| blob | 00e31cf22ec4bfb8a5ba7960cedfc5b1087e16c4 |
1 /* Optimize jump instructions, for GNU compiler.
2 Copyright (C) 1987, 88, 89, 91-96, 1997 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, 59 Temple Place - Suite 330,
19 Boston, MA 02111-1307, USA. */
22 /* This is the jump-optimization pass of the compiler.
23 It is run two or three times: once before cse, sometimes once after cse,
24 and once after reload (before final).
26 jump_optimize deletes unreachable code and labels that are not used.
27 It also deletes jumps that jump to the following insn,
28 and simplifies jumps around unconditional jumps and jumps
29 to unconditional jumps.
31 Each CODE_LABEL has a count of the times it is used
32 stored in the LABEL_NUSES internal field, and each JUMP_INSN
33 has one label that it refers to stored in the
34 JUMP_LABEL internal field. With this we can detect labels that
35 become unused because of the deletion of all the jumps that
36 formerly used them. The JUMP_LABEL info is sometimes looked
37 at by later passes.
39 Optionally, cross-jumping can be done. Currently it is done
40 only the last time (when after reload and before final).
41 In fact, the code for cross-jumping now assumes that register
42 allocation has been done, since it uses `rtx_renumbered_equal_p'.
44 Jump optimization is done after cse when cse's constant-propagation
45 causes jumps to become unconditional or to be deleted.
47 Unreachable loops are not detected here, because the labels
48 have references and the insns appear reachable from the labels.
49 find_basic_blocks in flow.c finds and deletes such loops.
51 The subroutines delete_insn, redirect_jump, and invert_jump are used
52 from other passes as well. */
55 #include <stdio.h>
67 /* ??? Eventually must record somehow the labels used by jumps
68 from nested functions. */
69 /* Pre-record the next or previous real insn for each label?
70 No, this pass is very fast anyway. */
71 /* Condense consecutive labels?
72 This would make life analysis faster, maybe. */
73 /* Optimize jump y; x: ... y: jumpif... x?
74 Don't know if it is worth bothering with. */
75 /* Optimize two cases of conditional jump to conditional jump?
76 This can never delete any instruction or make anything dead,
77 or even change what is live at any point.
78 So perhaps let combiner do it. */
80 /* Vector indexed by uid.
81 For each CODE_LABEL, index by its uid to get first unconditional jump
82 that jumps to the label.
83 For each JUMP_INSN, index by its uid to get the next unconditional jump
84 that jumps to the same label.
85 Element 0 is the start of a chain of all return insns.
86 (It is safe to use element 0 because insn uid 0 is not used. */
90 /* List of labels referred to from initializers.
91 These can never be deleted. */
92 rtx forced_labels;
94 /* Maximum index in jump_chain. */
98 /* Set nonzero by jump_optimize if control can fall through
99 to the end of the function. */
102 /* Indicates whether death notes are significant in cross jump analysis.
103 Normally they are not significant, because of A and B jump to C,
104 and R dies in A, it must die in B. But this might not be true after
105 stack register conversion, and we must compare death notes in that
106 case. */
121 \f
122 /* Delete no-op jumps and optimize jumps to jumps
123 and jumps around jumps.
124 Delete unused labels and unreachable code.
126 If CROSS_JUMP is 1, detect matching code
127 before a jump and its destination and unify them.
128 If CROSS_JUMP is 2, do cross-jumping, but pay attention to death notes.
130 If NOOP_MOVES is nonzero, delete no-op move insns.
132 If AFTER_REGSCAN is nonzero, then this jump pass is being run immediately
133 after regscan, and it is safe to use regno_first_uid and regno_last_uid.
135 If `optimize' is zero, don't change any code,
136 just determine whether control drops off the end of the function.
137 This case occurs when we have -W and not -O.
138 It works because `delete_insn' checks the value of `optimize'
139 and refrains from actually deleting when that is 0. */
141 void
143 rtx f;
147 {
152 rtx last_insn;
156 /* Initialize LABEL_NUSES and JUMP_LABEL fields. Delete any REG_LABEL
157 notes whose labels don't occur in the insn any more. */
160 {
167 {
172 }
176 }
178 max_uid++;
180 /* Delete insns following barriers, up to next label. */
183 {
185 {
188 {
192 else
194 }
195 /* INSN is now the code_label. */
196 }
197 else
199 }
201 /* Leave some extra room for labels and duplicate exit test insns
202 we make. */
207 /* Mark the label each jump jumps to.
208 Combine consecutive labels, and count uses of labels.
210 For each label, make a chain (using `jump_chain')
211 of all the *unconditional* jumps that jump to it;
212 also make a chain of all returns. */
217 {
220 {
222 {
226 }
228 {
231 }
232 }
233 }
235 /* Keep track of labels used from static data;
236 they cannot ever be deleted. */
243 /* Keep track of labels used for marking handlers for exception
244 regions; they cannot usually be deleted. */
251 /* Delete all labels already not referenced.
252 Also find the last insn. */
256 {
259 else
260 {
263 }
264 }
267 {
268 /* See if there is still a NOTE_INSN_FUNCTION_END in this function.
269 If so record that this function can drop off the end. */
272 {
275 /* One label can follow the end-note: the return label. */
277 /* Ordinary insns can follow it if returning a structure. */
279 /* If machine uses explicit RETURN insns, no epilogue,
280 then one of them follows the note. */
283 /* A barrier can follow the return insn. */
285 /* Other kinds of notes can follow also. */
289 }
291 /* Report if control can fall through at the end of the function. */
297 /* Zero the "deleted" flag of all the "deleted" insns. */
301 }
303 #ifdef HAVE_return
305 {
306 /* If we fall through to the epilogue, see if we can insert a RETURN insn
307 in front of it. If the machine allows it at this point (we might be
308 after reload for a leaf routine), it will improve optimization for it
309 to be there. */
315 {
318 }
319 }
320 #endif
324 {
328 {
331 /* Combine stack_adjusts with following push_insns. */
332 #ifdef PUSH_ROUNDING
339 {
340 rtx p;
346 /* Find all successive push insns. */
348 /* Don't convert more than three pushes;
349 that starts adding too many displaced addresses
350 and the whole thing starts becoming a losing
351 proposition. */
353 {
362 /* Allow a no-op move between the adjust and the push. */
371 pushes++;
376 }
378 /* Discard the amount pushed from the stack adjust;
379 maybe eliminate it entirely. */
381 {
384 }
385 else
389 /* Change the appropriate push insns to ordinary stores. */
392 {
406 /* If this push doesn't fully fit in the space
407 of the stack adjust that we deleted,
408 make another stack adjust here for what we
409 didn't use up. There should be peepholes
410 to recognize the resulting sequence of insns. */
412 {
415 p);
417 }
420 }
421 }
422 #endif
424 /* Detect and delete no-op move instructions
425 resulting from not allocating a parameter in a register. */
438 /* Detect and ignore no-op move instructions
439 resulting from smart or fortuitous register allocation. */
442 {
449 {
450 rtx trial;
457 {
458 /* DREG may have been the target of a REG_DEAD note in
459 the insn which makes INSN redundant. If so, reorg
460 would still think it is dead. So search for such a
461 note and delete it if we find it. */
467 {
470 }
471 #ifdef PRESERVE_DEATH_INFO_REGNO_P
472 /* Deleting insn could lose a death-note for SREG
473 so don't do it if final needs accurate
474 death-notes. */
477 {
478 /* Change this into a USE so that we won't emit
479 code for it, but still can keep the note. */
483 /* Remove all reg notes but the REG_DEAD one. */
486 }
487 else
488 #endif
490 }
491 }
496 {
497 /* This handles the case where we have two consecutive
498 assignments of the same constant to pseudos that didn't
499 get a hard reg. Each SET from the constant will be
500 converted into a SET of the spill register and an
501 output reload will be made following it. This produces
502 two loads of the same constant into the same spill
503 register. */
507 /* Look back for a death note for the first reg.
