| blob | 40258a5c0a2771d2228ea8184e30d0959d227d50 |
1 /* Optimize jump instructions, for GNU compiler.
2 Copyright (C) 1987, 88, 89, 91, 92, 93, 1994 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. */
116 \f
117 /* Delete no-op jumps and optimize jumps to jumps
118 and jumps around jumps.
119 Delete unused labels and unreachable code.
121 If CROSS_JUMP is 1, detect matching code
122 before a jump and its destination and unify them.
123 If CROSS_JUMP is 2, do cross-jumping, but pay attention to death notes.
125 If NOOP_MOVES is nonzero, delete no-op move insns.
127 If AFTER_REGSCAN is nonzero, then this jump pass is being run immediately
128 after regscan, and it is safe to use regno_first_uid and regno_last_uid.
130 If `optimize' is zero, don't change any code,
131 just determine whether control drops off the end of the function.
132 This case occurs when we have -W and not -O.
133 It works because `delete_insn' checks the value of `optimize'
134 and refrains from actually deleting when that is 0. */
136 void
138 rtx f;
142 {
147 rtx last_insn;
151 /* Initialize LABEL_NUSES and JUMP_LABEL fields. Delete any REG_LABEL
152 notes whose labels don't occur in the insn any more. */
155 {
162 {
167 }
171 }
173 max_uid++;
175 /* Delete insns following barriers, up to next label. */
178 {
180 {
183 {
187 else
189 }
190 /* INSN is now the code_label. */
191 }
192 else
194 }
196 /* Leave some extra room for labels and duplicate exit test insns
197 we make. */
202 /* Mark the label each jump jumps to.
203 Combine consecutive labels, and count uses of labels.
205 For each label, make a chain (using `jump_chain')
206 of all the *unconditional* jumps that jump to it;
207 also make a chain of all returns. */
212 {
215 {
217 {
221 }
223 {
226 }
227 }
228 }
230 /* Keep track of labels used from static data;
231 they cannot ever be deleted. */
236 /* Delete all labels already not referenced.
237 Also find the last insn. */
241 {
244 else
245 {
248 }
249 }
252 {
253 /* See if there is still a NOTE_INSN_FUNCTION_END in this function.
254 If so record that this function can drop off the end. */
257 {
260 /* One label can follow the end-note: the return label. */
262 /* Ordinary insns can follow it if returning a structure. */
264 /* If machine uses explicit RETURN insns, no epilogue,
265 then one of them follows the note. */
268 /* Other kinds of notes can follow also. */
272 }
274 /* Report if control can fall through at the end of the function. */
280 /* Zero the "deleted" flag of all the "deleted" insns. */
284 }
286 #ifdef HAVE_return
288 {
289 /* If we fall through to the epilogue, see if we can insert a RETURN insn
290 in front of it. If the machine allows it at this point (we might be
291 after reload for a leaf routine), it will improve optimization for it
292 to be there. */
298 {
301 }
302 }
303 #endif
307 {
311 {
314 /* Combine stack_adjusts with following push_insns. */
315 #ifdef PUSH_ROUNDING
322 {
323 rtx p;
329 /* Find all successive push insns. */
331 /* Don't convert more than three pushes;
332 that starts adding too many displaced addresses
333 and the whole thing starts becoming a losing
334 proposition. */
336 {
345 /* Allow a no-op move between the adjust and the push. */
354 pushes++;
359 }
361 /* Discard the amount pushed from the stack adjust;
362 maybe eliminate it entirely. */
364 {
367 }
368 else
372 /* Change the appropriate push insns to ordinary stores. */
375 {
389 /* If this push doesn't fully fit in the space
390 of the stack adjust that we deleted,
391 make another stack adjust here for what we
392 didn't use up. There should be peepholes
393 to recognize the resulting sequence of insns. */
395 {
398 p);
400 }
403 }
404 }
405 #endif
407 /* Detect and delete no-op move instructions
408 resulting from not allocating a parameter in a register. */
421 /* Detect and ignore no-op move instructions
422 resulting from smart or fortuitous register allocation. */
425 {
432 {
433 rtx trial;
438 #ifdef PRESERVE_DEATH_INFO_REGNO_P
439 /* Deleting insn could lose a death-note for SREG or DREG
440 so don't do it if final needs accurate death-notes. */
443 #endif
444 {
445 /* DREG may have been the target of a REG_DEAD note in
446 the insn which makes INSN redundant. If so, reorg
447 would still think it is dead. So search for such a
448 note and delete it if we find it. */
453 {
456 }
461 }
462 }
467 {
468 /* This handles the case where we have two consecutive
469 assignments of the same constant to pseudos that didn't
470 get a hard reg. Each SET from the constant will be
471 converted into a SET of the spill register and an
472 output reload will be made following it. This produces
473 two loads of the same constant into the same spill
474 register. */
478 /* Look back for a death note for the first reg.
479 If there is one, it is no longer accurate. */
481 {
485 {
488 }
490 }
492 /* Delete the second load of the value. */
494 }
495 }
497 {
498 /* If each part is a set between two identical registers or
499 a USE or CLOBBER, delete the insn. */
501 rtx tem;
504 {
514 }
518 }
520 in the big-endian case. */
521 /* Also delete insns to store bit fields if they are no-ops. */
530 }
532 }
534 /* If we haven't yet gotten to reload and we have just run regscan,
535 delete any insn that sets a register that isn't used elsewhere.
536 This helps some of the optimizations below by having less insns
537 being jumped around. */
541 {
549 /* We use regno_last_note_uid so as not to delete the setting
550 of a reg that's used in notes. A subsequent optimization
551 might arrange to use that reg for real. */
555 }
557 /* Now iterate optimizing jumps until nothing changes over one pass. */
560 {
564 {
565 rtx reallabelprev;
567 rtx nlabel;
569 #if 0
570 /* If NOT the first iteration, if this is the last jump pass
571 (just before final), do the special peephole optimizations.
572 Avoiding the first iteration gives ordinary jump opts
573 a chance to work before peephole opts. */
578 #endif
580 /* That could have deleted some insns after INSN, so check now
581 what the following insn is. */
585 /* See if this is a NOTE_INSN_LOOP_BEG followed by an unconditional
586 jump. Try to optimize by duplicating the loop exit test if so.
587 This is only safe immediately after regscan, because it uses
588 the values of regno_first_uid and regno_last_uid. */
593 {
596 {
600 }
601 }
609 /* Tension the labels in dispatch tables. */
616 /* If a dispatch table always goes to the same place,
617 get rid of it and replace the insn that uses it. */
621 {
636 /* Don't mess with a casesi insn. */
641 {
645 }
646 }
650 /* If a jump references the end of the function, try to turn
651 it into a RETURN insn, possibly a conditional one. */
658 /* Detect jump to following insn. */
660 {
664 }
666 /* If we have an unconditional jump preceded by a USE, try to put
667 the USE before the target and jump there. This simplifies many
668 of the optimizations below since we don't have to worry about
669 dealing with these USE insns. We only do this if the label
670 being branch to already has the identical USE or if code
671 never falls through to that label. */
680 {
682 {
685 }
691 }
693 /* Simplify if (...) x = a; else x = b; by converting it
694 to x = b; if (...) x = a;
695 if B is sufficiently simple, the test doesn't involve X,
696 and nothing in the test modifies B or X.
