| blob | e0d20a60caf21d148777b9039abf33dd178f244a |
1 /* Optimize jump instructions, for GNU compiler.
2 Copyright (C) 1987, 88, 89, 91-97, 1998 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. */
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. */
216 {
219 {
221 {
225 }
227 {
230 }
231 }
232 }
234 /* Keep track of labels used from static data;
235 they cannot ever be deleted. */
242 /* Keep track of labels used for marking handlers for exception
243 regions; they cannot usually be deleted. */
250 /* Delete all labels already not referenced.
251 Also find the last insn. */
255 {
258 else
259 {
262 }
263 }
266 {
267 /* See if there is still a NOTE_INSN_FUNCTION_END in this function.
268 If so record that this function can drop off the end. */
271 {
274 /* One label can follow the end-note: the return label. */
276 /* Ordinary insns can follow it if returning a structure. */
278 /* If machine uses explicit RETURN insns, no epilogue,
279 then one of them follows the note. */
282 /* A barrier can follow the return insn. */
284 /* Other kinds of notes can follow also. */
288 }
290 /* Report if control can fall through at the end of the function. */
296 /* Zero the "deleted" flag of all the "deleted" insns. */
300 }
302 #ifdef HAVE_return
304 {
305 /* If we fall through to the epilogue, see if we can insert a RETURN insn
306 in front of it. If the machine allows it at this point (we might be
307 after reload for a leaf routine), it will improve optimization for it
308 to be there. */
314 {
317 }
318 }
319 #endif
323 {
327 {
330 /* Combine stack_adjusts with following push_insns. */
331 #ifdef PUSH_ROUNDING
338 {
339 rtx p;
345 /* Find all successive push insns. */
347 /* Don't convert more than three pushes;
348 that starts adding too many displaced addresses
349 and the whole thing starts becoming a losing
350 proposition. */
352 {
361 /* Allow a no-op move between the adjust and the push. */
370 pushes++;
375 }
377 /* Discard the amount pushed from the stack adjust;
378 maybe eliminate it entirely. */
380 {
383 }
384 else
388 /* Change the appropriate push insns to ordinary stores. */
391 {
405 /* If this push doesn't fully fit in the space
406 of the stack adjust that we deleted,
407 make another stack adjust here for what we
408 didn't use up. There should be peepholes
409 to recognize the resulting sequence of insns. */
411 {
414 p);
416 }
419 }
420 }
421 #endif
423 /* Detect and delete no-op move instructions
424 resulting from not allocating a parameter in a register. */
437 /* Detect and ignore no-op move instructions
438 resulting from smart or fortuitous register allocation. */
441 {
448 {
449 rtx trial;
456 {
457 /* DREG may have been the target of a REG_DEAD note in
458 the insn which makes INSN redundant. If so, reorg
459 would still think it is dead. So search for such a
460 note and delete it if we find it. */
466 {
469 }
470 #ifdef PRESERVE_DEATH_INFO_REGNO_P
471 /* Deleting insn could lose a death-note for SREG
472 so don't do it if final needs accurate
473 death-notes. */
476 {
477 /* Change this into a USE so that we won't emit
478 code for it, but still can keep the note. */
482 /* Remove all reg notes but the REG_DEAD one. */
485 }
486 else
487 #endif
489 }
490 }
495 {
496 /* This handles the case where we have two consecutive
497 assignments of the same constant to pseudos that didn't
498 get a hard reg. Each SET from the constant will be
499 converted into a SET of the spill register and an
500 output reload will be made following it. This produces
501 two loads of the same constant into the same spill
502 register. */
506 /* Look back for a death note for the first reg.
507 If there is one, it is no longer accurate. */
509 {
513 {
516 }
518 }
520 /* Delete the second load of the value. */
522 }
523 }
525 {
526 /* If each part is a set between two identical registers or
527 a USE or CLOBBER, delete the insn. */
529 rtx tem;
532 {
542 }
546 }
547 /* Also delete insns to store bit fields if they are no-ops. */
548 /* Not worth the hair to detect this in the big-endian case. */
557 }
559 }
561 /* If we haven't yet gotten to reload and we have just run regscan,
562 delete any insn that sets a register that isn't used elsewhere.
563 This helps some of the optimizations below by having less insns
564 being jumped around. */
568 {
576 /* We use regno_last_note_uid so as not to delete the setting
577 of a reg that's used in notes. A subsequent optimization
578 might arrange to use that reg for real. */
583 }
585 /* Now iterate optimizing jumps until nothing changes over one pass. */
588 {
592 {
593 rtx reallabelprev;
595 rtx nlabel;
598 #if 0
599 /* If NOT the first iteration, if this is the last jump pass
600 (just before final), do the special peephole optimizations.
601 Avoiding the first iteration gives ordinary jump opts
602 a chance to work before peephole opts. */
607 #endif
609 /* That could have deleted some insns after INSN, so check now
610 what the following insn is. */
614 /* See if this is a NOTE_INSN_LOOP_BEG followed by an unconditional
615 jump. Try to optimize by duplicating the loop exit test if so.
616 This is only safe immediately after regscan, because it uses
617 the values of regno_first_uid and regno_last_uid. */
622 {
625 {
629 }
630 }
639 /* Tension the labels in dispatch tables. */
646 /* If a dispatch table always goes to the same place,
647 get rid of it and replace the insn that uses it. */
651 {
666 /* Don't mess with a casesi insn. */
671 {
675 }
676 }
680 /* If a jump references the end of the function, try to turn
681 it into a RETURN insn, possibly a conditional one. */
688 /* Detect jump to following insn. */
690 {
695 }
697 /* If we have an unconditional jump preceded by a USE, try to put
698 the USE before the target and jump there. This simplifies many
699 of the optimizations below since we don't have to worry about
700 dealing with these USE insns. We only do this if the label
701 being branch to already has the identical USE or if code
702 never falls through to that label. */
711 /* Don't do this optimization if we have a loop containing only
712 the USE instruction, and the loop start label has a usage
713 count of 1. This is because we will redo this optimization
714 everytime through the outer loop, and jump opt will never
715 exit. */
719 {
721 {
724 }
730 }
732 /* Simplify if (...) x = a; else x = b; by converting it
733 to x = b; if (...) x = a;
734 if B is sufficiently simple, the test doesn't involve X,
735 and nothing in the test modifies B or X.
737 If we have small register classes, we also can't do this if X
738 is a hard register.
740 If the "x = b;" insn has any REG_NOTES, we don't do this because
741 of the possibility that we are running after CSE and there is a
742 REG_EQUAL note that is only valid if the branch has already been
743 taken. If we move the insn with the REG_EQUAL note, we may
744 fold the comparison to always be false in a later CSE pass.
745 (We could also delete the REG_NOTES when moving the insn, but it
746 seems simpler to not move it.) An exception is that we can move
747 the insn if the only note is a REG_EQUAL or REG_EQUIV whose
748 value is the same as "b".
