lib/CodeGen/MLRegAllocEvictAdvisor.cpp

//===- MLRegAllocEvictAdvisor.cpp - ML eviction advisor -------------------===//
//
// 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 ML eviction advisor and reward injection pass
//
//===----------------------------------------------------------------------===//

#include "AllocationOrder.h"
#include "RegAllocEvictionAdvisor.h"
#include "RegAllocGreedy.h"
#include "llvm/Analysis/InteractiveModelRunner.h"
#include "llvm/Analysis/MLModelRunner.h"
#include "llvm/Analysis/TensorSpec.h"
#if defined(LLVM_HAVE_TF_AOT_REGALLOCEVICTMODEL) || defined(LLVM_HAVE_TFLITE)
#include "llvm/Analysis/ModelUnderTrainingRunner.h"
#include "llvm/Analysis/NoInferenceModelRunner.h"
#include "llvm/Analysis/Utils/TrainingLogger.h"
#endif
#include "MLRegAllocEvictAdvisor.h"
#include "llvm/Analysis/ReleaseModeModelRunner.h"
#include "llvm/CodeGen/CalcSpillWeights.h"
#include "llvm/CodeGen/LiveRegMatrix.h"
#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/RegisterClassInfo.h"
#include "llvm/CodeGen/VirtRegMap.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/PassRegistry.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/ErrorHandling.h"

#include <array>
#include <bitset>
#include <memory>

using namespace llvm;

#define DEBUG_TYPE "ml-regalloc"

// Generated header in release (AOT) mode
#if defined(LLVM_HAVE_TF_AOT_REGALLOCEVICTMODEL)
#include "RegAllocEvictModel.h"
using CompiledModelType = RegAllocEvictModel;
#else
using CompiledModelType = NoopSavedModelImpl;
#endif

static cl::opt<std::string> InteractiveChannelBaseName(
    "regalloc-evict-interactive-channel-base", cl::Hidden,
    cl::desc(
        "Base file path for the interactive mode. The incoming filename should "
        "have the name <regalloc-evict-interactive-channel-base>.in, while the "
        "outgoing name should be "
        "<regalloc-evict-interactive-channel-base>.out"));

// Options that only make sense in development mode
#ifdef LLVM_HAVE_TFLITE
#include "RegAllocScore.h"
#include "llvm/Analysis/Utils/TFUtils.h"

static cl::opt<std::string> TrainingLog(
    "regalloc-training-log", cl::Hidden,
    cl::desc("Training log for the register allocator eviction model"));

static cl::opt<std::string> ModelUnderTraining(
    "regalloc-model", cl::Hidden,
    cl::desc("The model being trained for register allocation eviction"));

static cl::opt<bool> EnableDevelopmentFeatures(
    "regalloc-enable-development-features", cl::Hidden,
    cl::desc("Whether or not to enable features under development for the ML "
             "regalloc advisor"));

#else
static const bool EnableDevelopmentFeatures = false;
#endif // #ifdef LLVM_HAVE_TFLITE

/// The score injection pass.
/// This pass calculates the score for a function and inserts it in the log, but
/// this happens only in development mode. It's a no-op otherwise.
namespace llvm {
extern cl::opt<unsigned> EvictInterferenceCutoff;

class RegAllocScoring : public MachineFunctionPass {
public:
  static char ID;

  RegAllocScoring() : MachineFunctionPass(ID) {
    initializeRegAllocScoringPass(*PassRegistry::getPassRegistry());
  }

  ~RegAllocScoring() override = default;

  StringRef getPassName() const override {
    return "Register Allocation Pass Scoring";
  }

  /// RegAllocReward analysis usage.
  void getAnalysisUsage(AnalysisUsage &AU) const override {
    AU.setPreservesAll();
    AU.addRequired<RegAllocEvictionAdvisorAnalysis>();
    AU.addRequired<RegAllocPriorityAdvisorAnalysis>();
    AU.addRequired<MachineBlockFrequencyInfo>();
    MachineFunctionPass::getAnalysisUsage(AU);
  }

  /// Performs this pass
  bool runOnMachineFunction(MachineFunction &) override;
};

char RegAllocScoring::ID = 0;
FunctionPass *createRegAllocScoringPass() { return new RegAllocScoring(); }

} // namespace llvm

INITIALIZE_PASS(RegAllocScoring, "regallocscoringpass",
                "Register Allocation Scoring Pass", false, false)

