Makefile.in (final.o): Depend on BASIC_BLOCK_H.

[gcc.git] / gcc / jump.c

/* Optimize jump instructions, for GNU compiler.
   Copyright (C) 1987, 1988, 1989, 1991, 1992, 1993, 1994, 1995, 1996, 1997
   1998, 1999, 2000 Free Software Foundation, Inc.

This file is part of GNU CC.

GNU CC 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.

GNU CC 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 GNU CC; see the file COPYING.  If not, write to
the Free Software Foundation, 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */


/* This is the jump-optimization pass of the compiler.
   It is run two or three times: once before cse, sometimes once after cse,
   and once after reload (before final).

   jump_optimize deletes unreachable code and labels that are not used.
   It also deletes jumps that jump to the following insn,
   and simplifies jumps around unconditional jumps and jumps
   to unconditional jumps.

   Each CODE_LABEL has a count of the times it is used
   stored in the LABEL_NUSES internal field, and each JUMP_INSN
   has one label that it refers to stored in the
   JUMP_LABEL internal field.  With this we can detect labels that
   become unused because of the deletion of all the jumps that
   formerly used them.  The JUMP_LABEL info is sometimes looked
   at by later passes.

   Optionally, cross-jumping can be done.  Currently it is done
   only the last time (when after reload and before final).
   In fact, the code for cross-jumping now assumes that register
   allocation has been done, since it uses `rtx_renumbered_equal_p'.

   Jump optimization is done after cse when cse's constant-propagation
   causes jumps to become unconditional or to be deleted.

   Unreachable loops are not detected here, because the labels
   have references and the insns appear reachable from the labels.
   find_basic_blocks in flow.c finds and deletes such loops.

   The subroutines delete_insn, redirect_jump, and invert_jump are used
   from other passes as well.  */

#include "config.h"
#include "system.h"
#include "rtl.h"
#include "tm_p.h"
#include "flags.h"
#include "hard-reg-set.h"
#include "regs.h"
#include "insn-config.h"
#include "insn-flags.h"
#include "insn-attr.h"
#include "recog.h"
#include "function.h"
#include "expr.h"
#include "real.h"
#include "except.h"
#include "toplev.h"

/* ??? Eventually must record somehow the labels used by jumps
   from nested functions.  */
/* Pre-record the next or previous real insn for each label?
   No, this pass is very fast anyway.  */
/* Condense consecutive labels?
   This would make life analysis faster, maybe.  */
/* Optimize jump y; x: ... y: jumpif... x?
   Don't know if it is worth bothering with.  */
/* Optimize two cases of conditional jump to conditional jump?
   This can never delete any instruction or make anything dead,
   or even change what is live at any point.
   So perhaps let combiner do it.  */

/* Vector indexed by uid.
   For each CODE_LABEL, index by its uid to get first unconditional jump
   that jumps to the label.
   For each JUMP_INSN, index by its uid to get the next unconditional jump
   that jumps to the same label.
   Element 0 is the start of a chain of all return insns.
   (It is safe to use element 0 because insn uid 0 is not used.  */

static rtx *jump_chain;

/* Maximum index in jump_chain.  */

static int max_jump_chain;

/* Set nonzero by jump_optimize if control can fall through
   to the end of the function.  */
int can_reach_end;

/* Indicates whether death notes are significant in cross jump analysis.
   Normally they are not significant, because of A and B jump to C,
   and R dies in A, it must die in B.  But this might not be true after
   stack register conversion, and we must compare death notes in that
   case.  */

static int cross_jump_death_matters = 0;

static int init_label_info              PARAMS ((rtx));
static void delete_barrier_successors   PARAMS ((rtx));
static void mark_all_labels             PARAMS ((rtx, int));
static rtx delete_unreferenced_labels   PARAMS ((rtx));
static void delete_noop_moves           PARAMS ((rtx));
static int calculate_can_reach_end      PARAMS ((rtx, int));
static int duplicate_loop_exit_test     PARAMS ((rtx));
static void find_cross_jump             PARAMS ((rtx, rtx, int, rtx *, rtx *));
static void do_cross_jump               PARAMS ((rtx, rtx, rtx));
static int jump_back_p                  PARAMS ((rtx, rtx));
static int tension_vector_labels        PARAMS ((rtx, int));
static void mark_jump_label             PARAMS ((rtx, rtx, int, int));
static void delete_computation          PARAMS ((rtx));
static void redirect_exp_1              PARAMS ((rtx *, rtx, rtx, rtx));
static void invert_exp_1                PARAMS ((rtx, rtx));
static void delete_from_jump_chain      PARAMS ((rtx));
static int delete_labelref_insn         PARAMS ((rtx, rtx, int));
static void mark_modified_reg           PARAMS ((rtx, rtx, void *));
static void redirect_tablejump          PARAMS ((rtx, rtx));
static void jump_optimize_1             PARAMS ((rtx, int, int, int, int, int));
static int returnjump_p_1               PARAMS ((rtx *, void *));
static void delete_prior_computation    PARAMS ((rtx, rtx));
\f
/* Main external entry point into the jump optimizer.  See comments before
   jump_optimize_1 for descriptions of the arguments.  */
void
jump_optimize (f, cross_jump, noop_moves, after_regscan)
     rtx f;
     int cross_jump;
     int noop_moves;
     int after_regscan;
{
  jump_optimize_1 (f, cross_jump, noop_moves, after_regscan, 0, 0);
}

/* Alternate entry into the jump optimizer.  This entry point only rebuilds
   the JUMP_LABEL field in jumping insns and REG_LABEL notes in non-jumping
   instructions.  */
void
rebuild_jump_labels (f)
     rtx f;
{
  jump_optimize_1 (f, 0, 0, 0, 1, 0);
}

/* Alternate entry into the jump optimizer.  Do only trivial optimizations.  */
void
jump_optimize_minimal (f)
     rtx f;
{
  jump_optimize_1 (f, 0, 0, 0, 0, 1);
}
\f
/* Delete no-op jumps and optimize jumps to jumps
   and jumps around jumps.
   Delete unused labels and unreachable code.

   If CROSS_JUMP is 1, detect matching code
   before a jump and its destination and unify them.
   If CROSS_JUMP is 2, do cross-jumping, but pay attention to death notes.

   If NOOP_MOVES is nonzero, delete no-op move insns.

   If AFTER_REGSCAN is nonzero, then this jump pass is being run immediately
   after regscan, and it is safe to use regno_first_uid and regno_last_uid.

   If MARK_LABELS_ONLY is nonzero, then we only rebuild the jump chain
   and JUMP_LABEL field for jumping insns.

   If `optimize' is zero, don't change any code,
   just determine whether control drops off the end of the function.
   This case occurs when we have -W and not -O.
   It works because `delete_insn' checks the value of `optimize'
   and refrains from actually deleting when that is 0.

   If MINIMAL is nonzero, then we only perform trivial optimizations:

     * Removal of unreachable code after BARRIERs.
     * Removal of unreferenced CODE_LABELs.
     * Removal of a jump to the next instruction.
     * Removal of a conditional jump followed by an unconditional jump
       to the same target as the conditional jump.
     * Simplify a conditional jump around an unconditional jump.
     * Simplify a jump to a jump.
     * Delete extraneous line number notes.
  */

static void
jump_optimize_1 (f, cross_jump, noop_moves, after_regscan,
                 mark_labels_only, minimal)
     rtx f;
     int cross_jump;
     int noop_moves;
     int after_regscan;
     int mark_labels_only;
     int minimal;
{
  register rtx insn, next;
  int changed;
  int old_max_reg;
  int first = 1;
  int max_uid = 0;
  rtx last_insn;

  cross_jump_death_matters = (cross_jump == 2);
  max_uid = init_label_info (f) + 1;

  /* If we are performing cross jump optimizations, then initialize
     tables mapping UIDs to EH regions to avoid incorrect movement
     of insns from one EH region to another.  */
  if (flag_exceptions && cross_jump)
    init_insn_eh_region (f, max_uid);

  if (! mark_labels_only)
    delete_barrier_successors (f);

  /* Leave some extra room for labels and duplicate exit test insns
     we make.  */
  max_jump_chain = max_uid * 14 / 10;
  jump_chain = (rtx *) xcalloc (max_jump_chain, sizeof (rtx));

  mark_all_labels (f, cross_jump);

  /* Keep track of labels used from static data;
     they cannot ever be deleted.  */

  for (insn = forced_labels; insn; insn = XEXP (insn, 1))
    LABEL_NUSES (XEXP (insn, 0))++;

  check_exception_handler_labels ();

  /* Keep track of labels used for marking handlers for exception
     regions; they cannot usually be deleted.  */

  for (insn = exception_handler_labels; insn; insn = XEXP (insn, 1))
    LABEL_NUSES (XEXP (insn, 0))++;

  /* Quit now if we just wanted to rebuild the JUMP_LABEL and REG_LABEL
     notes and recompute LABEL_NUSES.  */
  if (mark_labels_only)
    goto end;

  if (! minimal)
    exception_optimize ();

  last_insn = delete_unreferenced_labels (f);

  if (noop_moves)
    delete_noop_moves (f);

  /* If we haven't yet gotten to reload and we have just run regscan,
     delete any insn that sets a register that isn't used elsewhere.
     This helps some of the optimizations below by having less insns
     being jumped around.  */

  if (optimize && ! reload_completed && after_regscan)
    for (insn = f; insn; insn = next)
      {
        rtx set = single_set (insn);

        next = NEXT_INSN (insn);

        if (set && GET_CODE (SET_DEST (set)) == REG
            && REGNO (SET_DEST (set)) >= FIRST_PSEUDO_REGISTER
            && REGNO_FIRST_UID (REGNO (SET_DEST (set))) == INSN_UID (insn)
            /* We use regno_last_note_uid so as not to delete the setting
               of a reg that's used in notes.  A subsequent optimization
               might arrange to use that reg for real.  */             
            && REGNO_LAST_NOTE_UID (REGNO (SET_DEST (set))) == INSN_UID (insn)
            && ! side_effects_p (SET_SRC (set))
            && ! find_reg_note (insn, REG_RETVAL, 0)
            /* An ADDRESSOF expression can turn into a use of the internal arg
               pointer, so do not delete the initialization of the internal
               arg pointer yet.  If it is truly dead, flow will delete the
               initializing insn.  */
            && SET_DEST (set) != current_function_internal_arg_pointer)
          delete_insn (insn);
      }

  /* Now iterate optimizing jumps until nothing changes over one pass.  */
  changed = 1;
  old_max_reg = max_reg_num ();
  while (changed)
    {
      changed = 0;

      for (insn = f; insn; insn = next)
        {
          rtx reallabelprev;
          rtx temp, temp1, temp2 = NULL_RTX;
          rtx temp4 ATTRIBUTE_UNUSED;
          rtx nlabel;
          int this_is_simplejump, this_is_condjump;
          int this_is_condjump_in_parallel;

          next = NEXT_INSN (insn);

          /* See if this is a NOTE_INSN_LOOP_BEG followed by an unconditional
             jump.  Try to optimize by duplicating the loop exit test if so.
             This is only safe immediately after regscan, because it uses
             the values of regno_first_uid and regno_last_uid.  */
          if (after_regscan && GET_CODE (insn) == NOTE
              && NOTE_LINE_NUMBER (insn) == NOTE_INSN_LOOP_BEG
              && (temp1 = next_nonnote_insn (insn)) != 0
              && simplejump_p (temp1))
            {
              temp = PREV_INSN (insn);
              if (duplicate_loop_exit_test (insn))
                {
                  changed = 1;
                  next = NEXT_INSN (temp);
                  continue;
                }
            }

          if (GET_CODE (insn) != JUMP_INSN)
            continue;

          this_is_simplejump = simplejump_p (insn);
          this_is_condjump = condjump_p (insn);
          this_is_condjump_in_parallel = condjump_in_parallel_p (insn);

          /* Tension the labels in dispatch tables.  */

          if (GET_CODE (PATTERN (insn)) == ADDR_VEC)
            changed |= tension_vector_labels (PATTERN (insn), 0);
          if (GET_CODE (PATTERN (insn)) == ADDR_DIFF_VEC)
            changed |= tension_vector_labels (PATTERN (insn), 1);

          /* See if this jump goes to another jump and redirect if so.  */
          nlabel = follow_jumps (JUMP_LABEL (insn));
          if (nlabel != JUMP_LABEL (insn))
            changed |= redirect_jump (insn, nlabel);

          if (! optimize || minimal)
            continue;

          /* If a dispatch table always goes to the same place,
             get rid of it and replace the insn that uses it.  */

          if (GET_CODE (PATTERN (insn)) == ADDR_VEC
              || GET_CODE (PATTERN (insn)) == ADDR_DIFF_VEC)
            {
              int i;
              rtx pat = PATTERN (insn);
              int diff_vec_p = GET_CODE (PATTERN (insn)) == ADDR_DIFF_VEC;
              int len = XVECLEN (pat, diff_vec_p);
              rtx dispatch = prev_real_insn (insn);
              rtx set;

              for (i = 0; i < len; i++)
                if (XEXP (XVECEXP (pat, diff_vec_p, i), 0)
                    != XEXP (XVECEXP (pat, diff_vec_p, 0), 0))
                  break;

              if (i == len
                  && dispatch != 0
                  && GET_CODE (dispatch) == JUMP_INSN
                  && JUMP_LABEL (dispatch) != 0
                  /* Don't mess with a casesi insn. 
                     XXX according to the comment before computed_jump_p(),
                     all casesi insns should be a parallel of the jump
                     and a USE of a LABEL_REF.  */
                  && ! ((set = single_set (dispatch)) != NULL
                        && (GET_CODE (SET_SRC (set)) == IF_THEN_ELSE))
                  && next_real_insn (JUMP_LABEL (dispatch)) == insn)
                {
                  redirect_tablejump (dispatch,
                                      XEXP (XVECEXP (pat, diff_vec_p, 0), 0));
                  changed = 1;
                }
            }

          /* If a jump references the end of the function, try to turn
             it into a RETURN insn, possibly a conditional one.  */
          if (JUMP_LABEL (insn) != 0
              && (next_active_insn (JUMP_LABEL (insn)) == 0
                  || GET_CODE (PATTERN (next_active_insn (JUMP_LABEL (insn))))
                      == RETURN))
            changed |= redirect_jump (insn, NULL_RTX);

          reallabelprev = prev_active_insn (JUMP_LABEL (insn));

          /* Detect jump to following insn.  */
          if (reallabelprev == insn && this_is_condjump)
            {
              next = next_real_insn (JUMP_LABEL (insn));
              delete_jump (insn);
              changed = 1;
              continue;
            }

          /* Detect a conditional jump going to the same place
             as an immediately following unconditional jump.  */
          else if (this_is_condjump
                   && (temp = next_active_insn (insn)) != 0
                   && simplejump_p (temp)
                   && (next_active_insn (JUMP_LABEL (insn))
                       == next_active_insn (JUMP_LABEL (temp))))
            {
              /* Don't mess up test coverage analysis.  */
              temp2 = temp;
              if (flag_test_coverage && !reload_completed)
                for (temp2 = insn; temp2 != temp; temp2 = NEXT_INSN (temp2))
                  if (GET_CODE (temp2) == NOTE && NOTE_LINE_NUMBER (temp2) > 0)
                    break;
                  
              if (temp2 == temp)
                {
                  delete_jump (insn);
                  changed = 1;
                  continue;
                }
            }

          /* Detect a conditional jump jumping over an unconditional jump.  */

          else if ((this_is_condjump || this_is_condjump_in_parallel)
                   && ! this_is_simplejump
                   && reallabelprev != 0
                   && GET_CODE (reallabelprev) == JUMP_INSN
                   && prev_active_insn (reallabelprev) == insn
                   && no_labels_between_p (insn, reallabelprev)
                   && simplejump_p (reallabelprev))
            {
              /* When we invert the unconditional jump, we will be
                 decrementing the usage count of its old label.
                 Make sure that we don't delete it now because that
                 might cause the following code to be deleted.  */
              rtx prev_uses = prev_nonnote_insn (reallabelprev);
              rtx prev_label = JUMP_LABEL (insn);

              if (prev_label)
                ++LABEL_NUSES (prev_label);

              if (invert_jump (insn, JUMP_LABEL (reallabelprev)))
                {
                  /* It is very likely that if there are USE insns before
                     this jump, they hold REG_DEAD notes.  These REG_DEAD
                     notes are no longer valid due to this optimization,
                     and will cause the life-analysis that following passes
                     (notably delayed-branch scheduling) to think that
                     these registers are dead when they are not.

