| blob | e1382b38e87755920d8b477f99c70e5ce7c61aad |
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. */
65 /* ??? Eventually must record somehow the labels used by jumps
66 from nested functions. */
67 /* Pre-record the next or previous real insn for each label?
68 No, this pass is very fast anyway. */
69 /* Condense consecutive labels?
70 This would make life analysis faster, maybe. */
71 /* Optimize jump y; x: ... y: jumpif... x?
72 Don't know if it is worth bothering with. */
73 /* Optimize two cases of conditional jump to conditional jump?
74 This can never delete any instruction or make anything dead,
75 or even change what is live at any point.
76 So perhaps let combiner do it. */
78 /* Vector indexed by uid.
79 For each CODE_LABEL, index by its uid to get first unconditional jump
80 that jumps to the label.
81 For each JUMP_INSN, index by its uid to get the next unconditional jump
82 that jumps to the same label.
83 Element 0 is the start of a chain of all return insns.
84 (It is safe to use element 0 because insn uid 0 is not used. */
88 /* List of labels referred to from initializers.
89 These can never be deleted. */
90 rtx forced_labels;
92 /* Maximum index in jump_chain. */
96 /* Set nonzero by jump_optimize if control can fall through
97 to the end of the function. */
100 /* Indicates whether death notes are significant in cross jump analysis.
101 Normally they are not significant, because of A and B jump to C,
102 and R dies in A, it must die in B. But this might not be true after
103 stack register conversion, and we must compare death notes in that
104 case. */
118 \f
119 /* Delete no-op jumps and optimize jumps to jumps
120 and jumps around jumps.
121 Delete unused labels and unreachable code.
123 If CROSS_JUMP is 1, detect matching code
124 before a jump and its destination and unify them.
125 If CROSS_JUMP is 2, do cross-jumping, but pay attention to death notes.
127 If NOOP_MOVES is nonzero, delete no-op move insns.
129 If AFTER_REGSCAN is nonzero, then this jump pass is being run immediately
130 after regscan, and it is safe to use regno_first_uid and regno_last_uid.
132 If `optimize' is zero, don't change any code,
133 just determine whether control drops off the end of the function.
134 This case occurs when we have -W and not -O.
135 It works because `delete_insn' checks the value of `optimize'
136 and refrains from actually deleting when that is 0. */
138 void
140 rtx f;
144 {
149 rtx last_insn;
153 /* Initialize LABEL_NUSES and JUMP_LABEL fields. Delete any REG_LABEL
154 notes whose labels don't occur in the insn any more. */
157 {
164 {
169 }
173 }
175 max_uid++;
177 /* Delete insns following barriers, up to next label. */
180 {
182 {
185 {
189 else
191 }
192 /* INSN is now the code_label. */
193 }
194 else
196 }
198 /* Leave some extra room for labels and duplicate exit test insns
199 we make. */
204 /* Mark the label each jump jumps to.
205 Combine consecutive labels, and count uses of labels.
207 For each label, make a chain (using `jump_chain')
208 of all the *unconditional* jumps that jump to it;
209 also make a chain of all returns. */
214 {
217 {
219 {
223 }
225 {
228 }
229 }
230 }
232 /* Keep track of labels used from static data;
233 they cannot ever be deleted. */
240 /* Keep track of labels used for marking handlers for exception
241 regions; they cannot usually be deleted. */
248 /* Delete all labels already not referenced.
249 Also find the last insn. */
253 {
256 else
257 {
260 }
261 }
264 {
265 /* See if there is still a NOTE_INSN_FUNCTION_END in this function.
266 If so record that this function can drop off the end. */
269 {
272 /* One label can follow the end-note: the return label. */
274 /* Ordinary insns can follow it if returning a structure. */
276 /* If machine uses explicit RETURN insns, no epilogue,
277 then one of them follows the note. */
280 /* A barrier can follow the return insn. */
282 /* Other kinds of notes can follow also. */
286 }
288 /* Report if control can fall through at the end of the function. */
294 /* Zero the "deleted" flag of all the "deleted" insns. */
298 }
300 #ifdef HAVE_return
302 {
303 /* If we fall through to the epilogue, see if we can insert a RETURN insn
304 in front of it. If the machine allows it at this point (we might be
305 after reload for a leaf routine), it will improve optimization for it
306 to be there. */
312 {
315 }
316 }
317 #endif
321 {
325 {
328 /* Combine stack_adjusts with following push_insns. */
329 #ifdef PUSH_ROUNDING
336 {
337 rtx p;
343 /* Find all successive push insns. */
345 /* Don't convert more than three pushes;
346 that starts adding too many displaced addresses
347 and the whole thing starts becoming a losing
348 proposition. */
350 {
359 /* Allow a no-op move between the adjust and the push. */
368 pushes++;
373 }
375 /* Discard the amount pushed from the stack adjust;
376 maybe eliminate it entirely. */
378 {
381 }
382 else
386 /* Change the appropriate push insns to ordinary stores. */
389 {
403 /* If this push doesn't fully fit in the space
404 of the stack adjust that we deleted,
405 make another stack adjust here for what we
406 didn't use up. There should be peepholes
407 to recognize the resulting sequence of insns. */
409 {
412 p);
414 }
417 }
418 }
419 #endif
421 /* Detect and delete no-op move instructions
422 resulting from not allocating a parameter in a register. */
435 /* Detect and ignore no-op move instructions
436 resulting from smart or fortuitous register allocation. */
439 {
446 {
447 rtx trial;
454 {
455 /* DREG may have been the target of a REG_DEAD note in
456 the insn which makes INSN redundant. If so, reorg
457 would still think it is dead. So search for such a
458 note and delete it if we find it. */
464 {
467 }
468 #ifdef PRESERVE_DEATH_INFO_REGNO_P
469 /* Deleting insn could lose a death-note for SREG
470 so don't do it if final needs accurate
471 death-notes. */
474 {
475 /* Change this into a USE so that we won't emit
476 code for it, but still can keep the note. */
480 /* Remove all reg notes but the REG_DEAD one. */
483 }
484 else
485 #endif
487 }
488 }
493 {
494 /* This handles the case where we have two consecutive
495 assignments of the same constant to pseudos that didn't
496 get a hard reg. Each SET from the constant will be
497 converted into a SET of the spill register and an
498 output reload will be made following it. This produces
499 two loads of the same constant into the same spill
500 register. */
504 /* Look back for a death note for the first reg.
505 If there is one, it is no longer accurate. */
507 {
511 {
514 }
516 }
518 /* Delete the second load of the value. */
520 }
521 }
523 {
524 /* If each part is a set between two identical registers or
525 a USE or CLOBBER, delete the insn. */
527 rtx tem;
530 {
540 }
544 }
545 /* Also delete insns to store bit fields if they are no-ops. */
546 /* Not worth the hair to detect this in the big-endian case. */
555 }
557 }
559 /* If we haven't yet gotten to reload and we have just run regscan,
560 delete any insn that sets a register that isn't used elsewhere.
561 This helps some of the optimizations below by having less insns
562 being jumped around. */
566 {
574 /* We use regno_last_note_uid so as not to delete the setting
575 of a reg that's used in notes. A subsequent optimization
576 might arrange to use that reg for real. */
581 }
583 /* Now iterate optimizing jumps until nothing changes over one pass. */
586 {
590 {
591 rtx reallabelprev;
593 rtx nlabel;
596 #if 0
597 /* If NOT the first iteration, if this is the last jump pass
598 (just before final), do the special peephole optimizations.
599 Avoiding the first iteration gives ordinary jump opts
600 a chance to work before peephole opts. */
605 #endif
607 /* That could have deleted some insns after INSN, so check now
608 what the following insn is. */
612 /* See if this is a NOTE_INSN_LOOP_BEG followed by an unconditional
613 jump. Try to optimize by duplicating the loop exit test if so.
