| blob | ecdc3752af3c5cb5cf5fae4b2bc507802740e090 |
1 /* Perform instruction reorganizations for delay slot filling.
2 Copyright (C) 1992-2018 Free Software Foundation, Inc.
3 Contributed by Richard Kenner (kenner@vlsi1.ultra.nyu.edu).
4 Hacked by Michael Tiemann (tiemann@cygnus.com).
6 This file is part of GCC.
8 GCC is free software; you can redistribute it and/or modify it under
9 the terms of the GNU General Public License as published by the Free
10 Software Foundation; either version 3, or (at your option) any later
11 version.
13 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
14 WARRANTY; without even the implied warranty of MERCHANTABILITY or
15 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
16 for more details.
18 You should have received a copy of the GNU General Public License
19 along with GCC; see the file COPYING3. If not see
20 <http://www.gnu.org/licenses/>. */
22 /* Instruction reorganization pass.
24 This pass runs after register allocation and final jump
25 optimization. It should be the last pass to run before peephole.
26 It serves primarily to fill delay slots of insns, typically branch
27 and call insns. Other insns typically involve more complicated
28 interactions of data dependencies and resource constraints, and
29 are better handled by scheduling before register allocation (by the
30 function `schedule_insns').
32 The Branch Penalty is the number of extra cycles that are needed to
33 execute a branch insn. On an ideal machine, branches take a single
34 cycle, and the Branch Penalty is 0. Several RISC machines approach
35 branch delays differently:
37 The MIPS has a single branch delay slot. Most insns
38 (except other branches) can be used to fill this slot. When the
39 slot is filled, two insns execute in two cycles, reducing the
40 branch penalty to zero.
42 The SPARC always has a branch delay slot, but its effects can be
43 annulled when the branch is not taken. This means that failing to
44 find other sources of insns, we can hoist an insn from the branch
45 target that would only be safe to execute knowing that the branch
46 is taken.
48 The HP-PA always has a branch delay slot. For unconditional branches
49 its effects can be annulled when the branch is taken. The effects
50 of the delay slot in a conditional branch can be nullified for forward
51 taken branches, or for untaken backward branches. This means
52 we can hoist insns from the fall-through path for forward branches or
53 steal insns from the target of backward branches.
55 The TMS320C3x and C4x have three branch delay slots. When the three
56 slots are filled, the branch penalty is zero. Most insns can fill the
57 delay slots except jump insns.
59 Three techniques for filling delay slots have been implemented so far:
61 (1) `fill_simple_delay_slots' is the simplest, most efficient way
62 to fill delay slots. This pass first looks for insns which come
63 from before the branch and which are safe to execute after the
64 branch. Then it searches after the insn requiring delay slots or,
65 in the case of a branch, for insns that are after the point at
66 which the branch merges into the fallthrough code, if such a point
67 exists. When such insns are found, the branch penalty decreases
68 and no code expansion takes place.
70 (2) `fill_eager_delay_slots' is more complicated: it is used for
71 scheduling conditional jumps, or for scheduling jumps which cannot
72 be filled using (1). A machine need not have annulled jumps to use
73 this strategy, but it helps (by keeping more options open).
74 `fill_eager_delay_slots' tries to guess the direction the branch
75 will go; if it guesses right 100% of the time, it can reduce the
76 branch penalty as much as `fill_simple_delay_slots' does. If it
77 guesses wrong 100% of the time, it might as well schedule nops. When
78 `fill_eager_delay_slots' takes insns from the fall-through path of
79 the jump, usually there is no code expansion; when it takes insns
80 from the branch target, there is code expansion if it is not the
81 only way to reach that target.
83 (3) `relax_delay_slots' uses a set of rules to simplify code that
84 has been reorganized by (1) and (2). It finds cases where
85 conditional test can be eliminated, jumps can be threaded, extra
86 insns can be eliminated, etc. It is the job of (1) and (2) to do a
87 good job of scheduling locally; `relax_delay_slots' takes care of
88 making the various individual schedules work well together. It is
89 especially tuned to handle the control flow interactions of branch
90 insns. It does nothing for insns with delay slots that do not
91 branch.
93 On machines that use CC0, we are very conservative. We will not make
94 a copy of an insn involving CC0 since we want to maintain a 1-1
95 correspondence between the insn that sets and uses CC0. The insns are
96 allowed to be separated by placing an insn that sets CC0 (but not an insn
97 that uses CC0; we could do this, but it doesn't seem worthwhile) in a
98 delay slot. In that case, we point each insn at the other with REG_CC_USER
99 and REG_CC_SETTER notes. Note that these restrictions affect very few
100 machines because most RISC machines with delay slots will not use CC0
101 (the RT is the only known exception at this point). */
122 \f
123 /* First, some functions that were used before GCC got a control flow graph.
124 These functions are now only used here in reorg.c, and have therefore
125 been moved here to avoid inadvertent misuse elsewhere in the compiler. */
127 /* Return the last label to mark the same position as LABEL. Return LABEL
128 itself if it is null or any return rtx. */
130 static rtx
132 {
145 }
147 /* INSN uses CC0 and is being moved into a delay slot. Set up REG_CC_SETTER
148 and REG_CC_USER notes so we can find it. */
150 static void
152 {
160 }
161 \f
162 /* Insns which have delay slots that have not yet been filled. */
167 /* Define macros to refer to the first and last slot containing unfilled
168 insns. These are used because the list may move and its address
169 should be recomputed at each use. */
171 #define unfilled_slots_base \
172 ((rtx_insn **) obstack_base (&unfilled_slots_obstack))
174 #define unfilled_slots_next \
175 ((rtx_insn **) obstack_next_free (&unfilled_slots_obstack))
177 /* Points to the label before the end of the function, or before a
178 return insn. */
180 /* Likewise for a simple_return. */
183 /* Mapping between INSN_UID's and position in the code since INSN_UID's do
184 not always monotonically increase. */
187 /* Highest valid index in `uid_to_ruid'. */
215 rtx *);
237 \f
238 /* A wrapper around next_active_insn which takes care to return ret_rtx
239 unchanged. */
241 static rtx
243 {
247 }
248 \f
249 /* Return true iff INSN is a simplejump, or any kind of return insn. */
251 static bool
253 {
257 }
258 \f
259 /* Return TRUE if this insn should stop the search for insn to fill delay
260 slots. LABELS_P indicates that labels should terminate the search.
261 In all cases, jumps terminate the search. */
263 static int
265 {
269 /* If the insn can throw an exception that is caught within the function,
270 it may effectively perform a jump from the viewpoint of the function.
271 Therefore act like for a jump. */
276 {
289 /* OK unless it contains a delay slot or is an `asm' insn of some type.
290 We don't know anything about these. */
297 }
298 }
299 \f
300 /* Return TRUE if any resources are marked in both RES1 and RES2 or if either
301 resource set contains a volatile memory reference. Otherwise, return FALSE. */
303 static int
305 {
311 }
313 /* Return TRUE if any resource marked in RES, a `struct resources', is
314 referenced by INSN. If INCLUDE_DELAYED_EFFECTS is set, return if the called
315 routine is using those resources.
317 We compute this by computing all the resources referenced by INSN and
318 seeing if this conflicts with RES. It might be faster to directly check
319 ourselves, and this is the way it used to work, but it means duplicating
320 a large block of complex code. */
322 static int
325 {
331 }
333 /* Return TRUE if INSN modifies resources that are marked in RES.
