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      1 //===- ExecutionEngine.h - Abstract Execution Engine Interface --*- C++ -*-===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file defines the abstract interface that implements execution support
     11 // for LLVM.
     12 //
     13 //===----------------------------------------------------------------------===//
     14 
     15 #ifndef LLVM_EXECUTION_ENGINE_H
     16 #define LLVM_EXECUTION_ENGINE_H
     17 
     18 #include "llvm/MC/MCCodeGenInfo.h"
     19 #include "llvm/ADT/SmallVector.h"
     20 #include "llvm/ADT/StringRef.h"
     21 #include "llvm/ADT/ValueMap.h"
     22 #include "llvm/ADT/DenseMap.h"
     23 #include "llvm/Support/ErrorHandling.h"
     24 #include "llvm/Support/ValueHandle.h"
     25 #include "llvm/Support/Mutex.h"
     26 #include "llvm/Target/TargetMachine.h"
     27 #include "llvm/Target/TargetOptions.h"
     28 #include <vector>
     29 #include <map>
     30 #include <string>
     31 
     32 namespace llvm {
     33 
     34 struct GenericValue;
     35 class Constant;
     36 class ExecutionEngine;
     37 class Function;
     38 class GlobalVariable;
     39 class GlobalValue;
     40 class JITEventListener;
     41 class JITMemoryManager;
     42 class MachineCodeInfo;
     43 class Module;
     44 class MutexGuard;
     45 class TargetData;
     46 class Triple;
     47 class Type;
     48 
     49 /// \brief Helper class for helping synchronize access to the global address map
     50 /// table.
     51 class ExecutionEngineState {
     52 public:
     53   struct AddressMapConfig : public ValueMapConfig<const GlobalValue*> {
     54     typedef ExecutionEngineState *ExtraData;
     55     static sys::Mutex *getMutex(ExecutionEngineState *EES);
     56     static void onDelete(ExecutionEngineState *EES, const GlobalValue *Old);
     57     static void onRAUW(ExecutionEngineState *, const GlobalValue *,
     58                        const GlobalValue *);
     59   };
     60 
     61   typedef ValueMap<const GlobalValue *, void *, AddressMapConfig>
     62       GlobalAddressMapTy;
     63 
     64 private:
     65   ExecutionEngine &EE;
     66 
     67   /// GlobalAddressMap - A mapping between LLVM global values and their
     68   /// actualized version...
     69   GlobalAddressMapTy GlobalAddressMap;
     70 
     71   /// GlobalAddressReverseMap - This is the reverse mapping of GlobalAddressMap,
     72   /// used to convert raw addresses into the LLVM global value that is emitted
     73   /// at the address.  This map is not computed unless getGlobalValueAtAddress
     74   /// is called at some point.
     75   std::map<void *, AssertingVH<const GlobalValue> > GlobalAddressReverseMap;
     76 
     77 public:
     78   ExecutionEngineState(ExecutionEngine &EE);
     79 
     80   GlobalAddressMapTy &getGlobalAddressMap(const MutexGuard &) {
     81     return GlobalAddressMap;
     82   }
     83 
     84   std::map<void*, AssertingVH<const GlobalValue> > &
     85   getGlobalAddressReverseMap(const MutexGuard &) {
     86     return GlobalAddressReverseMap;
     87   }
     88 
     89   /// \brief Erase an entry from the mapping table.
     90   ///
     91   /// \returns The address that \arg ToUnmap was happed to.
     92   void *RemoveMapping(const MutexGuard &, const GlobalValue *ToUnmap);
     93 };
     94 
     95 /// \brief Abstract interface for implementation execution of LLVM modules,
     96 /// designed to support both interpreter and just-in-time (JIT) compiler
     97 /// implementations.
     98 class ExecutionEngine {
     99   /// The state object holding the global address mapping, which must be
    100   /// accessed synchronously.