698 If we have small register classes, we also can't do this if X
699 is a hard register.
701 If the "x = b;" insn has any REG_NOTES, we don't do this because
702 of the possibility that we are running after CSE and there is a
703 REG_EQUAL note that is only valid if the branch has already been
704 taken. If we move the insn with the REG_EQUAL note, we may
705 fold the comparison to always be false in a later CSE pass.
706 (We could also delete the REG_NOTES when moving the insn, but it
707 seems simpler to not move it.) An exception is that we can move
708 the insn if the only note is a REG_EQUAL or REG_EQUIV whose
709 value is the same as "b".
711 INSN is the branch over the `else' part.
713 We set:
715 TEMP to the jump insn preceding "x = a;"
716 TEMP1 to X
717 TEMP2 to the insn that sets "x = b;"
718 TEMP3 to the insn that sets "x = a;"
719 TEMP4 to the set of "x = b"; */
726 #ifdef SMALL_REGISTER_CLASSES
728 #endif
744 /* TEMP must skip over the "x = a;" insn */
747 /* There must be no other entries to the "x = b;" insn. */
749 /* INSN must either branch to the insn after TEMP2 or the insn
750 after TEMP2 must branch to the same place as INSN. */
755 {
756 /* The test expression, X, may be a complicated test with
757 multiple branches. See if we can find all the uses of
758 the label that TEMP branches to without hitting a CALL_INSN
759 or a jump to somewhere else. */
764 /* Set P to the first jump insn that goes around "x = a;". */
766 {
768 {
771 {
772 nuses--;
775 }
776 else
778 }
781 }
783 #ifdef HAVE_cc0
784 /* We cannot insert anything between a set of cc and its use
785 so if P uses cc0, we must back up to the previous insn. */
790 #endif
795 /* If we found all the uses and there was no data conflict, we
796 can move the assignment unless we can branch into the middle
797 from somewhere. */
804 {
808 /* Set NEXT to an insn that we know won't go away. */
811 /* Delete the jump around the set. Note that we must do
812 this before we redirect the test jumps so that it won't
813 delete the code immediately following the assignment
814 we moved (which might be a jump). */
818 /* We either have two consecutive labels or a jump to
819 a jump, so adjust all the JUMP_INSNs to branch to where
820 INSN branches to. */
827 }
828 }
830 #ifndef HAVE_cc0
831 /* If we have if (...) x = exp; and branches are expensive,
832 EXP is a single insn, does not have any side effects, cannot
833 trap, and is not too costly, convert this to
834 t = exp; if (...) x = t;
836 Don't do this when we have CC0 because it is unlikely to help
837 and we'd need to worry about where to place the new insn and
838 the potential for conflicts. We also can't do this when we have
839 notes on the insn for the same reason as above.
841 We set:
843 TEMP to the "x = exp;" insn.
844 TEMP1 to the single set in the "x = exp; insn.
845 TEMP2 to "x". */
860 #ifdef SMALL_REGISTER_CLASSES
862 #endif
869 {
873 {
879 }
880 }
882 /* Similarly, if it takes two insns to compute EXP but they
883 have the same destination. Here TEMP3 will be the second
884 insn and TEMP4 the SET from that insn. */
902 #ifdef SMALL_REGISTER_CLASSES
904 #endif
913 {
917 {
921 emit_insn_after_with_line_notes
927 }
928 }
930 /* Finally, handle the case where two insns are used to
931 compute EXP but a temporary register is used. Here we must
932 ensure that the temporary register is not used anywhere else. */
935 && after_regscan
963 #ifdef SMALL_REGISTER_CLASSES
965 #endif
970 {
974 {
983 }
984 }
987 /* We deal with four cases:
989 1) x = a; if (...) x = b; and either A or B is zero,
990 2) if (...) x = 0; and jumps are expensive,
991 3) x = a; if (...) x = b; and A and B are constants where all the
992 set bits in A are also set in B and jumps are expensive, and
993 4) x = a; if (...) x = b; and A and B non-zero, and jumps are
994 more expensive.
995 5) if (...) x = b; if jumps are even more expensive.
997 In each of these try to use a store-flag insn to avoid the jump.
998 (If the jump would be faster, the machine should not have
999 defined the scc insns!). These cases are often made by the
1000 previous optimization.
1002 INSN here is the jump around the store. We set:
1004 TEMP to the "x = b;" insn.
1005 TEMP1 to X.
1006 TEMP2 to B (const0_rtx in the second case).
1007 TEMP3 to A (X in the second case).
1008 TEMP4 to the condition being tested.
1009 TEMP5 to the earliest insn used to find the condition. */
1012 ! reload_completed
1014 /* Set TEMP to the "x = b;" insn. */
1019 #ifdef SMALL_REGISTER_CLASSES
1021 #endif
1026 /* Allow either form, but prefer the former if both apply.
1027 There is no point in using the old value of TEMP1 if
1028 it is a register, since cse will alias them. It can
1029 lose if the old value were a hard register since CSE
1030 won't replace hard registers. */
1033 /* Make the latter case look like x = x; if (...) x = 0; */
1037 #ifdef HAVE_conditional_move
1039 #endif
1041 /* INSN must either branch to the insn after TEMP or the insn
1042 after TEMP must branch to the same place as INSN. */
1048 /* We must be comparing objects whose modes imply the size.
1049 We could handle BLKmode if (1) emit_store_flag could
1050 and (2) we could find the size reliably. */
1053 /* If B is zero, OK; if A is zero, can only do (1) if we
1054 can reverse the condition. See if (3) applies possibly
1055 by reversing the condition. Prefer reversing to (4) when
1056 branches are very expensive. */
1066 insn)))))
1067 #ifdef HAVE_conditional_move
1069 #endif
1071 #ifdef HAVE_cc0
1072 /* If the previous insn sets CC0 and something else, we can't
1073 do this since we are going to delete that insn. */
1080 #endif
1081 )
1082 {
1086 rtx target;
1088 /* If necessary, reverse the condition. */
1091 else
1094 /* See if we can do this with a store-flag insn. */
1097 /* If CVAL is non-zero, normalize to -1. Otherwise,
1098 if UVAL is the constant 1, it is best to just compute
1099 the result directly. If UVAL is constant and STORE_FLAG_VALUE
1100 includes all of its bits, it is best to compute the flag
1101 value unnormalized and `and' it with UVAL. Otherwise,
1102 normalize to -1 and `and' with UVAL. */
1109 /* We will be putting the store-flag insn immediately in
1110 front of the comparison that was originally being done,
1111 so we know all the variables in TEMP4 will be valid.
1112 However, this might be in front of the assignment of
1113 A to VAR. If it is, it would clobber the store-flag
1114 we will be emitting.
