gcc/gensupport.c

/* Support routines for the various generation passes.
   Copyright (C) 2000, 2001, 2002, 2003, 2004
   Free Software Foundation, Inc.

   This file is part of GCC.

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

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

   You should have received a copy of the GNU General Public License
   along with GCC; see the file COPYING.  If not, write to the Free
   Software Foundation, 59 Temple Place - Suite 330, Boston, MA
   02111-1307, USA.  */

#include "bconfig.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "rtl.h"
#include "obstack.h"
#include "errors.h"
#include "hashtab.h"
#include "gensupport.h"


/* In case some macros used by files we include need it, define this here.  */
int target_flags;

int insn_elision = 1;

static struct obstack obstack;
struct obstack *rtl_obstack = &obstack;

static int sequence_num;
static int errors;

static int predicable_default;
static const char *predicable_true;
static const char *predicable_false;

static htab_t condition_table;

static char *base_dir = NULL;

/* We initially queue all patterns, process the define_insn and
   define_cond_exec patterns, then return them one at a time.  */

struct queue_elem
{
  rtx data;
  const char *filename;
  int lineno;
  struct queue_elem *next;
};

static struct queue_elem *define_attr_queue;
static struct queue_elem **define_attr_tail = &define_attr_queue;
static struct queue_elem *define_insn_queue;
static struct queue_elem **define_insn_tail = &define_insn_queue;
static struct queue_elem *define_cond_exec_queue;
static struct queue_elem **define_cond_exec_tail = &define_cond_exec_queue;
static struct queue_elem *other_queue;
static struct queue_elem **other_tail = &other_queue;

static void queue_pattern (rtx, struct queue_elem ***,
			   const char *, int);

/* Current maximum length of directory names in the search path
   for include files.  (Altered as we get more of them.)  */

size_t max_include_len;

struct file_name_list
  {
    struct file_name_list *next;
    const char *fname;
  };

struct file_name_list *first_dir_md_include = 0;  /* First dir to search */
        /* First dir to search for <file> */
struct file_name_list *first_bracket_include = 0;
struct file_name_list *last_dir_md_include = 0;        /* Last in chain */

static void remove_constraints (rtx);
static void process_rtx (rtx, int);

static int is_predicable (struct queue_elem *);
static void identify_predicable_attribute (void);
static int n_alternatives (const char *);
static void collect_insn_data (rtx, int *, int *);
static rtx alter_predicate_for_insn (rtx, int, int, int);
static const char *alter_test_for_insn (struct queue_elem *,
					struct queue_elem *);
static char *shift_output_template (char *, const char *, int);
static const char *alter_output_for_insn (struct queue_elem *,
					  struct queue_elem *,
					  int, int);
static void process_one_cond_exec (struct queue_elem *);
static void process_define_cond_exec (void);
static void process_include (rtx, int);
static char *save_string (const char *, int);

void
message_with_line (int lineno, const char *msg, ...)
{
  va_list ap;

  va_start (ap, msg);

  fprintf (stderr, "%s:%d: ", read_rtx_filename, lineno);
  vfprintf (stderr, msg, ap);
  fputc ('\n', stderr);

  va_end (ap);
}

/* Make a version of gen_rtx_CONST_INT so that GEN_INT can be used in
   the gensupport programs.  */

rtx
gen_rtx_CONST_INT (enum machine_mode mode ATTRIBUTE_UNUSED,
		   HOST_WIDE_INT arg)
{
  rtx rt = rtx_alloc (CONST_INT);

  XWINT (rt, 0) = arg;
  return rt;
}

/* Queue PATTERN on LIST_TAIL.  */

static void
queue_pattern (rtx pattern, struct queue_elem ***list_tail,
	       const char *filename, int lineno)
{
  struct queue_elem *e = xmalloc (sizeof (*e));
  e->data = pattern;
  e->filename = filename;
  e->lineno = lineno;
  e->next = NULL;
  **list_tail = e;
  *list_tail = &e->next;
}