    101   //
    102   // FIXME: There is no particular need the entire map needs to be
    103   // synchronized.  Wouldn't a reader-writer design be better here?
    104   ExecutionEngineState EEState;
    105 
    106   /// The target data for the platform for which execution is being performed.
    107   const TargetData *TD;
    108 
    109   /// Whether lazy JIT compilation is enabled.
    110   bool CompilingLazily;
    111 
    112   /// Whether JIT compilation of external global variables is allowed.
    113   bool GVCompilationDisabled;
    114 
    115   /// Whether the JIT should perform lookups of external symbols (e.g.,
    116   /// using dlsym).
    117   bool SymbolSearchingDisabled;
    118 
    119   friend class EngineBuilder;  // To allow access to JITCtor and InterpCtor.
    120 
    121 protected:
    122   /// The list of Modules that we are JIT'ing from.  We use a SmallVector to
    123   /// optimize for the case where there is only one module.
    124   SmallVector<Module*, 1> Modules;
    125 
    126   void setTargetData(const TargetData *td) { TD = td; }
    127 
    128   /// getMemoryforGV - Allocate memory for a global variable.
    129   virtual char *getMemoryForGV(const GlobalVariable *GV);
    130 
    131   // To avoid having libexecutionengine depend on the JIT and interpreter
    132   // libraries, the execution engine implementations set these functions to ctor
    133   // pointers at startup time if they are linked in.
    134   static ExecutionEngine *(*JITCtor)(
    135     Module *M,
    136     std::string *ErrorStr,
    137     JITMemoryManager *JMM,
    138     bool GVsWithCode,
    139     TargetMachine *TM);
    140   static ExecutionEngine *(*MCJITCtor)(
    141     Module *M,
    142     std::string *ErrorStr,
    143     JITMemoryManager *JMM,
    144     bool GVsWithCode,
    145     TargetMachine *TM);
    146   static ExecutionEngine *(*InterpCtor)(Module *M, std::string *ErrorStr);
    147 
    148   /// LazyFunctionCreator - If an unknown function is needed, this function
    149   /// pointer is invoked to create it.  If this returns null, the JIT will
    150   /// abort.
    151   void *(*LazyFunctionCreator)(const std::string &);
    152 
    153   /// ExceptionTableRegister - If Exception Handling is set, the JIT will
    154   /// register dwarf tables with this function.
    155   typedef void (*EERegisterFn)(void*);
    156   EERegisterFn ExceptionTableRegister;
    157   EERegisterFn ExceptionTableDeregister;
    158   /// This maps functions to their exception tables frames.
    159   DenseMap<const Function*, void*> AllExceptionTables;
    160 
    161 
    162 public:
    163   /// lock - This lock protects the ExecutionEngine, JIT, JITResolver and
    164   /// JITEmitter classes.  It must be held while changing the internal state of
    165   /// any of those classes.
    166   sys::Mutex lock;
    167 
    168   //===--------------------------------------------------------------------===//
    169   //  ExecutionEngine Startup
    170   //===--------------------------------------------------------------------===//
    171 
    172   virtual ~ExecutionEngine();
    173 
    174   /// create - This is the factory method for creating an execution engine which
    175   /// is appropriate for the current machine.  This takes ownership of the
    176   /// module.
    177   ///
    178   /// \param GVsWithCode - Allocating globals with code breaks
    179   /// freeMachineCodeForFunction and is probably unsafe and bad for performance.
    180   /// However, we have clients who depend on this behavior, so we must support
    181   /// it.  Eventually, when we're willing to break some backwards compatibility,
    182   /// this flag should be flipped to false, so that by default
    183   /// freeMachineCodeForFunction works.
    184   static ExecutionEngine *create(Module *M,
    185                                  bool ForceInterpreter = false,
    186                                  std::string *ErrorStr = 0,
    187                                  CodeGenOpt::Level OptLevel =
    188                                  CodeGenOpt::Default,
    189                                  bool GVsWithCode = true);
    190 
    191   /// createJIT - This is the factory method for creating a JIT for the current
    192   /// machine, it does not fall back to the interpreter.  This takes ownership
    193   /// of the Module and JITMemoryManager if successful.