1116 Therefore, emit into a temporary which will be copied to
1117 VAR immediately after TEMP. */
1121 VOIDmode,
1124 normalizep);
1126 {
1128 rtx seq;
1130 /* Put the store-flag insns in front of the first insn
1131 used to compute the condition to ensure that we
1132 use the same values of them as the current
1133 comparison. However, the remainder of the insns we
1134 generate will be placed directly in front of the
1135 jump insn, in case any of the pseudos we use
1136 are modified earlier. */
1145 /* Both CVAL and UVAL are non-zero. */
1147 {
1155 else
1156 {
1162 }
1164 /* If we usually make new pseudos, do so here. This
1165 turns out to help machines that have conditional
1166 move insns. */
1174 }
1176 {
1177 /* We know that either CVAL or UVAL is zero. If
1178 UVAL is zero, negate TARGET and `and' with CVAL.
1179 Otherwise, `and' with UVAL. */
1181 {
1185 }
1191 }
1197 #ifdef HAVE_cc0
1198 /* If INSN uses CC0, we must not separate it from the
1199 insn that sets cc0. */
1203 #endif
1213 }
1214 else
1216 }
1218 /* If branches are expensive, convert
1219 if (foo) bar++; to bar += (foo != 0);
1220 and similarly for "bar--;"
1222 INSN is the conditional branch around the arithmetic. We set:
1224 TEMP is the arithmetic insn.
1225 TEMP1 is the SET doing the arithmetic.
1226 TEMP2 is the operand being incremented or decremented.
1227 TEMP3 to the condition being tested.
1228 TEMP4 to the earliest insn used to find the condition. */
1231 #ifdef HAVE_incscc
1232 || HAVE_incscc
1233 #endif
1234 #ifdef HAVE_decscc
1235 || HAVE_decscc
1236 #endif
1237 )
1238 && ! reload_completed
1248 /* INSN must either branch to the insn after TEMP or the insn
1249 after TEMP must branch to the same place as INSN. */
1255 /* We must be comparing objects whose modes imply the size.
1256 We could handle BLKmode if (1) emit_store_flag could
1257 and (2) we could find the size reliably. */
1260 {
1266 /* It must be the case that TEMP2 is not modified in the range
1267 [TEMP4, INSN). The one exception we make is if the insn
1268 before INSN sets TEMP2 to something which is also unchanged
1269 in that range. In that case, we can move the initialization
1270 into our sequence. */
1279 {
1283 }
1289 VOIDmode,
1293 /* If we can do the store-flag, do the addition or
1294 subtraction. */
1303 {
1304 /* Put the result back in temp2 in case it isn't already.
1305 Then replace the jump, possible a CC0-setting insn in
1306 front of the jump, and TEMP, with the sequence we have
1307 made. */
1322 #ifdef HAVE_cc0
1324 #endif
1328 }
1329 else
1331 }
1333 /* Simplify if (...) x = 1; else {...} if (x) ...
1334 We recognize this case scanning backwards as well.
1336 TEMP is the assignment to x;
1337 TEMP1 is the label at the head of the second if. */
1338 /* ?? This should call get_condition to find the values being
1339 compared, instead of looking for a COMPARE insn when HAVE_cc0
1340 is not defined. This would allow it to work on the m88k. */
1341 /* ?? This optimization is only safe before cse is run if HAVE_cc0
1342 is not defined and the condition is tested by a separate compare
1343 insn. This is because the code below assumes that the result
1344 of the compare dies in the following branch.
1346 Not only that, but there might be other insns between the
1347 compare and branch whose results are live. Those insns need
1348 to be executed.
1350 A way to fix this is to move the insns at JUMP_LABEL (insn)
1351 to before INSN. If we are running before flow, they will
1352 be deleted if they aren't needed. But this doesn't work
1353 well after flow.
1355 This is really a special-case of jump threading, anyway. The
1356 right thing to do is to replace this and jump threading with
1357 much simpler code in cse.
1359 This code has been turned off in the non-cc0 case in the
1360 meantime. */
1362 #ifdef HAVE_cc0
1364 /* Safe to skip USE and CLOBBER insns here
1365 since they will not be deleted. */
1373 /* If we find that the next value tested is `x'
1374 (TEMP1 is the insn where this happens), win. */
1377 #ifdef HAVE_cc0
1378 /* Does temp1 `tst' the value of x? */
1382 #else
1383 /* Does temp1 compare the value of x against zero? */
1390 #endif
1392 {
1393 /* Get the if_then_else from the condjump. */
1396 {
1399 rtx cond
1402 rtx ultimate;
1408 else
1418 }
1419 }
1420 #endif
1422 #if 0
1423 /* @@ This needs a bit of work before it will be right.
1425 Any type of comparison can be accepted for the first and
1426 second compare. When rewriting the first jump, we must
1427 compute the what conditions can reach label3, and use the
1428 appropriate code. We can not simply reverse/swap the code
1429 of the first jump. In some cases, the second jump must be
1430 rewritten also.
1432 For example,
1433 < == converts to > ==
1434 < != converts to == >
1435 etc.
1437 If the code is written to only accept an '==' test for the second
1438 compare, then all that needs to be done is to swap the condition
1439 of the first branch.
1441 It is questionable whether we want this optimization anyways,
1442 since if the user wrote code like this because he/she knew that
1443 the jump to label1 is taken most of the time, then rewriting
1444 this gives slower code. */
1445 /* @@ This should call get_condition to find the values being
1446 compared, instead of looking for a COMPARE insn when HAVE_cc0
1447 is not defined. This would allow it to work on the m88k. */
1448 /* @@ This optimization is only safe before cse is run if HAVE_cc0
1449 is not defined and the condition is tested by a separate compare
1450 insn. This is because the code below assumes that the result
1451 of the compare dies in the following branch. */
1453 /* Simplify test a ~= b
1454 condjump label1;
1455 test a == b
1456 condjump label2;
1457 jump label3;
1458 label1:
1460 rewriting as
1461 test a ~~= b
1462 condjump label3
1463 test a == b
1464 condjump label2
1465 label1:
1467 where ~= is an inequality, e.g. >, and ~~= is the swapped
1468 inequality, e.g. <.
1470 We recognize this case scanning backwards.
1472 TEMP is the conditional jump to `label2';
1473 TEMP1 is the test for `a == b';
1474 TEMP2 is the conditional jump to `label1';
1475 TEMP3 is the test for `a ~= b'. */
1484 #ifdef HAVE_cc0
1486 #else
1490 #endif
1504 {
1509 {
1512 }
1516 }
1517 #endif
1518 /* Simplify if (...) {... x = 1;} if (x) ...
1520 We recognize this case backwards.
1522 TEMP is the test of `x';
1523 TEMP1 is the assignment to `x' at the end of the
1524 previous statement. */
1525 /* @@ This should call get_condition to find the values being
1526 compared, instead of looking for a COMPARE insn when HAVE_cc0
1527 is not defined. This would allow it to work on the m88k. */
1528 /* @@ This optimization is only safe before cse is run if HAVE_cc0
1529 is not defined and the condition is tested by a separate compare
1530 insn. This is because the code below assumes that the result
1531 of the compare dies in the following branch. */
1533 /* ??? This has to be turned off. The problem is that the
1534 unconditional jump might indirectly end up branching to the
1535 label between TEMP1 and TEMP. We can't detect this, in general,
1536 since it may become a jump to there after further optimizations.
