1 /* Instruction scheduling pass.
2 Copyright (C) 1992, 1993, 1994, 1995, 1996, 1997, 1998,
3 1999, 2000, 2001, 2002, 2003, 2004 Free Software Foundation, Inc.
4 Contributed by Michael Tiemann (tiemann@cygnus.com) Enhanced by,
5 and currently maintained by, Jim Wilson (wilson@cygnus.com)
7 This file is part of GCC.
9 GCC is free software; you can redistribute it and/or modify it under
10 the terms of the GNU General Public License as published by the Free
11 Software Foundation; either version 2, or (at your option) any later
14 GCC is distributed in the hope that it will be useful, but WITHOUT ANY
15 WARRANTY; without even the implied warranty of MERCHANTABILITY or
16 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
19 You should have received a copy of the GNU General Public License
20 along with GCC; see the file COPYING. If not, write to the Free
21 Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
26 #include "coretypes.h"
31 #include "hard-reg-set.h"
35 #include "insn-config.h"
36 #include "insn-attr.h"
40 #include "cfglayout.h"
42 #include "sched-int.h"
46 /* The number of insns to be scheduled in total. */
47 static int target_n_insns;
48 /* The number of insns scheduled so far. */
49 static int sched_n_insns;
51 /* Implementations of the sched_info functions for region scheduling. */
52 static void init_ready_list (void);
53 static int can_schedule_ready_p (rtx);
54 static int schedule_more_p (void);
55 static const char *ebb_print_insn (rtx, int);
56 static int rank (rtx, rtx);
57 static int contributes_to_priority (rtx, rtx);
58 static void compute_jump_reg_dependencies (rtx, regset, regset, regset);
59 static basic_block earliest_block_with_similiar_load (basic_block, rtx);
60 static void add_deps_for_risky_insns (rtx, rtx);
61 static basic_block schedule_ebb (rtx, rtx);
62 static basic_block fix_basic_block_boundaries (basic_block, basic_block, rtx,
64 static void add_missing_bbs (rtx, basic_block, basic_block);
66 /* Return nonzero if there are more insns that should be scheduled. */
69 schedule_more_p (void)
71 return sched_n_insns < target_n_insns;
74 /* Add all insns that are initially ready to the ready list READY. Called
75 once before scheduling a set of insns. */
78 init_ready_list (void)
80 rtx prev_head = current_sched_info->prev_head;
81 rtx next_tail = current_sched_info->next_tail;
88 /* Print debugging information. */
89 if (sched_verbose >= 5)
90 debug_dependencies ();
93 /* Initialize ready list with all 'ready' insns in target block.
94 Count number of insns in the target block being scheduled. */
95 for (insn = NEXT_INSN (prev_head); insn != next_tail; insn = NEXT_INSN (insn))
102 /* Called after taking INSN from the ready list. Returns nonzero if this
103 insn can be scheduled, nonzero if we should silently discard it. */
106 can_schedule_ready_p (rtx insn ATTRIBUTE_UNUSED)
112 /* Return a string that contains the insn uid and optionally anything else
113 necessary to identify this insn in an output. It's valid to use a
114 static buffer for this. The ALIGNED parameter should cause the string
115 to be formatted so that multiple output lines will line up nicely. */
118 ebb_print_insn (rtx insn, int aligned ATTRIBUTE_UNUSED)
122 sprintf (tmp, "%4d", INSN_UID (insn));
126 /* Compare priority of two insns. Return a positive number if the second
127 insn is to be preferred for scheduling, and a negative one if the first
128 is to be preferred. Zero if they are equally good. */
131 rank (rtx insn1, rtx insn2)
133 basic_block bb1 = BLOCK_FOR_INSN (insn1);
134 basic_block bb2 = BLOCK_FOR_INSN (insn2);
136 if (bb1->count > bb2->count
137 || bb1->frequency > bb2->frequency)
139 if (bb1->count < bb2->count
140 || bb1->frequency < bb2->frequency)
145 /* NEXT is an instruction that depends on INSN (a backward dependence);
146 return nonzero if we should include this dependence in priority
150 contributes_to_priority (rtx next ATTRIBUTE_UNUSED,
151 rtx insn ATTRIBUTE_UNUSED)
156 /* INSN is a JUMP_INSN, COND_SET is the set of registers that are
157 conditionally set before INSN. Store the set of registers that
158 must be considered as used by this jump in USED and that of
159 registers that must be considered as set in SET. */