334 INCLUDE_DELAYED_EFFECTS is set if the actions of that routine should be
335 included. CC0 is only modified if it is explicitly set; see comments
336 in front of mark_set_resources for details. */
338 static int
341 {
346 (include_delayed_effects
347 ? MARK_SRC_DEST_CALL
350 }
351 \f
352 /* Find a label at the end of the function or before a RETURN. If there
353 is none, try to make one. If that fails, returns 0.
355 The property of such a label is that it is placed just before the
356 epilogue or a bare RETURN insn, so that another bare RETURN can be
357 turned into a jump to the label unconditionally. In particular, the
358 label cannot be placed before a RETURN insn with a filled delay slot.
360 ??? There may be a problem with the current implementation. Suppose
361 we start with a bare RETURN insn and call find_end_label. It may set
362 function_return_label just before the RETURN. Suppose the machinery
363 is able to fill the delay slot of the RETURN insn afterwards. Then
364 function_return_label is no longer valid according to the property
365 described above and find_end_label will still return it unmodified.
366 Note that this is probably mitigated by the following observation:
367 once function_return_label is made, it is very likely the target of
368 a jump, so filling the delay slot of the RETURN will be much more
369 difficult.
370 KIND is either simple_return_rtx or ret_rtx, indicating which type of
371 return we're looking for. */
375 {
381 else
382 {
385 }
387 /* If we found one previously, return it. */
391 /* Otherwise, see if there is a label at the end of the function. If there
392 is, it must be that RETURN insns aren't needed, so that is our return
393 label and we don't have to do anything else. */
402 /* When a target threads its epilogue we might already have a
403 suitable return insn. If so put a label before it for the
404 function_return_label. */
408 {
413 /* Put the label before any USE insns that may precede the RETURN
414 insn. */
420 }
424 else
425 {
428 /* If the basic block reorder pass moves the return insn to
429 some other place try to locate it again and put our
430 function_return_label there. */
434 {
437 /* Put the label before any USE insns that may precede the
438 RETURN insn. */
443 }
444 else
445 {
447 /* The RETURN insn has its delay slot filled so we cannot
448 emit the label just before it. Since we already have
449 an epilogue and cannot emit a new RETURN, we cannot
450 emit the label at all. */
453 /* Otherwise, make a new label and emit a RETURN and BARRIER,
454 if needed. */
457 {
458 /* The return we make may have delay slots too. */
465 }
466 }
468 }
470 /* Show one additional use for this label so it won't go away until
471 we are done. */
475 }
476 \f
477 /* Put INSN and LIST together in a SEQUENCE rtx of LENGTH, and replace
478 the pattern of INSN with the SEQUENCE.
480 Returns the insn containing the SEQUENCE that replaces INSN. */
484 {
485 /* Allocate the rtvec to hold the insns and the SEQUENCE. */
490 /* If DELAY_INSN has a location, use it for SEQ_INSN. If DELAY_INSN does
491 not have a location, but one of the delayed insns does, we pick up a
492 location from there later. */
495 /* Unlink INSN from the insn chain, so that we can put it into
496 the SEQUENCE. Remember where we want to emit SEQUENCE in AFTER. */
501 /* Build our SEQUENCE and rebuild the insn chain. */
508 {
512 /* Show that this copy of the insn isn't deleted. */
515 /* Unlink insn from its original place, and re-emit it into
516 the sequence. */
520 /* SPARC assembler, for instance, emit warning when debug info is output
521 into the delay slot. */
527 {
530 {
532 /* Remove any REG_DEAD notes because we can't rely on them now
533 that the insn has been moved. */
539 /* Keep the label reference count up to date. */
546 }
547 }
548 }
551 /* Splice our SEQUENCE into the insn stream where INSN used to be. */
555 }
557 /* Add INSN to DELAY_LIST and return the head of the new list. The list must
558 be in the order in which the insns are to be executed. */
560 static void
562 {
563 /* If INSN has its block number recorded, clear it since we may
564 be moving the insn to a new block. */
567 }
568 \f
569 /* Delete INSN from the delay slot of the insn that it is in, which may
570 produce an insn with no delay slots. Return the new insn. */
574 {
580 /* We first must find the insn containing the SEQUENCE with INSN in its
581 delay slot. Do this by finding an insn, TRIAL, where
582 PREV_INSN (NEXT_INSN (TRIAL)) != TRIAL. */
587 ;
595 /* Create a delay list consisting of all the insns other than the one
596 we are deleting (unless we were the only one). */
603 /* Delete the old SEQUENCE, re-emit the insn that used to have the delay
604 list, and rebuild the delay list if non-empty. */
610 /* If there was a barrier after the old SEQUENCE, remit it. */
614 /* If there are any delay insns, remit them. Otherwise clear the
615 annul flag. */
623 /* Show we need to fill this insn again. */
627 }
628 \f
629 /* Delete INSN, a JUMP_INSN. If it is a conditional jump, we must track down
630 the insn that sets CC0 for it and delete it too. */
632 static void
634 {
635 /* Delete the insn that sets cc0 for us. On machines without cc0, we could
636 delete the insn that sets the condition code, but it is hard to find it.
637 Since this case is rare anyway, don't bother trying; there would likely
638 be other insns that became dead anyway, which we wouldn't know to
639 delete. */
642 {
645 /* If a reg-note was found, it points to an insn to set CC0. This
646 insn is in the delay list of some other insn. So delete it from
647 the delay list it was in. */
649 {
653 }
654 else
655 {
656 /* The insn setting CC0 is our previous insn, but it may be in
657 a delay slot. It will be the last insn in the delay slot, if
658 it is. */
667 else
669 }
670 }
673 }
674 \f
675 /* Counters for delay-slot filling. */
677 #define NUM_REORG_FUNCTIONS 2
678 #define MAX_DELAY_HISTOGRAM 3
679 #define MAX_REORG_PASSES 2
687 static void
689 {
694 }
695 \f
696 /* Optimize the following cases:
698 1. When a conditional branch skips over only one instruction,
699 use an annulling branch and put that insn in the delay slot.
700 Use either a branch that annuls when the condition if true or
701 invert the test with a branch that annuls when the condition is
702 false. This saves insns, since otherwise we must copy an insn
703 from the L1 target.
705 (orig) (skip) (otherwise)
706 Bcc.n L1 Bcc',a L1 Bcc,a L1'
707 insn insn insn2
708 L1: L1: L1:
709 insn2 insn2 insn2
710 insn3 insn3 L1':
711 insn3
713 2. When a conditional branch skips over only one instruction,
714 and after that, it unconditionally branches somewhere else,
715 perform the similar optimization. This saves executing the
716 second branch in the case where the inverted condition is true.
718 Bcc.n L1 Bcc',a L2
719 insn insn
720 L1: L1:
721 Bra L2 Bra L2
723 INSN is a JUMP_INSN.
725 This should be expanded to skip over N insns, where N is the number
726 of delay slots required. */
728 static void
730 {
747 /* There are two cases where we are just executing one insn (we assume
748 here that a branch requires only one insn; this should be generalized
749 at some point): Where the branch goes around a single insn or where
750 we have one insn followed by a branch to the same label we branch to.
