llvm-6502/include/llvm/ExecutionEngine/ExecutionEngine.h

//===- ExecutionEngine.h - Abstract Execution Engine Interface --*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the abstract interface that implements execution support
// for LLVM.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_EXECUTIONENGINE_EXECUTIONENGINE_H
#define LLVM_EXECUTIONENGINE_EXECUTIONENGINE_H

#include "llvm-c/ExecutionEngine.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/IR/ValueMap.h"
#include "llvm/MC/MCCodeGenInfo.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/Mutex.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
#include <map>
#include <string>
#include <vector>

namespace llvm {

struct GenericValue;
class Constant;
class DataLayout;
class ExecutionEngine;
class Function;
class GlobalVariable;
class GlobalValue;
class JITEventListener;
class JITMemoryManager;
class MachineCodeInfo;
class Module;
class MutexGuard;
class ObjectCache;
class RTDyldMemoryManager;
class Triple;
class Type;

namespace object {
  class Archive;
  class ObjectFile;
}

/// \brief Helper class for helping synchronize access to the global address map
/// table.  Access to this class should be serialized under a mutex.
class ExecutionEngineState {
public:
  struct AddressMapConfig : public ValueMapConfig<const GlobalValue*> {
    typedef ExecutionEngineState *ExtraData;
    static sys::Mutex *getMutex(ExecutionEngineState *EES);
    static void onDelete(ExecutionEngineState *EES, const GlobalValue *Old);
    static void onRAUW(ExecutionEngineState *, const GlobalValue *,
                       const GlobalValue *);
  };

  typedef ValueMap<const GlobalValue *, void *, AddressMapConfig>
      GlobalAddressMapTy;

private:
  ExecutionEngine &EE;

  /// GlobalAddressMap - A mapping between LLVM global values and their
  /// actualized version...
  GlobalAddressMapTy GlobalAddressMap;

  /// GlobalAddressReverseMap - This is the reverse mapping of GlobalAddressMap,
  /// used to convert raw addresses into the LLVM global value that is emitted
  /// at the address.  This map is not computed unless getGlobalValueAtAddress
  /// is called at some point.
  std::map<void *, AssertingVH<const GlobalValue> > GlobalAddressReverseMap;

public:
  ExecutionEngineState(ExecutionEngine &EE);

  GlobalAddressMapTy &getGlobalAddressMap() {
    return GlobalAddressMap;
  }

  std::map<void*, AssertingVH<const GlobalValue> > &
  getGlobalAddressReverseMap() {
    return GlobalAddressReverseMap;
  }

  /// \brief Erase an entry from the mapping table.
  ///
  /// \returns The address that \p ToUnmap was happed to.
  void *RemoveMapping(const GlobalValue *ToUnmap);
};

/// \brief Abstract interface for implementation execution of LLVM modules,
/// designed to support both interpreter and just-in-time (JIT) compiler
/// implementations.
class ExecutionEngine {
  /// The state object holding the global address mapping, which must be
  /// accessed synchronously.
  //
  // FIXME: There is no particular need the entire map needs to be
  // synchronized.  Wouldn't a reader-writer design be better here?
  ExecutionEngineState EEState;

  /// The target data for the platform for which execution is being performed.
  const DataLayout *DL;

  /// Whether lazy JIT compilation is enabled.
  bool CompilingLazily;

  /// Whether JIT compilation of external global variables is allowed.
  bool GVCompilationDisabled;

  /// Whether the JIT should perform lookups of external symbols (e.g.,
  /// using dlsym).
  bool SymbolSearchingDisabled;

  /// Whether the JIT should verify IR modules during compilation.
  bool VerifyModules;

  friend class EngineBuilder;  // To allow access to JITCtor and InterpCtor.

protected:
  /// The list of Modules that we are JIT'ing from.  We use a SmallVector to
  /// optimize for the case where there is only one module.
  SmallVector<Module*, 1> Modules;

  void setDataLayout(const DataLayout *Val) { DL = Val; }

  /// getMemoryforGV - Allocate memory for a global variable.
  virtual char *getMemoryForGV(const GlobalVariable *GV);

