| blob | 4025d8bbb218fdb1fd8413d3c9b91078ddcd85a4 |
1 /* Optimize jump instructions, for GNU compiler.
2 Copyright (C) 1987, 88, 89, 91, 92, 1993 Free Software Foundation, Inc.
4 This file is part of GNU CC.
6 GNU CC is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 2, or (at your option)
9 any later version.
11 GNU CC is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with GNU CC; see the file COPYING. If not, write to
18 the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */
21 /* This is the jump-optimization pass of the compiler.
22 It is run two or three times: once before cse, sometimes once after cse,
23 and once after reload (before final).
25 jump_optimize deletes unreachable code and labels that are not used.
26 It also deletes jumps that jump to the following insn,
27 and simplifies jumps around unconditional jumps and jumps
28 to unconditional jumps.
30 Each CODE_LABEL has a count of the times it is used
31 stored in the LABEL_NUSES internal field, and each JUMP_INSN
32 has one label that it refers to stored in the
33 JUMP_LABEL internal field. With this we can detect labels that
34 become unused because of the deletion of all the jumps that
35 formerly used them. The JUMP_LABEL info is sometimes looked
36 at by later passes.
38 Optionally, cross-jumping can be done. Currently it is done
39 only the last time (when after reload and before final).
40 In fact, the code for cross-jumping now assumes that register
41 allocation has been done, since it uses `rtx_renumbered_equal_p'.
43 Jump optimization is done after cse when cse's constant-propagation
44 causes jumps to become unconditional or to be deleted.
46 Unreachable loops are not detected here, because the labels
47 have references and the insns appear reachable from the labels.
48 find_basic_blocks in flow.c finds and deletes such loops.
50 The subroutines delete_insn, redirect_jump, and invert_jump are used
51 from other passes as well. */
63 /* ??? Eventually must record somehow the labels used by jumps
64 from nested functions. */
65 /* Pre-record the next or previous real insn for each label?
66 No, this pass is very fast anyway. */
67 /* Condense consecutive labels?
68 This would make life analysis faster, maybe. */
69 /* Optimize jump y; x: ... y: jumpif... x?
70 Don't know if it is worth bothering with. */
71 /* Optimize two cases of conditional jump to conditional jump?
72 This can never delete any instruction or make anything dead,
73 or even change what is live at any point.
74 So perhaps let combiner do it. */
76 /* Vector indexed by uid.
77 For each CODE_LABEL, index by its uid to get first unconditional jump
78 that jumps to the label.
79 For each JUMP_INSN, index by its uid to get the next unconditional jump
80 that jumps to the same label.
81 Element 0 is the start of a chain of all return insns.
82 (It is safe to use element 0 because insn uid 0 is not used. */
86 /* List of labels referred to from initializers.
87 These can never be deleted. */
88 rtx forced_labels;
90 /* Maximum index in jump_chain. */
94 /* Set nonzero by jump_optimize if control can fall through
95 to the end of the function. */
98 /* Indicates whether death notes are significant in cross jump analysis.
99 Normally they are not significant, because of A and B jump to C,
100 and R dies in A, it must die in B. But this might not be true after
101 stack register conversion, and we must compare death notes in that
102 case. */
119 \f
120 /* Delete no-op jumps and optimize jumps to jumps
121 and jumps around jumps.
122 Delete unused labels and unreachable code.
124 If CROSS_JUMP is 1, detect matching code
125 before a jump and its destination and unify them.
126 If CROSS_JUMP is 2, do cross-jumping, but pay attention to death notes.
128 If NOOP_MOVES is nonzero, delete no-op move insns.
130 If AFTER_REGSCAN is nonzero, then this jump pass is being run immediately
131 after regscan, and it is safe to use regno_first_uid and regno_last_uid.
133 If `optimize' is zero, don't change any code,
134 just determine whether control drops off the end of the function.
135 This case occurs when we have -W and not -O.
136 It works because `delete_insn' checks the value of `optimize'
137 and refrains from actually deleting when that is 0. */
139 void
141 rtx f;
145 {
150 rtx last_insn;
154 /* Initialize LABEL_NUSES and JUMP_LABEL fields. */
157 {
164 }
166 max_uid++;
168 /* Delete insns following barriers, up to next label. */
171 {
173 {
176 {
180 else
182 }
183 /* INSN is now the code_label. */
184 }
185 else
187 }
189 /* Leave some extra room for labels and duplicate exit test insns
190 we make. */
195 /* Mark the label each jump jumps to.
196 Combine consecutive labels, and count uses of labels.
198 For each label, make a chain (using `jump_chain')
199 of all the *unconditional* jumps that jump to it;
200 also make a chain of all returns. */
206 {
209 {
211 {
215 }
217 {
220 }
221 }
222 }
224 /* Keep track of labels used from static data;
225 they cannot ever be deleted. */
230 /* Delete all labels already not referenced.
231 Also find the last insn. */
235 {
238 else
239 {
242 }
243 }
246 {
247 /* See if there is still a NOTE_INSN_FUNCTION_END in this function.
248 If so record that this function can drop off the end. */
251 {
254 /* One label can follow the end-note: the return label. */
256 /* Ordinary insns can follow it if returning a structure. */
258 /* If machine uses explicit RETURN insns, no epilogue,
259 then one of them follows the note. */
262 /* Other kinds of notes can follow also. */
266 }
268 /* Report if control can fall through at the end of the function. */
274 /* Zero the "deleted" flag of all the "deleted" insns. */
278 }
280 #ifdef HAVE_return
282 {
283 /* If we fall through to the epilogue, see if we can insert a RETURN insn
284 in front of it. If the machine allows it at this point (we might be
285 after reload for a leaf routine), it will improve optimization for it
286 to be there. */
292 {
295 }
296 }
297 #endif
301 {
305 {
308 /* Combine stack_adjusts with following push_insns. */
309 #ifdef PUSH_ROUNDING
316 {
317 rtx p;
323 /* Find all successive push insns. */
325 /* Don't convert more than three pushes;
326 that starts adding too many displaced addresses
327 and the whole thing starts becoming a losing
328 proposition. */
330 {
339 /* Allow a no-op move between the adjust and the push. */
348 pushes++;
353 }
355 /* Discard the amount pushed from the stack adjust;
356 maybe eliminate it entirely. */
358 {
361 }
362 else
366 /* Change the appropriate push insns to ordinary stores. */
369 {
383 /* If this push doesn't fully fit in the space
384 of the stack adjust that we deleted,
385 make another stack adjust here for what we
386 didn't use up. There should be peepholes
387 to recognize the resulting sequence of insns. */
389 {
392 p);
394 }
397 }
398 }
399 #endif
401 /* Detect and delete no-op move instructions
402 resulting from not allocating a parameter in a register. */
415 /* Detect and ignore no-op move instructions
416 resulting from smart or fortuitous register allocation. */
419 {
426 {
427 rtx trial;
432 #ifdef PRESERVE_DEATH_INFO_REGNO_P
433 /* Deleting insn could lose a death-note for SREG or DREG
434 so don't do it if final needs accurate death-notes. */
437 #endif
438 {
439 /* DREG may have been the target of a REG_DEAD note in
440 the insn which makes INSN redundant. If so, reorg
441 would still think it is dead. So search for such a
442 note and delete it if we find it. */
447 {
450 }
455 }
456 }
461 {
462 /* This handles the case where we have two consecutive
463 assignments of the same constant to pseudos that didn't
464 get a hard reg. Each SET from the constant will be
465 converted into a SET of the spill register and an
466 output reload will be made following it. This produces
467 two loads of the same constant into the same spill
468 register. */
472 /* Look back for a death note for the first reg.
