GCC. |
6 | |
7 | GCC is free software; you can redistribute it and/or modify it |
8 | 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, but WITHOUT |
13 | ANY WARRANTY; without even the implied warranty of MERCHANTABILITY |
14 | or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public |
15 | 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 | /* This file implements the well known algorithm from Lengauer and Tarjan |
22 | to compute the dominators in a control flow graph. A basic block D is said |
23 | to dominate another block X, when all paths from the entry node of the CFG |
24 | to X go also over D. The dominance relation is a transitive reflexive |
25 | relation and its minimal transitive reduction is a tree, called the |
26 | dominator tree. So for each block X besides the entry block exists a |
27 | block I(X), called the immediate dominator of X, which is the parent of X |
28 | in the dominator tree. |
29 | |
30 | The algorithm computes this dominator tree implicitly by computing for |
31 | each block its immediate dominator. We use tree balancing and path |
32 | compression, so it's the O(e*a(e,v)) variant, where a(e,v) is the very |
33 | slowly growing functional inverse of the Ackerman function. */ |
34 | |
35 | #include "config.h" |
36 | #include "system.h" |
37 | #include "coretypes.h" |
38 | #include "backend.h" |
39 | #include "timevar.h" |
40 | #include "diagnostic-core.h" |
41 | #include "cfganal.h" |
42 | #include "et-forest.h" |
43 | #include "graphds.h" |
44 | |
45 | /* We name our nodes with integers, beginning with 1. Zero is reserved for |
46 | 'undefined' or 'end of list'. The name of each node is given by the dfs |
47 | number of the corresponding basic block. Please note, that we include the |
48 | artificial ENTRY_BLOCK (or EXIT_BLOCK in the post-dom case) in our lists to |
49 | support multiple entry points. Its dfs number is of course 1. */ |
50 | |
51 | /* Type of Basic Block aka. TBB */ |
52 | typedef unsigned int TBB; |
53 | |
54 | namespace { |
55 | |
56 | /* This class holds various arrays reflecting the (sub)structure of the |
57 | flowgraph. Most of them are of type TBB and are also indexed by TBB. */ |
58 | |
59 | class dom_info |
60 | { |
61 | public: |
62 | dom_info (function *, cdi_direction); |
63 | dom_info (vec <basic_block>, cdi_direction); |
64 | ~dom_info (); |
65 | void calc_dfs_tree (); |
66 | void calc_idoms (); |
67 | |
68 | inline basic_block get_idom (basic_block); |
69 | private: |
70 | void calc_dfs_tree_nonrec (basic_block); |
71 | void compress (TBB); |
72 | void dom_init (void); |
73 | TBB eval (TBB); |
74 | void link_roots (TBB, TBB); |
75 | |
76 | /* The parent of a node in the DFS tree. */ |
77 | TBB *m_dfs_parent; |
78 | /* For a node x m_key[x] is roughly the node nearest to the root from which |
79 | exists a way to x only over nodes behind x. Such a node is also called |
80 | semidominator. */ |
81 | TBB *m_key; |
82 | /* The value in m_path_min[x] is the node y on the path from x to the root of |
83 | the tree x is in with the smallest m_key[y]. */ |
84 | TBB *m_path_min; |
85 | /* m_bucket[x] points to the first node of the set of nodes having x as |
86 | key. */ |
87 | TBB *m_bucket; |
88 | /* And m_next_bucket[x] points to the next node. */ |
89 | TBB *m_next_bucket; |
90 | /* After the algorithm is done, m_dom[x] contains the immediate dominator |
91 | of x. */ |
92 | TBB *m_dom; |
93 | |
94 | /* The following few fields implement the structures needed for disjoint |
95 | sets. */ |
96 | /* m_set_chain[x] is the next node on the path from x to the representative |
97 | of the set containing x. If m_set_chain[x]==0 then x is a root. */ |
98 | TBB *m_set_chain; |
99 | /* m_set_size[x] is the number of elements in the set named by x. */ |
100 | unsigned int *m_set_size; |
101 | /* m_set_child[x] is used for balancing the tree representing a set. It can |
102 | be understood as the next sibling of x. */ |
103 | TBB *m_set_child; |
104 | |
105 | /* If b is the number of a basic block (BB->index), m_dfs_order[b] is the |
106 | number of that node in DFS order counted from 1. This is an index |
107 | into most of the other arrays in this structure. */ |
108 | TBB *m_dfs_order; |
109 | /* Points to last element in m_dfs_order array. */ |
110 | TBB *m_dfs_last; |
111 | /* If x is the DFS-index of a node which corresponds with a basic block, |
112 | m_dfs_to_bb[x] is that basic block. Note, that in our structure there are |
113 | more nodes that basic blocks, so only |
114 | m_dfs_to_bb[m_dfs_order[bb->index]]==bb is true for every basic block bb, |
115 | but not the opposite. */ |
116 | basic_block *m_dfs_to_bb; |
117 | |
118 | /* This is the next free DFS number when creating the DFS tree. */ |
119 | unsigned int m_dfsnum; |
120 | /* The number of nodes in the DFS tree (==m_dfsnum-1). */ |
121 | unsigned int m_nodes; |
122 | |
123 | /* Blocks with bits set here have a fake edge to EXIT. These are used |
124 | to turn a DFS forest into a proper tree. */ |
125 | bitmap m_fake_exit_edge; |
126 | |
127 | /* Number of basic blocks in the function being compiled. */ |
128 | unsigned m_n_basic_blocks; |
129 | |
130 | /* True, if we are computing postdominators (rather than dominators). */ |
131 | bool m_reverse; |
132 | |
133 | /* Start block (the entry block for forward problem, exit block for backward |
134 | problem). */ |
135 | basic_block m_start_block; |
136 | /* Ending block. */ |
137 | basic_block m_end_block; |
138 | }; |
139 | |
140 | } // anonymous namespace |
141 | |
142 | void debug_dominance_info (cdi_direction); |
143 | void debug_dominance_tree (cdi_direction, basic_block); |
144 | |
145 | /* Allocate and zero-initialize NUM elements of type T (T must be a |
146 | POD-type). Note: after transition to C++11 or later, |
147 | `x = new_zero_array <T> (num);' can be replaced with |
148 | `x = new T[num] {};'. */ |
149 | |
150 | template<typename T> |
151 | inline T *new_zero_array (unsigned num) |
152 | { |
153 | T *result = new T[num]; |
154 | memset (result, 0, sizeof (T) * num); |
155 | return result; |
156 | } |
157 | |
158 | /* Helper function for constructors to initialize a part of class members. */ |
159 | |
160 | void |
161 | dom_info::dom_init (void) |
162 | { |
163 | unsigned num = m_n_basic_blocks; |
164 | |
165 | m_dfs_parent = new_zero_array <TBB> (num); |
166 | m_dom = new_zero_array <TBB> (num); |
167 | |
168 | m_path_min = new TBB[num]; |
169 | m_key = new TBB[num]; |
170 | m_set_size = new unsigned int[num]; |
171 | for (unsigned i = 0; i < num; i++) |
172 | { |
173 | m_path_min[i] = m_key[i] = i; |
174 | m_set_size[i] = 1; |
175 | } |
176 | |
177 | m_bucket = new_zero_array <TBB> (num); |
178 | m_next_bucket = new_zero_array <TBB> (num); |
179 | |
180 | m_set_chain = new_zero_array <TBB> (num); |
181 | m_set_child = new_zero_array <TBB> (num); |
182 | |
183 | m_dfs_to_bb = new_zero_array <basic_block> (num); |
184 | |
185 | m_dfsnum = 1; |
186 | m_nodes = 0; |
187 | } |
188 | |
189 | /* Allocate all needed memory in a pessimistic fashion (so we round up). */ |
190 | |
191 | dom_info::dom_info (function *fn, cdi_direction dir) |
