explow.c

gcc库的原代码,对编程有很大帮助.

    }
#endif /* STACK_BOUNDARY */
  return size;
}

/* Save the stack pointer for the purpose in SAVE_LEVEL.  PSAVE is a pointer
   to a previously-created save area.  If no save area has been allocated,
   this function will allocate one.  If a save area is specified, it
   must be of the proper mode.

   The insns are emitted after insn AFTER, if nonzero, otherwise the insns
   are emitted at the current position.  */

void
emit_stack_save (save_level, psave, after)
     enum save_level save_level;
     rtx *psave;
     rtx after;
{
  rtx sa = *psave;
  /* The default is that we use a move insn and save in a Pmode object.  */
  rtx (*fcn) () = gen_move_insn;
  enum machine_mode mode = Pmode;

  /* See if this machine has anything special to do for this kind of save.  */
  switch (save_level)
    {
#ifdef HAVE_save_stack_block
    case SAVE_BLOCK:
      if (HAVE_save_stack_block)
	{
	  fcn = gen_save_stack_block;
	  mode = insn_operand_mode[CODE_FOR_save_stack_block][0];
	}
      break;
#endif
#ifdef HAVE_save_stack_function
    case SAVE_FUNCTION:
      if (HAVE_save_stack_function)
	{
	  fcn = gen_save_stack_function;
	  mode = insn_operand_mode[CODE_FOR_save_stack_function][0];
	}
      break;
#endif
#ifdef HAVE_save_stack_nonlocal
    case SAVE_NONLOCAL:
      if (HAVE_save_stack_nonlocal)
	{
	  fcn = gen_save_stack_nonlocal;
	  mode = insn_operand_mode[(int) CODE_FOR_save_stack_nonlocal][0];
	}
      break;
#endif
    }

  /* If there is no save area and we have to allocate one, do so.  Otherwise
     verify the save area is the proper mode.  */

  if (sa == 0)
    {
      if (mode != VOIDmode)
	{
	  if (save_level == SAVE_NONLOCAL)
	    *psave = sa = assign_stack_local (mode, GET_MODE_SIZE (mode), 0);
	  else
	    *psave = sa = gen_reg_rtx (mode);
	}
    }
  else
    {
      if (mode == VOIDmode || GET_MODE (sa) != mode)
	abort ();
    }

  if (after)
    {
      rtx seq;

      start_sequence ();
      /* We must validize inside the sequence, to ensure that any instructions
	 created by the validize call also get moved to the right place.  */
      if (sa != 0)
	sa = validize_mem (sa);
      emit_insn (fcn (sa, stack_pointer_rtx));
      seq = gen_sequence ();
      end_sequence ();
      emit_insn_after (seq, after);
    }
  else
    {
      if (sa != 0)
	sa = validize_mem (sa);
      emit_insn (fcn (sa, stack_pointer_rtx));
    }
}

/* Restore the stack pointer for the purpose in SAVE_LEVEL.  SA is the save
   area made by emit_stack_save.  If it is zero, we have nothing to do. 

   Put any emitted insns after insn AFTER, if nonzero, otherwise at 
   current position.  */

void
emit_stack_restore (save_level, sa, after)
     enum save_level save_level;
     rtx after;
     rtx sa;
{
  /* The default is that we use a move insn.  */
  rtx (*fcn) () = gen_move_insn;

  /* See if this machine has anything special to do for this kind of save.  */
  switch (save_level)
    {
#ifdef HAVE_restore_stack_block
    case SAVE_BLOCK:
      if (HAVE_restore_stack_block)
	fcn = gen_restore_stack_block;
      break;
#endif
#ifdef HAVE_restore_stack_function
    case SAVE_FUNCTION:
      if (HAVE_restore_stack_function)
	fcn = gen_restore_stack_function;
      break;
#endif
#ifdef HAVE_restore_stack_nonlocal

    case SAVE_NONLOCAL:
      if (HAVE_restore_stack_nonlocal)
	fcn = gen_restore_stack_nonlocal;
      break;
#endif
    }

  if (sa != 0)
    sa = validize_mem (sa);

  if (after)
    {
      rtx seq;

      start_sequence ();
      emit_insn (fcn (stack_pointer_rtx, sa));
      seq = gen_sequence ();
      end_sequence ();
      emit_insn_after (seq, after);
    }
  else
    emit_insn (fcn (stack_pointer_rtx, sa));
}

/* Return an rtx representing the address of an area of memory dynamically
   pushed on the stack.  This region of memory is always aligned to
   a multiple of BIGGEST_ALIGNMENT.

