explow.c

gcc库的原代码,对编程有很大帮助.

  /* We get better cse by rejecting indirect addressing at this stage.
     Let the combiner create indirect addresses where appropriate.
     For now, generate the code so that the subexpressions useful to share
     are visible.  But not if cse won't be done!  */
  else
    {
      if (! cse_not_expected && GET_CODE (x) != REG)
	x = break_out_memory_refs (x);

      /* At this point, any valid address is accepted.  */
      GO_IF_LEGITIMATE_ADDRESS (mode, x, win);

      /* If it was valid before but breaking out memory refs invalidated it,
	 use it the old way.  */
      if (memory_address_p (mode, oldx))
	goto win2;

      /* Perform machine-dependent transformations on X
	 in certain cases.  This is not necessary since the code
	 below can handle all possible cases, but machine-dependent
	 transformations can make better code.  */
      LEGITIMIZE_ADDRESS (x, oldx, mode, win);

      /* PLUS and MULT can appear in special ways
	 as the result of attempts to make an address usable for indexing.
	 Usually they are dealt with by calling force_operand, below.
	 But a sum containing constant terms is special
	 if removing them makes the sum a valid address:
	 then we generate that address in a register
	 and index off of it.  We do this because it often makes
	 shorter code, and because the addresses thus generated
	 in registers often become common subexpressions.  */
      if (GET_CODE (x) == PLUS)
	{
	  rtx constant_term = const0_rtx;
	  rtx y = eliminate_constant_term (x, &constant_term);
	  if (constant_term == const0_rtx
	      || ! memory_address_p (mode, y))
	    x = force_operand (x, NULL_RTX);
	  else
	    {
	      y = gen_rtx (PLUS, GET_MODE (x), copy_to_reg (y), constant_term);
	      if (! memory_address_p (mode, y))
		x = force_operand (x, NULL_RTX);
	      else
		x = y;
	    }
	}

      else if (GET_CODE (x) == MULT || GET_CODE (x) == MINUS)
	x = force_operand (x, NULL_RTX);

      /* If we have a register that's an invalid address,
	 it must be a hard reg of the wrong class.  Copy it to a pseudo.  */
      else if (GET_CODE (x) == REG)
	x = copy_to_reg (x);

      /* Last resort: copy the value to a register, since
	 the register is a valid address.  */
      else
	x = force_reg (Pmode, x);

      goto done;

    win2:
      x = oldx;
    win:
      if (flag_force_addr && ! cse_not_expected && GET_CODE (x) != REG
	  /* Don't copy an addr via a reg if it is one of our stack slots.  */
	  && ! (GET_CODE (x) == PLUS
		&& (XEXP (x, 0) == virtual_stack_vars_rtx
		    || XEXP (x, 0) == virtual_incoming_args_rtx)))
	{
	  if (general_operand (x, Pmode))
	    x = force_reg (Pmode, x);
	  else
	    x = force_operand (x, NULL_RTX);
	}
    }

 done:

  /* If we didn't change the address, we are done.  Otherwise, mark
     a reg as a pointer if we have REG or REG + CONST_INT.  */
  if (oldx == x)
    return x;
  else if (GET_CODE (x) == REG)
    mark_reg_pointer (x);
  else if (GET_CODE (x) == PLUS
	   && GET_CODE (XEXP (x, 0)) == REG
	   && GET_CODE (XEXP (x, 1)) == CONST_INT)
    mark_reg_pointer (XEXP (x, 0));

  /* OLDX may have been the address on a temporary.  Update the address
     to indicate that X is now used.  */
  update_temp_slot_address (oldx, x);

  return x;
}

/* Like `memory_address' but pretend `flag_force_addr' is 0.  */

rtx
memory_address_noforce (mode, x)
     enum machine_mode mode;
     rtx x;
{
  int ambient_force_addr = flag_force_addr;
  rtx val;

  flag_force_addr = 0;
  val = memory_address (mode, x);
  flag_force_addr = ambient_force_addr;
  return val;
}

/* Convert a mem ref into one with a valid memory address.
   Pass through anything else unchanged.  */

rtx
validize_mem (ref)
     rtx ref;
{
  if (GET_CODE (ref) != MEM)
    return ref;
  if (memory_address_p (GET_MODE (ref), XEXP (ref, 0)))
    return ref;
  /* Don't alter REF itself, since that is probably a stack slot.  */
  return change_address (ref, GET_MODE (ref), XEXP (ref, 0));
}

