//===-------- interface.cpp - Target independent OpenMP target RTL --------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Implementation of the interface to be used by Clang during the codegen of a
// target region.
//
//===----------------------------------------------------------------------===//

#include "OpenMP/OMPT/Interface.h"
#include "OffloadPolicy.h"
#include "OpenMP/OMPT/Callback.h"
#include "OpenMP/omp.h"
#include "PluginManager.h"
#include "omptarget.h"
#include "private.h"

#include "Shared/EnvironmentVar.h"
#include "Shared/Profile.h"

#include "Utils/ExponentialBackoff.h"

#include "llvm/Frontend/OpenMP/OMPConstants.h"

#include <cassert>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <memory>
#include <vector>

#ifdef OMPT_SUPPORT
using namespace llvm::omp::target::ompt;
#endif
using namespace llvm::omp::target::debug;

// If offload is enabled, ensure that device DeviceID has been initialized.
//
// The return bool indicates if the offload is to the host device
// There are three possible results:
// - Return false if the target device is ready for offload
// - Return true without reporting a runtime error if offload is
//   disabled, perhaps because the initial device was specified.
// - Report a runtime error and return true.
//
// If DeviceID == OFFLOAD_DEVICE_DEFAULT, set DeviceID to the default device.
// This step might be skipped if offload is disabled.
bool checkDevice(int64_t &DeviceID, ident_t *Loc) {
  if (OffloadPolicy::get(*PM).Kind == OffloadPolicy::DISABLED) {
    ODBG(ODT_Device) << "Offload is disabled";
    return true;
  }

  if (DeviceID == OFFLOAD_DEVICE_DEFAULT) {
    DeviceID = omp_get_default_device();
    ODBG(ODT_Device) << "Use default device id " << DeviceID;
  }

  // Proposed behavior for OpenMP 5.2 in OpenMP spec github issue 2669.
  if (omp_get_num_devices() == 0) {
    ODBG(ODT_Device) << "omp_get_num_devices() == 0 but offload is manadatory";
    handleTargetOutcome(false, Loc);
    return true;
  }

  if (DeviceID == omp_get_initial_device()) {
    ODBG(ODT_Device) << "Device is host (" << DeviceID
                     << "), returning as if offload is disabled";
    return true;
  }
  return false;
}

////////////////////////////////////////////////////////////////////////////////
/// adds requires flags
EXTERN void __tgt_register_requires(int64_t Flags) {
  MESSAGE("The %s function has been removed. Old OpenMP requirements will not "
          "be handled",
          __PRETTY_FUNCTION__);
}

EXTERN void __tgt_rtl_init() { initRuntime(); }
EXTERN void __tgt_rtl_deinit() { deinitRuntime(); }

////////////////////////////////////////////////////////////////////////////////
/// adds a target shared library to the target execution image
EXTERN void __tgt_register_lib(__tgt_bin_desc *Desc) {
  initRuntime();
  if (PM->delayRegisterLib(Desc))
    return;

  PM->registerLib(Desc);
}

////////////////////////////////////////////////////////////////////////////////
/// Initialize all available devices without registering any image
EXTERN void __tgt_init_all_rtls() {
  assert(PM && "Runtime not initialized");
  PM->initializeAllDevices();
}

////////////////////////////////////////////////////////////////////////////////
/// unloads a target shared library
EXTERN void __tgt_unregister_lib(__tgt_bin_desc *Desc) {
  PM->unregisterLib(Desc);

  deinitRuntime();
}

template <typename TargetAsyncInfoTy>
static inline void
targetData(ident_t *Loc, int64_t DeviceId, int32_t ArgNum, void **ArgsBase,
           void **Args, int64_t *ArgSizes, int64_t *ArgTypes,
           map_var_info_t *ArgNames, void **ArgMappers,
           TargetDataFuncPtrTy TargetDataFunction, const char *RegionTypeMsg,
           const char *RegionName) {
  assert(PM && "Runtime not initialized");
  static_assert(std::is_convertible_v<TargetAsyncInfoTy &, AsyncInfoTy &>,
                "TargetAsyncInfoTy must be convertible to AsyncInfoTy.");

