Mercurial > hg > CbC > CbC_gcc
annotate gcc/tree-ssa-threadupdate.c @ 55:77e2b8dfacca gcc-4.4.5
update it from 4.4.3 to 4.5.0
| author | ryoma <e075725@ie.u-ryukyu.ac.jp> |
|---|---|
| date | Fri, 12 Feb 2010 23:39:51 +0900 |
| parents | a06113de4d67 |
| children | b7f97abdc517 |
| rev | line source |
|---|---|
| 0 | 1 /* Thread edges through blocks and update the control flow and SSA graphs. |
| 2 Copyright (C) 2004, 2005, 2006, 2007, 2008 Free Software Foundation, | |
| 3 Inc. | |
| 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" | |
| 25 #include "tree.h" | |
| 26 #include "flags.h" | |
| 27 #include "rtl.h" | |
| 28 #include "tm_p.h" | |
| 29 #include "ggc.h" | |
| 30 #include "basic-block.h" | |
| 31 #include "output.h" | |
| 32 #include "expr.h" | |
| 33 #include "function.h" | |
| 34 #include "diagnostic.h" | |
| 35 #include "tree-flow.h" | |
| 36 #include "tree-dump.h" | |
| 37 #include "tree-pass.h" | |
| 38 #include "cfgloop.h" | |
| 39 | |
| 40 /* Given a block B, update the CFG and SSA graph to reflect redirecting | |
| 41 one or more in-edges to B to instead reach the destination of an | |
| 42 out-edge from B while preserving any side effects in B. | |
| 43 | |
| 44 i.e., given A->B and B->C, change A->B to be A->C yet still preserve the | |
| 45 side effects of executing B. | |
| 46 | |
| 47 1. Make a copy of B (including its outgoing edges and statements). Call | |
| 48 the copy B'. Note B' has no incoming edges or PHIs at this time. | |
| 49 | |
| 50 2. Remove the control statement at the end of B' and all outgoing edges | |
| 51 except B'->C. | |
| 52 | |
| 53 3. Add a new argument to each PHI in C with the same value as the existing | |
| 54 argument associated with edge B->C. Associate the new PHI arguments | |
| 55 with the edge B'->C. | |
| 56 | |
| 57 4. For each PHI in B, find or create a PHI in B' with an identical | |
| 58 PHI_RESULT. Add an argument to the PHI in B' which has the same | |
| 59 value as the PHI in B associated with the edge A->B. Associate | |
| 60 the new argument in the PHI in B' with the edge A->B. | |
| 61 | |
| 62 5. Change the edge A->B to A->B'. | |
| 63 | |
| 64 5a. This automatically deletes any PHI arguments associated with the | |
| 65 edge A->B in B. | |
| 66 | |
| 67 5b. This automatically associates each new argument added in step 4 | |
| 68 with the edge A->B'. | |
| 69 | |
| 70 6. Repeat for other incoming edges into B. | |
| 71 | |
| 72 7. Put the duplicated resources in B and all the B' blocks into SSA form. | |
| 73 | |
| 74 Note that block duplication can be minimized by first collecting the | |
| 75 set of unique destination blocks that the incoming edges should | |
| 76 be threaded to. Block duplication can be further minimized by using | |
| 77 B instead of creating B' for one destination if all edges into B are | |
| 78 going to be threaded to a successor of B. | |
| 79 | |
| 80 We further reduce the number of edges and statements we create by | |
| 81 not copying all the outgoing edges and the control statement in | |
| 82 step #1. We instead create a template block without the outgoing | |
| 83 edges and duplicate the template. */ | |
| 84 | |
| 85 | |
| 86 /* Steps #5 and #6 of the above algorithm are best implemented by walking | |
| 87 all the incoming edges which thread to the same destination edge at | |
| 88 the same time. That avoids lots of table lookups to get information | |
| 89 for the destination edge. | |
| 90 | |
| 91 To realize that implementation we create a list of incoming edges | |
| 92 which thread to the same outgoing edge. Thus to implement steps | |
| 93 #5 and #6 we traverse our hash table of outgoing edge information. | |
| 94 For each entry we walk the list of incoming edges which thread to | |
| 95 the current outgoing edge. */ | |
| 96 | |
| 97 struct el | |
| 98 { | |
| 99 edge e; | |
| 100 struct el *next; | |
| 101 }; | |
| 102 | |
| 103 /* Main data structure recording information regarding B's duplicate | |
| 104 blocks. */ | |
| 105 | |
| 106 /* We need to efficiently record the unique thread destinations of this | |
| 107 block and specific information associated with those destinations. We | |
| 108 may have many incoming edges threaded to the same outgoing edge. This | |
| 109 can be naturally implemented with a hash table. */ | |
| 110 | |
| 111 struct redirection_data | |
| 112 { | |
| 113 /* A duplicate of B with the trailing control statement removed and which | |
| 114 targets a single successor of B. */ | |
| 115 basic_block dup_block; | |
| 116 | |
| 117 /* An outgoing edge from B. DUP_BLOCK will have OUTGOING_EDGE->dest as | |
| 118 its single successor. */ | |
| 119 edge outgoing_edge; | |
| 120 | |
| 121 /* A list of incoming edges which we want to thread to | |
| 122 OUTGOING_EDGE->dest. */ | |
| 123 struct el *incoming_edges; | |
| 124 | |
| 125 /* Flag indicating whether or not we should create a duplicate block | |
| 126 for this thread destination. This is only true if we are threading | |
| 127 all incoming edges and thus are using BB itself as a duplicate block. */ | |
| 128 bool do_not_duplicate; | |
| 129 }; | |
| 130 | |
| 131 /* Main data structure to hold information for duplicates of BB. */ | |
