Re: [PATCH] Tree SRA and atomicity/volatility

["Richard Guenther" <richard.guenther@gmail.com>]

On 1/23/07, Mark Mitchell <mark@codesourcery.com> wrote:
> Eric Botcazou wrote:
>
> > 2007-01-06  Eric Botcazou  <ebotcazou@adacore.com>
> >
> >       * tree-sra.c (sra_walk_fns) <ldst>: Document new restriction.
> >       (sra_walk_modify_expr) <rhs_elt>: Treat the reference as a use
> >       if the lhs has side-effects.
> >       <lhs_elt>: Treat the reference as a use if the rhs has side-effects.
> >
> > :ADDPATCH Tree-SRA:
>
> I've read through this thread, and I think Eric's patch makes sense.  (I
> think Richard G. eventually came to the same conclusion, so I'm not
> claiming this is some brilliant insight on my part.)  Even in C, keeping
> volatile accesses "more atomic" seems like a good thing.  And,
> certainly, any possible pessimization by not doing individual accesses
> to move data out of volatile structures is going to be insignificant, to
> overall program runtime.

I agreed to fix the (possible) regression on the branches with Eric's patch.
I didn't agree to put the same fix on the mainline until we first had a
precise definition of what constraints the Ada frontend (seems to) put on
the middle-end.  And with the further conversation it looks to me what
the Ada frontend does/wants isn't what it communicates to the middle-end.

So I'm against applying the patch to the mainline without proper texi
documentation of what Ada does here (it should make little sense, too,
of course).

Richard.