* tree-cfg.c (tree_find_edge_insert_loc): Handle naked RETURN_EXPR.
[official-gcc.git] / gcc / tree-ssa-threadupdate.c
blob1b7733b0c9b878f3d26711c8f5a2f18568dcc2c0
1 /* Thread edges through blocks and update the control flow and SSA graphs.
2 Copyright (C) 2004, 2005 Free Software Foundation, Inc.
4 This file is part of GCC.
6 GCC is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 2, or (at your option)
9 any later version.
11 GCC is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with GCC; see the file COPYING. If not, write to
18 the Free Software Foundation, 51 Franklin Street, Fifth Floor,
19 Boston, MA 02110-1301, USA. */
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"
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.
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.
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.
50 2. Remove the control statement at the end of B' and all outgoing edges
51 except B'->C.
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.
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.
62 5. Change the edge A->B to A->B'.
64 5a. This automatically deletes any PHI arguments associated with the
65 edge A->B in B.
67 5b. This automatically associates each new argument added in step 4
68 with the edge A->B'.
70 6. Repeat for other incoming edges into B.
72 7. Put the duplicated resources in B and all the B' blocks into SSA form.
74 Note that block duplication can be minimized by first collecting the
75 the 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.
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. */
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.
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. */
97 struct el
99 edge e;
100 struct el *next;
103 /* Main data structure recording information regarding B's duplicate
104 blocks. */
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. */
111 struct redirection_data
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;
117 /* An outgoing edge from B. DUP_BLOCK will have OUTGOING_EDGE->dest as
118 its single successor. */
119 edge outgoing_edge;
121 /* A list of incoming edges which we want to thread to
122 OUTGOING_EDGE->dest. */
123 struct el *incoming_edges;
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;
131 /* Main data structure to hold information for duplicates of BB. */
132 static htab_t redirection_data;
134 bool rediscover_loops_after_threading;
136 /* Data structure of information to pass to hash table traversal routines. */
137 struct local_info
139 /* The current block we are working on. */
140 basic_block bb;
142 /* A template copy of BB with no outgoing edges or control statement that
143 we use for creating copies. */
144 basic_block template_block;
146 /* TRUE if we thread one or more jumps, FALSE otherwise. */
147 bool jumps_threaded;
150 /* Jump threading statistics. */
152 struct thread_stats_d
154 unsigned long num_threaded_edges;
157 struct thread_stats_d thread_stats;
160 /* Remove the last statement in block BB if it is a control statement
161 Also remove all outgoing edges except the edge which reaches DEST_BB.
162 If DEST_BB is NULL, then remove all outgoing edges. */
164 static void
165 remove_ctrl_stmt_and_useless_edges (basic_block bb, basic_block dest_bb)
167 block_stmt_iterator bsi;
168 edge e;
169 edge_iterator ei;
171 bsi = bsi_last (bb);
173 /* If the duplicate ends with a control statement, then remove it.
175 Note that if we are duplicating the template block rather than the
176 original basic block, then the duplicate might not have any real
177 statements in it. */
178 if (!bsi_end_p (bsi)
179 && bsi_stmt (bsi)
180 && (TREE_CODE (bsi_stmt (bsi)) == COND_EXPR
181 || TREE_CODE (bsi_stmt (bsi)) == GOTO_EXPR
182 || TREE_CODE (bsi_stmt (bsi)) == SWITCH_EXPR))
183 bsi_remove (&bsi);
185 for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
187 if (e->dest != dest_bb)
188 remove_edge (e);
189 else
190 ei_next (&ei);
194 /* Create a duplicate of BB which only reaches the destination of the edge
195 stored in RD. Record the duplicate block in RD. */
197 static void
198 create_block_for_threading (basic_block bb, struct redirection_data *rd)
200 /* We can use the generic block duplication code and simply remove
201 the stuff we do not need. */
202 rd->dup_block = duplicate_block (bb, NULL, NULL);
204 /* Zero out the profile, since the block is unreachable for now. */
205 rd->dup_block->frequency = 0;
206 rd->dup_block->count = 0;
208 /* The call to duplicate_block will copy everything, including the
209 useless COND_EXPR or SWITCH_EXPR at the end of BB. We just remove
210 the useless COND_EXPR or SWITCH_EXPR here rather than having a
211 specialized block copier. We also remove all outgoing edges
212 from the duplicate block. The appropriate edge will be created
213 later. */
214 remove_ctrl_stmt_and_useless_edges (rd->dup_block, NULL);
217 /* Hashing and equality routines for our hash table. */
218 static hashval_t
219 redirection_data_hash (const void *p)
221 edge e = ((struct redirection_data *)p)->outgoing_edge;
222 return e->dest->index;
225 static int
226 redirection_data_eq (const void *p1, const void *p2)
228 edge e1 = ((struct redirection_data *)p1)->outgoing_edge;
229 edge e2 = ((struct redirection_data *)p2)->outgoing_edge;
231 return e1 == e2;
234 /* Given an outgoing edge E lookup and return its entry in our hash table.