614 This is only safe immediately after regscan, because it uses
615 the values of regno_first_uid and regno_last_uid. */
620 {
623 {
627 }
628 }
637 /* Tension the labels in dispatch tables. */
644 /* If a dispatch table always goes to the same place,
645 get rid of it and replace the insn that uses it. */
649 {
664 /* Don't mess with a casesi insn. */
669 {
673 }
674 }
678 /* If a jump references the end of the function, try to turn
679 it into a RETURN insn, possibly a conditional one. */
686 /* Detect jump to following insn. */
688 {
693 }
695 /* If we have an unconditional jump preceded by a USE, try to put
696 the USE before the target and jump there. This simplifies many
697 of the optimizations below since we don't have to worry about
698 dealing with these USE insns. We only do this if the label
699 being branch to already has the identical USE or if code
700 never falls through to that label. */
709 /* Don't do this optimization if we have a loop containing only
710 the USE instruction, and the loop start label has a usage
711 count of 1. This is because we will redo this optimization
712 everytime through the outer loop, and jump opt will never
713 exit. */
717 {
719 {
722 }
728 }
730 /* Simplify if (...) x = a; else x = b; by converting it
731 to x = b; if (...) x = a;
732 if B is sufficiently simple, the test doesn't involve X,
733 and nothing in the test modifies B or X.
735 If we have small register classes, we also can't do this if X
736 is a hard register.
738 If the "x = b;" insn has any REG_NOTES, we don't do this because
739 of the possibility that we are running after CSE and there is a
740 REG_EQUAL note that is only valid if the branch has already been
741 taken. If we move the insn with the REG_EQUAL note, we may
742 fold the comparison to always be false in a later CSE pass.
743 (We could also delete the REG_NOTES when moving the insn, but it
744 seems simpler to not move it.) An exception is that we can move
745 the insn if the only note is a REG_EQUAL or REG_EQUIV whose
746 value is the same as "b".
748 INSN is the branch over the `else' part.
750 We set:
752 TEMP to the jump insn preceding "x = a;"
753 TEMP1 to X
754 TEMP2 to the insn that sets "x = b;"
755 TEMP3 to the insn that sets "x = a;"
756 TEMP4 to the set of "x = b"; */
763 #ifdef SMALL_REGISTER_CLASSES
764 && (! SMALL_REGISTER_CLASSES
766 #endif
782 /* TEMP must skip over the "x = a;" insn */
785 /* There must be no other entries to the "x = b;" insn. */
787 /* INSN must either branch to the insn after TEMP2 or the insn
788 after TEMP2 must branch to the same place as INSN. */
793 {
794 /* The test expression, X, may be a complicated test with
795 multiple branches. See if we can find all the uses of
796 the label that TEMP branches to without hitting a CALL_INSN
797 or a jump to somewhere else. */
802 /* Set P to the first jump insn that goes around "x = a;". */
804 {
806 {
809 {
810 nuses--;
813 }
814 else
816 }
819 }
821 #ifdef HAVE_cc0
822 /* We cannot insert anything between a set of cc and its use
823 so if P uses cc0, we must back up to the previous insn. */
828 #endif
833 /* If we found all the uses and there was no data conflict, we
834 can move the assignment unless we can branch into the middle
835 from somewhere. */
842 {
846 /* Set NEXT to an insn that we know won't go away. */
849 /* Delete the jump around the set. Note that we must do
850 this before we redirect the test jumps so that it won't
851 delete the code immediately following the assignment
852 we moved (which might be a jump). */
856 /* We either have two consecutive labels or a jump to
857 a jump, so adjust all the JUMP_INSNs to branch to where
858 INSN branches to. */
865 }
866 }
868 /* Simplify if (...) { x = a; goto l; } x = b; by converting it
869 to x = a; if (...) goto l; x = b;
870 if A is sufficiently simple, the test doesn't involve X,
871 and nothing in the test modifies A or X.
873 If we have small register classes, we also can't do this if X
874 is a hard register.
876 If the "x = a;" insn has any REG_NOTES, we don't do this because
877 of the possibility that we are running after CSE and there is a
878 REG_EQUAL note that is only valid if the branch has already been
879 taken. If we move the insn with the REG_EQUAL note, we may
880 fold the comparison to always be false in a later CSE pass.
881 (We could also delete the REG_NOTES when moving the insn, but it
882 seems simpler to not move it.) An exception is that we can move
883 the insn if the only note is a REG_EQUAL or REG_EQUIV whose
884 value is the same as "a".
886 INSN is the goto.
888 We set:
890 TEMP to the jump insn preceding "x = a;"
891 TEMP1 to X
892 TEMP2 to the insn that sets "x = b;"
893 TEMP3 to the insn that sets "x = a;"
894 TEMP4 to the set of "x = a"; */
901 #ifdef SMALL_REGISTER_CLASSES
902 && (! SMALL_REGISTER_CLASSES
904 #endif
921 /* TEMP must skip over the "x = a;" insn */
924 {
928 #ifdef HAVE_cc0
929 /* We cannot insert anything between a set of cc and its use. */
933 #endif
946 {
951 /* Set NEXT to an insn that we know won't go away. */
954 }
959 }
961 #ifndef HAVE_cc0
962 /* If we have if (...) x = exp; and branches are expensive,
963 EXP is a single insn, does not have any side effects, cannot
964 trap, and is not too costly, convert this to
965 t = exp; if (...) x = t;
967 Don't do this when we have CC0 because it is unlikely to help
968 and we'd need to worry about where to place the new insn and
969 the potential for conflicts. We also can't do this when we have
970 notes on the insn for the same reason as above.
972 We set:
974 TEMP to the "x = exp;" insn.
975 TEMP1 to the single set in the "x = exp; insn.
976 TEMP2 to "x". */
991 #ifdef SMALL_REGISTER_CLASSES
992 && (! SMALL_REGISTER_CLASSES
994 #endif
1001 {
1005 {
1011 }
1012 }
1014 /* Similarly, if it takes two insns to compute EXP but they
1015 have the same destination. Here TEMP3 will be the second
1016 insn and TEMP4 the SET from that insn. */
1034 #ifdef SMALL_REGISTER_CLASSES
1035 && (! SMALL_REGISTER_CLASSES
1037 #endif
1046 {
1050 {
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 #ifdef SMALL_REGISTER_CLASSES
1097 && (! SMALL_REGISTER_CLASSES
1099 #endif
1104 {
1108 {
1117 }
1118 }
1121 /* Try to use a conditional move (if the target has them), or a
1122 store-flag insn. The general case is:
1124 1) x = a; if (...) x = b; and
1125 2) if (...) x = b;
1127 If the jump would be faster, the machine should not have defined
1128 the movcc or scc insns!. These cases are often made by the
1129 previous optimization.
1131 The second case is treated as x = x; if (...) x = b;.
1133 INSN here is the jump around the store. We set:
1135 TEMP to the "x = b;" insn.
1136 TEMP1 to X.
1137 TEMP2 to B.
1138 TEMP3 to A (X in the second case).
1139 TEMP4 to the condition being tested.
1140 TEMP5 to the earliest insn used to find the condition. */
1143 ! reload_completed
1145 /* Set TEMP to the "x = b;" insn. */
1150 #ifdef SMALL_REGISTER_CLASSES
1151 && (! SMALL_REGISTER_CLASSES
1153 #endif
1156 /* ??? How about floating point constants? */
1158 /* Allow either form, but prefer the former if both apply.
1159 There is no point in using the old value of TEMP1 if
1160 it is a register, since cse will alias them. It can
1161 lose if the old value were a hard register since CSE
1162 won't replace hard registers. */
1164 /* Make the latter case look like x = x; if (...) x = b; */
1166 /* INSN must either branch to the insn after TEMP or the insn
1167 after TEMP must branch to the same place as INSN. */
1173 /* We must be comparing objects whose modes imply the size.
