| blob | 2b9218a776302076a0f92d2a9a33d2e9fd721558 |
1 /* Optimize jump instructions, for GNU compiler.
2 Copyright (C) 1987, 88, 89, 91-95, 1996 Free Software Foundation, Inc.b
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, 59 Temple Place - Suite 330,
19 Boston, MA 02111-1307, USA. */
22 /* This is the jump-optimization pass of the compiler.
23 It is run two or three times: once before cse, sometimes once after cse,
24 and once after reload (before final).
26 jump_optimize deletes unreachable code and labels that are not used.
27 It also deletes jumps that jump to the following insn,
28 and simplifies jumps around unconditional jumps and jumps
29 to unconditional jumps.
31 Each CODE_LABEL has a count of the times it is used
32 stored in the LABEL_NUSES internal field, and each JUMP_INSN
33 has one label that it refers to stored in the
34 JUMP_LABEL internal field. With this we can detect labels that
35 become unused because of the deletion of all the jumps that
36 formerly used them. The JUMP_LABEL info is sometimes looked
37 at by later passes.
39 Optionally, cross-jumping can be done. Currently it is done
40 only the last time (when after reload and before final).
41 In fact, the code for cross-jumping now assumes that register
42 allocation has been done, since it uses `rtx_renumbered_equal_p'.
44 Jump optimization is done after cse when cse's constant-propagation
45 causes jumps to become unconditional or to be deleted.
47 Unreachable loops are not detected here, because the labels
48 have references and the insns appear reachable from the labels.
49 find_basic_blocks in flow.c finds and deletes such loops.
51 The subroutines delete_insn, redirect_jump, and invert_jump are used
52 from other passes as well. */
64 /* ??? Eventually must record somehow the labels used by jumps
65 from nested functions. */
66 /* Pre-record the next or previous real insn for each label?
67 No, this pass is very fast anyway. */
68 /* Condense consecutive labels?
69 This would make life analysis faster, maybe. */
70 /* Optimize jump y; x: ... y: jumpif... x?
71 Don't know if it is worth bothering with. */
72 /* Optimize two cases of conditional jump to conditional jump?
73 This can never delete any instruction or make anything dead,
74 or even change what is live at any point.
75 So perhaps let combiner do it. */
77 /* Vector indexed by uid.
78 For each CODE_LABEL, index by its uid to get first unconditional jump
79 that jumps to the label.
80 For each JUMP_INSN, index by its uid to get the next unconditional jump
81 that jumps to the same label.
82 Element 0 is the start of a chain of all return insns.
83 (It is safe to use element 0 because insn uid 0 is not used. */
87 /* List of labels referred to from initializers.
88 These can never be deleted. */
89 rtx forced_labels;
91 /* Maximum index in jump_chain. */
95 /* Set nonzero by jump_optimize if control can fall through
96 to the end of the function. */
99 /* Indicates whether death notes are significant in cross jump analysis.
100 Normally they are not significant, because of A and B jump to C,
101 and R dies in A, it must die in B. But this might not be true after
102 stack register conversion, and we must compare death notes in that
103 case. */
117 \f
118 /* Delete no-op jumps and optimize jumps to jumps
119 and jumps around jumps.
120 Delete unused labels and unreachable code.
122 If CROSS_JUMP is 1, detect matching code
123 before a jump and its destination and unify them.
124 If CROSS_JUMP is 2, do cross-jumping, but pay attention to death notes.
126 If NOOP_MOVES is nonzero, delete no-op move insns.
128 If AFTER_REGSCAN is nonzero, then this jump pass is being run immediately
129 after regscan, and it is safe to use regno_first_uid and regno_last_uid.
131 If `optimize' is zero, don't change any code,
132 just determine whether control drops off the end of the function.
133 This case occurs when we have -W and not -O.
134 It works because `delete_insn' checks the value of `optimize'
135 and refrains from actually deleting when that is 0. */
137 void
139 rtx f;
143 {
148 rtx last_insn;
152 /* Initialize LABEL_NUSES and JUMP_LABEL fields. Delete any REG_LABEL
153 notes whose labels don't occur in the insn any more. */
156 {
163 {
168 }
172 }
174 max_uid++;
176 /* Delete insns following barriers, up to next label. */
179 {
181 {
184 {
188 else
190 }
191 /* INSN is now the code_label. */
192 }
193 else
195 }
197 /* Leave some extra room for labels and duplicate exit test insns
198 we make. */
203 /* Mark the label each jump jumps to.
204 Combine consecutive labels, and count uses of labels.
206 For each label, make a chain (using `jump_chain')
207 of all the *unconditional* jumps that jump to it;
208 also make a chain of all returns. */
213 {
216 {
218 {
222 }
224 {
227 }
228 }
229 }
231 /* Keep track of labels used from static data;
232 they cannot ever be deleted. */
237 /* Delete all labels already not referenced.
238 Also find the last insn. */
242 {
245 else
246 {
249 }
250 }
253 {
254 /* See if there is still a NOTE_INSN_FUNCTION_END in this function.
255 If so record that this function can drop off the end. */
258 {
261 /* One label can follow the end-note: the return label. */
263 /* Ordinary insns can follow it if returning a structure. */
265 /* If machine uses explicit RETURN insns, no epilogue,
266 then one of them follows the note. */
269 /* A barrier can follow the return insn. */
271 /* Other kinds of notes can follow also. */
275 }
277 /* Report if control can fall through at the end of the function. */
283 /* Zero the "deleted" flag of all the "deleted" insns. */
287 }
289 #ifdef HAVE_return
291 {
292 /* If we fall through to the epilogue, see if we can insert a RETURN insn
293 in front of it. If the machine allows it at this point (we might be
294 after reload for a leaf routine), it will improve optimization for it
295 to be there. */
301 {
304 }
305 }
306 #endif
310 {
314 {
317 /* Combine stack_adjusts with following push_insns. */
318 #ifdef PUSH_ROUNDING
325 {
326 rtx p;
332 /* Find all successive push insns. */
334 /* Don't convert more than three pushes;
335 that starts adding too many displaced addresses
336 and the whole thing starts becoming a losing
337 proposition. */
339 {
348 /* Allow a no-op move between the adjust and the push. */
357 pushes++;
362 }
364 /* Discard the amount pushed from the stack adjust;
365 maybe eliminate it entirely. */
367 {
370 }
371 else
375 /* Change the appropriate push insns to ordinary stores. */
378 {
392 /* If this push doesn't fully fit in the space
393 of the stack adjust that we deleted,
394 make another stack adjust here for what we
395 didn't use up. There should be peepholes
396 to recognize the resulting sequence of insns. */
398 {
401 p);
403 }
406 }
407 }
408 #endif
410 /* Detect and delete no-op move instructions
411 resulting from not allocating a parameter in a register. */
424 /* Detect and ignore no-op move instructions
425 resulting from smart or fortuitous register allocation. */
428 {
435 {
436 rtx trial;
441 #ifdef PRESERVE_DEATH_INFO_REGNO_P
442 /* Deleting insn could lose a death-note for SREG or DREG
443 so don't do it if final needs accurate death-notes. */
446 #endif
447 {
448 /* DREG may have been the target of a REG_DEAD note in
449 the insn which makes INSN redundant. If so, reorg
450 would still think it is dead. So search for such a
451 note and delete it if we find it. */
456 {
459 }
464 }
465 }
470 {
471 /* This handles the case where we have two consecutive
472 assignments of the same constant to pseudos that didn't
473 get a hard reg. Each SET from the constant will be
474 converted into a SET of the spill register and an
475 output reload will be made following it. This produces
476 two loads of the same constant into the same spill
477 register. */
481 /* Look back for a death note for the first reg.