236 If INSERT is true, then we insert the entry into the hash table if
237 it is not already present. INCOMING_EDGE is added to the list of incoming
238 edges associated with E in the hash table. */
240 static struct redirection_data *
241 lookup_redirection_data (edge e, edge incoming_edge, enum insert_option insert)
243 void **slot;
244 struct redirection_data *elt;
246 /* Build a hash table element so we can see if E is already
247 in the table. */
248 elt = xmalloc (sizeof (struct redirection_data));
249 elt->outgoing_edge = e;
250 elt->dup_block = NULL;
251 elt->do_not_duplicate = false;
252 elt->incoming_edges = NULL;
254 slot = htab_find_slot (redirection_data, elt, insert);
256 /* This will only happen if INSERT is false and the entry is not
257 in the hash table. */
258 if (slot == NULL)
260 free (elt);
261 return NULL;
264 /* This will only happen if E was not in the hash table and
265 INSERT is true. */
266 if (*slot == NULL)
268 *slot = (void *)elt;
269 elt->incoming_edges = xmalloc (sizeof (struct el));
270 elt->incoming_edges->e = incoming_edge;
271 elt->incoming_edges->next = NULL;
272 return elt;
274 /* E was in the hash table. */
275 else
277 /* Free ELT as we do not need it anymore, we will extract the
278 relevant entry from the hash table itself. */
279 free (elt);
281 /* Get the entry stored in the hash table. */
282 elt = (struct redirection_data *) *slot;
284 /* If insertion was requested, then we need to add INCOMING_EDGE
285 to the list of incoming edges associated with E. */
286 if (insert)
288 struct el *el = xmalloc (sizeof (struct el));
289 el->next = elt->incoming_edges;
290 el->e = incoming_edge;
291 elt->incoming_edges = el;
294 return elt;
298 /* Given a duplicate block and its single destination (both stored
299 in RD). Create an edge between the duplicate and its single
300 destination.
