reload.c

gcc库的原代码,对编程有很大帮助.

    secondary_type = type;
  else
    secondary_type = in_p ? RELOAD_FOR_INPUT_ADDRESS : RELOAD_FOR_OUTPUT_ADDRESS;

  *picode = CODE_FOR_nothing;

  /* If X is a paradoxical SUBREG, use the inner value to determine both the
     mode and object being reloaded.  */
  if (GET_CODE (x) == SUBREG
      && (GET_MODE_SIZE (GET_MODE (x))
	  > GET_MODE_SIZE (GET_MODE (SUBREG_REG (x)))))
    {
      x = SUBREG_REG (x);
      reload_mode = GET_MODE (x);
    }

  /* If X is a pseudo-register that has an equivalent MEM (actually, if it
     is still a pseudo-register by now, it *must* have an equivalent MEM
     but we don't want to assume that), use that equivalent when seeing if
     a secondary reload is needed since whether or not a reload is needed
     might be sensitive to the form of the MEM.  */

  if (GET_CODE (x) == REG && REGNO (x) >= FIRST_PSEUDO_REGISTER
      && reg_equiv_mem[REGNO (x)] != 0)
    x = reg_equiv_mem[REGNO (x)];

#ifdef SECONDARY_INPUT_RELOAD_CLASS
  if (in_p)
    class = SECONDARY_INPUT_RELOAD_CLASS (reload_class, reload_mode, x);
#endif

#ifdef SECONDARY_OUTPUT_RELOAD_CLASS
  if (! in_p)
    class = SECONDARY_OUTPUT_RELOAD_CLASS (reload_class, reload_mode, x);
#endif

  /* If we don't need any secondary registers, done.  */
  if (class == NO_REGS)
    return -1;

  /* Get a possible insn to use.  If the predicate doesn't accept X, don't
     use the insn.  */

  icode = (in_p ? reload_in_optab[(int) reload_mode]
	   : reload_out_optab[(int) reload_mode]);

  if (icode != CODE_FOR_nothing
      && insn_operand_predicate[(int) icode][in_p]
      && (! (insn_operand_predicate[(int) icode][in_p]) (x, reload_mode)))
    icode = CODE_FOR_nothing;

  /* If we will be using an insn, see if it can directly handle the reload
     register we will be using.  If it can, the secondary reload is for a
     scratch register.  If it can't, we will use the secondary reload for
     an intermediate register and require a tertiary reload for the scratch
     register.  */

  if (icode != CODE_FOR_nothing)
    {
      /* If IN_P is non-zero, the reload register will be the output in 
	 operand 0.  If IN_P is zero, the reload register will be the input
	 in operand 1.  Outputs should have an initial "=", which we must
	 skip.  */

      char insn_letter = insn_operand_constraint[(int) icode][!in_p][in_p];
      enum reg_class insn_class
	= (insn_letter == 'r' ? GENERAL_REGS
	   : REG_CLASS_FROM_LETTER (insn_letter));

      if (insn_class == NO_REGS
	  || (in_p && insn_operand_constraint[(int) icode][!in_p][0] != '=')
	  /* The scratch register's constraint must start with "=&".  */
	  || insn_operand_constraint[(int) icode][2][0] != '='
	  || insn_operand_constraint[(int) icode][2][1] != '&')
	abort ();

      if (reg_class_subset_p (reload_class, insn_class))
	mode = insn_operand_mode[(int) icode][2];
      else
	{
	  char t_letter = insn_operand_constraint[(int) icode][2][2];
	  class = insn_class;
	  t_mode = insn_operand_mode[(int) icode][2];
	  t_class = (t_letter == 'r' ? GENERAL_REGS
		     : REG_CLASS_FROM_LETTER (t_letter));
	  t_icode = icode;
	  icode = CODE_FOR_nothing;
	}
    }

  /* This case isn't valid, so fail.  Reload is allowed to use the same
     register for RELOAD_FOR_INPUT_ADDRESS and RELOAD_FOR_INPUT reloads, but
     in the case of a secondary register, we actually need two different
     registers for correct code.  We fail here to prevent the possibility of
     silently generating incorrect code later.

     The convention is that secondary input reloads are valid only if the
     secondary_class is different from class.  If you have such a case, you
     can not use secondary reloads, you must work around the problem some
     other way.

