Re: underlying type for enums

[Richard Henderson <rth at redhat dot com>]

On Wed, Dec 03, 2003 at 02:51:07AM +0000, Jamie Lokier wrote:
> If you were to say the type is an integer of the minimum number of
> bits required to represent all the enumerators, and set
> TYPE_MIN/MAX_VALUE according to that, will GCC assume that range for
> the purpose of optimisation?

In some places.  Perhaps only the switch generator at present.

> In particular, if you do that can GCC generate a sequence of
> shifts/masks that modify bits outside the bitfield s.e in this example?
> 
>     typedef enum { RED, GREEN, YELLOW } E;
>     struct { E e : 2; unsigned f : 1; } s;
>     E e2;
>     *(char *)&e2 = 4;
>     // Can this modify s.f?
>     s.e = (__typeof__(s.e)) e2;

I don't know.  Certainly we wouldn't at present.


r~