    194   ///
    195   /// Clients should make sure to initialize targets prior to calling this
    196   /// function.
    197   static ExecutionEngine *createJIT(Module *M,
    198                                     std::string *ErrorStr = 0,
    199                                     JITMemoryManager *JMM = 0,
    200                                     CodeGenOpt::Level OptLevel =
    201                                     CodeGenOpt::Default,
    202                                     bool GVsWithCode = true,
    203                                     Reloc::Model RM = Reloc::Default,
    204                                     CodeModel::Model CMM =
    205                                     CodeModel::JITDefault);
    206 
    207   /// addModule - Add a Module to the list of modules that we can JIT from.
    208   /// Note that this takes ownership of the Module: when the ExecutionEngine is
    209   /// destroyed, it destroys the Module as well.
    210   virtual void addModule(Module *M) {
    211     Modules.push_back(M);
    212   }
    213 
    214   //===--------------------------------------------------------------------===//
    215 
    216   const TargetData *getTargetData() const { return TD; }
    217 
    218   /// removeModule - Remove a Module from the list of modules.  Returns true if
    219   /// M is found.
    220   virtual bool removeModule(Module *M);
    221 
    222   /// FindFunctionNamed - Search all of the active modules to find the one that
    223   /// defines FnName.  This is very slow operation and shouldn't be used for
    224   /// general code.
    225   Function *FindFunctionNamed(const char *FnName);
    226 
    227   /// runFunction - Execute the specified function with the specified arguments,
    228   /// and return the result.
    229   virtual GenericValue runFunction(Function *F,
    230                                 const std::vector<GenericValue> &ArgValues) = 0;
    231 
    232   /// getPointerToNamedFunction - This method returns the address of the
    233   /// specified function by using the dlsym function call.  As such it is only
    234   /// useful for resolving library symbols, not code generated symbols.
    235   ///
    236   /// If AbortOnFailure is false and no function with the given name is
    237   /// found, this function silently returns a null pointer. Otherwise,
    238   /// it prints a message to stderr and aborts.
    239   ///
    240   virtual void *getPointerToNamedFunction(const std::string &Name,
    241                                           bool AbortOnFailure = true) = 0;
    242 
    243   /// mapSectionAddress - map a section to its target address space value.
    244   /// Map the address of a JIT section as returned from the memory manager
    245   /// to the address in the target process as the running code will see it.
    246   /// This is the address which will be used for relocation resolution.
    247   virtual void mapSectionAddress(void *LocalAddress, uint64_t TargetAddress) {
    248     llvm_unreachable("Re-mapping of section addresses not supported with this "
    249                      "EE!");
    250   }
    251 
    252   /// runStaticConstructorsDestructors - This method is used to execute all of
    253   /// the static constructors or destructors for a program.
    254   ///
    255   /// \param isDtors - Run the destructors instead of constructors.
    256   void runStaticConstructorsDestructors(bool isDtors);
    257 
    258   /// runStaticConstructorsDestructors - This method is used to execute all of
    259   /// the static constructors or destructors for a particular module.
    260   ///
    261   /// \param isDtors - Run the destructors instead of constructors.
    262   void runStaticConstructorsDestructors(Module *module, bool isDtors);
    263 
    264 
    265   /// runFunctionAsMain - This is a helper function which wraps runFunction to
    266   /// handle the common task of starting up main with the specified argc, argv,
    267   /// and envp parameters.
    268   int runFunctionAsMain(Function *Fn, const std::vector<std::string> &argv,
    269                         const char * const * envp);
    270 
    271 
    272   /// addGlobalMapping - Tell the execution engine that the specified global is
    273   /// at the specified location.  This is used internally as functions are JIT'd
    274   /// and as global variables are laid out in memory.  It can and should also be
    275   /// used by clients of the EE that want to have an LLVM global overlay
    276   /// existing data in memory.  Mappings are automatically removed when their
    277   /// GlobalValue is destroyed.