192 | { |
193 | m_n_basic_blocks = n_basic_blocks_for_fn (fn); |
194 | |
195 | dom_init (); |
196 | |
197 | unsigned last_bb_index = last_basic_block_for_fn (fn); |
198 | m_dfs_order = new_zero_array <TBB> (num: last_bb_index + 1); |
199 | m_dfs_last = &m_dfs_order[last_bb_index]; |
200 | |
201 | switch (dir) |
202 | { |
203 | case CDI_DOMINATORS: |
204 | m_reverse = false; |
205 | m_fake_exit_edge = NULL; |
206 | m_start_block = ENTRY_BLOCK_PTR_FOR_FN (fn); |
207 | m_end_block = EXIT_BLOCK_PTR_FOR_FN (fn); |
208 | break; |
209 | case CDI_POST_DOMINATORS: |
210 | m_reverse = true; |
211 | m_fake_exit_edge = BITMAP_ALLOC (NULL); |
212 | m_start_block = EXIT_BLOCK_PTR_FOR_FN (fn); |
213 | m_end_block = ENTRY_BLOCK_PTR_FOR_FN (fn); |
214 | break; |
215 | default: |
216 | gcc_unreachable (); |
217 | } |
218 | } |
219 | |
220 | /* Constructor for reducible region REGION. */ |
221 | |
222 | dom_info::dom_info (vec<basic_block> region, cdi_direction dir) |
223 | { |
224 | m_n_basic_blocks = region.length (); |
225 | unsigned nm1 = m_n_basic_blocks - 1; |
226 | |
227 | dom_init (); |
228 | |
229 | /* Determine max basic block index in region. */ |
230 | int max_index = region[0]->index; |
231 | for (unsigned i = 1; i <= nm1; i++) |
232 | if (region[i]->index > max_index) |
233 | max_index = region[i]->index; |
234 | max_index += 1; /* set index on the first bb out of region. */ |
235 | |
236 | m_dfs_order = new_zero_array <TBB> (num: max_index + 1); |
237 | m_dfs_last = &m_dfs_order[max_index]; |
238 | |
239 | m_fake_exit_edge = NULL; /* Assume that region is reducible. */ |
240 | |
241 | switch (dir) |
242 | { |
243 | case CDI_DOMINATORS: |
244 | m_reverse = false; |
245 | m_start_block = region[0]; |
246 | m_end_block = region[nm1]; |
247 | break; |
248 | case CDI_POST_DOMINATORS: |
249 | m_reverse = true; |
250 | m_start_block = region[nm1]; |
251 | m_end_block = region[0]; |
252 | break; |
253 | default: |
254 | gcc_unreachable (); |
255 | } |
256 | } |
257 | |
258 | inline basic_block |
259 | dom_info::get_idom (basic_block bb) |
260 | { |
261 | TBB d = m_dom[m_dfs_order[bb->index]]; |
262 | return m_dfs_to_bb[d]; |
263 | } |
264 | |
265 | /* Map dominance calculation type to array index used for various |
266 | dominance information arrays. This version is simple -- it will need |
267 | to be modified, obviously, if additional values are added to |
268 | cdi_direction. */ |
269 | |
270 | static inline unsigned int |
271 | dom_convert_dir_to_idx (cdi_direction dir) |
272 | { |
273 | gcc_checking_assert (dir == CDI_DOMINATORS || dir == CDI_POST_DOMINATORS); |
274 | return dir - 1; |
275 | } |
276 | |
277 | /* Free all allocated memory in dom_info. */ |
278 | |
279 | dom_info::~dom_info () |
280 | { |
281 | delete[] m_dfs_parent; |
282 | delete[] m_path_min; |
283 | delete[] m_key; |
284 | delete[] m_dom; |
285 | delete[] m_bucket; |
286 | delete[] m_next_bucket; |
287 | delete[] m_set_chain; |
288 | delete[] m_set_size; |
289 | delete[] m_set_child; |
290 | delete[] m_dfs_order; |
291 | delete[] m_dfs_to_bb; |
292 | BITMAP_FREE (m_fake_exit_edge); |
293 | } |
294 | |
295 | /* The nonrecursive variant of creating a DFS tree. BB is the starting basic |
296 | block for this tree and m_reverse is true, if predecessors should be visited |
297 | instead of successors of a node. After this is done all nodes reachable |
298 | from BB were visited, have assigned their dfs number and are linked together |
299 | to form a tree. */ |
300 | |
301 | void |
302 | dom_info::calc_dfs_tree_nonrec (basic_block bb) |
303 | { |
304 | edge_iterator *stack = new edge_iterator[m_n_basic_blocks + 1]; |
305 | int sp = 0; |
306 | unsigned d_i = dom_convert_dir_to_idx (dir: m_reverse ? CDI_POST_DOMINATORS |
307 | : CDI_DOMINATORS); |
308 | |
309 | /* Initialize the first edge. */ |
310 | edge_iterator ei = m_reverse ? ei_start (bb->preds) |
311 | : ei_start (bb->succs); |
312 | |
313 | /* When the stack is empty we break out of this loop. */ |
314 | while (1) |
315 | { |
316 | basic_block bn; |
317 | edge_iterator einext; |
318 | |
319 | /* This loop traverses edges e in depth first manner, and fills the |
320 | stack. */ |
321 | while (!ei_end_p (i: ei)) |
322 | { |
323 | edge e = ei_edge (i: ei); |
324 | |
325 | /* Deduce from E the current and the next block (BB and BN), and the |
326 | next edge. */ |
327 | if (m_reverse) |
328 | { |
329 | bn = e->src; |
330 | |
331 | /* If the next node BN is either already visited or a border |
332 | block or out of region the current edge is useless, and simply |
333 | overwritten with the next edge out of the current node. */ |
334 | if (bn == m_end_block || bn->dom[d_i] == NULL |
335 | || m_dfs_order[bn->index]) |
336 | { |
337 | ei_next (i: &ei); |
338 | continue; |
339 | } |
340 | bb = e->dest; |
341 | einext = ei_start (bn->preds); |
342 | } |
343 | else |
344 | { |
345 | bn = e->dest; |
346 | if (bn == m_end_block || bn->dom[d_i] == NULL |
347 | || m_dfs_order[bn->index]) |
348 | { |
349 | ei_next (i: &ei); |
350 | continue; |
351 | } |
352 | bb = e->src; |
353 | einext = ei_start (bn->succs); |
354 | } |
355 | |
356 | gcc_assert (bn != m_start_block); |
357 | |
358 | /* Fill the DFS tree info calculatable _before_ recursing. */ |
359 | TBB my_i; |
360 | if (bb != m_start_block) |
361 | my_i = m_dfs_order[bb->index]; |
362 | else |
363 | my_i = *m_dfs_last; |
364 | TBB child_i = m_dfs_order[bn->index] = m_dfsnum++; |
365 | m_dfs_to_bb[child_i] = bn; |
366 | m_dfs_parent[child_i] = my_i; |
367 | |
368 | /* Save the current point in the CFG on the stack, and recurse. */ |
369 | stack[sp++] = ei; |
370 | ei = einext; |
371 | } |
372 | |
373 | if (!sp) |
374 | break; |
375 | ei = stack[--sp]; |
376 | |
377 | /* OK. The edge-list was exhausted, meaning normally we would |
378 | end the recursion. After returning from the recursive call, |
379 | there were (may be) other statements which were run after a |
380 | child node was completely considered by DFS. Here is the |
381 | point to do it in the non-recursive variant. |
382 | E.g. The block just completed is in e->dest for forward DFS, |
383 | the block not yet completed (the parent of the one above) |
384 | in e->src. This could be used e.g. for computing the number of |
385 | descendants or the tree depth. */ |
386 | ei_next (i: &ei); |
387 | } |
388 | delete[] stack; |
389 | } |
390 | |
391 | /* The main entry for calculating the DFS tree or forest. m_reverse is true, |
392 | if we are interested in the reverse flow graph. In that case the result is |
393 | not necessarily a tree but a forest, because there may be nodes from which |
394 | the EXIT_BLOCK is unreachable. */ |
395 | |
396 | void |
397 | dom_info::calc_dfs_tree () |
398 | { |
399 | *m_dfs_last = m_dfsnum; |
400 | m_dfs_to_bb[m_dfsnum] = m_start_block; |
401 | m_dfsnum++; |
402 | |
403 | calc_dfs_tree_nonrec (bb: m_start_block); |
404 | |
405 | if (m_fake_exit_edge) |
406 | { |
407 | /* In the post-dom case we may have nodes without a path to EXIT_BLOCK. |
408 | They are reverse-unreachable. In the dom-case we disallow such |
409 | nodes, but in post-dom we have to deal with them. |