508 If there is one, it is no longer accurate. */
510 {
514 {
517 }
519 }
521 /* Delete the second load of the value. */
523 }
524 }
526 {
527 /* If each part is a set between two identical registers or
528 a USE or CLOBBER, delete the insn. */
530 rtx tem;
533 {
543 }
547 }
548 /* Also delete insns to store bit fields if they are no-ops. */
549 /* Not worth the hair to detect this in the big-endian case. */
558 }
560 }
562 /* If we haven't yet gotten to reload and we have just run regscan,
563 delete any insn that sets a register that isn't used elsewhere.
564 This helps some of the optimizations below by having less insns
565 being jumped around. */
569 {
577 /* We use regno_last_note_uid so as not to delete the setting
578 of a reg that's used in notes. A subsequent optimization
579 might arrange to use that reg for real. */
584 }
586 /* Now iterate optimizing jumps until nothing changes over one pass. */
589 {
593 {
594 rtx reallabelprev;
596 rtx nlabel;
599 #if 0
600 /* If NOT the first iteration, if this is the last jump pass
601 (just before final), do the special peephole optimizations.
602 Avoiding the first iteration gives ordinary jump opts
603 a chance to work before peephole opts. */
608 #endif
610 /* That could have deleted some insns after INSN, so check now
611 what the following insn is. */
615 /* See if this is a NOTE_INSN_LOOP_BEG followed by an unconditional
616 jump. Try to optimize by duplicating the loop exit test if so.
617 This is only safe immediately after regscan, because it uses
618 the values of regno_first_uid and regno_last_uid. */
623 {
626 {
630 }
631 }
640 /* Tension the labels in dispatch tables. */
647 /* If a dispatch table always goes to the same place,
648 get rid of it and replace the insn that uses it. */
652 {
667 /* Don't mess with a casesi insn. */
672 {
676 }
677 }
681 /* If a jump references the end of the function, try to turn
682 it into a RETURN insn, possibly a conditional one. */
689 /* Detect jump to following insn. */
691 {
696 }
698 /* If we have an unconditional jump preceded by a USE, try to put
699 the USE before the target and jump there. This simplifies many
700 of the optimizations below since we don't have to worry about
701 dealing with these USE insns. We only do this if the label
702 being branch to already has the identical USE or if code
703 never falls through to that label. */
712 /* Don't do this optimization if we have a loop containing only
713 the USE instruction, and the loop start label has a usage
714 count of 1. This is because we will redo this optimization
715 everytime through the outer loop, and jump opt will never
716 exit. */
720 {
722 {
725 }
731 }
733 /* Simplify if (...) x = a; else x = b; by converting it
734 to x = b; if (...) x = a;
735 if B is sufficiently simple, the test doesn't involve X,
736 and nothing in the test modifies B or X.
738 If we have small register classes, we also can't do this if X
739 is a hard register.
741 If the "x = b;" insn has any REG_NOTES, we don't do this because
742 of the possibility that we are running after CSE and there is a
743 REG_EQUAL note that is only valid if the branch has already been
744 taken. If we move the insn with the REG_EQUAL note, we may
745 fold the comparison to always be false in a later CSE pass.
746 (We could also delete the REG_NOTES when moving the insn, but it
747 seems simpler to not move it.) An exception is that we can move
748 the insn if the only note is a REG_EQUAL or REG_EQUIV whose
749 value is the same as "b".
751 INSN is the branch over the `else' part.
753 We set:
755 TEMP to the jump insn preceding "x = a;"
756 TEMP1 to X
757 TEMP2 to the insn that sets "x = b;"
758 TEMP3 to the insn that sets "x = a;"
759 TEMP4 to the set of "x = b"; */
766 && (! SMALL_REGISTER_CLASSES
783 /* TEMP must skip over the "x = a;" insn */
786 /* There must be no other entries to the "x = b;" insn. */
788 /* INSN must either branch to the insn after TEMP2 or the insn
789 after TEMP2 must branch to the same place as INSN. */
794 {
795 /* The test expression, X, may be a complicated test with
796 multiple branches. See if we can find all the uses of
797 the label that TEMP branches to without hitting a CALL_INSN
798 or a jump to somewhere else. */
803 /* Set P to the first jump insn that goes around "x = a;". */
805 {
807 {
810 {
811 nuses--;
814 }
815 else
817 }
820 }
822 #ifdef HAVE_cc0
823 /* We cannot insert anything between a set of cc and its use
824 so if P uses cc0, we must back up to the previous insn. */
829 #endif
834 /* If we found all the uses and there was no data conflict, we
835 can move the assignment unless we can branch into the middle
836 from somewhere. */
843 {
847 /* Set NEXT to an insn that we know won't go away. */
850 /* Delete the jump around the set. Note that we must do
851 this before we redirect the test jumps so that it won't
852 delete the code immediately following the assignment
853 we moved (which might be a jump). */
857 /* We either have two consecutive labels or a jump to
858 a jump, so adjust all the JUMP_INSNs to branch to where
859 INSN branches to. */
866 }
867 }
869 /* Simplify if (...) { x = a; goto l; } x = b; by converting it
870 to x = a; if (...) goto l; x = b;
871 if A is sufficiently simple, the test doesn't involve X,
872 and nothing in the test modifies A or X.
874 If we have small register classes, we also can't do this if X
875 is a hard register.
877 If the "x = a;" insn has any REG_NOTES, we don't do this because
878 of the possibility that we are running after CSE and there is a
879 REG_EQUAL note that is only valid if the branch has already been
880 taken. If we move the insn with the REG_EQUAL note, we may
881 fold the comparison to always be false in a later CSE pass.
882 (We could also delete the REG_NOTES when moving the insn, but it
883 seems simpler to not move it.) An exception is that we can move
884 the insn if the only note is a REG_EQUAL or REG_EQUIV whose
885 value is the same as "a".
887 INSN is the goto.
889 We set:
891 TEMP to the jump insn preceding "x = a;"
892 TEMP1 to X
893 TEMP2 to the insn that sets "x = b;"
894 TEMP3 to the insn that sets "x = a;"
895 TEMP4 to the set of "x = a"; */
902 && (! SMALL_REGISTER_CLASSES
919 /* TEMP must skip over the "x = a;" insn */
922 {
926 #ifdef HAVE_cc0
927 /* We cannot insert anything between a set of cc and its use. */
931 #endif
944 {
949 /* Set NEXT to an insn that we know won't go away. */
952 }
957 }
959 #ifndef HAVE_cc0
960 /* If we have if (...) x = exp; and branches are expensive,
961 EXP is a single insn, does not have any side effects, cannot
962 trap, and is not too costly, convert this to
963 t = exp; if (...) x = t;
965 Don't do this when we have CC0 because it is unlikely to help
966 and we'd need to worry about where to place the new insn and
967 the potential for conflicts. We also can't do this when we have
968 notes on the insn for the same reason as above.
970 We set:
972 TEMP to the "x = exp;" insn.
973 TEMP1 to the single set in the "x = exp; insn.
974 TEMP2 to "x". */
989 && (! SMALL_REGISTER_CLASSES
997 {
1002 {
1008 }
1009 }
1011 /* Similarly, if it takes two insns to compute EXP but they
1012 have the same destination. Here TEMP3 will be the second
1013 insn and TEMP4 the SET from that insn. */
1031 && (! SMALL_REGISTER_CLASSES
1041 {
1047 {
1048 /* Use the earliest of temp5 and temp6. */
1054 emit_insn_after_with_line_notes
1060 }
1061 }
1063 /* Finally, handle the case where two insns are used to
1064 compute EXP but a temporary register is used. Here we must
1065 ensure that the temporary register is not used anywhere else. */
1068 && after_regscan
1096 && (! SMALL_REGISTER_CLASSES
1102 {
1108 {
1109 /* Use the earliest of temp5 and temp6. */
1120 }
1121 }
1124 /* Try to use a conditional move (if the target has them), or a
1125 store-flag insn. The general case is:
1127 1) x = a; if (...) x = b; and
1128 2) if (...) x = b;
1130 If the jump would be faster, the machine should not have defined
1131 the movcc or scc insns!. These cases are often made by the
1132 previous optimization.
1134 The second case is treated as x = x; if (...) x = b;.
1136 INSN here is the jump around the store. We set:
1138 TEMP to the "x = b;" insn.
1139 TEMP1 to X.
1140 TEMP2 to B.
1141 TEMP3 to A (X in the second case).
1142 TEMP4 to the condition being tested.
1143 TEMP5 to the earliest insn used to find the condition. */
1146 ! reload_completed
1148 /* Set TEMP to the "x = b;" insn. */
1153 && (! SMALL_REGISTER_CLASSES
1157 /* ??? How about floating point constants? */
1159 /* Allow either form, but prefer the former if both apply.
