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 (struct ready_list *);
53 static int can_schedule_ready_p (rtx);
54 static int new_ready (rtx);
55 static int schedule_more_p (void);
56 static const char *ebb_print_insn (rtx, int);
57 static int rank (rtx, rtx);
58 static int contributes_to_priority (rtx, rtx);
59 static void compute_jump_reg_dependencies (rtx, regset, regset, regset);
60 static basic_block earliest_block_with_similiar_load (basic_block, rtx);
61 static void add_deps_for_risky_insns (rtx, rtx);
62 static basic_block schedule_ebb (rtx, rtx);
63 static basic_block fix_basic_block_boundaries (basic_block, basic_block, rtx,
65 static void add_missing_bbs (rtx, basic_block, basic_block);
67 /* Return nonzero if there are more insns that should be scheduled. */
70 schedule_more_p (void)
72 return sched_n_insns < target_n_insns;
75 /* Add all insns that are initially ready to the ready list READY. Called
76 once before scheduling a set of insns. */
79 init_ready_list (struct ready_list *ready)
81 rtx prev_head = current_sched_info->prev_head;
82 rtx next_tail = current_sched_info->next_tail;
89 /* Print debugging information. */
90 if (sched_verbose >= 5)
91 debug_dependencies ();
94 /* Initialize ready list with all 'ready' insns in target block.
95 Count number of insns in the target block being scheduled. */
96 for (insn = NEXT_INSN (prev_head); insn != next_tail; insn = NEXT_INSN (insn))
98 if (INSN_DEP_COUNT (insn) == 0)
99 ready_add (ready, insn);
104 /* Called after taking INSN from the ready list. Returns nonzero if this
105 insn can be scheduled, nonzero if we should silently discard it. */
108 can_schedule_ready_p (rtx insn ATTRIBUTE_UNUSED)
114 /* Called after INSN has all its dependencies resolved. Return nonzero
115 if it should be moved to the ready list or the queue, or zero if we
116 should silently discard it. */
118 new_ready (rtx next ATTRIBUTE_UNUSED)
123 /* Return a string that contains the insn uid and optionally anything else
124 necessary to identify this insn in an output. It's valid to use a
125 static buffer for this. The ALIGNED parameter should cause the string
126 to be formatted so that multiple output lines will line up nicely. */
129 ebb_print_insn (rtx insn, int aligned ATTRIBUTE_UNUSED)
133 sprintf (tmp, "%4d", INSN_UID (insn));
137 /* Compare priority of two insns. Return a positive number if the second
138 insn is to be preferred for scheduling, and a negative one if the first
139 is to be preferred. Zero if they are equally good. */
142 rank (rtx insn1, rtx insn2)
144 basic_block bb1 = BLOCK_FOR_INSN (insn1);
145 basic_block bb2 = BLOCK_FOR_INSN (insn2);
147 if (bb1->count > bb2->count
148 || bb1->frequency > bb2->frequency)
150 if (bb1->count < bb2->count
151 || bb1->frequency < bb2->frequency)
156 /* NEXT is an instruction that depends on INSN (a backward dependence);
157 return nonzero if we should include this dependence in priority
161 contributes_to_priority (rtx next ATTRIBUTE_UNUSED,
162 rtx insn ATTRIBUTE_UNUSED)
167 /* INSN is a JUMP_INSN, COND_SET is the set of registers that are
168 conditionally set before INSN. Store the set of registers that
169 must be considered as used by this jump in USED and that of
170 registers that must be considered as set in SET. */
173 compute_jump_reg_dependencies (rtx insn, regset cond_set, regset used,
176 basic_block b = BLOCK_FOR_INSN (insn);
180 FOR_EACH_EDGE (e, ei, b->succs)
181 if (e->flags & EDGE_FALLTHRU)
182 /* The jump may be a by-product of a branch that has been merged
183 in the main codepath after being conditionalized. Therefore
184 it may guard the fallthrough block from using a value that has
185 conditionally overwritten that of the main codepath. So we
186 consider that it restores the value of the main codepath. */
187 bitmap_and (set, e->dest->il.rtl->global_live_at_start, cond_set);
189 bitmap_ior_into (used, e->dest->il.rtl->global_live_at_start);
192 /* Used in schedule_insns to initialize current_sched_info for scheduling
193 regions (or single basic blocks). */
195 static struct sched_info ebb_sched_info =
198 can_schedule_ready_p,
203 contributes_to_priority,
204 compute_jump_reg_dependencies,
213 /* It is possible that ebb scheduling eliminated some blocks.
