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6de9cd9a | 1 | /* Generic dominator tree walker |
fa10beec RW |
2 | Copyright (C) 2003, 2004, 2005, 2007, 2008 Free Software Foundation, |
3 | Inc. | |
6de9cd9a DN |
4 | Contributed by Diego Novillo <dnovillo@redhat.com> |
5 | ||
6 | This file is part of GCC. | |
7 | ||
8 | GCC is free software; you can redistribute it and/or modify | |
9 | it under the terms of the GNU General Public License as published by | |
9dcd6f09 | 10 | the Free Software Foundation; either version 3, or (at your option) |
6de9cd9a DN |
11 | any later version. |
12 | ||
13 | GCC is distributed in the hope that it will be useful, | |
14 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
15 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
16 | GNU General Public License for more details. | |
17 | ||
18 | You should have received a copy of the GNU General Public License | |
9dcd6f09 NC |
19 | along with GCC; see the file COPYING3. If not see |
20 | <http://www.gnu.org/licenses/>. */ | |
6de9cd9a DN |
21 | |
22 | #include "config.h" | |
23 | #include "system.h" | |
24 | #include "coretypes.h" | |
25 | #include "tm.h" | |
26 | #include "tree.h" | |
27 | #include "basic-block.h" | |
28 | #include "tree-flow.h" | |
29 | #include "domwalk.h" | |
30 | #include "ggc.h" | |
31 | ||
32 | /* This file implements a generic walker for dominator trees. | |
33 | ||
34 | To understand the dominator walker one must first have a grasp of dominators, | |
35 | immediate dominators and the dominator tree. | |
36 | ||
37 | Dominators | |
38 | A block B1 is said to dominate B2 if every path from the entry to B2 must | |
39 | pass through B1. Given the dominance relationship, we can proceed to | |
40 | compute immediate dominators. Note it is not important whether or not | |
41 | our definition allows a block to dominate itself. | |
42 | ||
43 | Immediate Dominators: | |
44 | Every block in the CFG has no more than one immediate dominator. The | |
45 | immediate dominator of block BB must dominate BB and must not dominate | |
46 | any other dominator of BB and must not be BB itself. | |
47 | ||
48 | Dominator tree: | |
49 | If we then construct a tree where each node is a basic block and there | |
50 | is an edge from each block's immediate dominator to the block itself, then | |
51 | we have a dominator tree. | |
52 | ||
53 | ||
54 | [ Note this walker can also walk the post-dominator tree, which is | |
454ff5cb | 55 | defined in a similar manner. i.e., block B1 is said to post-dominate |
6de9cd9a DN |
56 | block B2 if all paths from B2 to the exit block must pass through |
57 | B1. ] | |
58 | ||
59 | For example, given the CFG | |
60 | ||
61 | 1 | |
62 | | | |
63 | 2 | |
64 | / \ | |
65 | 3 4 | |
66 | / \ | |
67 | +---------->5 6 | |
68 | | / \ / | |
69 | | +--->8 7 | |
70 | | | / | | |
71 | | +--9 11 | |
72 | | / | | |
73 | +--- 10 ---> 12 | |
74 | ||
75 | ||
76 | We have a dominator tree which looks like | |
77 | ||
78 | 1 | |
79 | | | |
80 | 2 | |
81 | / \ | |
82 | / \ | |
83 | 3 4 | |
84 | / / \ \ | |
85 | | | | | | |
86 | 5 6 7 12 | |
87 | | | | |
88 | 8 11 | |
89 | | | |
90 | 9 | |
91 | | | |
92 | 10 | |
93 | ||
94 | ||
95 | ||
96 | The dominator tree is the basis for a number of analysis, transformation | |
97 | and optimization algorithms that operate on a semi-global basis. | |
98 | ||
99 | The dominator walker is a generic routine which visits blocks in the CFG | |
100 | via a depth first search of the dominator tree. In the example above | |
101 | the dominator walker might visit blocks in the following order | |
102 | 1, 2, 3, 4, 5, 8, 9, 10, 6, 7, 11, 12. | |
103 | ||
104 | The dominator walker has a number of callbacks to perform actions | |
105 | during the walk of the dominator tree. There are two callbacks | |
106 | which walk statements, one before visiting the dominator children, | |
107 | one after visiting the dominator children. There is a callback | |
108 | before and after each statement walk callback. In addition, the | |