  TIMESCOPE_WITH_DETAILS_AND_IDENT("Runtime: Data Copy",
                                   "NumArgs=" + std::to_string(ArgNum), Loc);

  ODBG(ODT_Interface) << "Entering data " << RegionName << " region for device "
                      << DeviceId << " with " << ArgNum << " mappings";

  if (checkDevice(DeviceId, Loc)) {
    ODBG(ODT_Interface) << "Not offloading to device " << DeviceId;
    return;
  }

  if (getInfoLevel() & OMP_INFOTYPE_KERNEL_ARGS)
    printKernelArguments(Loc, DeviceId, ArgNum, ArgSizes, ArgTypes, ArgNames,
                         RegionTypeMsg);
  ODBG_OS(ODT_Kernel, [&](llvm::raw_ostream &Os) {
    for (int I = 0; I < ArgNum; ++I) {
      Os << "Entry " << llvm::format("%2d", I) << ": Base=" << ArgsBase[I]
         << ", Begin=" << Args[I] << ", Size=" << ArgSizes[I]
         << ", Type=" << llvm::format("0x%" PRIx64, ArgTypes[I]) << ", Name="
         << ((ArgNames) ? getNameFromMapping(ArgNames[I]) : "unknown") << "\n";
    }
  });

  auto DeviceOrErr = PM->getDevice(DeviceId);
  if (!DeviceOrErr)
    FATAL_MESSAGE(DeviceId, "%s", toString(DeviceOrErr.takeError()).c_str());

  TargetAsyncInfoTy TargetAsyncInfo(*DeviceOrErr);
  AsyncInfoTy &AsyncInfo = TargetAsyncInfo;

  /// RAII to establish tool anchors before and after data begin / end / update
  OMPT_IF_BUILT(assert((TargetDataFunction == targetDataBegin ||
                        TargetDataFunction == targetDataEnd ||
                        TargetDataFunction == targetDataUpdate) &&
                       "Encountered unexpected TargetDataFunction during "
                       "execution of targetData");
                auto CallbackFunctions =
                    (TargetDataFunction == targetDataBegin)
                        ? RegionInterface.getCallbacks<ompt_target_enter_data>()
                    : (TargetDataFunction == targetDataEnd)
                        ? RegionInterface.getCallbacks<ompt_target_exit_data>()
                        : RegionInterface.getCallbacks<ompt_target_update>();
                InterfaceRAII TargetDataRAII(CallbackFunctions, DeviceId,
                                             OMPT_GET_RETURN_ADDRESS);)

  int Rc = OFFLOAD_SUCCESS;

  // Allocate StateInfo for targetDataBegin and targetDataEnd to track
  // allocations, pointer attachments and deferred transfers.
  // This is not needed for targetDataUpdate.
  std::unique_ptr<StateInfoTy> StateInfo;
  if (TargetDataFunction == targetDataBegin ||
      TargetDataFunction == targetDataEnd)
    StateInfo = std::make_unique<StateInfoTy>();

  Rc = TargetDataFunction(Loc, *DeviceOrErr, ArgNum, ArgsBase, Args, ArgSizes,
                          ArgTypes, ArgNames, ArgMappers, AsyncInfo,
                          StateInfo.get(), /*FromMapper=*/false);

  if (Rc == OFFLOAD_SUCCESS) {
    // Process deferred ATTACH entries BEFORE synchronization
    if (StateInfo && !StateInfo->AttachEntries.empty())
      Rc = processAttachEntries(*DeviceOrErr, *StateInfo, AsyncInfo);