                     To prevent this trouble, we just remove the USE insns
                     from the insn chain.  */

                  while (prev_uses && GET_CODE (prev_uses) == INSN
                         && GET_CODE (PATTERN (prev_uses)) == USE)
                    {
                      rtx useless = prev_uses;
                      prev_uses = prev_nonnote_insn (prev_uses);
                      delete_insn (useless);
                    }

                  delete_insn (reallabelprev);
                  changed = 1;
                }

              /* We can now safely delete the label if it is unreferenced
                 since the delete_insn above has deleted the BARRIER.  */
              if (prev_label && --LABEL_NUSES (prev_label) == 0)
                delete_insn (prev_label);

              next = NEXT_INSN (insn);
            }

          /* If we have an unconditional jump preceded by a USE, try to put
             the USE before the target and jump there.  This simplifies many
             of the optimizations below since we don't have to worry about
             dealing with these USE insns.  We only do this if the label
             being branch to already has the identical USE or if code
             never falls through to that label.  */

          else if (this_is_simplejump
                   && (temp = prev_nonnote_insn (insn)) != 0
                   && GET_CODE (temp) == INSN
                   && GET_CODE (PATTERN (temp)) == USE
                   && (temp1 = prev_nonnote_insn (JUMP_LABEL (insn))) != 0
                   && (GET_CODE (temp1) == BARRIER
                       || (GET_CODE (temp1) == INSN
                           && rtx_equal_p (PATTERN (temp), PATTERN (temp1))))
                   /* Don't do this optimization if we have a loop containing
                      only the USE instruction, and the loop start label has
                      a usage count of 1.  This is because we will redo this
                      optimization everytime through the outer loop, and jump
                      opt will never exit.  */
                   && ! ((temp2 = prev_nonnote_insn (temp)) != 0
                         && temp2 == JUMP_LABEL (insn)
                         && LABEL_NUSES (temp2) == 1))
            {
              if (GET_CODE (temp1) == BARRIER)
                {
                  emit_insn_after (PATTERN (temp), temp1);
                  temp1 = NEXT_INSN (temp1);
                }

              delete_insn (temp);
              redirect_jump (insn, get_label_before (temp1));
              reallabelprev = prev_real_insn (temp1);
              changed = 1;
              next = NEXT_INSN (insn);
            }

#ifdef HAVE_trap
          /* Detect a conditional jump jumping over an unconditional trap.  */
          if (HAVE_trap
              && this_is_condjump && ! this_is_simplejump
              && reallabelprev != 0
              && GET_CODE (reallabelprev) == INSN
              && GET_CODE (PATTERN (reallabelprev)) == TRAP_IF
              && TRAP_CONDITION (PATTERN (reallabelprev)) == const_true_rtx
              && prev_active_insn (reallabelprev) == insn
              && no_labels_between_p (insn, reallabelprev)
              && (temp2 = get_condition (insn, &temp4))
              && can_reverse_comparison_p (temp2, insn))
            {
              rtx new = gen_cond_trap (reverse_condition (GET_CODE (temp2)),
                                       XEXP (temp2, 0), XEXP (temp2, 1),
                                       TRAP_CODE (PATTERN (reallabelprev)));

              if (new)
                {
                  emit_insn_before (new, temp4);
                  delete_insn (reallabelprev);
                  delete_jump (insn);
                  changed = 1;
                  continue;
                }
            }
          /* Detect a jump jumping to an unconditional trap.  */
          else if (HAVE_trap && this_is_condjump
                   && (temp = next_active_insn (JUMP_LABEL (insn)))
                   && GET_CODE (temp) == INSN
                   && GET_CODE (PATTERN (temp)) == TRAP_IF
                   && (this_is_simplejump
                       || (temp2 = get_condition (insn, &temp4))))
            {
              rtx tc = TRAP_CONDITION (PATTERN (temp));

              if (tc == const_true_rtx
                  || (! this_is_simplejump && rtx_equal_p (temp2, tc)))
                {
                  rtx new;
                  /* Replace an unconditional jump to a trap with a trap.  */
                  if (this_is_simplejump)
                    {
                      emit_barrier_after (emit_insn_before (gen_trap (), insn));
                      delete_jump (insn);
                      changed = 1;
                      continue;
                    }
                  new = gen_cond_trap (GET_CODE (temp2), XEXP (temp2, 0),
                                       XEXP (temp2, 1),
                                       TRAP_CODE (PATTERN (temp)));
                  if (new)
                    {
                      emit_insn_before (new, temp4);
                      delete_jump (insn);
                      changed = 1;
                      continue;
                    }
                }
              /* If the trap condition and jump condition are mutually
                 exclusive, redirect the jump to the following insn.  */
              else if (GET_RTX_CLASS (GET_CODE (tc)) == '<'
                       && ! this_is_simplejump
                       && swap_condition (GET_CODE (temp2)) == GET_CODE (tc)
                       && rtx_equal_p (XEXP (tc, 0), XEXP (temp2, 0))
                       && rtx_equal_p (XEXP (tc, 1), XEXP (temp2, 1))
                       && redirect_jump (insn, get_label_after (temp)))
                {
                  changed = 1;
                  continue;
                }
            }
#endif
          else
            {
              /* Now that the jump has been tensioned,
                 try cross jumping: check for identical code
                 before the jump and before its target label.  */

              /* First, cross jumping of conditional jumps:  */

              if (cross_jump && condjump_p (insn))
                {
                  rtx newjpos, newlpos;
                  rtx x = prev_real_insn (JUMP_LABEL (insn));

                  /* A conditional jump may be crossjumped
                     only if the place it jumps to follows
                     an opposing jump that comes back here.  */

                  if (x != 0 && ! jump_back_p (x, insn))
                    /* We have no opposing jump;
                       cannot cross jump this insn.  */
                    x = 0;

                  newjpos = 0;
                  /* TARGET is nonzero if it is ok to cross jump
                     to code before TARGET.  If so, see if matches.  */
                  if (x != 0)
                    find_cross_jump (insn, x, 2,
                                     &newjpos, &newlpos);

                  if (newjpos != 0)
                    {
                      do_cross_jump (insn, newjpos, newlpos);
                      /* Make the old conditional jump
                         into an unconditional one.  */
                      SET_SRC (PATTERN (insn))
                        = gen_rtx_LABEL_REF (VOIDmode, JUMP_LABEL (insn));
                      INSN_CODE (insn) = -1;
                      emit_barrier_after (insn);
                      /* Add to jump_chain unless this is a new label
                         whose UID is too large.  */
                      if (INSN_UID (JUMP_LABEL (insn)) < max_jump_chain)
                        {
                          jump_chain[INSN_UID (insn)]
                            = jump_chain[INSN_UID (JUMP_LABEL (insn))];
                          jump_chain[INSN_UID (JUMP_LABEL (insn))] = insn;
                        }
                      changed = 1;
                      next = insn;
                    }
                }

              /* Cross jumping of unconditional jumps:
                 a few differences.  */

              if (cross_jump && simplejump_p (insn))
                {
                  rtx newjpos, newlpos;
                  rtx target;

                  newjpos = 0;

                  /* TARGET is nonzero if it is ok to cross jump
                     to code before TARGET.  If so, see if matches.  */
                  find_cross_jump (insn, JUMP_LABEL (insn), 1,
                                   &newjpos, &newlpos);

                  /* If cannot cross jump to code before the label,
                     see if we can cross jump to another jump to
                     the same label.  */
                  /* Try each other jump to this label.  */
                  if (INSN_UID (JUMP_LABEL (insn)) < max_uid)
                    for (target = jump_chain[INSN_UID (JUMP_LABEL (insn))];
                         target != 0 && newjpos == 0;
                         target = jump_chain[INSN_UID (target)])
                      if (target != insn
                          && JUMP_LABEL (target) == JUMP_LABEL (insn)
                          /* Ignore TARGET if it's deleted.  */
                          && ! INSN_DELETED_P (target))
                        find_cross_jump (insn, target, 2,
                                         &newjpos, &newlpos);

                  if (newjpos != 0)
                    {
                      do_cross_jump (insn, newjpos, newlpos);
                      changed = 1;
                      next = insn;
                    }
                }

              /* This code was dead in the previous jump.c!  */
              if (cross_jump && GET_CODE (PATTERN (insn)) == RETURN)
                {
                  /* Return insns all "jump to the same place"
                     so we can cross-jump between any two of them.  */

                  rtx newjpos, newlpos, target;

                  newjpos = 0;

                  /* If cannot cross jump to code before the label,
                     see if we can cross jump to another jump to
                     the same label.  */
                  /* Try each other jump to this label.  */
                  for (target = jump_chain[0];
                       target != 0 && newjpos == 0;
                       target = jump_chain[INSN_UID (target)])
                    if (target != insn
                        && ! INSN_DELETED_P (target)
                        && GET_CODE (PATTERN (target)) == RETURN)
                      find_cross_jump (insn, target, 2,
                                       &newjpos, &newlpos);

                  if (newjpos != 0)
                    {
                      do_cross_jump (insn, newjpos, newlpos);
                      changed = 1;
                      next = insn;
                    }
                }
            }
        }

      first = 0;
    }

  /* Delete extraneous line number notes.
     Note that two consecutive notes for different lines are not really
     extraneous.  There should be some indication where that line belonged,
     even if it became empty.  */

  {
    rtx last_note = 0;

    for (insn = f; insn; insn = NEXT_INSN (insn))
      if (GET_CODE (insn) == NOTE && NOTE_LINE_NUMBER (insn) >= 0)
        {
          /* Delete this note if it is identical to previous note.  */
          if (last_note
              && NOTE_SOURCE_FILE (insn) == NOTE_SOURCE_FILE (last_note)
              && NOTE_LINE_NUMBER (insn) == NOTE_LINE_NUMBER (last_note))
            {
              delete_insn (insn);
              continue;
            }

          last_note = insn;
        }
  }

  /* CAN_REACH_END is persistent for each function.  Once set it should
     not be cleared.  This is especially true for the case where we
     delete the NOTE_FUNCTION_END note.  CAN_REACH_END is cleared by
     the front-end before compiling each function.  */
  if (! minimal && calculate_can_reach_end (last_insn, optimize != 0))
    can_reach_end = 1;

end:
  /* Clean up.  */
  free (jump_chain);
  jump_chain = 0;
}
\f
/* Initialize LABEL_NUSES and JUMP_LABEL fields.  Delete any REG_LABEL
   notes whose labels don't occur in the insn any more.  Returns the
   largest INSN_UID found.  */
static int
init_label_info (f)
     rtx f;
{
  int largest_uid = 0;
  rtx insn;

  for (insn = f; insn; insn = NEXT_INSN (insn))
    {
      if (GET_CODE (insn) == CODE_LABEL)
        LABEL_NUSES (insn) = (LABEL_PRESERVE_P (insn) != 0);
      else if (GET_CODE (insn) == JUMP_INSN)
        JUMP_LABEL (insn) = 0;
      else if (GET_CODE (insn) == INSN || GET_CODE (insn) == CALL_INSN)
        {
          rtx note, next;

          for (note = REG_NOTES (insn); note; note = next)
            {
              next = XEXP (note, 1);
              if (REG_NOTE_KIND (note) == REG_LABEL
                  && ! reg_mentioned_p (XEXP (note, 0), PATTERN (insn)))
                remove_note (insn, note);
            }
        }
      if (INSN_UID (insn) > largest_uid)
        largest_uid = INSN_UID (insn);
    }

  return largest_uid;
}

/* Delete insns following barriers, up to next label. 

   Also delete no-op jumps created by gcse.  */

static void
delete_barrier_successors (f)
     rtx f;
{
  rtx insn;

  for (insn = f; insn;)
    {
      if (GET_CODE (insn) == BARRIER)
        {
          insn = NEXT_INSN (insn);

          never_reached_warning (insn);

          while (insn != 0 && GET_CODE (insn) != CODE_LABEL)
            {
              if (GET_CODE (insn) == NOTE
                  && NOTE_LINE_NUMBER (insn) != NOTE_INSN_FUNCTION_END)
                insn = NEXT_INSN (insn);
              else
                insn = delete_insn (insn);
            }
          /* INSN is now the code_label.  */
        }

      /* Also remove (set (pc) (pc)) insns which can be created by
         gcse.  We eliminate such insns now to avoid having them
         cause problems later.  */
      else if (GET_CODE (insn) == JUMP_INSN
               && GET_CODE (PATTERN (insn)) == SET
               && SET_SRC (PATTERN (insn)) == pc_rtx
               && SET_DEST (PATTERN (insn)) == pc_rtx)
        insn = delete_insn (insn);

      else
        insn = NEXT_INSN (insn);
    }
}

/* Mark the label each jump jumps to.
   Combine consecutive labels, and count uses of labels.

   For each label, make a chain (using `jump_chain')
   of all the *unconditional* jumps that jump to it;
   also make a chain of all returns.

   CROSS_JUMP indicates whether we are doing cross jumping
   and if we are whether we will be paying attention to
   death notes or not.  */

static void
mark_all_labels (f, cross_jump)
     rtx f;
     int cross_jump;
{
  rtx insn;

  for (insn = f; insn; insn = NEXT_INSN (insn))
    if (GET_RTX_CLASS (GET_CODE (insn)) == 'i')
      {
        if (GET_CODE (insn) == CALL_INSN
            && GET_CODE (PATTERN (insn)) == CALL_PLACEHOLDER)
          {
            mark_all_labels (XEXP (PATTERN (insn), 0), cross_jump);
            mark_all_labels (XEXP (PATTERN (insn), 1), cross_jump);
            mark_all_labels (XEXP (PATTERN (insn), 2), cross_jump);
            continue;
          }
        
        mark_jump_label (PATTERN (insn), insn, cross_jump, 0);
        if (! INSN_DELETED_P (insn) && GET_CODE (insn) == JUMP_INSN)
          {
            if (JUMP_LABEL (insn) != 0 && simplejump_p (insn))
              {
                jump_chain[INSN_UID (insn)]
                  = jump_chain[INSN_UID (JUMP_LABEL (insn))];
                jump_chain[INSN_UID (JUMP_LABEL (insn))] = insn;
              }
            if (GET_CODE (PATTERN (insn)) == RETURN)
              {
                jump_chain[INSN_UID (insn)] = jump_chain[0];
                jump_chain[0] = insn;
              }
          }
      }
}

/* Delete all labels already not referenced.
   Also find and return the last insn.  */

static rtx
delete_unreferenced_labels (f)
     rtx f;
{
  rtx final = NULL_RTX;
  rtx insn;

  for (insn = f; insn; )
    {
      if (GET_CODE (insn) == CODE_LABEL
          && LABEL_NUSES (insn) == 0
          && LABEL_ALTERNATE_NAME (insn) == NULL)
        insn = delete_insn (insn);
      else
        {
          final = insn;
          insn = NEXT_INSN (insn);
        }
    }

  return final;
}

/* Delete various simple forms of moves which have no necessary
   side effect.  */

static void
delete_noop_moves (f)
     rtx f;
{
  rtx insn, next;

  for (insn = f; insn; )
    {
      next = NEXT_INSN (insn);

      if (GET_CODE (insn) == INSN)
        {
          register rtx body = PATTERN (insn);

          /* Detect and delete no-op move instructions
             resulting from not allocating a parameter in a register.  */

          if (GET_CODE (body) == SET
              && (SET_DEST (body) == SET_SRC (body)
                  || (GET_CODE (SET_DEST (body)) == MEM
                      && GET_CODE (SET_SRC (body)) == MEM
                      && rtx_equal_p (SET_SRC (body), SET_DEST (body))))
              && ! (GET_CODE (SET_DEST (body)) == MEM
                    && MEM_VOLATILE_P (SET_DEST (body)))
              && ! (GET_CODE (SET_SRC (body)) == MEM
                    && MEM_VOLATILE_P (SET_SRC (body))))
            delete_computation (insn);