214 Place blocks from FIRST to LAST before BEFORE. */
217 add_missing_bbs (rtx before, basic_block first, basic_block last)
219 for (; last != first->prev_bb; last = last->prev_bb)
221 before = emit_note_before (NOTE_INSN_BASIC_BLOCK, before);
222 NOTE_BASIC_BLOCK (before) = last;
223 BB_HEAD (last) = before;
224 BB_END (last) = before;
225 update_bb_for_insn (last);
229 /* Fixup the CFG after EBB scheduling. Re-recognize the basic
230 block boundaries in between HEAD and TAIL and update basic block
231 structures between BB and LAST. */
234 fix_basic_block_boundaries (basic_block bb, basic_block last, rtx head,
238 rtx last_inside = BB_HEAD (bb);
239 rtx aftertail = NEXT_INSN (tail);
243 for (; insn != aftertail; insn = NEXT_INSN (insn))
245 gcc_assert (!LABEL_P (insn));
246 /* Create new basic blocks just before first insn. */
247 if (inside_basic_block_p (insn))
253 /* Re-emit the basic block note for newly found BB header. */
256 note = emit_note_after (NOTE_INSN_BASIC_BLOCK, insn);
262 note = emit_note_before (NOTE_INSN_BASIC_BLOCK, insn);
270 /* Control flow instruction terminate basic block. It is possible
271 that we've eliminated some basic blocks (made them empty).
272 Find the proper basic block using BLOCK_FOR_INSN and arrange things in
273 a sensible way by inserting empty basic blocks as needed. */
274 if (control_flow_insn_p (insn) || (insn == tail && last_inside))
276 basic_block curr_bb = BLOCK_FOR_INSN (insn);
279 if (!control_flow_insn_p (insn))
281 if (bb == last->next_bb)
287 /* An obscure special case, where we do have partially dead
288 instruction scheduled after last control flow instruction.
289 In this case we can create new basic block. It is
290 always exactly one basic block last in the sequence. Handle
291 it by splitting the edge and repositioning the block.
292 This is somewhat hackish, but at least avoid cut&paste
294 A safer solution can be to bring the code into sequence,
295 do the split and re-emit it back in case this will ever
298 FOR_EACH_EDGE (f, ei, bb->prev_bb->succs)
299 if (f->flags & EDGE_FALLTHRU)
304 last = curr_bb = split_edge (f);
305 h = BB_HEAD (curr_bb);
306 BB_HEAD (curr_bb) = head;
307 BB_END (curr_bb) = insn;
308 /* Edge splitting created misplaced BASIC_BLOCK note, kill
312 /* It may happen that code got moved past unconditional jump in
313 case the code is completely dead. Kill it. */
316 rtx next = next_nonnote_insn (insn);
317 delete_insn_chain (head, insn);
318 /* We keep some notes in the way that may split barrier from the
320 if (BARRIER_P (next))
322 emit_barrier_after (prev_nonnote_insn (head));
330 BB_HEAD (curr_bb) = head;
331 BB_END (curr_bb) = insn;
332 add_missing_bbs (BB_HEAD (curr_bb), bb, curr_bb->prev_bb);
334 note = LABEL_P (head) ? NEXT_INSN (head) : head;
335 NOTE_BASIC_BLOCK (note) = curr_bb;
336 update_bb_for_insn (curr_bb);
337 bb = curr_bb->next_bb;
343 add_missing_bbs (BB_HEAD (last->next_bb), bb, last);
347 /* Returns the earliest block in EBB currently being processed where a
348 "similar load" 'insn2' is found, and hence LOAD_INSN can move
349 speculatively into the found block. All the following must hold:
351 (1) both loads have 1 base register (PFREE_CANDIDATEs).
