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

[Petr Hosek via cfe-dev]

That's useful to know and not something I was aware of, this might be a
sufficient reason to alter the LLVM_ENABLE_PER_TARGET_RUNTIME_DIR layout
and move libc++ out of the resource directory.

On Mon, Feb 25, 2019 at 2:32 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.
>>
>> 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
>>> <https://github.com/llvm/llvm-project/blob/master/libunwind/CMakeLists.txt#L189>,
>>> libc++abi
>>> <https://github.com/llvm/llvm-project/blob/master/libcxxabi/CMakeLists.txt#L179>
>>> and libc++
>>> <https://github.com/llvm/llvm-project/blob/master/libcxx/CMakeLists.txt#L419>)
>>> and Clang driver in one place
>>> <https://github.com/llvm/llvm-project/blob/master/clang/lib/Driver/ToolChain.cpp#L79>.
>>> 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.
>>> _______________________________________________
>>> cfe-dev mailing list
>>> cfe-dev at lists.llvm.org
>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>>
>>
>>
>> --
>> Regards,
>> Ilya Biryukov
>>
>
>
> --
> Regards,
> Ilya Biryukov
>
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