1160 There is no point in using the old value of TEMP1 if
1161 it is a register, since cse will alias them. It can
1162 lose if the old value were a hard register since CSE
1163 won't replace hard registers. */
1165 /* Make the latter case look like x = x; if (...) x = b; */
1167 /* INSN must either branch to the insn after TEMP or the insn
1168 after TEMP must branch to the same place as INSN. */
1174 /* We must be comparing objects whose modes imply the size.
1175 We could handle BLKmode if (1) emit_store_flag could
1176 and (2) we could find the size reliably. */
1178 /* Even if branches are cheap, the store_flag optimization
1179 can win when the operation to be performed can be
1180 expressed directly. */
1181 #ifdef HAVE_cc0
1182 /* If the previous insn sets CC0 and something else, we can't
1183 do this since we are going to delete that insn. */
1190 #endif
1191 )
1192 {
1193 #ifdef HAVE_conditional_move
1194 /* First try a conditional move. */
1195 {
1199 rtx target;
1201 /* Copy the compared variables into cond0 and cond1, so that
1202 any side effects performed in or after the old comparison,
1203 will not affect our compare which will come later. */
1204 /* ??? Is it possible to just use the comparison in the jump
1205 insn? After all, we're going to delete it. We'd have
1206 to modify emit_conditional_move to take a comparison rtx
1207 instead or write a new function. */
1209 /* We want the target to be able to simplify comparisons with
1210 zero (and maybe other constants as well), so don't create
1211 pseudos for them. There's no need to either. */
1215 else
1229 {
1232 /* Save the conditional move sequence but don't emit it
1233 yet. On some machines, like the alpha, it is possible
1234 that temp5 == insn, so next generate the sequence that
1235 saves the compared values and then emit both
1236 sequences ensuring seq1 occurs before seq2. */
1240 /* Now that we can't fail, generate the copy insns that
1241 preserve the compared values. */
1250 /* Insert conditional move after insn, to be sure that
1251 the jump and a possible compare won't be separated */
1254 /* ??? We can also delete the insn that sets X to A.
1255 Flow will do it too though. */
1261 }
1262 else
1264 }
1265 #endif
1267 /* That didn't work, try a store-flag insn.
1269 We further divide the cases into:
1271 1) x = a; if (...) x = b; and either A or B is zero,
1272 2) if (...) x = 0; and jumps are expensive,
1273 3) x = a; if (...) x = b; and A and B are constants where all
1274 the set bits in A are also set in B and jumps are expensive,
1275 4) x = a; if (...) x = b; and A and B non-zero, and jumps are
1276 more expensive, and
1277 5) if (...) x = b; if jumps are even more expensive. */
1281 /* Make the latter case look like
1282 x = x; if (...) x = 0; */
1287 /* If B is zero, OK; if A is zero, can only do (1) if we
1288 can reverse the condition. See if (3) applies possibly
1289 by reversing the condition. Prefer reversing to (4) when
1290 branches are very expensive. */
1294 /* Check that the mask is a power of two,
1295 so that it can probably be generated
1296 with a shift. */
1311 insn)))))
1313 )
1314 {
1318 rtx target;
1320 /* If necessary, reverse the condition. */
1323 else
1326 /* If CVAL is non-zero, normalize to -1. Otherwise, if UVAL
1327 is the constant 1, it is best to just compute the result
1328 directly. If UVAL is constant and STORE_FLAG_VALUE
1329 includes all of its bits, it is best to compute the flag
1330 value unnormalized and `and' it with UVAL. Otherwise,
1331 normalize to -1 and `and' with UVAL. */
1338 /* We will be putting the store-flag insn immediately in
1339 front of the comparison that was originally being done,
1340 so we know all the variables in TEMP4 will be valid.
1341 However, this might be in front of the assignment of
1342 A to VAR. If it is, it would clobber the store-flag
1343 we will be emitting.
1345 Therefore, emit into a temporary which will be copied to
1346 VAR immediately after TEMP. */
1351 VOIDmode,
1354 normalizep);
1356 {
1357 rtx seq;
1363 /* Put the store-flag insns in front of the first insn
1364 used to compute the condition to ensure that we
1365 use the same values of them as the current
1366 comparison. However, the remainder of the insns we
1367 generate will be placed directly in front of the
1368 jump insn, in case any of the pseudos we use
1369 are modified earlier. */
1375 /* Both CVAL and UVAL are non-zero. */
1377 {
1385 else
1386 {
1392 }
1394 /* If we usually make new pseudos, do so here. This
1395 turns out to help machines that have conditional
1396 move insns. */
1397 /* ??? Conditional moves have already been handled.
1398 This may be obsolete. */
1406 }
1408 {
1409 /* We know that either CVAL or UVAL is zero. If
1410 UVAL is zero, negate TARGET and `and' with CVAL.
1411 Otherwise, `and' with UVAL. */
1413 {
1417 }
1423 }
1428 #ifdef HAVE_cc0
1429 /* If INSN uses CC0, we must not separate it from the
1430 insn that sets cc0. */
1433 #endif
1441 }
1442 else
1444 }
1445 }
1447 /* If branches are expensive, convert
1448 if (foo) bar++; to bar += (foo != 0);
1449 and similarly for "bar--;"
1451 INSN is the conditional branch around the arithmetic. We set:
1453 TEMP is the arithmetic insn.
1454 TEMP1 is the SET doing the arithmetic.
1455 TEMP2 is the operand being incremented or decremented.
1456 TEMP3 to the condition being tested.
1457 TEMP4 to the earliest insn used to find the condition. */
1460 #ifdef HAVE_incscc
1461 || HAVE_incscc
1462 #endif
1463 #ifdef HAVE_decscc
1464 || HAVE_decscc
1465 #endif
1466 )
1467 && ! reload_completed
1479 /* INSN must either branch to the insn after TEMP or the insn
1480 after TEMP must branch to the same place as INSN. */
1486 /* We must be comparing objects whose modes imply the size.
1487 We could handle BLKmode if (1) emit_store_flag could
1488 and (2) we could find the size reliably. */
1491 {
1497 /* It must be the case that TEMP2 is not modified in the range
1498 [TEMP4, INSN). The one exception we make is if the insn
1499 before INSN sets TEMP2 to something which is also unchanged
1500 in that range. In that case, we can move the initialization
1501 into our sequence. */
1511 {
1515 }
1521 VOIDmode,
1525 /* If we can do the store-flag, do the addition or
1526 subtraction. */
1535 {
1536 /* Put the result back in temp2 in case it isn't already.
1537 Then replace the jump, possible a CC0-setting insn in
1538 front of the jump, and TEMP, with the sequence we have
1539 made. */
1554 #ifdef HAVE_cc0
1556 #endif
1560 }
1561 else
1563 }
1565 /* Simplify if (...) x = 1; else {...} if (x) ...
1566 We recognize this case scanning backwards as well.
1568 TEMP is the assignment to x;
1569 TEMP1 is the label at the head of the second if. */
1570 /* ?? This should call get_condition to find the values being
1571 compared, instead of looking for a COMPARE insn when HAVE_cc0
1572 is not defined. This would allow it to work on the m88k. */
1573 /* ?? This optimization is only safe before cse is run if HAVE_cc0
1574 is not defined and the condition is tested by a separate compare
1575 insn. This is because the code below assumes that the result
1576 of the compare dies in the following branch.
1578 Not only that, but there might be other insns between the
1579 compare and branch whose results are live. Those insns need
1580 to be executed.
1582 A way to fix this is to move the insns at JUMP_LABEL (insn)
1583 to before INSN. If we are running before flow, they will
1584 be deleted if they aren't needed. But this doesn't work
1585 well after flow.
1587 This is really a special-case of jump threading, anyway. The
1588 right thing to do is to replace this and jump threading with
1589 much simpler code in cse.
