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[gcc.git] / gcc / reg-stack.c

/* Register to Stack convert for GNU compiler.
   Copyright (C) 1990 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 pass converts stack-like registers from the "flat register
   file" model that gcc uses, to a stack convention that the 387 uses.

   * The form of the input:

   On input, the function consists of insn that have had their
   registers fully allocated to a set of "virtual" registers.  Note that
   the word "virtual" is used differently here than elsewhere in gcc: for
   each virtual stack reg, there is a hard reg, but the mapping between
   them is not known until this pass is run.  On output, hard register
   numbers have been substituted, and various pop and exchange insns have
   been emitted.  The hard register numbers and the virtual register
   numbers completely overlap - before this pass, all stack register
   numbers are virtual, and afterward they are all hard, with the
   exception of ASM_OPERANDS, which are discussed below.

   The virtual registers can be manipulated normally by gcc, and their
   semantics are the same as for normal registers.  After the hard
   register numbers are substituted, the semantics of an insn containing
   stack-like regs are not the same as for an insn with normal regs: for
   instance, it is not safe to delete an insn that appears to be a no-op
   move.  In general, no insn containing hard regs should be changed
   after this pass is done.

   * The form of the output:

   After this pass, hard register numbers represent the distance from
   the current top of stack to the desired register.  A reference to
   FIRST_STACK_REG references the top of stack, FIRST_STACK_REG + 1,
   represents the register just below that, and so forth.  Also, REG_DEAD
   notes indicate whether or not a stack register should be popped.

   A "swap" insn looks like a parallel of two patterns, where each
   pattern is a SET: one sets A to B, the other B to A.

   A "push" or "load" insn is a SET whose SET_DEST is FIRST_STACK_REG
   and whose SET_DEST is REG or MEM.  Any other SET_DEST, such as PLUS,
   will replace the existing stack top, not push a new value.

   A store insn is a SET whose SET_DEST is FIRST_STACK_REG, and whose
   SET_SRC is REG or MEM.

   The case where both the SET_SRC and SET_DEST FIRST_STACK_REG
   appears ambiguous.  As a special case, the presence of a REG_DEAD note
   for FIRST_STACK_REG differentiates between a load insn and a pop.

   If a REG_DEAD is present, the insn represents a "pop" that discards
   the top of the register stack.  If there is no REG_DEAD note, then the
   insn represents a "dup" or a push of the current top of stack onto the
   stack.

   * Methodology:

   Existing REG_DEAD and REG_UNUSED notes for stack registers are
   deleted and recreated from scratch.  REG_DEAD is never created for a
   SET_DEST, only REG_UNUSED.

   Before life analysis, the mode of each insn is set based on whether
   or not any stack registers are mentioned within that insn.  VOIDmode
   means that no regs are mentioned anyway, and QImode means that at
   least one pattern within the insn mentions stack registers.  This
   information is valid until after reg_to_stack returns, and is used
   from jump_optimize.

   * Limitations:

   Inline assembly isn't handled yet. */
\f
#include <stdio.h>
#include "config.h"
#include "tree.h"
#include "rtl.h"
#include "regs.h"
#include "hard-reg-set.h"
#include "flags.h"

#ifdef STACK_REGS

#define REG_STACK_SIZE (LAST_STACK_REG - FIRST_STACK_REG + 1)

/* True if the current function returns a real value. */
static int current_function_returns_real;

/* This is the basic stack record.  TOP is an index into REG[] such
   that REG[TOP] is the top of stack.  If TOP is -1 the stack is empty.

   If TOP is -2 the stack is not yet initialized: reg_set indicates
   which registers are live.  Stack initialization consists of placing
   each live reg in array `reg' and setting `top' appropriately. */

typedef struct stack_def
{
  int top;                      /* index to top stack element */
  HARD_REG_SET reg_set;         /* set of live registers */
  char reg[REG_STACK_SIZE];     /* register - stack mapping */
} *stack;

/* highest instruction uid */
static int max_uid = 0;

/* Number of basic blocks in the current function.  */
static int blocks;

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

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

/* Element N is nonzero if control can drop into basic block N */
static char *block_drops_in;

/* Element N says all about the stack at entry block N */
static stack block_stack_in;

/* Element N says all about the stack life at the end of block N */
static HARD_REG_SET *block_out_reg_set;

/* This is where the BLOCK_NUM values are really stored.  This is set
   up by find_blocks and used there and in life_analysis.  It can be used
   later, but only to look up an insn that is the head or tail of some
   block.  life_analysis and the stack register conversion process can
   add insns within a block. */
static short *block_number;

/* This is the register file for all register after conversion */
static rtx FP_mode_reg[FIRST_PSEUDO_REGISTER][(int) MAX_MACHINE_MODE];

/* ??? set of register to delete after ASM_OPERAND */
HARD_REG_SET asm_regs;

/* Get the basic block number of an insn.  See note at block_number
   definition are validity of this information. */

#define BLOCK_NUM(INSN)  \
  (((INSN_UID (INSN) > max_uid) \
    ? (short *)(abort() , 0)            \
    : block_number)[INSN_UID (INSN)])

extern rtx gen_jump ();
extern rtx gen_movdf ();
extern rtx find_regno_note ();
extern rtx emit_jump_insn_before ();
extern rtx emit_label_after ();

/* Forward declarations */

static void find_blocks ();
static void stack_reg_life_analysis ();
static void convert_regs ();
static void dump_stack_info ();
static void fatal_for_asm ();
\f
\f
/* Return non-zero if any stack register is mentioned somewhere within
   PAT. */

static int
stack_regs_mentioned_p (pat)
     register rtx pat;
{
  register char *fmt;
  register int i;

  if (STACK_REG_P (pat))
    return 1;

  fmt = GET_RTX_FORMAT (GET_CODE (pat));
  for (i = GET_RTX_LENGTH (GET_CODE (pat)) - 1; i >= 0; i--)
    {
      if (fmt[i] == 'E')
        {
          register int j;

          for (j = XVECLEN (pat, i) - 1; j >= 0; j--)
            if (stack_regs_mentioned_p (XVECEXP (pat, i, j)))
              return 1;
        }
      else if (fmt[i] == 'e' && stack_regs_mentioned_p (XEXP (pat, i)))
        return 1;
    }

  return 0;
}
\f
/* Convert register usage from "flat" register file usage to a "stack
   register file.  FIRST is the first insn in the function, FILE is the
   dump file, if used.

   First compute the beginning and end of each basic block.  Do a
   register life analysis on the stack registers, recording the result
   for the head and tail of each basic block.  The convert each insn one
   by one.  Run a last jump_optimize() pass, if optimizing, to eliminate
   any cross-jumping created when the converter inserts pop insns.*/

void
reg_to_stack (first, file)
     rtx first;
     FILE *file;
{
  register rtx insn;
  register int i;
  int stack_reg_seen = 0;
  enum machine_mode mode;

  current_function_returns_real
    = TREE_CODE (TREE_TYPE (DECL_RESULT (current_function_decl))) == REAL_TYPE;

  for (mode = GET_CLASS_NARROWEST_MODE (MODE_FLOAT); mode != VOIDmode;
       mode = GET_MODE_WIDER_MODE (mode))
    for (i = 0; i < FIRST_PSEUDO_REGISTER; i++)
      FP_mode_reg[i][(int) mode] = gen_rtx (REG, mode, i);