1174 We could handle BLKmode if (1) emit_store_flag could
1175 and (2) we could find the size reliably. */
1177 /* Even if branches are cheap, the store_flag optimization
1178 can win when the operation to be performed can be
1179 expressed directly. */
1180 #ifdef HAVE_cc0
1181 /* If the previous insn sets CC0 and something else, we can't
1182 do this since we are going to delete that insn. */
1189 #endif
1190 )
1191 {
1192 #ifdef HAVE_conditional_move
1193 /* First try a conditional move. */
1194 {
1198 rtx target;
1200 /* Copy the compared variables into cond0 and cond1, so that
1201 any side effects performed in or after the old comparison,
1202 will not affect our compare which will come later. */
1203 /* ??? Is it possible to just use the comparison in the jump
1204 insn? After all, we're going to delete it. We'd have
1205 to modify emit_conditional_move to take a comparison rtx
1206 instead or write a new function. */
1208 /* We want the target to be able to simplify comparisons with
1209 zero (and maybe other constants as well), so don't create
1210 pseudos for them. There's no need to either. */
1214 else
1228 {
1231 /* Save the conditional move sequence but don't emit it
1232 yet. On some machines, like the alpha, it is possible
1233 that temp5 == insn, so next generate the sequence that
1234 saves the compared values and then emit both
1235 sequences ensuring seq1 occurs before seq2. */
1239 /* Now that we can't fail, generate the copy insns that
1240 preserve the compared values. */
1249 /* Insert conditional move after insn, to be sure that
1250 the jump and a possible compare won't be separated */
1253 /* ??? We can also delete the insn that sets X to A.
1254 Flow will do it too though. */
1260 }
1261 else
1263 }
1264 #endif
1266 /* That didn't work, try a store-flag insn.
1268 We further divide the cases into:
1270 1) x = a; if (...) x = b; and either A or B is zero,
1271 2) if (...) x = 0; and jumps are expensive,
1272 3) x = a; if (...) x = b; and A and B are constants where all
1273 the set bits in A are also set in B and jumps are expensive,
1274 4) x = a; if (...) x = b; and A and B non-zero, and jumps are
1275 more expensive, and
1276 5) if (...) x = b; if jumps are even more expensive. */
1280 /* Make the latter case look like
1281 x = x; if (...) x = 0; */
1286 /* If B is zero, OK; if A is zero, can only do (1) if we
1287 can reverse the condition. See if (3) applies possibly
1288 by reversing the condition. Prefer reversing to (4) when
1289 branches are very expensive. */
1293 /* Check that the mask is a power of two,
1294 so that it can probably be generated
1295 with a shift. */
1310 insn)))))
1312 )
1313 {
1317 rtx target;
1319 /* If necessary, reverse the condition. */
1322 else
1325 /* If CVAL is non-zero, normalize to -1. Otherwise, if UVAL
1326 is the constant 1, it is best to just compute the result
1327 directly. If UVAL is constant and STORE_FLAG_VALUE
1328 includes all of its bits, it is best to compute the flag
1329 value unnormalized and `and' it with UVAL. Otherwise,
1330 normalize to -1 and `and' with UVAL. */
1337 /* We will be putting the store-flag insn immediately in
1338 front of the comparison that was originally being done,
1339 so we know all the variables in TEMP4 will be valid.
1340 However, this might be in front of the assignment of
1341 A to VAR. If it is, it would clobber the store-flag
1342 we will be emitting.
1344 Therefore, emit into a temporary which will be copied to
1345 VAR immediately after TEMP. */
1350 VOIDmode,
1353 normalizep);
1355 {
1356 rtx seq;
1362 /* Put the store-flag insns in front of the first insn
1363 used to compute the condition to ensure that we
1364 use the same values of them as the current
1365 comparison. However, the remainder of the insns we
1366 generate will be placed directly in front of the
1367 jump insn, in case any of the pseudos we use
1368 are modified earlier. */
1374 /* Both CVAL and UVAL are non-zero. */
1376 {
1384 else
1385 {
1391 }
1393 /* If we usually make new pseudos, do so here. This
1394 turns out to help machines that have conditional
1395 move insns. */
1396 /* ??? Conditional moves have already been handled.
1397 This may be obsolete. */
1405 }
1407 {
1408 /* We know that either CVAL or UVAL is zero. If
1409 UVAL is zero, negate TARGET and `and' with CVAL.
1410 Otherwise, `and' with UVAL. */
1412 {
1416 }
1422 }
1427 #ifdef HAVE_cc0
1428 /* If INSN uses CC0, we must not separate it from the
1429 insn that sets cc0. */
1432 #endif
1440 }
1441 else
1443 }
1444 }
1446 /* If branches are expensive, convert
1447 if (foo) bar++; to bar += (foo != 0);
1448 and similarly for "bar--;"
1450 INSN is the conditional branch around the arithmetic. We set:
1452 TEMP is the arithmetic insn.
1453 TEMP1 is the SET doing the arithmetic.
1454 TEMP2 is the operand being incremented or decremented.
1455 TEMP3 to the condition being tested.
1456 TEMP4 to the earliest insn used to find the condition. */
1459 #ifdef HAVE_incscc
1460 || HAVE_incscc
1461 #endif
1462 #ifdef HAVE_decscc
1463 || HAVE_decscc
1464 #endif
1465 )
1466 && ! reload_completed
1478 /* INSN must either branch to the insn after TEMP or the insn
1479 after TEMP must branch to the same place as INSN. */
1485 /* We must be comparing objects whose modes imply the size.
1486 We could handle BLKmode if (1) emit_store_flag could
1487 and (2) we could find the size reliably. */
1490 {
1496 /* It must be the case that TEMP2 is not modified in the range
1497 [TEMP4, INSN). The one exception we make is if the insn
1498 before INSN sets TEMP2 to something which is also unchanged
1499 in that range. In that case, we can move the initialization
1500 into our sequence. */
1510 {
1514 }
1520 VOIDmode,
1524 /* If we can do the store-flag, do the addition or
1525 subtraction. */
1534 {
1535 /* Put the result back in temp2 in case it isn't already.
1536 Then replace the jump, possible a CC0-setting insn in
1537 front of the jump, and TEMP, with the sequence we have
1538 made. */
1553 #ifdef HAVE_cc0
1555 #endif
1559 }
1560 else
1562 }
1564 /* Simplify if (...) x = 1; else {...} if (x) ...
1565 We recognize this case scanning backwards as well.
1567 TEMP is the assignment to x;
1568 TEMP1 is the label at the head of the second if. */
1569 /* ?? This should call get_condition to find the values being
1570 compared, instead of looking for a COMPARE insn when HAVE_cc0
1571 is not defined. This would allow it to work on the m88k. */
1572 /* ?? This optimization is only safe before cse is run if HAVE_cc0
1573 is not defined and the condition is tested by a separate compare
1574 insn. This is because the code below assumes that the result
1575 of the compare dies in the following branch.
1577 Not only that, but there might be other insns between the
1578 compare and branch whose results are live. Those insns need
1579 to be executed.
1581 A way to fix this is to move the insns at JUMP_LABEL (insn)
1582 to before INSN. If we are running before flow, they will
1583 be deleted if they aren't needed. But this doesn't work
1584 well after flow.
1586 This is really a special-case of jump threading, anyway. The
1587 right thing to do is to replace this and jump threading with
1588 much simpler code in cse.
1590 This code has been turned off in the non-cc0 case in the
1591 meantime. */
1593 #ifdef HAVE_cc0
1595 /* Safe to skip USE and CLOBBER insns here
1596 since they will not be deleted. */
1604 /* If we find that the next value tested is `x'
1605 (TEMP1 is the insn where this happens), win. */
1608 #ifdef HAVE_cc0
1609 /* Does temp1 `tst' the value of x? */
1613 #else
1614 /* Does temp1 compare the value of x against zero? */
1621 #endif
1623 {
1624 /* Get the if_then_else from the condjump. */
1627 {
1630 rtx cond
1633 rtx ultimate;
1639 else
1649 }
1650 }
1651 #endif
1653 #if 0
1654 /* @@ This needs a bit of work before it will be right.