    if (Rc == OFFLOAD_SUCCESS)
      Rc = AsyncInfo.synchronize();
  }

  handleTargetOutcome(Rc == OFFLOAD_SUCCESS, Loc);
}

/// creates host-to-target data mapping, stores it in the
/// libomptarget.so internal structure (an entry in a stack of data maps)
/// and passes the data to the device.
EXTERN void __tgt_target_data_begin_mapper(ident_t *Loc, int64_t DeviceId,
                                           int32_t ArgNum, void **ArgsBase,
                                           void **Args, int64_t *ArgSizes,
                                           int64_t *ArgTypes,
                                           map_var_info_t *ArgNames,
                                           void **ArgMappers) {
  OMPT_IF_BUILT(ReturnAddressSetterRAII RA(__builtin_return_address(0)));
  targetData<AsyncInfoTy>(Loc, DeviceId, ArgNum, ArgsBase, Args, ArgSizes,
                          ArgTypes, ArgNames, ArgMappers, targetDataBegin,
                          "Entering OpenMP data region with being_mapper",
                          "begin");
}

EXTERN void __tgt_target_data_begin_nowait_mapper(
    ident_t *Loc, int64_t DeviceId, int32_t ArgNum, void **ArgsBase,
    void **Args, int64_t *ArgSizes, int64_t *ArgTypes, map_var_info_t *ArgNames,
    void **ArgMappers, int32_t DepNum, void *DepList, int32_t NoAliasDepNum,
    void *NoAliasDepList) {
  OMPT_IF_BUILT(ReturnAddressSetterRAII RA(__builtin_return_address(0)));
  targetData<TaskAsyncInfoWrapperTy>(
      Loc, DeviceId, ArgNum, ArgsBase, Args, ArgSizes, ArgTypes, ArgNames,
      ArgMappers, targetDataBegin,
      "Entering OpenMP data region with being_nowait_mapper", "begin");
}

/// passes data from the target, releases target memory and destroys
/// the host-target mapping (top entry from the stack of data maps)
/// created by the last __tgt_target_data_begin.
EXTERN void __tgt_target_data_end_mapper(ident_t *Loc, int64_t DeviceId,
                                         int32_t ArgNum, void **ArgsBase,
                                         void **Args, int64_t *ArgSizes,
                                         int64_t *ArgTypes,
                                         map_var_info_t *ArgNames,
                                         void **ArgMappers) {
  OMPT_IF_BUILT(ReturnAddressSetterRAII RA(__builtin_return_address(0)));
  targetData<AsyncInfoTy>(Loc, DeviceId, ArgNum, ArgsBase, Args, ArgSizes,
                          ArgTypes, ArgNames, ArgMappers, targetDataEnd,
                          "Exiting OpenMP data region with end_mapper", "end");
}

EXTERN void __tgt_target_data_end_nowait_mapper(
    ident_t *Loc, int64_t DeviceId, int32_t ArgNum, void **ArgsBase,
    void **Args, int64_t *ArgSizes, int64_t *ArgTypes, map_var_info_t *ArgNames,
    void **ArgMappers, int32_t DepNum, void *DepList, int32_t NoAliasDepNum,
    void *NoAliasDepList) {
  OMPT_IF_BUILT(ReturnAddressSetterRAII RA(__builtin_return_address(0)));
  targetData<TaskAsyncInfoWrapperTy>(
      Loc, DeviceId, ArgNum, ArgsBase, Args, ArgSizes, ArgTypes, ArgNames,
      ArgMappers, targetDataEnd,
      "Exiting OpenMP data region with end_nowait_mapper", "end");
}

EXTERN void __tgt_target_data_update_mapper(ident_t *Loc, int64_t DeviceId,
                                            int32_t ArgNum, void **ArgsBase,
                                            void **Args, int64_t *ArgSizes,
                                            int64_t *ArgTypes,
                                            map_var_info_t *ArgNames,
                                            void **ArgMappers) {
  OMPT_IF_BUILT(ReturnAddressSetterRAII RA(__builtin_return_address(0)));
  targetData<AsyncInfoTy>(
      Loc, DeviceId, ArgNum, ArgsBase, Args, ArgSizes, ArgTypes, ArgNames,
      ArgMappers, targetDataUpdate,
      "Updating data within the OpenMP data region with update_mapper",
      "update");
}