  /* Count the basic blocks.  Also find maximum insn uid.  */
  {
    register RTX_CODE prev_code = JUMP_INSN;
    register RTX_CODE code;

    max_uid = 0;
    blocks = 0;
    for (insn = first; insn; insn = NEXT_INSN (insn))
      {
        /* Note that this loop must select the same block boundaries
           as code in find_blocks. */

        if (INSN_UID (insn) > max_uid)
          max_uid = INSN_UID (insn);

        code = GET_CODE (insn);

        if (code == CODE_LABEL
            || (prev_code != INSN
                && prev_code != CALL_INSN
                && prev_code != CODE_LABEL
                && (code == INSN || code == CALL_INSN || code == JUMP_INSN)))
          blocks++;

        /* Remember whether or not this insn mentions an FP regs.
           Check JUMP_INSNs too, in case someone creates a funny PARALLEL. */

        if ((GET_CODE (insn) == INSN || GET_CODE (insn) == CALL_INSN
             || GET_CODE (insn) == JUMP_INSN)
            && stack_regs_mentioned_p (PATTERN (insn)))
          {
            stack_reg_seen = 1;
            PUT_MODE (insn, QImode);
          }
        else
          PUT_MODE (insn, VOIDmode);

        if (code != NOTE)
          prev_code = code;
      }
  }

  /* If no stack register reference exists in this insn, there isn't
     anything to convert.  */

  if (! stack_reg_seen)
    return;

  /* If there are stack registers, there must be at least one block. */

  if (! blocks)
    abort ();

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

  block_begin = (rtx *) alloca (blocks * sizeof (rtx));
  block_end = (rtx *) alloca (blocks * sizeof (rtx));
  block_drops_in = (char *) alloca (blocks);

  block_stack_in = (stack) alloca (blocks * sizeof (struct stack_def));
  block_out_reg_set = (HARD_REG_SET *) alloca (blocks * sizeof (HARD_REG_SET));
  bzero (block_stack_in, blocks * sizeof (struct stack_def));
  bzero (block_out_reg_set, blocks * sizeof (HARD_REG_SET));

  block_number = (short *) alloca ((max_uid + 1) * sizeof (short));

  find_blocks (first);
  stack_reg_life_analysis (first);

  /* Dump the life analysis debug information before jump
     optimization, as that will destroy the LABEL_REFS we keep the
     information in. */

  if (file)
    dump_stack_info (file);

  convert_regs ();

  if (optimize)
    jump_optimize (first, 2, 0, 0);
}
\f
/* Check PAT, which is in INSN, for LABEL_REFs.  Add INSN to the
   label's chain of references, and note which insn contains each
   reference. */

static void
record_label_references (insn, pat)
     rtx insn, pat;
{
  register enum rtx_code code = GET_CODE (pat);
  register int i;
  register char *fmt;

  if (code == LABEL_REF)
    {
      register rtx label = XEXP (pat, 0);
      register rtx ref;

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

      /* Don't make a duplicate in the code_label's chain. */

      for (ref = LABEL_REFS (label); ref != label; ref = LABEL_NEXTREF (ref))
        if (CONTAINING_INSN (ref) == insn)
          return;

      CONTAINING_INSN (pat) = insn;
      LABEL_NEXTREF (pat) = LABEL_REFS (label);
      LABEL_REFS (label) = pat;

      return;
    }

  fmt = GET_RTX_FORMAT (code);
  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
    {
      if (fmt[i] == 'e')
        record_label_references (insn, XEXP (pat, i));
      if (fmt[i] == 'E')
        {
          register int j;
          for (j = 0; j < XVECLEN (pat, i); j++)
            record_label_references (insn, XVECEXP (pat, i, j));
        }
    }
}
\f
/* Return a pointer to the REG expression within PAT.  If PAT is not a
   REG, possible enclosed by a conversion rtx, return the inner part of
   PAT that stopped the search. */

static rtx *
get_true_reg (pat)
     rtx *pat;
{
  while (GET_CODE (*pat) == SUBREG
         || GET_CODE (*pat) == FLOAT
         || GET_CODE (*pat) == FIX
         || GET_CODE (*pat) == FLOAT_EXTEND
         || GET_CODE (*pat) == FLOAT_TRUNCATE)
    pat = & XEXP (*pat, 0);

  return pat;
}

/* If REG is a stack register that is marked dead in REGSTACK, then
   record that it is now live. If REG is not DEST, add a death note to
   INSN if there isn't one already.  If DEST is not a reg, it is safe to
   assume that it does not mention a reg anywhere within. */

static void
record_note_if_dead (insn, regstack, reg, dest)
     rtx insn;
     stack regstack;
     rtx reg, dest;
{
  reg = * get_true_reg (& reg);

  if (STACK_REG_P (reg))
    {
      if (! TEST_HARD_REG_BIT (regstack->reg_set, REGNO (reg)))
        {
          if ((! REG_P (dest) || REGNO (dest) != REGNO (reg))
              && ! find_regno_note (insn, REG_DEAD, REGNO (reg)))
            REG_NOTES (insn) = gen_rtx (EXPR_LIST,
                                        REG_DEAD, reg, REG_NOTES (insn));

          SET_HARD_REG_BIT (regstack->reg_set, REGNO (reg));
        }
    }
  else
    if (stack_regs_mentioned_p (reg))
      abort ();
}
\f
/* Scan PAT, which is part of INSN, and record the life & death of
   stack registers in REGSTACK.  If a register was dead, but is an input
   operand in this insn, then mark the register live and record a death
   note.

   If a register is dead after this insn, but is an output operand in
   this insn, record a REG_UNUSED note.

   This function does not know about SET_DESTs that are both input and
   output (such as ZERO_EXTRACT) - this cannot happen on a 387. */

static void
record_reg_life_pat (insn, regstack, pat)
     rtx insn;
     stack regstack;
     rtx pat;
{
  rtx src, dest;

  if (GET_CODE (pat) == CLOBBER
      && GET_CODE (PATTERN (insn)) == PARALLEL
      && GET_CODE (SET_SRC (XVECEXP (PATTERN (insn), 0, 0))) == ASM_OPERANDS)
    {
      if (STACK_REG_P (XEXP (pat, 0)))
        abort ();
      return;
    }

  if (GET_CODE (pat) != SET)
    return;

  dest = * get_true_reg (& SET_DEST (pat));

  /* The destination is dead before this insn.  If the destination is
     not used after this insn, record this with REG_UNUSED. */

  if (STACK_REG_P (dest))
    {
      /* ??? This check is unnecessary. */

      if (find_regno_note (insn, REG_UNUSED, REGNO (dest)))
        abort ();

      if (! TEST_HARD_REG_BIT (regstack->reg_set, REGNO (dest)))
        REG_NOTES (insn) = gen_rtx (EXPR_LIST, REG_UNUSED, dest,
                                    REG_NOTES (insn));

      CLEAR_HARD_REG_BIT (regstack->reg_set, REGNO (dest));
    }
  else
    if (dest != cc0_rtx && stack_regs_mentioned_p (dest))
      abort ();

  src = * get_true_reg (& SET_SRC (pat));

  switch (GET_CODE (src))
    {
      /* ??? get_true_reg will make some of these cases redundant. */

    case PLUS:
    case MINUS:
    case MULT:
    case DIV:
    case COMPARE:
      record_note_if_dead (insn, regstack, XEXP (src, 0), dest);
      record_note_if_dead (insn, regstack, XEXP (src, 1), dest);
      break;

    case ABS:
    case NEG:
    case SQRT:
    case FLOAT_EXTEND:
    case FLOAT_TRUNCATE:
    case FLOAT:
    case UNSIGNED_FLOAT:
      record_note_if_dead (insn, regstack, XEXP (src, 0), dest);
      break;

    case UNSIGNED_FIX:
    case FIX:
      src = XEXP (src, 0);
      if (GET_CODE (src) == FIX)
        record_note_if_dead (insn, regstack, XEXP (src, 0), dest);
      else
        record_note_if_dead (insn, regstack, src, dest);
      break;

    case ASM_OPERANDS:
      {
        register int j;

        /* ??? This needs much improvement */

        if (stack_regs_mentioned_p (pat))
          abort ();

        for (j = 0; j < XVECLEN (src, 3); j++)
          record_note_if_dead (insn, regstack, XVECEXP (src, 3, j), dest);
      }
      break;

    case REG:
      record_note_if_dead (insn, regstack, src, dest);
      break;

    default:
      /* If a stack register appears in the src RTL, it is a bug, and
         code should be added above to handle it. */

      if (stack_regs_mentioned_p (src))
        abort ();
    }
}
\f
/* Scan INSN, which is in BLOCK, and record the life & death of stack
   registers in REGSTACK.  This function is called to process insns from
   the last insn in a block to the first.  The actual scanning is done in
   record_reg_life_pat.

