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)
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. */
23 #include "coretypes.h"
30 #include "basic-block.h"
34 #include "diagnostic.h"
35 #include "tree-flow.h"
36 #include "tree-dump.h"
37 #include "tree-pass.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
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
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
67 5b. This automatically associates each new argument added in step 4
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. */
103 /* Main data structure recording information regarding B's duplicate
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. */
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. */
137 /* The current block we are working on. */
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. */
148 /* Passes which use the jump threading code register jump threading
149 opportunities as they are discovered. We keep the registered
150 jump threading opportunities in this vector as edge pairs
151 (original_edge, target_edge). */
152 static VEC(edge
,heap
) *threaded_edges
;
155 /* Jump threading statistics. */
157 struct thread_stats_d
159 unsigned long num_threaded_edges
;
162 struct thread_stats_d thread_stats
;
165 /* Remove the last statement in block BB if it is a control statement
166 Also remove all outgoing edges except the edge which reaches DEST_BB.
167 If DEST_BB is NULL, then remove all outgoing edges. */
170 remove_ctrl_stmt_and_useless_edges (basic_block bb
, basic_block dest_bb
)
172 block_stmt_iterator bsi
;
178 /* If the duplicate ends with a control statement, then remove it.
180 Note that if we are duplicating the template block rather than the
181 original basic block, then the duplicate might not have any real
185 && (TREE_CODE (bsi_stmt (bsi
)) == COND_EXPR
186 || TREE_CODE (bsi_stmt (bsi
)) == GOTO_EXPR
187 || TREE_CODE (bsi_stmt (bsi
)) == SWITCH_EXPR
))
188 bsi_remove (&bsi
, true);
190 for (ei
= ei_start (bb
->succs
); (e
= ei_safe_edge (ei
)); )
192 if (e
->dest
!= dest_bb
)
199 /* Create a duplicate of BB which only reaches the destination of the edge
200 stored in RD. Record the duplicate block in RD. */
203 create_block_for_threading (basic_block bb
, struct redirection_data
*rd
)
205 /* We can use the generic block duplication code and simply remove
206 the stuff we do not need. */
207 rd
->dup_block
= duplicate_block (bb
, NULL
, NULL
);
209 /* Zero out the profile, since the block is unreachable for now. */
210 rd
->dup_block
->frequency
= 0;
211 rd
->dup_block
->count
= 0;
213 /* The call to duplicate_block will copy everything, including the
214 useless COND_EXPR or SWITCH_EXPR at the end of BB. We just remove
215 the useless COND_EXPR or SWITCH_EXPR here rather than having a
216 specialized block copier. We also remove all outgoing edges
217 from the duplicate block. The appropriate edge will be created
219 remove_ctrl_stmt_and_useless_edges (rd
->dup_block
, NULL
);
222 /* Hashing and equality routines for our hash table. */
224 redirection_data_hash (const void *p
)
226 edge e
= ((struct redirection_data
*)p
)->outgoing_edge
;
227 return e
->dest
->index
;
231 redirection_data_eq (const void *p1
, const void *p2
)
233 edge e1
= ((struct redirection_data
*)p1
)->outgoing_edge
;
234 edge e2
= ((struct redirection_data
*)p2
)->outgoing_edge
;
239 /* Given an outgoing edge E lookup and return its entry in our hash table.
