Promotion of integer return types to int

[Alexandre Courbot <Alexandre dot Courbot at lifl dot fr>]

Hello everybody,

I couldn't help but notice that the C parser automatically promotes any type 
that can be promoted to int when used to return values. This happens in 
c-decl.c, line 5650:

  /* Promote the value to int before returning it.  */
  if (c_promoting_integer_type_p (restype))
    {
      /* It retains unsignedness if not really getting wider.  */
      if (TREE_UNSIGNED (restype)
	  && (TYPE_PRECISION (restype)
		  == TYPE_PRECISION (integer_type_node)))
	restype = unsigned_type_node;
      else
	restype = integer_type_node;
    }

c_promoting_integer_type_p always returns 1 when given a char or short type. 
As a consequence, the integer promotion is made at tree level and if I 
compile the following function:

unsigned char function_returns_char();

Then I have no way to know that the return type is char-sized. My backend is 
fooled and believes it is int-sized. This is a serious issue for me because I 
have to specify the return type of the functions in the assembler file and 
all the functions returning chars or shorts actually return ints.

Since I'm porting to an target for embedded devices (typically smartcards), 
this is a real issue and I wondered if the promotion couldn't be optional. 
I've noticed that someone already submitted a patch for this 
(http://gcc.gnu.org/ml/gcc-patches/2003-05/msg01630.html) but it hasn't been 
included. For my use I really need the return types not to be promoted, so 
I'll disable it, but I guess it could be useful to others if this feature was 
added. Maybe a new, dedicated macro? If not defined, the promotion would 
happen just as it does today. If no one bothers, shall I go ahead and submit 
a patch?

Thanks,
Alex.