Optimize based on possible enum class values?

[Jonathan Wakely]

On 19 May 2016 at 02:52, lh mouse wrote:
> -fstrict-enums
>
> This option is for C++ only.

In this example the enumeration type has a fixed underlying type, so
the valid values of the enumeration are all the valid values of the
underlying type, which allows 0-255. It can't assume that there isn't
code that does:

E e = E{255};

So -fstrict-enums isn't enough to tell the compiler that only the
values 0, 1 and 2 will be used.

As others have replied, __builtin_unreachable() can be used for that.