text: #ifndef LLVM_EXAMPLES_THINLTOJIT_DISCOVERYLAYER_H
  #define LLVM_EXAMPLES_THINLTOJIT_DISCOVERYLAYER_H
  
  #include "llvm/ExecutionEngine/JITSymbol.h"
  #include "llvm/ExecutionEngine/Orc/Core.h"
  #include "llvm/ExecutionEngine/Orc/IRCompileLayer.h"
  #include "llvm/ExecutionEngine/Orc/Layer.h"
  #include "llvm/ExecutionEngine/Orc/ThreadSafeModule.h"
  #include "llvm/IR/GlobalValue.h"
  #include "llvm/IR/IRBuilder.h"
  #include "llvm/Support/raw_ostream.h"
  
  #include "ThinLtoJIT.h"
  
  #include <atomic>
  #include <cstdint>
  #include <map>
  #include <mutex>
  #include <vector>
  
  namespace llvm {
  namespace orc {
  
  class ThinLtoInstrumentationLayer : public IRLayer {
  public:
    ThinLtoInstrumentationLayer(ExecutionSession &ES, IRCompileLayer &BaseLayer,
                                ThinLtoJIT::ExplicitMemoryBarrier MemFence,
                                unsigned FlagsPerBucket)
        : IRLayer(ES, BaseLayer.getManglingOptions()), BaseLayer(BaseLayer),
          MemFence(MemFence) {
      // TODO: So far we only allocate one bucket.
      allocateDiscoveryFlags(FlagsPerBucket);
    }
  
    ~ThinLtoInstrumentationLayer() override;
  
    void emit(MaterializationResponsibility R, ThreadSafeModule TSM) override;
  
    unsigned reserveDiscoveryFlags(unsigned Count);
    void registerDiscoveryFlagOwners(std::vector<GlobalValue::GUID> Guids,
                                     unsigned FirstIdx);
  
    void nudgeIntoDiscovery(std::vector<GlobalValue::GUID> Functions);
  
    std::vector<unsigned> takeFlagsThatFired();
    std::vector<GlobalValue::GUID> takeFlagOwners(std::vector<unsigned> Indexes);
  
    void dump(raw_ostream &OS);
  
  private:
    IRCompileLayer &BaseLayer;
    ThinLtoJIT::ExplicitMemoryBarrier MemFence;
  
    enum Flag : uint8_t { Clear = 0, Fired = 1 };
  
    // Lock-free read access.
    uint8_t *FlagsStorage;
    Flag *FlagsIncoming; // lock-free write by design
    Flag *FlagsHandled;
    unsigned NumFlagsAllocated;
    std::atomic<unsigned> NumFlagsUsed; // spin-lock
  
    // Acquire/release sync between writers and reader
    std::atomic<uint64_t> FlagsSync;
  
    // STL container requires locking for both, read and write access.
    mutable std::mutex DiscoveryFlagsInfoLock;
    std::map<unsigned, GlobalValue::GUID> FlagOwnersMap;
  
    void allocateDiscoveryFlags(unsigned MinFlags);
    void compileFunctionReachedFlagSetter(IRBuilder<> &B, Flag *F);
  };
  
  } // namespace orc
  } // namespace llvm
  
  #endif
  