| blob | 076f6950b11c98c10f6fd81c33ad1fa9bdbe85ac |
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. */
556 }
558 /* Now iterate optimizing jumps until nothing changes over one pass. */
561 {
565 {
566 rtx reallabelprev;
568 rtx nlabel;
571 #if 0
572 /* If NOT the first iteration, if this is the last jump pass
573 (just before final), do the special peephole optimizations.
574 Avoiding the first iteration gives ordinary jump opts
575 a chance to work before peephole opts. */
580 #endif
582 /* That could have deleted some insns after INSN, so check now
583 what the following insn is. */
587 /* See if this is a NOTE_INSN_LOOP_BEG followed by an unconditional
588 jump. Try to optimize by duplicating the loop exit test if so.
589 This is only safe immediately after regscan, because it uses
590 the values of regno_first_uid and regno_last_uid. */
595 {
598 {
602 }
603 }
612 /* Tension the labels in dispatch tables. */
619 /* If a dispatch table always goes to the same place,
620 get rid of it and replace the insn that uses it. */
624 {
639 /* Don't mess with a casesi insn. */
644 {
648 }
649 }
653 /* If a jump references the end of the function, try to turn
654 it into a RETURN insn, possibly a conditional one. */
661 /* Detect jump to following insn. */
663 {
667 }
669 /* If we have an unconditional jump preceded by a USE, try to put
670 the USE before the target and jump there. This simplifies many
671 of the optimizations below since we don't have to worry about
672 dealing with these USE insns. We only do this if the label
673 being branch to already has the identical USE or if code
674 never falls through to that label. */
683 {
685 {
688 }
694 }
696 /* Simplify if (...) x = a; else x = b; by converting it
697 to x = b; if (...) x = a;
698 if B is sufficiently simple, the test doesn't involve X,
699 and nothing in the test modifies B or X.
701 If we have small register classes, we also can't do this if X
702 is a hard register.
704 If the "x = b;" insn has any REG_NOTES, we don't do this because
705 of the possibility that we are running after CSE and there is a
706 REG_EQUAL note that is only valid if the branch has already been
707 taken. If we move the insn with the REG_EQUAL note, we may
708 fold the comparison to always be false in a later CSE pass.
709 (We could also delete the REG_NOTES when moving the insn, but it
710 seems simpler to not move it.) An exception is that we can move
711 the insn if the only note is a REG_EQUAL or REG_EQUIV whose
712 value is the same as "b".
714 INSN is the branch over the `else' part.
716 We set:
718 TEMP to the jump insn preceding "x = a;"
719 TEMP1 to X
720 TEMP2 to the insn that sets "x = b;"
721 TEMP3 to the insn that sets "x = a;"
722 TEMP4 to the set of "x = b"; */
729 #ifdef SMALL_REGISTER_CLASSES
731 #endif
747 /* TEMP must skip over the "x = a;" insn */
750 /* There must be no other entries to the "x = b;" insn. */
752 /* INSN must either branch to the insn after TEMP2 or the insn
753 after TEMP2 must branch to the same place as INSN. */
758 {
759 /* The test expression, X, may be a complicated test with
760 multiple branches. See if we can find all the uses of
761 the label that TEMP branches to without hitting a CALL_INSN
762 or a jump to somewhere else. */
767 /* Set P to the first jump insn that goes around "x = a;". */
769 {
771 {
774 {
775 nuses--;
778 }
779 else
781 }
784 }
786 #ifdef HAVE_cc0
787 /* We cannot insert anything between a set of cc and its use
788 so if P uses cc0, we must back up to the previous insn. */
793 #endif
798 /* If we found all the uses and there was no data conflict, we
799 can move the assignment unless we can branch into the middle
800 from somewhere. */
807 {
811 /* Set NEXT to an insn that we know won't go away. */
814 /* Delete the jump around the set. Note that we must do
815 this before we redirect the test jumps so that it won't
816 delete the code immediately following the assignment
817 we moved (which might be a jump). */
821 /* We either have two consecutive labels or a jump to
822 a jump, so adjust all the JUMP_INSNs to branch to where
823 INSN branches to. */
830 }
831 }
833 #ifndef HAVE_cc0
834 /* If we have if (...) x = exp; and branches are expensive,
835 EXP is a single insn, does not have any side effects, cannot
836 trap, and is not too costly, convert this to
837 t = exp; if (...) x = t;
839 Don't do this when we have CC0 because it is unlikely to help
840 and we'd need to worry about where to place the new insn and
841 the potential for conflicts. We also can't do this when we have
842 notes on the insn for the same reason as above.
844 We set:
846 TEMP to the "x = exp;" insn.
847 TEMP1 to the single set in the "x = exp; insn.
848 TEMP2 to "x". */
863 #ifdef SMALL_REGISTER_CLASSES
865 #endif
872 {
876 {
882 }
883 }
885 /* Similarly, if it takes two insns to compute EXP but they
886 have the same destination. Here TEMP3 will be the second
887 insn and TEMP4 the SET from that insn. */
905 #ifdef SMALL_REGISTER_CLASSES
907 #endif
916 {
920 {
924 emit_insn_after_with_line_notes
930 }
931 }
933 /* Finally, handle the case where two insns are used to
934 compute EXP but a temporary register is used. Here we must
935 ensure that the temporary register is not used anywhere else. */
938 && after_regscan
966 #ifdef SMALL_REGISTER_CLASSES
968 #endif
973 {
977 {
986 }
987 }
990 /* We deal with four cases:
992 1) x = a; if (...) x = b; and either A or B is zero,
993 2) if (...) x = 0; and jumps are expensive,
994 3) x = a; if (...) x = b; and A and B are constants where all the
995 set bits in A are also set in B and jumps are expensive, and
996 4) x = a; if (...) x = b; and A and B non-zero, and jumps are
997 more expensive.
998 5) if (...) x = b; if jumps are even more expensive.
1000 In each of these try to use a store-flag insn to avoid the jump.
1001 (If the jump would be faster, the machine should not have
1002 defined the scc insns!). These cases are often made by the
1003 previous optimization.
1005 INSN here is the jump around the store. We set:
1007 TEMP to the "x = b;" insn.
1008 TEMP1 to X.
1009 TEMP2 to B (const0_rtx in the second case).
1010 TEMP3 to A (X in the second case).
1011 TEMP4 to the condition being tested.
1012 TEMP5 to the earliest insn used to find the condition. */
1015 ! reload_completed
1017 /* Set TEMP to the "x = b;" insn. */
1022 #ifdef SMALL_REGISTER_CLASSES
1024 #endif
1029 /* Allow either form, but prefer the former if both apply.
