c4x.c

gcc-you can use this code to learn something about gcc, and inquire further into linux,

   the stack in reverse order (right to left).  GCC handles that for us.

   c4x_init_cumulative_args() is called at the start, so we can parse
   the args to see how many floating point arguments and how many
   integer (or pointer) arguments there are.  c4x_function_arg() is
   then called (sometimes repeatedly) for each argument (parsed left
   to right) to obtain the register to pass the argument in, or zero
   if the argument is to be passed on the stack.  Once the compiler is
   happy, c4x_function_arg_advance() is called.

   Don't use R0 to pass arguments in, we use 0 to indicate a stack
   argument.  */

static const int c4x_int_reglist[3][6] =
{
  {AR2_REGNO, R2_REGNO, R3_REGNO, RC_REGNO, RS_REGNO, RE_REGNO},
  {AR2_REGNO, R3_REGNO, RC_REGNO, RS_REGNO, RE_REGNO, 0},
  {AR2_REGNO, RC_REGNO, RS_REGNO, RE_REGNO, 0, 0}
};

static const int c4x_fp_reglist[2] = {R2_REGNO, R3_REGNO};


/* Initialize a variable CUM of type CUMULATIVE_ARGS for a call to a
   function whose data type is FNTYPE.
   For a library call, FNTYPE is  0.  */

void
c4x_init_cumulative_args (cum, fntype, libname)
     CUMULATIVE_ARGS *cum;	/* Argument info to initialize.  */
     tree fntype;		/* Tree ptr for function decl.  */
     rtx libname;		/* SYMBOL_REF of library name or 0.  */
{
  tree param, next_param;

  cum->floats = cum->ints = 0;
  cum->init = 0;
  cum->var = 0;
  cum->args = 0;

  if (TARGET_DEBUG)
    {
      fprintf (stderr, "\nc4x_init_cumulative_args (");
      if (fntype)
	{
	  tree ret_type = TREE_TYPE (fntype);

	  fprintf (stderr, "fntype code = %s, ret code = %s",
		   tree_code_name[(int) TREE_CODE (fntype)],
		   tree_code_name[(int) TREE_CODE (ret_type)]);
	}
      else
	fprintf (stderr, "no fntype");

      if (libname)
	fprintf (stderr, ", libname = %s", XSTR (libname, 0));
    }

  cum->prototype = (fntype && TYPE_ARG_TYPES (fntype));

  for (param = fntype ? TYPE_ARG_TYPES (fntype) : 0;
       param; param = next_param)
    {
      tree type;

      next_param = TREE_CHAIN (param);

      type = TREE_VALUE (param);
      if (type && type != void_type_node)
	{
	  enum machine_mode mode;

	  /* If the last arg doesn't have void type then we have
	     variable arguments.  */
	  if (! next_param)
	    cum->var = 1;

	  if ((mode = TYPE_MODE (type)))
	    {
	      if (! MUST_PASS_IN_STACK (mode, type))
		{
		  /* Look for float, double, or long double argument.  */
		  if (mode == QFmode || mode == HFmode)
		    cum->floats++;
		  /* Look for integer, enumeral, boolean, char, or pointer
		     argument.  */
		  else if (mode == QImode || mode == Pmode)
		    cum->ints++;
		}
	    }
	  cum->args++;
	}
    }

  if (TARGET_DEBUG)
    fprintf (stderr, "%s%s, args = %d)\n",
	     cum->prototype ? ", prototype" : "",
	     cum->var ? ", variable args" : "",
	     cum->args);
}


/* Update the data in CUM to advance over an argument
   of mode MODE and data type TYPE.
   (TYPE is null for libcalls where that information may not be available.)  */

void
c4x_function_arg_advance (cum, mode, type, named)
     CUMULATIVE_ARGS *cum;	/* Current arg information.  */
     enum machine_mode mode;	/* Current arg mode.  */
     tree type;			/* Type of the arg or 0 if lib support.  */
     int named;			/* Whether or not the argument was named.  */
{
  if (TARGET_DEBUG)
    fprintf (stderr, "c4x_function_adv(mode=%s, named=%d)\n\n",
	     GET_MODE_NAME (mode), named);
  if (! TARGET_MEMPARM 
      && named
      && type
      && ! MUST_PASS_IN_STACK (mode, type))
    {
      /* Look for float, double, or long double argument.  */
      if (mode == QFmode || mode == HFmode)
	cum->floats++;
      /* Look for integer, enumeral, boolean, char, or pointer argument.  */
      else if (mode == QImode || mode == Pmode)
	cum->ints++;
    }
  else if (! TARGET_MEMPARM && ! type)
    {
      /* Handle libcall arguments.  */
      if (mode == QFmode || mode == HFmode)
	cum->floats++;
      else if (mode == QImode || mode == Pmode)
	cum->ints++;
    }
  return;
}


