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[official-gcc.git] / gcc / tree-ssa-threadupdate.c
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1 /* Thread edges through blocks and update the control flow and SSA graphs.
2 Copyright (C) 2004, 2005, 2006 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 /* Data structure of information to pass to hash table traversal routines. */
135 struct local_info
137 /* The current block we are working on. */
138 basic_block bb;
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;
144 /* TRUE if we thread one or more jumps, FALSE otherwise. */
145 bool jumps_threaded;
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 DEF_VEC_ALLOC_P(edge,heap);
153 static VEC(edge,heap) *threaded_edges;
156 /* Jump threading statistics. */
158 struct thread_stats_d
160 unsigned long num_threaded_edges;
163 struct thread_stats_d thread_stats;
166 /* Remove the last statement in block BB if it is a control statement
167 Also remove all outgoing edges except the edge which reaches DEST_BB.
168 If DEST_BB is NULL, then remove all outgoing edges. */
170 static void
171 remove_ctrl_stmt_and_useless_edges (basic_block bb, basic_block dest_bb)
173 block_stmt_iterator bsi;
174 edge e;
175 edge_iterator ei;
177 bsi = bsi_last (bb);
179 /* If the duplicate ends with a control statement, then remove it.
181 Note that if we are duplicating the template block rather than the
182 original basic block, then the duplicate might not have any real
183 statements in it. */
184 if (!bsi_end_p (bsi)
185 && bsi_stmt (bsi)
186 && (TREE_CODE (bsi_stmt (bsi)) == COND_EXPR
187 || TREE_CODE (bsi_stmt (bsi)) == GOTO_EXPR
188 || TREE_CODE (bsi_stmt (bsi)) == SWITCH_EXPR))
189 bsi_remove (&bsi, true);
191 for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
193 if (e->dest != dest_bb)
194 remove_edge (e);
195 else
196 ei_next (&ei);
200 /* Create a duplicate of BB which only reaches the destination of the edge
201 stored in RD. Record the duplicate block in RD. */
203 static void
204 create_block_for_threading (basic_block bb, struct redirection_data *rd)
206 /* We can use the generic block duplication code and simply remove
207 the stuff we do not need. */
208 rd->dup_block = duplicate_block (bb, NULL, NULL);
210 /* Zero out the profile, since the block is unreachable for now. */
211 rd->dup_block->frequency = 0;
212 rd->dup_block->count = 0;
214 /* The call to duplicate_block will copy everything, including the
215 useless COND_EXPR or SWITCH_EXPR at the end of BB. We just remove
216 the useless COND_EXPR or SWITCH_EXPR here rather than having a
217 specialized block copier. We also remove all outgoing edges
218 from the duplicate block. The appropriate edge will be created
219 later. */
220 remove_ctrl_stmt_and_useless_edges (rd->dup_block, NULL);
223 /* Hashing and equality routines for our hash table. */
224 static hashval_t
225 redirection_data_hash (const void *p)
227 edge e = ((struct redirection_data *)p)->outgoing_edge;
228 return e->dest->index;
231 static int
232 redirection_data_eq (const void *p1, const void *p2)
234 edge e1 = ((struct redirection_data *)p1)->outgoing_edge;
235 edge e2 = ((struct redirection_data *)p2)->outgoing_edge;
237 return e1 == e2;
240 /* Given an outgoing edge E lookup and return its entry in our hash table.