751 In both of these cases, inverting the jump and annulling the delay
752 slot give the same effect in fewer insns. */
757 {
759 {
764 }
771 /* Also, if we are targeting an unconditional
772 branch, thread our jump to the target of that branch. Don't
773 change this into a RETURN here, because it may not accept what
774 we have in the delay slot. We'll fix this up later. */
776 {
782 {
783 /* Recompute the flags based on TARGET_LABEL since threading
784 the jump to TARGET_LABEL may change the direction of the
785 jump (which may change the circumstances in which the
786 delay slot is nullified). */
790 }
791 }
794 }
795 }
796 \f
797 /* Encode and return branch direction and prediction information for
798 INSN assuming it will jump to LABEL.
800 Non conditional branches return no direction information and
801 are predicted as very likely taken. */
803 static int
805 {
808 /* get_jump_flags can be passed any insn with delay slots, these may
809 be INSNs, CALL_INSNs, or JUMP_INSNs. Only JUMP_INSNs have branch
810 direction information, and only if they are conditional jumps.
812 If LABEL is a return, then there is no way to determine the branch
813 direction. */
819 flags
822 /* No valid direction information. */
823 else
827 }
829 /* Return truth value of the statement that this branch
830 is mostly taken. If we think that the branch is extremely likely
831 to be taken, we return 2. If the branch is slightly more likely to be
832 taken, return 1. If the branch is slightly less likely to be taken,
833 return 0 and if the branch is highly unlikely to be taken, return -1. */
835 static int
837 {
838 /* If branch probabilities are available, then use that number since it
839 always gives a correct answer. */
842 {
852 else
854 }
856 /* If there is no note, assume branches are not taken.
857 This should be rare. */
859 }
861 /* Return the condition under which INSN will branch to TARGET. If TARGET
862 is zero, return the condition under which INSN will return. If INSN is
863 an unconditional branch, return const_true_rtx. If INSN isn't a simple
864 type of jump, or it doesn't go to TARGET, return 0. */
866 static rtx
868 {
870 rtx src;
897 {
904 }
907 }
909 /* Return nonzero if CONDITION is more strict than the condition of
910 INSN, i.e., if INSN will always branch if CONDITION is true. */
912 static int
914 {
933 }
935 /* Return nonzero if redirecting JUMP to NEWLABEL does not invalidate
936 any insns already in the delay slot of JUMP. */
938 static int
940 {
944 /* Make sure all the delay slots of this jump would still
945 be valid after threading the jump. If they are still
946 valid, then return nonzero. */
951 #if ANNUL_IFFALSE_SLOTS
955 #endif
956 #if ANNUL_IFTRUE_SLOTS
960 #endif
965 }
967 /* Return nonzero if redirecting JUMP to NEWLABEL does not invalidate
968 any insns we wish to place in the delay slot of JUMP. */
970 static int
973 {
974 /* Make sure all the insns in DELAY_LIST would still be
975 valid after threading the jump. If they are still
976 valid, then return nonzero. */
983 #if ANNUL_IFFALSE_SLOTS
987 #endif
988 #if ANNUL_IFTRUE_SLOTS
992 #endif
997 }
999 /* DELAY_LIST is a list of insns that have already been placed into delay
1000 slots. See if all of them have the same annulling status as ANNUL_TRUE_P.
1001 If not, return 0; otherwise return 1. */
1003 static int
1006 {
1015 }
1016 \f
1017 /* INSN branches to an insn whose pattern SEQ is a SEQUENCE. Given that
1018 the condition tested by INSN is CONDITION and the resources shown in
1019 OTHER_NEEDED are needed after INSN, see whether INSN can take all the insns
1020 from SEQ's delay list, in addition to whatever insns it may execute
1021 (in DELAY_LIST). SETS and NEEDED are denote resources already set and
1022 needed while searching for delay slot insns. Return the concatenated
1023 delay list if possible, otherwise, return 0.
1025 SLOTS_TO_FILL is the total number of slots required by INSN, and
1026 PSLOTS_FILLED points to the number filled so far (also the number of
1027 insns in DELAY_LIST). It is updated with the number that have been
1028 filled from the SEQUENCE, if any.
1030 PANNUL_P points to a nonzero value if we already know that we need
1031 to annul INSN. If this routine determines that annulling is needed,
1032 it may set that value nonzero.
1034 PNEW_THREAD points to a location that is to receive the place at which
1035 execution should continue. */
1037 static void
1045 {
1055 /* We can't do anything if there are more delay slots in SEQ than we
1056 can handle, or if we don't know that it will be a taken branch.
1057 We know that it will be a taken branch if it is either an unconditional
1058 branch or a conditional branch with a stricter branch condition.
1060 Also, exit if the branch has more than one set, since then it is computing
1061 other results that can't be ignored, e.g. the HPPA mov&branch instruction.
1062 ??? It may be possible to move other sets into INSN in addition to
1063 moving the instructions in the delay slots.
1065 We can not steal the delay list if one of the instructions in the
1066 current delay_list modifies the condition codes and the jump in the
1067 sequence is a conditional jump. We can not do this because we can
1068 not change the direction of the jump because the condition codes
1069 will effect the direction of the jump in the sequence. */
1075 {
1079 }
1086 /* On some targets, branches with delay slots can have a limited
1087 displacement. Give the back end a chance to tell us we can't do
1088 this. */
1094 {
1101 /* If TRIAL sets CC0, we can't copy it, so we can't steal this
1102 delay list. */
1104 /* If TRIAL is from the fallthrough code of an annulled branch insn
1105 in SEQ, we cannot use it. */
1110 /* If this insn was already done (usually in a previous delay slot),
1111 pretend we put it in our delay slot. */
1116 /* We will end up re-vectoring this branch, so compute flags
1117 based on jumping to the new label. */
1131 {
1133 {
1134 /* Frame related instructions cannot go into annulled delay
1135 slots, it messes up the dwarf info. */
1139 }
1143 total_slots_filled++;
1147 }
1148 else
1150 }
1152 /* Record the effect of the instructions that were redundant and which
1153 we therefore decided not to copy. */
1156 {
1159 }
1161 /* Show the place to which we will be branching. */
1164 /* Add any new insns to the delay list and update the count of the
1165 number of slots filled. */
1173 }
1174 \f
1175 /* Similar to steal_delay_list_from_target except that SEQ is on the
1176 fallthrough path of INSN. Here we only do something if the delay insn
1177 of SEQ is an unconditional branch. In that case we steal its delay slot
1178 for INSN since unconditional branches are much easier to fill. */
1180 static void
1189 {
1197 /* We can't do anything if SEQ's delay insn isn't an
1198 unconditional branch. */
1204 {
1208 /* If TRIAL sets CC0, stealing it will move it too far from the use
1209 of CC0. */
1217 /* If this insn was already done, we don't need it. */
1219 {
1224 }
1234 {
1242 }
1243 else
1245 }
1249 }
1250 \f
1251 /* Try merging insns starting at THREAD which match exactly the insns in
1252 INSN's delay list.
1254 If all insns were matched and the insn was previously annulling, the
1255 annul bit will be cleared.