/* Define where to put the arguments to a function.  Value is zero to
   push the argument on the stack, or a hard register in which to
   store the argument.

   MODE is the argument's machine mode.
   TYPE is the data type of the argument (as a tree).
   This is null for libcalls where that information may
   not be available.
   CUM is a variable of type CUMULATIVE_ARGS which gives info about
   the preceding args and about the function being called.
   NAMED is nonzero if this argument is a named parameter
   (otherwise it is an extra parameter matching an ellipsis).  */

struct rtx_def *
c4x_function_arg (cum, mode, type, named)
     CUMULATIVE_ARGS *cum;	/* Current arg information.  */
     enum machine_mode mode;	/* Current arg mode.  */
     tree type;			/* Type of the arg or 0 if lib support.  */
     int named;			/* != 0 for normal args, == 0 for ... args.  */
{
  int reg = 0;			/* Default to passing argument on stack.  */

  if (! cum->init)
    {
      /* We can handle at most 2 floats in R2, R3.  */
      cum->maxfloats = (cum->floats > 2) ? 2 : cum->floats;

      /* We can handle at most 6 integers minus number of floats passed 
	 in registers.  */
      cum->maxints = (cum->ints > 6 - cum->maxfloats) ? 
	6 - cum->maxfloats : cum->ints;

      /* If there is no prototype, assume all the arguments are integers.  */
      if (! cum->prototype)
	cum->maxints = 6;

      cum->ints = cum->floats = 0;
      cum->init = 1;
    }

  /* This marks the last argument.  We don't need to pass this through
     to the call insn.  */
  if (type == void_type_node)
    return 0;

  if (! TARGET_MEMPARM 
      && named 
      && type
      && ! MUST_PASS_IN_STACK (mode, type))
    {
      /* Look for float, double, or long double argument.  */
      if (mode == QFmode || mode == HFmode)
	{
	  if (cum->floats < cum->maxfloats)
	    reg = c4x_fp_reglist[cum->floats];
	}
      /* Look for integer, enumeral, boolean, char, or pointer argument.  */
      else if (mode == QImode || mode == Pmode)
	{
	  if (cum->ints < cum->maxints)
	    reg = c4x_int_reglist[cum->maxfloats][cum->ints];
	}
    }
  else if (! TARGET_MEMPARM && ! type)
    {
      /* We could use a different argument calling model for libcalls,
         since we're only calling functions in libgcc.  Thus we could
         pass arguments for long longs in registers rather than on the
         stack.  In the meantime, use the odd TI format.  We make the
         assumption that we won't have more than two floating point
         args, six integer args, and that all the arguments are of the
         same mode.  */
      if (mode == QFmode || mode == HFmode)
	reg = c4x_fp_reglist[cum->floats];
      else if (mode == QImode || mode == Pmode)
	reg = c4x_int_reglist[0][cum->ints];
    }

  if (TARGET_DEBUG)
    {
      fprintf (stderr, "c4x_function_arg(mode=%s, named=%d",
	       GET_MODE_NAME (mode), named);
      if (reg)
	fprintf (stderr, ", reg=%s", reg_names[reg]);
      else
	fprintf (stderr, ", stack");
      fprintf (stderr, ")\n");
    }
  if (reg)
    return gen_rtx_REG (mode, reg);
  else
    return NULL_RTX;
}

