reload.c

GUN开源阻止下的编译器GCC


/* Transfer all replacements that used to be in reload FROM to be in
   reload TO.  */

void
transfer_replacements (to, from)
     int to, from;
{
  int i;

  for (i = 0; i < n_replacements; i++)
    if (replacements[i].what == from)
      replacements[i].what = to;
}

/* If there is only one output reload, and it is not for an earlyclobber
   operand, try to combine it with a (logically unrelated) input reload
   to reduce the number of reload registers needed.

   This is safe if the input reload does not appear in
   the value being output-reloaded, because this implies
   it is not needed any more once the original insn completes.

   If that doesn't work, see we can use any of the registers that
   die in this insn as a reload register.  We can if it is of the right
   class and does not appear in the value being output-reloaded.  */

static void
combine_reloads ()
{
  int i;
  int output_reload = -1;
  int secondary_out = -1;
  rtx note;

  /* Find the output reload; return unless there is exactly one
     and that one is mandatory.  */

  for (i = 0; i < n_reloads; i++)
    if (reload_out[i] != 0)
      {
	if (output_reload >= 0)
	  return;
	output_reload = i;
      }

  if (output_reload < 0 || reload_optional[output_reload])
    return;

  /* An input-output reload isn't combinable.  */

  if (reload_in[output_reload] != 0)
    return;

  /* If this reload is for an earlyclobber operand, we can't do anything.  */
  if (earlyclobber_operand_p (reload_out[output_reload]))
    return;

  /* Check each input reload; can we combine it?  */

  for (i = 0; i < n_reloads; i++)
    if (reload_in[i] && ! reload_optional[i] && ! reload_nocombine[i]
	/* Life span of this reload must not extend past main insn.  */
	&& reload_when_needed[i] != RELOAD_FOR_OUTPUT_ADDRESS
	&& reload_when_needed[i] != RELOAD_OTHER
	&& (CLASS_MAX_NREGS (reload_reg_class[i], reload_inmode[i])
	    == CLASS_MAX_NREGS (reload_reg_class[output_reload],
				reload_outmode[output_reload]))
	&& reload_inc[i] == 0
	&& reload_reg_rtx[i] == 0
#ifdef SECONDARY_MEMORY_NEEDED
	/* Don't combine two reloads with different secondary
	   memory locations.  */
	&& (secondary_memlocs_elim[(int) reload_outmode[output_reload]][reload_opnum[i]] == 0
	    || secondary_memlocs_elim[(int) reload_outmode[output_reload]][reload_opnum[output_reload]] == 0
	    || rtx_equal_p (secondary_memlocs_elim[(int) reload_outmode[output_reload]][reload_opnum[i]],
			    secondary_memlocs_elim[(int) reload_outmode[output_reload]][reload_opnum[output_reload]]))
#endif
#ifdef SMALL_REGISTER_CLASSES
	&& reload_reg_class[i] == reload_reg_class[output_reload]
#else
	&& (reg_class_subset_p (reload_reg_class[i],
				reload_reg_class[output_reload])
	    || reg_class_subset_p (reload_reg_class[output_reload],
				   reload_reg_class[i]))
#endif
	&& (MATCHES (reload_in[i], reload_out[output_reload])
	    /* Args reversed because the first arg seems to be
	       the one that we imagine being modified
	       while the second is the one that might be affected.  */
	    || (! reg_overlap_mentioned_for_reload_p (reload_out[output_reload],
						      reload_in[i])
		/* However, if the input is a register that appears inside
		   the output, then we also can't share.
		   Imagine (set (mem (reg 69)) (plus (reg 69) ...)).
		   If the same reload reg is used for both reg 69 and the
		   result to be stored in memory, then that result
		   will clobber the address of the memory ref.  */
		&& ! (GET_CODE (reload_in[i]) == REG
		      && reg_overlap_mentioned_for_reload_p (reload_in[i],
							     reload_out[output_reload]))))
	&& (reg_class_size[(int) reload_reg_class[i]]
#ifdef SMALL_REGISTER_CLASSES
	     || 1
#endif
	    )
	/* We will allow making things slightly worse by combining an
	   input and an output, but no worse than that.  */
	&& (reload_when_needed[i] == RELOAD_FOR_INPUT
	    || reload_when_needed[i] == RELOAD_FOR_OUTPUT))
      {
	int j;

	/* We have found a reload to combine with!  */
	reload_out[i] = reload_out[output_reload];
	reload_outmode[i] = reload_outmode[output_reload];
	/* Mark the old output reload as inoperative.  */
	reload_out[output_reload] = 0;
	/* The combined reload is needed for the entire insn.  */
	reload_when_needed[i] = RELOAD_OTHER;
	/* If the output reload had a secondary reload, copy it. */
	if (reload_secondary_out_reload[output_reload] != -1)
	  {
	    reload_secondary_out_reload[i]
	      = reload_secondary_out_reload[output_reload];
	    reload_secondary_out_icode[i]
	      = reload_secondary_out_icode[output_reload];
	  }

