Re: [RFC] More jump threading restrictions in the presence of loops.

[Jeff Law <jeffreyalaw@gmail.com>]

On 10/14/2021 3:25 AM, Aldy Hernandez wrote:
> PING.
>
> Note, that there are no PRs and nothing really dependent on this
> patch.  This has just been suggested as the right thing to do wrt
> loops.
>
> This patch fixes 6 XFAILs in our testsuite and has the added
> side-effect of fixing the aarch64 bootstrap problem (though the
> problem in the uninit code is still there).
>
> This is a fundamental change in what we've traditionally allowed for
> jump threading, but I think it's a good thing.  It also paves the way
> for combining the validity models for both the forward and the
> backward threaders.
>
> I am happy to field the PRs this may bring about, since every change
> in the cost model has us questioning whether we should or shouldn't
> thread a path.  But I may need some help from y'all if there's a
> missing thread that causes a regression in some other pass.  That
> being said, most of the issues that have come with the threader
> changes haven't been because we thread less, but because we thread
> more-- so perhaps restricting things is a good thing ;-).
Just chasing down fallout from the vectorizer changes first :-)

jeff