1537 If that jump is done, it will be deleted, so we will retry
1538 this optimization in the next pass, thus an infinite loop.
1540 The present code prevents this by putting the jump after the
1541 label, but this is not logically correct. */
1542 #if 0
1544 /* Safe to skip USE and CLOBBER insns here
1545 since they will not be deleted. */
1550 #ifdef HAVE_cc0
1553 #else
1554 /* Temp must be a compare insn, we can not accept a register
1555 to register move here, since it may not be simply a
1556 tst insn. */
1562 #endif
1563 /* May skip USE or CLOBBER insns here
1564 for checking for opportunity, since we
1565 take care of them later. */
1569 #ifdef HAVE_cc0
1571 #else
1574 #endif
1576 /* If this isn't true, cse will do the job. */
1578 {
1579 /* Get the if_then_else from the condjump. */
1584 {
1586 rtx last_insn;
1587 rtx ultimate;
1588 rtx p;
1590 /* Get the place that condjump will jump to
1591 if it is reached from here. */
1595 else
1597 /* Get it as a CODE_LABEL. */
1600 else
1601 /* Get the label out of the LABEL_REF. */
1604 /* Insert the jump immediately before TEMP, specifically
1605 after the label that is between TEMP1 and TEMP. */
1608 /* If we would be branching to the next insn, the jump
1609 would immediately be deleted and the re-inserted in
1610 a subsequent pass over the code. So don't do anything
1611 in that case. */
1614 {
1617 last_insn);
1622 {
1626 }
1629 }
1630 }
1631 }
1632 #endif
1633 /* Detect a conditional jump going to the same place
1634 as an immediately following unconditional jump. */
1640 {
1644 }
1645 /* Detect a conditional jump jumping over an unconditional jump. */
1653 {
1654 /* When we invert the unconditional jump, we will be
1655 decrementing the usage count of its old label.
1656 Make sure that we don't delete it now because that
1657 might cause the following code to be deleted. */
1665 {
1666 /* It is very likely that if there are USE insns before
1667 this jump, they hold REG_DEAD notes. These REG_DEAD
1668 notes are no longer valid due to this optimization,
1669 and will cause the life-analysis that following passes
1670 (notably delayed-branch scheduling) to think that
1671 these registers are dead when they are not.
1673 To prevent this trouble, we just remove the USE insns
1674 from the insn chain. */
1678 {
1682 }
1687 }
1689 /* We can now safely delete the label if it is unreferenced
1690 since the delete_insn above has deleted the BARRIER. */
1694 }
1695 else
1696 {
1697 /* Detect a jump to a jump. */
1702 {
1705 }
1707 /* Look for if (foo) bar; else break; */
1708 /* The insns look like this:
1709 insn = condjump label1;
1710 ...range1 (some insns)...
1711 jump label2;
1712 label1:
1713 ...range2 (some insns)...
1714 jump somewhere unconditionally
1715 label2: */
1716 {
1719 /* Don't do this optimization on the first round, so that
1720 jump-around-a-jump gets simplified before we ask here
1721 whether a jump is unconditional.
1723 Also don't do it when we are called after reload since
1724 it will confuse reorg. */
1727 /* Make sure INSN is something we can invert. */
1734 {
1741 /* Invert the jump condition, so we
1742 still execute the same insns in each case. */
1744 {
1750 /* Include in each range any notes before it, to be
1751 sure that we get the line number note if any, even
1752 if there are other notes here. */
1761 /* Don't move NOTEs for blocks or loops; shift them
1762 outside the ranges, where they'll stay put. */
1766 /* Get current surrounds of the 2 ranges. */
1772 /* Splice range2 where range1 was. */
1777 /* Splice range1 where range2 was. */
1784 }
1785 }
1786 }
1788 /* Now that the jump has been tensioned,
1789 try cross jumping: check for identical code
1790 before the jump and before its target label. */
1792 /* First, cross jumping of conditional jumps: */
1795 {
1799 /* A conditional jump may be crossjumped
1800 only if the place it jumps to follows
1801 an opposing jump that comes back here. */
1804 /* We have no opposing jump;
1805 cannot cross jump this insn. */
1809 /* TARGET is nonzero if it is ok to cross jump
1810 to code before TARGET. If so, see if matches. */
1816 {
1818 /* Make the old conditional jump
1819 into an unconditional one. */
1824 /* Add to jump_chain unless this is a new label
1825 whose UID is too large. */
1827 {
1831 }
1834 }
1835 }
1837 /* Cross jumping of unconditional jumps:
1838 a few differences. */
1841 {
1843 rtx target;
1847 /* TARGET is nonzero if it is ok to cross jump
1848 to code before TARGET. If so, see if matches. */
1852 /* If cannot cross jump to code before the label,
1853 see if we can cross jump to another jump to
1854 the same label. */
1855 /* Try each other jump to this label. */
1862 /* Ignore TARGET if it's deleted. */
1868 {
1872 }
1873 }
1875 /* This code was dead in the previous jump.c! */
1877 {
1878 /* Return insns all "jump to the same place"
1879 so we can cross-jump between any two of them. */
1885 /* If cannot cross jump to code before the label,
1886 see if we can cross jump to another jump to
1887 the same label. */
1888 /* Try each other jump to this label. */
1899 {
1903 }
1904 }
1905 }
1906 }
1909 }
1911 /* Delete extraneous line number notes.
1912 Note that two consecutive notes for different lines are not really
1913 extraneous. There should be some indication where that line belonged,
1914 even if it became empty. */
1916 {
1921 {
1922 /* Delete this note if it is identical to previous note. */
1926 {
1929 }
1932 }
1933 }
1935 #ifdef HAVE_return
1937 {
1938 /* If we fall through to the epilogue, see if we can insert a RETURN insn
1939 in front of it. If the machine allows it at this point (we might be
1940 after reload for a leaf routine), it will improve optimization for it
1941 to be there. We do this both here and at the start of this pass since
1942 the RETURN might have been deleted by some of our optimizations. */
1948 {
1951 }
1952 }
1953 #endif
1955 /* See if there is still a NOTE_INSN_FUNCTION_END in this function.
1956 If so, delete it, and record that this function can drop off the end. */
1959 {
1962 /* One label can follow the end-note: the return label. */
1964 /* Ordinary insns can follow it if returning a structure. */
1966 /* If machine uses explicit RETURN insns, no epilogue,
1967 then one of them follows the note. */
1970 /* Other kinds of notes can follow also. */
1974 }
1976 /* Report if control can fall through at the end of the function. */
1979 {
1982 }
1984 /* Show JUMP_CHAIN no longer valid. */
1986 }
1987 \f
1988 /* LOOP_START is a NOTE_INSN_LOOP_BEG note that is followed by an unconditional
1989 jump. Assume that this unconditional jump is to the exit test code. If
1990 the code is sufficiently simple, make a copy of it before INSN,
1991 followed by a jump to the exit of the loop. Then delete the unconditional
1992 jump after INSN.
