[llvm-dev] llvm-6 change from inlining to relocations causing ImageMagick+mesa crash

[Nicolai Hähnle-Montoro via llvm-dev]

The simplest bandaid fix for the time being is to make sure the LLVM
driver forcibly inlines everything. This is what graphics APIs are
still doing.

The next step is to implement proper linking in Mesa and make sure
it's used for those OpenCL applications. I have patches pending for
the graphics side of this (look for: "amd,radeonsi: add a real runtime
linker").

Cheers,
Nicolai

On Mon, Jun 3, 2019 at 2:06 AM James Harvey via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
>
> ImageMagick + mesa provided OpenCL has been failing for many people
> for some time now.  See
> https://github.com/ImageMagick/ImageMagick/issues/1366
>
> It was tracked down that ImageMagick commit 41a3cc9 and Mesa commit
> 9baacf were involved.
>
> There's been discussion about this on the Mesa list.  See
> https://lists.freedesktop.org/archives/mesa-dev/2019-June/219736.html
>
> Mesa dev Jan Vesely says behavior changed in llvm-6 that started
> causing GPU hangs/crashes in some situations, and their commit was
> just to prevent those.
>
> Specifically: "AMDGPU llvm backend used to inline all function calls
> until llvm-6. llvm-6+ uses functions calls and issues relocations for
> each function invocation. unhandled relocations lead to GPU
> hangs/crashes. either clover/mesa needs to handle relocations, or LLVM
> needs to stop using relocations for internal symbols (they are not
> needed)."
>
> I don't know all the specifics, of course, but it sounds like even if
> ImageMagick or mesa could be changed as a workaround, that the
> ultimate cause was a change in llvm-6 that is causing crashes and
> should be addressed.
>
> I'm trying to bring the 3 involved projects together.  At this time,
> we unfortunately don't have a specific llvm commit where the failure
> started.  If it's needed, please ask.  It's not something I'd be able
> to bisect, but I'd be able to see if I could find someone involved who
> would.
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