750 INSN is the branch over the `else' part.
752 We set:
754 TEMP to the jump insn preceding "x = a;"
755 TEMP1 to X
756 TEMP2 to the insn that sets "x = b;"
757 TEMP3 to the insn that sets "x = a;"
758 TEMP4 to the set of "x = b"; */
765 && (! SMALL_REGISTER_CLASSES
784 /* TEMP must skip over the "x = a;" insn */
787 /* There must be no other entries to the "x = b;" insn. */
789 /* INSN must either branch to the insn after TEMP2 or the insn
790 after TEMP2 must branch to the same place as INSN. */
795 {
796 /* The test expression, X, may be a complicated test with
797 multiple branches. See if we can find all the uses of
798 the label that TEMP branches to without hitting a CALL_INSN
799 or a jump to somewhere else. */
802 rtx p;
803 #ifdef HAVE_cc0
804 rtx q;
805 #endif
807 /* Set P to the first jump insn that goes around "x = a;". */
809 {
811 {
814 {
815 nuses--;
818 }
819 else
821 }
824 }
826 #ifdef HAVE_cc0
827 /* We cannot insert anything between a set of cc and its use
828 so if P uses cc0, we must back up to the previous insn. */
833 #endif
838 /* If we found all the uses and there was no data conflict, we
839 can move the assignment unless we can branch into the middle
840 from somewhere. */
847 {
851 /* Set NEXT to an insn that we know won't go away. */
854 /* Delete the jump around the set. Note that we must do
855 this before we redirect the test jumps so that it won't
856 delete the code immediately following the assignment
857 we moved (which might be a jump). */
861 /* We either have two consecutive labels or a jump to
862 a jump, so adjust all the JUMP_INSNs to branch to where
863 INSN branches to. */
870 }
871 }
873 /* Simplify if (...) { x = a; goto l; } x = b; by converting it
874 to x = a; if (...) goto l; x = b;
875 if A is sufficiently simple, the test doesn't involve X,
876 and nothing in the test modifies A or X.
878 If we have small register classes, we also can't do this if X
879 is a hard register.
881 If the "x = a;" insn has any REG_NOTES, we don't do this because
882 of the possibility that we are running after CSE and there is a
883 REG_EQUAL note that is only valid if the branch has already been
884 taken. If we move the insn with the REG_EQUAL note, we may
885 fold the comparison to always be false in a later CSE pass.
886 (We could also delete the REG_NOTES when moving the insn, but it
887 seems simpler to not move it.) An exception is that we can move
888 the insn if the only note is a REG_EQUAL or REG_EQUIV whose
889 value is the same as "a".
891 INSN is the goto.
893 We set:
895 TEMP to the jump insn preceding "x = a;"
896 TEMP1 to X
897 TEMP2 to the insn that sets "x = b;"
898 TEMP3 to the insn that sets "x = a;"
899 TEMP4 to the set of "x = a"; */
906 && (! SMALL_REGISTER_CLASSES
925 /* TEMP must skip over the "x = a;" insn */
928 {
932 #ifdef HAVE_cc0
933 /* We cannot insert anything between a set of cc and its use. */
937 #endif
950 {
955 /* Set NEXT to an insn that we know won't go away. */
958 }
963 }
965 #ifndef HAVE_cc0
966 /* If we have if (...) x = exp; and branches are expensive,
967 EXP is a single insn, does not have any side effects, cannot
968 trap, and is not too costly, convert this to
969 t = exp; if (...) x = t;
971 Don't do this when we have CC0 because it is unlikely to help
972 and we'd need to worry about where to place the new insn and
973 the potential for conflicts. We also can't do this when we have
974 notes on the insn for the same reason as above.
976 We set:
978 TEMP to the "x = exp;" insn.
979 TEMP1 to the single set in the "x = exp; insn.
980 TEMP2 to "x". */
995 && (! SMALL_REGISTER_CLASSES
1003 {
1008 {
1014 }
1015 }
1017 /* Similarly, if it takes two insns to compute EXP but they
1018 have the same destination. Here TEMP3 will be the second
1019 insn and TEMP4 the SET from that insn. */
1037 && (! SMALL_REGISTER_CLASSES
1047 {
1053 {
1054 /* Use the earliest of temp5 and temp6. */
1060 emit_insn_after_with_line_notes
1066 }
1067 }
1069 /* Finally, handle the case where two insns are used to
1070 compute EXP but a temporary register is used. Here we must
1071 ensure that the temporary register is not used anywhere else. */
1074 && after_regscan
1102 && (! SMALL_REGISTER_CLASSES
1108 {
1114 {
1115 /* Use the earliest of temp5 and temp6. */
1126 }
1127 }
1130 /* Try to use a conditional move (if the target has them), or a
1131 store-flag insn. The general case is:
1133 1) x = a; if (...) x = b; and
1134 2) if (...) x = b;
1136 If the jump would be faster, the machine should not have defined
1137 the movcc or scc insns!. These cases are often made by the
1138 previous optimization.
1140 The second case is treated as x = x; if (...) x = b;.
1142 INSN here is the jump around the store. We set:
1144 TEMP to the "x = b;" insn.
1145 TEMP1 to X.
1146 TEMP2 to B.
1147 TEMP3 to A (X in the second case).
1148 TEMP4 to the condition being tested.
1149 TEMP5 to the earliest insn used to find the condition. */
1152 ! reload_completed
1154 /* Set TEMP to the "x = b;" insn. */
1159 && (! SMALL_REGISTER_CLASSES
1164 /* ??? How about floating point constants? */
1166 /* Allow either form, but prefer the former if both apply.
1167 There is no point in using the old value of TEMP1 if
1168 it is a register, since cse will alias them. It can
1169 lose if the old value were a hard register since CSE
1170 won't replace hard registers. Avoid using TEMP3 if
1171 small register classes and it is a hard register. */
1175 /* Make the latter case look like x = x; if (...) x = b; */
1177 /* INSN must either branch to the insn after TEMP or the insn
1178 after TEMP must branch to the same place as INSN. */
1184 /* We must be comparing objects whose modes imply the size.
1185 We could handle BLKmode if (1) emit_store_flag could
1186 and (2) we could find the size reliably. */
1188 /* Even if branches are cheap, the store_flag optimization
1189 can win when the operation to be performed can be
1190 expressed directly. */
1191 #ifdef HAVE_cc0
1192 /* If the previous insn sets CC0 and something else, we can't
1193 do this since we are going to delete that insn. */
1200 #endif
1201 )
1202 {
1203 #ifdef HAVE_conditional_move
1204 /* First try a conditional move. */
1205 {
1209 rtx target;
1211 /* Copy the compared variables into cond0 and cond1, so that
1212 any side effects performed in or after the old comparison,
1213 will not affect our compare which will come later. */
1214 /* ??? Is it possible to just use the comparison in the jump
1215 insn? After all, we're going to delete it. We'd have
1216 to modify emit_conditional_move to take a comparison rtx
1217 instead or write a new function. */
1219 /* We want the target to be able to simplify comparisons with
1220 zero (and maybe other constants as well), so don't create
1221 pseudos for them. There's no need to either. */
1225 else
1239 {
1242 /* Save the conditional move sequence but don't emit it
1243 yet. On some machines, like the alpha, it is possible
1244 that temp5 == insn, so next generate the sequence that
1245 saves the compared values and then emit both
1246 sequences ensuring seq1 occurs before seq2. */
1250 /* Now that we can't fail, generate the copy insns that
1251 preserve the compared values. */
1260 /* Insert conditional move after insn, to be sure that
1261 the jump and a possible compare won't be separated */
1264 /* ??? We can also delete the insn that sets X to A.
1265 Flow will do it too though. */
1271 }
1272 else
1274 }
1275 #endif
1277 /* That didn't work, try a store-flag insn.
