[Polly] Build failure with shared lib at -O0 and lld

[aengelke]

Polly uses AllAnalysesOn<Loop>, which has an explicit template instantiation in LoopAnalysisManager.cpp/h. Therefore, there are multiple (weak) definitions for libLLVM.so, the Polly ones are hidden (STV_HIDDEN) due to -fvisibility-inlines-hidden while the explicit instantiation has default visibility. According to the gABI, the non-default visibility wins (implemented by LLD/Gold; with BFD, default wins). The symbol ends up with STV_HIDDEN in libLLVM.so and linking the unit tests therefore fails with undefined symbol: llvm::AllAnalysesOn<llvm::Loop>::ID().

(FWIW, this behavior was implemented in LLD in 78471f0 (2015).)

CMake command: cmake -DLLVM_ENABLE_PROJECTS="polly" -DLLVM_TARGETS_TO_BUILD="X86" -DLLVM_BUILD_EXAMPLES=OFF -DCMAKE_BUILD_TYPE=Release -DCMAKE_C_FLAGS_RELEASE=-O0 -DCMAKE_CXX_FLAGS_RELEASE=-O0 -G Ninja -DLLVM_ENABLE_ASSERTIONS=OFF -DLLVM_BUILD_LLVM_DYLIB=ON -DLLVM_LINK_LLVM_DYLIB=ON -DCMAKE_C_COMPILER=clang-19 -DCMAKE_CXX_COMPILER=clang++-19 -DLLVM_USE_LINKER=lld -B llvm-build-tmp -S llvm-project/llvm.

(cc @MaskRay – could we get a warning when a previously default-visible symbol gets hidden? Or are there cases where this is intended?)

[llvmbot]

@llvm/issue-subscribers-polly

Author: Alexis Engelke (aengelke)

Polly uses `AllAnalysesOn<Loop>`, which has an explicit template instantiation in LoopAnalysisManager.cpp/h. Therefore, there are multiple (weak) definitions for libLLVM.so, the Polly ones are hidden (`STV_HIDDEN`) due to `-fvisibility-inlines-hidden` while the explicit instantiation has default visibility. According to the gABI, the non-default visibility wins (implemented by LLD/Gold; with BFD, default wins). The symbol ends up with `STV_HIDDEN` in libLLVM.so and linking the unit tests therefore fails with `undefined symbol: llvm::AllAnalysesOn<llvm::Loop>::ID()`.

(FWIW, this behavior was implemented in LLD in 78471f0 (2015).)

CMake command: cmake -DLLVM_ENABLE_PROJECTS="polly" -DLLVM_TARGETS_TO_BUILD="X86" -DLLVM_BUILD_EXAMPLES=OFF -DCMAKE_BUILD_TYPE=Release -DCMAKE_C_FLAGS_RELEASE=-O0 -DCMAKE_CXX_FLAGS_RELEASE=-O0 -G Ninja -DLLVM_ENABLE_ASSERTIONS=OFF -DLLVM_BUILD_LLVM_DYLIB=ON -DLLVM_LINK_LLVM_DYLIB=ON -DCMAKE_C_COMPILER=clang-19 -DCMAKE_CXX_COMPILER=clang++-19 -DLLVM_USE_LINKER=lld -B llvm-build-tmp -S llvm-project/llvm.

(cc @MaskRay – could we get a warning when a previously default-visible symbol gets hidden? Or are there cases where this is intended?)

[MaskRay]

According to the gABI, the non-default visibility wins (implemented by LLD/Gold; with BFD, default wins).

GNU ld doesn't behave differently from gold / LLD. The non-default visibility wins per gABI

If different visibility attributes are specified for distinct references to or definitions of a symbol, the most constraining visibility attribute must be propagated to the resolving symbol in the linked object. The attributes, ordered from least to most constraining, are: STV_PROTECTED, STV_HIDDEN and STV_INTERNAL.

This is an intended behavior and allows users to constrain a symbol. I don't think we could implement a warning...

[Meinersbur]

This problem doesn't seem Polly-specific, but applies to any NPM pass plugin.

Anyway, use of AllAnalysisOn<Loop> in Polly will be removed in #125783.