| Issue |
174701
|
| Summary |
OpenMP configured as runtime breaks CLANG_DEFAULT_CXX_STDLIB=libc++ build
|
| Labels |
libc++
|
| Assignees |
|
| Reporter |
pkl97
|
When compiling clang like this, the build terminates during compiling of binaries in directory llvm-project/openmp/tools/omptest/src.
```
cmake -G "Ninja" \
-DCMAKE_BUILD_TYPE=Release \
-DCMAKE_INSTALL_PREFIX=install \
-DLLVM_ENABLE_PROJECTS="clang;clang-tools-extra;lld;lldb;polly" \
-DLLVM_ENABLE_RUNTIMES="compiler-rt;libcxx;libcxxabi;libunwind;openmp" \
-DCLANG_DEFAULT_CXX_STDLIB=libc++ \
-DCLANG_DEFAULT_LINKER=lld \
-DLLVM_BUILD_LLVM_DYLIB=ON \
-DLLVM_ENABLE_EH=ON \
-DLLVM_ENABLE_RTTI=ON \
-DLLVM_LINK_LLVM_DYLIB=ON \
-DLIBCXXABI_USE_LLVM_UNWINDER=OFF \
-DCOMPILER_RT_USE_LLVM_UNWINDER=OFF \
../llvm-project/llvm
cmake --build . --verbose > output_compile.txt 2>&1
```
This is the output of the compile run:
[output_compile.txt](https://github.com/user-attachments/files/24465191/output_compile.txt)
The error messages indicate that libc++ header files are needed but not found:
```
llvm-binaries/bin/../include/c++/v1/cctype:45:5: error: <cctype> tried including <ctype.h> but didn't find libc++'s <ctype.h> header.
This usually means that your header search paths are not configured properly.
The header search paths should contain the C++ Standard Library headers before
any C Standard Library.
142 45 | # error <cctype> tried including <ctype.h> but didn't find libc++'s <ctype.h> header. \
143 | ^
```
It turns out that CLANG_DEFAULT_CXX_STDLIB=libc++ triggers the problem. If this switch is removed then clang compiles fine.
However we need a clang version that by default picks libc++ as its C++ Standard Library.
The problem occurs since "openmp" had to be moved from LLVM_ENABLE_PROJECTS to LLVM_ENABLE_RUNTIMES.
Is this kind of build no longer supported or is this behavior a bug?
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