     Allow this when MODE is not reload_mode and assume that the generated
     code handles this case (it does on the Alpha, which is the only place
     this currently happens).  */

  if (in_p && class == reload_class && mode == reload_mode)
    abort ();

  /* If we need a tertiary reload, see if we have one we can reuse or else
     make a new one.  */

  if (t_class != NO_REGS)
    {
      for (t_reload = 0; t_reload < n_reloads; t_reload++)
	if (reload_secondary_p[t_reload]
	    && (reg_class_subset_p (t_class, reload_reg_class[t_reload])
		|| reg_class_subset_p (reload_reg_class[t_reload], t_class))
	    && ((in_p && reload_inmode[t_reload] == t_mode)
		|| (! in_p && reload_outmode[t_reload] == t_mode))
	    && ((in_p && (reload_secondary_in_icode[t_reload]
			  == CODE_FOR_nothing))
		|| (! in_p &&(reload_secondary_out_icode[t_reload]
			      == CODE_FOR_nothing)))
	    && (reg_class_size[(int) t_class] == 1
#ifdef SMALL_REGISTER_CLASSES
		|| 1
#endif
		)
	    && MERGABLE_RELOADS (secondary_type,
				 reload_when_needed[t_reload],
				 opnum, reload_opnum[t_reload]))
	  {
	    if (in_p)
	      reload_inmode[t_reload] = t_mode;
	    if (! in_p)
	      reload_outmode[t_reload] = t_mode;

	    if (reg_class_subset_p (t_class, reload_reg_class[t_reload]))
	      reload_reg_class[t_reload] = t_class;

	    reload_opnum[t_reload] = MIN (reload_opnum[t_reload], opnum);
	    reload_optional[t_reload] &= optional;
	    reload_secondary_p[t_reload] = 1;
	    if (MERGE_TO_OTHER (secondary_type, reload_when_needed[t_reload],
				opnum, reload_opnum[t_reload]))
	      reload_when_needed[t_reload] = RELOAD_OTHER;
	  }

      if (t_reload == n_reloads)
	{
	  /* We need to make a new tertiary reload for this register class.  */
	  reload_in[t_reload] = reload_out[t_reload] = 0;
	  reload_reg_class[t_reload] = t_class;
	  reload_inmode[t_reload] = in_p ? t_mode : VOIDmode;
	  reload_outmode[t_reload] = ! in_p ? t_mode : VOIDmode;
	  reload_reg_rtx[t_reload] = 0;
	  reload_optional[t_reload] = optional;
	  reload_inc[t_reload] = 0;
	  /* Maybe we could combine these, but it seems too tricky.  */
	  reload_nocombine[t_reload] = 1;
	  reload_in_reg[t_reload] = 0;
	  reload_opnum[t_reload] = opnum;
	  reload_when_needed[t_reload] = secondary_type;
	  reload_secondary_in_reload[t_reload] = -1;
	  reload_secondary_out_reload[t_reload] = -1;
	  reload_secondary_in_icode[t_reload] = CODE_FOR_nothing;
	  reload_secondary_out_icode[t_reload] = CODE_FOR_nothing;
	  reload_secondary_p[t_reload] = 1;

	  n_reloads++;
	}
    }

  /* See if we can reuse an existing secondary reload.  */
  for (s_reload = 0; s_reload < n_reloads; s_reload++)
    if (reload_secondary_p[s_reload]
	&& (reg_class_subset_p (class, reload_reg_class[s_reload])
	    || reg_class_subset_p (reload_reg_class[s_reload], class))
	&& ((in_p && reload_inmode[s_reload] == mode)
	    || (! in_p && reload_outmode[s_reload] == mode))
	&& ((in_p && reload_secondary_in_reload[s_reload] == t_reload)
	    || (! in_p && reload_secondary_out_reload[s_reload] == t_reload))
	&& ((in_p && reload_secondary_in_icode[s_reload] == t_icode)
	    || (! in_p && reload_secondary_out_icode[s_reload] == t_icode))
	&& (reg_class_size[(int) class] == 1
#ifdef SMALL_REGISTER_CLASSES
	    || 1
#endif
	    )
	&& MERGABLE_RELOADS (secondary_type, reload_when_needed[s_reload],
			     opnum, reload_opnum[s_reload]))
      {
	if (in_p)
	  reload_inmode[s_reload] = mode;
	if (! in_p)
	  reload_outmode[s_reload] = mode;

	if (reg_class_subset_p (class, reload_reg_class[s_reload]))
	  reload_reg_class[s_reload] = class;

	reload_opnum[s_reload] = MIN (reload_opnum[s_reload], opnum);
	reload_optional[s_reload] &= optional;
	reload_secondary_p[s_reload] = 1;
	if (MERGE_TO_OTHER (secondary_type, reload_when_needed[s_reload],
			    opnum, reload_opnum[s_reload]))
	  reload_when_needed[s_reload] = RELOAD_OTHER;
      }

  if (s_reload == n_reloads)
    {
      /* We need to make a new secondary reload for this register class.  */
      reload_in[s_reload] = reload_out[s_reload] = 0;
      reload_reg_class[s_reload] = class;

      reload_inmode[s_reload] = in_p ? mode : VOIDmode;
      reload_outmode[s_reload] = ! in_p ? mode : VOIDmode;
      reload_reg_rtx[s_reload] = 0;
      reload_optional[s_reload] = optional;
      reload_inc[s_reload] = 0;
      /* Maybe we could combine these, but it seems too tricky.  */
      reload_nocombine[s_reload] = 1;
      reload_in_reg[s_reload] = 0;
      reload_opnum[s_reload] = opnum;
      reload_when_needed[s_reload] = secondary_type;
      reload_secondary_in_reload[s_reload] = in_p ? t_reload : -1;
      reload_secondary_out_reload[s_reload] = ! in_p ? t_reload : -1;
      reload_secondary_in_icode[s_reload] = in_p ? t_icode : CODE_FOR_nothing; 
      reload_secondary_out_icode[s_reload]
	= ! in_p ? t_icode : CODE_FOR_nothing;
      reload_secondary_p[s_reload] = 1;

      n_reloads++;

