Re: Build with LTO / -flto on macOS

Hi,

On 2024-07-19 15:36:29 -0400, Tom Lane wrote:
> Andres Freund <andres(at)anarazel(dot)de> writes:
> > On 2024-07-19 11:06:47 -0400, Tom Lane wrote:
> >> 2. Do we really want to encourage people to build with -flto?
>
> > The only case I know where we do rely on compilation units providing some
> > level of boundaries is on compilers where we don't know how to emit a compiler
> > barrier. That's probably a fallback we ought to remove one of these days...
>
> Hm. We've moved our platform/toolchain goalposts far enough in the
> last few releases that that might not be too big a lift. Do you
> know offhand which supported platforms still have a problem there?
>
> (mumble AIX mumble)

In 16 it looks like the only case might indeed have been [drumroll] AIX with
xlc (with gcc . And there it it looks like it'd have been trivial to implement
[1].

We've been talking about requiring 32 bit atomics and a spinlock
implementation - this imo fits in well with that, without proper barriers it's
pretty much impossible to have correct spinlocks and, even more so, any lock
free construct, of which we have a bunch.

IOW, let's rip out the fallback implementation for compiler and memory
barriers and fix the fallout, if there is any.

Greetings,

Andres Freund

[1] I think it'd just be __fence(). Looks like it's been present for a while,
found it in "IBM XL C/C++ for AIX, V10.1 Compiler Reference Version 10.1",
which looks to be from 2008.