[llvm-dev] wasteful cmake defaults

[Michael Kruse via llvm-dev]

Am Do., 19. Nov. 2020 um 03:33 Uhr schrieb David Chisnall
<David.Chisnall at cl.cam.ac.uk>:
> > Since I am not
> > the admin of that machine, I have to compile clang (and gcc) with a
> > prefix in my home directory.
>
> As I recall, nothing in the LLVM install hard codes the install
> location.  Deb packages are just ar archives, RPMs are just cpio
> archives, so users without admin access could just grab the latest
> nightly package for their distro and extract it into their home
> directory.  We could provide a script for that (or, to be more friendly,
> build a .txz from the same directory tree).

Why is this preferable over compiling from source? We provide
documentation to compile from source, but not how to extract files
from distribution packages and where clang expects them.
Even if one would consider that, there are reasons to compile from
source such as optimizing the binary for the concrete CPU
(-match=native) and not having to trust a 3rd party that the compiled
binary corresponds to the sources (not that I would argue like that,
but I know people who compile from source, including their kernel, on
principle).


> > Second, for OpenMP target offloading, we recommend users to compile
> > the latest trunk because it is under heavy development. In practice,
> > if you are using target offloading, you have to compile it yourself
> > because it needs to match the installed version of CUDA (or ROCm) and
> > I have yet to see a distribution where OpenMP target offloading works
> > out of the box.
>
> That sounds unfortunate.  I presume that there is a long-term plan for
> fixing this?

I hope. It is somewhat difficult to provide offloading plugins for all
vendors at the same time (Nvidia+AMD+NEC+...) that each also have
different versions.

Michael