1257 For each insn that is merged, if the branch is or will be non-annulling,
1258 we delete the merged insn. */
1260 static void
1262 {
1278 /* If this is not an annulling branch, take into account anything needed in
1279 INSN's delay slot. This prevents two increments from being incorrectly
1280 folded into one. If we are annulling, this would be the correct
1281 thing to do. (The alternative, looking at things set in NEXT_TO_MATCH
1282 will essentially disable this optimization. This method is somewhat of
1283 a kludge, but I don't see a better way.) */
1291 {
1297 /* TRIAL must be a CALL_INSN or INSN. Skip USE and CLOBBER. */
1303 /* We can't share an insn that sets cc0. */
1309 /* Update next_trial, in case try_split succeeded. */
1311 /* Likewise THREAD. */
1314 /* Have to test this condition if annul condition is different
1315 from (and less restrictive than) non-annulling one. */
1317 {
1320 {
1327 }
1328 else
1335 }
1339 }
1341 /* See if we stopped on a filled insn. If we did, try to see if its
1342 delay slots match. */
1348 {
1352 /* Account for resources set/needed by the filled insn. */
1357 {
1361 /* Account for resources set by the insn following NEXT_TO_MATCH
1362 inside INSN's delay list. */
1366 /* Account for resources set by the insn before DTRIAL and inside
1367 TRIAL's delay list. */
1376 /* Check that DTRIAL and NEXT_TO_MATCH does not reference a
1377 resource modified between them (only dtrial is checked because
1378 next_to_match and dtrial shall to be equal in order to hit
1379 this line) */
1382 {
1384 {
1392 }
1393 else
1401 }
1402 else
1403 {
1404 /* Keep track of the set/referenced resources for the delay
1405 slots of any trial insns we encounter. */
1408 }
1409 }
1410 }
1412 /* If all insns in the delay slot have been matched and we were previously
1413 annulling the branch, we need not any more. In that case delete all the
1414 merged insns. Also clear the INSN_FROM_TARGET_P bit of each insn in
1415 the delay list so that we know that it isn't only being used at the
1416 target. */
1418 {
1422 {
1427 }
1428 else
1429 {
1432 }
1438 }
1439 }
1440 \f
1441 /* See if INSN is redundant with an insn in front of TARGET. Often this
1442 is called when INSN is a candidate for a delay slot of TARGET.
1443 DELAY_LIST are insns that will be placed in delay slots of TARGET in front
1444 of INSN. Often INSN will be redundant with an insn in a delay slot of
1445 some previous insn. This happens when we have a series of branches to the
1446 same label; in that case the first insn at the target might want to go
1447 into each of the delay slots.
1449 If we are not careful, this routine can take up a significant fraction
1450 of the total compilation time (4%), but only wins rarely. Hence we
1451 speed this routine up by making two passes. The first pass goes back
1452 until it hits a label and sees if it finds an insn with an identical
1453 pattern. Only in this (relatively rare) event does it check for
1454 data conflicts.
1456 We do not split insns we encounter. This could cause us not to find a
1457 redundant insn, but the cost of splitting seems greater than the possible
1458 gain in rare cases. */
1462 {
1466 rtx pat;
1471 /* If INSN has any REG_UNUSED notes, it can't match anything since we
1472 are allowed to not actually assign to such a register. */
1476 /* Scan backwards looking for a match. */
1481 {
1482 /* (use (insn))s can come immediately after a barrier if the
1483 label that used to precede them has been deleted as dead.
1484 See delete_related_insns. */
1497 {
1498 /* Stop for a CALL and its delay slots because it is difficult to
1499 track its resource needs correctly. */
1503 /* Stop for an INSN or JUMP_INSN with delayed effects and its delay
1504 slots because it is difficult to track its resource needs
1505 correctly. */
1513 /* See if any of the insns in the delay slot match, updating
1514 resource requirements as we go. */
1521 /* If found a match, exit this loop early. */
1524 }
1529 }
1531 /* If we didn't find an insn that matches, return 0. */
1535 /* See what resources this insn sets and needs. If they overlap, or
1536 if this insn references CC0, it can't be redundant. */
1543 /* If TARGET is a SEQUENCE, get the main insn. */
1549 /* The insn requiring the delay may not set anything needed or set by
1550 INSN. */
1555 /* Insns we pass may not set either NEEDED or SET, so merge them for
1556 simpler tests. */
1560 /* This insn isn't redundant if it conflicts with an insn that either is
1561 or will be in a delay slot of TARGET. */
1575 /* Scan backwards until we reach a label or an insn that uses something
1576 INSN sets or sets something insn uses or sets. */
1582 {
1592 {
1596 /* If this is a CALL_INSN and its delay slots, it is hard to track
1597 the resource needs properly, so give up. */
1601 /* If this is an INSN or JUMP_INSN with delayed effects, it
1602 is hard to track the resource needs properly, so give up. */
1613 /* See if any of the insns in the delay slot match, updating
1614 resource requirements as we go. */
1616 {
1619 /* If an insn will be annulled if the branch is false, it isn't
1620 considered as a possible duplicate insn. */
1623 {
1624 /* Show that this insn will be used in the sequel. */
1627 }
1629 /* Unless this is an annulled insn from the target of a branch,
1630 we must stop if it sets anything needed or set by INSN. */
1634 }
1636 /* If the insn requiring the delay slot conflicts with INSN, we
1637 must stop. */
1640 }
1641 else
1642 {
1643 /* See if TRIAL is the same as INSN. */
1648 /* Can't go any further if TRIAL conflicts with INSN. */
1651 }
1652 }
1655 }
1656 \f
1657 /* Return 1 if THREAD can only be executed in one way. If LABEL is nonzero,
1658 it is the target of the branch insn being scanned. If ALLOW_FALLTHROUGH
1659 is nonzero, we are allowed to fall into this thread; otherwise, we are
1660 not.
1662 If LABEL is used more than one or we pass a label other than LABEL before
1663 finding an active insn, we do not own this thread. */
1665 static int
1667 {
1671 /* We don't own the function end. */
1675 /* We have a non-NULL insn. */
1678 /* Get the first active insn, or THREAD_INSN, if it is an active insn. */
1689 /* Ensure that we reach a BARRIER before any insn or label. */
1701 }
1702 \f
1703 /* Called when INSN is being moved from a location near the target of a jump.
1704 We leave a marker of the form (use (INSN)) immediately in front of WHERE
1705 for mark_target_live_regs. These markers will be deleted at the end.
1707 We used to try to update the live status of registers if WHERE is at
1708 the start of a basic block, but that can't work since we may remove a
1709 BARRIER in relax_delay_slots. */
1711 static void
1713 {
1716 /* INSN might be making a value live in a block where it didn't use to
1717 be. So recompute liveness information for this block. */
1719 }
1721 /* Similar to REDIRECT_JUMP except that we update the BB_TICKS entry for
1722 the basic block containing the jump. */
1724 static int
1726 {
1729 }
1731 /* Called when INSN is being moved forward into a delay slot of DELAYED_INSN.
1732 We check every instruction between INSN and DELAYED_INSN for REG_DEAD notes
1733 that reference values used in INSN. If we find one, then we move the
1734 REG_DEAD note to INSN.
1736 This is needed to handle the case where a later insn (after INSN) has a
1737 REG_DEAD note for a register used by INSN, and this later insn subsequently
1738 gets moved before a CODE_LABEL because it is a redundant insn. In this
1739 case, mark_target_live_regs may be confused into thinking the register
1740 is dead because it sees a REG_DEAD note immediately before a CODE_LABEL. */
1742 static void
1744 {
1751 {
1759 {
1760 /* Move the REG_DEAD note from P to INSN. */
1764 }
1765 }
1766 }
1768 /* Called when an insn redundant with start_insn is deleted. If there
1769 is a REG_DEAD note for the target of start_insn between start_insn
1770 and stop_insn, then the REG_DEAD note needs to be deleted since the
1771 value no longer dies there.