109 | dominator walker manages allocation/deallocation of data structures | |
110 | which are local to each block visited. | |
111 | ||
112 | The dominator walker is meant to provide a generic means to build a pass | |
113 | which can analyze or transform/optimize a function based on walking | |
114 | the dominator tree. One simply fills in the dominator walker data | |
115 | structure with the appropriate callbacks and calls the walker. | |
116 | ||
117 | We currently use the dominator walker to prune the set of variables | |
118 | which might need PHI nodes (which can greatly improve compile-time | |
119 | performance in some cases). | |
120 | ||
121 | We also use the dominator walker to rewrite the function into SSA form | |
122 | which reduces code duplication since the rewriting phase is inherently | |
123 | a walk of the dominator tree. | |
124 | ||
110abdbc | 125 | And (of course), we use the dominator walker to drive our dominator |
6de9cd9a DN |
126 | optimizer, which is a semi-global optimizer. |
127 | ||
128 | TODO: | |
129 | ||
130 | Walking statements is based on the block statement iterator abstraction, | |
131 | which is currently an abstraction over walking tree statements. Thus | |
132 | the dominator walker is currently only useful for trees. */ | |
133 | ||
134 | /* Recursively walk the dominator tree. | |
135 | ||
136 | WALK_DATA contains a set of callbacks to perform pass-specific | |
137 | actions during the dominator walk as well as a stack of block local | |
138 | data maintained during the dominator walk. | |
139 | ||
140 | BB is the basic block we are currently visiting. */ | |
141 | ||
142 | void | |
143 | walk_dominator_tree (struct dom_walk_data *walk_data, basic_block bb) | |
144 | { | |
145 | void *bd = NULL; | |
146 | basic_block dest; | |
726a989a | 147 | gimple_stmt_iterator gsi; |
0bca51f0 | 148 | bool is_interesting; |
df648b94 JH |
149 | basic_block *worklist = XNEWVEC (basic_block, n_basic_blocks * 2); |
150 | int sp = 0; | |
0bca51f0 | 151 | |
df648b94 | 152 | while (true) |
6de9cd9a | 153 | { |
df648b94 | 154 | /* Don't worry about unreachable blocks. */ |
515f36eb RG |
155 | if (EDGE_COUNT (bb->preds) > 0 |
156 | || bb == ENTRY_BLOCK_PTR | |
157 | || bb == EXIT_BLOCK_PTR) | |
6de9cd9a | 158 | { |
df648b94 JH |
159 | /* If block BB is not interesting to the caller, then none of the |
160 | callbacks that walk the statements in BB are going to be | |
161 | executed. */ | |
162 | is_interesting = walk_data->interesting_blocks == NULL | |
163 | || TEST_BIT (walk_data->interesting_blocks, | |
164 | bb->index); | |
165 | ||
166 | /* Callback to initialize the local data structure. */ | |
167 | if (walk_data->initialize_block_local_data) | |
168 | { | |
169 | bool recycled; | |
170 | ||
726a989a RB |
171 | /* First get some local data, reusing any local data |
172 | pointer we may have saved. */ | |
df648b94 JH |
173 | if (VEC_length (void_p, walk_data->free_block_data) > 0) |
174 | { | |
175 | bd = VEC_pop (void_p, walk_data->free_block_data); | |
176 | recycled = 1; | |
177 | } | |
178 | else | |
179 | { | |
180 | bd = xcalloc (1, walk_data->block_local_data_size); | |
181 | recycled = 0; | |
182 | } | |
183 | ||
184 | /* Push the local data into the local data stack. */ | |
185 | VEC_safe_push (void_p, heap, walk_data->block_data_stack, bd); | |
186 | ||
187 | /* Call the initializer. */ | |
188 | walk_data->initialize_block_local_data (walk_data, bb, | |
189 | recycled); | |
190 | ||
191 | } | |
192 | ||
193 | /* Callback for operations to execute before we have walked the | |
194 | dominator children, but before we walk statements. */ | |
195 | if (walk_data->before_dom_children_before_stmts) | |
196 | (*walk_data->before_dom_children_before_stmts) (walk_data, bb); | |
197 | ||
198 | /* Statement walk before walking dominator children. */ | |
199 | if (is_interesting && walk_data->before_dom_children_walk_stmts) | |
200 | { | |
201 | if (walk_data->walk_stmts_backward) | |