/* C[34]x arguments grow in weird ways (downwards) that the standard
   varargs stuff can't handle..  */
rtx
c4x_va_arg (valist, type)
     tree valist, type;
{
  tree t;

  t = build (PREDECREMENT_EXPR, TREE_TYPE (valist), valist,
	     build_int_2 (int_size_in_bytes (type), 0));
  TREE_SIDE_EFFECTS (t) = 1;

  return expand_expr (t, NULL_RTX, Pmode, EXPAND_NORMAL);
}


static int
c4x_isr_reg_used_p (regno)
     unsigned int regno;
{
  /* Don't save/restore FP or ST, we handle them separately.  */
  if (regno == FRAME_POINTER_REGNUM
      || IS_ST_REGNO (regno))
    return 0;

  /* We could be a little smarter abut saving/restoring DP.
     We'll only save if for the big memory model or if
     we're paranoid. ;-)  */
  if (IS_DP_REGNO (regno))
    return ! TARGET_SMALL || TARGET_PARANOID;

  /* Only save/restore regs in leaf function that are used.  */
  if (c4x_leaf_function)
    return regs_ever_live[regno] && fixed_regs[regno] == 0;

  /* Only save/restore regs that are used by the ISR and regs
     that are likely to be used by functions the ISR calls
     if they are not fixed.  */
  return IS_EXT_REGNO (regno)
    || ((regs_ever_live[regno] || call_used_regs[regno]) 
	&& fixed_regs[regno] == 0);
}


static int
c4x_leaf_function_p ()
{
  /* A leaf function makes no calls, so we only need
     to save/restore the registers we actually use.
     For the global variable leaf_function to be set, we need
     to define LEAF_REGISTERS and all that it entails.
     Let's check ourselves...   */

  if (lookup_attribute ("leaf_pretend",
			TYPE_ATTRIBUTES (TREE_TYPE (current_function_decl))))
    return 1;

  /* Use the leaf_pretend attribute at your own risk.  This is a hack
     to speed up ISRs that call a function infrequently where the
     overhead of saving and restoring the additional registers is not
     warranted.  You must save and restore the additional registers
     required by the called function.  Caveat emptor.  Here's enough
     rope...  */

  if (leaf_function_p ())
    return 1;

  return 0;
}


static int
c4x_assembler_function_p ()
{
  tree type;

  type = TREE_TYPE (current_function_decl);
  return (lookup_attribute ("assembler", TYPE_ATTRIBUTES (type)) != NULL)
    || (lookup_attribute ("naked", TYPE_ATTRIBUTES (type)) != NULL);
}


int
c4x_interrupt_function_p ()
{
  if (lookup_attribute ("interrupt",
			TYPE_ATTRIBUTES (TREE_TYPE (current_function_decl))))
    return 1;

  /* Look for TI style c_intnn.  */
  return current_function_name[0] == 'c'
    && current_function_name[1] == '_'
    && current_function_name[2] == 'i'
    && current_function_name[3] == 'n' 
    && current_function_name[4] == 't'
    && ISDIGIT (current_function_name[5])
    && ISDIGIT (current_function_name[6]);
}

void
c4x_expand_prologue ()
{
  unsigned int regno;
  int size = get_frame_size ();
  rtx insn;

  /* In functions where ar3 is not used but frame pointers are still
     specified, frame pointers are not adjusted (if >= -O2) and this
     is used so it won't needlessly push the frame pointer.  */
  int dont_push_ar3;

  /* For __assembler__ function don't build a prologue.  */
  if (c4x_assembler_function_p ())
    {
      return;
    }
  
  /* For __interrupt__ function build specific prologue.  */
  if (c4x_interrupt_function_p ())
    {
      c4x_leaf_function = c4x_leaf_function_p ();
      
      insn = emit_insn (gen_push_st ());
      RTX_FRAME_RELATED_P (insn) = 1;
      if (size)
	{
          insn = emit_insn (gen_pushqi ( gen_rtx_REG (QImode, AR3_REGNO)));
          RTX_FRAME_RELATED_P (insn) = 1;
	  insn = emit_insn (gen_movqi (gen_rtx_REG (QImode, AR3_REGNO),
				       gen_rtx_REG (QImode, SP_REGNO)));
          RTX_FRAME_RELATED_P (insn) = 1;
	  /* We require that an ISR uses fewer than 32768 words of
	     local variables, otherwise we have to go to lots of
	     effort to save a register, load it with the desired size,
	     adjust the stack pointer, and then restore the modified
	     register.  Frankly, I think it is a poor ISR that
	     requires more than 32767 words of local temporary
	     storage!  */
	  if (size > 32767)
	    error ("ISR %s requires %d words of local vars, max is 32767",
		   current_function_name, size);