242 If INSERT is true, then we insert the entry into the hash table if
243 it is not already present. INCOMING_EDGE is added to the list of incoming
244 edges associated with E in the hash table. */
246 static struct redirection_data *
247 lookup_redirection_data (edge e, edge incoming_edge, enum insert_option insert)
249 void **slot;
250 struct redirection_data *elt;
252 /* Build a hash table element so we can see if E is already
253 in the table. */
254 elt = XNEW (struct redirection_data);
255 elt->outgoing_edge = e;
256 elt->dup_block = NULL;
257 elt->do_not_duplicate = false;
258 elt->incoming_edges = NULL;
260 slot = htab_find_slot (redirection_data, elt, insert);
262 /* This will only happen if INSERT is false and the entry is not
263 in the hash table. */
264 if (slot == NULL)
266 free (elt);
267 return NULL;
270 /* This will only happen if E was not in the hash table and
271 INSERT is true. */
272 if (*slot == NULL)
274 *slot = (void *)elt;
275 elt->incoming_edges = XNEW (struct el);
276 elt->incoming_edges->e = incoming_edge;
277 elt->incoming_edges->next = NULL;
278 return elt;
280 /* E was in the hash table. */
281 else
283 /* Free ELT as we do not need it anymore, we will extract the
284 relevant entry from the hash table itself. */
285 free (elt);
287 /* Get the entry stored in the hash table. */
288 elt = (struct redirection_data *) *slot;
290 /* If insertion was requested, then we need to add INCOMING_EDGE
291 to the list of incoming edges associated with E. */
292 if (insert)
294 struct el *el = XNEW (struct el);
295 el->next = elt->incoming_edges;
296 el->e = incoming_edge;
297 elt->incoming_edges = el;
300 return elt;
304 /* Given a duplicate block and its single destination (both stored
305 in RD). Create an edge between the duplicate and its single
306 destination.
308 Add an additional argument to any PHI nodes at the single
309 destination. */
311 static void
312 create_edge_and_update_destination_phis (struct redirection_data *rd)
314 edge e = make_edge (rd->dup_block, rd->outgoing_edge->dest, EDGE_FALLTHRU);
315 tree phi;
317 e->probability = REG_BR_PROB_BASE;
318 e->count = rd->dup_block->count;
320 /* If there are any PHI nodes at the destination of the outgoing edge
321 from the duplicate block, then we will need to add a new argument
322 to them. The argument should have the same value as the argument
323 associated with the outgoing edge stored in RD. */
324 for (phi = phi_nodes (e->dest); phi; phi = PHI_CHAIN (phi))
326 int indx = rd->outgoing_edge->dest_idx;
327 add_phi_arg (phi, PHI_ARG_DEF (phi, indx), e);
331 /* Hash table traversal callback routine to create duplicate blocks. */
333 static int
334 create_duplicates (void **slot, void *data)
336 struct redirection_data *rd = (struct redirection_data *) *slot;
337 struct local_info *local_info = (struct local_info *)data;
339 /* If this entry should not have a duplicate created, then there's
340 nothing to do. */
341 if (rd->do_not_duplicate)
342 return 1;
344 /* Create a template block if we have not done so already. Otherwise
345 use the template to create a new block. */
346 if (local_info->template_block == NULL)
348 create_block_for_threading (local_info->bb, rd);
349 local_info->template_block = rd->dup_block;
351 /* We do not create any outgoing edges for the template. We will
352 take care of that in a later traversal. That way we do not
353 create edges that are going to just be deleted. */
355 else
357 create_block_for_threading (local_info->template_block, rd);
359 /* Go ahead and wire up outgoing edges and update PHIs for the duplicate
360 block. */
361 create_edge_and_update_destination_phis (rd);
364 /* Keep walking the hash table. */
365 return 1;
368 /* We did not create any outgoing edges for the template block during
369 block creation. This hash table traversal callback creates the
370 outgoing edge for the template block. */
372 static int
373 fixup_template_block (void **slot, void *data)
375 struct redirection_data *rd = (struct redirection_data *) *slot;
376 struct local_info *local_info = (struct local_info *)data;
378 /* If this is the template block, then create its outgoing edges
379 and halt the hash table traversal. */
380 if (rd->dup_block && rd->dup_block == local_info->template_block)
382 create_edge_and_update_destination_phis (rd);
383 return 0;
386 return 1;
389 /* Not all jump threading requests are useful. In particular some
390 jump threading requests can create irreducible regions which are
391 undesirable.
