1 /* Localize comdats.
2 Copyright (C) 2014-2018 Free Software Foundation, Inc.
3
4 This file is part of GCC.
5
6 GCC is free software; you can redistribute it and/or modify it under
7 the terms of the GNU General Public License as published by the Free
8 Software Foundation; either version 3, or (at your option) any later
9 version.
10
11 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
12 WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 for more details.
15
16 You should have received a copy of the GNU General Public License
17 along with GCC; see the file COPYING3. If not see
18 <http://www.gnu.org/licenses/>. */
19
20 /* This is very simple pass that looks for static symbols that are used
21 exlusively by symbol within one comdat group. In this case it makes
22 sense to bring the symbol itself into the group to avoid dead code
23 that would arrise when the comdat group from current unit is replaced
24 by a different copy. Consider for example:
25
26 static int q(void)
27 {
28 ....
29 }
30 inline int t(void)
31 {
32 return q();
33 }
34
35 if Q is used only by T, it makes sense to put Q into T's comdat group.
36
37 The pass solve simple dataflow across the callgraph trying to prove what
38 symbols are used exclusively from a given comdat group.
39
40 The implementation maintains a queue linked by AUX pointer terminated by
41 pointer value 1. Lattice values are NULL for TOP, actual comdat group, or
42 ERROR_MARK_NODE for bottom.
43
44 TODO: When symbol is used only by comdat symbols, but from different groups,
45 it would make sense to produce a new comdat group for it with anonymous name.
46
47 TODO2: We can't mix variables and functions within one group. Currently
48 we just give up on references of symbols of different types. We also should
49 handle this by anonymous comdat group section. */
50
51 #include "config.h"
52 #include "system.h"
53 #include "coretypes.h"
54 #include "tm.h"
55 #include "tree.h"
56 #include "tree-pass.h"
57 #include "cgraph.h"
58
59 /* Main dataflow loop propagating comdat groups across
60 the symbol table. All references to SYMBOL are examined
61 and NEWGROUP is updated accordingly. MAP holds current lattice
62 values for individual symbols. */
63
64 tree
propagate_comdat_group(struct symtab_node * symbol,tree newgroup,hash_map<symtab_node *,tree> & map)65 propagate_comdat_group (struct symtab_node *symbol,
66 tree newgroup, hash_map<symtab_node *, tree> &map)
67 {
68 int i;
69 struct ipa_ref *ref;
70
71 /* Walk all references to SYMBOL, recursively dive into aliases. */
72
73 for (i = 0;
74 symbol->iterate_referring (i, ref)
75 && newgroup != error_mark_node; i++)
76 {
77 struct symtab_node *symbol2 = ref->referring;
78
79 if (ref->use == IPA_REF_ALIAS)
80 {
81 newgroup = propagate_comdat_group (symbol2, newgroup, map);
82 continue;
83 }
84
85 /* One COMDAT group can not hold both variables and functions at
86 a same time. For now we just go to BOTTOM, in future we may
87 invent special comdat groups for this case. */
88
89 if (symbol->type != symbol2->type)
90 {
91 newgroup = error_mark_node;
92 break;
93 }
94
95 /* If we see inline clone, its comdat group actually
96 corresponds to the comdat group of the function it is inlined
97 to. */
98
99 if (cgraph_node * cn = dyn_cast <cgraph_node *> (symbol2))
100 {
101 if (cn->global.inlined_to)
102 symbol2 = cn->global.inlined_to;
103 }
104
105 /* The actual merge operation. */
106
107 tree *val2 = map.get (symbol2);
108
109 if (val2 && *val2 != newgroup)
110 {
111 if (!newgroup)
112 newgroup = *val2;
113 else
114 newgroup = error_mark_node;
115 }
116 }
117
118 /* If we analyze function, walk also callers. */
119
120 cgraph_node *cnode = dyn_cast <cgraph_node *> (symbol);
121
122 if (cnode)
123 for (struct cgraph_edge * edge = cnode->callers;
124 edge && newgroup != error_mark_node; edge = edge->next_caller)
125 {
126 struct symtab_node *symbol2 = edge->caller;
127
128 if (cgraph_node * cn = dyn_cast <cgraph_node *> (symbol2))
129 {
130 /* Thunks can not call across section boundary. */
131 if (cn->thunk.thunk_p)
132 newgroup = propagate_comdat_group (symbol2, newgroup, map);
133 /* If we see inline clone, its comdat group actually
134 corresponds to the comdat group of the function it
135 is inlined to. */
136 if (cn->global.inlined_to)
137 symbol2 = cn->global.inlined_to;
138 }
139
140 /* The actual merge operation. */
141
142 tree *val2 = map.get (symbol2);
143
144 if (val2 && *val2 != newgroup)
145 {
146 if (!newgroup)
147 newgroup = *val2;
148 else
149 newgroup = error_mark_node;
150 }
151 }
152 return newgroup;
153 }
154
155
156 /* Add all references of SYMBOL that are defined into queue started by FIRST
157 and linked by AUX pointer (unless they are already enqueued).
