[vtk-developers] Various issues on my dashboards... help needed...

Thu Aug 17 11:29:44 EDT 2017

I agree, the scope for disabling the warnings should be as small as
possible -- Leave the warnings on, and then if we find one that's
harmless, just push/pop the warnings around the template function. Ken
pointed me at a few of these warnings a couple weeks ago and we ended
up fixing a few real template resolution bugs these warnings uncovered
that severely affected performance.

I took a closer look through these and fixed a few harmless warnings
that could be easily addressed without pragmas. See
https://gitlab.kitware.com/vtk/vtk/merge_requests/3163

The vtkXMLWriter patch will probably still throw warnings after that
MR is merged, but they can be safely ignored with the others. That
patch just makes the optimization more robust in the case that e.g.
vtkFloatArray is in the dispatch list, instead of
vtkAOSDataArrayTemplate<float> (Generic template parameters are used
before the compiler will check inheritance).

There were two in places I'm not familiar with, so I'll leave those
for someone more familiar with these classes:

Filters/General/vtkQuadraturePointsUtilities.hxx:119
Rendering/Context2D/vtkContextActor.cxx:88

The rest (overloads with AOS/SOA specific arguments) can be safely
ignored. Sean, would you mind patching those? I don't have a suitable
version of clang to test on so it'd probably faster if you could test
locally. Most of those are in files generated from
Common/Core/Testing/Cxx/TestDataArrayAPI.cxx.in, so realistically
there are only a couple places that need patching.

Allie

On Thu, Aug 17, 2017 at 9:46 AM, Ken Martin <ken.martin at kitware.com> wrote:
> I think the warning is valuable. I do not believe it applies to general
> class templates that have external linkage.
>
> I believe in this case the error is specifically due to the fact the
> templated function in question has internal linkage. By defining it  inside
> an anonymous namespace the templated function cannot be used anywhere else,
> and yet it is unused. So the compiler warns us.
>
> Potential fixes could be to
>
> - pull that struct (CheckShallowCopy) out of the anonymous namespace (I
> think that changes its linkage to external)
>
> - do an ifdef to remove the function for this test case
>
> - declare that function in CheckShallowCopy as extern forcing it to have
> external linkage
>
> I'm not 100% sure which if any of those solutions would work but that would
> be my guess. Maybe Sean could give one of them a shot on his system?
>
>
> Dave here is the llvm thread I looked at last time that talks a bit about
> this
>
> https://reviews.llvm.org/D29877
>
>
>
>
> On Wed, Aug 16, 2017 at 8:37 PM, David Cole via vtk-developers
> <vtk-developers at vtk.org> wrote:
>>
>> In this thread :
>> http://public.kitware.com/pipermail/vtk-developers/2017-August/035314.html
>> , Ken Martin said
>>
>> "the llvm folks added this due to some ODR violation checking.
>> That having it unused can cause it to be defined multiple times in a
>> translation unit for some reason."
>>
>> Despite my Google skillz, I could not find what exactly he was
>> referring to, and a search on the quoted "-Wunused-template" doesn't
>> help much. Or I didn't dig deep enough.
>>
>> Anyhow:
>>
>> I think you should favor limiting the disabled bit of the warning to
>> the scope where you know it's safe to ignore, and not just put a
>> blanket suppression on it. Each warning is useful to somebody for some
>> code, and ignoring them everywhere by a global compile flag is not the
>> best way to suppress a warning in a handful of files among thousands.
>>
>>
>> Just my opinion ... but there you have it.
>>
>> David C.
>>
>>
>>
>>
>>
>> On Wed, Aug 16, 2017 at 7:06 PM, Sean McBride <sean at rogue-research.com>
>> wrote:
>> > On Wed, 16 Aug 2017 13:54:26 -0400, Allie Vacanti said:
>> >
>> >>> Allison, do you think you can work on the data array warnings?
>> >>>
>> >>> I think if both Allison and I take care of those it should whittle
>> >>> down the
>> >>> list to a more manageable size to start getting others to help out
>> >>> with.
>> >>
>> >>I think we should just disable the unused-template warnings. Most of
>> >>these cases depend on the ArrayDispatch configuration and can't be
>> >>removed without breaking features, even though some builds don't use
>> >>them.
>> >
>> > Allie,
>> >
>> > OK, so we just have to decide if we should:
>> >  a) use "#pragma clang diagnostic ignored" to disable this warning for
>> > the ArrayDispatch file(s)
>> > or
>> >  b) I just add -Wno-unused-template to disable it everywhere and always
>> >
>> > I guess it depends if the warning is generally useful (except for the
>> > funky case of ArrayDispatch stuff), or generally useless.
>> >
>> > Cheers,
>> >
>> > --
>> > ____________________________________________________________
>> > Sean McBride, B. Eng                 sean at rogue-research.com
>> > Rogue Research                        www.rogue-research.com
>> > Mac Software Developer              Montréal, Québec, Canada
>> >
>> >
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>
>
> --
> Ken Martin PhD
> Distinguished Engineer
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