/* Return a modified copy of X with its memory address copied
   into a temporary register to protect it from side effects.
   If X is not a MEM, it is returned unchanged (and not copied).
   Perhaps even if it is a MEM, if there is no need to change it.  */

rtx
stabilize (x)
     rtx x;
{
  register rtx addr;
  if (GET_CODE (x) != MEM)
    return x;
  addr = XEXP (x, 0);
  if (rtx_unstable_p (addr))
    {
      rtx temp = copy_all_regs (addr);
      rtx mem;
      if (GET_CODE (temp) != REG)
	temp = copy_to_reg (temp);
      mem = gen_rtx (MEM, GET_MODE (x), temp);

      /* Mark returned memref with in_struct if it's in an array or
	 structure.  Copy const and volatile from original memref.  */

      MEM_IN_STRUCT_P (mem) = MEM_IN_STRUCT_P (x) || GET_CODE (addr) == PLUS;
      RTX_UNCHANGING_P (mem) = RTX_UNCHANGING_P (x);
      MEM_VOLATILE_P (mem) = MEM_VOLATILE_P (x);
      return mem;
    }
  return x;
}

/* Copy the value or contents of X to a new temp reg and return that reg.  */

rtx
copy_to_reg (x)
     rtx x;
{
  register rtx temp = gen_reg_rtx (GET_MODE (x));
 
  /* If not an operand, must be an address with PLUS and MULT so
     do the computation.  */ 
  if (! general_operand (x, VOIDmode))
    x = force_operand (x, temp);
  
  if (x != temp)
    emit_move_insn (temp, x);

  return temp;
}

/* Like copy_to_reg but always give the new register mode Pmode
   in case X is a constant.  */

rtx
copy_addr_to_reg (x)
     rtx x;
{
  return copy_to_mode_reg (Pmode, x);
}

/* Like copy_to_reg but always give the new register mode MODE
   in case X is a constant.  */

rtx
copy_to_mode_reg (mode, x)
     enum machine_mode mode;
     rtx x;
{
  register rtx temp = gen_reg_rtx (mode);
  
  /* If not an operand, must be an address with PLUS and MULT so
     do the computation.  */ 
  if (! general_operand (x, VOIDmode))
    x = force_operand (x, temp);

  if (GET_MODE (x) != mode && GET_MODE (x) != VOIDmode)
    abort ();
  if (x != temp)
    emit_move_insn (temp, x);
  return temp;
}

/* Load X into a register if it is not already one.
   Use mode MODE for the register.
   X should be valid for mode MODE, but it may be a constant which
   is valid for all integer modes; that's why caller must specify MODE.

   The caller must not alter the value in the register we return,
   since we mark it as a "constant" register.  */

rtx
force_reg (mode, x)
     enum machine_mode mode;
     rtx x;
{
  register rtx temp, insn, set;

  if (GET_CODE (x) == REG)
    return x;
  temp = gen_reg_rtx (mode);
  insn = emit_move_insn (temp, x);

  /* Let optimizers know that TEMP's value never changes
     and that X can be substituted for it.  Don't get confused
     if INSN set something else (such as a SUBREG of TEMP).  */
  if (CONSTANT_P (x)
      && (set = single_set (insn)) != 0
      && SET_DEST (set) == temp)
    {
      rtx note = find_reg_note (insn, REG_EQUAL, NULL_RTX);

      if (note)
	XEXP (note, 0) = x;
      else
	REG_NOTES (insn) = gen_rtx (EXPR_LIST, REG_EQUAL, x, REG_NOTES (insn));
    }
  return temp;
}

/* If X is a memory ref, copy its contents to a new temp reg and return
   that reg.  Otherwise, return X.  */

rtx
force_not_mem (x)
     rtx x;
{
  register rtx temp;
  if (GET_CODE (x) != MEM || GET_MODE (x) == BLKmode)
    return x;
  temp = gen_reg_rtx (GET_MODE (x));
  emit_move_insn (temp, x);
  return temp;
}

/* Copy X to TARGET (if it's nonzero and a reg)
   or to a new temp reg and return that reg.
   MODE is the mode to use for X in case it is a constant.  */

rtx
copy_to_suggested_reg (x, target, mode)
     rtx x, target;
     enum machine_mode mode;
{
  register rtx temp;

  if (target && GET_CODE (target) == REG)
    temp = target;
  else
    temp = gen_reg_rtx (mode);

  emit_move_insn (temp, x);
  return temp;
}

/* Return the mode to use to store a scalar of TYPE and MODE.
   PUNSIGNEDP points to the signedness of the type and may be adjusted
   to show what signedness to use on extension operations.