473 If there is one, it is no longer accurate. */
475 {
479 {
482 }
484 }
486 /* Delete the second load of the value. */
488 }
489 }
491 {
492 /* If each part is a set between two identical registers or
493 a USE or CLOBBER, delete the insn. */
495 rtx tem;
498 {
508 }
512 }
514 in the big-endian case. */
515 /* Also delete insns to store bit fields if they are no-ops. */
524 }
526 }
528 /* If we haven't yet gotten to reload and we have just run regscan,
529 delete any insn that sets a register that isn't used elsewhere.
530 This helps some of the optimizations below by having less insns
531 being jumped around. */
535 {
546 }
548 /* Now iterate optimizing jumps until nothing changes over one pass. */
551 {
555 {
556 rtx reallabelprev;
558 rtx nlabel;
560 #if 0
561 /* If NOT the first iteration, if this is the last jump pass
562 (just before final), do the special peephole optimizations.
563 Avoiding the first iteration gives ordinary jump opts
564 a chance to work before peephole opts. */
569 #endif
571 /* That could have deleted some insns after INSN, so check now
572 what the following insn is. */
576 /* See if this is a NOTE_INSN_LOOP_BEG followed by an unconditional
577 jump. Try to optimize by duplicating the loop exit test if so.
578 This is only safe immediately after regscan, because it uses
579 the values of regno_first_uid and regno_last_uid. */
584 {
587 {
591 }
592 }
600 /* Tension the labels in dispatch tables. */
607 /* If a dispatch table always goes to the same place,
608 get rid of it and replace the insn that uses it. */
612 {
627 /* Don't mess with a casesi insn. */
632 {
636 }
637 }
641 /* If a jump references the end of the function, try to turn
642 it into a RETURN insn, possibly a conditional one. */
649 /* Detect jump to following insn. */
651 {
655 }
657 /* If we have an unconditional jump preceded by a USE, try to put
658 the USE before the target and jump there. This simplifies many
659 of the optimizations below since we don't have to worry about
660 dealing with these USE insns. We only do this if the label
661 being branch to already has the identical USE or if code
662 never falls through to that label. */
671 {
673 {
676 }
682 }
684 /* Simplify if (...) x = a; else x = b; by converting it
685 to x = b; if (...) x = a;
686 if B is sufficiently simple, the test doesn't involve X,
687 and nothing in the test modifies B or X.
689 If we have small register classes, we also can't do this if X
690 is a hard register.
692 If the "x = b;" insn has any REG_NOTES, we don't do this because
693 of the possibility that we are running after CSE and there is a
694 REG_EQUAL note that is only valid if the branch has already been
695 taken. If we move the insn with the REG_EQUAL note, we may
696 fold the comparison to always be false in a later CSE pass.
697 (We could also delete the REG_NOTES when moving the insn, but it
698 seems simpler to not move it.) An exception is that we can move
699 the insn if the only note is a REG_EQUAL or REG_EQUIV whose
700 value is the same as "b".
702 INSN is the branch over the `else' part.
704 We set:
706 TEMP to the jump insn preceding "x = a;"
707 TEMP1 to X
708 TEMP2 to the insn that sets "x = b;"
709 TEMP3 to the insn that sets "x = a;"
710 TEMP4 to the set of "x = b"; */
717 #ifdef SMALL_REGISTER_CLASSES
719 #endif
735 /* TEMP must skip over the "x = a;" insn */
738 /* There must be no other entries to the "x = b;" insn. */
740 /* INSN must either branch to the insn after TEMP2 or the insn
741 after TEMP2 must branch to the same place as INSN. */
746 {
747 /* The test expression, X, may be a complicated test with
748 multiple branches. See if we can find all the uses of
749 the label that TEMP branches to without hitting a CALL_INSN
750 or a jump to somewhere else. */
755 /* Set P to the first jump insn that goes around "x = a;". */
757 {
759 {
762 {
763 nuses--;
766 }
767 else
769 }
772 }
774 #ifdef HAVE_cc0
775 /* We cannot insert anything between a set of cc and its use
776 so if P uses cc0, we must back up to the previous insn. */
781 #endif
786 /* If we found all the uses and there was no data conflict, we
787 can move the assignment unless we can branch into the middle
788 from somewhere. */
795 {
799 /* Set NEXT to an insn that we know won't go away. */
802 /* Delete the jump around the set. Note that we must do
803 this before we redirect the test jumps so that it won't
804 delete the code immediately following the assignment
805 we moved (which might be a jump). */
809 /* We either have two consecutive labels or a jump to
810 a jump, so adjust all the JUMP_INSNs to branch to where
811 INSN branches to. */
818 }
819 }
821 #ifndef HAVE_cc0
822 /* If we have if (...) x = exp; and branches are expensive,
823 EXP is a single insn, does not have any side effects, cannot
824 trap, and is not too costly, convert this to
825 t = exp; if (...) x = t;
827 Don't do this when we have CC0 because it is unlikely to help
828 and we'd need to worry about where to place the new insn and
829 the potential for conflicts. We also can't do this when we have
830 notes on the insn for the same reason as above.
832 We set:
834 TEMP to the "x = exp;" insn.
835 TEMP1 to the single set in the "x = exp; insn.
836 TEMP2 to "x". */
851 #ifdef SMALL_REGISTER_CLASSES
853 #endif
860 {
864 {
869 }
870 }
872 /* Similarly, if it takes two insns to compute EXP but they
873 have the same destination. Here TEMP3 will be the second
874 insn and TEMP4 the SET from that insn. */
892 #ifdef SMALL_REGISTER_CLASSES
894 #endif
903 {
907 {
911 emit_insn_after_with_line_notes
916 }
917 }
919 /* Finally, handle the case where two insns are used to
920 compute EXP but a temporary register is used. Here we must
921 ensure that the temporary register is not used anywhere else. */
924 && after_regscan
948 #ifdef SMALL_REGISTER_CLASSES
950 #endif
955 {
959 {
967 }
968 }
971 /* We deal with four cases:
973 1) x = a; if (...) x = b; and either A or B is zero,
974 2) if (...) x = 0; and jumps are expensive,
975 3) x = a; if (...) x = b; and A and B are constants where all the
976 set bits in A are also set in B and jumps are expensive, and
977 4) x = a; if (...) x = b; and A and B non-zero, and jumps are
978 more expensive.
979 5) if (...) x = b; if jumps are even more expensive.
981 In each of these try to use a store-flag insn to avoid the jump.
982 (If the jump would be faster, the machine should not have
983 defined the scc insns!). These cases are often made by the
984 previous optimization.
986 INSN here is the jump around the store. We set:
988 TEMP to the "x = b;" insn.
989 TEMP1 to X.
990 TEMP2 to B (const0_rtx in the second case).
991 TEMP3 to A (X in the second case).
992 TEMP4 to the condition being tested.
993 TEMP5 to the earliest insn used to find the condition. */
996 ! reload_completed
998 /* Set TEMP to the "x = b;" insn. */
1003 #ifdef SMALL_REGISTER_CLASSES
1005 #endif
1010 /* Allow either form, but prefer the former if both apply.