1279 We further divide the cases into:
1281 1) x = a; if (...) x = b; and either A or B is zero,
1282 2) if (...) x = 0; and jumps are expensive,
1283 3) x = a; if (...) x = b; and A and B are constants where all
1284 the set bits in A are also set in B and jumps are expensive,
1285 4) x = a; if (...) x = b; and A and B non-zero, and jumps are
1286 more expensive, and
1287 5) if (...) x = b; if jumps are even more expensive. */
1291 /* Make the latter case look like
1292 x = x; if (...) x = 0; */
1297 /* If B is zero, OK; if A is zero, can only do (1) if we
1298 can reverse the condition. See if (3) applies possibly
1299 by reversing the condition. Prefer reversing to (4) when
1300 branches are very expensive. */
1304 /* Check that the mask is a power of two,
1305 so that it can probably be generated
1306 with a shift. */
1321 insn)))))
1323 )
1324 {
1328 rtx target;
1330 /* If necessary, reverse the condition. */
1333 else
1336 /* If CVAL is non-zero, normalize to -1. Otherwise, if UVAL
1337 is the constant 1, it is best to just compute the result
1338 directly. If UVAL is constant and STORE_FLAG_VALUE
1339 includes all of its bits, it is best to compute the flag
1340 value unnormalized and `and' it with UVAL. Otherwise,
1341 normalize to -1 and `and' with UVAL. */
1348 /* We will be putting the store-flag insn immediately in
1349 front of the comparison that was originally being done,
1350 so we know all the variables in TEMP4 will be valid.
1351 However, this might be in front of the assignment of
1352 A to VAR. If it is, it would clobber the store-flag
1353 we will be emitting.
1355 Therefore, emit into a temporary which will be copied to
1356 VAR immediately after TEMP. */
1361 VOIDmode,
1364 normalizep);
1366 {
1367 rtx seq;
1373 /* Put the store-flag insns in front of the first insn
1374 used to compute the condition to ensure that we
1375 use the same values of them as the current
1376 comparison. However, the remainder of the insns we
1377 generate will be placed directly in front of the
1378 jump insn, in case any of the pseudos we use
1379 are modified earlier. */
1385 /* Both CVAL and UVAL are non-zero. */
1387 {
1395 else
1396 {
1402 }
1404 /* If we usually make new pseudos, do so here. This
1405 turns out to help machines that have conditional
1406 move insns. */
1407 /* ??? Conditional moves have already been handled.
1408 This may be obsolete. */
1416 }
1418 {
1419 /* We know that either CVAL or UVAL is zero. If
1420 UVAL is zero, negate TARGET and `and' with CVAL.
1421 Otherwise, `and' with UVAL. */
1423 {
1427 }
1433 }
1438 #ifdef HAVE_cc0
1439 /* If INSN uses CC0, we must not separate it from the
1440 insn that sets cc0. */
1443 #endif
1451 }
1452 else
1454 }
1455 }
1457 /* If branches are expensive, convert
1458 if (foo) bar++; to bar += (foo != 0);
1459 and similarly for "bar--;"
1461 INSN is the conditional branch around the arithmetic. We set:
1463 TEMP is the arithmetic insn.
1464 TEMP1 is the SET doing the arithmetic.
1465 TEMP2 is the operand being incremented or decremented.
1466 TEMP3 to the condition being tested.
1467 TEMP4 to the earliest insn used to find the condition. */
1470 #ifdef HAVE_incscc
1471 || HAVE_incscc
1472 #endif
1473 #ifdef HAVE_decscc
1474 || HAVE_decscc
1475 #endif
1476 )
1477 && ! reload_completed
1489 /* INSN must either branch to the insn after TEMP or the insn
1490 after TEMP must branch to the same place as INSN. */
1496 /* We must be comparing objects whose modes imply the size.
1497 We could handle BLKmode if (1) emit_store_flag could
1498 and (2) we could find the size reliably. */
1501 {
1507 /* It must be the case that TEMP2 is not modified in the range
1508 [TEMP4, INSN). The one exception we make is if the insn
1509 before INSN sets TEMP2 to something which is also unchanged
1510 in that range. In that case, we can move the initialization
1511 into our sequence. */
1521 {
1525 }
1531 VOIDmode,
1535 /* If we can do the store-flag, do the addition or
1536 subtraction. */
1545 {
1546 /* Put the result back in temp2 in case it isn't already.
1547 Then replace the jump, possible a CC0-setting insn in
1548 front of the jump, and TEMP, with the sequence we have
1549 made. */
1564 #ifdef HAVE_cc0
1566 #endif
1570 }
1571 else
1573 }
1575 /* Simplify if (...) x = 1; else {...} if (x) ...
1576 We recognize this case scanning backwards as well.
1578 TEMP is the assignment to x;
1579 TEMP1 is the label at the head of the second if. */
1580 /* ?? This should call get_condition to find the values being
1581 compared, instead of looking for a COMPARE insn when HAVE_cc0
1582 is not defined. This would allow it to work on the m88k. */
1583 /* ?? This optimization is only safe before cse is run if HAVE_cc0
1584 is not defined and the condition is tested by a separate compare
1585 insn. This is because the code below assumes that the result
1586 of the compare dies in the following branch.
1588 Not only that, but there might be other insns between the
1589 compare and branch whose results are live. Those insns need
1590 to be executed.
1592 A way to fix this is to move the insns at JUMP_LABEL (insn)
1593 to before INSN. If we are running before flow, they will
1594 be deleted if they aren't needed. But this doesn't work
1595 well after flow.
1597 This is really a special-case of jump threading, anyway. The
1598 right thing to do is to replace this and jump threading with
1599 much simpler code in cse.
1601 This code has been turned off in the non-cc0 case in the
1602 meantime. */
1604 #ifdef HAVE_cc0
1606 /* Safe to skip USE and CLOBBER insns here
1607 since they will not be deleted. */
1615 /* If we find that the next value tested is `x'
1616 (TEMP1 is the insn where this happens), win. */
1619 #ifdef HAVE_cc0
1620 /* Does temp1 `tst' the value of x? */
1624 #else
1625 /* Does temp1 compare the value of x against zero? */
1632 #endif
1634 {
1635 /* Get the if_then_else from the condjump. */
1638 {
1641 rtx cond
1644 rtx ultimate;
1650 else
1660 }
1661 }
1662 #endif
1664 #if 0
1665 /* @@ This needs a bit of work before it will be right.
1667 Any type of comparison can be accepted for the first and
1668 second compare. When rewriting the first jump, we must
1669 compute the what conditions can reach label3, and use the
1670 appropriate code. We can not simply reverse/swap the code
1671 of the first jump. In some cases, the second jump must be
1672 rewritten also.
1674 For example,
1675 < == converts to > ==
1676 < != converts to == >
1677 etc.
1679 If the code is written to only accept an '==' test for the second
1680 compare, then all that needs to be done is to swap the condition
1681 of the first branch.
1683 It is questionable whether we want this optimization anyways,
1684 since if the user wrote code like this because he/she knew that
1685 the jump to label1 is taken most of the time, then rewriting
1686 this gives slower code. */
1687 /* @@ This should call get_condition to find the values being
1688 compared, instead of looking for a COMPARE insn when HAVE_cc0
1689 is not defined. This would allow it to work on the m88k. */
1690 /* @@ This optimization is only safe before cse is run if HAVE_cc0
1691 is not defined and the condition is tested by a separate compare
1692 insn. This is because the code below assumes that the result
1693 of the compare dies in the following branch. */
1695 /* Simplify test a ~= b
1696 condjump label1;
1697 test a == b
1698 condjump label2;
1699 jump label3;
1700 label1:
1702 rewriting as
1703 test a ~~= b
1704 condjump label3
1705 test a == b
1706 condjump label2
1707 label1:
1709 where ~= is an inequality, e.g. >, and ~~= is the swapped
1710 inequality, e.g. <.
1712 We recognize this case scanning backwards.
1714 TEMP is the conditional jump to `label2';
1715 TEMP1 is the test for `a == b';
1716 TEMP2 is the conditional jump to `label1';
1717 TEMP3 is the test for `a ~= b'. */
1726 #ifdef HAVE_cc0
1728 #else
1732 #endif
1746 {
1751 {
1754 }
1758 }
1759 #endif
1760 /* Simplify if (...) {... x = 1;} if (x) ...