1656 Any type of comparison can be accepted for the first and
1657 second compare. When rewriting the first jump, we must
1658 compute the what conditions can reach label3, and use the
1659 appropriate code. We can not simply reverse/swap the code
1660 of the first jump. In some cases, the second jump must be
1661 rewritten also.
1663 For example,
1664 < == converts to > ==
1665 < != converts to == >
1666 etc.
1668 If the code is written to only accept an '==' test for the second
1669 compare, then all that needs to be done is to swap the condition
1670 of the first branch.
1672 It is questionable whether we want this optimization anyways,
1673 since if the user wrote code like this because he/she knew that
1674 the jump to label1 is taken most of the time, then rewriting
1675 this gives slower code. */
1676 /* @@ This should call get_condition to find the values being
1677 compared, instead of looking for a COMPARE insn when HAVE_cc0
1678 is not defined. This would allow it to work on the m88k. */
1679 /* @@ This optimization is only safe before cse is run if HAVE_cc0
1680 is not defined and the condition is tested by a separate compare
1681 insn. This is because the code below assumes that the result
1682 of the compare dies in the following branch. */
1684 /* Simplify test a ~= b
1685 condjump label1;
1686 test a == b
1687 condjump label2;
1688 jump label3;
1689 label1:
1691 rewriting as
1692 test a ~~= b
1693 condjump label3
1694 test a == b
1695 condjump label2
1696 label1:
1698 where ~= is an inequality, e.g. >, and ~~= is the swapped
1699 inequality, e.g. <.
1701 We recognize this case scanning backwards.
1703 TEMP is the conditional jump to `label2';
1704 TEMP1 is the test for `a == b';
1705 TEMP2 is the conditional jump to `label1';
1706 TEMP3 is the test for `a ~= b'. */
1715 #ifdef HAVE_cc0
1717 #else
1721 #endif
1735 {
1740 {
1743 }
1747 }
1748 #endif
1749 /* Simplify if (...) {... x = 1;} if (x) ...
1751 We recognize this case backwards.
1753 TEMP is the test of `x';
1754 TEMP1 is the assignment to `x' at the end of the
1755 previous statement. */
1756 /* @@ This should call get_condition to find the values being
1757 compared, instead of looking for a COMPARE insn when HAVE_cc0
1758 is not defined. This would allow it to work on the m88k. */
1759 /* @@ This optimization is only safe before cse is run if HAVE_cc0
1760 is not defined and the condition is tested by a separate compare
1761 insn. This is because the code below assumes that the result
1762 of the compare dies in the following branch. */
1764 /* ??? This has to be turned off. The problem is that the
1765 unconditional jump might indirectly end up branching to the
1766 label between TEMP1 and TEMP. We can't detect this, in general,
1767 since it may become a jump to there after further optimizations.
1768 If that jump is done, it will be deleted, so we will retry
1769 this optimization in the next pass, thus an infinite loop.
1771 The present code prevents this by putting the jump after the
1772 label, but this is not logically correct. */
1773 #if 0
1775 /* Safe to skip USE and CLOBBER insns here
1776 since they will not be deleted. */
1781 #ifdef HAVE_cc0
1784 #else
1785 /* Temp must be a compare insn, we can not accept a register
1786 to register move here, since it may not be simply a
1787 tst insn. */
1793 #endif
1794 /* May skip USE or CLOBBER insns here
1795 for checking for opportunity, since we
1796 take care of them later. */
1800 #ifdef HAVE_cc0
1802 #else
1805 #endif
1807 /* If this isn't true, cse will do the job. */
1809 {
1810 /* Get the if_then_else from the condjump. */
1815 {
1817 rtx last_insn;
1818 rtx ultimate;
1819 rtx p;
1821 /* Get the place that condjump will jump to
1822 if it is reached from here. */
1826 else
1828 /* Get it as a CODE_LABEL. */
1831 else
1832 /* Get the label out of the LABEL_REF. */
1835 /* Insert the jump immediately before TEMP, specifically
1836 after the label that is between TEMP1 and TEMP. */
1839 /* If we would be branching to the next insn, the jump
1840 would immediately be deleted and the re-inserted in
1841 a subsequent pass over the code. So don't do anything
1842 in that case. */
1845 {
1848 last_insn);
1853 {
1857 }
1860 }
1861 }
1862 }
1863 #endif
1864 /* Detect a conditional jump going to the same place
1865 as an immediately following unconditional jump. */
1871 {
1875 }
1876 /* Detect a conditional jump jumping over an unconditional jump. */
1879 && ! this_is_simplejump
1885 {
1886 /* When we invert the unconditional jump, we will be
1887 decrementing the usage count of its old label.
1888 Make sure that we don't delete it now because that
1889 might cause the following code to be deleted. */
1897 {
1898 /* It is very likely that if there are USE insns before
1899 this jump, they hold REG_DEAD notes. These REG_DEAD
1900 notes are no longer valid due to this optimization,
1901 and will cause the life-analysis that following passes
1902 (notably delayed-branch scheduling) to think that
1903 these registers are dead when they are not.
1905 To prevent this trouble, we just remove the USE insns
1906 from the insn chain. */
1910 {
1914 }
1919 }
1921 /* We can now safely delete the label if it is unreferenced
1922 since the delete_insn above has deleted the BARRIER. */
1926 }
1927 else
1928 {
1929 /* Detect a jump to a jump. */
1934 {
1937 }
1939 /* Look for if (foo) bar; else break; */
1940 /* The insns look like this:
1941 insn = condjump label1;
1942 ...range1 (some insns)...
1943 jump label2;
1944 label1:
1945 ...range2 (some insns)...
1946 jump somewhere unconditionally
1947 label2: */
1948 {
1951 /* Don't do this optimization on the first round, so that
1952 jump-around-a-jump gets simplified before we ask here
1953 whether a jump is unconditional.
1955 Also don't do it when we are called after reload since
1956 it will confuse reorg. */
1959 /* Make sure INSN is something we can invert. */
1966 {
1973 /* Invert the jump condition, so we
1974 still execute the same insns in each case. */
1976 {
1981 rtx rangenext;
1983 /* Include in each range any notes before it, to be
1984 sure that we get the line number note if any, even
1985 if there are other notes here. */
1994 /* Don't move NOTEs for blocks or loops; shift them
1995 outside the ranges, where they'll stay put. */
1999 /* Get current surrounds of the 2 ranges. */
2005 /* Splice range2 where range1 was. */
2010 /* Splice range1 where range2 was. */
2016 /* Check for a loop end note between the end of
2017 range2, and the next code label. If there is one,
2018 then what we have really seen is
2019 if (foo) break; end_of_loop;
2020 and moved the break sequence outside the loop.
2021 We must move the LOOP_END note to where the
2022 loop really ends now, or we will confuse loop
2023 optimization. Stop if we find a LOOP_BEG note
2024 first, since we don't want to move the LOOP_END
2025 note in that case. */
2027 {
2030 {
2033 {
2044 }
2048 }
2049 }
2052 }
2053 }
2054 }
2056 /* Now that the jump has been tensioned,
2057 try cross jumping: check for identical code
2058 before the jump and before its target label. */
2060 /* First, cross jumping of conditional jumps: */
2063 {
2067 /* A conditional jump may be crossjumped
2068 only if the place it jumps to follows
2069 an opposing jump that comes back here. */
2072 /* We have no opposing jump;
2073 cannot cross jump this insn. */
2077 /* TARGET is nonzero if it is ok to cross jump
2078 to code before TARGET. If so, see if matches. */
2084 {
2086 /* Make the old conditional jump
2087 into an unconditional one. */
2092 /* Add to jump_chain unless this is a new label
2093 whose UID is too large. */
2095 {
2099 }
2102 }
2103 }
2105 /* Cross jumping of unconditional jumps:
2106 a few differences. */
2109 {
2111 rtx target;
2115 /* TARGET is nonzero if it is ok to cross jump
2116 to code before TARGET. If so, see if matches. */
2120 /* If cannot cross jump to code before the label,
2121 see if we can cross jump to another jump to
2122 the same label. */
2123 /* Try each other jump to this label. */
2130 /* Ignore TARGET if it's deleted. */
2136 {
2140 }
2141 }
2143 /* This code was dead in the previous jump.c! */
2145 {
2146 /* Return insns all "jump to the same place"
2147 so we can cross-jump between any two of them. */
2153 /* If cannot cross jump to code before the label,
2154 see if we can cross jump to another jump to
2155 the same label. */
2156 /* Try each other jump to this label. */
2167 {
2171 }
2172 }
2173 }
2174 }
2177 }
2179 /* Delete extraneous line number notes.
