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1382992b | 1 | /* Rename SSA copies. |
2 | Copyright (C) 2004-2015 Free Software Foundation, Inc. | |
3 | Contributed by Andrew MacLeod <amacleod@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 | |
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, | |
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 | |
18 | along with GCC; see the file COPYING3. If not see | |
19 | <http://www.gnu.org/licenses/>. */ | |
20 | ||
21 | #include "config.h" | |
22 | #include "system.h" | |
23 | #include "coretypes.h" | |
24 | #include "tm.h" | |
1382992b | 25 | #include "alias.h" |
26 | #include "symtab.h" | |
27 | #include "tree.h" | |
28 | #include "fold-const.h" | |
29 | #include "predict.h" | |
30 | #include "hard-reg-set.h" | |
31 | #include "function.h" | |
32 | #include "dominance.h" | |
33 | #include "cfg.h" | |
34 | #include "basic-block.h" | |
35 | #include "tree-ssa-alias.h" | |
36 | #include "internal-fn.h" | |
37 | #include "gimple-expr.h" | |
1382992b | 38 | #include "gimple.h" |
39 | #include "gimple-iterator.h" | |
40 | #include "flags.h" | |
41 | #include "tree-pretty-print.h" | |
42 | #include "bitmap.h" | |
43 | #include "gimple-ssa.h" | |
44 | #include "stringpool.h" | |
45 | #include "tree-ssanames.h" | |
46 | #include "rtl.h" | |
47 | #include "insn-config.h" | |
48 | #include "expmed.h" | |
49 | #include "dojump.h" | |
50 | #include "explow.h" | |
51 | #include "calls.h" | |
52 | #include "emit-rtl.h" | |
53 | #include "varasm.h" | |
54 | #include "stmt.h" | |
55 | #include "expr.h" | |
56 | #include "tree-dfa.h" | |
57 | #include "tree-inline.h" | |
58 | #include "tree-ssa-live.h" | |
59 | #include "tree-pass.h" | |
60 | #include "langhooks.h" | |
61 | ||
62 | static struct | |
63 | { | |
64 | /* Number of copies coalesced. */ | |
65 | int coalesced; | |
66 | } stats; | |
67 | ||
68 | /* The following routines implement the SSA copy renaming phase. | |
69 | ||
70 | This optimization looks for copies between 2 SSA_NAMES, either through a | |
71 | direct copy, or an implicit one via a PHI node result and its arguments. | |
72 | ||
73 | Each copy is examined to determine if it is possible to rename the base | |
74 | variable of one of the operands to the same variable as the other operand. | |
75 | i.e. | |
76 | T.3_5 = <blah> | |
77 | a_1 = T.3_5 | |
78 | ||
79 | If this copy couldn't be copy propagated, it could possibly remain in the | |
80 | program throughout the optimization phases. After SSA->normal, it would | |
81 | become: | |
82 | ||
83 | T.3 = <blah> | |
84 | a = T.3 | |
85 | ||
86 | Since T.3_5 is distinct from all other SSA versions of T.3, there is no | |
87 | fundamental reason why the base variable needs to be T.3, subject to | |
88 | certain restrictions. This optimization attempts to determine if we can | |
89 | change the base variable on copies like this, and result in code such as: | |
90 | ||
91 | a_5 = <blah> | |
92 | a_1 = a_5 | |
93 | ||
94 | This gives the SSA->normal pass a shot at coalescing a_1 and a_5. If it is | |
95 | possible, the copy goes away completely. If it isn't possible, a new temp | |
96 | will be created for a_5, and you will end up with the exact same code: | |
97 | ||
98 | a.8 = <blah> | |