   Any required stack pointer alignment is preserved.

   SIZE is an rtx representing the size of the area.
   TARGET is a place in which the address can be placed.

   KNOWN_ALIGN is the alignment (in bits) that we know SIZE has.  */

rtx
allocate_dynamic_stack_space (size, target, known_align)
     rtx size;
     rtx target;
     int known_align;
{
  /* If we're asking for zero bytes, it doesn't matter what we point
     to since we can't dereference it.  But return a reasonable
     address anyway.  */
  if (size == const0_rtx)
    return virtual_stack_dynamic_rtx;

  /* Otherwise, show we're calling alloca or equivalent.  */
  current_function_calls_alloca = 1;

  /* Ensure the size is in the proper mode.  */
  if (GET_MODE (size) != VOIDmode && GET_MODE (size) != Pmode)
    size = convert_to_mode (Pmode, size, 1);

  /* We will need to ensure that the address we return is aligned to
     BIGGEST_ALIGNMENT.  If STACK_DYNAMIC_OFFSET is defined, we don't
     always know its final value at this point in the compilation (it 
     might depend on the size of the outgoing parameter lists, for
     example), so we must align the value to be returned in that case.
     (Note that STACK_DYNAMIC_OFFSET will have a default non-zero value if
     STACK_POINTER_OFFSET or ACCUMULATE_OUTGOING_ARGS are defined).
     We must also do an alignment operation on the returned value if
     the stack pointer alignment is less strict that BIGGEST_ALIGNMENT.

     If we have to align, we must leave space in SIZE for the hole
     that might result from the alignment operation.  */

#if defined (STACK_DYNAMIC_OFFSET) || defined (STACK_POINTER_OFFSET) || defined (ALLOCATE_OUTGOING_ARGS) || ! defined (STACK_BOUNDARY)
#define MUST_ALIGN 1
#else
#define MUST_ALIGN (STACK_BOUNDARY < BIGGEST_ALIGNMENT)
#endif

  if (MUST_ALIGN)
    {
      if (GET_CODE (size) == CONST_INT)
	size = GEN_INT (INTVAL (size)
			+ (BIGGEST_ALIGNMENT / BITS_PER_UNIT - 1));
      else
	size = expand_binop (Pmode, add_optab, size,
			     GEN_INT (BIGGEST_ALIGNMENT / BITS_PER_UNIT - 1),
			     NULL_RTX, 1, OPTAB_LIB_WIDEN);
    }

#ifdef SETJMP_VIA_SAVE_AREA
  /* If setjmp restores regs from a save area in the stack frame,
     avoid clobbering the reg save area.  Note that the offset of
     virtual_incoming_args_rtx includes the preallocated stack args space.
     It would be no problem to clobber that, but it's on the wrong side
     of the old save area.  */
  {
    rtx dynamic_offset
      = expand_binop (Pmode, sub_optab, virtual_stack_dynamic_rtx,
		      stack_pointer_rtx, NULL_RTX, 1, OPTAB_LIB_WIDEN);
    size = expand_binop (Pmode, add_optab, size, dynamic_offset,
			 NULL_RTX, 1, OPTAB_LIB_WIDEN);
  }
#endif /* SETJMP_VIA_SAVE_AREA */

  /* Round the size to a multiple of the required stack alignment.
     Since the stack if presumed to be rounded before this allocation,
     this will maintain the required alignment.

     If the stack grows downward, we could save an insn by subtracting
     SIZE from the stack pointer and then aligning the stack pointer.
     The problem with this is that the stack pointer may be unaligned
     between the execution of the subtraction and alignment insns and
     some machines do not allow this.  Even on those that do, some
     signal handlers malfunction if a signal should occur between those
     insns.  Since this is an extremely rare event, we have no reliable
     way of knowing which systems have this problem.  So we avoid even
     momentarily mis-aligning the stack.  */

#ifdef STACK_BOUNDARY
  /* If we added a variable amount to SIZE,
     we can no longer assume it is aligned.  */
#if !defined (SETJMP_VIA_SAVE_AREA)
  if (MUST_ALIGN || known_align % STACK_BOUNDARY != 0)
#endif
    size = round_push (size);
#endif

  do_pending_stack_adjust ();

  /* Don't use a TARGET that isn't a pseudo.  */
  if (target == 0 || GET_CODE (target) != REG
      || REGNO (target) < FIRST_PSEUDO_REGISTER)
    target = gen_reg_rtx (Pmode);

  mark_reg_pointer (target);