1591 This code has been turned off in the non-cc0 case in the
1592 meantime. */
1594 #ifdef HAVE_cc0
1596 /* Safe to skip USE and CLOBBER insns here
1597 since they will not be deleted. */
1605 /* If we find that the next value tested is `x'
1606 (TEMP1 is the insn where this happens), win. */
1609 #ifdef HAVE_cc0
1610 /* Does temp1 `tst' the value of x? */
1614 #else
1615 /* Does temp1 compare the value of x against zero? */
1622 #endif
1624 {
1625 /* Get the if_then_else from the condjump. */
1628 {
1631 rtx cond
1634 rtx ultimate;
1640 else
1650 }
1651 }
1652 #endif
1654 #if 0
1655 /* @@ This needs a bit of work before it will be right.
1657 Any type of comparison can be accepted for the first and
1658 second compare. When rewriting the first jump, we must
1659 compute the what conditions can reach label3, and use the
1660 appropriate code. We can not simply reverse/swap the code
1661 of the first jump. In some cases, the second jump must be
1662 rewritten also.
1664 For example,
1665 < == converts to > ==
1666 < != converts to == >
1667 etc.
1669 If the code is written to only accept an '==' test for the second
1670 compare, then all that needs to be done is to swap the condition
1671 of the first branch.
1673 It is questionable whether we want this optimization anyways,
1674 since if the user wrote code like this because he/she knew that
1675 the jump to label1 is taken most of the time, then rewriting
1676 this gives slower code. */
1677 /* @@ This should call get_condition to find the values being
1678 compared, instead of looking for a COMPARE insn when HAVE_cc0
1679 is not defined. This would allow it to work on the m88k. */
1680 /* @@ This optimization is only safe before cse is run if HAVE_cc0
1681 is not defined and the condition is tested by a separate compare
1682 insn. This is because the code below assumes that the result
1683 of the compare dies in the following branch. */
1685 /* Simplify test a ~= b
1686 condjump label1;
1687 test a == b
1688 condjump label2;
1689 jump label3;
1690 label1:
1692 rewriting as
1693 test a ~~= b
1694 condjump label3
1695 test a == b
1696 condjump label2
1697 label1:
1699 where ~= is an inequality, e.g. >, and ~~= is the swapped
1700 inequality, e.g. <.
1702 We recognize this case scanning backwards.
1704 TEMP is the conditional jump to `label2';
1705 TEMP1 is the test for `a == b';
1706 TEMP2 is the conditional jump to `label1';
1707 TEMP3 is the test for `a ~= b'. */
1716 #ifdef HAVE_cc0
1718 #else
1722 #endif
1736 {
1741 {
1744 }
1748 }
1749 #endif
1750 /* Simplify if (...) {... x = 1;} if (x) ...
1752 We recognize this case backwards.
1754 TEMP is the test of `x';
1755 TEMP1 is the assignment to `x' at the end of the
1756 previous statement. */
1757 /* @@ This should call get_condition to find the values being
1758 compared, instead of looking for a COMPARE insn when HAVE_cc0
1759 is not defined. This would allow it to work on the m88k. */
1760 /* @@ This optimization is only safe before cse is run if HAVE_cc0
1761 is not defined and the condition is tested by a separate compare
1762 insn. This is because the code below assumes that the result
1763 of the compare dies in the following branch. */
1765 /* ??? This has to be turned off. The problem is that the
1766 unconditional jump might indirectly end up branching to the
1767 label between TEMP1 and TEMP. We can't detect this, in general,
1768 since it may become a jump to there after further optimizations.
1769 If that jump is done, it will be deleted, so we will retry
1770 this optimization in the next pass, thus an infinite loop.
1772 The present code prevents this by putting the jump after the
1773 label, but this is not logically correct. */
1774 #if 0
1776 /* Safe to skip USE and CLOBBER insns here
1777 since they will not be deleted. */
1782 #ifdef HAVE_cc0
1785 #else
1786 /* Temp must be a compare insn, we can not accept a register
1787 to register move here, since it may not be simply a
1788 tst insn. */
1794 #endif
1795 /* May skip USE or CLOBBER insns here
1796 for checking for opportunity, since we
1797 take care of them later. */
1801 #ifdef HAVE_cc0
1803 #else
1806 #endif
1808 /* If this isn't true, cse will do the job. */
1810 {
1811 /* Get the if_then_else from the condjump. */
1816 {
1818 rtx last_insn;
1819 rtx ultimate;
1820 rtx p;
1822 /* Get the place that condjump will jump to
1823 if it is reached from here. */
1827 else
1829 /* Get it as a CODE_LABEL. */
1832 else
1833 /* Get the label out of the LABEL_REF. */
1836 /* Insert the jump immediately before TEMP, specifically
1837 after the label that is between TEMP1 and TEMP. */
1840 /* If we would be branching to the next insn, the jump
1841 would immediately be deleted and the re-inserted in
1842 a subsequent pass over the code. So don't do anything
1843 in that case. */
1846 {
1849 last_insn);
1854 {
1858 }
1861 }
1862 }
1863 }
1864 #endif
1865 /* Detect a conditional jump going to the same place
1866 as an immediately following unconditional jump. */
1872 {
1875 /* ??? Optional. Disables some optimizations, but makes
1876 gcov output more accurate with -O. */
1883 {
1887 }
1888 }
1889 /* Detect a conditional jump jumping over an unconditional jump. */
1892 && ! this_is_simplejump
1898 {
1899 /* When we invert the unconditional jump, we will be
1900 decrementing the usage count of its old label.
1901 Make sure that we don't delete it now because that
1902 might cause the following code to be deleted. */
1910 {
1911 /* It is very likely that if there are USE insns before
1912 this jump, they hold REG_DEAD notes. These REG_DEAD
1913 notes are no longer valid due to this optimization,
1914 and will cause the life-analysis that following passes
1915 (notably delayed-branch scheduling) to think that
1916 these registers are dead when they are not.
1918 To prevent this trouble, we just remove the USE insns
1919 from the insn chain. */
1923 {
1927 }
1932 }
1934 /* We can now safely delete the label if it is unreferenced
1935 since the delete_insn above has deleted the BARRIER. */
1939 }
1940 else
1941 {
1942 /* Detect a jump to a jump. */
1947 {
1950 }
1952 /* Look for if (foo) bar; else break; */
1953 /* The insns look like this:
1954 insn = condjump label1;
1955 ...range1 (some insns)...
1956 jump label2;
1957 label1:
1958 ...range2 (some insns)...
1959 jump somewhere unconditionally
1960 label2: */
1961 {
1964 /* Don't do this optimization on the first round, so that
1965 jump-around-a-jump gets simplified before we ask here
1966 whether a jump is unconditional.
1968 Also don't do it when we are called after reload since
1969 it will confuse reorg. */
1972 /* Make sure INSN is something we can invert. */
1979 {
1986 /* Invert the jump condition, so we
1987 still execute the same insns in each case. */
1989 {
1994 rtx rangenext;
1996 /* Include in each range any notes before it, to be
1997 sure that we get the line number note if any, even
1998 if there are other notes here. */
2007 /* Don't move NOTEs for blocks or loops; shift them
2008 outside the ranges, where they'll stay put. */
2012 /* Get current surrounds of the 2 ranges. */
2018 /* Splice range2 where range1 was. */
2023 /* Splice range1 where range2 was. */
2029 /* Check for a loop end note between the end of
2030 range2, and the next code label. If there is one,
2031 then what we have really seen is
2032 if (foo) break; end_of_loop;
2033 and moved the break sequence outside the loop.