241 If INSERT is true, then we insert the entry into the hash table if
242 it is not already present. INCOMING_EDGE is added to the list of incoming
243 edges associated with E in the hash table. */
245 static struct redirection_data
*
246 lookup_redirection_data (edge e
, edge incoming_edge
, enum insert_option insert
)
249 struct redirection_data
*elt
;
251 /* Build a hash table element so we can see if E is already
253 elt
= XNEW (struct redirection_data
);
254 elt
->outgoing_edge
= e
;
255 elt
->dup_block
= NULL
;
256 elt
->do_not_duplicate
= false;
257 elt
->incoming_edges
= NULL
;
259 slot
= htab_find_slot (redirection_data
, elt
, insert
);
261 /* This will only happen if INSERT is false and the entry is not
262 in the hash table. */
269 /* This will only happen if E was not in the hash table and
274 elt
->incoming_edges
= XNEW (struct el
);
275 elt
->incoming_edges
->e
= incoming_edge
;
276 elt
->incoming_edges
->next
= NULL
;
279 /* E was in the hash table. */
282 /* Free ELT as we do not need it anymore, we will extract the
283 relevant entry from the hash table itself. */
286 /* Get the entry stored in the hash table. */
287 elt
= (struct redirection_data
*) *slot
;
289 /* If insertion was requested, then we need to add INCOMING_EDGE
290 to the list of incoming edges associated with E. */
293 struct el
*el
= XNEW (struct el
);
294 el
->next
= elt
->incoming_edges
;
295 el
->e
= incoming_edge
;
296 elt
->incoming_edges
= el
;
303 /* Given a duplicate block and its single destination (both stored
304 in RD). Create an edge between the duplicate and its single
307 Add an additional argument to any PHI nodes at the single
311 create_edge_and_update_destination_phis (struct redirection_data
*rd
)
313 edge e
= make_edge (rd
->dup_block
, rd
->outgoing_edge
->dest
, EDGE_FALLTHRU
);
316 e
->probability
= REG_BR_PROB_BASE
;
317 e
->count
= rd
->dup_block
->count
;
318 e
->aux
= rd
->outgoing_edge
->aux
;
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. */
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
341 if (rd
->do_not_duplicate
)
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. */
357 create_block_for_threading (local_info
->template_block
, rd
);
359 /* Go ahead and wire up outgoing edges and update PHIs for the duplicate
361 create_edge_and_update_destination_phis (rd
);
364 /* Keep walking the hash table. */
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. */
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
);
389 /* Hash table traversal callback to redirect each incoming edge
390 associated with this hash table element to its new destination. */
393 redirect_edges (void **slot
, void *data
)
395 struct redirection_data
*rd
= (struct redirection_data
*) *slot
;
396 struct local_info
*local_info
= (struct local_info
*)data
;
397 struct el
*next
, *el
;
399 /* Walk over all the incoming edges associated associated with this
401 for (el
= rd
->incoming_edges
; el
; el
= next
)
405 /* Go ahead and free this element from the list. Doing this now
406 avoids the need for another list walk when we destroy the hash
411 /* Go ahead and clear E->aux. It's not needed anymore and failure
412 to clear it will cause all kinds of unpleasant problems later. */
415 thread_stats
.num_threaded_edges
++;
421 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
422 fprintf (dump_file
, " Threaded jump %d --> %d to %d\n",
423 e
->src
->index
, e
->dest
->index
, rd
->dup_block
->index
);
425 rd
->dup_block
->count
+= e
->count
;
426 rd
->dup_block
->frequency
+= EDGE_FREQUENCY (e
);
427 EDGE_SUCC (rd
->dup_block
, 0)->count
+= e
->count
;
428 /* Redirect the incoming edge to the appropriate duplicate
430 e2
= redirect_edge_and_branch (e
, rd
->dup_block
);
431 gcc_assert (e
== e2
);
432 flush_pending_stmts (e2
);
436 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
437 fprintf (dump_file
, " Threaded jump %d --> %d to %d\n",
438 e
->src
->index
, e
->dest
->index
, local_info
->bb
->index
);
440 /* We are using BB as the duplicate. Remove the unnecessary
441 outgoing edges and statements from BB. */
442 remove_ctrl_stmt_and_useless_edges (local_info
->bb
,
443 rd
->outgoing_edge
->dest
);
445 /* And fixup the flags on the single remaining edge. */
446 single_succ_edge (local_info
->bb
)->flags
447 &= ~(EDGE_TRUE_VALUE
| EDGE_FALSE_VALUE
| EDGE_ABNORMAL
);
448 single_succ_edge (local_info
->bb
)->flags
|= EDGE_FALLTHRU
;
452 /* Indicate that we actually threaded one or more jumps. */
453 if (rd
->incoming_edges
)
454 local_info
->jumps_threaded
= true;
459 /* Return true if this block has no executable statements other than
460 a simple ctrl flow instruction. When the number of outgoing edges
461 is one, this is equivalent to a "forwarder" block. */
464 redirection_block_p (basic_block bb
)
466 block_stmt_iterator bsi
;
468 /* Advance to the first executable statement. */
469 bsi
= bsi_start (bb
);
470 while (!bsi_end_p (bsi
)
471 && (TREE_CODE (bsi_stmt (bsi
)) == LABEL_EXPR
472 || IS_EMPTY_STMT (bsi_stmt (bsi
))))
475 /* Check if this is an empty block. */
479 /* Test that we've reached the terminating control statement. */
480 return bsi_stmt (bsi
)
481 && (TREE_CODE (bsi_stmt (bsi
)) == COND_EXPR
482 || TREE_CODE (bsi_stmt (bsi
)) == GOTO_EXPR
483 || TREE_CODE (bsi_stmt (bsi
)) == SWITCH_EXPR
);
486 /* BB is a block which ends with a COND_EXPR or SWITCH_EXPR and when BB
487 is reached via one or more specific incoming edges, we know which
488 outgoing edge from BB will be traversed.
