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[gcc.git] / gcc / flow.c

/* Data flow analysis for GNU compiler.
   Copyright (C) 1987, 1988, 1992 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, 675 Mass Ave, Cambridge, MA 02139, USA.  */


/* This file contains the data flow analysis pass of the compiler.
   It computes data flow information
   which tells combine_instructions which insns to consider combining
   and controls register allocation.

   Additional data flow information that is too bulky to record
   is generated during the analysis, and is used at that time to
   create autoincrement and autodecrement addressing.

   The first step is dividing the function into basic blocks.
   find_basic_blocks does this.  Then life_analysis determines
   where each register is live and where it is dead.

   ** find_basic_blocks **

   find_basic_blocks divides the current function's rtl
   into basic blocks.  It records the beginnings and ends of the
   basic blocks in the vectors basic_block_head and basic_block_end,
   and the number of blocks in n_basic_blocks.

   find_basic_blocks also finds any unreachable loops
   and deletes them.

   ** life_analysis **

   life_analysis is called immediately after find_basic_blocks.
   It uses the basic block information to determine where each
   hard or pseudo register is live.

   ** live-register info **

   The information about where each register is live is in two parts:
   the REG_NOTES of insns, and the vector basic_block_live_at_start.

   basic_block_live_at_start has an element for each basic block,
   and the element is a bit-vector with a bit for each hard or pseudo
   register.  The bit is 1 if the register is live at the beginning
   of the basic block.

   Two types of elements can be added to an insn's REG_NOTES.  
   A REG_DEAD note is added to an insn's REG_NOTES for any register
   that meets both of two conditions:  The value in the register is not
   needed in subsequent insns and the insn does not replace the value in
   the register (in the case of multi-word hard registers, the value in
   each register must be replaced by the insn to avoid a REG_DEAD note).

   In the vast majority of cases, an object in a REG_DEAD note will be
   used somewhere in the insn.  The (rare) exception to this is if an
   insn uses a multi-word hard register and only some of the registers are
   needed in subsequent insns.  In that case, REG_DEAD notes will be
   provided for those hard registers that are not subsequently needed.
   Partial REG_DEAD notes of this type do not occur when an insn sets
   only some of the hard registers used in such a multi-word operand;
   omitting REG_DEAD notes for objects stored in an insn is optional and
   the desire to do so does not justify the complexity of the partial
   REG_DEAD notes.

   REG_UNUSED notes are added for each register that is set by the insn
   but is unused subsequently (if every register set by the insn is unused
   and the insn does not reference memory or have some other side-effect,
   the insn is deleted instead).  If only part of a multi-word hard
   register is used in a subsequent insn, REG_UNUSED notes are made for
   the parts that will not be used.

   To determine which registers are live after any insn, one can
   start from the beginning of the basic block and scan insns, noting
   which registers are set by each insn and which die there.

   ** Other actions of life_analysis **

   life_analysis sets up the LOG_LINKS fields of insns because the
   information needed to do so is readily available.

   life_analysis deletes insns whose only effect is to store a value
   that is never used.

   life_analysis notices cases where a reference to a register as
   a memory address can be combined with a preceding or following
   incrementation or decrementation of the register.  The separate
   instruction to increment or decrement is deleted and the address
   is changed to a POST_INC or similar rtx.

   Each time an incrementing or decrementing address is created,
   a REG_INC element is added to the insn's REG_NOTES list.

   life_analysis fills in certain vectors containing information about
   register usage: reg_n_refs, reg_n_deaths, reg_n_sets, reg_live_length,
   reg_n_calls_crosses and reg_basic_block.  */
\f
#include <stdio.h>
#include "config.h"
#include "rtl.h"
#include "basic-block.h"
#include "insn-config.h"
#include "regs.h"
#include "hard-reg-set.h"
#include "flags.h"
#include "output.h"

#include "obstack.h"
#define obstack_chunk_alloc xmalloc
#define obstack_chunk_free free

extern int xmalloc ();
extern void free ();

/* List of labels that must never be deleted.  */
extern rtx forced_labels;

/* Get the basic block number of an insn.
   This info should not be expected to remain available
   after the end of life_analysis.  */

/* This is the limit of the allocated space in the following two arrays.  */

static int max_uid_for_flow;

#define BLOCK_NUM(INSN)  uid_block_number[INSN_UID (INSN)]

/* This is where the BLOCK_NUM values are really stored.
   This is set up by find_basic_blocks and used there and in life_analysis,
   and then freed.  */

static short *uid_block_number;

/* INSN_VOLATILE (insn) is 1 if the insn refers to anything volatile.  */

#define INSN_VOLATILE(INSN) uid_volatile[INSN_UID (INSN)]
static char *uid_volatile;

/* Number of basic blocks in the current function.  */

int n_basic_blocks;

/* Maximum register number used in this function, plus one.  */

int max_regno;

/* Maximum number of SCRATCH rtx's used in any basic block of this function. */

int max_scratch;

/* Number of SCRATCH rtx's in the current block.  */

static int num_scratch;

/* Indexed by n, gives number of basic block that  (REG n) is used in.
   If the value is REG_BLOCK_GLOBAL (-2),
   it means (REG n) is used in more than one basic block.
   REG_BLOCK_UNKNOWN (-1) means it hasn't been seen yet so we don't know.
   This information remains valid for the rest of the compilation
   of the current function; it is used to control register allocation.  */

short *reg_basic_block;

/* Indexed by n, gives number of times (REG n) is used or set, each
   weighted by its loop-depth.
   This information remains valid for the rest of the compilation
   of the current function; it is used to control register allocation.  */

int *reg_n_refs;

/* Indexed by N, gives number of places register N dies.
   This information remains valid for the rest of the compilation
   of the current function; it is used to control register allocation.  */

short *reg_n_deaths;

/* Indexed by N, gives 1 if that reg is live across any CALL_INSNs.
   This information remains valid for the rest of the compilation
   of the current function; it is used to control register allocation.  */

int *reg_n_calls_crossed;

/* Total number of instructions at which (REG n) is live.
   The larger this is, the less priority (REG n) gets for
   allocation in a real register.
   This information remains valid for the rest of the compilation
   of the current function; it is used to control register allocation.

   local-alloc.c may alter this number to change the priority.

   Negative values are special.
   -1 is used to mark a pseudo reg which has a constant or memory equivalent
   and is used infrequently enough that it should not get a hard register.
   -2 is used to mark a pseudo reg for a parameter, when a frame pointer
   is not required.  global-alloc.c makes an allocno for this but does
   not try to assign a hard register to it.  */

int *reg_live_length;

/* Element N is the next insn that uses (hard or pseudo) register number N
   within the current basic block; or zero, if there is no such insn.
   This is valid only during the final backward scan in propagate_block.  */

static rtx *reg_next_use;

/* Size of a regset for the current function,
   in (1) bytes and (2) elements.  */

int regset_bytes;
int regset_size;

/* Element N is first insn in basic block N.
   This info lasts until we finish compiling the function.  */

rtx *basic_block_head;

/* Element N is last insn in basic block N.
   This info lasts until we finish compiling the function.  */

rtx *basic_block_end;

/* Element N is a regset describing the registers live
   at the start of basic block N.
   This info lasts until we finish compiling the function.  */

regset *basic_block_live_at_start;

/* Regset of regs live when calls to `setjmp'-like functions happen.  */

regset regs_live_at_setjmp;

/* List made of EXPR_LIST rtx's which gives pairs of pseudo registers
   that have to go in the same hard reg.
   The first two regs in the list are a pair, and the next two
   are another pair, etc.  */
rtx regs_may_share;

/* Element N is nonzero if control can drop into basic block N
   from the preceding basic block.  Freed after life_analysis.  */

static char *basic_block_drops_in;

/* Element N is depth within loops of the last insn in basic block number N.
   Freed after life_analysis.  */

static short *basic_block_loop_depth;

/* Element N nonzero if basic block N can actually be reached.
   Vector exists only during find_basic_blocks.  */

static char *block_live_static;

/* Depth within loops of basic block being scanned for lifetime analysis,
   plus one.  This is the weight attached to references to registers.  */

static int loop_depth;

/* During propagate_block, this is non-zero if the value of CC0 is live.  */

static int cc0_live;

/* During propagate_block, this contains the last MEM stored into.  It
   is used to eliminate consecutive stores to the same location.  */

static rtx last_mem_set;

/* Set of registers that may be eliminable.  These are handled specially
   in updating regs_ever_live.  */

static HARD_REG_SET elim_reg_set;

/* Forward declarations */
static void find_basic_blocks ();
static void life_analysis ();
static void mark_label_ref ();
void allocate_for_life_analysis (); /* Used also in stupid_life_analysis */
static void init_regset_vector ();
static void propagate_block ();
static void mark_set_regs ();
static void mark_used_regs ();
static int insn_dead_p ();
static int libcall_dead_p ();
static int try_pre_increment ();
static int try_pre_increment_1 ();
static rtx find_use_as_address ();
void dump_flow_info ();
\f
/* Find basic blocks of the current function and perform data flow analysis.
   F is the first insn of the function and NREGS the number of register numbers
   in use.  */

void
flow_analysis (f, nregs, file)
     rtx f;
     int nregs;
     FILE *file;
{
  register rtx insn;
  register int i;
  rtx nonlocal_label_list = nonlocal_label_rtx_list ();

#ifdef ELIMINABLE_REGS
  static struct {int from, to; } eliminables[] = ELIMINABLE_REGS;
#endif

  /* Record which registers will be eliminated.  We use this in
     mark_used_regs. */

  CLEAR_HARD_REG_SET (elim_reg_set);

#ifdef ELIMINABLE_REGS
  for (i = 0; i < sizeof eliminables / sizeof eliminables[0]; i++)
    SET_HARD_REG_BIT (elim_reg_set, eliminables[i].from);
#else
  SET_HARD_REG_BIT (elim_reg_set, FRAME_POINTER_REGNUM);
#endif

  /* Count the basic blocks.  Also find maximum insn uid value used.  */

  {
    register RTX_CODE prev_code = JUMP_INSN;
    register RTX_CODE code;

    max_uid_for_flow = 0;

    for (insn = f, i = 0; insn; insn = NEXT_INSN (insn))
      {
        code = GET_CODE (insn);
        if (INSN_UID (insn) > max_uid_for_flow)
          max_uid_for_flow = INSN_UID (insn);
        if (code == CODE_LABEL
            || (GET_RTX_CLASS (code) == 'i'
                && (prev_code == JUMP_INSN
                    || (prev_code == CALL_INSN
                        && nonlocal_label_list != 0)
                    || prev_code == BARRIER)))
          i++;
        if (code != NOTE)
          prev_code = code;
      }
  }

#ifdef AUTO_INC_DEC
  /* Leave space for insns we make in some cases for auto-inc.  These cases
     are rare, so we don't need too much space.  */
  max_uid_for_flow += max_uid_for_flow / 10;
#endif

  /* Allocate some tables that last till end of compiling this function
     and some needed only in find_basic_blocks and life_analysis.  */

  n_basic_blocks = i;
  basic_block_head = (rtx *) oballoc (n_basic_blocks * sizeof (rtx));
  basic_block_end = (rtx *) oballoc (n_basic_blocks * sizeof (rtx));
  basic_block_drops_in = (char *) alloca (n_basic_blocks);
  basic_block_loop_depth = (short *) alloca (n_basic_blocks * sizeof (short));
  uid_block_number
    = (short *) alloca ((max_uid_for_flow + 1) * sizeof (short));
  uid_volatile = (char *) alloca (max_uid_for_flow + 1);
  bzero (uid_volatile, max_uid_for_flow + 1);

  find_basic_blocks (f, nonlocal_label_list);
  life_analysis (f, nregs);
  if (file)
    dump_flow_info (file);

  basic_block_drops_in = 0;
  uid_block_number = 0;
  basic_block_loop_depth = 0;
}
\f
/* Find all basic blocks of the function whose first insn is F.
   Store the correct data in the tables that describe the basic blocks,
   set up the chains of references for each CODE_LABEL, and
   delete any entire basic blocks that cannot be reached.