   FOR_CALL is non-zero if this call is promoting args for a call.  */

enum machine_mode
promote_mode (type, mode, punsignedp, for_call)
     tree type;
     enum machine_mode mode;
     int *punsignedp;
     int for_call;
{
  enum tree_code code = TREE_CODE (type);
  int unsignedp = *punsignedp;

#ifdef PROMOTE_FOR_CALL_ONLY
  if (! for_call)
    return mode;
#endif

  switch (code)
    {
#ifdef PROMOTE_MODE
    case INTEGER_TYPE:   case ENUMERAL_TYPE:   case BOOLEAN_TYPE:
    case CHAR_TYPE:      case REAL_TYPE:       case OFFSET_TYPE:
      PROMOTE_MODE (mode, unsignedp, type);
      break;
#endif

#ifdef POINTERS_EXTEND_UNSIGNED
    case POINTER_TYPE:
      mode = Pmode;
      unsignedp = POINTERS_EXTEND_UNSIGNED;
      break;
#endif
    }

  *punsignedp = unsignedp;
  return mode;
}

/* Adjust the stack pointer by ADJUST (an rtx for a number of bytes).
   This pops when ADJUST is positive.  ADJUST need not be constant.  */

void
adjust_stack (adjust)
     rtx adjust;
{
  rtx temp;
  adjust = protect_from_queue (adjust, 0);

  if (adjust == const0_rtx)
    return;

  temp = expand_binop (Pmode,
#ifdef STACK_GROWS_DOWNWARD
		       add_optab,
#else
		       sub_optab,
#endif
		       stack_pointer_rtx, adjust, stack_pointer_rtx, 0,
		       OPTAB_LIB_WIDEN);

  if (temp != stack_pointer_rtx)
    emit_move_insn (stack_pointer_rtx, temp);
}

/* Adjust the stack pointer by minus ADJUST (an rtx for a number of bytes).
   This pushes when ADJUST is positive.  ADJUST need not be constant.  */

void
anti_adjust_stack (adjust)
     rtx adjust;
{
  rtx temp;
  adjust = protect_from_queue (adjust, 0);

  if (adjust == const0_rtx)
    return;

  temp = expand_binop (Pmode,
#ifdef STACK_GROWS_DOWNWARD
		       sub_optab,
#else
		       add_optab,
#endif
		       stack_pointer_rtx, adjust, stack_pointer_rtx, 0,
		       OPTAB_LIB_WIDEN);

  if (temp != stack_pointer_rtx)
    emit_move_insn (stack_pointer_rtx, temp);
}

/* Round the size of a block to be pushed up to the boundary required
   by this machine.  SIZE is the desired size, which need not be constant.  */

rtx
round_push (size)
     rtx size;
{
#ifdef STACK_BOUNDARY
  int align = STACK_BOUNDARY / BITS_PER_UNIT;
  if (align == 1)
    return size;
  if (GET_CODE (size) == CONST_INT)
    {
      int new = (INTVAL (size) + align - 1) / align * align;
      if (INTVAL (size) != new)
	size = GEN_INT (new);
    }
  else
    {
      /* CEIL_DIV_EXPR needs to worry about the addition overflowing,
	 but we know it can't.  So add ourselves and then do TRUNC_DIV_EXPR. */
      size = expand_binop (Pmode, add_optab, size, GEN_INT (align - 1),
			   NULL_RTX, 1, OPTAB_LIB_WIDEN);
      size = expand_divmod (0, TRUNC_DIV_EXPR, Pmode, size, GEN_INT (align),
			    NULL_RTX, 1);
      size = expand_mult (Pmode, size, GEN_INT (align), NULL_RTX, 1);