482 If there is one, it is no longer accurate. */
484 {
488 {
491 }
493 }
495 /* Delete the second load of the value. */
497 }
498 }
500 {
501 /* If each part is a set between two identical registers or
502 a USE or CLOBBER, delete the insn. */
504 rtx tem;
507 {
517 }
521 }
522 /* Also delete insns to store bit fields if they are no-ops. */
523 /* Not worth the hair to detect this in the big-endian case. */
532 }
534 }
536 /* If we haven't yet gotten to reload and we have just run regscan,
537 delete any insn that sets a register that isn't used elsewhere.
538 This helps some of the optimizations below by having less insns
539 being jumped around. */
543 {
551 /* We use regno_last_note_uid so as not to delete the setting
552 of a reg that's used in notes. A subsequent optimization
553 might arrange to use that reg for real. */
558 }
560 /* Now iterate optimizing jumps until nothing changes over one pass. */
563 {
567 {
568 rtx reallabelprev;
570 rtx nlabel;
573 #if 0
574 /* If NOT the first iteration, if this is the last jump pass
575 (just before final), do the special peephole optimizations.
576 Avoiding the first iteration gives ordinary jump opts
577 a chance to work before peephole opts. */
582 #endif
584 /* That could have deleted some insns after INSN, so check now
585 what the following insn is. */
589 /* See if this is a NOTE_INSN_LOOP_BEG followed by an unconditional
590 jump. Try to optimize by duplicating the loop exit test if so.
591 This is only safe immediately after regscan, because it uses
592 the values of regno_first_uid and regno_last_uid. */
597 {
600 {
604 }
605 }
614 /* Tension the labels in dispatch tables. */
621 /* If a dispatch table always goes to the same place,
622 get rid of it and replace the insn that uses it. */
626 {
641 /* Don't mess with a casesi insn. */
646 {
650 }
651 }
655 /* If a jump references the end of the function, try to turn
656 it into a RETURN insn, possibly a conditional one. */
663 /* Detect jump to following insn. */
665 {
670 }
672 /* If we have an unconditional jump preceded by a USE, try to put
673 the USE before the target and jump there. This simplifies many
674 of the optimizations below since we don't have to worry about
675 dealing with these USE insns. We only do this if the label
676 being branch to already has the identical USE or if code
677 never falls through to that label. */
686 /* Don't do this optimization if we have a loop containing only
687 the USE instruction, and the loop start label has a usage
688 count of 1. This is because we will redo this optimization
689 everytime through the outer loop, and jump opt will never
690 exit. */
694 {
696 {
699 }
705 }
707 /* Simplify if (...) x = a; else x = b; by converting it
708 to x = b; if (...) x = a;
709 if B is sufficiently simple, the test doesn't involve X,
710 and nothing in the test modifies B or X.
712 If we have small register classes, we also can't do this if X
713 is a hard register.
715 If the "x = b;" insn has any REG_NOTES, we don't do this because
716 of the possibility that we are running after CSE and there is a
717 REG_EQUAL note that is only valid if the branch has already been
718 taken. If we move the insn with the REG_EQUAL note, we may
719 fold the comparison to always be false in a later CSE pass.
720 (We could also delete the REG_NOTES when moving the insn, but it
721 seems simpler to not move it.) An exception is that we can move
722 the insn if the only note is a REG_EQUAL or REG_EQUIV whose
723 value is the same as "b".
725 INSN is the branch over the `else' part.
727 We set:
729 TEMP to the jump insn preceding "x = a;"
730 TEMP1 to X
731 TEMP2 to the insn that sets "x = b;"
732 TEMP3 to the insn that sets "x = a;"
733 TEMP4 to the set of "x = b"; */
740 #ifdef SMALL_REGISTER_CLASSES
742 #endif
758 /* TEMP must skip over the "x = a;" insn */
761 /* There must be no other entries to the "x = b;" insn. */
763 /* INSN must either branch to the insn after TEMP2 or the insn
764 after TEMP2 must branch to the same place as INSN. */
769 {
770 /* The test expression, X, may be a complicated test with
771 multiple branches. See if we can find all the uses of
772 the label that TEMP branches to without hitting a CALL_INSN
773 or a jump to somewhere else. */
778 /* Set P to the first jump insn that goes around "x = a;". */
780 {
782 {
785 {
786 nuses--;
789 }
790 else
792 }
795 }
797 #ifdef HAVE_cc0
798 /* We cannot insert anything between a set of cc and its use
799 so if P uses cc0, we must back up to the previous insn. */
804 #endif
809 /* If we found all the uses and there was no data conflict, we
810 can move the assignment unless we can branch into the middle
811 from somewhere. */
818 {
822 /* Set NEXT to an insn that we know won't go away. */
825 /* Delete the jump around the set. Note that we must do
826 this before we redirect the test jumps so that it won't
827 delete the code immediately following the assignment
828 we moved (which might be a jump). */
832 /* We either have two consecutive labels or a jump to
833 a jump, so adjust all the JUMP_INSNs to branch to where
834 INSN branches to. */
841 }
842 }
844 #ifndef HAVE_cc0
845 /* If we have if (...) x = exp; and branches are expensive,
846 EXP is a single insn, does not have any side effects, cannot
847 trap, and is not too costly, convert this to
848 t = exp; if (...) x = t;
850 Don't do this when we have CC0 because it is unlikely to help
851 and we'd need to worry about where to place the new insn and
852 the potential for conflicts. We also can't do this when we have
853 notes on the insn for the same reason as above.
855 We set:
857 TEMP to the "x = exp;" insn.
858 TEMP1 to the single set in the "x = exp; insn.
859 TEMP2 to "x". */
874 #ifdef SMALL_REGISTER_CLASSES
876 #endif
883 {
887 {
893 }
894 }
896 /* Similarly, if it takes two insns to compute EXP but they
897 have the same destination. Here TEMP3 will be the second
898 insn and TEMP4 the SET from that insn. */
916 #ifdef SMALL_REGISTER_CLASSES
918 #endif
927 {
931 {
935 emit_insn_after_with_line_notes
941 }
942 }
944 /* Finally, handle the case where two insns are used to
945 compute EXP but a temporary register is used. Here we must
946 ensure that the temporary register is not used anywhere else. */
949 && after_regscan
977 #ifdef SMALL_REGISTER_CLASSES
979 #endif
984 {
988 {
997 }
998 }
1001 /* Try to use a conditional move (if the target has them), or a
1002 store-flag insn. The general case is:
1004 1) x = a; if (...) x = b; and
1005 2) if (...) x = b;
1007 If the jump would be faster, the machine should not have defined
1008 the movcc or scc insns!. These cases are often made by the
1009 previous optimization.
1011 The second case is treated as x = x; if (...) x = b;.
1013 INSN here is the jump around the store. We set:
1015 TEMP to the "x = b;" insn.
1016 TEMP1 to X.
1017 TEMP2 to B.
1018 TEMP3 to A (X in the second case).
1019 TEMP4 to the condition being tested.
1020 TEMP5 to the earliest insn used to find the condition. */
1023 ! reload_completed
1025 /* Set TEMP to the "x = b;" insn. */
1030 #ifdef SMALL_REGISTER_CLASSES
1032 #endif
1035 /* ??? How about floating point constants? */
1037 /* Allow either form, but prefer the former if both apply.
1038 There is no point in using the old value of TEMP1 if
1039 it is a register, since cse will alias them. It can
1040 lose if the old value were a hard register since CSE
1041 won't replace hard registers. */
1043 /* Make the latter case look like x = x; if (...) x = b; */
1045 /* INSN must either branch to the insn after TEMP or the insn
1046 after TEMP must branch to the same place as INSN. */
1052 /* We must be comparing objects whose modes imply the size.