99 | a = a.8 | |
100 | ||
101 | The other benefit of performing this optimization relates to what variables | |
102 | are chosen in copies. Gimplification of the program uses temporaries for | |
103 | a lot of things. expressions like | |
104 | ||
105 | a_1 = <blah> | |
106 | <blah2> = a_1 | |
107 | ||
108 | get turned into | |
109 | ||
110 | T.3_5 = <blah> | |
111 | a_1 = T.3_5 | |
112 | <blah2> = a_1 | |
113 | ||
114 | Copy propagation is done in a forward direction, and if we can propagate | |
115 | through the copy, we end up with: | |
116 | ||
117 | T.3_5 = <blah> | |
118 | <blah2> = T.3_5 | |
119 | ||
120 | The copy is gone, but so is all reference to the user variable 'a'. By | |
121 | performing this optimization, we would see the sequence: | |
122 | ||
123 | a_5 = <blah> | |
124 | a_1 = a_5 | |
125 | <blah2> = a_1 | |
126 | ||
127 | which copy propagation would then turn into: | |
128 | ||
129 | a_5 = <blah> | |
130 | <blah2> = a_5 | |
131 | ||
132 | and so we still retain the user variable whenever possible. */ | |
133 | ||
134 | ||
135 | /* Coalesce the partitions in MAP representing VAR1 and VAR2 if it is valid. | |
136 | Choose a representative for the partition, and send debug info to DEBUG. */ | |
137 | ||
138 | static void | |
139 | copy_rename_partition_coalesce (var_map map, tree var1, tree var2, FILE *debug) | |
140 | { | |
141 | int p1, p2, p3; | |
142 | tree root1, root2; | |
143 | tree rep1, rep2; | |
144 | bool ign1, ign2, abnorm; | |
145 | ||
146 | gcc_assert (TREE_CODE (var1) == SSA_NAME); | |
147 | gcc_assert (TREE_CODE (var2) == SSA_NAME); | |
148 | ||
149 | register_ssa_partition (map, var1); | |
150 | register_ssa_partition (map, var2); | |
151 | ||
152 | p1 = partition_find (map->var_partition, SSA_NAME_VERSION (var1)); | |
153 | p2 = partition_find (map->var_partition, SSA_NAME_VERSION (var2)); | |
154 | ||
155 | if (debug) | |
156 | { | |
157 | fprintf (debug, "Try : "); | |
158 | print_generic_expr (debug, var1, TDF_SLIM); | |
159 | fprintf (debug, "(P%d) & ", p1); | |
160 | print_generic_expr (debug, var2, TDF_SLIM); | |
161 | fprintf (debug, "(P%d)", p2); | |
162 | } | |
163 | ||
164 | gcc_assert (p1 != NO_PARTITION); | |
165 | gcc_assert (p2 != NO_PARTITION); | |
166 | ||
167 | if (p1 == p2) | |
168 | { | |
169 | if (debug) | |
170 | fprintf (debug, " : Already coalesced.\n"); | |
171 | return; | |
172 | } | |
173 | ||
174 | rep1 = partition_to_var (map, p1); | |
175 | rep2 = partition_to_var (map, p2); | |
176 | root1 = SSA_NAME_VAR (rep1); | |
177 | root2 = SSA_NAME_VAR (rep2); | |
178 | if (!root1 && !root2) | |
179 | return; | |
180 | ||
181 | /* Don't coalesce if one of the variables occurs in an abnormal PHI. */ | |
182 | abnorm = (SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rep1) | |
183 | || SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rep2)); | |
184 | if (abnorm) | |
185 | { | |
186 | if (debug) | |
187 | fprintf (debug, " : Abnormal PHI barrier. No coalesce.\n"); | |
188 | return; | |
189 | } | |
190 | ||
191 | /* Partitions already have the same root, simply merge them. */ | |
192 | if (root1 == root2) | |
193 | { | |
194 | p1 = partition_union (map->var_partition, p1, p2); | |
195 | if (debug) | |
