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1 /* Perform instruction reorganizations for delay slot filling.
2 Copyright (C) 1992-2016 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 {
851 else
853 }
855 /* If there is no note, assume branches are not taken.
856 This should be rare. */
858 }
860 /* Return the condition under which INSN will branch to TARGET. If TARGET
861 is zero, return the condition under which INSN will return. If INSN is
862 an unconditional branch, return const_true_rtx. If INSN isn't a simple
863 type of jump, or it doesn't go to TARGET, return 0. */
865 static rtx
867 {
869 rtx src;
896 {
903 }
906 }
908 /* Return nonzero if CONDITION is more strict than the condition of
909 INSN, i.e., if INSN will always branch if CONDITION is true. */
911 static int
913 {
932 }
934 /* Return nonzero if redirecting JUMP to NEWLABEL does not invalidate
935 any insns already in the delay slot of JUMP. */
937 static int
939 {
943 /* Make sure all the delay slots of this jump would still
944 be valid after threading the jump. If they are still
945 valid, then return nonzero. */
950 #if ANNUL_IFFALSE_SLOTS
954 #endif
955 #if ANNUL_IFTRUE_SLOTS
959 #endif
964 }
966 /* Return nonzero if redirecting JUMP to NEWLABEL does not invalidate
967 any insns we wish to place in the delay slot of JUMP. */
969 static int
972 {
973 /* Make sure all the insns in DELAY_LIST would still be
974 valid after threading the jump. If they are still
975 valid, then return nonzero. */
982 #if ANNUL_IFFALSE_SLOTS
986 #endif
987 #if ANNUL_IFTRUE_SLOTS
991 #endif
996 }
998 /* DELAY_LIST is a list of insns that have already been placed into delay
999 slots. See if all of them have the same annulling status as ANNUL_TRUE_P.
1000 If not, return 0; otherwise return 1. */
1002 static int
1005 {
1014 }
1015 \f
1016 /* INSN branches to an insn whose pattern SEQ is a SEQUENCE. Given that
1017 the condition tested by INSN is CONDITION and the resources shown in
1018 OTHER_NEEDED are needed after INSN, see whether INSN can take all the insns
1019 from SEQ's delay list, in addition to whatever insns it may execute
1020 (in DELAY_LIST). SETS and NEEDED are denote resources already set and
1021 needed while searching for delay slot insns. Return the concatenated
1022 delay list if possible, otherwise, return 0.
1024 SLOTS_TO_FILL is the total number of slots required by INSN, and
1025 PSLOTS_FILLED points to the number filled so far (also the number of
1026 insns in DELAY_LIST). It is updated with the number that have been
1027 filled from the SEQUENCE, if any.
1029 PANNUL_P points to a nonzero value if we already know that we need
1030 to annul INSN. If this routine determines that annulling is needed,
1031 it may set that value nonzero.
1033 PNEW_THREAD points to a location that is to receive the place at which
1034 execution should continue. */
1036 static void
1043 {
1053 /* We can't do anything if there are more delay slots in SEQ than we
1054 can handle, or if we don't know that it will be a taken branch.
1055 We know that it will be a taken branch if it is either an unconditional
1056 branch or a conditional branch with a stricter branch condition.
1058 Also, exit if the branch has more than one set, since then it is computing
1059 other results that can't be ignored, e.g. the HPPA mov&branch instruction.
1060 ??? It may be possible to move other sets into INSN in addition to
1061 moving the instructions in the delay slots.
1063 We can not steal the delay list if one of the instructions in the
1064 current delay_list modifies the condition codes and the jump in the
1065 sequence is a conditional jump. We can not do this because we can
1066 not change the direction of the jump because the condition codes
1067 will effect the direction of the jump in the sequence. */
1073 {
1077 }
1084 /* On some targets, branches with delay slots can have a limited
1085 displacement. Give the back end a chance to tell us we can't do
1086 this. */
1092 {
1099 /* If TRIAL sets CC0, we can't copy it, so we can't steal this
1100 delay list. */
1102 /* If TRIAL is from the fallthrough code of an annulled branch insn
1103 in SEQ, we cannot use it. */
1108 /* If this insn was already done (usually in a previous delay slot),
1109 pretend we put it in our delay slot. */
1114 /* We will end up re-vectoring this branch, so compute flags
1115 based on jumping to the new label. */
1129 {
1131 {
1132 /* Frame related instructions cannot go into annulled delay
1133 slots, it messes up the dwarf info. */
1137 }
1141 total_slots_filled++;
1145 }
1146 else
1148 }
1150 /* Record the effect of the instructions that were redundant and which
1151 we therefore decided not to copy. */
1156 /* Show the place to which we will be branching. */
1159 /* Add any new insns to the delay list and update the count of the
1160 number of slots filled. */
1168 }
1169 \f
1170 /* Similar to steal_delay_list_from_target except that SEQ is on the
1171 fallthrough path of INSN. Here we only do something if the delay insn
1172 of SEQ is an unconditional branch. In that case we steal its delay slot
1173 for INSN since unconditional branches are much easier to fill. */
1175 static void
1184 {
1192 /* We can't do anything if SEQ's delay insn isn't an
1193 unconditional branch. */
1199 {
1202 /* If TRIAL sets CC0, stealing it will move it too far from the use
1203 of CC0. */
1211 /* If this insn was already done, we don't need it. */
1213 {
1217 }
1227 {
1235 }
1236 else
1238 }
1242 }
1243 \f
1244 /* Try merging insns starting at THREAD which match exactly the insns in
1245 INSN's delay list.
1247 If all insns were matched and the insn was previously annulling, the
1248 annul bit will be cleared.