/* Recursively remove constraints from an rtx.  */

static void
remove_constraints (rtx part)
{
  int i, j;
  const char *format_ptr;

  if (part == 0)
    return;

  if (GET_CODE (part) == MATCH_OPERAND)
    XSTR (part, 2) = "";
  else if (GET_CODE (part) == MATCH_SCRATCH)
    XSTR (part, 1) = "";

  format_ptr = GET_RTX_FORMAT (GET_CODE (part));

  for (i = 0; i < GET_RTX_LENGTH (GET_CODE (part)); i++)
    switch (*format_ptr++)
      {
      case 'e':
      case 'u':
	remove_constraints (XEXP (part, i));
	break;
      case 'E':
	if (XVEC (part, i) != NULL)
	  for (j = 0; j < XVECLEN (part, i); j++)
	    remove_constraints (XVECEXP (part, i, j));
	break;
      }
}

/* Process an include file assuming that it lives in gcc/config/{target}/
   if the include looks like (include "file").  */

static void
process_include (rtx desc, int lineno)
{
  const char *filename = XSTR (desc, 0);
  const char *old_filename;
  int old_lineno;
  char *pathname;
  FILE *input_file;

  /* If specified file name is absolute, skip the include stack.  */
  if (! IS_ABSOLUTE_PATH (filename))
    {
      struct file_name_list *stackp;

      /* Search directory path, trying to open the file.  */
      for (stackp = first_dir_md_include; stackp; stackp = stackp->next)
	{
	  static const char sep[2] = { DIR_SEPARATOR, '\0' };

	  pathname = concat (stackp->fname, sep, filename, NULL);
	  input_file = fopen (pathname, "r");
	  if (input_file != NULL)
	    goto success;
	  free (pathname);
	}
    }

  if (base_dir)
    pathname = concat (base_dir, filename, NULL);
  else
    pathname = xstrdup (filename);
  input_file = fopen (pathname, "r");
  if (input_file == NULL)
    {
      free (pathname);
      message_with_line (lineno, "include file `%s' not found", filename);
      errors = 1;
      return;
    }
 success:

  /* Save old cursor; setup new for the new file.  Note that "lineno" the
     argument to this function is the beginning of the include statement,
     while read_rtx_lineno has already been advanced.  */
  old_filename = read_rtx_filename;
  old_lineno = read_rtx_lineno;
  read_rtx_filename = pathname;
  read_rtx_lineno = 1;

  /* Read the entire file.  */
  while (1)
    {
      rtx desc;
      int c;

      c = read_skip_spaces (input_file);
      if (c == EOF)
	break;

      ungetc (c, input_file);
      lineno = read_rtx_lineno;
      desc = read_rtx (input_file);
      process_rtx (desc, lineno);
    }

  /* Do not free pathname.  It is attached to the various rtx queue
     elements.  */

  read_rtx_filename = old_filename;
  read_rtx_lineno = old_lineno;

  fclose (input_file);
}

/* Process a top level rtx in some way, queuing as appropriate.  */

static void
process_rtx (rtx desc, int lineno)
{
  switch (GET_CODE (desc))
    {
    case DEFINE_INSN:
      queue_pattern (desc, &define_insn_tail, read_rtx_filename, lineno);
      break;

    case DEFINE_COND_EXEC:
      queue_pattern (desc, &define_cond_exec_tail, read_rtx_filename, lineno);
      break;

    case DEFINE_ATTR:
      queue_pattern (desc, &define_attr_tail, read_rtx_filename, lineno);
      break;

    case INCLUDE:
      process_include (desc, lineno);
      break;

    case DEFINE_INSN_AND_SPLIT:
      {
	const char *split_cond;
	rtx split;
	rtvec attr;
	int i;

	/* Create a split with values from the insn_and_split.  */
	split = rtx_alloc (DEFINE_SPLIT);

	i = XVECLEN (desc, 1);
	XVEC (split, 0) = rtvec_alloc (i);
	while (--i >= 0)
	  {
	    XVECEXP (split, 0, i) = copy_rtx (XVECEXP (desc, 1, i));
	    remove_constraints (XVECEXP (split, 0, i));
	  }

	/* If the split condition starts with "&&", append it to the
	   insn condition to create the new split condition.  */
	split_cond = XSTR (desc, 4);
	if (split_cond[0] == '&' && split_cond[1] == '&')
	  split_cond = concat (XSTR (desc, 2), split_cond, NULL);
	XSTR (split, 1) = split_cond;
	XVEC (split, 2) = XVEC (desc, 5);
	XSTR (split, 3) = XSTR (desc, 6);