410 | |
411 | There are two situations in which this occurs. First, noreturn |
412 | functions. Second, infinite loops. In the first case we need to |
413 | pretend that there is an edge to the exit block. In the second |
414 | case, we wind up with a forest. We need to process all noreturn |
415 | blocks before we know if we've got any infinite loops. */ |
416 | |
417 | basic_block b; |
418 | bool saw_unconnected = false; |
419 | |
420 | FOR_BB_BETWEEN (b, m_start_block->prev_bb, m_end_block, prev_bb) |
421 | { |
422 | if (EDGE_COUNT (b->succs) > 0) |
423 | { |
424 | if (m_dfs_order[b->index] == 0) |
425 | saw_unconnected = true; |
426 | continue; |
427 | } |
428 | bitmap_set_bit (m_fake_exit_edge, b->index); |
429 | m_dfs_order[b->index] = m_dfsnum; |
430 | m_dfs_to_bb[m_dfsnum] = b; |
431 | m_dfs_parent[m_dfsnum] = *m_dfs_last; |
432 | m_dfsnum++; |
433 | calc_dfs_tree_nonrec (bb: b); |
434 | } |
435 | |
436 | if (saw_unconnected) |
437 | { |
438 | FOR_BB_BETWEEN (b, m_start_block->prev_bb, m_end_block, prev_bb) |
439 | { |
440 | if (m_dfs_order[b->index]) |
441 | continue; |
442 | basic_block b2 = dfs_find_deadend (b); |
443 | gcc_checking_assert (m_dfs_order[b2->index] == 0); |
444 | bitmap_set_bit (m_fake_exit_edge, b2->index); |
445 | m_dfs_order[b2->index] = m_dfsnum; |
446 | m_dfs_to_bb[m_dfsnum] = b2; |
447 | m_dfs_parent[m_dfsnum] = *m_dfs_last; |
448 | m_dfsnum++; |
449 | calc_dfs_tree_nonrec (bb: b2); |
450 | gcc_checking_assert (m_dfs_order[b->index]); |
451 | } |
452 | } |
453 | } |
454 | |
455 | m_nodes = m_dfsnum - 1; |
456 | |
457 | /* This aborts e.g. when there is _no_ path from ENTRY to EXIT at all. */ |
458 | gcc_assert (m_nodes == (unsigned int) m_n_basic_blocks - 1); |
459 | } |
460 | |
461 | /* Compress the path from V to the root of its set and update path_min at the |
462 | same time. After compress(di, V) set_chain[V] is the root of the set V is |
463 | in and path_min[V] is the node with the smallest key[] value on the path |
464 | from V to that root. */ |
465 | |
466 | void |
467 | dom_info::compress (TBB v) |
468 | { |
469 | /* Btw. It's not worth to unrecurse compress() as the depth is usually not |
470 | greater than 5 even for huge graphs (I've not seen call depth > 4). |
471 | Also performance wise compress() ranges _far_ behind eval(). */ |
472 | TBB parent = m_set_chain[v]; |
473 | if (m_set_chain[parent]) |
474 | { |
475 | compress (v: parent); |
476 | if (m_key[m_path_min[parent]] < m_key[m_path_min[v]]) |
477 | m_path_min[v] = m_path_min[parent]; |
478 | m_set_chain[v] = m_set_chain[parent]; |
479 | } |
480 | } |
481 | |
482 | /* Compress the path from V to the set root of V if needed (when the root has |
483 | changed since the last call). Returns the node with the smallest key[] |
484 | value on the path from V to the root. */ |
485 | |
486 | inline TBB |
487 | dom_info::eval (TBB v) |
488 | { |
489 | /* The representative of the set V is in, also called root (as the set |
490 | representation is a tree). */ |
491 | TBB rep = m_set_chain[v]; |
492 | |
493 | /* V itself is the root. */ |
494 | if (!rep) |
495 | return m_path_min[v]; |
496 | |
497 | /* Compress only if necessary. */ |
498 | if (m_set_chain[rep]) |
499 | { |
500 | compress (v); |
501 | rep = m_set_chain[v]; |
502 | } |
503 | |
504 | if (m_key[m_path_min[rep]] >= m_key[m_path_min[v]]) |
505 | return m_path_min[v]; |
506 | else |
507 | return m_path_min[rep]; |
508 | } |
509 | |
510 | /* This essentially merges the two sets of V and W, giving a single set with |
511 | the new root V. The internal representation of these disjoint sets is a |
512 | balanced tree. Currently link(V,W) is only used with V being the parent |
513 | of W. */ |
514 | |
515 | void |
516 | dom_info::link_roots (TBB v, TBB w) |
517 | { |
518 | TBB s = w; |
519 | |
520 | /* Rebalance the tree. */ |
521 | while (m_key[m_path_min[w]] < m_key[m_path_min[m_set_child[s]]]) |
522 | { |
523 | if (m_set_size[s] + m_set_size[m_set_child[m_set_child[s]]] |
524 | >= 2 * m_set_size[m_set_child[s]]) |
525 | { |
526 | m_set_chain[m_set_child[s]] = s; |
527 | m_set_child[s] = m_set_child[m_set_child[s]]; |
528 | } |
529 | else |
530 | { |
531 | m_set_size[m_set_child[s]] = m_set_size[s]; |
532 | s = m_set_chain[s] = m_set_child[s]; |
533 | } |
534 | } |
535 | |
536 | m_path_min[s] = m_path_min[w]; |
537 | m_set_size[v] += m_set_size[w]; |
538 | if (m_set_size[v] < 2 * m_set_size[w]) |
539 | std::swap (a&: m_set_child[v], b&: s); |
540 | |
541 | /* Merge all subtrees. */ |
542 | while (s) |
543 | { |
544 | m_set_chain[s] = v; |
545 | s = m_set_child[s]; |
546 | } |
547 | } |
548 | |
549 | /* This calculates the immediate dominators (or post-dominators). THIS is our |
550 | working structure and should hold the DFS forest. |
551 | On return the immediate dominator to node V is in m_dom[V]. */ |
552 | |
553 | void |
554 | dom_info::calc_idoms () |
555 | { |
556 | /* Go backwards in DFS order, to first look at the leafs. */ |
557 | for (TBB v = m_nodes; v > 1; v--) |
558 | { |
559 | basic_block bb = m_dfs_to_bb[v]; |
560 | edge e; |
561 | |
562 | TBB par = m_dfs_parent[v]; |
563 | TBB k = v; |
564 | |
565 | edge_iterator ei = m_reverse ? ei_start (bb->succs) |
566 | : ei_start (bb->preds); |
567 | edge_iterator einext; |
568 | |
569 | if (m_fake_exit_edge) |
570 | { |
571 | /* If this block has a fake edge to exit, process that first. */ |
572 | if (bitmap_bit_p (m_fake_exit_edge, bb->index)) |
573 | { |
574 | einext = ei; |
575 | einext.index = 0; |
576 | goto do_fake_exit_edge; |
577 | } |
578 | } |
579 | |
580 | /* Search all direct predecessors for the smallest node with a path |
581 | to them. That way we have the smallest node with also a path to |
582 | us only over nodes behind us. In effect we search for our |
583 | semidominator. */ |
584 | while (!ei_end_p (i: ei)) |
585 | { |
586 | basic_block b; |
587 | TBB k1; |
588 | |
589 | e = ei_edge (i: ei); |
590 | b = m_reverse ? e->dest : e->src; |
591 | einext = ei; |
592 | ei_next (i: &einext); |
593 | |
594 | if (b == m_start_block) |
595 | { |
596 | do_fake_exit_edge: |
597 | k1 = *m_dfs_last; |
598 | } |
599 | else |
600 | k1 = m_dfs_order[b->index]; |
601 | |
602 | /* Call eval() only if really needed. If k1 is above V in DFS tree, |
603 | then we know, that eval(k1) == k1 and key[k1] == k1. */ |
604 | if (k1 > v) |
605 | k1 = m_key[eval (v: k1)]; |
606 | if (k1 < k) |
607 | k = k1; |
608 | |
609 | ei = einext; |
610 | } |
611 | |
612 | m_key[v] = k; |
613 | link_roots (v: par, w: v); |
614 | m_next_bucket[v] = m_bucket[k]; |
615 | m_bucket[k] = v; |
616 | |
617 | /* Transform semidominators into dominators. */ |
618 | for (TBB w = m_bucket[par]; w; w = m_next_bucket[w]) |
619 | { |
620 | k = eval (v: w); |
621 | if (m_key[k] < m_key[w]) |
622 | m_dom[w] = k; |
623 | else |
624 | m_dom[w] = par; |
625 | } |
626 | /* We don't need to cleanup next_bucket[]. */ |
627 | m_bucket[par] = 0; |
628 | } |
629 | |
630 | /* Explicitly define the dominators. */ |
631 | m_dom[1] = 0; |
632 | for (TBB v = 2; v <= m_nodes; v++) |
633 | if (m_dom[v] != m_key[v]) |
634 | m_dom[v] = m_dom[m_dom[v]]; |