EXTERN void __tgt_target_data_update_nowait_mapper(
    ident_t *Loc, int64_t DeviceId, int32_t ArgNum, void **ArgsBase,
    void **Args, int64_t *ArgSizes, int64_t *ArgTypes, map_var_info_t *ArgNames,
    void **ArgMappers, int32_t DepNum, void *DepList, int32_t NoAliasDepNum,
    void *NoAliasDepList) {
  OMPT_IF_BUILT(ReturnAddressSetterRAII RA(__builtin_return_address(0)));
  targetData<TaskAsyncInfoWrapperTy>(
      Loc, DeviceId, ArgNum, ArgsBase, Args, ArgSizes, ArgTypes, ArgNames,
      ArgMappers, targetDataUpdate,
      "Updating data within the OpenMP data region with update_nowait_mapper",
      "update");
}

/// Holds dynamically allocated argument arrays when upgrading old-format
/// kernel arguments to include the dyn_ptr slot.
struct UpgradedArgBuffersTy {
  llvm::SmallVector<void *, 0> BasePtrs;
  llvm::SmallVector<void *, 0> Ptrs;
  llvm::SmallVector<int64_t, 0> Sizes;
  llvm::SmallVector<int64_t, 0> Types;
  llvm::SmallVector<map_var_info_t, 0> Names;
  llvm::SmallVector<void *, 0> Mappers;
};

static KernelArgsTy *upgradeKernelArgs(KernelArgsTy *KernelArgs,
                                       KernelArgsTy &LocalKernelArgs,
                                       UpgradedArgBuffersTy &Bufs,
                                       int32_t NumTeams, int32_t ThreadLimit) {
  if (KernelArgs->Version > OMP_KERNEL_ARG_VERSION)
    ODBG(ODT_Interface) << "Unexpected ABI version: " << KernelArgs->Version;

  // Versions before OMP_KERNEL_ARG_MIN_VERSION_WITH_DYN_PTR used an older
  // struct layout missing several fields. Reconstruct a complete struct.
  if (KernelArgs->Version < OMP_KERNEL_ARG_MIN_VERSION_WITH_DYN_PTR) {
    // Maintain the version so the runtime can match the device ABI.
    LocalKernelArgs.Version = KernelArgs->Version;
    LocalKernelArgs.NumArgs = KernelArgs->NumArgs;
    LocalKernelArgs.ArgBasePtrs = KernelArgs->ArgBasePtrs;
    LocalKernelArgs.ArgPtrs = KernelArgs->ArgPtrs;
    LocalKernelArgs.ArgSizes = KernelArgs->ArgSizes;
    LocalKernelArgs.ArgTypes = KernelArgs->ArgTypes;
    LocalKernelArgs.ArgNames = KernelArgs->ArgNames;
    LocalKernelArgs.ArgMappers = KernelArgs->ArgMappers;
    LocalKernelArgs.Tripcount = KernelArgs->Tripcount;
    LocalKernelArgs.Flags = KernelArgs->Flags;
    LocalKernelArgs.DynCGroupMem = 0;
    LocalKernelArgs.NumTeams[0] = NumTeams;
    LocalKernelArgs.NumTeams[1] = 1;
    LocalKernelArgs.NumTeams[2] = 1;
    LocalKernelArgs.ThreadLimit[0] = ThreadLimit;
    LocalKernelArgs.ThreadLimit[1] = 1;
    LocalKernelArgs.ThreadLimit[2] = 1;
    return &LocalKernelArgs;
  }

  // FIXME: This is a WA to "calibrate" the bad work done in the front end.
  // Delete this ugly code after the front end emits proper values.
  auto CorrectMultiDim = [](uint32_t (&Val)[3]) {
    if (Val[1] == 0)
      Val[1] = 1;
    if (Val[2] == 0)
      Val[2] = 1;
  };
  CorrectMultiDim(KernelArgs->ThreadLimit);
  CorrectMultiDim(KernelArgs->NumTeams);

  // Version 3 put the implicit argument at the front with no storage.
  if (KernelArgs->Version == OMP_KERNEL_ARG_MIN_VERSION_WITH_DYN_PTR) {
    uint32_t NewSize = KernelArgs->NumArgs + 1;

