mvanhorn opened a new pull request, #20162: URL: https://github.com/apache/tvm/pull/20162
TVM sets `CMAKE_CXX_STANDARD` to 20 globally, then adds the vendored `tvm-ffi` project, whose sources are intended to compile as C++17. Because CMake's `cxx_std_17` feature is a minimum rather than an exact standard, the parent setting causes `tvm-ffi` sources to compile as C++20 and exposes a recursive `std::optional` constraint failure with the reporter's newer Clang/GCC standard-library combination. The reporter's attempted local standard isolation allowed compilation to progress through the original error, while the later LLVM link errors came from the separately configured ROCm LLVM toolchain. No prior or competing PR is recorded in the supplied issue bundle. ## Testing - Configure a normal Ninja build and confirm compile commands for `3rdparty/tvm-ffi` contain an explicit C++17 mode or no newer-standard flag, while TVM `src/` commands retain C++20. - Configure with a compiler whose default language mode is already C++17 and confirm the validation accepts an omitted explicit C++17 flag for `tvm-ffi` without weakening the C++20 assertion for TVM. - Exercise the existing CI build path and confirm the original `std::optional<tvm::ffi::Optional<VisitInterrupt>>` compilation failure no longer occurs on a modern Clang using GCC 16 standard-library headers. - Deliberately allow the dependency to inherit a C++20 flag and confirm the build driver stops before compilation with a diagnostic that identifies the mismatched `tvm-ffi` compile command. ## What changed In `CMakeLists.txt`, save TVM's C++20 setting immediately before `add_subdirectory(3rdparty/tvm-ffi)`, temporarily select C++17 while the dependency creates its targets, and restore the saved value immediately afterward so all subsequent TVM targets retain the project standard. Keep the change at the parent/dependency boundary rather than altering `tvm-ffi` headers or adding a source-level workaround for the reported template instantiation. Extend `tests/scripts/task_build.py` after CMake configuration to inspect the generated compile database and assert that C++ sources under `3rdparty/tvm-ffi` are not compiled with a C++20 flag while representative TVM C++ sources still are. Fixes #20042 -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