2034 We must move the LOOP_END note to where the
2035 loop really ends now, or we will confuse loop
2036 optimization. Stop if we find a LOOP_BEG note
2037 first, since we don't want to move the LOOP_END
2038 note in that case. */
2040 {
2043 {
2046 {
2057 }
2061 }
2062 }
2065 }
2066 }
2067 }
2069 /* Now that the jump has been tensioned,
2070 try cross jumping: check for identical code
2071 before the jump and before its target label. */
2073 /* First, cross jumping of conditional jumps: */
2076 {
2080 /* A conditional jump may be crossjumped
2081 only if the place it jumps to follows
2082 an opposing jump that comes back here. */
2085 /* We have no opposing jump;
2086 cannot cross jump this insn. */
2090 /* TARGET is nonzero if it is ok to cross jump
2091 to code before TARGET. If so, see if matches. */
2097 {
2099 /* Make the old conditional jump
2100 into an unconditional one. */
2105 /* Add to jump_chain unless this is a new label
2106 whose UID is too large. */
2108 {
2112 }
2115 }
2116 }
2118 /* Cross jumping of unconditional jumps:
2119 a few differences. */
2122 {
2124 rtx target;
2128 /* TARGET is nonzero if it is ok to cross jump
2129 to code before TARGET. If so, see if matches. */
2133 /* If cannot cross jump to code before the label,
2134 see if we can cross jump to another jump to
2135 the same label. */
2136 /* Try each other jump to this label. */
2143 /* Ignore TARGET if it's deleted. */
2149 {
2153 }
2154 }
2156 /* This code was dead in the previous jump.c! */
2158 {
2159 /* Return insns all "jump to the same place"
2160 so we can cross-jump between any two of them. */
2166 /* If cannot cross jump to code before the label,
2167 see if we can cross jump to another jump to
2168 the same label. */
2169 /* Try each other jump to this label. */
2180 {
2184 }
2185 }
2186 }
2187 }
2190 }
2192 /* Delete extraneous line number notes.
2193 Note that two consecutive notes for different lines are not really
2194 extraneous. There should be some indication where that line belonged,
2195 even if it became empty. */
2197 {
2202 {
2203 /* Delete this note if it is identical to previous note. */
2207 {
2210 }
2213 }
2214 }
2216 #ifdef HAVE_return
2218 {
2219 /* If we fall through to the epilogue, see if we can insert a RETURN insn
2220 in front of it. If the machine allows it at this point (we might be
2221 after reload for a leaf routine), it will improve optimization for it
2222 to be there. We do this both here and at the start of this pass since
2223 the RETURN might have been deleted by some of our optimizations. */
2229 {
2232 }
2233 }
2234 #endif
2236 /* See if there is still a NOTE_INSN_FUNCTION_END in this function.
2237 If so, delete it, and record that this function can drop off the end. */
2240 {
2243 /* One label can follow the end-note: the return label. */
2245 /* Ordinary insns can follow it if returning a structure. */
2247 /* If machine uses explicit RETURN insns, no epilogue,
2248 then one of them follows the note. */
2251 /* A barrier can follow the return insn. */
2253 /* Other kinds of notes can follow also. */
2257 }
2259 /* Report if control can fall through at the end of the function. */
2262 {
2265 }
2267 /* Show JUMP_CHAIN no longer valid. */
2269 }
2270 \f
2271 /* LOOP_START is a NOTE_INSN_LOOP_BEG note that is followed by an unconditional
2272 jump. Assume that this unconditional jump is to the exit test code. If
2273 the code is sufficiently simple, make a copy of it before INSN,
2274 followed by a jump to the exit of the loop. Then delete the unconditional
2275 jump after INSN.
2277 Return 1 if we made the change, else 0.
2279 This is only safe immediately after a regscan pass because it uses the
2280 values of regno_first_uid and regno_last_uid. */
2282 static int
2284 rtx loop_start;
2285 {
2290 rtx lastexit;
2294 /* Scan the exit code. We do not perform this optimization if any insn:
2296 is a CALL_INSN
2297 is a CODE_LABEL
2298 has a REG_RETVAL or REG_LIBCALL note (hard to adjust)
2299 is a NOTE_INSN_LOOP_BEG because this means we have a nested loop
2300 is a NOTE_INSN_BLOCK_{BEG,END} because duplicating these notes
2301 are not valid
2303 Also, don't do this if the exit code is more than 20 insns. */
2306 insn
2310 {
2312 {
2317 /* We could be in front of the wrong NOTE_INSN_LOOP_END if there is
2318 a jump immediately after the loop start that branches outside
2319 the loop but within an outer loop, near the exit test.
2320 If we copied this exit test and created a phony
2321 NOTE_INSN_LOOP_VTOP, this could make instructions immediately
2322 before the exit test look like these could be safely moved
2323 out of the loop even if they actually may be never executed.
2324 This can be avoided by checking here for NOTE_INSN_LOOP_CONT. */
2341 }
2342 }
2344 /* Unless INSN is zero, we can do the optimization. */
2350 /* See if any insn sets a register only used in the loop exit code and
2351 not a user variable. If so, replace it with a new register. */
2360 {
2366 {
2367 /* We can do the replacement. Allocate reg_map if this is the
2368 first replacement we found. */
2370 {
2373 }
2378 }
2379 }
2381 /* Now copy each insn. */
2384 {
2389 /* Only copy line-number notes. */
2391 {
2394 }
2404 /* Copy all REG_NOTES except REG_LABEL since mark_jump_label will
2405 make them. */
2421 {
2425 }
2427 /* If this is a simple jump, add it to the jump chain. */
2431 {
2435 }
2440 }
2442 /* Now clean up by emitting a jump to the end label and deleting the jump
2443 at the start of the loop. */
2445 {
2447 loop_start);
2451 {
2455 }
2457 }
2459 /* Mark the exit code as the virtual top of the converted loop. */
2465 }
2466 \f
2467 /* Move all block-beg, block-end, loop-beg, loop-cont, loop-vtop, and
2468 loop-end notes between START and END out before START. Assume that
2469 END is not such a note. START may be such a note. Returns the value
2470 of the new starting insn, which may be different if the original start
2471 was such a note. */
2473 rtx
2476 {
2477 rtx insn;
2478 rtx next;
2481 {
2490 {
2493 else
2494 {
2502 }
2503 }
2504 }
2507 }
2508 \f
2509 /* Compare the instructions before insn E1 with those before E2
2510 to find an opportunity for cross jumping.
2511 (This means detecting identical sequences of insns followed by
2512 jumps to the same place, or followed by a label and a jump
2513 to that label, and replacing one with a jump to the other.)
2515 Assume E1 is a jump that jumps to label E2
2516 (that is not always true but it might as well be).
2517 Find the longest possible equivalent sequences
2518 and store the first insns of those sequences into *F1 and *F2.
2519 Store zero there if no equivalent preceding instructions are found.
2521 We give up if we find a label in stream 1.
2522 Actually we could transfer that label into stream 2. */
2524 static void
2529 {
2536 rtx prev1;
2542 {
2552 /* Don't allow the range of insns preceding E1 or E2
2553 to include the other (E2 or E1). */
2557 /* If we will get to this code by jumping, those jumps will be
2558 tensioned to go directly to the new label (before I2),
2559 so this cross-jumping won't cost extra. So reduce the minimum. */
2561 {
2564 }
2572 /* If this is a CALL_INSN, compare register usage information.
2573 If we don't check this on stack register machines, the two
2574 CALL_INSNs might be merged leaving reg-stack.c with mismatching
2575 numbers of stack registers in the same basic block.
2576 If we don't check this on machines with delay slots, a delay slot may
2577 be filled that clobbers a parameter expected by the subroutine.
2579 ??? We take the simple route for now and assume that if they're
2580 equal, they were constructed identically. */
2587 #ifdef STACK_REGS
2588 /* If cross_jump_death_matters is not 0, the insn's mode
2589 indicates whether or not the insn contains any stack-like
2590 regs. */
2593 {
2594 /* If register stack conversion has already been done, then
2595 death notes must also be compared before it is certain that
2596 the two instruction streams match. */
2598 rtx note;
2618 done:
2619 ;
2620 }
2621 #endif
2623 /* Don't allow old-style asm or volatile extended asms to be accepted
2624 for cross jumping purposes. It is conceptually correct to allow
2625 them, since cross-jumping preserves the dynamic instruction order
2626 even though it is changing the static instruction order. However,
2627 if an asm is being used to emit an assembler pseudo-op, such as
2628 the MIPS `.set reorder' pseudo-op, then the static instruction order
2629 matters and it must be preserved. */
2637 {
2638 /* The following code helps take care of G++ cleanups. */
2639 rtx equiv1;
2640 rtx equiv2;
2647 /* If the equivalences are not to a constant, they may
2648 reference pseudos that no longer exist, so we can't
2649 use them. */
2652 {
2657 {
2664 }
2665 }
2667 /* Insns fail to match; cross jumping is limited to the following
2668 insns. */
2670 #ifdef HAVE_cc0
2671 /* Don't allow the insn after a compare to be shared by
2672 cross-jumping unless the compare is also shared.
