Mercurial > hg > CbC > CbC_gcc
annotate gcc/tree-ssa-threadupdate.c @ 63:b7f97abdc517 gcc-4.6-20100522
update gcc from gcc-4.5.0 to gcc-4.6
| author | ryoma <e075725@ie.u-ryukyu.ac.jp> |
|---|---|
| date | Mon, 24 May 2010 12:47:05 +0900 |
| parents | 77e2b8dfacca |
| children | f6334be47118 |
| 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 "tm_p.h" | |
| 28 #include "basic-block.h" | |
| 29 #include "output.h" | |
| 30 #include "expr.h" | |
| 31 #include "function.h" | |
| 32 #include "diagnostic.h" | |
| 33 #include "tree-flow.h" | |
| 34 #include "tree-dump.h" | |
| 35 #include "tree-pass.h" | |
| 36 #include "cfgloop.h" | |
| 37 | |
| 38 /* Given a block B, update the CFG and SSA graph to reflect redirecting | |
| 39 one or more in-edges to B to instead reach the destination of an | |
| 40 out-edge from B while preserving any side effects in B. | |
| 41 | |
| 42 i.e., given A->B and B->C, change A->B to be A->C yet still preserve the | |
| 43 side effects of executing B. | |
| 44 | |
| 45 1. Make a copy of B (including its outgoing edges and statements). Call | |
| 46 the copy B'. Note B' has no incoming edges or PHIs at this time. | |
| 47 | |
| 48 2. Remove the control statement at the end of B' and all outgoing edges | |
| 49 except B'->C. | |
| 50 | |
| 51 3. Add a new argument to each PHI in C with the same value as the existing | |
| 52 argument associated with edge B->C. Associate the new PHI arguments | |
| 53 with the edge B'->C. | |
| 54 | |
| 55 4. For each PHI in B, find or create a PHI in B' with an identical | |
| 56 PHI_RESULT. Add an argument to the PHI in B' which has the same | |
| 57 value as the PHI in B associated with the edge A->B. Associate | |
| 58 the new argument in the PHI in B' with the edge A->B. | |
| 59 | |
| 60 5. Change the edge A->B to A->B'. | |
| 61 | |
| 62 5a. This automatically deletes any PHI arguments associated with the | |
| 63 edge A->B in B. | |
| 64 | |
| 65 5b. This automatically associates each new argument added in step 4 | |
| 66 with the edge A->B'. | |
| 67 | |
| 68 6. Repeat for other incoming edges into B. | |
| 69 | |
| 70 7. Put the duplicated resources in B and all the B' blocks into SSA form. | |
| 71 | |
| 72 Note that block duplication can be minimized by first collecting the | |
| 73 set of unique destination blocks that the incoming edges should | |
| 74 be threaded to. Block duplication can be further minimized by using | |
| 75 B instead of creating B' for one destination if all edges into B are | |
| 76 going to be threaded to a successor of B. | |
| 77 | |
| 78 We further reduce the number of edges and statements we create by | |
| 79 not copying all the outgoing edges and the control statement in | |
| 80 step #1. We instead create a template block without the outgoing | |
| 81 edges and duplicate the template. */ | |
| 82 | |
| 83 | |
| 84 /* Steps #5 and #6 of the above algorithm are best implemented by walking | |
| 85 all the incoming edges which thread to the same destination edge at | |
| 86 the same time. That avoids lots of table lookups to get information | |
| 87 for the destination edge. | |
| 88 | |
| 89 To realize that implementation we create a list of incoming edges | |
| 90 which thread to the same outgoing edge. Thus to implement steps | |
| 91 #5 and #6 we traverse our hash table of outgoing edge information. | |
| 92 For each entry we walk the list of incoming edges which thread to | |
| 93 the current outgoing edge. */ | |
| 94 | |
| 95 struct el | |
| 96 { | |
| 97 edge e; | |
| 98 struct el *next; | |
| 99 }; | |
| 100 | |
| 101 /* Main data structure recording information regarding B's duplicate | |
| 102 blocks. */ | |
| 103 | |
| 104 /* We need to efficiently record the unique thread destinations of this | |
| 105 block and specific information associated with those destinations. We | |
| 106 may have many incoming edges threaded to the same outgoing edge. This | |
| 107 can be naturally implemented with a hash table. */ | |
| 108 | |
| 109 struct redirection_data | |
| 110 { | |
| 111 /* A duplicate of B with the trailing control statement removed and which | |
| 112 targets a single successor of B. */ | |
| 113 basic_block dup_block; | |
| 114 | |
| 115 /* An outgoing edge from B. DUP_BLOCK will have OUTGOING_EDGE->dest as | |
| 116 its single successor. */ | |
| 117 edge outgoing_edge; | |
| 118 | |
| 119 /* A list of incoming edges which we want to thread to | |
| 120 OUTGOING_EDGE->dest. */ | |
| 121 struct el *incoming_edges; | |
| 122 | |
| 123 /* Flag indicating whether or not we should create a duplicate block | |
| 124 for this thread destination. This is only true if we are threading | |
| 125 all incoming edges and thus are using BB itself as a duplicate block. */ | |
| 126 bool do_not_duplicate; | |
| 127 }; | |
| 128 | |
| 129 /* Main data structure to hold information for duplicates of BB. */ | |
| 130 static htab_t redirection_data; | |
| 131 | |
| 132 /* Data structure of information to pass to hash table traversal routines. */ | |
| 133 struct local_info | |
| 134 { | |
| 135 /* The current block we are working on. */ | |
| 136 basic_block bb; | |
| 137 | |