| 132 static htab_t redirection_data; | |
| 133 | |
| 134 /* Data structure of information to pass to hash table traversal routines. */ | |
| 135 struct local_info | |
| 136 { | |
| 137 /* The current block we are working on. */ | |
| 138 basic_block bb; | |
| 139 | |
| 140 /* A template copy of BB with no outgoing edges or control statement that | |
| 141 we use for creating copies. */ | |
| 142 basic_block template_block; | |
| 143 | |
| 144 /* TRUE if we thread one or more jumps, FALSE otherwise. */ | |
| 145 bool jumps_threaded; | |
| 146 }; | |
| 147 | |
| 148 /* Passes which use the jump threading code register jump threading | |
| 149 opportunities as they are discovered. We keep the registered | |
| 150 jump threading opportunities in this vector as edge pairs | |
| 151 (original_edge, target_edge). */ | |
| 152 static VEC(edge,heap) *threaded_edges; | |
| 153 | |
| 154 | |
| 155 /* Jump threading statistics. */ | |
| 156 | |
| 157 struct thread_stats_d | |
| 158 { | |
| 159 unsigned long num_threaded_edges; | |
| 160 }; | |
| 161 | |
| 162 struct thread_stats_d thread_stats; | |
| 163 | |
| 164 | |
| 165 /* Remove the last statement in block BB if it is a control statement | |
| 166 Also remove all outgoing edges except the edge which reaches DEST_BB. | |
| 167 If DEST_BB is NULL, then remove all outgoing edges. */ | |
| 168 | |
| 169 static void | |
| 170 remove_ctrl_stmt_and_useless_edges (basic_block bb, basic_block dest_bb) | |
| 171 { | |
| 172 gimple_stmt_iterator gsi; | |
| 173 edge e; | |
| 174 edge_iterator ei; | |
| 175 | |
| 176 gsi = gsi_last_bb (bb); | |
| 177 | |
| 178 /* If the duplicate ends with a control statement, then remove it. | |
| 179 | |
| 180 Note that if we are duplicating the template block rather than the | |
| 181 original basic block, then the duplicate might not have any real | |
| 182 statements in it. */ | |
| 183 if (!gsi_end_p (gsi) | |
| 184 && gsi_stmt (gsi) | |
| 185 && (gimple_code (gsi_stmt (gsi)) == GIMPLE_COND | |
| 186 || gimple_code (gsi_stmt (gsi)) == GIMPLE_GOTO | |
| 187 || gimple_code (gsi_stmt (gsi)) == GIMPLE_SWITCH)) | |
| 188 gsi_remove (&gsi, true); | |
| 189 | |
| 190 for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); ) | |
| 191 { | |
| 192 if (e->dest != dest_bb) | |
| 193 remove_edge (e); | |
| 194 else | |
| 195 ei_next (&ei); | |
| 196 } | |
| 197 } | |
| 198 | |
| 199 /* Create a duplicate of BB which only reaches the destination of the edge | |
| 200 stored in RD. Record the duplicate block in RD. */ | |
| 201 | |
| 202 static void | |
| 203 create_block_for_threading (basic_block bb, struct redirection_data *rd) | |
| 204 { | |
| 205 /* We can use the generic block duplication code and simply remove | |
| 206 the stuff we do not need. */ | |
| 207 rd->dup_block = duplicate_block (bb, NULL, NULL); | |
| 208 | |
| 209 /* Zero out the profile, since the block is unreachable for now. */ | |
| 210 rd->dup_block->frequency = 0; | |
| 211 rd->dup_block->count = 0; | |
| 212 | |
| 213 /* The call to duplicate_block will copy everything, including the | |
| 214 useless COND_EXPR or SWITCH_EXPR at the end of BB. We just remove | |
| 215 the useless COND_EXPR or SWITCH_EXPR here rather than having a | |
| 216 specialized block copier. We also remove all outgoing edges | |
| 217 from the duplicate block. The appropriate edge will be created | |
| 218 later. */ | |
| 219 remove_ctrl_stmt_and_useless_edges (rd->dup_block, NULL); | |
| 220 } | |
| 221 | |
| 222 /* Hashing and equality routines for our hash table. */ | |
| 223 static hashval_t | |
| 224 redirection_data_hash (const void *p) | |
| 225 { | |
| 226 edge e = ((const struct redirection_data *)p)->outgoing_edge; | |
| 227 return e->dest->index; | |
| 228 } | |
| 229 | |
| 230 static int | |
| 231 redirection_data_eq (const void *p1, const void *p2) | |
| 232 { | |
| 233 edge e1 = ((const struct redirection_data *)p1)->outgoing_edge; | |
| 234 edge e2 = ((const struct redirection_data *)p2)->outgoing_edge; | |
| 235 | |
| 236 return e1 == e2; | |
| 237 } | |
| 238 | |
| 239 /* Given an outgoing edge E lookup and return its entry in our hash table. | |
| 240 | |
| 241 If INSERT is true, then we insert the entry into the hash table if | |
| 242 it is not already present. INCOMING_EDGE is added to the list of incoming | |
| 243 edges associated with E in the hash table. */ | |
| 244 | |
| 245 static struct redirection_data * | |
| 246 lookup_redirection_data (edge e, edge incoming_edge, enum insert_option insert) | |
| 247 { | |
| 248 void **slot; | |
| 249 struct redirection_data *elt; | |
| 250 | |
| 251 /* Build a hash table element so we can see if E is already | |
| 252 in the table. */ | |
| 253 elt = XNEW (struct redirection_data); | |
| 254 elt->outgoing_edge = e; | |
| 255 elt->dup_block = NULL; | |
| 256 elt->do_not_duplicate = false; | |
| 257 elt->incoming_edges = NULL; | |
| 258 | |
| 259 slot = htab_find_slot (redirection_data, elt, insert); | |
| 260 | |
| 261 /* This will only happen if INSERT is false and the entry is not | |
| 262 in the hash table. */ | |
| 263 if (slot == NULL) | |
| 264 { | |
| 265 free (elt); | |
| 266 return NULL; | |
| 267 } | |
| 268 | |
| 269 /* This will only happen if E was not in the hash table and | |