1250 For each insn that is merged, if the branch is or will be non-annulling,
1251 we delete the merged insn. */
1253 static void
1255 {
1271 /* If this is not an annulling branch, take into account anything needed in
1272 INSN's delay slot. This prevents two increments from being incorrectly
1273 folded into one. If we are annulling, this would be the correct
1274 thing to do. (The alternative, looking at things set in NEXT_TO_MATCH
1275 will essentially disable this optimization. This method is somewhat of
1276 a kludge, but I don't see a better way.) */
1284 {
1290 /* TRIAL must be a CALL_INSN or INSN. Skip USE and CLOBBER. */
1296 /* We can't share an insn that sets cc0. */
1302 /* Update next_trial, in case try_split succeeded. */
1304 /* Likewise THREAD. */
1307 /* Have to test this condition if annul condition is different
1308 from (and less restrictive than) non-annulling one. */
1310 {
1313 {
1320 }
1321 else
1328 }
1332 }
1334 /* See if we stopped on a filled insn. If we did, try to see if its
1335 delay slots match. */
1341 {
1345 /* Account for resources set/needed by the filled insn. */
1350 {
1354 /* Account for resources set by the insn following NEXT_TO_MATCH
1355 inside INSN's delay list. */
1359 /* Account for resources set by the insn before DTRIAL and inside
1360 TRIAL's delay list. */
1369 /* Check that DTRIAL and NEXT_TO_MATCH does not reference a
1370 resource modified between them (only dtrial is checked because
1371 next_to_match and dtrial shall to be equal in order to hit
1372 this line) */
1375 {
1377 {
1385 }
1386 else
1394 }
1395 else
1396 {
1397 /* Keep track of the set/referenced resources for the delay
1398 slots of any trial insns we encounter. */
1401 }
1402 }
1403 }
1405 /* If all insns in the delay slot have been matched and we were previously
1406 annulling the branch, we need not any more. In that case delete all the
1407 merged insns. Also clear the INSN_FROM_TARGET_P bit of each insn in
1408 the delay list so that we know that it isn't only being used at the
1409 target. */
1411 {
1415 {
1420 }
1421 else
1422 {
1425 }
1431 }
1432 }
1433 \f
1434 /* See if INSN is redundant with an insn in front of TARGET. Often this
1435 is called when INSN is a candidate for a delay slot of TARGET.
1436 DELAY_LIST are insns that will be placed in delay slots of TARGET in front
1437 of INSN. Often INSN will be redundant with an insn in a delay slot of
1438 some previous insn. This happens when we have a series of branches to the
1439 same label; in that case the first insn at the target might want to go
1440 into each of the delay slots.
1442 If we are not careful, this routine can take up a significant fraction
1443 of the total compilation time (4%), but only wins rarely. Hence we
1444 speed this routine up by making two passes. The first pass goes back
1445 until it hits a label and sees if it finds an insn with an identical
1446 pattern. Only in this (relatively rare) event does it check for
1447 data conflicts.
1449 We do not split insns we encounter. This could cause us not to find a
1450 redundant insn, but the cost of splitting seems greater than the possible
1451 gain in rare cases. */
1455 {
1459 rtx pat;
1464 /* If INSN has any REG_UNUSED notes, it can't match anything since we
1465 are allowed to not actually assign to such a register. */
1469 /* Scan backwards looking for a match. */
1474 {
1475 /* (use (insn))s can come immediately after a barrier if the
1476 label that used to precede them has been deleted as dead.
1477 See delete_related_insns. */
1490 {
1491 /* Stop for a CALL and its delay slots because it is difficult to
1492 track its resource needs correctly. */
1496 /* Stop for an INSN or JUMP_INSN with delayed effects and its delay
1497 slots because it is difficult to track its resource needs
1498 correctly. */
1506 /* See if any of the insns in the delay slot match, updating
1507 resource requirements as we go. */
1514 /* If found a match, exit this loop early. */
1517 }
1522 }
1524 /* If we didn't find an insn that matches, return 0. */
1528 /* See what resources this insn sets and needs. If they overlap, or
1529 if this insn references CC0, it can't be redundant. */
1536 /* If TARGET is a SEQUENCE, get the main insn. */
1542 /* The insn requiring the delay may not set anything needed or set by
1543 INSN. */
1548 /* Insns we pass may not set either NEEDED or SET, so merge them for
1549 simpler tests. */
1553 /* This insn isn't redundant if it conflicts with an insn that either is
1554 or will be in a delay slot of TARGET. */
1568 /* Scan backwards until we reach a label or an insn that uses something
1569 INSN sets or sets something insn uses or sets. */
1575 {
1585 {
1589 /* If this is a CALL_INSN and its delay slots, it is hard to track
1590 the resource needs properly, so give up. */
1594 /* If this is an INSN or JUMP_INSN with delayed effects, it
1595 is hard to track the resource needs properly, so give up. */
1606 /* See if any of the insns in the delay slot match, updating
1607 resource requirements as we go. */
1609 {
1612 /* If an insn will be annulled if the branch is false, it isn't
1613 considered as a possible duplicate insn. */
1616 {
1617 /* Show that this insn will be used in the sequel. */
1620 }
1622 /* Unless this is an annulled insn from the target of a branch,
1623 we must stop if it sets anything needed or set by INSN. */
1627 }
1629 /* If the insn requiring the delay slot conflicts with INSN, we
1630 must stop. */
1633 }
1634 else
1635 {
1636 /* See if TRIAL is the same as INSN. */
1641 /* Can't go any further if TRIAL conflicts with INSN. */
1644 }
1645 }
1648 }
1649 \f
1650 /* Return 1 if THREAD can only be executed in one way. If LABEL is nonzero,
1651 it is the target of the branch insn being scanned. If ALLOW_FALLTHROUGH
1652 is nonzero, we are allowed to fall into this thread; otherwise, we are
1653 not.
