Per discussion on discord and various feature requests across bindings (Haskell and Rust bindings authors have asked me directly), we should be building a link-ready MLIR-C dylib which exports the C API and can be used without linking to anything else.
This patch:
* Adds a new MLIR-C aggregate shared library (libMLIR-C.so), which is similar in name and function to libLLVM-C.so.
* It is guarded by the new CMake option MLIR_BUILD_MLIR_C_DYLIB, which has a similar purpose/name to the LLVM_BUILD_LLVM_C_DYLIB option.
* On all platforms, this will work with both static, BUILD_SHARED_LIBS, and libMLIR builds, if supported:
* In static builds: libMLIR-C.so will export the CAPI symbols and statically link all dependencies into itself.
* In BUILD_SHARED_LIBS: libMLIR-C.so will export the CAPI symbols and have dynamic dependencies on implementation shared libraries.
* In libMLIR.so mode: same as static. libMLIR.so was not finished for actual linking use within the project. An eventual relayering so that libMLIR-C.so depends on libMLIR.so is possible but requires first re-engineering the latter to use the aggregate facility.
* On Linux, exported symbols are filtered to only the CAPI. On others (MacOS, Windows), all symbols are exported. A CMake status is printed unless if global visibility is hidden indicating that this has not yet been implemented. The library should still work, but it will be larger and more likely to conflict until fixed. Someone should look at lifting the corresponding support from libLLVM-C.so and adapting. Or, for special uses, just build with `-DCMAKE_CXX_VISIBILITY_PRESET=hidden -DCMAKE_C_VISIBILITY_PRESET=hidden`.
* Includes fixes to execution engine symbol export macros to enable default visibility. Without this, the advice to use hidden visibility would have resulted in test failures and unusable execution engine support libraries.
Differential Revision: https://reviews.llvm.org/D113731
Expose the debug flag as a readable and assignable property of a
dedicated class instead of a write-only function. Actually test the fact
of setting the flag. Move test to a dedicated file, it has zero relation
to context_managers.py where it was added.
Arguably, it should be promoted from mlir.ir to mlir module, but we are
not re-exporting the latter and this functionality is purposefully
hidden so can stay in IR for now. Drop unnecessary export code.
Refactor C API and put Debug into a separate library, fix it to actually
set the flag to the given value.
Reviewed By: nicolasvasilache
Differential Revision: https://reviews.llvm.org/D100757