490 We want to redirect those incoming edges to the target of the
491 appropriate outgoing edge. Doing so avoids a conditional branch
492 and may expose new optimization opportunities. Note that we have
493 to update dominator tree and SSA graph after such changes.
495 The key to keeping the SSA graph update manageable is to duplicate
496 the side effects occurring in BB so that those side effects still
497 occur on the paths which bypass BB after redirecting edges.
499 We accomplish this by creating duplicates of BB and arranging for
500 the duplicates to unconditionally pass control to one specific
501 successor of BB. We then revector the incoming edges into BB to
502 the appropriate duplicate of BB.
504 If NOLOOP_ONLY is true, we only perform the threading as long as it
505 does not affect the structure of the loops in a nontrivial way. */
508 thread_block (basic_block bb
, bool noloop_only
)
510 /* E is an incoming edge into BB that we may or may not want to
511 redirect to a duplicate of BB. */
514 struct local_info local_info
;
515 struct loop
*loop
= bb
->loop_father
;
517 /* ALL indicates whether or not all incoming edges into BB should
518 be threaded to a duplicate of BB. */
521 /* To avoid scanning a linear array for the element we need we instead
522 use a hash table. For normal code there should be no noticeable
523 difference. However, if we have a block with a large number of
524 incoming and outgoing edges such linear searches can get expensive. */
525 redirection_data
= htab_create (EDGE_COUNT (bb
->succs
),
526 redirection_data_hash
,
530 /* If we thread the latch of the loop to its exit, the loop ceases to
531 exist. Make sure we do not restrict ourselves in order to preserve
533 if (loop
->header
== bb
)
535 e
= loop_latch_edge (loop
);
538 if (e2
&& loop_exit_edge_p (loop
, e2
))
545 /* Record each unique threaded destination into a hash table for
546 efficient lookups. */
547 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
552 /* If NOLOOP_ONLY is true, we only allow threading through the
553 header of a loop to exit edges. */
555 && bb
== bb
->loop_father
->header
556 && !loop_exit_edge_p (bb
->loop_father
, e2
)))
562 update_bb_profile_for_threading (e
->dest
, EDGE_FREQUENCY (e
),
565 /* Insert the outgoing edge into the hash table if it is not
566 already in the hash table. */
567 lookup_redirection_data (e2
, e
, INSERT
);
570 /* If we are going to thread all incoming edges to an outgoing edge, then
571 BB will become unreachable. Rather than just throwing it away, use
572 it for one of the duplicates. Mark the first incoming edge with the
573 DO_NOT_DUPLICATE attribute. */
576 edge e
= EDGE_PRED (bb
, 0)->aux
;
577 lookup_redirection_data (e
, NULL
, NO_INSERT
)->do_not_duplicate
= true;
580 /* We do not update dominance info. */
581 free_dominance_info (CDI_DOMINATORS
);
583 /* Now create duplicates of BB.
585 Note that for a block with a high outgoing degree we can waste
586 a lot of time and memory creating and destroying useless edges.
588 So we first duplicate BB and remove the control structure at the
589 tail of the duplicate as well as all outgoing edges from the
590 duplicate. We then use that duplicate block as a template for
591 the rest of the duplicates. */
592 local_info
.template_block
= NULL
;
594 local_info
.jumps_threaded
= false;
595 htab_traverse (redirection_data
, create_duplicates
, &local_info
);
597 /* The template does not have an outgoing edge. Create that outgoing
598 edge and update PHI nodes as the edge's target as necessary.