| 138 /* A template copy of BB with no outgoing edges or control statement that | |
| 139 we use for creating copies. */ | |
| 140 basic_block template_block; | |
| 141 | |
| 142 /* TRUE if we thread one or more jumps, FALSE otherwise. */ | |
| 143 bool jumps_threaded; | |
| 144 }; | |
| 145 | |
| 146 /* Passes which use the jump threading code register jump threading | |
| 147 opportunities as they are discovered. We keep the registered | |
| 148 jump threading opportunities in this vector as edge pairs | |
| 149 (original_edge, target_edge). */ | |
| 150 static VEC(edge,heap) *threaded_edges; | |
| 151 | |
| 152 | |
| 153 /* Jump threading statistics. */ | |
| 154 | |
| 155 struct thread_stats_d | |
| 156 { | |
| 157 unsigned long num_threaded_edges; | |
| 158 }; | |
| 159 | |
| 160 struct thread_stats_d thread_stats; | |
| 161 | |
| 162 | |
| 163 /* Remove the last statement in block BB if it is a control statement | |
| 164 Also remove all outgoing edges except the edge which reaches DEST_BB. | |
| 165 If DEST_BB is NULL, then remove all outgoing edges. */ | |
| 166 | |
| 167 static void | |
| 168 remove_ctrl_stmt_and_useless_edges (basic_block bb, basic_block dest_bb) | |
| 169 { | |
| 170 gimple_stmt_iterator gsi; | |
| 171 edge e; | |
| 172 edge_iterator ei; | |
| 173 | |
| 174 gsi = gsi_last_bb (bb); | |
| 175 | |
| 176 /* If the duplicate ends with a control statement, then remove it. | |
| 177 | |
| 178 Note that if we are duplicating the template block rather than the | |
| 179 original basic block, then the duplicate might not have any real | |
| 180 statements in it. */ | |
| 181 if (!gsi_end_p (gsi) | |
| 182 && gsi_stmt (gsi) | |
| 183 && (gimple_code (gsi_stmt (gsi)) == GIMPLE_COND | |
| 184 || gimple_code (gsi_stmt (gsi)) == GIMPLE_GOTO | |
| 185 || gimple_code (gsi_stmt (gsi)) == GIMPLE_SWITCH)) | |
| 186 gsi_remove (&gsi, true); | |
| 187 | |
| 188 for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); ) | |
| 189 { | |
| 190 if (e->dest != dest_bb) | |
| 191 remove_edge (e); | |
| 192 else | |
| 193 ei_next (&ei); | |
| 194 } | |
| 195 } | |
| 196 | |
| 197 /* Create a duplicate of BB which only reaches the destination of the edge | |
| 198 stored in RD. Record the duplicate block in RD. */ | |
| 199 | |
| 200 static void | |
| 201 create_block_for_threading (basic_block bb, struct redirection_data *rd) | |
| 202 { | |
| 203 /* We can use the generic block duplication code and simply remove | |
| 204 the stuff we do not need. */ | |
| 205 rd->dup_block = duplicate_block (bb, NULL, NULL); | |
| 206 | |
| 207 /* Zero out the profile, since the block is unreachable for now. */ | |
| 208 rd->dup_block->frequency = 0; | |
| 209 rd->dup_block->count = 0; | |
| 210 | |
| 211 /* The call to duplicate_block will copy everything, including the | |
| 212 useless COND_EXPR or SWITCH_EXPR at the end of BB. We just remove | |
| 213 the useless COND_EXPR or SWITCH_EXPR here rather than having a | |
| 214 specialized block copier. We also remove all outgoing edges | |
| 215 from the duplicate block. The appropriate edge will be created | |
| 216 later. */ | |
| 217 remove_ctrl_stmt_and_useless_edges (rd->dup_block, NULL); | |
| 218 } | |
| 219 | |
| 220 /* Hashing and equality routines for our hash table. */ | |
| 221 static hashval_t | |
| 222 redirection_data_hash (const void *p) | |
| 223 { | |
| 224 edge e = ((const struct redirection_data *)p)->outgoing_edge; | |
| 225 return e->dest->index; | |
| 226 } | |
| 227 | |
| 228 static int | |
| 229 redirection_data_eq (const void *p1, const void *p2) | |
| 230 { | |
| 231 edge e1 = ((const struct redirection_data *)p1)->outgoing_edge; | |
| 232 edge e2 = ((const struct redirection_data *)p2)->outgoing_edge; | |
| 233 | |
| 234 return e1 == e2; | |
| 235 } | |
| 236 | |
| 237 /* Given an outgoing edge E lookup and return its entry in our hash table. | |
| 238 | |
| 239 If INSERT is true, then we insert the entry into the hash table if | |
| 240 it is not already present. INCOMING_EDGE is added to the list of incoming | |
| 241 edges associated with E in the hash table. */ | |
| 242 | |
| 243 static struct redirection_data * | |
| 244 lookup_redirection_data (edge e, edge incoming_edge, enum insert_option insert) | |
| 245 { | |
| 246 void **slot; | |
| 247 struct redirection_data *elt; | |
| 248 | |
| 249 /* Build a hash table element so we can see if E is already | |
| 250 in the table. */ | |
| 251 elt = XNEW (struct redirection_data); | |
| 252 elt->outgoing_edge = e; | |
| 253 elt->dup_block = NULL; | |
| 254 elt->do_not_duplicate = false; | |
| 255 elt->incoming_edges = NULL; | |
| 256 | |
| 257 slot = htab_find_slot (redirection_data, elt, insert); | |
| 258 | |
| 259 /* This will only happen if INSERT is false and the entry is not | |
| 260 in the hash table. */ | |
| 261 if (slot == NULL) | |
| 262 { | |
| 263 free (elt); | |
| 264 return NULL; | |
| 265 } | |
| 266 | |
| 267 /* This will only happen if E was not in the hash table and | |
| 268 INSERT is true. */ | |
| 269 if (*slot == NULL) | |
| 270 { | |
| 271 *slot = (void *)elt; | |
| 272 elt->incoming_edges = XNEW (struct el); | |
| 273 elt->incoming_edges->e = incoming_edge; | |