158 Walk recursively inlined functions. */
159
160 void
enqueue_references(symtab_node ** first,symtab_node * symbol)161 enqueue_references (symtab_node **first,
162 symtab_node *symbol)
163 {
164 int i;
165 struct ipa_ref *ref = NULL;
166
167 for (i = 0; symbol->iterate_reference (i, ref); i++)
168 {
169 symtab_node *node = ref->referred->ultimate_alias_target ();
170
171 /* Always keep thunks in same sections as target function. */
172 if (is_a <cgraph_node *>(node))
173 node = dyn_cast <cgraph_node *> (node)->function_symbol ();
174 if (!node->aux && node->definition)
175 {
176 node->aux = *first;
177 *first = node;
178 }
179 }
180
181 if (cgraph_node *cnode = dyn_cast <cgraph_node *> (symbol))
182 {
183 struct cgraph_edge *edge;
184
185 for (edge = cnode->callees; edge; edge = edge->next_callee)
186 if (!edge->inline_failed)
187 enqueue_references (first, edge->callee);
188 else
189 {
190 symtab_node *node = edge->callee->ultimate_alias_target ();
191
192 /* Always keep thunks in same sections as target function. */
193 if (is_a <cgraph_node *>(node))
194 node = dyn_cast <cgraph_node *> (node)->function_symbol ();
195 if (!node->aux && node->definition)
196 {
197 node->aux = *first;
198 *first = node;
199 }
200 }
201 }
202 }
203
204 /* Set comdat group of SYMBOL to GROUP.
205 Callback for for_node_and_aliases. */
206
207 bool
set_comdat_group(symtab_node * symbol,void * head_p)208 set_comdat_group (symtab_node *symbol,
209 void *head_p)
210 {
211 symtab_node *head = (symtab_node *)head_p;
212
213 gcc_assert (!symbol->get_comdat_group ());
214 if (symbol->real_symbol_p ())
215 {
216 symbol->set_comdat_group (head->get_comdat_group ());
217 symbol->add_to_same_comdat_group (head);
218 }
219 return false;
220 }
221
222 /* Set comdat group of SYMBOL to GROUP.
223 Callback for for_node_thunks_and_aliases. */
224
225 bool
set_comdat_group_1(cgraph_node * symbol,void * head_p)226 set_comdat_group_1 (cgraph_node *symbol,
227 void *head_p)
228 {
229 return set_comdat_group (symbol, head_p);
230 }
231
232 /* The actual pass with the main dataflow loop. */
233
234 static unsigned int
ipa_comdats(void)235 ipa_comdats (void)
236 {
237 hash_map<symtab_node *, tree> map (251);
238 hash_map<tree, symtab_node *> comdat_head_map (251);
239 symtab_node *symbol;
240 bool comdat_group_seen = false;
241 symtab_node *first = (symtab_node *) (void *) 1;
242 tree group;
243
244 /* Start the dataflow by assigning comdat group to symbols that are in comdat
245 groups already. All other externally visible symbols must stay, we use
246 ERROR_MARK_NODE as bottom for the propagation. */
247
248 FOR_EACH_DEFINED_SYMBOL (symbol)
249 if (!symbol->real_symbol_p ())
250 ;
251 else if ((group = symbol->get_comdat_group ()) != NULL)
252 {
253 map.put (symbol, group);
254 comdat_head_map.put (group, symbol);
255 comdat_group_seen = true;
256
257 /* Mark the symbol so we won't waste time visiting it for dataflow. */
258 symbol->aux = (symtab_node *) (void *) 1;
259 }
260 /* See symbols that can not be privatized to comdats; that is externally
261 visible symbols or otherwise used ones. We also do not want to mangle
262 user section names. */
263 else if (symbol->externally_visible
264 || symbol->force_output
265 || symbol->used_from_other_partition
266 || TREE_THIS_VOLATILE (symbol->decl)
267 || symbol->get_section ()
268 || (TREE_CODE (symbol->decl) == FUNCTION_DECL
269 && (DECL_STATIC_CONSTRUCTOR (symbol->decl)
270 || DECL_STATIC_DESTRUCTOR (symbol->decl))))
271 {
272 symtab_node *target = symbol->ultimate_alias_target ();
273
274 /* Always keep thunks in same sections as target function. */
275 if (is_a <cgraph_node *>(target))
276 target = dyn_cast <cgraph_node *> (target)->function_symbol ();
277 map.put (target, error_mark_node);
278
279 /* Mark the symbol so we won't waste time visiting it for dataflow. */