// ===================================
// Common ML Advisor declarations
// ===================================
namespace {
// The model can only accept a specified number of opcodes and will error it if
// fed an opcode it hasn't seen before. This constant sets the current cutoff.
static const int OpcodeValueCutoff = 17716;

// Most features are as described above, so we'll reuse this vector in defining
// them.
static const std::vector<int64_t> PerLiveRangeShape{1, NumberOfInterferences};

// --------------
// Features table
// --------------
// For each interfering live range (incl. the candidate) we collect a number of
// features. However, because the features are of different types (and because
// of ML best practices), we organize the tensors per feature, not per
// candidate. Each such tensor has a scalar value corresponding to the
// interferring live range at that position, in the order in AllocationOrder.
// The last position corresponds to the virt reg seeking allocation.
// Exception to all that is the progression feature, which is just a scalar (see
// its documentation for details).
// Note on naming: the "_by_max" are normalized using the largest value of that
// tensor, as observed in the current decision making stage (i.e. for the
// current call to the advisor's tryFindEvictionCandidate)
//
// The feature list format: type, name, shape, documentation.
// Note: we can really just use int64 and float, hence the modeling of some
// bools as int64 values.
#define RA_EVICT_FEATURES_LIST(M)                                              \
  M(int64_t, mask, PerLiveRangeShape,                                          \
    "boolean values, 0 for unavailable candidates (i.e. if a position is 0, "  \
    "it "                                                                      \
    "can't be evicted)")                                                       \
  M(int64_t, is_free, PerLiveRangeShape,                                       \
    "boolean values, 1 if this phys reg is actually free (no interferences)")  \
  M(float, nr_urgent, PerLiveRangeShape,                                       \
    "number of 'urgent' intervals, normalized. Urgent are those that are OK "  \
    "to break cascades")                                                       \
  M(float, nr_broken_hints, PerLiveRangeShape,                                 \
    "if this position were evicted, how many broken hints would there be")     \
  M(int64_t, is_hint, PerLiveRangeShape,                                       \
    "is this a preferred phys reg for the candidate")                          \
  M(int64_t, is_local, PerLiveRangeShape,                                      \
    "is this live range local to a basic block")                               \
  M(float, nr_rematerializable, PerLiveRangeShape,                             \
    "nr rematerializable ranges")                                              \
  M(float, nr_defs_and_uses, PerLiveRangeShape,                                \
    "bb freq - weighed nr defs and uses")                                      \
  M(float, weighed_reads_by_max, PerLiveRangeShape,                            \
    "bb freq - weighed nr of reads, normalized")                               \
  M(float, weighed_writes_by_max, PerLiveRangeShape,                           \
    "bb feq - weighed nr of writes, normalized")                               \
  M(float, weighed_read_writes_by_max, PerLiveRangeShape,                      \
    "bb freq - weighed nr of uses that are both read and writes, normalized")  \
  M(float, weighed_indvars_by_max, PerLiveRangeShape,                          \
    "bb freq - weighed nr of uses that are indvars, normalized")               \
  M(float, hint_weights_by_max, PerLiveRangeShape,                             \
    "bb freq - weighed nr of uses that are hints, normalized")                 \
  M(float, start_bb_freq_by_max, PerLiveRangeShape,                            \
    "the freq in the start block, normalized")                                 \
  M(float, end_bb_freq_by_max, PerLiveRangeShape,                              \
    "freq of end block, normalized")                                           \
  M(float, hottest_bb_freq_by_max, PerLiveRangeShape,                          \
    "hottest BB freq, normalized")                                             \
  M(float, liverange_size, PerLiveRangeShape,                                  \
    "size (instr index diff) of the LR")                                       \
  M(float, use_def_density, PerLiveRangeShape,                                 \
    "the max weight, as computed by the manual heuristic")                     \
  M(int64_t, max_stage, PerLiveRangeShape,                                     \
    "largest stage of an interval in this LR")                                 \
  M(int64_t, min_stage, PerLiveRangeShape,                                     \
    "lowest stage of an interval in this LR")                                  \
  M(float, progress, {1}, "ratio of current queue size to initial size")

#ifdef LLVM_HAVE_TFLITE
#define RA_EVICT_FIRST_DEVELOPMENT_FEATURE(M)                                  \
  M(int64_t, instructions, InstructionsShape,                                  \
    "Opcodes of the instructions covered by the eviction problem")