| 274 elt->incoming_edges->next = NULL; | |
| 275 return elt; | |
| 276 } | |
| 277 /* E was in the hash table. */ | |
| 278 else | |
| 279 { | |
| 280 /* Free ELT as we do not need it anymore, we will extract the | |
| 281 relevant entry from the hash table itself. */ | |
| 282 free (elt); | |
| 283 | |
| 284 /* Get the entry stored in the hash table. */ | |
| 285 elt = (struct redirection_data *) *slot; | |
| 286 | |
| 287 /* If insertion was requested, then we need to add INCOMING_EDGE | |
| 288 to the list of incoming edges associated with E. */ | |
| 289 if (insert) | |
| 290 { | |
| 291 struct el *el = XNEW (struct el); | |
| 292 el->next = elt->incoming_edges; | |
| 293 el->e = incoming_edge; | |
| 294 elt->incoming_edges = el; | |
| 295 } | |
| 296 | |
| 297 return elt; | |
| 298 } | |
| 299 } | |
| 300 | |
| 301 /* Given a duplicate block and its single destination (both stored | |
| 302 in RD). Create an edge between the duplicate and its single | |
| 303 destination. | |
| 304 | |
| 305 Add an additional argument to any PHI nodes at the single | |
| 306 destination. */ | |
| 307 | |
| 308 static void | |
| 309 create_edge_and_update_destination_phis (struct redirection_data *rd) | |
| 310 { | |
| 311 edge e = make_edge (rd->dup_block, rd->outgoing_edge->dest, EDGE_FALLTHRU); | |
| 312 gimple_stmt_iterator gsi; | |
| 313 | |
| 314 rescan_loop_exit (e, true, false); | |
| 315 e->probability = REG_BR_PROB_BASE; | |
| 316 e->count = rd->dup_block->count; | |
| 317 e->aux = rd->outgoing_edge->aux; | |
| 318 | |
| 319 /* If there are any PHI nodes at the destination of the outgoing edge | |
| 320 from the duplicate block, then we will need to add a new argument | |
| 321 to them. The argument should have the same value as the argument | |
| 322 associated with the outgoing edge stored in RD. */ | |
| 323 for (gsi = gsi_start_phis (e->dest); !gsi_end_p (gsi); gsi_next (&gsi)) | |
| 324 { | |
| 325 gimple phi = gsi_stmt (gsi); | |
|
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326 source_location locus; |
| 0 | 327 int indx = rd->outgoing_edge->dest_idx; |
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328 |
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329 locus = gimple_phi_arg_location (phi, indx); |
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330 add_phi_arg (phi, gimple_phi_arg_def (phi, indx), e, locus); |
| 0 | 331 } |
| 332 } | |
| 333 | |
| 334 /* Hash table traversal callback routine to create duplicate blocks. */ | |
| 335 | |
| 336 static int | |
| 337 create_duplicates (void **slot, void *data) | |
| 338 { | |
| 339 struct redirection_data *rd = (struct redirection_data *) *slot; | |
| 340 struct local_info *local_info = (struct local_info *)data; | |
| 341 | |
| 342 /* If this entry should not have a duplicate created, then there's | |
| 343 nothing to do. */ | |
| 344 if (rd->do_not_duplicate) | |
| 345 return 1; | |
| 346 | |
| 347 /* Create a template block if we have not done so already. Otherwise | |
| 348 use the template to create a new block. */ | |
| 349 if (local_info->template_block == NULL) | |
| 350 { | |
| 351 create_block_for_threading (local_info->bb, rd); | |
| 352 local_info->template_block = rd->dup_block; | |
| 353 | |
| 354 /* We do not create any outgoing edges for the template. We will | |
| 355 take care of that in a later traversal. That way we do not | |
| 356 create edges that are going to just be deleted. */ | |
| 357 } | |
| 358 else | |
| 359 { | |
| 360 create_block_for_threading (local_info->template_block, rd); | |
| 361 | |
| 362 /* Go ahead and wire up outgoing edges and update PHIs for the duplicate | |
| 363 block. */ | |
| 364 create_edge_and_update_destination_phis (rd); | |
| 365 } | |
| 366 | |
| 367 /* Keep walking the hash table. */ | |
| 368 return 1; | |
| 369 } | |
| 370 | |
| 371 /* We did not create any outgoing edges for the template block during | |
| 372 block creation. This hash table traversal callback creates the | |
| 373 outgoing edge for the template block. */ | |
| 374 | |
| 375 static int | |
| 376 fixup_template_block (void **slot, void *data) | |
| 377 { | |
| 378 struct redirection_data *rd = (struct redirection_data *) *slot; | |
| 379 struct local_info *local_info = (struct local_info *)data; | |
| 380 | |
| 381 /* If this is the template block, then create its outgoing edges | |
| 382 and halt the hash table traversal. */ | |
| 383 if (rd->dup_block && rd->dup_block == local_info->template_block) | |
| 384 { | |
| 385 create_edge_and_update_destination_phis (rd); | |
| 386 return 0; | |
| 387 } | |
| 388 | |
| 389 return 1; | |
| 390 } | |
| 391 | |
| 392 /* Hash table traversal callback to redirect each incoming edge | |
| 393 associated with this hash table element to its new destination. */ | |
| 394 | |
| 395 static int | |
| 396 redirect_edges (void **slot, void *data) | |
| 397 { | |
| 398 struct redirection_data *rd = (struct redirection_data *) *slot; | |
| 399 struct local_info *local_info = (struct local_info *)data; | |
| 400 struct el *next, *el; | |
| 401 | |
| 402 /* Walk over all the incoming edges associated associated with this | |
| 403 hash table entry. */ | |