  // To avoid having libexecutionengine depend on the JIT and interpreter
  // libraries, the execution engine implementations set these functions to ctor
  // pointers at startup time if they are linked in.
  static ExecutionEngine *(*JITCtor)(
    Module *M,
    std::string *ErrorStr,
    JITMemoryManager *JMM,
    bool GVsWithCode,
    TargetMachine *TM);
  static ExecutionEngine *(*MCJITCtor)(
    Module *M,
    std::string *ErrorStr,
    RTDyldMemoryManager *MCJMM,
    TargetMachine *TM);
  static ExecutionEngine *(*InterpCtor)(Module *M, std::string *ErrorStr);

  /// LazyFunctionCreator - If an unknown function is needed, this function
  /// pointer is invoked to create it.  If this returns null, the JIT will
  /// abort.
  void *(*LazyFunctionCreator)(const std::string &);

public:
  /// lock - This lock protects the ExecutionEngine, MCJIT, JIT, JITResolver and
  /// JITEmitter classes.  It must be held while changing the internal state of
  /// any of those classes.
  sys::Mutex lock;

  //===--------------------------------------------------------------------===//
  //  ExecutionEngine Startup
  //===--------------------------------------------------------------------===//

  virtual ~ExecutionEngine();

  /// addModule - Add a Module to the list of modules that we can JIT from.
  /// Note that this takes ownership of the Module: when the ExecutionEngine is
  /// destroyed, it destroys the Module as well.
  virtual void addModule(Module *M) {
    Modules.push_back(M);
  }

  /// addObjectFile - Add an ObjectFile to the execution engine.
  ///
  /// This method is only supported by MCJIT.  MCJIT will immediately load the
  /// object into memory and adds its symbols to the list used to resolve
  /// external symbols while preparing other objects for execution.
  ///
  /// Objects added using this function will not be made executable until
  /// needed by another object.
  ///
  /// MCJIT will take ownership of the ObjectFile.
  virtual void addObjectFile(std::unique_ptr<object::ObjectFile> O);

  /// addArchive - Add an Archive to the execution engine.
  ///
  /// This method is only supported by MCJIT.  MCJIT will use the archive to
  /// resolve external symbols in objects it is loading.  If a symbol is found
  /// in the Archive the contained object file will be extracted (in memory)
  /// and loaded for possible execution.
  virtual void addArchive(std::unique_ptr<object::Archive> A);

  //===--------------------------------------------------------------------===//

  const DataLayout *getDataLayout() const { return DL; }

  /// removeModule - Remove a Module from the list of modules.  Returns true if
  /// M is found.
  virtual bool removeModule(Module *M);

  /// FindFunctionNamed - Search all of the active modules to find the one that
  /// defines FnName.  This is very slow operation and shouldn't be used for
  /// general code.
  virtual Function *FindFunctionNamed(const char *FnName);

  /// runFunction - Execute the specified function with the specified arguments,
  /// and return the result.
  virtual GenericValue runFunction(Function *F,
                                const std::vector<GenericValue> &ArgValues) = 0;

  /// getPointerToNamedFunction - This method returns the address of the
  /// specified function by using the dlsym function call.  As such it is only
  /// useful for resolving library symbols, not code generated symbols.
  ///
  /// If AbortOnFailure is false and no function with the given name is
  /// found, this function silently returns a null pointer. Otherwise,
  /// it prints a message to stderr and aborts.
  ///
  /// This function is deprecated for the MCJIT execution engine.
  ///
  /// FIXME: the JIT and MCJIT interfaces should be disentangled or united
  /// again, if possible.
  ///
  virtual void *getPointerToNamedFunction(const std::string &Name,
                                          bool AbortOnFailure = true) = 0;

  /// mapSectionAddress - map a section to its target address space value.
  /// Map the address of a JIT section as returned from the memory manager
  /// to the address in the target process as the running code will see it.
  /// This is the address which will be used for relocation resolution.
  virtual void mapSectionAddress(const void *LocalAddress, uint64_t TargetAddress) {
    llvm_unreachable("Re-mapping of section addresses not supported with this "
                     "EE!");
  }

  /// generateCodeForModule - Run code generationen for the specified module and
  /// load it into memory.
  ///
  /// When this function has completed, all code and data for the specified
  /// module, and any module on which this module depends, will be generated
  /// and loaded into memory, but relocations will not yet have been applied
  /// and all memory will be readable and writable but not executable.
  ///
  /// This function is primarily useful when generating code for an external
  /// target, allowing the client an opportunity to remap section addresses
  /// before relocations are applied.  Clients that intend to execute code
  /// locally can use the getFunctionAddress call, which will generate code
  /// and apply final preparations all in one step.
  ///
  /// This method has no effect for the legacy JIT engine or the interpeter.
  virtual void generateCodeForModule(Module *M) {}