196 | fprintf (debug, " : Same root, coalesced --> P%d.\n", p1); | |
197 | return; | |
198 | } | |
199 | ||
200 | /* Never attempt to coalesce 2 different parameters. */ | |
201 | if ((root1 && TREE_CODE (root1) == PARM_DECL) | |
202 | && (root2 && TREE_CODE (root2) == PARM_DECL)) | |
203 | { | |
204 | if (debug) | |
205 | fprintf (debug, " : 2 different PARM_DECLS. No coalesce.\n"); | |
206 | return; | |
207 | } | |
208 | ||
209 | if ((root1 && TREE_CODE (root1) == RESULT_DECL) | |
210 | != (root2 && TREE_CODE (root2) == RESULT_DECL)) | |
211 | { | |
212 | if (debug) | |
213 | fprintf (debug, " : One root a RESULT_DECL. No coalesce.\n"); | |
214 | return; | |
215 | } | |
216 | ||
217 | ign1 = !root1 || (TREE_CODE (root1) == VAR_DECL && DECL_IGNORED_P (root1)); | |
218 | ign2 = !root2 || (TREE_CODE (root2) == VAR_DECL && DECL_IGNORED_P (root2)); | |
219 | ||
220 | /* Refrain from coalescing user variables, if requested. */ | |
221 | if (!ign1 && !ign2) | |
222 | { | |
223 | if (flag_ssa_coalesce_vars && DECL_FROM_INLINE (root2)) | |
224 | ign2 = true; | |
225 | else if (flag_ssa_coalesce_vars && DECL_FROM_INLINE (root1)) | |
226 | ign1 = true; | |
227 | else if (flag_ssa_coalesce_vars != 2) | |
228 | { | |
229 | if (debug) | |
230 | fprintf (debug, " : 2 different USER vars. No coalesce.\n"); | |
231 | return; | |
232 | } | |
233 | else | |
234 | ign2 = true; | |
235 | } | |
236 | ||
237 | /* If both values have default defs, we can't coalesce. If only one has a | |
238 | tag, make sure that variable is the new root partition. */ | |
239 | if (root1 && ssa_default_def (cfun, root1)) | |
240 | { | |
241 | if (root2 && ssa_default_def (cfun, root2)) | |
242 | { | |
243 | if (debug) | |
244 | fprintf (debug, " : 2 default defs. No coalesce.\n"); | |
245 | return; | |
246 | } | |
247 | else | |
248 | { | |
249 | ign2 = true; | |
250 | ign1 = false; | |
251 | } | |
252 | } | |
253 | else if (root2 && ssa_default_def (cfun, root2)) | |
254 | { | |
255 | ign1 = true; | |
256 | ign2 = false; | |
257 | } | |
258 | ||
259 | /* Do not coalesce if we cannot assign a symbol to the partition. */ | |
260 | if (!(!ign2 && root2) | |
261 | && !(!ign1 && root1)) | |
262 | { | |
263 | if (debug) | |
264 | fprintf (debug, " : Choosen variable has no root. No coalesce.\n"); | |
265 | return; | |
266 | } | |
267 | ||
268 | /* Don't coalesce if the new chosen root variable would be read-only. | |
269 | If both ign1 && ign2, then the root var of the larger partition | |
270 | wins, so reject in that case if any of the root vars is TREE_READONLY. | |
271 | Otherwise reject only if the root var, on which replace_ssa_name_symbol | |
272 | will be called below, is readonly. */ | |
273 | if (((root1 && TREE_READONLY (root1)) && ign2) | |
274 | || ((root2 && TREE_READONLY (root2)) && ign1)) | |
275 | { | |
276 | if (debug) | |
277 | fprintf (debug, " : Readonly variable. No coalesce.\n"); | |
278 | return; | |
279 | } | |
280 | ||
281 | /* Don't coalesce if the two variables aren't type compatible . */ | |
282 | if (!types_compatible_p (TREE_TYPE (var1), TREE_TYPE (var2)) | |
283 | /* There is a disconnect between the middle-end type-system and | |
284 | VRP, avoid coalescing enum types with different bounds. */ | |
285 | || ((TREE_CODE (TREE_TYPE (var1)) == ENUMERAL_TYPE | |