    278   void addGlobalMapping(const GlobalValue *GV, void *Addr);
    279 
    280   /// clearAllGlobalMappings - Clear all global mappings and start over again,
    281   /// for use in dynamic compilation scenarios to move globals.
    282   void clearAllGlobalMappings();
    283 
    284   /// clearGlobalMappingsFromModule - Clear all global mappings that came from a
    285   /// particular module, because it has been removed from the JIT.
    286   void clearGlobalMappingsFromModule(Module *M);
    287 
    288   /// updateGlobalMapping - Replace an existing mapping for GV with a new
    289   /// address.  This updates both maps as required.  If "Addr" is null, the
    290   /// entry for the global is removed from the mappings.  This returns the old
    291   /// value of the pointer, or null if it was not in the map.
    292   void *updateGlobalMapping(const GlobalValue *GV, void *Addr);
    293 
    294   /// getPointerToGlobalIfAvailable - This returns the address of the specified
    295   /// global value if it is has already been codegen'd, otherwise it returns
    296   /// null.
    297   void *getPointerToGlobalIfAvailable(const GlobalValue *GV);
    298 
    299   /// getPointerToGlobal - This returns the address of the specified global
    300   /// value. This may involve code generation if it's a function.
    301   void *getPointerToGlobal(const GlobalValue *GV);
    302 
    303   /// getPointerToFunction - The different EE's represent function bodies in
    304   /// different ways.  They should each implement this to say what a function
    305   /// pointer should look like.  When F is destroyed, the ExecutionEngine will
    306   /// remove its global mapping and free any machine code.  Be sure no threads
    307   /// are running inside F when that happens.
    308   virtual void *getPointerToFunction(Function *F) = 0;
    309 
    310   /// getPointerToBasicBlock - The different EE's represent basic blocks in
    311   /// different ways.  Return the representation for a blockaddress of the
    312   /// specified block.
    313   virtual void *getPointerToBasicBlock(BasicBlock *BB) = 0;
    314 
    315   /// getPointerToFunctionOrStub - If the specified function has been
    316   /// code-gen'd, return a pointer to the function.  If not, compile it, or use
    317   /// a stub to implement lazy compilation if available.  See
    318   /// getPointerToFunction for the requirements on destroying F.
    319   virtual void *getPointerToFunctionOrStub(Function *F) {
    320     // Default implementation, just codegen the function.
    321     return getPointerToFunction(F);
    322   }
    323 
    324   // The JIT overrides a version that actually does this.
    325   virtual void runJITOnFunction(Function *, MachineCodeInfo * = 0) { }
    326 
    327   /// getGlobalValueAtAddress - Return the LLVM global value object that starts
    328   /// at the specified address.
    329   ///
    330   const GlobalValue *getGlobalValueAtAddress(void *Addr);
    331 
    332   /// StoreValueToMemory - Stores the data in Val of type Ty at address Ptr.
    333   /// Ptr is the address of the memory at which to store Val, cast to
    334   /// GenericValue *.  It is not a pointer to a GenericValue containing the
    335   /// address at which to store Val.
    336   void StoreValueToMemory(const GenericValue &Val, GenericValue *Ptr,
    337                           Type *Ty);
    338 
    339   void InitializeMemory(const Constant *Init, void *Addr);
    340 
    341   /// recompileAndRelinkFunction - This method is used to force a function which
    342   /// has already been compiled to be compiled again, possibly after it has been
    343   /// modified.  Then the entry to the old copy is overwritten with a branch to
    344   /// the new copy.  If there was no old copy, this acts just like
    345   /// VM::getPointerToFunction().