  /// finalizeObject - ensure the module is fully processed and is usable.
  ///
  /// It is the user-level function for completing the process of making the
  /// object usable for execution.  It should be called after sections within an
  /// object have been relocated using mapSectionAddress.  When this method is
  /// called the MCJIT execution engine will reapply relocations for a loaded
  /// object.  This method has no effect for the legacy JIT engine or the
  /// interpeter.
  virtual void finalizeObject() {}

  /// runStaticConstructorsDestructors - This method is used to execute all of
  /// the static constructors or destructors for a program.
  ///
  /// \param isDtors - Run the destructors instead of constructors.
  virtual void runStaticConstructorsDestructors(bool isDtors);

  /// runStaticConstructorsDestructors - This method is used to execute all of
  /// the static constructors or destructors for a particular module.
  ///
  /// \param isDtors - Run the destructors instead of constructors.
  void runStaticConstructorsDestructors(Module *module, bool isDtors);


  /// runFunctionAsMain - This is a helper function which wraps runFunction to
  /// handle the common task of starting up main with the specified argc, argv,
  /// and envp parameters.
  int runFunctionAsMain(Function *Fn, const std::vector<std::string> &argv,
                        const char * const * envp);


  /// addGlobalMapping - Tell the execution engine that the specified global is
  /// at the specified location.  This is used internally as functions are JIT'd
  /// and as global variables are laid out in memory.  It can and should also be
  /// used by clients of the EE that want to have an LLVM global overlay
  /// existing data in memory.  Mappings are automatically removed when their
  /// GlobalValue is destroyed.
  void addGlobalMapping(const GlobalValue *GV, void *Addr);

  /// clearAllGlobalMappings - Clear all global mappings and start over again,
  /// for use in dynamic compilation scenarios to move globals.
  void clearAllGlobalMappings();

  /// clearGlobalMappingsFromModule - Clear all global mappings that came from a
  /// particular module, because it has been removed from the JIT.
  void clearGlobalMappingsFromModule(Module *M);

  /// updateGlobalMapping - Replace an existing mapping for GV with a new
  /// address.  This updates both maps as required.  If "Addr" is null, the
  /// entry for the global is removed from the mappings.  This returns the old
  /// value of the pointer, or null if it was not in the map.
  void *updateGlobalMapping(const GlobalValue *GV, void *Addr);

  /// getPointerToGlobalIfAvailable - This returns the address of the specified
  /// global value if it is has already been codegen'd, otherwise it returns
  /// null.
  ///
  /// This function is deprecated for the MCJIT execution engine.  It doesn't
  /// seem to be needed in that case, but an equivalent can be added if it is.
  void *getPointerToGlobalIfAvailable(const GlobalValue *GV);

  /// getPointerToGlobal - This returns the address of the specified global
  /// value. This may involve code generation if it's a function.
  ///
  /// This function is deprecated for the MCJIT execution engine.  Use
  /// getGlobalValueAddress instead.
  void *getPointerToGlobal(const GlobalValue *GV);

  /// getPointerToFunction - The different EE's represent function bodies in
  /// different ways.  They should each implement this to say what a function
  /// pointer should look like.  When F is destroyed, the ExecutionEngine will
  /// remove its global mapping and free any machine code.  Be sure no threads
  /// are running inside F when that happens.
  ///
  /// This function is deprecated for the MCJIT execution engine.  Use
  /// getFunctionAddress instead.
  virtual void *getPointerToFunction(Function *F) = 0;

  /// getPointerToBasicBlock - The different EE's represent basic blocks in
  /// different ways.  Return the representation for a blockaddress of the
  /// specified block.
  ///
  /// This function will not be implemented for the MCJIT execution engine.
  virtual void *getPointerToBasicBlock(BasicBlock *BB) = 0;

  /// getPointerToFunctionOrStub - If the specified function has been
  /// code-gen'd, return a pointer to the function.  If not, compile it, or use
  /// a stub to implement lazy compilation if available.  See
  /// getPointerToFunction for the requirements on destroying F.
  ///
  /// This function is deprecated for the MCJIT execution engine.  Use
  /// getFunctionAddress instead.
  virtual void *getPointerToFunctionOrStub(Function *F) {
    // Default implementation, just codegen the function.
    return getPointerToFunction(F);
  }