   If a register is live after a CALL_INSN, but is not a value return
   register for that CALL_INSN, then code is emitted to initialize that
   register.  The block_end[] data is kept accurate.

   Existing death and unset notes for stack registers are deleted
   before processing the insn. */

static void
record_reg_life (insn, block, regstack)
     rtx insn;
     int block;
     stack regstack;
{
  rtx note, *note_link;

  if ((GET_CODE (insn) != INSN && GET_CODE (insn) != CALL_INSN)
      || INSN_DELETED_P (insn))
    return;

  /* Strip death notes for stack regs from this insn */

  note_link = &REG_NOTES(insn);
  for (note = *note_link; note; note = XEXP (note, 1))
    if (STACK_REG_P (XEXP (note, 0))
        && (REG_NOTE_KIND (note) == REG_DEAD
            || REG_NOTE_KIND (note) == REG_UNUSED))
      *note_link = XEXP (note, 1);
    else
      note_link = &XEXP (note, 1);

  /* Process all patterns in the insn. */

  if (GET_CODE (PATTERN (insn)) == PARALLEL)
    {
      register int i;

      for (i = 0; i < XVECLEN (PATTERN (insn), 0); i++)
        record_reg_life_pat (insn, regstack, XVECEXP (PATTERN (insn), 0, i));
    }
  else if (GET_MODE (insn) == QImode)
    record_reg_life_pat (insn, regstack, PATTERN (insn));

  /* There might be a reg that is live after a function call.
     Initialize it to zero so that the program does not crash.  See comment
     towards the end of stack_reg_life_analysis(). */

  if (GET_CODE (insn) == CALL_INSN)
    {
      int reg = FIRST_FLOAT_REG;

      /* If a stack reg is mentioned in a CALL_INSN, it must be as the
         return value; conversely, if a float is returned, a stack reg
         must be mentioned. */

      if (stack_regs_mentioned_p (PATTERN (insn)))
        reg++;

      for (; reg <= LAST_STACK_REG; reg++)
        if (TEST_HARD_REG_BIT (regstack->reg_set, reg))
          {
            rtx init, pat;

            /* The insn will use virtual register numbers, and so
               convert_regs is expected to process these.  But BLOCK_NUM
               cannot be used on these insns, because they do not appear in
               block_number[]. */

            pat = gen_rtx (SET, VOIDmode, FP_mode_reg[reg][(int) DFmode],
                           CONST0_RTX (DFmode));
            init = emit_insn_after (pat, insn);
            PUT_MODE (init, QImode);

            CLEAR_HARD_REG_BIT (regstack->reg_set, reg);

            /* If the CALL_INSN was the end of a block, move the
               block_end to point to the new insn. */

            if (block_end[block] == insn)
              block_end[block] = init;
          }

      /* Some regs do not survive a CALL */

      AND_COMPL_HARD_REG_SET (regstack->reg_set, call_used_reg_set);
    }
}
\f
/* Find all basic blocks of the function, which starts with FIRST.
   For each JUMP_INSN, build the chain of LABEL_REFS on each CODE_LABEL. */

static void
find_blocks (first)
     rtx first;
{
  register rtx insn;
  register int block;
  register RTX_CODE prev_code = BARRIER;
  register RTX_CODE code;

  /* Record where all the blocks start and end.
     Record which basic blocks control can drop in to. */

  block = -1;
  for (insn = first; insn; insn = NEXT_INSN (insn))
    {
      /* Note that this loop must select the same block boundaries
         as code in reg_to_stack. */

      code = GET_CODE (insn);

      if (code == CODE_LABEL
          || (prev_code != INSN
              && prev_code != CALL_INSN
              && prev_code != CODE_LABEL
              && (code == INSN || code == CALL_INSN || code == JUMP_INSN)))
        {
          block_begin[++block] = insn;
          block_end[block] = insn;
          block_drops_in[block] = prev_code != BARRIER;
        }
      else if (code == INSN || code == CALL_INSN || code == JUMP_INSN)
        block_end[block] = insn;

      BLOCK_NUM (insn) = block;

      if (code == CODE_LABEL)
        LABEL_REFS (insn) = insn; /* delete old chain */

      if (code != NOTE)
        prev_code = code;
    }

  if (block + 1 != blocks)
    abort ();

  /* generate all label references to the correspondending jump insn */
  for (block = 0; block < blocks; block++)
    {
      insn = block_end[block];

      if (GET_CODE (insn) == JUMP_INSN)
        record_label_references (insn, PATTERN (insn));
    }
}
\f
/* Determine the which registers are live at the start of each basic
   block of the function whose first insn is FIRST.

   First, if the function returns a real_type, mark the function
   return type as live at each return point, as the RTL may not give any
   hint that the register is live.

   Then, start with the last block and work back to the first block.
   Similarly, work backwards within each block, insn by insn, recording
   which regs are die and which are used (and therefore live) in the
   hard reg set of block_stack_in[].

   After processing each basic block, if there is a label at the start
   of the block, propagate the live registers to all jumps to this block.

   As a special case, if there are regs live in this block, that are
   not live in a block containing a jump to this label, and the block
   containing the jump has already been processed, we must propagate this
   block's entry register life back to the block containing the jump, and
   restart life analysis from there.

   In the worst case, this function may traverse the insns
   REG_STACK_SIZE times.  This is necessary, since a jump towards the end
   of the insns may not know that a reg is live at a target that is early
   in the insns.  So we back up and start over with the new reg live.

   If there are registers that are live at the start of the function,
   insns are emitted to initialize these registers.  Something similar is
   done after CALL_INSNs in record_reg_life. */

static void
stack_reg_life_analysis (first)
     rtx first;
{
  int reg, block;
  struct stack_def regstack;

  if (current_function_returns_real)
    {
      /* Find all RETURN insns and mark them. */

      for (block = blocks - 1; block >= 0; block--)
        if (GET_CODE (block_end[block]) == JUMP_INSN
            && GET_CODE (PATTERN (block_end[block])) == RETURN)
          SET_HARD_REG_BIT (block_out_reg_set[block], FIRST_STACK_REG);

      /* Mark of the end of last block if we "fall off" the end of the
         function into the epilogue. */

      if (GET_CODE (block_end[blocks-1]) != JUMP_INSN
          || GET_CODE (PATTERN (block_end[blocks-1])) == RETURN)
        SET_HARD_REG_BIT (block_out_reg_set[blocks-1], FIRST_STACK_REG);
    }

  /* now scan all blocks backward for stack register use */

  block = blocks - 1;
  while (block >= 0)
    {
      register rtx insn, prev;

      /* current register status at last instruction */

      COPY_HARD_REG_SET (regstack.reg_set, block_out_reg_set[block]);

      prev = block_end[block];
      do
        {
          insn = prev;
          prev = PREV_INSN (insn);