1011 There is no point in using the old value of TEMP1 if
1012 it is a register, since cse will alias them. It can
1013 lose if the old value were a hard register since CSE
1014 won't replace hard registers. */
1017 /* Make the latter case look like x = x; if (...) x = 0; */
1021 #ifdef HAVE_conditional_move
1023 #endif
1025 /* INSN must either branch to the insn after TEMP or the insn
1026 after TEMP must branch to the same place as INSN. */
1032 /* We must be comparing objects whose modes imply the size.
1033 We could handle BLKmode if (1) emit_store_flag could
1034 and (2) we could find the size reliably. */
1037 /* If B is zero, OK; if A is zero, can only do (1) if we
1038 can reverse the condition. See if (3) applies possibly
1039 by reversing the condition. Prefer reversing to (4) when
1040 branches are very expensive. */
1050 insn)))))
1051 #ifdef HAVE_conditional_move
1053 #endif
1055 #ifdef HAVE_cc0
1056 /* If the previous insn sets CC0 and something else, we can't
1057 do this since we are going to delete that insn. */
1064 #endif
1065 )
1066 {
1070 rtx target;
1072 /* If necessary, reverse the condition. */
1075 else
1078 /* See if we can do this with a store-flag insn. */
1081 /* If CVAL is non-zero, normalize to -1. Otherwise,
1082 if UVAL is the constant 1, it is best to just compute
1083 the result directly. If UVAL is constant and STORE_FLAG_VALUE
1084 includes all of its bits, it is best to compute the flag
1085 value unnormalized and `and' it with UVAL. Otherwise,
1086 normalize to -1 and `and' with UVAL. */
1093 /* We will be putting the store-flag insn immediately in
1094 front of the comparison that was originally being done,
1095 so we know all the variables in TEMP4 will be valid.
1096 However, this might be in front of the assignment of
1097 A to VAR. If it is, it would clobber the store-flag
1098 we will be emitting.
1100 Therefore, emit into a temporary which will be copied to
1101 VAR immediately after TEMP. */
1105 VOIDmode,
1108 normalizep);
1110 {
1112 rtx seq;
1114 /* Put the store-flag insns in front of the first insn
1115 used to compute the condition to ensure that we
1116 use the same values of them as the current
1117 comparison. However, the remainder of the insns we
1118 generate will be placed directly in front of the
1119 jump insn, in case any of the pseudos we use
1120 are modified earlier. */
1129 /* Both CVAL and UVAL are non-zero. */
1131 {
1139 else
1140 {
1146 }
1148 /* If we usually make new pseudos, do so here. This
1149 turns out to help machines that have conditional
1150 move insns. */
1158 }
1160 {
1161 /* We know that either CVAL or UVAL is zero. If
1162 UVAL is zero, negate TARGET and `and' with CVAL.
1163 Otherwise, `and' with UVAL. */
1165 {
1169 }
1175 }
1181 #ifdef HAVE_cc0
1182 /* If INSN uses CC0, we must not separate it from the
1183 insn that sets cc0. */
1187 #endif
1197 }
1198 else
1200 }
1202 /* If branches are expensive, convert
1203 if (foo) bar++; to bar += (foo != 0);
1204 and similarly for "bar--;"
1206 INSN is the conditional branch around the arithmetic. We set:
1208 TEMP is the arithmetic insn.
1209 TEMP1 is the SET doing the arithmetic.
1210 TEMP2 is the operand being incremented or decremented.
1211 TEMP3 to the condition being tested.
1212 TEMP4 to the earliest insn used to find the condition. */
1215 #ifdef HAVE_incscc
1216 || HAVE_incscc
1217 #endif
1218 #ifdef HAVE_decscc
1219 || HAVE_decscc
1220 #endif
1221 )
1222 && ! reload_completed
1232 /* INSN must either branch to the insn after TEMP or the insn
1233 after TEMP must branch to the same place as INSN. */
1239 /* We must be comparing objects whose modes imply the size.
1240 We could handle BLKmode if (1) emit_store_flag could
1241 and (2) we could find the size reliably. */
1244 {
1250 /* It must be the case that TEMP2 is not modified in the range
1251 [TEMP4, INSN). The one exception we make is if the insn
1252 before INSN sets TEMP2 to something which is also unchanged
1253 in that range. In that case, we can move the initialization
1254 into our sequence. */
1263 {
1267 }
1273 VOIDmode,
1277 /* If we can do the store-flag, do the addition or
1278 subtraction. */
1287 {
1288 /* Put the result back in temp2 in case it isn't already.
1289 Then replace the jump, possible a CC0-setting insn in
1290 front of the jump, and TEMP, with the sequence we have
1291 made. */
1306 #ifdef HAVE_cc0
1308 #endif
1312 }
1313 else
1315 }
1317 /* Simplify if (...) x = 1; else {...} if (x) ...
1318 We recognize this case scanning backwards as well.
1320 TEMP is the assignment to x;
1321 TEMP1 is the label at the head of the second if. */
1322 /* ?? This should call get_condition to find the values being
1323 compared, instead of looking for a COMPARE insn when HAVE_cc0
1324 is not defined. This would allow it to work on the m88k. */
1325 /* ?? This optimization is only safe before cse is run if HAVE_cc0
1326 is not defined and the condition is tested by a separate compare
1327 insn. This is because the code below assumes that the result
1328 of the compare dies in the following branch.
1330 Not only that, but there might be other insns between the
1331 compare and branch whose results are live. Those insns need
1332 to be executed.
1334 A way to fix this is to move the insns at JUMP_LABEL (insn)
1335 to before INSN. If we are running before flow, they will
1336 be deleted if they aren't needed. But this doesn't work
1337 well after flow.
1339 This is really a special-case of jump threading, anyway. The
1340 right thing to do is to replace this and jump threading with
1341 much simpler code in cse.
1343 This code has been turned off in the non-cc0 case in the
1344 meantime. */
1346 #ifdef HAVE_cc0
1348 /* Safe to skip USE and CLOBBER insns here
1349 since they will not be deleted. */
1357 /* If we find that the next value tested is `x'
1358 (TEMP1 is the insn where this happens), win. */
1361 #ifdef HAVE_cc0
1362 /* Does temp1 `tst' the value of x? */
1366 #else
1367 /* Does temp1 compare the value of x against zero? */
1374 #endif
1376 {
1377 /* Get the if_then_else from the condjump. */
1380 {
1383 rtx cond
1386 rtx ultimate;
1392 else
1402 }
1403 }
1404 #endif
1406 #if 0
1407 /* @@ This needs a bit of work before it will be right.
1409 Any type of comparison can be accepted for the first and
1410 second compare. When rewriting the first jump, we must
1411 compute the what conditions can reach label3, and use the
1412 appropriate code. We can not simply reverse/swap the code
1413 of the first jump. In some cases, the second jump must be
1414 rewritten also.
1416 For example,
1417 < == converts to > ==
1418 < != converts to == >
1419 etc.
1421 If the code is written to only accept an '==' test for the second
1422 compare, then all that needs to be done is to swap the condition
1423 of the first branch.