| 270 INSERT is true. */ | |
| 271 if (*slot == NULL) | |
| 272 { | |
| 273 *slot = (void *)elt; | |
| 274 elt->incoming_edges = XNEW (struct el); | |
| 275 elt->incoming_edges->e = incoming_edge; | |
| 276 elt->incoming_edges->next = NULL; | |
| 277 return elt; | |
| 278 } | |
| 279 /* E was in the hash table. */ | |
| 280 else | |
| 281 { | |
| 282 /* Free ELT as we do not need it anymore, we will extract the | |
| 283 relevant entry from the hash table itself. */ | |
| 284 free (elt); | |
| 285 | |
| 286 /* Get the entry stored in the hash table. */ | |
| 287 elt = (struct redirection_data *) *slot; | |
| 288 | |
| 289 /* If insertion was requested, then we need to add INCOMING_EDGE | |
| 290 to the list of incoming edges associated with E. */ | |
| 291 if (insert) | |
| 292 { | |
| 293 struct el *el = XNEW (struct el); | |
| 294 el->next = elt->incoming_edges; | |
| 295 el->e = incoming_edge; | |
| 296 elt->incoming_edges = el; | |
| 297 } | |
| 298 | |
| 299 return elt; | |
| 300 } | |
| 301 } | |
| 302 | |
| 303 /* Given a duplicate block and its single destination (both stored | |
| 304 in RD). Create an edge between the duplicate and its single | |
| 305 destination. | |
| 306 | |
| 307 Add an additional argument to any PHI nodes at the single | |
| 308 destination. */ | |
| 309 | |
| 310 static void | |
| 311 create_edge_and_update_destination_phis (struct redirection_data *rd) | |
| 312 { | |
| 313 edge e = make_edge (rd->dup_block, rd->outgoing_edge->dest, EDGE_FALLTHRU); | |
| 314 gimple_stmt_iterator gsi; | |
| 315 | |
| 316 rescan_loop_exit (e, true, false); | |
| 317 e->probability = REG_BR_PROB_BASE; | |
| 318 e->count = rd->dup_block->count; | |
| 319 e->aux = rd->outgoing_edge->aux; | |
| 320 | |
| 321 /* If there are any PHI nodes at the destination of the outgoing edge | |
| 322 from the duplicate block, then we will need to add a new argument | |
| 323 to them. The argument should have the same value as the argument | |
| 324 associated with the outgoing edge stored in RD. */ | |
| 325 for (gsi = gsi_start_phis (e->dest); !gsi_end_p (gsi); gsi_next (&gsi)) | |
| 326 { | |
| 327 gimple phi = gsi_stmt (gsi); | |
|
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328 source_location locus; |
| 0 | 329 int indx = rd->outgoing_edge->dest_idx; |
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330 |
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331 locus = gimple_phi_arg_location (phi, indx); |
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332 add_phi_arg (phi, gimple_phi_arg_def (phi, indx), e, locus); |
| 0 | 333 } |
| 334 } | |
| 335 | |
| 336 /* Hash table traversal callback routine to create duplicate blocks. */ | |
| 337 | |
| 338 static int | |
| 339 create_duplicates (void **slot, void *data) | |
| 340 { | |
| 341 struct redirection_data *rd = (struct redirection_data *) *slot; | |
| 342 struct local_info *local_info = (struct local_info *)data; | |
| 343 | |
| 344 /* If this entry should not have a duplicate created, then there's | |
| 345 nothing to do. */ | |
| 346 if (rd->do_not_duplicate) | |
| 347 return 1; | |
| 348 | |
| 349 /* Create a template block if we have not done so already. Otherwise | |
| 350 use the template to create a new block. */ | |
| 351 if (local_info->template_block == NULL) | |
| 352 { | |
| 353 create_block_for_threading (local_info->bb, rd); | |
| 354 local_info->template_block = rd->dup_block; | |
| 355 | |
| 356 /* We do not create any outgoing edges for the template. We will | |
| 357 take care of that in a later traversal. That way we do not | |
| 358 create edges that are going to just be deleted. */ | |
| 359 } | |
| 360 else | |
| 361 { | |
| 362 create_block_for_threading (local_info->template_block, rd); | |
| 363 | |
| 364 /* Go ahead and wire up outgoing edges and update PHIs for the duplicate | |
| 365 block. */ | |
| 366 create_edge_and_update_destination_phis (rd); | |
| 367 } | |
| 368 | |
| 369 /* Keep walking the hash table. */ | |
| 370 return 1; | |
| 371 } | |
| 372 | |
| 373 /* We did not create any outgoing edges for the template block during | |
| 374 block creation. This hash table traversal callback creates the | |
| 375 outgoing edge for the template block. */ | |
| 376 | |
| 377 static int | |
| 378 fixup_template_block (void **slot, void *data) | |
| 379 { | |
| 380 struct redirection_data *rd = (struct redirection_data *) *slot; | |
| 381 struct local_info *local_info = (struct local_info *)data; | |
| 382 | |
| 383 /* If this is the template block, then create its outgoing edges | |
| 384 and halt the hash table traversal. */ | |
| 385 if (rd->dup_block && rd->dup_block == local_info->template_block) | |
| 386 { | |
| 387 create_edge_and_update_destination_phis (rd); | |
| 388 return 0; | |
| 389 } | |
| 390 | |
| 391 return 1; | |
| 392 } | |
| 393 | |
| 394 /* Hash table traversal callback to redirect each incoming edge | |
| 395 associated with this hash table element to its new destination. */ | |
| 396 | |
| 397 static int | |
| 398 redirect_edges (void **slot, void *data) | |
| 399 { | |
| 400 struct redirection_data *rd = (struct redirection_data *) *slot; | |
| 401 struct local_info *local_info = (struct local_info *)data; | |