1655 If LABEL is used more than one or we pass a label other than LABEL before
1656 finding an active insn, we do not own this thread. */
1658 static int
1660 {
1664 /* We don't own the function end. */
1668 /* We have a non-NULL insn. */
1671 /* Get the first active insn, or THREAD_INSN, if it is an active insn. */
1682 /* Ensure that we reach a BARRIER before any insn or label. */
1694 }
1695 \f
1696 /* Called when INSN is being moved from a location near the target of a jump.
1697 We leave a marker of the form (use (INSN)) immediately in front
1698 of WHERE for mark_target_live_regs. These markers will be deleted when
1699 reorg finishes.
1701 We used to try to update the live status of registers if WHERE is at
1702 the start of a basic block, but that can't work since we may remove a
1703 BARRIER in relax_delay_slots. */
1705 static void
1707 {
1708 /* Ignore if this was in a delay slot and it came from the target of
1709 a branch. */
1715 /* INSN might be making a value live in a block where it didn't use to
1716 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 REDUNDANT_INSN.
1802 This handles the case of udivmodXi4 instructions which optimize their
1803 output depending on whether any REG_UNUSED notes are present.
1804 we must make sure that INSN calculates as many results as REDUNDANT_INSN
1805 does. */
1807 static void
1809 {
1813 {
1823 }
1824 }
1825 \f
1828 /* Return the label before INSN, or put a new label there. If SIBLING is
1829 non-zero, it is another label associated with the new label (if any),
1830 typically the former target of the jump that will be redirected to
1831 the new label. */
1835 {
1838 /* Find an existing label at this point
1839 or make a new one if there is none. */
1843 {
1850 {
1853 }
1854 }
1856 }
1858 /* Scan a function looking for insns that need a delay slot and find insns to
1859 put into the delay slot.
1861 NON_JUMPS_P is nonzero if we are to only try to fill non-jump insns (such
1862 as calls). We do these first since we don't want jump insns (that are
1863 easier to fill) to get the only insns that could be used for non-jump insns.
1864 When it is zero, only try to fill JUMP_INSNs.
1866 When slots are filled in this manner, the insns (including the
1867 delay_insn) are put together in a SEQUENCE rtx. In this fashion,
1868 it is possible to tell whether a delay slot has really been filled
1869 or not. `final' knows how to deal with this, by communicating
1870 through FINAL_SEQUENCE. */
1872 static void
1874 {
1876 rtx pat;
1884 {
1886 /* Get the next insn to fill. If it has already had any slots assigned,
1887 we can't do anything with it. Maybe we'll improve this later. */
1898 /* It may have been that this insn used to need delay slots, but
1899 now doesn't; ignore in that case. This can happen, for example,
1900 on the HP PA RISC, where the number of delay slots depends on
1901 what insns are nearby. */
1904 /* Some machine description have defined instructions to have
1905 delay slots only in certain circumstances which may depend on
1906 nearby insns (which change due to reorg's actions).
1908 For example, the PA port normally has delay slots for unconditional
1909 jumps.
1911 However, the PA port claims such jumps do not have a delay slot
1912 if they are immediate successors of certain CALL_INSNs. This
1913 allows the port to favor filling the delay slot of the call with
1914 the unconditional jump. */
1918 /* This insn needs, or can use, some delay slots. SLOTS_TO_FILL
1919 says how many. After initialization, first try optimizing
1921 call _foo call _foo
1922 nop add %o7,.-L1,%o7
1923 b,a L1
1924 nop
1926 If this case applies, the delay slot of the call is filled with
1927 the unconditional jump. This is done first to avoid having the
1928 delay slot of the call filled in the backward scan. Also, since
1929 the unconditional jump is likely to also have a delay slot, that
1930 insn must exist when it is subsequently scanned.