          /* If the insn is a CALL_INSN, we need to ensure that
             everything dies.  But otherwise don't process unless there
             are some stack regs present. */

          if (GET_MODE (insn) == QImode || GET_CODE (insn) == CALL_INSN)
            record_reg_life (insn, block, &regstack);

        } while (insn != block_begin[block]);

      /* Set the state at the start of the block.  Mark that no
         register mapping information known yet. */

      COPY_HARD_REG_SET (block_stack_in[block].reg_set, regstack.reg_set);
      block_stack_in[block].top = -2;

      /* If there is a label, propagate our register life to all jumps
         to this label. */

      if (GET_CODE (insn) == CODE_LABEL)
        {
          register rtx label;
          int must_restart = 0;

          for (label = LABEL_REFS (insn); label != insn;
               label = LABEL_NEXTREF (label))
            {
              int jump_block = BLOCK_NUM (CONTAINING_INSN (label));

              if (jump_block < block)
                IOR_HARD_REG_SET (block_out_reg_set[jump_block],
                                  block_stack_in[block].reg_set);
              else
                {
                  /* The block containing the jump has already been
                     processed.  If there are registers that were not known
                     to be live then, but are live now, we must back up
                     and restart life analysis from that point with the new
                     life information. */

                  GO_IF_HARD_REG_SUBSET (block_stack_in[block].reg_set,
                                         block_out_reg_set[jump_block],
                                         win);

                  IOR_HARD_REG_SET (block_out_reg_set[jump_block],
                                    block_stack_in[block].reg_set);

                  block = jump_block;
                  must_restart = 1;

                win:
                  ;
                }
            }
          if (must_restart)
            continue;
        }

      if (block_drops_in[block])
        IOR_HARD_REG_SET (block_out_reg_set[block-1],
                          block_stack_in[block].reg_set);

      block -= 1;
    }

  {
    /* If any reg is live at the start of the first block of a
       function, then we must guarantee that the reg holds some value by
       generating our own "load" of that register.  Otherwise a 387 would
       fault trying to access an empty register. */

    HARD_REG_SET empty_regs;
    CLEAR_HARD_REG_SET (empty_regs);
    GO_IF_HARD_REG_SUBSET (block_stack_in[0].reg_set, empty_regs,
                           no_live_regs);
  }

  /* Load zero into each live register.  The fact that a register
     appears live at the function start does not necessarily imply an error
     in the user program: it merely means that we could not determine that
     there wasn't such an error, just as -Wunused sometimes gives
     "incorrect" warnings.  In those cases, these initializations will do
     no harm.

     Note that we are inserting virtual register references here:
     these insns must be processed by convert_regs later.  Also, these
     insns will not be in block_number, so BLOCK_NUM() will fail for them. */

  for (reg = LAST_STACK_REG; reg >= FIRST_STACK_REG; reg--)
    if (TEST_HARD_REG_BIT (block_stack_in[0].reg_set, reg))
      {
        rtx init_rtx;

        init_rtx = gen_rtx (SET, VOIDmode, FP_mode_reg[reg][(int) DFmode],
                            CONST0_RTX (DFmode));
        block_begin[0] = emit_insn_after (init_rtx, first);
        PUT_MODE (block_begin[0], QImode);

        CLEAR_HARD_REG_BIT (block_stack_in[0].reg_set, reg);
      }

 no_live_regs:
  ;
}
\f
/*****************************************************************************
   This section deals with stack register substition, and forms the second
   pass over the RTL.
 *****************************************************************************/

/* Replace REG, which is a pointer to a stack reg RTX, with an RTX for
   the desired hard REGNO. */

static void
replace_reg (reg, regno)
     rtx *reg;
     int regno;
{
  if (regno < FIRST_STACK_REG || regno > LAST_STACK_REG
      || ! STACK_REG_P (*reg))
    abort ();

  if (GET_MODE_CLASS (GET_MODE (*reg)) != MODE_FLOAT)
    abort;

  *reg = FP_mode_reg[regno][(int) GET_MODE (*reg)];
}

/* Remove a note of type NOTE, which must be found, for register
   number REGNO from INSN.  Remove only one such note. */

static void
remove_regno_note (insn, note, regno)
     rtx insn;
     enum reg_note note;
     int regno;
{
  register rtx *note_link, this;

  note_link = &REG_NOTES(insn);
  for (this = *note_link; this; this = XEXP (this, 1))
    if (REG_NOTE_KIND (this) == note
        && REG_P (XEXP (this, 0)) && REGNO (XEXP (this, 0)) == regno)
      {
        *note_link = XEXP (this, 1);
        return;
      }
    else
      note_link = &XEXP (this, 1);

  abort ();
}

/* Find the hard register number of virtual register REG in REGSTACK.
   The hard register number is relative to the top of the stack.  -1 is
   returned if the register is not found. */

static int
get_hard_regnum (regstack, reg)
     stack regstack;
     rtx reg;
{
  int i;

  if (! STACK_REG_P (reg))
    abort ();

  for (i = regstack->top; i >= 0; i--)
    if (regstack->reg[i] == REGNO (reg))
      break;

  return i >= 0 ? (FIRST_STACK_REG + regstack->top - i) : -1;
}

/* Delete INSN from the RTL.  Mark the insn, but don't remove it from
   the chain of insns.  Doing so could confuse block_begin and block_end
   if this were the only insn in the block. */

static void
delete_insn_for_stacker (insn)
     rtx insn;
{
  PUT_CODE (insn, NOTE);
  NOTE_LINE_NUMBER (insn) = NOTE_INSN_DELETED;
  NOTE_SOURCE_FILE (insn) = 0;
  INSN_DELETED_P (insn) = 1;
}
\f
/* Emit an insn to pop virtual register REG before or after INSN.
   REGSTACK is the stack state after INSN and is updated to reflect this
   pop.  WHEN is either emit_insn_before or emit_insn_after.  A pop insn
   is represented as a SET whose destination is the register to be popped
   and source is the top of stack.  A death note for the top of stack
   cases the movdf pattern to pop. */

static rtx
emit_pop_insn (insn, regstack, reg, when)
     rtx insn;
     stack regstack;
     rtx reg;
     rtx (*when)();
{
  rtx pop_insn, pop_rtx;
  int hard_regno;

  hard_regno = get_hard_regnum (regstack, reg);

  if (hard_regno < FIRST_STACK_REG)
    abort ();

  pop_rtx = gen_rtx (SET, VOIDmode, FP_mode_reg[hard_regno][(int) DFmode],
                     FP_mode_reg[FIRST_STACK_REG][(int) DFmode]);

  pop_insn = (*when) (pop_rtx, insn);
  PUT_MODE (pop_insn, VOIDmode);

  REG_NOTES (pop_insn) = gen_rtx (EXPR_LIST, REG_DEAD,
                                  FP_mode_reg[FIRST_STACK_REG][(int) DFmode],
                                  REG_NOTES (pop_insn));

  regstack->reg[regstack->top - (hard_regno - FIRST_STACK_REG)]
    = regstack->reg[regstack->top];
  regstack->top -= 1;
  CLEAR_HARD_REG_BIT (regstack->reg_set, REGNO (reg));

  return pop_insn;
}
\f
/* Emit an insn before or after INSN to swap virtual register REG with the
   top of stack.  WHEN should be `emit_insn_before' or `emit_insn_before'
   REGSTACK is the stack state before the swap, and is updated to reflect
   the swap.  A swap insn is represented as a PARALLEL of two patterns:
   each pattern moves one reg to the other.