| 402 struct el *next, *el; | |
| 403 | |
| 404 /* Walk over all the incoming edges associated associated with this | |
| 405 hash table entry. */ | |
| 406 for (el = rd->incoming_edges; el; el = next) | |
| 407 { | |
| 408 edge e = el->e; | |
| 409 | |
| 410 /* Go ahead and free this element from the list. Doing this now | |
| 411 avoids the need for another list walk when we destroy the hash | |
| 412 table. */ | |
| 413 next = el->next; | |
| 414 free (el); | |
| 415 | |
| 416 /* Go ahead and clear E->aux. It's not needed anymore and failure | |
| 417 to clear it will cause all kinds of unpleasant problems later. */ | |
| 418 e->aux = NULL; | |
| 419 | |
| 420 thread_stats.num_threaded_edges++; | |
| 421 | |
| 422 if (rd->dup_block) | |
| 423 { | |
| 424 edge e2; | |
| 425 | |
| 426 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 427 fprintf (dump_file, " Threaded jump %d --> %d to %d\n", | |
| 428 e->src->index, e->dest->index, rd->dup_block->index); | |
| 429 | |
| 430 rd->dup_block->count += e->count; | |
| 431 rd->dup_block->frequency += EDGE_FREQUENCY (e); | |
| 432 EDGE_SUCC (rd->dup_block, 0)->count += e->count; | |
| 433 /* Redirect the incoming edge to the appropriate duplicate | |
| 434 block. */ | |
| 435 e2 = redirect_edge_and_branch (e, rd->dup_block); | |
| 436 gcc_assert (e == e2); | |
| 437 flush_pending_stmts (e2); | |
| 438 } | |
| 439 else | |
| 440 { | |
| 441 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 442 fprintf (dump_file, " Threaded jump %d --> %d to %d\n", | |
| 443 e->src->index, e->dest->index, local_info->bb->index); | |
| 444 | |
| 445 /* We are using BB as the duplicate. Remove the unnecessary | |
| 446 outgoing edges and statements from BB. */ | |
| 447 remove_ctrl_stmt_and_useless_edges (local_info->bb, | |
| 448 rd->outgoing_edge->dest); | |
| 449 | |
| 450 /* Fixup the flags on the single remaining edge. */ | |
| 451 single_succ_edge (local_info->bb)->flags | |
| 452 &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE | EDGE_ABNORMAL); | |
| 453 single_succ_edge (local_info->bb)->flags |= EDGE_FALLTHRU; | |
| 454 | |
| 455 /* And adjust count and frequency on BB. */ | |
| 456 local_info->bb->count = e->count; | |
| 457 local_info->bb->frequency = EDGE_FREQUENCY (e); | |
| 458 } | |
| 459 } | |
| 460 | |
| 461 /* Indicate that we actually threaded one or more jumps. */ | |
| 462 if (rd->incoming_edges) | |
| 463 local_info->jumps_threaded = true; | |
| 464 | |
| 465 return 1; | |
| 466 } | |
| 467 | |
| 468 /* Return true if this block has no executable statements other than | |
| 469 a simple ctrl flow instruction. When the number of outgoing edges | |
| 470 is one, this is equivalent to a "forwarder" block. */ | |
| 471 | |
| 472 static bool | |
| 473 redirection_block_p (basic_block bb) | |
| 474 { | |
| 475 gimple_stmt_iterator gsi; | |
| 476 | |
| 477 /* Advance to the first executable statement. */ | |
| 478 gsi = gsi_start_bb (bb); | |
| 479 while (!gsi_end_p (gsi) | |
| 480 && (gimple_code (gsi_stmt (gsi)) == GIMPLE_LABEL | |
|
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parents:
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481 || is_gimple_debug (gsi_stmt (gsi)) |
| 0 | 482 || gimple_nop_p (gsi_stmt (gsi)))) |
| 483 gsi_next (&gsi); | |
|
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484 |
| 0 | 485 /* Check if this is an empty block. */ |
| 486 if (gsi_end_p (gsi)) | |
| 487 return true; | |
| 488 | |
| 489 /* Test that we've reached the terminating control statement. */ | |
| 490 return gsi_stmt (gsi) | |
| 491 && (gimple_code (gsi_stmt (gsi)) == GIMPLE_COND | |
| 492 || gimple_code (gsi_stmt (gsi)) == GIMPLE_GOTO | |
| 493 || gimple_code (gsi_stmt (gsi)) == GIMPLE_SWITCH); | |
| 494 } | |
| 495 | |
| 496 /* BB is a block which ends with a COND_EXPR or SWITCH_EXPR and when BB | |
| 497 is reached via one or more specific incoming edges, we know which | |
| 498 outgoing edge from BB will be traversed. | |
| 499 | |
| 500 We want to redirect those incoming edges to the target of the | |
| 501 appropriate outgoing edge. Doing so avoids a conditional branch | |
| 502 and may expose new optimization opportunities. Note that we have | |
| 503 to update dominator tree and SSA graph after such changes. | |
| 504 | |
| 505 The key to keeping the SSA graph update manageable is to duplicate | |
| 506 the side effects occurring in BB so that those side effects still | |
| 507 occur on the paths which bypass BB after redirecting edges. | |
| 508 | |
| 509 We accomplish this by creating duplicates of BB and arranging for | |
| 510 the duplicates to unconditionally pass control to one specific | |
| 511 successor of BB. We then revector the incoming edges into BB to | |
| 512 the appropriate duplicate of BB. | |
| 513 | |
| 514 If NOLOOP_ONLY is true, we only perform the threading as long as it | |
| 515 does not affect the structure of the loops in a nontrivial way. */ | |
| 516 | |
| 517 static bool | |
| 518 thread_block (basic_block bb, bool noloop_only) | |
| 519 { | |
| 520 /* E is an incoming edge into BB that we may or may not want to | |
| 521 redirect to a duplicate of BB. */ | |
| 522 edge e, e2; | |
| 523 edge_iterator ei; | |
| 524 struct local_info local_info; | |
