[Bug rtl-optimization/96015] [10/11 Regression] gcc-10.1.0 miscompiles Python on hppa

["marxin at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96015

--- Comment #28 from Martin Liška <marxin at gcc dot gnu.org> ---
(In reply to Sergei Trofimovich from comment #25)
> (In reply to Sergei Trofimovich from comment #22)
> > (In reply to Martin Liška from comment #17)
> > > For me tree optimized dump is correct, so likely a target issue.
> > 
> > Yeah, I agree. I finally understood why memory loads disappear (duh!).
> > 
> > > @Sergei: Is GCC 9 working properly?
> > > Would it be possible to bisect that?
> > 
> > gcc-9 seems to work, bu I'm not sure if it's intentional or unrelated
> > optimization passes change the code enough.
> > 
> > I'll try to cook up even smaller example given that -fno-delayed-branch
> > seems to be a culprit and then bisect gcc.
> 
> Bisected down to:
> 
> $ git bisect good
> 8c3785c43d490d4f234e21c9dee6bb1bb8d1dbdf is the first bad commit
> commit 8c3785c43d490d4f234e21c9dee6bb1bb8d1dbdf
> Author: Martin Liska <mliska@suse.cz>
> Date:   Wed Dec 4 11:13:49 2019 +0100
> 
>     Initialize a BB count in switch lowering.
> 
>     2019-12-04  Martin Liska  <mliska@suse.cz>
> 
>             * tree-switch-conversion.c
> (switch_decision_tree::try_switch_expansion):
>             Initialize count of newly created BB.
> 
>     From-SVN: r278959
> 
>  gcc/ChangeLog                | 5 +++++
>  gcc/tree-switch-conversion.c | 1 +
>  2 files changed, 6 insertions(+)

Thank you for the bisection. However, this one is not a culprit commit, it only
made it visible.
Let's wait for can Erik find out.