635 | } |
636 | |
637 | /* Assign dfs numbers starting from NUM to NODE and its sons. */ |
638 | |
639 | static void |
640 | assign_dfs_numbers (struct et_node *node, int *num) |
641 | { |
642 | et_node *n = node; |
643 | while (1) |
644 | { |
645 | n->dfs_num_in = (*num)++; |
646 | if (n->son) |
647 | n = n->son; |
648 | else |
649 | { |
650 | while (!n->right || n->right == n->father->son) |
651 | { |
652 | n->dfs_num_out = (*num)++; |
653 | if (n == node) |
654 | return; |
655 | n = n->father; |
656 | } |
657 | n->dfs_num_out = (*num)++; |
658 | n = n->right; |
659 | } |
660 | } |
661 | } |
662 | |
663 | /* Compute the data necessary for fast resolving of dominator queries in a |
664 | static dominator tree. */ |
665 | |
666 | static void |
667 | compute_dom_fast_query (enum cdi_direction dir) |
668 | { |
669 | int num = 0; |
670 | basic_block bb; |
671 | unsigned int dir_index = dom_convert_dir_to_idx (dir); |
672 | |
673 | gcc_checking_assert (dom_info_available_p (dir)); |
674 | |
675 | if (dom_computed[dir_index] == DOM_OK) |
676 | return; |
677 | |
678 | FOR_ALL_BB_FN (bb, cfun) |
679 | { |
680 | if (!bb->dom[dir_index]->father) |
681 | assign_dfs_numbers (node: bb->dom[dir_index], num: &num); |
682 | } |
683 | |
684 | dom_computed[dir_index] = DOM_OK; |
685 | } |
686 | |
687 | /* Analogous to the previous function but compute the data for reducible |
688 | region REGION. */ |
689 | |
690 | static void |
691 | compute_dom_fast_query_in_region (enum cdi_direction dir, |
692 | vec<basic_block> region) |
693 | { |
694 | int num = 0; |
695 | basic_block bb; |
696 | unsigned int dir_index = dom_convert_dir_to_idx (dir); |
697 | |
698 | gcc_checking_assert (dom_info_available_p (dir)); |
699 | |
700 | if (dom_computed[dir_index] == DOM_OK) |
701 | return; |
702 | |
703 | /* Assign dfs numbers for region nodes except for entry and exit nodes. */ |
704 | for (unsigned int i = 1; i < region.length () - 1; i++) |
705 | { |
706 | bb = region[i]; |
707 | if (!bb->dom[dir_index]->father) |
708 | assign_dfs_numbers (node: bb->dom[dir_index], num: &num); |
709 | } |
710 | |
711 | dom_computed[dir_index] = DOM_OK; |
712 | } |
713 | |
714 | /* The main entry point into this module. DIR is set depending on whether |
715 | we want to compute dominators or postdominators. If COMPUTE_FAST_QUERY |
716 | is false then the DFS numbers allowing for a O(1) dominance query |
717 | are not computed. */ |
718 | |
719 | void |
720 | calculate_dominance_info (cdi_direction dir, bool compute_fast_query) |
721 | { |
722 | unsigned int dir_index = dom_convert_dir_to_idx (dir); |
723 | |
724 | if (dom_computed[dir_index] == DOM_OK) |
725 | { |
726 | checking_verify_dominators (dir); |
727 | return; |
728 | } |
729 | |
730 | timevar_push (tv: TV_DOMINANCE); |
731 | if (!dom_info_available_p (dir)) |
732 | { |
733 | gcc_assert (!n_bbs_in_dom_tree[dir_index]); |
734 | |
735 | basic_block b; |
736 | FOR_ALL_BB_FN (b, cfun) |
737 | { |
738 | b->dom[dir_index] = et_new_tree (data: b); |
739 | } |
740 | n_bbs_in_dom_tree[dir_index] = n_basic_blocks_for_fn (cfun); |
741 | |
742 | dom_info di (cfun, dir); |
743 | di.calc_dfs_tree (); |
744 | di.calc_idoms (); |
745 | |
746 | FOR_EACH_BB_FN (b, cfun) |
747 | { |
748 | if (basic_block d = di.get_idom (bb: b)) |
749 | et_set_father (b->dom[dir_index], d->dom[dir_index]); |
750 | } |
751 | |
752 | dom_computed[dir_index] = DOM_NO_FAST_QUERY; |
753 | } |
754 | else |
755 | checking_verify_dominators (dir); |
756 | |
757 | if (compute_fast_query) |
758 | compute_dom_fast_query (dir); |
759 | |
760 | timevar_pop (tv: TV_DOMINANCE); |
761 | } |
762 | |
763 | /* Analogous to the previous function but compute dominance info for regions |
764 | which are single entry, multiple exit regions for CDI_DOMINATORs and |
765 | multiple entry, single exit regions for CDI_POST_DOMINATORs. */ |
766 | |
767 | void |
768 | calculate_dominance_info_for_region (cdi_direction dir, |
769 | vec<basic_block> region) |
770 | { |
771 | unsigned int dir_index = dom_convert_dir_to_idx (dir); |
772 | basic_block bb; |
773 | unsigned int i; |
774 | |
775 | if (dom_computed[dir_index] == DOM_OK) |
776 | return; |
777 | |
778 | timevar_push (tv: TV_DOMINANCE); |
779 | /* Assume that dom info is not partially computed. */ |
780 | gcc_assert (!dom_info_available_p (dir)); |
781 | |
782 | FOR_EACH_VEC_ELT (region, i, bb) |
783 | { |
784 | bb->dom[dir_index] = et_new_tree (data: bb); |
785 | } |
786 | dom_info di (region, dir); |
787 | di.calc_dfs_tree (); |
788 | di.calc_idoms (); |
789 | |
790 | FOR_EACH_VEC_ELT (region, i, bb) |
791 | if (basic_block d = di.get_idom (bb)) |
792 | et_set_father (bb->dom[dir_index], d->dom[dir_index]); |
793 | |
794 | dom_computed[dir_index] = DOM_NO_FAST_QUERY; |
795 | compute_dom_fast_query_in_region (dir, region); |
796 | |
797 | timevar_pop (tv: TV_DOMINANCE); |
798 | } |
799 | |
800 | /* Free dominance information for direction DIR. */ |
801 | void |
802 | free_dominance_info (function *fn, enum cdi_direction dir) |
803 | { |
804 | basic_block bb; |
805 | unsigned int dir_index = dom_convert_dir_to_idx (dir); |
806 | |
807 | if (!dom_info_available_p (fn, dir)) |
808 | return; |
809 | |
810 | FOR_ALL_BB_FN (bb, fn) |
811 | { |
812 | et_free_tree_force (bb->dom[dir_index]); |
813 | bb->dom[dir_index] = NULL; |
814 | } |
815 | et_free_pools (); |
816 | |
817 | fn->cfg->x_n_bbs_in_dom_tree[dir_index] = 0; |
818 | |
819 | fn->cfg->x_dom_computed[dir_index] = DOM_NONE; |
820 | } |
821 | |
822 | void |
823 | free_dominance_info (enum cdi_direction dir) |
824 | { |
825 | free_dominance_info (cfun, dir); |
826 | } |
827 | |
828 | /* Free dominance information for direction DIR in region REGION. */ |
829 | |
830 | void |
831 | free_dominance_info_for_region (function *fn, |
832 | enum cdi_direction dir, |
833 | vec<basic_block> region) |
834 | { |
835 | basic_block bb; |
836 | unsigned int i; |
837 | unsigned int dir_index = dom_convert_dir_to_idx (dir); |
838 | |
839 | if (!dom_info_available_p (dir)) |
840 | return; |
841 | |
842 | FOR_EACH_VEC_ELT (region, i, bb) |
843 | { |
844 | et_free_tree_force (bb->dom[dir_index]); |
845 | bb->dom[dir_index] = NULL; |
846 | } |
847 | et_free_pools (); |
848 | |
849 | fn->cfg->x_dom_computed[dir_index] = DOM_NONE; |
850 | |
851 | fn->cfg->x_n_bbs_in_dom_tree[dir_index] = 0; |
852 | } |
853 | |
854 | /* Return the immediate dominator of basic block BB. */ |
855 | basic_block |
856 | get_immediate_dominator (enum cdi_direction dir, basic_block bb) |
857 | { |
858 | unsigned int dir_index = dom_convert_dir_to_idx (dir); |
859 | struct et_node *node = bb->dom[dir_index]; |
860 | |
861 | gcc_checking_assert (dom_computed[dir_index]); |
862 | |
863 | if (!node->father) |
864 | return NULL; |
865 | |
866 | return (basic_block) node->father->data; |
867 | } |
868 | |
869 | /* Set the immediate dominator of the block possibly removing |
870 | existing edge. NULL can be used to remove any edge. */ |
871 | void |
872 | set_immediate_dominator (enum cdi_direction dir, basic_block bb, |
873 | basic_block dominated_by) |
874 | { |
875 | unsigned int dir_index = dom_convert_dir_to_idx (dir); |
