Re: [jani:device-info-inheritance-v3 3/19] drivers/gpu/drm/i915/i915_pci.c:212:2: error: initializer element is not a compile-time constant

[Jani Nikula <jani.nikula@linux.intel.com>]

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On Mon, 09 Mar 2020, Nick Desaulniers <ndesaulniers@google.com> wrote:
> On Mon, Mar 9, 2020 at 1:32 AM Jani Nikula <jani.nikula@linux.intel.com> wrote:
>>
>> On Fri, 06 Mar 2020, Nick Desaulniers <ndesaulniers@google.com> wrote:
>> > Based on the tree, I think this report was meant to go to Jani (cc'ed)?
>>
>> It baffles me that the build bot burns resources on building random
>> branches in my personal repositories.
>
> It uses a branch naming convention to avoid testing branches:
> https://github.com/intel/lkp-tests/wiki/LKP-FAQ#is-there-a-way-not-to-trigger-kbuild-tests-on-a-specific-branch
>
> But in this case, it seems it caught a build breakage even further
> upstream, which is valuable, right?

I guess, though I usually only use it to share some half-baked
stuff. Perhaps I'll also start using it for build testing some of the
more obscure ideas. ;)

>> That said, this builds on GCC 8 just fine. Is clang not able to do this?
>
> Places that require integer constant expressions can be very subtle.
> See this recent example in i915 for example:
> https://github.com/ClangBuiltLinux/linux/issues/918
> Sometimes reproducing also depends on some configs.  In this case,
> it's not as I've fetched your branch and can repro on defconfig.

Yeah, reminds me of earlier issues with GCC and Clang having different
order in certain checks and optimizations, leading to Clang warnings in
code that GCC just optimized away.

> This is definitely our bug: https://bugs.llvm.org/show_bug.cgi?id=45157

Any idea if older GCC is also limited in this regard? What versions does
the kbuild bot test?

BR,
Jani.



-- 
Jani Nikula, Intel Open Source Graphics Center