   NONLOCAL_LABEL_LIST is the same local variable from flow_analysis.  */

static void
find_basic_blocks (f, nonlocal_label_list)
     rtx f, nonlocal_label_list;
{
  register rtx insn;
  register int i;
  register char *block_live = (char *) alloca (n_basic_blocks);
  register char *block_marked = (char *) alloca (n_basic_blocks);
  /* List of label_refs to all labels whose addresses are taken
     and used as data.  */
  rtx label_value_list = 0;

  block_live_static = block_live;
  bzero (block_live, n_basic_blocks);
  bzero (block_marked, n_basic_blocks);

  /* Initialize with just block 0 reachable and no blocks marked.  */
  if (n_basic_blocks > 0)
    block_live[0] = 1;

  /* Initialize the ref chain of each label to 0.  */
  /* Record where all the blocks start and end and their depth in loops.  */
  /* For each insn, record the block it is in.  */
  /* Also mark as reachable any blocks headed by labels that
     must not be deleted.  */

  {
    register RTX_CODE prev_code = JUMP_INSN;
    register RTX_CODE code;
    int depth = 1;

    for (insn = f, i = -1; insn; insn = NEXT_INSN (insn))
      {
        code = GET_CODE (insn);
        if (code == NOTE)
          {
            if (NOTE_LINE_NUMBER (insn) == NOTE_INSN_LOOP_BEG)
              depth++;
            else if (NOTE_LINE_NUMBER (insn) == NOTE_INSN_LOOP_END)
              depth--;
          }
        /* A basic block starts at label, or after something that can jump.  */
        else if (code == CODE_LABEL
                 || (GET_RTX_CLASS (code) == 'i'
                     && (prev_code == JUMP_INSN
                         || (prev_code == CALL_INSN
                             && nonlocal_label_list != 0)
                         || prev_code == BARRIER)))
          {
            basic_block_head[++i] = insn;
            basic_block_end[i] = insn;
            basic_block_loop_depth[i] = depth;
            if (code == CODE_LABEL)
              {
                LABEL_REFS (insn) = insn;
                /* Any label that cannot be deleted
                   is considered to start a reachable block.  */
                if (LABEL_PRESERVE_P (insn))
                  block_live[i] = 1;
              }
          }
        else if (GET_RTX_CLASS (code) == 'i')
          {
            basic_block_end[i] = insn;
            basic_block_loop_depth[i] = depth;
          }

        /* Make a list of all labels referred to other than by jumps.  */
        if (code == INSN || code == CALL_INSN)
          {
            rtx note = find_reg_note (insn, REG_LABEL, 0);
            if (note != 0)
              label_value_list = gen_rtx (EXPR_LIST, VOIDmode, XEXP (note, 0),
                                          label_value_list);
          }

        BLOCK_NUM (insn) = i;

        /* Don't separare a CALL_INSN from following CLOBBER insns.  This is
           a kludge that will go away when each CALL_INSN records its
           USE and CLOBBERs.  */

        if (code != NOTE
            && ! (prev_code == CALL_INSN && code == INSN
                  && GET_CODE (PATTERN (insn)) == CLOBBER))
          prev_code = code;
      }
    if (i + 1 != n_basic_blocks)
      abort ();
  }

  /* Don't delete the labels that are referenced by non-jump instructions.  */
  {
    register rtx x;
    for (x = label_value_list; x; x = XEXP (x, 1))
      block_live[BLOCK_NUM (XEXP (x, 0))] = 1;
  }

  /* Record which basic blocks control can drop in to.  */

  {
    register int i;
    for (i = 0; i < n_basic_blocks; i++)
      {
        register rtx insn = PREV_INSN (basic_block_head[i]);
        /* TEMP1 is used to avoid a bug in Sequent's compiler.  */
        register int temp1;
        while (insn && GET_CODE (insn) == NOTE)
          insn = PREV_INSN (insn);
        temp1 = insn && GET_CODE (insn) != BARRIER;
        basic_block_drops_in[i] = temp1;
      }
  }

  /* Now find which basic blocks can actually be reached
     and put all jump insns' LABEL_REFS onto the ref-chains
     of their target labels.  */

  if (n_basic_blocks > 0)
    {
      int something_marked = 1;

      /* Find all indirect jump insns and mark them as possibly jumping
         to all the labels whose addresses are explicitly used.
         This is because, when there are computed gotos,
         we can't tell which labels they jump to, of all the possibilities.  */

      for (insn = f; insn; insn = NEXT_INSN (insn))
        if (GET_CODE (insn) == JUMP_INSN
            && GET_CODE (PATTERN (insn)) == SET
            && SET_DEST (PATTERN (insn)) == pc_rtx
            && GET_CODE (SET_SRC (PATTERN (insn))) == REG)
          {
            rtx x;
            for (x = label_value_list; x; x = XEXP (x, 1))
              mark_label_ref (gen_rtx (LABEL_REF, VOIDmode, XEXP (x, 0)),
                              insn, 0);
            for (x = forced_labels; x; x = XEXP (x, 1))
              mark_label_ref (gen_rtx (LABEL_REF, VOIDmode, XEXP (x, 0)),
                              insn, 0);
          }

      /* Find all call insns and mark them as possibly jumping
         to all the nonlocal goto handler labels.  */

      for (insn = f; insn; insn = NEXT_INSN (insn))
        if (GET_CODE (insn) == CALL_INSN)
          {
            rtx x;
            for (x = nonlocal_label_list; x; x = XEXP (x, 1))
              mark_label_ref (gen_rtx (LABEL_REF, VOIDmode, XEXP (x, 0)),
                              insn, 0);
            /* ??? This could be made smarter:
               in some cases it's possible to tell that certain
               calls will not do a nonlocal goto.

               For example, if the nested functions that do the
               nonlocal gotos do not have their addresses taken, then
               only calls to those functions or to other nested
               functions that use them could possibly do nonlocal
               gotos.  */
          }

      /* Pass over all blocks, marking each block that is reachable
         and has not yet been marked.
         Keep doing this until, in one pass, no blocks have been marked.
         Then blocks_live and blocks_marked are identical and correct.
         In addition, all jumps actually reachable have been marked.  */

      while (something_marked)
        {
          something_marked = 0;
          for (i = 0; i < n_basic_blocks; i++)
            if (block_live[i] && !block_marked[i])
              {
                block_marked[i] = 1;
                something_marked = 1;
                if (i + 1 < n_basic_blocks && basic_block_drops_in[i + 1])
                  block_live[i + 1] = 1;
                insn = basic_block_end[i];
                if (GET_CODE (insn) == JUMP_INSN)
                  mark_label_ref (PATTERN (insn), insn, 0);
              }
        }

      /* Now delete the code for any basic blocks that can't be reached.
         They can occur because jump_optimize does not recognize
         unreachable loops as unreachable.  */

      for (i = 0; i < n_basic_blocks; i++)
        if (!block_live[i])
          {
            insn = basic_block_head[i];
            while (1)
              {
                if (GET_CODE (insn) == BARRIER)
                  abort ();
                if (GET_CODE (insn) != NOTE)
                  {
                    PUT_CODE (insn, NOTE);
                    NOTE_LINE_NUMBER (insn) = NOTE_INSN_DELETED;
                    NOTE_SOURCE_FILE (insn) = 0;
                  }
                if (insn == basic_block_end[i])
                  {
                    /* BARRIERs are between basic blocks, not part of one.
                       Delete a BARRIER if the preceding jump is deleted.
                       We cannot alter a BARRIER into a NOTE
                       because it is too short; but we can really delete
                       it because it is not part of a basic block.  */
                    if (NEXT_INSN (insn) != 0
                        && GET_CODE (NEXT_INSN (insn)) == BARRIER)
                      delete_insn (NEXT_INSN (insn));
                    break;
                  }
                insn = NEXT_INSN (insn);
              }
            /* Each time we delete some basic blocks,
               see if there is a jump around them that is
               being turned into a no-op.  If so, delete it.  */

            if (block_live[i - 1])
              {
                register int j;
                for (j = i; j < n_basic_blocks; j++)
                  if (block_live[j])
                    {
                      rtx label;
                      insn = basic_block_end[i - 1];
                      if (GET_CODE (insn) == JUMP_INSN
                          /* An unconditional jump is the only possibility
                             we must check for, since a conditional one
                             would make these blocks live.  */
                          && simplejump_p (insn)
                          && (label = XEXP (SET_SRC (PATTERN (insn)), 0), 1)
                          && INSN_UID (label) != 0
                          && BLOCK_NUM (label) == j)
                        {
                          PUT_CODE (insn, NOTE);
                          NOTE_LINE_NUMBER (insn) = NOTE_INSN_DELETED;
                          NOTE_SOURCE_FILE (insn) = 0;
                          if (GET_CODE (NEXT_INSN (insn)) != BARRIER)
                            abort ();
                          delete_insn (NEXT_INSN (insn));
                        }
                      break;
                    }
              }
          }
    }
}
\f
/* Check expression X for label references;
   if one is found, add INSN to the label's chain of references.