876 | struct et_node *node = bb->dom[dir_index]; |
877 | |
878 | gcc_checking_assert (dom_computed[dir_index]); |
879 | |
880 | if (node->father) |
881 | { |
882 | if (node->father->data == dominated_by) |
883 | return; |
884 | et_split (node); |
885 | } |
886 | |
887 | if (dominated_by) |
888 | et_set_father (node, dominated_by->dom[dir_index]); |
889 | |
890 | if (dom_computed[dir_index] == DOM_OK) |
891 | dom_computed[dir_index] = DOM_NO_FAST_QUERY; |
892 | } |
893 | |
894 | /* Returns the list of basic blocks immediately dominated by BB, in the |
895 | direction DIR. */ |
896 | auto_vec<basic_block> |
897 | get_dominated_by (enum cdi_direction dir, basic_block bb) |
898 | { |
899 | unsigned int dir_index = dom_convert_dir_to_idx (dir); |
900 | struct et_node *node = bb->dom[dir_index], *son = node->son, *ason; |
901 | auto_vec<basic_block> bbs; |
902 | |
903 | gcc_checking_assert (dom_computed[dir_index]); |
904 | |
905 | if (!son) |
906 | return bbs; |
907 | |
908 | bbs.safe_push (obj: (basic_block) son->data); |
909 | for (ason = son->right; ason != son; ason = ason->right) |
910 | bbs.safe_push (obj: (basic_block) ason->data); |
911 | |
912 | return bbs; |
913 | } |
914 | |
915 | /* Returns the list of basic blocks that are immediately dominated (in |
916 | direction DIR) by some block between N_REGION ones stored in REGION, |
917 | except for blocks in the REGION itself. */ |
918 | |
919 | auto_vec<basic_block> |
920 | get_dominated_by_region (enum cdi_direction dir, basic_block *region, |
921 | unsigned n_region) |
922 | { |
923 | unsigned i; |
924 | basic_block dom; |
925 | auto_vec<basic_block> doms; |
926 | |
927 | for (i = 0; i < n_region; i++) |
928 | region[i]->flags |= BB_DUPLICATED; |
929 | for (i = 0; i < n_region; i++) |
930 | for (dom = first_dom_son (dir, region[i]); |
931 | dom; |
932 | dom = next_dom_son (dir, dom)) |
933 | if (!(dom->flags & BB_DUPLICATED)) |
934 | doms.safe_push (obj: dom); |
935 | for (i = 0; i < n_region; i++) |
936 | region[i]->flags &= ~BB_DUPLICATED; |
937 | |
938 | return doms; |
939 | } |
940 | |
941 | /* Returns the list of basic blocks including BB dominated by BB, in the |
942 | direction DIR up to DEPTH in the dominator tree. The DEPTH of zero will |
943 | produce a vector containing all dominated blocks. The vector will be sorted |
944 | in preorder. */ |
945 | |
946 | auto_vec<basic_block> |
947 | get_dominated_to_depth (enum cdi_direction dir, basic_block bb, int depth) |
948 | { |
949 | auto_vec<basic_block> bbs; |
950 | unsigned i; |
951 | unsigned next_level_start; |
952 | |
953 | i = 0; |
954 | bbs.safe_push (obj: bb); |
955 | next_level_start = 1; /* = bbs.length (); */ |
956 | |
957 | do |
958 | { |
959 | basic_block son; |
960 | |
961 | bb = bbs[i++]; |
962 | for (son = first_dom_son (dir, bb); |
963 | son; |
964 | son = next_dom_son (dir, son)) |
965 | bbs.safe_push (obj: son); |
966 | |
967 | if (i == next_level_start && --depth) |
968 | next_level_start = bbs.length (); |
969 | } |
970 | while (i < next_level_start); |
971 | |
972 | return bbs; |
973 | } |
974 | |
975 | /* Returns the list of basic blocks including BB dominated by BB, in the |
976 | direction DIR. The vector will be sorted in preorder. */ |
977 | |
978 | auto_vec<basic_block> |
979 | get_all_dominated_blocks (enum cdi_direction dir, basic_block bb) |
980 | { |
981 | return get_dominated_to_depth (dir, bb, depth: 0); |
982 | } |
983 | |
984 | /* Redirect all edges pointing to BB to TO. */ |
985 | void |
986 | redirect_immediate_dominators (enum cdi_direction dir, basic_block bb, |
987 | basic_block to) |
988 | { |
989 | unsigned int dir_index = dom_convert_dir_to_idx (dir); |
990 | struct et_node *bb_node, *to_node, *son; |
991 | |
992 | bb_node = bb->dom[dir_index]; |
993 | to_node = to->dom[dir_index]; |
994 | |
995 | gcc_checking_assert (dom_computed[dir_index]); |
996 | |
997 | if (!bb_node->son) |
998 | return; |
999 | |
1000 | while (bb_node->son) |
1001 | { |
1002 | son = bb_node->son; |
1003 | |
1004 | et_split (son); |
1005 | et_set_father (son, to_node); |
1006 | } |
1007 | |
1008 | if (dom_computed[dir_index] == DOM_OK) |
1009 | dom_computed[dir_index] = DOM_NO_FAST_QUERY; |
1010 | } |
1011 | |
1012 | /* Find first basic block in the tree dominating both BB1 and BB2. */ |
1013 | basic_block |
1014 | nearest_common_dominator (enum cdi_direction dir, basic_block bb1, basic_block bb2) |
1015 | { |
1016 | unsigned int dir_index = dom_convert_dir_to_idx (dir); |
1017 | |
1018 | gcc_checking_assert (dom_computed[dir_index]); |
1019 | |
1020 | if (!bb1) |
1021 | return bb2; |
1022 | if (!bb2) |
1023 | return bb1; |
1024 | |
1025 | return (basic_block) et_nca (bb1->dom[dir_index], bb2->dom[dir_index])->data; |
1026 | } |
1027 | |
1028 | |
1029 | /* Find the nearest common dominator for the basic blocks in BLOCKS, |
1030 | using dominance direction DIR. */ |
1031 | |
1032 | basic_block |
1033 | nearest_common_dominator_for_set (enum cdi_direction dir, bitmap blocks) |
1034 | { |
1035 | unsigned i, first; |
1036 | bitmap_iterator bi; |
1037 | basic_block dom; |
1038 | |
1039 | first = bitmap_first_set_bit (blocks); |
1040 | dom = BASIC_BLOCK_FOR_FN (cfun, first); |
1041 | EXECUTE_IF_SET_IN_BITMAP (blocks, 0, i, bi) |
1042 | if (dom != BASIC_BLOCK_FOR_FN (cfun, i)) |
1043 | dom = nearest_common_dominator (dir, bb1: dom, BASIC_BLOCK_FOR_FN (cfun, i)); |
1044 | |
1045 | return dom; |
1046 | } |
1047 | |
1048 | /* Given a dominator tree, we can determine whether one thing |
1049 | dominates another in constant time by using two DFS numbers: |
1050 | |
1051 | 1. The number for when we visit a node on the way down the tree |
1052 | 2. The number for when we visit a node on the way back up the tree |
1053 | |
1054 | You can view these as bounds for the range of dfs numbers the |
1055 | nodes in the subtree of the dominator tree rooted at that node |
1056 | will contain. |
1057 | |
1058 | The dominator tree is always a simple acyclic tree, so there are |
1059 | only three possible relations two nodes in the dominator tree have |
1060 | to each other: |
1061 | |
1062 | 1. Node A is above Node B (and thus, Node A dominates node B) |
1063 | |
1064 | A |
1065 | | |
1066 | C |
1067 | / \ |
1068 | B D |
1069 | |
1070 | |
1071 | In the above case, DFS_Number_In of A will be <= DFS_Number_In of |
1072 | B, and DFS_Number_Out of A will be >= DFS_Number_Out of B. This is |
1073 | because we must hit A in the dominator tree *before* B on the walk |
1074 | down, and we will hit A *after* B on the walk back up |
1075 | |
1076 | 2. Node A is below node B (and thus, node B dominates node A) |
1077 | |
1078 | |
1079 | B |
1080 | | |
1081 | A |
1082 | / \ |
1083 | C D |
1084 | |
1085 | In the above case, DFS_Number_In of A will be >= DFS_Number_In of |
1086 | B, and DFS_Number_Out of A will be <= DFS_Number_Out of B. |
1087 | |
1088 | This is because we must hit A in the dominator tree *after* B on |
1089 | the walk down, and we will hit A *before* B on the walk back up |
1090 | |
1091 | 3. Node A and B are siblings (and thus, neither dominates the other) |
1092 | |
1093 | C |
1094 | | |