	/* Fix up the DEFINE_INSN.  */
	attr = XVEC (desc, 7);
	PUT_CODE (desc, DEFINE_INSN);
	XVEC (desc, 4) = attr;

	/* Queue them.  */
	queue_pattern (desc, &define_insn_tail, read_rtx_filename, lineno);
	queue_pattern (split, &other_tail, read_rtx_filename, lineno);
	break;
      }

    default:
      queue_pattern (desc, &other_tail, read_rtx_filename, lineno);
      break;
    }
}

/* Return true if attribute PREDICABLE is true for ELEM, which holds
   a DEFINE_INSN.  */

static int
is_predicable (struct queue_elem *elem)
{
  rtvec vec = XVEC (elem->data, 4);
  const char *value;
  int i;

  if (! vec)
    return predicable_default;

  for (i = GET_NUM_ELEM (vec) - 1; i >= 0; --i)
    {
      rtx sub = RTVEC_ELT (vec, i);
      switch (GET_CODE (sub))
	{
	case SET_ATTR:
	  if (strcmp (XSTR (sub, 0), "predicable") == 0)
	    {
	      value = XSTR (sub, 1);
	      goto found;
	    }
	  break;

	case SET_ATTR_ALTERNATIVE:
	  if (strcmp (XSTR (sub, 0), "predicable") == 0)
	    {
	      message_with_line (elem->lineno,
				 "multiple alternatives for `predicable'");
	      errors = 1;
	      return 0;
	    }
	  break;

	case SET:
	  if (GET_CODE (SET_DEST (sub)) != ATTR
	      || strcmp (XSTR (SET_DEST (sub), 0), "predicable") != 0)
	    break;
	  sub = SET_SRC (sub);
	  if (GET_CODE (sub) == CONST_STRING)
	    {
	      value = XSTR (sub, 0);
	      goto found;
	    }

	  /* ??? It would be possible to handle this if we really tried.
	     It's not easy though, and I'm not going to bother until it
	     really proves necessary.  */
	  message_with_line (elem->lineno,
			     "non-constant value for `predicable'");
	  errors = 1;
	  return 0;

	default:
	  abort ();
	}
    }

  return predicable_default;

 found:
  /* Verify that predicability does not vary on the alternative.  */
  /* ??? It should be possible to handle this by simply eliminating
     the non-predicable alternatives from the insn.  FRV would like
     to do this.  Delay this until we've got the basics solid.  */
  if (strchr (value, ',') != NULL)
    {
      message_with_line (elem->lineno,
			 "multiple alternatives for `predicable'");
      errors = 1;
      return 0;
    }

  /* Find out which value we're looking at.  */
  if (strcmp (value, predicable_true) == 0)
    return 1;
  if (strcmp (value, predicable_false) == 0)
    return 0;

  message_with_line (elem->lineno,
		     "unknown value `%s' for `predicable' attribute",
		     value);
  errors = 1;
  return 0;
}

/* Examine the attribute "predicable"; discover its boolean values
   and its default.  */

static void
identify_predicable_attribute (void)
{
  struct queue_elem *elem;
  char *p_true, *p_false;
  const char *value;

  /* Look for the DEFINE_ATTR for `predicable', which must exist.  */
  for (elem = define_attr_queue; elem ; elem = elem->next)
    if (strcmp (XSTR (elem->data, 0), "predicable") == 0)
      goto found;

  message_with_line (define_cond_exec_queue->lineno,
		     "attribute `predicable' not defined");
  errors = 1;
  return;

 found:
  value = XSTR (elem->data, 1);
  p_false = xstrdup (value);
  p_true = strchr (p_false, ',');
  if (p_true == NULL || strchr (++p_true, ',') != NULL)
    {
      message_with_line (elem->lineno,
			 "attribute `predicable' is not a boolean");
      errors = 1;
      return;
    }
  p_true[-1] = '\0';

  predicable_true = p_true;
  predicable_false = p_false;

  switch (GET_CODE (XEXP (elem->data, 2)))
    {
    case CONST_STRING:
      value = XSTR (XEXP (elem->data, 2), 0);
      break;

    case CONST:
      message_with_line (elem->lineno,
			 "attribute `predicable' cannot be const");
      errors = 1;
      return;

    default:
      message_with_line (elem->lineno,
			 "attribute `predicable' must have a constant default");
      errors = 1;
      return;
    }

  if (strcmp (value, p_true) == 0)
    predicable_default = 1;
  else if (strcmp (value, p_false) == 0)
    predicable_default = 0;
  else
    {
      message_with_line (elem->lineno,
			 "unknown value `%s' for `predicable' attribute",
			 value);
      errors = 1;
    }
}