   CHECKDUP means check for and avoid creating duplicate references
   from the same insn.  Such duplicates do no serious harm but
   can slow life analysis.  CHECKDUP is set only when duplicates
   are likely.  */

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

  /* We can be called with NULL when scanning label_value_list.  */
  if (x == 0)
    return;

  code = GET_CODE (x);
  if (code == LABEL_REF)
    {
      register rtx label = XEXP (x, 0);
      register rtx y;
      if (GET_CODE (label) != CODE_LABEL)
        abort ();
      /* If the label was never emitted, this insn is junk,
         but avoid a crash trying to refer to BLOCK_NUM (label).
         This can happen as a result of a syntax error
         and a diagnostic has already been printed.  */
      if (INSN_UID (label) == 0)
        return;
      CONTAINING_INSN (x) = insn;
      /* if CHECKDUP is set, check for duplicate ref from same insn
         and don't insert.  */
      if (checkdup)
        for (y = LABEL_REFS (label); y != label; y = LABEL_NEXTREF (y))
          if (CONTAINING_INSN (y) == insn)
            return;
      LABEL_NEXTREF (x) = LABEL_REFS (label);
      LABEL_REFS (label) = x;
      block_live_static[BLOCK_NUM (label)] = 1;
      return;
    }

  fmt = GET_RTX_FORMAT (code);
  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
    {
      if (fmt[i] == 'e')
        mark_label_ref (XEXP (x, i), insn, 0);
      if (fmt[i] == 'E')
        {
          register int j;
          for (j = 0; j < XVECLEN (x, i); j++)
            mark_label_ref (XVECEXP (x, i, j), insn, 1);
        }
    }
}
\f
/* Determine which registers are live at the start of each
   basic block of the function whose first insn is F.
   NREGS is the number of registers used in F.
   We allocate the vector basic_block_live_at_start
   and the regsets that it points to, and fill them with the data.
   regset_size and regset_bytes are also set here.  */

static void
life_analysis (f, nregs)
     rtx f;
     int nregs;
{
  register regset tem;
  int first_pass;
  int changed;
  /* For each basic block, a bitmask of regs
     live on exit from the block.  */
  regset *basic_block_live_at_end;
  /* For each basic block, a bitmask of regs
     live on entry to a successor-block of this block.
     If this does not match basic_block_live_at_end,
     that must be updated, and the block must be rescanned.  */
  regset *basic_block_new_live_at_end;
  /* For each basic block, a bitmask of regs
     whose liveness at the end of the basic block
     can make a difference in which regs are live on entry to the block.
     These are the regs that are set within the basic block,
     possibly excluding those that are used after they are set.  */
  regset *basic_block_significant;
  register int i;
  rtx insn;

  struct obstack flow_obstack;

  gcc_obstack_init (&flow_obstack);

  max_regno = nregs;

  bzero (regs_ever_live, sizeof regs_ever_live);

  /* Allocate and zero out many data structures
     that will record the data from lifetime analysis.  */

  allocate_for_life_analysis ();

  reg_next_use = (rtx *) alloca (nregs * sizeof (rtx));
  bzero (reg_next_use, nregs * sizeof (rtx));

  /* Set up several regset-vectors used internally within this function.
     Their meanings are documented above, with their declarations.  */

  basic_block_live_at_end = (regset *) alloca (n_basic_blocks * sizeof (regset));
  /* Don't use alloca since that leads to a crash rather than an error message
     if there isn't enough space.
     Don't use oballoc since we may need to allocate other things during
     this function on the temporary obstack.  */
  tem = (regset) obstack_alloc (&flow_obstack, n_basic_blocks * regset_bytes);
  bzero (tem, n_basic_blocks * regset_bytes);
  init_regset_vector (basic_block_live_at_end, tem, n_basic_blocks, regset_bytes);

  basic_block_new_live_at_end = (regset *) alloca (n_basic_blocks * sizeof (regset));
  tem = (regset) obstack_alloc (&flow_obstack, n_basic_blocks * regset_bytes);
  bzero (tem, n_basic_blocks * regset_bytes);
  init_regset_vector (basic_block_new_live_at_end, tem, n_basic_blocks, regset_bytes);

  basic_block_significant = (regset *) alloca (n_basic_blocks * sizeof (regset));
  tem = (regset) obstack_alloc (&flow_obstack, n_basic_blocks * regset_bytes);
  bzero (tem, n_basic_blocks * regset_bytes);
  init_regset_vector (basic_block_significant, tem, n_basic_blocks, regset_bytes);

  /* Record which insns refer to any volatile memory
     or for any reason can't be deleted just because they are dead stores.
     Also, delete any insns that copy a register to itself. */

  for (insn = f; insn; insn = NEXT_INSN (insn))
    {
      enum rtx_code code1 = GET_CODE (insn);
      if (code1 == CALL_INSN)
        INSN_VOLATILE (insn) = 1;
      else if (code1 == INSN || code1 == JUMP_INSN)
        {
          /* Delete (in effect) any obvious no-op moves.  */
          if (GET_CODE (PATTERN (insn)) == SET
              && GET_CODE (SET_DEST (PATTERN (insn))) == REG
              && GET_CODE (SET_SRC (PATTERN (insn))) == REG
              && REGNO (SET_DEST (PATTERN (insn))) ==
                        REGNO (SET_SRC (PATTERN (insn)))
              /* Insns carrying these notes are useful later on.  */
              && ! find_reg_note (insn, REG_EQUAL, 0))
            {
              PUT_CODE (insn, NOTE);
              NOTE_LINE_NUMBER (insn) = NOTE_INSN_DELETED;
              NOTE_SOURCE_FILE (insn) = 0;
            }
          else if (GET_CODE (PATTERN (insn)) == PARALLEL)
            {
              /* If nothing but SETs of registers to themselves,
                 this insn can also be deleted.  */
              for (i = 0; i < XVECLEN (PATTERN (insn), 0); i++)
                {
                  rtx tem = XVECEXP (PATTERN (insn), 0, i);

                  if (GET_CODE (tem) == USE
                      || GET_CODE (tem) == CLOBBER)
                    continue;
                    
                  if (GET_CODE (tem) != SET
                      || GET_CODE (SET_DEST (tem)) != REG
                      || GET_CODE (SET_SRC (tem)) != REG
                      || REGNO (SET_DEST (tem)) != REGNO (SET_SRC (tem)))
                    break;
                }
                
              if (i == XVECLEN (PATTERN (insn), 0)
                  /* Insns carrying these notes are useful later on.  */
                  && ! find_reg_note (insn, REG_EQUAL, 0))
                {
                  PUT_CODE (insn, NOTE);
                  NOTE_LINE_NUMBER (insn) = NOTE_INSN_DELETED;
                  NOTE_SOURCE_FILE (insn) = 0;
                }
              else
                INSN_VOLATILE (insn) = volatile_refs_p (PATTERN (insn));
            }
          else if (GET_CODE (PATTERN (insn)) != USE)
            INSN_VOLATILE (insn) = volatile_refs_p (PATTERN (insn));
          /* A SET that makes space on the stack cannot be dead.
             (Such SETs occur only for allocating variable-size data,
             so they will always have a PLUS or MINUS according to the
             direction of stack growth.)
             Even if this function never uses this stack pointer value,
             signal handlers do!  */
          else if (code1 == INSN && GET_CODE (PATTERN (insn)) == SET
                   && SET_DEST (PATTERN (insn)) == stack_pointer_rtx
#ifdef STACK_GROWS_DOWNWARD
                   && GET_CODE (SET_SRC (PATTERN (insn))) == MINUS
#else
                   && GET_CODE (SET_SRC (PATTERN (insn))) == PLUS
#endif
                   && XEXP (SET_SRC (PATTERN (insn)), 0) == stack_pointer_rtx)
            INSN_VOLATILE (insn) = 1;
        }
    }

  if (n_basic_blocks > 0)
#ifdef EXIT_IGNORE_STACK
    if (! EXIT_IGNORE_STACK
        || (! FRAME_POINTER_REQUIRED && flag_omit_frame_pointer))
#endif
      {
        /* If exiting needs the right stack value,
           consider the stack pointer live at the end of the function.  */
        basic_block_live_at_end[n_basic_blocks - 1]
          [STACK_POINTER_REGNUM / REGSET_ELT_BITS]
            |= 1 << (STACK_POINTER_REGNUM % REGSET_ELT_BITS);
        basic_block_new_live_at_end[n_basic_blocks - 1]
          [STACK_POINTER_REGNUM / REGSET_ELT_BITS]
            |= 1 << (STACK_POINTER_REGNUM % REGSET_ELT_BITS);
      }

  /* Mark all global registers as being live at the end of the function
     since they may be referenced by our caller.  */

  if (n_basic_blocks > 0)
    for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
      if (global_regs[i])
        {
          basic_block_live_at_end[n_basic_blocks - 1]
            [i / REGSET_ELT_BITS] |= 1 << (i % REGSET_ELT_BITS);
          basic_block_new_live_at_end[n_basic_blocks - 1]
            [i / REGSET_ELT_BITS] |= 1 << (i % REGSET_ELT_BITS);
        }

  /* Propagate life info through the basic blocks
     around the graph of basic blocks.

     This is a relaxation process: each time a new register
     is live at the end of the basic block, we must scan the block
     to determine which registers are, as a consequence, live at the beginning
     of that block.  These registers must then be marked live at the ends
     of all the blocks that can transfer control to that block.
     The process continues until it reaches a fixed point.  */

  first_pass = 1;
  changed = 1;
  while (changed)
    {
      changed = 0;
      for (i = n_basic_blocks - 1; i >= 0; i--)
        {
          int consider = first_pass;
          int must_rescan = first_pass;
          register int j;

          if (!first_pass)
            {
              /* Set CONSIDER if this block needs thinking about at all
                 (that is, if the regs live now at the end of it
                 are not the same as were live at the end of it when
                 we last thought about it).
                 Set must_rescan if it needs to be thought about
                 instruction by instruction (that is, if any additional
                 reg that is live at the end now but was not live there before
                 is one of the significant regs of this basic block).  */

              for (j = 0; j < regset_size; j++)
                {
                  register int x = (basic_block_new_live_at_end[i][j]
                                    & ~basic_block_live_at_end[i][j]);
                  if (x)
                    consider = 1;
                  if (x & basic_block_significant[i][j])
                    {
                      must_rescan = 1;
                      consider = 1;
                      break;
                    }
                }

              if (! consider)
                continue;
            }

          /* The live_at_start of this block may be changing,
             so another pass will be required after this one.  */
          changed = 1;

          if (! must_rescan)
            {
              /* No complete rescan needed;
                 just record those variables newly known live at end
                 as live at start as well.  */
              for (j = 0; j < regset_size; j++)
                {
                  register int x = basic_block_new_live_at_end[i][j]
                        & ~basic_block_live_at_end[i][j];
                  basic_block_live_at_start[i][j] |= x;
                  basic_block_live_at_end[i][j] |= x;
                }
            }
          else
            {
              /* Update the basic_block_live_at_start
                 by propagation backwards through the block.  */
              bcopy (basic_block_new_live_at_end[i],
                     basic_block_live_at_end[i], regset_bytes);
              bcopy (basic_block_live_at_end[i],
                     basic_block_live_at_start[i], regset_bytes);
              propagate_block (basic_block_live_at_start[i],
                               basic_block_head[i], basic_block_end[i], 0,
                               first_pass ? basic_block_significant[i] : 0,
                               i);
            }

          {
            register rtx jump, head;
            /* Update the basic_block_new_live_at_end's of the block
               that falls through into this one (if any).  */
            head = basic_block_head[i];
            jump = PREV_INSN (head);
            if (basic_block_drops_in[i])
              {
                register int from_block = BLOCK_NUM (jump);
                register int j;
                for (j = 0; j < regset_size; j++)
                  basic_block_new_live_at_end[from_block][j]
                    |= basic_block_live_at_start[i][j];
              }
            /* Update the basic_block_new_live_at_end's of
               all the blocks that jump to this one.  */
            if (GET_CODE (head) == CODE_LABEL)
              for (jump = LABEL_REFS (head);
                   jump != head;
                   jump = LABEL_NEXTREF (jump))
                {
                  register int from_block = BLOCK_NUM (CONTAINING_INSN (jump));
                  register int j;
                  for (j = 0; j < regset_size; j++)
                    basic_block_new_live_at_end[from_block][j]
                      |= basic_block_live_at_start[i][j];
                }
          }
#ifdef USE_C_ALLOCA
          alloca (0);
#endif
        }
      first_pass = 0;
    }

  /* The only pseudos that are live at the beginning of the function are
     those that were not set anywhere in the function.  local-alloc doesn't
     know how to handle these correctly, so mark them as not local to any
     one basic block.  */

  if (n_basic_blocks > 0)
    for (i = FIRST_PSEUDO_REGISTER; i < max_regno; i++)
      if (basic_block_live_at_start[0][i / REGSET_ELT_BITS]
          & (1 << (i % REGSET_ELT_BITS)))
        reg_basic_block[i] = REG_BLOCK_GLOBAL;

  /* Now the life information is accurate.
     Make one more pass over each basic block
     to delete dead stores, create autoincrement addressing
     and record how many times each register is used, is set, or dies.