1762 We recognize this case backwards.
1764 TEMP is the test of `x';
1765 TEMP1 is the assignment to `x' at the end of the
1766 previous statement. */
1767 /* @@ This should call get_condition to find the values being
1768 compared, instead of looking for a COMPARE insn when HAVE_cc0
1769 is not defined. This would allow it to work on the m88k. */
1770 /* @@ This optimization is only safe before cse is run if HAVE_cc0
1771 is not defined and the condition is tested by a separate compare
1772 insn. This is because the code below assumes that the result
1773 of the compare dies in the following branch. */
1775 /* ??? This has to be turned off. The problem is that the
1776 unconditional jump might indirectly end up branching to the
1777 label between TEMP1 and TEMP. We can't detect this, in general,
1778 since it may become a jump to there after further optimizations.
1779 If that jump is done, it will be deleted, so we will retry
1780 this optimization in the next pass, thus an infinite loop.
1782 The present code prevents this by putting the jump after the
1783 label, but this is not logically correct. */
1784 #if 0
1786 /* Safe to skip USE and CLOBBER insns here
1787 since they will not be deleted. */
1792 #ifdef HAVE_cc0
1795 #else
1796 /* Temp must be a compare insn, we can not accept a register
1797 to register move here, since it may not be simply a
1798 tst insn. */
1804 #endif
1805 /* May skip USE or CLOBBER insns here
1806 for checking for opportunity, since we
1807 take care of them later. */
1811 #ifdef HAVE_cc0
1813 #else
1816 #endif
1818 /* If this isn't true, cse will do the job. */
1820 {
1821 /* Get the if_then_else from the condjump. */
1826 {
1828 rtx last_insn;
1829 rtx ultimate;
1830 rtx p;
1832 /* Get the place that condjump will jump to
1833 if it is reached from here. */
1837 else
1839 /* Get it as a CODE_LABEL. */
1842 else
1843 /* Get the label out of the LABEL_REF. */
1846 /* Insert the jump immediately before TEMP, specifically
1847 after the label that is between TEMP1 and TEMP. */
1850 /* If we would be branching to the next insn, the jump
1851 would immediately be deleted and the re-inserted in
1852 a subsequent pass over the code. So don't do anything
1853 in that case. */
1856 {
1859 last_insn);
1864 {
1868 }
1871 }
1872 }
1873 }
1874 #endif
1875 /* Detect a conditional jump going to the same place
1876 as an immediately following unconditional jump. */
1882 {
1885 /* ??? Optional. Disables some optimizations, but makes
1886 gcov output more accurate with -O. */
1893 {
1897 }
1898 }
1899 /* Detect a conditional jump jumping over an unconditional jump. */
1902 && ! this_is_simplejump
1908 {
1909 /* When we invert the unconditional jump, we will be
1910 decrementing the usage count of its old label.
1911 Make sure that we don't delete it now because that
1912 might cause the following code to be deleted. */
1920 {
1921 /* It is very likely that if there are USE insns before
1922 this jump, they hold REG_DEAD notes. These REG_DEAD
1923 notes are no longer valid due to this optimization,
1924 and will cause the life-analysis that following passes
1925 (notably delayed-branch scheduling) to think that
1926 these registers are dead when they are not.
1928 To prevent this trouble, we just remove the USE insns
1929 from the insn chain. */
1933 {
1937 }
1942 }
1944 /* We can now safely delete the label if it is unreferenced
1945 since the delete_insn above has deleted the BARRIER. */
1949 }
1950 else
1951 {
1952 /* Detect a jump to a jump. */
1957 {
1960 }
1962 /* Look for if (foo) bar; else break; */
1963 /* The insns look like this:
1964 insn = condjump label1;
1965 ...range1 (some insns)...
1966 jump label2;
1967 label1:
1968 ...range2 (some insns)...
1969 jump somewhere unconditionally
1970 label2: */
1971 {
1974 /* Don't do this optimization on the first round, so that
1975 jump-around-a-jump gets simplified before we ask here
1976 whether a jump is unconditional.
1978 Also don't do it when we are called after reload since
1979 it will confuse reorg. */
1982 /* Make sure INSN is something we can invert. */
1989 {
1996 /* Invert the jump condition, so we
1997 still execute the same insns in each case. */
1999 {
2004 rtx rangenext;
2006 /* Include in each range any notes before it, to be
2007 sure that we get the line number note if any, even
2008 if there are other notes here. */
2017 /* Don't move NOTEs for blocks or loops; shift them
2018 outside the ranges, where they'll stay put. */
2022 /* Get current surrounds of the 2 ranges. */
2028 /* Splice range2 where range1 was. */
2033 /* Splice range1 where range2 was. */
2039 /* Check for a loop end note between the end of
2040 range2, and the next code label. If there is one,
2041 then what we have really seen is
2042 if (foo) break; end_of_loop;
2043 and moved the break sequence outside the loop.
2044 We must move the LOOP_END note to where the
2045 loop really ends now, or we will confuse loop
2046 optimization. Stop if we find a LOOP_BEG note
2047 first, since we don't want to move the LOOP_END
2048 note in that case. */
2050 {
2053 {
2056 {
2067 }
2071 }
2072 }
2075 }
2076 }
2077 }
2079 /* Now that the jump has been tensioned,
2080 try cross jumping: check for identical code
2081 before the jump and before its target label. */
2083 /* First, cross jumping of conditional jumps: */
2086 {
2090 /* A conditional jump may be crossjumped
2091 only if the place it jumps to follows
2092 an opposing jump that comes back here. */
2095 /* We have no opposing jump;
2096 cannot cross jump this insn. */
2100 /* TARGET is nonzero if it is ok to cross jump
2101 to code before TARGET. If so, see if matches. */
2107 {
2109 /* Make the old conditional jump
2110 into an unconditional one. */
2115 /* Add to jump_chain unless this is a new label
2116 whose UID is too large. */
2118 {
2122 }
2125 }
2126 }
2128 /* Cross jumping of unconditional jumps:
2129 a few differences. */
2132 {
2134 rtx target;
2138 /* TARGET is nonzero if it is ok to cross jump
2139 to code before TARGET. If so, see if matches. */
2143 /* If cannot cross jump to code before the label,
2144 see if we can cross jump to another jump to
2145 the same label. */
2146 /* Try each other jump to this label. */
2153 /* Ignore TARGET if it's deleted. */
2159 {
2163 }
2164 }
2166 /* This code was dead in the previous jump.c! */
2168 {
2169 /* Return insns all "jump to the same place"
2170 so we can cross-jump between any two of them. */
2176 /* If cannot cross jump to code before the label,
2177 see if we can cross jump to another jump to
2178 the same label. */
2179 /* Try each other jump to this label. */
2190 {
2194 }
2195 }
2196 }
2197 }
2200 }
2202 /* Delete extraneous line number notes.
2203 Note that two consecutive notes for different lines are not really
2204 extraneous. There should be some indication where that line belonged,
2205 even if it became empty. */
2207 {
2212 {
2213 /* Delete this note if it is identical to previous note. */
2217 {
2220 }
2223 }
2224 }
2226 #ifdef HAVE_return
2228 {
2229 /* If we fall through to the epilogue, see if we can insert a RETURN insn
2230 in front of it. If the machine allows it at this point (we might be
2231 after reload for a leaf routine), it will improve optimization for it
2232 to be there. We do this both here and at the start of this pass since
2233 the RETURN might have been deleted by some of our optimizations. */
2239 {
2242 }
2243 }
2244 #endif
2246 /* See if there is still a NOTE_INSN_FUNCTION_END in this function.