          /* Detect and ignore no-op move instructions
             resulting from smart or fortuitous register allocation.  */

          else if (GET_CODE (body) == SET)
            {
              int sreg = true_regnum (SET_SRC (body));
              int dreg = true_regnum (SET_DEST (body));

              if (sreg == dreg && sreg >= 0)
                delete_insn (insn);
              else if (sreg >= 0 && dreg >= 0)
                {
                  rtx trial;
                  rtx tem = find_equiv_reg (NULL_RTX, insn, 0,
                                            sreg, NULL_PTR, dreg,
                                            GET_MODE (SET_SRC (body)));

                  if (tem != 0
                      && GET_MODE (tem) == GET_MODE (SET_DEST (body)))
                    {
                      /* DREG may have been the target of a REG_DEAD note in
                         the insn which makes INSN redundant.  If so, reorg
                         would still think it is dead.  So search for such a
                         note and delete it if we find it.  */
                      if (! find_regno_note (insn, REG_UNUSED, dreg))
                        for (trial = prev_nonnote_insn (insn);
                             trial && GET_CODE (trial) != CODE_LABEL;
                             trial = prev_nonnote_insn (trial))
                          if (find_regno_note (trial, REG_DEAD, dreg))
                            {
                              remove_death (dreg, trial);
                              break;
                            }

                      /* Deleting insn could lose a death-note for SREG.  */
                      if ((trial = find_regno_note (insn, REG_DEAD, sreg)))
                        {
                          /* Change this into a USE so that we won't emit
                             code for it, but still can keep the note.  */
                          PATTERN (insn)
                            = gen_rtx_USE (VOIDmode, XEXP (trial, 0));
                          INSN_CODE (insn) = -1;
                          /* Remove all reg notes but the REG_DEAD one.  */
                          REG_NOTES (insn) = trial;
                          XEXP (trial, 1) = NULL_RTX;
                        }
                      else
                        delete_insn (insn);
                    }
                }
              else if (dreg >= 0 && CONSTANT_P (SET_SRC (body))
                       && find_equiv_reg (SET_SRC (body), insn, 0, dreg,
                                          NULL_PTR, 0,
                                          GET_MODE (SET_DEST (body))))
                {
                  /* This handles the case where we have two consecutive
                     assignments of the same constant to pseudos that didn't
                     get a hard reg.  Each SET from the constant will be
                     converted into a SET of the spill register and an
                     output reload will be made following it.  This produces
                     two loads of the same constant into the same spill
                     register.  */

                  rtx in_insn = insn;

                  /* Look back for a death note for the first reg.
                     If there is one, it is no longer accurate.  */
                  while (in_insn && GET_CODE (in_insn) != CODE_LABEL)
                    {
                      if ((GET_CODE (in_insn) == INSN
                           || GET_CODE (in_insn) == JUMP_INSN)
                          && find_regno_note (in_insn, REG_DEAD, dreg))
                        {
                          remove_death (dreg, in_insn);
                          break;
                        }
                      in_insn = PREV_INSN (in_insn);
                    }

                  /* Delete the second load of the value.  */
                  delete_insn (insn);
                }
            }
          else if (GET_CODE (body) == PARALLEL)
            {
              /* If each part is a set between two identical registers or
                 a USE or CLOBBER, delete the insn.  */
              int i, sreg, dreg;
              rtx tem;

              for (i = XVECLEN (body, 0) - 1; i >= 0; i--)
                {
                  tem = XVECEXP (body, 0, i);
                  if (GET_CODE (tem) == USE || GET_CODE (tem) == CLOBBER)
                    continue;

                  if (GET_CODE (tem) != SET
                      || (sreg = true_regnum (SET_SRC (tem))) < 0
                      || (dreg = true_regnum (SET_DEST (tem))) < 0
                      || dreg != sreg)
                    break;
                }
                  
              if (i < 0)
                delete_insn (insn);
            }
          /* Also delete insns to store bit fields if they are no-ops.  */
          /* Not worth the hair to detect this in the big-endian case.  */
          else if (! BYTES_BIG_ENDIAN
                   && GET_CODE (body) == SET
                   && GET_CODE (SET_DEST (body)) == ZERO_EXTRACT
                   && XEXP (SET_DEST (body), 2) == const0_rtx
                   && XEXP (SET_DEST (body), 0) == SET_SRC (body)
                   && ! (GET_CODE (SET_SRC (body)) == MEM
                         && MEM_VOLATILE_P (SET_SRC (body))))
            delete_insn (insn);
        }
      insn = next;
    }
}

/* See if there is still a NOTE_INSN_FUNCTION_END in this function.
   If so indicate that this function can drop off the end by returning
   1, else return 0.

   CHECK_DELETED indicates whether we must check if the note being
   searched for has the deleted flag set.

   DELETE_FINAL_NOTE indicates whether we should delete the note
   if we find it.  */

static int
calculate_can_reach_end (last, delete_final_note)
     rtx last;
     int delete_final_note;
{
  rtx insn = last;
  int n_labels = 1;

  while (insn != NULL_RTX)
    {
      int ok = 0;

      /* One label can follow the end-note: the return label.  */
      if (GET_CODE (insn) == CODE_LABEL && n_labels-- > 0)
        ok = 1;
      /* Ordinary insns can follow it if returning a structure.  */
      else if (GET_CODE (insn) == INSN)
        ok = 1;
      /* If machine uses explicit RETURN insns, no epilogue,
         then one of them follows the note.  */
      else if (GET_CODE (insn) == JUMP_INSN
               && GET_CODE (PATTERN (insn)) == RETURN)
        ok = 1;
      /* A barrier can follow the return insn.  */
      else if (GET_CODE (insn) == BARRIER)
        ok = 1;
      /* Other kinds of notes can follow also.  */
      else if (GET_CODE (insn) == NOTE
               && NOTE_LINE_NUMBER (insn) != NOTE_INSN_FUNCTION_END)
        ok = 1;

      if (ok != 1)
        break;

      insn = PREV_INSN (insn);
    }

  /* See if we backed up to the appropriate type of note.  */
  if (insn != NULL_RTX
      && GET_CODE (insn) == NOTE
      && NOTE_LINE_NUMBER (insn) == NOTE_INSN_FUNCTION_END)
    {
      if (delete_final_note)
        delete_insn (insn);
      return 1;
    }

  return 0;
}

/* LOOP_START is a NOTE_INSN_LOOP_BEG note that is followed by an unconditional
   jump.  Assume that this unconditional jump is to the exit test code.  If
   the code is sufficiently simple, make a copy of it before INSN,
   followed by a jump to the exit of the loop.  Then delete the unconditional
   jump after INSN.

   Return 1 if we made the change, else 0.

   This is only safe immediately after a regscan pass because it uses the
   values of regno_first_uid and regno_last_uid.  */

static int
duplicate_loop_exit_test (loop_start)
     rtx loop_start;
{
  rtx insn, set, reg, p, link;
  rtx copy = 0, first_copy = 0;
  int num_insns = 0;
  rtx exitcode = NEXT_INSN (JUMP_LABEL (next_nonnote_insn (loop_start)));
  rtx lastexit;
  int max_reg = max_reg_num ();
  rtx *reg_map = 0;

  /* Scan the exit code.  We do not perform this optimization if any insn:

         is a CALL_INSN
         is a CODE_LABEL
         has a REG_RETVAL or REG_LIBCALL note (hard to adjust)
         is a NOTE_INSN_LOOP_BEG because this means we have a nested loop
         is a NOTE_INSN_BLOCK_{BEG,END} because duplicating these notes
              is not valid.

     We also do not do this if we find an insn with ASM_OPERANDS.  While
     this restriction should not be necessary, copying an insn with
     ASM_OPERANDS can confuse asm_noperands in some cases.

     Also, don't do this if the exit code is more than 20 insns.  */

  for (insn = exitcode;
       insn
       && ! (GET_CODE (insn) == NOTE
             && NOTE_LINE_NUMBER (insn) == NOTE_INSN_LOOP_END);
       insn = NEXT_INSN (insn))
    {
      switch (GET_CODE (insn))
        {
        case CODE_LABEL:
        case CALL_INSN:
          return 0;
        case NOTE:
          /* We could be in front of the wrong NOTE_INSN_LOOP_END if there is
             a jump immediately after the loop start that branches outside
             the loop but within an outer loop, near the exit test.
             If we copied this exit test and created a phony
             NOTE_INSN_LOOP_VTOP, this could make instructions immediately
             before the exit test look like these could be safely moved
             out of the loop even if they actually may be never executed.
             This can be avoided by checking here for NOTE_INSN_LOOP_CONT.  */

          if (NOTE_LINE_NUMBER (insn) == NOTE_INSN_LOOP_BEG
              || NOTE_LINE_NUMBER (insn) == NOTE_INSN_LOOP_CONT)
            return 0;

          if (optimize < 2
              && (NOTE_LINE_NUMBER (insn) == NOTE_INSN_BLOCK_BEG
                  || NOTE_LINE_NUMBER (insn) == NOTE_INSN_BLOCK_END))
            /* If we were to duplicate this code, we would not move
               the BLOCK notes, and so debugging the moved code would
               be difficult.  Thus, we only move the code with -O2 or
               higher.  */
            return 0;

          break;
        case JUMP_INSN:
        case INSN:
          /* The code below would grossly mishandle REG_WAS_0 notes,
             so get rid of them here.  */
          while ((p = find_reg_note (insn, REG_WAS_0, NULL_RTX)) != 0)
            remove_note (insn, p);
          if (++num_insns > 20
              || find_reg_note (insn, REG_RETVAL, NULL_RTX)
              || find_reg_note (insn, REG_LIBCALL, NULL_RTX))
            return 0;
          break;
        default:
          break;
        }
    }

  /* Unless INSN is zero, we can do the optimization.  */
  if (insn == 0)
    return 0;

  lastexit = insn;

  /* See if any insn sets a register only used in the loop exit code and
     not a user variable.  If so, replace it with a new register.  */
  for (insn = exitcode; insn != lastexit; insn = NEXT_INSN (insn))
    if (GET_CODE (insn) == INSN
        && (set = single_set (insn)) != 0
        && ((reg = SET_DEST (set), GET_CODE (reg) == REG)
            || (GET_CODE (reg) == SUBREG
                && (reg = SUBREG_REG (reg), GET_CODE (reg) == REG)))
        && REGNO (reg) >= FIRST_PSEUDO_REGISTER
        && REGNO_FIRST_UID (REGNO (reg)) == INSN_UID (insn))
      {
        for (p = NEXT_INSN (insn); p != lastexit; p = NEXT_INSN (p))
          if (REGNO_LAST_UID (REGNO (reg)) == INSN_UID (p))
            break;

        if (p != lastexit)
          {
            /* We can do the replacement.  Allocate reg_map if this is the
               first replacement we found.  */
            if (reg_map == 0)
              reg_map = (rtx *) xcalloc (max_reg, sizeof (rtx));

            REG_LOOP_TEST_P (reg) = 1;

            reg_map[REGNO (reg)] = gen_reg_rtx (GET_MODE (reg));
          }
      }

  /* Now copy each insn.  */
  for (insn = exitcode; insn != lastexit; insn = NEXT_INSN (insn))
    {
      switch (GET_CODE (insn))
        {
        case BARRIER:
          copy = emit_barrier_before (loop_start);
          break;
        case NOTE:
          /* Only copy line-number notes.  */
          if (NOTE_LINE_NUMBER (insn) >= 0)
            {
              copy = emit_note_before (NOTE_LINE_NUMBER (insn), loop_start);
              NOTE_SOURCE_FILE (copy) = NOTE_SOURCE_FILE (insn);
            }
          break;
          
        case INSN:
          copy = emit_insn_before (copy_insn (PATTERN (insn)), loop_start);
          if (reg_map)
            replace_regs (PATTERN (copy), reg_map, max_reg, 1);
          
          mark_jump_label (PATTERN (copy), copy, 0, 0);
          
          /* Copy all REG_NOTES except REG_LABEL since mark_jump_label will
             make them.  */
          for (link = REG_NOTES (insn); link; link = XEXP (link, 1))
            if (REG_NOTE_KIND (link) != REG_LABEL)
              {
                if (GET_CODE (link) == EXPR_LIST)
                  REG_NOTES (copy)
                    = copy_insn_1 (gen_rtx_EXPR_LIST (REG_NOTE_KIND (link),
                                                      XEXP (link, 0),
                                                      REG_NOTES (copy)));
                else
                  REG_NOTES (copy)
                    = copy_insn_1 (gen_rtx_INSN_LIST (REG_NOTE_KIND (link),
                                                      XEXP (link, 0),
                                                      REG_NOTES (copy)));
              }

          if (reg_map && REG_NOTES (copy))
            replace_regs (REG_NOTES (copy), reg_map, max_reg, 1);
          break;
          
        case JUMP_INSN:
          copy = emit_jump_insn_before (copy_insn (PATTERN (insn)), loop_start);
          if (reg_map)
            replace_regs (PATTERN (copy), reg_map, max_reg, 1);
          mark_jump_label (PATTERN (copy), copy, 0, 0);
          if (REG_NOTES (insn))
            {
              REG_NOTES (copy) = copy_insn_1 (REG_NOTES (insn));
              if (reg_map)
                replace_regs (REG_NOTES (copy), reg_map, max_reg, 1);
            }
          
          /* If this is a simple jump, add it to the jump chain.  */
          
          if (INSN_UID (copy) < max_jump_chain && JUMP_LABEL (copy)
              && simplejump_p (copy))
            {
              jump_chain[INSN_UID (copy)]
                = jump_chain[INSN_UID (JUMP_LABEL (copy))];
              jump_chain[INSN_UID (JUMP_LABEL (copy))] = copy;
            }
          break;
          
        default:
          abort ();
        }

      /* Record the first insn we copied.  We need it so that we can
         scan the copied insns for new pseudo registers.  */
      if (! first_copy)
        first_copy = copy;
    }

  /* Now clean up by emitting a jump to the end label and deleting the jump
     at the start of the loop.  */
  if (! copy || GET_CODE (copy) != BARRIER)
    {
      copy = emit_jump_insn_before (gen_jump (get_label_after (insn)),
                                    loop_start);

      /* Record the first insn we copied.  We need it so that we can
         scan the copied insns for new pseudo registers.   This may not
         be strictly necessary since we should have copied at least one
         insn above.  But I am going to be safe.  */
      if (! first_copy)
        first_copy = copy;

      mark_jump_label (PATTERN (copy), copy, 0, 0);
      if (INSN_UID (copy) < max_jump_chain
          && INSN_UID (JUMP_LABEL (copy)) < max_jump_chain)
        {
          jump_chain[INSN_UID (copy)]
            = jump_chain[INSN_UID (JUMP_LABEL (copy))];
          jump_chain[INSN_UID (JUMP_LABEL (copy))] = copy;
        }
      emit_barrier_before (loop_start);
    }

  /* Now scan from the first insn we copied to the last insn we copied
     (copy) for new pseudo registers.  Do this after the code to jump to
     the end label since that might create a new pseudo too.  */
  reg_scan_update (first_copy, copy, max_reg);

  /* Mark the exit code as the virtual top of the converted loop.  */
  emit_note_before (NOTE_INSN_LOOP_VTOP, exitcode);

  delete_insn (next_nonnote_insn (loop_start));
  
  /* Clean up.  */
  if (reg_map)
    free (reg_map);

  return 1;
}
\f
/* Move all block-beg, block-end, loop-beg, loop-cont, loop-vtop, loop-end,
   eh-beg, eh-end notes between START and END out before START.  Assume that
   END is not such a note.  START may be such a note.  Returns the value
   of the new starting insn, which may be different if the original start
   was such a note.  */

rtx
squeeze_notes (start, end)
     rtx start, end;
{
  rtx insn;
  rtx next;

  for (insn = start; insn != end; insn = next)
    {
      next = NEXT_INSN (insn);
      if (GET_CODE (insn) == NOTE
          && (NOTE_LINE_NUMBER (insn) == NOTE_INSN_BLOCK_END
              || NOTE_LINE_NUMBER (insn) == NOTE_INSN_BLOCK_BEG
              || NOTE_LINE_NUMBER (insn) == NOTE_INSN_LOOP_BEG
              || NOTE_LINE_NUMBER (insn) == NOTE_INSN_LOOP_END
              || NOTE_LINE_NUMBER (insn) == NOTE_INSN_LOOP_CONT
              || NOTE_LINE_NUMBER (insn) == NOTE_INSN_LOOP_VTOP
              || NOTE_LINE_NUMBER (insn) == NOTE_INSN_EH_REGION_BEG
              || NOTE_LINE_NUMBER (insn) == NOTE_INSN_EH_REGION_END))
        {
          if (insn == start)
            start = next;
          else
            {
              rtx prev = PREV_INSN (insn);
              PREV_INSN (insn) = PREV_INSN (start);
              NEXT_INSN (insn) = start;
              NEXT_INSN (PREV_INSN (insn)) = insn;
              PREV_INSN (NEXT_INSN (insn)) = insn;
              NEXT_INSN (prev) = next;
              PREV_INSN (next) = prev;
            }
        }
    }

  return start;
}
\f
/* Compare the instructions before insn E1 with those before E2
   to find an opportunity for cross jumping.
   (This means detecting identical sequences of insns followed by
   jumps to the same place, or followed by a label and a jump
   to that label, and replacing one with a jump to the other.)