    Bufs.BasePtrs.resize(NewSize, nullptr);
    Bufs.Ptrs.resize(NewSize, nullptr);
    Bufs.Sizes.resize(NewSize, 0);
    Bufs.Types.resize(NewSize, 0);
    Bufs.Names.resize(NewSize, nullptr);
    Bufs.Mappers.resize(NewSize, nullptr);

    for (uint32_t I = 0; I < KernelArgs->NumArgs; ++I) {
      Bufs.BasePtrs[I] = KernelArgs->ArgBasePtrs[I];
      Bufs.Ptrs[I] = KernelArgs->ArgPtrs[I];
      Bufs.Sizes[I] = KernelArgs->ArgSizes[I];
      Bufs.Types[I] = KernelArgs->ArgTypes[I];
      if (KernelArgs->ArgNames)
        Bufs.Names[I] = KernelArgs->ArgNames[I];
      if (KernelArgs->ArgMappers)
        Bufs.Mappers[I] = KernelArgs->ArgMappers[I];
    }

    Bufs.Types[KernelArgs->NumArgs] =
        OMP_TGT_MAPTYPE_TARGET_PARAM | OMP_TGT_MAPTYPE_LITERAL;

    LocalKernelArgs = *KernelArgs;
    LocalKernelArgs.NumArgs = NewSize;
    LocalKernelArgs.ArgBasePtrs = Bufs.BasePtrs.data();
    LocalKernelArgs.ArgPtrs = Bufs.Ptrs.data();
    LocalKernelArgs.ArgSizes = Bufs.Sizes.data();
    LocalKernelArgs.ArgTypes = Bufs.Types.data();
    LocalKernelArgs.ArgNames = Bufs.Names.data();
    LocalKernelArgs.ArgMappers = Bufs.Mappers.data();
    return &LocalKernelArgs;
  }

  return KernelArgs;
}

template <typename TargetAsyncInfoTy>
static inline int targetKernel(ident_t *Loc, int64_t DeviceId, int32_t NumTeams,
                               int32_t ThreadLimit, void *HostPtr,
                               KernelArgsTy *KernelArgs) {
  assert(PM && "Runtime not initialized");
  static_assert(std::is_convertible_v<TargetAsyncInfoTy &, AsyncInfoTy &>,
                "Target AsyncInfoTy must be convertible to AsyncInfoTy.");
  ODBG(ODT_Interface) << "Entering target region for device " << DeviceId
                      << " with entry point " << HostPtr;

  if (checkDevice(DeviceId, Loc)) {
    ODBG(ODT_Interface) << "Not offloading to device " << DeviceId;
    return OMP_TGT_FAIL;
  }

  bool IsTeams = NumTeams != -1;
  if (!IsTeams)
    KernelArgs->NumTeams[0] = NumTeams = 1;

  KernelArgsTy LocalKernelArgs;
  UpgradedArgBuffersTy UpgradedBufs;
  KernelArgs = upgradeKernelArgs(KernelArgs, LocalKernelArgs, UpgradedBufs,
                                 NumTeams, ThreadLimit);

  TIMESCOPE_WITH_DETAILS_AND_IDENT(
      "Runtime: target exe",
      "NumTeams=" + std::to_string(NumTeams) +
          ";NumArgs=" + std::to_string(KernelArgs->NumArgs),
      Loc);

  // The implicit dyn_ptr slot is always the last entry for versions that
  // support it.  Exclude it from user-facing info output.
  uint32_t UserArgCount = KernelArgs->NumArgs;
  if (KernelArgs->Version >= OMP_KERNEL_ARG_MIN_VERSION_WITH_DYN_PTR &&
      UserArgCount > 0)
    --UserArgCount;

  if (getInfoLevel() & OMP_INFOTYPE_KERNEL_ARGS)
    printKernelArguments(Loc, DeviceId, UserArgCount, KernelArgs->ArgSizes,
                         KernelArgs->ArgTypes, KernelArgs->ArgNames,
                         "Entering OpenMP kernel");