286 | || TREE_CODE (TREE_TYPE (var2)) == ENUMERAL_TYPE) | |
287 | && TREE_TYPE (var1) != TREE_TYPE (var2))) | |
288 | { | |
289 | if (debug) | |
290 | fprintf (debug, " : Incompatible types. No coalesce.\n"); | |
291 | return; | |
292 | } | |
293 | ||
294 | /* Merge the two partitions. */ | |
295 | p3 = partition_union (map->var_partition, p1, p2); | |
296 | ||
297 | /* Set the root variable of the partition to the better choice, if there is | |
298 | one. */ | |
299 | if (!ign2 && root2) | |
300 | replace_ssa_name_symbol (partition_to_var (map, p3), root2); | |
301 | else if (!ign1 && root1) | |
302 | replace_ssa_name_symbol (partition_to_var (map, p3), root1); | |
303 | else | |
304 | gcc_unreachable (); | |
305 | ||
306 | if (debug) | |
307 | { | |
308 | fprintf (debug, " --> P%d ", p3); | |
309 | print_generic_expr (debug, SSA_NAME_VAR (partition_to_var (map, p3)), | |
310 | TDF_SLIM); | |
311 | fprintf (debug, "\n"); | |
312 | } | |
313 | } | |
314 | ||
315 | ||
316 | namespace { | |
317 | ||
318 | const pass_data pass_data_rename_ssa_copies = | |
319 | { | |
320 | GIMPLE_PASS, /* type */ | |
321 | "copyrename", /* name */ | |
322 | OPTGROUP_NONE, /* optinfo_flags */ | |
323 | TV_TREE_COPY_RENAME, /* tv_id */ | |
324 | ( PROP_cfg | PROP_ssa ), /* properties_required */ | |
325 | 0, /* properties_provided */ | |
326 | 0, /* properties_destroyed */ | |
327 | 0, /* todo_flags_start */ | |
328 | 0, /* todo_flags_finish */ | |
329 | }; | |
330 | ||
331 | class pass_rename_ssa_copies : public gimple_opt_pass | |
332 | { | |
333 | public: | |
334 | pass_rename_ssa_copies (gcc::context *ctxt) | |
335 | : gimple_opt_pass (pass_data_rename_ssa_copies, ctxt) | |
336 | {} | |
337 | ||
338 | /* opt_pass methods: */ | |
339 | opt_pass * clone () { return new pass_rename_ssa_copies (m_ctxt); } | |
340 | virtual bool gate (function *) { return flag_tree_copyrename != 0; } | |
341 | virtual unsigned int execute (function *); | |
342 | ||
343 | }; // class pass_rename_ssa_copies | |
344 | ||
345 | /* This function will make a pass through the IL, and attempt to coalesce any | |
346 | SSA versions which occur in PHI's or copies. Coalescing is accomplished by | |
347 | changing the underlying root variable of all coalesced version. This will | |
348 | then cause the SSA->normal pass to attempt to coalesce them all to the same | |
349 | variable. */ | |
350 | ||
351 | unsigned int | |
352 | pass_rename_ssa_copies::execute (function *fun) | |
353 | { | |
354 | var_map map; | |
355 | basic_block bb; | |
356 | tree var, part_var; | |
357 | gimple stmt; | |
358 | unsigned x; | |
359 | FILE *debug; | |
360 | ||
361 | memset (&stats, 0, sizeof (stats)); | |
362 | ||
363 | if (dump_file && (dump_flags & TDF_DETAILS)) | |
364 | debug = dump_file; | |
365 | else | |
366 | debug = NULL; | |
367 | ||
368 | map = init_var_map (num_ssa_names); | |
369 | ||
370 | FOR_EACH_BB_FN (bb, fun) | |
371 | { | |
372 | /* Scan for real copies. */ | |
373 | for (gimple_stmt_iterator gsi = gsi_start_bb (bb); !gsi_end_p (gsi); | |
374 | gsi_next (&gsi)) | |
375 | { | |
376 | stmt = gsi_stmt (gsi); | |
377 | if (gimple_assign_ssa_name_copy_p (stmt)) | |
378 | { | |
379 | tree lhs = gimple_assign_lhs (stmt); | |