1053 We could handle BLKmode if (1) emit_store_flag could
1054 and (2) we could find the size reliably. */
1056 /* No point in doing any of this if branches are cheap or we
1057 don't have conditional moves. */
1059 #ifdef HAVE_conditional_move
1061 #endif
1062 )
1063 #ifdef HAVE_cc0
1064 /* If the previous insn sets CC0 and something else, we can't
1065 do this since we are going to delete that insn. */
1072 #endif
1073 )
1074 {
1075 #ifdef HAVE_conditional_move
1076 /* First try a conditional move. */
1077 {
1081 rtx target;
1083 /* Copy the compared variables into cond0 and cond1, so that
1084 any side effects performed in or after the old comparison,
1085 will not affect our compare which will come later. */
1086 /* ??? Is it possible to just use the comparison in the jump
1087 insn? After all, we're going to delete it. We'd have
1088 to modify emit_conditional_move to take a comparison rtx
1089 instead or write a new function. */
1091 /* We want the target to be able to simplify comparisons with
1092 zero (and maybe other constants as well), so don't create
1093 pseudos for them. There's no need to either. */
1097 else
1111 {
1114 /* Save the conditional move sequence but don't emit it
1115 yet. On some machines, like the alpha, it is possible
1116 that temp5 == insn, so next generate the sequence that
1117 saves the compared values and then emit both
1118 sequences ensuring seq1 occurs before seq2. */
1122 /* Now that we can't fail, generate the copy insns that
1123 preserve the compared values. */
1134 /* ??? We can also delete the insn that sets X to A.
1135 Flow will do it too though. */
1141 }
1142 else
1144 }
1145 #endif
1147 /* That didn't work, try a store-flag insn.
1149 We further divide the cases into:
1151 1) x = a; if (...) x = b; and either A or B is zero,
1152 2) if (...) x = 0; and jumps are expensive,
1153 3) x = a; if (...) x = b; and A and B are constants where all
1154 the set bits in A are also set in B and jumps are expensive,
1155 4) x = a; if (...) x = b; and A and B non-zero, and jumps are
1156 more expensive, and
1157 5) if (...) x = b; if jumps are even more expensive. */
1161 /* Make the latter case look like
1162 x = x; if (...) x = 0; */
1167 /* If B is zero, OK; if A is zero, can only do (1) if we
1168 can reverse the condition. See if (3) applies possibly
1169 by reversing the condition. Prefer reversing to (4) when
1170 branches are very expensive. */
1180 insn)))))
1182 )
1183 {
1187 rtx target;
1189 /* If necessary, reverse the condition. */
1192 else
1195 /* If CVAL is non-zero, normalize to -1. Otherwise, if UVAL
1196 is the constant 1, it is best to just compute the result
1197 directly. If UVAL is constant and STORE_FLAG_VALUE
1198 includes all of its bits, it is best to compute the flag
1199 value unnormalized and `and' it with UVAL. Otherwise,
1200 normalize to -1 and `and' with UVAL. */
1207 /* We will be putting the store-flag insn immediately in
1208 front of the comparison that was originally being done,
1209 so we know all the variables in TEMP4 will be valid.
1210 However, this might be in front of the assignment of
1211 A to VAR. If it is, it would clobber the store-flag
1212 we will be emitting.
1214 Therefore, emit into a temporary which will be copied to
1215 VAR immediately after TEMP. */
1220 VOIDmode,
1223 normalizep);
1225 {
1226 rtx seq;
1232 /* Put the store-flag insns in front of the first insn
1233 used to compute the condition to ensure that we
1234 use the same values of them as the current
1235 comparison. However, the remainder of the insns we
1236 generate will be placed directly in front of the
1237 jump insn, in case any of the pseudos we use
1238 are modified earlier. */
1244 /* Both CVAL and UVAL are non-zero. */
1246 {
1254 else
1255 {
1261 }
1263 /* If we usually make new pseudos, do so here. This
1264 turns out to help machines that have conditional
1265 move insns. */
1266 /* ??? Conditional moves have already been handled.
1267 This may be obsolete. */
1275 }
1277 {
1278 /* We know that either CVAL or UVAL is zero. If
1279 UVAL is zero, negate TARGET and `and' with CVAL.
1280 Otherwise, `and' with UVAL. */
1282 {
1286 }
1292 }
1297 #ifdef HAVE_cc0
1298 /* If INSN uses CC0, we must not separate it from the
1299 insn that sets cc0. */
1302 #endif
1310 }
1311 else
1313 }
1314 }
1316 /* If branches are expensive, convert
1317 if (foo) bar++; to bar += (foo != 0);
1318 and similarly for "bar--;"
1320 INSN is the conditional branch around the arithmetic. We set:
1322 TEMP is the arithmetic insn.
1323 TEMP1 is the SET doing the arithmetic.
1324 TEMP2 is the operand being incremented or decremented.
1325 TEMP3 to the condition being tested.
1326 TEMP4 to the earliest insn used to find the condition. */
1329 #ifdef HAVE_incscc
1330 || HAVE_incscc
1331 #endif
1332 #ifdef HAVE_decscc
1333 || HAVE_decscc
1334 #endif
1335 )
1336 && ! reload_completed
1348 /* INSN must either branch to the insn after TEMP or the insn
1349 after TEMP must branch to the same place as INSN. */
1355 /* We must be comparing objects whose modes imply the size.
1356 We could handle BLKmode if (1) emit_store_flag could
1357 and (2) we could find the size reliably. */
1360 {
1366 /* It must be the case that TEMP2 is not modified in the range
1367 [TEMP4, INSN). The one exception we make is if the insn
1368 before INSN sets TEMP2 to something which is also unchanged
1369 in that range. In that case, we can move the initialization
1370 into our sequence. */
1379 {
1383 }
1389 VOIDmode,
1393 /* If we can do the store-flag, do the addition or
1394 subtraction. */
1403 {
1404 /* Put the result back in temp2 in case it isn't already.
1405 Then replace the jump, possible a CC0-setting insn in
1406 front of the jump, and TEMP, with the sequence we have
1407 made. */
1422 #ifdef HAVE_cc0
1424 #endif
1428 }
1429 else
1431 }
1433 /* Simplify if (...) x = 1; else {...} if (x) ...
1434 We recognize this case scanning backwards as well.
1436 TEMP is the assignment to x;
1437 TEMP1 is the label at the head of the second if. */
1438 /* ?? This should call get_condition to find the values being
1439 compared, instead of looking for a COMPARE insn when HAVE_cc0
1440 is not defined. This would allow it to work on the m88k. */
1441 /* ?? This optimization is only safe before cse is run if HAVE_cc0
1442 is not defined and the condition is tested by a separate compare
1443 insn. This is because the code below assumes that the result
1444 of the compare dies in the following branch.
1446 Not only that, but there might be other insns between the
1447 compare and branch whose results are live. Those insns need
1448 to be executed.
1450 A way to fix this is to move the insns at JUMP_LABEL (insn)
1451 to before INSN. If we are running before flow, they will
1452 be deleted if they aren't needed. But this doesn't work
1453 well after flow.
1455 This is really a special-case of jump threading, anyway. The
1456 right thing to do is to replace this and jump threading with
1457 much simpler code in cse.
1459 This code has been turned off in the non-cc0 case in the
1460 meantime. */
1462 #ifdef HAVE_cc0
1464 /* Safe to skip USE and CLOBBER insns here
1465 since they will not be deleted. */
1473 /* If we find that the next value tested is `x'
1474 (TEMP1 is the insn where this happens), win. */
1477 #ifdef HAVE_cc0
1478 /* Does temp1 `tst' the value of x? */
1482 #else
1483 /* Does temp1 compare the value of x against zero? */
1490 #endif
1492 {
1493 /* Get the if_then_else from the condjump. */
1496 {
1499 rtx cond
1502 rtx ultimate;
1508 else
1518 }
1519 }
1520 #endif
1522 #if 0
1523 /* @@ This needs a bit of work before it will be right.