#ifdef SECONDARY_MEMORY_NEEDED
      /* If we need a memory location to copy between the two reload regs,
	 set it up now.  */

      if (in_p && icode == CODE_FOR_nothing
	  && SECONDARY_MEMORY_NEEDED (class, reload_class, reload_mode))
	get_secondary_mem (x, reload_mode, opnum, type);

      if (! in_p && icode == CODE_FOR_nothing
	  && SECONDARY_MEMORY_NEEDED (reload_class, class, reload_mode))
	get_secondary_mem (x, reload_mode, opnum, type);
#endif
    }

  *picode = icode;
  return s_reload;
}
#endif /* HAVE_SECONDARY_RELOADS */

#ifdef SECONDARY_MEMORY_NEEDED

/* Return a memory location that will be used to copy X in mode MODE.  
   If we haven't already made a location for this mode in this insn,
   call find_reloads_address on the location being returned.  */

rtx
get_secondary_mem (x, mode, opnum, type)
     rtx x;
     enum machine_mode mode;
     int opnum;
     enum reload_type type;
{
  rtx loc;
  int mem_valid;

  /* By default, if MODE is narrower than a word, widen it to a word.
     This is required because most machines that require these memory
     locations do not support short load and stores from all registers
     (e.g., FP registers).  */

#ifdef SECONDARY_MEMORY_NEEDED_MODE
  mode = SECONDARY_MEMORY_NEEDED_MODE (mode);
#else
  if (GET_MODE_BITSIZE (mode) < BITS_PER_WORD)
    mode = mode_for_size (BITS_PER_WORD, GET_MODE_CLASS (mode), 0);
#endif

  /* If we already have made a MEM for this operand in MODE, return it.  */
  if (secondary_memlocs_elim[(int) mode][opnum] != 0)
    return secondary_memlocs_elim[(int) mode][opnum];

  /* If this is the first time we've tried to get a MEM for this mode, 
     allocate a new one.  `something_changed' in reload will get set
     by noticing that the frame size has changed.  */

  if (secondary_memlocs[(int) mode] == 0)
    {
#ifdef SECONDARY_MEMORY_NEEDED_RTX
      secondary_memlocs[(int) mode] = SECONDARY_MEMORY_NEEDED_RTX (mode);
#else
      secondary_memlocs[(int) mode]
	= assign_stack_local (mode, GET_MODE_SIZE (mode), 0);
#endif
    }

  /* Get a version of the address doing any eliminations needed.  If that
     didn't give us a new MEM, make a new one if it isn't valid.  */

  loc = eliminate_regs (secondary_memlocs[(int) mode], VOIDmode, NULL_RTX);
  mem_valid = strict_memory_address_p (mode, XEXP (loc, 0));

  if (! mem_valid && loc == secondary_memlocs[(int) mode])
    loc = copy_rtx (loc);

  /* The only time the call below will do anything is if the stack
     offset is too large.  In that case IND_LEVELS doesn't matter, so we
     can just pass a zero.  Adjust the type to be the address of the
     corresponding object.  If the address was valid, save the eliminated
     address.  If it wasn't valid, we need to make a reload each time, so
     don't save it.  */

  if (! mem_valid)
    {
      type =  (type == RELOAD_FOR_INPUT ? RELOAD_FOR_INPUT_ADDRESS
	       : type == RELOAD_FOR_OUTPUT ? RELOAD_FOR_OUTPUT_ADDRESS
	       : RELOAD_OTHER);

      find_reloads_address (mode, NULL_PTR, XEXP (loc, 0), &XEXP (loc, 0),
			    opnum, type, 0);
    }

  secondary_memlocs_elim[(int) mode][opnum] = loc;
  return loc;
}

/* Clear any secondary memory locations we've made.  */

void
clear_secondary_mem ()
{
  bzero ((char *) secondary_memlocs, sizeof secondary_memlocs);
}
#endif /* SECONDARY_MEMORY_NEEDED */

/* Record one reload that needs to be performed.
   IN is an rtx saying where the data are to be found before this instruction.
   OUT says where they must be stored after the instruction.
   (IN is zero for data not read, and OUT is zero for data not written.)
   INLOC and OUTLOC point to the places in the instructions where
   IN and OUT were found.
   If IN and OUT are both non-zero, it means the same register must be used
   to reload both IN and OUT.

   CLASS is a register class required for the reloaded data.
   INMODE is the machine mode that the instruction requires
   for the reg that replaces IN and OUTMODE is likewise for OUT.

   If IN is zero, then OUT's location and mode should be passed as
   INLOC and INMODE.