1425 It is questionable whether we want this optimization anyways,
1426 since if the user wrote code like this because he/she knew that
1427 the jump to label1 is taken most of the time, then rewriting
1428 this gives slower code. */
1429 /* @@ This should call get_condition to find the values being
1430 compared, instead of looking for a COMPARE insn when HAVE_cc0
1431 is not defined. This would allow it to work on the m88k. */
1432 /* @@ This optimization is only safe before cse is run if HAVE_cc0
1433 is not defined and the condition is tested by a separate compare
1434 insn. This is because the code below assumes that the result
1435 of the compare dies in the following branch. */
1437 /* Simplify test a ~= b
1438 condjump label1;
1439 test a == b
1440 condjump label2;
1441 jump label3;
1442 label1:
1444 rewriting as
1445 test a ~~= b
1446 condjump label3
1447 test a == b
1448 condjump label2
1449 label1:
1451 where ~= is an inequality, e.g. >, and ~~= is the swapped
1452 inequality, e.g. <.
1454 We recognize this case scanning backwards.
1456 TEMP is the conditional jump to `label2';
1457 TEMP1 is the test for `a == b';
1458 TEMP2 is the conditional jump to `label1';
1459 TEMP3 is the test for `a ~= b'. */
1468 #ifdef HAVE_cc0
1470 #else
1474 #endif
1488 {
1493 {
1496 }
1500 }
1501 #endif
1502 /* Simplify if (...) {... x = 1;} if (x) ...
1504 We recognize this case backwards.
1506 TEMP is the test of `x';
1507 TEMP1 is the assignment to `x' at the end of the
1508 previous statement. */
1509 /* @@ This should call get_condition to find the values being
1510 compared, instead of looking for a COMPARE insn when HAVE_cc0
1511 is not defined. This would allow it to work on the m88k. */
1512 /* @@ This optimization is only safe before cse is run if HAVE_cc0
1513 is not defined and the condition is tested by a separate compare
1514 insn. This is because the code below assumes that the result
1515 of the compare dies in the following branch. */
1517 /* ??? This has to be turned off. The problem is that the
1518 unconditional jump might indirectly end up branching to the
1519 label between TEMP1 and TEMP. We can't detect this, in general,
1520 since it may become a jump to there after further optimizations.
1521 If that jump is done, it will be deleted, so we will retry
1522 this optimization in the next pass, thus an infinite loop.
1524 The present code prevents this by putting the jump after the
1525 label, but this is not logically correct. */
1526 #if 0
1528 /* Safe to skip USE and CLOBBER insns here
1529 since they will not be deleted. */
1534 #ifdef HAVE_cc0
1537 #else
1538 /* Temp must be a compare insn, we can not accept a register
1539 to register move here, since it may not be simply a
1540 tst insn. */
1546 #endif
1547 /* May skip USE or CLOBBER insns here
1548 for checking for opportunity, since we
1549 take care of them later. */
1553 #ifdef HAVE_cc0
1555 #else
1558 #endif
1560 /* If this isn't true, cse will do the job. */
1562 {
1563 /* Get the if_then_else from the condjump. */
1568 {
1570 rtx last_insn;
1571 rtx ultimate;
1572 rtx p;
1574 /* Get the place that condjump will jump to
1575 if it is reached from here. */
1579 else
1581 /* Get it as a CODE_LABEL. */
1584 else
1585 /* Get the label out of the LABEL_REF. */
1588 /* Insert the jump immediately before TEMP, specifically
1589 after the label that is between TEMP1 and TEMP. */
1592 /* If we would be branching to the next insn, the jump
1593 would immediately be deleted and the re-inserted in
1594 a subsequent pass over the code. So don't do anything
1595 in that case. */
1598 {
1601 last_insn);
1606 {
1610 }
1613 }
1614 }
1615 }
1616 #endif
1617 /* Detect a conditional jump going to the same place
1618 as an immediately following unconditional jump. */
1624 {
1628 }
1629 /* Detect a conditional jump jumping over an unconditional jump. */
1637 {
1638 /* When we invert the unconditional jump, we will be
1639 decrementing the usage count of its old label.
1640 Make sure that we don't delete it now because that
1641 might cause the following code to be deleted. */
1648 {
1649 /* It is very likely that if there are USE insns before
1650 this jump, they hold REG_DEAD notes. These REG_DEAD
1651 notes are no longer valid due to this optimization,
1652 and will cause the life-analysis that following passes
1653 (notably delayed-branch scheduling) to think that
1654 these registers are dead when they are not.
1656 To prevent this trouble, we just remove the USE insns
1657 from the insn chain. */
1661 {
1665 }
1670 }
1672 /* We can now safely delete the label if it is unreferenced
1673 since the delete_insn above has deleted the BARRIER. */
1677 }
1678 else
1679 {
1680 /* Detect a jump to a jump. */
1685 {
1688 }
1690 /* Look for if (foo) bar; else break; */
1691 /* The insns look like this:
1692 insn = condjump label1;
1693 ...range1 (some insns)...
1694 jump label2;
1695 label1:
1696 ...range2 (some insns)...
1697 jump somewhere unconditionally
1698 label2: */
1699 {
1702 /* Don't do this optimization on the first round, so that
1703 jump-around-a-jump gets simplified before we ask here
1704 whether a jump is unconditional.
1706 Also don't do it when we are called after reload since
1707 it will confuse reorg. */
1710 /* Make sure INSN is something we can invert. */
1717 {
1724 /* Invert the jump condition, so we
1725 still execute the same insns in each case. */
1727 {
1733 /* Include in each range any line number before it. */
1744 /* Don't move NOTEs for blocks or loops; shift them
1745 outside the ranges, where they'll stay put. */
1749 /* Get current surrounds of the 2 ranges. */
1755 /* Splice range2 where range1 was. */
1760 /* Splice range1 where range2 was. */
1767 }
1768 }
1769 }
1771 /* Now that the jump has been tensioned,
1772 try cross jumping: check for identical code
1773 before the jump and before its target label. */
1775 /* First, cross jumping of conditional jumps: */
1778 {
1782 /* A conditional jump may be crossjumped
1783 only if the place it jumps to follows
1784 an opposing jump that comes back here. */
1787 /* We have no opposing jump;
1788 cannot cross jump this insn. */
1792 /* TARGET is nonzero if it is ok to cross jump
1793 to code before TARGET. If so, see if matches. */
1799 {
1801 /* Make the old conditional jump
1802 into an unconditional one. */
1807 /* Add to jump_chain unless this is a new label
1808 whose UID is too large. */
1810 {
1814 }
1817 }
1818 }
1820 /* Cross jumping of unconditional jumps:
1821 a few differences. */
1824 {
1826 rtx target;
1830 /* TARGET is nonzero if it is ok to cross jump
1831 to code before TARGET. If so, see if matches. */
1835 /* If cannot cross jump to code before the label,
1836 see if we can cross jump to another jump to
1837 the same label. */
1838 /* Try each other jump to this label. */
1845 /* Ignore TARGET if it's deleted. */
1851 {
1855 }
1856 }
1858 /* This code was dead in the previous jump.c! */
1860 {
1861 /* Return insns all "jump to the same place"
1862 so we can cross-jump between any two of them. */
1868 /* If cannot cross jump to code before the label,
1869 see if we can cross jump to another jump to
1870 the same label. */
1871 /* Try each other jump to this label. */
1882 {
1886 }
1887 }
1888 }
1889 }
1892 }
1894 /* Delete extraneous line number notes.