1773 If the REG_DEAD note isn't deleted, then mark_target_live_regs may be
1774 confused into thinking the register is dead. */
1776 static void
1778 {
1785 {
1793 {
1796 }
1797 }
1798 }
1800 /* Delete any REG_UNUSED notes that exist on INSN but not on OTHER_INSN.
1802 This handles the case of udivmodXi4 instructions which optimize their
1803 output depending on whether any REG_UNUSED notes are present. We must
1804 make sure that INSN calculates as many results as OTHER_INSN does. */
1806 static void
1808 {
1812 {
1821 }
1822 }
1823 \f
1826 /* Return the label before INSN, or put a new label there. If SIBLING is
1827 non-zero, it is another label associated with the new label (if any),
1828 typically the former target of the jump that will be redirected to
1829 the new label. */
1833 {
1836 /* Find an existing label at this point
1837 or make a new one if there is none. */
1841 {
1848 {
1851 }
1852 }
1854 }
1856 /* Scan a function looking for insns that need a delay slot and find insns to
1857 put into the delay slot.
1859 NON_JUMPS_P is nonzero if we are to only try to fill non-jump insns (such
1860 as calls). We do these first since we don't want jump insns (that are
1861 easier to fill) to get the only insns that could be used for non-jump insns.
1862 When it is zero, only try to fill JUMP_INSNs.
1864 When slots are filled in this manner, the insns (including the
1865 delay_insn) are put together in a SEQUENCE rtx. In this fashion,
1866 it is possible to tell whether a delay slot has really been filled
1867 or not. `final' knows how to deal with this, by communicating
1868 through FINAL_SEQUENCE. */
1870 static void
1872 {
1874 rtx pat;
1882 {
1884 /* Get the next insn to fill. If it has already had any slots assigned,
1885 we can't do anything with it. Maybe we'll improve this later. */
1896 /* It may have been that this insn used to need delay slots, but
1897 now doesn't; ignore in that case. This can happen, for example,
1898 on the HP PA RISC, where the number of delay slots depends on
1899 what insns are nearby. */
1902 /* Some machine description have defined instructions to have
1903 delay slots only in certain circumstances which may depend on
1904 nearby insns (which change due to reorg's actions).
1906 For example, the PA port normally has delay slots for unconditional
1907 jumps.
1909 However, the PA port claims such jumps do not have a delay slot
1910 if they are immediate successors of certain CALL_INSNs. This
1911 allows the port to favor filling the delay slot of the call with
1912 the unconditional jump. */
1916 /* This insn needs, or can use, some delay slots. SLOTS_TO_FILL
1917 says how many. After initialization, first try optimizing
1919 call _foo call _foo
1920 nop add %o7,.-L1,%o7
1921 b,a L1
1922 nop
1924 If this case applies, the delay slot of the call is filled with
1925 the unconditional jump. This is done first to avoid having the
1926 delay slot of the call filled in the backward scan. Also, since
1927 the unconditional jump is likely to also have a delay slot, that
1928 insn must exist when it is subsequently scanned.
1930 This is tried on each insn with delay slots as some machines
1931 have insns which perform calls, but are not represented as
1932 CALL_INSNs. */
1939 else
1948 {
1950 slots_filled++;
1953 /* TRIAL may have had its delay slot filled, then unfilled. When
1954 the delay slot is unfilled, TRIAL is placed back on the unfilled
1955 slots obstack. Unfortunately, it is placed on the end of the
1956 obstack, not in its original location. Therefore, we must search
1957 from entry i + 1 to the end of the unfilled slots obstack to
1958 try and find TRIAL. */
1961 tmp++;
1963 /* Remove the unconditional jump from consideration for delay slot
1964 filling and unthread it. */
1967 {
1974 }
1975 }
1977 /* Now, scan backwards from the insn to search for a potential
1978 delay-slot candidate. Stop searching when a label or jump is hit.
1980 For each candidate, if it is to go into the delay slot (moved
1981 forward in execution sequence), it must not need or set any resources
1982 that were set by later insns and must not set any resources that
1983 are needed for those insns.
1985 The delay slot insn itself sets resources unless it is a call
1986 (in which case the called routine, not the insn itself, is doing
1987 the setting). */
1990 {
1991 /* If the flags register is dead after the insn, then we want to be
1992 able to accept a candidate that clobbers it. For this purpose,
1993 we need to filter the flags register during life analysis, so
1994 that it doesn't create RAW and WAW dependencies, while still
1995 creating the necessary WAR dependencies. */
1996 bool filter_flags
2005 {
2008 }
2013 {
2016 /* This must be an INSN or CALL_INSN. */
2019 /* Stand-alone USE and CLOBBER are just for flow. */
2023 /* Check for resource conflict first, to avoid unnecessary
2024 splitting. */
2030 /* Can't separate set of cc0 from its use. */
2033 {
2037 {
2038 /* In this case, we are searching backward, so if we
2039 find insns to put on the delay list, we want
2040 to put them at the head, rather than the
2041 tail, of the list. */
2050 }
2051 }
2055 {
2057 /* If the flags register is set, then it doesn't create RAW
2058 dependencies any longer and it also doesn't create WAW
2059 dependencies since it's dead after the original insn. */
2061 {
2064 }
2065 }
2067 }
2068 }
2070 /* If all needed slots haven't been filled, we come here. */
2072 /* Try to optimize case of jumping around a single insn. */
2079 {
2083 }
2085 /* Try to get insns from beyond the insn needing the delay slot.
2086 These insns can neither set or reference resources set in insns being
2087 skipped, cannot set resources in the insn being skipped, and, if this
2088 is a CALL_INSN (or a CALL_INSN is passed), cannot trap (because the
2089 call might not return).
2091 There used to be code which continued past the target label if
2092 we saw all uses of the target label. This code did not work,
2093 because it failed to account for some instructions which were
2094 both annulled and marked as from the target. This can happen as a
2095 result of optimize_skip. Since this code was redundant with
2096 fill_eager_delay_slots anyways, it was just deleted. */
2099 /* If this instruction could throw an exception which is
2100 caught in the same function, then it's not safe to fill
2101 the delay slot with an instruction from beyond this
2102 point. For example, consider:
2104 int i = 2;
2106 try {
2107 f();
2108 i = 3;
2109 } catch (...) {}
2111 return i;
2113 Even though `i' is a local variable, we must be sure not
2114 to put `i = 3' in the delay slot if `f' might throw an
2115 exception.
2117 Presumably, we should also check to see if we could get
2118 back to this function via `setjmp'. */
2121 {
2135 {
2138 /* This must be an INSN or CALL_INSN. */
2141 /* Stand-alone USE and CLOBBER are just for flow. */
2145 /* If this already has filled delay slots, get the insn needing
2146 the delay slots. */
2149 else
2152 /* Stop our search when seeing a jump. */
2156 /* See if we have a resource problem before we try to split. */
2166 {
2176 }
2181 /* Ensure we don't put insns between the setting of cc and the
2182 comparison by moving a setting of cc into an earlier delay
2183 slot since these insns could clobber the condition code. */
2186 /* If this is a call, we might not get here. */
2189 }
2191 /* If there are slots left to fill and our search was stopped by an
2192 unconditional branch, try the insn at the branch target. We can
2193 redirect the branch if it works.
