bc-optab.c

gcc库的原代码,对编程有很大帮助.

  enum typecode to;
  int cost;
  struct conversion_list *prev;
};

/* Determine if it is "reasonable" to add a given conversion to
   a given list of conversions.  The following criteria define
   "reasonable" conversion lists:
   * No typecode appears more than once in the sequence (no loops).
   * At most one conversion from integer to float or vice versa is present.
   * Either sign extensions or zero extensions may be present, but not both.
   * No widening conversions occur after a signed/unsigned conversion.
   * The sequence of sizes must be strict nonincreasing or nondecreasing.  */
static int
conversion_reasonable_p (conversion, list)
     struct conversion_info *conversion;
     struct conversion_list *list;
{
  struct conversion_list *curr;
  int curr_size, prev_size;
  int has_int_float, has_float_int;
  int has_sign_extend, has_zero_extend;
  int has_signed_unsigned, has_unsigned_signed;

  has_int_float = 0;
  has_float_int = 0;
  has_sign_extend = 0;
  has_zero_extend = 0;
  has_signed_unsigned = 0;
  has_unsigned_signed = 0;

  /* Make sure the destination typecode doesn't already appear in
     the list.  */
  for (curr = list; curr; curr = curr->prev)
    if (conversion->to == curr->to)
      return 0;

  /* Check for certain kinds of conversions.  */
  if (TYPECODE_INTEGER_P (conversion->from)
      && TYPECODE_FLOAT_P (conversion->to))
    has_int_float = 1;
  if (TYPECODE_FLOAT_P (conversion->from)
      && TYPECODE_INTEGER_P (conversion->to))
    has_float_int = 1;
  if (TYPECODE_SIGNED_P (conversion->from)
      && TYPECODE_SIGNED_P (conversion->to)
      && GET_TYPECODE_SIZE (conversion->from)
      < GET_TYPECODE_SIZE (conversion->to))
    has_sign_extend = 1;
  if (TYPECODE_UNSIGNED_P (conversion->from)
      && TYPECODE_UNSIGNED_P (conversion->to)
      && GET_TYPECODE_SIZE (conversion->from)
      < GET_TYPECODE_SIZE (conversion->to))
    has_zero_extend = 1;

  for (curr = list; curr && curr->prev; curr = curr->prev)
    {
      if (TYPECODE_INTEGER_P (curr->prev->to)
	  && TYPECODE_FLOAT_P (curr->to))
	has_int_float = 1;
      if (TYPECODE_FLOAT_P (curr->prev->to)
	  && TYPECODE_INTEGER_P (curr->to))
	has_float_int = 1;
      if (TYPECODE_SIGNED_P (curr->prev->to)
	  && TYPECODE_SIGNED_P (curr->to)
	  && GET_TYPECODE_SIZE (curr->prev->to)
	  < GET_TYPECODE_SIZE (curr->to))
	has_sign_extend = 1;
      if (TYPECODE_UNSIGNED_P (curr->prev->to)
	  && TYPECODE_UNSIGNED_P (curr->to)
	  && GET_TYPECODE_SIZE (curr->prev->to)
	  < GET_TYPECODE_SIZE (curr->to))
	has_zero_extend = 1;
      if (TYPECODE_SIGNED_P (curr->prev->to)
	  && TYPECODE_UNSIGNED_P (curr->to))
	has_signed_unsigned = 1;
      if (TYPECODE_UNSIGNED_P (curr->prev->to)
	  && TYPECODE_SIGNED_P (curr->to))
	has_unsigned_signed = 1;
    }

  if (TYPECODE_INTEGER_P (conversion->from)
      && TYPECODE_INTEGER_P (conversion->to)
      && GET_TYPECODE_SIZE (conversion->to)
      > GET_TYPECODE_SIZE (conversion->from)
      && (has_signed_unsigned || has_unsigned_signed))
    return 0;

  if (has_float_int && has_int_float || has_sign_extend && has_zero_extend)
    return 0;

  /* Make sure the sequence of destination typecode sizes is
     strictly nondecreasing or strictly nonincreasing.  */
  prev_size = GET_TYPECODE_SIZE (conversion->to);
  for (curr = list; curr; curr = curr->prev)
    {
      curr_size = GET_TYPECODE_SIZE (curr->to);
      if (curr_size != prev_size)
	break;
    }
  if (!curr)
    return 1;

  if (curr_size < prev_size)
    for (prev_size = curr_size; curr; curr = curr->prev)
      {
	curr_size = GET_TYPECODE_SIZE (curr->to);
	if (curr_size > prev_size)
	  return 0;
	prev_size = curr_size;
      }
  else
    for (prev_size = curr_size; curr; curr = curr->prev)
      {
	curr_size = GET_TYPECODE_SIZE (curr->to);
	if (curr_size < prev_size)
	  return 0;
	prev_size = curr_size;
      }
  return 1;
}