     To save time, we operate directly in basic_block_live_at_end[i],
     thus destroying it (in fact, converting it into a copy of
     basic_block_live_at_start[i]).  This is ok now because
     basic_block_live_at_end[i] is no longer used past this point.  */

  max_scratch = 0;

  for (i = 0; i < n_basic_blocks; i++)
    {
      propagate_block (basic_block_live_at_end[i],
                       basic_block_head[i], basic_block_end[i], 1, 0, i);
#ifdef USE_C_ALLOCA
      alloca (0);
#endif
    }

#if 0
  /* Something live during a setjmp should not be put in a register
     on certain machines which restore regs from stack frames
     rather than from the jmpbuf.
     But we don't need to do this for the user's variables, since
     ANSI says only volatile variables need this.  */
#ifdef LONGJMP_RESTORE_FROM_STACK
  for (i = FIRST_PSEUDO_REGISTER; i < nregs; i++)
    if (regs_live_at_setjmp[i / REGSET_ELT_BITS] & (1 << (i % REGSET_ELT_BITS))
        && regno_reg_rtx[i] != 0 && ! REG_USERVAR_P (regno_reg_rtx[i]))
      {
        reg_live_length[i] = -1;
        reg_basic_block[i] = -1;
      }
#endif
#endif

  /* We have a problem with any pseudoreg that
     lives across the setjmp.  ANSI says that if a
     user variable does not change in value
     between the setjmp and the longjmp, then the longjmp preserves it.
     This includes longjmp from a place where the pseudo appears dead.
     (In principle, the value still exists if it is in scope.)
     If the pseudo goes in a hard reg, some other value may occupy
     that hard reg where this pseudo is dead, thus clobbering the pseudo.
     Conclusion: such a pseudo must not go in a hard reg.  */
  for (i = FIRST_PSEUDO_REGISTER; i < nregs; i++)
    if (regs_live_at_setjmp[i / REGSET_ELT_BITS] & (1 << (i % REGSET_ELT_BITS))
        && regno_reg_rtx[i] != 0)
      {
        reg_live_length[i] = -1;
        reg_basic_block[i] = -1;
      }

  obstack_free (&flow_obstack, 0);
}
\f
/* Subroutines of life analysis.  */

/* Allocate the permanent data structures that represent the results
   of life analysis.  Not static since used also for stupid life analysis.  */

void
allocate_for_life_analysis ()
{
  register int i;
  register regset tem;

  regset_size = ((max_regno + REGSET_ELT_BITS - 1) / REGSET_ELT_BITS);
  regset_bytes = regset_size * sizeof (*(regset)0);

  reg_n_refs = (int *) oballoc (max_regno * sizeof (int));
  bzero (reg_n_refs, max_regno * sizeof (int));

  reg_n_sets = (short *) oballoc (max_regno * sizeof (short));
  bzero (reg_n_sets, max_regno * sizeof (short));

  reg_n_deaths = (short *) oballoc (max_regno * sizeof (short));
  bzero (reg_n_deaths, max_regno * sizeof (short));

  reg_live_length = (int *) oballoc (max_regno * sizeof (int));
  bzero (reg_live_length, max_regno * sizeof (int));

  reg_n_calls_crossed = (int *) oballoc (max_regno * sizeof (int));
  bzero (reg_n_calls_crossed, max_regno * sizeof (int));

  reg_basic_block = (short *) oballoc (max_regno * sizeof (short));
  for (i = 0; i < max_regno; i++)
    reg_basic_block[i] = REG_BLOCK_UNKNOWN;

  basic_block_live_at_start = (regset *) oballoc (n_basic_blocks * sizeof (regset));
  tem = (regset) oballoc (n_basic_blocks * regset_bytes);
  bzero (tem, n_basic_blocks * regset_bytes);
  init_regset_vector (basic_block_live_at_start, tem, n_basic_blocks, regset_bytes);

  regs_live_at_setjmp = (regset) oballoc (regset_bytes);
  bzero (regs_live_at_setjmp, regset_bytes);
}

/* Make each element of VECTOR point at a regset,
   taking the space for all those regsets from SPACE.
   SPACE is of type regset, but it is really as long as NELTS regsets.
   BYTES_PER_ELT is the number of bytes in one regset.  */

static void
init_regset_vector (vector, space, nelts, bytes_per_elt)
     regset *vector;
     regset space;
     int nelts;
     int bytes_per_elt;
{
  register int i;
  register regset p = space;

  for (i = 0; i < nelts; i++)
    {
      vector[i] = p;
      p += bytes_per_elt / sizeof (*p);
    }
}
\f
/* Compute the registers live at the beginning of a basic block
   from those live at the end.

   When called, OLD contains those live at the end.
   On return, it contains those live at the beginning.
   FIRST and LAST are the first and last insns of the basic block.

   FINAL is nonzero if we are doing the final pass which is not
   for computing the life info (since that has already been done)
   but for acting on it.  On this pass, we delete dead stores,
   set up the logical links and dead-variables lists of instructions,
   and merge instructions for autoincrement and autodecrement addresses.

   SIGNIFICANT is nonzero only the first time for each basic block.
   If it is nonzero, it points to a regset in which we store
   a 1 for each register that is set within the block.

   BNUM is the number of the basic block.  */

static void
propagate_block (old, first, last, final, significant, bnum)
     register regset old;
     rtx first;
     rtx last;
     int final;
     regset significant;
     int bnum;
{
  register rtx insn;
  rtx prev;
  regset live;
  regset dead;

  /* The following variables are used only if FINAL is nonzero.  */
  /* This vector gets one element for each reg that has been live
     at any point in the basic block that has been scanned so far.
     SOMETIMES_MAX says how many elements are in use so far.
     In each element, OFFSET is the byte-number within a regset
     for the register described by the element, and BIT is a mask
     for that register's bit within the byte.  */
  register struct foo { short offset; short bit; } *regs_sometimes_live;
  int sometimes_max = 0;
  /* This regset has 1 for each reg that we have seen live so far.
     It and REGS_SOMETIMES_LIVE are updated together.  */
  regset maxlive;

  /* The loop depth may change in the middle of a basic block.  Since we
     scan from end to beginning, we start with the depth at the end of the
     current basic block, and adjust as we pass ends and starts of loops.  */
  loop_depth = basic_block_loop_depth[bnum];

  dead = (regset) alloca (regset_bytes);
  live = (regset) alloca (regset_bytes);

  cc0_live = 0;
  last_mem_set = 0;

  /* Include any notes at the end of the block in the scan.
     This is in case the block ends with a call to setjmp.  */

  while (NEXT_INSN (last) != 0 && GET_CODE (NEXT_INSN (last)) == NOTE)
    {
      /* Look for loop boundaries, we are going forward here.  */
      last = NEXT_INSN (last);
      if (NOTE_LINE_NUMBER (last) == NOTE_INSN_LOOP_BEG)
        loop_depth++;
      else if (NOTE_LINE_NUMBER (last) == NOTE_INSN_LOOP_END)
        loop_depth--;
    }

  if (final)
    {
      register int i, offset, bit;

      num_scratch = 0;
      maxlive = (regset) alloca (regset_bytes);
      bcopy (old, maxlive, regset_bytes);
      regs_sometimes_live
        = (struct foo *) alloca (max_regno * sizeof (struct foo));

      /* Process the regs live at the end of the block.
         Enter them in MAXLIVE and REGS_SOMETIMES_LIVE.
         Also mark them as not local to any one basic block.  */

      for (offset = 0, i = 0; offset < regset_size; offset++)
        for (bit = 1; bit; bit <<= 1, i++)
          {
            if (i == max_regno)
              break;
            if (old[offset] & bit)
              {
                reg_basic_block[i] = REG_BLOCK_GLOBAL;
                regs_sometimes_live[sometimes_max].offset = offset;
                regs_sometimes_live[sometimes_max].bit = i % REGSET_ELT_BITS;
                sometimes_max++;
              }
          }
    }

  /* Scan the block an insn at a time from end to beginning.  */

  for (insn = last; ; insn = prev)
    {
      prev = PREV_INSN (insn);

      /* Look for loop boundaries, remembering that we are going backwards.  */
      if (GET_CODE (insn) == NOTE
          && NOTE_LINE_NUMBER (insn) == NOTE_INSN_LOOP_END)
        loop_depth++;
      else if (GET_CODE (insn) == NOTE
               && NOTE_LINE_NUMBER (insn) == NOTE_INSN_LOOP_BEG)
        loop_depth--;

      /* If we have LOOP_DEPTH == 0, there has been a bookkeeping error. 
         Abort now rather than setting register status incorrectly.  */
      if (loop_depth == 0)
        abort ();

      /* If this is a call to `setjmp' et al,
         warn if any non-volatile datum is live.  */

      if (final && GET_CODE (insn) == NOTE
          && NOTE_LINE_NUMBER (insn) == NOTE_INSN_SETJMP)
        {
          int i;
          for (i = 0; i < regset_size; i++)
            regs_live_at_setjmp[i] |= old[i];
        }

      /* Update the life-status of regs for this insn.
         First DEAD gets which regs are set in this insn
         then LIVE gets which regs are used in this insn.
         Then the regs live before the insn
         are those live after, with DEAD regs turned off,
         and then LIVE regs turned on.  */

      if (GET_RTX_CLASS (GET_CODE (insn)) == 'i')
        {
          register int i;
          rtx note = find_reg_note (insn, REG_RETVAL, 0);
          int insn_is_dead
            = (insn_dead_p (PATTERN (insn), old, 0)
               /* Don't delete something that refers to volatile storage!  */
               && ! INSN_VOLATILE (insn));
          int libcall_is_dead 
            = (insn_is_dead && note != 0
               && libcall_dead_p (PATTERN (insn), old, note, insn));

          /* If an instruction consists of just dead store(s) on final pass,
             "delete" it by turning it into a NOTE of type NOTE_INSN_DELETED.
             We could really delete it with delete_insn, but that
             can cause trouble for first or last insn in a basic block.  */
          if (final && insn_is_dead)
            {
              PUT_CODE (insn, NOTE);
              NOTE_LINE_NUMBER (insn) = NOTE_INSN_DELETED;
              NOTE_SOURCE_FILE (insn) = 0;