600 We do this after creating all the duplicates to avoid creating
601 unnecessary edges. */
602 htab_traverse (redirection_data
, fixup_template_block
, &local_info
);
604 /* The hash table traversals above created the duplicate blocks (and the
605 statements within the duplicate blocks). This loop creates PHI nodes for
606 the duplicated blocks and redirects the incoming edges into BB to reach
607 the duplicates of BB. */
608 htab_traverse (redirection_data
, redirect_edges
, &local_info
);
610 /* Done with this block. Clear REDIRECTION_DATA. */
611 htab_delete (redirection_data
);
612 redirection_data
= NULL
;
614 /* Indicate to our caller whether or not any jumps were threaded. */
615 return local_info
.jumps_threaded
;
618 /* Threads edge E through E->dest to the edge E->aux. Returns the copy
619 of E->dest created during threading, or E->dest if it was not necessary
620 to copy it (E is its single predecessor). */
623 thread_single_edge (edge e
)
625 basic_block bb
= e
->dest
;
627 struct redirection_data rd
;
628 struct local_info local_info
;
632 thread_stats
.num_threaded_edges
++;
634 if (single_pred_p (bb
))
636 /* If BB has just a single predecessor, we should only remove the
637 control statements at its end, and successors except for ETO. */
638 remove_ctrl_stmt_and_useless_edges (bb
, eto
->dest
);
642 /* Otherwise, we need to create a copy. */
643 update_bb_profile_for_threading (bb
, EDGE_FREQUENCY (e
), e
->count
, eto
);
646 rd
.outgoing_edge
= eto
;
648 create_block_for_threading (bb
, &rd
);
649 create_edge_and_update_destination_phis (&rd
);
651 if (dump_file
&& (dump_flags
& TDF_DETAILS
))
652 fprintf (dump_file
, " Threaded jump %d --> %d to %d\n",
653 e
->src
->index
, e
->dest
->index
, rd
.dup_block
->index
);
655 rd
.dup_block
->count
= e
->count
;
656 rd
.dup_block
->frequency
= EDGE_FREQUENCY (e
);
657 single_succ_edge (rd
.dup_block
)->count
= e
->count
;
658 redirect_edge_and_branch (e
, rd
.dup_block
);
659 flush_pending_stmts (e
);
664 /* Callback for dfs_enumerate_from. Returns true if BB is different
665 from STOP and DBDS_CE_STOP. */
667 static basic_block dbds_ce_stop
;
669 dbds_continue_enumeration_p (basic_block bb
, void *stop
)
671 return (bb
!= (basic_block
) stop
672 && bb
!= dbds_ce_stop
);
675 /* Evaluates the dominance relationship of latch of the LOOP and BB, and
676 returns the state. */
680 /* BB does not dominate latch of the LOOP. */
682 /* The LOOP is broken (there is no path from the header to its latch. */
684 /* BB dominates the latch of the LOOP. */
688 static enum bb_dom_status
689 determine_bb_domination_status (struct loop
*loop
, basic_block bb
)
691 basic_block
*bblocks
;
693 bool bb_reachable
= false;
697 #ifdef ENABLE_CHECKING
698 /* This function assumes BB is a successor of LOOP->header. */
702 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
704 if (e
->src
== loop
->header
)
715 if (bb
== loop
->latch
)
716 return DOMST_DOMINATING
;
718 /* Check that BB dominates LOOP->latch, and that it is back-reachable
721 bblocks
= XCNEWVEC (basic_block
, loop
->num_nodes
);
722 dbds_ce_stop
= loop
->header
;
723 nblocks
= dfs_enumerate_from (loop
->latch
, 1, dbds_continue_enumeration_p
,
724 bblocks
, loop
->num_nodes
, bb
);
725 for (i
= 0; i
< nblocks
; i
++)
726 FOR_EACH_EDGE (e
, ei
, bblocks
[i
]->preds
)
728 if (e
->src
== loop
->header
)
731 return DOMST_NONDOMINATING
;
738 return (bb_reachable
? DOMST_DOMINATING
: DOMST_LOOP_BROKEN
);
741 /* Thread jumps through the header of LOOP. Returns true if cfg changes.
742 If MAY_PEEL_LOOP_HEADERS is false, we avoid threading from entry edges
743 to the inside of the loop. */
746 thread_through_loop_header (struct loop
*loop
, bool may_peel_loop_headers
)
748 basic_block header
= loop
->header
;
749 edge e
, tgt_edge
, latch
= loop_latch_edge (loop
);
751 basic_block tgt_bb
, atgt_bb
;
752 enum bb_dom_status domst
;
754 /* We have already threaded through headers to exits, so all the threading
755 requests now are to the inside of the loop. We need to avoid creating
756 irreducible regions (i.e., loops with more than one entry block), and
757 also loop with several latch edges, or new subloops of the loop (although
758 there are cases where it might be appropriate, it is difficult to decide,
759 and doing it wrongly may confuse other optimizers).