393 This routine will examine the BB's incoming edges for jump threading
394 requests which, if acted upon, would create irreducible regions. Any
395 such jump threading requests found will be pruned away. */
397 static void
398 prune_undesirable_thread_requests (basic_block bb)
400 edge e;
401 edge_iterator ei;
402 bool may_create_irreducible_region = false;
403 unsigned int num_outgoing_edges_into_loop = 0;
405 /* For the heuristics below, we need to know if BB has more than
406 one outgoing edge into a loop. */
407 FOR_EACH_EDGE (e, ei, bb->succs)
408 num_outgoing_edges_into_loop += ((e->flags & EDGE_LOOP_EXIT) == 0);
410 if (num_outgoing_edges_into_loop > 1)
412 edge backedge = NULL;
414 /* Consider the effect of threading the edge (0, 1) to 2 on the left
415 CFG to produce the right CFG:
420 1<--+ 2<--------+
421 / \ | | |
422 2 3 | 4<----+ |
423 \ / | / \ | |
424 4---+ E 1-- | --+
425 | | |
426 E 3---+
429 Threading the (0, 1) edge to 2 effectively creates two loops
430 (2, 4, 1) and (4, 1, 3) which are neither disjoint nor nested.
431 This is not good.
433 However, we do need to be able to thread (0, 1) to 2 or 3
434 in the left CFG below (which creates the middle and right
435 CFGs with nested loops).
437 0 0 0
438 | | |
439 1<--+ 2<----+ 3<-+<-+
440 /| | | | | | |
441 2 | | 3<-+ | 1--+ |
442 \| | | | | | |
443 3---+ 1--+--+ 2-----+
446 A safe heuristic appears to be to only allow threading if BB
447 has a single incoming backedge from one of its direct successors. */
449 FOR_EACH_EDGE (e, ei, bb->preds)
451 if (e->flags & EDGE_DFS_BACK)
453 if (backedge)
455 backedge = NULL;
456 break;
458 else
460 backedge = e;
465 if (backedge && find_edge (bb, backedge->src))
467 else
468 may_create_irreducible_region = true;
470 else
472 edge dest = NULL;
474 /* If we thread across the loop entry block (BB) into the
475 loop and BB is still reached from outside the loop, then
476 we would create an irreducible CFG. Consider the effect
477 of threading the edge (1, 4) to 5 on the left CFG to produce
478 the right CFG
481 / \ / \
482 1 2 1 2
483 \ / | |
484 4<----+ 5<->4
485 / \ | |
486 E 5---+ E
489 Threading the (1, 4) edge to 5 creates two entry points
490 into the loop (4, 5) (one from block 1, the other from
491 block 2). A classic irreducible region.
493 So look at all of BB's incoming edges which are not
494 backedges and which are not threaded to the loop exit.
495 If that subset of incoming edges do not all thread
496 to the same block, then threading any of them will create
497 an irreducible region. */
499 FOR_EACH_EDGE (e, ei, bb->preds)
501 edge e2;
503 /* We ignore back edges for now. This may need refinement
504 as threading a backedge creates an inner loop which
505 we would need to verify has a single entry point.
507 If all backedges thread to new locations, then this
508 block will no longer have incoming backedges and we
509 need not worry about creating irreducible regions
510 by threading through BB. I don't think this happens
511 enough in practice to worry about it. */
512 if (e->flags & EDGE_DFS_BACK)
513 continue;
515 /* If the incoming edge threads to the loop exit, then it
516 is clearly safe. */
517 e2 = e->aux;
518 if (e2 && (e2->flags & EDGE_LOOP_EXIT))
519 continue;
521 /* E enters the loop header and is not threaded. We can
522 not allow any other incoming edges to thread into
523 the loop as that would create an irreducible region. */
524 if (!e2)
526 may_create_irreducible_region = true;
527 break;
530 /* We know that this incoming edge threads to a block inside
531 the loop. This edge must thread to the same target in
532 the loop as any previously seen threaded edges. Otherwise
533 we will create an irreducible region. */
534 if (!dest)
535 dest = e2;
536 else if (e2 != dest)
538 may_create_irreducible_region = true;
539 break;
544 /* If we might create an irreducible region, then cancel any of
545 the jump threading requests for incoming edges which are
546 not backedges and which do not thread to the exit block. */
547 if (may_create_irreducible_region)