              /* If this insn is copying the return value from a library call,
                 delete the entire library call.  */
              if (libcall_is_dead)
                {
                  rtx first = XEXP (note, 0);
                  rtx p = insn;
                  while (INSN_DELETED_P (first))
                    first = NEXT_INSN (first);
                  while (p != first)
                    {
                      p = PREV_INSN (p);
                      PUT_CODE (p, NOTE);
                      NOTE_LINE_NUMBER (p) = NOTE_INSN_DELETED;
                      NOTE_SOURCE_FILE (p) = 0;
                    }
                }
              goto flushed;
            }

          for (i = 0; i < regset_size; i++)
            {
              dead[i] = 0;      /* Faster than bzero here */
              live[i] = 0;      /* since regset_size is usually small */
            }

          /* See if this is an increment or decrement that can be
             merged into a following memory address.  */
#ifdef AUTO_INC_DEC
          {
            register rtx x = PATTERN (insn);
            /* Does this instruction increment or decrement a register?  */
            if (final && GET_CODE (x) == SET
                && GET_CODE (SET_DEST (x)) == REG
                && (GET_CODE (SET_SRC (x)) == PLUS
                    || GET_CODE (SET_SRC (x)) == MINUS)
                && XEXP (SET_SRC (x), 0) == SET_DEST (x)
                && GET_CODE (XEXP (SET_SRC (x), 1)) == CONST_INT
                /* Ok, look for a following memory ref we can combine with.
                   If one is found, change the memory ref to a PRE_INC
                   or PRE_DEC, cancel this insn, and return 1.
                   Return 0 if nothing has been done.  */
                && try_pre_increment_1 (insn))
              goto flushed;
          }
#endif /* AUTO_INC_DEC */

          /* If this is not the final pass, and this insn is copying the
             value of a library call and it's dead, don't scan the
             insns that perform the library call, so that the call's
             arguments are not marked live.  */
          if (libcall_is_dead)
            {
              /* Mark the dest reg as `significant'.  */
              mark_set_regs (old, dead, PATTERN (insn), 0, significant);

              insn = XEXP (note, 0);
              prev = PREV_INSN (insn);
            }
          else if (GET_CODE (PATTERN (insn)) == SET
                   && SET_DEST (PATTERN (insn)) == stack_pointer_rtx
                   && GET_CODE (SET_SRC (PATTERN (insn))) == PLUS
                   && XEXP (SET_SRC (PATTERN (insn)), 0) == stack_pointer_rtx
                   && GET_CODE (XEXP (SET_SRC (PATTERN (insn)), 1)) == CONST_INT)
            /* We have an insn to pop a constant amount off the stack.
               (Such insns use PLUS regardless of the direction of the stack,
               and any insn to adjust the stack by a constant is always a pop.)
               These insns, if not dead stores, have no effect on life.  */
            ;
          else
            {
              /* LIVE gets the regs used in INSN;
                 DEAD gets those set by it.  Dead insns don't make anything
                 live.  */

              mark_set_regs (old, dead, PATTERN (insn), final ? insn : 0,
                             significant);

              /* If an insn doesn't use CC0, it becomes dead since we 
                 assume that every insn clobbers it.  So show it dead here;
                 mark_used_regs will set it live if it is referenced.  */
              cc0_live = 0;

              if (! insn_is_dead)
                mark_used_regs (old, live, PATTERN (insn), final, insn);

              /* Sometimes we may have inserted something before INSN (such as
                 a move) when we make an auto-inc.  So ensure we will scan
                 those insns.  */
#ifdef AUTO_INC_DEC
              prev = PREV_INSN (insn);
#endif

              if (! insn_is_dead && GET_CODE (insn) == CALL_INSN)
                {
                  register int i;

                  /* Each call clobbers all call-clobbered regs that are not
                     global.  Note that the function-value reg is a
                     call-clobbered reg, and mark_set_regs has already had
                     a chance to handle it.  */

                  for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
                    if (call_used_regs[i] && ! global_regs[i])
                      dead[i / REGSET_ELT_BITS]
                        |= (1 << (i % REGSET_ELT_BITS));

                  /* The stack ptr is used (honorarily) by a CALL insn.  */
                  live[STACK_POINTER_REGNUM / REGSET_ELT_BITS]
                    |= (1 << (STACK_POINTER_REGNUM % REGSET_ELT_BITS));

                  /* Calls may also reference any of the global registers,
                     so they are made live.  */

                  for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
                    if (global_regs[i])
                      live[i / REGSET_ELT_BITS]
                        |= (1 << (i % REGSET_ELT_BITS));

                  /* Calls also clobber memory.  */
                  last_mem_set = 0;
                }

              /* Update OLD for the registers used or set.  */
              for (i = 0; i < regset_size; i++)
                {
                  old[i] &= ~dead[i];
                  old[i] |= live[i];
                }

              if (GET_CODE (insn) == CALL_INSN && final)
                {
                  /* Any regs live at the time of a call instruction
                     must not go in a register clobbered by calls.
                     Find all regs now live and record this for them.  */

                  register struct foo *p = regs_sometimes_live;

                  for (i = 0; i < sometimes_max; i++, p++)
                    if (old[p->offset] & (1 << p->bit))
                      reg_n_calls_crossed[p->offset * REGSET_ELT_BITS + p->bit]+= 1;
                }
            }

          /* On final pass, add any additional sometimes-live regs
             into MAXLIVE and REGS_SOMETIMES_LIVE.
             Also update counts of how many insns each reg is live at.  */

          if (final)
            {
              for (i = 0; i < regset_size; i++)
                {
                  register int diff = live[i] & ~maxlive[i];

                  if (diff)
                    {
                      register int regno;
                      maxlive[i] |= diff;
                      for (regno = 0; diff && regno < REGSET_ELT_BITS; regno++)
                        if (diff & (1 << regno))
                          {
                            regs_sometimes_live[sometimes_max].offset = i;
                            regs_sometimes_live[sometimes_max].bit = regno;
                            diff &= ~ (1 << regno);
                            sometimes_max++;
                          }
                    }
                }

              {
                register struct foo *p = regs_sometimes_live;
                for (i = 0; i < sometimes_max; i++, p++)
                  {
                    if (old[p->offset] & (1 << p->bit))
                      reg_live_length[p->offset * REGSET_ELT_BITS + p->bit]++;
                  }
              }
            }
        }
    flushed: ;
      if (insn == first)
        break;
    }

  if (num_scratch > max_scratch)
    max_scratch = num_scratch;
}
\f
/* Return 1 if X (the body of an insn, or part of it) is just dead stores
   (SET expressions whose destinations are registers dead after the insn).
   NEEDED is the regset that says which regs are alive after the insn.

   Unless CALL_OK is non-zero, an insn is needed if it contains a CALL.  */

static int
insn_dead_p (x, needed, call_ok)
     rtx x;
     regset needed;
     int call_ok;
{
  register RTX_CODE code = GET_CODE (x);
  /* If setting something that's a reg or part of one,
     see if that register's altered value will be live.  */

  if (code == SET)
    {
      register rtx r = SET_DEST (x);
      /* A SET that is a subroutine call cannot be dead.  */
      if (! call_ok && GET_CODE (SET_SRC (x)) == CALL)
        return 0;

#ifdef HAVE_cc0
      if (GET_CODE (r) == CC0)
        return ! cc0_live;
#endif
      
      if (GET_CODE (r) == MEM && last_mem_set && ! MEM_VOLATILE_P (r)
          && rtx_equal_p (r, last_mem_set))
        return 1;

      while (GET_CODE (r) == SUBREG
             || GET_CODE (r) == STRICT_LOW_PART
             || GET_CODE (r) == ZERO_EXTRACT
             || GET_CODE (r) == SIGN_EXTRACT)
        r = SUBREG_REG (r);

      if (GET_CODE (r) == REG)
        {
          register int regno = REGNO (r);
          register int offset = regno / REGSET_ELT_BITS;
          register int bit = 1 << (regno % REGSET_ELT_BITS);

          if ((regno < FIRST_PSEUDO_REGISTER && global_regs[regno])
              /* Make sure insns to set frame pointer aren't deleted.  */
              || regno == FRAME_POINTER_REGNUM
#if FRAME_POINTER_REGNUM != ARG_POINTER_REGNUM
              /* Make sure insns to set arg pointer are never deleted
                 (if the arg pointer isn't fixed, there will be a USE for
                 it, so we can treat it normally). */
              || (regno == ARG_POINTER_REGNUM && fixed_regs[regno])
#endif
              || (needed[offset] & bit) != 0)
            return 0;

          /* If this is a hard register, verify that subsequent words are
             not needed.  */
          if (regno < FIRST_PSEUDO_REGISTER)
            {
              int n = HARD_REGNO_NREGS (regno, GET_MODE (r));

              while (--n > 0)
                if ((needed[(regno + n) / REGSET_ELT_BITS]
                     & 1 << ((regno + n) % REGSET_ELT_BITS)) != 0)
                  return 0;
            }

          return 1;
        }
    }
  /* If performing several activities,
     insn is dead if each activity is individually dead.
     Also, CLOBBERs and USEs can be ignored; a CLOBBER or USE
     that's inside a PARALLEL doesn't make the insn worth keeping.  */
  else if (code == PARALLEL)
    {
      register int i = XVECLEN (x, 0);
      for (i--; i >= 0; i--)
        {
          rtx elt = XVECEXP (x, 0, i);
          if (!insn_dead_p (elt, needed, call_ok)
              && GET_CODE (elt) != CLOBBER
              && GET_CODE (elt) != USE)
            return 0;
        }
      return 1;
    }
  /* We do not check CLOBBER or USE here.
     An insn consisting of just a CLOBBER or just a USE
     should not be deleted.  */
  return 0;
}

/* If X is the pattern of the last insn in a libcall, and assuming X is dead,
   return 1 if the entire library call is dead.
   This is true if X copies a register (hard or pseudo)
   and if the hard return  reg of the call insn is dead.
   (The caller should have tested the destination of X already for death.)

   If this insn doesn't just copy a register, then we don't
   have an ordinary libcall.  In that case, cse could not have
   managed to substitute the source for the dest later on,
   so we can assume the libcall is dead.

   NEEDED is the bit vector of pseudoregs live before this insn.
   NOTE is the REG_RETVAL note of the insn.  INSN is the insn itself.  */

static int
libcall_dead_p (x, needed, note, insn)
     rtx x;
     regset needed;
     rtx note;
     rtx insn;
{
  register RTX_CODE code = GET_CODE (x);

  if (code == SET)
    {
      register rtx r = SET_SRC (x);
      if (GET_CODE (r) == REG)
        {
          rtx call = XEXP (note, 0);
          register int i;

          /* Find the call insn.  */
          while (call != insn && GET_CODE (call) != CALL_INSN)
            call = NEXT_INSN (call);

          /* If there is none, do nothing special,
             since ordinary death handling can understand these insns.  */
          if (call == insn)
            return 0;

          /* See if the hard reg holding the value is dead.
             If this is a PARALLEL, find the call within it.  */
          call = PATTERN (call);
          if (GET_CODE (call) == PARALLEL)
            {
              for (i = XVECLEN (call, 0) - 1; i >= 0; i--)
                if (GET_CODE (XVECEXP (call, 0, i)) == SET
                    && GET_CODE (SET_SRC (XVECEXP (call, 0, i))) == CALL)
                  break;

              if (i < 0)
                abort ();

              call = XVECEXP (call, 0, i);
            }

          return insn_dead_p (call, needed, 1);
        }
    }
  return 1;
}

/* Return 1 if register REGNO was used before it was set.
   In other words, if it is live at function entry.  */

int
regno_uninitialized (regno)
     int regno;
{
  if (n_basic_blocks == 0)
    return 0;

  return (basic_block_live_at_start[0][regno / REGSET_ELT_BITS]
          & (1 << (regno % REGSET_ELT_BITS)));
}

/* 1 if register REGNO was alive at a place where `setjmp' was called
   and was set more than once or is an argument.
   Such regs may be clobbered by `longjmp'.  */

int
regno_clobbered_at_setjmp (regno)
     int regno;
{
  if (n_basic_blocks == 0)
    return 0;

  return ((reg_n_sets[regno] > 1
           || (basic_block_live_at_start[0][regno / REGSET_ELT_BITS]
               & (1 << (regno % REGSET_ELT_BITS))))
          && (regs_live_at_setjmp[regno / REGSET_ELT_BITS]
              & (1 << (regno % REGSET_ELT_BITS))));
}
\f
/* Process the registers that are set within X.
   Their bits are set to 1 in the regset DEAD,
   because they are dead prior to this insn.