1525 Any type of comparison can be accepted for the first and
1526 second compare. When rewriting the first jump, we must
1527 compute the what conditions can reach label3, and use the
1528 appropriate code. We can not simply reverse/swap the code
1529 of the first jump. In some cases, the second jump must be
1530 rewritten also.
1532 For example,
1533 < == converts to > ==
1534 < != converts to == >
1535 etc.
1537 If the code is written to only accept an '==' test for the second
1538 compare, then all that needs to be done is to swap the condition
1539 of the first branch.
1541 It is questionable whether we want this optimization anyways,
1542 since if the user wrote code like this because he/she knew that
1543 the jump to label1 is taken most of the time, then rewriting
1544 this gives slower code. */
1545 /* @@ This should call get_condition to find the values being
1546 compared, instead of looking for a COMPARE insn when HAVE_cc0
1547 is not defined. This would allow it to work on the m88k. */
1548 /* @@ This optimization is only safe before cse is run if HAVE_cc0
1549 is not defined and the condition is tested by a separate compare
1550 insn. This is because the code below assumes that the result
1551 of the compare dies in the following branch. */
1553 /* Simplify test a ~= b
1554 condjump label1;
1555 test a == b
1556 condjump label2;
1557 jump label3;
1558 label1:
1560 rewriting as
1561 test a ~~= b
1562 condjump label3
1563 test a == b
1564 condjump label2
1565 label1:
1567 where ~= is an inequality, e.g. >, and ~~= is the swapped
1568 inequality, e.g. <.
1570 We recognize this case scanning backwards.
1572 TEMP is the conditional jump to `label2';
1573 TEMP1 is the test for `a == b';
1574 TEMP2 is the conditional jump to `label1';
1575 TEMP3 is the test for `a ~= b'. */
1584 #ifdef HAVE_cc0
1586 #else
1590 #endif
1604 {
1609 {
1612 }
1616 }
1617 #endif
1618 /* Simplify if (...) {... x = 1;} if (x) ...
1620 We recognize this case backwards.
1622 TEMP is the test of `x';
1623 TEMP1 is the assignment to `x' at the end of the
1624 previous statement. */
1625 /* @@ This should call get_condition to find the values being
1626 compared, instead of looking for a COMPARE insn when HAVE_cc0
1627 is not defined. This would allow it to work on the m88k. */
1628 /* @@ This optimization is only safe before cse is run if HAVE_cc0
1629 is not defined and the condition is tested by a separate compare
1630 insn. This is because the code below assumes that the result
1631 of the compare dies in the following branch. */
1633 /* ??? This has to be turned off. The problem is that the
1634 unconditional jump might indirectly end up branching to the
1635 label between TEMP1 and TEMP. We can't detect this, in general,
1636 since it may become a jump to there after further optimizations.
1637 If that jump is done, it will be deleted, so we will retry
1638 this optimization in the next pass, thus an infinite loop.
1640 The present code prevents this by putting the jump after the
1641 label, but this is not logically correct. */
1642 #if 0
1644 /* Safe to skip USE and CLOBBER insns here
1645 since they will not be deleted. */
1650 #ifdef HAVE_cc0
1653 #else
1654 /* Temp must be a compare insn, we can not accept a register
1655 to register move here, since it may not be simply a
1656 tst insn. */
1662 #endif
1663 /* May skip USE or CLOBBER insns here
1664 for checking for opportunity, since we
1665 take care of them later. */
1669 #ifdef HAVE_cc0
1671 #else
1674 #endif
1676 /* If this isn't true, cse will do the job. */
1678 {
1679 /* Get the if_then_else from the condjump. */
1684 {
1686 rtx last_insn;
1687 rtx ultimate;
1688 rtx p;
1690 /* Get the place that condjump will jump to
1691 if it is reached from here. */
1695 else
1697 /* Get it as a CODE_LABEL. */
1700 else
1701 /* Get the label out of the LABEL_REF. */
1704 /* Insert the jump immediately before TEMP, specifically
1705 after the label that is between TEMP1 and TEMP. */
1708 /* If we would be branching to the next insn, the jump
1709 would immediately be deleted and the re-inserted in
1710 a subsequent pass over the code. So don't do anything
1711 in that case. */
1714 {
1717 last_insn);
1722 {
1726 }
1729 }
1730 }
1731 }
1732 #endif
1733 /* Detect a conditional jump going to the same place
1734 as an immediately following unconditional jump. */
1740 {
1744 }
1745 /* Detect a conditional jump jumping over an unconditional jump. */
1748 && ! this_is_simplejump
1754 {
1755 /* When we invert the unconditional jump, we will be
1756 decrementing the usage count of its old label.
1757 Make sure that we don't delete it now because that
1758 might cause the following code to be deleted. */
1766 {
1767 /* It is very likely that if there are USE insns before
1768 this jump, they hold REG_DEAD notes. These REG_DEAD
1769 notes are no longer valid due to this optimization,
1770 and will cause the life-analysis that following passes
1771 (notably delayed-branch scheduling) to think that
1772 these registers are dead when they are not.
1774 To prevent this trouble, we just remove the USE insns
1775 from the insn chain. */
1779 {
1783 }
1788 }
1790 /* We can now safely delete the label if it is unreferenced
1791 since the delete_insn above has deleted the BARRIER. */
1795 }
1796 else
1797 {
1798 /* Detect a jump to a jump. */
1803 {
1806 }
1808 /* Look for if (foo) bar; else break; */
1809 /* The insns look like this:
1810 insn = condjump label1;
1811 ...range1 (some insns)...
1812 jump label2;
1813 label1:
1814 ...range2 (some insns)...
1815 jump somewhere unconditionally
1816 label2: */
1817 {
1820 /* Don't do this optimization on the first round, so that
1821 jump-around-a-jump gets simplified before we ask here
1822 whether a jump is unconditional.
1824 Also don't do it when we are called after reload since
1825 it will confuse reorg. */
1828 /* Make sure INSN is something we can invert. */
1835 {
1842 /* Invert the jump condition, so we
1843 still execute the same insns in each case. */
1845 {
1850 rtx rangenext;
1852 /* Include in each range any notes before it, to be
1853 sure that we get the line number note if any, even
1854 if there are other notes here. */
1863 /* Don't move NOTEs for blocks or loops; shift them
1864 outside the ranges, where they'll stay put. */
1868 /* Get current surrounds of the 2 ranges. */
1874 /* Splice range2 where range1 was. */
1879 /* Splice range1 where range2 was. */
1885 /* Check for a loop end note between the end of
1886 range2, and the next code label. If there is one,
1887 then what we have really seen is
1888 if (foo) break; end_of_loop;
1889 and moved the break sequence outside the loop.