2247 If so, delete it, and record that this function can drop off the end. */
2250 {
2253 /* One label can follow the end-note: the return label. */
2255 /* Ordinary insns can follow it if returning a structure. */
2257 /* If machine uses explicit RETURN insns, no epilogue,
2258 then one of them follows the note. */
2261 /* A barrier can follow the return insn. */
2263 /* Other kinds of notes can follow also. */
2267 }
2269 /* Report if control can fall through at the end of the function. */
2272 {
2275 }
2277 /* Show JUMP_CHAIN no longer valid. */
2279 }
2280 \f
2281 /* LOOP_START is a NOTE_INSN_LOOP_BEG note that is followed by an unconditional
2282 jump. Assume that this unconditional jump is to the exit test code. If
2283 the code is sufficiently simple, make a copy of it before INSN,
2284 followed by a jump to the exit of the loop. Then delete the unconditional
2285 jump after INSN.
2287 Return 1 if we made the change, else 0.
2289 This is only safe immediately after a regscan pass because it uses the
2290 values of regno_first_uid and regno_last_uid. */
2292 static int
2294 rtx loop_start;
2295 {
2300 rtx lastexit;
2304 /* Scan the exit code. We do not perform this optimization if any insn:
2306 is a CALL_INSN
2307 is a CODE_LABEL
2308 has a REG_RETVAL or REG_LIBCALL note (hard to adjust)
2309 is a NOTE_INSN_LOOP_BEG because this means we have a nested loop
2310 is a NOTE_INSN_BLOCK_{BEG,END} because duplicating these notes
2311 are not valid
2313 Also, don't do this if the exit code is more than 20 insns. */
2316 insn
2320 {
2322 {
2327 /* We could be in front of the wrong NOTE_INSN_LOOP_END if there is
2328 a jump immediately after the loop start that branches outside
2329 the loop but within an outer loop, near the exit test.
2330 If we copied this exit test and created a phony
2331 NOTE_INSN_LOOP_VTOP, this could make instructions immediately
2332 before the exit test look like these could be safely moved
2333 out of the loop even if they actually may be never executed.
2334 This can be avoided by checking here for NOTE_INSN_LOOP_CONT. */
2351 }
2352 }
2354 /* Unless INSN is zero, we can do the optimization. */
2360 /* See if any insn sets a register only used in the loop exit code and
2361 not a user variable. If so, replace it with a new register. */
2370 {
2376 {
2377 /* We can do the replacement. Allocate reg_map if this is the
2378 first replacement we found. */
2380 {
2383 }
2388 }
2389 }
2391 /* Now copy each insn. */
2394 {
2399 /* Only copy line-number notes. */
2401 {
2404 }
2414 /* Copy all REG_NOTES except REG_LABEL since mark_jump_label will
2415 make them. */
2432 {
2436 }
2438 /* If this is a simple jump, add it to the jump chain. */
2442 {
2446 }
2451 }
2453 /* Now clean up by emitting a jump to the end label and deleting the jump
2454 at the start of the loop. */
2456 {
2458 loop_start);
2462 {
2466 }
2468 }
2470 /* Mark the exit code as the virtual top of the converted loop. */
2476 }
2477 \f
2478 /* Move all block-beg, block-end, loop-beg, loop-cont, loop-vtop, and
2479 loop-end notes between START and END out before START. Assume that
2480 END is not such a note. START may be such a note. Returns the value
2481 of the new starting insn, which may be different if the original start
2482 was such a note. */
2484 rtx
2487 {
2488 rtx insn;
2489 rtx next;
2492 {
2501 {
2504 else
2505 {
2513 }
2514 }
2515 }
2518 }
2519 \f
2520 /* Compare the instructions before insn E1 with those before E2
2521 to find an opportunity for cross jumping.
2522 (This means detecting identical sequences of insns followed by
2523 jumps to the same place, or followed by a label and a jump
2524 to that label, and replacing one with a jump to the other.)
2526 Assume E1 is a jump that jumps to label E2
2527 (that is not always true but it might as well be).
2528 Find the longest possible equivalent sequences
2529 and store the first insns of those sequences into *F1 and *F2.
2530 Store zero there if no equivalent preceding instructions are found.
2532 We give up if we find a label in stream 1.
2533 Actually we could transfer that label into stream 2. */
2535 static void
2540 {
2552 {
2562 /* Don't allow the range of insns preceding E1 or E2
2563 to include the other (E2 or E1). */
2567 /* If we will get to this code by jumping, those jumps will be
2568 tensioned to go directly to the new label (before I2),
2569 so this cross-jumping won't cost extra. So reduce the minimum. */
2571 {
2574 }
2582 /* If this is a CALL_INSN, compare register usage information.
2583 If we don't check this on stack register machines, the two
2584 CALL_INSNs might be merged leaving reg-stack.c with mismatching
2585 numbers of stack registers in the same basic block.
2586 If we don't check this on machines with delay slots, a delay slot may
2587 be filled that clobbers a parameter expected by the subroutine.
2589 ??? We take the simple route for now and assume that if they're
2590 equal, they were constructed identically. */
2597 #ifdef STACK_REGS
2598 /* If cross_jump_death_matters is not 0, the insn's mode
2599 indicates whether or not the insn contains any stack-like
2600 regs. */
2603 {
2604 /* If register stack conversion has already been done, then
2605 death notes must also be compared before it is certain that
2606 the two instruction streams match. */
2608 rtx note;
2628 done:
2629 ;
2630 }
2631 #endif
2633 /* Don't allow old-style asm or volatile extended asms to be accepted
2634 for cross jumping purposes. It is conceptually correct to allow
2635 them, since cross-jumping preserves the dynamic instruction order
2636 even though it is changing the static instruction order. However,
2637 if an asm is being used to emit an assembler pseudo-op, such as
2638 the MIPS `.set reorder' pseudo-op, then the static instruction order
2639 matters and it must be preserved. */
2647 {
2648 /* The following code helps take care of G++ cleanups. */
2649 rtx equiv1;
2650 rtx equiv2;
2657 /* If the equivalences are not to a constant, they may
2658 reference pseudos that no longer exist, so we can't
2659 use them. */
2662 {
2667 {
2674 }
2675 }
2677 /* Insns fail to match; cross jumping is limited to the following
2678 insns. */
2680 #ifdef HAVE_cc0
2681 /* Don't allow the insn after a compare to be shared by
2682 cross-jumping unless the compare is also shared.
2683 Here, if either of these non-matching insns is a compare,
2684 exclude the following insn from possible cross-jumping. */
2687 #endif
2689 /* If cross-jumping here will feed a jump-around-jump
2690 optimization, this jump won't cost extra, so reduce
2691 the minimum. */
2697 }
2699 win:
2701 {
2702 /* Ok, this insn is potentially includable in a cross-jump here. */
2705 }
2706 }
2710 }
2712 static void
2715 {
2716 /* Find an existing label at this point
2717 or make a new one if there is none. */
2720 /* Make the same jump insn jump to the new point. */
2722 {
2723 /* Remove from jump chain of returns. */
2725 /* Change the insn. */
2730 /* Add to new the jump chain. */
2733 {
2736 }
2737 }
2738 else
2741 /* Delete the matching insns before the jump. Also, remove any REG_EQUAL
2742 or REG_EQUIV note in the NEWLPOS stream that isn't also present in
2743 the NEWJPOS stream. */
2746 {
2747 rtx lnote;
2759 }
2760 }
2761 \f
2762 /* Return the label before INSN, or put a new label there. */
2764 rtx
2766 rtx insn;
2767 {
2768 rtx label;
2770 /* Find an existing label at this point
2771 or make a new one if there is none. */
2775 {
2781 }
2783 }
2785 /* Return the label after INSN, or put a new label there. */
2787 rtx
2789 rtx insn;
2790 {
2791 rtx label;
2793 /* Find an existing label at this point
2794 or make a new one if there is none. */
2798 {
2802 }
2804 }
2805 \f
2806 /* Return 1 if INSN is a jump that jumps to right after TARGET
2807 only on the condition that TARGET itself would drop through.