/* Return the number of alternatives in constraint S.  */

static int
n_alternatives (const char *s)
{
  int n = 1;

  if (s)
    while (*s)
      n += (*s++ == ',');

  return n;
}

/* Determine how many alternatives there are in INSN, and how many
   operands.  */

static void
collect_insn_data (rtx pattern, int *palt, int *pmax)
{
  const char *fmt;
  enum rtx_code code;
  int i, j, len;

  code = GET_CODE (pattern);
  switch (code)
    {
    case MATCH_OPERAND:
      i = n_alternatives (XSTR (pattern, 2));
      *palt = (i > *palt ? i : *palt);
      /* Fall through.  */

    case MATCH_OPERATOR:
    case MATCH_SCRATCH:
    case MATCH_PARALLEL:
    case MATCH_INSN:
      i = XINT (pattern, 0);
      if (i > *pmax)
	*pmax = i;
      break;

    default:
      break;
    }

  fmt = GET_RTX_FORMAT (code);
  len = GET_RTX_LENGTH (code);
  for (i = 0; i < len; i++)
    {
      switch (fmt[i])
	{
	case 'e': case 'u':
	  collect_insn_data (XEXP (pattern, i), palt, pmax);
	  break;

	case 'V':
	  if (XVEC (pattern, i) == NULL)
	    break;
	  /* Fall through.  */
	case 'E':
	  for (j = XVECLEN (pattern, i) - 1; j >= 0; --j)
	    collect_insn_data (XVECEXP (pattern, i, j), palt, pmax);
	  break;

	case 'i': case 'w': case '0': case 's': case 'S': case 'T':
	  break;

	default:
	  abort ();
	}
    }
}

static rtx
alter_predicate_for_insn (rtx pattern, int alt, int max_op, int lineno)
{
  const char *fmt;
  enum rtx_code code;
  int i, j, len;

  code = GET_CODE (pattern);
  switch (code)
    {
    case MATCH_OPERAND:
      {
	const char *c = XSTR (pattern, 2);

	if (n_alternatives (c) != 1)
	  {
	    message_with_line (lineno,
			       "too many alternatives for operand %d",
			       XINT (pattern, 0));
	    errors = 1;
	    return NULL;
	  }

	/* Replicate C as needed to fill out ALT alternatives.  */
	if (c && *c && alt > 1)
	  {
	    size_t c_len = strlen (c);
	    size_t len = alt * (c_len + 1);
	    char *new_c = xmalloc (len);

	    memcpy (new_c, c, c_len);
	    for (i = 1; i < alt; ++i)
	      {
		new_c[i * (c_len + 1) - 1] = ',';
		memcpy (&new_c[i * (c_len + 1)], c, c_len);
	      }
	    new_c[len - 1] = '\0';
	    XSTR (pattern, 2) = new_c;
	  }
      }
      /* Fall through.  */

    case MATCH_OPERATOR:
    case MATCH_SCRATCH:
    case MATCH_PARALLEL:
    case MATCH_INSN:
      XINT (pattern, 0) += max_op;
      break;

    default:
      break;
    }

  fmt = GET_RTX_FORMAT (code);
  len = GET_RTX_LENGTH (code);
  for (i = 0; i < len; i++)
    {
      rtx r;

      switch (fmt[i])
	{
	case 'e': case 'u':
	  r = alter_predicate_for_insn (XEXP (pattern, i), alt,
					max_op, lineno);
	  if (r == NULL)
	    return r;
	  break;

	case 'E':
	  for (j = XVECLEN (pattern, i) - 1; j >= 0; --j)
	    {
	      r = alter_predicate_for_insn (XVECEXP (pattern, i, j),
					    alt, max_op, lineno);
	      if (r == NULL)
		return r;
	    }
	  break;

	case 'i': case 'w': case '0': case 's':
	  break;