| 525 struct loop *loop = bb->loop_father; | |
| 526 | |
| 527 /* ALL indicates whether or not all incoming edges into BB should | |
| 528 be threaded to a duplicate of BB. */ | |
| 529 bool all = true; | |
| 530 | |
| 531 /* To avoid scanning a linear array for the element we need we instead | |
| 532 use a hash table. For normal code there should be no noticeable | |
| 533 difference. However, if we have a block with a large number of | |
| 534 incoming and outgoing edges such linear searches can get expensive. */ | |
| 535 redirection_data = htab_create (EDGE_COUNT (bb->succs), | |
| 536 redirection_data_hash, | |
| 537 redirection_data_eq, | |
| 538 free); | |
| 539 | |
| 540 /* If we thread the latch of the loop to its exit, the loop ceases to | |
| 541 exist. Make sure we do not restrict ourselves in order to preserve | |
| 542 this loop. */ | |
| 543 if (loop->header == bb) | |
| 544 { | |
| 545 e = loop_latch_edge (loop); | |
| 546 e2 = (edge) e->aux; | |
| 547 | |
| 548 if (e2 && loop_exit_edge_p (loop, e2)) | |
| 549 { | |
| 550 loop->header = NULL; | |
| 551 loop->latch = NULL; | |
| 552 } | |
| 553 } | |
| 554 | |
| 555 /* Record each unique threaded destination into a hash table for | |
| 556 efficient lookups. */ | |
| 557 FOR_EACH_EDGE (e, ei, bb->preds) | |
| 558 { | |
| 559 e2 = (edge) e->aux; | |
| 560 | |
| 561 if (!e2 | |
| 562 /* If NOLOOP_ONLY is true, we only allow threading through the | |
| 563 header of a loop to exit edges. */ | |
| 564 || (noloop_only | |
| 565 && bb == bb->loop_father->header | |
| 566 && !loop_exit_edge_p (bb->loop_father, e2))) | |
| 567 { | |
| 568 all = false; | |
| 569 continue; | |
| 570 } | |
| 571 | |
| 572 update_bb_profile_for_threading (e->dest, EDGE_FREQUENCY (e), | |
| 573 e->count, (edge) e->aux); | |
| 574 | |
| 575 /* Insert the outgoing edge into the hash table if it is not | |
| 576 already in the hash table. */ | |
| 577 lookup_redirection_data (e2, e, INSERT); | |
| 578 } | |
| 579 | |
| 580 /* If we are going to thread all incoming edges to an outgoing edge, then | |
| 581 BB will become unreachable. Rather than just throwing it away, use | |
| 582 it for one of the duplicates. Mark the first incoming edge with the | |
| 583 DO_NOT_DUPLICATE attribute. */ | |
| 584 if (all) | |
| 585 { | |
| 586 edge e = (edge) EDGE_PRED (bb, 0)->aux; | |
| 587 lookup_redirection_data (e, NULL, NO_INSERT)->do_not_duplicate = true; | |
| 588 } | |
| 589 | |
| 590 /* We do not update dominance info. */ | |
| 591 free_dominance_info (CDI_DOMINATORS); | |
| 592 | |
| 593 /* Now create duplicates of BB. | |
| 594 | |
| 595 Note that for a block with a high outgoing degree we can waste | |
| 596 a lot of time and memory creating and destroying useless edges. | |
| 597 | |
| 598 So we first duplicate BB and remove the control structure at the | |
| 599 tail of the duplicate as well as all outgoing edges from the | |
| 600 duplicate. We then use that duplicate block as a template for | |
| 601 the rest of the duplicates. */ | |
| 602 local_info.template_block = NULL; | |
| 603 local_info.bb = bb; | |
| 604 local_info.jumps_threaded = false; | |
| 605 htab_traverse (redirection_data, create_duplicates, &local_info); | |
| 606 | |
| 607 /* The template does not have an outgoing edge. Create that outgoing | |
| 608 edge and update PHI nodes as the edge's target as necessary. | |
| 609 | |
| 610 We do this after creating all the duplicates to avoid creating | |
| 611 unnecessary edges. */ | |
| 612 htab_traverse (redirection_data, fixup_template_block, &local_info); | |
| 613 | |
| 614 /* The hash table traversals above created the duplicate blocks (and the | |
| 615 statements within the duplicate blocks). This loop creates PHI nodes for | |
| 616 the duplicated blocks and redirects the incoming edges into BB to reach | |
| 617 the duplicates of BB. */ | |
| 618 htab_traverse (redirection_data, redirect_edges, &local_info); | |
| 619 | |
| 620 /* Done with this block. Clear REDIRECTION_DATA. */ | |
| 621 htab_delete (redirection_data); | |
| 622 redirection_data = NULL; | |
| 623 | |
| 624 /* Indicate to our caller whether or not any jumps were threaded. */ | |
| 625 return local_info.jumps_threaded; | |
| 626 } | |
| 627 | |
| 628 /* Threads edge E through E->dest to the edge E->aux. Returns the copy | |
| 629 of E->dest created during threading, or E->dest if it was not necessary | |
| 630 to copy it (E is its single predecessor). */ | |
| 631 | |
| 632 static basic_block | |
| 633 thread_single_edge (edge e) | |
| 634 { | |
| 635 basic_block bb = e->dest; | |
| 636 edge eto = (edge) e->aux; | |
| 637 struct redirection_data rd; | |
| 638 | |
| 639 e->aux = NULL; | |
| 640 | |
| 641 thread_stats.num_threaded_edges++; | |
| 642 | |
| 643 if (single_pred_p (bb)) | |
| 644 { | |
| 645 /* If BB has just a single predecessor, we should only remove the | |
| 646 control statements at its end, and successors except for ETO. */ | |
| 647 remove_ctrl_stmt_and_useless_edges (bb, eto->dest); | |
| 648 | |
| 649 /* And fixup the flags on the single remaining edge. */ | |
| 650 eto->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE | EDGE_ABNORMAL); | |
| 651 eto->flags |= EDGE_FALLTHRU; | |