#define RA_EVICT_REST_DEVELOPMENT_FEATURES(M)                                  \
  M(int64_t, instructions_mapping, InstructionsMappingShape,                   \
    "A binary matrix mapping LRs to instruction opcodes")                      \
  M(float, mbb_frequencies, MBBFrequencyShape,                                 \
    "A vector of machine basic block frequencies")                             \
  M(int64_t, mbb_mapping, InstructionsShape,                                   \
    "A vector of indicies mapping instructions to MBBs")
#else
#define RA_EVICT_FIRST_DEVELOPMENT_FEATURE(M)
#define RA_EVICT_REST_DEVELOPMENT_FEATURES(M)
#endif

// The model learns to pick one of the mask == 1 interferences. This is the
// name of the output tensor. The contract with the model is that the output
// will be guaranteed to be to a mask == 1 position. Using a macro here to
// avoid 'not used' warnings (and keep cond compilation to a minimum)
#define DecisionName "index_to_evict"
static const TensorSpec DecisionSpec =
    TensorSpec::createSpec<int64_t>(DecisionName, {1});

// Named features index.
enum FeatureIDs {
#define _FEATURE_IDX_SIMPLE(_, name, __, ___) name
#define _FEATURE_IDX(A, B, C, D) _FEATURE_IDX_SIMPLE(A, B, C, D),
  RA_EVICT_FEATURES_LIST(_FEATURE_IDX) FeatureCount,
#ifdef LLVM_HAVE_TFLITE
  RA_EVICT_FIRST_DEVELOPMENT_FEATURE(_FEATURE_IDX_SIMPLE) = FeatureCount,
#else
  RA_EVICT_FIRST_DEVELOPMENT_FEATURE(_FEATURE_IDX)
#endif // #ifdef LLVM_HAVE_TFLITE
  RA_EVICT_REST_DEVELOPMENT_FEATURES(_FEATURE_IDX) FeaturesWithDevelopmentCount
#undef _FEATURE_IDX
#undef _FEATURE_IDX_SIMPLE
};

// The ML advisor will typically have a sparse input to the evaluator, because
// various phys regs won't be available. It's easier (maintenance-wise) to
// bulk-reset the state of the evaluator each time we are about to use it
// again.
template <typename T> size_t getTotalSize(const std::vector<int64_t> &Shape) {
  size_t Ret = sizeof(T);
  for (const auto V : Shape)
    Ret *= V;
  return Ret;
}

void resetInputs(MLModelRunner &Runner) {
#define _RESET(TYPE, NAME, SHAPE, __)                                          \
  std::memset(Runner.getTensorUntyped(FeatureIDs::NAME), 0,                    \
              getTotalSize<TYPE>(SHAPE));
  RA_EVICT_FEATURES_LIST(_RESET)
  if (EnableDevelopmentFeatures) {
    RA_EVICT_FIRST_DEVELOPMENT_FEATURE(_RESET)
    RA_EVICT_REST_DEVELOPMENT_FEATURES(_RESET)
#undef _RESET
  }
}

// Per-live interval components that get aggregated into the feature values
// that will be passed to the evaluator.
struct LIFeatureComponents {
  double R = 0;
  double W = 0;
  double RW = 0;
  double IndVarUpdates = 0;
  double HintWeights = 0.0;
  int64_t NrDefsAndUses = 0;
  float HottestBlockFreq = 0.0;
  bool IsRemat = false;
};

using CandidateRegList =
    std::array<std::pair<MCRegister, bool>, NumberOfInterferences>;
using FeaturesListNormalizer =
    llvm::SmallVector<float, FeatureIDs::FeatureCount>;

/// The ML evictor (commonalities between release and development mode)
class MLEvictAdvisor : public RegAllocEvictionAdvisor {
public:
  MLEvictAdvisor(const MachineFunction &MF, const RAGreedy &RA,
                 MLModelRunner *Runner, const MachineBlockFrequencyInfo &MBFI,
                 const MachineLoopInfo &Loops);

protected:
  const RegAllocEvictionAdvisor &getDefaultAdvisor() const {
    return static_cast<const RegAllocEvictionAdvisor &>(DefaultAdvisor);
  }

  // The assumption is that if the Runner could not be constructed, we emit-ed
  // error, and we shouldn't be asking for it here.
  const MLModelRunner &getRunner() const { return *Runner; }

