osprey/kg++fe/gnu/sched-ebb.c

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/* Instruction scheduling pass.
   Copyright (C) 1992, 1993, 1994, 1995, 1996, 1997, 1998,
   1999, 2000, 2001, 2002 Free Software Foundation, Inc.
   Contributed by Michael Tiemann (tiemann@cygnus.com) Enhanced by,
   and currently maintained by, Jim Wilson (wilson@cygnus.com)

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 2, or (at your option) any later
version.

GCC is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING.  If not, write to the Free
Software Foundation, 59 Temple Place - Suite 330, Boston, MA
02111-1307, USA.  */

#include "config.h"
#include "system.h"
#include "toplev.h"
#include "rtl.h"
#include "tm_p.h"
#include "hard-reg-set.h"
#include "basic-block.h"
#include "regs.h"
#include "function.h"
#include "flags.h"
#include "insn-config.h"
#include "insn-attr.h"
#include "except.h"
#include "toplev.h"
#include "recog.h"
#include "cfglayout.h"
#include "sched-int.h"

/* The number of insns to be scheduled in total.  */
static int target_n_insns;
/* The number of insns scheduled so far.  */
static int sched_n_insns;

/* Implementations of the sched_info functions for region scheduling.  */
static void init_ready_list PARAMS ((struct ready_list *));
static int can_schedule_ready_p PARAMS ((rtx));
static int new_ready PARAMS ((rtx));
static int schedule_more_p PARAMS ((void));
static const char *ebb_print_insn PARAMS ((rtx, int));
static int rank PARAMS ((rtx, rtx));
static int contributes_to_priority PARAMS ((rtx, rtx));
static void compute_jump_reg_dependencies PARAMS ((rtx, regset, regset,
               regset));
static basic_block earliest_block_with_similiar_load PARAMS ((basic_block,
                    rtx));
static void add_deps_for_risky_insns PARAMS ((rtx, rtx));
static void schedule_ebb PARAMS ((rtx, rtx));

/* Return nonzero if there are more insns that should be scheduled.  */

static int
schedule_more_p ()
{
  return sched_n_insns < target_n_insns;
}

/* Add all insns that are initially ready to the ready list READY.  Called
   once before scheduling a set of insns.  */

static void
init_ready_list (ready)
     struct ready_list *ready;
{
  rtx prev_head = current_sched_info->prev_head;
  rtx next_tail = current_sched_info->next_tail;
  rtx insn;

  target_n_insns = 0;
  sched_n_insns = 0;

#if 0
  /* Print debugging information.  */
  if (sched_verbose >= 5)
    debug_dependencies ();
#endif

  /* Initialize ready list with all 'ready' insns in target block.
     Count number of insns in the target block being scheduled.  */
  for (insn = NEXT_INSN (prev_head); insn != next_tail; insn = NEXT_INSN (insn))
    {
      rtx next;

      if (! INSN_P (insn))
  continue;
      next = NEXT_INSN (insn);

      if (INSN_DEP_COUNT (insn) == 0
    && (! INSN_P (next) || SCHED_GROUP_P (next) == 0))
  ready_add (ready, insn);
      if (!(SCHED_GROUP_P (insn)))
  target_n_insns++;
    }
}

/* Called after taking INSN from the ready list.  Returns nonzero if this
   insn can be scheduled, nonzero if we should silently discard it.  */

static int
can_schedule_ready_p (insn)
     rtx insn ATTRIBUTE_UNUSED;
{
  sched_n_insns++;
  return 1;
}

/* Called after INSN has all its dependencies resolved.  Return nonzero
   if it should be moved to the ready list or the queue, or zero if we
   should silently discard it.  */
static int
new_ready (next)
     rtx next ATTRIBUTE_UNUSED;
{
  return 1;
}

/* Return a string that contains the insn uid and optionally anything else
   necessary to identify this insn in an output.  It's valid to use a
   static buffer for this.  The ALIGNED parameter should cause the string
   to be formatted so that multiple output lines will line up nicely.  */

static const char *
ebb_print_insn (insn, aligned)
     rtx insn;
     int aligned ATTRIBUTE_UNUSED;
{
  static char tmp[80];

  sprintf (tmp, "%4d", INSN_UID (insn));
  return tmp;
}

/* Compare priority of two insns.  Return a positive number if the second
   insn is to be preferred for scheduling, and a negative one if the first
   is to be preferred.  Zero if they are equally good.  */

static int
rank (insn1, insn2)
     rtx insn1 ATTRIBUTE_UNUSED, insn2 ATTRIBUTE_UNUSED;
{
  return 0;
}

/* NEXT is an instruction that depends on INSN (a backward dependence);
   return nonzero if we should include this dependence in priority
   calculations.  */

static int
contributes_to_priority (next, insn)
     rtx next ATTRIBUTE_UNUSED, insn ATTRIBUTE_UNUSED;
{
  return 1;
}