302 Add an additional argument to any PHI nodes at the single
303 destination. */
305 static void
306 create_edge_and_update_destination_phis (struct redirection_data *rd)
308 edge e = make_edge (rd->dup_block, rd->outgoing_edge->dest, EDGE_FALLTHRU);
309 tree phi;
311 e->probability = REG_BR_PROB_BASE;
312 e->count = rd->dup_block->count;
314 /* If there are any PHI nodes at the destination of the outgoing edge
315 from the duplicate block, then we will need to add a new argument
316 to them. The argument should have the same value as the argument
317 associated with the outgoing edge stored in RD. */
318 for (phi = phi_nodes (e->dest); phi; phi = PHI_CHAIN (phi))
320 int indx = rd->outgoing_edge->dest_idx;
321 add_phi_arg (phi, PHI_ARG_DEF (phi, indx), e);
325 /* Hash table traversal callback routine to create duplicate blocks. */
327 static int
328 create_duplicates (void **slot, void *data)
330 struct redirection_data *rd = (struct redirection_data *) *slot;
331 struct local_info *local_info = (struct local_info *)data;
333 /* If this entry should not have a duplicate created, then there's
334 nothing to do. */
335 if (rd->do_not_duplicate)
336 return 1;
338 /* Create a template block if we have not done so already. Otherwise
339 use the template to create a new block. */
340 if (local_info->template_block == NULL)
342 create_block_for_threading (local_info->bb, rd);
343 local_info->template_block = rd->dup_block;
345 /* We do not create any outgoing edges for the template. We will
346 take care of that in a later traversal. That way we do not
347 create edges that are going to just be deleted. */
349 else
351 create_block_for_threading (local_info->template_block, rd);
353 /* Go ahead and wire up outgoing edges and update PHIs for the duplicate
354 block. */
355 create_edge_and_update_destination_phis (rd);
358 /* Keep walking the hash table. */
359 return 1;
362 /* We did not create any outgoing edges for the template block during
363 block creation. This hash table traversal callback creates the
364 outgoing edge for the template block. */
366 static int
367 fixup_template_block (void **slot, void *data)
369 struct redirection_data *rd = (struct redirection_data *) *slot;
370 struct local_info *local_info = (struct local_info *)data;
372 /* If this is the template block, then create its outgoing edges
373 and halt the hash table traversal. */
374 if (rd->dup_block && rd->dup_block == local_info->template_block)
376 create_edge_and_update_destination_phis (rd);
377 return 0;
380 return 1;
383 /* Not all jump threading requests are useful. In particular some
384 jump threading requests can create irreducible regions which are
385 undesirable.
387 This routine will examine the BB's incoming edges for jump threading
388 requests which, if acted upon, would create irreducible regions. Any
389 such jump threading requests found will be pruned away. */
391 static void
392 prune_undesirable_thread_requests (basic_block bb)
394 edge e;
395 edge_iterator ei;
396 bool may_create_irreducible_region = false;
397 unsigned int num_outgoing_edges_into_loop = 0;
399 /* For the heuristics below, we need to know if BB has more than
400 one outgoing edge into a loop. */
401 FOR_EACH_EDGE (e, ei, bb->succs)
402 num_outgoing_edges_into_loop += ((e->flags & EDGE_LOOP_EXIT) == 0);
404 if (num_outgoing_edges_into_loop > 1)
406 edge backedge = NULL;
408 /* Consider the effect of threading the edge (0, 1) to 2 on the left
409 CFG to produce the right CFG:
414 1<--+ 2<--------+
415 / \ | | |
416 2 3 | 4<----+ |
417 \ / | / \ | |
418 4---+ E 1-- | --+
419 | | |
420 E 3---+
423 Threading the (0, 1) edge to 2 effectively creates two loops
424 (2, 4, 1) and (4, 1, 3) which are neither disjoint nor nested.
425 This is not good.
427 However, we do need to be able to thread (0, 1) to 2 or 3
428 in the left CFG below (which creates the middle and right
429 CFGs with nested loops).
431 0 0 0
432 | | |
433 1<--+ 2<----+ 3<-+<-+
434 /| | | | | | |
435 2 | | 3<-+ | 1--+ |
436 \| | | | | | |
437 3---+ 1--+--+ 2-----+
440 A safe heuristic appears to be to only allow threading if BB
441 has a single incoming backedge from one of its direct successors. */
443 FOR_EACH_EDGE (e, ei, bb->preds)
445 if (e->flags & EDGE_DFS_BACK)
447 if (backedge)
449 backedge = NULL;
450 break;
452 else
454 backedge = e;
459 if (backedge && find_edge (bb, backedge->src))
461 else
462 may_create_irreducible_region = true;
464 else
466 edge dest = NULL;
468 /* If we thread across the loop entry block (BB) into the
469 loop and BB is still reached from outside the loop, then
470 we would create an irreducible CFG. Consider the effect
471 of threading the edge (1, 4) to 5 on the left CFG to produce
472 the right CFG
475 / \ / \
476 1 2 1 2
477 \ / | |
478 4<----+ 5<->4
479 / \ | |
480 E 5---+ E
483 Threading the (1, 4) edge to 5 creates two entry points
484 into the loop (4, 5) (one from block 1, the other from
485 block 2). A classic irreducible region.