| 404 for (el = rd->incoming_edges; el; el = next) | |
| 405 { | |
| 406 edge e = el->e; | |
| 407 | |
| 408 /* Go ahead and free this element from the list. Doing this now | |
| 409 avoids the need for another list walk when we destroy the hash | |
| 410 table. */ | |
| 411 next = el->next; | |
| 412 free (el); | |
| 413 | |
| 414 /* Go ahead and clear E->aux. It's not needed anymore and failure | |
| 415 to clear it will cause all kinds of unpleasant problems later. */ | |
| 416 e->aux = NULL; | |
| 417 | |
| 418 thread_stats.num_threaded_edges++; | |
| 419 | |
| 420 if (rd->dup_block) | |
| 421 { | |
| 422 edge e2; | |
| 423 | |
| 424 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 425 fprintf (dump_file, " Threaded jump %d --> %d to %d\n", | |
| 426 e->src->index, e->dest->index, rd->dup_block->index); | |
| 427 | |
| 428 rd->dup_block->count += e->count; | |
| 429 rd->dup_block->frequency += EDGE_FREQUENCY (e); | |
| 430 EDGE_SUCC (rd->dup_block, 0)->count += e->count; | |
| 431 /* Redirect the incoming edge to the appropriate duplicate | |
| 432 block. */ | |
| 433 e2 = redirect_edge_and_branch (e, rd->dup_block); | |
| 434 gcc_assert (e == e2); | |
| 435 flush_pending_stmts (e2); | |
| 436 } | |
| 437 else | |
| 438 { | |
| 439 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 440 fprintf (dump_file, " Threaded jump %d --> %d to %d\n", | |
| 441 e->src->index, e->dest->index, local_info->bb->index); | |
| 442 | |
| 443 /* We are using BB as the duplicate. Remove the unnecessary | |
| 444 outgoing edges and statements from BB. */ | |
| 445 remove_ctrl_stmt_and_useless_edges (local_info->bb, | |
| 446 rd->outgoing_edge->dest); | |
| 447 | |
| 448 /* Fixup the flags on the single remaining edge. */ | |
| 449 single_succ_edge (local_info->bb)->flags | |
| 450 &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE | EDGE_ABNORMAL); | |
| 451 single_succ_edge (local_info->bb)->flags |= EDGE_FALLTHRU; | |
| 452 | |
| 453 /* And adjust count and frequency on BB. */ | |
| 454 local_info->bb->count = e->count; | |
| 455 local_info->bb->frequency = EDGE_FREQUENCY (e); | |
| 456 } | |
| 457 } | |
| 458 | |
| 459 /* Indicate that we actually threaded one or more jumps. */ | |
| 460 if (rd->incoming_edges) | |
| 461 local_info->jumps_threaded = true; | |
| 462 | |
| 463 return 1; | |
| 464 } | |
| 465 | |
| 466 /* Return true if this block has no executable statements other than | |
| 467 a simple ctrl flow instruction. When the number of outgoing edges | |
| 468 is one, this is equivalent to a "forwarder" block. */ | |
| 469 | |
| 470 static bool | |
| 471 redirection_block_p (basic_block bb) | |
| 472 { | |
| 473 gimple_stmt_iterator gsi; | |
| 474 | |
| 475 /* Advance to the first executable statement. */ | |
| 476 gsi = gsi_start_bb (bb); | |
| 477 while (!gsi_end_p (gsi) | |
| 478 && (gimple_code (gsi_stmt (gsi)) == GIMPLE_LABEL | |
|
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479 || is_gimple_debug (gsi_stmt (gsi)) |
| 0 | 480 || gimple_nop_p (gsi_stmt (gsi)))) |
| 481 gsi_next (&gsi); | |
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482 |
| 0 | 483 /* Check if this is an empty block. */ |
| 484 if (gsi_end_p (gsi)) | |
| 485 return true; | |
| 486 | |
| 487 /* Test that we've reached the terminating control statement. */ | |
| 488 return gsi_stmt (gsi) | |
| 489 && (gimple_code (gsi_stmt (gsi)) == GIMPLE_COND | |
| 490 || gimple_code (gsi_stmt (gsi)) == GIMPLE_GOTO | |
| 491 || gimple_code (gsi_stmt (gsi)) == GIMPLE_SWITCH); | |
| 492 } | |
| 493 | |
| 494 /* BB is a block which ends with a COND_EXPR or SWITCH_EXPR and when BB | |
| 495 is reached via one or more specific incoming edges, we know which | |
| 496 outgoing edge from BB will be traversed. | |
| 497 | |
| 498 We want to redirect those incoming edges to the target of the | |
| 499 appropriate outgoing edge. Doing so avoids a conditional branch | |
| 500 and may expose new optimization opportunities. Note that we have | |
| 501 to update dominator tree and SSA graph after such changes. | |
| 502 | |
| 503 The key to keeping the SSA graph update manageable is to duplicate | |
| 504 the side effects occurring in BB so that those side effects still | |
| 505 occur on the paths which bypass BB after redirecting edges. | |
| 506 | |
| 507 We accomplish this by creating duplicates of BB and arranging for | |
| 508 the duplicates to unconditionally pass control to one specific | |
| 509 successor of BB. We then revector the incoming edges into BB to | |
| 510 the appropriate duplicate of BB. | |
| 511 | |
| 512 If NOLOOP_ONLY is true, we only perform the threading as long as it | |
| 513 does not affect the structure of the loops in a nontrivial way. */ | |
| 514 | |
| 515 static bool | |
| 516 thread_block (basic_block bb, bool noloop_only) | |
| 517 { | |
| 518 /* E is an incoming edge into BB that we may or may not want to | |
| 519 redirect to a duplicate of BB. */ | |
| 520 edge e, e2; | |
| 521 edge_iterator ei; | |
| 522 struct local_info local_info; | |
| 523 struct loop *loop = bb->loop_father; | |
| 524 | |
| 525 /* ALL indicates whether or not all incoming edges into BB should | |
| 526 be threaded to a duplicate of BB. */ | |
