find_package(LLVM) fails to find shared libztd and errors out on Windows, when using Clang
#306
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Filed llvm/llvm-project#121345. |
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That doesn't seem to be the case. It is possible that I've messed something up but I've just set Visual Studio 2022, and Conda environment with Clang. Clang reports https://cmake.org/cmake/help/latest/variable/MSVC.html#variable:MSVC says:
And indeed, if I set |
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And indeed, if I replace |
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I've proposed llvm/llvm-project#121437 to do that. https://dev.azure.com/conda-forge/feedstock-builds/_build/results?buildId=1129626&view=logs&j=535b614b-9e28-51ef-eb67-d0aa83d01d61&t=c0e5205c-8699-555e-ce93-e93093f402f2 seems to confirm that it fixed the issue in question (note the |
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Thanks, I was wondering if MinGW could be affected — but this is definitely cleaner than trying to maintain an opt-out list of compilers or guessing based on static library suffix. |
Instead of unconditionally assuming MSVC-alike behavior for WIN32 that could negatively impact MSVC, use `CMAKE_CXX_SIMULATE_ID` to detect Clang using MSVC ABI. Note that this variable is unset for MSVC itself, so use it alternatively to MSVC. Thanks to @isuruf for the suggestion (conda-forge/llvmdev-feedstock#306 (comment)).
Solution to issue cannot be found in the documentation.
Issue
When trying to get triton-feedstock working on Windows, with Clang used as the compiler, CMake would fail with:
Full Azure log: azure-log.txt
I don't have a Windows setup to test this properly, but my reading of the code leads to the following conclusion (that I've originally stated in conda-forge/triton-feedstock#29 (comment)):
https://github.com/llvm/llvm-project/blob/e21dc4bd5474d04b8e62d7331362edcc5648d7e5/llvm/cmake/modules/Findzstd.cmake
When MSVC is used,
zstd_STATIC_LIBRARY_SUFFIXis_static.lib$, otherwise it's just.lib$. So when using MSVC,zstd.lib(andlibzstd.libwould too) triggers the second clause in thezstd_FOUNDcondition, causing it to perform explicit lookup forbin/zstd.dll. On the other hand, when using Clang, it just treatslibzstd.libas a static library (the first clause) and doesn't bother beyond that. So effectively, with MSVC it finds both static and shared libraries, and with Clang only the former.Now, since LLVM in Conda is built with MSVC, it uses the shared zstd library and includes references to the dependency on this library in the installed CMake files. However, these files don't include the zstd library target itself — instead, they're triggering another lookup in reverse dependencies. Since the lookup is now performed with Clang and it doesn't find the shared library, the dependencies are unsatisfied.
And perhaps the worst part, it is possible that I've actually broken it there. I specifically see the shared library logic for MSVC has been added in llvm/llvm-project@e7fc754 — perhaps the condition there should check for Windows rather than MSVC. But it's outside my expertise to change that.
Installed packages
Environment info
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