162 compute_jump_reg_dependencies (rtx insn, regset cond_set, regset used,
165 basic_block b = BLOCK_FOR_INSN (insn);
169 FOR_EACH_EDGE (e, ei, b->succs)
170 if (e->flags & EDGE_FALLTHRU)
171 /* The jump may be a by-product of a branch that has been merged
172 in the main codepath after being conditionalized. Therefore
173 it may guard the fallthrough block from using a value that has
174 conditionally overwritten that of the main codepath. So we
175 consider that it restores the value of the main codepath. */
176 bitmap_and (set, e->dest->il.rtl->global_live_at_start, cond_set);
178 bitmap_ior_into (used, e->dest->il.rtl->global_live_at_start);
181 /* Used in schedule_insns to initialize current_sched_info for scheduling
182 regions (or single basic blocks). */
184 static struct sched_info ebb_sched_info =
187 can_schedule_ready_p,
192 contributes_to_priority,
193 compute_jump_reg_dependencies,
202 /* It is possible that ebb scheduling eliminated some blocks.
203 Place blocks from FIRST to LAST before BEFORE. */
206 add_missing_bbs (rtx before, basic_block first, basic_block last)
208 for (; last != first->prev_bb; last = last->prev_bb)
210 before = emit_note_before (NOTE_INSN_BASIC_BLOCK, before);
211 NOTE_BASIC_BLOCK (before) = last;
212 BB_HEAD (last) = before;
213 BB_END (last) = before;
214 update_bb_for_insn (last);
218 /* Fixup the CFG after EBB scheduling. Re-recognize the basic
219 block boundaries in between HEAD and TAIL and update basic block
220 structures between BB and LAST. */
223 fix_basic_block_boundaries (basic_block bb, basic_block last, rtx head,
227 rtx last_inside = BB_HEAD (bb);
228 rtx aftertail = NEXT_INSN (tail);
232 for (; insn != aftertail; insn = NEXT_INSN (insn))
234 gcc_assert (!LABEL_P (insn));
235 /* Create new basic blocks just before first insn. */
236 if (inside_basic_block_p (insn))
242 /* Re-emit the basic block note for newly found BB header. */
245 note = emit_note_after (NOTE_INSN_BASIC_BLOCK, insn);
251 note = emit_note_before (NOTE_INSN_BASIC_BLOCK, insn);
259 /* Control flow instruction terminate basic block. It is possible
260 that we've eliminated some basic blocks (made them empty).
261 Find the proper basic block using BLOCK_FOR_INSN and arrange things in
262 a sensible way by inserting empty basic blocks as needed. */
263 if (control_flow_insn_p (insn) || (insn == tail && last_inside))
265 basic_block curr_bb = BLOCK_FOR_INSN (insn);
268 if (!control_flow_insn_p (insn))
270 if (bb == last->next_bb)
276 /* An obscure special case, where we do have partially dead
277 instruction scheduled after last control flow instruction.
278 In this case we can create new basic block. It is
279 always exactly one basic block last in the sequence. Handle
280 it by splitting the edge and repositioning the block.
281 This is somewhat hackish, but at least avoid cut&paste
283 A safer solution can be to bring the code into sequence,
284 do the split and re-emit it back in case this will ever
287 FOR_EACH_EDGE (f, ei, bb->prev_bb->succs)
288 if (f->flags & EDGE_FALLTHRU)
293 last = curr_bb = split_edge (f);
294 h = BB_HEAD (curr_bb);
295 BB_HEAD (curr_bb) = head;
296 BB_END (curr_bb) = insn;
297 /* Edge splitting created misplaced BASIC_BLOCK note, kill
301 /* It may happen that code got moved past unconditional jump in
302 case the code is completely dead. Kill it. */
305 rtx next = next_nonnote_insn (insn);
306 delete_insn_chain (head, insn);
307 /* We keep some notes in the way that may split barrier from the
309 if (BARRIER_P (next))
311 emit_barrier_after (prev_nonnote_insn (head));
319 BB_HEAD (curr_bb) = head;
320 BB_END (curr_bb) = insn;
321 add_missing_bbs (BB_HEAD (curr_bb), bb, curr_bb->prev_bb);
323 note = LABEL_P (head) ? NEXT_INSN (head) : head;
324 NOTE_BASIC_BLOCK (note) = curr_bb;
325 update_bb_for_insn (curr_bb);
326 bb = curr_bb->next_bb;
332 add_missing_bbs (BB_HEAD (last->next_bb), bb, last);
336 /* Returns the earliest block in EBB currently being processed where a
337 "similar load" 'insn2' is found, and hence LOAD_INSN can move
338 speculatively into the found block. All the following must hold:
340 (1) both loads have 1 base register (PFREE_CANDIDATEs).