#ifdef SECONDARY_MEMORY_NEEDED
	/* Copy any secondary MEM.  */
	if (secondary_memlocs_elim[(int) reload_outmode[output_reload]][reload_opnum[output_reload]] != 0)
	  secondary_memlocs_elim[(int) reload_outmode[output_reload]][reload_opnum[i]]
	    = secondary_memlocs_elim[(int) reload_outmode[output_reload]][reload_opnum[output_reload]];
#endif
	/* If required, minimize the register class. */
	if (reg_class_subset_p (reload_reg_class[output_reload],
				reload_reg_class[i]))
	  reload_reg_class[i] = reload_reg_class[output_reload];

	/* Transfer all replacements from the old reload to the combined.  */
	for (j = 0; j < n_replacements; j++)
	  if (replacements[j].what == output_reload)
	    replacements[j].what = i;

	return;
      }

  /* If this insn has only one operand that is modified or written (assumed
     to be the first),  it must be the one corresponding to this reload.  It
     is safe to use anything that dies in this insn for that output provided
     that it does not occur in the output (we already know it isn't an
     earlyclobber.  If this is an asm insn, give up.  */

  if (INSN_CODE (this_insn) == -1)
    return;

  for (i = 1; i < insn_n_operands[INSN_CODE (this_insn)]; i++)
    if (insn_operand_constraint[INSN_CODE (this_insn)][i][0] == '='
	|| insn_operand_constraint[INSN_CODE (this_insn)][i][0] == '+')
      return;

  /* See if some hard register that dies in this insn and is not used in
     the output is the right class.  Only works if the register we pick
     up can fully hold our output reload.  */
  for (note = REG_NOTES (this_insn); note; note = XEXP (note, 1))
    if (REG_NOTE_KIND (note) == REG_DEAD
	&& GET_CODE (XEXP (note, 0)) == REG
	&& ! reg_overlap_mentioned_for_reload_p (XEXP (note, 0),
						 reload_out[output_reload])
	&& REGNO (XEXP (note, 0)) < FIRST_PSEUDO_REGISTER
	&& HARD_REGNO_MODE_OK (REGNO (XEXP (note, 0)), reload_outmode[output_reload])
	&& TEST_HARD_REG_BIT (reg_class_contents[(int) reload_reg_class[output_reload]],
			      REGNO (XEXP (note, 0)))
	&& (HARD_REGNO_NREGS (REGNO (XEXP (note, 0)), reload_outmode[output_reload])
	    <= HARD_REGNO_NREGS (REGNO (XEXP (note, 0)), GET_MODE (XEXP (note, 0))))
	/* Ensure that a secondary or tertiary reload for this output
	   won't want this register.  */
        && ((secondary_out = reload_secondary_out_reload[output_reload]) == -1
            || (! (TEST_HARD_REG_BIT
		    (reg_class_contents[(int) reload_reg_class[secondary_out]],
		     REGNO (XEXP (note, 0))))
		&& ((secondary_out = reload_secondary_out_reload[secondary_out]) == -1
		    ||  ! (TEST_HARD_REG_BIT
			   (reg_class_contents[(int) reload_reg_class[secondary_out]],
			    REGNO (XEXP (note, 0)))))))
	&& ! fixed_regs[REGNO (XEXP (note, 0))])
      {
	reload_reg_rtx[output_reload] = gen_rtx (REG,
						 reload_outmode[output_reload],
						 REGNO (XEXP (note, 0)));
	return;
      }
}

/* Try to find a reload register for an in-out reload (expressions IN and OUT).
   See if one of IN and OUT is a register that may be used;
   this is desirable since a spill-register won't be needed.
   If so, return the register rtx that proves acceptable.

   INLOC and OUTLOC are locations where IN and OUT appear in the insn.
   CLASS is the register class required for the reload.

   If FOR_REAL is >= 0, it is the number of the reload,
   and in some cases when it can be discovered that OUT doesn't need
   to be computed, clear out reload_out[FOR_REAL].