   Assume E1 is a jump that jumps to label E2
   (that is not always true but it might as well be).
   Find the longest possible equivalent sequences
   and store the first insns of those sequences into *F1 and *F2.
   Store zero there if no equivalent preceding instructions are found.

   We give up if we find a label in stream 1.
   Actually we could transfer that label into stream 2.  */

static void
find_cross_jump (e1, e2, minimum, f1, f2)
     rtx e1, e2;
     int minimum;
     rtx *f1, *f2;
{
  register rtx i1 = e1, i2 = e2;
  register rtx p1, p2;
  int lose = 0;

  rtx last1 = 0, last2 = 0;
  rtx afterlast1 = 0, afterlast2 = 0;

  *f1 = 0;
  *f2 = 0;

  while (1)
    {
      i1 = prev_nonnote_insn (i1);

      i2 = PREV_INSN (i2);
      while (i2 && (GET_CODE (i2) == NOTE || GET_CODE (i2) == CODE_LABEL))
        i2 = PREV_INSN (i2);

      if (i1 == 0)
        break;

      /* Don't allow the range of insns preceding E1 or E2
         to include the other (E2 or E1).  */
      if (i2 == e1 || i1 == e2)
        break;

      /* If we will get to this code by jumping, those jumps will be
         tensioned to go directly to the new label (before I2),
         so this cross-jumping won't cost extra.  So reduce the minimum.  */
      if (GET_CODE (i1) == CODE_LABEL)
        {
          --minimum;
          break;
        }

      if (i2 == 0 || GET_CODE (i1) != GET_CODE (i2))
        break;

      /* Avoid moving insns across EH regions if either of the insns
         can throw.  */
      if (flag_exceptions
          && (asynchronous_exceptions || GET_CODE (i1) == CALL_INSN)
          && !in_same_eh_region (i1, i2))
        break;

      p1 = PATTERN (i1);
      p2 = PATTERN (i2);
        
      /* If this is a CALL_INSN, compare register usage information.
         If we don't check this on stack register machines, the two
         CALL_INSNs might be merged leaving reg-stack.c with mismatching
         numbers of stack registers in the same basic block.
         If we don't check this on machines with delay slots, a delay slot may
         be filled that clobbers a parameter expected by the subroutine.

         ??? We take the simple route for now and assume that if they're
         equal, they were constructed identically.  */

      if (GET_CODE (i1) == CALL_INSN
          && ! rtx_equal_p (CALL_INSN_FUNCTION_USAGE (i1),
                            CALL_INSN_FUNCTION_USAGE (i2)))
        lose = 1;

#ifdef STACK_REGS
      /* If cross_jump_death_matters is not 0, the insn's mode
         indicates whether or not the insn contains any stack-like
         regs.  */

      if (!lose && cross_jump_death_matters && stack_regs_mentioned (i1))
        {
          /* If register stack conversion has already been done, then
             death notes must also be compared before it is certain that
             the two instruction streams match.  */

          rtx note;
          HARD_REG_SET i1_regset, i2_regset;

          CLEAR_HARD_REG_SET (i1_regset);
          CLEAR_HARD_REG_SET (i2_regset);

          for (note = REG_NOTES (i1); note; note = XEXP (note, 1))
            if (REG_NOTE_KIND (note) == REG_DEAD
                && STACK_REG_P (XEXP (note, 0)))
              SET_HARD_REG_BIT (i1_regset, REGNO (XEXP (note, 0)));

          for (note = REG_NOTES (i2); note; note = XEXP (note, 1))
            if (REG_NOTE_KIND (note) == REG_DEAD
                && STACK_REG_P (XEXP (note, 0)))
              SET_HARD_REG_BIT (i2_regset, REGNO (XEXP (note, 0)));

          GO_IF_HARD_REG_EQUAL (i1_regset, i2_regset, done);

          lose = 1;

        done:
          ;
        }
#endif

      /* Don't allow old-style asm or volatile extended asms to be accepted
         for cross jumping purposes.  It is conceptually correct to allow
         them, since cross-jumping preserves the dynamic instruction order
         even though it is changing the static instruction order.  However,
         if an asm is being used to emit an assembler pseudo-op, such as
         the MIPS `.set reorder' pseudo-op, then the static instruction order
         matters and it must be preserved.  */
      if (GET_CODE (p1) == ASM_INPUT || GET_CODE (p2) == ASM_INPUT
          || (GET_CODE (p1) == ASM_OPERANDS && MEM_VOLATILE_P (p1))
          || (GET_CODE (p2) == ASM_OPERANDS && MEM_VOLATILE_P (p2)))
        lose = 1;

      if (lose || GET_CODE (p1) != GET_CODE (p2)
          || ! rtx_renumbered_equal_p (p1, p2))
        {
          /* The following code helps take care of G++ cleanups.  */
          rtx equiv1;
          rtx equiv2;

          if (!lose && GET_CODE (p1) == GET_CODE (p2)
              && ((equiv1 = find_reg_note (i1, REG_EQUAL, NULL_RTX)) != 0
                  || (equiv1 = find_reg_note (i1, REG_EQUIV, NULL_RTX)) != 0)
              && ((equiv2 = find_reg_note (i2, REG_EQUAL, NULL_RTX)) != 0
                  || (equiv2 = find_reg_note (i2, REG_EQUIV, NULL_RTX)) != 0)
              /* If the equivalences are not to a constant, they may
                 reference pseudos that no longer exist, so we can't
                 use them.  */
              && CONSTANT_P (XEXP (equiv1, 0))
              && rtx_equal_p (XEXP (equiv1, 0), XEXP (equiv2, 0)))
            {
              rtx s1 = single_set (i1);
              rtx s2 = single_set (i2);
              if (s1 != 0 && s2 != 0
                  && rtx_renumbered_equal_p (SET_DEST (s1), SET_DEST (s2)))
                {
                  validate_change (i1, &SET_SRC (s1), XEXP (equiv1, 0), 1);
                  validate_change (i2, &SET_SRC (s2), XEXP (equiv2, 0), 1);
                  if (! rtx_renumbered_equal_p (p1, p2))
                    cancel_changes (0);
                  else if (apply_change_group ())
                    goto win;
                }
            }

          /* Insns fail to match; cross jumping is limited to the following
             insns.  */

#ifdef HAVE_cc0
          /* Don't allow the insn after a compare to be shared by
             cross-jumping unless the compare is also shared.
             Here, if either of these non-matching insns is a compare,
             exclude the following insn from possible cross-jumping.  */
          if (sets_cc0_p (p1) || sets_cc0_p (p2))
            last1 = afterlast1, last2 = afterlast2, ++minimum;
#endif

          /* If cross-jumping here will feed a jump-around-jump
             optimization, this jump won't cost extra, so reduce
             the minimum.  */
          if (GET_CODE (i1) == JUMP_INSN
              && JUMP_LABEL (i1)
              && prev_real_insn (JUMP_LABEL (i1)) == e1)
            --minimum;
          break;
        }

    win:
      if (GET_CODE (p1) != USE && GET_CODE (p1) != CLOBBER)
        {
          /* Ok, this insn is potentially includable in a cross-jump here.  */
          afterlast1 = last1, afterlast2 = last2;
          last1 = i1, last2 = i2, --minimum;
        }
    }

  if (minimum <= 0 && last1 != 0 && last1 != e1)
    *f1 = last1, *f2 = last2;
}

static void
do_cross_jump (insn, newjpos, newlpos)
     rtx insn, newjpos, newlpos;
{
  /* Find an existing label at this point
     or make a new one if there is none.  */
  register rtx label = get_label_before (newlpos);

  /* Make the same jump insn jump to the new point.  */
  if (GET_CODE (PATTERN (insn)) == RETURN)
    {
      /* Remove from jump chain of returns.  */
      delete_from_jump_chain (insn);
      /* Change the insn.  */
      PATTERN (insn) = gen_jump (label);
      INSN_CODE (insn) = -1;
      JUMP_LABEL (insn) = label;
      LABEL_NUSES (label)++;
      /* Add to new the jump chain.  */
      if (INSN_UID (label) < max_jump_chain
          && INSN_UID (insn) < max_jump_chain)
        {
          jump_chain[INSN_UID (insn)] = jump_chain[INSN_UID (label)];
          jump_chain[INSN_UID (label)] = insn;
        }
    }
  else
    redirect_jump (insn, label);

  /* Delete the matching insns before the jump.  Also, remove any REG_EQUAL
     or REG_EQUIV note in the NEWLPOS stream that isn't also present in
     the NEWJPOS stream.  */

  while (newjpos != insn)
    {
      rtx lnote;

      for (lnote = REG_NOTES (newlpos); lnote; lnote = XEXP (lnote, 1))
        if ((REG_NOTE_KIND (lnote) == REG_EQUAL
             || REG_NOTE_KIND (lnote) == REG_EQUIV)
            && ! find_reg_note (newjpos, REG_EQUAL, XEXP (lnote, 0))
            && ! find_reg_note (newjpos, REG_EQUIV, XEXP (lnote, 0)))
          remove_note (newlpos, lnote);

      delete_insn (newjpos);
      newjpos = next_real_insn (newjpos);
      newlpos = next_real_insn (newlpos);
    }
}
\f
/* Return the label before INSN, or put a new label there.  */

rtx
get_label_before (insn)
     rtx insn;
{
  rtx label;

  /* Find an existing label at this point
     or make a new one if there is none.  */
  label = prev_nonnote_insn (insn);

  if (label == 0 || GET_CODE (label) != CODE_LABEL)
    {
      rtx prev = PREV_INSN (insn);

      label = gen_label_rtx ();
      emit_label_after (label, prev);
      LABEL_NUSES (label) = 0;
    }
  return label;
}

/* Return the label after INSN, or put a new label there.  */

rtx
get_label_after (insn)
     rtx insn;
{
  rtx label;

  /* Find an existing label at this point
     or make a new one if there is none.  */
  label = next_nonnote_insn (insn);

  if (label == 0 || GET_CODE (label) != CODE_LABEL)
    {
      label = gen_label_rtx ();
      emit_label_after (label, insn);
      LABEL_NUSES (label) = 0;
    }
  return label;
}
\f
/* Return 1 if INSN is a jump that jumps to right after TARGET
   only on the condition that TARGET itself would drop through.
   Assumes that TARGET is a conditional jump.  */

static int
jump_back_p (insn, target)
     rtx insn, target;
{
  rtx cinsn, ctarget;
  enum rtx_code codei, codet;

  if (simplejump_p (insn) || ! condjump_p (insn)
      || simplejump_p (target)
      || target != prev_real_insn (JUMP_LABEL (insn)))
    return 0;

  cinsn = XEXP (SET_SRC (PATTERN (insn)), 0);
  ctarget = XEXP (SET_SRC (PATTERN (target)), 0);

  codei = GET_CODE (cinsn);
  codet = GET_CODE (ctarget);

  if (XEXP (SET_SRC (PATTERN (insn)), 1) == pc_rtx)
    {
      if (! can_reverse_comparison_p (cinsn, insn))
        return 0;
      codei = reverse_condition (codei);
    }

  if (XEXP (SET_SRC (PATTERN (target)), 2) == pc_rtx)
    {
      if (! can_reverse_comparison_p (ctarget, target))
        return 0;
      codet = reverse_condition (codet);
    }

  return (codei == codet
          && rtx_renumbered_equal_p (XEXP (cinsn, 0), XEXP (ctarget, 0))
          && rtx_renumbered_equal_p (XEXP (cinsn, 1), XEXP (ctarget, 1)));
}
\f
/* Given a comparison, COMPARISON, inside a conditional jump insn, INSN,
   return non-zero if it is safe to reverse this comparison.  It is if our
   floating-point is not IEEE, if this is an NE or EQ comparison, or if
   this is known to be an integer comparison.  */

int
can_reverse_comparison_p (comparison, insn)
     rtx comparison;
     rtx insn;
{
  rtx arg0;

  /* If this is not actually a comparison, we can't reverse it.  */
  if (GET_RTX_CLASS (GET_CODE (comparison)) != '<')
    return 0;

  if (TARGET_FLOAT_FORMAT != IEEE_FLOAT_FORMAT
      /* If this is an NE comparison, it is safe to reverse it to an EQ
         comparison and vice versa, even for floating point.  If no operands
         are NaNs, the reversal is valid.  If some operand is a NaN, EQ is
         always false and NE is always true, so the reversal is also valid.  */
      || flag_fast_math
      || GET_CODE (comparison) == NE
      || GET_CODE (comparison) == EQ)
    return 1;

  arg0 = XEXP (comparison, 0);

  /* Make sure ARG0 is one of the actual objects being compared.  If we
     can't do this, we can't be sure the comparison can be reversed. 

     Handle cc0 and a MODE_CC register.  */
  if ((GET_CODE (arg0) == REG && GET_MODE_CLASS (GET_MODE (arg0)) == MODE_CC)
#ifdef HAVE_cc0
      || arg0 == cc0_rtx
#endif
      )
    {
      rtx prev = prev_nonnote_insn (insn);
      rtx set;

      /* First see if the condition code mode alone if enough to say we can
         reverse the condition.  If not, then search backwards for a set of
         ARG0. We do not need to check for an insn clobbering it since valid
         code will contain set a set with no intervening clobber.  But
         stop when we reach a label.  */
#ifdef REVERSIBLE_CC_MODE
      if (GET_MODE_CLASS (GET_MODE (arg0)) == MODE_CC
          && REVERSIBLE_CC_MODE (GET_MODE (arg0)))
        return 1;
#endif
        
      for (prev = prev_nonnote_insn (insn);
           prev != 0 && GET_CODE (prev) != CODE_LABEL;
           prev = prev_nonnote_insn (prev))
        if ((set = single_set (prev)) != 0
            && rtx_equal_p (SET_DEST (set), arg0))
          {
            arg0 = SET_SRC (set);

            if (GET_CODE (arg0) == COMPARE)
              arg0 = XEXP (arg0, 0);
            break;
          }
    }

  /* We can reverse this if ARG0 is a CONST_INT or if its mode is
     not VOIDmode and neither a MODE_CC nor MODE_FLOAT type.  */
  return (GET_CODE (arg0) == CONST_INT
          || (GET_MODE (arg0) != VOIDmode
              && GET_MODE_CLASS (GET_MODE (arg0)) != MODE_CC
              && GET_MODE_CLASS (GET_MODE (arg0)) != MODE_FLOAT));
}

/* Given an rtx-code for a comparison, return the code for the negated
   comparison.  If no such code exists, return UNKNOWN.