/* INSN is a JUMP_INSN, COND_SET is the set of registers that are
   conditionally set before INSN.  Store the set of registers that
   must be considered as used by this jump in USED and that of
   registers that must be considered as set in SET.  */

static void
compute_jump_reg_dependencies (insn, cond_set, used, set)
     rtx insn;
     regset cond_set, used, set;
{
  basic_block b = BLOCK_FOR_INSN (insn);
  edge e;
  for (e = b->succ; e; e = e->succ_next)
    if (e->flags & EDGE_FALLTHRU)
      /* The jump may be a by-product of a branch that has been merged
   in the main codepath after being conditionalized.  Therefore
   it may guard the fallthrough block from using a value that has
   conditionally overwritten that of the main codepath.  So we
   consider that it restores the value of the main codepath.  */
      bitmap_operation (set, e->dest->global_live_at_start, cond_set,
      BITMAP_AND);
    else
      bitmap_operation (used, used, e->dest->global_live_at_start,
      BITMAP_IOR);
}

/* Used in schedule_insns to initialize current_sched_info for scheduling
   regions (or single basic blocks).  */

static struct sched_info ebb_sched_info =
{
  init_ready_list,
  can_schedule_ready_p,
  schedule_more_p,
  new_ready,
  rank,
  ebb_print_insn,
  contributes_to_priority,
  compute_jump_reg_dependencies,

  NULL, NULL,
  NULL, NULL,
  0, 1
};

/* Returns the earliest block in EBB currently being processed where a
   "similar load" 'insn2' is found, and hence LOAD_INSN can move
   speculatively into the found block.  All the following must hold:

   (1) both loads have 1 base register (PFREE_CANDIDATEs).
   (2) load_insn and load2 have a def-use dependence upon
   the same insn 'insn1'.

   From all these we can conclude that the two loads access memory
   addresses that differ at most by a constant, and hence if moving
   load_insn would cause an exception, it would have been caused by
   load2 anyhow.

   The function uses list (given by LAST_BLOCK) of already processed
   blocks in EBB.  The list is formed in `add_deps_for_risky_insns'.  */

static basic_block
earliest_block_with_similiar_load (last_block, load_insn)
     basic_block last_block;
     rtx load_insn;
{
  rtx back_link;
  basic_block bb, earliest_block = NULL;

  for (back_link = LOG_LINKS (load_insn);
       back_link;
       back_link = XEXP (back_link, 1))
    {
      rtx insn1 = XEXP (back_link, 0);

      if (GET_MODE (back_link) == VOIDmode)
  {
    /* Found a DEF-USE dependence (insn1, load_insn).  */
    rtx fore_link;

    for (fore_link = INSN_DEPEND (insn1);
         fore_link;
         fore_link = XEXP (fore_link, 1))
      {
        rtx insn2 = XEXP (fore_link, 0);
        basic_block insn2_block = BLOCK_FOR_INSN (insn2);

        if (GET_MODE (fore_link) == VOIDmode)
    {
      if (earliest_block != NULL
          && earliest_block->index < insn2_block->index)
        continue;

      /* Found a DEF-USE dependence (insn1, insn2).  */
      if (haifa_classify_insn (insn2) != PFREE_CANDIDATE)
        /* insn2 not guaranteed to be a 1 base reg load.  */
        continue;
      
      for (bb = last_block; bb; bb = bb->aux)
        if (insn2_block == bb)
          break;

      if (!bb)
        /* insn2 is the similar load.  */
        earliest_block = insn2_block;
    }
      }
  }
    }

  return earliest_block;
}

/* The following function adds dependecies between jumps and risky
   insns in given ebb.  */

static void
add_deps_for_risky_insns (head, tail)
     rtx head, tail;
{
  rtx insn, prev;
  int class;
  rtx last_jump = NULL_RTX;
  rtx next_tail = NEXT_INSN (tail);
  basic_block last_block = NULL, bb;
  
  for (insn = head; insn != next_tail; insn = NEXT_INSN (insn))
    if (GET_CODE (insn) == JUMP_INSN)
      {
  bb = BLOCK_FOR_INSN (insn);
  bb->aux = last_block;
  last_block = bb;
  last_jump = insn;
      }
    else if (INSN_P (insn) && last_jump != NULL_RTX)
      {
  class = haifa_classify_insn (insn);
  prev = last_jump;
  switch (class)
    {
    case PFREE_CANDIDATE:
      if (flag_schedule_speculative_load)
        {
    bb = earliest_block_with_similiar_load (last_block, insn);
    if (bb)
      {
        bb = bb->aux;
        if (!bb)
          break;
        prev = bb->end;
      }
        }
      /* FALLTHRU */
    case TRAP_RISKY:
    case IRISKY:
    case PRISKY_CANDIDATE:
      /* ??? We could implement better checking PRISKY_CANDIATEs
         analogous to sched-rgn.c.  */
      /* We can not change the mode of the backward
         dependency because REG_DEP_ANTI has the lowest
         rank.  */
      if (add_dependence (insn, prev, REG_DEP_ANTI))
        add_forward_dependence (prev, insn, REG_DEP_ANTI);
            break;
      
          default:
            break;
    }
      }
  /* Maintain the invariant that bb->aux is clear after use.  */
  while (last_block)
    {
      bb = last_block->aux;
      last_block->aux = NULL;
      last_block = bb;
    }
}