761 We could handle more general cases here. However, the intention is to
762 preserve some information about the loop, which is impossible if its
763 structure changes significantly, in a way that is not well understood.
764 Thus we only handle few important special cases, in which also updating
765 of the loop-carried information should be feasible:
767 1) Propagation of latch edge to a block that dominates the latch block
768 of a loop. This aims to handle the following idiom:
779 After threading the latch edge, this becomes
790 The original header of the loop is moved out of it, and we may thread
791 the remaining edges through it without further constraints.
793 2) All entry edges are propagated to a single basic block that dominates
794 the latch block of the loop. This aims to handle the following idiom
795 (normally created for "for" loops):
818 /* Threading through the header won't improve the code if the header has just
820 if (single_succ_p (header
))
825 tgt_edge
= latch
->aux
;
826 tgt_bb
= tgt_edge
->dest
;
828 else if (!may_peel_loop_headers
829 && !redirection_block_p (loop
->header
))
835 FOR_EACH_EDGE (e
, ei
, header
->preds
)
842 /* If latch is not threaded, and there is a header
843 edge that is not threaded, we would create loop
844 with multiple entries. */
849 atgt_bb
= tgt_edge
->dest
;
852 /* Two targets of threading would make us create loop
853 with multiple entries. */
854 else if (tgt_bb
!= atgt_bb
)
860 /* There are no threading requests. */
864 /* Redirecting to empty loop latch is useless. */
865 if (tgt_bb
== loop
->latch
866 && empty_block_p (loop
->latch
))
870 /* The target block must dominate the loop latch, otherwise we would be
871 creating a subloop. */
872 domst
= determine_bb_domination_status (loop
, tgt_bb
);
873 if (domst
== DOMST_NONDOMINATING
)
875 if (domst
== DOMST_LOOP_BROKEN
)
877 /* If the loop ceased to exist, mark it as such, and thread through its
881 return thread_block (header
, false);
884 if (tgt_bb
->loop_father
->header
== tgt_bb
)
886 /* If the target of the threading is a header of a subloop, we need
887 to create a preheader for it, so that the headers of the two loops
889 if (EDGE_COUNT (tgt_bb
->preds
) > 2)
891 tgt_bb
= create_preheader (tgt_bb
->loop_father
, 0);
892 gcc_assert (tgt_bb
!= NULL
);
895 tgt_bb
= split_edge (tgt_edge
);
900 /* First handle the case latch edge is redirected. */
901 loop
->latch
= thread_single_edge (latch
);
902 gcc_assert (single_succ (loop
->latch
) == tgt_bb
);
903 loop
->header
= tgt_bb
;
905 /* Thread the remaining edges through the former header. */
906 thread_block (header
, false);
910 basic_block new_preheader
;
912 /* Now consider the case entry edges are redirected to the new entry
913 block. Remember one entry edge, so that we can find the new
914 preheader (its destination after threading). */
915 FOR_EACH_EDGE (e
, ei
, header
->preds
)
921 /* The duplicate of the header is the new preheader of the loop. Ensure
922 that it is placed correctly in the loop hierarchy. */
923 set_loop_copy (loop
, loop_outer (loop
));
925 thread_block (header
, false);
926 set_loop_copy (loop
, NULL
);
927 new_preheader
= e
->dest
;
929 /* Create the new latch block. This is always necessary, as the latch
930 must have only a single successor, but the original header had at
931 least two successors. */
933 mfb_kj_edge
= single_succ_edge (new_preheader
);
934 loop
->header
= mfb_kj_edge
->dest
;
935 latch
= make_forwarder_block (tgt_bb
, mfb_keep_just
, NULL
);
936 loop
->header
= latch
->dest
;
937 loop
->latch
= latch
->src
;
943 /* We failed to thread anything. Cancel the requests. */
944 FOR_EACH_EDGE (e
, ei
, header
->preds
)
951 /* Walk through the registered jump threads and convert them into a
952 form convenient for this pass.