| 652 | |
| 653 return bb; | |
| 654 } | |
| 655 | |
| 656 /* Otherwise, we need to create a copy. */ | |
| 657 update_bb_profile_for_threading (bb, EDGE_FREQUENCY (e), e->count, eto); | |
| 658 | |
| 659 rd.outgoing_edge = eto; | |
| 660 | |
| 661 create_block_for_threading (bb, &rd); | |
| 662 create_edge_and_update_destination_phis (&rd); | |
| 663 | |
| 664 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 665 fprintf (dump_file, " Threaded jump %d --> %d to %d\n", | |
| 666 e->src->index, e->dest->index, rd.dup_block->index); | |
| 667 | |
| 668 rd.dup_block->count = e->count; | |
| 669 rd.dup_block->frequency = EDGE_FREQUENCY (e); | |
| 670 single_succ_edge (rd.dup_block)->count = e->count; | |
| 671 redirect_edge_and_branch (e, rd.dup_block); | |
| 672 flush_pending_stmts (e); | |
| 673 | |
| 674 return rd.dup_block; | |
| 675 } | |
| 676 | |
| 677 /* Callback for dfs_enumerate_from. Returns true if BB is different | |
| 678 from STOP and DBDS_CE_STOP. */ | |
| 679 | |
| 680 static basic_block dbds_ce_stop; | |
| 681 static bool | |
| 682 dbds_continue_enumeration_p (const_basic_block bb, const void *stop) | |
| 683 { | |
| 684 return (bb != (const_basic_block) stop | |
| 685 && bb != dbds_ce_stop); | |
| 686 } | |
| 687 | |
| 688 /* Evaluates the dominance relationship of latch of the LOOP and BB, and | |
| 689 returns the state. */ | |
| 690 | |
| 691 enum bb_dom_status | |
| 692 { | |
| 693 /* BB does not dominate latch of the LOOP. */ | |
| 694 DOMST_NONDOMINATING, | |
| 695 /* The LOOP is broken (there is no path from the header to its latch. */ | |
| 696 DOMST_LOOP_BROKEN, | |
| 697 /* BB dominates the latch of the LOOP. */ | |
| 698 DOMST_DOMINATING | |
| 699 }; | |
| 700 | |
| 701 static enum bb_dom_status | |
| 702 determine_bb_domination_status (struct loop *loop, basic_block bb) | |
| 703 { | |
| 704 basic_block *bblocks; | |
| 705 unsigned nblocks, i; | |
| 706 bool bb_reachable = false; | |
| 707 edge_iterator ei; | |
| 708 edge e; | |
| 709 | |
| 710 #ifdef ENABLE_CHECKING | |
| 711 /* This function assumes BB is a successor of LOOP->header. */ | |
| 712 { | |
| 713 bool ok = false; | |
| 714 | |
| 715 FOR_EACH_EDGE (e, ei, bb->preds) | |
| 716 { | |
| 717 if (e->src == loop->header) | |
| 718 { | |
| 719 ok = true; | |
| 720 break; | |
| 721 } | |
| 722 } | |
| 723 | |
| 724 gcc_assert (ok); | |
| 725 } | |
| 726 #endif | |
| 727 | |
| 728 if (bb == loop->latch) | |
| 729 return DOMST_DOMINATING; | |
| 730 | |
| 731 /* Check that BB dominates LOOP->latch, and that it is back-reachable | |
| 732 from it. */ | |
| 733 | |
| 734 bblocks = XCNEWVEC (basic_block, loop->num_nodes); | |
| 735 dbds_ce_stop = loop->header; | |
| 736 nblocks = dfs_enumerate_from (loop->latch, 1, dbds_continue_enumeration_p, | |
| 737 bblocks, loop->num_nodes, bb); | |
| 738 for (i = 0; i < nblocks; i++) | |
| 739 FOR_EACH_EDGE (e, ei, bblocks[i]->preds) | |
| 740 { | |
| 741 if (e->src == loop->header) | |
| 742 { | |
| 743 free (bblocks); | |
| 744 return DOMST_NONDOMINATING; | |
| 745 } | |
| 746 if (e->src == bb) | |
| 747 bb_reachable = true; | |
| 748 } | |
| 749 | |
| 750 free (bblocks); | |
| 751 return (bb_reachable ? DOMST_DOMINATING : DOMST_LOOP_BROKEN); | |
| 752 } | |
| 753 | |
| 754 /* Thread jumps through the header of LOOP. Returns true if cfg changes. | |
| 755 If MAY_PEEL_LOOP_HEADERS is false, we avoid threading from entry edges | |
| 756 to the inside of the loop. */ | |
| 757 | |
| 758 static bool | |
| 759 thread_through_loop_header (struct loop *loop, bool may_peel_loop_headers) | |
| 760 { | |
| 761 basic_block header = loop->header; | |
| 762 edge e, tgt_edge, latch = loop_latch_edge (loop); | |
| 763 edge_iterator ei; | |
| 764 basic_block tgt_bb, atgt_bb; | |
| 765 enum bb_dom_status domst; | |
| 766 | |
| 767 /* We have already threaded through headers to exits, so all the threading | |
| 768 requests now are to the inside of the loop. We need to avoid creating | |
| 769 irreducible regions (i.e., loops with more than one entry block), and | |
| 770 also loop with several latch edges, or new subloops of the loop (although | |
| 771 there are cases where it might be appropriate, it is difficult to decide, | |
| 772 and doing it wrongly may confuse other optimizers). | |
| 773 | |
| 774 We could handle more general cases here. However, the intention is to | |
| 775 preserve some information about the loop, which is impossible if its | |
| 776 structure changes significantly, in a way that is not well understood. | |
| 777 Thus we only handle few important special cases, in which also updating | |
| 778 of the loop-carried information should be feasible: | |
| 779 | |
| 780 1) Propagation of latch edge to a block that dominates the latch block | |
| 781 of a loop. This aims to handle the following idiom: | |
| 782 | |
| 783 first = 1; | |
| 784 while (1) | |
| 785 { | |
| 786 if (first) | |
| 787 initialize; | |
| 788 first = 0; | |
| 789 body; | |
| 790 } | |
| 791 | |
| 792 After threading the latch edge, this becomes | |
| 793 | |
| 794 first = 1; | |
| 795 if (first) | |
| 796 initialize; | |
| 797 while (1) | |
| 798 { | |
| 799 first = 0; | |
| 800 body; | |
| 801 } | |
| 802 | |
