1 /* Web construction code for GNU compiler.
2 Contributed by Jan Hubicka.
3 Copyright (C) 2001, 2002, 2004, 2006
4 Free Software Foundation, Inc.
5
6 This file is part of GCC.
7
8 GCC is free software; you can redistribute it and/or modify it under
9 the terms of the GNU General Public License as published by the Free
10 Software Foundation; either version 2, or (at your option) any later
11 version.
12
13 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
14 WARRANTY; without even the implied warranty of MERCHANTABILITY or
15 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
16 for more details.
17
18 You should have received a copy of the GNU General Public License
19 along with GCC; see the file COPYING. If not, write to the Free
20 Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
21 02110-1301, USA. */
22
23 /* Simple optimization pass that splits independent uses of each pseudo,
24 increasing effectiveness of other optimizations. The optimization can
25 serve as an example of use for the dataflow module.
26
27 We don't split registers with REG_USERVAR set unless -fmessy-debugging
28 is specified, because debugging information about such split variables
29 is almost unusable.
30
31 TODO
32 - Add code to keep debugging up-to-date after splitting user variable
33 pseudos. This can be done by keeping track of all the pseudos used
34 for the variable and using life analysis information before reload
35 to determine which one is live and, in case more than one are live,
36 choose the one with the latest definition.
37
38 Other optimization passes can benefit from the infrastructure too.
39
40 - We may use profile information and ignore infrequent use for the
41 purpose of web unifying, inserting the compensation code later to
42 implement full induction variable expansion for loops (currently
43 we expand only if the induction variable is dead afterward, which
44 is often the case). */
45
46 #include "config.h"
47 #include "system.h"
48 #include "coretypes.h"
49 #include "tm.h"
50 #include "toplev.h"
51
52 #include "rtl.h"
53 #include "hard-reg-set.h"
54 #include "flags.h"
55 #include "obstack.h"
56 #include "basic-block.h"
57 #include "output.h"
58 #include "df.h"
59 #include "function.h"
60 #include "timevar.h"
61 #include "tree-pass.h"
62
63
64 static rtx entry_register (struct web_entry *, struct df_ref *, char *);
65 static void replace_ref (struct df_ref *, rtx);
66
67 /* Find the root of unionfind tree (the representative of set). */
68
69 struct web_entry *
unionfind_root(struct web_entry * element)70 unionfind_root (struct web_entry *element)
71 {
72 struct web_entry *element1 = element, *element2;
73
74 while (element->pred)
75 element = element->pred;
76 while (element1->pred)
77 {
78 element2 = element1->pred;
79 element1->pred = element;
80 element1 = element2;
81 }
82 return element;
83 }
84
85 /* Union sets.
86 Return true if FIRST and SECOND points to the same web entry structure and
87 nothing is done. Otherwise, return false. */
88
89 bool
unionfind_union(struct web_entry * first,struct web_entry * second)90 unionfind_union (struct web_entry *first, struct web_entry *second)
91 {
92 first = unionfind_root (first);
93 second = unionfind_root (second);
94 if (first == second)
95 return true;
96 second->pred = first;
97 return false;
98 }
99
100 /* For each use, all possible defs reaching it must come in the same
101 register, union them.
102 FUN is the function that does the union. */
103
104 void
union_defs(struct df * df,struct df_ref * use,struct web_entry * def_entry,struct web_entry * use_entry,bool (* fun)(struct web_entry *,struct web_entry *))105 union_defs (struct df *df, struct df_ref *use, struct web_entry *def_entry,
106 struct web_entry *use_entry,
107 bool (*fun) (struct web_entry *, struct web_entry *))
108 {
109 rtx insn = DF_REF_INSN (use);
110 struct df_link *link = DF_REF_CHAIN (use);
111 struct df_ref *use_link;
112 struct df_ref *def_link;
113 rtx set;
114
115 if (insn)
116 {
117 use_link = DF_INSN_USES (df, insn);
118 def_link = DF_INSN_DEFS (df, insn);
119 set = single_set (insn);
120 }
121 else
122 {
123 use_link = NULL;
124 def_link = NULL;
125 set = NULL;
126 }
127
128 /* Some instructions may use match_dup for their operands. In case the
129 operands are dead, we will assign them different pseudos, creating
130 invalid instructions, so union all uses of the same operand for each
131 insn. */
132
133 while (use_link)
134 {
135 if (use != use_link
136 && DF_REF_REAL_REG (use) == DF_REF_REAL_REG (use_link))
137 (*fun) (use_entry + DF_REF_ID (use),
138 use_entry + DF_REF_ID (use_link));
139 use_link = use_link->next_ref;
140 }
141
142 /* Recognize trivial noop moves and attempt to keep them as noop.