2195 Don't do this if the insn at the branch target is a branch. */
2197 && trial
2212 {
2213 /* See comment in relax_delay_slots about necessity of using
2214 next_real_insn here. */
2219 else
2223 {
2226 slots_filled++;
2228 new_label);
2229 }
2230 }
2231 }
2233 /* If this is an unconditional jump, then try to get insns from the
2234 target of the jump. */
2253 }
2254 }
2255 \f
2256 /* Follow any unconditional jump at LABEL, for the purpose of redirecting JUMP;
2257 return the ultimate label reached by any such chain of jumps.
2258 Return a suitable return rtx if the chain ultimately leads to a
2259 return instruction.
2260 If LABEL is not followed by a jump, return LABEL.
2261 If the chain loops or we can't find end, return LABEL,
2262 since that tells caller to avoid changing the insn.
2263 If the returned label is obtained by following a crossing jump,
2264 set *CROSSING to true, otherwise set it to false. */
2266 static rtx
2268 {
2288 depth++)
2289 {
2292 /* If we have found a cycle, make the insn jump to itself. */
2296 /* Cannot follow returns and cannot look through tablejumps. */
2310 }
2314 }
2316 /* Try to find insns to place in delay slots.
2318 INSN is the jump needing SLOTS_TO_FILL delay slots. It tests CONDITION
2319 or is an unconditional branch if CONDITION is const_true_rtx.
2320 *PSLOTS_FILLED is updated with the number of slots that we have filled.
2322 THREAD is a flow-of-control, either the insns to be executed if the
2323 branch is true or if the branch is false, THREAD_IF_TRUE says which.
2325 OPPOSITE_THREAD is the thread in the opposite direction. It is used
2326 to see if any potential delay slot insns set things needed there.
2328 LIKELY is nonzero if it is extremely likely that the branch will be
2329 taken and THREAD_IF_TRUE is set. This is used for the branch at the
2330 end of a loop back up to the top.
2332 OWN_THREAD is true if we are the only user of the thread, i.e. it is
2333 the target of the jump when we are the only jump going there.
2335 If OWN_THREAD is false, it must be the "true" thread of a jump. In that
2336 case, we can only take insns from the head of the thread for our delay
2337 slot. We then adjust the jump to point after the insns we have taken. */
2339 static void
2344 {
2345 rtx new_thread;
2352 /* Validate our arguments. */
2358 /* If our thread is the end of subroutine, we can't get any delay
2359 insns from that. */
2365 /* If this is an unconditional branch, nothing is needed at the
2366 opposite thread. Otherwise, compute what is needed there. */
2369 else
2372 /* If the insn at THREAD can be split, do it here to avoid having to
2373 update THREAD and NEW_THREAD if it is done in the loop below. Also
2374 initialize NEW_THREAD. */
2378 /* Scan insns at THREAD. We are looking for an insn that can be removed
2379 from THREAD (it neither sets nor references resources that were set
2380 ahead of it and it doesn't set anything needs by the insns ahead of
2381 it) and that either can be placed in an annulling insn or aren't
2382 needed at OPPOSITE_THREAD. */
2387 /* If we do not own this thread, we must stop as soon as we find
2388 something that we can't put in a delay slot, since all we can do
2389 is branch into THREAD at a later point. Therefore, labels stop
2390 the search if this is not the `true' thread. */
2395 {
2398 /* If we have passed a label, we no longer own this thread. */
2400 {
2403 }
2409 /* If TRIAL conflicts with the insns ahead of it, we lose. Also,
2410 don't separate or copy insns that set and use CC0. */
2417 {
2420 /* If TRIAL is redundant with some insn before INSN, we don't
2421 actually need to add it to the delay list; we can merely pretend
2422 we did. */
2424 {
2427 {
2430 {
2434 }
2437 }
2438 else
2439 {
2442 }
2445 }
2447 /* There are two ways we can win: If TRIAL doesn't set anything
2448 needed at the opposite thread and can't trap, or if it can
2449 go into an annulled delay slot. But we want neither to copy
2450 nor to speculate frame-related insns. */
2457 {
2467 }
2471 {
2484 {
2488 winner:
2493 /* If we own this thread, delete the insn. If this is the
2494 destination of a branch, show that a basic block status
2495 may have been updated. In any case, mark the new
2496 starting point of this thread. */
2498 {
2499 rtx note;
2503 {
2507 }
2509 /* We are moving this insn, not deleting it. We must
2510 temporarily increment the use count on any referenced
2511 label lest it be deleted by delete_related_insns. */
2517 {
2518 /* REG_LABEL_OPERAND could be
2519 NOTE_INSN_DELETED_LABEL too. */
2522 else
2525 }
2536 {
2537 /* REG_LABEL_OPERAND could be
2538 NOTE_INSN_DELETED_LABEL too. */
2541 else
2544 }
2547 }
2548 else
2558 {
2559 /* Even though we have filled all the slots, we
2560 may be branching to a location that has a
2561 redundant insn. Skip any if so. */
2568 && (prior_insn
2571 {
2572 /* We know we do not own the thread, so no need
2573 to call update_block and delete_insn. */
2576 new_thread
2578 }
2580 }
2583 }
2584 }
2585 }
2587 /* This insn can't go into a delay slot. */
2592 /* Ensure we don't put insns between the setting of cc and the comparison
2593 by moving a setting of cc into an earlier delay slot since these insns
2594 could clobber the condition code. */
2597 /* If this insn is a register-register copy and the next insn has
2598 a use of our destination, change it to use our source. That way,
2599 it will become a candidate for our delay slot the next time
2600 through this loop. This case occurs commonly in loops that
2601 scan a list.
2603 We could check for more complex cases than those tested below,
2604 but it doesn't seem worth it. It might also be a good idea to try
2605 to swap the two insns. That might do better.
2607 We can't do this if the next insn modifies our destination, because
2608 that would make the replacement into the insn invalid. We also can't
2609 do this if it modifies our source, because it might be an earlyclobber
2610 operand. This latter test also prevents updating the contents of
2611 a PRE_INC. We also can't do this if there's overlap of source and
2612 destination. Overlap may happen for larger-than-register-size modes. */
2618 {
2628 }
2629 }
2631 /* If we stopped on a branch insn that has delay slots, see if we can
2632 steal some of the insns in those slots. */
2636 {
2638 /* If this is the `true' thread, we will want to follow the jump,
2639 so we can only do this if we have taken everything up to here. */
2641 {
2647 /* If we owned the thread and are told that it branched
2648 elsewhere, make sure we own the thread at the new location. */
2651 }
2657 }
2659 /* If we haven't found anything for this delay slot and it is very
2660 likely that the branch will be taken, see if the insn at our target
2661 increments or decrements a register with an increment that does not
2662 depend on the destination register. If so, try to place the opposite
2663 arithmetic insn after the jump insn and put the arithmetic insn in the
2664 delay slot. If we can't do this, return. */
2671 {
2673 rtx dest;
2674 rtx src;
2676 /* We know "new_thread" is an insn due to NONJUMP_INSN_P (new_thread)
2677 above. */
2694 {
2696 rtx new_arith;
2699 /* If this is a constant adjustment, use the same code with
2700 the negated constant. Otherwise, reverse the sense of the
2701 arithmetic. */
2705 else
2714 {
2717 }
2720 {
2723 {
2727 }
2729 }
2730 else
2739 }
2740 }
2745 /* If we are to branch into the middle of this thread, find an appropriate
2746 label or make a new one if none, and redirect INSN to it. If we hit the
2747 end of the function, use the end-of-function label. */
2749 {
2750 rtx label;
2766 else
2771 {
2775 }
2776 }
2777 }
2778 \f
2779 /* Make another attempt to find insns to place in delay slots.
