On Sat, 16 Sep 2023, Jason Merrill wrote:
> On 9/15/23 12:03, Patrick Palka wrote:
> > Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> > trunk?
> >
> > -- >8 --
> >
> > Here convert_to_void always completes the type of an INDIRECT_REF or
> > VAR_DECL expression, but according to [expr.context] an lvalue-to-rvalue
> > conversion is applied to a discarded-value expression only if "the
> > expression is a glvalue of volatile-qualified type". This patch restricts
> > convert_to_void's type completion accordingly.
> >
> > PR c++/111419
> >
> > gcc/cp/ChangeLog:
> >
> > * cvt.cc (convert_to_void) <case INDIRECT_REF>: Only call
> > complete_type if the type is volatile and the INDIRECT_REF
> > isn't an implicit one.
>
> Hmm, what does implicit have to do with it? The expression forms listed in
> https://eel.is/c++draft/expr.context#2 include "id-expression"...
When there's an implicit INDIRECT_REF, I reckoned the type of the
id-expression is really a reference type, which can't be cv-qualified?
>
> > diff --git a/gcc/testsuite/g++.dg/expr/discarded1a.C
> > b/gcc/testsuite/g++.dg/expr/discarded1a.C
> > new file mode 100644
> > index 00000000000..5516ff46fe9
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/expr/discarded1a.C
> > @@ -0,0 +1,16 @@
> > +// PR c++/111419
> > +
> > +struct Incomplete;
> > +
> > +template<class T, int> struct Holder { T t; }; // { dg-error "incomplete" }
> > +
> > +extern volatile Holder<Incomplete, 0> a;
> > +extern volatile Holder<Incomplete, 1>& b;
> > +extern volatile Holder<Incomplete, 2>* c;
> > +
> > +int main() {
> > + a; // { dg-message "required from here" }
> > + b; // { dg-warning "implicit dereference will not access object" }
> > + // { dg-bogus "required from here" "" { target *-*-* } .-1 }
>
> ...so it seems to me this line should get the lvalue-rvalue conversion (and
> not the warning about no access).
>
> > + *c; // { dg-message "required from here" }
> > +}
>
>
