On Thu, Jun 22, 2023 at 03:53:33PM -0400, Olivier Dion wrote:
> On Thu, 22 Jun 2023, "Paul E. McKenney" <paul...@kernel.org> wrote:
>
> > I suggest C11 volatile atomic load/store. Load/store fusing is permitted
> > for non-volatile atomic loads and stores, and such fusing can ruin your
> > code's entire day. ;-)
>
> Good catch. Seems like not a problem on GCC (yet), but Clang is extremely
> aggressive and seems to do store fusing on some corner cases [0].
>
> However, I do not find any simple reproducer of load/store fusing. Do
> you have example of such fusing, or is this a precaution? In the
> meantime, back to reading the standard to be certain :-)
>
> [0] https://godbolt.org/z/odKG9a75a
I certainly have heard a number of compiler writers thinking in terms
of doing load/store fusing, some of whom were trying to get rid of the
volatile variants in order to remove an impediment to their mission of
optimizing all programs out of existence. ;-)
I therefore suggest taking this possibility quite seriously.
Thanx, Paul
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