487 So look at all of BB's incoming edges which are not
488 backedges and which are not threaded to the loop exit.
489 If that subset of incoming edges do not all thread
490 to the same block, then threading any of them will create
491 an irreducible region. */
493 FOR_EACH_EDGE (e, ei, bb->preds)
495 edge e2;
497 /* We ignore back edges for now. This may need refinement
498 as threading a backedge creates an inner loop which
499 we would need to verify has a single entry point.
501 If all backedges thread to new locations, then this
502 block will no longer have incoming backedges and we
503 need not worry about creating irreducible regions
504 by threading through BB. I don't think this happens
505 enough in practice to worry about it. */
506 if (e->flags & EDGE_DFS_BACK)
507 continue;
509 /* If the incoming edge threads to the loop exit, then it
510 is clearly safe. */
511 e2 = e->aux;
512 if (e2 && (e2->flags & EDGE_LOOP_EXIT))
513 continue;
515 /* E enters the loop header and is not threaded. We can
516 not allow any other incoming edges to thread into
517 the loop as that would create an irreducible region. */
518 if (!e2)
520 may_create_irreducible_region = true;
521 break;
524 /* We know that this incoming edge threads to a block inside
525 the loop. This edge must thread to the same target in
526 the loop as any previously seen threaded edges. Otherwise
527 we will create an irreducible region. */
528 if (!dest)
529 dest = e2;
530 else if (e2 != dest)
532 may_create_irreducible_region = true;
533 break;
538 /* If we might create an irreducible region, then cancel any of
539 the jump threading requests for incoming edges which are
540 not backedges and which do not thread to the exit block. */
541 if (may_create_irreducible_region)
543 FOR_EACH_EDGE (e, ei, bb->preds)
545 edge e2;
547 /* Ignore back edges. */
548 if (e->flags & EDGE_DFS_BACK)
549 continue;
551 e2 = e->aux;
553 /* If this incoming edge was not threaded, then there is
554 nothing to do. */
555 if (!e2)
556 continue;
558 /* If this incoming edge threaded to the loop exit,
559 then it can be ignored as it is safe. */
560 if (e2->flags & EDGE_LOOP_EXIT)
561 continue;
563 if (e2)
565 /* This edge threaded into the loop and the jump thread
566 request must be cancelled. */
567 if (dump_file && (dump_flags & TDF_DETAILS))
568 fprintf (dump_file, " Not threading jump %d --> %d to %d\n",
569 e->src->index, e->dest->index, e2->dest->index);
570 e->aux = NULL;
576 /* Hash table traversal callback to redirect each incoming edge
577 associated with this hash table element to its new destination. */
579 static int
580 redirect_edges (void **slot, void *data)
582 struct redirection_data *rd = (struct redirection_data *) *slot;
583 struct local_info *local_info = (struct local_info *)data;
584 struct el *next, *el;
586 /* Walk over all the incoming edges associated associated with this
587 hash table entry. */
588 for (el = rd->incoming_edges; el; el = next)
590 edge e = el->e;
592 /* Go ahead and free this element from the list. Doing this now
593 avoids the need for another list walk when we destroy the hash
594 table. */
595 next = el->next;
596 free (el);
598 /* Go ahead and clear E->aux. It's not needed anymore and failure
599 to clear it will cause all kinds of unpleasant problems later. */
600 e->aux = NULL;
602 thread_stats.num_threaded_edges++;
604 if (rd->dup_block)
606 edge e2;
608 if (dump_file && (dump_flags & TDF_DETAILS))
609 fprintf (dump_file, " Threaded jump %d --> %d to %d\n",
610 e->src->index, e->dest->index, rd->dup_block->index);
612 rd->dup_block->count += e->count;
613 rd->dup_block->frequency += EDGE_FREQUENCY (e);
614 EDGE_SUCC (rd->dup_block, 0)->count += e->count;
615 /* Redirect the incoming edge to the appropriate duplicate
616 block. */
617 e2 = redirect_edge_and_branch (e, rd->dup_block);
618 flush_pending_stmts (e2);
620 if ((dump_file && (dump_flags & TDF_DETAILS))
621 && e->src != e2->src)
622 fprintf (dump_file, " basic block %d created\n", e2->src->index);
624 else
626 if (dump_file && (dump_flags & TDF_DETAILS))