   WATCH OUT!  reverse_condition is not safe to use on a jump that might
   be acting on the results of an IEEE floating point comparison, because
   of the special treatment of non-signaling nans in comparisons.  
   Use can_reverse_comparison_p to be sure.  */

enum rtx_code
reverse_condition (code)
     enum rtx_code code;
{
  switch (code)
    {
    case EQ:
      return NE;
    case NE:
      return EQ;
    case GT:
      return LE;
    case GE:
      return LT;
    case LT:
      return GE;
    case LE:
      return GT;
    case GTU:
      return LEU;
    case GEU:
      return LTU;
    case LTU:
      return GEU;
    case LEU:
      return GTU;
    case UNORDERED:
      return ORDERED;
    case ORDERED:
      return UNORDERED;

    case UNLT:
    case UNLE:
    case UNGT:
    case UNGE:
    case UNEQ:
    case LTGT:
      return UNKNOWN;

    default:
      abort ();
    }
}

/* Similar, but we're allowed to generate unordered comparisons, which
   makes it safe for IEEE floating-point.  Of course, we have to recognize
   that the target will support them too...  */

enum rtx_code
reverse_condition_maybe_unordered (code)
     enum rtx_code code;
{
  /* Non-IEEE formats don't have unordered conditions.  */
  if (TARGET_FLOAT_FORMAT != IEEE_FLOAT_FORMAT)
    return reverse_condition (code);

  switch (code)
    {
    case EQ:
      return NE;
    case NE:
      return EQ;
    case GT:
      return UNLE;
    case GE:
      return UNLT;
    case LT:
      return UNGE;
    case LE:
      return UNGT;
    case LTGT:
      return UNEQ;
    case GTU:
      return LEU;
    case GEU:
      return LTU;
    case LTU:
      return GEU;
    case LEU:
      return GTU;
    case UNORDERED:
      return ORDERED;
    case ORDERED:
      return UNORDERED;
    case UNLT:
      return GE;
    case UNLE:
      return GT;
    case UNGT:
      return LE;
    case UNGE:
      return LT;
    case UNEQ:
      return LTGT;

    default:
      abort ();
    }
}

/* Similar, but return the code when two operands of a comparison are swapped.
   This IS safe for IEEE floating-point.  */

enum rtx_code
swap_condition (code)
     enum rtx_code code;
{
  switch (code)
    {
    case EQ:
    case NE:
    case UNORDERED:
    case ORDERED:
    case UNEQ:
    case LTGT:
      return code;

    case GT:
      return LT;
    case GE:
      return LE;
    case LT:
      return GT;
    case LE:
      return GE;
    case GTU:
      return LTU;
    case GEU:
      return LEU;
    case LTU:
      return GTU;
    case LEU:
      return GEU;
    case UNLT:
      return UNGT;
    case UNLE:
      return UNGE;
    case UNGT:
      return UNLT;
    case UNGE:
      return UNLE;

    default:
      abort ();
    }
}

/* Given a comparison CODE, return the corresponding unsigned comparison.
   If CODE is an equality comparison or already an unsigned comparison,
   CODE is returned.  */

enum rtx_code
unsigned_condition (code)
     enum rtx_code code;
{
  switch (code)
    {
    case EQ:
    case NE:
    case GTU:
    case GEU:
    case LTU:
    case LEU:
      return code;

    case GT:
      return GTU;
    case GE:
      return GEU;
    case LT:
      return LTU;
    case LE:
      return LEU;

    default:
      abort ();
    }
}

/* Similarly, return the signed version of a comparison.  */

enum rtx_code
signed_condition (code)
     enum rtx_code code;
{
  switch (code)
    {
    case EQ:
    case NE:
    case GT:
    case GE:
    case LT:
    case LE:
      return code;

    case GTU:
      return GT;
    case GEU:
      return GE;
    case LTU:
      return LT;
    case LEU:
      return LE;

    default:
      abort ();
    }
}
\f
/* Return non-zero if CODE1 is more strict than CODE2, i.e., if the
   truth of CODE1 implies the truth of CODE2.  */

int
comparison_dominates_p (code1, code2)
     enum rtx_code code1, code2;
{
  if (code1 == code2)
    return 1;

  switch (code1)
    {
    case EQ:
      if (code2 == LE || code2 == LEU || code2 == GE || code2 == GEU
          || code2 == ORDERED)
        return 1;
      break;

    case LT:
      if (code2 == LE || code2 == NE || code2 == ORDERED)
        return 1;
      break;

    case GT:
      if (code2 == GE || code2 == NE || code2 == ORDERED)
        return 1;
      break;

    case GE:
    case LE:
      if (code2 == ORDERED)
        return 1;
      break;

    case LTGT:
      if (code2 == NE || code2 == ORDERED)
        return 1;
      break;

    case LTU:
      if (code2 == LEU || code2 == NE)
        return 1;
      break;

    case GTU:
      if (code2 == GEU || code2 == NE)
        return 1;
      break;

    case UNORDERED:
      if (code2 == NE)
        return 1;
      break;
      
    default:
      break;
    }

  return 0;
}
\f
/* Return 1 if INSN is an unconditional jump and nothing else.  */

int
simplejump_p (insn)
     rtx insn;
{
  return (GET_CODE (insn) == JUMP_INSN
          && GET_CODE (PATTERN (insn)) == SET
          && GET_CODE (SET_DEST (PATTERN (insn))) == PC
          && GET_CODE (SET_SRC (PATTERN (insn))) == LABEL_REF);
}

/* Return nonzero if INSN is a (possibly) conditional jump
   and nothing more.  */

int
condjump_p (insn)
     rtx insn;
{
  register rtx x = PATTERN (insn);

  if (GET_CODE (x) != SET
      || GET_CODE (SET_DEST (x)) != PC)
    return 0;

  x = SET_SRC (x);
  if (GET_CODE (x) == LABEL_REF)
    return 1;
  else return (GET_CODE (x) == IF_THEN_ELSE
               && ((GET_CODE (XEXP (x, 2)) == PC
                    && (GET_CODE (XEXP (x, 1)) == LABEL_REF
                        || GET_CODE (XEXP (x, 1)) == RETURN))
                   || (GET_CODE (XEXP (x, 1)) == PC
                       && (GET_CODE (XEXP (x, 2)) == LABEL_REF
                           || GET_CODE (XEXP (x, 2)) == RETURN))));

  return 0;
}

/* Return nonzero if INSN is a (possibly) conditional jump inside a
   PARALLEL.  */

int
condjump_in_parallel_p (insn)
     rtx insn;
{
  register rtx x = PATTERN (insn);

  if (GET_CODE (x) != PARALLEL)
    return 0;
  else
    x = XVECEXP (x, 0, 0);

  if (GET_CODE (x) != SET)
    return 0;
  if (GET_CODE (SET_DEST (x)) != PC)
    return 0;
  if (GET_CODE (SET_SRC (x)) == LABEL_REF)
    return 1;
  if (GET_CODE (SET_SRC (x)) != IF_THEN_ELSE)
    return 0;
  if (XEXP (SET_SRC (x), 2) == pc_rtx
      && (GET_CODE (XEXP (SET_SRC (x), 1)) == LABEL_REF
          || GET_CODE (XEXP (SET_SRC (x), 1)) == RETURN))
    return 1;
  if (XEXP (SET_SRC (x), 1) == pc_rtx
      && (GET_CODE (XEXP (SET_SRC (x), 2)) == LABEL_REF
          || GET_CODE (XEXP (SET_SRC (x), 2)) == RETURN))
    return 1;
  return 0;
}

/* Return the label of a conditional jump.  */

rtx
condjump_label (insn)
     rtx insn;
{
  register rtx x = PATTERN (insn);

  if (GET_CODE (x) == PARALLEL)
    x = XVECEXP (x, 0, 0);
  if (GET_CODE (x) != SET)
    return NULL_RTX;
  if (GET_CODE (SET_DEST (x)) != PC)
    return NULL_RTX;
  x = SET_SRC (x);
  if (GET_CODE (x) == LABEL_REF)
    return x;
  if (GET_CODE (x) != IF_THEN_ELSE)
    return NULL_RTX;
  if (XEXP (x, 2) == pc_rtx && GET_CODE (XEXP (x, 1)) == LABEL_REF)
    return XEXP (x, 1);
  if (XEXP (x, 1) == pc_rtx && GET_CODE (XEXP (x, 2)) == LABEL_REF)
    return XEXP (x, 2);
  return NULL_RTX;
}

/* Return true if INSN is a (possibly conditional) return insn.  */

static int
returnjump_p_1 (loc, data)
     rtx *loc;
     void *data ATTRIBUTE_UNUSED;
{
  rtx x = *loc;
  return x && GET_CODE (x) == RETURN;
}

int
returnjump_p (insn)
     rtx insn;
{
  return for_each_rtx (&PATTERN (insn), returnjump_p_1, NULL);
}

/* Return true if INSN is a jump that only transfers control and
   nothing more.  */

int
onlyjump_p (insn)
     rtx insn;
{
  rtx set;

  if (GET_CODE (insn) != JUMP_INSN)
    return 0;

  set = single_set (insn);
  if (set == NULL)
    return 0;
  if (GET_CODE (SET_DEST (set)) != PC)
    return 0;
  if (side_effects_p (SET_SRC (set)))
    return 0;

  return 1;
}

#ifdef HAVE_cc0

/* Return 1 if X is an RTX that does nothing but set the condition codes
   and CLOBBER or USE registers.
   Return -1 if X does explicitly set the condition codes,
   but also does other things.  */

int
sets_cc0_p (x)
     rtx x ATTRIBUTE_UNUSED;
{
  if (GET_CODE (x) == SET && SET_DEST (x) == cc0_rtx)
    return 1;
  if (GET_CODE (x) == PARALLEL)
    {
      int i;
      int sets_cc0 = 0;
      int other_things = 0;
      for (i = XVECLEN (x, 0) - 1; i >= 0; i--)
        {
          if (GET_CODE (XVECEXP (x, 0, i)) == SET
              && SET_DEST (XVECEXP (x, 0, i)) == cc0_rtx)
            sets_cc0 = 1;
          else if (GET_CODE (XVECEXP (x, 0, i)) == SET)
            other_things = 1;
        }
      return ! sets_cc0 ? 0 : other_things ? -1 : 1;
    }
  return 0;
}
#endif
\f
/* Follow any unconditional jump at LABEL;
   return the ultimate label reached by any such chain of jumps.
   If LABEL is not followed by a jump, return LABEL.
   If the chain loops or we can't find end, return LABEL,
   since that tells caller to avoid changing the insn.

   If RELOAD_COMPLETED is 0, we do not chain across a NOTE_INSN_LOOP_BEG or
   a USE or CLOBBER.  */

rtx
follow_jumps (label)
     rtx label;
{
  register rtx insn;
  register rtx next;
  register rtx value = label;
  register int depth;

  for (depth = 0;
       (depth < 10
        && (insn = next_active_insn (value)) != 0
        && GET_CODE (insn) == JUMP_INSN
        && ((JUMP_LABEL (insn) != 0 && simplejump_p (insn))
            || GET_CODE (PATTERN (insn)) == RETURN)
        && (next = NEXT_INSN (insn))
        && GET_CODE (next) == BARRIER);
       depth++)
    {
      /* Don't chain through the insn that jumps into a loop
         from outside the loop,
         since that would create multiple loop entry jumps
         and prevent loop optimization.  */
      rtx tem;
      if (!reload_completed)
        for (tem = value; tem != insn; tem = NEXT_INSN (tem))
          if (GET_CODE (tem) == NOTE
              && (NOTE_LINE_NUMBER (tem) == NOTE_INSN_LOOP_BEG
                  /* ??? Optional.  Disables some optimizations, but makes
                     gcov output more accurate with -O.  */
                  || (flag_test_coverage && NOTE_LINE_NUMBER (tem) > 0)))
            return value;

      /* If we have found a cycle, make the insn jump to itself.  */
      if (JUMP_LABEL (insn) == label)
        return label;

      tem = next_active_insn (JUMP_LABEL (insn));
      if (tem && (GET_CODE (PATTERN (tem)) == ADDR_VEC
                  || GET_CODE (PATTERN (tem)) == ADDR_DIFF_VEC))
        break;

      value = JUMP_LABEL (insn);
    }
  if (depth == 10)
    return label;
  return value;
}

/* Assuming that field IDX of X is a vector of label_refs,
   replace each of them by the ultimate label reached by it.
   Return nonzero if a change is made.
   If IGNORE_LOOPS is 0, we do not chain across a NOTE_INSN_LOOP_BEG.  */

static int
tension_vector_labels (x, idx)
     register rtx x;
     register int idx;
{
  int changed = 0;
  register int i;
  for (i = XVECLEN (x, idx) - 1; i >= 0; i--)
    {
      register rtx olabel = XEXP (XVECEXP (x, idx, i), 0);
      register rtx nlabel = follow_jumps (olabel);
      if (nlabel && nlabel != olabel)
        {
          XEXP (XVECEXP (x, idx, i), 0) = nlabel;
          ++LABEL_NUSES (nlabel);
          if (--LABEL_NUSES (olabel) == 0)
            delete_insn (olabel);
          changed = 1;
        }
    }
  return changed;
}
\f
/* Find all CODE_LABELs referred to in X, and increment their use counts.
   If INSN is a JUMP_INSN and there is at least one CODE_LABEL referenced
   in INSN, then store one of them in JUMP_LABEL (INSN).
   If INSN is an INSN or a CALL_INSN and there is at least one CODE_LABEL
   referenced in INSN, add a REG_LABEL note containing that label to INSN.
   Also, when there are consecutive labels, canonicalize on the last of them.

   Note that two labels separated by a loop-beginning note
   must be kept distinct if we have not yet done loop-optimization,
   because the gap between them is where loop-optimize
   will want to move invariant code to.  CROSS_JUMP tells us
   that loop-optimization is done with.

   Once reload has completed (CROSS_JUMP non-zero), we need not consider
   two labels distinct if they are separated by only USE or CLOBBER insns.  */

static void
mark_jump_label (x, insn, cross_jump, in_mem)
     register rtx x;
     rtx insn;
     int cross_jump;
     int in_mem;
{
  register RTX_CODE code = GET_CODE (x);
  register int i;
  register const char *fmt;

  switch (code)
    {
    case PC:
    case CC0:
    case REG:
    case SUBREG:
    case CONST_INT:
    case CONST_DOUBLE:
    case CLOBBER:
    case CALL:
      return;

    case MEM:
      in_mem = 1;
      break;

    case SYMBOL_REF:
      if (!in_mem)
        return;

      /* If this is a constant-pool reference, see if it is a label.  */
      if (CONSTANT_POOL_ADDRESS_P (x))
        mark_jump_label (get_pool_constant (x), insn, cross_jump, in_mem);
      break;

    case LABEL_REF:
      {
        rtx label = XEXP (x, 0);
        rtx olabel = label;
        rtx note;
        rtx next;

        /* Ignore remaining references to unreachable labels that
           have been deleted.  */
        if (GET_CODE (label) == NOTE
            && NOTE_LINE_NUMBER (label) == NOTE_INSN_DELETED_LABEL)
          break;

        if (GET_CODE (label) != CODE_LABEL)
          abort ();

        /* Ignore references to labels of containing functions.  */
        if (LABEL_REF_NONLOCAL_P (x))
          break;

        /* If there are other labels following this one,
           replace it with the last of the consecutive labels.  */
        for (next = NEXT_INSN (label); next; next = NEXT_INSN (next))
          {
            if (GET_CODE (next) == CODE_LABEL)
              label = next;
            else if (cross_jump && GET_CODE (next) == INSN
                     && (GET_CODE (PATTERN (next)) == USE
                         || GET_CODE (PATTERN (next)) == CLOBBER))
              continue;
            else if (GET_CODE (next) != NOTE)
              break;
            else if (! cross_jump
                     && (NOTE_LINE_NUMBER (next) == NOTE_INSN_LOOP_BEG
                         || NOTE_LINE_NUMBER (next) == NOTE_INSN_FUNCTION_END
                         /* ??? Optional.  Disables some optimizations, but
                            makes gcov output more accurate with -O.  */
                         || (flag_test_coverage && NOTE_LINE_NUMBER (next) > 0)))
              break;
          }

        XEXP (x, 0) = label;
        if (! insn || ! INSN_DELETED_P (insn))
          ++LABEL_NUSES (label);

        if (insn)
          {
            if (GET_CODE (insn) == JUMP_INSN)
              JUMP_LABEL (insn) = label;

            /* If we've changed OLABEL and we had a REG_LABEL note
               for it, update it as well.  */
            else if (label != olabel
                     && (note = find_reg_note (insn, REG_LABEL, olabel)) != 0)
              XEXP (note, 0) = label;

            /* Otherwise, add a REG_LABEL note for LABEL unless there already
               is one.  */
            else if (! find_reg_note (insn, REG_LABEL, label))
              {
                /* This code used to ignore labels which refered to dispatch
                   tables to avoid flow.c generating worse code.

                   However, in the presense of global optimizations like
                   gcse which call find_basic_blocks without calling
                   life_analysis, not recording such labels will lead
                   to compiler aborts because of inconsistencies in the
                   flow graph.  So we go ahead and record the label.