/* Exhaustively search all reasonable conversions to find one to
   convert the given types.  */
static struct conversion_recipe
deduce_conversion (from, to)
     enum typecode from, to;
{
  struct rl
    {
      struct conversion_list *list;
      struct rl *next;
    } *prev, curr, *good, *temp;
  struct conversion_list *conv, *best;
  int i, cost, bestcost;
  struct conversion_recipe result;
  struct obstack recipe_obstack;


  obstack_init (&recipe_obstack);
  curr.next = (struct rl *) obstack_alloc (&recipe_obstack, sizeof (struct rl));
  curr.next->list =
    (struct conversion_list *) obstack_alloc (&recipe_obstack,
					      sizeof (struct conversion_list));
  curr.next->list->opcode = -1;
  curr.next->list->to = from;
  curr.next->list->cost = 0;
  curr.next->list->prev = 0;
  curr.next->next = 0;
  good = 0;

  while (curr.next)
    {
      /* Remove successful conversions from further consideration.  */
      for (prev = &curr; prev; prev = prev->next)
	if (prev->next && prev->next->list->to == to)
	  {
	    temp = prev->next->next;
	    prev->next->next = good;
	    good = prev->next;
	    prev->next = temp;
	  }

      /* Go through each of the pending conversion chains, trying
	 all possible candidate conversions on them.  */
      for (prev = curr.next, curr.next = 0; prev; prev = prev->next)
	for (i = 0; i < NUM_CONVERSIONS; ++i)
	  if (conversion_info[i].from == prev->list->to
	      && conversion_reasonable_p (&conversion_info[i], prev->list))
	    {
	      temp = (struct rl *) obstack_alloc (&recipe_obstack,
						  sizeof (struct rl));
	      temp->list = (struct conversion_list *)
		obstack_alloc (&recipe_obstack,
			       sizeof (struct conversion_list));
	      temp->list->opcode = conversion_info[i].opcode;
	      temp->list->to = conversion_info[i].to;
	      temp->list->cost = conversion_info[i].cost;
	      temp->list->prev = prev->list;
	      temp->next = curr.next;
	      curr.next = temp;
	    }
    }

  bestcost = BIG_ARBITRARY_NUMBER;
  best = 0;
  for (temp = good; temp; temp = temp->next)
    {
      for (conv = temp->list, cost = 0; conv; conv = conv->prev)
	cost += conv->cost;
      if (cost < bestcost)
	{
	  bestcost = cost;
	  best = temp->list;
	}
    }

  if (!best)
    abort ();

  for (i = 0, conv = best; conv; conv = conv->prev)
    if (conv->opcode != -1)
      ++i;

  result.opcodes = (unsigned char *) xmalloc (i);
  result.nopcodes = i;
  for (conv = best; conv; conv = conv->prev)
    if (conv->opcode != -1)
      result.opcodes[--i] = conv->opcode;
  result.cost = bestcost;
  obstack_free (&recipe_obstack, 0);
  return result;
}

#define DEDUCE_CONVERSION(FROM, TO)				\
  (conversion_recipe[(int) FROM][(int) TO].opcodes ? 0		\
   : (conversion_recipe[(int) FROM][(int) TO]			\
       = deduce_conversion (FROM, TO), 0))


/* Emit a conversion between the given scalar types.  */
void
emit_typecode_conversion (from, to)
     enum typecode from, to;
{
  int i;

  DEDUCE_CONVERSION (from, to);
  for (i = 0; i < conversion_recipe[(int) from][(int) to].nopcodes; ++i)
    bc_emit_instruction (conversion_recipe[(int) from][(int) to].opcodes[i]);
}


/* Initialize mode_to_code_map[] */
void
bc_init_mode_to_code_map ()
{
  int mode;

  for (mode = 0; mode < MAX_MACHINE_MODE + 1; mode++)
    {
      signed_mode_to_code_map[mode] = 
	unsigned_mode_to_code_map[mode] =
	  LAST_AND_UNUSED_TYPECODE;
    }

#define DEF_MODEMAP(SYM, CODE, UCODE, CONST, LOAD, STORE) \
  { signed_mode_to_code_map[(int) SYM] = CODE; \
    unsigned_mode_to_code_map[(int) SYM] = UCODE; }
#include "modemap.def"
#undef DEF_MODEMAP

  /* Initialize opcode maps for const, load, and store */
  bc_init_mode_to_opcode_maps ();
}