| 527 bool all = true; | |
| 528 | |
| 529 /* To avoid scanning a linear array for the element we need we instead | |
| 530 use a hash table. For normal code there should be no noticeable | |
| 531 difference. However, if we have a block with a large number of | |
| 532 incoming and outgoing edges such linear searches can get expensive. */ | |
| 533 redirection_data = htab_create (EDGE_COUNT (bb->succs), | |
| 534 redirection_data_hash, | |
| 535 redirection_data_eq, | |
| 536 free); | |
| 537 | |
| 538 /* If we thread the latch of the loop to its exit, the loop ceases to | |
| 539 exist. Make sure we do not restrict ourselves in order to preserve | |
| 540 this loop. */ | |
| 541 if (loop->header == bb) | |
| 542 { | |
| 543 e = loop_latch_edge (loop); | |
| 544 e2 = (edge) e->aux; | |
| 545 | |
| 546 if (e2 && loop_exit_edge_p (loop, e2)) | |
| 547 { | |
| 548 loop->header = NULL; | |
| 549 loop->latch = NULL; | |
| 550 } | |
| 551 } | |
| 552 | |
| 553 /* Record each unique threaded destination into a hash table for | |
| 554 efficient lookups. */ | |
| 555 FOR_EACH_EDGE (e, ei, bb->preds) | |
| 556 { | |
| 557 e2 = (edge) e->aux; | |
| 558 | |
| 559 if (!e2 | |
| 560 /* If NOLOOP_ONLY is true, we only allow threading through the | |
| 561 header of a loop to exit edges. */ | |
| 562 || (noloop_only | |
| 563 && bb == bb->loop_father->header | |
| 564 && !loop_exit_edge_p (bb->loop_father, e2))) | |
| 565 { | |
| 566 all = false; | |
| 567 continue; | |
| 568 } | |
| 569 | |
| 570 update_bb_profile_for_threading (e->dest, EDGE_FREQUENCY (e), | |
| 571 e->count, (edge) e->aux); | |
| 572 | |
| 573 /* Insert the outgoing edge into the hash table if it is not | |
| 574 already in the hash table. */ | |
| 575 lookup_redirection_data (e2, e, INSERT); | |
| 576 } | |
| 577 | |
| 578 /* If we are going to thread all incoming edges to an outgoing edge, then | |
| 579 BB will become unreachable. Rather than just throwing it away, use | |
| 580 it for one of the duplicates. Mark the first incoming edge with the | |
| 581 DO_NOT_DUPLICATE attribute. */ | |
| 582 if (all) | |
| 583 { | |
| 584 edge e = (edge) EDGE_PRED (bb, 0)->aux; | |
| 585 lookup_redirection_data (e, NULL, NO_INSERT)->do_not_duplicate = true; | |
| 586 } | |
| 587 | |
| 588 /* We do not update dominance info. */ | |
| 589 free_dominance_info (CDI_DOMINATORS); | |
| 590 | |
| 591 /* Now create duplicates of BB. | |
| 592 | |
| 593 Note that for a block with a high outgoing degree we can waste | |
| 594 a lot of time and memory creating and destroying useless edges. | |
| 595 | |
| 596 So we first duplicate BB and remove the control structure at the | |
| 597 tail of the duplicate as well as all outgoing edges from the | |
| 598 duplicate. We then use that duplicate block as a template for | |
| 599 the rest of the duplicates. */ | |
| 600 local_info.template_block = NULL; | |
| 601 local_info.bb = bb; | |
| 602 local_info.jumps_threaded = false; | |
| 603 htab_traverse (redirection_data, create_duplicates, &local_info); | |
| 604 | |
| 605 /* The template does not have an outgoing edge. Create that outgoing | |
| 606 edge and update PHI nodes as the edge's target as necessary. | |
| 607 | |
| 608 We do this after creating all the duplicates to avoid creating | |
| 609 unnecessary edges. */ | |
| 610 htab_traverse (redirection_data, fixup_template_block, &local_info); | |
| 611 | |
| 612 /* The hash table traversals above created the duplicate blocks (and the | |
| 613 statements within the duplicate blocks). This loop creates PHI nodes for | |
| 614 the duplicated blocks and redirects the incoming edges into BB to reach | |
| 615 the duplicates of BB. */ | |
| 616 htab_traverse (redirection_data, redirect_edges, &local_info); | |
| 617 | |
| 618 /* Done with this block. Clear REDIRECTION_DATA. */ | |
| 619 htab_delete (redirection_data); | |
| 620 redirection_data = NULL; | |
| 621 | |
| 622 /* Indicate to our caller whether or not any jumps were threaded. */ | |
| 623 return local_info.jumps_threaded; | |
| 624 } | |
| 625 | |
| 626 /* Threads edge E through E->dest to the edge E->aux. Returns the copy | |
| 627 of E->dest created during threading, or E->dest if it was not necessary | |
| 628 to copy it (E is its single predecessor). */ | |
| 629 | |
| 630 static basic_block | |
| 631 thread_single_edge (edge e) | |
| 632 { | |
| 633 basic_block bb = e->dest; | |
| 634 edge eto = (edge) e->aux; | |
| 635 struct redirection_data rd; | |
| 636 | |
| 637 e->aux = NULL; | |
| 638 | |
| 639 thread_stats.num_threaded_edges++; | |
| 640 | |
| 641 if (single_pred_p (bb)) | |
| 642 { | |
| 643 /* If BB has just a single predecessor, we should only remove the | |
| 644 control statements at its end, and successors except for ETO. */ | |
| 645 remove_ctrl_stmt_and_useless_edges (bb, eto->dest); | |
| 646 | |
| 647 /* And fixup the flags on the single remaining edge. */ | |
| 648 eto->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE | EDGE_ABNORMAL); | |
| 649 eto->flags |= EDGE_FALLTHRU; | |
| 650 | |
| 651 return bb; | |
| 652 } | |
| 653 | |
| 654 /* Otherwise, we need to create a copy. */ | |
