Failures building glibc with mainline GCC

[Jeff Law]

On 7/30/2021 10:19 AM, Aldy Hernandez via Libc-alpha wrote:
> There's a new jump threader in GCC which is much more aggressive, and
> may trigger latent problems with other warning passes, especially
> -Warray-bounds, -Woverflow, and -Wuninitialized.
>
> Do your problems go away if you take out commit 2e96b5f14e?
>
> I have notes throughout the commit analyzing variants of the above
> warnings (for example my addendum to gcc.c-torture/compile/pr83510.c).
> So far, all the warnings I've seen are legitimate jump threading
> opportunities that we are now doing, but which throw off the warning
> passes.
>
> Before the inclusion of the new threader, I had warned that this could
> happen.  Perhaps we'll have to come up a way to reduce the false
> positives.
I should be able to get you testcases for at least some of these.  I 
strongly suspect it's the new threader.  First up will be the iconf 
stringop-overflow failures which should hit your inbox shortly.

Jeff