1890 We must move the LOOP_END note to where the
1891 loop really ends now, or we will confuse loop
1892 optimization. Stop if we find a LOOP_BEG note
1893 first, since we don't want to move the LOOP_END
1894 note in that case. */
1896 {
1899 {
1902 {
1913 }
1917 }
1918 }
1921 }
1922 }
1923 }
1925 /* Now that the jump has been tensioned,
1926 try cross jumping: check for identical code
1927 before the jump and before its target label. */
1929 /* First, cross jumping of conditional jumps: */
1932 {
1936 /* A conditional jump may be crossjumped
1937 only if the place it jumps to follows
1938 an opposing jump that comes back here. */
1941 /* We have no opposing jump;
1942 cannot cross jump this insn. */
1946 /* TARGET is nonzero if it is ok to cross jump
1947 to code before TARGET. If so, see if matches. */
1953 {
1955 /* Make the old conditional jump
1956 into an unconditional one. */
1961 /* Add to jump_chain unless this is a new label
1962 whose UID is too large. */
1964 {
1968 }
1971 }
1972 }
1974 /* Cross jumping of unconditional jumps:
1975 a few differences. */
1978 {
1980 rtx target;
1984 /* TARGET is nonzero if it is ok to cross jump
1985 to code before TARGET. If so, see if matches. */
1989 /* If cannot cross jump to code before the label,
1990 see if we can cross jump to another jump to
1991 the same label. */
1992 /* Try each other jump to this label. */
1999 /* Ignore TARGET if it's deleted. */
2005 {
2009 }
2010 }
2012 /* This code was dead in the previous jump.c! */
2014 {
2015 /* Return insns all "jump to the same place"
2016 so we can cross-jump between any two of them. */
2022 /* If cannot cross jump to code before the label,
2023 see if we can cross jump to another jump to
2024 the same label. */
2025 /* Try each other jump to this label. */
2036 {
2040 }
2041 }
2042 }
2043 }
2046 }
2048 /* Delete extraneous line number notes.
2049 Note that two consecutive notes for different lines are not really
2050 extraneous. There should be some indication where that line belonged,
2051 even if it became empty. */
2053 {
2058 {
2059 /* Delete this note if it is identical to previous note. */
2063 {
2066 }
2069 }
2070 }
2072 #ifdef HAVE_return
2074 {
2075 /* If we fall through to the epilogue, see if we can insert a RETURN insn
2076 in front of it. If the machine allows it at this point (we might be
2077 after reload for a leaf routine), it will improve optimization for it
2078 to be there. We do this both here and at the start of this pass since
2079 the RETURN might have been deleted by some of our optimizations. */
2085 {
2088 }
2089 }
2090 #endif
2092 /* See if there is still a NOTE_INSN_FUNCTION_END in this function.
2093 If so, delete it, and record that this function can drop off the end. */
2096 {
2099 /* One label can follow the end-note: the return label. */
2101 /* Ordinary insns can follow it if returning a structure. */
2103 /* If machine uses explicit RETURN insns, no epilogue,
2104 then one of them follows the note. */
2107 /* A barrier can follow the return insn. */
2109 /* Other kinds of notes can follow also. */
2113 }
2115 /* Report if control can fall through at the end of the function. */
2118 {
2121 }
2123 /* Show JUMP_CHAIN no longer valid. */
2125 }
2126 \f
2127 /* LOOP_START is a NOTE_INSN_LOOP_BEG note that is followed by an unconditional
2128 jump. Assume that this unconditional jump is to the exit test code. If
2129 the code is sufficiently simple, make a copy of it before INSN,
2130 followed by a jump to the exit of the loop. Then delete the unconditional
2131 jump after INSN.
2133 Return 1 if we made the change, else 0.
2135 This is only safe immediately after a regscan pass because it uses the
2136 values of regno_first_uid and regno_last_uid. */
2138 static int
2140 rtx loop_start;
2141 {
2146 rtx lastexit;
2150 /* Scan the exit code. We do not perform this optimization if any insn:
2152 is a CALL_INSN
2153 is a CODE_LABEL
2154 has a REG_RETVAL or REG_LIBCALL note (hard to adjust)
2155 is a NOTE_INSN_LOOP_BEG because this means we have a nested loop
2156 is a NOTE_INSN_BLOCK_{BEG,END} because duplicating these notes
2157 are not valid
2159 Also, don't do this if the exit code is more than 20 insns. */
2162 insn
2166 {
2168 {
2173 /* We could be in front of the wrong NOTE_INSN_LOOP_END if there is
2174 a jump immediately after the loop start that branches outside
2175 the loop but within an outer loop, near the exit test.
2176 If we copied this exit test and created a phony
2177 NOTE_INSN_LOOP_VTOP, this could make instructions immediately
2178 before the exit test look like these could be safely moved
2179 out of the loop even if they actually may be never executed.
2180 This can be avoided by checking here for NOTE_INSN_LOOP_CONT. */
2195 }
2196 }
2198 /* Unless INSN is zero, we can do the optimization. */
2204 /* See if any insn sets a register only used in the loop exit code and
2205 not a user variable. If so, replace it with a new register. */
2214 {
2220 {
2221 /* We can do the replacement. Allocate reg_map if this is the
2222 first replacement we found. */
2224 {
2227 }
2232 }
2233 }
2235 /* Now copy each insn. */
2238 {
2243 /* Only copy line-number notes. */
2245 {
2248 }
2258 /* Copy all REG_NOTES except REG_LABEL since mark_jump_label will
2259 make them. */
2275 {
2279 }
2281 /* If this is a simple jump, add it to the jump chain. */
2285 {
2289 }
2294 }
2296 /* Now clean up by emitting a jump to the end label and deleting the jump
2297 at the start of the loop. */
2299 {
2301 loop_start);
2305 {
2309 }
2311 }
2313 /* Mark the exit code as the virtual top of the converted loop. */
2319 }
2320 \f
2321 /* Move all block-beg, block-end, loop-beg, loop-cont, loop-vtop, and
2322 loop-end notes between START and END out before START. Assume that
2323 END is not such a note. START may be such a note. Returns the value
2324 of the new starting insn, which may be different if the original start
2325 was such a note. */
2327 rtx
2330 {
2331 rtx insn;
2332 rtx next;
2335 {
2344 {
2347 else
2348 {
2356 }
2357 }
2358 }
2361 }
2362 \f
2363 /* Compare the instructions before insn E1 with those before E2
2364 to find an opportunity for cross jumping.
2365 (This means detecting identical sequences of insns followed by
2366 jumps to the same place, or followed by a label and a jump
2367 to that label, and replacing one with a jump to the other.)
2369 Assume E1 is a jump that jumps to label E2
2370 (that is not always true but it might as well be).
2371 Find the longest possible equivalent sequences
2372 and store the first insns of those sequences into *F1 and *F2.
2373 Store zero there if no equivalent preceding instructions are found.
2375 We give up if we find a label in stream 1.
2376 Actually we could transfer that label into stream 2. */
2378 static void
2383 {
2390 rtx prev1;
2396 {
2406 /* Don't allow the range of insns preceding E1 or E2
2407 to include the other (E2 or E1). */
2411 /* If we will get to this code by jumping, those jumps will be
2412 tensioned to go directly to the new label (before I2),
2413 so this cross-jumping won't cost extra. So reduce the minimum. */
2415 {
2418 }
2426 /* If this is a CALL_INSN, compare register usage information.
2427 If we don't check this on stack register machines, the two
2428 CALL_INSNs might be merged leaving reg-stack.c with mismatching
2429 numbers of stack registers in the same basic block.
2430 If we don't check this on machines with delay slots, a delay slot may
2431 be filled that clobbers a parameter expected by the subroutine.
2433 ??? We take the simple route for now and assume that if they're
2434 equal, they were constructed identically. */
2441 #ifdef STACK_REGS
2442 /* If cross_jump_death_matters is not 0, the insn's mode
2443 indicates whether or not the insn contains any stack-like
2444 regs. */
2447 {
2448 /* If register stack conversion has already been done, then
2449 death notes must also be compared before it is certain that
2450 the two instruction streams match. */
2452 rtx note;
2472 done:
2473 ;
2474 }
2475 #endif
2479 {
2480 /* The following code helps take care of G++ cleanups. */
2481 rtx equiv1;
2482 rtx equiv2;
2489 /* If the equivalences are not to a constant, they may
2490 reference pseudos that no longer exist, so we can't
2491 use them. */
2494 {
2499 {
2506 }
2507 }
2509 /* Insns fail to match; cross jumping is limited to the following
2510 insns. */
2512 #ifdef HAVE_cc0
2513 /* Don't allow the insn after a compare to be shared by
2514 cross-jumping unless the compare is also shared.