   If INSN is nonzero, it is the insn being processed
   and the fact that it is nonzero implies this is the FINAL pass
   in propagate_block.  In this case, various info about register
   usage is stored, LOG_LINKS fields of insns are set up.  */

static void mark_set_1 ();

static void
mark_set_regs (needed, dead, x, insn, significant)
     regset needed;
     regset dead;
     rtx x;
     rtx insn;
     regset significant;
{
  register RTX_CODE code = GET_CODE (x);

  if (code == SET || code == CLOBBER)
    mark_set_1 (needed, dead, x, insn, significant);
  else if (code == PARALLEL)
    {
      register int i;
      for (i = XVECLEN (x, 0) - 1; i >= 0; i--)
        {
          code = GET_CODE (XVECEXP (x, 0, i));
          if (code == SET || code == CLOBBER)
            mark_set_1 (needed, dead, XVECEXP (x, 0, i), insn, significant);
        }
    }
}

/* Process a single SET rtx, X.  */

static void
mark_set_1 (needed, dead, x, insn, significant)
     regset needed;
     regset dead;
     rtx x;
     rtx insn;
     regset significant;
{
  register int regno;
  register rtx reg = SET_DEST (x);

  /* Modifying just one hardware register of a multi-reg value
     or just a byte field of a register
     does not mean the value from before this insn is now dead.
     But it does mean liveness of that register at the end of the block
     is significant.

     Within mark_set_1, however, we treat it as if the register is
     indeed modified.  mark_used_regs will, however, also treat this
     register as being used.  Thus, we treat these insns as setting a
     new value for the register as a function of its old value.  This
     cases LOG_LINKS to be made appropriately and this will help combine.  */

  while (GET_CODE (reg) == SUBREG || GET_CODE (reg) == ZERO_EXTRACT
         || GET_CODE (reg) == SIGN_EXTRACT
         || GET_CODE (reg) == STRICT_LOW_PART)
    reg = XEXP (reg, 0);

  /* If we are writing into memory or into a register mentioned in the
     address of the last thing stored into memory, show we don't know
     what the last store was.  If we are writing memory, save the address
     unless it is volatile.  */
  if (GET_CODE (reg) == MEM
      || (GET_CODE (reg) == REG
          && last_mem_set != 0 && reg_overlap_mentioned_p (reg, last_mem_set)))
    last_mem_set = 0;
    
  if (GET_CODE (reg) == MEM && ! side_effects_p (reg)
      /* There are no REG_INC notes for SP, so we can't assume we'll see 
         everything that invalidates it.  To be safe, don't eliminate any
         stores though SP; none of them should be redundant anyway.  */
      && ! reg_mentioned_p (stack_pointer_rtx, reg))
    last_mem_set = reg;

  if (GET_CODE (reg) == REG
      && (regno = REGNO (reg), regno != FRAME_POINTER_REGNUM)
#if FRAME_POINTER_REGNUM != ARG_POINTER_REGNUM
      && ! (regno == ARG_POINTER_REGNUM && fixed_regs[regno])
#endif
      && ! (regno < FIRST_PSEUDO_REGISTER && global_regs[regno]))
    /* && regno != STACK_POINTER_REGNUM) -- let's try without this.  */
    {
      register int offset = regno / REGSET_ELT_BITS;
      register int bit = 1 << (regno % REGSET_ELT_BITS);
      int all_needed = (needed[offset] & bit) != 0;
      int some_needed = (needed[offset] & bit) != 0;

      /* Mark it as a significant register for this basic block.  */
      if (significant)
        significant[offset] |= bit;

      /* Mark it as as dead before this insn.  */
      dead[offset] |= bit;

      /* A hard reg in a wide mode may really be multiple registers.
         If so, mark all of them just like the first.  */
      if (regno < FIRST_PSEUDO_REGISTER)
        {
          int n;

          /* Nothing below is needed for the stack pointer; get out asap.
             Eg, log links aren't needed, since combine won't use them.  */
          if (regno == STACK_POINTER_REGNUM)
            return;

          n = HARD_REGNO_NREGS (regno, GET_MODE (reg));
          while (--n > 0)
            {
              if (significant)
                significant[(regno + n) / REGSET_ELT_BITS]
                  |= 1 << ((regno + n) % REGSET_ELT_BITS);
              dead[(regno + n) / REGSET_ELT_BITS]
                |= 1 << ((regno + n) % REGSET_ELT_BITS);
              some_needed |= (needed[(regno + n) / REGSET_ELT_BITS]
                              & 1 << ((regno + n) % REGSET_ELT_BITS));
              all_needed &= (needed[(regno + n) / REGSET_ELT_BITS]
                             & 1 << ((regno + n) % REGSET_ELT_BITS));
            }
        }
      /* Additional data to record if this is the final pass.  */
      if (insn)
        {
          register rtx y = reg_next_use[regno];
          register int blocknum = BLOCK_NUM (insn);

          /* If this is a hard reg, record this function uses the reg.  */

          if (regno < FIRST_PSEUDO_REGISTER)
            {
              register int i;
              int endregno = regno + HARD_REGNO_NREGS (regno, GET_MODE (reg));

              for (i = regno; i < endregno; i++)
                {
                  regs_ever_live[i] = 1;
                  reg_n_sets[i]++;
                }
            }
          else
            {
              /* Keep track of which basic blocks each reg appears in.  */

              if (reg_basic_block[regno] == REG_BLOCK_UNKNOWN)
                reg_basic_block[regno] = blocknum;
              else if (reg_basic_block[regno] != blocknum)
                reg_basic_block[regno] = REG_BLOCK_GLOBAL;

              /* Count (weighted) references, stores, etc.  This counts a
                 register twice if it is modified, but that is correct.  */
              reg_n_sets[regno]++;

              reg_n_refs[regno] += loop_depth;
                  
              /* The insns where a reg is live are normally counted
                 elsewhere, but we want the count to include the insn
                 where the reg is set, and the normal counting mechanism
                 would not count it.  */
              reg_live_length[regno]++;
            }

          /* The next use is no longer "next", since a store intervenes.  */
          reg_next_use[regno] = 0;

          if (all_needed)
            {
              /* Make a logical link from the next following insn
                 that uses this register, back to this insn.
                 The following insns have already been processed.

                 We don't build a LOG_LINK for hard registers containing
                 in ASM_OPERANDs.  If these registers get replaced,
                 we might wind up changing the semantics of the insn,
                 even if reload can make what appear to be valid assignments
                 later.  */
              if (y && (BLOCK_NUM (y) == blocknum)
                  && (regno >= FIRST_PSEUDO_REGISTER
                      || asm_noperands (PATTERN (y)) < 0))
                LOG_LINKS (y)
                  = gen_rtx (INSN_LIST, VOIDmode, insn, LOG_LINKS (y));
            }
          else if (! some_needed)
            {
              /* Note that dead stores have already been deleted when possible
                 If we get here, we have found a dead store that cannot
                 be eliminated (because the same insn does something useful).
                 Indicate this by marking the reg being set as dying here.  */
              REG_NOTES (insn)
                = gen_rtx (EXPR_LIST, REG_UNUSED, reg, REG_NOTES (insn));
              reg_n_deaths[REGNO (reg)]++;
            }
          else
            {
              /* This is a case where we 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.  This case should
                 be rare.  */

              int i;

              for (i = HARD_REGNO_NREGS (regno, GET_MODE (reg)) - 1;
                   i >= 0; i--)
                if ((needed[(regno + i) / REGSET_ELT_BITS]
                     & 1 << ((regno + i) % REGSET_ELT_BITS)) == 0)
                  REG_NOTES (insn)
                    = gen_rtx (EXPR_LIST, REG_UNUSED,
                               gen_rtx (REG, word_mode, regno + i),
                               REG_NOTES (insn));
            }
        }
    }

  /* If this is the last pass and this is a SCRATCH, show it will be dying
     here and count it.  */
  else if (GET_CODE (reg) == SCRATCH && insn != 0)
    {
      REG_NOTES (insn)
        = gen_rtx (EXPR_LIST, REG_UNUSED, reg, REG_NOTES (insn));
      num_scratch++;
    }
}
\f
#ifdef AUTO_INC_DEC

/* X is a MEM found in INSN.  See if we can convert it into an auto-increment
   reference.  */

static void
find_auto_inc (needed, x, insn)
     regset needed;
     rtx x;
     rtx insn;
{
  rtx addr = XEXP (x, 0);
  int offset = 0;

  /* Here we detect use of an index register which might be good for
     postincrement, postdecrement, preincrement, or predecrement.  */

  if (GET_CODE (addr) == PLUS && GET_CODE (XEXP (addr, 1)) == CONST_INT)
    offset = INTVAL (XEXP (addr, 1)), addr = XEXP (addr, 0);

  if (GET_CODE (addr) == REG)
    {
      register rtx y;
      register int size = GET_MODE_SIZE (GET_MODE (x));
      rtx use;
      rtx incr;
      int regno = REGNO (addr);

      /* Is the next use an increment that might make auto-increment? */
      incr = reg_next_use[regno];
      if (incr && GET_CODE (PATTERN (incr)) == SET
          && BLOCK_NUM (incr) == BLOCK_NUM (insn)
          /* Can't add side effects to jumps; if reg is spilled and
             reloaded, there's no way to store back the altered value.  */
          && GET_CODE (insn) != JUMP_INSN
          && (y = SET_SRC (PATTERN (incr)), GET_CODE (y) == PLUS)
          && XEXP (y, 0) == addr
          && GET_CODE (XEXP (y, 1)) == CONST_INT
          && (0
#ifdef HAVE_POST_INCREMENT
              || (INTVAL (XEXP (y, 1)) == size && offset == 0)
#endif
#ifdef HAVE_POST_DECREMENT
              || (INTVAL (XEXP (y, 1)) == - size && offset == 0)
#endif
#ifdef HAVE_PRE_INCREMENT
              || (INTVAL (XEXP (y, 1)) == size && offset == size)
#endif
#ifdef HAVE_PRE_DECREMENT
              || (INTVAL (XEXP (y, 1)) == - size && offset == - size)
#endif
              )
          /* Make sure this reg appears only once in this insn.  */
          && (use = find_use_as_address (PATTERN (insn), addr, offset),
              use != 0 && use != (rtx) 1))
        {
          int win = 0;
          rtx q = SET_DEST (PATTERN (incr));

          if (dead_or_set_p (incr, addr))
            win = 1;
          else if (GET_CODE (q) == REG && ! reg_used_between_p (q, insn, incr))
            {
              /* We have *p followed by q = p+size.
                 Both p and q must be live afterward,
                 and q must be dead before.
                 Change it to q = p, ...*q..., q = q+size.
                 Then fall into the usual case.  */
              rtx insns, temp;

              start_sequence ();
              emit_move_insn (q, addr);
              insns = get_insns ();
              end_sequence ();