1932 This is tried on each insn with delay slots as some machines
1933 have insns which perform calls, but are not represented as
1934 CALL_INSNs. */
1941 else
1950 {
1952 slots_filled++;
1955 /* TRIAL may have had its delay slot filled, then unfilled. When
1956 the delay slot is unfilled, TRIAL is placed back on the unfilled
1957 slots obstack. Unfortunately, it is placed on the end of the
1958 obstack, not in its original location. Therefore, we must search
1959 from entry i + 1 to the end of the unfilled slots obstack to
1960 try and find TRIAL. */
1963 tmp++;
1965 /* Remove the unconditional jump from consideration for delay slot
1966 filling and unthread it. */
1969 {
1976 }
1977 }
1979 /* Now, scan backwards from the insn to search for a potential
1980 delay-slot candidate. Stop searching when a label or jump is hit.
1982 For each candidate, if it is to go into the delay slot (moved
1983 forward in execution sequence), it must not need or set any resources
1984 that were set by later insns and must not set any resources that
1985 are needed for those insns.
1987 The delay slot insn itself sets resources unless it is a call
1988 (in which case the called routine, not the insn itself, is doing
1989 the setting). */
1992 {
1993 /* If the flags register is dead after the insn, then we want to be
1994 able to accept a candidate that clobbers it. For this purpose,
1995 we need to filter the flags register during life analysis, so
1996 that it doesn't create RAW and WAW dependencies, while still
1997 creating the necessary WAR dependencies. */
1998 bool filter_flags
2007 {
2010 }
2015 {
2018 /* This must be an INSN or CALL_INSN. */
2021 /* Stand-alone USE and CLOBBER are just for flow. */
2025 /* Check for resource conflict first, to avoid unnecessary
2026 splitting. */
2032 /* Can't separate set of cc0 from its use. */
2035 {
2039 {
2040 /* In this case, we are searching backward, so if we
2041 find insns to put on the delay list, we want
2042 to put them at the head, rather than the
2043 tail, of the list. */
2052 }
2053 }
2057 {
2059 /* If the flags register is set, then it doesn't create RAW
2060 dependencies any longer and it also doesn't create WAW
2061 dependencies since it's dead after the original insn. */
2063 {
2066 }
2067 }
2069 }
2070 }
2072 /* If all needed slots haven't been filled, we come here. */
2074 /* Try to optimize case of jumping around a single insn. */
2081 {
2085 }
2087 /* Try to get insns from beyond the insn needing the delay slot.
2088 These insns can neither set or reference resources set in insns being
2089 skipped, cannot set resources in the insn being skipped, and, if this
2090 is a CALL_INSN (or a CALL_INSN is passed), cannot trap (because the
2091 call might not return).
2093 There used to be code which continued past the target label if
2094 we saw all uses of the target label. This code did not work,
2095 because it failed to account for some instructions which were
2096 both annulled and marked as from the target. This can happen as a
2097 result of optimize_skip. Since this code was redundant with
2098 fill_eager_delay_slots anyways, it was just deleted. */
2101 /* If this instruction could throw an exception which is
2102 caught in the same function, then it's not safe to fill
2103 the delay slot with an instruction from beyond this
2104 point. For example, consider:
2106 int i = 2;
2108 try {
2109 f();
2110 i = 3;
2111 } catch (...) {}
2113 return i;
2115 Even though `i' is a local variable, we must be sure not
2116 to put `i = 3' in the delay slot if `f' might throw an
2117 exception.
2119 Presumably, we should also check to see if we could get
2120 back to this function via `setjmp'. */
2123 {
2137 {
2140 /* This must be an INSN or CALL_INSN. */
2143 /* Stand-alone USE and CLOBBER are just for flow. */
2147 /* If this already has filled delay slots, get the insn needing
2148 the delay slots. */
2151 else
2154 /* Stop our search when seeing a jump. */
2158 /* See if we have a resource problem before we try to split. */
2168 {
2178 }
2183 /* Ensure we don't put insns between the setting of cc and the
2184 comparison by moving a setting of cc into an earlier delay
2185 slot since these insns could clobber the condition code. */
2188 /* If this is a call, we might not get here. */
2191 }
2193 /* If there are slots left to fill and our search was stopped by an
2194 unconditional branch, try the insn at the branch target. We can
2195 redirect the branch if it works.
2197 Don't do this if the insn at the branch target is a branch. */
2199 && trial
2214 {
2215 /* See comment in relax_delay_slots about necessity of using
2216 next_real_insn here. */
2221 else
2225 {
2228 slots_filled++;
2230 new_label);
2231 }
2232 }
2233 }
2235 /* If this is an unconditional jump, then try to get insns from the
2236 target of the jump. */
2255 }
2256 }
2257 \f
2258 /* Follow any unconditional jump at LABEL, for the purpose of redirecting JUMP;
2259 return the ultimate label reached by any such chain of jumps.
2260 Return a suitable return rtx if the chain ultimately leads to a
2261 return instruction.
2262 If LABEL is not followed by a jump, return LABEL.
2263 If the chain loops or we can't find end, return LABEL,
2264 since that tells caller to avoid changing the insn.
2265 If the returned label is obtained by following a crossing jump,
2266 set *CROSSING to true, otherwise set it to false. */
2268 static rtx
2270 {
2290 depth++)
2291 {
2294 /* If we have found a cycle, make the insn jump to itself. */
2298 /* Cannot follow returns and cannot look through tablejumps. */
2312 }
2316 }
2318 /* Try to find insns to place in delay slots.
