Hi,
On Wed, 6 Jun 2007, Paolo Bonzini wrote:
> > > No, I think on the contrary that TYPE_MIN/MAX_VALUE *is* a useful
> > > thing to have in the middle-end.
> >
> > For what, if we don't want to do optimization based on it?
>
> We don't *always* want to do optimization based on it.
That's a strange statement, either we want to do optimization based on
them (and I'm of that opinion), or we don't. If we want to then we need
to set them to sensible values, hence your suggestion to _not_ set MIN/MAX
for enums seems to imply that you do not want to optimize based on that,
i.e. you contradict yourself :-)
Now, if we were to make use of MIN/MAX in vrp to the full extent possible,
then indeed for this example:
> enum E { V = 1 };
> static const E E_MIN = V;
> static const E E_MAX = V;
> bool valid(E v) { return v >= E_MIN && v <= E_MAX; }
> int main() { return valid(E(2)); }
(let's read this as pseudo code, not using C or C++ semantic) then vrp may
validly assume that the valid() predicate is true all the time. It may
assume that because the type in which the compare happens is 'E' (because
all operands, even 'v' is of that type), so it's a tautology.
I'm not sure why Ian thinks that vrp (properly extended to make
really use of MIN/MAX) would draw the conclusion that valid might ever be
false.