Re: [RFC] LKMM: Add volatile_if()

Segher Boessenkool
2021-06-07T18:23:01Z

On Mon, Jun 07, 2021 at 09:07:58PM +0300, Alexander Monakov wrote:
> On Mon, 7 Jun 2021, Segher Boessenkool wrote:
>
> > > So the barrier which is a compiler barrier but not a machine barrier is
> > > __atomic_signal_fence(model), but internally GCC will not treat it smarter
> > > than an asm-with-memory-clobber today.
> >
> > It will do nothing for relaxed ordering, and do blockage for everything
> > else. Can it do anything weaker than that?
>
> It's a "blockage instruction" after transitioning to RTL, but before that,
> on GIMPLE, the compiler sees it properly as a corresponding built-in, and
> may optimize according to given memory model. And on RTL, well, if anyone
> cares they'll need to invent RTL representation for it, I guess.

My question was if anything weaker is *valid* :-) (And if so, why!)

Segher