2673 Here, if either of these non-matching insns is a compare,
2674 exclude the following insn from possible cross-jumping. */
2677 #endif
2679 /* If cross-jumping here will feed a jump-around-jump
2680 optimization, this jump won't cost extra, so reduce
2681 the minimum. */
2687 }
2689 win:
2691 {
2692 /* Ok, this insn is potentially includable in a cross-jump here. */
2695 }
2696 }
2700 }
2702 static void
2705 {
2706 /* Find an existing label at this point
2707 or make a new one if there is none. */
2710 /* Make the same jump insn jump to the new point. */
2712 {
2713 /* Remove from jump chain of returns. */
2715 /* Change the insn. */
2720 /* Add to new the jump chain. */
2723 {
2726 }
2727 }
2728 else
2731 /* Delete the matching insns before the jump. Also, remove any REG_EQUAL
2732 or REG_EQUIV note in the NEWLPOS stream that isn't also present in
2733 the NEWJPOS stream. */
2736 {
2737 rtx lnote;
2749 }
2750 }
2751 \f
2752 /* Return the label before INSN, or put a new label there. */
2754 rtx
2756 rtx insn;
2757 {
2758 rtx label;
2760 /* Find an existing label at this point
2761 or make a new one if there is none. */
2765 {
2771 }
2773 }
2775 /* Return the label after INSN, or put a new label there. */
2777 rtx
2779 rtx insn;
2780 {
2781 rtx label;
2783 /* Find an existing label at this point
2784 or make a new one if there is none. */
2788 {
2792 }
2794 }
2795 \f
2796 /* Return 1 if INSN is a jump that jumps to right after TARGET
2797 only on the condition that TARGET itself would drop through.
2798 Assumes that TARGET is a conditional jump. */
2800 static int
2803 {
2819 {
2823 }
2826 {
2830 }
2835 }
2836 \f
2837 /* Given a comparison, COMPARISON, inside a conditional jump insn, INSN,
2838 return non-zero if it is safe to reverse this comparison. It is if our
2839 floating-point is not IEEE, if this is an NE or EQ comparison, or if
2840 this is known to be an integer comparison. */
2842 int
2844 rtx comparison;
2845 rtx insn;
2846 {
2847 rtx arg0;
2849 /* If this is not actually a comparison, we can't reverse it. */
2854 /* If this is an NE comparison, it is safe to reverse it to an EQ
2855 comparison and vice versa, even for floating point. If no operands
2856 are NaNs, the reversal is valid. If some operand is a NaN, EQ is
2857 always false and NE is always true, so the reversal is also valid. */
2858 || flag_fast_math
2865 /* Make sure ARG0 is one of the actual objects being compared. If we
2866 can't do this, we can't be sure the comparison can be reversed.
2868 Handle cc0 and a MODE_CC register. */
2870 #ifdef HAVE_cc0
2872 #endif
2873 )
2874 {
2885 }
2887 /* We can reverse this if ARG0 is a CONST_INT or if its mode is
2888 not VOIDmode and neither a MODE_CC nor MODE_FLOAT type. */
2893 }
2895 /* Given an rtx-code for a comparison, return the code
2896 for the negated comparison.
2897 WATCH OUT! reverse_condition is not safe to use on a jump
2898 that might be acting on the results of an IEEE floating point comparison,
2899 because of the special treatment of non-signaling nans in comparisons.
2900 Use can_reverse_comparison_p to be sure. */
2902 enum rtx_code
2905 {
2907 {
2941 }
2942 }
2944 /* Similar, but return the code when two operands of a comparison are swapped.
2945 This IS safe for IEEE floating-point. */
2947 enum rtx_code
2950 {
2952 {
2984 }
2985 }
2987 /* Given a comparison CODE, return the corresponding unsigned comparison.
2988 If CODE is an equality comparison or already an unsigned comparison,
2989 CODE is returned. */
2991 enum rtx_code
2994 {
2996 {
3019 }
3020 }
3022 /* Similarly, return the signed version of a comparison. */
3024 enum rtx_code
3027 {
3029 {
3052 }
3053 }
3054 \f
3055 /* Return non-zero if CODE1 is more strict than CODE2, i.e., if the
3056 truth of CODE1 implies the truth of CODE2. */
3058 int
3061 {
3066 {
3094 }
3097 }
3098 \f
3099 /* Return 1 if INSN is an unconditional jump and nothing else. */
3101 int
3103 rtx insn;
3104 {
3109 }
3111 /* Return nonzero if INSN is a (possibly) conditional jump
3112 and nothing more. */
3114 int
3116 rtx insn;
3117 {
3136 }
3138 /* Return nonzero if INSN is a (possibly) conditional jump
3139 and nothing more. */
3141 int
3143 rtx insn;
3144 {
3149 else
3169 }
3171 /* Return 1 if X is an RTX that does nothing but set the condition codes
3172 and CLOBBER or USE registers.
3173 Return -1 if X does explicitly set the condition codes,
3174 but also does other things. */
3176 int
3178 rtx x;
3179 {
3180 #ifdef HAVE_cc0
3184 {
3189 {
3195 }
3197 }
3199 #else
3201 #endif
3202 }
3203 \f
3204 /* Follow any unconditional jump at LABEL;
3205 return the ultimate label reached by any such chain of jumps.
3206 If LABEL is not followed by a jump, return LABEL.
3207 If the chain loops or we can't find end, return LABEL,
3208 since that tells caller to avoid changing the insn.
3210 If RELOAD_COMPLETED is 0, we do not chain across a NOTE_INSN_LOOP_BEG or
3211 a USE or CLOBBER. */
3213 rtx
3215 rtx label;
3216 {
3230 depth++)
3231 {
3232 /* Don't chain through the insn that jumps into a loop
3233 from outside the loop,
3234 since that would create multiple loop entry jumps
3235 and prevent loop optimization. */
3236 rtx tem;
3241 /* ??? Optional. Disables some optimizations, but makes
3242 gcov output more accurate with -O. */
3246 /* If we have found a cycle, make the insn jump to itself. */
3256 }
3260 }
3262 /* Assuming that field IDX of X is a vector of label_refs,
3263 replace each of them by the ultimate label reached by it.
3264 Return nonzero if a change is made.
3265 If IGNORE_LOOPS is 0, we do not chain across a NOTE_INSN_LOOP_BEG. */
3267 static int
3271 {
3275 {
3279 {
3285 }
3286 }
3288 }
3289 \f
3290 /* Find all CODE_LABELs referred to in X, and increment their use counts.
3291 If INSN is a JUMP_INSN and there is at least one CODE_LABEL referenced
3292 in INSN, then store one of them in JUMP_LABEL (INSN).
3293 If INSN is an INSN or a CALL_INSN and there is at least one CODE_LABEL
3294 referenced in INSN, add a REG_LABEL note containing that label to INSN.
3295 Also, when there are consecutive labels, canonicalize on the last of them.
3297 Note that two labels separated by a loop-beginning note
3298 must be kept distinct if we have not yet done loop-optimization,
3299 because the gap between them is where loop-optimize
3300 will want to move invariant code to. CROSS_JUMP tells us
3301 that loop-optimization is done with.
3303 Once reload has completed (CROSS_JUMP non-zero), we need not consider
3304 two labels distinct if they are separated by only USE or CLOBBER insns. */
3306 static void
3309 rtx insn;
3311 {
3317 {
3330 /* If this is a constant-pool reference, see if it is a label. */
3337 {
3340 rtx note;
3341 rtx next;
3346 /* Ignore references to labels of containing functions. */
3350 /* If there are other labels following this one,
3351 replace it with the last of the consecutive labels. */
3353 {
3365 /* ??? Optional. Disables some optimizations, but
3366 makes gcov output more accurate with -O. */
3369 }
3375 {
3379 /* If we've changed OLABEL and we had a REG_LABEL note
3380 for it, update it as well. */
3385 /* Otherwise, add a REG_LABEL note for LABEL unless there already
3386 is one. */
3388 {
3390 /* Don't record labels that refer to dispatch tables.
3391 This is not necessary, since the tablejump
3392 references the same label.