352 (2) load_insn and load2 have a def-use dependence upon
353 the same insn 'insn1'.
355 From all these we can conclude that the two loads access memory
356 addresses that differ at most by a constant, and hence if moving
357 load_insn would cause an exception, it would have been caused by
360 The function uses list (given by LAST_BLOCK) of already processed
361 blocks in EBB. The list is formed in `add_deps_for_risky_insns'. */
364 earliest_block_with_similiar_load (basic_block last_block, rtx load_insn)
367 basic_block bb, earliest_block = NULL;
369 for (back_link = LOG_LINKS (load_insn);
371 back_link = XEXP (back_link, 1))
373 rtx insn1 = XEXP (back_link, 0);
375 if (GET_MODE (back_link) == VOIDmode)
377 /* Found a DEF-USE dependence (insn1, load_insn). */
380 for (fore_link = INSN_DEPEND (insn1);
382 fore_link = XEXP (fore_link, 1))
384 rtx insn2 = XEXP (fore_link, 0);
385 basic_block insn2_block = BLOCK_FOR_INSN (insn2);
387 if (GET_MODE (fore_link) == VOIDmode)
389 if (earliest_block != NULL
390 && earliest_block->index < insn2_block->index)
393 /* Found a DEF-USE dependence (insn1, insn2). */
394 if (haifa_classify_insn (insn2) != PFREE_CANDIDATE)
395 /* insn2 not guaranteed to be a 1 base reg load. */
398 for (bb = last_block; bb; bb = bb->aux)
399 if (insn2_block == bb)
403 /* insn2 is the similar load. */
404 earliest_block = insn2_block;
410 return earliest_block;
413 /* The following function adds dependencies between jumps and risky
414 insns in given ebb. */
417 add_deps_for_risky_insns (rtx head, rtx tail)
421 rtx last_jump = NULL_RTX;
422 rtx next_tail = NEXT_INSN (tail);
423 basic_block last_block = NULL, bb;
425 for (insn = head; insn != next_tail; insn = NEXT_INSN (insn))
426 if (control_flow_insn_p (insn))
428 bb = BLOCK_FOR_INSN (insn);
429 bb->aux = last_block;
433 else if (INSN_P (insn) && last_jump != NULL_RTX)
435 class = haifa_classify_insn (insn);
439 case PFREE_CANDIDATE:
440 if (flag_schedule_speculative_load)
442 bb = earliest_block_with_similiar_load (last_block, insn);
454 case PRISKY_CANDIDATE:
455 /* ??? We could implement better checking PRISKY_CANDIDATEs
456 analogous to sched-rgn.c. */
457 /* We can not change the mode of the backward
458 dependency because REG_DEP_ANTI has the lowest
460 if (! sched_insns_conditions_mutex_p (insn, prev))
462 if (!(current_sched_info->flags & DO_SPECULATION))
464 enum DEPS_ADJUST_RESULT res;
466 res = add_or_update_back_dep (insn, prev,
467 REG_DEP_ANTI, DEP_ANTI);
469 if (res == DEP_CREATED)
470 add_forw_dep (insn, LOG_LINKS (insn));
472 gcc_assert (res != DEP_CHANGED);
475 add_or_update_back_forw_dep (insn, prev, REG_DEP_ANTI,
476 set_dep_weak (DEP_ANTI,
487 /* Maintain the invariant that bb->aux is clear after use. */
490 bb = last_block->aux;
491 last_block->aux = NULL;
496 /* Schedule a single extended basic block, defined by the boundaries HEAD
500 schedule_ebb (rtx head, rtx tail)
504 struct deps tmp_deps;
505 basic_block first_bb = BLOCK_FOR_INSN (head);
506 basic_block last_bb = BLOCK_FOR_INSN (tail);
508 if (no_real_insns_p (head, tail))
509 return BLOCK_FOR_INSN (tail);
513 /* Compute LOG_LINKS. */
514 init_deps (&tmp_deps);
515 sched_analyze (&tmp_deps, head, tail);