  /// getGlobalValueAddress - Return the address of the specified global
  /// value. This may involve code generation.
  ///
  /// This function should not be called with the JIT or interpreter engines.
  virtual uint64_t getGlobalValueAddress(const std::string &Name) {
    // Default implementation for JIT and interpreter.  MCJIT will override this.
    // JIT and interpreter clients should use getPointerToGlobal instead.
    return 0;
  }

  /// getFunctionAddress - Return the address of the specified function.
  /// This may involve code generation.
  virtual uint64_t getFunctionAddress(const std::string &Name) {
    // Default implementation for JIT and interpreter.  MCJIT will override this.
    // JIT and interpreter clients should use getPointerToFunction instead.
    return 0;
  }

  // The JIT overrides a version that actually does this.
  virtual void runJITOnFunction(Function *, MachineCodeInfo * = nullptr) { }

  /// getGlobalValueAtAddress - Return the LLVM global value object that starts
  /// at the specified address.
  ///
  const GlobalValue *getGlobalValueAtAddress(void *Addr);

  /// StoreValueToMemory - Stores the data in Val of type Ty at address Ptr.
  /// Ptr is the address of the memory at which to store Val, cast to
  /// GenericValue *.  It is not a pointer to a GenericValue containing the
  /// address at which to store Val.
  void StoreValueToMemory(const GenericValue &Val, GenericValue *Ptr,
                          Type *Ty);

  void InitializeMemory(const Constant *Init, void *Addr);

  /// recompileAndRelinkFunction - This method is used to force a function which
  /// has already been compiled to be compiled again, possibly after it has been
  /// modified.  Then the entry to the old copy is overwritten with a branch to
  /// the new copy.  If there was no old copy, this acts just like
  /// VM::getPointerToFunction().
  virtual void *recompileAndRelinkFunction(Function *F) = 0;

  /// freeMachineCodeForFunction - Release memory in the ExecutionEngine
  /// corresponding to the machine code emitted to execute this function, useful
  /// for garbage-collecting generated code.
  virtual void freeMachineCodeForFunction(Function *F) = 0;

  /// getOrEmitGlobalVariable - Return the address of the specified global
  /// variable, possibly emitting it to memory if needed.  This is used by the
  /// Emitter.
  ///
  /// This function is deprecated for the MCJIT execution engine.  Use
  /// getGlobalValueAddress instead.
  virtual void *getOrEmitGlobalVariable(const GlobalVariable *GV) {
    return getPointerToGlobal((const GlobalValue *)GV);
  }

  /// Registers a listener to be called back on various events within
  /// the JIT.  See JITEventListener.h for more details.  Does not
  /// take ownership of the argument.  The argument may be NULL, in
  /// which case these functions do nothing.
  virtual void RegisterJITEventListener(JITEventListener *) {}
  virtual void UnregisterJITEventListener(JITEventListener *) {}

  /// Sets the pre-compiled object cache.  The ownership of the ObjectCache is
  /// not changed.  Supported by MCJIT but not JIT.
  virtual void setObjectCache(ObjectCache *) {
    llvm_unreachable("No support for an object cache");
  }

  /// setProcessAllSections (MCJIT Only): By default, only sections that are
  /// "required for execution" are passed to the RTDyldMemoryManager, and other
  /// sections are discarded. Passing 'true' to this method will cause
  /// RuntimeDyld to pass all sections to its RTDyldMemoryManager regardless
  /// of whether they are "required to execute" in the usual sense.
  ///
  /// Rationale: Some MCJIT clients want to be able to inspect metadata
  /// sections (e.g. Dwarf, Stack-maps) to enable functionality or analyze
  /// performance. Passing these sections to the memory manager allows the
  /// client to make policy about the relevant sections, rather than having
  /// MCJIT do it.
  virtual void setProcessAllSections(bool ProcessAllSections) {
    llvm_unreachable("No support for ProcessAllSections option");
  }

  /// Return the target machine (if available).
  virtual TargetMachine *getTargetMachine() { return nullptr; }