/* Schedule a single extended basic block, defined by the boundaries HEAD
   and TAIL.  */

static void
schedule_ebb (head, tail)
     rtx head, tail;
{
  int n_insns;
  struct deps tmp_deps;

  if (no_real_insns_p (head, tail))
    return;

  init_deps_global ();

  /* Compute LOG_LINKS.  */
  init_deps (&tmp_deps);
  sched_analyze (&tmp_deps, head, tail);
  free_deps (&tmp_deps);

  /* Compute INSN_DEPEND.  */
  compute_forward_dependences (head, tail);

  add_deps_for_risky_insns (head, tail);

  /* Set priorities.  */
  n_insns = set_priorities (head, tail);

  current_sched_info->prev_head = PREV_INSN (head);
  current_sched_info->next_tail = NEXT_INSN (tail);

  if (write_symbols != NO_DEBUG)
    {
      save_line_notes (0, head, tail);
      rm_line_notes (head, tail);
    }

  /* rm_other_notes only removes notes which are _inside_ the
     block---that is, it won't remove notes before the first real insn
     or after the last real insn of the block.  So if the first insn
     has a REG_SAVE_NOTE which would otherwise be emitted before the
     insn, it is redundant with the note before the start of the
     block, and so we have to take it out.  */
  if (INSN_P (head))
    {
      rtx note;

      for (note = REG_NOTES (head); note; note = XEXP (note, 1))
  if (REG_NOTE_KIND (note) == REG_SAVE_NOTE)
    {
      remove_note (head, note);
      note = XEXP (note, 1);
      remove_note (head, note);
    }
    }

  /* Remove remaining note insns from the block, save them in
     note_list.  These notes are restored at the end of
     schedule_block ().  */
  rm_other_notes (head, tail);

  current_sched_info->queue_must_finish_empty = 1;

  schedule_block (-1, n_insns);

  /* Sanity check: verify that all region insns were scheduled.  */
  if (sched_n_insns != n_insns)
    abort ();
  head = current_sched_info->head;
  tail = current_sched_info->tail;

  if (write_symbols != NO_DEBUG)
    restore_line_notes (head, tail);

  finish_deps_global ();
}

/* The one entry point in this file.  DUMP_FILE is the dump file for
   this pass.  */

void
schedule_ebbs (dump_file)
     FILE *dump_file;
{
  basic_block bb;

  /* Taking care of this degenerate case makes the rest of
     this code simpler.  */
  if (n_basic_blocks == 0)
    return;

  sched_init (dump_file);

  current_sched_info = &ebb_sched_info;

  allocate_reg_life_data ();
  compute_bb_for_insn ();

  /* Schedule every region in the subroutine.  */
  FOR_EACH_BB (bb)
    {
      rtx head = bb->head;
      rtx tail;

      for (;;)
  {
    edge e;
    tail = bb->end;
    if (bb->next_bb == EXIT_BLOCK_PTR
        || GET_CODE (bb->next_bb->head) == CODE_LABEL)
      break;
    for (e = bb->succ; e; e = e->succ_next)
      if ((e->flags & EDGE_FALLTHRU) != 0)
        break;
    if (! e)
      break;
    if (GET_CODE (tail) == JUMP_INSN)
      {
        rtx x = find_reg_note (tail, REG_BR_PROB, 0);
        if (x)
    {
      int pred_val = INTVAL (XEXP (x, 0));
      if (pred_val > REG_BR_PROB_BASE / 2)
        break;
    }
      }

    bb = bb->next_bb;
  }

      /* Blah.  We should fix the rest of the code not to get confused by
   a note or two.  */
      while (head != tail)
  {
    if (GET_CODE (head) == NOTE)
      head = NEXT_INSN (head);
    else if (GET_CODE (tail) == NOTE)
      tail = PREV_INSN (tail);
    else if (GET_CODE (head) == CODE_LABEL)
      head = NEXT_INSN (head);
    else
      break;
  }

      schedule_ebb (head, tail);
    }

  /* It doesn't make much sense to try and update life information here - we
     probably messed up even the flow graph.  */

  /* Reposition the prologue and epilogue notes in case we moved the
     prologue/epilogue insns.  */
  if (reload_completed)
    reposition_prologue_and_epilogue_notes (get_insns ());

  if (write_symbols != NO_DEBUG)
    rm_redundant_line_notes ();

  sched_finish ();
}

---