1895 Note that two consecutive notes for different lines are not really
1896 extraneous. There should be some indication where that line belonged,
1897 even if it became empty. */
1899 {
1904 {
1905 /* Delete this note if it is identical to previous note. */
1909 {
1912 }
1915 }
1916 }
1918 /* See if there is still a NOTE_INSN_FUNCTION_END in this function.
1919 If so, delete it, and record that this function can drop off the end. */
1922 {
1925 /* One label can follow the end-note: the return label. */
1927 /* Ordinary insns can follow it if returning a structure. */
1929 /* If machine uses explicit RETURN insns, no epilogue,
1930 then one of them follows the note. */
1933 /* Other kinds of notes can follow also. */
1937 }
1939 /* Report if control can fall through at the end of the function. */
1942 {
1945 }
1947 /* Show JUMP_CHAIN no longer valid. */
1949 }
1950 \f
1951 /* LOOP_START is a NOTE_INSN_LOOP_BEG note that is followed by an unconditional
1952 jump. Assume that this unconditional jump is to the exit test code. If
1953 the code is sufficiently simple, make a copy of it before INSN,
1954 followed by a jump to the exit of the loop. Then delete the unconditional
1955 jump after INSN.
1957 Note that it is possible we can get confused here if the jump immediately
1958 after the loop start branches outside the loop but within an outer loop.
1959 If we are near the exit of that loop, we will copy its exit test. This
1960 will not generate incorrect code, but could suppress some optimizations.
1961 However, such cases are degenerate loops anyway.
1963 Return 1 if we made the change, else 0.
1965 This is only safe immediately after a regscan pass because it uses the
1966 values of regno_first_uid and regno_last_uid. */
1968 static int
1970 rtx loop_start;
1971 {
1976 rtx lastexit;
1980 /* Scan the exit code. We do not perform this optimization if any insn:
1982 is a CALL_INSN
1983 is a CODE_LABEL
1984 has a REG_RETVAL or REG_LIBCALL note (hard to adjust)
1985 is a NOTE_INSN_LOOP_BEG because this means we have a nested loop
1986 is a NOTE_INSN_BLOCK_{BEG,END} because duplicating these notes
1987 are not valid
1989 Also, don't do this if the exit code is more than 20 insns. */
1992 insn
1996 {
1998 {
2015 }
2016 }
2018 /* Unless INSN is zero, we can do the optimization. */
2024 /* See if any insn sets a register only used in the loop exit code and
2025 not a user variable. If so, replace it with a new register. */
2032 {
2038 {
2039 /* We can do the replacement. Allocate reg_map if this is the
2040 first replacement we found. */
2042 {
2045 }
2051 }
2052 }
2054 /* Now copy each insn. */
2057 {
2062 /* Only copy line-number notes. */
2064 {
2067 }
2077 /* Copy all REG_NOTES except REG_LABEL since mark_jump_label will
2078 make them. */
2094 {
2098 }
2100 /* If this is a simple jump, add it to the jump chain. */
2104 {
2108 }
2113 }
2115 /* Now clean up by emitting a jump to the end label and deleting the jump
2116 at the start of the loop. */
2118 {
2120 loop_start);
2124 {
2128 }
2130 }
2134 /* Mark the exit code as the virtual top of the converted loop. */
2138 }
2139 \f
2140 /* Move all block-beg, block-end, loop-beg, loop-cont, loop-vtop, and
2141 loop-end notes between START and END out before START. Assume that
2142 END is not such a note. START may be such a note. Returns the value
2143 of the new starting insn, which may be different if the original start
2144 was such a note. */
2146 rtx
2149 {
2150 rtx insn;
2151 rtx next;
2154 {
2163 {
2166 else
2167 {
2175 }
2176 }
2177 }
2180 }
2181 \f
2182 /* Compare the instructions before insn E1 with those before E2
2183 to find an opportunity for cross jumping.
2184 (This means detecting identical sequences of insns followed by
2185 jumps to the same place, or followed by a label and a jump
2186 to that label, and replacing one with a jump to the other.)
2188 Assume E1 is a jump that jumps to label E2
2189 (that is not always true but it might as well be).
2190 Find the longest possible equivalent sequences
2191 and store the first insns of those sequences into *F1 and *F2.
2192 Store zero there if no equivalent preceding instructions are found.
2194 We give up if we find a label in stream 1.
2195 Actually we could transfer that label into stream 2. */
2197 static void
2202 {
2209 rtx prev1;
2215 {
2225 /* Don't allow the range of insns preceding E1 or E2
2226 to include the other (E2 or E1). */
2230 /* If we will get to this code by jumping, those jumps will be
2231 tensioned to go directly to the new label (before I2),
2232 so this cross-jumping won't cost extra. So reduce the minimum. */
2234 {
2237 }
2245 #ifdef STACK_REGS
2246 /* If cross_jump_death_matters is not 0, the insn's mode
2247 indicates whether or not the insn contains any stack-like
2248 regs. */
2251 {
2252 /* If register stack conversion has already been done, then
2253 death notes must also be compared before it is certain that
2254 the two instruction streams match. */
2256 rtx note;
2276 done:
2277 ;
2278 }
2279 #endif
2283 {
2284 /* The following code helps take care of G++ cleanups. */
2285 rtx equiv1;
2286 rtx equiv2;
2293 /* If the equivalences are not to a constant, they may
2294 reference pseudos that no longer exist, so we can't
2295 use them. */
2298 {
2303 {
2310 }
2311 }
2313 /* Insns fail to match; cross jumping is limited to the following
2314 insns. */
2316 #ifdef HAVE_cc0
2317 /* Don't allow the insn after a compare to be shared by
2318 cross-jumping unless the compare is also shared.
2319 Here, if either of these non-matching insns is a compare,
2320 exclude the following insn from possible cross-jumping. */
2323 #endif
2325 /* If cross-jumping here will feed a jump-around-jump
2326 optimization, this jump won't cost extra, so reduce
2327 the minimum. */
2333 }
2335 win:
