Re: PR 40752: -Wconversion generates false warnings for operands not larger than target type

[Paolo Carlini <paolo dot carlini at oracle dot com>]

Hi,

On 05/09/2012 02:54 PM, Manuel López-Ibáñez wrote:
> On 7 May 2012 16:52, Paolo Carlini<paolo.carlini@oracle.com>  wrote:
> > Hi,
> >
> >
> > On 06/11/2010 10:23 PM, Manuel López-Ibáñez wrote:
> > > On 11 August 2009 02:01, Joseph S. Myers<joseph@codesourcery.com>    wrote:
> > > > On Tue, 11 Aug 2009, Manuel López-Ibáñez wrote:
> > > >
> > > > > Modified the patch to make use of the new c-c++-common testsuite.
> > > > > Bootstrapped and regression tested on x86_64-linux-gnu.
> > > > >
> > > > > OK for trunk?
> > > > I still think the warnings for these cases are mostly correct (there are
> > > > cases where you may be able to make deductions about the range of
> > > > possible
> > > > values of the expression being converted) and appropriate, and if
> > > > disabled
> > > > should be disabled under some separate -Wno-conversion-whatever option.
> > > -Wno-conversion-after-promotion ?
> > >
> > > I am not sure what would be a good name, but I think it is worth to
> > > allow silencing these warnings, so suggestions are welcome.
> > it looks like this PR is still open today, and I think resolving it one way
> > or the other isn't much work... Thus I'm asking: shall we actually have a
> > new -Wno-conversion-after-promotion? Or, alternately - the issue came up
> > quite often in recent times, because other widespread compilers don't warn -
> > suppress the warning only in case of conditional expressions:
> >
> > char
> > foo(bool haveBar, char bar_)
> > {
> >   return haveBar ? bar_ : 0;
> > };
> >
> > What do you think?
> I think Joseph has said before that if the range can be deduced to
> stay within limits of the target type, then we should never warn, no
> new option needed. This is exactly the case if you recurse only on
> conditional expression operands and casts, and it will fix the warning
> above. The other cases should be deal separately.
Good, I even have a patch essentially ready for that, but can you point 
me to that detailed feedback? I couldn't find it when I looked for it.

Thanks
Paolo.