Add CPPINTEROP_EXTRA_INTERPRETER_ARGS env variable to pass extra arguments.

This patch also teaches CppInterOp to pass down arguments directly to llvm. For
example -mllvm -debug-only=jitlink to subscribe for debug output for a specific
debug type.

Author: vgvassilev

include/clang/Interpreter/CppInterOp.h

@@ -113,6 +113,10 @@ namespace Cpp {
   };
 
   /// Enables or disables the debugging printouts on stderr.
+  /// Debugging output can be enabled also by the environment variable
+  /// CPPINTEROP_EXTRA_INTERPRETER_ARGS. For example,
+  /// CPPINTEROP_EXTRA_INTERPRETER_ARGS="-mllvm -debug-only=jitcall" to produce
+  /// only debug output for jitcall events.
   void EnableDebugOutput(bool value = true);
 
   ///\returns true if the debugging printouts on stderr are enabled.
@@ -296,6 +300,11 @@ namespace Cpp {
   /// Returns the argument name of function as string.
   std::string GetFunctionArgName(TCppFunction_t func, TCppIndex_t param_index);
 
+  /// Creates an instance of the interpreter we need for the various interop
+  /// services.
+  ///\param[in] Args - the list of arguments for interpreter constructor.
+  ///\param[in] CPPINTEROP_EXTRA_INTERPRETER_ARGS - an env variable, if defined,
+  ///           adds additional arguments to the interpreter.
   TInterp_t CreateInterpreter(const std::vector<const char *> &Args = {});
 
   TCppSema_t GetSema(TInterp_t interp);

lib/Interpreter/CppInterOp.cpp

@@ -2429,7 +2429,40 @@ namespace Cpp {
                                            "-std=c++14"};
     ClingArgv.insert(ClingArgv.begin(), MainExecutableName.c_str());
     ClingArgv.insert(ClingArgv.end(), Args.begin(), Args.end());
-    return new compat::Interpreter(ClingArgv.size(), &ClingArgv[0]);
+
+    // Process externally passed arguments if present.
+    std::vector<std::string> ExtraArgs;
+    llvm::Optional<std::string> EnvOpt
+      = llvm::sys::Process::GetEnv("CPPINTEROP_EXTRA_INTERPRETER_ARGS");
+    if (EnvOpt) {
+      StringRef Env(*EnvOpt);
+      while (!Env.empty()) {
+        StringRef Arg;
+        std::tie(Arg, Env) = Env.split(' ');
+        ExtraArgs.push_back(Arg.str());
+      }
+    }
+    std::transform(ExtraArgs.begin(), ExtraArgs.end(),
+                   std::back_inserter(ClingArgv),
+                   [&](const std::string& str) { return str.c_str(); });
+
+    auto I = new compat::Interpreter(ClingArgv.size(), &ClingArgv[0]);
+
+    // Honor -mllvm.
+    //
+    // FIXME: Remove this, one day.
+    // This should happen AFTER plugins have been loaded!
+    const CompilerInstance* Clang = I->getCI();
+    if (!Clang->getFrontendOpts().LLVMArgs.empty()) {
+      unsigned NumArgs = Clang->getFrontendOpts().LLVMArgs.size();
+      auto Args = std::make_unique<const char*[]>(NumArgs + 2);
+      Args[0] = "clang (LLVM option parsing)";
+      for (unsigned i = 0; i != NumArgs; ++i)
+        Args[i + 1] = Clang->getFrontendOpts().LLVMArgs[i].c_str();
+      Args[NumArgs + 1] = nullptr;
+      llvm::cl::ParseCommandLineOptions(NumArgs + 1, Args.get());
+    }
+    return I;
   }
 
   TCppSema_t GetSema(TInterp_t interp) {