2337 {
2338 /* Ok, this insn is potentially includable in a cross-jump here. */
2341 }
2342 }
2344 /* We have to be careful that we do not cross-jump into the middle of
2345 USE-CALL_INSN-CLOBBER sequence. This sequence is used instead of
2346 putting the USE and CLOBBERs inside the CALL_INSN. The delay slot
2347 scheduler needs to know what registers are used and modified by the
2348 CALL_INSN and needs the adjacent USE and CLOBBERs to do so.
2350 ??? At some point we should probably change this so that these are
2351 part of the CALL_INSN. The way we are doing it now is a kludge that
2352 is now causing trouble. */
2358 {
2359 /* Remove this CALL_INSN from the range we can cross-jump. */
2363 minimum++;
2364 }
2366 /* Skip past CLOBBERS since they may be right after a CALL_INSN. It
2367 isn't worth checking for the CALL_INSN. */
2373 }
2375 static void
2378 {
2379 /* Find an existing label at this point
2380 or make a new one if there is none. */
2383 /* Make the same jump insn jump to the new point. */
2385 {
2386 /* Remove from jump chain of returns. */
2388 /* Change the insn. */
2393 /* Add to new the jump chain. */
2396 {
2399 }
2400 }
2401 else
2404 /* Delete the matching insns before the jump. Also, remove any REG_EQUAL
2405 or REG_EQUIV note in the NEWLPOS stream that isn't also present in
2406 the NEWJPOS stream. */
2409 {
2410 rtx lnote;
2422 }
2423 }
2424 \f
2425 /* Return the label before INSN, or put a new label there. */
2427 rtx
2429 rtx insn;
2430 {
2431 rtx label;
2433 /* Find an existing label at this point
2434 or make a new one if there is none. */
2438 {
2441 /* Don't put a label between a CALL_INSN and USE insns that precede
2442 it. */
2453 }
2455 }
2457 /* Return the label after INSN, or put a new label there. */
2459 rtx
2461 rtx insn;
2462 {
2463 rtx label;
2465 /* Find an existing label at this point
2466 or make a new one if there is none. */
2470 {
2471 /* Don't put a label between a CALL_INSN and CLOBBER insns
2472 following it. */
2484 }
2486 }
2487 \f
2488 /* Return 1 if INSN is a jump that jumps to right after TARGET
2489 only on the condition that TARGET itself would drop through.
2490 Assumes that TARGET is a conditional jump. */
2492 static int
2495 {
2511 {
2515 }
2518 {
2522 }
2527 }
2528 \f
2529 /* Given a comparison, COMPARISON, inside a conditional jump insn, INSN,
2530 return non-zero if it is safe to reverse this comparison. It is if our
2531 floating-point is not IEEE, if this is an NE or EQ comparison, or if
2532 this is known to be an integer comparison. */
2534 int
2536 rtx comparison;
2537 rtx insn;
2538 {
2539 rtx arg0;
2541 /* If this is not actually a comparison, we can't reverse it. */
2546 /* If this is an NE comparison, it is safe to reverse it to an EQ
2547 comparison and vice versa, even for floating point. If no operands
2548 are NaNs, the reversal is valid. If some operand is a NaN, EQ is
2549 always false and NE is always true, so the reversal is also valid. */
2556 /* Make sure ARG0 is one of the actual objects being compared. If we
2557 can't do this, we can't be sure the comparison can be reversed.
2559 Handle cc0 and a MODE_CC register. */
2561 #ifdef HAVE_cc0
2563 #endif
2564 )
2565 {
2576 }
2578 /* We can reverse this if ARG0 is a CONST_INT or if its mode is
2579 not VOIDmode and neither a MODE_CC nor MODE_FLOAT type. */
2584 }
2586 /* Given an rtx-code for a comparison, return the code
2587 for the negated comparison.
2588 WATCH OUT! reverse_condition is not safe to use on a jump
2589 that might be acting on the results of an IEEE floating point comparison,
2590 because of the special treatment of non-signaling nans in comparisons.
2591 Use can_reverse_comparison_p to be sure. */
2593 enum rtx_code
2596 {
2598 {
2632 }
2633 }
2635 /* Similar, but return the code when two operands of a comparison are swapped.
2636 This IS safe for IEEE floating-point. */
2638 enum rtx_code
2641 {
2643 {
2675 }
2676 }
2678 /* Given a comparison CODE, return the corresponding unsigned comparison.
2679 If CODE is an equality comparison or already an unsigned comparison,
2680 CODE is returned. */
2682 enum rtx_code
2685 {
2687 {
2710 }
2711 }
2713 /* Similarly, return the signed version of a comparison. */
2715 enum rtx_code
2718 {
2720 {
2743 }
2744 }
2745 \f
2746 /* Return non-zero if CODE1 is more strict than CODE2, i.e., if the
2747 truth of CODE1 implies the truth of CODE2. */
2749 int
2752 {
2757 {
2782 }
2785 }
2786 \f
2787 /* Return 1 if INSN is an unconditional jump and nothing else. */
2789 int
2791 rtx insn;
2792 {
2797 }
2799 /* Return nonzero if INSN is a (possibly) conditional jump
2800 and nothing more. */
2802 int
2804 rtx insn;
2805 {
2824 }
2826 /* Return 1 if X is an RTX that does nothing but set the condition codes
2827 and CLOBBER or USE registers.
2828 Return -1 if X does explicitly set the condition codes,
2829 but also does other things. */
2831 int
2833 rtx x;
2834 {
2835 #ifdef HAVE_cc0
2839 {
2844 {
2850 }
2852 }
2854 #else
2856 #endif
2857 }
2858 \f
2859 /* Follow any unconditional jump at LABEL;
2860 return the ultimate label reached by any such chain of jumps.
2861 If LABEL is not followed by a jump, return LABEL.
2862 If the chain loops or we can't find end, return LABEL,
2863 since that tells caller to avoid changing the insn.
2865 If RELOAD_COMPLETED is 0, we do not chain across a NOTE_INSN_LOOP_BEG or
2866 a USE or CLOBBER. */
2868 rtx
2870 rtx label;
2871 {
2884 depth++)
2885 {
2886 /* Don't chain through the insn that jumps into a loop
2887 from outside the loop,
2888 since that would create multiple loop entry jumps
2889 and prevent loop optimization. */
2890 rtx tem;
2897 /* If we have found a cycle, make the insn jump to itself. */
2901 }
2905 }
2907 /* Assuming that field IDX of X is a vector of label_refs,
2908 replace each of them by the ultimate label reached by it.
2909 Return nonzero if a change is made.
2910 If IGNORE_LOOPS is 0, we do not chain across a NOTE_INSN_LOOP_BEG. */
2912 static int
2916 {
2920 {
2924 {
2930 }
2931 }
2933 }
2934 \f
2935 /* Find all CODE_LABELs referred to in X, and increment their use counts.
2936 If INSN is a JUMP_INSN and there is at least one CODE_LABEL referenced
2937 in INSN, then store one of them in JUMP_LABEL (INSN).
2938 If INSN is an INSN or a CALL_INSN and there is at least one CODE_LABEL
2939 referenced in INSN, add a REG_LABEL note containing that label to INSN.
2940 Also, when there are consecutive labels, canonicalize on the last of them.
2942 Note that two labels separated by a loop-beginning note
2943 must be kept distinct if we have not yet done loop-optimization,
2944 because the gap between them is where loop-optimize
2945 will want to move invariant code to. CROSS_JUMP tells us
2946 that loop-optimization is done with.
2948 Once reload has completed (CROSS_JUMP non-zero), we need not consider
2949 two labels distinct if they are separated by only USE or CLOBBER insns. */
2951 static void
2954 rtx insn;
2956 {
2962 {
2975 /* If this is a constant-pool reference, see if it is a label. */
2982 {
2987 /* Ignore references to labels of containing functions. */
2990 /* If there are other labels following this one,
2991 replace it with the last of the consecutive labels. */
2993 {
3006 }
3010 {
3014 {
3016 /* Don't record labels that refer to dispatch tables.
3017 This is not necessary, since the tablejump
3018 references the same label.
