Re: lambda-switch regression

[Martin Sebor <msebor at gmail dot com>]

On 11/15/2017 10:38 AM, David Malcolm wrote:
> On Wed, 2017-11-15 at 12:25 -0500, David Malcolm wrote:
> > On Wed, 2017-11-15 at 12:06 -0500, David Malcolm wrote:
> > > On Wed, 2017-11-15 at 08:03 -0500, Nathan Sidwell wrote:
> > > > g++.dg/lambda/lambda-switch.C Has recently regressed.
> > >
> > > g++.dg/cpp0x/lambda/lambda-switch.C
> > >
> > > > It appears the
> > > > location of a warning message has moved.
> > > >
> > > > 	  l = []()		// { dg-warning "statement will never
> > > > be executed" }
> > > > 	    {
> > > > 	    case 3:		// { dg-error "case" }
> > > > 	      break;		// { dg-error "break" }
> > > > 	    };  <--- warning now here
> > > >
> > > > We seem to be diagnosing the last line of the statement, not the
> > > > first.
> > > > That seems not a useful.
> > > >
> > > > I've not investigated what patch may have caused this, on the
> > > > chance
> > > > someone might already know?
> > > >
> > > > nathan
> > >
> > > The warning was added in r236597 (aka
> > > 1398da0f786e120bb0b407e84f412aa9fc6d80ee):
> > >
> > > +2016-05-23  Marek Polacek  <polacek@redhat.com>
> > > +
> > > +       PR c/49859
> > > +       * common.opt (Wswitch-unreachable): New option.
> > > +       * doc/invoke.texi: Document -Wswitch-unreachable.
> > > +       * gimplify.c (gimplify_switch_expr): Implement the
> > > -Wswitch-
> > > unreachable
> > > +       warning.
> > >
> > > which had it at there (23:7).
> > >
> > > r244705 (aka 3ef7eab185e1463c7dbfa2a8d1af5d0120cf9f76) moved the
> > > warning from 23:7 up to the "[] ()" at 19:6 in:
> > >
> > > +2017-01-20  Marek Polacek  <polacek@redhat.com>
> > > +
> > > +       PR c/64279
> > > [...snip...]
> > > +       * g++.dg/cpp0x/lambda/lambda-switch.C: Move dg-warning.
> > >
> > > I tried it with some working copies I have to hand:
> > > - works for me with r254387 (2017-11-03)
> > > - fails for me with r254700 (2017-11-13)
> > >
> > > so hopefully that helps track it down.
> > >
> > > Dave
> >
> > Searching in the November archives of the gcc-regression ML for
> > "lambda-switch.c":
> >
> > https://gcc.gnu.org/cgi-bin/search.cgi?wm=wrd&form=extended&m=all&s=D
> > &q=lambda-switch.c&ul=%2Fml%2Fgcc-regression%2F2017-11%2F%25
> >
> > showed e.g.:
> >   https://gcc.gnu.org/ml/gcc-regression/2017-11/msg00173.html
> >    "Regressions on trunk at revision 254648 vs revision 254623"
> >
> > which says this is a new failure somewhere in that range; so it
> > presumably happened sometime on 2017-11-10 after r254623 and up to
> > (maybe ==) r254648.
> >
> > Looking at:
> >    svn log -r r254623:r254648 |less
> > nothing jumps out at me as being related.
> >
> > Hope this is helpful
> > Dave
>
> Actually, https://gcc.gnu.org/ml/gcc-regression/2017-11/msg00157.html
> has a tighter range: r254628 vs r254635.
>
> Looking at:
>   svn log -r r254628:r254635 |less
> I see msebor's r254630 ("PR c/81117 - Improve buffer overflow checking
> in strncpy") has:
>
>         * gimple.c (gimple_build_call_from_tree): Set call location.
>
> with:
> +  gimple_set_location (call, EXPR_LOCATION (t));
>
> Maybe that's it?  (nothing else in that commit range seems to affect
> locations).

Yes, that's it.  Before the change there would be no location
associated with a GIMPLE call seen in gimple-fold.  The location
would only get added later, after folding.

The purpose of the lambda-switch.C test is to verify GCC doesn't
ICE on the ill-formed code.  The warning is incidental to the test
case so I've adjusted it to filter it out.

Martin