3393 And if we did record them, flow.c would make worse code. */
3400 }
3401 }
3403 }
3405 /* Do walk the labels in a vector, but not the first operand of an
3406 ADDR_DIFF_VEC. Don't set the JUMP_LABEL of a vector. */
3409 {
3414 }
3419 }
3423 {
3427 {
3431 }
3432 }
3433 }
3435 /* If all INSN does is set the pc, delete it,
3436 and delete the insn that set the condition codes for it
3437 if that's what the previous thing was. */
3439 void
3441 rtx insn;
3442 {
3447 }
3449 /* Delete INSN and recursively delete insns that compute values used only
3450 by INSN. This uses the REG_DEAD notes computed during flow analysis.
3451 If we are running before flow.c, we need do nothing since flow.c will
3452 delete dead code. We also can't know if the registers being used are
3453 dead or not at this point.
3455 Otherwise, look at all our REG_DEAD notes. If a previous insn does
3456 nothing other than set a register that dies in this insn, we can delete
3457 that insn as well.
3459 On machines with CC0, if CC0 is used in this insn, we may be able to
3460 delete the insn that set it. */
3462 static void
3464 rtx insn;
3465 {
3468 #ifdef HAVE_cc0
3470 {
3472 /* We assume that at this stage
3473 CC's are always set explicitly
3474 and always immediately before the jump that
3475 will use them. So if the previous insn
3476 exists to set the CC's, delete it
3477 (unless it performs auto-increments, etc.). */
3480 {
3484 else
3485 /* Otherwise, show that cc0 won't be used. */
3488 }
3489 }
3490 #endif
3493 {
3494 rtx our_prev;
3499 /* Verify that the REG_NOTE is legitimate. */
3506 {
3507 /* If we reach a SEQUENCE, it is too complex to try to
3508 do anything with it, so give up. */
3514 /* reorg creates USEs that look like this. We leave them
3515 alone because reorg needs them for its own purposes. */
3519 {
3524 {
3525 /* If we find a SET of something else, we can't
3526 delete the insn. */
3531 {
3537 }
3541 }
3547 }
3549 /* If OUR_PREV references the register that dies here, it is an
3550 additional use. Hence any prior SET isn't dead. However, this
3551 insn becomes the new place for the REG_DEAD note. */
3554 {
3558 }
3559 }
3560 }
3563 }
3564 \f
3565 /* Delete insn INSN from the chain of insns and update label ref counts.
3566 May delete some following insns as a consequence; may even delete
3567 a label elsewhere and insns that follow it.
3569 Returns the first insn after INSN that was not deleted. */
3571 rtx
3574 {
3583 /* This insn is already deleted => return first following nondeleted. */
3587 /* Don't delete user-declared labels. Convert them to special NOTEs
3588 instead. */
3591 {
3596 }
3597 else
3598 /* Mark this insn as deleted. */
3601 /* If this is an unconditional jump, delete it from the jump chain. */
3605 /* If instruction is followed by a barrier,
3606 delete the barrier too. */
3609 {
3612 }
3614 /* Patch out INSN (and the barrier if any) */
3617 {
3619 {
3624 }
3627 {
3631 }
3635 }
3637 /* If deleting a jump, decrement the count of the label,
3638 and delete the label if it is now unused. */
3642 {
3643 /* This can delete NEXT or PREV,
3644 either directly if NEXT is JUMP_LABEL (INSN),
3645 or indirectly through more levels of jumps. */
3647 /* I feel a little doubtful about this loop,
3648 but I see no clean and sure alternative way
3649 to find the first insn after INSN that is not now deleted.
3650 I hope this works. */
3654 }
3656 /* Likewise if we're deleting a dispatch table. */
3661 {
3672 }
3677 /* If INSN was a label and a dispatch table follows it,
3678 delete the dispatch table. The tablejump must have gone already.
3679 It isn't useful to fall through into a table. */
3688 /* If INSN was a label, delete insns following it if now unreachable. */
3691 {
3697 {
3701 /* Keep going past other deleted labels to delete what follows. */
3704 else
3705 /* Note: if this deletes a jump, it can cause more
3706 deletion of unreachable code, after a different label.
3707 As long as the value from this recursive call is correct,
3708 this invocation functions correctly. */
3710 }
3711 }
3714 }
3716 /* Advance from INSN till reaching something not deleted
3717 then return that. May return INSN itself. */
3719 rtx
3721 rtx insn;
3722 {
3726 }
3727 \f
3728 /* Delete a range of insns from FROM to TO, inclusive.
3729 This is for the sake of peephole optimization, so assume
3730 that whatever these insns do will still be done by a new
3731 peephole insn that will replace them. */
3733 void
3736 {
3740 {
3745 {
3748 /* Patch this insn out of the chain. */
3749 /* We don't do this all at once, because we
3750 must preserve all NOTEs. */
3756 }
3761 }
3763 /* Note that if TO is an unconditional jump
3764 we *do not* delete the BARRIER that follows,
3765 since the peephole that replaces this sequence
3766 is also an unconditional jump in that case. */
3767 }
3768 \f
3769 /* Invert the condition of the jump JUMP, and make it jump
3770 to label NLABEL instead of where it jumps now. */
3772 int
3775 {
3776 /* We have to either invert the condition and change the label or
3777 do neither. Either operation could fail. We first try to invert
3778 the jump. If that succeeds, we try changing the label. If that fails,
3779 we invert the jump back to what it was. */
3785 {
3787 {
3790 /* An inverted jump means that a probability taken becomes a
3791 probability not taken. Subtract the branch probability from the
3792 probability base to convert it back to a taken probability.
3793 (We don't flip the probability on a branch that's never taken. */
3796 }
3799 }
3802 /* This should just be putting it back the way it was. */
3806 }
3808 /* Invert the jump condition of rtx X contained in jump insn, INSN.
3810 Return 1 if we can do so, 0 if we cannot find a way to do so that
3811 matches a pattern. */
3813 int
3815 rtx x;
3816 rtx insn;
3817 {
3825 {
3829 /* We can do this in two ways: The preferable way, which can only
3830 be done if this is not an integer comparison, is to reverse
3831 the comparison code. Otherwise, swap the THEN-part and ELSE-part
3832 of the IF_THEN_ELSE. If we can't do either, fail. */
3845 }
3849 {
3854 {
3859 }
3860 }
3863 }
3864 \f
3865 /* Make jump JUMP jump to label NLABEL instead of where it jumps now.
3866 If the old jump target label is unused as a result,
3867 it and the code following it may be deleted.
3869 If NLABEL is zero, we are to turn the jump into a (possibly conditional)
3870 RETURN insn.
3872 The return value will be 1 if the change was made, 0 if it wasn't (this
3873 can only occur for NLABEL == 0). */
3875 int
3878 {
3887 /* If this is an unconditional branch, delete it from the jump_chain of
3888 OLABEL and add it to the jump_chain of NLABEL (assuming both labels
3889 have UID's in range and JUMP_CHAIN is valid). */
3892 {
3898 {
3901 }
3902 }
3912 }
3914 /* Delete the instruction JUMP from any jump chain it might be on. */
3916 static void
3918 rtx jump;
3919 {
3923 /* Handle unconditional jumps. */
3928 /* Handle return insns. */
3935 else
3936 {
3937 rtx insn;
3943 {
3946 }
3947 }
3948 }
3950 /* If NLABEL is nonzero, throughout the rtx at LOC,
3951 alter (LABEL_REF OLABEL) to (LABEL_REF NLABEL). If OLABEL is
3952 zero, alter (RETURN) to (LABEL_REF NLABEL).
3954 If NLABEL is zero, alter (LABEL_REF OLABEL) to (RETURN) and check
3955 validity with validate_change. Convert (set (pc) (label_ref olabel))
3956 to (return).
3958 Return 0 if we found a change we would like to make but it is invalid.
3959 Otherwise, return 1. */
3961 int
3965 rtx insn;
3966 {
3973 {
3975 {
3978 else
3981 }
3982 }
3984 {
3989 }
3998 {
4003 {
4008 }
4009 }
4012 }
4013 \f
4014 /* Make jump JUMP jump to label NLABEL, assuming it used to be a tablejump.