1030 There is no point in using the old value of TEMP1 if
1031 it is a register, since cse will alias them. It can
1032 lose if the old value were a hard register since CSE
1033 won't replace hard registers. */
1036 /* Make the latter case look like x = x; if (...) x = 0; */
1040 #ifdef HAVE_conditional_move
1041 || HAVE_conditional_move
1042 #endif
1044 /* INSN must either branch to the insn after TEMP or the insn
1045 after TEMP must branch to the same place as INSN. */
1051 /* We must be comparing objects whose modes imply the size.
1052 We could handle BLKmode if (1) emit_store_flag could
1053 and (2) we could find the size reliably. */
1056 /* If B is zero, OK; if A is zero, can only do (1) if we
1057 can reverse the condition. See if (3) applies possibly
1058 by reversing the condition. Prefer reversing to (4) when
1059 branches are very expensive. */
1069 insn)))))
1070 #ifdef HAVE_conditional_move
1071 || HAVE_conditional_move
1072 #endif
1074 #ifdef HAVE_cc0
1075 /* If the previous insn sets CC0 and something else, we can't
1076 do this since we are going to delete that insn. */
1083 #endif
1084 )
1085 {
1089 rtx target;
1091 /* If necessary, reverse the condition. */
1094 else
1097 /* See if we can do this with a store-flag insn. */
1100 /* If CVAL is non-zero, normalize to -1. Otherwise,
1101 if UVAL is the constant 1, it is best to just compute
1102 the result directly. If UVAL is constant and STORE_FLAG_VALUE
1103 includes all of its bits, it is best to compute the flag
1104 value unnormalized and `and' it with UVAL. Otherwise,
1105 normalize to -1 and `and' with UVAL. */
1112 /* We will be putting the store-flag insn immediately in
1113 front of the comparison that was originally being done,
1114 so we know all the variables in TEMP4 will be valid.
1115 However, this might be in front of the assignment of
1116 A to VAR. If it is, it would clobber the store-flag
1117 we will be emitting.
1119 Therefore, emit into a temporary which will be copied to
1120 VAR immediately after TEMP. */
1124 VOIDmode,
1127 normalizep);
1129 {
1131 rtx seq;
1133 /* Put the store-flag insns in front of the first insn
1134 used to compute the condition to ensure that we
1135 use the same values of them as the current
1136 comparison. However, the remainder of the insns we
1137 generate will be placed directly in front of the
1138 jump insn, in case any of the pseudos we use
1139 are modified earlier. */
1148 /* Both CVAL and UVAL are non-zero. */
1150 {
1158 else
1159 {
1165 }
1167 /* If we usually make new pseudos, do so here. This
1168 turns out to help machines that have conditional
1169 move insns. */
1177 }
1179 {
1180 /* We know that either CVAL or UVAL is zero. If
1181 UVAL is zero, negate TARGET and `and' with CVAL.
1182 Otherwise, `and' with UVAL. */
1184 {
1188 }
1194 }
1200 #ifdef HAVE_cc0
1201 /* If INSN uses CC0, we must not separate it from the
1202 insn that sets cc0. */
1206 #endif
1216 }
1217 else
1219 }
1221 /* If branches are expensive, convert
1222 if (foo) bar++; to bar += (foo != 0);
1223 and similarly for "bar--;"
1225 INSN is the conditional branch around the arithmetic. We set:
1227 TEMP is the arithmetic insn.
1228 TEMP1 is the SET doing the arithmetic.
1229 TEMP2 is the operand being incremented or decremented.
1230 TEMP3 to the condition being tested.
1231 TEMP4 to the earliest insn used to find the condition. */
1234 #ifdef HAVE_incscc
1235 || HAVE_incscc
1236 #endif
1237 #ifdef HAVE_decscc
1238 || HAVE_decscc
1239 #endif
1240 )
1241 && ! reload_completed
1251 /* INSN must either branch to the insn after TEMP or the insn
1252 after TEMP must branch to the same place as INSN. */
1258 /* We must be comparing objects whose modes imply the size.
1259 We could handle BLKmode if (1) emit_store_flag could
1260 and (2) we could find the size reliably. */
1263 {
1269 /* It must be the case that TEMP2 is not modified in the range
1270 [TEMP4, INSN). The one exception we make is if the insn
1271 before INSN sets TEMP2 to something which is also unchanged
1272 in that range. In that case, we can move the initialization
1273 into our sequence. */
1282 {
1286 }
1292 VOIDmode,
1296 /* If we can do the store-flag, do the addition or
1297 subtraction. */
1306 {
1307 /* Put the result back in temp2 in case it isn't already.
1308 Then replace the jump, possible a CC0-setting insn in
1309 front of the jump, and TEMP, with the sequence we have
1310 made. */
1325 #ifdef HAVE_cc0
1327 #endif
1331 }
1332 else
1334 }
1336 /* Simplify if (...) x = 1; else {...} if (x) ...
1337 We recognize this case scanning backwards as well.
1339 TEMP is the assignment to x;
1340 TEMP1 is the label at the head of the second if. */
1341 /* ?? This should call get_condition to find the values being
1342 compared, instead of looking for a COMPARE insn when HAVE_cc0
1343 is not defined. This would allow it to work on the m88k. */
1344 /* ?? This optimization is only safe before cse is run if HAVE_cc0
1345 is not defined and the condition is tested by a separate compare
1346 insn. This is because the code below assumes that the result
1347 of the compare dies in the following branch.
1349 Not only that, but there might be other insns between the
1350 compare and branch whose results are live. Those insns need
1351 to be executed.
1353 A way to fix this is to move the insns at JUMP_LABEL (insn)
1354 to before INSN. If we are running before flow, they will
1355 be deleted if they aren't needed. But this doesn't work
1356 well after flow.
1358 This is really a special-case of jump threading, anyway. The
1359 right thing to do is to replace this and jump threading with
1360 much simpler code in cse.