341 (2) load_insn and load2 have a def-use dependence upon
342 the same insn 'insn1'.
344 From all these we can conclude that the two loads access memory
345 addresses that differ at most by a constant, and hence if moving
346 load_insn would cause an exception, it would have been caused by
349 The function uses list (given by LAST_BLOCK) of already processed
350 blocks in EBB. The list is formed in `add_deps_for_risky_insns'. */
353 earliest_block_with_similiar_load (basic_block last_block, rtx load_insn)
356 basic_block bb, earliest_block = NULL;
358 for (back_link = LOG_LINKS (load_insn);
360 back_link = XEXP (back_link, 1))
362 rtx insn1 = XEXP (back_link, 0);
364 if (GET_MODE (back_link) == VOIDmode)
366 /* Found a DEF-USE dependence (insn1, load_insn). */
369 for (fore_link = INSN_DEPEND (insn1);
371 fore_link = XEXP (fore_link, 1))
373 rtx insn2 = XEXP (fore_link, 0);
374 basic_block insn2_block = BLOCK_FOR_INSN (insn2);
376 if (GET_MODE (fore_link) == VOIDmode)
378 if (earliest_block != NULL
379 && earliest_block->index < insn2_block->index)
382 /* Found a DEF-USE dependence (insn1, insn2). */
383 if (haifa_classify_insn (insn2) != PFREE_CANDIDATE)
384 /* insn2 not guaranteed to be a 1 base reg load. */
387 for (bb = last_block; bb; bb = bb->aux)
388 if (insn2_block == bb)
392 /* insn2 is the similar load. */
393 earliest_block = insn2_block;
399 return earliest_block;
402 /* The following function adds dependencies between jumps and risky
403 insns in given ebb. */
406 add_deps_for_risky_insns (rtx head, rtx tail)
410 rtx last_jump = NULL_RTX;
411 rtx next_tail = NEXT_INSN (tail);
412 basic_block last_block = NULL, bb;
414 for (insn = head; insn != next_tail; insn = NEXT_INSN (insn))
415 if (control_flow_insn_p (insn))
417 bb = BLOCK_FOR_INSN (insn);
418 bb->aux = last_block;
422 else if (INSN_P (insn) && last_jump != NULL_RTX)
424 class = haifa_classify_insn (insn);
428 case PFREE_CANDIDATE:
429 if (flag_schedule_speculative_load)
431 bb = earliest_block_with_similiar_load (last_block, insn);
443 case PRISKY_CANDIDATE:
444 /* ??? We could implement better checking PRISKY_CANDIDATEs
445 analogous to sched-rgn.c. */
446 /* We can not change the mode of the backward
447 dependency because REG_DEP_ANTI has the lowest
449 if (! sched_insns_conditions_mutex_p (insn, prev))
451 if (!(current_sched_info->flags & DO_SPECULATION))
453 enum DEPS_ADJUST_RESULT res;
455 res = add_or_update_back_dep (insn, prev,
456 REG_DEP_ANTI, DEP_ANTI);
458 if (res == DEP_CREATED)
459 add_forw_dep (insn, LOG_LINKS (insn));
461 gcc_assert (res != DEP_CHANGED);
464 add_or_update_back_forw_dep (insn, prev, REG_DEP_ANTI,
465 set_dep_weak (DEP_ANTI,
476 /* Maintain the invariant that bb->aux is clear after use. */
479 bb = last_block->aux;
480 last_block->aux = NULL;
485 /* Schedule a single extended basic block, defined by the boundaries HEAD
489 schedule_ebb (rtx head, rtx tail)
493 struct deps tmp_deps;
494 basic_block first_bb = BLOCK_FOR_INSN (head);
495 basic_block last_bb = BLOCK_FOR_INSN (tail);
497 if (no_real_insns_p (head, tail))
498 return BLOCK_FOR_INSN (tail);
502 /* Compute LOG_LINKS. */
503 init_deps (&tmp_deps);
504 sched_analyze (&tmp_deps, head, tail);
505 free_deps (&tmp_deps);
507 /* Compute INSN_DEPEND. */