2808 Assumes that TARGET is a conditional jump. */
2810 static int
2813 {
2829 {
2833 }
2836 {
2840 }
2845 }
2846 \f
2847 /* Given a comparison, COMPARISON, inside a conditional jump insn, INSN,
2848 return non-zero if it is safe to reverse this comparison. It is if our
2849 floating-point is not IEEE, if this is an NE or EQ comparison, or if
2850 this is known to be an integer comparison. */
2852 int
2854 rtx comparison;
2855 rtx insn;
2856 {
2857 rtx arg0;
2859 /* If this is not actually a comparison, we can't reverse it. */
2864 /* If this is an NE comparison, it is safe to reverse it to an EQ
2865 comparison and vice versa, even for floating point. If no operands
2866 are NaNs, the reversal is valid. If some operand is a NaN, EQ is
2867 always false and NE is always true, so the reversal is also valid. */
2868 || flag_fast_math
2875 /* Make sure ARG0 is one of the actual objects being compared. If we
2876 can't do this, we can't be sure the comparison can be reversed.
2878 Handle cc0 and a MODE_CC register. */
2880 #ifdef HAVE_cc0
2882 #endif
2883 )
2884 {
2895 }
2897 /* We can reverse this if ARG0 is a CONST_INT or if its mode is
2898 not VOIDmode and neither a MODE_CC nor MODE_FLOAT type. */
2903 }
2905 /* Given an rtx-code for a comparison, return the code
2906 for the negated comparison.
2907 WATCH OUT! reverse_condition is not safe to use on a jump
2908 that might be acting on the results of an IEEE floating point comparison,
2909 because of the special treatment of non-signaling nans in comparisons.
2910 Use can_reverse_comparison_p to be sure. */
2912 enum rtx_code
2915 {
2917 {
2951 }
2952 }
2954 /* Similar, but return the code when two operands of a comparison are swapped.
2955 This IS safe for IEEE floating-point. */
2957 enum rtx_code
2960 {
2962 {
2994 }
2995 }
2997 /* Given a comparison CODE, return the corresponding unsigned comparison.
2998 If CODE is an equality comparison or already an unsigned comparison,
2999 CODE is returned. */
3001 enum rtx_code
3004 {
3006 {
3029 }
3030 }
3032 /* Similarly, return the signed version of a comparison. */
3034 enum rtx_code
3037 {
3039 {
3062 }
3063 }
3064 \f
3065 /* Return non-zero if CODE1 is more strict than CODE2, i.e., if the
3066 truth of CODE1 implies the truth of CODE2. */
3068 int
3071 {
3076 {
3104 }
3107 }
3108 \f
3109 /* Return 1 if INSN is an unconditional jump and nothing else. */
3111 int
3113 rtx insn;
3114 {
3119 }
3121 /* Return nonzero if INSN is a (possibly) conditional jump
3122 and nothing more. */
3124 int
3126 rtx insn;
3127 {
3146 }
3148 /* Return nonzero if INSN is a (possibly) conditional jump
3149 and nothing more. */
3151 int
3153 rtx insn;
3154 {
3159 else
3179 }
3181 /* Return 1 if X is an RTX that does nothing but set the condition codes
3182 and CLOBBER or USE registers.
3183 Return -1 if X does explicitly set the condition codes,
3184 but also does other things. */
3186 int
3188 rtx x;
3189 {
3190 #ifdef HAVE_cc0
3194 {
3199 {
3205 }
3207 }
3209 #else
3211 #endif
3212 }
3213 \f
3214 /* Follow any unconditional jump at LABEL;
3215 return the ultimate label reached by any such chain of jumps.
3216 If LABEL is not followed by a jump, return LABEL.
3217 If the chain loops or we can't find end, return LABEL,
3218 since that tells caller to avoid changing the insn.
3220 If RELOAD_COMPLETED is 0, we do not chain across a NOTE_INSN_LOOP_BEG or
3221 a USE or CLOBBER. */
3223 rtx
3225 rtx label;
3226 {
3240 depth++)
3241 {
3242 /* Don't chain through the insn that jumps into a loop
3243 from outside the loop,
3244 since that would create multiple loop entry jumps
3245 and prevent loop optimization. */
3246 rtx tem;
3251 /* ??? Optional. Disables some optimizations, but makes
3252 gcov output more accurate with -O. */
3256 /* If we have found a cycle, make the insn jump to itself. */
3266 }
3270 }
3272 /* Assuming that field IDX of X is a vector of label_refs,
3273 replace each of them by the ultimate label reached by it.
3274 Return nonzero if a change is made.
3275 If IGNORE_LOOPS is 0, we do not chain across a NOTE_INSN_LOOP_BEG. */
3277 static int
3281 {
3285 {
3289 {
3295 }
3296 }
3298 }
3299 \f
3300 /* Find all CODE_LABELs referred to in X, and increment their use counts.
3301 If INSN is a JUMP_INSN and there is at least one CODE_LABEL referenced
3302 in INSN, then store one of them in JUMP_LABEL (INSN).
3303 If INSN is an INSN or a CALL_INSN and there is at least one CODE_LABEL
3304 referenced in INSN, add a REG_LABEL note containing that label to INSN.
3305 Also, when there are consecutive labels, canonicalize on the last of them.
3307 Note that two labels separated by a loop-beginning note
3308 must be kept distinct if we have not yet done loop-optimization,
3309 because the gap between them is where loop-optimize
3310 will want to move invariant code to. CROSS_JUMP tells us
3311 that loop-optimization is done with.
3313 Once reload has completed (CROSS_JUMP non-zero), we need not consider
3314 two labels distinct if they are separated by only USE or CLOBBER insns. */
3316 static void
3319 rtx insn;
3321 {
3327 {
3340 /* If this is a constant-pool reference, see if it is a label. */
3347 {
3350 rtx note;
3351 rtx next;
3356 /* Ignore references to labels of containing functions. */
3360 /* If there are other labels following this one,
3361 replace it with the last of the consecutive labels. */
3363 {
3375 /* ??? Optional. Disables some optimizations, but
3376 makes gcov output more accurate with -O. */
3379 }
3386 {
3390 /* If we've changed OLABEL and we had a REG_LABEL note
3391 for it, update it as well. */
3396 /* Otherwise, add a REG_LABEL note for LABEL unless there already
3397 is one. */
3399 {
3401 /* Don't record labels that refer to dispatch tables.
3402 This is not necessary, since the tablejump
3403 references the same label.
3404 And if we did record them, flow.c would make worse code. */
3411 }
3412 }
3414 }
3416 /* Do walk the labels in a vector, but not the first operand of an
3417 ADDR_DIFF_VEC. Don't set the JUMP_LABEL of a vector. */
3421 {
3426 }
3431 }
3435 {
3439 {
3443 }
3444 }
3445 }
3447 /* If all INSN does is set the pc, delete it,
3448 and delete the insn that set the condition codes for it
3449 if that's what the previous thing was. */
3451 void
3453 rtx insn;
3454 {
3459 }
3461 /* Delete INSN and recursively delete insns that compute values used only
3462 by INSN. This uses the REG_DEAD notes computed during flow analysis.
3463 If we are running before flow.c, we need do nothing since flow.c will
3464 delete dead code. We also can't know if the registers being used are
3465 dead or not at this point.
3467 Otherwise, look at all our REG_DEAD notes. If a previous insn does
3468 nothing other than set a register that dies in this insn, we can delete
3469 that insn as well.