  /// This just calls Evaluate on the Runner, but in the development mode
  /// case, if we're just capturing the log of the default advisor, it needs
  /// to call the latter instead, so we need to pass all the necessary
  /// parameters for it. In the development case, it will also log.
  virtual int64_t
  tryFindEvictionCandidatePosition(const LiveInterval &VirtReg,
                                   const AllocationOrder &Order,
                                   unsigned OrderLimit, uint8_t CostPerUseLimit,
                                   const SmallVirtRegSet &FixedRegisters) const;

  /// Load the features of the given VirtReg (allocated or not) at column Pos,
  /// but if  that can't be evicted, return false instead.
  bool
  loadInterferenceFeatures(const LiveInterval &VirtReg, MCRegister PhysReg,
                           bool IsHint, const SmallVirtRegSet &FixedRegisters,
                           llvm::SmallVectorImpl<float> &Largest, size_t Pos,
                           SmallVectorImpl<LRStartEndInfo> &LRPosInfo) const;

private:
  static float getInitialQueueSize(const MachineFunction &MF);

  MCRegister tryFindEvictionCandidate(
      const LiveInterval &VirtReg, const AllocationOrder &Order,
      uint8_t CostPerUseLimit,
      const SmallVirtRegSet &FixedRegisters) const override;

  void extractFeatures(const SmallVectorImpl<const LiveInterval *> &Intervals,
                       llvm::SmallVectorImpl<float> &Largest, size_t Pos,
                       int64_t IsHint, int64_t LocalIntfsCount, float NrUrgent,
                       SmallVectorImpl<LRStartEndInfo> &LRPosInfo) const;

  // Point-in-time: we didn't learn this, so we always delegate to the
  // default.
  bool canEvictHintInterference(
      const LiveInterval &VirtReg, MCRegister PhysReg,
      const SmallVirtRegSet &FixedRegisters) const override {
    return getDefaultAdvisor().canEvictHintInterference(VirtReg, PhysReg,
                                                        FixedRegisters);
  }

  const LIFeatureComponents &
  getLIFeatureComponents(const LiveInterval &LI) const;

  // Hold on to a default advisor for:
  // 1) the implementation of canEvictHintInterference, because we didn't
  // learn that nuance yet; 2) for bootstrapping (logging) in the development
  // mode case.
  const DefaultEvictionAdvisor DefaultAdvisor;
  MLModelRunner *const Runner;
  const MachineBlockFrequencyInfo &MBFI;
  const MachineLoopInfo &Loops;

  // Indices of those features we don't want to normalize.
  // This could be static and shared, but its initialization is non-trivial.
  std::bitset<FeatureIDs::FeatureCount> DoNotNormalize;
  const float InitialQSize;

  using RegID = unsigned;
  mutable DenseMap<RegID, LIFeatureComponents> CachedFeatures;
};

#define _DECL_FEATURES(type, name, shape, _)                                   \
  TensorSpec::createSpec<type>(#name, shape),

// ===================================
// Release (AOT) - specifics
// ===================================
class ReleaseModeEvictionAdvisorAnalysis final
    : public RegAllocEvictionAdvisorAnalysis {
public:
  ReleaseModeEvictionAdvisorAnalysis()
      : RegAllocEvictionAdvisorAnalysis(AdvisorMode::Release) {
    if (EnableDevelopmentFeatures) {
      InputFeatures = {RA_EVICT_FEATURES_LIST(
          _DECL_FEATURES) RA_EVICT_FIRST_DEVELOPMENT_FEATURE(_DECL_FEATURES)
                           RA_EVICT_REST_DEVELOPMENT_FEATURES(_DECL_FEATURES)};
    } else {
      InputFeatures = {RA_EVICT_FEATURES_LIST(_DECL_FEATURES)};
    }
  }
  // support for isa<> and dyn_cast.
  static bool classof(const RegAllocEvictionAdvisorAnalysis *R) {
    return R->getAdvisorMode() == AdvisorMode::Release;
  }

private:
  std::vector<TensorSpec> InputFeatures;

  void getAnalysisUsage(AnalysisUsage &AU) const override {
    AU.addRequired<MachineBlockFrequencyInfo>();
    AU.addRequired<MachineLoopInfo>();
    RegAllocEvictionAdvisorAnalysis::getAnalysisUsage(AU);
  }

