clang-interpreter: use LLVM interpreter if JIT is unavailable

Update the strategy in r212083 to try JIT first and otherwise fall back to the
interpreter. This gives the best of both worlds and still builds fine with no
targets enabled.

Requires supporting changes from LLVM r212086.

llvm-svn: 212087

clang/examples/clang-interpreter/CMakeLists.txt

@@ -2,7 +2,9 @@ set(LLVM_LINK_COMPONENTS
   Core
   ExecutionEngine
   Interpreter
+  JIT
   Support
+  native
   )
 
 add_clang_executable(clang-interpreter

clang/examples/clang-interpreter/README.txt

@@ -10,8 +10,7 @@ It demonstrates the following features:
  3. Invoking the Clang compiler to lex, parse, syntax check, and then generate
     LLVM code.
 
- 4. Use the LLVM interpreter functionality to execute the final module, with
-    guidance on how to extend the demo with JIT execution.
+ 4. Use the LLVM JIT functionality to execute the final module.
 
 The implementation has many limitations and is not designed to be a full fledged
 C interpreter. It is designed to demonstrate a simple but functional use of the

clang/examples/clang-interpreter/main.cpp

@@ -18,6 +18,7 @@
 #include "clang/Frontend/TextDiagnosticPrinter.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ExecutionEngine/ExecutionEngine.h"
+#include "llvm/ExecutionEngine/JIT.h"
 #include "llvm/IR/Module.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Host.h"
@@ -42,12 +43,11 @@ std::string GetExecutablePath(const char *Argv0) {
 }
 
 static int Execute(llvm::Module *Mod, char * const *envp) {
-  // To JIT instead of interpreting, call llvm::InitializeNativeTarget() here
-  // and pass ForceInterpreter=false to ExecutionEngine::create().
+  llvm::InitializeNativeTarget();
 
   std::string Error;
   std::unique_ptr<llvm::ExecutionEngine> EE(
-      llvm::ExecutionEngine::create(Mod, /*ForceInterpreter*/ true, &Error));
+      llvm::ExecutionEngine::create(Mod, /*ForceInterpreter*/ false, &Error));
   if (!EE) {
     llvm::errs() << "unable to make execution engine: " << Error << "\n";
     return 255;