549 FOR_EACH_EDGE (e, ei, bb->preds)
551 edge e2;
553 /* Ignore back edges. */
554 if (e->flags & EDGE_DFS_BACK)
555 continue;
557 e2 = e->aux;
559 /* If this incoming edge was not threaded, then there is
560 nothing to do. */
561 if (!e2)
562 continue;
564 /* If this incoming edge threaded to the loop exit,
565 then it can be ignored as it is safe. */
566 if (e2->flags & EDGE_LOOP_EXIT)
567 continue;
569 if (e2)
571 /* This edge threaded into the loop and the jump thread
572 request must be cancelled. */
573 if (dump_file && (dump_flags & TDF_DETAILS))
574 fprintf (dump_file, " Not threading jump %d --> %d to %d\n",
575 e->src->index, e->dest->index, e2->dest->index);
576 e->aux = NULL;
582 /* Hash table traversal callback to redirect each incoming edge
583 associated with this hash table element to its new destination. */
585 static int
586 redirect_edges (void **slot, void *data)
588 struct redirection_data *rd = (struct redirection_data *) *slot;
589 struct local_info *local_info = (struct local_info *)data;
590 struct el *next, *el;
592 /* Walk over all the incoming edges associated associated with this
593 hash table entry. */
594 for (el = rd->incoming_edges; el; el = next)
596 edge e = el->e;
598 /* Go ahead and free this element from the list. Doing this now
599 avoids the need for another list walk when we destroy the hash
600 table. */
601 next = el->next;
602 free (el);
604 /* Go ahead and clear E->aux. It's not needed anymore and failure
605 to clear it will cause all kinds of unpleasant problems later. */
606 e->aux = NULL;
608 thread_stats.num_threaded_edges++;
610 if (rd->dup_block)
612 edge e2;
614 if (dump_file && (dump_flags & TDF_DETAILS))
615 fprintf (dump_file, " Threaded jump %d --> %d to %d\n",
616 e->src->index, e->dest->index, rd->dup_block->index);
618 rd->dup_block->count += e->count;
619 rd->dup_block->frequency += EDGE_FREQUENCY (e);
620 EDGE_SUCC (rd->dup_block, 0)->count += e->count;
621 /* Redirect the incoming edge to the appropriate duplicate
622 block. */
623 e2 = redirect_edge_and_branch (e, rd->dup_block);
624 flush_pending_stmts (e2);
626 if ((dump_file && (dump_flags & TDF_DETAILS))
627 && e->src != e2->src)
628 fprintf (dump_file, " basic block %d created\n", e2->src->index);
630 else
632 if (dump_file && (dump_flags & TDF_DETAILS))
633 fprintf (dump_file, " Threaded jump %d --> %d to %d\n",
634 e->src->index, e->dest->index, local_info->bb->index);
636 /* We are using BB as the duplicate. Remove the unnecessary
637 outgoing edges and statements from BB. */
638 remove_ctrl_stmt_and_useless_edges (local_info->bb,
639 rd->outgoing_edge->dest);
641 /* And fixup the flags on the single remaining edge. */
642 single_succ_edge (local_info->bb)->flags
643 &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE | EDGE_ABNORMAL);
644 single_succ_edge (local_info->bb)->flags |= EDGE_FALLTHRU;
648 /* Indicate that we actually threaded one or more jumps. */
649 if (rd->incoming_edges)
650 local_info->jumps_threaded = true;
652 return 1;
655 /* Return true if this block has no executable statements other than
656 a simple ctrl flow instruction. When the number of outgoing edges
657 is one, this is equivalent to a "forwarder" block. */
659 static bool
660 redirection_block_p (basic_block bb)
662 block_stmt_iterator bsi;
664 /* Advance to the first executable statement. */
665 bsi = bsi_start (bb);
666 while (!bsi_end_p (bsi)
667 && (TREE_CODE (bsi_stmt (bsi)) == LABEL_EXPR
668 || IS_EMPTY_STMT (bsi_stmt (bsi))))
669 bsi_next (&bsi);
671 /* Check if this is an empty block. */
672 if (bsi_end_p (bsi))
673 return true;
675 /* Test that we've reached the terminating control statement. */
676 return bsi_stmt (bsi)
677 && (TREE_CODE (bsi_stmt (bsi)) == COND_EXPR
678 || TREE_CODE (bsi_stmt (bsi)) == GOTO_EXPR
679 || TREE_CODE (bsi_stmt (bsi)) == SWITCH_EXPR);
682 /* BB is a block which ends with a COND_EXPR or SWITCH_EXPR and when BB
683 is reached via one or more specific incoming edges, we know which
684 outgoing edge from BB will be traversed.
