Re: -fprofile-update=atomic vs. 32-bit architectures

[Richard Biener <richard.guenther@gmail.com>]

On Tue, Nov 8, 2022 at 1:00 PM Sebastian Huber
<sebastian.huber@embedded-brains.de> wrote:
>
> On 08.11.22 11:25, Richard Biener wrote:
> >> How do I get ((unsigned int *) &val) + 1 from tree addr?
> >>
> >> It would be great to have a code example for the construction of the "if
> >> (f()) f();".
> > I think for the function above we need to emit __atomic_fetch_add_8,
> > not the emulated form because we cannot insert the required control
> > flow (if (f()) f()) on an edge.  The __atomic_fetch_add_8 should then be
> > lowered after the instrumentation took place.
>
> Ok, I am not a compiler expert, so I have just a vague feeling how this
> works. I am not sure which piece is responsible for the "lowering" of
> this particular __atomic_fetch_add_8. I guess we don't want to split all
> __atomic_fetch_add_8 into this if (f()) f(); form?

I think we should do it right after the profile instrumentation commits
the edge insertions.  And yes, we only want to lower those that
are not natively supported (but have native support for fetch_add_4).
Not sure how to determine this.

>
> >
> > There's currently no helper to create a diamond so the canonical
> > way is to create a GIMPLE_COND, split the block after this stmt,
> > split the outgoing edge and then redirect edges to form a half-diamond.
> > move_sese_in_condition has most of that CFG manipulation (but
> > it performs sth different)
>
> Thanks, I will probably able to do this with a bit trial and error.
>
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