1994 Note that it is possible we can get confused here if the jump immediately
1995 after the loop start branches outside the loop but within an outer loop.
1996 If we are near the exit of that loop, we will copy its exit test. This
1997 will not generate incorrect code, but could suppress some optimizations.
1998 However, such cases are degenerate loops anyway.
2000 Return 1 if we made the change, else 0.
2002 This is only safe immediately after a regscan pass because it uses the
2003 values of regno_first_uid and regno_last_uid. */
2005 static int
2007 rtx loop_start;
2008 {
2013 rtx lastexit;
2017 /* Scan the exit code. We do not perform this optimization if any insn:
2019 is a CALL_INSN
2020 is a CODE_LABEL
2021 has a REG_RETVAL or REG_LIBCALL note (hard to adjust)
2022 is a NOTE_INSN_LOOP_BEG because this means we have a nested loop
2023 is a NOTE_INSN_BLOCK_{BEG,END} because duplicating these notes
2024 are not valid
2026 Also, don't do this if the exit code is more than 20 insns. */
2029 insn
2033 {
2035 {
2052 }
2053 }
2055 /* Unless INSN is zero, we can do the optimization. */
2061 /* See if any insn sets a register only used in the loop exit code and
2062 not a user variable. If so, replace it with a new register. */
2069 {
2075 {
2076 /* We can do the replacement. Allocate reg_map if this is the
2077 first replacement we found. */
2079 {
2082 }
2088 }
2089 }
2091 /* Now copy each insn. */
2094 {
2099 /* Only copy line-number notes. */
2101 {
2104 }
2114 /* Copy all REG_NOTES except REG_LABEL since mark_jump_label will
2115 make them. */
2131 {
2135 }
2137 /* If this is a simple jump, add it to the jump chain. */
2141 {
2145 }
2150 }
2152 /* Now clean up by emitting a jump to the end label and deleting the jump
2153 at the start of the loop. */
2155 {
2157 loop_start);
2161 {
2165 }
2167 }
2171 /* Mark the exit code as the virtual top of the converted loop. */
2175 }
2176 \f
2177 /* Move all block-beg, block-end, loop-beg, loop-cont, loop-vtop, and
2178 loop-end notes between START and END out before START. Assume that
2179 END is not such a note. START may be such a note. Returns the value
2180 of the new starting insn, which may be different if the original start
2181 was such a note. */
2183 rtx
2186 {
2187 rtx insn;
2188 rtx next;
2191 {
2200 {
2203 else
2204 {
2212 }
2213 }
2214 }
2217 }
2218 \f
2219 /* Compare the instructions before insn E1 with those before E2
2220 to find an opportunity for cross jumping.
2221 (This means detecting identical sequences of insns followed by
2222 jumps to the same place, or followed by a label and a jump
2223 to that label, and replacing one with a jump to the other.)
2225 Assume E1 is a jump that jumps to label E2
2226 (that is not always true but it might as well be).
2227 Find the longest possible equivalent sequences
2228 and store the first insns of those sequences into *F1 and *F2.
2229 Store zero there if no equivalent preceding instructions are found.
2231 We give up if we find a label in stream 1.
2232 Actually we could transfer that label into stream 2. */
2234 static void
2239 {
2246 rtx prev1;
2252 {
2262 /* Don't allow the range of insns preceding E1 or E2
2263 to include the other (E2 or E1). */
2267 /* If we will get to this code by jumping, those jumps will be
2268 tensioned to go directly to the new label (before I2),
2269 so this cross-jumping won't cost extra. So reduce the minimum. */
2271 {
2274 }
2282 /* If this is a CALL_INSN, compare register usage information.
2283 If we don't check this on stack register machines, the two
2284 CALL_INSNs might be merged leaving reg-stack.c with mismatching
2285 numbers of stack registers in the same basic block.
2286 If we don't check this on machines with delay slots, a delay slot may
2287 be filled that clobbers a parameter expected by the subroutine.
2289 ??? We take the simple route for now and assume that if they're
2290 equal, they were constructed identically. */
2297 #ifdef STACK_REGS
2298 /* If cross_jump_death_matters is not 0, the insn's mode
2299 indicates whether or not the insn contains any stack-like
2300 regs. */
2303 {
2304 /* If register stack conversion has already been done, then
2305 death notes must also be compared before it is certain that
2306 the two instruction streams match. */
2308 rtx note;
2328 done:
2329 ;
2330 }
2331 #endif
2335 {
2336 /* The following code helps take care of G++ cleanups. */
2337 rtx equiv1;
2338 rtx equiv2;
2345 /* If the equivalences are not to a constant, they may
2346 reference pseudos that no longer exist, so we can't
2347 use them. */
2350 {
2355 {
2362 }
2363 }
2365 /* Insns fail to match; cross jumping is limited to the following
2366 insns. */
2368 #ifdef HAVE_cc0
2369 /* Don't allow the insn after a compare to be shared by
2370 cross-jumping unless the compare is also shared.
2371 Here, if either of these non-matching insns is a compare,
2372 exclude the following insn from possible cross-jumping. */
2375 #endif
2377 /* If cross-jumping here will feed a jump-around-jump
2378 optimization, this jump won't cost extra, so reduce
2379 the minimum. */
2385 }
2387 win:
2389 {
2390 /* Ok, this insn is potentially includable in a cross-jump here. */
2393 }
2394 }
2398 }
2400 static void
2403 {
2404 /* Find an existing label at this point
2405 or make a new one if there is none. */
2408 /* Make the same jump insn jump to the new point. */
2410 {
2411 /* Remove from jump chain of returns. */
2413 /* Change the insn. */
2418 /* Add to new the jump chain. */
2421 {
2424 }
2425 }
2426 else
2429 /* Delete the matching insns before the jump. Also, remove any REG_EQUAL
2430 or REG_EQUIV note in the NEWLPOS stream that isn't also present in
2431 the NEWJPOS stream. */
2434 {
2435 rtx lnote;
2447 }
2448 }
2449 \f
2450 /* Return the label before INSN, or put a new label there. */
2452 rtx
2454 rtx insn;
2455 {
2456 rtx label;
2458 /* Find an existing label at this point
2459 or make a new one if there is none. */
2463 {
2469 }
2471 }
2473 /* Return the label after INSN, or put a new label there. */
2475 rtx
2477 rtx insn;
2478 {
2479 rtx label;
2481 /* Find an existing label at this point
2482 or make a new one if there is none. */
2486 {
2490 }
2492 }
2493 \f
2494 /* Return 1 if INSN is a jump that jumps to right after TARGET
2495 only on the condition that TARGET itself would drop through.