2781 We previously looked for insns located in front of the delay insn
2782 and, for non-jump delay insns, located behind the delay insn.
2784 Here only try to schedule jump insns and try to move insns from either
2785 the target or the following insns into the delay slot. If annulling is
2786 supported, we will be likely to do this. Otherwise, we can do this only
2787 if safe. */
2789 static void
2791 {
2797 {
2798 rtx condition;
2815 /* Some machine description have defined instructions to have
2816 delay slots only in certain circumstances which may depend on
2817 nearby insns (which change due to reorg's actions).
2819 For example, the PA port normally has delay slots for unconditional
2820 jumps.
2822 However, the PA port claims such jumps do not have a delay slot
2823 if they are immediate successors of certain CALL_INSNs. This
2824 allows the port to favor filling the delay slot of the call with
2825 the unconditional jump. */
2836 /* Get the next active fallthrough and target insns and see if we own
2837 them. Then see whether the branch is likely true. We don't need
2838 to do a lot of this for unconditional branches. */
2844 {
2848 }
2849 else
2850 {
2854 }
2856 /* If this insn is expected to branch, first try to get insns from our
2857 target, then our fallthrough insns. If it is not expected to branch,
2858 try the other order. */
2861 {
2864 own_target,
2868 {
2869 /* Even though we didn't find anything for delay slots,
2870 we might have found a redundant insn which we deleted
2871 from the thread that was filled. So we have to recompute
2872 the next insn at the target. */
2880 }
2881 }
2882 else
2883 {
2893 }
2903 }
2904 }
2905 \f
2908 /* Recursively delete prior insns that compute the value (used only by INSN
2909 which the caller is deleting) stored in the register mentioned by NOTE
2910 which is a REG_DEAD note associated with INSN. */
2912 static void
2914 {
2922 {
2925 /* If we reach a CALL which is not calling a const function
2926 or the callee pops the arguments, then give up. */
2932 /* If we reach a SEQUENCE, it is too complex to try to
2933 do anything with it, so give up. We can be run during
2934 and after reorg, so SEQUENCE rtl can legitimately show
2935 up here. */
2941 /* reorg creates USEs that look like this. We leave them
2942 alone because reorg needs them for its own purposes. */
2946 {
2951 {
2952 /* If we find a SET of something else, we can't
2953 delete the insn. */
2958 {
2964 }
2968 }
2971 {
2981 /* We may have a multi-word hard register and some, but not
2982 all, of the words of the register are needed in subsequent
2983 insns. Write REG_UNUSED notes for those parts that were not
2984 needed. */
2987 {
2998 }
2999 }
3002 }
3004 /* If PAT references the register that dies here, it is an
3005 additional use. Hence any prior SET isn't dead. However, this
3006 insn becomes the new place for the REG_DEAD note. */
3008 {
3012 }
3013 }
3014 }
3016 /* Delete INSN and recursively delete insns that compute values used only
3017 by INSN. This uses the REG_DEAD notes computed during flow analysis.
3019 Look at all our REG_DEAD notes. If a previous insn does nothing other
3020 than set a register that dies in this insn, we can delete that insn
3021 as well.
3023 On machines with CC0, if CC0 is used in this insn, we may be able to
3024 delete the insn that set it. */
3026 static void
3028 {
3032 {
3034 /* We assume that at this stage
3035 CC's are always set explicitly
3036 and always immediately before the jump that
3037 will use them. So if the previous insn
3038 exists to set the CC's, delete it
3039 (unless it performs auto-increments, etc.). */
3042 {
3046 else
3047 /* Otherwise, show that cc0 won't be used. */
3049 }
3050 }
3053 {
3057 /* Verify that the REG_NOTE is legitimate. */
3062 }
3065 }
3067 /* If all INSN does is set the pc, delete it,
3068 and delete the insn that set the condition codes for it
3069 if that's what the previous thing was. */
3071 static void
3073 {
3078 }
3082 {
3085 {
3091 }
3093 }
3095 /* Return TRUE if there is a NOTE_INSN_SWITCH_TEXT_SECTIONS note in between
3096 BEG and END. */
3098 static bool
3100 {
3106 }
3108 \f
3109 /* Once we have tried two ways to fill a delay slot, make a pass over the
3110 code to try to improve the results and to do such things as more jump
3111 threading. */
3113 static void
3115 {
3119 rtx target_label;
3121 /* Look at every JUMP_INSN and see if we can improve it. */
3123 {
3129 /* If this is a jump insn, see if it now jumps to a jump, jumps to
3130 the next insn, or jumps to a label that is not the last of a
3131 group of consecutive labels. */
3135 {
3137 target_label
3147 {
3150 }
3153 {
3157 }
3159 /* See if this jump conditionally branches around an unconditional
3160 jump. If so, invert this jump and point it to the target of the
3161 second jump. Check if it's possible on the target. */
3164 && target_label
3169 {
3172 /* Be careful how we do this to avoid deleting code or
3173 labels that are momentarily dead. See similar optimization
3174 in jump.c.
3176 We also need to ensure we properly handle the case when
3177 invert_jump fails. */
3184 {
3187 }
3196 }
3197 }
3199 /* If this is an unconditional jump and the previous insn is a
3200 conditional jump, try reversing the condition of the previous
3201 insn and swapping our targets. The next pass might be able to
3202 fill the slots.
3204 Don't do this if we expect the conditional branch to be true, because
3205 we would then be making the more common case longer. */
3212 {
3218 }
3220 /* Now look only at cases where we have a filled delay slot. */
3227 /* See if the first insn in the delay slot is redundant with some
3228 previous insn. Remove it from the delay slot if so; then set up
3229 to reprocess this insn. */
3231 {
3237 }
3239 /* See if we have a RETURN insn with a filled delay slot followed
3240 by a RETURN insn with an unfilled a delay slot. If so, we can delete
3241 the first RETURN (but not its delay insn). This gives the same
3242 effect in fewer instructions.
3244 Only do so if optimizing for size since this results in slower, but
3245 smaller code. */
3248 && next
3251 {
3255 /* Delete the RETURN and just execute the delay list insns.
3257 We do this by deleting the INSN containing the SEQUENCE, then
3258 re-emitting the insns separately, and then deleting the RETURN.
3259 This allows the count of the jump target to be properly
3260 decremented.
3262 Note that we need to change the INSN_UID of the re-emitted insns
3263 since it is used to hash the insns for mark_target_live_regs and
3264 the re-emitted insns will no longer be wrapped up in a SEQUENCE.