2515 Here, if either of these non-matching insns is a compare,
2516 exclude the following insn from possible cross-jumping. */
2519 #endif
2521 /* If cross-jumping here will feed a jump-around-jump
2522 optimization, this jump won't cost extra, so reduce
2523 the minimum. */
2529 }
2531 win:
2533 {
2534 /* Ok, this insn is potentially includable in a cross-jump here. */
2537 }
2538 }
2542 }
2544 static void
2547 {
2548 /* Find an existing label at this point
2549 or make a new one if there is none. */
2552 /* Make the same jump insn jump to the new point. */
2554 {
2555 /* Remove from jump chain of returns. */
2557 /* Change the insn. */
2562 /* Add to new the jump chain. */
2565 {
2568 }
2569 }
2570 else
2573 /* Delete the matching insns before the jump. Also, remove any REG_EQUAL
2574 or REG_EQUIV note in the NEWLPOS stream that isn't also present in
2575 the NEWJPOS stream. */
2578 {
2579 rtx lnote;
2591 }
2592 }
2593 \f
2594 /* Return the label before INSN, or put a new label there. */
2596 rtx
2598 rtx insn;
2599 {
2600 rtx label;
2602 /* Find an existing label at this point
2603 or make a new one if there is none. */
2607 {
2613 }
2615 }
2617 /* Return the label after INSN, or put a new label there. */
2619 rtx
2621 rtx insn;
2622 {
2623 rtx label;
2625 /* Find an existing label at this point
2626 or make a new one if there is none. */
2630 {
2634 }
2636 }
2637 \f
2638 /* Return 1 if INSN is a jump that jumps to right after TARGET
2639 only on the condition that TARGET itself would drop through.
2640 Assumes that TARGET is a conditional jump. */
2642 static int
2645 {
2661 {
2665 }
2668 {
2672 }
2677 }
2678 \f
2679 /* Given a comparison, COMPARISON, inside a conditional jump insn, INSN,
2680 return non-zero if it is safe to reverse this comparison. It is if our
2681 floating-point is not IEEE, if this is an NE or EQ comparison, or if
2682 this is known to be an integer comparison. */
2684 int
2686 rtx comparison;
2687 rtx insn;
2688 {
2689 rtx arg0;
2691 /* If this is not actually a comparison, we can't reverse it. */
2696 /* If this is an NE comparison, it is safe to reverse it to an EQ
2697 comparison and vice versa, even for floating point. If no operands
2698 are NaNs, the reversal is valid. If some operand is a NaN, EQ is
2699 always false and NE is always true, so the reversal is also valid. */
2700 || flag_fast_math
2707 /* Make sure ARG0 is one of the actual objects being compared. If we
2708 can't do this, we can't be sure the comparison can be reversed.
2710 Handle cc0 and a MODE_CC register. */
2712 #ifdef HAVE_cc0
2714 #endif
2715 )
2716 {
2727 }
2729 /* We can reverse this if ARG0 is a CONST_INT or if its mode is
2730 not VOIDmode and neither a MODE_CC nor MODE_FLOAT type. */
2735 }
2737 /* Given an rtx-code for a comparison, return the code
2738 for the negated comparison.
2739 WATCH OUT! reverse_condition is not safe to use on a jump
2740 that might be acting on the results of an IEEE floating point comparison,
2741 because of the special treatment of non-signaling nans in comparisons.
2742 Use can_reverse_comparison_p to be sure. */
2744 enum rtx_code
2747 {
2749 {
2783 }
2784 }
2786 /* Similar, but return the code when two operands of a comparison are swapped.
2787 This IS safe for IEEE floating-point. */
2789 enum rtx_code
2792 {
2794 {
2826 }
2827 }
2829 /* Given a comparison CODE, return the corresponding unsigned comparison.
2830 If CODE is an equality comparison or already an unsigned comparison,
2831 CODE is returned. */
2833 enum rtx_code
2836 {
2838 {
2861 }
2862 }
2864 /* Similarly, return the signed version of a comparison. */
2866 enum rtx_code
2869 {
2871 {
2894 }
2895 }
2896 \f
2897 /* Return non-zero if CODE1 is more strict than CODE2, i.e., if the
2898 truth of CODE1 implies the truth of CODE2. */
2900 int
2903 {
2908 {
2933 }
2936 }
2937 \f
2938 /* Return 1 if INSN is an unconditional jump and nothing else. */
2940 int
2942 rtx insn;
2943 {
2948 }
2950 /* Return nonzero if INSN is a (possibly) conditional jump
2951 and nothing more. */
2953 int
2955 rtx insn;
2956 {
2975 }
2977 /* Return nonzero if INSN is a (possibly) conditional jump
2978 and nothing more. */
2980 int
2982 rtx insn;
2983 {
2988 else
3008 }
3010 /* Return 1 if X is an RTX that does nothing but set the condition codes
3011 and CLOBBER or USE registers.
3012 Return -1 if X does explicitly set the condition codes,
3013 but also does other things. */
3015 int
3017 rtx x;
3018 {
3019 #ifdef HAVE_cc0
3023 {
3028 {
3034 }
3036 }
3038 #else
3040 #endif
3041 }
3042 \f
3043 /* Follow any unconditional jump at LABEL;
3044 return the ultimate label reached by any such chain of jumps.
3045 If LABEL is not followed by a jump, return LABEL.
3046 If the chain loops or we can't find end, return LABEL,
3047 since that tells caller to avoid changing the insn.
3049 If RELOAD_COMPLETED is 0, we do not chain across a NOTE_INSN_LOOP_BEG or
3050 a USE or CLOBBER. */
3052 rtx
3054 rtx label;
3055 {
3069 depth++)
3070 {
3071 /* Don't chain through the insn that jumps into a loop
3072 from outside the loop,
3073 since that would create multiple loop entry jumps
3074 and prevent loop optimization. */
3075 rtx tem;
3082 /* If we have found a cycle, make the insn jump to itself. */
3092 }
3096 }
3098 /* Assuming that field IDX of X is a vector of label_refs,
3099 replace each of them by the ultimate label reached by it.
3100 Return nonzero if a change is made.
3101 If IGNORE_LOOPS is 0, we do not chain across a NOTE_INSN_LOOP_BEG. */
3103 static int
3107 {
3111 {
3115 {
3121 }
3122 }
3124 }
3125 \f
3126 /* Find all CODE_LABELs referred to in X, and increment their use counts.
3127 If INSN is a JUMP_INSN and there is at least one CODE_LABEL referenced
3128 in INSN, then store one of them in JUMP_LABEL (INSN).
3129 If INSN is an INSN or a CALL_INSN and there is at least one CODE_LABEL
3130 referenced in INSN, add a REG_LABEL note containing that label to INSN.
3131 Also, when there are consecutive labels, canonicalize on the last of them.
3133 Note that two labels separated by a loop-beginning note
3134 must be kept distinct if we have not yet done loop-optimization,
3135 because the gap between them is where loop-optimize
3136 will want to move invariant code to. CROSS_JUMP tells us
3137 that loop-optimization is done with.
3139 Once reload has completed (CROSS_JUMP non-zero), we need not consider
3140 two labels distinct if they are separated by only USE or CLOBBER insns. */
3142 static void
3145 rtx insn;
3147 {
3153 {
3166 /* If this is a constant-pool reference, see if it is a label. */
3173 {
3176 rtx note;
3177 rtx next;
3182 /* Ignore references to labels of containing functions. */
3186 /* If there are other labels following this one,
3187 replace it with the last of the consecutive labels. */
3189 {
3202 }
3208 {
3212 /* If we've changed OLABEL and we had a REG_LABEL note
3213 for it, update it as well. */
3218 /* Otherwise, add a REG_LABEL note for LABEL unless there already
3219 is one. */
3221 {
3223 /* Don't record labels that refer to dispatch tables.
