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