  ODBG_OS(ODT_Kernel, [&](llvm::raw_ostream &Os) {
    for (uint32_t I = 0; I < KernelArgs->NumArgs; ++I) {
      Os << "Entry" << llvm::format("%2d", I)
         << ": Base=" << KernelArgs->ArgBasePtrs[I]
         << ", Begin=" << KernelArgs->ArgPtrs[I]
         << ", Size=" << KernelArgs->ArgSizes[I]
         << ", Type=" << llvm::format("0x%" PRIx64, KernelArgs->ArgTypes[I])
         << ", Name="
         << (KernelArgs->ArgNames
                 ? getNameFromMapping(KernelArgs->ArgNames[I]).c_str()
                 : "unknown")
         << "\n";
    }
  });

  auto DeviceOrErr = PM->getDevice(DeviceId);
  if (!DeviceOrErr)
    FATAL_MESSAGE(DeviceId, "%s", toString(DeviceOrErr.takeError()).c_str());

  TargetAsyncInfoTy TargetAsyncInfo(*DeviceOrErr);
  AsyncInfoTy &AsyncInfo = TargetAsyncInfo;
  /// RAII to establish tool anchors before and after target region
  OMPT_IF_BUILT(InterfaceRAII TargetRAII(
                    RegionInterface.getCallbacks<ompt_target>(), DeviceId,
                    /*CodePtr=*/OMPT_GET_RETURN_ADDRESS);)

  int Rc = OFFLOAD_SUCCESS;
  Rc = target(Loc, *DeviceOrErr, HostPtr, *KernelArgs, AsyncInfo);
  { // required to show synchronization
    TIMESCOPE_WITH_DETAILS_AND_IDENT("Runtime: synchronize", "", Loc);
    if (Rc == OFFLOAD_SUCCESS)
      Rc = AsyncInfo.synchronize();

    handleTargetOutcome(Rc == OFFLOAD_SUCCESS, Loc);
    assert(Rc == OFFLOAD_SUCCESS && "__tgt_target_kernel unexpected failure!");
  }
  return OMP_TGT_SUCCESS;
}

/// Implements a kernel entry that executes the target region on the specified
/// device.
///
/// \param Loc Source location associated with this target region.
/// \param DeviceId The device to execute this region, -1 indicated the default.
/// \param NumTeams Number of teams to launch the region with, -1 indicates a
///                 non-teams region and 0 indicates it was unspecified.
/// \param ThreadLimit Limit to the number of threads to use in the kernel
///                    launch, 0 indicates it was unspecified.
/// \param HostPtr  The pointer to the host function registered with the kernel.
/// \param Args     All arguments to this kernel launch (see struct definition).
EXTERN int __tgt_target_kernel(ident_t *Loc, int64_t DeviceId, int32_t NumTeams,
                               int32_t ThreadLimit, void *HostPtr,
                               KernelArgsTy *KernelArgs) {
  OMPT_IF_BUILT(ReturnAddressSetterRAII RA(__builtin_return_address(0)));
  if (KernelArgs->Flags.NoWait)
    return targetKernel<TaskAsyncInfoWrapperTy>(
        Loc, DeviceId, NumTeams, ThreadLimit, HostPtr, KernelArgs);
  return targetKernel<AsyncInfoTy>(Loc, DeviceId, NumTeams, ThreadLimit,
                                   HostPtr, KernelArgs);
}

/// Activates the record replay mechanism.
/// \param DeviceId The device identifier to execute the target region.
/// \param MemorySize The number of bytes to be (pre-)allocated
///                   by the record replay allocator.
/// /param IsRecord Activates the record replay mechanism in
///                 'record' or 'replay' mode.
/// /param SaveOutput Store the device memory after kernel
///                   execution on persistent storage.
/// /param EmitReport Emit a summary report after the recording.
/// /param OutputDirPath The output directory where the record replay files
/// should be stored. An empty string or nullptr indicates the current working
/// directory should be used.
EXTERN int __tgt_activate_record_replay(int64_t DeviceId, uint64_t MemorySize,
                                        void *VAddr, bool IsRecord,
                                        bool SaveOutput, bool EmitReport,
                                        const char *OutputDirPath) {
  assert(PM && "Runtime not initialized");
  OMPT_IF_BUILT(ReturnAddressSetterRAII RA(__builtin_return_address(0)));
  auto DeviceOrErr = PM->getDevice(DeviceId);
  if (!DeviceOrErr)
    FATAL_MESSAGE(DeviceId, "%s", toString(DeviceOrErr.takeError()).c_str());