2320 INSN is the jump needing SLOTS_TO_FILL delay slots. It tests CONDITION
2321 or is an unconditional branch if CONDITION is const_true_rtx.
2322 *PSLOTS_FILLED is updated with the number of slots that we have filled.
2324 THREAD is a flow-of-control, either the insns to be executed if the
2325 branch is true or if the branch is false, THREAD_IF_TRUE says which.
2327 OPPOSITE_THREAD is the thread in the opposite direction. It is used
2328 to see if any potential delay slot insns set things needed there.
2330 LIKELY is nonzero if it is extremely likely that the branch will be
2331 taken and THREAD_IF_TRUE is set. This is used for the branch at the
2332 end of a loop back up to the top.
2334 OWN_THREAD and OWN_OPPOSITE_THREAD are true if we are the only user of the
2335 thread. I.e., it is the fallthrough code of our jump or the target of the
2336 jump when we are the only jump going there.
2338 If OWN_THREAD is false, it must be the "true" thread of a jump. In that
2339 case, we can only take insns from the head of the thread for our delay
2340 slot. We then adjust the jump to point after the insns we have taken. */
2342 static void
2347 {
2348 rtx new_thread;
2355 /* Validate our arguments. */
2361 /* If our thread is the end of subroutine, we can't get any delay
2362 insns from that. */
2368 /* If this is an unconditional branch, nothing is needed at the
2369 opposite thread. Otherwise, compute what is needed there. */
2372 else
2375 /* If the insn at THREAD can be split, do it here to avoid having to
2376 update THREAD and NEW_THREAD if it is done in the loop below. Also
2377 initialize NEW_THREAD. */
2381 /* Scan insns at THREAD. We are looking for an insn that can be removed
2382 from THREAD (it neither sets nor references resources that were set
2383 ahead of it and it doesn't set anything needs by the insns ahead of
2384 it) and that either can be placed in an annulling insn or aren't
2385 needed at OPPOSITE_THREAD. */
2390 /* If we do not own this thread, we must stop as soon as we find
2391 something that we can't put in a delay slot, since all we can do
2392 is branch into THREAD at a later point. Therefore, labels stop
2393 the search if this is not the `true' thread. */
2398 {
2401 /* If we have passed a label, we no longer own this thread. */
2403 {
2406 }
2412 /* If TRIAL conflicts with the insns ahead of it, we lose. Also,
2413 don't separate or copy insns that set and use CC0. */
2420 {
2423 /* If TRIAL is redundant with some insn before INSN, we don't
2424 actually need to add it to the delay list; we can merely pretend
2425 we did. */
2427 {
2430 {
2433 {
2437 }
2440 }
2441 else
2442 {
2445 }
2448 }
2450 /* There are two ways we can win: If TRIAL doesn't set anything
2451 needed at the opposite thread and can't trap, or if it can
2452 go into an annulled delay slot. But we want neither to copy
2453 nor to speculate frame-related insns. */
2460 {
2470 }
2474 {
2487 {
2491 winner:
2496 /* If we own this thread, delete the insn. If this is the
2497 destination of a branch, show that a basic block status
2498 may have been updated. In any case, mark the new
2499 starting point of this thread. */
2501 {
2502 rtx note;
2506 {
2510 }
2512 /* We are moving this insn, not deleting it. We must
2513 temporarily increment the use count on any referenced
2514 label lest it be deleted by delete_related_insns. */
2520 {
2521 /* REG_LABEL_OPERAND could be
2522 NOTE_INSN_DELETED_LABEL too. */
2525 else
2528 }
2539 {
2540 /* REG_LABEL_OPERAND could be
2541 NOTE_INSN_DELETED_LABEL too. */
2544 else
2547 }
2550 }
2551 else
2561 {
2562 /* Even though we have filled all the slots, we
2563 may be branching to a location that has a
2564 redundant insn. Skip any if so. */
2571 && (prior_insn
2574 {
2575 /* We know we do not own the thread, so no need
2576 to call update_block and delete_insn. */
2579 new_thread
2581 }
2583 }
2586 }
2587 }
2588 }
2590 /* This insn can't go into a delay slot. */
2595 /* Ensure we don't put insns between the setting of cc and the comparison
2596 by moving a setting of cc into an earlier delay slot since these insns
2597 could clobber the condition code. */
2600 /* If this insn is a register-register copy and the next insn has
2601 a use of our destination, change it to use our source. That way,
2602 it will become a candidate for our delay slot the next time
2603 through this loop. This case occurs commonly in loops that
2604 scan a list.
2606 We could check for more complex cases than those tested below,
2607 but it doesn't seem worth it. It might also be a good idea to try
2608 to swap the two insns. That might do better.