954 Any block which has incoming edges threaded to outgoing edges
955 will have its entry in THREADED_BLOCK set.
957 Any threaded edge will have its new outgoing edge stored in the
958 original edge's AUX field.
960 This form avoids the need to walk all the edges in the CFG to
961 discover blocks which need processing and avoids unnecessary
962 hash table lookups to map from threaded edge to new target. */
965 mark_threaded_blocks (bitmap threaded_blocks
)
969 bitmap tmp
= BITMAP_ALLOC (NULL
);
974 for (i
= 0; i
< VEC_length (edge
, threaded_edges
); i
+= 2)
976 edge e
= VEC_index (edge
, threaded_edges
, i
);
977 edge e2
= VEC_index (edge
, threaded_edges
, i
+ 1);
980 bitmap_set_bit (tmp
, e
->dest
->index
);
983 /* If optimizing for size, only thread through block if we don't have
984 to duplicate it or it's an otherwise empty redirection block. */
987 EXECUTE_IF_SET_IN_BITMAP (tmp
, 0, i
, bi
)
989 bb
= BASIC_BLOCK (i
);
990 if (EDGE_COUNT (bb
->preds
) > 1
991 && !redirection_block_p (bb
))
993 FOR_EACH_EDGE (e
, ei
, bb
->preds
)
997 bitmap_set_bit (threaded_blocks
, i
);
1001 bitmap_copy (threaded_blocks
, tmp
);
1007 /* Walk through all blocks and thread incoming edges to the appropriate
1008 outgoing edge for each edge pair recorded in THREADED_EDGES.
1010 It is the caller's responsibility to fix the dominance information
1011 and rewrite duplicated SSA_NAMEs back into SSA form.
1013 If MAY_PEEL_LOOP_HEADERS is false, we avoid threading edges through
1014 loop headers if it does not simplify the loop.
1016 Returns true if one or more edges were threaded, false otherwise. */
1019 thread_through_all_blocks (bool may_peel_loop_headers
)
1021 bool retval
= false;
1024 bitmap threaded_blocks
;
1028 /* We must know about loops in order to preserve them. */
1029 gcc_assert (current_loops
!= NULL
);
1031 if (threaded_edges
== NULL
)
1034 threaded_blocks
= BITMAP_ALLOC (NULL
);
1035 memset (&thread_stats
, 0, sizeof (thread_stats
));
1037 mark_threaded_blocks (threaded_blocks
);
1039 initialize_original_copy_tables ();
1041 /* First perform the threading requests that do not affect
1043 EXECUTE_IF_SET_IN_BITMAP (threaded_blocks
, 0, i
, bi
)
1045 basic_block bb
= BASIC_BLOCK (i
);
1047 if (EDGE_COUNT (bb
->preds
) > 0)
1048 retval
|= thread_block (bb
, true);
1051 /* Then perform the threading through loop headers. We start with the
1052 innermost loop, so that the changes in cfg we perform won't affect
1053 further threading. */
1054 FOR_EACH_LOOP (li
, loop
, LI_FROM_INNERMOST
)
1057 || !bitmap_bit_p (threaded_blocks
, loop
->header
->index
))
1060 retval
|= thread_through_loop_header (loop
, may_peel_loop_headers
);
1063 if (dump_file
&& (dump_flags
& TDF_STATS
))
1064 fprintf (dump_file
, "\nJumps threaded: %lu\n",
1065 thread_stats
.num_threaded_edges
);
1067 free_original_copy_tables ();
1069 BITMAP_FREE (threaded_blocks
);
1070 threaded_blocks
= NULL
;
1071 VEC_free (edge
, heap
, threaded_edges
);
1072 threaded_edges
= NULL
;
1077 /* Register a jump threading opportunity. We queue up all the jump
1078 threading opportunities discovered by a pass and update the CFG
1079 and SSA form all at once.
1081 E is the edge we can thread, E2 is the new target edge. ie, we
1082 are effectively recording that E->dest can be changed to E2->dest
1083 after fixing the SSA graph. */
1086 register_jump_thread (edge e
, edge e2
)
1088 if (threaded_edges
== NULL
)
1089 threaded_edges
= VEC_alloc (edge
, heap
, 10);
1091 VEC_safe_push (edge
, heap
, threaded_edges
, e
);
1092 VEC_safe_push (edge
, heap
, threaded_edges
, e2
);