-fvisibility-inlines-hidden hinders symbol export from CXCppInterOp.cpp for emscripten use case

[anutosh491]

Description of bug

Not sure about the native use case (haven't looked into that) but we had this untill now

CppInterOp/lib/Interpreter/CMakeLists.txt

Lines 7 to 11 in 59b7c11

	add_llvm_library(clangCppInterOp
	SHARED
	CppInterOp.cpp
	CXCppInterOp.cpp

I guess we all assumed that this was enough to have symbols out of CXCppInterOp.cpp being exposed just like the other source files.

But recently while reviewing #483 I realized that not even a single symbol out of this file is being exported.

This is the reason, these symbols have been manually exported in the PR
https://github.com/compiler-research/CppInterOp/pull/483/files#diff-054935aee7c0887220251f89b2179dbc4a0c418a69bca9f74854305ae7c0f967R31-R37

What operating system was you using when the bug occured?

Other

What is the architechture of the cpu on your system?

Other

What did you build CppInterOp against?

Clang-repl (LLVM19)

[anutosh491]

Steps to go about this

1. Trying the following on our current libclangCppInterOp.so would give about 498 symbols

emnm --debug-syms libclangCppInterOp.so > test.txt

2. These are the Compile flags and Link flags we currently use

CXX_FLAGS =  -fPIC -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough  -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -ffunction-sections -fdata-sections -fno-common -Woverloaded-virtual -Wcast-qual -fno-strict-aliasing -Wno-long-long -Wall -W -Wno-unused-parameter -Wwrite-strings  -Wno-sign-compare -O3 -DNDEBUG -std=c++17 -fPIC -s SIDE_MODULE=1 -UNDEBUG

/Users/anutosh491/micromamba/envs/xeus-cpp-wasm-build/opt/emsdk/upstream/emscripten/em++ -fPIC  -fPIC -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough  -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -ffunction-sections -fdata-sections -fno-common -Woverloaded-virtual -Wcast-qual -fno-strict-aliasing -pedantic -Wno-long-long -Wall -W -Wno-unused-parameter -Wwrite-strings -O3 -DNDEBUG  -Wl,--gc-sections -s WASM_BIGINT -O2 -g0 -s WASM=1 -sWASM_BIGINT -L/Users/anutosh491/micromamba/envs/xeus-cpp-wasm-host/lib -Wl,-z,defs -s SIDE_MODULE=1  -o ../libclangCppInterOp.so @CMakeFiles/clangCppInterOp.dir/objects1.rsp @CMakeFiles/clangCppInterOp.dir/linkLibs.rsp

3. Once we remove -fvisibility-inlines-hidden from these and try emnm --debug-syms libclangCppInterOp.so > test.txt again, you would see somewhere around 530 symbols I think (which would those 498 from libclangCppInterOp.so + all symbols out of CXCppInterOp.cpp)

And we then won't have to export them the way we do cause these symbols should be a part libclangCppInterOp.so

[anutosh491]

What I think might be happening is the compiler is considering these function to be potentially inlined and hence the -fvisibility-inlines-hidden flag sets the default visibility to hidden, causing the symbols from CXCppInterOp.cpp to not be exported in the shared library (libclangCppInterOp.so). Since these symbols are not in the dynamic symbol table, they cannot be accessed during linking or at runtime.

So yeah to fix this we have 3 options

1. add a flag to overwrite it
2. remove the flag from where it comes (llvm)
3. built llvm in a way that doesn't introduce this flag