1362 This code has been turned off in the non-cc0 case in the
1363 meantime. */
1365 #ifdef HAVE_cc0
1367 /* Safe to skip USE and CLOBBER insns here
1368 since they will not be deleted. */
1376 /* If we find that the next value tested is `x'
1377 (TEMP1 is the insn where this happens), win. */
1380 #ifdef HAVE_cc0
1381 /* Does temp1 `tst' the value of x? */
1385 #else
1386 /* Does temp1 compare the value of x against zero? */
1393 #endif
1395 {
1396 /* Get the if_then_else from the condjump. */
1399 {
1402 rtx cond
1405 rtx ultimate;
1411 else
1421 }
1422 }
1423 #endif
1425 #if 0
1426 /* @@ This needs a bit of work before it will be right.
1428 Any type of comparison can be accepted for the first and
1429 second compare. When rewriting the first jump, we must
1430 compute the what conditions can reach label3, and use the
1431 appropriate code. We can not simply reverse/swap the code
1432 of the first jump. In some cases, the second jump must be
1433 rewritten also.
1435 For example,
1436 < == converts to > ==
1437 < != converts to == >
1438 etc.
1440 If the code is written to only accept an '==' test for the second
1441 compare, then all that needs to be done is to swap the condition
1442 of the first branch.
1444 It is questionable whether we want this optimization anyways,
1445 since if the user wrote code like this because he/she knew that
1446 the jump to label1 is taken most of the time, then rewriting
1447 this gives slower code. */
1448 /* @@ This should call get_condition to find the values being
1449 compared, instead of looking for a COMPARE insn when HAVE_cc0
1450 is not defined. This would allow it to work on the m88k. */
1451 /* @@ This optimization is only safe before cse is run if HAVE_cc0
1452 is not defined and the condition is tested by a separate compare
1453 insn. This is because the code below assumes that the result
1454 of the compare dies in the following branch. */
1456 /* Simplify test a ~= b
1457 condjump label1;
1458 test a == b
1459 condjump label2;
1460 jump label3;
1461 label1:
1463 rewriting as
1464 test a ~~= b
1465 condjump label3
1466 test a == b
1467 condjump label2
1468 label1:
1470 where ~= is an inequality, e.g. >, and ~~= is the swapped
1471 inequality, e.g. <.
1473 We recognize this case scanning backwards.
1475 TEMP is the conditional jump to `label2';
1476 TEMP1 is the test for `a == b';
1477 TEMP2 is the conditional jump to `label1';
1478 TEMP3 is the test for `a ~= b'. */
1487 #ifdef HAVE_cc0
1489 #else
1493 #endif
1507 {
1512 {
1515 }
1519 }
1520 #endif
1521 /* Simplify if (...) {... x = 1;} if (x) ...
1523 We recognize this case backwards.
1525 TEMP is the test of `x';
1526 TEMP1 is the assignment to `x' at the end of the
1527 previous statement. */
1528 /* @@ This should call get_condition to find the values being
1529 compared, instead of looking for a COMPARE insn when HAVE_cc0
1530 is not defined. This would allow it to work on the m88k. */
1531 /* @@ This optimization is only safe before cse is run if HAVE_cc0
1532 is not defined and the condition is tested by a separate compare
1533 insn. This is because the code below assumes that the result
1534 of the compare dies in the following branch. */
1536 /* ??? This has to be turned off. The problem is that the
1537 unconditional jump might indirectly end up branching to the
1538 label between TEMP1 and TEMP. We can't detect this, in general,
1539 since it may become a jump to there after further optimizations.
1540 If that jump is done, it will be deleted, so we will retry
1541 this optimization in the next pass, thus an infinite loop.
1543 The present code prevents this by putting the jump after the
1544 label, but this is not logically correct. */
1545 #if 0
1547 /* Safe to skip USE and CLOBBER insns here
1548 since they will not be deleted. */
1553 #ifdef HAVE_cc0
1556 #else
1557 /* Temp must be a compare insn, we can not accept a register
1558 to register move here, since it may not be simply a
1559 tst insn. */
1565 #endif
1566 /* May skip USE or CLOBBER insns here
1567 for checking for opportunity, since we
1568 take care of them later. */
1572 #ifdef HAVE_cc0
1574 #else
1577 #endif
1579 /* If this isn't true, cse will do the job. */
1581 {
1582 /* Get the if_then_else from the condjump. */
1587 {
1589 rtx last_insn;
1590 rtx ultimate;
1591 rtx p;
1593 /* Get the place that condjump will jump to
1594 if it is reached from here. */
1598 else
1600 /* Get it as a CODE_LABEL. */
1603 else
1604 /* Get the label out of the LABEL_REF. */
1607 /* Insert the jump immediately before TEMP, specifically
1608 after the label that is between TEMP1 and TEMP. */
1611 /* If we would be branching to the next insn, the jump
1612 would immediately be deleted and the re-inserted in
1613 a subsequent pass over the code. So don't do anything
1614 in that case. */
1617 {
1620 last_insn);
1625 {
1629 }
1632 }
1633 }
1634 }
1635 #endif
1636 /* Detect a conditional jump going to the same place
1637 as an immediately following unconditional jump. */
1643 {
1647 }
1648 /* Detect a conditional jump jumping over an unconditional jump. */
1651 && ! this_is_simplejump
1657 {
1658 /* When we invert the unconditional jump, we will be
1659 decrementing the usage count of its old label.
1660 Make sure that we don't delete it now because that
1661 might cause the following code to be deleted. */
1669 {
1670 /* It is very likely that if there are USE insns before
1671 this jump, they hold REG_DEAD notes. These REG_DEAD
1672 notes are no longer valid due to this optimization,
1673 and will cause the life-analysis that following passes
1674 (notably delayed-branch scheduling) to think that
1675 these registers are dead when they are not.
1677 To prevent this trouble, we just remove the USE insns
1678 from the insn chain. */
1682 {
1686 }
1691 }
1693 /* We can now safely delete the label if it is unreferenced
1694 since the delete_insn above has deleted the BARRIER. */
1698 }
1699 else
1700 {
1701 /* Detect a jump to a jump. */
1706 {
1709 }
1711 /* Look for if (foo) bar; else break; */
1712 /* The insns look like this:
1713 insn = condjump label1;
1714 ...range1 (some insns)...
1715 jump label2;
1716 label1:
1717 ...range2 (some insns)...
1718 jump somewhere unconditionally
1719 label2: */
1720 {
1723 /* Don't do this optimization on the first round, so that
1724 jump-around-a-jump gets simplified before we ask here
1725 whether a jump is unconditional.