508 compute_forward_dependences (head, tail);
510 add_deps_for_risky_insns (head, tail);
512 if (targetm.sched.dependencies_evaluation_hook)
513 targetm.sched.dependencies_evaluation_hook (head, tail);
515 /* Set priorities. */
516 current_sched_info->sched_max_insns_priority = 0;
517 n_insns = set_priorities (head, tail);
518 current_sched_info->sched_max_insns_priority++;
520 current_sched_info->prev_head = PREV_INSN (head);
521 current_sched_info->next_tail = NEXT_INSN (tail);
523 if (write_symbols != NO_DEBUG)
525 save_line_notes (first_bb->index, head, tail);
526 rm_line_notes (head, tail);
529 /* rm_other_notes only removes notes which are _inside_ the
530 block---that is, it won't remove notes before the first real insn
531 or after the last real insn of the block. So if the first insn
532 has a REG_SAVE_NOTE which would otherwise be emitted before the
533 insn, it is redundant with the note before the start of the
534 block, and so we have to take it out. */
539 for (note = REG_NOTES (head); note; note = XEXP (note, 1))
540 if (REG_NOTE_KIND (note) == REG_SAVE_NOTE)
541 remove_note (head, note);
544 /* Remove remaining note insns from the block, save them in
545 note_list. These notes are restored at the end of
546 schedule_block (). */
547 rm_other_notes (head, tail);
549 current_sched_info->queue_must_finish_empty = 1;
551 schedule_block (-1, n_insns);
553 /* Sanity check: verify that all region insns were scheduled. */
554 gcc_assert (sched_n_insns == n_insns);
555 head = current_sched_info->head;
556 tail = current_sched_info->tail;
558 if (write_symbols != NO_DEBUG)
559 restore_line_notes (head, tail);
560 b = fix_basic_block_boundaries (first_bb, last_bb, head, tail);
562 finish_deps_global ();
566 /* The one entry point in this file. */
572 int probability_cutoff;
574 if (profile_info && flag_branch_probabilities)
575 probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY_FEEDBACK);
577 probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY);
578 probability_cutoff = REG_BR_PROB_BASE / 100 * probability_cutoff;
580 /* Taking care of this degenerate case makes the rest of
581 this code simpler. */
582 if (n_basic_blocks == NUM_FIXED_BLOCKS)
585 /* We need current_sched_info in init_dependency_caches, which is
586 invoked via sched_init. */
587 current_sched_info = &ebb_sched_info;
591 compute_bb_for_insn ();
593 /* Schedule every region in the subroutine. */
596 rtx head = BB_HEAD (bb);
604 if (bb->next_bb == EXIT_BLOCK_PTR
605 || LABEL_P (BB_HEAD (bb->next_bb)))
607 FOR_EACH_EDGE (e, ei, bb->succs)
608 if ((e->flags & EDGE_FALLTHRU) != 0)
612 if (e->probability <= probability_cutoff)
617 /* Blah. We should fix the rest of the code not to get confused by
622 head = NEXT_INSN (head);
623 else if (NOTE_P (tail))
624 tail = PREV_INSN (tail);
625 else if (LABEL_P (head))
626 head = NEXT_INSN (head);
631 bb = schedule_ebb (head, tail);
634 /* Updating life info can be done by local propagation over the modified
637 /* Reposition the prologue and epilogue notes in case we moved the
638 prologue/epilogue insns. */
639 if (reload_completed)
640 reposition_prologue_and_epilogue_notes (get_insns ());
642 if (write_symbols != NO_DEBUG)
643 rm_redundant_line_notes ();