3266 Clear the from target bit, since these insns are no longer
3267 in delay slots. */
3280 }
3282 /* Now look only at the cases where we have a filled JUMP_INSN. */
3293 /* If this jump goes to another unconditional jump, thread it, but
3294 don't convert a jump into a RETURN here. */
3296 delay_jump_insn,
3303 {
3308 }
3310 /* If the first insn at TARGET_LABEL is redundant with a previous
3311 insn, redirect the jump to the following insn and process again.
3312 We use next_real_insn instead of next_active_insn so we
3313 don't skip USE-markers, or we'll end up with incorrect
3314 liveness info. */
3319 {
3320 /* Figure out where to emit the special USE insn so we don't
3321 later incorrectly compute register live/death info. */
3327 {
3328 /* Insert the special USE insn and update dataflow info.
3329 We know "trial" is an insn here as it is the output of
3330 next_real_insn () above. */
3333 /* Now emit a label before the special USE insn, and
3334 redirect our jump to the new label. */
3339 }
3340 }
3342 /* Similarly, if it is an unconditional jump with one insn in its
3343 delay list and that insn is redundant, thread the jump. */
3351 {
3359 {
3364 }
3365 }
3367 /* See if we have a simple (conditional) jump that is useless. */
3373 /* If the last insn in the delay slot sets CC0 for some insn,
3374 various code assumes that it is in a delay slot. We could
3375 put it back where it belonged and delete the register notes,
3376 but it doesn't seem worthwhile in this uncommon case. */
3377 && (!HAVE_cc0
3380 {
3384 /* All this insn does is execute its delay list and jump to the
3385 following insn. So delete the jump and just execute the delay
3386 list insns.
3388 We do this by deleting the INSN containing the SEQUENCE, then
3389 re-emitting the insns separately, and then deleting the jump.
3390 This allows the count of the jump target to be properly
3391 decremented.
3393 Note that we need to change the INSN_UID of the re-emitted insns
3394 since it is used to hash the insns for mark_target_live_regs and
3395 the re-emitted insns will no longer be wrapped up in a SEQUENCE.
3397 Clear the from target bit, since these insns are no longer
3398 in delay slots. */
3411 }
3413 /* See if this is an unconditional jump around a single insn which is
3414 identical to the one in its delay slot. In this case, we can just
3415 delete the branch and the insn in its delay slot. */
3421 {
3424 }
3426 /* See if this jump (with its delay slots) conditionally branches
3427 around an unconditional jump (without delay slots). If so, invert
3428 this jump and point it to the target of the second jump. We cannot
3429 do this for annulled jumps, though. Again, don't convert a jump to
3430 a RETURN here. */
3437 {
3444 /* find_end_label can generate a new label. Check this first. */
3449 {
3450 /* Be careful how we do this to avoid deleting code or labels
3451 that are momentarily dead. See similar optimization in
3452 jump.c */
3457 {
3460 /* Must update the INSN_FROM_TARGET_P bits now that
3461 the branch is reversed, so that mark_target_live_regs
3462 will handle the delay slot insn correctly. */
3464 {
3467 }
3471 }
3476 }
3477 }
3479 /* If we own the thread opposite the way this insn branches, see if we
3480 can merge its delay slots with following insns. */
3489 /* If we get here, we haven't deleted INSN. But we may have deleted
3490 NEXT, so recompute it. */
3492 }
3493 }
3494 \f
3496 /* Look for filled jumps to the end of function label. We can try to convert
3497 them into RETURN insns if the insns in the delay slot are valid for the
3498 RETURN as well. */
3500 static void
3502 {
3509 /* See if there is a RETURN insn in the function other than the one we
3510 made for END_OF_FUNCTION_LABEL. If so, set up anything we can't change
3511 into a RETURN to jump to it. */
3514 {
3518 else
3521 }
3523 /* Show an extra usage of REAL_RETURN_LABEL so it won't go away if it
3524 was equal to END_OF_FUNCTION_LABEL. */
3530 /* Clear the list of insns to fill so we can use it. */
3534 {
3538 /* Only look at filled JUMP_INSNs that go to the end of function
3539 label. */
3552 {
3555 }
3557 {
3560 }
3561 else
3566 /* If we can't make the jump into a RETURN, try to redirect it to the best
3567 RETURN and go on to the next insn. */
3569 {
3570 /* Make sure redirecting the jump will not invalidate the delay
3571 slot insns. */
3575 }
3577 /* See if this RETURN can accept the insns current in its delay slot.
3578 It can if it has more or an equal number of slots and the contents
3579 of each is valid. */
3584 {
3587 #if ANNUL_IFFALSE_SLOTS
3592 #endif
3593 #if ANNUL_IFTRUE_SLOTS
3598 #endif
3602 }
3603 else
3609 /* We have to do something with this insn. If it is an unconditional
3610 RETURN, delete the SEQUENCE and output the individual insns,
3611 followed by the RETURN. Then set things up so we try to find
3612 insns for its delay slots, if it needs some. */
3614 {
3619 {
3623 }
3631 }
3632 else
3633 /* It is probably more efficient to keep this with its current
3634 delay slot as a branch to a RETURN. */
3636 }
3638 /* Now delete REAL_RETURN_LABEL if we never used it. Then try to fill any
3639 new delay slots we have created. */
3648 }
3649 \f
3650 /* Try to find insns to place in delay slots. */
3652 static void
3654 {
3659 /* If the current function has no insns other than the prologue and
3660 epilogue, then do not try to fill any delay slots. */
3664 /* Find the highest INSN_UID and allocate and initialize our map from
3665 INSN_UID's to position in code. */
3667 {
3673 }
3679 /* Initialize the list of insns that need filling. */
3681 {
3684 }
3687 {
3688 rtx target;
3690 /* Skip vector tables. We can't get attributes for them. */
3701 /* Ensure all jumps go to the last of a set of consecutive labels. */
3708 }
3712 /* Show we haven't computed an end-of-function label yet. */
3715 /* Initialize the statistics for this function. */
3719 /* Now do the delay slot filling. Try everything twice in case earlier
3720 changes make more slots fillable. */
3724 reorg_pass_number++)
3725 {
3731 }
3733 /* If we made an end of function label, indicate that it is now
3734 safe to delete it by undoing our prior adjustment to LABEL_NUSES.
3735 If it is now unused, delete it. */
3749 /* Delete any USE insns made by update_block; subsequent passes don't need
3750 them or know how to deal with them. */
3752 {
3758 }
3762 /* It is not clear why the line below is needed, but it does seem to be. */
3766 {
3773 reorg_pass_number++)
3774 {
3777 {
3786 {
3792 }
3794 }
3795 }
3799 {
3804 {
3806 {
3807 rtx control;
3814 else
3816 }
3819 }
3820 }
3824 {
3826 {
3831 }
3832 }
3836 {
3840 {
3842 {
3847 }
3848 }
3850 }
3853 }
3856 {
3859 }
3864 }
3865 \f
3866 /* Run delay slot optimization. */
3867 static unsigned int
3869 {
3874 }
3879 {
3889 };
3892 {
3896 {}
3898 /* opt_pass methods: */
3901 {
3903 }
3907 bool
3909 {
3910 /* At -O0 dataflow info isn't updated after RA. */
3915 }
3919 rtl_opt_pass *
3921 {
3923 }
3925 /* Machine dependent reorg pass. */
3930 {
3940 };
3943 {
3947 {}
3949 /* opt_pass methods: */
3951 {
3953 }
3956 {
3959 }
3965 rtl_opt_pass *
3967 {
3969 }