2496 Assumes that TARGET is a conditional jump. */
2498 static int
2501 {
2517 {
2521 }
2524 {
2528 }
2533 }
2534 \f
2535 /* Given a comparison, COMPARISON, inside a conditional jump insn, INSN,
2536 return non-zero if it is safe to reverse this comparison. It is if our
2537 floating-point is not IEEE, if this is an NE or EQ comparison, or if
2538 this is known to be an integer comparison. */
2540 int
2542 rtx comparison;
2543 rtx insn;
2544 {
2545 rtx arg0;
2547 /* If this is not actually a comparison, we can't reverse it. */
2552 /* If this is an NE comparison, it is safe to reverse it to an EQ
2553 comparison and vice versa, even for floating point. If no operands
2554 are NaNs, the reversal is valid. If some operand is a NaN, EQ is
2555 always false and NE is always true, so the reversal is also valid. */
2556 || flag_fast_math
2563 /* Make sure ARG0 is one of the actual objects being compared. If we
2564 can't do this, we can't be sure the comparison can be reversed.
2566 Handle cc0 and a MODE_CC register. */
2568 #ifdef HAVE_cc0
2570 #endif
2571 )
2572 {
2583 }
2585 /* We can reverse this if ARG0 is a CONST_INT or if its mode is
2586 not VOIDmode and neither a MODE_CC nor MODE_FLOAT type. */
2591 }
2593 /* Given an rtx-code for a comparison, return the code
2594 for the negated comparison.
2595 WATCH OUT! reverse_condition is not safe to use on a jump
2596 that might be acting on the results of an IEEE floating point comparison,
2597 because of the special treatment of non-signaling nans in comparisons.
2598 Use can_reverse_comparison_p to be sure. */
2600 enum rtx_code
2603 {
2605 {
2639 }
2640 }
2642 /* Similar, but return the code when two operands of a comparison are swapped.
2643 This IS safe for IEEE floating-point. */
2645 enum rtx_code
2648 {
2650 {
2682 }
2683 }
2685 /* Given a comparison CODE, return the corresponding unsigned comparison.
2686 If CODE is an equality comparison or already an unsigned comparison,
2687 CODE is returned. */
2689 enum rtx_code
2692 {
2694 {
2717 }
2718 }
2720 /* Similarly, return the signed version of a comparison. */
2722 enum rtx_code
2725 {
2727 {
2750 }
2751 }
2752 \f
2753 /* Return non-zero if CODE1 is more strict than CODE2, i.e., if the
2754 truth of CODE1 implies the truth of CODE2. */
2756 int
2759 {
2764 {
2789 }
2792 }
2793 \f
2794 /* Return 1 if INSN is an unconditional jump and nothing else. */
2796 int
2798 rtx insn;
2799 {
2804 }
2806 /* Return nonzero if INSN is a (possibly) conditional jump
2807 and nothing more. */
2809 int
2811 rtx insn;
2812 {
2831 }
2833 /* Return 1 if X is an RTX that does nothing but set the condition codes
2834 and CLOBBER or USE registers.
2835 Return -1 if X does explicitly set the condition codes,
2836 but also does other things. */
2838 int
2840 rtx x;
2841 {
2842 #ifdef HAVE_cc0
2846 {
2851 {
2857 }
2859 }
2861 #else
2863 #endif
2864 }
2865 \f
2866 /* Follow any unconditional jump at LABEL;
2867 return the ultimate label reached by any such chain of jumps.
2868 If LABEL is not followed by a jump, return LABEL.
2869 If the chain loops or we can't find end, return LABEL,
2870 since that tells caller to avoid changing the insn.
2872 If RELOAD_COMPLETED is 0, we do not chain across a NOTE_INSN_LOOP_BEG or
2873 a USE or CLOBBER. */
2875 rtx
2877 rtx label;
2878 {
2891 depth++)
2892 {
2893 /* Don't chain through the insn that jumps into a loop
2894 from outside the loop,
2895 since that would create multiple loop entry jumps
2896 and prevent loop optimization. */
2897 rtx tem;
2904 /* If we have found a cycle, make the insn jump to itself. */
2914 }
2918 }
2920 /* Assuming that field IDX of X is a vector of label_refs,
2921 replace each of them by the ultimate label reached by it.
2922 Return nonzero if a change is made.
2923 If IGNORE_LOOPS is 0, we do not chain across a NOTE_INSN_LOOP_BEG. */
2925 static int
2929 {
2933 {
2937 {
2943 }
2944 }
2946 }
2947 \f
2948 /* Find all CODE_LABELs referred to in X, and increment their use counts.
2949 If INSN is a JUMP_INSN and there is at least one CODE_LABEL referenced
2950 in INSN, then store one of them in JUMP_LABEL (INSN).
2951 If INSN is an INSN or a CALL_INSN and there is at least one CODE_LABEL
2952 referenced in INSN, add a REG_LABEL note containing that label to INSN.
2953 Also, when there are consecutive labels, canonicalize on the last of them.
2955 Note that two labels separated by a loop-beginning note
2956 must be kept distinct if we have not yet done loop-optimization,
2957 because the gap between them is where loop-optimize
2958 will want to move invariant code to. CROSS_JUMP tells us
2959 that loop-optimization is done with.
2961 Once reload has completed (CROSS_JUMP non-zero), we need not consider
2962 two labels distinct if they are separated by only USE or CLOBBER insns. */
2964 static void
2967 rtx insn;
2969 {
2975 {
2988 /* If this is a constant-pool reference, see if it is a label. */
2995 {
2998 rtx note;
2999 rtx next;
3004 /* Ignore references to labels of containing functions. */
3008 /* If there are other labels following this one,
3009 replace it with the last of the consecutive labels. */
3011 {
3024 }
3030 {
3034 /* If we've changed OLABEL and we had a REG_LABEL note
3035 for it, update it as well. */
3040 /* Otherwise, add a REG_LABEL note for LABEL unless there already
3041 is one. */
3043 {
3045 /* Don't record labels that refer to dispatch tables.
3046 This is not necessary, since the tablejump
3047 references the same label.
3048 And if we did record them, flow.c would make worse code. */
3055 }
3056 }
3058 }
3060 /* Do walk the labels in a vector, but not the first operand of an
3061 ADDR_DIFF_VEC. Don't set the JUMP_LABEL of a vector. */
3064 {
3070 }
3071 }
3075 {
3079 {
3083 }
3084 }
3085 }
3087 /* If all INSN does is set the pc, delete it,
3088 and delete the insn that set the condition codes for it
3089 if that's what the previous thing was. */
3091 void
3093 rtx insn;
3094 {
3099 }
3101 /* Delete INSN and recursively delete insns that compute values used only
3102 by INSN. This uses the REG_DEAD notes computed during flow analysis.
3103 If we are running before flow.c, we need do nothing since flow.c will
3104 delete dead code. We also can't know if the registers being used are
3105 dead or not at this point.
3107 Otherwise, look at all our REG_DEAD notes. If a previous insn does
3108 nothing other than set a register that dies in this insn, we can delete
3109 that insn as well.