3471 On machines with CC0, if CC0 is used in this insn, we may be able to
3472 delete the insn that set it. */
3474 static void
3476 rtx insn;
3477 {
3480 #ifdef HAVE_cc0
3482 {
3484 /* We assume that at this stage
3485 CC's are always set explicitly
3486 and always immediately before the jump that
3487 will use them. So if the previous insn
3488 exists to set the CC's, delete it
3489 (unless it performs auto-increments, etc.). */
3492 {
3496 else
3497 /* Otherwise, show that cc0 won't be used. */
3500 }
3501 }
3502 #endif
3505 {
3506 rtx our_prev;
3511 /* Verify that the REG_NOTE is legitimate. */
3518 {
3519 /* If we reach a SEQUENCE, it is too complex to try to
3520 do anything with it, so give up. */
3526 /* reorg creates USEs that look like this. We leave them
3527 alone because reorg needs them for its own purposes. */
3531 {
3536 {
3537 /* If we find a SET of something else, we can't
3538 delete the insn. */
3543 {
3549 }
3553 }
3559 }
3561 /* If OUR_PREV references the register that dies here, it is an
3562 additional use. Hence any prior SET isn't dead. However, this
3563 insn becomes the new place for the REG_DEAD note. */
3566 {
3570 }
3571 }
3572 }
3575 }
3576 \f
3577 /* Delete insn INSN from the chain of insns and update label ref counts.
3578 May delete some following insns as a consequence; may even delete
3579 a label elsewhere and insns that follow it.
3581 Returns the first insn after INSN that was not deleted. */
3583 rtx
3586 {
3595 /* This insn is already deleted => return first following nondeleted. */
3599 /* Don't delete user-declared labels. Convert them to special NOTEs
3600 instead. */
3603 {
3608 }
3609 else
3610 /* Mark this insn as deleted. */
3613 /* If this is an unconditional jump, delete it from the jump chain. */
3617 /* If instruction is followed by a barrier,
3618 delete the barrier too. */
3621 {
3624 }
3626 /* Patch out INSN (and the barrier if any) */
3629 {
3631 {
3636 }
3639 {
3643 }
3647 }
3649 /* If deleting a jump, decrement the count of the label,
3650 and delete the label if it is now unused. */
3654 {
3655 /* This can delete NEXT or PREV,
3656 either directly if NEXT is JUMP_LABEL (INSN),
3657 or indirectly through more levels of jumps. */
3659 /* I feel a little doubtful about this loop,
3660 but I see no clean and sure alternative way
3661 to find the first insn after INSN that is not now deleted.
3662 I hope this works. */
3666 }
3668 /* Likewise if we're deleting a dispatch table. */
3673 {
3684 }
3689 /* If INSN was a label and a dispatch table follows it,
3690 delete the dispatch table. The tablejump must have gone already.
3691 It isn't useful to fall through into a table. */
3700 /* If INSN was a label, delete insns following it if now unreachable. */
3703 {
3709 {
3713 /* Keep going past other deleted labels to delete what follows. */
3716 else
3717 /* Note: if this deletes a jump, it can cause more
3718 deletion of unreachable code, after a different label.
3719 As long as the value from this recursive call is correct,
3720 this invocation functions correctly. */
3722 }
3723 }
3726 }
3728 /* Advance from INSN till reaching something not deleted
3729 then return that. May return INSN itself. */
3731 rtx
3733 rtx insn;
3734 {
3738 }
3739 \f
3740 /* Delete a range of insns from FROM to TO, inclusive.
3741 This is for the sake of peephole optimization, so assume
3742 that whatever these insns do will still be done by a new
3743 peephole insn that will replace them. */
3745 void
3748 {
3752 {
3757 {
3760 /* Patch this insn out of the chain. */
3761 /* We don't do this all at once, because we
3762 must preserve all NOTEs. */
3768 }
3773 }
3775 /* Note that if TO is an unconditional jump
3776 we *do not* delete the BARRIER that follows,
3777 since the peephole that replaces this sequence
3778 is also an unconditional jump in that case. */
3779 }
3780 \f
3781 /* Invert the condition of the jump JUMP, and make it jump
3782 to label NLABEL instead of where it jumps now. */
3784 int
3787 {
3788 /* We have to either invert the condition and change the label or
3789 do neither. Either operation could fail. We first try to invert
3790 the jump. If that succeeds, we try changing the label. If that fails,
3791 we invert the jump back to what it was. */
3797 {
3799 {
3802 /* An inverted jump means that a probability taken becomes a
3803 probability not taken. Subtract the branch probability from the
3804 probability base to convert it back to a taken probability.
3805 (We don't flip the probability on a branch that's never taken. */
3808 }
3811 }
3814 /* This should just be putting it back the way it was. */
3818 }
3820 /* Invert the jump condition of rtx X contained in jump insn, INSN.
3822 Return 1 if we can do so, 0 if we cannot find a way to do so that
3823 matches a pattern. */
3825 int
3827 rtx x;
3828 rtx insn;
3829 {
3837 {
3841 /* We can do this in two ways: The preferable way, which can only
3842 be done if this is not an integer comparison, is to reverse
3843 the comparison code. Otherwise, swap the THEN-part and ELSE-part
3844 of the IF_THEN_ELSE. If we can't do either, fail. */
3857 }
3861 {
3866 {
3871 }
3872 }
3875 }
3876 \f
3877 /* Make jump JUMP jump to label NLABEL instead of where it jumps now.
3878 If the old jump target label is unused as a result,
3879 it and the code following it may be deleted.
3881 If NLABEL is zero, we are to turn the jump into a (possibly conditional)
3882 RETURN insn.
3884 The return value will be 1 if the change was made, 0 if it wasn't (this
3885 can only occur for NLABEL == 0). */
3887 int
3890 {
3899 /* If this is an unconditional branch, delete it from the jump_chain of
3900 OLABEL and add it to the jump_chain of NLABEL (assuming both labels
3901 have UID's in range and JUMP_CHAIN is valid). */
3904 {
3910 {
3913 }
3914 }
3924 }
3926 /* Delete the instruction JUMP from any jump chain it might be on. */
3928 static void
3930 rtx jump;
3931 {
3935 /* Handle unconditional jumps. */
3940 /* Handle return insns. */
3947 else
3948 {
3949 rtx insn;
3955 {
3958 }
3959 }
3960 }
3962 /* If NLABEL is nonzero, throughout the rtx at LOC,
3963 alter (LABEL_REF OLABEL) to (LABEL_REF NLABEL). If OLABEL is
3964 zero, alter (RETURN) to (LABEL_REF NLABEL).
3966 If NLABEL is zero, alter (LABEL_REF OLABEL) to (RETURN) and check
3967 validity with validate_change. Convert (set (pc) (label_ref olabel))
3968 to (return).
3970 Return 0 if we found a change we would like to make but it is invalid.
3971 Otherwise, return 1. */
3973 int
3977 rtx insn;
3978 {
3985 {
3987 {
3990 else
3993 }
3994 }
3996 {
4001 }
4010 {
4015 {
4020 }
4021 }
4024 }
4025 \f
4026 /* Make jump JUMP jump to label NLABEL, assuming it used to be a tablejump.
4028 If the old jump target label (before the dispatch table) becomes unused,
4029 it and the dispatch table may be deleted. In that case, find the insn
4030 before the jump references that label and delete it and logical successors
4031 too. */
4033 static void
4036 {
4039 /* Add this jump to the jump_chain of NLABEL. */
4042 {
4045 }
4053 {
4056 }
4057 }
4059 /* Find the insn referencing LABEL that is a logical predecessor of INSN.