2610 We can't do this if the next insn modifies our destination, because
2611 that would make the replacement into the insn invalid. We also can't
2612 do this if it modifies our source, because it might be an earlyclobber
2613 operand. This latter test also prevents updating the contents of
2614 a PRE_INC. We also can't do this if there's overlap of source and
2615 destination. Overlap may happen for larger-than-register-size modes. */
2621 {
2631 }
2632 }
2634 /* If we stopped on a branch insn that has delay slots, see if we can
2635 steal some of the insns in those slots. */
2639 {
2641 /* If this is the `true' thread, we will want to follow the jump,
2642 so we can only do this if we have taken everything up to here. */
2644 {
2650 /* If we owned the thread and are told that it branched
2651 elsewhere, make sure we own the thread at the new location. */
2654 }
2660 }
2662 /* If we haven't found anything for this delay slot and it is very
2663 likely that the branch will be taken, see if the insn at our target
2664 increments or decrements a register with an increment that does not
2665 depend on the destination register. If so, try to place the opposite
2666 arithmetic insn after the jump insn and put the arithmetic insn in the
2667 delay slot. If we can't do this, return. */
2674 {
2676 rtx dest;
2677 rtx src;
2679 /* We know "new_thread" is an insn due to NONJUMP_INSN_P (new_thread)
2680 above. */
2697 {
2699 rtx new_arith;
2702 /* If this is a constant adjustment, use the same code with
2703 the negated constant. Otherwise, reverse the sense of the
2704 arithmetic. */
2708 else
2717 {
2720 }
2723 {
2726 {
2730 }
2732 }
2733 else
2742 }
2743 }
2748 /* If we are to branch into the middle of this thread, find an appropriate
2749 label or make a new one if none, and redirect INSN to it. If we hit the
2750 end of the function, use the end-of-function label. */
2752 {
2753 rtx label;
2769 else
2774 {
2778 }
2779 }
2780 }
2781 \f
2782 /* Make another attempt to find insns to place in delay slots.
2784 We previously looked for insns located in front of the delay insn
2785 and, for non-jump delay insns, located behind the delay insn.
2787 Here only try to schedule jump insns and try to move insns from either
2788 the target or the following insns into the delay slot. If annulling is
2789 supported, we will be likely to do this. Otherwise, we can do this only
2790 if safe. */
2792 static void
2794 {
2800 {
2801 rtx condition;
2818 /* Some machine description have defined instructions to have
2819 delay slots only in certain circumstances which may depend on
2820 nearby insns (which change due to reorg's actions).
2822 For example, the PA port normally has delay slots for unconditional
2823 jumps.
2825 However, the PA port claims such jumps do not have a delay slot
2826 if they are immediate successors of certain CALL_INSNs. This
2827 allows the port to favor filling the delay slot of the call with
2828 the unconditional jump. */
2839 /* Get the next active fallthrough and target insns and see if we own
2840 them. Then see whether the branch is likely true. We don't need
2841 to do a lot of this for unconditional branches. */
2847 {
2851 }
2852 else
2853 {
2857 }
2859 /* If this insn is expected to branch, first try to get insns from our
2860 target, then our fallthrough insns. If it is not expected to branch,
2861 try the other order. */
2864 {
2867 own_target,
2871 {
2872 /* Even though we didn't find anything for delay slots,
2873 we might have found a redundant insn which we deleted
2874 from the thread that was filled. So we have to recompute
2875 the next insn at the target. */
2883 }
2884 }
2885 else
2886 {
2896 }
2906 }
2907 }
2908 \f
2911 /* Recursively delete prior insns that compute the value (used only by INSN
2912 which the caller is deleting) stored in the register mentioned by NOTE
2913 which is a REG_DEAD note associated with INSN. */
2915 static void
2917 {
2925 {
2928 /* If we reach a CALL which is not calling a const function
2929 or the callee pops the arguments, then give up. */
2935 /* If we reach a SEQUENCE, it is too complex to try to
2936 do anything with it, so give up. We can be run during
2937 and after reorg, so SEQUENCE rtl can legitimately show
2938 up here. */
2944 /* reorg creates USEs that look like this. We leave them
2945 alone because reorg needs them for its own purposes. */
2949 {
2954 {
2955 /* If we find a SET of something else, we can't
2956 delete the insn. */
2961 {
2967 }
2971 }
2974 {
2984 /* We may have a multi-word hard register and some, but not
2985 all, of the words of the register are needed in subsequent
2986 insns. Write REG_UNUSED notes for those parts that were not
2987 needed. */
2990 {
3001 }
3002 }
3005 }
3007 /* If PAT references the register that dies here, it is an
3008 additional use. Hence any prior SET isn't dead. However, this
3009 insn becomes the new place for the REG_DEAD note. */
3011 {
3015 }
3016 }
3017 }
3019 /* Delete INSN and recursively delete insns that compute values used only
3020 by INSN. This uses the REG_DEAD notes computed during flow analysis.
3022 Look at all our REG_DEAD notes. If a previous insn does nothing other
3023 than set a register that dies in this insn, we can delete that insn
3024 as well.