627 fprintf (dump_file, " Threaded jump %d --> %d to %d\n",
628 e->src->index, e->dest->index, local_info->bb->index);
630 /* We are using BB as the duplicate. Remove the unnecessary
631 outgoing edges and statements from BB. */
632 remove_ctrl_stmt_and_useless_edges (local_info->bb,
633 rd->outgoing_edge->dest);
635 /* And fixup the flags on the single remaining edge. */
636 single_succ_edge (local_info->bb)->flags
637 &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE | EDGE_ABNORMAL);
638 single_succ_edge (local_info->bb)->flags |= EDGE_FALLTHRU;
642 /* Indicate that we actually threaded one or more jumps. */
643 if (rd->incoming_edges)
644 local_info->jumps_threaded = true;
646 return 1;
649 /* BB is a block which ends with a COND_EXPR or SWITCH_EXPR and when BB
650 is reached via one or more specific incoming edges, we know which
651 outgoing edge from BB will be traversed.
653 We want to redirect those incoming edges to the target of the
654 appropriate outgoing edge. Doing so avoids a conditional branch
655 and may expose new optimization opportunities. Note that we have
656 to update dominator tree and SSA graph after such changes.
658 The key to keeping the SSA graph update manageable is to duplicate
659 the side effects occurring in BB so that those side effects still
660 occur on the paths which bypass BB after redirecting edges.
662 We accomplish this by creating duplicates of BB and arranging for
663 the duplicates to unconditionally pass control to one specific
664 successor of BB. We then revector the incoming edges into BB to
665 the appropriate duplicate of BB.
667 BB and its duplicates will have assignments to the same set of
668 SSA_NAMEs. Right now, we just call into update_ssa to update the
669 SSA graph for those names.
671 We are also going to experiment with a true incremental update
672 scheme for the duplicated resources. One of the interesting
673 properties we can exploit here is that all the resources set
674 in BB will have the same IDFS, so we have one IDFS computation
675 per block with incoming threaded edges, which can lower the
676 cost of the true incremental update algorithm. */
678 static bool
679 thread_block (basic_block bb)
681 /* E is an incoming edge into BB that we may or may not want to
682 redirect to a duplicate of BB. */
683 edge e;
684 edge_iterator ei;
685 struct local_info local_info;
687 /* FOUND_BACKEDGE indicates that we found an incoming backedge
688 into BB, in which case we may ignore certain jump threads
689 to avoid creating irreducible regions. */
690 bool found_backedge = false;
692 /* ALL indicates whether or not all incoming edges into BB should
693 be threaded to a duplicate of BB. */
694 bool all = true;
696 /* To avoid scanning a linear array for the element we need we instead
697 use a hash table. For normal code there should be no noticeable
698 difference. However, if we have a block with a large number of
699 incoming and outgoing edges such linear searches can get expensive. */
700 redirection_data = htab_create (EDGE_COUNT (bb->succs),
701 redirection_data_hash,
702 redirection_data_eq,
703 free);
705 FOR_EACH_EDGE (e, ei, bb->preds)
706 found_backedge |= ((e->flags & EDGE_DFS_BACK) != 0);
708 /* If BB has incoming backedges, then threading across BB might
709 introduce an irreducible region, which would be undesirable
710 as that inhibits various optimizations later. Prune away
711 any jump threading requests which we know will result in
712 an irreducible region. */
713 if (found_backedge)
714 prune_undesirable_thread_requests (bb);
716 /* Record each unique threaded destination into a hash table for
717 efficient lookups. */
718 FOR_EACH_EDGE (e, ei, bb->preds)
720 if (!e->aux)
722 all = false;
724 else
726 edge e2 = e->aux;
727 update_bb_profile_for_threading (e->dest, EDGE_FREQUENCY (e),
728 e->count, e->aux);
730 /* If we thread to a loop exit edge, then we will need to
731 rediscover the loop exit edges. While it may seem that
732 the new edge is a loop exit edge, that is not the case.