              /* If anything in INSNS have UID's that don't fit within the
                 extra space we allocate earlier, we can't make this auto-inc.
                 This should never happen.  */
              for (temp = insns; temp; temp = NEXT_INSN (temp))
                {
                  if (INSN_UID (temp) > max_uid_for_flow)
                    return;
                  BLOCK_NUM (temp) = BLOCK_NUM (insn);
                }

              emit_insns_before (insns, insn);

              if (basic_block_head[BLOCK_NUM (insn)] == insn)
                basic_block_head[BLOCK_NUM (insn)] = insns;

              XEXP (x, 0) = q;
              XEXP (y, 0) = q;

              /* INCR will become a NOTE and INSN won't contain a
                 use of ADDR.  If a use of ADDR was just placed in
                 the insn before INSN, make that the next use. 
                 Otherwise, invalidate it.  */
              if (GET_CODE (PREV_INSN (insn)) == INSN
                  && GET_CODE (PATTERN (PREV_INSN (insn))) == SET
                  && SET_SRC (PATTERN (PREV_INSN (insn))) == addr)
                reg_next_use[regno] = PREV_INSN (insn);
              else
                reg_next_use[regno] = 0;

              addr = q;
              regno = REGNO (q);
              win = 1;

              /* REGNO is now used in INCR which is below INSN, but
                 it previously wasn't live here.  If we don't mark
                 it as needed, we'll put a REG_DEAD note for it
                 on this insn, which is incorrect.  */
              needed[regno / REGSET_ELT_BITS]
                |= 1 << (regno % REGSET_ELT_BITS);

              /* If there are any calls between INSN and INCR, show
                 that REGNO now crosses them.  */
              for (temp = insn; temp != incr; temp = NEXT_INSN (temp))
                if (GET_CODE (temp) == CALL_INSN)
                  reg_n_calls_crossed[regno]++;
            }

          if (win)
            {
              /* We have found a suitable auto-increment: do POST_INC around
                 the register here, and patch out the increment instruction 
                 that follows. */
              XEXP (x, 0) = gen_rtx ((INTVAL (XEXP (y, 1)) == size
                                      ? (offset ? PRE_INC : POST_INC)
                                      : (offset ? PRE_DEC : POST_DEC)),
                                     Pmode, addr);

              /* Record that this insn has an implicit side effect.  */
              REG_NOTES (insn)
                = gen_rtx (EXPR_LIST, REG_INC, addr, REG_NOTES (insn));

              /* Modify the old increment-insn to simply copy
                 the already-incremented value of our register.  */
              SET_SRC (PATTERN (incr)) = addr;
              /* Indicate insn must be re-recognized.  */
              INSN_CODE (incr) = -1;

              /* If that makes it a no-op (copying the register into itself)
                 then delete it so it won't appear to be a "use" and a "set"
                 of this register.  */
              if (SET_DEST (PATTERN (incr)) == addr)
                {
                  PUT_CODE (incr, NOTE);
                  NOTE_LINE_NUMBER (incr) = NOTE_INSN_DELETED;
                  NOTE_SOURCE_FILE (incr) = 0;
                }

              if (regno >= FIRST_PSEUDO_REGISTER)
                {
                  /* Count an extra reference to the reg.  When a reg is
                     incremented, spilling it is worse, so we want to make
                     that less likely.  */
                  reg_n_refs[regno] += loop_depth;
                  /* Count the increment as a setting of the register,
                     even though it isn't a SET in rtl.  */
                  reg_n_sets[regno]++;
                }
            }
        }
    }
}
#endif /* AUTO_INC_DEC */
\f
/* Scan expression X and store a 1-bit in LIVE for each reg it uses.
   This is done assuming the registers needed from X
   are those that have 1-bits in NEEDED.

   On the final pass, FINAL is 1.  This means try for autoincrement
   and count the uses and deaths of each pseudo-reg.

   INSN is the containing instruction.  If INSN is dead, this function is not
   called.  */

static void
mark_used_regs (needed, live, x, final, insn)
     regset needed;
     regset live;
     rtx x;
     rtx insn;
     int final;
{
  register RTX_CODE code;
  register int regno;
  int i;

 retry:
  code = GET_CODE (x);
  switch (code)
    {
    case LABEL_REF:
    case SYMBOL_REF:
    case CONST_INT:
    case CONST:
    case CONST_DOUBLE:
    case PC:
    case CLOBBER:
    case ADDR_VEC:
    case ADDR_DIFF_VEC:
    case ASM_INPUT:
      return;

#ifdef HAVE_cc0
    case CC0:
      cc0_live = 1;
      return;
#endif

    case MEM:
      /* Invalidate the data for the last MEM stored.  We could do this only
         if the addresses conflict, but this doesn't seem worthwhile.  */
      last_mem_set = 0;

#ifdef AUTO_INC_DEC
      if (final)
        find_auto_inc (needed, x, insn);
#endif
      break;

    case REG:
      /* See a register other than being set
         => mark it as needed.  */

      regno = REGNO (x);
      {
        register int offset = regno / REGSET_ELT_BITS;
        register int bit = 1 << (regno % REGSET_ELT_BITS);
        int all_needed = (needed[offset] & bit) != 0;
        int some_needed = (needed[offset] & bit) != 0;

        live[offset] |= bit;
        /* A hard reg in a wide mode may really be multiple registers.
           If so, mark all of them just like the first.  */
        if (regno < FIRST_PSEUDO_REGISTER)
          {
            int n;

            /* For stack ptr or fixed arg pointer,
               nothing below can be necessary, so waste no more time.  */
            if (regno == STACK_POINTER_REGNUM
#if FRAME_POINTER_REGNUM != ARG_POINTER_REGNUM
                || (regno == ARG_POINTER_REGNUM && fixed_regs[regno])
#endif
                || regno == FRAME_POINTER_REGNUM)
              {
                /* If this is a register we are going to try to eliminate,
                   don't mark it live here.  If we are successful in
                   eliminating it, it need not be live unless it is used for
                   pseudos, in which case it will have been set live when
                   it was allocated to the pseudos.  If the register will not
                   be eliminated, reload will set it live at that point.  */

                if (! TEST_HARD_REG_BIT (elim_reg_set, regno))
                  regs_ever_live[regno] = 1;
                return;
              }
            /* No death notes for global register variables;
               their values are live after this function exits.  */
            if (global_regs[regno])
              return;

            n = HARD_REGNO_NREGS (regno, GET_MODE (x));
            while (--n > 0)
              {
                live[(regno + n) / REGSET_ELT_BITS]
                  |= 1 << ((regno + n) % REGSET_ELT_BITS);
                some_needed |= (needed[(regno + n) / REGSET_ELT_BITS]
                                & 1 << ((regno + n) % REGSET_ELT_BITS));
                all_needed &= (needed[(regno + n) / REGSET_ELT_BITS]
                               & 1 << ((regno + n) % REGSET_ELT_BITS));
              }
          }
        if (final)
          {
            /* Record where each reg is used, so when the reg
               is set we know the next insn that uses it.  */

            reg_next_use[regno] = insn;

            if (regno < FIRST_PSEUDO_REGISTER)
              {
                /* If a hard reg is being used,
                   record that this function does use it.  */

                i = HARD_REGNO_NREGS (regno, GET_MODE (x));
                if (i == 0)
                  i = 1;
                do
                  regs_ever_live[regno + --i] = 1;
                while (i > 0);
              }
            else
              {
                /* Keep track of which basic block each reg appears in.  */

                register int blocknum = BLOCK_NUM (insn);

                if (reg_basic_block[regno] == REG_BLOCK_UNKNOWN)
                  reg_basic_block[regno] = blocknum;
                else if (reg_basic_block[regno] != blocknum)
                  reg_basic_block[regno] = REG_BLOCK_GLOBAL;

                /* Count (weighted) number of uses of each reg.  */

                reg_n_refs[regno] += loop_depth;
              }

            /* Record and count the insns in which a reg dies.
               If it is used in this insn and was dead below the insn
               then it dies in this insn.  If it was set in this insn,
               we do not make a REG_DEAD note; likewise if we already
               made such a note.  */

            if (! all_needed
                && ! dead_or_set_p (insn, x)
#if 0
                && (regno >= FIRST_PSEUDO_REGISTER || ! fixed_regs[regno])
#endif
                )
              {
                /* If none of the words in X is needed, make a REG_DEAD
                   note.  Otherwise, we must make partial REG_DEAD notes.  */
                if (! some_needed)
                  {
                    REG_NOTES (insn)
                      = gen_rtx (EXPR_LIST, REG_DEAD, x, REG_NOTES (insn));
                    reg_n_deaths[regno]++;
                  }
                else
                  {
                    int i;

                    /* Don't make a REG_DEAD note for a part of a register
                       that is set in the insn.  */

                    for (i = HARD_REGNO_NREGS (regno, GET_MODE (x)) - 1;
                         i >= 0; i--)
                      if ((needed[(regno + i) / REGSET_ELT_BITS]
                           & 1 << ((regno + i) % REGSET_ELT_BITS)) == 0
                          && ! dead_or_set_regno_p (insn, regno + i))
                        REG_NOTES (insn)
                          = gen_rtx (EXPR_LIST, REG_DEAD,
                                     gen_rtx (REG, word_mode, regno + i),
                                     REG_NOTES (insn));
                  }
              }
          }
      }
      return;

    case SET:
      {
        register rtx testreg = SET_DEST (x);
        int mark_dest = 0;

        /* If storing into MEM, don't show it as being used.  But do
           show the address as being used.  */
        if (GET_CODE (testreg) == MEM)
          {
#ifdef AUTO_INC_DEC
            if (final)
              find_auto_inc (needed, testreg, insn);
#endif
            mark_used_regs (needed, live, XEXP (testreg, 0), final, insn);
            mark_used_regs (needed, live, SET_SRC (x), final, insn);
            return;
          }
            
        /* Storing in STRICT_LOW_PART is like storing in a reg
           in that this SET might be dead, so ignore it in TESTREG.
           but in some other ways it is like using the reg.