3111 On machines with CC0, if CC0 is used in this insn, we may be able to
3112 delete the insn that set it. */
3114 static void
3116 rtx insn;
3117 {
3120 #ifdef HAVE_cc0
3122 {
3124 /* We assume that at this stage
3125 CC's are always set explicitly
3126 and always immediately before the jump that
3127 will use them. So if the previous insn
3128 exists to set the CC's, delete it
3129 (unless it performs auto-increments, etc.). */
3132 {
3136 else
3137 /* Otherwise, show that cc0 won't be used. */
3140 }
3141 }
3142 #endif
3145 {
3146 rtx our_prev;
3151 /* Verify that the REG_NOTE is legitimate. */
3158 {
3159 /* If we reach a SEQUENCE, it is too complex to try to
3160 do anything with it, so give up. */
3166 /* reorg creates USEs that look like this. We leave them
3167 alone because reorg needs them for its own purposes. */
3171 {
3176 {
3177 /* If we find a SET of something else, we can't
3178 delete the insn. */
3183 {
3189 }
3193 }
3199 }
3201 /* If OUR_PREV references the register that dies here, it is an
3202 additional use. Hence any prior SET isn't dead. However, this
3203 insn becomes the new place for the REG_DEAD note. */
3206 {
3210 }
3211 }
3212 }
3215 }
3216 \f
3217 /* Delete insn INSN from the chain of insns and update label ref counts.
3218 May delete some following insns as a consequence; may even delete
3219 a label elsewhere and insns that follow it.
3221 Returns the first insn after INSN that was not deleted. */
3223 rtx
3226 {
3235 /* This insn is already deleted => return first following nondeleted. */
3239 /* Don't delete user-declared labels. Convert them to special NOTEs
3240 instead. */
3243 {
3248 }
3249 else
3250 /* Mark this insn as deleted. */
3253 /* If this is an unconditional jump, delete it from the jump chain. */
3257 /* If instruction is followed by a barrier,
3258 delete the barrier too. */
3261 {
3264 }
3266 /* Patch out INSN (and the barrier if any) */
3269 {
3271 {
3276 }
3279 {
3283 }
3287 }
3289 /* If deleting a jump, decrement the count of the label,
3290 and delete the label if it is now unused. */
3294 {
3295 /* This can delete NEXT or PREV,
3296 either directly if NEXT is JUMP_LABEL (INSN),
3297 or indirectly through more levels of jumps. */
3299 /* I feel a little doubtful about this loop,
3300 but I see no clean and sure alternative way
3301 to find the first insn after INSN that is not now deleted.
3302 I hope this works. */
3306 }
3311 /* If INSN was a label and a dispatch table follows it,
3312 delete the dispatch table. The tablejump must have gone already.
3313 It isn't useful to fall through into a table. */
3322 /* If INSN was a label, delete insns following it if now unreachable. */
3325 {
3331 {
3335 /* Keep going past other deleted labels to delete what follows. */
3338 else
3339 /* Note: if this deletes a jump, it can cause more
3340 deletion of unreachable code, after a different label.
3341 As long as the value from this recursive call is correct,
3342 this invocation functions correctly. */
3344 }
3345 }
3348 }
3350 /* Advance from INSN till reaching something not deleted
3351 then return that. May return INSN itself. */
3353 rtx
3355 rtx insn;
3356 {
3360 }
3361 \f
3362 /* Delete a range of insns from FROM to TO, inclusive.
3363 This is for the sake of peephole optimization, so assume
3364 that whatever these insns do will still be done by a new
3365 peephole insn that will replace them. */
3367 void
3370 {
3374 {
3379 {
3382 /* Patch this insn out of the chain. */
3383 /* We don't do this all at once, because we
3384 must preserve all NOTEs. */
3390 }
3395 }
3397 /* Note that if TO is an unconditional jump
3398 we *do not* delete the BARRIER that follows,
3399 since the peephole that replaces this sequence
3400 is also an unconditional jump in that case. */
3401 }
3402 \f
3403 /* Invert the condition of the jump JUMP, and make it jump
3404 to label NLABEL instead of where it jumps now. */
3406 int
3409 {
3410 /* We have to either invert the condition and change the label or
3411 do neither. Either operation could fail. We first try to invert
3412 the jump. If that succeeds, we try changing the label. If that fails,
3413 we invert the jump back to what it was. */
3422 /* This should just be putting it back the way it was. */
3426 }
3428 /* Invert the jump condition of rtx X contained in jump insn, INSN.
3430 Return 1 if we can do so, 0 if we cannot find a way to do so that
3431 matches a pattern. */
3433 int
3435 rtx x;
3436 rtx insn;
3437 {
3445 {
3449 /* We can do this in two ways: The preferable way, which can only
3450 be done if this is not an integer comparison, is to reverse
3451 the comparison code. Otherwise, swap the THEN-part and ELSE-part
3452 of the IF_THEN_ELSE. If we can't do either, fail. */
3465 }
3469 {
3474 {
3479 }
3480 }
3483 }
3484 \f
3485 /* Make jump JUMP jump to label NLABEL instead of where it jumps now.
3486 If the old jump target label is unused as a result,
3487 it and the code following it may be deleted.
3489 If NLABEL is zero, we are to turn the jump into a (possibly conditional)
3490 RETURN insn.
3492 The return value will be 1 if the change was made, 0 if it wasn't (this
3493 can only occur for NLABEL == 0). */
3495 int
3498 {
3507 /* If this is an unconditional branch, delete it from the jump_chain of
3508 OLABEL and add it to the jump_chain of NLABEL (assuming both labels
3509 have UID's in range and JUMP_CHAIN is valid). */
3512 {
3518 {
3521 }
3522 }
3532 }
3534 /* Delete the instruction JUMP from any jump chain it might be on. */
3536 static void
3538 rtx jump;
3539 {
3543 /* Handle unconditional jumps. */
3548 /* Handle return insns. */
3555 else
3556 {
3557 rtx insn;
3563 {
3566 }
3567 }
3568 }
3570 /* If NLABEL is nonzero, throughout the rtx at LOC,
3571 alter (LABEL_REF OLABEL) to (LABEL_REF NLABEL). If OLABEL is
3572 zero, alter (RETURN) to (LABEL_REF NLABEL).
3574 If NLABEL is zero, alter (LABEL_REF OLABEL) to (RETURN) and check
3575 validity with validate_change. Convert (set (pc) (label_ref olabel))
3576 to (return).
3578 Return 0 if we found a change we would like to make but it is invalid.
3579 Otherwise, return 1. */
3581 int
3585 rtx insn;
3586 {
3593 {
3595 {
3598 else
3601 }
3602 }
3604 {
3609 }
3618 {
3623 {
3628 }
3629 }
3632 }
3633 \f
3634 /* Make jump JUMP jump to label NLABEL, assuming it used to be a tablejump.
3636 If the old jump target label (before the dispatch table) becomes unused,
3637 it and the dispatch table may be deleted. In that case, find the insn
3638 before the jump references that label and delete it and logical successors
3639 too. */
3641 static void
3644 {
3647 /* Add this jump to the jump_chain of NLABEL. */
3650 {
3653 }
3661 {
3664 }
3665 }
3667 /* Find the insn referencing LABEL that is a logical predecessor of INSN.