	  insn = emit_insn (gen_addqi3 (gen_rtx_REG (QImode, SP_REGNO),
				        gen_rtx_REG (QImode, SP_REGNO),
					GEN_INT (size)));
          RTX_FRAME_RELATED_P (insn) = 1;
	}
      for (regno = 0; regno < FIRST_PSEUDO_REGISTER; regno++)
	{
	  if (c4x_isr_reg_used_p (regno))
	    {
	      if (regno == DP_REGNO)
		{
		  insn = emit_insn (gen_push_dp ());
                  RTX_FRAME_RELATED_P (insn) = 1;
		}
	      else
		{
                  insn = emit_insn (gen_pushqi (gen_rtx_REG (QImode, regno)));
                  RTX_FRAME_RELATED_P (insn) = 1;
		  if (IS_EXT_REGNO (regno))
		    {
                      insn = emit_insn (gen_pushqf
					(gen_rtx_REG (QFmode, regno)));
                      RTX_FRAME_RELATED_P (insn) = 1;
		    }
		}
	    }
	}
      /* We need to clear the repeat mode flag if the ISR is
         going to use a RPTB instruction or uses the RC, RS, or RE
         registers.  */
      if (regs_ever_live[RC_REGNO] 
	  || regs_ever_live[RS_REGNO] 
	  || regs_ever_live[RE_REGNO])
	{
          insn = emit_insn (gen_andn_st (GEN_INT(~0x100)));
          RTX_FRAME_RELATED_P (insn) = 1;
	}

      /* Reload DP reg if we are paranoid about some turkey
         violating small memory model rules.  */
      if (TARGET_SMALL && TARGET_PARANOID)
	{
          insn = emit_insn (gen_set_ldp_prologue
			    (gen_rtx_REG (QImode, DP_REGNO),
			     gen_rtx_SYMBOL_REF (QImode, "data_sec")));
          RTX_FRAME_RELATED_P (insn) = 1;
	}
    }
  else
    {
      if (frame_pointer_needed)
	{
	  if ((size != 0)
	      || (current_function_args_size != 0)
	      || (optimize < 2))
	    {
              insn = emit_insn (gen_pushqi ( gen_rtx_REG (QImode, AR3_REGNO)));
              RTX_FRAME_RELATED_P (insn) = 1;
	      insn = emit_insn (gen_movqi (gen_rtx_REG (QImode, AR3_REGNO),
				           gen_rtx_REG (QImode, SP_REGNO)));
              RTX_FRAME_RELATED_P (insn) = 1;
	      dont_push_ar3 = 1;
	    }
	  else
	    {
	      /* Since ar3 is not used, we don't need to push it.  */
	      dont_push_ar3 = 1;
	    }
	}
      else
	{
	  /* If we use ar3, we need to push it.   */
	  dont_push_ar3 = 0;
	  if ((size != 0) || (current_function_args_size != 0))
	    {
	      /* If we are omitting the frame pointer, we still have
	         to make space for it so the offsets are correct
	         unless we don't use anything on the stack at all.  */
	      size += 1;
	    }
	}
      
      if (size > 32767)
	{
	  /* Local vars are too big, it will take multiple operations
	     to increment SP.  */
	  if (TARGET_C3X)
	    {
	      insn = emit_insn (gen_movqi (gen_rtx_REG (QImode, R1_REGNO),
					   GEN_INT(size >> 16)));
              RTX_FRAME_RELATED_P (insn) = 1;
	      insn = emit_insn (gen_lshrqi3 (gen_rtx_REG (QImode, R1_REGNO),
					     gen_rtx_REG (QImode, R1_REGNO),
					     GEN_INT(-16)));
              RTX_FRAME_RELATED_P (insn) = 1;
	    }
	  else
	    {
	      insn = emit_insn (gen_movqi (gen_rtx_REG (QImode, R1_REGNO),
					   GEN_INT(size & ~0xffff)));
              RTX_FRAME_RELATED_P (insn) = 1;
	    }
	  insn = emit_insn (gen_iorqi3 (gen_rtx_REG (QImode, R1_REGNO),