  std::unique_ptr<RegAllocEvictionAdvisor>
  getAdvisor(const MachineFunction &MF, const RAGreedy &RA) override {
    if (!Runner) {
      if (InteractiveChannelBaseName.empty())
        Runner = std::make_unique<ReleaseModeModelRunner<CompiledModelType>>(
            MF.getFunction().getContext(), InputFeatures, DecisionName);
      else
        Runner = std::make_unique<InteractiveModelRunner>(
            MF.getFunction().getContext(), InputFeatures, DecisionSpec,
            InteractiveChannelBaseName + ".out",
            InteractiveChannelBaseName + ".in");
    }
    return std::make_unique<MLEvictAdvisor>(
        MF, RA, Runner.get(), getAnalysis<MachineBlockFrequencyInfo>(),
        getAnalysis<MachineLoopInfo>());
  }
  std::unique_ptr<MLModelRunner> Runner;
};

// ===================================
// Development mode-specifics
// ===================================
//
// Features we log
#ifdef LLVM_HAVE_TFLITE
static const TensorSpec Reward = TensorSpec::createSpec<float>("reward", {1});

// Features we bind on the model. The tensor names have a prefix, and we also
// need to include some tensors that are expected to be present by the
// training algo.
// TODO: can we just get rid of these?
#define _DECL_TRAIN_FEATURES(type, name, shape, _)                             \
  TensorSpec::createSpec<type>(std::string("action_") + #name, shape),

class DevelopmentModeEvictAdvisor : public MLEvictAdvisor {
public:
  DevelopmentModeEvictAdvisor(const MachineFunction &MF, const RAGreedy &RA,
                              MLModelRunner *Runner,
                              const MachineBlockFrequencyInfo &MBFI,
                              const MachineLoopInfo &Loops, Logger *Log)
      : MLEvictAdvisor(MF, RA, Runner, MBFI, Loops), Log(Log) {}

private:
  int64_t tryFindEvictionCandidatePosition(
      const LiveInterval &VirtReg, const AllocationOrder &Order,
      unsigned OrderLimit, uint8_t CostPerUseLimit,
      const SmallVirtRegSet &FixedRegisters) const override;

  Logger *const Log;
};

class DevelopmentModeEvictionAdvisorAnalysis final
    : public RegAllocEvictionAdvisorAnalysis {
public:
  DevelopmentModeEvictionAdvisorAnalysis()
      : RegAllocEvictionAdvisorAnalysis(AdvisorMode::Development) {
    if (EnableDevelopmentFeatures) {
      InputFeatures = {RA_EVICT_FEATURES_LIST(
          _DECL_FEATURES) RA_EVICT_FIRST_DEVELOPMENT_FEATURE(_DECL_FEATURES)
                           RA_EVICT_REST_DEVELOPMENT_FEATURES(_DECL_FEATURES)};
      TrainingInputFeatures = {
          RA_EVICT_FEATURES_LIST(_DECL_TRAIN_FEATURES)
              RA_EVICT_FIRST_DEVELOPMENT_FEATURE(_DECL_TRAIN_FEATURES)
                  RA_EVICT_REST_DEVELOPMENT_FEATURES(_DECL_TRAIN_FEATURES)
                      TensorSpec::createSpec<float>("action_discount", {1}),
          TensorSpec::createSpec<int32_t>("action_step_type", {1}),
          TensorSpec::createSpec<float>("action_reward", {1})};
    } else {
      InputFeatures = {RA_EVICT_FEATURES_LIST(_DECL_FEATURES)};
      TrainingInputFeatures = {
          RA_EVICT_FEATURES_LIST(_DECL_TRAIN_FEATURES)
              TensorSpec::createSpec<float>("action_discount", {1}),
          TensorSpec::createSpec<int32_t>("action_step_type", {1}),
          TensorSpec::createSpec<float>("action_reward", {1})};
    }
  }
  // support for isa<> and dyn_cast.
  static bool classof(const RegAllocEvictionAdvisorAnalysis *R) {
    return R->getAdvisorMode() == AdvisorMode::Development;
  }

  void logRewardIfNeeded(const MachineFunction &MF,
                         llvm::function_ref<float()> GetReward) override {
    if (!Log || !Log->hasAnyObservationForContext(MF.getName()))
      return;
    // The function pass manager would run all the function passes for a
    // function, so we assume the last context belongs to this function. If
    // this invariant ever changes, we can implement at that time switching
    // contexts. At this point, it'd be an error
    if (Log->currentContext() != MF.getName()) {
      MF.getFunction().getContext().emitError(
          "The training log context shouldn't have had changed.");
    }
    if (Log->hasObservationInProgress())
      Log->logReward<float>(GetReward());
  }