3668 If we found one, delete it and then delete this insn if DELETE_THIS is
3669 non-zero. Return non-zero if INSN or a predecessor references LABEL. */
3671 static int
3675 {
3677 rtx link;
3681 {
3683 {
3686 }
3687 else
3689 }
3693 {
3695 {
3698 }
3699 else
3701 }
3704 }
3705 \f
3706 /* Like rtx_equal_p except that it considers two REGs as equal
3707 if they renumber to the same value and considers two commutative
3708 operations to be the same if the order of the operands has been
3709 reversed. */
3711 int
3714 {
3725 {
3732 /* If we haven't done any renumbering, don't
3733 make any assumptions. */
3738 {
3743 {
3746 }
3747 }
3749 else
3750 {
3754 }
3757 {
3762 {
3765 }
3766 }
3768 else
3769 {
3773 }
3776 }
3778 /* Now we have disposed of all the cases
3779 in which different rtx codes can match. */
3784 {
3795 /* We can't assume nonlocal labels have their following insns yet. */
3799 /* Two label-refs are equivalent if they point at labels
3800 in the same position in the instruction stream. */
3806 }
3808 /* (MULT:SI x y) and (MULT:HI x y) are NOT equivalent. */
3813 /* For commutative operations, the RTX match if the operand match in any
3814 order. Also handle the simple binary and unary cases without a loop. */
3826 /* Compare the elements. If any pair of corresponding elements
3827 fail to match, return 0 for the whole things. */
3831 {
3834 {
3858 /* fall through. */
3872 }
3873 }
3875 }
3876 \f
3877 /* If X is a hard register or equivalent to one or a subregister of one,
3878 return the hard register number. If X is a pseudo register that was not
3879 assigned a hard register, return the pseudo register number. Otherwise,
3880 return -1. Any rtx is valid for X. */
3882 int
3884 rtx x;
3885 {
3887 {
3891 }
3893 {
3897 }
3899 }
3900 \f
3901 /* Optimize code of the form:
3903 for (x = a[i]; x; ...)
3904 ...
3905 for (x = a[i]; x; ...)
3906 ...
3907 foo:
3909 Loop optimize will change the above code into
3911 if (x = a[i])
3912 for (;;)
3913 { ...; if (! (x = ...)) break; }
3914 if (x = a[i])
3915 for (;;)
3916 { ...; if (! (x = ...)) break; }
3917 foo:
3919 In general, if the first test fails, the program can branch
3920 directly to `foo' and skip the second try which is doomed to fail.
3921 We run this after loop optimization and before flow analysis. */
3923 /* When comparing the insn patterns, we track the fact that different
3924 pseudo-register numbers may have been used in each computation.
3925 The following array stores an equivalence -- same_regs[I] == J means
3926 that pseudo register I was used in the first set of tests in a context
3927 where J was used in the second set. We also count the number of such
3928 pending equivalences. If nonzero, the expressions really aren't the
3929 same. */
3935 /* Track any registers modified between the target of the first jump and
3936 the second jump. They never compare equal. */
3940 /* Record if memory was modified. */
3944 /* Called via note_stores on each insn between the target of the first
3945 branch and the second branch. It marks any changed registers. */
3947 static void
3949 rtx dest;
3950 rtx x;
3951 {
3966 else
3969 }
3971 /* F is the first insn in the chain of insns. */
3973 void
3975 rtx f;
3978 {
3979 /* Basic algorithm is to find a conditional branch,
3980 the label it may branch to, and the branch after
3981 that label. If the two branches test the same condition,
3982 walk back from both branch paths until the insn patterns
3983 differ, or code labels are hit. If we make it back to
3984 the target of the first branch, then we know that the first branch
3985 will either always succeed or always fail depending on the relative
3986 senses of the two branches. So adjust the first branch accordingly
3987 in this case. */
3996 /* Allocate register tables and quick-reset table. */
4004 {
4008 {
4009 /* Get to a candidate branch insn. */
4023 /* Look for a branch after the target. Record any registers and
4024 memory modified between the target and the branch. Stop when we
4025 get to a label since we can't know what was changed there. */
4027 {
4032 {
4033 /* If this is an unconditional jump and is the only use of
4034 its target label, we can follow it. */
4038 {
4041 }
4042 else
4044 }
4050 {
4059 }
4062 }
4064 /* Check the next candidate branch insn from the label
4065 of the first. */
4073 /* Get the comparison codes and operands, reversing the
4074 codes if appropriate. If we don't have comparison codes,
4075 we can't do anything. */
4088 /* If they test the same things and knowing that B1 branches
4089 tells us whether or not B2 branches, check if we
4090 can thread the branch. */
4095 {
4100 {
4102 {
4103 /* We have reached the target of the first branch.
4104 If there are no pending register equivalents,
4105 we know that this branch will either always
4106 succeed (if the senses of the two branches are
4107 the same) or always fail (if not). */
4108 rtx new_label;
4115 else
4119 {
4124 {
4125 /* Don't thread to the loop label. If a loop
4126 label is reused, loop optimization will
4127 be disabled for that loop. */
4130 }
4132 }
4134 }
4136 /* If either of these is not a normal insn (it might be
4137 a JUMP_INSN, CALL_INSN, or CODE_LABEL) we fail. (NOTEs
4138 have already been skipped above.) Similarly, fail
4139 if the insns are different. */
4148 }
4149 }
4150 }
4151 }
4152 }
4153 \f
4154 /* This is like RTX_EQUAL_P except that it knows about our handling of
4155 possibly equivalent registers and knows to consider volatile and
4156 modified objects as not equal.
4158 YINSN is the insn containing Y. */
4160 int
4163 rtx yinsn;
4164 {
4171 /* Rtx's of different codes cannot be equal. */
4175 /* (MULT:SI x y) and (MULT:HI x y) are NOT equivalent.
4176 (REG:SI x) and (REG:HI x) are NOT equivalent. */
4181 /* For commutative operations, the RTX match if the operand match in any
4182 order. Also handle the simple binary and unary cases without a loop. */
4194 /* Handle special-cases first. */
4196 {
4201 /* If neither is user variable or hard register, check for possible
4202 equivalence. */
4209 {
4211 num_same_regs++;
4213 /* If this is the first time we are seeing a register on the `Y'
4214 side, see if it is the last use. If not, we can't thread the
4215 jump, so mark it as not equivalent. */
4220 }
4221 else
4227 /* If memory modified or either volatile, not equivalent.
4228 Else, check address. */
4241 /* Cancel a pending `same_regs' if setting equivalenced registers.
4242 Then process source. */
4245 {
4247 {
4249 num_same_regs--;
4250 }
4253 }
4254 else
4265 }
4272 {
4274 {
4288 /* Two vectors must have the same length. */
4292 /* And the corresponding elements must match. */
4311 /* These are just backpointers, so they don't matter. */
4317 /* It is believed that rtx's at this level will never
4318 contain anything but integers and other rtx's,
4319 except for within LABEL_REFs and SYMBOL_REFs. */
4322 }
4323 }
4325 }