1727 Also don't do it when we are called after reload since
1728 it will confuse reorg. */
1731 /* Make sure INSN is something we can invert. */
1738 {
1745 /* Invert the jump condition, so we
1746 still execute the same insns in each case. */
1748 {
1754 /* Include in each range any notes before it, to be
1755 sure that we get the line number note if any, even
1756 if there are other notes here. */
1765 /* Don't move NOTEs for blocks or loops; shift them
1766 outside the ranges, where they'll stay put. */
1770 /* Get current surrounds of the 2 ranges. */
1776 /* Splice range2 where range1 was. */
1781 /* Splice range1 where range2 was. */
1788 }
1789 }
1790 }
1792 /* Now that the jump has been tensioned,
1793 try cross jumping: check for identical code
1794 before the jump and before its target label. */
1796 /* First, cross jumping of conditional jumps: */
1799 {
1803 /* A conditional jump may be crossjumped
1804 only if the place it jumps to follows
1805 an opposing jump that comes back here. */
1808 /* We have no opposing jump;
1809 cannot cross jump this insn. */
1813 /* TARGET is nonzero if it is ok to cross jump
1814 to code before TARGET. If so, see if matches. */
1820 {
1822 /* Make the old conditional jump
1823 into an unconditional one. */
1828 /* Add to jump_chain unless this is a new label
1829 whose UID is too large. */
1831 {
1835 }
1838 }
1839 }
1841 /* Cross jumping of unconditional jumps:
1842 a few differences. */
1845 {
1847 rtx target;
1851 /* TARGET is nonzero if it is ok to cross jump
1852 to code before TARGET. If so, see if matches. */
1856 /* If cannot cross jump to code before the label,
1857 see if we can cross jump to another jump to
1858 the same label. */
1859 /* Try each other jump to this label. */
1866 /* Ignore TARGET if it's deleted. */
1872 {
1876 }
1877 }
1879 /* This code was dead in the previous jump.c! */
1881 {
1882 /* Return insns all "jump to the same place"
1883 so we can cross-jump between any two of them. */
1889 /* If cannot cross jump to code before the label,
1890 see if we can cross jump to another jump to
1891 the same label. */
1892 /* Try each other jump to this label. */
1903 {
1907 }
1908 }
1909 }
1910 }
1913 }
1915 /* Delete extraneous line number notes.
1916 Note that two consecutive notes for different lines are not really
1917 extraneous. There should be some indication where that line belonged,
1918 even if it became empty. */
1920 {
1925 {
1926 /* Delete this note if it is identical to previous note. */
1930 {
1933 }
1936 }
1937 }
1939 #ifdef HAVE_return
1941 {
1942 /* If we fall through to the epilogue, see if we can insert a RETURN insn
1943 in front of it. If the machine allows it at this point (we might be
1944 after reload for a leaf routine), it will improve optimization for it
1945 to be there. We do this both here and at the start of this pass since
1946 the RETURN might have been deleted by some of our optimizations. */
1952 {
1955 }
1956 }
1957 #endif
1959 /* See if there is still a NOTE_INSN_FUNCTION_END in this function.
1960 If so, delete it, and record that this function can drop off the end. */
1963 {
1966 /* One label can follow the end-note: the return label. */
1968 /* Ordinary insns can follow it if returning a structure. */
1970 /* If machine uses explicit RETURN insns, no epilogue,
1971 then one of them follows the note. */
1974 /* Other kinds of notes can follow also. */
1978 }
1980 /* Report if control can fall through at the end of the function. */
1983 {
1986 }
1988 /* Show JUMP_CHAIN no longer valid. */
1990 }
1991 \f
1992 /* LOOP_START is a NOTE_INSN_LOOP_BEG note that is followed by an unconditional
1993 jump. Assume that this unconditional jump is to the exit test code. If
1994 the code is sufficiently simple, make a copy of it before INSN,
1995 followed by a jump to the exit of the loop. Then delete the unconditional
1996 jump after INSN.
1998 Note that it is possible we can get confused here if the jump immediately
1999 after the loop start branches outside the loop but within an outer loop.
2000 If we are near the exit of that loop, we will copy its exit test. This
2001 will not generate incorrect code, but could suppress some optimizations.
2002 However, such cases are degenerate loops anyway.
2004 Return 1 if we made the change, else 0.
2006 This is only safe immediately after a regscan pass because it uses the
2007 values of regno_first_uid and regno_last_uid. */
2009 static int
2011 rtx loop_start;
2012 {
2017 rtx lastexit;
2021 /* Scan the exit code. We do not perform this optimization if any insn:
2023 is a CALL_INSN
2024 is a CODE_LABEL
2025 has a REG_RETVAL or REG_LIBCALL note (hard to adjust)
2026 is a NOTE_INSN_LOOP_BEG because this means we have a nested loop
2027 is a NOTE_INSN_BLOCK_{BEG,END} because duplicating these notes
2028 are not valid
2030 Also, don't do this if the exit code is more than 20 insns. */
2033 insn
2037 {
2039 {
2056 }
2057 }
2059 /* Unless INSN is zero, we can do the optimization. */
2065 /* See if any insn sets a register only used in the loop exit code and
2066 not a user variable. If so, replace it with a new register. */
2073 {
2079 {
2080 /* We can do the replacement. Allocate reg_map if this is the
2081 first replacement we found. */
2083 {
2086 }
2092 }
2093 }
2095 /* Now copy each insn. */
2098 {
2103 /* Only copy line-number notes. */
2105 {
2108 }
2118 /* Copy all REG_NOTES except REG_LABEL since mark_jump_label will
2119 make them. */
2135 {
2139 }
2141 /* If this is a simple jump, add it to the jump chain. */
2145 {
2149 }
2154 }
2156 /* Now clean up by emitting a jump to the end label and deleting the jump
2157 at the start of the loop. */
2159 {
2161 loop_start);
2165 {
2169 }
2171 }
2175 /* Mark the exit code as the virtual top of the converted loop. */
2179 }
2180 \f
2181 /* Move all block-beg, block-end, loop-beg, loop-cont, loop-vtop, and
2182 loop-end notes between START and END out before START. Assume that
2183 END is not such a note. START may be such a note. Returns the value
2184 of the new starting insn, which may be different if the original start
2185 was such a note. */
2187 rtx
2190 {
2191 rtx insn;
2192 rtx next;
2195 {
2204 {
2207 else
2208 {
2216 }
2217 }
2218 }
2221 }
2222 \f
2223 /* Compare the instructions before insn E1 with those before E2
2224 to find an opportunity for cross jumping.