                   It may also be the case that the optimization argument
                   is no longer valid because of the more accurate cfg
                   we build in find_basic_blocks -- it no longer pessimizes
                   code when it finds a REG_LABEL note.  */
                REG_NOTES (insn) = gen_rtx_INSN_LIST (REG_LABEL, label,
                                                      REG_NOTES (insn));
              }
          }
        return;
      }

  /* Do walk the labels in a vector, but not the first operand of an
     ADDR_DIFF_VEC.  Don't set the JUMP_LABEL of a vector.  */
    case ADDR_VEC:
    case ADDR_DIFF_VEC:
      if (! INSN_DELETED_P (insn))
        {
          int eltnum = code == ADDR_DIFF_VEC ? 1 : 0;

          for (i = 0; i < XVECLEN (x, eltnum); i++)
            mark_jump_label (XVECEXP (x, eltnum, i), NULL_RTX, 
                    cross_jump, in_mem);
        }
      return;
      
    default:
      break;
    }

  fmt = GET_RTX_FORMAT (code);
  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
    {
      if (fmt[i] == 'e')
        mark_jump_label (XEXP (x, i), insn, cross_jump, in_mem);
      else if (fmt[i] == 'E')
        {
          register int j;
          for (j = 0; j < XVECLEN (x, i); j++)
            mark_jump_label (XVECEXP (x, i, j), insn, cross_jump, in_mem);
        }
    }
}

/* If all INSN does is set the pc, delete it,
   and delete the insn that set the condition codes for it
   if that's what the previous thing was.  */

void
delete_jump (insn)
     rtx insn;
{
  register rtx set = single_set (insn);

  if (set && GET_CODE (SET_DEST (set)) == PC)
    delete_computation (insn);
}

/* Verify INSN is a BARRIER and delete it.  */

void
delete_barrier (insn)
     rtx insn;
{
  if (GET_CODE (insn) != BARRIER)
    abort ();

  delete_insn (insn);
}

/* Recursively delete prior insns that compute the value (used only by INSN
   which the caller is deleting) stored in the register mentioned by NOTE
   which is a REG_DEAD note associated with INSN.  */

static void
delete_prior_computation (note, insn)
     rtx note;
     rtx insn;
{
  rtx our_prev;
  rtx reg = XEXP (note, 0);

  for (our_prev = prev_nonnote_insn (insn);
       our_prev && (GET_CODE (our_prev) == INSN
                    || GET_CODE (our_prev) == CALL_INSN);
       our_prev = prev_nonnote_insn (our_prev))
    {
      rtx pat = PATTERN (our_prev);

      /* If we reach a CALL which is not calling a const function
         or the callee pops the arguments, then give up.  */
      if (GET_CODE (our_prev) == CALL_INSN
          && (! CONST_CALL_P (our_prev)
              || GET_CODE (pat) != SET || GET_CODE (SET_SRC (pat)) != CALL))
        break;

      /* If we reach a SEQUENCE, it is too complex to try to
         do anything with it, so give up.  */
      if (GET_CODE (pat) == SEQUENCE)
        break;

      if (GET_CODE (pat) == USE
          && GET_CODE (XEXP (pat, 0)) == INSN)
        /* reorg creates USEs that look like this.  We leave them
           alone because reorg needs them for its own purposes.  */
        break;

      if (reg_set_p (reg, pat))
        {
          if (side_effects_p (pat) && GET_CODE (our_prev) != CALL_INSN)
            break;

          if (GET_CODE (pat) == PARALLEL)
            {
              /* If we find a SET of something else, we can't
                 delete the insn.  */

              int i;

              for (i = 0; i < XVECLEN (pat, 0); i++)
                {
                  rtx part = XVECEXP (pat, 0, i);

                  if (GET_CODE (part) == SET
                      && SET_DEST (part) != reg)
                    break;
                }

              if (i == XVECLEN (pat, 0))
                delete_computation (our_prev);
            }
          else if (GET_CODE (pat) == SET
                   && GET_CODE (SET_DEST (pat)) == REG)
            {
              int dest_regno = REGNO (SET_DEST (pat));
              int dest_endregno
                    = dest_regno + (dest_regno < FIRST_PSEUDO_REGISTER 
                      ? HARD_REGNO_NREGS (dest_regno,
                                GET_MODE (SET_DEST (pat))) : 1);
              int regno = REGNO (reg);
              int endregno = regno + (regno < FIRST_PSEUDO_REGISTER 
                             ? HARD_REGNO_NREGS (regno, GET_MODE (reg)) : 1);

              if (dest_regno >= regno
                  && dest_endregno <= endregno)
                delete_computation (our_prev);

              /* We may have a multi-word hard register and some, but not
                 all, of the words of the register are needed in subsequent
                 insns.  Write REG_UNUSED notes for those parts that were not
                 needed.  */
              else if (dest_regno <= regno
                       && dest_endregno >= endregno)
                {
                  int i;

                  REG_NOTES (our_prev)
                    = gen_rtx_EXPR_LIST (REG_UNUSED, reg, REG_NOTES (our_prev));

                  for (i = dest_regno; i < dest_endregno; i++)
                    if (! find_regno_note (our_prev, REG_UNUSED, i))
                      break;

                  if (i == dest_endregno)
                    delete_computation (our_prev);
                }
            }

          break;
        }

      /* If PAT references the register that dies here, it is an
         additional use.  Hence any prior SET isn't dead.  However, this
         insn becomes the new place for the REG_DEAD note.  */
      if (reg_overlap_mentioned_p (reg, pat))
        {
          XEXP (note, 1) = REG_NOTES (our_prev);
          REG_NOTES (our_prev) = note;
          break;
        }
    }
}

/* Delete INSN and recursively delete insns that compute values used only
   by INSN.  This uses the REG_DEAD notes computed during flow analysis.
   If we are running before flow.c, we need do nothing since flow.c will
   delete dead code.  We also can't know if the registers being used are
   dead or not at this point.

   Otherwise, look at all our REG_DEAD notes.  If a previous insn does
   nothing other than set a register that dies in this insn, we can delete
   that insn as well.

   On machines with CC0, if CC0 is used in this insn, we may be able to
   delete the insn that set it.  */

static void
delete_computation (insn)
     rtx insn;
{
  rtx note, next;
  rtx set;

#ifdef HAVE_cc0
  if (reg_referenced_p (cc0_rtx, PATTERN (insn)))
    {
      rtx prev = prev_nonnote_insn (insn);
      /* We assume that at this stage
         CC's are always set explicitly
         and always immediately before the jump that
         will use them.  So if the previous insn
         exists to set the CC's, delete it
         (unless it performs auto-increments, etc.).  */
      if (prev && GET_CODE (prev) == INSN
          && sets_cc0_p (PATTERN (prev)))
        {
          if (sets_cc0_p (PATTERN (prev)) > 0
              && ! side_effects_p (PATTERN (prev)))
            delete_computation (prev);
          else
            /* Otherwise, show that cc0 won't be used.  */
            REG_NOTES (prev) = gen_rtx_EXPR_LIST (REG_UNUSED,
                                                  cc0_rtx, REG_NOTES (prev));
        }
    }
#endif

#ifdef INSN_SCHEDULING
  /* ?!? The schedulers do not keep REG_DEAD notes accurate after
     reload has completed.  The schedulers need to be fixed.  Until
     they are, we must not rely on the death notes here.  */
  if (reload_completed && flag_schedule_insns_after_reload)
    {
      delete_insn (insn);
      return;
    }
#endif

  /* The REG_DEAD note may have been omitted for a register
     which is both set and used by the insn.  */
  set = single_set (insn);
  if (set && GET_CODE (SET_DEST (set)) == REG)
    {
    int dest_regno = REGNO (SET_DEST (set));
    int dest_endregno
          = dest_regno + (dest_regno < FIRST_PSEUDO_REGISTER 
            ? HARD_REGNO_NREGS (dest_regno,
                                GET_MODE (SET_DEST (set))) : 1);
    int i;

    for (i = dest_regno; i < dest_endregno; i++)
      {
        if (! refers_to_regno_p (i, i + 1, SET_SRC (set), NULL_PTR)
            || find_regno_note (insn, REG_DEAD, i))
          continue;

        note = gen_rtx_EXPR_LIST (REG_DEAD, (i < FIRST_PSEUDO_REGISTER
                                             ? gen_rtx_REG (reg_raw_mode[i], i)
                                             : SET_DEST (set)), NULL_RTX);
        delete_prior_computation (note, insn);
      }
    }

  for (note = REG_NOTES (insn); note; note = next)
    {
      next = XEXP (note, 1);

      if (REG_NOTE_KIND (note) != REG_DEAD
          /* Verify that the REG_NOTE is legitimate.  */
          || GET_CODE (XEXP (note, 0)) != REG)
        continue;

      delete_prior_computation (note, insn);
    }

  delete_insn (insn);
}
\f
/* Delete insn INSN from the chain of insns and update label ref counts.
   May delete some following insns as a consequence; may even delete
   a label elsewhere and insns that follow it.

   Returns the first insn after INSN that was not deleted.  */

rtx
delete_insn (insn)
     register rtx insn;
{
  register rtx next = NEXT_INSN (insn);
  register rtx prev = PREV_INSN (insn);
  register int was_code_label = (GET_CODE (insn) == CODE_LABEL);
  register int dont_really_delete = 0;

  while (next && INSN_DELETED_P (next))
    next = NEXT_INSN (next);

  /* This insn is already deleted => return first following nondeleted.  */
  if (INSN_DELETED_P (insn))
    return next;

  if (was_code_label)
    remove_node_from_expr_list (insn, &nonlocal_goto_handler_labels);

  /* Don't delete user-declared labels.  When optimizing, convert them
     to special NOTEs instead.  When not optimizing, leave them alone.  */
  if (was_code_label && LABEL_NAME (insn) != 0)
    {
      if (! optimize)
        dont_really_delete = 1;
      else if (! dont_really_delete)
        {
          const char *name = LABEL_NAME (insn);
          PUT_CODE (insn, NOTE);
          NOTE_LINE_NUMBER (insn) = NOTE_INSN_DELETED_LABEL;
          NOTE_SOURCE_FILE (insn) = name;
          dont_really_delete = 1;
        }
    }
  else
    /* Mark this insn as deleted.  */
    INSN_DELETED_P (insn) = 1;

  /* If this is an unconditional jump, delete it from the jump chain.  */
  if (simplejump_p (insn))
    delete_from_jump_chain (insn);

  /* If instruction is followed by a barrier,
     delete the barrier too.  */

  if (next != 0 && GET_CODE (next) == BARRIER)
    {
      INSN_DELETED_P (next) = 1;
      next = NEXT_INSN (next);
    }

  /* Patch out INSN (and the barrier if any) */

  if (! dont_really_delete)
    {
      if (prev)
        {
          NEXT_INSN (prev) = next;
          if (GET_CODE (prev) == INSN && GET_CODE (PATTERN (prev)) == SEQUENCE)
            NEXT_INSN (XVECEXP (PATTERN (prev), 0,
                                XVECLEN (PATTERN (prev), 0) - 1)) = next;
        }

      if (next)
        {
          PREV_INSN (next) = prev;
          if (GET_CODE (next) == INSN && GET_CODE (PATTERN (next)) == SEQUENCE)
            PREV_INSN (XVECEXP (PATTERN (next), 0, 0)) = prev;
        }

      if (prev && NEXT_INSN (prev) == 0)
        set_last_insn (prev);
    }

  /* If deleting a jump, decrement the count of the label,
     and delete the label if it is now unused.  */

  if (GET_CODE (insn) == JUMP_INSN && JUMP_LABEL (insn))
    {
      rtx lab = JUMP_LABEL (insn), lab_next;

      if (--LABEL_NUSES (lab) == 0)
        {
          /* This can delete NEXT or PREV,
             either directly if NEXT is JUMP_LABEL (INSN),
             or indirectly through more levels of jumps.  */
          delete_insn (lab);

          /* I feel a little doubtful about this loop,
             but I see no clean and sure alternative way
             to find the first insn after INSN that is not now deleted.
             I hope this works.  */
          while (next && INSN_DELETED_P (next))
            next = NEXT_INSN (next);
          return next;
        }
      else if ((lab_next = next_nonnote_insn (lab)) != NULL
               && GET_CODE (lab_next) == JUMP_INSN
               && (GET_CODE (PATTERN (lab_next)) == ADDR_VEC
                   || GET_CODE (PATTERN (lab_next)) == ADDR_DIFF_VEC))
        {
          /* If we're deleting the tablejump, delete the dispatch table.
             We may not be able to kill the label immediately preceeding
             just yet, as it might be referenced in code leading up to
             the tablejump.  */
          delete_insn (lab_next);
        }
    }

  /* Likewise if we're deleting a dispatch table.  */

  if (GET_CODE (insn) == JUMP_INSN
      && (GET_CODE (PATTERN (insn)) == ADDR_VEC
          || GET_CODE (PATTERN (insn)) == ADDR_DIFF_VEC))
    {
      rtx pat = PATTERN (insn);
      int i, diff_vec_p = GET_CODE (pat) == ADDR_DIFF_VEC;
      int len = XVECLEN (pat, diff_vec_p);

      for (i = 0; i < len; i++)
        if (--LABEL_NUSES (XEXP (XVECEXP (pat, diff_vec_p, i), 0)) == 0)
          delete_insn (XEXP (XVECEXP (pat, diff_vec_p, i), 0));
      while (next && INSN_DELETED_P (next))
        next = NEXT_INSN (next);
      return next;
    }

  while (prev && (INSN_DELETED_P (prev) || GET_CODE (prev) == NOTE))
    prev = PREV_INSN (prev);

  /* If INSN was a label and a dispatch table follows it,
     delete the dispatch table.  The tablejump must have gone already.
     It isn't useful to fall through into a table.  */

  if (was_code_label
      && NEXT_INSN (insn) != 0
      && GET_CODE (NEXT_INSN (insn)) == JUMP_INSN
      && (GET_CODE (PATTERN (NEXT_INSN (insn))) == ADDR_VEC
          || GET_CODE (PATTERN (NEXT_INSN (insn))) == ADDR_DIFF_VEC))
    next = delete_insn (NEXT_INSN (insn));

  /* If INSN was a label, delete insns following it if now unreachable.  */

  if (was_code_label && prev && GET_CODE (prev) == BARRIER)
    {
      register RTX_CODE code;
      while (next != 0
             && (GET_RTX_CLASS (code = GET_CODE (next)) == 'i'
                 || code == NOTE || code == BARRIER
                 || (code == CODE_LABEL && INSN_DELETED_P (next))))
        {
          if (code == NOTE
              && NOTE_LINE_NUMBER (next) != NOTE_INSN_FUNCTION_END)
            next = NEXT_INSN (next);
          /* Keep going past other deleted labels to delete what follows.  */
          else if (code == CODE_LABEL && INSN_DELETED_P (next))
            next = NEXT_INSN (next);
          else
            /* Note: if this deletes a jump, it can cause more
               deletion of unreachable code, after a different label.
               As long as the value from this recursive call is correct,
               this invocation functions correctly.  */
            next = delete_insn (next);
        }
    }

  return next;
}

/* Advance from INSN till reaching something not deleted
   then return that.  May return INSN itself.  */

rtx
next_nondeleted_insn (insn)
     rtx insn;
{
  while (INSN_DELETED_P (insn))
    insn = NEXT_INSN (insn);
  return insn;
}
\f
/* Delete a range of insns from FROM to TO, inclusive.
   This is for the sake of peephole optimization, so assume
   that whatever these insns do will still be done by a new
   peephole insn that will replace them.  */

void
delete_for_peephole (from, to)
     register rtx from, to;
{
  register rtx insn = from;

  while (1)
    {
      register rtx next = NEXT_INSN (insn);
      register rtx prev = PREV_INSN (insn);

      if (GET_CODE (insn) != NOTE)
        {
          INSN_DELETED_P (insn) = 1;

          /* Patch this insn out of the chain.  */
          /* We don't do this all at once, because we
             must preserve all NOTEs.  */
          if (prev)
            NEXT_INSN (prev) = next;

          if (next)
            PREV_INSN (next) = prev;
        }

      if (insn == to)
        break;
      insn = next;
    }

  /* Note that if TO is an unconditional jump
     we *do not* delete the BARRIER that follows,
     since the peephole that replaces this sequence
     is also an unconditional jump in that case.  */
}
\f
/* We have determined that INSN is never reached, and are about to
   delete it.  Print a warning if the user asked for one.