3026 On machines with CC0, if CC0 is used in this insn, we may be able to
3027 delete the insn that set it. */
3029 static void
3031 {
3035 {
3037 /* We assume that at this stage
3038 CC's are always set explicitly
3039 and always immediately before the jump that
3040 will use them. So if the previous insn
3041 exists to set the CC's, delete it
3042 (unless it performs auto-increments, etc.). */
3045 {
3049 else
3050 /* Otherwise, show that cc0 won't be used. */
3052 }
3053 }
3056 {
3060 /* Verify that the REG_NOTE is legitimate. */
3065 }
3068 }
3070 /* If all INSN does is set the pc, delete it,
3071 and delete the insn that set the condition codes for it
3072 if that's what the previous thing was. */
3074 static void
3076 {
3081 }
3085 {
3088 {
3094 }
3096 }
3098 /* Return TRUE if there is a NOTE_INSN_SWITCH_TEXT_SECTIONS note in between
3099 BEG and END. */
3101 static bool
3103 {
3109 }
3111 \f
3112 /* Once we have tried two ways to fill a delay slot, make a pass over the
3113 code to try to improve the results and to do such things as more jump
3114 threading. */
3116 static void
3118 {
3121 rtx trial;
3123 rtx target_label;
3125 /* Look at every JUMP_INSN and see if we can improve it. */
3127 {
3133 /* If this is a jump insn, see if it now jumps to a jump, jumps to
3134 the next insn, or jumps to a label that is not the last of a
3135 group of consecutive labels. */
3139 {
3141 target_label
3151 {
3154 }
3157 {
3161 }
3163 /* See if this jump conditionally branches around an unconditional
3164 jump. If so, invert this jump and point it to the target of the
3165 second jump. Check if it's possible on the target. */
3168 && target_label
3173 {
3176 /* Be careful how we do this to avoid deleting code or
3177 labels that are momentarily dead. See similar optimization
3178 in jump.c.
3180 We also need to ensure we properly handle the case when
3181 invert_jump fails. */
3188 {
3191 }
3200 }
3201 }
3203 /* If this is an unconditional jump and the previous insn is a
3204 conditional jump, try reversing the condition of the previous
3205 insn and swapping our targets. The next pass might be able to
3206 fill the slots.
3208 Don't do this if we expect the conditional branch to be true, because
3209 we would then be making the more common case longer. */
3216 {
3222 }
3224 /* Now look only at cases where we have a filled delay slot. */
3231 /* See if the first insn in the delay slot is redundant with some
3232 previous insn. Remove it from the delay slot if so; then set up
3233 to reprocess this insn. */
3235 {
3240 }
3242 /* See if we have a RETURN insn with a filled delay slot followed
3243 by a RETURN insn with an unfilled a delay slot. If so, we can delete
3244 the first RETURN (but not its delay insn). This gives the same
3245 effect in fewer instructions.
3247 Only do so if optimizing for size since this results in slower, but
3248 smaller code. */
3251 && next
3254 {
3258 /* Delete the RETURN and just execute the delay list insns.
3260 We do this by deleting the INSN containing the SEQUENCE, then
3261 re-emitting the insns separately, and then deleting the RETURN.
3262 This allows the count of the jump target to be properly
3263 decremented.
3265 Note that we need to change the INSN_UID of the re-emitted insns
3266 since it is used to hash the insns for mark_target_live_regs and
3267 the re-emitted insns will no longer be wrapped up in a SEQUENCE.
3269 Clear the from target bit, since these insns are no longer
3270 in delay slots. */
3283 }
3285 /* Now look only at the cases where we have a filled JUMP_INSN. */
3296 /* If this jump goes to another unconditional jump, thread it, but
3297 don't convert a jump into a RETURN here. */
3299 delay_jump_insn,
3306 {
3311 }
3313 /* If the first insn at TARGET_LABEL is redundant with a previous
3314 insn, redirect the jump to the following insn and process again.
3315 We use next_real_insn instead of next_active_insn so we
3316 don't skip USE-markers, or we'll end up with incorrect
3317 liveness info. */
3322 {
3323 /* Figure out where to emit the special USE insn so we don't
3324 later incorrectly compute register live/death info. */
3330 {
3331 /* Insert the special USE insn and update dataflow info.
3332 We know "trial" is an insn here as it is the output of
3333 next_real_insn () above. */
3336 /* Now emit a label before the special USE insn, and
3337 redirect our jump to the new label. */
3342 }
3343 }
3345 /* Similarly, if it is an unconditional jump with one insn in its
3346 delay list and that insn is redundant, thread the jump. */
3354 {
3362 {
3367 }
3368 }
3370 /* See if we have a simple (conditional) jump that is useless. */
3375 /* If the last insn in the delay slot sets CC0 for some insn,
3376 various code assumes that it is in a delay slot. We could
3377 put it back where it belonged and delete the register notes,
3378 but it doesn't seem worthwhile in this uncommon case. */
3379 && (!HAVE_cc0
3382 {
3386 /* All this insn does is execute its delay list and jump to the
3387 following insn. So delete the jump and just execute the delay
3388 list insns.
3390 We do this by deleting the INSN containing the SEQUENCE, then
3391 re-emitting the insns separately, and then deleting the jump.
3392 This allows the count of the jump target to be properly
3393 decremented.
3395 Note that we need to change the INSN_UID of the re-emitted insns
3396 since it is used to hash the insns for mark_target_live_regs and
3397 the re-emitted insns will no longer be wrapped up in a SEQUENCE.