	default:
	  abort ();
	}
    }

  return pattern;
}

static const char *
alter_test_for_insn (struct queue_elem *ce_elem,
		     struct queue_elem *insn_elem)
{
  const char *ce_test, *insn_test;

  ce_test = XSTR (ce_elem->data, 1);
  insn_test = XSTR (insn_elem->data, 2);
  if (!ce_test || *ce_test == '\0')
    return insn_test;
  if (!insn_test || *insn_test == '\0')
    return ce_test;

  return concat ("(", ce_test, ") && (", insn_test, ")", NULL);
}

/* Adjust all of the operand numbers in OLD to match the shift they'll
   get from an operand displacement of DISP.  Return a pointer after the
   adjusted string.  */

static char *
shift_output_template (char *new, const char *old, int disp)
{
  while (*old)
    {
      char c = *old++;
      *new++ = c;
      if (c == '%')
	{
	  c = *old++;
	  if (ISDIGIT ((unsigned char) c))
	    c += disp;
	  else if (ISALPHA (c))
	    {
	      *new++ = c;
	      c = *old++ + disp;
	    }
	  *new++ = c;
	}
    }

  return new;
}

static const char *
alter_output_for_insn (struct queue_elem *ce_elem,
		       struct queue_elem *insn_elem,
		       int alt, int max_op)
{
  const char *ce_out, *insn_out;
  char *new, *p;
  size_t len, ce_len, insn_len;

  /* ??? Could coordinate with genoutput to not duplicate code here.  */

  ce_out = XSTR (ce_elem->data, 2);
  insn_out = XTMPL (insn_elem->data, 3);
  if (!ce_out || *ce_out == '\0')
    return insn_out;

  ce_len = strlen (ce_out);
  insn_len = strlen (insn_out);

  if (*insn_out == '*')
    /* You must take care of the predicate yourself.  */
    return insn_out;

  if (*insn_out == '@')
    {
      len = (ce_len + 1) * alt + insn_len + 1;
      p = new = xmalloc (len);

      do
	{
	  do
	    *p++ = *insn_out++;
	  while (ISSPACE ((unsigned char) *insn_out));

	  if (*insn_out != '#')
	    {
	      p = shift_output_template (p, ce_out, max_op);
	      *p++ = ' ';
	    }

	  do
	    *p++ = *insn_out++;
	  while (*insn_out && *insn_out != '\n');
	}
      while (*insn_out);
      *p = '\0';
    }
  else
    {
      len = ce_len + 1 + insn_len + 1;
      new = xmalloc (len);

      p = shift_output_template (new, ce_out, max_op);
      *p++ = ' ';
      memcpy (p, insn_out, insn_len + 1);
    }

  return new;
}

/* Replicate insns as appropriate for the given DEFINE_COND_EXEC.  */

static void
process_one_cond_exec (struct queue_elem *ce_elem)
{
  struct queue_elem *insn_elem;
  for (insn_elem = define_insn_queue; insn_elem ; insn_elem = insn_elem->next)
    {
      int alternatives, max_operand;
      rtx pred, insn, pattern;

      if (! is_predicable (insn_elem))
	continue;

      alternatives = 1;
      max_operand = -1;
      collect_insn_data (insn_elem->data, &alternatives, &max_operand);
      max_operand += 1;

      if (XVECLEN (ce_elem->data, 0) != 1)
	{
	  message_with_line (ce_elem->lineno,
			     "too many patterns in predicate");
	  errors = 1;
	  return;
	}

      pred = copy_rtx (XVECEXP (ce_elem->data, 0, 0));
      pred = alter_predicate_for_insn (pred, alternatives, max_operand,
				       ce_elem->lineno);
      if (pred == NULL)
	return;

      /* Construct a new pattern for the new insn.  */
      insn = copy_rtx (insn_elem->data);
      XSTR (insn, 0) = "";
      pattern = rtx_alloc (COND_EXEC);
      XEXP (pattern, 0) = pred;
      if (XVECLEN (insn, 1) == 1)
	{
	  XEXP (pattern, 1) = XVECEXP (insn, 1, 0);
	  XVECEXP (insn, 1, 0) = pattern;
	  PUT_NUM_ELEM (XVEC (insn, 1), 1);
	}
      else
	{
	  XEXP (pattern, 1) = rtx_alloc (PARALLEL);
	  XVEC (XEXP (pattern, 1), 0) = XVEC (insn, 1);
	  XVEC (insn, 1) = rtvec_alloc (1);
	  XVECEXP (insn, 1, 0) = pattern;
	}