  /// DisableLazyCompilation - When lazy compilation is off (the default), the
  /// JIT will eagerly compile every function reachable from the argument to
  /// getPointerToFunction.  If lazy compilation is turned on, the JIT will only
  /// compile the one function and emit stubs to compile the rest when they're
  /// first called.  If lazy compilation is turned off again while some lazy
  /// stubs are still around, and one of those stubs is called, the program will
  /// abort.
  ///
  /// In order to safely compile lazily in a threaded program, the user must
  /// ensure that 1) only one thread at a time can call any particular lazy
  /// stub, and 2) any thread modifying LLVM IR must hold the JIT's lock
  /// (ExecutionEngine::lock) or otherwise ensure that no other thread calls a
  /// lazy stub.  See http://llvm.org/PR5184 for details.
  void DisableLazyCompilation(bool Disabled = true) {
    CompilingLazily = !Disabled;
  }
  bool isCompilingLazily() const {
    return CompilingLazily;
  }
  // Deprecated in favor of isCompilingLazily (to reduce double-negatives).
  // Remove this in LLVM 2.8.
  bool isLazyCompilationDisabled() const {
    return !CompilingLazily;
  }

  /// DisableGVCompilation - If called, the JIT will abort if it's asked to
  /// allocate space and populate a GlobalVariable that is not internal to
  /// the module.
  void DisableGVCompilation(bool Disabled = true) {
    GVCompilationDisabled = Disabled;
  }
  bool isGVCompilationDisabled() const {
    return GVCompilationDisabled;
  }

  /// DisableSymbolSearching - If called, the JIT will not try to lookup unknown
  /// symbols with dlsym.  A client can still use InstallLazyFunctionCreator to
  /// resolve symbols in a custom way.
  void DisableSymbolSearching(bool Disabled = true) {
    SymbolSearchingDisabled = Disabled;
  }
  bool isSymbolSearchingDisabled() const {
    return SymbolSearchingDisabled;
  }

  /// Enable/Disable IR module verification.
  ///
  /// Note: Module verification is enabled by default in Debug builds, and
  /// disabled by default in Release. Use this method to override the default.
  void setVerifyModules(bool Verify) {
    VerifyModules = Verify;
  }
  bool getVerifyModules() const {
    return VerifyModules;
  }

  /// InstallLazyFunctionCreator - If an unknown function is needed, the
  /// specified function pointer is invoked to create it.  If it returns null,
  /// the JIT will abort.
  void InstallLazyFunctionCreator(void* (*P)(const std::string &)) {
    LazyFunctionCreator = P;
  }

protected:
  explicit ExecutionEngine(Module *M);

  void emitGlobals();

  void EmitGlobalVariable(const GlobalVariable *GV);

  GenericValue getConstantValue(const Constant *C);
  void LoadValueFromMemory(GenericValue &Result, GenericValue *Ptr,
                           Type *Ty);
};

namespace EngineKind {
  // These are actually bitmasks that get or-ed together.
  enum Kind {
    JIT         = 0x1,
    Interpreter = 0x2
  };
  const static Kind Either = (Kind)(JIT | Interpreter);
}

/// EngineBuilder - Builder class for ExecutionEngines.  Use this by
/// stack-allocating a builder, chaining the various set* methods, and
/// terminating it with a .create() call.
class EngineBuilder {
private:
  Module *M;
  EngineKind::Kind WhichEngine;
  std::string *ErrorStr;
  CodeGenOpt::Level OptLevel;
  RTDyldMemoryManager *MCJMM;
  JITMemoryManager *JMM;
  bool AllocateGVsWithCode;
  TargetOptions Options;
  Reloc::Model RelocModel;
  CodeModel::Model CMModel;
  std::string MArch;
  std::string MCPU;
  SmallVector<std::string, 4> MAttrs;
  bool UseMCJIT;
  bool VerifyModules;

  /// InitEngine - Does the common initialization of default options.
  void InitEngine();

public:
  /// EngineBuilder - Constructor for EngineBuilder.  If create() is called and
  /// is successful, the created engine takes ownership of the module.
  EngineBuilder(Module *m) : M(m) {
    InitEngine();
  }

  /// setEngineKind - Controls whether the user wants the interpreter, the JIT,
  /// or whichever engine works.  This option defaults to EngineKind::Either.
  EngineBuilder &setEngineKind(EngineKind::Kind w) {
    WhichEngine = w;
    return *this;
  }

  /// setMCJITMemoryManager - Sets the MCJIT memory manager to use. This allows
  /// clients to customize their memory allocation policies for the MCJIT. This
  /// is only appropriate for the MCJIT; setting this and configuring the builder
  /// to create anything other than MCJIT will cause a runtime error. If create()
  /// is called and is successful, the created engine takes ownership of the
  /// memory manager. This option defaults to NULL. Using this option nullifies
  /// the setJITMemoryManager() option.
  EngineBuilder &setMCJITMemoryManager(RTDyldMemoryManager *mcjmm) {
    MCJMM = mcjmm;
    JMM = nullptr;
    return *this;
  }