380 | tree rhs = gimple_assign_rhs1 (stmt); | |
381 | ||
382 | copy_rename_partition_coalesce (map, lhs, rhs, debug); | |
383 | } | |
384 | } | |
385 | } | |
386 | ||
387 | FOR_EACH_BB_FN (bb, fun) | |
388 | { | |
389 | /* Treat PHI nodes as copies between the result and each argument. */ | |
390 | for (gphi_iterator gsi = gsi_start_phis (bb); !gsi_end_p (gsi); | |
391 | gsi_next (&gsi)) | |
392 | { | |
393 | size_t i; | |
394 | tree res; | |
395 | gphi *phi = gsi.phi (); | |
396 | res = gimple_phi_result (phi); | |
397 | ||
398 | /* Do not process virtual SSA_NAMES. */ | |
399 | if (virtual_operand_p (res)) | |
400 | continue; | |
401 | ||
402 | /* Make sure to only use the same partition for an argument | |
403 | as the result but never the other way around. */ | |
404 | if (SSA_NAME_VAR (res) | |
405 | && !DECL_IGNORED_P (SSA_NAME_VAR (res))) | |
406 | for (i = 0; i < gimple_phi_num_args (phi); i++) | |
407 | { | |
408 | tree arg = PHI_ARG_DEF (phi, i); | |
409 | if (TREE_CODE (arg) == SSA_NAME) | |
410 | copy_rename_partition_coalesce (map, res, arg, | |
411 | debug); | |
412 | } | |
413 | /* Else if all arguments are in the same partition try to merge | |
414 | it with the result. */ | |
415 | else | |
416 | { | |
417 | int all_p_same = -1; | |
418 | int p = -1; | |
419 | for (i = 0; i < gimple_phi_num_args (phi); i++) | |
420 | { | |
421 | tree arg = PHI_ARG_DEF (phi, i); | |
422 | if (TREE_CODE (arg) != SSA_NAME) | |
423 | { | |
424 | all_p_same = 0; | |
425 | break; | |
426 | } | |
427 | else if (all_p_same == -1) | |
428 | { | |
429 | p = partition_find (map->var_partition, | |
430 | SSA_NAME_VERSION (arg)); | |
431 | all_p_same = 1; | |
432 | } | |
433 | else if (all_p_same == 1 | |
434 | && p != partition_find (map->var_partition, | |
435 | SSA_NAME_VERSION (arg))) | |
436 | { | |
437 | all_p_same = 0; | |
438 | break; | |
439 | } | |
440 | } | |
441 | if (all_p_same == 1) | |
442 | copy_rename_partition_coalesce (map, res, | |
443 | PHI_ARG_DEF (phi, 0), | |
444 | debug); | |
445 | } | |
446 | } | |
447 | } | |
448 | ||
449 | if (debug) | |
450 | dump_var_map (debug, map); | |
451 | ||
452 | /* Now one more pass to make all elements of a partition share the same | |
453 | root variable. */ | |
454 | ||
455 | for (x = 1; x < num_ssa_names; x++) | |
456 | { | |
457 | part_var = partition_to_var (map, x); | |
458 | if (!part_var) | |
459 | continue; | |
460 | var = ssa_name (x); | |
461 | if (SSA_NAME_VAR (var) == SSA_NAME_VAR (part_var)) | |
462 | continue; | |
463 | if (debug) | |
464 | { | |
465 | fprintf (debug, "Coalesced "); | |
466 | print_generic_expr (debug, var, TDF_SLIM); | |
467 | fprintf (debug, " to "); | |
468 | print_generic_expr (debug, part_var, TDF_SLIM); | |
469 | fprintf (debug, "\n"); | |
470 | } | |
471 | stats.coalesced++; | |
472 | replace_ssa_name_symbol (var, SSA_NAME_VAR (part_var)); | |
473 | } | |
474 | ||
475 | statistics_counter_event (fun, "copies coalesced", | |
476 | stats.coalesced); | |
477 | delete_var_map (map); | |
478 | return 0; | |
479 | } | |
480 | ||
481 | } // anon namespace | |
482 | ||
483 | gimple_opt_pass * | |
484 | make_pass_rename_ssa_copies (gcc::context *ctxt) | |
485 | { | |
486 | return new pass_rename_ssa_copies (ctxt); | |
487 | } |