   If FOR_REAL is -1, this should not be done, because this call
   is just to see if a register can be found, not to find and install it.  */

static rtx
find_dummy_reload (real_in, real_out, inloc, outloc,
		   inmode, outmode, class, for_real)
     rtx real_in, real_out;
     rtx *inloc, *outloc;
     enum machine_mode inmode, outmode;
     enum reg_class class;
     int for_real;
{
  rtx in = real_in;
  rtx out = real_out;
  int in_offset = 0;
  int out_offset = 0;
  rtx value = 0;

  /* If operands exceed a word, we can't use either of them
     unless they have the same size.  */
  if (GET_MODE_SIZE (outmode) != GET_MODE_SIZE (inmode)
      && (GET_MODE_SIZE (outmode) > UNITS_PER_WORD
	  || GET_MODE_SIZE (inmode) > UNITS_PER_WORD))
    return 0;

  /* Find the inside of any subregs.  */
  while (GET_CODE (out) == SUBREG)
    {
      out_offset = SUBREG_WORD (out);
      out = SUBREG_REG (out);
    }
  while (GET_CODE (in) == SUBREG)
    {
      in_offset = SUBREG_WORD (in);
      in = SUBREG_REG (in);
    }

  /* Narrow down the reg class, the same way push_reload will;
     otherwise we might find a dummy now, but push_reload won't.  */
  class = PREFERRED_RELOAD_CLASS (in, class);

  /* See if OUT will do.  */
  if (GET_CODE (out) == REG
      && REGNO (out) < FIRST_PSEUDO_REGISTER)
    {
      register int regno = REGNO (out) + out_offset;
      int nwords = HARD_REGNO_NREGS (regno, outmode);
      rtx saved_rtx;

      /* When we consider whether the insn uses OUT,
	 ignore references within IN.  They don't prevent us
	 from copying IN into OUT, because those refs would
	 move into the insn that reloads IN.

	 However, we only ignore IN in its role as this reload.
	 If the insn uses IN elsewhere and it contains OUT,
	 that counts.  We can't be sure it's the "same" operand
	 so it might not go through this reload.  */
      saved_rtx = *inloc;
      *inloc = const0_rtx;

      if (regno < FIRST_PSEUDO_REGISTER
	  /* A fixed reg that can overlap other regs better not be used
	     for reloading in any way.  */
#ifdef OVERLAPPING_REGNO_P
	  && ! (fixed_regs[regno] && OVERLAPPING_REGNO_P (regno))
#endif
	  && ! refers_to_regno_for_reload_p (regno, regno + nwords,
					     PATTERN (this_insn), outloc))
	{
	  int i;
	  for (i = 0; i < nwords; i++)
	    if (! TEST_HARD_REG_BIT (reg_class_contents[(int) class],
				     regno + i))
	      break;

	  if (i == nwords)
	    {
	      if (GET_CODE (real_out) == REG)
		value = real_out;
	      else
		value = gen_rtx (REG, outmode, regno);
	    }
	}

      *inloc = saved_rtx;
    }

  /* Consider using IN if OUT was not acceptable
     or if OUT dies in this insn (like the quotient in a divmod insn).
     We can't use IN unless it is dies in this insn,
     which means we must know accurately which hard regs are live.
     Also, the result can't go in IN if IN is used within OUT.  */
  if (hard_regs_live_known
      && GET_CODE (in) == REG
      && REGNO (in) < FIRST_PSEUDO_REGISTER
      && (value == 0
	  || find_reg_note (this_insn, REG_UNUSED, real_out))
      && find_reg_note (this_insn, REG_DEAD, real_in)
      && !fixed_regs[REGNO (in)]
      && HARD_REGNO_MODE_OK (REGNO (in),
			     /* The only case where out and real_out might
				have different modes is where real_out
				is a subreg, and in that case, out
				has a real mode.  */
			     (GET_MODE (out) != VOIDmode
			      ? GET_MODE (out) : outmode)))
    {
      register int regno = REGNO (in) + in_offset;
      int nwords = HARD_REGNO_NREGS (regno, inmode);

      if (! refers_to_regno_for_reload_p (regno, regno + nwords, out, NULL_PTR)
	  && ! hard_reg_set_here_p (regno, regno + nwords,
				    PATTERN (this_insn)))
	{
	  int i;
	  for (i = 0; i < nwords; i++)
	    if (! TEST_HARD_REG_BIT (reg_class_contents[(int) class],
				     regno + i))
	      break;

	  if (i == nwords)
	    {
	      /* If we were going to use OUT as the reload reg
		 and changed our mind, it means OUT is a dummy that
		 dies here.  So don't bother copying value to it.  */
	      if (for_real >= 0 && value == real_out)
		reload_out[for_real] = 0;
	      if (GET_CODE (real_in) == REG)
		value = real_in;
	      else
		value = gen_rtx (REG, inmode, regno);
	    }
	}
    }

  return value;
}

/* This page contains subroutines used mainly for determining
   whether the IN or an OUT of a reload can serve as the
   reload register.  */

/* Return 1 if X is an op