  /// setJITMemoryManager - Sets the JIT memory manager to use.  This allows
  /// clients to customize their memory allocation policies.  This is only
  /// appropriate for either JIT or MCJIT; setting this and configuring the
  /// builder to create an interpreter will cause a runtime error. If create()
  /// is called and is successful, the created engine takes ownership of the
  /// memory manager.  This option defaults to NULL. This option overrides
  /// setMCJITMemoryManager() as well.
  EngineBuilder &setJITMemoryManager(JITMemoryManager *jmm) {
    MCJMM = nullptr;
    JMM = jmm;
    return *this;
  }

  /// setErrorStr - Set the error string to write to on error.  This option
  /// defaults to NULL.
  EngineBuilder &setErrorStr(std::string *e) {
    ErrorStr = e;
    return *this;
  }

  /// setOptLevel - Set the optimization level for the JIT.  This option
  /// defaults to CodeGenOpt::Default.
  EngineBuilder &setOptLevel(CodeGenOpt::Level l) {
    OptLevel = l;
    return *this;
  }

  /// setTargetOptions - Set the target options that the ExecutionEngine
  /// target is using. Defaults to TargetOptions().
  EngineBuilder &setTargetOptions(const TargetOptions &Opts) {
    Options = Opts;
    return *this;
  }

  /// setRelocationModel - Set the relocation model that the ExecutionEngine
  /// target is using. Defaults to target specific default "Reloc::Default".
  EngineBuilder &setRelocationModel(Reloc::Model RM) {
    RelocModel = RM;
    return *this;
  }

  /// setCodeModel - Set the CodeModel that the ExecutionEngine target
  /// data is using. Defaults to target specific default
  /// "CodeModel::JITDefault".
  EngineBuilder &setCodeModel(CodeModel::Model M) {
    CMModel = M;
    return *this;
  }

  /// setAllocateGVsWithCode - Sets whether global values should be allocated
  /// into the same buffer as code.  For most applications this should be set
  /// to false.  Allocating globals with code breaks freeMachineCodeForFunction
  /// and is probably unsafe and bad for performance.  However, we have clients
  /// who depend on this behavior, so we must support it.  This option defaults
  /// to false so that users of the new API can safely use the new memory
  /// manager and free machine code.
  EngineBuilder &setAllocateGVsWithCode(bool a) {
    AllocateGVsWithCode = a;
    return *this;
  }

  /// setMArch - Override the architecture set by the Module's triple.
  EngineBuilder &setMArch(StringRef march) {
    MArch.assign(march.begin(), march.end());
    return *this;
  }

  /// setMCPU - Target a specific cpu type.
  EngineBuilder &setMCPU(StringRef mcpu) {
    MCPU.assign(mcpu.begin(), mcpu.end());
    return *this;
  }

  /// setUseMCJIT - Set whether the MC-JIT implementation should be used
  /// (experimental).
  EngineBuilder &setUseMCJIT(bool Value) {
    UseMCJIT = Value;
    return *this;
  }

  /// setVerifyModules - Set whether the JIT implementation should verify
  /// IR modules during compilation.
  EngineBuilder &setVerifyModules(bool Verify) {
    VerifyModules = Verify;
    return *this;
  }

  /// setMAttrs - Set cpu-specific attributes.
  template<typename StringSequence>
  EngineBuilder &setMAttrs(const StringSequence &mattrs) {
    MAttrs.clear();
    MAttrs.append(mattrs.begin(), mattrs.end());
    return *this;
  }

  TargetMachine *selectTarget();

  /// selectTarget - Pick a target either via -march or by guessing the native
  /// arch.  Add any CPU features specified via -mcpu or -mattr.
  TargetMachine *selectTarget(const Triple &TargetTriple,
                              StringRef MArch,
                              StringRef MCPU,
                              const SmallVectorImpl<std::string>& MAttrs);

  ExecutionEngine *create() {
    return create(selectTarget());
  }

  ExecutionEngine *create(TargetMachine *TM);
};

// Create wrappers for C Binding types (see CBindingWrapping.h).
DEFINE_SIMPLE_CONVERSION_FUNCTIONS(ExecutionEngine, LLVMExecutionEngineRef)

} // End llvm namespace

#endif