3019 And if we did record them, flow.c would make worse code. */
3024 {
3027 /* Record in the note whether label is nonlocal. */
3030 }
3031 }
3032 }
3034 }
3036 /* Do walk the labels in a vector, but not the first operand of an
3037 ADDR_DIFF_VEC. Don't set the JUMP_LABEL of a vector. */
3040 {
3046 }
3047 }
3051 {
3055 {
3059 }
3060 }
3061 }
3063 /* If all INSN does is set the pc, delete it,
3064 and delete the insn that set the condition codes for it
3065 if that's what the previous thing was. */
3067 void
3069 rtx insn;
3070 {
3075 }
3077 /* Delete INSN and recursively delete insns that compute values used only
3078 by INSN. This uses the REG_DEAD notes computed during flow analysis.
3079 If we are running before flow.c, we need do nothing since flow.c will
3080 delete dead code. We also can't know if the registers being used are
3081 dead or not at this point.
3083 Otherwise, look at all our REG_DEAD notes. If a previous insn does
3084 nothing other than set a register that dies in this insn, we can delete
3085 that insn as well.
3087 On machines with CC0, if CC0 is used in this insn, we may be able to
3088 delete the insn that set it. */
3090 void
3092 rtx insn;
3093 {
3096 #ifdef HAVE_cc0
3098 {
3100 /* We assume that at this stage
3101 CC's are always set explicitly
3102 and always immediately before the jump that
3103 will use them. So if the previous insn
3104 exists to set the CC's, delete it
3105 (unless it performs auto-increments, etc.). */
3108 {
3112 else
3113 /* Otherwise, show that cc0 won't be used. */
3116 }
3117 }
3118 #endif
3121 {
3122 rtx our_prev;
3127 /* Verify that the REG_NOTE is legitimate. */
3134 {
3135 /* If we reach a SEQUENCE, it is too complex to try to
3136 do anything with it, so give up. */
3142 /* reorg creates USEs that look like this. We leave them
3143 alone because reorg needs them for its own purposes. */
3147 {
3152 {
3153 /* If we find a SET of something else, we can't
3154 delete the insn. */
3159 {
3165 }
3169 }
3175 }
3177 /* If OUR_PREV references the register that dies here, it is an
3178 additional use. Hence any prior SET isn't dead. However, this
3179 insn becomes the new place for the REG_DEAD note. */
3182 {
3186 }
3187 }
3188 }
3191 }
3192 \f
3193 /* Delete insn INSN from the chain of insns and update label ref counts.
3194 May delete some following insns as a consequence; may even delete
3195 a label elsewhere and insns that follow it.
3197 Returns the first insn after INSN that was not deleted. */
3199 rtx
3202 {
3211 /* This insn is already deleted => return first following nondeleted. */
3215 /* Don't delete user-declared labels. Convert them to special NOTEs
3216 instead. */
3219 {
3224 }
3225 else
3226 /* Mark this insn as deleted. */
3229 /* If this is an unconditional jump, delete it from the jump chain. */
3233 /* If instruction is followed by a barrier,
3234 delete the barrier too. */
3237 {
3240 }
3242 /* Patch out INSN (and the barrier if any) */
3245 {
3247 {
3252 }
3255 {
3259 }
3263 }
3265 /* If deleting a jump, decrement the count of the label,
3266 and delete the label if it is now unused. */
3270 {
3271 /* This can delete NEXT or PREV,
3272 either directly if NEXT is JUMP_LABEL (INSN),
3273 or indirectly through more levels of jumps. */
3275 /* I feel a little doubtful about this loop,
3276 but I see no clean and sure alternative way
3277 to find the first insn after INSN that is not now deleted.
3278 I hope this works. */
3282 }
3287 /* If INSN was a label and a dispatch table follows it,
3288 delete the dispatch table. The tablejump must have gone already.
3289 It isn't useful to fall through into a table. */
3298 /* If INSN was a label, delete insns following it if now unreachable. */
3301 {
3308 {
3312 /* Keep going past other deleted labels to delete what follows. */
3315 else
3316 /* Note: if this deletes a jump, it can cause more
3317 deletion of unreachable code, after a different label.
3318 As long as the value from this recursive call is correct,
3319 this invocation functions correctly. */
3321 }
3322 }
3325 }
3327 /* Advance from INSN till reaching something not deleted
3328 then return that. May return INSN itself. */
3330 rtx
3332 rtx insn;
3333 {
3337 }
3338 \f
3339 /* Delete a range of insns from FROM to TO, inclusive.
3340 This is for the sake of peephole optimization, so assume
3341 that whatever these insns do will still be done by a new
3342 peephole insn that will replace them. */
3344 void
3347 {
3351 {
3356 {
3359 /* Patch this insn out of the chain. */
3360 /* We don't do this all at once, because we
3361 must preserve all NOTEs. */
3367 }
3372 }
3374 /* Note that if TO is an unconditional jump
3375 we *do not* delete the BARRIER that follows,
3376 since the peephole that replaces this sequence
3377 is also an unconditional jump in that case. */
3378 }
3379 \f
3380 /* Invert the condition of the jump JUMP, and make it jump
3381 to label NLABEL instead of where it jumps now. */
3383 int
3386 {
3389 /* We have to either invert the condition and change the label or
3390 do neither. Either operation could fail. We first try to invert
3391 the jump. If that succeeds, we try changing the label. If that fails,
3392 we invert the jump back to what it was. */
3401 /* This should just be putting it back the way it was. */
3405 }
3407 /* Invert the jump condition of rtx X contained in jump insn, INSN.
3409 Return 1 if we can do so, 0 if we cannot find a way to do so that
3410 matches a pattern. */
3412 int
3414 rtx x;
3415 rtx insn;
3416 {
3424 {
3428 /* We can do this in two ways: The preferable way, which can only
3429 be done if this is not an integer comparison, is to reverse
3430 the comparison code. Otherwise, swap the THEN-part and ELSE-part
3431 of the IF_THEN_ELSE. If we can't do either, fail. */
3444 }
3448 {
3453 {
3458 }
3459 }
3462 }
3463 \f
3464 /* Make jump JUMP jump to label NLABEL instead of where it jumps now.
3465 If the old jump target label is unused as a result,
3466 it and the code following it may be deleted.
3468 If NLABEL is zero, we are to turn the jump into a (possibly conditional)
3469 RETURN insn.
3471 The return value will be 1 if the change was made, 0 if it wasn't (this
3472 can only occur for NLABEL == 0). */
3474 int
3477 {
3486 /* If this is an unconditional branch, delete it from the jump_chain of
3487 OLABEL and add it to the jump_chain of NLABEL (assuming both labels
3488 have UID's in range and JUMP_CHAIN is valid). */
3491 {
3497 {
3500 }
3501 }
3511 }
3513 /* Delete the instruction JUMP from any jump chain it might be on. */
3515 static void
3517 rtx jump;
3518 {
3522 /* Handle unconditional jumps. */
3527 /* Handle return insns. */
3534 else
3535 {
3536 rtx insn;
3542 {
3545 }
3546 }
3547 }
3549 /* If NLABEL is nonzero, throughout the rtx at LOC,
3550 alter (LABEL_REF OLABEL) to (LABEL_REF NLABEL). If OLABEL is
3551 zero, alter (RETURN) to (LABEL_REF NLABEL).
3553 If NLABEL is zero, alter (LABEL_REF OLABEL) to (RETURN) and check
3554 validity with validate_change. Convert (set (pc) (label_ref olabel))
3555 to (return).