      XSTR (insn, 2) = alter_test_for_insn (ce_elem, insn_elem);
      XTMPL (insn, 3) = alter_output_for_insn (ce_elem, insn_elem,
					      alternatives, max_operand);

      /* ??? Set `predicable' to false.  Not crucial since it's really
         only used here, and we won't reprocess this new pattern.  */

      /* Put the new pattern on the `other' list so that it
	 (a) is not reprocessed by other define_cond_exec patterns
	 (b) appears after all normal define_insn patterns.

	 ??? B is debatable.  If one has normal insns that match
	 cond_exec patterns, they will be preferred over these
	 generated patterns.  Whether this matters in practice, or if
	 it's a good thing, or whether we should thread these new
	 patterns into the define_insn chain just after their generator
	 is something we'll have to experiment with.  */

      queue_pattern (insn, &other_tail, insn_elem->filename,
		     insn_elem->lineno);
    }
}

/* If we have any DEFINE_COND_EXEC patterns, expand the DEFINE_INSN
   patterns appropriately.  */

static void
process_define_cond_exec (void)
{
  struct queue_elem *elem;

  identify_predicable_attribute ();
  if (errors)
    return;

  for (elem = define_cond_exec_queue; elem ; elem = elem->next)
    process_one_cond_exec (elem);
}

static char *
save_string (const char *s, int len)
{
  char *result = xmalloc (len + 1);

  memcpy (result, s, len);
  result[len] = 0;
  return result;
}


/* The entry point for initializing the reader.  */

int
init_md_reader_args (int argc, char **argv)
{
  int i;
  const char *in_fname;

  max_include_len = 0;
  in_fname = NULL;
  for (i = 1; i < argc; i++)
    {
      if (argv[i][0] != '-')
	{
	  if (in_fname == NULL)
	    in_fname = argv[i];
	}
      else
	{
	  int c = argv[i][1];
	  switch (c)
	    {
	    case 'I':		/* Add directory to path for includes.  */
	      {
		struct file_name_list *dirtmp;

		dirtmp = xmalloc (sizeof (struct file_name_list));
		dirtmp->next = 0;	/* New one goes on the end */
		if (first_dir_md_include == 0)
		  first_dir_md_include = dirtmp;
		else
		  last_dir_md_include->next = dirtmp;
		last_dir_md_include = dirtmp;	/* Tail follows the last one */
		if (argv[i][1] == 'I' && argv[i][2] != 0)
		  dirtmp->fname = argv[i] + 2;
		else if (i + 1 == argc)
		  fatal ("directory name missing after -I option");
		else
		  dirtmp->fname = argv[++i];
		if (strlen (dirtmp->fname) > max_include_len)
		  max_include_len = strlen (dirtmp->fname);
	      }
	      break;
	    default:
	      fatal ("invalid option `%s'", argv[i]);

	    }
	}
    }
    return init_md_reader (in_fname);
}

/* The entry point for initializing the reader.  */

int
init_md_reader (const char *filename)
{
  FILE *input_file;
  int c;
  size_t i;
  char *lastsl;

  lastsl = strrchr (filename, '/');
  if (lastsl != NULL)
    base_dir = save_string (filename, lastsl - filename + 1 );

  read_rtx_filename = filename;
  input_file = fopen (filename, "r");
  if (input_file == 0)
    {
      perror (filename);
      return FATAL_EXIT_CODE;
    }

  /* Initialize the table of insn conditions.  */
  condition_table = htab_create (n_insn_conditions,
				 hash_c_test, cmp_c_test, NULL);

  for (i = 0; i < n_insn_conditions; i++)
    *(htab_find_slot (condition_table, &insn_conditions[i], INSERT))
      = (void *) &insn_conditions[i];

  obstack_init (rtl_obstack);
  errors = 0;
  sequence_num = 0;

  /* Read the entire file.  */
  while (1)
    {
      rtx desc;
      int lineno;

      c = read_skip_spaces (input_file);
      if (c == EOF)
        break;

      ungetc (c, input_file);
      lineno = read_rtx_lineno;
      desc = read_rtx (input_file);
      process_rtx (desc, lineno);
    }
  fclose (input_file);