| 655 update_bb_profile_for_threading (bb, EDGE_FREQUENCY (e), e->count, eto); | |
| 656 | |
| 657 rd.outgoing_edge = eto; | |
| 658 | |
| 659 create_block_for_threading (bb, &rd); | |
| 660 create_edge_and_update_destination_phis (&rd); | |
| 661 | |
| 662 if (dump_file && (dump_flags & TDF_DETAILS)) | |
| 663 fprintf (dump_file, " Threaded jump %d --> %d to %d\n", | |
| 664 e->src->index, e->dest->index, rd.dup_block->index); | |
| 665 | |
| 666 rd.dup_block->count = e->count; | |
| 667 rd.dup_block->frequency = EDGE_FREQUENCY (e); | |
| 668 single_succ_edge (rd.dup_block)->count = e->count; | |
| 669 redirect_edge_and_branch (e, rd.dup_block); | |
| 670 flush_pending_stmts (e); | |
| 671 | |
| 672 return rd.dup_block; | |
| 673 } | |
| 674 | |
| 675 /* Callback for dfs_enumerate_from. Returns true if BB is different | |
| 676 from STOP and DBDS_CE_STOP. */ | |
| 677 | |
| 678 static basic_block dbds_ce_stop; | |
| 679 static bool | |
| 680 dbds_continue_enumeration_p (const_basic_block bb, const void *stop) | |
| 681 { | |
| 682 return (bb != (const_basic_block) stop | |
| 683 && bb != dbds_ce_stop); | |
| 684 } | |
| 685 | |
| 686 /* Evaluates the dominance relationship of latch of the LOOP and BB, and | |
| 687 returns the state. */ | |
| 688 | |
| 689 enum bb_dom_status | |
| 690 { | |
| 691 /* BB does not dominate latch of the LOOP. */ | |
| 692 DOMST_NONDOMINATING, | |
| 693 /* The LOOP is broken (there is no path from the header to its latch. */ | |
| 694 DOMST_LOOP_BROKEN, | |
| 695 /* BB dominates the latch of the LOOP. */ | |
| 696 DOMST_DOMINATING | |
| 697 }; | |
| 698 | |
| 699 static enum bb_dom_status | |
| 700 determine_bb_domination_status (struct loop *loop, basic_block bb) | |
| 701 { | |
| 702 basic_block *bblocks; | |
| 703 unsigned nblocks, i; | |
| 704 bool bb_reachable = false; | |
| 705 edge_iterator ei; | |
| 706 edge e; | |
| 707 | |
| 708 #ifdef ENABLE_CHECKING | |
| 709 /* This function assumes BB is a successor of LOOP->header. */ | |
| 710 { | |
| 711 bool ok = false; | |
| 712 | |
| 713 FOR_EACH_EDGE (e, ei, bb->preds) | |
| 714 { | |
| 715 if (e->src == loop->header) | |
| 716 { | |
| 717 ok = true; | |
| 718 break; | |
| 719 } | |
| 720 } | |
| 721 | |
| 722 gcc_assert (ok); | |
| 723 } | |
| 724 #endif | |
| 725 | |
| 726 if (bb == loop->latch) | |
| 727 return DOMST_DOMINATING; | |
| 728 | |
| 729 /* Check that BB dominates LOOP->latch, and that it is back-reachable | |
| 730 from it. */ | |
| 731 | |
| 732 bblocks = XCNEWVEC (basic_block, loop->num_nodes); | |
| 733 dbds_ce_stop = loop->header; | |
| 734 nblocks = dfs_enumerate_from (loop->latch, 1, dbds_continue_enumeration_p, | |
| 735 bblocks, loop->num_nodes, bb); | |
| 736 for (i = 0; i < nblocks; i++) | |
| 737 FOR_EACH_EDGE (e, ei, bblocks[i]->preds) | |
| 738 { | |
| 739 if (e->src == loop->header) | |
| 740 { | |
| 741 free (bblocks); | |
| 742 return DOMST_NONDOMINATING; | |
| 743 } | |
| 744 if (e->src == bb) | |
| 745 bb_reachable = true; | |
| 746 } | |
| 747 | |
| 748 free (bblocks); | |
| 749 return (bb_reachable ? DOMST_DOMINATING : DOMST_LOOP_BROKEN); | |
| 750 } | |
| 751 | |
| 752 /* Thread jumps through the header of LOOP. Returns true if cfg changes. | |
| 753 If MAY_PEEL_LOOP_HEADERS is false, we avoid threading from entry edges | |
| 754 to the inside of the loop. */ | |
| 755 | |
| 756 static bool | |
| 757 thread_through_loop_header (struct loop *loop, bool may_peel_loop_headers) | |
| 758 { | |
| 759 basic_block header = loop->header; | |
| 760 edge e, tgt_edge, latch = loop_latch_edge (loop); | |
| 761 edge_iterator ei; | |
| 762 basic_block tgt_bb, atgt_bb; | |
| 763 enum bb_dom_status domst; | |
| 764 | |
| 765 /* We have already threaded through headers to exits, so all the threading | |
| 766 requests now are to the inside of the loop. We need to avoid creating | |
| 767 irreducible regions (i.e., loops with more than one entry block), and | |
| 768 also loop with several latch edges, or new subloops of the loop (although | |
| 769 there are cases where it might be appropriate, it is difficult to decide, | |
| 770 and doing it wrongly may confuse other optimizers). | |
| 771 | |
| 772 We could handle more general cases here. However, the intention is to | |
| 773 preserve some information about the loop, which is impossible if its | |
| 774 structure changes significantly, in a way that is not well understood. | |
| 775 Thus we only handle few important special cases, in which also updating | |
| 776 of the loop-carried information should be feasible: | |
| 777 | |
| 778 1) Propagation of latch edge to a block that dominates the latch block | |
| 779 of a loop. This aims to handle the following idiom: | |
| 780 | |
| 781 first = 1; | |
| 782 while (1) | |
| 783 { | |
| 784 if (first) | |
| 785 initialize; | |
| 786 first = 0; | |
| 787 body; | |
| 788 } | |
| 789 | |
| 790 After threading the latch edge, this becomes | |
| 791 | |
| 792 first = 1; | |
| 793 if (first) | |
| 794 initialize; | |
| 795 while (1) | |
| 796 { | |
| 797 first = 0; | |
| 798 body; | |
| 799 } | |
| 800 | |
| 801 The original header of the loop is moved out of it, and we may thread | |
| 802 the remaining edges through it without further constraints. | |