3399 Clear the from target bit, since these insns are no longer
3400 in delay slots. */
3413 }
3415 /* See if this is an unconditional jump around a single insn which is
3416 identical to the one in its delay slot. In this case, we can just
3417 delete the branch and the insn in its delay slot. */
3423 {
3426 }
3428 /* See if this jump (with its delay slots) conditionally branches
3429 around an unconditional jump (without delay slots). If so, invert
3430 this jump and point it to the target of the second jump. We cannot
3431 do this for annulled jumps, though. Again, don't convert a jump to
3432 a RETURN here. */
3439 {
3446 /* find_end_label can generate a new label. Check this first. */
3451 {
3452 /* Be careful how we do this to avoid deleting code or labels
3453 that are momentarily dead. See similar optimization in
3454 jump.c */
3459 {
3462 /* Must update the INSN_FROM_TARGET_P bits now that
3463 the branch is reversed, so that mark_target_live_regs
3464 will handle the delay slot insn correctly. */
3466 {
3469 }
3473 }
3478 }
3479 }
3481 /* If we own the thread opposite the way this insn branches, see if we
3482 can merge its delay slots with following insns. */
3491 /* If we get here, we haven't deleted INSN. But we may have deleted
3492 NEXT, so recompute it. */
3494 }
3495 }
3496 \f
3498 /* Look for filled jumps to the end of function label. We can try to convert
3499 them into RETURN insns if the insns in the delay slot are valid for the
3500 RETURN as well. */
3502 static void
3504 {
3511 /* See if there is a RETURN insn in the function other than the one we
3512 made for END_OF_FUNCTION_LABEL. If so, set up anything we can't change
3513 into a RETURN to jump to it. */
3516 {
3520 else
3523 }
3525 /* Show an extra usage of REAL_RETURN_LABEL so it won't go away if it
3526 was equal to END_OF_FUNCTION_LABEL. */
3532 /* Clear the list of insns to fill so we can use it. */
3536 {
3540 /* Only look at filled JUMP_INSNs that go to the end of function
3541 label. */
3554 {
3557 }
3559 {
3562 }
3563 else
3568 /* If we can't make the jump into a RETURN, try to redirect it to the best
3569 RETURN and go on to the next insn. */
3571 {
3572 /* Make sure redirecting the jump will not invalidate the delay
3573 slot insns. */
3577 }
3579 /* See if this RETURN can accept the insns current in its delay slot.
3580 It can if it has more or an equal number of slots and the contents
3581 of each is valid. */
3586 {
3589 #if ANNUL_IFFALSE_SLOTS
3594 #endif
3595 #if ANNUL_IFTRUE_SLOTS
3600 #endif
3604 }
3605 else
3611 /* We have to do something with this insn. If it is an unconditional
3612 RETURN, delete the SEQUENCE and output the individual insns,
3613 followed by the RETURN. Then set things up so we try to find
3614 insns for its delay slots, if it needs some. */
3616 {
3628 }
3629 else
3630 /* It is probably more efficient to keep this with its current
3631 delay slot as a branch to a RETURN. */
3633 }
3635 /* Now delete REAL_RETURN_LABEL if we never used it. Then try to fill any
3636 new delay slots we have created. */
3645 }
3646 \f
3647 /* Try to find insns to place in delay slots. */
3649 static void
3651 {
3656 /* If the current function has no insns other than the prologue and
3657 epilogue, then do not try to fill any delay slots. */
3661 /* Find the highest INSN_UID and allocate and initialize our map from
3662 INSN_UID's to position in code. */
3664 {
3670 }
3676 /* Initialize the list of insns that need filling. */
3678 {
3681 }
3684 {
3685 rtx target;
3687 /* Skip vector tables. We can't get attributes for them. */
3698 /* Ensure all jumps go to the last of a set of consecutive labels. */
3705 }
3709 /* Show we haven't computed an end-of-function label yet. */
3712 /* Initialize the statistics for this function. */
3716 /* Now do the delay slot filling. Try everything twice in case earlier
3717 changes make more slots fillable. */
3721 reorg_pass_number++)
3722 {
3728 }
3730 /* If we made an end of function label, indicate that it is now
3731 safe to delete it by undoing our prior adjustment to LABEL_NUSES.
3732 If it is now unused, delete it. */
3746 /* Delete any USE insns made by update_block; subsequent passes don't need
3747 them or know how to deal with them. */
3749 {
3755 }
3759 /* It is not clear why the line below is needed, but it does seem to be. */
3763 {
3770 reorg_pass_number++)
3771 {
3774 {
3783 {
3789 }
3791 }
3792 }
3796 {
3801 {
3803 {
3804 rtx control;
3811 else
3813 }
3816 }
3817 }
3821 {
3823 {
3828 }
3829 }
3833 {
3837 {
3839 {
3844 }
3845 }
3847 }
3850 }
3853 {
3856 }
3861 }
3862 \f
3863 /* Run delay slot optimization. */
3864 static unsigned int
3866 {
3871 }
3876 {
3886 };
3889 {
3893 {}
3895 /* opt_pass methods: */
3898 {
3900 }
3904 bool
3906 {
3907 /* At -O0 dataflow info isn't updated after RA. */
3912 }
3916 rtl_opt_pass *
3918 {
3920 }
3922 /* Machine dependent reorg pass. */
3927 {
3937 };
3940 {
3944 {}
3946 /* opt_pass methods: */
3948 {
3950 }
3953 {
3956 }
3962 rtl_opt_pass *
3964 {
3966 }