On Wed, Sep 19, 2018 at 9:50 PM, Marek Polacek <pola...@redhat.com> wrote: > Aaaand this addresses > <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87150#c11>, > as I promised earlier. I hope I got it right. > > Bootstrapped/regtested on x86_64-linux, ok for trunk? > > 2018-09-19 Marek Polacek <pola...@redhat.com> > > PR c++/87109 - wrong ctor with maybe-rvalue semantics. > * call.c (build_user_type_conversion_1): Refine the maybe-rvalue > check to only return if we're converting from a base class. > > * g++.dg/cpp0x/ref-qual19.C: Adjust the expected results. > * g++.dg/cpp0x/ref-qual20.C: New test. > > diff --git gcc/cp/call.c gcc/cp/call.c > index ddf0ed044a0..4bbd77b9cef 100644 > --- gcc/cp/call.c > +++ gcc/cp/call.c > @@ -4034,9 +4034,13 @@ build_user_type_conversion_1 (tree totype, tree expr, > int flags, > conv->bad_p = true; > > /* We're performing the maybe-rvalue overload resolution and > - a conversion function is in play. This isn't going to work > - because we would not end up with a suitable constructor. */ > - if ((flags & LOOKUP_PREFER_RVALUE) && !DECL_CONSTRUCTOR_P (cand->fn)) > + a conversion function is in play. If we're converting from > + a base class to a derived class, reject the conversion. */ > + if ((flags & LOOKUP_PREFER_RVALUE) > + && !DECL_CONSTRUCTOR_P (cand->fn) > + && CLASS_TYPE_P (fromtype) > + && CLASS_TYPE_P (totype) > + && DERIVED_FROM_P (fromtype, totype))
Here fromtype is the type we're converting from, and what we want to reject is converting the return value of the conversion op to a base class. CLASS_TYPE_P (fromtype) will always be true, since it has a conversion op. And I think we also want to handle the case of totype being a reference. Jason