280 symbol->aux = (symtab_node *) (void *) 1;
281 }
282 else
283 {
284 /* Enqueue symbol for dataflow. */
285 symbol->aux = first;
286 first = symbol;
287 }
288
289 if (!comdat_group_seen)
290 {
291 FOR_EACH_DEFINED_SYMBOL (symbol)
292 symbol->aux = NULL;
293 return 0;
294 }
295
296 /* The actual dataflow. */
297
298 while (first != (void *) 1)
299 {
300 tree group = NULL;
301 tree newgroup, *val;
302
303 symbol = first;
304 first = (symtab_node *)first->aux;
305
306 /* Get current lattice value of SYMBOL. */
307 val = map.get (symbol);
308 if (val)
309 group = *val;
310
311 /* If it is bottom, there is nothing to do; do not clear AUX
312 so we won't re-queue the symbol. */
313 if (group == error_mark_node)
314 continue;
315
316 newgroup = propagate_comdat_group (symbol, group, map);
317
318 /* If nothing changed, proceed to next symbol. */
319 if (newgroup == group)
320 {
321 symbol->aux = NULL;
322 continue;
323 }
324
325 /* Update lattice value and enqueue all references for re-visiting. */
326 gcc_assert (newgroup);
327 if (val)
328 *val = newgroup;
329 else
330 map.put (symbol, newgroup);
331 enqueue_references (&first, symbol);
332
333 /* We may need to revisit the symbol unless it is BOTTOM. */
334 if (newgroup != error_mark_node)
335 symbol->aux = NULL;
336 }
337
338 /* Finally assign symbols to the sections. */
339
340 FOR_EACH_DEFINED_SYMBOL (symbol)
341 {
342 struct cgraph_node *fun;
343 symbol->aux = NULL;
344 if (!symbol->get_comdat_group ()
345 && !symbol->alias
346 && (!(fun = dyn_cast <cgraph_node *> (symbol))
347 || !fun->thunk.thunk_p)
348 && symbol->real_symbol_p ())
349 {
350 tree *val = map.get (symbol);
351
352 /* A NULL here means that SYMBOL is unreachable in the definition
353 of ipa-comdats. Either ipa-comdats is wrong about this or someone
354 forgot to cleanup and remove unreachable functions earlier. */
355 gcc_assert (val);
356
357 tree group = *val;
358
359 if (group == error_mark_node)
360 continue;
361 if (dump_file)
362 {
363 fprintf (dump_file, "Localizing symbol\n");
364 symbol->dump (dump_file);
365 fprintf (dump_file, "To group: %s\n", IDENTIFIER_POINTER (group));
366 }
367 if (is_a <cgraph_node *> (symbol))
368 dyn_cast <cgraph_node *>(symbol)->call_for_symbol_thunks_and_aliases
369 (set_comdat_group_1,
370 *comdat_head_map.get (group),
371 true);
372 else
373 symbol->call_for_symbol_and_aliases
374 (set_comdat_group,
375 *comdat_head_map.get (group),
376 true);
377 }
378 }
379 return 0;
380 }
381
382 namespace {
383
384 const pass_data pass_data_ipa_comdats =
385 {
386 IPA_PASS, /* type */
387 "comdats", /* name */
388 OPTGROUP_NONE, /* optinfo_flags */
389 TV_IPA_COMDATS, /* tv_id */
390 0, /* properties_required */
391 0, /* properties_provided */
392 0, /* properties_destroyed */
393 0, /* todo_flags_start */
394 0, /* todo_flags_finish */
395 };
396
397 class pass_ipa_comdats : public ipa_opt_pass_d
398 {
399 public:
pass_ipa_comdats(gcc::context * ctxt)400 pass_ipa_comdats (gcc::context *ctxt)
401 : ipa_opt_pass_d (pass_data_ipa_comdats, ctxt,
402 NULL, /* generate_summary */
403 NULL, /* write_summary */
404 NULL, /* read_summary */
405 NULL, /* write_optimization_summary */
406 NULL, /* read_optimization_summary */
407 NULL, /* stmt_fixup */
408 0, /* function_transform_todo_flags_start */
409 NULL, /* function_transform */
410 NULL) /* variable_transform */
411 {}
412
413 /* opt_pass methods: */
414 virtual bool gate (function *);
execute(function *)415 virtual unsigned int execute (function *) { return ipa_comdats (); }
416
417 }; // class pass_ipa_comdats
418
419 bool
gate(function *)420 pass_ipa_comdats::gate (function *)
421 {
422 return HAVE_COMDAT_GROUP;
423 }
424
425 } // anon namespace
426
427 ipa_opt_pass_d *
make_pass_ipa_comdats(gcc::context * ctxt)428 make_pass_ipa_comdats (gcc::context *ctxt)
429 {
430 return new pass_ipa_comdats (ctxt);
431 }
432