Remove pinning cxx_version in get_stdopt for xeus-cpp-lite

[anutosh491]

Currently we only support c++ 20 based wasm kernel and this flag is passed to our wasm interpreter here

xeus-cpp/src/xinterpreter.cpp

Lines 29 to 33 in dc14222

	void* createInterpreter(const Args &ExtraArgs = {}) {
	Args ClangArgs = {/*"-xc++"*/"-v"}; // ? {"-Xclang", "-emit-llvm-only", "-Xclang", "-diagnostic-log-file", "-Xclang", "-", "-xc++"};
	#ifdef EMSCRIPTEN
	ClangArgs.push_back("-std=c++20");
	#else

This is the only place where essentially we should be hardcoing the version 20 before we start supporting multiple wasm kernels.

Currently get_stdopt is framed like this

    static std::string get_stdopt()
    {
        // We need to find what's the C++ version the interpreter runs with.
#ifndef EMSCRIPTEN
        const char* code = R"(
int __get_cxx_version () {
#if __cplusplus > 202302L
    return 26;
#elif __cplusplus > 202002L
    return 23;
#elif __cplusplus >  201703L
    return 20;
#elif __cplusplus > 201402L
    return 17;
#elif __cplusplus > 201103L || (defined(_WIN32) && _MSC_VER >= 1900)
    return 14;
#elif __cplusplus >= 201103L
   return 11;
#else
  return 0;
#endif
  }
__get_cxx_version ()
      )";
        auto cxx_version = Cpp::Evaluate(code);
        return std::to_string(cxx_version);
#else
        return "20";
#endif
    }
    

But we should simply have

    static std::string get_stdopt()
    {
        // We need to find what's the C++ version the interpreter runs with.
        const char* code = R"(
int __get_cxx_version () {
#if __cplusplus > 202302L
    return 26;
#elif __cplusplus > 202002L
    return 23;
#elif __cplusplus >  201703L
    return 20;
#elif __cplusplus > 201402L
    return 17;
#elif __cplusplus > 201103L || (defined(_WIN32) && _MSC_VER >= 1900)
    return 14;
#elif __cplusplus >= 201103L
   return 11;
#else
  return 0;
#endif
  }
__get_cxx_version()
      )";
        auto cxx_version = Cpp::Evaluate(code);
        return std::to_string(cxx_version);
    }

That is basically run the __get_cxx_version as a first side module and fetch the version through Evaluate rather than hardcode it, cause xeus-cpp-lite should be able to run the code from get_stdopt anyways.

[anutosh491]

Currently if we do it, we end up with

Which is expected.

[anutosh491]

This happens because of how __clang_Interpreter_SetValueNoAlloc is defined (https://github.com/llvm/llvm-project/blob/5656cbca52545e608f6fb8b7c9a778c7c9b4b468/clang/lib/Interpreter/InterpreterValuePrinter.cpp#L313)

So the solution is as follows.

1. First expose the symbol through libclangCppInterOp.so

Probably adding the following below this block(https://github.com/compiler-research/CppInterOp/blob/c446c3e2c43a1d3f374c739295d1484d5349274e/lib/Interpreter/CMakeLists.txt#L7-L19) would suffice.

  target_link_options(clangCppInterOp PRIVATE
    "-Wl,--export=__clang_Interpreter_SetValueNoAlloc"
  )

2. Check if the symbol is being exported by libclangCppInterop.so. We might expect something like this

wasm-objdump -x libclangCppInterOp.so | grep __clang_Interpreter_SetValueNoAlloc

- func[854] sig=6 <__clang_Interpreter_SetValueNoAlloc>
 - func[854] <__clang_Interpreter_SetValueNoAlloc> -> "__clang_Interpreter_SetValueNoAlloc"
 - func[854] size=3144 <__clang_Interpreter_SetValueNoAlloc>

3. Further it should be exposed in xcpp.wasm (through libclangCppInterOp.so ... this might happen itself without intervention) so that the first side module can make use of it. Probably should see the following in xcpp.wasm

(func $__clang_Interpreter_SetValueNoAlloc (;480;) (export "__clang_Interpreter_SetValueNoAlloc") (param $var0 i32) (param $var1 i32) (param $var2 i32) (param $var3 i32)