4060 If we found one, delete it and then delete this insn if DELETE_THIS is
4061 non-zero. Return non-zero if INSN or a predecessor references LABEL. */
4063 static int
4067 {
4069 rtx link;
4073 {
4075 {
4078 }
4079 else
4081 }
4085 {
4087 {
4090 }
4091 else
4093 }
4096 }
4097 \f
4098 /* Like rtx_equal_p except that it considers two REGs as equal
4099 if they renumber to the same value and considers two commutative
4100 operations to be the same if the order of the operands has been
4101 reversed. */
4103 int
4106 {
4117 {
4124 /* If we haven't done any renumbering, don't
4125 make any assumptions. */
4130 {
4135 {
4138 }
4139 }
4141 else
4142 {
4146 }
4149 {
4154 {
4157 }
4158 }
4160 else
4161 {
4165 }
4168 }
4170 /* Now we have disposed of all the cases
4171 in which different rtx codes can match. */
4176 {
4187 /* We can't assume nonlocal labels have their following insns yet. */
4191 /* Two label-refs are equivalent if they point at labels
4192 in the same position in the instruction stream. */
4201 }
4203 /* (MULT:SI x y) and (MULT:HI x y) are NOT equivalent. */
4208 /* For commutative operations, the RTX match if the operand match in any
4209 order. Also handle the simple binary and unary cases without a loop. */
4221 /* Compare the elements. If any pair of corresponding elements
4222 fail to match, return 0 for the whole things. */
4226 {
4229 {
4253 /* fall through. */
4267 }
4268 }
4270 }
4271 \f
4272 /* If X is a hard register or equivalent to one or a subregister of one,
4273 return the hard register number. If X is a pseudo register that was not
4274 assigned a hard register, return the pseudo register number. Otherwise,
4275 return -1. Any rtx is valid for X. */
4277 int
4279 rtx x;
4280 {
4282 {
4286 }
4288 {
4292 }
4294 }
4295 \f
4296 /* Optimize code of the form:
4298 for (x = a[i]; x; ...)
4299 ...
4300 for (x = a[i]; x; ...)
4301 ...
4302 foo:
4304 Loop optimize will change the above code into
4306 if (x = a[i])
4307 for (;;)
4308 { ...; if (! (x = ...)) break; }
4309 if (x = a[i])
4310 for (;;)
4311 { ...; if (! (x = ...)) break; }
4312 foo:
4314 In general, if the first test fails, the program can branch
4315 directly to `foo' and skip the second try which is doomed to fail.
4316 We run this after loop optimization and before flow analysis. */
4318 /* When comparing the insn patterns, we track the fact that different
4319 pseudo-register numbers may have been used in each computation.
4320 The following array stores an equivalence -- same_regs[I] == J means
4321 that pseudo register I was used in the first set of tests in a context
4322 where J was used in the second set. We also count the number of such
4323 pending equivalences. If nonzero, the expressions really aren't the
4324 same. */
4330 /* Track any registers modified between the target of the first jump and
4331 the second jump. They never compare equal. */
4335 /* Record if memory was modified. */
4339 /* Called via note_stores on each insn between the target of the first
4340 branch and the second branch. It marks any changed registers. */
4342 static void
4344 rtx dest;
4345 rtx x;
4346 {
4361 else
4364 }
4366 /* F is the first insn in the chain of insns. */
4368 void
4370 rtx f;
4373 {
4374 /* Basic algorithm is to find a conditional branch,
4375 the label it may branch to, and the branch after
4376 that label. If the two branches test the same condition,
4377 walk back from both branch paths until the insn patterns
4378 differ, or code labels are hit. If we make it back to
4379 the target of the first branch, then we know that the first branch
4380 will either always succeed or always fail depending on the relative
4381 senses of the two branches. So adjust the first branch accordingly
4382 in this case. */
4391 /* Allocate register tables and quick-reset table. */
4399 {
4403 {
4404 /* Get to a candidate branch insn. */
4419 /* Look for a branch after the target. Record any registers and
4420 memory modified between the target and the branch. Stop when we
4421 get to a label since we can't know what was changed there. */
4423 {
4428 {
4429 /* If this is an unconditional jump and is the only use of
4430 its target label, we can follow it. */
4434 {
4437 }
4438 else
4440 }
4446 {
4455 }
4458 }
4460 /* Check the next candidate branch insn from the label
4461 of the first. */
4469 /* Get the comparison codes and operands, reversing the
4470 codes if appropriate. If we don't have comparison codes,
4471 we can't do anything. */
4484 /* If they test the same things and knowing that B1 branches
4485 tells us whether or not B2 branches, check if we
4486 can thread the branch. */
4493 b1))))
4494 {
4499 {
4501 {
4502 /* We have reached the target of the first branch.
4503 If there are no pending register equivalents,
4504 we know that this branch will either always
4505 succeed (if the senses of the two branches are
4506 the same) or always fail (if not). */
4507 rtx new_label;
4514 else
4518 {
4523 {
4524 /* Don't thread to the loop label. If a loop
4525 label is reused, loop optimization will
4526 be disabled for that loop. */
4529 }
4531 }
4533 }
4535 /* If either of these is not a normal insn (it might be
4536 a JUMP_INSN, CALL_INSN, or CODE_LABEL) we fail. (NOTEs
4537 have already been skipped above.) Similarly, fail
4538 if the insns are different. */
4547 }
4548 }
4549 }
4550 }
4551 }
4552 \f
4553 /* This is like RTX_EQUAL_P except that it knows about our handling of
4554 possibly equivalent registers and knows to consider volatile and
4555 modified objects as not equal.
4557 YINSN is the insn containing Y. */
4559 int
4562 rtx yinsn;
4563 {
4570 /* Rtx's of different codes cannot be equal. */
4574 /* (MULT:SI x y) and (MULT:HI x y) are NOT equivalent.
4575 (REG:SI x) and (REG:HI x) are NOT equivalent. */
4580 /* For floating-point, consider everything unequal. This is a bit
4581 pessimistic, but this pass would only rarely do anything for FP
4582 anyway. */
4587 /* For commutative operations, the RTX match if the operand match in any
4588 order. Also handle the simple binary and unary cases without a loop. */
4600 /* Handle special-cases first. */
4602 {
4607 /* If neither is user variable or hard register, check for possible
4608 equivalence. */
4615 {
4617 num_same_regs++;
4619 /* If this is the first time we are seeing a register on the `Y'
4620 side, see if it is the last use. If not, we can't thread the
4621 jump, so mark it as not equivalent. */
4626 }
4627 else
4633 /* If memory modified or either volatile, not equivalent.
4634 Else, check address. */
4647 /* Cancel a pending `same_regs' if setting equivalenced registers.
4648 Then process source. */
4651 {
4653 {
4655 num_same_regs--;
4656 }
4659 }
4660 else
4674 }
4681 {
4683 {
4697 /* Two vectors must have the same length. */
4701 /* And the corresponding elements must match. */
4720 /* These are just backpointers, so they don't matter. */
4726 /* It is believed that rtx's at this level will never
4727 contain anything but integers and other rtx's,
4728 except for within LABEL_REFs and SYMBOL_REFs. */
4731 }
4732 }
4734 }
4735 \f
4737 /* Return the insn that NEW can be safely inserted in front of starting at
4738 the jump insn INSN. Return 0 if it is not safe to do this jump
4739 optimization. Note that NEW must contain a single set. */
4741 static rtx
4743 rtx insn;
4745 {
4747 rtx prev;
4749 /* If NEW does not clobber, it is safe to insert NEW before INSN. */
4756 insn))
4762 /* There is a good chance that the previous insn PREV sets the thing
4763 being clobbered (often the CC in a hard reg). If PREV does not
4764 use what NEW sets, we can insert NEW before PREV. */
4770 insn)
4772 prev))
4776 }