bug#46495: 28.0.50; [native-comp] Build fails for 32bit --with-wide-int

[Andrea Corallo]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Andrea Corallo <akrl@sdf.org>
>> Cc: andrewjmoreton@gmail.com, 46495@debbugs.gnu.org
>> Date: Tue, 16 Feb 2021 16:30:46 +0000
>> 
>> I did some GCC debugging (the crash is there) using my reduced
>> reproducer and clearly look (for my case at least) this is a libgccjit
>> bug that we trigger only generating code for 32bit wide-int.
>
> So GCC 10 has a bug when it generates code which manipulates 64-bit
> integers, is that what you are saying?

It's not strictly related to the integer size.  On 32bit wide-int we
indeed we generate significantly different code respect to 64bit.  For
one case of this GCC manage to prove that a piece of code will deference
a null pointer (this code in reality is unreachable) and tries to add a
call to __builtin_trap () in place.  Unfortunately the libgccjit
front-end is not initializing this built-in declaration.  This is as far
as I've analyzed the problem for now.

>> GCC trunk is broken but as you've anticipated 9 is working (just
>> finished an Emacs bootstrap).
>
> Thanks, this is good to know.  I think we should add an entry to
> etc/PROBLEMS about this.

Will do, still wants to try 10 to be sure.

> Does the buggy behavior of GCC 10 happen regardless of optimization
> level?

I think -O0 should spot this as copy-prop is not running.  We might have
a better (more narrowed) ways to work around this but I need to
investigate more.  Will follow-up.

>> This evening I'll open a bug on the GCC bugzilla and link it here.
>> Would be nice to fix it before the end of stage4... :/
>
> Thanks.

Welcome

  Andrea