2225 (This means detecting identical sequences of insns followed by
2226 jumps to the same place, or followed by a label and a jump
2227 to that label, and replacing one with a jump to the other.)
2229 Assume E1 is a jump that jumps to label E2
2230 (that is not always true but it might as well be).
2231 Find the longest possible equivalent sequences
2232 and store the first insns of those sequences into *F1 and *F2.
2233 Store zero there if no equivalent preceding instructions are found.
2235 We give up if we find a label in stream 1.
2236 Actually we could transfer that label into stream 2. */
2238 static void
2243 {
2250 rtx prev1;
2256 {
2266 /* Don't allow the range of insns preceding E1 or E2
2267 to include the other (E2 or E1). */
2271 /* If we will get to this code by jumping, those jumps will be
2272 tensioned to go directly to the new label (before I2),
2273 so this cross-jumping won't cost extra. So reduce the minimum. */
2275 {
2278 }
2286 /* If this is a CALL_INSN, compare register usage information.
2287 If we don't check this on stack register machines, the two
2288 CALL_INSNs might be merged leaving reg-stack.c with mismatching
2289 numbers of stack registers in the same basic block.
2290 If we don't check this on machines with delay slots, a delay slot may
2291 be filled that clobbers a parameter expected by the subroutine.
2293 ??? We take the simple route for now and assume that if they're
2294 equal, they were constructed identically. */
2301 #ifdef STACK_REGS
2302 /* If cross_jump_death_matters is not 0, the insn's mode
2303 indicates whether or not the insn contains any stack-like
2304 regs. */
2307 {
2308 /* If register stack conversion has already been done, then
2309 death notes must also be compared before it is certain that
2310 the two instruction streams match. */
2312 rtx note;
2332 done:
2333 ;
2334 }
2335 #endif
2339 {
2340 /* The following code helps take care of G++ cleanups. */
2341 rtx equiv1;
2342 rtx equiv2;
2349 /* If the equivalences are not to a constant, they may
2350 reference pseudos that no longer exist, so we can't
2351 use them. */
2354 {
2359 {
2366 }
2367 }
2369 /* Insns fail to match; cross jumping is limited to the following
2370 insns. */
2372 #ifdef HAVE_cc0
2373 /* Don't allow the insn after a compare to be shared by
2374 cross-jumping unless the compare is also shared.
2375 Here, if either of these non-matching insns is a compare,
2376 exclude the following insn from possible cross-jumping. */
2379 #endif
2381 /* If cross-jumping here will feed a jump-around-jump
2382 optimization, this jump won't cost extra, so reduce
2383 the minimum. */
2389 }
2391 win:
2393 {
2394 /* Ok, this insn is potentially includable in a cross-jump here. */
2397 }
2398 }
2402 }
2404 static void
2407 {
2408 /* Find an existing label at this point
2409 or make a new one if there is none. */
2412 /* Make the same jump insn jump to the new point. */
2414 {
2415 /* Remove from jump chain of returns. */
2417 /* Change the insn. */
2422 /* Add to new the jump chain. */
2425 {
2428 }
2429 }
2430 else
2433 /* Delete the matching insns before the jump. Also, remove any REG_EQUAL
2434 or REG_EQUIV note in the NEWLPOS stream that isn't also present in
2435 the NEWJPOS stream. */
2438 {
2439 rtx lnote;
2451 }
2452 }
2453 \f
2454 /* Return the label before INSN, or put a new label there. */
2456 rtx
2458 rtx insn;
2459 {
2460 rtx label;
2462 /* Find an existing label at this point
2463 or make a new one if there is none. */
2467 {
2473 }
2475 }
2477 /* Return the label after INSN, or put a new label there. */
2479 rtx
2481 rtx insn;
2482 {
2483 rtx label;
2485 /* Find an existing label at this point
2486 or make a new one if there is none. */
2490 {
2494 }
2496 }
2497 \f
2498 /* Return 1 if INSN is a jump that jumps to right after TARGET
2499 only on the condition that TARGET itself would drop through.
2500 Assumes that TARGET is a conditional jump. */
2502 static int
2505 {
2521 {
2525 }
2528 {
2532 }
2537 }
2538 \f
2539 /* Given a comparison, COMPARISON, inside a conditional jump insn, INSN,
2540 return non-zero if it is safe to reverse this comparison. It is if our
2541 floating-point is not IEEE, if this is an NE or EQ comparison, or if
2542 this is known to be an integer comparison. */
2544 int
2546 rtx comparison;
2547 rtx insn;
2548 {
2549 rtx arg0;
2551 /* If this is not actually a comparison, we can't reverse it. */
2556 /* If this is an NE comparison, it is safe to reverse it to an EQ
2557 comparison and vice versa, even for floating point. If no operands
2558 are NaNs, the reversal is valid. If some operand is a NaN, EQ is
2559 always false and NE is always true, so the reversal is also valid. */
2560 || flag_fast_math
2567 /* Make sure ARG0 is one of the actual objects being compared. If we
2568 can't do this, we can't be sure the comparison can be reversed.
2570 Handle cc0 and a MODE_CC register. */
2572 #ifdef HAVE_cc0
2574 #endif
2575 )
2576 {
2587 }
2589 /* We can reverse this if ARG0 is a CONST_INT or if its mode is
2590 not VOIDmode and neither a MODE_CC nor MODE_FLOAT type. */
2595 }
2597 /* Given an rtx-code for a comparison, return the code
2598 for the negated comparison.
2599 WATCH OUT! reverse_condition is not safe to use on a jump
2600 that might be acting on the results of an IEEE floating point comparison,
2601 because of the special treatment of non-signaling nans in comparisons.
2602 Use can_reverse_comparison_p to be sure. */
2604 enum rtx_code
2607 {
2609 {
2643 }
2644 }
2646 /* Similar, but return the code when two operands of a comparison are swapped.
2647 This IS safe for IEEE floating-point. */
2649 enum rtx_code
2652 {
2654 {
2686 }
2687 }
2689 /* Given a comparison CODE, return the corresponding unsigned comparison.