| 803 | |
| 804 2) All entry edges are propagated to a single basic block that dominates | |
| 805 the latch block of the loop. This aims to handle the following idiom | |
| 806 (normally created for "for" loops): | |
| 807 | |
| 808 i = 0; | |
| 809 while (1) | |
| 810 { | |
| 811 if (i >= 100) | |
| 812 break; | |
| 813 body; | |
| 814 i++; | |
| 815 } | |
| 816 | |
| 817 This becomes | |
| 818 | |
| 819 i = 0; | |
| 820 while (1) | |
| 821 { | |
| 822 body; | |
| 823 i++; | |
| 824 if (i >= 100) | |
| 825 break; | |
| 826 } | |
| 827 */ | |
| 828 | |
| 829 /* Threading through the header won't improve the code if the header has just | |
| 830 one successor. */ | |
| 831 if (single_succ_p (header)) | |
| 832 goto fail; | |
| 833 | |
| 834 if (latch->aux) | |
| 835 { | |
| 836 tgt_edge = (edge) latch->aux; | |
| 837 tgt_bb = tgt_edge->dest; | |
| 838 } | |
| 839 else if (!may_peel_loop_headers | |
| 840 && !redirection_block_p (loop->header)) | |
| 841 goto fail; | |
| 842 else | |
| 843 { | |
| 844 tgt_bb = NULL; | |
| 845 tgt_edge = NULL; | |
| 846 FOR_EACH_EDGE (e, ei, header->preds) | |
| 847 { | |
| 848 if (!e->aux) | |
| 849 { | |
| 850 if (e == latch) | |
| 851 continue; | |
| 852 | |
| 853 /* If latch is not threaded, and there is a header | |
| 854 edge that is not threaded, we would create loop | |
| 855 with multiple entries. */ | |
| 856 goto fail; | |
| 857 } | |
| 858 | |
| 859 tgt_edge = (edge) e->aux; | |
| 860 atgt_bb = tgt_edge->dest; | |
| 861 if (!tgt_bb) | |
| 862 tgt_bb = atgt_bb; | |
| 863 /* Two targets of threading would make us create loop | |
| 864 with multiple entries. */ | |
| 865 else if (tgt_bb != atgt_bb) | |
| 866 goto fail; | |
| 867 } | |
| 868 | |
| 869 if (!tgt_bb) | |
| 870 { | |
| 871 /* There are no threading requests. */ | |
| 872 return false; | |
| 873 } | |
| 874 | |
| 875 /* Redirecting to empty loop latch is useless. */ | |
| 876 if (tgt_bb == loop->latch | |
| 877 && empty_block_p (loop->latch)) | |
| 878 goto fail; | |
| 879 } | |
| 880 | |
| 881 /* The target block must dominate the loop latch, otherwise we would be | |
| 882 creating a subloop. */ | |
| 883 domst = determine_bb_domination_status (loop, tgt_bb); | |
| 884 if (domst == DOMST_NONDOMINATING) | |
| 885 goto fail; | |
| 886 if (domst == DOMST_LOOP_BROKEN) | |
| 887 { | |
| 888 /* If the loop ceased to exist, mark it as such, and thread through its | |
| 889 original header. */ | |
| 890 loop->header = NULL; | |
| 891 loop->latch = NULL; | |
| 892 return thread_block (header, false); | |
| 893 } | |
| 894 | |
| 895 if (tgt_bb->loop_father->header == tgt_bb) | |
| 896 { | |
| 897 /* If the target of the threading is a header of a subloop, we need | |
| 898 to create a preheader for it, so that the headers of the two loops | |
| 899 do not merge. */ | |
| 900 if (EDGE_COUNT (tgt_bb->preds) > 2) | |
| 901 { | |
| 902 tgt_bb = create_preheader (tgt_bb->loop_father, 0); | |
| 903 gcc_assert (tgt_bb != NULL); | |
| 904 } | |
| 905 else | |
| 906 tgt_bb = split_edge (tgt_edge); | |
| 907 } | |
|
55
77e2b8dfacca
update it from 4.4.3 to 4.5.0
ryoma <e075725@ie.u-ryukyu.ac.jp>
parents:
0
diff
changeset
|
908 |
| 0 | 909 if (latch->aux) |
| 910 { | |
| 911 /* First handle the case latch edge is redirected. */ | |
| 912 loop->latch = thread_single_edge (latch); | |
| 913 gcc_assert (single_succ (loop->latch) == tgt_bb); | |
| 914 loop->header = tgt_bb; | |
| 915 | |
| 916 /* Thread the remaining edges through the former header. */ | |
| 917 thread_block (header, false); | |
| 918 } | |
| 919 else | |
| 920 { | |
| 921 basic_block new_preheader; | |
| 922 | |
| 923 /* Now consider the case entry edges are redirected to the new entry | |
| 924 block. Remember one entry edge, so that we can find the new | |
| 925 preheader (its destination after threading). */ | |
| 926 FOR_EACH_EDGE (e, ei, header->preds) | |
| 927 { | |
| 928 if (e->aux) | |
| 929 break; | |
| 930 } | |
| 931 | |
| 932 /* The duplicate of the header is the new preheader of the loop. Ensure | |
| 933 that it is placed correctly in the loop hierarchy. */ | |
| 934 set_loop_copy (loop, loop_outer (loop)); | |
| 935 | |
| 936 thread_block (header, false); | |
| 937 set_loop_copy (loop, NULL); | |
| 938 new_preheader = e->dest; | |
| 939 | |
| 940 /* Create the new latch block. This is always necessary, as the latch | |
| 941 must have only a single successor, but the original header had at | |
| 942 least two successors. */ | |
| 943 loop->latch = NULL; | |
| 944 mfb_kj_edge = single_succ_edge (new_preheader); | |
| 945 loop->header = mfb_kj_edge->dest; | |
| 946 latch = make_forwarder_block (tgt_bb, mfb_keep_just, NULL); | |
| 947 loop->header = latch->dest; | |
| 948 loop->latch = latch->src; | |
| 949 } | |
|
55
77e2b8dfacca
update it from 4.4.3 to 4.5.0
ryoma <e075725@ie.u-ryukyu.ac.jp>
parents:
0
diff
changeset
|
950 |
| 0 | 951 return true; |
| 952 | |
| 953 fail: | |
| 954 /* We failed to thread anything. Cancel the requests. */ | |
| 955 FOR_EACH_EDGE (e, ei, header->preds) | |
| 956 { | |
| 957 e->aux = NULL; | |
| 958 } | |
| 959 return false; | |
| 960 } | |
| 961 | |
