On Tue, Mar 23, 2021 at 04:59:53PM -0400, Jason Merrill via Gcc-patches wrote:
> On 3/8/21 7:34 PM, Marek Polacek wrote:
> > On Fri, Mar 05, 2021 at 05:03:45PM -0500, Jason Merrill wrote:
> > > On 3/4/21 9:37 PM, Marek Polacek wrote:
> > > > This PR complains that we issue a -Wconversion warning in
> > > >
> > > > template <int N> struct X {};
> > > > template <class T> X<sizeof(T)> foo();
> > > >
> > > > saying "conversion from 'long unsigned int' to 'int' may change value".
> > > > While it's not technically wrong, I suspect -Wconversion warnings aren't
> > > > all that useful for value-dependent expressions. So this patch disables
> > > > them, though I'm open to other ideas.
> > >
> > > How about suppressing -Wconversion in
> > > build_converted_constant_expr_internal? If the size_t value ended up
> > > being
> > > too large for the int parameter, we would give an error about overflow in
> > > a
> > > constant expression, not just a warning.
> >
> > That works for me too. As you say, if we convert to a type that cannot
> > represent all the values of the original type, we give a pedantic-error
> > warning in check_narrowing.
> >
> > I've slightly enhanced the test, too.
> >
> > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/10?
>
> OK.
Thanks, pushed.
> I tried Martin's testcase, and get the expected
>
> wa.C:2:35: error: narrowing conversion of ‘256’ from ‘long unsigned int’ to
> ‘char’ [-Wnarrowing]
>
> Don't you?
Huh, I really don't:
$ ./cc1plus -quiet q.C -Wall -W -pedantic -Wnarrowing
# nothing
How can that be?
Marek