686 We want to redirect those incoming edges to the target of the
687 appropriate outgoing edge. Doing so avoids a conditional branch
688 and may expose new optimization opportunities. Note that we have
689 to update dominator tree and SSA graph after such changes.
691 The key to keeping the SSA graph update manageable is to duplicate
692 the side effects occurring in BB so that those side effects still
693 occur on the paths which bypass BB after redirecting edges.
695 We accomplish this by creating duplicates of BB and arranging for
696 the duplicates to unconditionally pass control to one specific
697 successor of BB. We then revector the incoming edges into BB to
698 the appropriate duplicate of BB.
700 BB and its duplicates will have assignments to the same set of
701 SSA_NAMEs. Right now, we just call into update_ssa to update the
702 SSA graph for those names.
704 We are also going to experiment with a true incremental update
705 scheme for the duplicated resources. One of the interesting
706 properties we can exploit here is that all the resources set
707 in BB will have the same IDFS, so we have one IDFS computation
708 per block with incoming threaded edges, which can lower the
709 cost of the true incremental update algorithm. */
711 static bool
712 thread_block (basic_block bb)
714 /* E is an incoming edge into BB that we may or may not want to
715 redirect to a duplicate of BB. */
716 edge e;
717 edge_iterator ei;
718 struct local_info local_info;
720 /* FOUND_BACKEDGE indicates that we found an incoming backedge
721 into BB, in which case we may ignore certain jump threads
722 to avoid creating irreducible regions. */
723 bool found_backedge = false;
725 /* ALL indicates whether or not all incoming edges into BB should
726 be threaded to a duplicate of BB. */
727 bool all = true;
729 /* If optimizing for size, only thread this block if we don't have
730 to duplicate it or it's an otherwise empty redirection block. */
731 if (optimize_size
732 && EDGE_COUNT (bb->preds) > 1
733 && !redirection_block_p (bb))
735 FOR_EACH_EDGE (e, ei, bb->preds)
736 e->aux = NULL;
737 return false;
740 /* To avoid scanning a linear array for the element we need we instead
741 use a hash table. For normal code there should be no noticeable
742 difference. However, if we have a block with a large number of
743 incoming and outgoing edges such linear searches can get expensive. */
744 redirection_data = htab_create (EDGE_COUNT (bb->succs),
745 redirection_data_hash,
746 redirection_data_eq,
747 free);
749 FOR_EACH_EDGE (e, ei, bb->preds)
750 found_backedge |= ((e->flags & EDGE_DFS_BACK) != 0);
752 /* If BB has incoming backedges, then threading across BB might
753 introduce an irreducible region, which would be undesirable
754 as that inhibits various optimizations later. Prune away
755 any jump threading requests which we know will result in
756 an irreducible region. */
757 if (found_backedge)
758 prune_undesirable_thread_requests (bb);
760 /* Record each unique threaded destination into a hash table for
761 efficient lookups. */
762 FOR_EACH_EDGE (e, ei, bb->preds)
764 if (!e->aux)
766 all = false;
768 else
770 edge e2 = e->aux;
771 update_bb_profile_for_threading (e->dest, EDGE_FREQUENCY (e),
772 e->count, e->aux);
774 /* Insert the outgoing edge into the hash table if it is not
775 already in the hash table. */
776 lookup_redirection_data (e2, e, INSERT);
780 /* If we are going to thread all incoming edges to an outgoing edge, then
781 BB will become unreachable. Rather than just throwing it away, use
782 it for one of the duplicates. Mark the first incoming edge with the
783 DO_NOT_DUPLICATE attribute. */
784 if (all)
786 edge e = EDGE_PRED (bb, 0)->aux;
787 lookup_redirection_data (e, NULL, NO_INSERT)->do_not_duplicate = true;
790 /* Now create duplicates of BB.
792 Note that for a block with a high outgoing degree we can waste
793 a lot of time and memory creating and destroying useless edges.