| 962 /* Walk through the registered jump threads and convert them into a | |
| 963 form convenient for this pass. | |
| 964 | |
| 965 Any block which has incoming edges threaded to outgoing edges | |
| 966 will have its entry in THREADED_BLOCK set. | |
| 967 | |
| 968 Any threaded edge will have its new outgoing edge stored in the | |
| 969 original edge's AUX field. | |
| 970 | |
| 971 This form avoids the need to walk all the edges in the CFG to | |
| 972 discover blocks which need processing and avoids unnecessary | |
| 973 hash table lookups to map from threaded edge to new target. */ | |
| 974 | |
| 975 static void | |
| 976 mark_threaded_blocks (bitmap threaded_blocks) | |
| 977 { | |
| 978 unsigned int i; | |
| 979 bitmap_iterator bi; | |
| 980 bitmap tmp = BITMAP_ALLOC (NULL); | |
| 981 basic_block bb; | |
| 982 edge e; | |
| 983 edge_iterator ei; | |
| 984 | |
| 985 for (i = 0; i < VEC_length (edge, threaded_edges); i += 2) | |
| 986 { | |
| 987 edge e = VEC_index (edge, threaded_edges, i); | |
| 988 edge e2 = VEC_index (edge, threaded_edges, i + 1); | |
| 989 | |
| 990 e->aux = e2; | |
| 991 bitmap_set_bit (tmp, e->dest->index); | |
| 992 } | |
| 993 | |
| 994 /* If optimizing for size, only thread through block if we don't have | |
| 995 to duplicate it or it's an otherwise empty redirection block. */ | |
| 996 if (optimize_function_for_size_p (cfun)) | |
| 997 { | |
| 998 EXECUTE_IF_SET_IN_BITMAP (tmp, 0, i, bi) | |
| 999 { | |
| 1000 bb = BASIC_BLOCK (i); | |
| 1001 if (EDGE_COUNT (bb->preds) > 1 | |
| 1002 && !redirection_block_p (bb)) | |
| 1003 { | |
| 1004 FOR_EACH_EDGE (e, ei, bb->preds) | |
| 1005 e->aux = NULL; | |
| 1006 } | |
| 1007 else | |
| 1008 bitmap_set_bit (threaded_blocks, i); | |
| 1009 } | |
| 1010 } | |
| 1011 else | |
| 1012 bitmap_copy (threaded_blocks, tmp); | |
| 1013 | |
| 1014 BITMAP_FREE(tmp); | |
| 1015 } | |
| 1016 | |
| 1017 | |
| 1018 /* Walk through all blocks and thread incoming edges to the appropriate | |
| 1019 outgoing edge for each edge pair recorded in THREADED_EDGES. | |
| 1020 | |
| 1021 It is the caller's responsibility to fix the dominance information | |
| 1022 and rewrite duplicated SSA_NAMEs back into SSA form. | |
| 1023 | |
| 1024 If MAY_PEEL_LOOP_HEADERS is false, we avoid threading edges through | |
| 1025 loop headers if it does not simplify the loop. | |
| 1026 | |
| 1027 Returns true if one or more edges were threaded, false otherwise. */ | |
| 1028 | |
| 1029 bool | |
| 1030 thread_through_all_blocks (bool may_peel_loop_headers) | |
| 1031 { | |
| 1032 bool retval = false; | |
| 1033 unsigned int i; | |
| 1034 bitmap_iterator bi; | |
| 1035 bitmap threaded_blocks; | |
| 1036 struct loop *loop; | |
| 1037 loop_iterator li; | |
| 1038 | |
| 1039 /* We must know about loops in order to preserve them. */ | |
| 1040 gcc_assert (current_loops != NULL); | |
| 1041 | |
| 1042 if (threaded_edges == NULL) | |
| 1043 return false; | |
| 1044 | |
| 1045 threaded_blocks = BITMAP_ALLOC (NULL); | |
| 1046 memset (&thread_stats, 0, sizeof (thread_stats)); | |
| 1047 | |
| 1048 mark_threaded_blocks (threaded_blocks); | |
| 1049 | |
| 1050 initialize_original_copy_tables (); | |
| 1051 | |
| 1052 /* First perform the threading requests that do not affect | |
| 1053 loop structure. */ | |
| 1054 EXECUTE_IF_SET_IN_BITMAP (threaded_blocks, 0, i, bi) | |
| 1055 { | |
| 1056 basic_block bb = BASIC_BLOCK (i); | |
| 1057 | |
| 1058 if (EDGE_COUNT (bb->preds) > 0) | |
| 1059 retval |= thread_block (bb, true); | |
| 1060 } | |
| 1061 | |
| 1062 /* Then perform the threading through loop headers. We start with the | |
| 1063 innermost loop, so that the changes in cfg we perform won't affect | |
| 1064 further threading. */ | |
| 1065 FOR_EACH_LOOP (li, loop, LI_FROM_INNERMOST) | |
| 1066 { | |
| 1067 if (!loop->header | |
| 1068 || !bitmap_bit_p (threaded_blocks, loop->header->index)) | |
| 1069 continue; | |
| 1070 | |
| 1071 retval |= thread_through_loop_header (loop, may_peel_loop_headers); | |
| 1072 } | |
| 1073 | |
| 1074 statistics_counter_event (cfun, "Jumps threaded", | |
| 1075 thread_stats.num_threaded_edges); | |
| 1076 | |
| 1077 free_original_copy_tables (); | |
| 1078 | |
| 1079 BITMAP_FREE (threaded_blocks); | |
| 1080 threaded_blocks = NULL; | |
| 1081 VEC_free (edge, heap, threaded_edges); | |
| 1082 threaded_edges = NULL; | |
| 1083 | |
| 1084 if (retval) | |
| 1085 loops_state_set (LOOPS_NEED_FIXUP); | |
| 1086 | |
| 1087 return retval; | |
| 1088 } | |
| 1089 | |
| 1090 /* Register a jump threading opportunity. We queue up all the jump | |
| 1091 threading opportunities discovered by a pass and update the CFG | |
| 1092 and SSA form all at once. | |
| 1093 | |
| 1094 E is the edge we can thread, E2 is the new target edge, i.e., we | |
| 1095 are effectively recording that E->dest can be changed to E2->dest | |
| 1096 after fixing the SSA graph. */ | |
| 1097 | |
| 1098 void | |
| 1099 register_jump_thread (edge e, edge e2) | |
| 1100 { | |
| 1101 if (threaded_edges == NULL) | |
| 1102 threaded_edges = VEC_alloc (edge, heap, 10); | |
| 1103 | |
| 1104 VEC_safe_push (edge, heap, threaded_edges, e); | |
| 1105 VEC_safe_push (edge, heap, threaded_edges, e2); | |
| 1106 } |