   If REG is already at the top of the stack, no insn is emitted. */

static void
emit_hard_swap_insn (insn, regstack, hard_regno, when)
     rtx insn;
     stack regstack;
     int hard_regno;
     rtx (*when)();
{
  rtx gen_swapdf();
  rtx swap_rtx, swap_insn;
  int tmp, other;

  if (hard_regno == FIRST_STACK_REG)
    return;

  swap_rtx = gen_swapdf (FP_mode_reg[hard_regno][(int) DFmode],
                         FP_mode_reg[FIRST_STACK_REG][(int) DFmode]);
  swap_insn = (*when) (swap_rtx, insn);
  PUT_MODE (swap_insn, VOIDmode);

  other = regstack->top - (hard_regno - FIRST_STACK_REG);

  tmp = regstack->reg[other];
  regstack->reg[other] = regstack->reg[regstack->top];
  regstack->reg[regstack->top] = tmp;
}

/* Emit an insn before or after INSN to swap virtual register REG with the
   top of stack.  See comments before emit_hard_swap_insn. */

static void
emit_swap_insn (insn, regstack, reg, when)
     rtx insn;
     stack regstack;
     rtx reg;
     rtx (*when)();
{
  int hard_regno;

  hard_regno = get_hard_regnum (regstack, reg);

  emit_hard_swap_insn (insn, regstack, hard_regno, when);
}
\f
/* Handle a move to or from a stack register in PAT, which is in INSN.
   REGSTACK is the current stack. */

static void
move_for_stack_reg (insn, regstack, pat)
     rtx insn;
     stack regstack;
     rtx pat;
{
  rtx *src =  get_true_reg (&SET_SRC (pat));
  rtx *dest = get_true_reg (&SET_DEST (pat));
  rtx note;

  if (STACK_REG_P (*src) && STACK_REG_P (*dest))
    {
      /* Write from one stack reg to another.  If SRC dies here, then
         just change the register mapping and delete the insn. */

      note = find_regno_note (insn, REG_DEAD, REGNO (*src));
      if (note)
        {
          int i;

          /* If this is a no-op move, there must not be a REG_DEAD note. */
          if (REGNO (*src) == REGNO (*dest))
            abort ();

          for (i = regstack->top; i >= 0; i--)
            if (regstack->reg[i] == REGNO (*src))
              break;

          /* The source must be live, and the dest must be dead. */
          if (i < 0 || get_hard_regnum (regstack, *dest) >= FIRST_STACK_REG)
            abort ();

          /* It is possible that the dest is unused after this insn.
             If so, just pop the src. */

          if (find_regno_note (insn, REG_UNUSED, REGNO (*dest)))
            {
              emit_pop_insn (insn, regstack, *src, emit_insn_after);

              delete_insn_for_stacker (insn);
              return;
            }

          regstack->reg[i] = REGNO (*dest);

          SET_HARD_REG_BIT (regstack->reg_set, REGNO (*dest));
          CLEAR_HARD_REG_BIT (regstack->reg_set, REGNO (*src));

          delete_insn_for_stacker (insn);

          return;
        }

      /* The source reg does not die. */

      /* If this appears to be a no-op move, delete it, or else it
         will confuse the machine description output patterns. But if
         it is REG_UNUSED, we must pop the reg now, as per-insn processing
         for REG_UNUSED will not work for deleted insns. */

      if (REGNO (*src) == REGNO (*dest))
        {
          if (find_regno_note (insn, REG_UNUSED, REGNO (*dest)))
            emit_pop_insn (insn, regstack, *dest, emit_insn_after);

          delete_insn_for_stacker (insn);
          return;
        }

      /* The destination ought to be dead */
      if (get_hard_regnum (regstack, *dest) >= FIRST_STACK_REG)
        abort ();

      replace_reg (src, get_hard_regnum (regstack, *src));

      regstack->reg[++regstack->top] = REGNO (*dest);
      SET_HARD_REG_BIT (regstack->reg_set, REGNO (*dest));
      replace_reg (dest, FIRST_STACK_REG);
    }
  else if (STACK_REG_P (*src))
    {
      /* Save from a stack reg to MEM, or possibly integer reg.  Since
         only top of stack may be saved, emit an exchange first if
         needs be. */

      emit_swap_insn (insn, regstack, *src, emit_insn_before);

      note = find_regno_note (insn, REG_DEAD, REGNO (*src));
      if (note)
        {
          replace_reg (&XEXP (note, 0), FIRST_STACK_REG);
          regstack->top--;
          CLEAR_HARD_REG_BIT (regstack->reg_set, REGNO (*src));
        }

      replace_reg (src, FIRST_STACK_REG);
    }
  else if (STACK_REG_P (*dest))
    {
      /* Load from MEM, or possibly integer REG or constant, into the
         stack regs.  The actual target is always the top of the
         stack. The stack mapping is changed to reflect that DEST is
         now at top of stack.  */

      /* The destination ought to be dead */
      if (get_hard_regnum (regstack, *dest) >= FIRST_STACK_REG)
        abort ();

      if (regstack->top >= REG_STACK_SIZE)
        abort ();

      regstack->reg[++regstack->top] = REGNO (*dest);
      SET_HARD_REG_BIT (regstack->reg_set, REGNO (*dest));
      replace_reg (dest, FIRST_STACK_REG);
    }
  else
    abort ();
}
\f
/* Handle a comparison.  Special care needs to be taken to avoid
   causing comparisons that a 387 cannot do correctly, such as EQ.

   Also, a pop insn may need to be emitted.  The 387 does have an
   `fcompp' insn that can pop two regs, but it is sometimes too expensive
   to do this - a `fcomp' followed by a `fstpl %st(0)' may be easier to
   set up. */

static void
compare_for_stack_reg (insn, regstack, pat)
     rtx insn;
     stack regstack;
     rtx pat;
{
  rtx *src1, *src2;
  rtx src1_note, src2_note;

  src1 = get_true_reg (&XEXP (SET_SRC (pat), 0));
  src2 = get_true_reg (&XEXP (SET_SRC (pat), 1));

  /* The first argument must always be a stack reg. */
  /* ??? why? */

  if (! STACK_REG_P (*src1))
    abort ();

  /* We will fix any death note later. */

  src1_note = find_regno_note (insn, REG_DEAD, REGNO (*src1));

  if (STACK_REG_P (*src2))
    src2_note = find_regno_note (insn, REG_DEAD, REGNO (*src2));
  else
    src2_note = 0;

  emit_swap_insn (insn, regstack, *src1, emit_insn_before);

  replace_reg (src1, FIRST_STACK_REG);

  if (STACK_REG_P (*src2))
    replace_reg (src2, get_hard_regnum (regstack, *src2));

  if (src1_note)
    {
      CLEAR_HARD_REG_BIT (regstack->reg_set, REGNO (XEXP (src1_note, 0)));
      replace_reg (&XEXP (src1_note, 0), FIRST_STACK_REG);
      regstack->top--;
    }