795 So we first duplicate BB and remove the control structure at the
796 tail of the duplicate as well as all outgoing edges from the
797 duplicate. We then use that duplicate block as a template for
798 the rest of the duplicates. */
799 local_info.template_block = NULL;
800 local_info.bb = bb;
801 local_info.jumps_threaded = false;
802 htab_traverse (redirection_data, create_duplicates, &local_info);
804 /* The template does not have an outgoing edge. Create that outgoing
805 edge and update PHI nodes as the edge's target as necessary.
807 We do this after creating all the duplicates to avoid creating
808 unnecessary edges. */
809 htab_traverse (redirection_data, fixup_template_block, &local_info);
811 /* The hash table traversals above created the duplicate blocks (and the
812 statements within the duplicate blocks). This loop creates PHI nodes for
813 the duplicated blocks and redirects the incoming edges into BB to reach
814 the duplicates of BB. */
815 htab_traverse (redirection_data, redirect_edges, &local_info);
817 /* Done with this block. Clear REDIRECTION_DATA. */
818 htab_delete (redirection_data);
819 redirection_data = NULL;
821 /* Indicate to our caller whether or not any jumps were threaded. */
822 return local_info.jumps_threaded;
825 /* Walk through the registered jump threads and convert them into a
826 form convenient for this pass.
828 Any block which has incoming edges threaded to outgoing edges
829 will have its entry in THREADED_BLOCK set.
831 Any threaded edge will have its new outgoing edge stored in the
832 original edge's AUX field.
834 This form avoids the need to walk all the edges in the CFG to
835 discover blocks which need processing and avoids unnecessary
836 hash table lookups to map from threaded edge to new target. */
838 static void
839 mark_threaded_blocks (bitmap threaded_blocks)
841 unsigned int i;
843 for (i = 0; i < VEC_length (edge, threaded_edges); i += 2)
845 edge e = VEC_index (edge, threaded_edges, i);
846 edge e2 = VEC_index (edge, threaded_edges, i + 1);
848 e->aux = e2;
849 bitmap_set_bit (threaded_blocks, e->dest->index);
854 /* Walk through all blocks and thread incoming edges to the appropriate
855 outgoing edge for each edge pair recorded in THREADED_EDGES.
857 It is the caller's responsibility to fix the dominance information
858 and rewrite duplicated SSA_NAMEs back into SSA form.
860 Returns true if one or more edges were threaded, false otherwise. */
862 bool
863 thread_through_all_blocks (void)
865 bool retval = false;
866 unsigned int i;
867 bitmap_iterator bi;
868 bitmap threaded_blocks;
870 if (threaded_edges == NULL)
871 return false;
873 threaded_blocks = BITMAP_ALLOC (NULL);
874 memset (&thread_stats, 0, sizeof (thread_stats));
876 mark_threaded_blocks (threaded_blocks);
878 EXECUTE_IF_SET_IN_BITMAP (threaded_blocks, 0, i, bi)
880 basic_block bb = BASIC_BLOCK (i);
882 if (EDGE_COUNT (bb->preds) > 0)
883 retval |= thread_block (bb);
886 if (dump_file && (dump_flags & TDF_STATS))
887 fprintf (dump_file, "\nJumps threaded: %lu\n",
888 thread_stats.num_threaded_edges);
890 BITMAP_FREE (threaded_blocks);
891 threaded_blocks = NULL;
892 VEC_free (edge, heap, threaded_edges);
893 threaded_edges = NULL;
894 return retval;
897 /* Register a jump threading opportunity. We queue up all the jump
898 threading opportunities discovered by a pass and update the CFG
899 and SSA form all at once.
901 E is the edge we can thread, E2 is the new target edge. ie, we
902 are effectively recording that E->dest can be changed to E2->dest
903 after fixing the SSA graph. */
905 void
906 register_jump_thread (edge e, edge e2)
908 if (threaded_edges == NULL)
909 threaded_edges = VEC_alloc (edge, heap, 10);
911 VEC_safe_push (edge, heap, threaded_edges, e);
912 VEC_safe_push (edge, heap, threaded_edges, e2);