   To try to make this warning more useful, this should only be called
   once per basic block not reached, and it only warns when the basic
   block contains more than one line from the current function, and
   contains at least one operation.  CSE and inlining can duplicate insns,
   so it's possible to get spurious warnings from this.  */

void
never_reached_warning (avoided_insn)
     rtx avoided_insn;
{
  rtx insn;
  rtx a_line_note = NULL;
  int two_avoided_lines = 0;
  int contains_insn = 0;
  
  if (! warn_notreached)
    return;

  /* Scan forwards, looking at LINE_NUMBER notes, until
     we hit a LABEL or we run out of insns.  */
  
  for (insn = avoided_insn; insn != NULL; insn = NEXT_INSN (insn))
    {
       if (GET_CODE (insn) == CODE_LABEL)
         break;
       else if (GET_CODE (insn) == NOTE         /* A line number note? */ 
                && NOTE_LINE_NUMBER (insn) >= 0)
        {
          if (a_line_note == NULL)
            a_line_note = insn;
          else
            two_avoided_lines |= (NOTE_LINE_NUMBER (a_line_note)
                                  != NOTE_LINE_NUMBER (insn));
        }
       else if (GET_RTX_CLASS (GET_CODE (insn)) == 'i')
         contains_insn = 1;
    }
  if (two_avoided_lines && contains_insn)
    warning_with_file_and_line (NOTE_SOURCE_FILE (a_line_note),
                                NOTE_LINE_NUMBER (a_line_note),
                                "will never be executed");
}
\f
/* Throughout LOC, redirect OLABEL to NLABEL.  Treat null OLABEL or
   NLABEL as a return.  Accrue modifications into the change group.  */

static void
redirect_exp_1 (loc, olabel, nlabel, insn)
     rtx *loc;
     rtx olabel, nlabel;
     rtx insn;
{
  register rtx x = *loc;
  register RTX_CODE code = GET_CODE (x);
  register int i;
  register const char *fmt;

  if (code == LABEL_REF)
    {
      if (XEXP (x, 0) == olabel)
        {
          rtx n;
          if (nlabel)
            n = gen_rtx_LABEL_REF (VOIDmode, nlabel);
          else
            n = gen_rtx_RETURN (VOIDmode); 

          validate_change (insn, loc, n, 1);
          return;
        }
    }
  else if (code == RETURN && olabel == 0)
    {
      x = gen_rtx_LABEL_REF (VOIDmode, nlabel);
      if (loc == &PATTERN (insn))
        x = gen_rtx_SET (VOIDmode, pc_rtx, x);
      validate_change (insn, loc, x, 1);
      return;
    }

  if (code == SET && nlabel == 0 && SET_DEST (x) == pc_rtx
      && GET_CODE (SET_SRC (x)) == LABEL_REF
      && XEXP (SET_SRC (x), 0) == olabel)
    {
      validate_change (insn, loc, gen_rtx_RETURN (VOIDmode), 1);
      return;
    }

  fmt = GET_RTX_FORMAT (code);
  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
    {
      if (fmt[i] == 'e')
        redirect_exp_1 (&XEXP (x, i), olabel, nlabel, insn);
      else if (fmt[i] == 'E')
        {
          register int j;
          for (j = 0; j < XVECLEN (x, i); j++)
            redirect_exp_1 (&XVECEXP (x, i, j), olabel, nlabel, insn);
        }
    }
}

/* Similar, but apply the change group and report success or failure.  */

int
redirect_exp (loc, olabel, nlabel, insn)
     rtx *loc;
     rtx olabel, nlabel;
     rtx insn;
{
  redirect_exp_1 (loc, olabel, nlabel, insn);
  if (num_validated_changes () == 0)
    return 0;

  return apply_change_group ();
}

/* Make JUMP go to NLABEL instead of where it jumps now.  Accrue
   the modifications into the change group.  Return false if we did
   not see how to do that.  */

int
redirect_jump_1 (jump, nlabel)
     rtx jump, nlabel;
{
  int ochanges = num_validated_changes ();
  redirect_exp_1 (&PATTERN (jump), JUMP_LABEL (jump), nlabel, jump);
  return num_validated_changes () > ochanges;
}

/* Make JUMP go to NLABEL instead of where it jumps now.  If the old
   jump target label is unused as a result, it and the code following
   it may be deleted.

   If NLABEL is zero, we are to turn the jump into a (possibly conditional)
   RETURN insn.

   The return value will be 1 if the change was made, 0 if it wasn't
   (this can only occur for NLABEL == 0).  */

int
redirect_jump (jump, nlabel)
     rtx jump, nlabel;
{
  register rtx olabel = JUMP_LABEL (jump);

  if (nlabel == olabel)
    return 1;

  if (! redirect_exp (&PATTERN (jump), olabel, nlabel, jump))
    return 0;

  /* If this is an unconditional branch, delete it from the jump_chain of
     OLABEL and add it to the jump_chain of NLABEL (assuming both labels
     have UID's in range and JUMP_CHAIN is valid).  */
  if (jump_chain && (simplejump_p (jump)
                     || GET_CODE (PATTERN (jump)) == RETURN))
    {
      int label_index = nlabel ? INSN_UID (nlabel) : 0;

      delete_from_jump_chain (jump);
      if (label_index < max_jump_chain
          && INSN_UID (jump) < max_jump_chain)
        {
          jump_chain[INSN_UID (jump)] = jump_chain[label_index];
          jump_chain[label_index] = jump;
        }
    }

  JUMP_LABEL (jump) = nlabel;
  if (nlabel)
    ++LABEL_NUSES (nlabel);

  /* If we're eliding the jump over exception cleanups at the end of a
     function, move the function end note so that -Wreturn-type works.  */
  if (olabel && NEXT_INSN (olabel)
      && GET_CODE (NEXT_INSN (olabel)) == NOTE
      && NOTE_LINE_NUMBER (NEXT_INSN (olabel)) == NOTE_INSN_FUNCTION_END)
    emit_note_after (NOTE_INSN_FUNCTION_END, nlabel);

  if (olabel && --LABEL_NUSES (olabel) == 0)
    delete_insn (olabel);

  return 1;
}

/* Invert the jump condition of rtx X contained in jump insn, INSN.  
   Accrue the modifications into the change group.  */

static void
invert_exp_1 (x, insn)
     rtx x;
     rtx insn;
{
  register RTX_CODE code;
  register int i;
  register const char *fmt;

  code = GET_CODE (x);

  if (code == IF_THEN_ELSE)
    {
      register rtx comp = XEXP (x, 0);
      register rtx tem;

      /* We can do this in two ways:  The preferable way, which can only
         be done if this is not an integer comparison, is to reverse
         the comparison code.  Otherwise, swap the THEN-part and ELSE-part
         of the IF_THEN_ELSE.  If we can't do either, fail.  */

      if (can_reverse_comparison_p (comp, insn))
        {
          validate_change (insn, &XEXP (x, 0),
                           gen_rtx_fmt_ee (reverse_condition (GET_CODE (comp)),
                                           GET_MODE (comp), XEXP (comp, 0),
                                           XEXP (comp, 1)),
                           1);
          return;
        }
                                       
      tem = XEXP (x, 1);
      validate_change (insn, &XEXP (x, 1), XEXP (x, 2), 1);
      validate_change (insn, &XEXP (x, 2), tem, 1);
      return;
    }

  fmt = GET_RTX_FORMAT (code);
  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
    {
      if (fmt[i] == 'e')
        invert_exp_1 (XEXP (x, i), insn);
      else if (fmt[i] == 'E')
        {
          register int j;
          for (j = 0; j < XVECLEN (x, i); j++)
            invert_exp_1 (XVECEXP (x, i, j), insn);
        }
    }
}

/* Invert the jump condition of rtx X contained in jump insn, INSN. 

   Return 1 if we can do so, 0 if we cannot find a way to do so that
   matches a pattern.  */

int
invert_exp (x, insn)
     rtx x;
     rtx insn;
{
  invert_exp_1 (x, insn);
  if (num_validated_changes () == 0)
    return 0;

  return apply_change_group ();
}

/* Invert the condition of the jump JUMP, and make it jump to label
   NLABEL instead of where it jumps now.  Accrue changes into the
   change group.  Return false if we didn't see how to perform the
   inversion and redirection.  */

int
invert_jump_1 (jump, nlabel)
     rtx jump, nlabel;
{
  int ochanges;

  ochanges = num_validated_changes ();
  invert_exp_1 (PATTERN (jump), jump);
  if (num_validated_changes () == ochanges)
    return 0;

  return redirect_jump_1 (jump, nlabel);
}

/* Invert the condition of the jump JUMP, and make it jump to label
   NLABEL instead of where it jumps now.  Return true if successful.  */

int
invert_jump (jump, nlabel)
     rtx jump, nlabel;
{
  /* We have to either invert the condition and change the label or
     do neither.  Either operation could fail.  We first try to invert
     the jump. If that succeeds, we try changing the label.  If that fails,
     we invert the jump back to what it was.  */

  if (! invert_exp (PATTERN (jump), jump))
    return 0;

  if (redirect_jump (jump, nlabel))
    {
      /* An inverted jump means that a probability taken becomes a
         probability not taken.  Subtract the branch probability from the
         probability base to convert it back to a taken probability.  */

      rtx note = find_reg_note (jump, REG_BR_PROB, NULL_RTX);
      if (note)
        XEXP (note, 0) = GEN_INT (REG_BR_PROB_BASE - INTVAL (XEXP (note, 0)));

      return 1;
    }

  if (! invert_exp (PATTERN (jump), jump))
    /* This should just be putting it back the way it was.  */
    abort ();

  return 0;
}

/* Delete the instruction JUMP from any jump chain it might be on.  */

static void
delete_from_jump_chain (jump)
     rtx jump;
{
  int index;
  rtx olabel = JUMP_LABEL (jump);

  /* Handle unconditional jumps.  */
  if (jump_chain && olabel != 0
      && INSN_UID (olabel) < max_jump_chain
      && simplejump_p (jump))
    index = INSN_UID (olabel);
  /* Handle return insns.  */
  else if (jump_chain && GET_CODE (PATTERN (jump)) == RETURN)
    index = 0;
  else return;

  if (jump_chain[index] == jump)
    jump_chain[index] = jump_chain[INSN_UID (jump)];
  else
    {
      rtx insn;

      for (insn = jump_chain[index];
           insn != 0;
           insn = jump_chain[INSN_UID (insn)])
        if (jump_chain[INSN_UID (insn)] == jump)
          {
            jump_chain[INSN_UID (insn)] = jump_chain[INSN_UID (jump)];
            break;
          }
    }
}
\f
/* Make jump JUMP jump to label NLABEL, assuming it used to be a tablejump.

   If the old jump target label (before the dispatch table) becomes unused,
   it and the dispatch table may be deleted.  In that case, find the insn
   before the jump references that label and delete it and logical successors
   too.  */

static void
redirect_tablejump (jump, nlabel)
     rtx jump, nlabel;
{
  register rtx olabel = JUMP_LABEL (jump);

  /* Add this jump to the jump_chain of NLABEL.  */
  if (jump_chain && INSN_UID (nlabel) < max_jump_chain
      && INSN_UID (jump) < max_jump_chain)
    {
      jump_chain[INSN_UID (jump)] = jump_chain[INSN_UID (nlabel)];
      jump_chain[INSN_UID (nlabel)] = jump;
    }

  PATTERN (jump) = gen_jump (nlabel);
  JUMP_LABEL (jump) = nlabel;
  ++LABEL_NUSES (nlabel);
  INSN_CODE (jump) = -1;

  if (--LABEL_NUSES (olabel) == 0)
    {
      delete_labelref_insn (jump, olabel, 0);
      delete_insn (olabel);
    }
}

/* Find the insn referencing LABEL that is a logical predecessor of INSN.
   If we found one, delete it and then delete this insn if DELETE_THIS is
   non-zero.  Return non-zero if INSN or a predecessor references LABEL.  */

static int
delete_labelref_insn (insn, label, delete_this)
     rtx insn, label;
     int delete_this;
{
  int deleted = 0;
  rtx link;

  if (GET_CODE (insn) != NOTE
      && reg_mentioned_p (label, PATTERN (insn)))
    {
      if (delete_this)
        {
          delete_insn (insn);
          deleted = 1;
        }
      else
        return 1;
    }

  for (link = LOG_LINKS (insn); link; link = XEXP (link, 1))
    if (delete_labelref_insn (XEXP (link, 0), label, 1))
      {
        if (delete_this)
          {
            delete_insn (insn);
            deleted = 1;
          }
        else
          return 1;
      }

  return deleted;
}
\f
/* Like rtx_equal_p except that it considers two REGs as equal
   if they renumber to the same value and considers two commutative
   operations to be the same if the order of the operands has been
   reversed.

   ??? Addition is not commutative on the PA due to the weird implicit
   space register selection rules for memory addresses.  Therefore, we
   don't consider a + b == b + a.

   We could/should make this test a little tighter.  Possibly only
   disabling it on the PA via some backend macro or only disabling this
   case when the PLUS is inside a MEM.  */

int
rtx_renumbered_equal_p (x, y)
     rtx x, y;
{
  register int i;
  register RTX_CODE code = GET_CODE (x);
  register const char *fmt;
      
  if (x == y)
    return 1;

  if ((code == REG || (code == SUBREG && GET_CODE (SUBREG_REG (x)) == REG))
      && (GET_CODE (y) == REG || (GET_CODE (y) == SUBREG
                                  && GET_CODE (SUBREG_REG (y)) == REG)))
    {
      int reg_x = -1, reg_y = -1;
      int word_x = 0, word_y = 0;

      if (GET_MODE (x) != GET_MODE (y))
        return 0;

      /* If we haven't done any renumbering, don't
         make any assumptions.  */
      if (reg_renumber == 0)
        return rtx_equal_p (x, y);

      if (code == SUBREG)
        {
          reg_x = REGNO (SUBREG_REG (x));
          word_x = SUBREG_WORD (x);

          if (reg_renumber[reg_x] >= 0)
            {
              reg_x = reg_renumber[reg_x] + word_x;
              word_x = 0;
            }
        }

      else
        {
          reg_x = REGNO (x);
          if (reg_renumber[reg_x] >= 0)
            reg_x = reg_renumber[reg_x];
        }

      if (GET_CODE (y) == SUBREG)
        {
          reg_y = REGNO (SUBREG_REG (y));
          word_y = SUBREG_WORD (y);

          if (reg_renumber[reg_y] >= 0)
            {
              reg_y = reg_renumber[reg_y];
              word_y = 0;
            }
        }

      else
        {
          reg_y = REGNO (y);
          if (reg_renumber[reg_y] >= 0)
            reg_y = reg_renumber[reg_y];
        }

      return reg_x >= 0 && reg_x == reg_y && word_x == word_y;
    }

  /* Now we have disposed of all the cases 
     in which different rtx codes can match.  */
  if (code != GET_CODE (y))
    return 0;

  switch (code)
    {
    case PC:
    case CC0:
    case ADDR_VEC:
    case ADDR_DIFF_VEC:
      return 0;

    case CONST_INT:
      return INTVAL (x) == INTVAL (y);

    case LABEL_REF:
      /* We can't assume nonlocal labels have their following insns yet.  */
      if (LABEL_REF_NONLOCAL_P (x) || LABEL_REF_NONLOCAL_P (y))
        return XEXP (x, 0) == XEXP (y, 0);

      /* Two label-refs are equivalent if they point at labels
         in the same position in the instruction stream.  */
      return (next_real_insn (XEXP (x, 0))
              == next_real_insn (XEXP (y, 0)));

    case SYMBOL_REF:
      return XSTR (x, 0) == XSTR (y, 0);

    case CODE_LABEL:
      /* If we didn't match EQ equality above, they aren't the same.  */
      return 0;

    default:
      break;
    }

  /* (MULT:SI x y) and (MULT:HI x y) are NOT equivalent.  */

  if (GET_MODE (x) != GET_MODE (y))
    return 0;

  /* For commutative operations, the RTX match if the operand match in any
     order.  Also handle the simple binary and unary cases without a loop.