  /* If the second operand dies, handle that.  But if the operands are
     the same stack register, don't bother, because only one death is
     needed, and it was just handled. */

  if (src2_note
      && ! (STACK_REG_P (*src1)
            && STACK_REG_P (*src2)
            && REGNO (*src1) == REGNO (*src2)))
    {
      /* As a special case, two regs may die in this insn if src2 is
         next to top of stack and the top of stack also dies.  Since
         we have already popped src1, "next to top of stack" is really
         at top (FIRST_STACK_REG) now. */

      if (get_hard_regnum (regstack, XEXP (src2_note, 0)) == FIRST_STACK_REG
          && src1_note)
        {
          CLEAR_HARD_REG_BIT (regstack->reg_set, REGNO (XEXP (src2_note, 0)));
          replace_reg (&XEXP (src2_note, 0), FIRST_STACK_REG + 1);
          regstack->top--;
        }
      else
        {
          /* The 386 can only represent death of the first operand in
             the case handled above.  In all other cases, emit a separate
             pop and remove the death note from here. */

          remove_regno_note (insn, REG_DEAD, REGNO (XEXP (src2_note, 0)));

          emit_pop_insn (insn, regstack, XEXP (src2_note, 0),
                         emit_insn_after);
        }
    }
}
\f
/* Substitute new registers in PAT, which is part of INSN.  REGSTACK
   is the current register layout. */

static void
subst_stack_regs_pat (insn, regstack, pat)
     rtx insn;
     stack regstack;
     rtx pat;
{
  rtx *dest, *src;
  rtx *src1 = 0, *src2;
  rtx src1_note, src2_note;

  if (GET_CODE (pat) != SET)
    return;

  dest = get_true_reg (&SET_DEST (pat));
  src  = get_true_reg (&SET_SRC (pat));

  /* See if this is a `movM' pattern, and handle elsewhere if so. */

  if (*dest != cc0_rtx
      && (STACK_REG_P (*src)
          || (STACK_REG_P (*dest)
              && (GET_CODE (*src) == REG || GET_CODE (*src) == MEM
                  || GET_CODE (*src) == CONST_DOUBLE))))
    move_for_stack_reg (insn, regstack, pat);
  else
    switch (GET_CODE (SET_SRC (pat)))
      {
      case COMPARE:
        compare_for_stack_reg (insn, regstack, pat);
        break;

      case CALL:
        regstack->reg[++regstack->top] = REGNO (*dest);
        SET_HARD_REG_BIT (regstack->reg_set, REGNO (*dest));
        replace_reg (dest, FIRST_STACK_REG);
        break;

      case REG:
        /* This is a `tstM2' case. */
        if (*dest != cc0_rtx)
          abort ();

        src1 = src;

        /* Fall through. */

      case SQRT:
      case ABS:
      case NEG:
        /* These insns only operate on the top of the stack. DEST might
           be cc0_rtx if we're processing a tstM pattern. Also, it's
           possible that the tstM case results in a REG_DEAD note on the
           source.  */

        if (src1 == 0)
          src1 = get_true_reg (&XEXP (SET_SRC (pat), 0));

        emit_swap_insn (insn, regstack, *src1, emit_insn_before);

        src1_note = find_regno_note (insn, REG_DEAD, REGNO (*src1));

        if (STACK_REG_P (*dest))
          replace_reg (dest, FIRST_STACK_REG);

        if (src1_note)
          {
            replace_reg (&XEXP (src1_note, 0), FIRST_STACK_REG);
            regstack->top--;
            CLEAR_HARD_REG_BIT (regstack->reg_set, REGNO (*src1));
          }

        replace_reg (src1, FIRST_STACK_REG);

        break;

      case MINUS:
      case DIV:
        /* On i386, reversed forms of subM3 and divM3 exist for
           MODE_FLOAT, so the same code that works for addM3 and mulM3
           can be used. */
      case MULT:
      case PLUS:
        /* These insns can accept the top of stack as a destination
           from a stack reg or mem, or can use the top of stack as a
           source and some other stack register (possibly top of stack)
           as a destination. */

        src1 = get_true_reg (&XEXP (SET_SRC (pat), 0));
        src2 = get_true_reg (&XEXP (SET_SRC (pat), 1));

        /* We will fix any death note later. */

        if (STACK_REG_P (*src1))
          src1_note = find_regno_note (insn, REG_DEAD, REGNO (*src1));
        else
          src1_note = 0;
        if (STACK_REG_P (*src2))
          src2_note = find_regno_note (insn, REG_DEAD, REGNO (*src2));
        else
          src2_note = 0;

        /* If either operand is not a stack register, then the dest
           must be top of stack. */

        if (! STACK_REG_P (*src1) || ! STACK_REG_P (*src2))
          emit_swap_insn (insn, regstack, *dest, emit_insn_before);
        else
          {
            /* Both operands are REG.  If neither operand is already
               at the top of stack, choose to make the one that is the dest
               the new top of stack.

               ??? A later optimization here would be to look forward
               in the insns and see which source reg will be needed at top
               of stack soonest. */

            int src1_hard_regnum, src2_hard_regnum;

            src1_hard_regnum = get_hard_regnum (regstack, *src1);
            src2_hard_regnum = get_hard_regnum (regstack, *src2);
            if (src1_hard_regnum == -1 || src2_hard_regnum == -1)
              abort ();

            if (src1_hard_regnum != FIRST_STACK_REG
                && src2_hard_regnum != FIRST_STACK_REG)
              emit_swap_insn (insn, regstack, *dest, emit_insn_before);
          }

        if (STACK_REG_P (*src1))
          replace_reg (src1, get_hard_regnum (regstack, *src1));
        if (STACK_REG_P (*src2))
          replace_reg (src2, get_hard_regnum (regstack, *src2));

        if (src1_note)
          {
            /* If the register that dies is at the top of stack, then
               the destination is somewhere else - merely substitute it.
               But if the reg that dies is not at top of stack, then
               move the top of stack to the dead reg, as though we had
               done the insn and then a store-with-pop. */

            if (REGNO (XEXP (src1_note, 0)) == regstack->reg[regstack->top])
              {
                SET_HARD_REG_BIT (regstack->reg_set, REGNO (*dest));
                replace_reg (dest, get_hard_regnum (regstack, *dest));
              }
            else
              {
                int regno = get_hard_regnum (regstack, XEXP (src1_note, 0));

                SET_HARD_REG_BIT (regstack->reg_set, REGNO (*dest));
                replace_reg (dest, regno);

                regstack->reg[regstack->top - (regno - FIRST_STACK_REG)]
                  = regstack->reg[regstack->top];
              }

            CLEAR_HARD_REG_BIT (regstack->reg_set,
                                REGNO (XEXP (src1_note, 0)));
            replace_reg (&XEXP (src1_note, 0), FIRST_STACK_REG);
            regstack->top--;
          }
        else if (src2_note)
          {
            if (REGNO (XEXP (src2_note, 0)) == regstack->reg[regstack->top])
              {
                SET_HARD_REG_BIT (regstack->reg_set, REGNO (*dest));
                replace_reg (dest, get_hard_regnum (regstack, *dest));
              }
            else
              {
                int regno = get_hard_regnum (regstack, XEXP (src2_note, 0));

                SET_HARD_REG_BIT (regstack->reg_set, REGNO (*dest));
                replace_reg (dest, regno);

                regstack->reg[regstack->top - (regno - FIRST_STACK_REG)]
                  = regstack->reg[regstack->top];
              }

            CLEAR_HARD_REG_BIT (regstack->reg_set,
                                REGNO (XEXP (src2_note, 0)));
            replace_reg (&XEXP (src2_note, 0), FIRST_STACK_REG);
            regstack->top--;
          }
        else
          {
            SET_HARD_REG_BIT (regstack->reg_set, REGNO (*dest));
            replace_reg (dest, get_hard_regnum (regstack, *dest));
          }

        break;

      default:
        abort ();
      }
}
\f
/* Substitute stack hard reg numbers for stack virtual registers in
   INSN.  Non-stack register numbers are not changed.  REGSTACK is the
   current stack content.  Insns may be emitted as needed to arrange the
   stack for the 387 based on the contents of the insn. */

static void
subst_stack_regs (insn, regstack)
     rtx insn;
     stack regstack;
{
  register rtx *note_link, note;
  register int i;

  if ((GET_CODE (insn) != INSN && GET_CODE (insn) != CALL_INSN)
      || INSN_DELETED_P (insn))
    return;

