Re: [PATCH 1/5] std::latch: reduce internal implementation from ptrdiff_t to int

[Hans-Peter Nilsson]

On Fri, 26 Feb 2021, Thiago Macieira via Gcc-patches wrote:

> On Friday, 26 February 2021 11:31:00 PST Andreas Schwab wrote:
> > On Feb 26 2021, Thiago Macieira wrote:
> > > On Friday, 26 February 2021 10:14:42 PST Andreas Schwab wrote:
> > >> On Feb 26 2021, Thiago Macieira via Gcc-patches wrote:
> > >> > -    alignas(__alignof__(ptrdiff_t)) ptrdiff_t _M_a;
> > >> > +    alignas(__alignof__(int)) int _M_a;
> > >>
> > >> Futexes must be aligned to 4 bytes.
> > >
> > > Agreed, but doesn't this accomplish that?
> >
> > No.  It uses whatever alignment the type already has, and is an
> > elaborate no-op.
>
> I thought so too when I read the original line. But I expected it was written
> like that for a reason, especially since the same pattern appears in other
> places.
>
> I can change to "alignas(4)" (which is a GCC extension, I believe). Is that
> the correct solution?

IMNSHO make use of the corresponding atomic type.  Then there'd
be no need for separate what's-the-right-align-curse games.

brgds, H-P