2180 Note that two consecutive notes for different lines are not really
2181 extraneous. There should be some indication where that line belonged,
2182 even if it became empty. */
2184 {
2189 {
2190 /* Delete this note if it is identical to previous note. */
2194 {
2197 }
2200 }
2201 }
2203 #ifdef HAVE_return
2205 {
2206 /* If we fall through to the epilogue, see if we can insert a RETURN insn
2207 in front of it. If the machine allows it at this point (we might be
2208 after reload for a leaf routine), it will improve optimization for it
2209 to be there. We do this both here and at the start of this pass since
2210 the RETURN might have been deleted by some of our optimizations. */
2216 {
2219 }
2220 }
2221 #endif
2223 /* See if there is still a NOTE_INSN_FUNCTION_END in this function.
2224 If so, delete it, and record that this function can drop off the end. */
2227 {
2230 /* One label can follow the end-note: the return label. */
2232 /* Ordinary insns can follow it if returning a structure. */
2234 /* If machine uses explicit RETURN insns, no epilogue,
2235 then one of them follows the note. */
2238 /* A barrier can follow the return insn. */
2240 /* Other kinds of notes can follow also. */
2244 }
2246 /* Report if control can fall through at the end of the function. */
2249 {
2252 }
2254 /* Show JUMP_CHAIN no longer valid. */
2256 }
2257 \f
2258 /* LOOP_START is a NOTE_INSN_LOOP_BEG note that is followed by an unconditional
2259 jump. Assume that this unconditional jump is to the exit test code. If
2260 the code is sufficiently simple, make a copy of it before INSN,
2261 followed by a jump to the exit of the loop. Then delete the unconditional
2262 jump after INSN.
2264 Return 1 if we made the change, else 0.
2266 This is only safe immediately after a regscan pass because it uses the
2267 values of regno_first_uid and regno_last_uid. */
2269 static int
2271 rtx loop_start;
2272 {
2277 rtx lastexit;
2281 /* Scan the exit code. We do not perform this optimization if any insn:
2283 is a CALL_INSN
2284 is a CODE_LABEL
2285 has a REG_RETVAL or REG_LIBCALL note (hard to adjust)
2286 is a NOTE_INSN_LOOP_BEG because this means we have a nested loop
2287 is a NOTE_INSN_BLOCK_{BEG,END} because duplicating these notes
2288 are not valid
2290 Also, don't do this if the exit code is more than 20 insns. */
2293 insn
2297 {
2299 {
2304 /* We could be in front of the wrong NOTE_INSN_LOOP_END if there is
2305 a jump immediately after the loop start that branches outside
2306 the loop but within an outer loop, near the exit test.
2307 If we copied this exit test and created a phony
2308 NOTE_INSN_LOOP_VTOP, this could make instructions immediately
2309 before the exit test look like these could be safely moved
2310 out of the loop even if they actually may be never executed.
2311 This can be avoided by checking here for NOTE_INSN_LOOP_CONT. */
2326 }
2327 }
2329 /* Unless INSN is zero, we can do the optimization. */
2335 /* See if any insn sets a register only used in the loop exit code and
2336 not a user variable. If so, replace it with a new register. */
2345 {
2351 {
2352 /* We can do the replacement. Allocate reg_map if this is the
2353 first replacement we found. */
2355 {
2358 }
2363 }
2364 }
2366 /* Now copy each insn. */
2369 {
2374 /* Only copy line-number notes. */
2376 {
2379 }
2389 /* Copy all REG_NOTES except REG_LABEL since mark_jump_label will
2390 make them. */
2406 {
2410 }
2412 /* If this is a simple jump, add it to the jump chain. */
2416 {
2420 }
2425 }
2427 /* Now clean up by emitting a jump to the end label and deleting the jump
2428 at the start of the loop. */
2430 {
2432 loop_start);
2436 {
2440 }
2442 }
2444 /* Mark the exit code as the virtual top of the converted loop. */
2450 }
2451 \f
2452 /* Move all block-beg, block-end, loop-beg, loop-cont, loop-vtop, and
2453 loop-end notes between START and END out before START. Assume that
2454 END is not such a note. START may be such a note. Returns the value
2455 of the new starting insn, which may be different if the original start
2456 was such a note. */
2458 rtx
2461 {
2462 rtx insn;
2463 rtx next;
2466 {
2475 {
2478 else
2479 {
2487 }
2488 }
2489 }
2492 }
2493 \f
2494 /* Compare the instructions before insn E1 with those before E2
2495 to find an opportunity for cross jumping.
2496 (This means detecting identical sequences of insns followed by
2497 jumps to the same place, or followed by a label and a jump
2498 to that label, and replacing one with a jump to the other.)
2500 Assume E1 is a jump that jumps to label E2
2501 (that is not always true but it might as well be).
2502 Find the longest possible equivalent sequences
2503 and store the first insns of those sequences into *F1 and *F2.
2504 Store zero there if no equivalent preceding instructions are found.
2506 We give up if we find a label in stream 1.
2507 Actually we could transfer that label into stream 2. */
2509 static void
2514 {
2521 rtx prev1;
2527 {
2537 /* Don't allow the range of insns preceding E1 or E2
2538 to include the other (E2 or E1). */
2542 /* If we will get to this code by jumping, those jumps will be
2543 tensioned to go directly to the new label (before I2),
2544 so this cross-jumping won't cost extra. So reduce the minimum. */
2546 {
2549 }
2557 /* If this is a CALL_INSN, compare register usage information.
2558 If we don't check this on stack register machines, the two
2559 CALL_INSNs might be merged leaving reg-stack.c with mismatching
2560 numbers of stack registers in the same basic block.
2561 If we don't check this on machines with delay slots, a delay slot may
2562 be filled that clobbers a parameter expected by the subroutine.
2564 ??? We take the simple route for now and assume that if they're
2565 equal, they were constructed identically. */
2572 #ifdef STACK_REGS
2573 /* If cross_jump_death_matters is not 0, the insn's mode
2574 indicates whether or not the insn contains any stack-like
2575 regs. */
2578 {
2579 /* If register stack conversion has already been done, then
2580 death notes must also be compared before it is certain that
2581 the two instruction streams match. */
2583 rtx note;
2603 done:
2604 ;
2605 }
2606 #endif
2608 /* Don't allow old-style asm or volatile extended asms to be accepted
2609 for cross jumping purposes. It is conceptually correct to allow
2610 them, since cross-jumping preserves the dynamic instruction order
2611 even though it is changing the static instruction order. However,
2612 if an asm is being used to emit an assembler pseudo-op, such as
2613 the MIPS `.set reorder' pseudo-op, then the static instruction order
2614 matters and it must be preserved. */
2622 {
2623 /* The following code helps take care of G++ cleanups. */
2624 rtx equiv1;
2625 rtx equiv2;
2632 /* If the equivalences are not to a constant, they may
2633 reference pseudos that no longer exist, so we can't
2634 use them. */
2637 {
2642 {
2649 }
2650 }
2652 /* Insns fail to match; cross jumping is limited to the following
2653 insns. */
2655 #ifdef HAVE_cc0
2656 /* Don't allow the insn after a compare to be shared by
2657 cross-jumping unless the compare is also shared.