  int Rc = target_activate_rr(*DeviceOrErr, MemorySize, VAddr, IsRecord,
                              SaveOutput, EmitReport, OutputDirPath);
  if (Rc != OFFLOAD_SUCCESS) {
    ODBG(ODT_Interface) << "Record replay failed to activate in device "
                        << DeviceId;
    return OMP_TGT_FAIL;
  }
  return OMP_TGT_SUCCESS;
}

/// Implements a target kernel entry that replays a pre-recorded kernel.
/// \param Loc Source location associated with this target region (unused).
/// \param DeviceId The device identifier to execute the target region.
/// \param HostPtr A pointer to an address that uniquely identifies the kernel.
/// \param DeviceMemory A pointer to an array storing device memory data to move
///                     prior to kernel execution.
/// \param DeviceMemorySize The size of the above device memory data in bytes.
/// \param TgtArgs An array of pointers of the pre-recorded target kernel
///                arguments.
/// \param TgtOffsets An array of pointers of the pre-recorded target kernel
///                   argument offsets.
/// \param NumArgs The number of kernel arguments.
/// \param NumTeams Number of teams to launch the target region with.
/// \param ThreadLimit Limit to the number of threads to use in kernel
///                    execution.
/// \param LoopTripCount The pre-recorded value of the loop tripcount, if any.
/// \return OMP_TGT_SUCCESS on success, OMP_TGT_FAIL on failure.
EXTERN int __tgt_target_kernel_replay(
    ident_t *Loc, int64_t DeviceId, void *HostPtr, void *DeviceMemory,
    int64_t DeviceMemorySize, const llvm::offloading::EntryTy *Globals,
    int32_t NumGlobals, void **TgtArgs, ptrdiff_t *TgtOffsets, int32_t NumArgs,
    int32_t NumTeams, int32_t ThreadLimit, uint32_t SharedMemorySize,
    uint64_t LoopTripCount, KernelReplayOutcomeTy *ReplayOutcome) {
  assert(PM && "Runtime not initialized");
  OMPT_IF_BUILT(ReturnAddressSetterRAII RA(__builtin_return_address(0)));
  if (checkDevice(DeviceId, Loc)) {
    ODBG(ODT_Interface) << "Not offloading to device " << DeviceId;
    return OMP_TGT_FAIL;
  }
  auto DeviceOrErr = PM->getDevice(DeviceId);
  if (!DeviceOrErr)
    FATAL_MESSAGE(DeviceId, "%s", toString(DeviceOrErr.takeError()).c_str());

  /// RAII to establish tool anchors before and after target region
  OMPT_IF_BUILT(InterfaceRAII TargetRAII(
                    RegionInterface.getCallbacks<ompt_target>(), DeviceId,
                    /*CodePtr=*/OMPT_GET_RETURN_ADDRESS);)

  AsyncInfoTy AsyncInfo(*DeviceOrErr);
  int Rc = target_replay(
      Loc, *DeviceOrErr, HostPtr, DeviceMemory, DeviceMemorySize, Globals,
      NumGlobals, TgtArgs, TgtOffsets, NumArgs, NumTeams, ThreadLimit,
      SharedMemorySize, LoopTripCount, AsyncInfo, ReplayOutcome);

  if (Rc == OFFLOAD_SUCCESS)
    Rc = AsyncInfo.synchronize();

  if (Rc != OFFLOAD_SUCCESS) {
    ODBG(ODT_Interface) << "Kernel replay failed in device " << DeviceId;
    return OMP_TGT_FAIL;
  }
  return OMP_TGT_SUCCESS;
}