3224 This is not necessary, since the tablejump
3225 references the same label.
3226 And if we did record them, flow.c would make worse code. */
3233 }
3234 }
3236 }
3238 /* Do walk the labels in a vector, but not the first operand of an
3239 ADDR_DIFF_VEC. Don't set the JUMP_LABEL of a vector. */
3242 {
3248 }
3249 }
3253 {
3257 {
3261 }
3262 }
3263 }
3265 /* If all INSN does is set the pc, delete it,
3266 and delete the insn that set the condition codes for it
3267 if that's what the previous thing was. */
3269 void
3271 rtx insn;
3272 {
3277 }
3279 /* Delete INSN and recursively delete insns that compute values used only
3280 by INSN. This uses the REG_DEAD notes computed during flow analysis.
3281 If we are running before flow.c, we need do nothing since flow.c will
3282 delete dead code. We also can't know if the registers being used are
3283 dead or not at this point.
3285 Otherwise, look at all our REG_DEAD notes. If a previous insn does
3286 nothing other than set a register that dies in this insn, we can delete
3287 that insn as well.
3289 On machines with CC0, if CC0 is used in this insn, we may be able to
3290 delete the insn that set it. */
3292 static void
3294 rtx insn;
3295 {
3298 #ifdef HAVE_cc0
3300 {
3302 /* We assume that at this stage
3303 CC's are always set explicitly
3304 and always immediately before the jump that
3305 will use them. So if the previous insn
3306 exists to set the CC's, delete it
3307 (unless it performs auto-increments, etc.). */
3310 {
3314 else
3315 /* Otherwise, show that cc0 won't be used. */
3318 }
3319 }
3320 #endif
3323 {
3324 rtx our_prev;
3329 /* Verify that the REG_NOTE is legitimate. */
3336 {
3337 /* If we reach a SEQUENCE, it is too complex to try to
3338 do anything with it, so give up. */
3344 /* reorg creates USEs that look like this. We leave them
3345 alone because reorg needs them for its own purposes. */
3349 {
3354 {
3355 /* If we find a SET of something else, we can't
3356 delete the insn. */
3361 {
3367 }
3371 }
3377 }
3379 /* If OUR_PREV references the register that dies here, it is an
3380 additional use. Hence any prior SET isn't dead. However, this
3381 insn becomes the new place for the REG_DEAD note. */
3384 {
3388 }
3389 }
3390 }
3393 }
3394 \f
3395 /* Delete insn INSN from the chain of insns and update label ref counts.
3396 May delete some following insns as a consequence; may even delete
3397 a label elsewhere and insns that follow it.
3399 Returns the first insn after INSN that was not deleted. */
3401 rtx
3404 {
3413 /* This insn is already deleted => return first following nondeleted. */
3417 /* Don't delete user-declared labels. Convert them to special NOTEs
3418 instead. */
3421 {
3426 }
3427 else
3428 /* Mark this insn as deleted. */
3431 /* If this is an unconditional jump, delete it from the jump chain. */
3435 /* If instruction is followed by a barrier,
3436 delete the barrier too. */
3439 {
3442 }
3444 /* Patch out INSN (and the barrier if any) */
3447 {
3449 {
3454 }
3457 {
3461 }
3465 }
3467 /* If deleting a jump, decrement the count of the label,
3468 and delete the label if it is now unused. */
3472 {
3473 /* This can delete NEXT or PREV,
3474 either directly if NEXT is JUMP_LABEL (INSN),
3475 or indirectly through more levels of jumps. */
3477 /* I feel a little doubtful about this loop,
3478 but I see no clean and sure alternative way
3479 to find the first insn after INSN that is not now deleted.
3480 I hope this works. */
3484 }
3486 /* Likewise if we're deleting a dispatch table. */
3491 {
3502 }
3507 /* If INSN was a label and a dispatch table follows it,
3508 delete the dispatch table. The tablejump must have gone already.
3509 It isn't useful to fall through into a table. */
3518 /* If INSN was a label, delete insns following it if now unreachable. */
3521 {
3527 {
3531 /* Keep going past other deleted labels to delete what follows. */
3534 else
3535 /* Note: if this deletes a jump, it can cause more
3536 deletion of unreachable code, after a different label.
3537 As long as the value from this recursive call is correct,
3538 this invocation functions correctly. */
3540 }
3541 }
3544 }
3546 /* Advance from INSN till reaching something not deleted
3547 then return that. May return INSN itself. */
3549 rtx
3551 rtx insn;
3552 {
3556 }
3557 \f
3558 /* Delete a range of insns from FROM to TO, inclusive.
3559 This is for the sake of peephole optimization, so assume
3560 that whatever these insns do will still be done by a new
3561 peephole insn that will replace them. */
3563 void
3566 {
3570 {
3575 {
3578 /* Patch this insn out of the chain. */
3579 /* We don't do this all at once, because we
3580 must preserve all NOTEs. */
3586 }
3591 }
3593 /* Note that if TO is an unconditional jump
3594 we *do not* delete the BARRIER that follows,
3595 since the peephole that replaces this sequence
3596 is also an unconditional jump in that case. */
3597 }
3598 \f
3599 /* Invert the condition of the jump JUMP, and make it jump
3600 to label NLABEL instead of where it jumps now. */
3602 int
3605 {
3606 /* We have to either invert the condition and change the label or
3607 do neither. Either operation could fail. We first try to invert
3608 the jump. If that succeeds, we try changing the label. If that fails,
3609 we invert the jump back to what it was. */
3618 /* This should just be putting it back the way it was. */
3622 }
3624 /* Invert the jump condition of rtx X contained in jump insn, INSN.
3626 Return 1 if we can do so, 0 if we cannot find a way to do so that
3627 matches a pattern. */
3629 int
3631 rtx x;
3632 rtx insn;
3633 {
3641 {
3645 /* We can do this in two ways: The preferable way, which can only
3646 be done if this is not an integer comparison, is to reverse
3647 the comparison code. Otherwise, swap the THEN-part and ELSE-part
3648 of the IF_THEN_ELSE. If we can't do either, fail. */
3661 }
3665 {
3670 {
3675 }
3676 }
3679 }
3680 \f
3681 /* Make jump JUMP jump to label NLABEL instead of where it jumps now.
3682 If the old jump target label is unused as a result,
3683 it and the code following it may be deleted.
3685 If NLABEL is zero, we are to turn the jump into a (possibly conditional)
3686 RETURN insn.
3688 The return value will be 1 if the change was made, 0 if it wasn't (this
3689 can only occur for NLABEL == 0). */
3691 int
3694 {
3703 /* If this is an unconditional branch, delete it from the jump_chain of
3704 OLABEL and add it to the jump_chain of NLABEL (assuming both labels
3705 have UID's in range and JUMP_CHAIN is valid). */
3708 {
3714 {
3717 }
3718 }
3728 }
3730 /* Delete the instruction JUMP from any jump chain it might be on. */
3732 static void
3734 rtx jump;
3735 {
3739 /* Handle unconditional jumps. */
3744 /* Handle return insns. */
3751 else
3752 {
3753 rtx insn;
3759 {
3762 }
3763 }
3764 }
3766 /* If NLABEL is nonzero, throughout the rtx at LOC,
3767 alter (LABEL_REF OLABEL) to (LABEL_REF NLABEL). If OLABEL is
3768 zero, alter (RETURN) to (LABEL_REF NLABEL).
3770 If NLABEL is zero, alter (LABEL_REF OLABEL) to (RETURN) and check
3771 validity with validate_change. Convert (set (pc) (label_ref olabel))
3772 to (return).