  /* Process define_cond_exec patterns.  */
  if (define_cond_exec_queue != NULL)
    process_define_cond_exec ();

  return errors ? FATAL_EXIT_CODE : SUCCESS_EXIT_CODE;
}

/* The entry point for reading a single rtx from an md file.  */

rtx
read_md_rtx (int *lineno, int *seqnr)
{
  struct queue_elem **queue, *elem;
  rtx desc;

 discard:

  /* Read all patterns from a given queue before moving on to the next.  */
  if (define_attr_queue != NULL)
    queue = &define_attr_queue;
  else if (define_insn_queue != NULL)
    queue = &define_insn_queue;
  else if (other_queue != NULL)
    queue = &other_queue;
  else
    return NULL_RTX;

  elem = *queue;
  *queue = elem->next;
  desc = elem->data;
  read_rtx_filename = elem->filename;
  *lineno = elem->lineno;
  *seqnr = sequence_num;

  free (elem);

  /* Discard insn patterns which we know can never match (because
     their C test is provably always false).  If insn_elision is
     false, our caller needs to see all the patterns.  Note that the
     elided patterns are never counted by the sequence numbering; it
     it is the caller's responsibility, when insn_elision is false, not
     to use elided pattern numbers for anything.  */
  switch (GET_CODE (desc))
    {
    case DEFINE_INSN:
    case DEFINE_EXPAND:
      if (maybe_eval_c_test (XSTR (desc, 2)) != 0)
	sequence_num++;
      else if (insn_elision)
	goto discard;
      break;

    case DEFINE_SPLIT:
    case DEFINE_PEEPHOLE:
    case DEFINE_PEEPHOLE2:
      if (maybe_eval_c_test (XSTR (desc, 1)) != 0)
	sequence_num++;
      else if (insn_elision)
	    goto discard;
      break;

    default:
      break;
    }

  return desc;
}

/* Helper functions for insn elision.  */

/* Compute a hash function of a c_test structure, which is keyed
   by its ->expr field.  */
hashval_t
hash_c_test (const void *x)
{
  const struct c_test *a = (const struct c_test *) x;
  const unsigned char *base, *s = (const unsigned char *) a->expr;
  hashval_t hash;
  unsigned char c;
  unsigned int len;

  base = s;
  hash = 0;

  while ((c = *s++) != '\0')
    {
      hash += c + (c << 17);
      hash ^= hash >> 2;
    }

  len = s - base;
  hash += len + (len << 17);
  hash ^= hash >> 2;

  return hash;
}

/* Compare two c_test expression structures.  */
int
cmp_c_test (const void *x, const void *y)
{
  const struct c_test *a = (const struct c_test *) x;
  const struct c_test *b = (const struct c_test *) y;

  return !strcmp (a->expr, b->expr);
}

/* Given a string representing a C test expression, look it up in the
   condition_table and report whether or not its value is known
   at compile time.  Returns a tristate: 1 for known true, 0 for
   known false, -1 for unknown.  */
int
maybe_eval_c_test (const char *expr)
{
  const struct c_test *test;
  struct c_test dummy;

  if (expr[0] == 0)
    return 1;

  if (insn_elision_unavailable)
    return -1;

  dummy.expr = expr;
  test = htab_find (condition_table, &dummy);
  if (!test)
    abort ();

  return test->value;
}

/* Given a string, return the number of comma-separated elements in it.
   Return 0 for the null string.  */
int
n_comma_elts (const char *s)
{
  int n;

  if (*s == '\0')
    return 0;

  for (n = 1; *s; s++)
    if (*s == ',')
      n++;

  return n;
}

/* Given a pointer to a (char *), return a pointer to the beginning of the
   next comma-separated element in the string.  Advance the pointer given
   to the end of that element.  Return NULL if at end of string.  Caller
   is responsible for copying the string if necessary.  White space between
   a comma and an element is ignored.  */

const char *
scan_comma_elt (const char **pstr)
{
  const char *start;
  const char *p = *pstr;

  if (*p == ',')
    p++;
  while (ISSPACE(*p))
    p++;

  if (*p == '\0')
    return NULL;

  start = p;

  while (*p != ',' && *p != '\0')
    p++;

  *pstr = p;
  return start;
}