505e049aa0
LLD has a bug regarding ordering of static link libraries in the ELF backend, which has been reported as #116669.
CMake 3.31.0 started properly deduplicating static libraries for LLD causing the following linking failure for `libclang-cpp.so` with `-DLLVM_LINK_LLVM_DYLIB=ON`:
```
ld.lld: error: undefined symbol: llvm::omp::getOpenMPClauseName(llvm::omp::Clause)
>>> referenced by OpenMPKinds.cpp
>>> tools/clang/lib/Basic/CMakeFiles/obj.clangBasic.dir/OpenMPKinds.cpp.o:(clang::getOpenMPSimpleClauseTypeName(llvm::omp::Clause, unsigned int))
>>> referenced by SemaOpenMP.cpp
>>> tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaOpenMP.cpp.o:(clang::SemaOpenMP::CheckOMPRequiresDecl(clang::SourceLocation, llvm::ArrayRef<clang::OMPClause*>))
>>> referenced by SemaOpenMP.cpp
>>> tools/clang/lib/Sema/CMakeFiles/obj.clangSema.dir/SemaOpenMP.cpp.o:(clang::SemaOpenMP::CheckOMPRequiresDecl(clang::SourceLocation, llvm::ArrayRef<clang::OMPClause*>))
>>> referenced 166 more times
[tons more]
```
CMake 3.31 also introduced CMP0179, which builds on CMP0156 and makes the deduplication consistent across platforms.
By coincidence this works around the above LLD deficiency and is the fix that CMake 3.31.1 will implement.
However, the fix is to ignore CMP0156 unless CMP0179 is also enabled, i.e. no more deduplication.
So enable CMP0179 to keep the benefits of deduplication from CMP0156 on LLD and fix the build for CMake 3.31.0.
See: #116669
See: https://gitlab.kitware.com/cmake/cmake/-/issues/26447
Fixes: cb90d5b
50 lines
1.9 KiB
CMake
50 lines
1.9 KiB
CMake
# CMake policy settings shared between LLVM projects
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# CMP0116: Ninja generators transform `DEPFILE`s from `add_custom_command()`
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# New in CMake 3.20. https://cmake.org/cmake/help/latest/policy/CMP0116.html
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if(POLICY CMP0116)
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cmake_policy(SET CMP0116 OLD)
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endif()
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# MSVC debug information format flags are selected via
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# CMAKE_MSVC_DEBUG_INFORMATION_FORMAT, instead of
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# embedding flags in e.g. CMAKE_CXX_FLAGS_RELEASE.
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# New in CMake 3.25.
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#
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# Supports debug info with SCCache
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# (https://github.com/mozilla/sccache?tab=readme-ov-file#usage)
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# avoiding “fatal error C1041: cannot open program database; if
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# multiple CL.EXE write to the same .PDB file, please use /FS"
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if(POLICY CMP0141)
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cmake_policy(SET CMP0141 NEW)
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endif()
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# CMP0144: find_package() uses uppercase <PackageName>_ROOT variables.
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# New in CMake 3.27: https://cmake.org/cmake/help/latest/policy/CMP0144.html
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if(POLICY CMP0144)
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cmake_policy(SET CMP0144 NEW)
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endif()
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# CMP0147: Visual Studio Generators build custom commands in parallel.
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# New in CMake 3.27: https://cmake.org/cmake/help/latest/policy/CMP0147.html
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if(POLICY CMP0147)
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cmake_policy(SET CMP0147 NEW)
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endif()
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# CMP0156: De-duplicate libraries on link lines based on linker capabilities.
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# New in CMake 3.29: https://cmake.org/cmake/help/latest/policy/CMP0156.html
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# Avoids the deluge of 'ld: warning: ignoring duplicate libraries' warnings when
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# building with the Apple linker.
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if(POLICY CMP0156)
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cmake_policy(SET CMP0156 NEW)
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# CMP0179: De-duplication of static libraries on link lines keeps first occurrence.
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# Dependent on CMP0156=NEW. Unifies the behaviour across platforms.
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# Works around a LLD bug ELF backend bug (#116669) and required for CMP0156
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# to have an effect for affected versions. Also fixes building with CMake 3.31.0,
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# which lacked the workaround of ignoring CMP0156 unless this is enabled.
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if(POLICY CMP0179)
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cmake_policy(SET CMP0179 NEW)
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endif()
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endif()
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