3774 Return 0 if we found a change we would like to make but it is invalid.
3775 Otherwise, return 1. */
3777 int
3781 rtx insn;
3782 {
3789 {
3791 {
3794 else
3797 }
3798 }
3800 {
3805 }
3814 {
3819 {
3824 }
3825 }
3828 }
3829 \f
3830 /* Make jump JUMP jump to label NLABEL, assuming it used to be a tablejump.
3832 If the old jump target label (before the dispatch table) becomes unused,
3833 it and the dispatch table may be deleted. In that case, find the insn
3834 before the jump references that label and delete it and logical successors
3835 too. */
3837 static void
3840 {
3843 /* Add this jump to the jump_chain of NLABEL. */
3846 {
3849 }
3857 {
3860 }
3861 }
3863 /* Find the insn referencing LABEL that is a logical predecessor of INSN.
3864 If we found one, delete it and then delete this insn if DELETE_THIS is
3865 non-zero. Return non-zero if INSN or a predecessor references LABEL. */
3867 static int
3871 {
3873 rtx link;
3877 {
3879 {
3882 }
3883 else
3885 }
3889 {
3891 {
3894 }
3895 else
3897 }
3900 }
3901 \f
3902 /* Like rtx_equal_p except that it considers two REGs as equal
3903 if they renumber to the same value and considers two commutative
3904 operations to be the same if the order of the operands has been
3905 reversed. */
3907 int
3910 {
3921 {
3928 /* If we haven't done any renumbering, don't
3929 make any assumptions. */
3934 {
3939 {
3942 }
3943 }
3945 else
3946 {
3950 }
3953 {
3958 {
3961 }
3962 }
3964 else
3965 {
3969 }
3972 }
3974 /* Now we have disposed of all the cases
3975 in which different rtx codes can match. */
3980 {
3991 /* We can't assume nonlocal labels have their following insns yet. */
3995 /* Two label-refs are equivalent if they point at labels
3996 in the same position in the instruction stream. */
4002 }
4004 /* (MULT:SI x y) and (MULT:HI x y) are NOT equivalent. */
4009 /* For commutative operations, the RTX match if the operand match in any
4010 order. Also handle the simple binary and unary cases without a loop. */
4022 /* Compare the elements. If any pair of corresponding elements
4023 fail to match, return 0 for the whole things. */
4027 {
4030 {
4054 /* fall through. */
4068 }
4069 }
4071 }
4072 \f
4073 /* If X is a hard register or equivalent to one or a subregister of one,
4074 return the hard register number. If X is a pseudo register that was not
4075 assigned a hard register, return the pseudo register number. Otherwise,
4076 return -1. Any rtx is valid for X. */
4078 int
4080 rtx x;
4081 {
4083 {
4087 }
4089 {
4093 }
4095 }
4096 \f
4097 /* Optimize code of the form:
4099 for (x = a[i]; x; ...)
4100 ...
4101 for (x = a[i]; x; ...)
4102 ...
4103 foo:
4105 Loop optimize will change the above code into
4107 if (x = a[i])
4108 for (;;)
4109 { ...; if (! (x = ...)) break; }
4110 if (x = a[i])
4111 for (;;)
4112 { ...; if (! (x = ...)) break; }
4113 foo:
4115 In general, if the first test fails, the program can branch
4116 directly to `foo' and skip the second try which is doomed to fail.
4117 We run this after loop optimization and before flow analysis. */
4119 /* When comparing the insn patterns, we track the fact that different
4120 pseudo-register numbers may have been used in each computation.
4121 The following array stores an equivalence -- same_regs[I] == J means
4122 that pseudo register I was used in the first set of tests in a context
4123 where J was used in the second set. We also count the number of such
4124 pending equivalences. If nonzero, the expressions really aren't the
4125 same. */
4131 /* Track any registers modified between the target of the first jump and
4132 the second jump. They never compare equal. */
4136 /* Record if memory was modified. */
4140 /* Called via note_stores on each insn between the target of the first
4141 branch and the second branch. It marks any changed registers. */
4143 static void
4145 rtx dest;
4146 rtx x;
4147 {
4162 else
4165 }
4167 /* F is the first insn in the chain of insns. */
4169 void
4171 rtx f;
4174 {
4175 /* Basic algorithm is to find a conditional branch,
4176 the label it may branch to, and the branch after
4177 that label. If the two branches test the same condition,
4178 walk back from both branch paths until the insn patterns
4179 differ, or code labels are hit. If we make it back to
4180 the target of the first branch, then we know that the first branch
4181 will either always succeed or always fail depending on the relative
4182 senses of the two branches. So adjust the first branch accordingly
4183 in this case. */
4192 /* Allocate register tables and quick-reset table. */
4200 {
4204 {
4205 /* Get to a candidate branch insn. */
4220 /* Look for a branch after the target. Record any registers and
4221 memory modified between the target and the branch. Stop when we
4222 get to a label since we can't know what was changed there. */
4224 {
4229 {
4230 /* If this is an unconditional jump and is the only use of
4231 its target label, we can follow it. */
4235 {
4238 }
4239 else
4241 }
4247 {
4256 }
4259 }
4261 /* Check the next candidate branch insn from the label
4262 of the first. */
4270 /* Get the comparison codes and operands, reversing the
4271 codes if appropriate. If we don't have comparison codes,
4272 we can't do anything. */
4285 /* If they test the same things and knowing that B1 branches
4286 tells us whether or not B2 branches, check if we
4287 can thread the branch. */
4292 {
4297 {
4299 {
4300 /* We have reached the target of the first branch.
4301 If there are no pending register equivalents,
4302 we know that this branch will either always
4303 succeed (if the senses of the two branches are
4304 the same) or always fail (if not). */
4305 rtx new_label;
4312 else
4316 {
4321 {
4322 /* Don't thread to the loop label. If a loop
4323 label is reused, loop optimization will
4324 be disabled for that loop. */
4327 }
4329 }
4331 }
4333 /* If either of these is not a normal insn (it might be
4334 a JUMP_INSN, CALL_INSN, or CODE_LABEL) we fail. (NOTEs
4335 have already been skipped above.) Similarly, fail
4336 if the insns are different. */
4345 }
4346 }
4347 }
4348 }
4349 }
4350 \f
4351 /* This is like RTX_EQUAL_P except that it knows about our handling of
4352 possibly equivalent registers and knows to consider volatile and
4353 modified objects as not equal.
4355 YINSN is the insn containing Y. */
4357 int
4360 rtx yinsn;
4361 {
4368 /* Rtx's of different codes cannot be equal. */
4372 /* (MULT:SI x y) and (MULT:HI x y) are NOT equivalent.
4373 (REG:SI x) and (REG:HI x) are NOT equivalent. */
4378 /* For commutative operations, the RTX match if the operand match in any
4379 order. Also handle the simple binary and unary cases without a loop. */
4391 /* Handle special-cases first. */
4393 {
4398 /* If neither is user variable or hard register, check for possible
4399 equivalence. */
4406 {
4408 num_same_regs++;
4410 /* If this is the first time we are seeing a register on the `Y'
4411 side, see if it is the last use. If not, we can't thread the
4412 jump, so mark it as not equivalent. */
4417 }
4418 else
4424 /* If memory modified or either volatile, not equivalent.
4425 Else, check address. */
4438 /* Cancel a pending `same_regs' if setting equivalenced registers.
4439 Then process source. */
4442 {
4444 {
4446 num_same_regs--;
4447 }
4450 }
4451 else
4462 }
4469 {
4471 {
4485 /* Two vectors must have the same length. */
4489 /* And the corresponding elements must match. */
4508 /* These are just backpointers, so they don't matter. */
4514 /* It is believed that rtx's at this level will never
4515 contain anything but integers and other rtx's,
4516 except for within LABEL_REFs and SYMBOL_REFs. */
4519 }
4520 }
4522 }