2658 Here, if either of these non-matching insns is a compare,
2659 exclude the following insn from possible cross-jumping. */
2662 #endif
2664 /* If cross-jumping here will feed a jump-around-jump
2665 optimization, this jump won't cost extra, so reduce
2666 the minimum. */
2672 }
2674 win:
2676 {
2677 /* Ok, this insn is potentially includable in a cross-jump here. */
2680 }
2681 }
2685 }
2687 static void
2690 {
2691 /* Find an existing label at this point
2692 or make a new one if there is none. */
2695 /* Make the same jump insn jump to the new point. */
2697 {
2698 /* Remove from jump chain of returns. */
2700 /* Change the insn. */
2705 /* Add to new the jump chain. */
2708 {
2711 }
2712 }
2713 else
2716 /* Delete the matching insns before the jump. Also, remove any REG_EQUAL
2717 or REG_EQUIV note in the NEWLPOS stream that isn't also present in
2718 the NEWJPOS stream. */
2721 {
2722 rtx lnote;
2734 }
2735 }
2736 \f
2737 /* Return the label before INSN, or put a new label there. */
2739 rtx
2741 rtx insn;
2742 {
2743 rtx label;
2745 /* Find an existing label at this point
2746 or make a new one if there is none. */
2750 {
2756 }
2758 }
2760 /* Return the label after INSN, or put a new label there. */
2762 rtx
2764 rtx insn;
2765 {
2766 rtx label;
2768 /* Find an existing label at this point
2769 or make a new one if there is none. */
2773 {
2777 }
2779 }
2780 \f
2781 /* Return 1 if INSN is a jump that jumps to right after TARGET
2782 only on the condition that TARGET itself would drop through.
2783 Assumes that TARGET is a conditional jump. */
2785 static int
2788 {
2804 {
2808 }
2811 {
2815 }
2820 }
2821 \f
2822 /* Given a comparison, COMPARISON, inside a conditional jump insn, INSN,
2823 return non-zero if it is safe to reverse this comparison. It is if our
2824 floating-point is not IEEE, if this is an NE or EQ comparison, or if
2825 this is known to be an integer comparison. */
2827 int
2829 rtx comparison;
2830 rtx insn;
2831 {
2832 rtx arg0;
2834 /* If this is not actually a comparison, we can't reverse it. */
2839 /* If this is an NE comparison, it is safe to reverse it to an EQ
2840 comparison and vice versa, even for floating point. If no operands
2841 are NaNs, the reversal is valid. If some operand is a NaN, EQ is
2842 always false and NE is always true, so the reversal is also valid. */
2843 || flag_fast_math
2850 /* Make sure ARG0 is one of the actual objects being compared. If we
2851 can't do this, we can't be sure the comparison can be reversed.
2853 Handle cc0 and a MODE_CC register. */
2855 #ifdef HAVE_cc0
2857 #endif
2858 )
2859 {
2870 }
2872 /* We can reverse this if ARG0 is a CONST_INT or if its mode is
2873 not VOIDmode and neither a MODE_CC nor MODE_FLOAT type. */
2878 }
2880 /* Given an rtx-code for a comparison, return the code
2881 for the negated comparison.
2882 WATCH OUT! reverse_condition is not safe to use on a jump
2883 that might be acting on the results of an IEEE floating point comparison,
2884 because of the special treatment of non-signaling nans in comparisons.
2885 Use can_reverse_comparison_p to be sure. */
2887 enum rtx_code
2890 {
2892 {
2926 }
2927 }
2929 /* Similar, but return the code when two operands of a comparison are swapped.
2930 This IS safe for IEEE floating-point. */
2932 enum rtx_code
2935 {
2937 {
2969 }
2970 }
2972 /* Given a comparison CODE, return the corresponding unsigned comparison.
2973 If CODE is an equality comparison or already an unsigned comparison,
2974 CODE is returned. */
2976 enum rtx_code
2979 {
2981 {
3004 }
3005 }
3007 /* Similarly, return the signed version of a comparison. */
3009 enum rtx_code
3012 {
3014 {
3037 }
3038 }
3039 \f
3040 /* Return non-zero if CODE1 is more strict than CODE2, i.e., if the
3041 truth of CODE1 implies the truth of CODE2. */
3043 int
3046 {
3051 {
3076 }
3079 }
3080 \f
3081 /* Return 1 if INSN is an unconditional jump and nothing else. */
3083 int
3085 rtx insn;
3086 {
3091 }
3093 /* Return nonzero if INSN is a (possibly) conditional jump
3094 and nothing more. */
3096 int
3098 rtx insn;
3099 {
3118 }
3120 /* Return nonzero if INSN is a (possibly) conditional jump
3121 and nothing more. */
3123 int
3125 rtx insn;
3126 {
3131 else
3151 }
3153 /* Return 1 if X is an RTX that does nothing but set the condition codes
3154 and CLOBBER or USE registers.
3155 Return -1 if X does explicitly set the condition codes,
3156 but also does other things. */
3158 int
3160 rtx x;
3161 {
3162 #ifdef HAVE_cc0
3166 {
3171 {
3177 }
3179 }
3181 #else
3183 #endif
3184 }
3185 \f
3186 /* Follow any unconditional jump at LABEL;
3187 return the ultimate label reached by any such chain of jumps.
3188 If LABEL is not followed by a jump, return LABEL.
3189 If the chain loops or we can't find end, return LABEL,
3190 since that tells caller to avoid changing the insn.
3192 If RELOAD_COMPLETED is 0, we do not chain across a NOTE_INSN_LOOP_BEG or
3193 a USE or CLOBBER. */
3195 rtx
3197 rtx label;
3198 {
3212 depth++)
3213 {
3214 /* Don't chain through the insn that jumps into a loop
3215 from outside the loop,
3216 since that would create multiple loop entry jumps
3217 and prevent loop optimization. */
3218 rtx tem;
3225 /* If we have found a cycle, make the insn jump to itself. */
3235 }
3239 }
3241 /* Assuming that field IDX of X is a vector of label_refs,
3242 replace each of them by the ultimate label reached by it.
3243 Return nonzero if a change is made.
3244 If IGNORE_LOOPS is 0, we do not chain across a NOTE_INSN_LOOP_BEG. */
3246 static int
3250 {
3254 {
3258 {
3264 }
3265 }
3267 }
3268 \f
3269 /* Find all CODE_LABELs referred to in X, and increment their use counts.
3270 If INSN is a JUMP_INSN and there is at least one CODE_LABEL referenced
3271 in INSN, then store one of them in JUMP_LABEL (INSN).
3272 If INSN is an INSN or a CALL_INSN and there is at least one CODE_LABEL
3273 referenced in INSN, add a REG_LABEL note containing that label to INSN.
3274 Also, when there are consecutive labels, canonicalize on the last of them.
3276 Note that two labels separated by a loop-beginning note
3277 must be kept distinct if we have not yet done loop-optimization,
3278 because the gap between them is where loop-optimize
3279 will want to move invariant code to. CROSS_JUMP tells us
3280 that loop-optimization is done with.
3282 Once reload has completed (CROSS_JUMP non-zero), we need not consider
3283 two labels distinct if they are separated by only USE or CLOBBER insns. */
3285 static void
3288 rtx insn;
3290 {
3296 {
3309 /* If this is a constant-pool reference, see if it is a label. */
3316 {
3319 rtx note;
3320 rtx next;
3325 /* Ignore references to labels of containing functions. */
3329 /* If there are other labels following this one,
3330 replace it with the last of the consecutive labels. */
3332 {
3345 }
3351 {
3355 /* If we've changed OLABEL and we had a REG_LABEL note
3356 for it, update it as well. */
3361 /* Otherwise, add a REG_LABEL note for LABEL unless there already
3362 is one. */
3364 {
3366 /* Don't record labels that refer to dispatch tables.