| 803 The original header of the loop is moved out of it, and we may thread | |
| 804 the remaining edges through it without further constraints. | |
| 805 | |
| 806 2) All entry edges are propagated to a single basic block that dominates | |
| 807 the latch block of the loop. This aims to handle the following idiom | |
| 808 (normally created for "for" loops): | |
| 809 | |
| 810 i = 0; | |
| 811 while (1) | |
| 812 { | |
| 813 if (i >= 100) | |
| 814 break; | |
| 815 body; | |
| 816 i++; | |
| 817 } | |
| 818 | |
| 819 This becomes | |
| 820 | |
| 821 i = 0; | |
| 822 while (1) | |
| 823 { | |
| 824 body; | |
| 825 i++; | |
| 826 if (i >= 100) | |
| 827 break; | |
| 828 } | |
| 829 */ | |
| 830 | |
| 831 /* Threading through the header won't improve the code if the header has just | |
| 832 one successor. */ | |
| 833 if (single_succ_p (header)) | |
| 834 goto fail; | |
| 835 | |
| 836 if (latch->aux) | |
| 837 { | |
| 838 tgt_edge = (edge) latch->aux; | |
| 839 tgt_bb = tgt_edge->dest; | |
| 840 } | |
| 841 else if (!may_peel_loop_headers | |
| 842 && !redirection_block_p (loop->header)) | |
| 843 goto fail; | |
| 844 else | |
| 845 { | |
| 846 tgt_bb = NULL; | |
| 847 tgt_edge = NULL; | |
| 848 FOR_EACH_EDGE (e, ei, header->preds) | |
| 849 { | |
| 850 if (!e->aux) | |
| 851 { | |
| 852 if (e == latch) | |
| 853 continue; | |
| 854 | |
| 855 /* If latch is not threaded, and there is a header | |
| 856 edge that is not threaded, we would create loop | |
| 857 with multiple entries. */ | |
| 858 goto fail; | |
| 859 } | |
| 860 | |
| 861 tgt_edge = (edge) e->aux; | |
| 862 atgt_bb = tgt_edge->dest; | |
| 863 if (!tgt_bb) | |
| 864 tgt_bb = atgt_bb; | |
| 865 /* Two targets of threading would make us create loop | |
| 866 with multiple entries. */ | |
| 867 else if (tgt_bb != atgt_bb) | |
| 868 goto fail; | |
| 869 } | |
| 870 | |
| 871 if (!tgt_bb) | |
| 872 { | |
| 873 /* There are no threading requests. */ | |
| 874 return false; | |
| 875 } | |
| 876 | |
| 877 /* Redirecting to empty loop latch is useless. */ | |
| 878 if (tgt_bb == loop->latch | |
| 879 && empty_block_p (loop->latch)) | |
| 880 goto fail; | |
| 881 } | |
| 882 | |
| 883 /* The target block must dominate the loop latch, otherwise we would be | |
| 884 creating a subloop. */ | |
| 885 domst = determine_bb_domination_status (loop, tgt_bb); | |
| 886 if (domst == DOMST_NONDOMINATING) | |
| 887 goto fail; | |
| 888 if (domst == DOMST_LOOP_BROKEN) | |
| 889 { | |
| 890 /* If the loop ceased to exist, mark it as such, and thread through its | |
| 891 original header. */ | |
| 892 loop->header = NULL; | |
| 893 loop->latch = NULL; | |
| 894 return thread_block (header, false); | |
| 895 } | |
| 896 | |
| 897 if (tgt_bb->loop_father->header == tgt_bb) | |
| 898 { | |
| 899 /* If the target of the threading is a header of a subloop, we need | |
| 900 to create a preheader for it, so that the headers of the two loops | |
| 901 do not merge. */ | |
| 902 if (EDGE_COUNT (tgt_bb->preds) > 2) | |
| 903 { | |
| 904 tgt_bb = create_preheader (tgt_bb->loop_father, 0); | |
| 905 gcc_assert (tgt_bb != NULL); | |
| 906 } | |
| 907 else | |
| 908 tgt_bb = split_edge (tgt_edge); | |
| 909 } | |
|
55
77e2b8dfacca
update it from 4.4.3 to 4.5.0
ryoma <e075725@ie.u-ryukyu.ac.jp>
parents:
0
diff
changeset
|
910 |
| 0 | 911 if (latch->aux) |
| 912 { | |
| 913 /* First handle the case latch edge is redirected. */ | |
| 914 loop->latch = thread_single_edge (latch); | |
| 915 gcc_assert (single_succ (loop->latch) == tgt_bb); | |
| 916 loop->header = tgt_bb; | |
| 917 | |
| 918 /* Thread the remaining edges through the former header. */ | |
| 919 thread_block (header, false); | |
| 920 } | |
| 921 else | |
| 922 { | |
| 923 basic_block new_preheader; | |
| 924 | |
| 925 /* Now consider the case entry edges are redirected to the new entry | |
| 926 block. Remember one entry edge, so that we can find the new | |
| 927 preheader (its destination after threading). */ | |
| 928 FOR_EACH_EDGE (e, ei, header->preds) | |
| 929 { | |
| 930 if (e->aux) | |
| 931 break; | |
| 932 } | |
| 933 | |
| 934 /* The duplicate of the header is the new preheader of the loop. Ensure | |
| 935 that it is placed correctly in the loop hierarchy. */ | |
| 936 set_loop_copy (loop, loop_outer (loop)); | |
| 937 | |
| 938 thread_block (header, false); | |
| 939 set_loop_copy (loop, NULL); | |
| 940 new_preheader = e->dest; | |
| 941 | |
| 942 /* Create the new latch block. This is always necessary, as the latch | |
| 943 must have only a single successor, but the original header had at | |
| 944 least two successors. */ | |
| 945 loop->latch = NULL; | |
| 946 mfb_kj_edge = single_succ_edge (new_preheader); | |
| 947 loop->header = mfb_kj_edge->dest; | |
| 948 latch = make_forwarder_block (tgt_bb, mfb_keep_just, NULL); | |
| 949 loop->header = latch->dest; | |
| 950 loop->latch = latch->src; | |
| 951 } | |
|
55
77e2b8dfacca
update it from 4.4.3 to 4.5.0
ryoma <e075725@ie.u-ryukyu.ac.jp>
parents:
0
diff
changeset
|
952 |
| 0 | 953 return true; |
| 954 | |
| 955 fail: | |
| 956 /* We failed to thread anything. Cancel the requests. */ | |
| 957 FOR_EACH_EDGE (e, ei, header->preds) | |
| 958 { | |
| 959 e->aux = NULL; | |
| 960 } | |
| 961 return false; | |
| 962 } | |