           Storing in a SUBREG or a bit field is like storing the entire
           register in that if the register's value is not used
           then this SET is not needed.  */
        while (GET_CODE (testreg) == STRICT_LOW_PART
               || GET_CODE (testreg) == ZERO_EXTRACT
               || GET_CODE (testreg) == SIGN_EXTRACT
               || GET_CODE (testreg) == SUBREG)
          {
            /* Modifying a single register in an alternate mode
               does not use any of the old value.  But these other
               ways of storing in a register do use the old value.  */
            if (GET_CODE (testreg) == SUBREG
                && !(REG_SIZE (SUBREG_REG (testreg)) > REG_SIZE (testreg)))
              ;
            else
              mark_dest = 1;

            testreg = XEXP (testreg, 0);
          }

        /* If this is a store into a register,
           recursively scan the value being stored.  */

        if (GET_CODE (testreg) == REG
            && (regno = REGNO (testreg), regno != FRAME_POINTER_REGNUM)
#if FRAME_POINTER_REGNUM != ARG_POINTER_REGNUM
            && ! (regno == ARG_POINTER_REGNUM && fixed_regs[regno])
#endif
            && ! (regno < FIRST_PSEUDO_REGISTER && global_regs[regno]))
          {
            mark_used_regs (needed, live, SET_SRC (x), final, insn);
            if (mark_dest)
              mark_used_regs (needed, live, SET_DEST (x), final, insn);
            return;
          }
      }
      break;

    case RETURN:
      /* If exiting needs the right stack value, consider this insn as
         using the stack pointer.  In any event, consider it as using
         all global registers.  */

#ifdef EXIT_IGNORE_STACK
      if (! EXIT_IGNORE_STACK
          || (! FRAME_POINTER_REQUIRED && flag_omit_frame_pointer))
#endif
        live[STACK_POINTER_REGNUM / REGSET_ELT_BITS]
          |= 1 << (STACK_POINTER_REGNUM % REGSET_ELT_BITS);

      for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
        if (global_regs[i])
          live[i / REGSET_ELT_BITS] |= 1 << (i % REGSET_ELT_BITS);
      break;
    }

  /* Recursively scan the operands of this expression.  */

  {
    register char *fmt = GET_RTX_FORMAT (code);
    register int i;
    
    for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
      {
        if (fmt[i] == 'e')
          {
            /* Tail recursive case: save a function call level.  */
            if (i == 0)
              {
                x = XEXP (x, 0);
                goto retry;
              }
            mark_used_regs (needed, live, XEXP (x, i), final, insn);
          }
        else if (fmt[i] == 'E')
          {
            register int j;
            for (j = 0; j < XVECLEN (x, i); j++)
              mark_used_regs (needed, live, XVECEXP (x, i, j), final, insn);
          }
      }
  }
}
\f
#ifdef AUTO_INC_DEC

static int
try_pre_increment_1 (insn)
     rtx insn;
{
  /* Find the next use of this reg.  If in same basic block,
     make it do pre-increment or pre-decrement if appropriate.  */
  rtx x = PATTERN (insn);
  int amount = ((GET_CODE (SET_SRC (x)) == PLUS ? 1 : -1)
                * INTVAL (XEXP (SET_SRC (x), 1)));
  int regno = REGNO (SET_DEST (x));
  rtx y = reg_next_use[regno];
  if (y != 0
      && BLOCK_NUM (y) == BLOCK_NUM (insn)
      && try_pre_increment (y, SET_DEST (PATTERN (insn)),
                            amount))
    {
      /* We have found a suitable auto-increment
         and already changed insn Y to do it.
         So flush this increment-instruction.  */
      PUT_CODE (insn, NOTE);
      NOTE_LINE_NUMBER (insn) = NOTE_INSN_DELETED;
      NOTE_SOURCE_FILE (insn) = 0;
      /* Count a reference to this reg for the increment
         insn we are deleting.  When a reg is incremented.
         spilling it is worse, so we want to make that
         less likely.  */
      if (regno >= FIRST_PSEUDO_REGISTER)
        {
          reg_n_refs[regno] += loop_depth;
          reg_n_sets[regno]++;
        }
      return 1;
    }
  return 0;
}

/* Try to change INSN so that it does pre-increment or pre-decrement
   addressing on register REG in order to add AMOUNT to REG.
   AMOUNT is negative for pre-decrement.
   Returns 1 if the change could be made.
   This checks all about the validity of the result of modifying INSN.  */

static int
try_pre_increment (insn, reg, amount)
     rtx insn, reg;
     int amount;
{
  register rtx use;

  /* Nonzero if we can try to make a pre-increment or pre-decrement.
     For example, addl $4,r1; movl (r1),... can become movl +(r1),...  */
  int pre_ok = 0;
  /* Nonzero if we can try to make a post-increment or post-decrement.
     For example, addl $4,r1; movl -4(r1),... can become movl (r1)+,...
     It is possible for both PRE_OK and POST_OK to be nonzero if the machine
     supports both pre-inc and post-inc, or both pre-dec and post-dec.  */
  int post_ok = 0;

  /* Nonzero if the opportunity actually requires post-inc or post-dec.  */
  int do_post = 0;

  /* From the sign of increment, see which possibilities are conceivable
     on this target machine.  */
#ifdef HAVE_PRE_INCREMENT
  if (amount > 0)
    pre_ok = 1;
#endif
#ifdef HAVE_POST_INCREMENT
  if (amount > 0)
    post_ok = 1;
#endif

#ifdef HAVE_PRE_DECREMENT
  if (amount < 0)
    pre_ok = 1;
#endif
#ifdef HAVE_POST_DECREMENT
  if (amount < 0)
    post_ok = 1;
#endif

  if (! (pre_ok || post_ok))
    return 0;

  /* It is not safe to add a side effect to a jump insn
     because if the incremented register is spilled and must be reloaded
     there would be no way to store the incremented value back in memory.  */

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

  use = 0;
  if (pre_ok)
    use = find_use_as_address (PATTERN (insn), reg, 0);
  if (post_ok && (use == 0 || use == (rtx) 1))
    {
      use = find_use_as_address (PATTERN (insn), reg, -amount);
      do_post = 1;
    }

  if (use == 0 || use == (rtx) 1)
    return 0;

  if (GET_MODE_SIZE (GET_MODE (use)) != (amount > 0 ? amount : - amount))
    return 0;

  XEXP (use, 0) = gen_rtx (amount > 0
                           ? (do_post ? POST_INC : PRE_INC)
                           : (do_post ? POST_DEC : PRE_DEC),
                           Pmode, reg);

  /* Record that this insn now has an implicit side effect on X.  */
  REG_NOTES (insn) = gen_rtx (EXPR_LIST, REG_INC, reg, REG_NOTES (insn));
  return 1;
}

#endif /* AUTO_INC_DEC */
\f
/* Find the place in the rtx X where REG is used as a memory address.
   Return the MEM rtx that so uses it.
   If PLUSCONST is nonzero, search instead for a memory address equivalent to
   (plus REG (const_int PLUSCONST)).

   If such an address does not appear, return 0.
   If REG appears more than once, or is used other than in such an address,
   return (rtx)1.  */

static rtx
find_use_as_address (x, reg, plusconst)
     register rtx x;
     rtx reg;
     int plusconst;
{
  enum rtx_code code = GET_CODE (x);
  char *fmt = GET_RTX_FORMAT (code);
  register int i;
  register rtx value = 0;
  register rtx tem;

  if (code == MEM && XEXP (x, 0) == reg && plusconst == 0)
    return x;

  if (code == MEM && GET_CODE (XEXP (x, 0)) == PLUS
      && XEXP (XEXP (x, 0), 0) == reg
      && GET_CODE (XEXP (XEXP (x, 0), 1)) == CONST_INT
      && INTVAL (XEXP (XEXP (x, 0), 1)) == plusconst)
    return x;

  if (code == SIGN_EXTRACT || code == ZERO_EXTRACT)
    {
      /* If REG occurs inside a MEM used in a bit-field reference,
         that is unacceptable.  */
      if (find_use_as_address (XEXP (x, 0), reg, 0) != 0)
        return (rtx) 1;
    }

  if (x == reg)
    return (rtx) 1;

  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
    {
      if (fmt[i] == 'e')
        {
          tem = find_use_as_address (XEXP (x, i), reg, plusconst);
          if (value == 0)
            value = tem;
          else if (tem != 0)
            return (rtx) 1;
        }
      if (fmt[i] == 'E')
        {
          register int j;
          for (j = XVECLEN (x, i) - 1; j >= 0; j--)
            {
              tem = find_use_as_address (XVECEXP (x, i, j), reg, plusconst);
              if (value == 0)
                value = tem;
              else if (tem != 0)
                return (rtx) 1;
            }
        }
    }

  return value;
}
\f
/* Write information about registers and basic blocks into FILE.
   This is part of making a debugging dump.  */

void
dump_flow_info (file)
     FILE *file;
{
  register int i;
  static char *reg_class_names[] = REG_CLASS_NAMES;

  fprintf (file, "%d registers.\n", max_regno);

  for (i = FIRST_PSEUDO_REGISTER; i < max_regno; i++)
    if (reg_n_refs[i])
      {
        enum reg_class class;
        fprintf (file, "\nRegister %d used %d times across %d insns",
                 i, reg_n_refs[i], reg_live_length[i]);
        if (reg_basic_block[i] >= 0)
          fprintf (file, " in block %d", reg_basic_block[i]);
        if (reg_n_deaths[i] != 1)
          fprintf (file, "; dies in %d places", reg_n_deaths[i]);
        if (reg_n_calls_crossed[i] == 1)
          fprintf (file, "; crosses 1 call");
        else if (reg_n_calls_crossed[i])
          fprintf (file, "; crosses %d calls", reg_n_calls_crossed[i]);
        if (PSEUDO_REGNO_BYTES (i) != UNITS_PER_WORD)
          fprintf (file, "; %d bytes", PSEUDO_REGNO_BYTES (i));
        class = reg_preferred_class (i);
        if (class != GENERAL_REGS)
          {
            if (reg_preferred_or_nothing (i))
              fprintf (file, "; %s or none", reg_class_names[(int) class]);
            else
              fprintf (file, "; pref %s", reg_class_names[(int) class]);
          }
        if (REGNO_POINTER_FLAG (i))
          fprintf (file, "; pointer");
        fprintf (file, ".\n");
      }
  fprintf (file, "\n%d basic blocks.\n", n_basic_blocks);
  for (i = 0; i < n_basic_blocks; i++)
    {
      register rtx head, jump;
      register int regno;
      fprintf (file, "\nBasic block %d: first insn %d, last %d.\n",
               i,
               INSN_UID (basic_block_head[i]),
               INSN_UID (basic_block_end[i]));
      /* The control flow graph's storage is freed
         now when flow_analysis returns.
         Don't try to print it if it is gone.  */
      if (basic_block_drops_in)
        {
          fprintf (file, "Reached from blocks: ");
          head = basic_block_head[i];
          if (GET_CODE (head) == CODE_LABEL)
            for (jump = LABEL_REFS (head);
                 jump != head;
                 jump = LABEL_NEXTREF (jump))
              {
                register int from_block = BLOCK_NUM (CONTAINING_INSN (jump));
                fprintf (file, " %d", from_block);
              }
          if (basic_block_drops_in[i])
            fprintf (file, " previous");
        }
      fprintf (file, "\nRegisters live at start:");
      for (regno = 0; regno < max_regno; regno++)
        {
          register int offset = regno / REGSET_ELT_BITS;
          register int bit = 1 << (regno % REGSET_ELT_BITS);
          if (basic_block_live_at_start[i][offset] & bit)
              fprintf (file, " %d", regno);
        }
      fprintf (file, "\n");
    }
  fprintf (file, "\n");
}