3557 Return 0 if we found a change we would like to make but it is invalid.
3558 Otherwise, return 1. */
3560 int
3564 rtx insn;
3565 {
3572 {
3574 {
3577 else
3580 }
3581 }
3583 {
3588 }
3597 {
3602 {
3607 }
3608 }
3611 }
3612 \f
3613 /* Make jump JUMP jump to label NLABEL, assuming it used to be a tablejump.
3615 If the old jump target label (before the dispatch table) becomes unused,
3616 it and the dispatch table may be deleted. In that case, find the insn
3617 before the jump references that label and delete it and logical successors
3618 too. */
3620 void
3623 {
3626 /* Add this jump to the jump_chain of NLABEL. */
3629 {
3632 }
3640 {
3643 }
3644 }
3646 /* Find the insn referencing LABEL that is a logical predecessor of INSN.
3647 If we found one, delete it and then delete this insn if DELETE_THIS is
3648 non-zero. Return non-zero if INSN or a predecessor references LABEL. */
3650 static int
3654 {
3656 rtx link;
3660 {
3662 {
3665 }
3666 else
3668 }
3672 {
3674 {
3677 }
3678 else
3680 }
3683 }
3684 \f
3685 /* Like rtx_equal_p except that it considers two REGs as equal
3686 if they renumber to the same value. */
3688 int
3691 {
3701 {
3707 /* If we haven't done any renumbering, don't
3708 make any assumptions. */
3713 {
3718 }
3719 else
3720 {
3724 }
3726 {
3731 }
3732 else
3733 {
3737 }
3739 }
3740 /* Now we have disposed of all the cases
3741 in which different rtx codes can match. */
3745 {
3756 /* We can't assume nonlocal labels have their following insns yet. */
3759 /* Two label-refs are equivalent if they point at labels
3760 in the same position in the instruction stream. */
3766 }
3768 /* (MULT:SI x y) and (MULT:HI x y) are NOT equivalent. */
3773 /* Compare the elements. If any pair of corresponding elements
3774 fail to match, return 0 for the whole things. */
3778 {
3781 {
3805 /* fall through. */
3819 }
3820 }
3822 }
3823 \f
3824 /* If X is a hard register or equivalent to one or a subregister of one,
3825 return the hard register number. If X is a pseudo register that was not
3826 assigned a hard register, return the pseudo register number. Otherwise,
3827 return -1. Any rtx is valid for X. */
3829 int
3831 rtx x;
3832 {
3834 {
3838 }
3840 {
3844 }
3846 }
3847 \f
3848 /* Optimize code of the form:
3850 for (x = a[i]; x; ...)
3851 ...
3852 for (x = a[i]; x; ...)
3853 ...
3854 foo:
3856 Loop optimize will change the above code into
3858 if (x = a[i])
3859 for (;;)
3860 { ...; if (! (x = ...)) break; }
3861 if (x = a[i])
3862 for (;;)
3863 { ...; if (! (x = ...)) break; }
3864 foo:
3866 In general, if the first test fails, the program can branch
3867 directly to `foo' and skip the second try which is doomed to fail.
3868 We run this after loop optimization and before flow analysis. */
3870 /* When comparing the insn patterns, we track the fact that different
3871 pseudo-register numbers may have been used in each computation.
3872 The following array stores an equivalence -- same_regs[I] == J means
3873 that pseudo register I was used in the first set of tests in a context
3874 where J was used in the second set. We also count the number of such
3875 pending equivalences. If nonzero, the expressions really aren't the
3876 same. */
3882 /* Track any registers modified between the target of the first jump and
3883 the second jump. They never compare equal. */
3887 /* Record if memory was modified. */
3891 /* Called via note_stores on each insn between the target of the first
3892 branch and the second branch. It marks any changed registers. */
3894 static void
3896 rtx dest;
3897 rtx x;
3898 {
3913 else
3916 }
3918 /* F is the first insn in the chain of insns. */
3920 void
3922 rtx f;
3925 {
3926 /* Basic algorithm is to find a conditional branch,
3927 the label it may branch to, and the branch after
3928 that label. If the two branches test the same condition,
3929 walk back from both branch paths until the insn patterns
3930 differ, or code labels are hit. If we make it back to
3931 the target of the first branch, then we know that the first branch
3932 will either always succeed or always fail depending on the relative
3933 senses of the two branches. So adjust the first branch accordingly
3934 in this case. */
3943 /* Allocate register tables and quick-reset table. */
3951 {
3955 {
3956 /* Get to a candidate branch insn. */
3970 /* Look for a branch after the target. Record any registers and
3971 memory modified between the target and the branch. Stop when we
3972 get to a label since we can't know what was changed there. */
3974 {
3979 {
3980 /* If this is an unconditional jump and is the only use of
3981 its target label, we can follow it. */
3985 {
3988 }
3989 else
3991 }
3997 {
4005 }
4008 }
4010 /* Check the next candidate branch insn from the label
4011 of the first. */
4019 /* Get the comparison codes and operands, reversing the
4020 codes if appropriate. If we don't have comparison codes,
4021 we can't do anything. */
4034 /* If they test the same things and knowing that B1 branches
4035 tells us whether or not B2 branches, check if we
4036 can thread the branch. */
4041 {
4046 {
4051 {
4052 /* We have reached the target of the first branch.
4053 If there are no pending register equivalents,
4054 we know that this branch will either always
4055 succeed (if the senses of the two branches are
4056 the same) or always fail (if not). */
4057 rtx new_label;
4064 else
4071 }
4073 /* If either of these is not a normal insn (it might be
4074 a JUMP_INSN, CALL_INSN, or CODE_LABEL) we fail. (NOTEs
4075 have already been skipped above.) Similarly, fail
4076 if the insns are different. */
4085 }
4086 }
4087 }
4088 }
4089 }
4090 \f
4091 /* This is like RTX_EQUAL_P except that it knows about our handling of
4092 possibly equivalent registers and knows to consider volatile and
4093 modified objects as not equal.
4095 YINSN is the insn containing Y. */
4097 int
4100 rtx yinsn;
4101 {
4108 /* Rtx's of different codes cannot be equal. */
4112 /* (MULT:SI x y) and (MULT:HI x y) are NOT equivalent.
4113 (REG:SI x) and (REG:HI x) are NOT equivalent. */
4118 /* Handle special-cases first. */
4120 {
4125 /* If neither is user variable or hard register, check for possible
4126 equivalence. */
4133 {
4135 num_same_regs++;
4137 /* If this is the first time we are seeing a register on the `Y'
4138 side, see if it is the last use. If not, we can't thread the
4139 jump, so mark it as not equivalent. */
4144 }
4145 else
4151 /* If memory modified or either volatile, not equivalent.
4152 Else, check address. */
4165 /* Cancel a pending `same_regs' if setting equivalenced registers.
4166 Then process source. */
4169 {
4171 {
4173 num_same_regs--;
4174 }
4177 }
4178 else
4189 }
4196 {
4198 {
4212 /* Two vectors must have the same length. */
4216 /* And the corresponding elements must match. */
4235 /* These are just backpointers, so they don't matter. */
4241 /* It is believed that rtx's at this level will never
4242 contain anything but integers and other rtx's,
4243 except for within LABEL_REFs and SYMBOL_REFs. */
4246 }
4247 }
4249 }