Bug#882781: clang is missing a dependency on libomp-dev

[Sylvestre Ledru]

On 26/11/2017 23:47, Alexander Kurtz wrote:
> Hi!
>
> On Sun, 2017-11-26 at 22:27 +0100, Sylvestre Ledru wrote:
>> For now, I am not planning to add this a mandatory dep. openmp is a
>> niche and I don't think
>> we should have a hard dependency for every clang user.
>> By the way libomp-dev is suggested by clang packages.
> In theory, you are right, clang should not depend on library packages
> just for convenience. However libomp-dev is special here, because its
> usage is usually hidden: Typical OpenMP tutorials look like this:
>
> 	cc -fopenmp foo.c
>
> or maybe
>
> 	cc -fopenmp -o foo.o foo.c
> 	cc -fopenmp -o foo   foo.o
>
> and this works on GCC. The fact that this doesn't work with clang isn't
> even the problem here, the fact that step 1 from above works, while
> step 2 doesn't is. If users expected to need to link a library in for
> this to work, things would be fine, but they don't (which arguably is
> the real problem here, but thanks to GCC that's just the way it is).
>
> TL;DR: If you want to write cross-compiler Makefiles, you use
> -fopenmp for both compiling and linking, because the actual OpenMP
> libraries differ between GCC and clang. And this breaks for clang.
>
> And last but not least, libomp-dev pulls in 238 KB, which is about 0.4%
> of the 59.1 MB clang pulls in:
Well, this won't be true in a future upload. I split clang & clang-tools;
clang should be about 9mb now.
> If you don't want a hard dependency (which I still think would be the
> correct thing to do since "a command line argument of clang doesn't
> actually work without it"), would you perhaps consider a Recommends: ?
>
Sure, I fixed that in the vcs!

Thanks
S


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