On Fri, 2020-07-17 at 13:00 -0600, Martin Sebor via Gcc-patches wrote: > The recent enhancement to treat the implicit this pointer argument > as nonnull in member functions triggers spurious -Wnonnull for > the synthesized conditional expression the C++ front end replaces > the pointer with in some static_cast expressions. The front end > already sets the no-warning bit for the test but not for the whole > conditional expression, so the attached fix extends the same solution > to it. > > The consequence of this fix is that user-written code like this: > > static_cast<T*>(p ? p : 0)->f (); > or > static_cast<T*>(p ? p : nullptr)->f (); > > don't trigger the warning because they are both transformed into > the same expression as: > > static_cast<T*>(p)->f (); > > What still does trigger it is this: > > static_cast<T*>(p ? p : (T*)0)->f (); > > because here it's the inner COND_EXPR's no-warning bit that's set > (the outer one is clear), whereas in the former expressions it's > the other way around. It would be nice if this worked consistently > but I didn't see an easy way to do that and more than a quick fix > seems outside the scope for this bug. > > Another case reported by someone else in the same bug involves > a dynamic_cast. A simplified test case goes something like this: > > if (dynamic_cast<T*>(p)) > dynamic_cast<T*>(p)->f (); > > The root cause is the same: the front end emitting the COND_EXPR > > ((p != 0) ? ((T*)__dynamic_cast(p, (& _ZTI1B), (& _ZTI1C), 0)) : 0) > > I decided not to suppress the warning in this case because doing > so would also suppress it in unconditional calls with the result > of the cast: > > dynamic_cast<T*>(p)->f (); > > and that doesn't seem helpful. Instead, I'd suggest to make > the second cast in the if statement to reference to T&: > > if (dynamic_cast<T*>(p)) > dynamic_cast<T&>(*p).f (); Hmmm, I wonder if this would fix a handful of errors I got when doing the testing of the Ranger work for Aldy. Let me throw the new version into the tester and respin just the failing packages.
Jeff >
