Re: [C++ PATCH] Don't allow taking the address of an rvalue reference (PR c++/35153)

[Mark Mitchell <mark at codesourcery dot com>]

Doug Gregor wrote:

> > So, I think your check should go in build_unary_op -- unless for some
> > reason it can't, like if there's a compiler-generated need to take the
> > address of the rvalue reference,
>
> Bingo. This is exactly what happened---compiler-generated code was
> going through build_unary_op, and triggering this error when it was
> okay to take the address of the result.

OK.

> > and we're going through build_unary_op
> > instead of build_address.
>
> I didn't think of that. build_address doesn't do the
> ADDR_EXPR/INDIRECT_REF simplification, which some of the current
> callers of build_unary_op(ADDR_EXPR...) might rely on. So, I can try
> to change the compiler-generated calls to build_unary_op(ADDR_EXPR...)
> into build_address, and move the address-of-rvalue check into
> build_unary_op, if you'd still prefer that implementation.

Yes, I think that's the Right Answer.  If anything in the front end 
depends on that simplification for compiler-generated code, it seems 
busted on its face to me -- and one certainly hopes that the middle-end 
is plenty smart enough to work this out these days.

In general, the front end is going to be simpler and more reliable if we 
clearly differentiate between compiler-generated implicit stuff (the 
sort of thing that would be generated during IL lowering) and user-level 
stuff.

Thanks,

--
Mark Mitchell
CodeSourcery
mark@codesourcery.com
(650) 331-3385 x713