#ifndef STACK_GROWS_DOWNWARD
  emit_move_insn (target, virtual_stack_dynamic_rtx);
#endif

  /* Perform the required allocation from the stack.  Some systems do
     this differently than simply incrementing/decrementing from the
     stack pointer.  */
#ifdef HAVE_allocate_stack
  if (HAVE_allocate_stack)
    {
      enum machine_mode mode
	= insn_operand_mode[(int) CODE_FOR_allocate_stack][0];

      size = convert_modes (mode, ptr_mode, size, 1);

      if (insn_operand_predicate[(int) CODE_FOR_allocate_stack][0]
	  && ! ((*insn_operand_predicate[(int) CODE_FOR_allocate_stack][0])
		(size, mode)))
	size = copy_to_mode_reg (mode, size);

      emit_insn (gen_allocate_stack (size));
    }
  else
#endif
    {
      size = convert_modes (Pmode, ptr_mode, size, 1);
      anti_adjust_stack (size);
    }

#ifdef STACK_GROWS_DOWNWARD
  emit_move_insn (target, virtual_stack_dynamic_rtx);
#endif

  if (MUST_ALIGN)
    {
      /* 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. */
      target = expand_binop (Pmode, add_optab, target,
			     GEN_INT (BIGGEST_ALIGNMENT / BITS_PER_UNIT - 1),
			     NULL_RTX, 1, OPTAB_LIB_WIDEN);
      target = expand_divmod (0, TRUNC_DIV_EXPR, Pmode, target,
			      GEN_INT (BIGGEST_ALIGNMENT / BITS_PER_UNIT),
			      NULL_RTX, 1);
      target = expand_mult (Pmode, target,
			    GEN_INT (BIGGEST_ALIGNMENT / BITS_PER_UNIT),
			    NULL_RTX, 1);
    }
  
  /* Some systems require a particular insn to refer to the stack
     to make the pages exist.  */
#ifdef HAVE_probe
  if (HAVE_probe)
    emit_insn (gen_probe ());
#endif

  /* Record the new stack level for nonlocal gotos.  */
  if (nonlocal_goto_handler_slot != 0)
    emit_stack_save (SAVE_NONLOCAL, &nonlocal_goto_stack_level, NULL_RTX);

  return target;
}

/* Return an rtx representing the register or memory location
   in which a scalar value of data type VALTYPE
   was returned by a function call to function FUNC.
   FUNC is a FUNCTION_DECL node if the precise function is known,
   otherwise 0.  */

rtx
hard_function_value (valtype, func)
     tree valtype;
     tree func;
{
  rtx val = FUNCTION_VALUE (valtype, func);
  if (GET_CODE (val) == REG
      && GET_MODE (val) == BLKmode)
    {
      int bytes = int_size_in_bytes (valtype);
      enum machine_mode tmpmode;
      for (tmpmode = GET_CLASS_NARROWEST_MODE (MODE_INT);
           tmpmode != MAX_MACHINE_MODE;
           tmpmode = GET_MODE_WIDER_MODE (tmpmode))
        {
          /* Have we found a large enough mode?  */
          if (GET_MODE_SIZE (tmpmode) >= bytes)
            break;
        }

      /* No suitable mode found.  */
      if (tmpmode == MAX_MACHINE_MODE)
        abort ();

      PUT_MODE (val, tmpmode);
    }      
  return val;
}

/* Return an rtx representing the register or memory location
   in which a scalar value of mode MODE was returned by a library call.  */

rtx
hard_libcall_value (mode)
     enum machine_mode mode;
{
  return LIBCALL_VALUE (mode);
}

/* Look up the tree code for a given rtx code
   to provide the arithmetic operation for REAL_ARITHMETIC.
   The function returns an int because the caller may not know
   what `enum tree_code' means.  */

int
rtx_to_tree_code (code)
     enum rtx_code code;
{
  enum tree_code tcode;

  switch (code)
    {
    case PLUS:
      tcode = PLUS_EXPR;
      break;
    case MINUS:
      tcode = MINUS_EXPR;
      break;
    case MULT:
      tcode = MULT_EXPR;
      break;
    case DIV:
      tcode = RDIV_EXPR;
      break;
    case SMIN:
      tcode = MIN_EXPR;
      break;
    case SMAX:
      tcode = MAX_EXPR;
      break;
    default:
      tcode = LAST_AND_UNUSED_TREE_CODE;
      break;
    }
  return ((int) tcode);
}