    346   virtual void *recompileAndRelinkFunction(Function *F) = 0;
    347 
    348   /// freeMachineCodeForFunction - Release memory in the ExecutionEngine
    349   /// corresponding to the machine code emitted to execute this function, useful
    350   /// for garbage-collecting generated code.
    351   virtual void freeMachineCodeForFunction(Function *F) = 0;
    352 
    353   /// getOrEmitGlobalVariable - Return the address of the specified global
    354   /// variable, possibly emitting it to memory if needed.  This is used by the
    355   /// Emitter.
    356   virtual void *getOrEmitGlobalVariable(const GlobalVariable *GV) {
    357     return getPointerToGlobal((GlobalValue*)GV);
    358   }
    359 
    360   /// Registers a listener to be called back on various events within
    361   /// the JIT.  See JITEventListener.h for more details.  Does not
    362   /// take ownership of the argument.  The argument may be NULL, in
    363   /// which case these functions do nothing.
    364   virtual void RegisterJITEventListener(JITEventListener *) {}
    365   virtual void UnregisterJITEventListener(JITEventListener *) {}
    366 
    367   /// DisableLazyCompilation - When lazy compilation is off (the default), the
    368   /// JIT will eagerly compile every function reachable from the argument to
    369   /// getPointerToFunction.  If lazy compilation is turned on, the JIT will only
    370   /// compile the one function and emit stubs to compile the rest when they're
    371   /// first called.  If lazy compilation is turned off again while some lazy
    372   /// stubs are still around, and one of those stubs is called, the program will
    373   /// abort.
    374   ///
    375   /// In order to safely compile lazily in a threaded program, the user must
    376   /// ensure that 1) only one thread at a time can call any particular lazy
    377   /// stub, and 2) any thread modifying LLVM IR must hold the JIT's lock
    378   /// (ExecutionEngine::lock) or otherwise ensure that no other thread calls a
    379   /// lazy stub.  See http://llvm.org/PR5184 for details.
    380   void DisableLazyCompilation(bool Disabled = true) {
    381     CompilingLazily = !Disabled;
    382   }
    383   bool isCompilingLazily() const {
    384     return CompilingLazily;
    385   }
    386   // Deprecated in favor of isCompilingLazily (to reduce double-negatives).
    387   // Remove this in LLVM 2.8.
    388   bool isLazyCompilationDisabled() const {
    389     return !CompilingLazily;
    390   }
    391 
    392   /// DisableGVCompilation - If called, the JIT will abort if it's asked to
    393   /// allocate space and populate a GlobalVariable that is not internal to
    394   /// the module.
    395   void DisableGVCompilation(bool Disabled = true) {
    396     GVCompilationDisabled = Disabled;
    397   }
    398   bool isGVCompilationDisabled() const {
    399     return GVCompilationDisabled;
    400   }
    401 
    402   /// DisableSymbolSearching - If called, the JIT will not try to lookup unknown
    403   /// symbols with dlsym.  A client can still use InstallLazyFunctionCreator to
    404   /// resolve symbols in a custom way.
    405   void DisableSymbolSearching(bool Disabled = true) {
    406     SymbolSearchingDisabled = Disabled;
    407   }
    408   bool isSymbolSearchingDisabled() const {
    409     return SymbolSearchingDisabled;
    410   }
    411 
    412   /// InstallLazyFunctionCreator - If an unknown function is needed, the
    413   /// specified function pointer is invoked to create it.  If it returns null,
    414   /// the JIT will abort.
    415   void InstallLazyFunctionCreator(void* (*P)(const std::string &)) {
    416     LazyFunctionCreator = P;
    417   }
    418 
    419   /// InstallExceptionTableRegister - The JIT will use the given function
    420   /// to register the exception tables it generates.
    421   void InstallExceptionTableRegister(EERegisterFn F) {
    422     ExceptionTableRegister = F;
    423   }
    424   void InstallExceptionTableDeregister(EERegisterFn F) {
    425     ExceptionTableDeregister = F;
    426   }
    427 
    428   /// RegisterTable - Registers the given pointer as an exception table.  It
    429   /// uses the ExceptionTableRegister function.