1095 | D |
1096 | / \ |
1097 | A B |
1098 | |
1099 | In the above case, DFS_Number_In of A will *always* be <= |
1100 | DFS_Number_In of B, and DFS_Number_Out of A will *always* be <= |
1101 | DFS_Number_Out of B. This is because we will always finish the dfs |
1102 | walk of one of the subtrees before the other, and thus, the dfs |
1103 | numbers for one subtree can't intersect with the range of dfs |
1104 | numbers for the other subtree. If you swap A and B's position in |
1105 | the dominator tree, the comparison changes direction, but the point |
1106 | is that both comparisons will always go the same way if there is no |
1107 | dominance relationship. |
1108 | |
1109 | Thus, it is sufficient to write |
1110 | |
1111 | A_Dominates_B (node A, node B) |
1112 | { |
1113 | return DFS_Number_In(A) <= DFS_Number_In(B) |
1114 | && DFS_Number_Out (A) >= DFS_Number_Out(B); |
1115 | } |
1116 | |
1117 | A_Dominated_by_B (node A, node B) |
1118 | { |
1119 | return DFS_Number_In(A) >= DFS_Number_In(B) |
1120 | && DFS_Number_Out (A) <= DFS_Number_Out(B); |
1121 | } */ |
1122 | |
1123 | /* Return TRUE in case BB1 is dominated by BB2. */ |
1124 | bool |
1125 | dominated_by_p (enum cdi_direction dir, const_basic_block bb1, const_basic_block bb2) |
1126 | { |
1127 | unsigned int dir_index = dom_convert_dir_to_idx (dir); |
1128 | struct et_node *n1 = bb1->dom[dir_index], *n2 = bb2->dom[dir_index]; |
1129 | |
1130 | gcc_checking_assert (dom_computed[dir_index]); |
1131 | |
1132 | if (dom_computed[dir_index] == DOM_OK) |
1133 | return (n1->dfs_num_in >= n2->dfs_num_in |
1134 | && n1->dfs_num_out <= n2->dfs_num_out); |
1135 | |
1136 | return et_below (n1, n2); |
1137 | } |
1138 | |
1139 | /* Returns the entry dfs number for basic block BB, in the direction DIR. */ |
1140 | |
1141 | unsigned |
1142 | bb_dom_dfs_in (enum cdi_direction dir, basic_block bb) |
1143 | { |
1144 | unsigned int dir_index = dom_convert_dir_to_idx (dir); |
1145 | struct et_node *n = bb->dom[dir_index]; |
1146 | |
1147 | gcc_checking_assert (dom_computed[dir_index] == DOM_OK); |
1148 | return n->dfs_num_in; |
1149 | } |
1150 | |
1151 | /* Returns the exit dfs number for basic block BB, in the direction DIR. */ |
1152 | |
1153 | unsigned |
1154 | bb_dom_dfs_out (enum cdi_direction dir, basic_block bb) |
1155 | { |
1156 | unsigned int dir_index = dom_convert_dir_to_idx (dir); |
1157 | struct et_node *n = bb->dom[dir_index]; |
1158 | |
1159 | gcc_checking_assert (dom_computed[dir_index] == DOM_OK); |
1160 | return n->dfs_num_out; |
1161 | } |
1162 | |
1163 | /* Verify invariants of dominator structure. */ |
1164 | DEBUG_FUNCTION void |
1165 | verify_dominators (cdi_direction dir) |
1166 | { |
1167 | gcc_assert (dom_info_available_p (dir)); |
1168 | |
1169 | dom_info di (cfun, dir); |
1170 | di.calc_dfs_tree (); |
1171 | di.calc_idoms (); |
1172 | |
1173 | bool err = false; |
1174 | basic_block bb; |
1175 | FOR_EACH_BB_FN (bb, cfun) |
1176 | { |
1177 | basic_block imm_bb = get_immediate_dominator (dir, bb); |
1178 | if (!imm_bb) |
1179 | { |
1180 | error ("dominator of %d status unknown" , bb->index); |
1181 | err = true; |
1182 | continue; |
1183 | } |
1184 | |
1185 | basic_block imm_bb_correct = di.get_idom (bb); |
1186 | if (imm_bb != imm_bb_correct) |
1187 | { |
1188 | error ("dominator of %d should be %d, not %d" , |
1189 | bb->index, imm_bb_correct->index, imm_bb->index); |
1190 | err = true; |
1191 | } |
1192 | } |
1193 | |
1194 | gcc_assert (!err); |
1195 | } |
1196 | |
1197 | /* Determine immediate dominator (or postdominator, according to DIR) of BB, |
1198 | assuming that dominators of other blocks are correct. We also use it to |
1199 | recompute the dominators in a restricted area, by iterating it until it |
1200 | reaches a fixed point. */ |
1201 | |
1202 | basic_block |
1203 | recompute_dominator (enum cdi_direction dir, basic_block bb) |
1204 | { |
1205 | unsigned int dir_index = dom_convert_dir_to_idx (dir); |
1206 | basic_block dom_bb = NULL; |
1207 | edge e; |
1208 | edge_iterator ei; |
1209 | |
1210 | gcc_checking_assert (dom_computed[dir_index]); |
1211 | |
1212 | if (dir == CDI_DOMINATORS) |
1213 | { |
1214 | FOR_EACH_EDGE (e, ei, bb->preds) |
1215 | { |
1216 | if (!dominated_by_p (dir, bb1: e->src, bb2: bb)) |
1217 | dom_bb = nearest_common_dominator (dir, bb1: dom_bb, bb2: e->src); |
1218 | } |
1219 | } |
1220 | else |
1221 | { |
1222 | FOR_EACH_EDGE (e, ei, bb->succs) |
1223 | { |
1224 | if (!dominated_by_p (dir, bb1: e->dest, bb2: bb)) |
1225 | dom_bb = nearest_common_dominator (dir, bb1: dom_bb, bb2: e->dest); |
1226 | } |
1227 | } |
1228 | |
1229 | return dom_bb; |
1230 | } |
1231 | |
1232 | /* Use simple heuristics (see iterate_fix_dominators) to determine dominators |
1233 | of BBS. We assume that all the immediate dominators except for those of the |
1234 | blocks in BBS are correct. If CONSERVATIVE is true, we also assume that the |
1235 | currently recorded immediate dominators of blocks in BBS really dominate the |
1236 | blocks. The basic blocks for that we determine the dominator are removed |
1237 | from BBS. */ |
1238 | |
1239 | static void |
1240 | prune_bbs_to_update_dominators (vec<basic_block> &bbs, |
1241 | bool conservative) |
1242 | { |
1243 | unsigned i; |
1244 | bool single; |
1245 | basic_block bb, dom = NULL; |
1246 | edge_iterator ei; |
1247 | edge e; |
1248 | |
1249 | for (i = 0; bbs.iterate (ix: i, ptr: &bb);) |
1250 | { |
1251 | if (bb == ENTRY_BLOCK_PTR_FOR_FN (cfun)) |
1252 | goto succeed; |
1253 | |
1254 | if (single_pred_p (bb)) |
1255 | { |
1256 | set_immediate_dominator (dir: CDI_DOMINATORS, bb, dominated_by: single_pred (bb)); |
1257 | goto succeed; |
1258 | } |
1259 | |
1260 | if (!conservative) |
1261 | goto fail; |
1262 | |
1263 | single = true; |
1264 | dom = NULL; |
1265 | FOR_EACH_EDGE (e, ei, bb->preds) |
1266 | { |
1267 | if (dominated_by_p (dir: CDI_DOMINATORS, bb1: e->src, bb2: bb)) |
1268 | continue; |
1269 | |
1270 | if (!dom) |
1271 | dom = e->src; |
1272 | else |
1273 | { |
1274 | single = false; |
1275 | dom = nearest_common_dominator (dir: CDI_DOMINATORS, bb1: dom, bb2: e->src); |
1276 | } |
1277 | } |
1278 | |
1279 | gcc_assert (dom != NULL); |
1280 | if (single |
1281 | || find_edge (dom, bb)) |
1282 | { |
1283 | set_immediate_dominator (dir: CDI_DOMINATORS, bb, dominated_by: dom); |
1284 | goto succeed; |
1285 | } |
1286 | |
1287 | fail: |
1288 | i++; |
1289 | continue; |
1290 | |
1291 | succeed: |
1292 | bbs.unordered_remove (ix: i); |
1293 | } |
1294 | } |
1295 | |
1296 | /* Returns root of the dominance tree in the direction DIR that contains |
1297 | BB. */ |
1298 | |
1299 | static basic_block |
1300 | root_of_dom_tree (enum cdi_direction dir, basic_block bb) |
1301 | { |
1302 | return (basic_block) et_root (bb->dom[dom_convert_dir_to_idx (dir)])->data; |
1303 | } |
1304 | |
1305 | /* See the comment in iterate_fix_dominators. Finds the immediate dominators |
1306 | for the sons of Y, found using the SON and BROTHER arrays representing |
1307 | the dominance tree of graph G. BBS maps the vertices of G to the basic |
1308 | blocks. */ |
1309 | |
1310 | static void |