/* Given a machine mode return the preferred typecode.  */
enum typecode
preferred_typecode (mode, unsignedp)
     enum machine_mode mode;
     int unsignedp;
{
  enum typecode code = (unsignedp
			? unsigned_mode_to_code_map
			: signed_mode_to_code_map) [MIN ((int) mode,
							 (int) MAX_MACHINE_MODE)];

  if (code == LAST_AND_UNUSED_TYPECODE)
    abort ();

  return code;
}


/* Expand a conversion between the given types.  */
void
bc_expand_conversion (from, to)
     tree from, to;
{
  enum typecode fcode, tcode;

  fcode = preferred_typecode (TYPE_MODE (from), TREE_UNSIGNED (from));
  tcode = preferred_typecode (TYPE_MODE (to), TREE_UNSIGNED (to));

  emit_typecode_conversion (fcode, tcode);
}

/* Expand a conversion of the given type to a truth value.  */
void
bc_expand_truth_conversion (from)
     tree from;
{
  enum typecode fcode;

  fcode = preferred_typecode (TYPE_MODE (from), TREE_UNSIGNED (from));
  emit_typecode_conversion (fcode, Tcode);
}

/* Emit an appropriate binary operation.  */
void
bc_expand_binary_operation (optab, resulttype, arg0, arg1)
     struct binary_operator optab[];
     tree resulttype, arg0, arg1;
{
  int i, besti, cost, bestcost;
  enum typecode resultcode, arg0code, arg1code;
  
  resultcode = preferred_typecode (TYPE_MODE (resulttype), TREE_UNSIGNED (resulttype));
  arg0code = preferred_typecode (TYPE_MODE (TREE_TYPE (arg0)), TREE_UNSIGNED (resulttype));
  arg1code = preferred_typecode (TYPE_MODE (TREE_TYPE (arg1)), TREE_UNSIGNED (resulttype));

  besti = -1;
  bestcost = BIG_ARBITRARY_NUMBER;

  for (i = 0; optab[i].opcode != -1; ++i)
    {
      cost = 0;
      DEDUCE_CONVERSION (arg0code, optab[i].arg0);
      cost += conversion_recipe[(int) arg0code][(int) optab[i].arg0].cost;
      DEDUCE_CONVERSION (arg1code, optab[i].arg1);
      cost += conversion_recipe[(int) arg1code][(int) optab[i].arg1].cost;
      if (cost < bestcost)
	{
	  besti = i;
	  bestcost = cost;
	}
    }

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

  expand_expr (arg1, 0, VOIDmode, 0);
  emit_typecode_conversion (arg1code, optab[besti].arg1);
  expand_expr (arg0, 0, VOIDmode, 0);
  emit_typecode_conversion (arg0code, optab[besti].arg0);
  bc_emit_instruction (optab[besti].opcode);
  emit_typecode_conversion (optab[besti].result, resultcode);
}

/* Emit an appropriate unary operation.  */
void
bc_expand_unary_operation (optab, resulttype, arg0)
     struct unary_operator optab[];
     tree resulttype, arg0;
{
  int i, besti, cost, bestcost;
  enum typecode resultcode, arg0code;
  
  resultcode = preferred_typecode (TYPE_MODE (resulttype), TREE_UNSIGNED (resulttype));
  arg0code = preferred_typecode (TYPE_MODE (TREE_TYPE (arg0)), TREE_UNSIGNED (TREE_TYPE (arg0)));

  besti = -1;
  bestcost = BIG_ARBITRARY_NUMBER;

  for (i = 0; optab[i].opcode != -1; ++i)
    {
      DEDUCE_CONVERSION (arg0code, optab[i].arg0);
      cost = conversion_recipe[(int) arg0code][(int) optab[i].arg0].cost;
      if (cost < bestcost)
	{
	  besti = i;
	  bestcost = cost;
	}
    }

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

  expand_expr (arg0, 0, VOIDmode, 0);
  emit_typecode_conversion (arg0code, optab[besti].arg0);
  bc_emit_instruction (optab[besti].opcode);
  emit_typecode_conversion (optab[besti].result, resultcode);
}


/* Emit an appropriate increment.  */
void
bc_expand_increment (optab, type)
     struct increment_operator optab[];
     tree type;
{
  enum typecode code;
  int i;

  code = preferred_typecode (TYPE_MODE (type), TREE_UNSIGNED (type));
  for (i = 0; (int) optab[i].opcode >= 0; ++i)
    if (code == optab[i].arg)
      {
	bc_emit_instruction (optab[i].opcode);
	return;
      }
  abort ();
}