2690 If CODE is an equality comparison or already an unsigned comparison,
2691 CODE is returned. */
2693 enum rtx_code
2696 {
2698 {
2721 }
2722 }
2724 /* Similarly, return the signed version of a comparison. */
2726 enum rtx_code
2729 {
2731 {
2754 }
2755 }
2756 \f
2757 /* Return non-zero if CODE1 is more strict than CODE2, i.e., if the
2758 truth of CODE1 implies the truth of CODE2. */
2760 int
2763 {
2768 {
2793 }
2796 }
2797 \f
2798 /* Return 1 if INSN is an unconditional jump and nothing else. */
2800 int
2802 rtx insn;
2803 {
2808 }
2810 /* Return nonzero if INSN is a (possibly) conditional jump
2811 and nothing more. */
2813 int
2815 rtx insn;
2816 {
2835 }
2837 /* Return nonzero if INSN is a (possibly) conditional jump
2838 and nothing more. */
2840 int
2842 rtx insn;
2843 {
2848 else
2868 }
2870 /* Return 1 if X is an RTX that does nothing but set the condition codes
2871 and CLOBBER or USE registers.
2872 Return -1 if X does explicitly set the condition codes,
2873 but also does other things. */
2875 int
2877 rtx x;
2878 {
2879 #ifdef HAVE_cc0
2883 {
2888 {
2894 }
2896 }
2898 #else
2900 #endif
2901 }
2902 \f
2903 /* Follow any unconditional jump at LABEL;
2904 return the ultimate label reached by any such chain of jumps.
2905 If LABEL is not followed by a jump, return LABEL.
2906 If the chain loops or we can't find end, return LABEL,
2907 since that tells caller to avoid changing the insn.
2909 If RELOAD_COMPLETED is 0, we do not chain across a NOTE_INSN_LOOP_BEG or
2910 a USE or CLOBBER. */
2912 rtx
2914 rtx label;
2915 {
2928 depth++)
2929 {
2930 /* Don't chain through the insn that jumps into a loop
2931 from outside the loop,
2932 since that would create multiple loop entry jumps
2933 and prevent loop optimization. */
2934 rtx tem;
2941 /* If we have found a cycle, make the insn jump to itself. */
2951 }
2955 }
2957 /* Assuming that field IDX of X is a vector of label_refs,
2958 replace each of them by the ultimate label reached by it.
2959 Return nonzero if a change is made.
2960 If IGNORE_LOOPS is 0, we do not chain across a NOTE_INSN_LOOP_BEG. */
2962 static int
2966 {
2970 {
2974 {
2980 }
2981 }
2983 }
2984 \f
2985 /* Find all CODE_LABELs referred to in X, and increment their use counts.
2986 If INSN is a JUMP_INSN and there is at least one CODE_LABEL referenced
2987 in INSN, then store one of them in JUMP_LABEL (INSN).
2988 If INSN is an INSN or a CALL_INSN and there is at least one CODE_LABEL
2989 referenced in INSN, add a REG_LABEL note containing that label to INSN.
2990 Also, when there are consecutive labels, canonicalize on the last of them.
2992 Note that two labels separated by a loop-beginning note
2993 must be kept distinct if we have not yet done loop-optimization,
2994 because the gap between them is where loop-optimize
2995 will want to move invariant code to. CROSS_JUMP tells us
2996 that loop-optimization is done with.
2998 Once reload has completed (CROSS_JUMP non-zero), we need not consider
2999 two labels distinct if they are separated by only USE or CLOBBER insns. */
3001 static void
3004 rtx insn;
3006 {
3012 {
3025 /* If this is a constant-pool reference, see if it is a label. */
3032 {
3035 rtx note;
3036 rtx next;
3041 /* Ignore references to labels of containing functions. */
3045 /* If there are other labels following this one,
3046 replace it with the last of the consecutive labels. */
3048 {
3061 }
3067 {
3071 /* If we've changed OLABEL and we had a REG_LABEL note
3072 for it, update it as well. */
3077 /* Otherwise, add a REG_LABEL note for LABEL unless there already
3078 is one. */
3080 {
3082 /* Don't record labels that refer to dispatch tables.
3083 This is not necessary, since the tablejump
3084 references the same label.
3085 And if we did record them, flow.c would make worse code. */
3092 }
3093 }
3095 }
3097 /* Do walk the labels in a vector, but not the first operand of an
3098 ADDR_DIFF_VEC. Don't set the JUMP_LABEL of a vector. */
3101 {
3107 }
3108 }
3112 {
3116 {
3120 }
3121 }
3122 }
3124 /* If all INSN does is set the pc, delete it,
3125 and delete the insn that set the condition codes for it
3126 if that's what the previous thing was. */
3128 void
3130 rtx insn;
3131 {
3136 }
3138 /* Delete INSN and recursively delete insns that compute values used only
3139 by INSN. This uses the REG_DEAD notes computed during flow analysis.
3140 If we are running before flow.c, we need do nothing since flow.c will
3141 delete dead code. We also can't know if the registers being used are
3142 dead or not at this point.
3144 Otherwise, look at all our REG_DEAD notes. If a previous insn does
3145 nothing other than set a register that dies in this insn, we can delete
3146 that insn as well.
3148 On machines with CC0, if CC0 is used in this insn, we may be able to
3149 delete the insn that set it. */
3151 static void
3153 rtx insn;
3154 {
3157 #ifdef HAVE_cc0
3159 {
3161 /* We assume that at this stage
3162 CC's are always set explicitly
3163 and always immediately before the jump that
3164 will use them. So if the previous insn
3165 exists to set the CC's, delete it
3166 (unless it performs auto-increments, etc.). */
3169 {
3173 else
3174 /* Otherwise, show that cc0 won't be used. */
3177 }
3178 }
3179 #endif
3182 {
3183 rtx our_prev;
3188 /* Verify that the REG_NOTE is legitimate. */
3195 {
3196 /* If we reach a SEQUENCE, it is too complex to try to
3197 do anything with it, so give up. */
3203 /* reorg creates USEs that look like this. We leave them
3204 alone because reorg needs them for its own purposes. */
3208 {
3213 {
3214 /* If we find a SET of something else, we can't
3215 delete the insn. */
3220 {
3226 }
3230 }
3236 }
3238 /* If OUR_PREV references the register that dies here, it is an
3239 additional use. Hence any prior SET isn't dead. However, this
3240 insn becomes the new place for the REG_DEAD note. */
3243 {
3247 }
3248 }
3249 }
3252 }
3253 \f
3254 /* Delete insn INSN from the chain of insns and update label ref counts.
3255 May delete some following insns as a consequence; may even delete
3256 a label elsewhere and insns that follow it.