1311 | determine_dominators_for_sons (struct graph *g, vec<basic_block> bbs, |
1312 | int y, int *son, int *brother) |
1313 | { |
1314 | bitmap gprime; |
1315 | int i, a, nc; |
1316 | vec<int> *sccs; |
1317 | basic_block bb, dom, ybb; |
1318 | unsigned si; |
1319 | edge e; |
1320 | edge_iterator ei; |
1321 | |
1322 | if (son[y] == -1) |
1323 | return; |
1324 | if (y == (int) bbs.length ()) |
1325 | ybb = ENTRY_BLOCK_PTR_FOR_FN (cfun); |
1326 | else |
1327 | ybb = bbs[y]; |
1328 | |
1329 | if (brother[son[y]] == -1) |
1330 | { |
1331 | /* Handle the common case Y has just one son specially. */ |
1332 | bb = bbs[son[y]]; |
1333 | set_immediate_dominator (dir: CDI_DOMINATORS, bb, |
1334 | dominated_by: recompute_dominator (dir: CDI_DOMINATORS, bb)); |
1335 | identify_vertices (g, y, son[y]); |
1336 | return; |
1337 | } |
1338 | |
1339 | gprime = BITMAP_ALLOC (NULL); |
1340 | for (a = son[y]; a != -1; a = brother[a]) |
1341 | bitmap_set_bit (gprime, a); |
1342 | |
1343 | nc = graphds_scc (g, gprime); |
1344 | BITMAP_FREE (gprime); |
1345 | |
1346 | /* ??? Needed to work around the pre-processor confusion with |
1347 | using a multi-argument template type as macro argument. */ |
1348 | typedef vec<int> vec_int_heap; |
1349 | sccs = XCNEWVEC (vec_int_heap, nc); |
1350 | for (a = son[y]; a != -1; a = brother[a]) |
1351 | sccs[g->vertices[a].component].safe_push (obj: a); |
1352 | |
1353 | for (i = nc - 1; i >= 0; i--) |
1354 | { |
1355 | dom = NULL; |
1356 | FOR_EACH_VEC_ELT (sccs[i], si, a) |
1357 | { |
1358 | bb = bbs[a]; |
1359 | FOR_EACH_EDGE (e, ei, bb->preds) |
1360 | { |
1361 | if (root_of_dom_tree (dir: CDI_DOMINATORS, bb: e->src) != ybb) |
1362 | continue; |
1363 | |
1364 | dom = nearest_common_dominator (dir: CDI_DOMINATORS, bb1: dom, bb2: e->src); |
1365 | } |
1366 | } |
1367 | |
1368 | gcc_assert (dom != NULL); |
1369 | FOR_EACH_VEC_ELT (sccs[i], si, a) |
1370 | { |
1371 | bb = bbs[a]; |
1372 | set_immediate_dominator (dir: CDI_DOMINATORS, bb, dominated_by: dom); |
1373 | } |
1374 | } |
1375 | |
1376 | for (i = 0; i < nc; i++) |
1377 | sccs[i].release (); |
1378 | free (ptr: sccs); |
1379 | |
1380 | for (a = son[y]; a != -1; a = brother[a]) |
1381 | identify_vertices (g, y, a); |
1382 | } |
1383 | |
1384 | /* Recompute dominance information for basic blocks in the set BBS. The |
1385 | function assumes that the immediate dominators of all the other blocks |
1386 | in CFG are correct, and that there are no unreachable blocks. |
1387 | |
1388 | If CONSERVATIVE is true, we additionally assume that all the ancestors of |
1389 | a block of BBS in the current dominance tree dominate it. */ |
1390 | |
1391 | void |
1392 | iterate_fix_dominators (enum cdi_direction dir, vec<basic_block> &bbs, |
1393 | bool conservative) |
1394 | { |
1395 | unsigned i; |
1396 | basic_block bb, dom; |
1397 | struct graph *g; |
1398 | int n, y; |
1399 | size_t dom_i; |
1400 | edge e; |
1401 | edge_iterator ei; |
1402 | int *parent, *son, *brother; |
1403 | unsigned int dir_index = dom_convert_dir_to_idx (dir); |
1404 | |
1405 | /* We only support updating dominators. There are some problems with |
1406 | updating postdominators (need to add fake edges from infinite loops |
1407 | and noreturn functions), and since we do not currently use |
1408 | iterate_fix_dominators for postdominators, any attempt to handle these |
1409 | problems would be unused, untested, and almost surely buggy. We keep |
1410 | the DIR argument for consistency with the rest of the dominator analysis |
1411 | interface. */ |
1412 | gcc_checking_assert (dir == CDI_DOMINATORS && dom_computed[dir_index]); |
1413 | |
1414 | /* The algorithm we use takes inspiration from the following papers, although |
1415 | the details are quite different from any of them: |
1416 | |
1417 | [1] G. Ramalingam, T. Reps, An Incremental Algorithm for Maintaining the |
1418 | Dominator Tree of a Reducible Flowgraph |
1419 | [2] V. C. Sreedhar, G. R. Gao, Y.-F. Lee: Incremental computation of |
1420 | dominator trees |
1421 | [3] K. D. Cooper, T. J. Harvey and K. Kennedy: A Simple, Fast Dominance |
1422 | Algorithm |
1423 | |
1424 | First, we use the following heuristics to decrease the size of the BBS |
1425 | set: |
1426 | a) if BB has a single predecessor, then its immediate dominator is this |
1427 | predecessor |
1428 | additionally, if CONSERVATIVE is true: |
1429 | b) if all the predecessors of BB except for one (X) are dominated by BB, |
1430 | then X is the immediate dominator of BB |
1431 | c) if the nearest common ancestor of the predecessors of BB is X and |
1432 | X -> BB is an edge in CFG, then X is the immediate dominator of BB |
1433 | |
1434 | Then, we need to establish the dominance relation among the basic blocks |
1435 | in BBS. We split the dominance tree by removing the immediate dominator |
1436 | edges from BBS, creating a forest F. We form a graph G whose vertices |
1437 | are BBS and ENTRY and X -> Y is an edge of G if there exists an edge |
1438 | X' -> Y in CFG such that X' belongs to the tree of the dominance forest |
1439 | whose root is X. We then determine dominance tree of G. Note that |
1440 | for X, Y in BBS, X dominates Y in CFG if and only if X dominates Y in G. |
1441 | In this step, we can use arbitrary algorithm to determine dominators. |
1442 | We decided to prefer the algorithm [3] to the algorithm of |
1443 | Lengauer and Tarjan, since the set BBS is usually small (rarely exceeding |
1444 | 10 during gcc bootstrap), and [3] should perform better in this case. |
1445 | |
1446 | Finally, we need to determine the immediate dominators for the basic |
1447 | blocks of BBS. If the immediate dominator of X in G is Y, then |
1448 | the immediate dominator of X in CFG belongs to the tree of F rooted in |
1449 | Y. We process the dominator tree T of G recursively, starting from leaves. |
1450 | Suppose that X_1, X_2, ..., X_k are the sons of Y in T, and that the |
1451 | subtrees of the dominance tree of CFG rooted in X_i are already correct. |
1452 | Let G' be the subgraph of G induced by {X_1, X_2, ..., X_k}. We make |
1453 | the following observations: |
1454 | (i) the immediate dominator of all blocks in a strongly connected |
1455 | component of G' is the same |
1456 | (ii) if X has no predecessors in G', then the immediate dominator of X |
1457 | is the nearest common ancestor of the predecessors of X in the |
1458 | subtree of F rooted in Y |
1459 | Therefore, it suffices to find the topological ordering of G', and |
1460 | process the nodes X_i in this order using the rules (i) and (ii). |
1461 | Then, we contract all the nodes X_i with Y in G, so that the further |
1462 | steps work correctly. */ |
1463 | |
1464 | if (!conservative) |
1465 | { |
1466 | /* Split the tree now. If the idoms of blocks in BBS are not |
1467 | conservatively correct, setting the dominators using the |
1468 | heuristics in prune_bbs_to_update_dominators could |
1469 | create cycles in the dominance "tree", and cause ICE. */ |
1470 | FOR_EACH_VEC_ELT (bbs, i, bb) |
1471 | set_immediate_dominator (dir: CDI_DOMINATORS, bb, NULL); |
1472 | } |
1473 | |