143 While most of noop moves should be removed, we still keep some
144 of them at libcall boundaries and such. */
145
146 if (set
147 && SET_SRC (set) == DF_REF_REG (use)
148 && SET_SRC (set) == SET_DEST (set))
149 {
150 while (def_link)
151 {
152 if (DF_REF_REAL_REG (use) == DF_REF_REAL_REG (def_link))
153 (*fun) (use_entry + DF_REF_ID (use),
154 def_entry + DF_REF_ID (def_link));
155 def_link = def_link->next_ref;
156 }
157 }
158 while (link)
159 {
160 (*fun) (use_entry + DF_REF_ID (use),
161 def_entry + DF_REF_ID (link->ref));
162 link = link->next;
163 }
164
165 /* A READ_WRITE use requires the corresponding def to be in the same
166 register. Find it and union. */
167 if (use->flags & DF_REF_READ_WRITE)
168 {
169 struct df_ref *link;
170
171 if (DF_REF_INSN (use))
172 link = DF_INSN_DEFS (df, DF_REF_INSN (use));
173 else
174 link = NULL;
175
176 while (link)
177 {
178 if (DF_REF_REAL_REG (link) == DF_REF_REAL_REG (use))
179 (*fun) (use_entry + DF_REF_ID (use),
180 def_entry + DF_REF_ID (link));
181 link = link->next_ref;
182 }
183 }
184 }
185
186 /* Find the corresponding register for the given entry. */
187
188 static rtx
entry_register(struct web_entry * entry,struct df_ref * ref,char * used)189 entry_register (struct web_entry *entry, struct df_ref *ref, char *used)
190 {
191 struct web_entry *root;
192 rtx reg, newreg;
193
194 /* Find the corresponding web and see if it has been visited. */
195 root = unionfind_root (entry);
196 if (root->reg)
197 return root->reg;
198
199 /* We are seeing this web for the first time, do the assignment. */
200 reg = DF_REF_REAL_REG (ref);
201
202 /* In case the original register is already assigned, generate new one. */
203 if (!used[REGNO (reg)])
204 newreg = reg, used[REGNO (reg)] = 1;
205 else if (REG_USERVAR_P (reg) && 0/*&& !flag_messy_debugging*/)
206 {
207 newreg = reg;
208 if (dump_file)
209 fprintf (dump_file,
210 "New web forced to keep reg=%i (user variable)\n",
211 REGNO (reg));
212 }
213 else
214 {
215 newreg = gen_reg_rtx (GET_MODE (reg));
216 REG_USERVAR_P (newreg) = REG_USERVAR_P (reg);
217 REG_POINTER (newreg) = REG_POINTER (reg);
218 REG_ATTRS (newreg) = REG_ATTRS (reg);
219 if (dump_file)
220 fprintf (dump_file, "Web oldreg=%i newreg=%i\n", REGNO (reg),
221 REGNO (newreg));
222 }
223
224 root->reg = newreg;
225 return newreg;
226 }
227
228 /* Replace the reference by REG. */
229
230 static void
replace_ref(struct df_ref * ref,rtx reg)231 replace_ref (struct df_ref *ref, rtx reg)
232 {
233 rtx oldreg = DF_REF_REAL_REG (ref);
234 rtx *loc = DF_REF_REAL_LOC (ref);
235
236 if (oldreg == reg)
237 return;
238 if (dump_file)
239 fprintf (dump_file, "Updating insn %i (%i->%i)\n",
240 INSN_UID (DF_REF_INSN (ref)), REGNO (oldreg), REGNO (reg));
241 *loc = reg;
242 }
243
244 /* Main entry point. */
245
246 static void
web_main(void)247 web_main (void)
248 {
249 struct df *df;
250 struct web_entry *def_entry;
251 struct web_entry *use_entry;
252 unsigned int i;
253 int max = max_reg_num ();
254 char *used;
255
256 df = df_init (DF_EQUIV_NOTES);
257 df_chain_add_problem (df, DF_UD_CHAIN);
258 df_analyze (df);
259 df_reorganize_refs (&df->def_info);
260 df_reorganize_refs (&df->use_info);
261
262 def_entry = XCNEWVEC (struct web_entry, DF_DEFS_SIZE (df));
263 use_entry = XCNEWVEC (struct web_entry, DF_USES_SIZE (df));
264 used = XCNEWVEC (char, max);
265
266 if (dump_file)
267 df_dump (df, dump_file);
268
269 /* Produce the web. */
270 for (i = 0; i < DF_USES_SIZE (df); i++)
271 union_defs (df, DF_USES_GET (df, i), def_entry, use_entry, unionfind_union);
272
273 /* Update the instruction stream, allocating new registers for split pseudos
274 in progress. */
275 for (i = 0; i < DF_USES_SIZE (df); i++)
276 replace_ref (DF_USES_GET (df, i),
277 entry_register (use_entry + i, DF_USES_GET (df, i), used));
278 for (i = 0; i < DF_DEFS_SIZE (df); i++)
279 replace_ref (DF_DEFS_GET (df, i),
280 entry_register (def_entry + i, DF_DEFS_GET (df, i), used));
281
282 /* Dataflow information is corrupt here, but it can be easily updated
283 by creating new entries for new registers and updates or calling
284 df_insns_modify. */
285 free (def_entry);
286 free (use_entry);
287 free (used);
288 df_finish (df);
289 df = NULL;
290 }
291
292 static bool
gate_handle_web(void)293 gate_handle_web (void)
294 {
295 return (optimize > 0 && flag_web);
296 }
297
298 static unsigned int
rest_of_handle_web(void)299 rest_of_handle_web (void)
300 {
301 web_main ();
302 delete_trivially_dead_insns (get_insns (), max_reg_num ());
303 cleanup_cfg (CLEANUP_EXPENSIVE);
304 reg_scan (get_insns (), max_reg_num ());
305 return 0;
306 }
307
308 struct tree_opt_pass pass_web =
309 {
310 "web", /* name */
311 gate_handle_web, /* gate */
312 rest_of_handle_web, /* execute */
313 NULL, /* sub */
314 NULL, /* next */
315 0, /* static_pass_number */
316 TV_WEB, /* tv_id */
317 0, /* properties_required */
318 0, /* properties_provided */
319 0, /* properties_destroyed */
320 0, /* todo_flags_start */
321 TODO_dump_func, /* todo_flags_finish */
322 'Z' /* letter */
323 };
324
325