| 963 | |
| 964 /* Walk through the registered jump threads and convert them into a | |
| 965 form convenient for this pass. | |
| 966 | |
| 967 Any block which has incoming edges threaded to outgoing edges | |
| 968 will have its entry in THREADED_BLOCK set. | |
| 969 | |
| 970 Any threaded edge will have its new outgoing edge stored in the | |
| 971 original edge's AUX field. | |
| 972 | |
| 973 This form avoids the need to walk all the edges in the CFG to | |
| 974 discover blocks which need processing and avoids unnecessary | |
| 975 hash table lookups to map from threaded edge to new target. */ | |
| 976 | |
| 977 static void | |
| 978 mark_threaded_blocks (bitmap threaded_blocks) | |
| 979 { | |
| 980 unsigned int i; | |
| 981 bitmap_iterator bi; | |
| 982 bitmap tmp = BITMAP_ALLOC (NULL); | |
| 983 basic_block bb; | |
| 984 edge e; | |
| 985 edge_iterator ei; | |
| 986 | |
| 987 for (i = 0; i < VEC_length (edge, threaded_edges); i += 2) | |
| 988 { | |
| 989 edge e = VEC_index (edge, threaded_edges, i); | |
| 990 edge e2 = VEC_index (edge, threaded_edges, i + 1); | |
| 991 | |
| 992 e->aux = e2; | |
| 993 bitmap_set_bit (tmp, e->dest->index); | |
| 994 } | |
| 995 | |
| 996 /* If optimizing for size, only thread through block if we don't have | |
| 997 to duplicate it or it's an otherwise empty redirection block. */ | |
| 998 if (optimize_function_for_size_p (cfun)) | |
| 999 { | |
| 1000 EXECUTE_IF_SET_IN_BITMAP (tmp, 0, i, bi) | |
| 1001 { | |
| 1002 bb = BASIC_BLOCK (i); | |
| 1003 if (EDGE_COUNT (bb->preds) > 1 | |
| 1004 && !redirection_block_p (bb)) | |
| 1005 { | |
| 1006 FOR_EACH_EDGE (e, ei, bb->preds) | |
| 1007 e->aux = NULL; | |
| 1008 } | |
| 1009 else | |
| 1010 bitmap_set_bit (threaded_blocks, i); | |
| 1011 } | |
| 1012 } | |
| 1013 else | |
| 1014 bitmap_copy (threaded_blocks, tmp); | |
| 1015 | |
| 1016 BITMAP_FREE(tmp); | |
| 1017 } | |
| 1018 | |
| 1019 | |
| 1020 /* Walk through all blocks and thread incoming edges to the appropriate | |
| 1021 outgoing edge for each edge pair recorded in THREADED_EDGES. | |
| 1022 | |
| 1023 It is the caller's responsibility to fix the dominance information | |
| 1024 and rewrite duplicated SSA_NAMEs back into SSA form. | |
| 1025 | |
| 1026 If MAY_PEEL_LOOP_HEADERS is false, we avoid threading edges through | |
| 1027 loop headers if it does not simplify the loop. | |
| 1028 | |
| 1029 Returns true if one or more edges were threaded, false otherwise. */ | |
| 1030 | |
| 1031 bool | |
| 1032 thread_through_all_blocks (bool may_peel_loop_headers) | |
| 1033 { | |
| 1034 bool retval = false; | |
| 1035 unsigned int i; | |
| 1036 bitmap_iterator bi; | |
| 1037 bitmap threaded_blocks; | |
| 1038 struct loop *loop; | |
| 1039 loop_iterator li; | |
| 1040 | |
| 1041 /* We must know about loops in order to preserve them. */ | |
| 1042 gcc_assert (current_loops != NULL); | |
| 1043 | |
| 1044 if (threaded_edges == NULL) | |
| 1045 return false; | |
| 1046 | |
| 1047 threaded_blocks = BITMAP_ALLOC (NULL); | |
| 1048 memset (&thread_stats, 0, sizeof (thread_stats)); | |
| 1049 | |
| 1050 mark_threaded_blocks (threaded_blocks); | |
| 1051 | |
| 1052 initialize_original_copy_tables (); | |
| 1053 | |
| 1054 /* First perform the threading requests that do not affect | |
| 1055 loop structure. */ | |
| 1056 EXECUTE_IF_SET_IN_BITMAP (threaded_blocks, 0, i, bi) | |
| 1057 { | |
| 1058 basic_block bb = BASIC_BLOCK (i); | |
| 1059 | |
| 1060 if (EDGE_COUNT (bb->preds) > 0) | |
| 1061 retval |= thread_block (bb, true); | |
| 1062 } | |
| 1063 | |
| 1064 /* Then perform the threading through loop headers. We start with the | |
| 1065 innermost loop, so that the changes in cfg we perform won't affect | |
| 1066 further threading. */ | |
| 1067 FOR_EACH_LOOP (li, loop, LI_FROM_INNERMOST) | |
| 1068 { | |
| 1069 if (!loop->header | |
| 1070 || !bitmap_bit_p (threaded_blocks, loop->header->index)) | |
| 1071 continue; | |
| 1072 | |
| 1073 retval |= thread_through_loop_header (loop, may_peel_loop_headers); | |
| 1074 } | |
| 1075 | |
| 1076 statistics_counter_event (cfun, "Jumps threaded", | |
| 1077 thread_stats.num_threaded_edges); | |
| 1078 | |
| 1079 free_original_copy_tables (); | |
| 1080 | |
| 1081 BITMAP_FREE (threaded_blocks); | |
| 1082 threaded_blocks = NULL; | |
| 1083 VEC_free (edge, heap, threaded_edges); | |
| 1084 threaded_edges = NULL; | |
| 1085 | |
| 1086 if (retval) | |
| 1087 loops_state_set (LOOPS_NEED_FIXUP); | |
| 1088 | |
| 1089 return retval; | |
| 1090 } | |
| 1091 | |
| 1092 /* Register a jump threading opportunity. We queue up all the jump | |
| 1093 threading opportunities discovered by a pass and update the CFG | |
| 1094 and SSA form all at once. | |
| 1095 | |
| 1096 E is the edge we can thread, E2 is the new target edge, i.e., we | |
| 1097 are effectively recording that E->dest can be changed to E2->dest | |
| 1098 after fixing the SSA graph. */ | |
| 1099 | |
| 1100 void | |
| 1101 register_jump_thread (edge e, edge e2) | |
| 1102 { | |
| 1103 if (threaded_edges == NULL) | |
| 1104 threaded_edges = VEC_alloc (edge, heap, 10); | |
| 1105 | |
| 1106 VEC_safe_push (edge, heap, threaded_edges, e); | |
| 1107 VEC_safe_push (edge, heap, threaded_edges, e2); | |
| 1108 } |