    430   void RegisterTable(const Function *fn, void* res) {
    431     if (ExceptionTableRegister) {
    432       ExceptionTableRegister(res);
    433       AllExceptionTables[fn] = res;
    434     }
    435   }
    436 
    437   /// DeregisterTable - Deregisters the exception frame previously registered
    438   /// for the given function.
    439   void DeregisterTable(const Function *Fn) {
    440     if (ExceptionTableDeregister) {
    441       DenseMap<const Function*, void*>::iterator frame =
    442         AllExceptionTables.find(Fn);
    443       if(frame != AllExceptionTables.end()) {
    444         ExceptionTableDeregister(frame->second);
    445         AllExceptionTables.erase(frame);
    446       }
    447     }
    448   }
    449 
    450   /// DeregisterAllTables - Deregisters all previously registered pointers to an
    451   /// exception tables.  It uses the ExceptionTableoDeregister function.
    452   void DeregisterAllTables();
    453 
    454 protected:
    455   explicit ExecutionEngine(Module *M);
    456 
    457   void emitGlobals();
    458 
    459   void EmitGlobalVariable(const GlobalVariable *GV);
    460 
    461   GenericValue getConstantValue(const Constant *C);
    462   void LoadValueFromMemory(GenericValue &Result, GenericValue *Ptr,
    463                            Type *Ty);
    464 };
    465 
    466 namespace EngineKind {
    467   // These are actually bitmasks that get or-ed together.
    468   enum Kind {
    469     JIT         = 0x1,
    470     Interpreter = 0x2
    471   };
    472   const static Kind Either = (Kind)(JIT | Interpreter);
    473 }
    474 
    475 /// EngineBuilder - Builder class for ExecutionEngines.  Use this by
    476 /// stack-allocating a builder, chaining the various set* methods, and
    477 /// terminating it with a .create() call.
    478 class EngineBuilder {
    479 private:
    480   Module *M;
    481   EngineKind::Kind WhichEngine;
    482   std::string *ErrorStr;
    483   CodeGenOpt::Level OptLevel;
    484   JITMemoryManager *JMM;
    485   bool AllocateGVsWithCode;
    486   TargetOptions Options;
    487   Reloc::Model RelocModel;
    488   CodeModel::Model CMModel;
    489   std::string MArch;
    490   std::string MCPU;
    491   SmallVector<std::string, 4> MAttrs;
    492   bool UseMCJIT;
    493 
    494   /// InitEngine - Does the common initialization of default options.
    495   void InitEngine() {
    496     WhichEngine = EngineKind::Either;
    497     ErrorStr = NULL;
    498     OptLevel = CodeGenOpt::Default;
    499     JMM = NULL;
    500     Options = TargetOptions();
    501     AllocateGVsWithCode = false;
    502     RelocModel = Reloc::Default;
    503     CMModel = CodeModel::JITDefault;
    504     UseMCJIT = false;
    505   }
    506 
    507 public:
    508   /// EngineBuilder - Constructor for EngineBuilder.  If create() is called and
    509   /// is successful, the created engine takes ownership of the module.
    510   EngineBuilder(Module *m) : M(m) {
    511     InitEngine();
    512   }
    513 
    514   /// setEngineKind - Controls whether the user wants the interpreter, the JIT,
    515   /// or whichever engine works.  This option defaults to EngineKind::Either.
    516   EngineBuilder &setEngineKind(EngineKind::Kind w) {
    517     WhichEngine = w;
    518     return *this;
    519   }
    520 
    521   /// setJITMemoryManager - Sets the memory manager to use.  This allows
    522   /// clients to customize their memory allocation policies.  If create() is
    523   /// called and is successful, the created engine takes ownership of the
    524   /// memory manager.  This option defaults to NULL.