3367 This is not necessary, since the tablejump
3368 references the same label.
3369 And if we did record them, flow.c would make worse code. */
3376 }
3377 }
3379 }
3381 /* Do walk the labels in a vector, but not the first operand of an
3382 ADDR_DIFF_VEC. Don't set the JUMP_LABEL of a vector. */
3385 {
3391 }
3392 }
3396 {
3400 {
3404 }
3405 }
3406 }
3408 /* If all INSN does is set the pc, delete it,
3409 and delete the insn that set the condition codes for it
3410 if that's what the previous thing was. */
3412 void
3414 rtx insn;
3415 {
3420 }
3422 /* Delete INSN and recursively delete insns that compute values used only
3423 by INSN. This uses the REG_DEAD notes computed during flow analysis.
3424 If we are running before flow.c, we need do nothing since flow.c will
3425 delete dead code. We also can't know if the registers being used are
3426 dead or not at this point.
3428 Otherwise, look at all our REG_DEAD notes. If a previous insn does
3429 nothing other than set a register that dies in this insn, we can delete
3430 that insn as well.
3432 On machines with CC0, if CC0 is used in this insn, we may be able to
3433 delete the insn that set it. */
3435 static void
3437 rtx insn;
3438 {
3441 #ifdef HAVE_cc0
3443 {
3445 /* We assume that at this stage
3446 CC's are always set explicitly
3447 and always immediately before the jump that
3448 will use them. So if the previous insn
3449 exists to set the CC's, delete it
3450 (unless it performs auto-increments, etc.). */
3453 {
3457 else
3458 /* Otherwise, show that cc0 won't be used. */
3461 }
3462 }
3463 #endif
3466 {
3467 rtx our_prev;
3472 /* Verify that the REG_NOTE is legitimate. */
3479 {
3480 /* If we reach a SEQUENCE, it is too complex to try to
3481 do anything with it, so give up. */
3487 /* reorg creates USEs that look like this. We leave them
3488 alone because reorg needs them for its own purposes. */
3492 {
3497 {
3498 /* If we find a SET of something else, we can't
3499 delete the insn. */
3504 {
3510 }
3514 }
3520 }
3522 /* If OUR_PREV references the register that dies here, it is an
3523 additional use. Hence any prior SET isn't dead. However, this
3524 insn becomes the new place for the REG_DEAD note. */
3527 {
3531 }
3532 }
3533 }
3536 }
3537 \f
3538 /* Delete insn INSN from the chain of insns and update label ref counts.
3539 May delete some following insns as a consequence; may even delete
3540 a label elsewhere and insns that follow it.
3542 Returns the first insn after INSN that was not deleted. */
3544 rtx
3547 {
3556 /* This insn is already deleted => return first following nondeleted. */
3560 /* Don't delete user-declared labels. Convert them to special NOTEs
3561 instead. */
3564 {
3569 }
3570 else
3571 /* Mark this insn as deleted. */
3574 /* If this is an unconditional jump, delete it from the jump chain. */
3578 /* If instruction is followed by a barrier,
3579 delete the barrier too. */
3582 {
3585 }
3587 /* Patch out INSN (and the barrier if any) */
3590 {
3592 {
3597 }
3600 {
3604 }
3608 }
3610 /* If deleting a jump, decrement the count of the label,
3611 and delete the label if it is now unused. */
3615 {
3616 /* This can delete NEXT or PREV,
3617 either directly if NEXT is JUMP_LABEL (INSN),
3618 or indirectly through more levels of jumps. */
3620 /* I feel a little doubtful about this loop,
3621 but I see no clean and sure alternative way
3622 to find the first insn after INSN that is not now deleted.
3623 I hope this works. */
3627 }
3629 /* Likewise if we're deleting a dispatch table. */
3634 {
3645 }
3650 /* If INSN was a label and a dispatch table follows it,
3651 delete the dispatch table. The tablejump must have gone already.
3652 It isn't useful to fall through into a table. */
3661 /* If INSN was a label, delete insns following it if now unreachable. */
3664 {
3670 {
3674 /* Keep going past other deleted labels to delete what follows. */
3677 else
3678 /* Note: if this deletes a jump, it can cause more
3679 deletion of unreachable code, after a different label.
3680 As long as the value from this recursive call is correct,
3681 this invocation functions correctly. */
3683 }
3684 }
3687 }
3689 /* Advance from INSN till reaching something not deleted
3690 then return that. May return INSN itself. */
3692 rtx
3694 rtx insn;
3695 {
3699 }
3700 \f
3701 /* Delete a range of insns from FROM to TO, inclusive.
3702 This is for the sake of peephole optimization, so assume
3703 that whatever these insns do will still be done by a new
3704 peephole insn that will replace them. */
3706 void
3709 {
3713 {
3718 {
3721 /* Patch this insn out of the chain. */
3722 /* We don't do this all at once, because we
3723 must preserve all NOTEs. */
3729 }
3734 }
3736 /* Note that if TO is an unconditional jump
3737 we *do not* delete the BARRIER that follows,
3738 since the peephole that replaces this sequence
3739 is also an unconditional jump in that case. */
3740 }
3741 \f
3742 /* Invert the condition of the jump JUMP, and make it jump
3743 to label NLABEL instead of where it jumps now. */
3745 int
3748 {
3749 /* We have to either invert the condition and change the label or
3750 do neither. Either operation could fail. We first try to invert
3751 the jump. If that succeeds, we try changing the label. If that fails,
3752 we invert the jump back to what it was. */
3761 /* This should just be putting it back the way it was. */
3765 }
3767 /* Invert the jump condition of rtx X contained in jump insn, INSN.
3769 Return 1 if we can do so, 0 if we cannot find a way to do so that
3770 matches a pattern. */
3772 int
3774 rtx x;
3775 rtx insn;
3776 {
3784 {
3788 /* We can do this in two ways: The preferable way, which can only
3789 be done if this is not an integer comparison, is to reverse
3790 the comparison code. Otherwise, swap the THEN-part and ELSE-part
3791 of the IF_THEN_ELSE. If we can't do either, fail. */
3804 }
3808 {
3813 {
3818 }
3819 }
3822 }
3823 \f
3824 /* Make jump JUMP jump to label NLABEL instead of where it jumps now.
3825 If the old jump target label is unused as a result,
3826 it and the code following it may be deleted.
3828 If NLABEL is zero, we are to turn the jump into a (possibly conditional)
3829 RETURN insn.
3831 The return value will be 1 if the change was made, 0 if it wasn't (this
3832 can only occur for NLABEL == 0). */
3834 int
3837 {
3846 /* If this is an unconditional branch, delete it from the jump_chain of
3847 OLABEL and add it to the jump_chain of NLABEL (assuming both labels
3848 have UID's in range and JUMP_CHAIN is valid). */
3851 {
3857 {
3860 }
3861 }
3871 }
3873 /* Delete the instruction JUMP from any jump chain it might be on. */
3875 static void
3877 rtx jump;
3878 {
3882 /* Handle unconditional jumps. */
3887 /* Handle return insns. */
3894 else
3895 {
3896 rtx insn;
3902 {
3905 }
3906 }
3907 }
3909 /* If NLABEL is nonzero, throughout the rtx at LOC,
3910 alter (LABEL_REF OLABEL) to (LABEL_REF NLABEL). If OLABEL is
3911 zero, alter (RETURN) to (LABEL_REF NLABEL).
3913 If NLABEL is zero, alter (LABEL_REF OLABEL) to (RETURN) and check
3914 validity with validate_change. Convert (set (pc) (label_ref olabel))
3915 to (return).