3258 Returns the first insn after INSN that was not deleted. */
3260 rtx
3263 {
3272 /* This insn is already deleted => return first following nondeleted. */
3276 /* Don't delete user-declared labels. Convert them to special NOTEs
3277 instead. */
3280 {
3285 }
3286 else
3287 /* Mark this insn as deleted. */
3290 /* If this is an unconditional jump, delete it from the jump chain. */
3294 /* If instruction is followed by a barrier,
3295 delete the barrier too. */
3298 {
3301 }
3303 /* Patch out INSN (and the barrier if any) */
3306 {
3308 {
3313 }
3316 {
3320 }
3324 }
3326 /* If deleting a jump, decrement the count of the label,
3327 and delete the label if it is now unused. */
3331 {
3332 /* This can delete NEXT or PREV,
3333 either directly if NEXT is JUMP_LABEL (INSN),
3334 or indirectly through more levels of jumps. */
3336 /* I feel a little doubtful about this loop,
3337 but I see no clean and sure alternative way
3338 to find the first insn after INSN that is not now deleted.
3339 I hope this works. */
3343 }
3348 /* If INSN was a label and a dispatch table follows it,
3349 delete the dispatch table. The tablejump must have gone already.
3350 It isn't useful to fall through into a table. */
3359 /* If INSN was a label, delete insns following it if now unreachable. */
3362 {
3368 {
3372 /* Keep going past other deleted labels to delete what follows. */
3375 else
3376 /* Note: if this deletes a jump, it can cause more
3377 deletion of unreachable code, after a different label.
3378 As long as the value from this recursive call is correct,
3379 this invocation functions correctly. */
3381 }
3382 }
3385 }
3387 /* Advance from INSN till reaching something not deleted
3388 then return that. May return INSN itself. */
3390 rtx
3392 rtx insn;
3393 {
3397 }
3398 \f
3399 /* Delete a range of insns from FROM to TO, inclusive.
3400 This is for the sake of peephole optimization, so assume
3401 that whatever these insns do will still be done by a new
3402 peephole insn that will replace them. */
3404 void
3407 {
3411 {
3416 {
3419 /* Patch this insn out of the chain. */
3420 /* We don't do this all at once, because we
3421 must preserve all NOTEs. */
3427 }
3432 }
3434 /* Note that if TO is an unconditional jump
3435 we *do not* delete the BARRIER that follows,
3436 since the peephole that replaces this sequence
3437 is also an unconditional jump in that case. */
3438 }
3439 \f
3440 /* Invert the condition of the jump JUMP, and make it jump
3441 to label NLABEL instead of where it jumps now. */
3443 int
3446 {
3447 /* We have to either invert the condition and change the label or
3448 do neither. Either operation could fail. We first try to invert
3449 the jump. If that succeeds, we try changing the label. If that fails,
3450 we invert the jump back to what it was. */
3459 /* This should just be putting it back the way it was. */
3463 }
3465 /* Invert the jump condition of rtx X contained in jump insn, INSN.
3467 Return 1 if we can do so, 0 if we cannot find a way to do so that
3468 matches a pattern. */
3470 int
3472 rtx x;
3473 rtx insn;
3474 {
3482 {
3486 /* We can do this in two ways: The preferable way, which can only
3487 be done if this is not an integer comparison, is to reverse
3488 the comparison code. Otherwise, swap the THEN-part and ELSE-part
3489 of the IF_THEN_ELSE. If we can't do either, fail. */
3502 }
3506 {
3511 {
3516 }
3517 }
3520 }
3521 \f
3522 /* Make jump JUMP jump to label NLABEL instead of where it jumps now.
3523 If the old jump target label is unused as a result,
3524 it and the code following it may be deleted.
3526 If NLABEL is zero, we are to turn the jump into a (possibly conditional)
3527 RETURN insn.
3529 The return value will be 1 if the change was made, 0 if it wasn't (this
3530 can only occur for NLABEL == 0). */
3532 int
3535 {
3544 /* If this is an unconditional branch, delete it from the jump_chain of
3545 OLABEL and add it to the jump_chain of NLABEL (assuming both labels
3546 have UID's in range and JUMP_CHAIN is valid). */
3549 {
3555 {
3558 }
3559 }
3569 }
3571 /* Delete the instruction JUMP from any jump chain it might be on. */
3573 static void
3575 rtx jump;
3576 {
3580 /* Handle unconditional jumps. */
3585 /* Handle return insns. */
3592 else
3593 {
3594 rtx insn;
3600 {
3603 }
3604 }
3605 }
3607 /* If NLABEL is nonzero, throughout the rtx at LOC,
3608 alter (LABEL_REF OLABEL) to (LABEL_REF NLABEL). If OLABEL is
3609 zero, alter (RETURN) to (LABEL_REF NLABEL).
3611 If NLABEL is zero, alter (LABEL_REF OLABEL) to (RETURN) and check
3612 validity with validate_change. Convert (set (pc) (label_ref olabel))
3613 to (return).
3615 Return 0 if we found a change we would like to make but it is invalid.
3616 Otherwise, return 1. */
3618 int
3622 rtx insn;
3623 {
3630 {
3632 {
3635 else
3638 }
3639 }
3641 {
3646 }
3655 {
3660 {
3665 }
3666 }
3669 }
3670 \f
3671 /* Make jump JUMP jump to label NLABEL, assuming it used to be a tablejump.
3673 If the old jump target label (before the dispatch table) becomes unused,
3674 it and the dispatch table may be deleted. In that case, find the insn
3675 before the jump references that label and delete it and logical successors
3676 too. */
3678 static void
3681 {
3684 /* Add this jump to the jump_chain of NLABEL. */
3687 {
3690 }
3698 {
3701 }
3702 }
3704 /* Find the insn referencing LABEL that is a logical predecessor of INSN.