4016 If the old jump target label (before the dispatch table) becomes unused,
4017 it and the dispatch table may be deleted. In that case, find the insn
4018 before the jump references that label and delete it and logical successors
4019 too. */
4021 static void
4024 {
4027 /* Add this jump to the jump_chain of NLABEL. */
4030 {
4033 }
4041 {
4044 }
4045 }
4047 /* Find the insn referencing LABEL that is a logical predecessor of INSN.
4048 If we found one, delete it and then delete this insn if DELETE_THIS is
4049 non-zero. Return non-zero if INSN or a predecessor references LABEL. */
4051 static int
4055 {
4057 rtx link;
4061 {
4063 {
4066 }
4067 else
4069 }
4073 {
4075 {
4078 }
4079 else
4081 }
4084 }
4085 \f
4086 /* Like rtx_equal_p except that it considers two REGs as equal
4087 if they renumber to the same value and considers two commutative
4088 operations to be the same if the order of the operands has been
4089 reversed. */
4091 int
4094 {
4105 {
4112 /* If we haven't done any renumbering, don't
4113 make any assumptions. */
4118 {
4123 {
4126 }
4127 }
4129 else
4130 {
4134 }
4137 {
4142 {
4145 }
4146 }
4148 else
4149 {
4153 }
4156 }
4158 /* Now we have disposed of all the cases
4159 in which different rtx codes can match. */
4164 {
4175 /* We can't assume nonlocal labels have their following insns yet. */
4179 /* Two label-refs are equivalent if they point at labels
4180 in the same position in the instruction stream. */
4189 }
4191 /* (MULT:SI x y) and (MULT:HI x y) are NOT equivalent. */
4196 /* For commutative operations, the RTX match if the operand match in any
4197 order. Also handle the simple binary and unary cases without a loop. */
4209 /* Compare the elements. If any pair of corresponding elements
4210 fail to match, return 0 for the whole things. */
4214 {
4217 {
4241 /* fall through. */
4255 }
4256 }
4258 }
4259 \f
4260 /* If X is a hard register or equivalent to one or a subregister of one,
4261 return the hard register number. If X is a pseudo register that was not
4262 assigned a hard register, return the pseudo register number. Otherwise,
4263 return -1. Any rtx is valid for X. */
4265 int
4267 rtx x;
4268 {
4270 {
4274 }
4276 {
4280 }
4282 }
4283 \f
4284 /* Optimize code of the form:
4286 for (x = a[i]; x; ...)
4287 ...
4288 for (x = a[i]; x; ...)
4289 ...
4290 foo:
4292 Loop optimize will change the above code into
4294 if (x = a[i])
4295 for (;;)
4296 { ...; if (! (x = ...)) break; }
4297 if (x = a[i])
4298 for (;;)
4299 { ...; if (! (x = ...)) break; }
4300 foo:
4302 In general, if the first test fails, the program can branch
4303 directly to `foo' and skip the second try which is doomed to fail.
4304 We run this after loop optimization and before flow analysis. */
4306 /* When comparing the insn patterns, we track the fact that different
4307 pseudo-register numbers may have been used in each computation.
4308 The following array stores an equivalence -- same_regs[I] == J means
4309 that pseudo register I was used in the first set of tests in a context
4310 where J was used in the second set. We also count the number of such
4311 pending equivalences. If nonzero, the expressions really aren't the
4312 same. */
4318 /* Track any registers modified between the target of the first jump and
4319 the second jump. They never compare equal. */
4323 /* Record if memory was modified. */
4327 /* Called via note_stores on each insn between the target of the first
4328 branch and the second branch. It marks any changed registers. */
4330 static void
4332 rtx dest;
4333 rtx x;
4334 {
4349 else
4352 }
4354 /* F is the first insn in the chain of insns. */
4356 void
4358 rtx f;
4361 {
4362 /* Basic algorithm is to find a conditional branch,
4363 the label it may branch to, and the branch after
4364 that label. If the two branches test the same condition,
4365 walk back from both branch paths until the insn patterns
4366 differ, or code labels are hit. If we make it back to
4367 the target of the first branch, then we know that the first branch
4368 will either always succeed or always fail depending on the relative
4369 senses of the two branches. So adjust the first branch accordingly
4370 in this case. */
4379 /* Allocate register tables and quick-reset table. */
4387 {
4391 {
4392 /* Get to a candidate branch insn. */
4407 /* Look for a branch after the target. Record any registers and
4408 memory modified between the target and the branch. Stop when we
4409 get to a label since we can't know what was changed there. */
4411 {
4416 {
4417 /* If this is an unconditional jump and is the only use of
4418 its target label, we can follow it. */
4422 {
4425 }
4426 else
4428 }
4434 {
4443 }
4446 }
4448 /* Check the next candidate branch insn from the label
4449 of the first. */
4457 /* Get the comparison codes and operands, reversing the
4458 codes if appropriate. If we don't have comparison codes,
4459 we can't do anything. */
4472 /* If they test the same things and knowing that B1 branches
4473 tells us whether or not B2 branches, check if we
4474 can thread the branch. */
4481 b1))))
4482 {
4487 {
4489 {
4490 /* We have reached the target of the first branch.
4491 If there are no pending register equivalents,
4492 we know that this branch will either always
4493 succeed (if the senses of the two branches are
4494 the same) or always fail (if not). */
4495 rtx new_label;
4502 else
4506 {
4511 {
4512 /* Don't thread to the loop label. If a loop
4513 label is reused, loop optimization will
4514 be disabled for that loop. */
4517 }
4519 }
4521 }
4523 /* If either of these is not a normal insn (it might be
4524 a JUMP_INSN, CALL_INSN, or CODE_LABEL) we fail. (NOTEs
4525 have already been skipped above.) Similarly, fail
4526 if the insns are different. */
4535 }
4536 }
4537 }
4538 }
4539 }
4540 \f
4541 /* This is like RTX_EQUAL_P except that it knows about our handling of
4542 possibly equivalent registers and knows to consider volatile and
4543 modified objects as not equal.
4545 YINSN is the insn containing Y. */
4547 int
4550 rtx yinsn;
4551 {
4558 /* Rtx's of different codes cannot be equal. */
4562 /* (MULT:SI x y) and (MULT:HI x y) are NOT equivalent.
4563 (REG:SI x) and (REG:HI x) are NOT equivalent. */
4568 /* For floating-point, consider everything unequal. This is a bit
4569 pessimistic, but this pass would only rarely do anything for FP
4570 anyway. */
4575 /* For commutative operations, the RTX match if the operand match in any
4576 order. Also handle the simple binary and unary cases without a loop. */
4588 /* Handle special-cases first. */
4590 {
4595 /* If neither is user variable or hard register, check for possible
4596 equivalence. */
4603 {
4605 num_same_regs++;
4607 /* If this is the first time we are seeing a register on the `Y'
4608 side, see if it is the last use. If not, we can't thread the
4609 jump, so mark it as not equivalent. */
4614 }
4615 else
4621 /* If memory modified or either volatile, not equivalent.
4622 Else, check address. */
4635 /* Cancel a pending `same_regs' if setting equivalenced registers.
4636 Then process source. */
4639 {
4641 {
4643 num_same_regs--;
4644 }
4647 }
4648 else
4662 }
4669 {
4671 {
4685 /* Two vectors must have the same length. */
4689 /* And the corresponding elements must match. */
4708 /* These are just backpointers, so they don't matter. */
4714 /* It is believed that rtx's at this level will never
4715 contain anything but integers and other rtx's,
4716 except for within LABEL_REFs and SYMBOL_REFs. */
4719 }
4720 }
4722 }
4723 \f
4725 /* Return the insn that NEW can be safely inserted in front of starting at
4726 the jump insn INSN. Return 0 if it is not safe to do this jump
4727 optimization. Note that NEW must contain a single set. */
4729 static rtx
4731 rtx insn;
4733 {
4735 rtx prev;
4737 /* If NEW does not clobber, it is safe to insert NEW before INSN. */
4744 insn))
4750 /* There is a good chance that the previous insn PREV sets the thing
4751 being clobbered (often the CC in a hard reg). If PREV does not
4752 use what NEW sets, we can insert NEW before PREV. */
4758 insn)
4760 prev))
4764 }