  /* The stack should be empty at a call. */

  if (GET_CODE (insn) == CALL_INSN)
    for (i = FIRST_STACK_REG; i <= LAST_STACK_REG; i++)
      if (TEST_HARD_REG_BIT (regstack->reg_set, i))
        abort ();

  /* Do the actual substitution if any stack regs are mentioned.
     Since we only record whether entire insn mentions stack regs, and
     subst_stack_regs_pat only works for patterns that contain stack regs,
     we must check each pattern in a parallel here.  A call_value_pop could
     fail otherwise. */

  if (GET_MODE (insn) == QImode)
    {
      if (GET_CODE (PATTERN (insn)) == PARALLEL)
        for (i = 0; i < XVECLEN (PATTERN (insn) , 0); i++)
          {
            if (stack_regs_mentioned_p (XVECEXP (PATTERN (insn), 0, i)))
              subst_stack_regs_pat (insn, regstack,
                                    XVECEXP (PATTERN (insn), 0, i));
          }
      else
        subst_stack_regs_pat (insn, regstack, PATTERN (insn));
    }

  /* subst_stack_regs_pat may have deleted a no-op insn.  If so, any
     REG_UNUSED will already have been dealt with, so just return. */

  if (INSN_DELETED_P (insn))
    return;

  /* If there is a REG_UNUSED note on a stack register on this insn,
     the indicated reg must be popped.  The REG_UNUSED note is removed,
     since the form of the newly emitted pop insn references the reg,
     making it no longer `unset'. */

  note_link = &REG_NOTES(insn);
  for (note = *note_link; note; note = XEXP (note, 1))
    if (REG_NOTE_KIND (note) == REG_UNUSED && STACK_REG_P (XEXP (note, 0)))
      {
        *note_link = XEXP (note, 1);
        emit_pop_insn (insn, regstack, XEXP (note, 0),
                       emit_insn_after);
      }
    else
      note_link = &XEXP (note, 1);
}
\f
/* Change the organization of the stack so that it fits a new basic
   block.  Some registers might have to be popped, but there can never be
   a register live in the new block that is not now live.

   Insert any needed insns after INSN.  OLD is the original stack
   layout, and NEW is the desired form.  OLD is updated to reflect the
   code emitted, ie, it will be the same as NEW upon return.

   This function will not preserve block_end[].  But that information
   is no longer needed once this has executed. */

static void
change_stack (insn, old, new)
     rtx insn;
     stack old;
     stack new;
{
  int reg;

  /* We will be inserting new insns after INSN, by first finding the
     next insn, and inserting before it. */

  insn = NEXT_INSN (insn);

  /* Pop any registers that are not needed in the new block. */

  for (reg = old->top; reg >= 0; reg--)
    if (! TEST_HARD_REG_BIT (new->reg_set, old->reg[reg]))
      emit_pop_insn (insn, old, FP_mode_reg[old->reg[reg]][(int) DFmode],
                     emit_insn_before);

  if (new->top == -2)
    {
      /* If the new block has never been processed, then it can inherit
         the old stack order. */

      new->top = old->top;
      bcopy (old->reg, new->reg, sizeof (new->reg));
    }
  else
    {
      /* This block has been entered before, and we must match the
         previously selected stack order. */

      /* By now, the only difference should be the order of the stack,
         not their depth or liveliness. */

      GO_IF_HARD_REG_EQUAL (old->reg_set, new->reg_set, win);

      abort ();

    win:

      if (old->top != new->top)
        abort ();

      /* Loop here emitting swaps until the stack is correct.  The
         worst case number of swaps emitted is N + 2, where N is the
         depth of the stack.  In some cases, the reg at the top of
         stack may be correct, but swapped anyway in order to fix
         other regs.  But since we never swap any other reg away from
         its correct slot, this algorithm will converge. */

      do
        {
          /* Swap the reg at top of stack into the position it is
             supposed to be in, until the correct top of stack appears. */

          while (old->reg[old->top] != new->reg[new->top])
            {
              for (reg = new->top; reg >= 0; reg--)
                if (new->reg[reg] == old->reg[old->top])
                  break;

              if (reg == -1)
                abort ();

              emit_swap_insn (insn, old,
                              FP_mode_reg[old->reg[reg]][(int) DFmode],
                              emit_insn_before);
            }

          /* See if any regs remain incorrect.  If so, bring an
             incorrect reg to the top of stack, and let the while loop
             above fix it. */

          for (reg = new->top; reg >= 0; reg--)
            if (new->reg[reg] != old->reg[reg])
              {
                emit_swap_insn (insn, old,
                                FP_mode_reg[old->reg[reg]][(int) DFmode],
                                emit_insn_before);
                break;
              }
        } while (reg >= 0);

      /* At this point there must be no differences. */

      for (reg = old->top; reg >= 0; reg--)
        if (old->reg[reg] != new->reg[reg])
          abort ();
    }
}
\f
/* Check PAT, which points to RTL in INSN, for a LABEL_REF.  If it is
   found, ensure that a jump from INSN to the code_label to which the
   label_ref points ends up with the same stack as that at the
   code_label.  Do this by inserting insns just before the code_label to
   pop and rotate the stack until it is in the correct order.  REGSTACK
   is the order of the register stack in INSN.

   Any code that is emitted here must not be later processed as part
   of any block, as it will already contain hard register numbers. */

static void
goto_block_pat (insn, regstack, pat)
     rtx insn;
     stack regstack;
     rtx pat;
{
  rtx label;
  rtx new_jump, new_label, new_barrier;
  rtx *ref;
  stack label_stack;
  struct stack_def temp_stack;
  int reg;

  if (GET_CODE (pat) != LABEL_REF)
    {
      int i, j;
      char *fmt = GET_RTX_FORMAT (GET_CODE (pat));

      for (i = GET_RTX_LENGTH (GET_CODE (pat)) - 1; i >= 0; i--)
        {
          if (fmt[i] == 'e')
            goto_block_pat (insn, regstack, XEXP (pat, i));
          if (fmt[i] == 'E')
            for (j = 0; j < XVECLEN (pat, i); j++)
              goto_block_pat (insn, regstack, XVECEXP (pat, i, j));
        }
      return;
    }

  label = XEXP (pat, 0);
  if (GET_CODE (label) != CODE_LABEL)
    abort ();

  /* First, see if in fact anything needs to be done to the stack at all. */

  label_stack = &block_stack_in[BLOCK_NUM (label)];

  if (label_stack->top == -2)
    {
      /* If the target block hasn't had a stack order selected, then
         we need merely ensure that no pops are needed. */

      for (reg = regstack->top; reg >= 0; reg--)
        if (! TEST_HARD_REG_BIT (label_stack->reg_set, regstack->reg[reg]))
          break;

      if (reg == -1)
        {
          /* change_stack will not emit any code in this case. */

          change_stack (label, regstack, label_stack);
          return;
        }
    }
  else if (label_stack->top == regstack->top)
    {
      for (reg = label_stack->top; reg >= 0; reg--)
        if (label_stack->reg[reg] != regstack->reg[reg])
          break;

      if (reg == -1)
        return;
    }

  /* At least one insn will need to be inserted before label.  Insert
     a jump around the code we are about to emit.  Emit a label for the new
     code, and point the original insn at this new label. We can't use
     redirect_jump here, because we're using fld[4] of the code labels as
     LABEL_REF chains, no NUSES counters. */

  new_jump = emit_jump_insn_before (gen_jump (label), label);
  record_label_references (new_jump, PATTERN (new_jump));
  JUMP_LABEL (new_jump) = label;

  new_barrier = emit_barrier_after (new_jump);

  new_label = gen_label_rtx ();
  emit_label_after (new_label, new_barrier);
  LABEL_REFS (new_label) = new_label;