// Get the current number of components for a user-defined mapper.
EXTERN int64_t __tgt_mapper_num_components(void *RtMapperHandle) {
  auto *MapperComponentsPtr = (struct MapperComponentsTy *)RtMapperHandle;
  int64_t Size = MapperComponentsPtr->Components.size();
  ODBG(ODT_Interface) << "__tgt_mapper_num_components(Handle=" << RtMapperHandle
                      << ") returns " << Size;
  return Size;
}

// Push back one component for a user-defined mapper.
EXTERN void __tgt_push_mapper_component(void *RtMapperHandle, void *Base,
                                        void *Begin, int64_t Size, int64_t Type,
                                        void *Name) {
  ODBG(ODT_Interface) << "__tgt_push_mapper_component(Handle=" << RtMapperHandle
                      << ") adds an entry (Base=" << Base << ", Begin=" << Begin
                      << ", Size=" << Size
                      << ", Type=" << llvm::format("0x%" PRIx64, Type)
                      << ", Name="
                      << ((Name) ? getNameFromMapping(Name) : "unknown") << ")";
  auto *MapperComponentsPtr = (struct MapperComponentsTy *)RtMapperHandle;
  MapperComponentsPtr->Components.push_back(
      MapComponentInfoTy(Base, Begin, Size, Type, Name));
}

EXTERN void __tgt_set_info_flag(uint32_t NewInfoLevel) {
  assert(PM && "Runtime not initialized");
  std::atomic<uint32_t> &InfoLevel = getInfoLevelInternal();
  InfoLevel.store(NewInfoLevel);
}

EXTERN int __tgt_print_device_info(int64_t DeviceId) {
  assert(PM && "Runtime not initialized");
  auto DeviceOrErr = PM->getDevice(DeviceId);
  if (!DeviceOrErr)
    FATAL_MESSAGE(DeviceId, "%s", toString(DeviceOrErr.takeError()).c_str());

  return DeviceOrErr->printDeviceInfo();
}

EXTERN void __tgt_target_nowait_query(void **AsyncHandle) {
  assert(PM && "Runtime not initialized");
  OMPT_IF_BUILT(ReturnAddressSetterRAII RA(__builtin_return_address(0)));

  if (!AsyncHandle || !*AsyncHandle) {
    FATAL_MESSAGE0(
        1, "Receive an invalid async handle from the current OpenMP task. Is "
           "this a target nowait region?\n");
  }

  // Exponential backoff tries to optimally decide if a thread should just query
  // for the device operations (work/spin wait on them) or block until they are
  // completed (use device side blocking mechanism). This allows the runtime to
  // adapt itself when there are a lot of long-running target regions in-flight.
  static thread_local utils::ExponentialBackoff QueryCounter(
      Int64Envar("OMPTARGET_QUERY_COUNT_MAX", 10),
      Int64Envar("OMPTARGET_QUERY_COUNT_THRESHOLD", 5),
      Envar<float>("OMPTARGET_QUERY_COUNT_BACKOFF_FACTOR", 0.5f));

  auto *AsyncInfo = (AsyncInfoTy *)*AsyncHandle;

  // If the thread is actively waiting on too many target nowait regions, we
  // should use the blocking sync type.
  if (QueryCounter.isAboveThreshold())
    AsyncInfo->SyncType = AsyncInfoTy::SyncTy::BLOCKING;

  if (AsyncInfo->synchronize())
    FATAL_MESSAGE0(1, "Error while querying the async queue for completion.\n");
  // If there are device operations still pending, return immediately without
  // deallocating the handle and increase the current thread query count.
  if (!AsyncInfo->isDone()) {
    QueryCounter.increment();
    return;
  }

  // When a thread successfully completes a target nowait region, we
  // exponentially backoff its query counter by the query factor.
  QueryCounter.decrement();

  // Delete the handle and unset it from the OpenMP task data.
  delete AsyncInfo;
  *AsyncHandle = nullptr;
}

EXTERN void __tgt_register_rpc_callback(unsigned (*Callback)(void *,
                                                             unsigned)) {
  for (auto &Plugin : PM->plugins())
    if (Plugin.is_initialized())
      Plugin.getRPCServer().registerCallback(Callback);
}