[cfe-dev] RFC: Place libs in Clang-dedicated directories (affects openmp, libcxx, libunwind, compiler-rt)

[Joel E. Denny via cfe-dev]

Hi Ilya,

On Mon, Feb 25, 2019 at 5:32 AM Ilya Biryukov <ibiryukov at google.com> wrote:
>
> > From this point of view, what LLVM_ENABLE_PER_TARGET_RUNTIME_DIR breaks the tools and the proposed alternative fixes this problem
> what  LLVM_ENABLE_PER_TARGET_RUNTIME_DIR does now ...
>
> On Mon, Feb 25, 2019 at 11:31 AM Ilya Biryukov <ibiryukov at google.com> wrote:
>>
>> Using the resource-dir in the header search paths would break tools that use compilation database, e.g. clang-tidy and clangd.
>> They override the resource-dir as it's very common for them to be built from a different revision than the used compiler. They rely on the fact that the same standard library can be found with the overridden resouce-dir.
>>
>> From this point of view, what LLVM_ENABLE_PER_TARGET_RUNTIME_DIR breaks the tools and the proposed alternative fixes this problem.

Thanks for pointing this out.  I'd like to better understand, but I'm
only familiar with clang-tidy and clangd from a high level.  Can you
explain a bit more about how they interact with the used compiler and
how they use the overridden resource directory?

Thanks.

Joel

>>
>> On Mon, Feb 25, 2019 at 11:17 AM Petr Hosek via cfe-dev <cfe-dev at lists.llvm.org> wrote:
>>>
>>> On Wed, Feb 20, 2019 at 6:14 PM Joel E. Denny <jdenny.ornl at gmail.com> wrote:
>>>>
>>>> My alternative to LLVM_ENABLE_PER_TARGET_RUNTIME_DIR is the preceding
>>>> bullets.  In other words, you wouldn't need to specify
>>>> LLVM_ENABLE_PER_TARGET_RUNTIME_DIR because it would effectively be
>>>> always on (except the directories might be different than now if the
>>>> version locking issue is important, as noted above).  Is that what
>>>> you're asking?
>>>
>>>
>>> That would be my preference. I always hoped that LLVM_ENABLE_PER_TARGET_RUNTIME_DIR would eventually become the default. It would be nice to finish the Darwin support so we can completely deprecate the old layout, but I don't know how far along beanz is in his effort. We should also update openmp to stop using the custom Android-specific runtime layout.
>>>
>>> There's also the unresolved question of where should libc++ headers and libraries go. Currently, in LLVM_ENABLE_PER_TARGET_RUNTIME_DIR we use the resource dir, but some people expressed the opinion that we shouldn't be using these for libc++ et al. since they're not version-locked to Clang. This is different from what GCC does (e.g. GCC would use $prefix/lib/gcc/x86_64-linux-gnu/8/libstdc++.a) and it's one of the reasons why I used the resource dir for libc++ et al. when implementing LLVM_ENABLE_PER_TARGET_RUNTIME_DIR.
>>>
>>> So concretely, today LLVM_ENABLE_PER_TARGET_RUNTIME_DIR uses the following layout:
>>>
>>> headers: $prefix/lib/clang/$version/include(/$triple)(/c++/v1)
>>> libraries: $prefix/lib/clang/$version/$triple/lib/$name.$ext
>>>
>>> The alternative that doesn't use resource dir for libc++ would be the following:
>>>
>>> compiler-rt:
>>>   headers: $prefix/lib/clang/$version/include
>>>   libraries: $prefix/lib/clang/$version/$triple/lib/$name.$ext
>>>
>>> libc++, libc++abi, libunwind:
>>>   headers: $prefix/include/c++/v1
>>>   libraries: $prefix/lib/$triple/$name.$ext
>>>
>>> Making this change should be trivial, it's the matter of changing three CMakeLists.txt files (libunwind, libc++abi and libc++) and Clang driver in one place. However, if we're going to make that change, I'd like to get a broader consensus. It'd be also useful to get feedback from libc++ maintainers on this.
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>>
>>
>>
>> --
>> Regards,
>> Ilya Biryukov
>
>
>
> --
> Regards,
> Ilya Biryukov