  /* The old label_ref will no longer point to the code_label if now uses,
     so strip the label_ref from the code_label's chain of references. */

  for (ref = &LABEL_REFS (label); *ref != label; ref = &LABEL_NEXTREF (*ref))
    if (*ref == pat)
      break;

  if (*ref == label)
    abort ();

  *ref = LABEL_NEXTREF (*ref);

  XEXP (pat, 0) = new_label;
  record_label_references (insn, PATTERN (insn));

  if (JUMP_LABEL (insn) == label)
    JUMP_LABEL (insn) = new_label;

  /* Now emit the needed code. */

  temp_stack = *regstack;

  change_stack (new_label, &temp_stack, label_stack);
}
\f
/* Traverse all basic blocks in a function, converting the register
   refereces in each insn from the "flat" register file that gcc uses, to
   the stack-like registers the 387 uses. */

static void
convert_regs ()
{
  register int block, reg;
  register rtx insn, next;
  struct stack_def regstack;

  for (block = 0; block < blocks; block++)
    {
      if (block_stack_in[block].top == -2)
        {
          /* This block has not been previously encountered.  Choose a
             default mapping for any stack regs live on entry */

          block_stack_in[block].top = -1;

          for (reg = LAST_STACK_REG; reg >= FIRST_STACK_REG; reg--)
            if (TEST_HARD_REG_BIT (block_stack_in[block].reg_set, reg))
              block_stack_in[block].reg[++block_stack_in[block].top] = reg;
        }

      /* Process all insns in this block.  Keep track of `next' here,
         so that we don't process any insns emitted while making
         substitutions in INSN. */

      next = block_begin[block];
      regstack = block_stack_in[block];
      do
        {
          insn = next;
          next = NEXT_INSN (insn);

          /* Don't bother processing unless there is a stack reg
             mentioned.

             ??? For now, process CALL_INSNs too to make sure that the
             stack regs are dead after a call.  Remove this eventually. */

          if (GET_MODE (insn) == QImode || GET_CODE (insn) == CALL_INSN)
            subst_stack_regs (insn, &regstack);

        } while (insn != block_end[block]);

      /* Something failed if the stack life doesn't match. */

      GO_IF_HARD_REG_EQUAL (regstack.reg_set, block_out_reg_set[block], win);

      abort ();

    win:

      /* Adjust the stack of this block on exit to match the stack of
         the target block, or copy stack information into stack of
         jump target if the target block's stack order hasn't been set
         yet. */

      if (GET_CODE (insn) == JUMP_INSN)
        goto_block_pat (insn, &regstack, PATTERN (insn));

      /* Likewise handle the case where we fall into the next block. */

      if ((block < blocks - 1) && block_drops_in[block+1])
        change_stack (insn, &regstack, &block_stack_in[block+1]);
    }

  /* If the last basic block is the end of a loop, and that loop has
     regs live at its start, then the last basic block will have regs live
     at its end that need to be popped before the function returns. */

  for (reg = regstack.top; reg >= 0; reg--)
    if (! current_function_returns_real
        || regstack.reg[reg] != FIRST_STACK_REG)
      insn = emit_pop_insn (insn, &regstack,
                            FP_mode_reg[regstack.reg[reg]][(int) DFmode],
                            emit_insn_after);
}
\f
/* Check expression PAT, which is in INSN, for label references.  if
   one is found, print the block number of destination to FILE. */

static void
print_blocks (file, insn, pat)
     FILE *file;
     rtx insn, pat;
{
  register RTX_CODE code = GET_CODE (pat);
  register int i;
  register char *fmt;

  if (code == LABEL_REF)
    {
      register rtx label = XEXP (pat, 0);

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

      fprintf (file, " %d", BLOCK_NUM (label));

      return;
    }

  fmt = GET_RTX_FORMAT (code);
  for (i = GET_RTX_LENGTH (code) - 1; i >= 0; i--)
    {
      if (fmt[i] == 'e')
        print_blocks (file, insn, XEXP (pat, i));
      if (fmt[i] == 'E')
        {
          register int j;
          for (j = 0; j < XVECLEN (pat, i); j++)
            print_blocks (file, insn, XVECEXP (pat, i, j));
        }
    }
}
\f
/* Write information about stack registers and stack blocks into FILE.
   This is part of making a debugging dump.  */
static void
dump_stack_info (file)
     FILE *file;
{
  register int block;

  fprintf (file, "\n%d stack blocks.\n", blocks);
  for (block = 0; block < blocks; block++)
    {
      register rtx head, jump, end;
      register int regno;

      fprintf (file, "\nStack block %d: first insn %d, last %d.\n",
               block, INSN_UID (block_begin[block]),
               INSN_UID (block_end[block]));

      head = block_begin[block];

      fprintf (file, "Reached from blocks: ");
      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 (block_drops_in[block])
        fprintf (file, " previous");

      fprintf (file, "\nlive stack registers on block entry: ");
      for (regno = FIRST_STACK_REG; regno <= LAST_STACK_REG ; regno++)
        {
          if (TEST_HARD_REG_BIT (block_stack_in[block].reg_set, regno))
            fprintf (file, "%d ", regno);
        }

      fprintf (file, "\nlive stack registers on block exit: ");
      for (regno = FIRST_STACK_REG; regno <= LAST_STACK_REG ; regno++)
        {
          if (TEST_HARD_REG_BIT (block_out_reg_set[block], regno))
            fprintf (file, "%d ", regno);
        }

      end = block_end[block];

      fprintf (file, "\nJumps to blocks: ");
      if (GET_CODE (end) == JUMP_INSN)
        print_blocks (file, end, PATTERN (end));

      if (block + 1 < blocks && block_drops_in[block+1])
        fprintf (file, " next");
      else if (block + 1 == blocks
               || (GET_CODE (end) == JUMP_INSN
                   && GET_CODE (PATTERN (end)) == RETURN))
        fprintf (file, " return");

      fprintf (file, "\n");
    }
}
\f
/* Report an error at line LINE of file FILE.
   S is a string and an arg for `printf'.  */

/* Report an fatal error at the line number of the insn INSN (ASM_OPERAND).
   S1, S2 is a string and an arg for `printf'. */

static void
fatal_for_asm (insn, s1, s2)
     rtx insn;
     char *s1, *s2;
{
  char *filename;
  int line;
  rtx body = PATTERN (insn);
  rtx asmop = 0;

  /* Find the (or one of the) ASM_OPERANDS in the insn.  */
  if (GET_CODE (body) == SET && GET_CODE (SET_SRC (body)) == ASM_OPERANDS)
    asmop = SET_SRC (body);
  else if (GET_CODE (body) == ASM_OPERANDS)
    asmop = body;
  else if (GET_CODE (body) == PARALLEL
           && GET_CODE (XVECEXP (body, 0, 0)) == SET)
    asmop = SET_SRC (XVECEXP (body, 0, 0));
  else if (GET_CODE (body) == PARALLEL
           && GET_CODE (XVECEXP (body, 0, 0)) == ASM_OPERANDS)
    asmop = XVECEXP (body, 0, 0);
  else
    abort ();

  filename = ASM_OPERANDS_SOURCE_FILE (asmop);
  line = ASM_OPERANDS_SOURCE_LINE (asmop);

  fprintf (stderr, s1);
  debug_rtx (insn);

  error_with_file_and_line (filename, line, s2, NULL, NULL);
  exit (34);
}
#endif /* STACK_REGS */