726a989a RB |
202 | for (gsi = gsi_last (bb_seq (bb)); !gsi_end_p (gsi); |
203 | gsi_prev (&gsi)) | |
df648b94 | 204 | (*walk_data->before_dom_children_walk_stmts) (walk_data, bb, |
726a989a | 205 | gsi); |
df648b94 | 206 | else |
726a989a | 207 | for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi)) |
df648b94 | 208 | (*walk_data->before_dom_children_walk_stmts) (walk_data, bb, |
726a989a | 209 | gsi); |
df648b94 JH |
210 | } |
211 | ||
212 | /* Callback for operations to execute before we have walked the | |
213 | dominator children, and after we walk statements. */ | |
214 | if (walk_data->before_dom_children_after_stmts) | |
215 | (*walk_data->before_dom_children_after_stmts) (walk_data, bb); | |
216 | ||
217 | /* Mark the current BB to be popped out of the recursion stack | |
fa10beec | 218 | once children are processed. */ |
df648b94 JH |
219 | worklist[sp++] = bb; |
220 | worklist[sp++] = NULL; | |
221 | ||
222 | for (dest = first_dom_son (walk_data->dom_direction, bb); | |
223 | dest; dest = next_dom_son (walk_data->dom_direction, dest)) | |
224 | worklist[sp++] = dest; | |
6de9cd9a | 225 | } |
df648b94 JH |
226 | /* NULL is used to signalize pop operation in recursion stack. */ |
227 | while (sp > 0 && !worklist[sp - 1]) | |
6de9cd9a | 228 | { |
df648b94 JH |
229 | --sp; |
230 | bb = worklist[--sp]; | |
231 | is_interesting = walk_data->interesting_blocks == NULL | |
232 | || TEST_BIT (walk_data->interesting_blocks, | |
233 | bb->index); | |
234 | /* Callback for operations to execute after we have walked the | |
235 | dominator children, but before we walk statements. */ | |
236 | if (walk_data->after_dom_children_before_stmts) | |
237 | (*walk_data->after_dom_children_before_stmts) (walk_data, bb); | |
238 | ||
239 | /* Statement walk after walking dominator children. */ | |
240 | if (is_interesting && walk_data->after_dom_children_walk_stmts) | |
241 | { | |
242 | if (walk_data->walk_stmts_backward) | |
726a989a RB |
243 | for (gsi = gsi_last (bb_seq (bb)); !gsi_end_p (gsi); |
244 | gsi_prev (&gsi)) | |
df648b94 | 245 | (*walk_data->after_dom_children_walk_stmts) (walk_data, bb, |
726a989a | 246 | gsi); |
df648b94 | 247 | else |
726a989a | 248 | for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi)) |
df648b94 | 249 | (*walk_data->after_dom_children_walk_stmts) (walk_data, bb, |
726a989a | 250 | gsi); |
df648b94 JH |
251 | } |
252 | ||
253 | /* Callback for operations to execute after we have walked the | |
254 | dominator children and after we have walked statements. */ | |
255 | if (walk_data->after_dom_children_after_stmts) | |
256 | (*walk_data->after_dom_children_after_stmts) (walk_data, bb); | |
257 | ||
258 | if (walk_data->initialize_block_local_data) | |
259 | { | |
260 | /* And finally pop the record off the block local data stack. */ | |
261 | bd = VEC_pop (void_p, walk_data->block_data_stack); | |
262 | /* And save the block data so that we can re-use it. */ | |
263 | VEC_safe_push (void_p, heap, walk_data->free_block_data, bd); | |
264 | } | |
6de9cd9a | 265 | } |
df648b94 JH |
266 | if (sp) |
267 | bb = worklist[--sp]; | |
6de9cd9a | 268 | else |
df648b94 | 269 | break; |
6de9cd9a | 270 | } |
df648b94 | 271 | free (worklist); |
6de9cd9a DN |
272 | } |
273 | ||
274 | void | |
275 | init_walk_dominator_tree (struct dom_walk_data *walk_data) | |
276 | { | |
ea497bb8 KH |
277 | walk_data->free_block_data = NULL; |
278 | walk_data->block_data_stack = NULL; | |
6de9cd9a DN |
279 | } |
280 | ||
281 | void | |
282 | fini_walk_dominator_tree (struct dom_walk_data *walk_data) | |
283 | { | |
284 | if (walk_data->initialize_block_local_data) | |
285 | { | |
ea497bb8 KH |
286 | while (VEC_length (void_p, walk_data->free_block_data) > 0) |
287 | free (VEC_pop (void_p, walk_data->free_block_data)); | |
6de9cd9a | 288 | } |
ea497bb8 KH |
289 | |
290 | VEC_free (void_p, heap, walk_data->free_block_data); | |
291 | VEC_free (void_p, heap, walk_data->block_data_stack); | |
6de9cd9a | 292 | } |