3705 If we found one, delete it and then delete this insn if DELETE_THIS is
3706 non-zero. Return non-zero if INSN or a predecessor references LABEL. */
3708 static int
3712 {
3714 rtx link;
3718 {
3720 {
3723 }
3724 else
3726 }
3730 {
3732 {
3735 }
3736 else
3738 }
3741 }
3742 \f
3743 /* Like rtx_equal_p except that it considers two REGs as equal
3744 if they renumber to the same value and considers two commutative
3745 operations to be the same if the order of the operands has been
3746 reversed. */
3748 int
3751 {
3762 {
3769 /* If we haven't done any renumbering, don't
3770 make any assumptions. */
3775 {
3780 {
3783 }
3784 }
3786 else
3787 {
3791 }
3794 {
3799 {
3802 }
3803 }
3805 else
3806 {
3810 }
3813 }
3815 /* Now we have disposed of all the cases
3816 in which different rtx codes can match. */
3821 {
3832 /* We can't assume nonlocal labels have their following insns yet. */
3836 /* Two label-refs are equivalent if they point at labels
3837 in the same position in the instruction stream. */
3843 }
3845 /* (MULT:SI x y) and (MULT:HI x y) are NOT equivalent. */
3850 /* For commutative operations, the RTX match if the operand match in any
3851 order. Also handle the simple binary and unary cases without a loop. */
3863 /* Compare the elements. If any pair of corresponding elements
3864 fail to match, return 0 for the whole things. */
3868 {
3871 {
3895 /* fall through. */
3909 }
3910 }
3912 }
3913 \f
3914 /* If X is a hard register or equivalent to one or a subregister of one,
3915 return the hard register number. If X is a pseudo register that was not
3916 assigned a hard register, return the pseudo register number. Otherwise,
3917 return -1. Any rtx is valid for X. */
3919 int
3921 rtx x;
3922 {
3924 {
3928 }
3930 {
3934 }
3936 }
3937 \f
3938 /* Optimize code of the form:
3940 for (x = a[i]; x; ...)
3941 ...
3942 for (x = a[i]; x; ...)
3943 ...
3944 foo:
3946 Loop optimize will change the above code into
3948 if (x = a[i])
3949 for (;;)
3950 { ...; if (! (x = ...)) break; }
3951 if (x = a[i])
3952 for (;;)
3953 { ...; if (! (x = ...)) break; }
3954 foo:
3956 In general, if the first test fails, the program can branch
3957 directly to `foo' and skip the second try which is doomed to fail.
3958 We run this after loop optimization and before flow analysis. */
3960 /* When comparing the insn patterns, we track the fact that different
3961 pseudo-register numbers may have been used in each computation.
3962 The following array stores an equivalence -- same_regs[I] == J means
3963 that pseudo register I was used in the first set of tests in a context
3964 where J was used in the second set. We also count the number of such
3965 pending equivalences. If nonzero, the expressions really aren't the
3966 same. */
3972 /* Track any registers modified between the target of the first jump and
3973 the second jump. They never compare equal. */
3977 /* Record if memory was modified. */
3981 /* Called via note_stores on each insn between the target of the first
3982 branch and the second branch. It marks any changed registers. */
3984 static void
3986 rtx dest;
3987 rtx x;
3988 {
4003 else
4006 }
4008 /* F is the first insn in the chain of insns. */
4010 void
4012 rtx f;
4015 {
4016 /* Basic algorithm is to find a conditional branch,
4017 the label it may branch to, and the branch after
4018 that label. If the two branches test the same condition,
4019 walk back from both branch paths until the insn patterns
4020 differ, or code labels are hit. If we make it back to
4021 the target of the first branch, then we know that the first branch
4022 will either always succeed or always fail depending on the relative
4023 senses of the two branches. So adjust the first branch accordingly
4024 in this case. */
4033 /* Allocate register tables and quick-reset table. */
4041 {
4045 {
4046 /* Get to a candidate branch insn. */
4061 /* Look for a branch after the target. Record any registers and
4062 memory modified between the target and the branch. Stop when we
4063 get to a label since we can't know what was changed there. */
4065 {
4070 {
4071 /* If this is an unconditional jump and is the only use of
4072 its target label, we can follow it. */
4076 {
4079 }
4080 else
4082 }
4088 {
4097 }
4100 }
4102 /* Check the next candidate branch insn from the label
4103 of the first. */
4111 /* Get the comparison codes and operands, reversing the
4112 codes if appropriate. If we don't have comparison codes,
4113 we can't do anything. */
4126 /* If they test the same things and knowing that B1 branches
4127 tells us whether or not B2 branches, check if we
4128 can thread the branch. */
4133 {
4138 {
4140 {
4141 /* We have reached the target of the first branch.
4142 If there are no pending register equivalents,
4143 we know that this branch will either always
4144 succeed (if the senses of the two branches are
4145 the same) or always fail (if not). */
4146 rtx new_label;
4153 else
4157 {
4162 {
4163 /* Don't thread to the loop label. If a loop
4164 label is reused, loop optimization will
4165 be disabled for that loop. */
4168 }
4170 }
4172 }
4174 /* If either of these is not a normal insn (it might be
4175 a JUMP_INSN, CALL_INSN, or CODE_LABEL) we fail. (NOTEs
4176 have already been skipped above.) Similarly, fail
4177 if the insns are different. */
4186 }
4187 }
4188 }
4189 }
4190 }
4191 \f
4192 /* This is like RTX_EQUAL_P except that it knows about our handling of
4193 possibly equivalent registers and knows to consider volatile and
4194 modified objects as not equal.
4196 YINSN is the insn containing Y. */
4198 int
4201 rtx yinsn;
4202 {
4209 /* Rtx's of different codes cannot be equal. */
4213 /* (MULT:SI x y) and (MULT:HI x y) are NOT equivalent.
4214 (REG:SI x) and (REG:HI x) are NOT equivalent. */
4219 /* For commutative operations, the RTX match if the operand match in any
4220 order. Also handle the simple binary and unary cases without a loop. */
4232 /* Handle special-cases first. */
4234 {
4239 /* If neither is user variable or hard register, check for possible
4240 equivalence. */
4247 {
4249 num_same_regs++;
4251 /* If this is the first time we are seeing a register on the `Y'
4252 side, see if it is the last use. If not, we can't thread the
4253 jump, so mark it as not equivalent. */
4258 }
4259 else
4265 /* If memory modified or either volatile, not equivalent.
4266 Else, check address. */
4279 /* Cancel a pending `same_regs' if setting equivalenced registers.
4280 Then process source. */
4283 {
4285 {
4287 num_same_regs--;
4288 }
4291 }
4292 else
4303 }
4310 {
4312 {
4326 /* Two vectors must have the same length. */
4330 /* And the corresponding elements must match. */
4349 /* These are just backpointers, so they don't matter. */
4355 /* It is believed that rtx's at this level will never
4356 contain anything but integers and other rtx's,
4357 except for within LABEL_REFs and SYMBOL_REFs. */
4360 }
4361 }
4363 }