     ??? Don't consider PLUS a commutative operator; see comments above.  */
  if ((code == EQ || code == NE || GET_RTX_CLASS (code) == 'c')
      && code != PLUS)
    return ((rtx_renumbered_equal_p (XEXP (x, 0), XEXP (y, 0))
             && rtx_renumbered_equal_p (XEXP (x, 1), XEXP (y, 1)))
            || (rtx_renumbered_equal_p (XEXP (x, 0), XEXP (y, 1))
                && rtx_renumbered_equal_p (XEXP (x, 1), XEXP (y, 0))));
  else if (GET_RTX_CLASS (code) == '<' || GET_RTX_CLASS (code) == '2')
    return (rtx_renumbered_equal_p (XEXP (x, 0), XEXP (y, 0))
            && rtx_renumbered_equal_p (XEXP (x, 1), XEXP (y, 1)));
  else if (GET_RTX_CLASS (code) == '1')
    return rtx_renumbered_equal_p (XEXP (x, 0), XEXP (y, 0));

  /* Compare the elements.  If any pair of corresponding elements
     fail to match, return 0 for the whole things.  */

  fmt = GET_RTX_FORMAT (code);
  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
    {
      register int j;
      switch (fmt[i])
        {
        case 'w':
          if (XWINT (x, i) != XWINT (y, i))
            return 0;
          break;

        case 'i':
          if (XINT (x, i) != XINT (y, i))
            return 0;
          break;

        case 's':
          if (strcmp (XSTR (x, i), XSTR (y, i)))
            return 0;
          break;

        case 'e':
          if (! rtx_renumbered_equal_p (XEXP (x, i), XEXP (y, i)))
            return 0;
          break;

        case 'u':
          if (XEXP (x, i) != XEXP (y, i))
            return 0;
          /* fall through.  */
        case '0':
          break;

        case 'E':
          if (XVECLEN (x, i) != XVECLEN (y, i))
            return 0;
          for (j = XVECLEN (x, i) - 1; j >= 0; j--)
            if (!rtx_renumbered_equal_p (XVECEXP (x, i, j), XVECEXP (y, i, j)))
              return 0;
          break;

        default:
          abort ();
        }
    }
  return 1;
}
\f
/* If X is a hard register or equivalent to one or a subregister of one,
   return the hard register number.  If X is a pseudo register that was not
   assigned a hard register, return the pseudo register number.  Otherwise,
   return -1.  Any rtx is valid for X.  */

int
true_regnum (x)
     rtx x;
{
  if (GET_CODE (x) == REG)
    {
      if (REGNO (x) >= FIRST_PSEUDO_REGISTER && reg_renumber[REGNO (x)] >= 0)
        return reg_renumber[REGNO (x)];
      return REGNO (x);
    }
  if (GET_CODE (x) == SUBREG)
    {
      int base = true_regnum (SUBREG_REG (x));
      if (base >= 0 && base < FIRST_PSEUDO_REGISTER)
        return SUBREG_WORD (x) + base;
    }
  return -1;
}
\f
/* Optimize code of the form:

        for (x = a[i]; x; ...)
          ...
        for (x = a[i]; x; ...)
          ...
      foo:

   Loop optimize will change the above code into

        if (x = a[i])
          for (;;)
             { ...; if (! (x = ...)) break; }
        if (x = a[i])
          for (;;)
             { ...; if (! (x = ...)) break; }
      foo:

   In general, if the first test fails, the program can branch
   directly to `foo' and skip the second try which is doomed to fail.
   We run this after loop optimization and before flow analysis.  */
   
/* When comparing the insn patterns, we track the fact that different
   pseudo-register numbers may have been used in each computation.
   The following array stores an equivalence -- same_regs[I] == J means
   that pseudo register I was used in the first set of tests in a context
   where J was used in the second set.  We also count the number of such
   pending equivalences.  If nonzero, the expressions really aren't the
   same.  */

static int *same_regs;

static int num_same_regs;

/* Track any registers modified between the target of the first jump and
   the second jump.  They never compare equal.  */

static char *modified_regs;

/* Record if memory was modified.  */

static int modified_mem;

/* Called via note_stores on each insn between the target of the first 
   branch and the second branch.  It marks any changed registers.  */

static void
mark_modified_reg (dest, x, data)
     rtx dest;
     rtx x ATTRIBUTE_UNUSED;
     void *data ATTRIBUTE_UNUSED;
{
  int regno;
  unsigned int i;

  if (GET_CODE (dest) == SUBREG)
    dest = SUBREG_REG (dest);

  if (GET_CODE (dest) == MEM)
    modified_mem = 1;

  if (GET_CODE (dest) != REG)
    return;

  regno = REGNO (dest);
  if (regno >= FIRST_PSEUDO_REGISTER)
    modified_regs[regno] = 1;
  else
    for (i = 0; i < HARD_REGNO_NREGS (regno, GET_MODE (dest)); i++)
      modified_regs[regno + i] = 1;
}

/* F is the first insn in the chain of insns.  */
   
void
thread_jumps (f, max_reg, flag_before_loop)
     rtx f;
     int max_reg;
     int flag_before_loop;
{
  /* Basic algorithm is to find a conditional branch,
     the label it may branch to, and the branch after
     that label.  If the two branches test the same condition,
     walk back from both branch paths until the insn patterns
     differ, or code labels are hit.  If we make it back to
     the target of the first branch, then we know that the first branch
     will either always succeed or always fail depending on the relative
     senses of the two branches.  So adjust the first branch accordingly
     in this case.  */
     
  rtx label, b1, b2, t1, t2;
  enum rtx_code code1, code2;
  rtx b1op0, b1op1, b2op0, b2op1;
  int changed = 1;
  int i;
  int *all_reset;

  /* Allocate register tables and quick-reset table.  */
  modified_regs = (char *) xmalloc (max_reg * sizeof (char));
  same_regs = (int *) xmalloc (max_reg * sizeof (int));
  all_reset = (int *) xmalloc (max_reg * sizeof (int));
  for (i = 0; i < max_reg; i++)
    all_reset[i] = -1;
    
  while (changed)
    {
      changed = 0;

      for (b1 = f; b1; b1 = NEXT_INSN (b1))
        {
          /* Get to a candidate branch insn.  */
          if (GET_CODE (b1) != JUMP_INSN
              || ! condjump_p (b1) || simplejump_p (b1)
              || JUMP_LABEL (b1) == 0)
            continue;

          bzero (modified_regs, max_reg * sizeof (char));
          modified_mem = 0;

          bcopy ((char *) all_reset, (char *) same_regs,
                 max_reg * sizeof (int));
          num_same_regs = 0;

          label = JUMP_LABEL (b1);

          /* Look for a branch after the target.  Record any registers and
             memory modified between the target and the branch.  Stop when we
             get to a label since we can't know what was changed there.  */
          for (b2 = NEXT_INSN (label); b2; b2 = NEXT_INSN (b2))
            {
              if (GET_CODE (b2) == CODE_LABEL)
                break;

              else if (GET_CODE (b2) == JUMP_INSN)
                {
                  /* If this is an unconditional jump and is the only use of
                     its target label, we can follow it.  */
                  if (simplejump_p (b2)
                      && JUMP_LABEL (b2) != 0
                      && LABEL_NUSES (JUMP_LABEL (b2)) == 1)
                    {
                      b2 = JUMP_LABEL (b2);
                      continue;
                    }
                  else
                    break;
                }

              if (GET_CODE (b2) != CALL_INSN && GET_CODE (b2) != INSN)
                continue;

              if (GET_CODE (b2) == CALL_INSN)
                {
                  modified_mem = 1;
                  for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
                    if (call_used_regs[i] && ! fixed_regs[i]
                        && i != STACK_POINTER_REGNUM
                        && i != FRAME_POINTER_REGNUM
                        && i != HARD_FRAME_POINTER_REGNUM
                        && i != ARG_POINTER_REGNUM)
                      modified_regs[i] = 1;
                }

              note_stores (PATTERN (b2), mark_modified_reg, NULL);
            }

          /* Check the next candidate branch insn from the label
             of the first.  */
          if (b2 == 0
              || GET_CODE (b2) != JUMP_INSN
              || b2 == b1
              || ! condjump_p (b2)
              || simplejump_p (b2))
            continue;

          /* Get the comparison codes and operands, reversing the
             codes if appropriate.  If we don't have comparison codes,
             we can't do anything.  */
          b1op0 = XEXP (XEXP (SET_SRC (PATTERN (b1)), 0), 0);
          b1op1 = XEXP (XEXP (SET_SRC (PATTERN (b1)), 0), 1);
          code1 = GET_CODE (XEXP (SET_SRC (PATTERN (b1)), 0));
          if (XEXP (SET_SRC (PATTERN (b1)), 1) == pc_rtx)
            code1 = reverse_condition (code1);

          b2op0 = XEXP (XEXP (SET_SRC (PATTERN (b2)), 0), 0);
          b2op1 = XEXP (XEXP (SET_SRC (PATTERN (b2)), 0), 1);
          code2 = GET_CODE (XEXP (SET_SRC (PATTERN (b2)), 0));
          if (XEXP (SET_SRC (PATTERN (b2)), 1) == pc_rtx)
            code2 = reverse_condition (code2);

          /* If they test the same things and knowing that B1 branches
             tells us whether or not B2 branches, check if we
             can thread the branch.  */
          if (rtx_equal_for_thread_p (b1op0, b2op0, b2)
              && rtx_equal_for_thread_p (b1op1, b2op1, b2)
              && (comparison_dominates_p (code1, code2)
                  || (can_reverse_comparison_p (XEXP (SET_SRC (PATTERN (b1)),
                                                      0),
                                                b1)
                      && comparison_dominates_p (code1, reverse_condition (code2)))))

            {
              t1 = prev_nonnote_insn (b1);
              t2 = prev_nonnote_insn (b2);
              
              while (t1 != 0 && t2 != 0)
                {
                  if (t2 == label)
                    {
                      /* We have reached the target of the first branch.
                         If there are no pending register equivalents,
                         we know that this branch will either always
                         succeed (if the senses of the two branches are
                         the same) or always fail (if not).  */
                      rtx new_label;

                      if (num_same_regs != 0)
                        break;

                      if (comparison_dominates_p (code1, code2))
                        new_label = JUMP_LABEL (b2);
                      else
                        new_label = get_label_after (b2);

                      if (JUMP_LABEL (b1) != new_label)
                        {
                          rtx prev = PREV_INSN (new_label);

                          if (flag_before_loop
                              && GET_CODE (prev) == NOTE
                              && NOTE_LINE_NUMBER (prev) == NOTE_INSN_LOOP_BEG)
                            {
                              /* Don't thread to the loop label.  If a loop
                                 label is reused, loop optimization will
                                 be disabled for that loop.  */
                              new_label = gen_label_rtx ();
                              emit_label_after (new_label, PREV_INSN (prev));
                            }
                          changed |= redirect_jump (b1, new_label);
                        }
                      break;
                    }
                    
                  /* If either of these is not a normal insn (it might be
                     a JUMP_INSN, CALL_INSN, or CODE_LABEL) we fail.  (NOTEs
                     have already been skipped above.)  Similarly, fail
                     if the insns are different.  */
                  if (GET_CODE (t1) != INSN || GET_CODE (t2) != INSN
                      || recog_memoized (t1) != recog_memoized (t2)
                      || ! rtx_equal_for_thread_p (PATTERN (t1),
                                                   PATTERN (t2), t2))
                    break;
                    
                  t1 = prev_nonnote_insn (t1);
                  t2 = prev_nonnote_insn (t2);
                }
            }
        }
    }

  /* Clean up.  */
  free (modified_regs);
  free (same_regs);
  free (all_reset);
}
\f
/* This is like RTX_EQUAL_P except that it knows about our handling of
   possibly equivalent registers and knows to consider volatile and
   modified objects as not equal.
   
   YINSN is the insn containing Y.  */

int
rtx_equal_for_thread_p (x, y, yinsn)
     rtx x, y;
     rtx yinsn;
{
  register int i;
  register int j;
  register enum rtx_code code;
  register const char *fmt;

  code = GET_CODE (x);
  /* Rtx's of different codes cannot be equal.  */
  if (code != GET_CODE (y))
    return 0;

  /* (MULT:SI x y) and (MULT:HI x y) are NOT equivalent.
     (REG:SI x) and (REG:HI x) are NOT equivalent.  */

  if (GET_MODE (x) != GET_MODE (y))
    return 0;

  /* For floating-point, consider everything unequal.  This is a bit
     pessimistic, but this pass would only rarely do anything for FP
     anyway.  */
  if (TARGET_FLOAT_FORMAT == IEEE_FLOAT_FORMAT
      && FLOAT_MODE_P (GET_MODE (x)) && ! flag_fast_math)
    return 0;

  /* For commutative operations, the RTX match if the operand match in any
     order.  Also handle the simple binary and unary cases without a loop.  */
  if (code == EQ || code == NE || GET_RTX_CLASS (code) == 'c')
    return ((rtx_equal_for_thread_p (XEXP (x, 0), XEXP (y, 0), yinsn)
             && rtx_equal_for_thread_p (XEXP (x, 1), XEXP (y, 1), yinsn))
            || (rtx_equal_for_thread_p (XEXP (x, 0), XEXP (y, 1), yinsn)
                && rtx_equal_for_thread_p (XEXP (x, 1), XEXP (y, 0), yinsn)));
  else if (GET_RTX_CLASS (code) == '<' || GET_RTX_CLASS (code) == '2')
    return (rtx_equal_for_thread_p (XEXP (x, 0), XEXP (y, 0), yinsn)
            && rtx_equal_for_thread_p (XEXP (x, 1), XEXP (y, 1), yinsn));
  else if (GET_RTX_CLASS (code) == '1')
    return rtx_equal_for_thread_p (XEXP (x, 0), XEXP (y, 0), yinsn);

  /* Handle special-cases first.  */
  switch (code)
    {
    case REG:
      if (REGNO (x) == REGNO (y) && ! modified_regs[REGNO (x)])
        return 1;

      /* If neither is user variable or hard register, check for possible
         equivalence.  */
      if (REG_USERVAR_P (x) || REG_USERVAR_P (y)
          || REGNO (x) < FIRST_PSEUDO_REGISTER
          || REGNO (y) < FIRST_PSEUDO_REGISTER)
        return 0;

      if (same_regs[REGNO (x)] == -1)
        {
          same_regs[REGNO (x)] = REGNO (y);
          num_same_regs++;

          /* If this is the first time we are seeing a register on the `Y'
             side, see if it is the last use.  If not, we can't thread the 
             jump, so mark it as not equivalent.  */
          if (REGNO_LAST_UID (REGNO (y)) != INSN_UID (yinsn))
            return 0;

          return 1;
        }
      else
        return (same_regs[REGNO (x)] == (int) REGNO (y));

      break;

    case MEM:
      /* If memory modified or either volatile, not equivalent.
         Else, check address.  */
      if (modified_mem || MEM_VOLATILE_P (x) || MEM_VOLATILE_P (y))
        return 0;

      return rtx_equal_for_thread_p (XEXP (x, 0), XEXP (y, 0), yinsn);

    case ASM_INPUT:
      if (MEM_VOLATILE_P (x) || MEM_VOLATILE_P (y))
        return 0;

      break;

    case SET:
      /* Cancel a pending `same_regs' if setting equivalenced registers.
         Then process source.  */
      if (GET_CODE (SET_DEST (x)) == REG
          && GET_CODE (SET_DEST (y)) == REG)
        {
          if (same_regs[REGNO (SET_DEST (x))] == (int) REGNO (SET_DEST (y)))
            {
              same_regs[REGNO (SET_DEST (x))] = -1;
              num_same_regs--;
            }
          else if (REGNO (SET_DEST (x)) != REGNO (SET_DEST (y)))
            return 0;
        }
      else
        if (rtx_equal_for_thread_p (SET_DEST (x), SET_DEST (y), yinsn) == 0)
          return 0;

      return rtx_equal_for_thread_p (SET_SRC (x), SET_SRC (y), yinsn);

    case LABEL_REF:
      return XEXP (x, 0) == XEXP (y, 0);

    case SYMBOL_REF:
      return XSTR (x, 0) == XSTR (y, 0);
      
    default:
      break;
    }

  if (x == y)
    return 1;

  fmt = GET_RTX_FORMAT (code);
  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
    {
      switch (fmt[i])
        {
        case 'w':
          if (XWINT (x, i) != XWINT (y, i))
            return 0;
          break;

        case 'n':
        case 'i':
          if (XINT (x, i) != XINT (y, i))
            return 0;
          break;

        case 'V':
        case 'E':
          /* Two vectors must have the same length.  */
          if (XVECLEN (x, i) != XVECLEN (y, i))
            return 0;

          /* And the corresponding elements must match.  */
          for (j = 0; j < XVECLEN (x, i); j++)
            if (rtx_equal_for_thread_p (XVECEXP (x, i, j),
                                        XVECEXP (y, i, j), yinsn) == 0)
              return 0;
          break;

        case 'e':
          if (rtx_equal_for_thread_p (XEXP (x, i), XEXP (y, i), yinsn) == 0)
            return 0;
          break;

        case 'S':
        case 's':
          if (strcmp (XSTR (x, i), XSTR (y, i)))
            return 0;
          break;

        case 'u':
          /* These are just backpointers, so they don't matter.  */
          break;

        case '0':
        case 't':
          break;

          /* It is believed that rtx's at this level will never
             contain anything but integers and other rtx's,
             except for within LABEL_REFs and SYMBOL_REFs.  */
        default:
          abort ();
        }
    }
  return 1;
}