516 free_deps (&tmp_deps);
518 /* Compute INSN_DEPEND. */
519 compute_forward_dependences (head, tail);
521 add_deps_for_risky_insns (head, tail);
523 if (targetm.sched.dependencies_evaluation_hook)
524 targetm.sched.dependencies_evaluation_hook (head, tail);
526 /* Set priorities. */
527 n_insns = set_priorities (head, tail);
529 current_sched_info->prev_head = PREV_INSN (head);
530 current_sched_info->next_tail = NEXT_INSN (tail);
532 if (write_symbols != NO_DEBUG)
534 save_line_notes (first_bb->index, head, tail);
535 rm_line_notes (head, tail);
538 /* rm_other_notes only removes notes which are _inside_ the
539 block---that is, it won't remove notes before the first real insn
540 or after the last real insn of the block. So if the first insn
541 has a REG_SAVE_NOTE which would otherwise be emitted before the
542 insn, it is redundant with the note before the start of the
543 block, and so we have to take it out. */
548 for (note = REG_NOTES (head); note; note = XEXP (note, 1))
549 if (REG_NOTE_KIND (note) == REG_SAVE_NOTE)
550 remove_note (head, note);
553 /* Remove remaining note insns from the block, save them in
554 note_list. These notes are restored at the end of
555 schedule_block (). */
556 rm_other_notes (head, tail);
558 current_sched_info->queue_must_finish_empty = 1;
560 schedule_block (-1, n_insns);
562 /* Sanity check: verify that all region insns were scheduled. */
563 gcc_assert (sched_n_insns == n_insns);
564 head = current_sched_info->head;
565 tail = current_sched_info->tail;
567 if (write_symbols != NO_DEBUG)
568 restore_line_notes (head, tail);
569 b = fix_basic_block_boundaries (first_bb, last_bb, head, tail);
571 finish_deps_global ();
575 /* The one entry point in this file. */
581 int probability_cutoff;
583 if (profile_info && flag_branch_probabilities)
584 probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY_FEEDBACK);
586 probability_cutoff = PARAM_VALUE (TRACER_MIN_BRANCH_PROBABILITY);
587 probability_cutoff = REG_BR_PROB_BASE / 100 * probability_cutoff;
589 /* Taking care of this degenerate case makes the rest of
590 this code simpler. */
591 if (n_basic_blocks == NUM_FIXED_BLOCKS)
594 /* We need current_sched_info in init_dependency_caches, which is
595 invoked via sched_init. */
596 current_sched_info = &ebb_sched_info;
600 compute_bb_for_insn ();
602 /* Schedule every region in the subroutine. */
605 rtx head = BB_HEAD (bb);
613 if (bb->next_bb == EXIT_BLOCK_PTR
614 || LABEL_P (BB_HEAD (bb->next_bb)))
616 FOR_EACH_EDGE (e, ei, bb->succs)
617 if ((e->flags & EDGE_FALLTHRU) != 0)
621 if (e->probability <= probability_cutoff)
626 /* Blah. We should fix the rest of the code not to get confused by
631 head = NEXT_INSN (head);
632 else if (NOTE_P (tail))
633 tail = PREV_INSN (tail);
634 else if (LABEL_P (head))
635 head = NEXT_INSN (head);
640 bb = schedule_ebb (head, tail);
643 /* Updating life info can be done by local propagation over the modified
646 /* Reposition the prologue and epilogue notes in case we moved the
647 prologue/epilogue insns. */
648 if (reload_completed)
649 reposition_prologue_and_epilogue_notes (get_insns ());
651 if (write_symbols != NO_DEBUG)
652 rm_redundant_line_notes ();