733 Consider threading the edge (5,6) to E in the CFG on the
734 left which creates the CFG on the right:
737 0<--+ 0<---+
738 / \ | / \ |
739 1 2 | 1 2 |
740 / \ | | / \ | |
741 3 4 | | 3 4 6--+
742 \ / | | \ /
743 5 | | 5
744 \ / | |
745 6---+ E
749 After threading, the edge (0, 1) is the loop exit edge and
750 the nodes 0, 2, 6 are the only nodes in the loop. */
751 if (e2->flags & EDGE_LOOP_EXIT)
752 rediscover_loops_after_threading = true;
754 /* Insert the outgoing edge into the hash table if it is not
755 already in the hash table. */
756 lookup_redirection_data (e2, e, INSERT);
760 /* If we are going to thread all incoming edges to an outgoing edge, then
761 BB will become unreachable. Rather than just throwing it away, use
762 it for one of the duplicates. Mark the first incoming edge with the
763 DO_NOT_DUPLICATE attribute. */
764 if (all)
766 edge e = EDGE_PRED (bb, 0)->aux;
767 lookup_redirection_data (e, NULL, NO_INSERT)->do_not_duplicate = true;
770 /* Now create duplicates of BB.
772 Note that for a block with a high outgoing degree we can waste
773 a lot of time and memory creating and destroying useless edges.
775 So we first duplicate BB and remove the control structure at the
776 tail of the duplicate as well as all outgoing edges from the
777 duplicate. We then use that duplicate block as a template for
778 the rest of the duplicates. */
779 local_info.template_block = NULL;
780 local_info.bb = bb;
781 local_info.jumps_threaded = false;
782 htab_traverse (redirection_data, create_duplicates, &local_info);
784 /* The template does not have an outgoing edge. Create that outgoing
785 edge and update PHI nodes as the edge's target as necessary.
787 We do this after creating all the duplicates to avoid creating
788 unnecessary edges. */
789 htab_traverse (redirection_data, fixup_template_block, &local_info);
791 /* The hash table traversals above created the duplicate blocks (and the
792 statements within the duplicate blocks). This loop creates PHI nodes for
793 the duplicated blocks and redirects the incoming edges into BB to reach
794 the duplicates of BB. */
795 htab_traverse (redirection_data, redirect_edges, &local_info);
797 /* Done with this block. Clear REDIRECTION_DATA. */
798 htab_delete (redirection_data);
799 redirection_data = NULL;
801 /* Indicate to our caller whether or not any jumps were threaded. */
802 return local_info.jumps_threaded;
805 /* Walk through all blocks and thread incoming edges to the block's
806 destinations as requested. This is the only entry point into this
807 file.
809 Blocks which have one or more incoming edges have INCOMING_EDGE_THREADED
810 set in the block's annotation.
812 Each edge that should be threaded has the new destination edge stored in
813 the original edge's AUX field.
815 This routine (or one of its callees) will clear INCOMING_EDGE_THREADED
816 in the block annotations and the AUX field in the edges.
818 It is the caller's responsibility to fix the dominance information
819 and rewrite duplicated SSA_NAMEs back into SSA form.
821 Returns true if one or more edges were threaded, false otherwise. */
823 bool
824 thread_through_all_blocks (bitmap threaded_blocks)
826 bool retval = false;
827 unsigned int i;
828 bitmap_iterator bi;
830 rediscover_loops_after_threading = false;
831 memset (&thread_stats, 0, sizeof (thread_stats));
833 EXECUTE_IF_SET_IN_BITMAP (threaded_blocks, 0, i, bi)
835 basic_block bb = BASIC_BLOCK (i);
837 if (EDGE_COUNT (bb->preds) > 0)
838 retval |= thread_block (bb);
841 if (dump_file && (dump_flags & TDF_STATS))
842 fprintf (dump_file, "\nJumps threaded: %lu\n",
843 thread_stats.num_threaded_edges);
845 return retval;