    525   EngineBuilder &setJITMemoryManager(JITMemoryManager *jmm) {
    526     JMM = jmm;
    527     return *this;
    528   }
    529 
    530   /// setErrorStr - Set the error string to write to on error.  This option
    531   /// defaults to NULL.
    532   EngineBuilder &setErrorStr(std::string *e) {
    533     ErrorStr = e;
    534     return *this;
    535   }
    536 
    537   /// setOptLevel - Set the optimization level for the JIT.  This option
    538   /// defaults to CodeGenOpt::Default.
    539   EngineBuilder &setOptLevel(CodeGenOpt::Level l) {
    540     OptLevel = l;
    541     return *this;
    542   }
    543 
    544   /// setTargetOptions - Set the target options that the ExecutionEngine
    545   /// target is using. Defaults to TargetOptions().
    546   EngineBuilder &setTargetOptions(const TargetOptions &Opts) {
    547     Options = Opts;
    548     return *this;
    549   }
    550 
    551   /// setRelocationModel - Set the relocation model that the ExecutionEngine
    552   /// target is using. Defaults to target specific default "Reloc::Default".
    553   EngineBuilder &setRelocationModel(Reloc::Model RM) {
    554     RelocModel = RM;
    555     return *this;
    556   }
    557 
    558   /// setCodeModel - Set the CodeModel that the ExecutionEngine target
    559   /// data is using. Defaults to target specific default
    560   /// "CodeModel::JITDefault".
    561   EngineBuilder &setCodeModel(CodeModel::Model M) {
    562     CMModel = M;
    563     return *this;
    564   }
    565 
    566   /// setAllocateGVsWithCode - Sets whether global values should be allocated
    567   /// into the same buffer as code.  For most applications this should be set
    568   /// to false.  Allocating globals with code breaks freeMachineCodeForFunction
    569   /// and is probably unsafe and bad for performance.  However, we have clients
    570   /// who depend on this behavior, so we must support it.  This option defaults
    571   /// to false so that users of the new API can safely use the new memory
    572   /// manager and free machine code.
    573   EngineBuilder &setAllocateGVsWithCode(bool a) {
    574     AllocateGVsWithCode = a;
    575     return *this;
    576   }
    577 
    578   /// setMArch - Override the architecture set by the Module's triple.
    579   EngineBuilder &setMArch(StringRef march) {
    580     MArch.assign(march.begin(), march.end());
    581     return *this;
    582   }
    583 
    584   /// setMCPU - Target a specific cpu type.
    585   EngineBuilder &setMCPU(StringRef mcpu) {
    586     MCPU.assign(mcpu.begin(), mcpu.end());
    587     return *this;
    588   }
    589 
    590   /// setUseMCJIT - Set whether the MC-JIT implementation should be used
    591   /// (experimental).
    592   EngineBuilder &setUseMCJIT(bool Value) {
    593     UseMCJIT = Value;
    594     return *this;
    595   }
    596 
    597   /// setMAttrs - Set cpu-specific attributes.
    598   template<typename StringSequence>
    599   EngineBuilder &setMAttrs(const StringSequence &mattrs) {
    600     MAttrs.clear();
    601     MAttrs.append(mattrs.begin(), mattrs.end());
    602     return *this;
    603   }
    604 
    605   TargetMachine *selectTarget();
    606 
    607   /// selectTarget - Pick a target either via -march or by guessing the native
    608   /// arch.  Add any CPU features specified via -mcpu or -mattr.
    609   TargetMachine *selectTarget(const Triple &TargetTriple,
    610                               StringRef MArch,
    611                               StringRef MCPU,
    612                               const SmallVectorImpl<std::string>& MAttrs);
    613 
    614   ExecutionEngine *create() {
    615     return create(selectTarget());
    616   }
    617 
    618   ExecutionEngine *create(TargetMachine *TM);
    619 };
    620 
    621 } // End llvm namespace
    622 
    623 #endif
    624