1474 | prune_bbs_to_update_dominators (bbs, conservative); |
1475 | n = bbs.length (); |
1476 | |
1477 | if (n == 0) |
1478 | return; |
1479 | |
1480 | if (n == 1) |
1481 | { |
1482 | bb = bbs[0]; |
1483 | set_immediate_dominator (dir: CDI_DOMINATORS, bb, |
1484 | dominated_by: recompute_dominator (dir: CDI_DOMINATORS, bb)); |
1485 | return; |
1486 | } |
1487 | |
1488 | timevar_push (tv: TV_DOMINANCE); |
1489 | |
1490 | /* Construct the graph G. */ |
1491 | hash_map<basic_block, int> map (251); |
1492 | FOR_EACH_VEC_ELT (bbs, i, bb) |
1493 | { |
1494 | /* If the dominance tree is conservatively correct, split it now. */ |
1495 | if (conservative) |
1496 | set_immediate_dominator (dir: CDI_DOMINATORS, bb, NULL); |
1497 | map.put (k: bb, v: i); |
1498 | } |
1499 | map.put (ENTRY_BLOCK_PTR_FOR_FN (cfun), v: n); |
1500 | |
1501 | g = new_graph (n + 1); |
1502 | for (y = 0; y < g->n_vertices; y++) |
1503 | g->vertices[y].data = BITMAP_ALLOC (NULL); |
1504 | FOR_EACH_VEC_ELT (bbs, i, bb) |
1505 | { |
1506 | FOR_EACH_EDGE (e, ei, bb->preds) |
1507 | { |
1508 | dom = root_of_dom_tree (dir: CDI_DOMINATORS, bb: e->src); |
1509 | if (dom == bb) |
1510 | continue; |
1511 | |
1512 | dom_i = *map.get (k: dom); |
1513 | |
1514 | /* Do not include parallel edges to G. */ |
1515 | if (!bitmap_set_bit ((bitmap) g->vertices[dom_i].data, i)) |
1516 | continue; |
1517 | |
1518 | add_edge (g, dom_i, i); |
1519 | } |
1520 | } |
1521 | for (y = 0; y < g->n_vertices; y++) |
1522 | BITMAP_FREE (g->vertices[y].data); |
1523 | |
1524 | /* Find the dominator tree of G. */ |
1525 | son = XNEWVEC (int, n + 1); |
1526 | brother = XNEWVEC (int, n + 1); |
1527 | parent = XNEWVEC (int, n + 1); |
1528 | graphds_domtree (g, n, parent, son, brother); |
1529 | |
1530 | /* Finally, traverse the tree and find the immediate dominators. */ |
1531 | for (y = n; son[y] != -1; y = son[y]) |
1532 | continue; |
1533 | while (y != -1) |
1534 | { |
1535 | determine_dominators_for_sons (g, bbs, y, son, brother); |
1536 | |
1537 | if (brother[y] != -1) |
1538 | { |
1539 | y = brother[y]; |
1540 | while (son[y] != -1) |
1541 | y = son[y]; |
1542 | } |
1543 | else |
1544 | y = parent[y]; |
1545 | } |
1546 | |
1547 | free (ptr: son); |
1548 | free (ptr: brother); |
1549 | free (ptr: parent); |
1550 | |
1551 | free_graph (g); |
1552 | |
1553 | timevar_pop (tv: TV_DOMINANCE); |
1554 | } |
1555 | |
1556 | void |
1557 | add_to_dominance_info (enum cdi_direction dir, basic_block bb) |
1558 | { |
1559 | unsigned int dir_index = dom_convert_dir_to_idx (dir); |
1560 | |
1561 | gcc_checking_assert (dom_computed[dir_index] && !bb->dom[dir_index]); |
1562 | |
1563 | n_bbs_in_dom_tree[dir_index]++; |
1564 | |
1565 | bb->dom[dir_index] = et_new_tree (data: bb); |
1566 | |
1567 | if (dom_computed[dir_index] == DOM_OK) |
1568 | dom_computed[dir_index] = DOM_NO_FAST_QUERY; |
1569 | } |
1570 | |
1571 | void |
1572 | delete_from_dominance_info (enum cdi_direction dir, basic_block bb) |
1573 | { |
1574 | unsigned int dir_index = dom_convert_dir_to_idx (dir); |
1575 | |
1576 | gcc_checking_assert (dom_computed[dir_index]); |
1577 | |
1578 | et_free_tree (bb->dom[dir_index]); |
1579 | bb->dom[dir_index] = NULL; |
1580 | n_bbs_in_dom_tree[dir_index]--; |
1581 | |
1582 | if (dom_computed[dir_index] == DOM_OK) |
1583 | dom_computed[dir_index] = DOM_NO_FAST_QUERY; |
1584 | } |
1585 | |
1586 | /* Returns the first son of BB in the dominator or postdominator tree |
1587 | as determined by DIR. */ |
1588 | |
1589 | basic_block |
1590 | first_dom_son (enum cdi_direction dir, basic_block bb) |
1591 | { |
1592 | unsigned int dir_index = dom_convert_dir_to_idx (dir); |
1593 | struct et_node *son = bb->dom[dir_index]->son; |
1594 | |
1595 | return (basic_block) (son ? son->data : NULL); |
1596 | } |
1597 | |
1598 | /* Returns the next dominance son after BB in the dominator or postdominator |
1599 | tree as determined by DIR, or NULL if it was the last one. */ |
1600 | |
1601 | basic_block |
1602 | next_dom_son (enum cdi_direction dir, basic_block bb) |
1603 | { |
1604 | unsigned int dir_index = dom_convert_dir_to_idx (dir); |
1605 | struct et_node *next = bb->dom[dir_index]->right; |
1606 | |
1607 | return (basic_block) (next->father->son == next ? NULL : next->data); |
1608 | } |
1609 | |
1610 | /* Return dominance availability for dominance info DIR. */ |
1611 | |
1612 | enum dom_state |
1613 | dom_info_state (function *fn, enum cdi_direction dir) |
1614 | { |
1615 | if (!fn->cfg) |
1616 | return DOM_NONE; |
1617 | |
1618 | unsigned int dir_index = dom_convert_dir_to_idx (dir); |
1619 | return fn->cfg->x_dom_computed[dir_index]; |
1620 | } |
1621 | |
1622 | enum dom_state |
1623 | dom_info_state (enum cdi_direction dir) |
1624 | { |
1625 | return dom_info_state (cfun, dir); |
1626 | } |
1627 | |
1628 | /* Set the dominance availability for dominance info DIR to NEW_STATE. */ |
1629 | |
1630 | void |
1631 | set_dom_info_availability (enum cdi_direction dir, enum dom_state new_state) |
1632 | { |
1633 | unsigned int dir_index = dom_convert_dir_to_idx (dir); |
1634 | |
1635 | dom_computed[dir_index] = new_state; |
1636 | } |
1637 | |
1638 | /* Returns true if dominance information for direction DIR is available. */ |
1639 | |
1640 | bool |
1641 | dom_info_available_p (function *fn, enum cdi_direction dir) |
1642 | { |
1643 | return dom_info_state (fn, dir) != DOM_NONE; |
1644 | } |
1645 | |
1646 | bool |
1647 | dom_info_available_p (enum cdi_direction dir) |
1648 | { |
1649 | return dom_info_available_p (cfun, dir); |
1650 | } |
1651 | |
1652 | DEBUG_FUNCTION void |
1653 | debug_dominance_info (enum cdi_direction dir) |
1654 | { |
1655 | basic_block bb, bb2; |
1656 | FOR_EACH_BB_FN (bb, cfun) |
1657 | if ((bb2 = get_immediate_dominator (dir, bb))) |
1658 | fprintf (stderr, format: "%i %i\n" , bb->index, bb2->index); |
1659 | } |
1660 | |
1661 | /* Prints to stderr representation of the dominance tree (for direction DIR) |
1662 | rooted in ROOT, indented by INDENT tabulators. If INDENT_FIRST is false, |
1663 | the first line of the output is not indented. */ |
1664 | |
1665 | static void |
1666 | debug_dominance_tree_1 (enum cdi_direction dir, basic_block root, |
1667 | unsigned indent, bool indent_first) |
1668 | { |
1669 | basic_block son; |
1670 | unsigned i; |
1671 | bool first = true; |
1672 | |
1673 | if (indent_first) |
1674 | for (i = 0; i < indent; i++) |
1675 | fprintf (stderr, format: "\t" ); |
1676 | fprintf (stderr, format: "%d\t" , root->index); |
1677 | |
1678 | for (son = first_dom_son (dir, bb: root); |
1679 | son; |
1680 | son = next_dom_son (dir, bb: son)) |
1681 | { |
1682 | debug_dominance_tree_1 (dir, root: son, indent: indent + 1, indent_first: !first); |
1683 | first = false; |
1684 | } |
1685 | |
1686 | if (first) |
1687 | fprintf (stderr, format: "\n" ); |
1688 | } |
1689 | |
1690 | /* Prints to stderr representation of the dominance tree (for direction DIR) |
1691 | rooted in ROOT. */ |
1692 | |
1693 | DEBUG_FUNCTION void |
1694 | debug_dominance_tree (enum cdi_direction dir, basic_block root) |
1695 | { |
1696 | debug_dominance_tree_1 (dir, root, indent: 0, indent_first: false); |
1697 | } |
1698 | |