3917 Return 0 if we found a change we would like to make but it is invalid.
3918 Otherwise, return 1. */
3920 int
3924 rtx insn;
3925 {
3932 {
3934 {
3937 else
3940 }
3941 }
3943 {
3948 }
3957 {
3962 {
3967 }
3968 }
3971 }
3972 \f
3973 /* Make jump JUMP jump to label NLABEL, assuming it used to be a tablejump.
3975 If the old jump target label (before the dispatch table) becomes unused,
3976 it and the dispatch table may be deleted. In that case, find the insn
3977 before the jump references that label and delete it and logical successors
3978 too. */
3980 static void
3983 {
3986 /* Add this jump to the jump_chain of NLABEL. */
3989 {
3992 }
4000 {
4003 }
4004 }
4006 /* Find the insn referencing LABEL that is a logical predecessor of INSN.
4007 If we found one, delete it and then delete this insn if DELETE_THIS is
4008 non-zero. Return non-zero if INSN or a predecessor references LABEL. */
4010 static int
4014 {
4016 rtx link;
4020 {
4022 {
4025 }
4026 else
4028 }
4032 {
4034 {
4037 }
4038 else
4040 }
4043 }
4044 \f
4045 /* Like rtx_equal_p except that it considers two REGs as equal
4046 if they renumber to the same value and considers two commutative
4047 operations to be the same if the order of the operands has been
4048 reversed. */
4050 int
4053 {
4064 {
4071 /* If we haven't done any renumbering, don't
4072 make any assumptions. */
4077 {
4082 {
4085 }
4086 }
4088 else
4089 {
4093 }
4096 {
4101 {
4104 }
4105 }
4107 else
4108 {
4112 }
4115 }
4117 /* Now we have disposed of all the cases
4118 in which different rtx codes can match. */
4123 {
4134 /* We can't assume nonlocal labels have their following insns yet. */
4138 /* Two label-refs are equivalent if they point at labels
4139 in the same position in the instruction stream. */
4145 }
4147 /* (MULT:SI x y) and (MULT:HI x y) are NOT equivalent. */
4152 /* For commutative operations, the RTX match if the operand match in any
4153 order. Also handle the simple binary and unary cases without a loop. */
4165 /* Compare the elements. If any pair of corresponding elements
4166 fail to match, return 0 for the whole things. */
4170 {
4173 {
4197 /* fall through. */
4211 }
4212 }
4214 }
4215 \f
4216 /* If X is a hard register or equivalent to one or a subregister of one,
4217 return the hard register number. If X is a pseudo register that was not
4218 assigned a hard register, return the pseudo register number. Otherwise,
4219 return -1. Any rtx is valid for X. */
4221 int
4223 rtx x;
4224 {
4226 {
4230 }
4232 {
4236 }
4238 }
4239 \f
4240 /* Optimize code of the form:
4242 for (x = a[i]; x; ...)
4243 ...
4244 for (x = a[i]; x; ...)
4245 ...
4246 foo:
4248 Loop optimize will change the above code into
4250 if (x = a[i])
4251 for (;;)
4252 { ...; if (! (x = ...)) break; }
4253 if (x = a[i])
4254 for (;;)
4255 { ...; if (! (x = ...)) break; }
4256 foo:
4258 In general, if the first test fails, the program can branch
4259 directly to `foo' and skip the second try which is doomed to fail.
4260 We run this after loop optimization and before flow analysis. */
4262 /* When comparing the insn patterns, we track the fact that different
4263 pseudo-register numbers may have been used in each computation.
4264 The following array stores an equivalence -- same_regs[I] == J means
4265 that pseudo register I was used in the first set of tests in a context
4266 where J was used in the second set. We also count the number of such
4267 pending equivalences. If nonzero, the expressions really aren't the
4268 same. */
4274 /* Track any registers modified between the target of the first jump and
4275 the second jump. They never compare equal. */
4279 /* Record if memory was modified. */
4283 /* Called via note_stores on each insn between the target of the first
4284 branch and the second branch. It marks any changed registers. */
4286 static void
4288 rtx dest;
4289 rtx x;
4290 {
4305 else
4308 }
4310 /* F is the first insn in the chain of insns. */
4312 void
4314 rtx f;
4317 {
4318 /* Basic algorithm is to find a conditional branch,
4319 the label it may branch to, and the branch after
4320 that label. If the two branches test the same condition,
4321 walk back from both branch paths until the insn patterns
4322 differ, or code labels are hit. If we make it back to
4323 the target of the first branch, then we know that the first branch
4324 will either always succeed or always fail depending on the relative
4325 senses of the two branches. So adjust the first branch accordingly
4326 in this case. */
4335 /* Allocate register tables and quick-reset table. */
4343 {
4347 {
4348 /* Get to a candidate branch insn. */
4363 /* Look for a branch after the target. Record any registers and
4364 memory modified between the target and the branch. Stop when we
4365 get to a label since we can't know what was changed there. */
4367 {
4372 {
4373 /* If this is an unconditional jump and is the only use of
4374 its target label, we can follow it. */
4378 {
4381 }
4382 else
4384 }
4390 {
4399 }
4402 }
4404 /* Check the next candidate branch insn from the label
4405 of the first. */
4413 /* Get the comparison codes and operands, reversing the
4414 codes if appropriate. If we don't have comparison codes,
4415 we can't do anything. */
4428 /* If they test the same things and knowing that B1 branches
4429 tells us whether or not B2 branches, check if we
4430 can thread the branch. */
4435 {
4440 {
4442 {
4443 /* We have reached the target of the first branch.
4444 If there are no pending register equivalents,
4445 we know that this branch will either always
4446 succeed (if the senses of the two branches are
4447 the same) or always fail (if not). */
4448 rtx new_label;
4455 else
4459 {
4464 {
4465 /* Don't thread to the loop label. If a loop
4466 label is reused, loop optimization will
4467 be disabled for that loop. */
4470 }
4472 }
4474 }
4476 /* If either of these is not a normal insn (it might be
4477 a JUMP_INSN, CALL_INSN, or CODE_LABEL) we fail. (NOTEs
4478 have already been skipped above.) Similarly, fail
4479 if the insns are different. */
4488 }
4489 }
4490 }
4491 }
4492 }
4493 \f
4494 /* This is like RTX_EQUAL_P except that it knows about our handling of
4495 possibly equivalent registers and knows to consider volatile and
4496 modified objects as not equal.
4498 YINSN is the insn containing Y. */
4500 int
4503 rtx yinsn;
4504 {
4511 /* Rtx's of different codes cannot be equal. */
4515 /* (MULT:SI x y) and (MULT:HI x y) are NOT equivalent.
4516 (REG:SI x) and (REG:HI x) are NOT equivalent. */
4521 /* For floating-point, consider everything unequal. This is a bit
4522 pessimistic, but this pass would only rarely do anything for FP
4523 anyway. */
4528 /* For commutative operations, the RTX match if the operand match in any
4529 order. Also handle the simple binary and unary cases without a loop. */
4541 /* Handle special-cases first. */
4543 {
4548 /* If neither is user variable or hard register, check for possible
4549 equivalence. */
4556 {
4558 num_same_regs++;
4560 /* If this is the first time we are seeing a register on the `Y'
4561 side, see if it is the last use. If not, we can't thread the
4562 jump, so mark it as not equivalent. */
4567 }
4568 else
4574 /* If memory modified or either volatile, not equivalent.
4575 Else, check address. */
4588 /* Cancel a pending `same_regs' if setting equivalenced registers.
4589 Then process source. */
4592 {
4594 {
4596 num_same_regs--;
4597 }
4600 }
4601 else
4612 }
4619 {
4621 {
4635 /* Two vectors must have the same length. */
4639 /* And the corresponding elements must match. */
4658 /* These are just backpointers, so they don't matter. */
4664 /* It is believed that rtx's at this level will never
4665 contain anything but integers and other rtx's,
4666 except for within LABEL_REFs and SYMBOL_REFs. */
4669 }
4670 }
4672 }