private:
  std::vector<TensorSpec> InputFeatures;
  std::vector<TensorSpec> TrainingInputFeatures;

  void getAnalysisUsage(AnalysisUsage &AU) const override {
    AU.addRequired<MachineBlockFrequencyInfo>();
    AU.addRequired<MachineLoopInfo>();
    RegAllocEvictionAdvisorAnalysis::getAnalysisUsage(AU);
  }

  bool doInitialization(Module &M) override {
    LLVMContext &Ctx = M.getContext();
    if (ModelUnderTraining.empty() && TrainingLog.empty()) {
      Ctx.emitError("Regalloc development mode should be requested with at "
                    "least logging enabled and/or a training model");
      return false;
    }
    if (ModelUnderTraining.empty())
      Runner = std::make_unique<NoInferenceModelRunner>(Ctx, InputFeatures);
    else
      Runner = ModelUnderTrainingRunner::createAndEnsureValid(
          Ctx, ModelUnderTraining, DecisionName, TrainingInputFeatures);
    if (!Runner) {
      Ctx.emitError("Regalloc: could not set up the model runner");
      return false;
    }
    if (TrainingLog.empty())
      return false;
    std::error_code EC;
    auto OS = std::make_unique<raw_fd_ostream>(TrainingLog, EC);
    if (EC) {
      M.getContext().emitError(EC.message() + ":" + TrainingLog);
      return false;
    }
    std::vector<TensorSpec> LFS = InputFeatures;
    if (auto *MUTR = dyn_cast<ModelUnderTrainingRunner>(Runner.get()))
      append_range(LFS, MUTR->extraOutputsForLoggingSpecs());
    // We always log the output; in particular, if we're not evaluating, we
    // don't have an output spec json file. That's why we handle the
    // 'normal' output separately.
    LFS.push_back(DecisionSpec);

    Log = std::make_unique<Logger>(std::move(OS), LFS, Reward,
                                   /*IncludeReward*/ true);
    return false;
  }

  std::unique_ptr<RegAllocEvictionAdvisor>
  getAdvisor(const MachineFunction &MF, const RAGreedy &RA) override {
    if (!Runner)
      return nullptr;
    if (Log)
      Log->switchContext(MF.getName());
    return std::make_unique<DevelopmentModeEvictAdvisor>(
        MF, RA, Runner.get(), getAnalysis<MachineBlockFrequencyInfo>(),
        getAnalysis<MachineLoopInfo>(), Log.get());
  }

  std::unique_ptr<MLModelRunner> Runner;
  std::unique_ptr<Logger> Log;
};

#endif //#ifdef LLVM_HAVE_TFLITE
} // namespace

float MLEvictAdvisor::getInitialQueueSize(const MachineFunction &MF) {
  auto &MRI = MF.getRegInfo();
  float Ret = 0.0;
  for (unsigned I = 0, E = MRI.getNumVirtRegs(); I != E; ++I) {
    Register Reg = Register::index2VirtReg(I);
    if (MRI.reg_nodbg_empty(Reg))
      continue;
    ++Ret;
  }
  return Ret;
}

MLEvictAdvisor::MLEvictAdvisor(const MachineFunction &MF, const RAGreedy &RA,
                               MLModelRunner *Runner,
                               const MachineBlockFrequencyInfo &MBFI,
                               const MachineLoopInfo &Loops)
    : RegAllocEvictionAdvisor(MF, RA), DefaultAdvisor(MF, RA),
      Runner(std::move(Runner)), MBFI(MBFI), Loops(Loops),
      InitialQSize(MLEvictAdvisor::getInitialQueueSize(MF)) {
  assert(this->Runner);
  Runner->switchContext(MF.getName());
  DoNotNormalize.set(FeatureIDs::mask);
  DoNotNormalize.set(FeatureIDs::is_free);
  DoNotNormalize.set(FeatureIDs::is_hint);
  DoNotNormalize.set(FeatureIDs::is_local);
  DoNotNormalize.set(FeatureIDs::min_stage);
  DoNotNormalize.set(FeatureIDs::max_stage);
  DoNotNormalize.set(FeatureIDs::progress);
}

int64_t MLEvictAdvisor::tryFindEvictionCandidatePosition(
    const LiveInterval &, const AllocationOrder &, unsigned, uint8_t,
    const SmallVirtRegSet &) const {
  int64_t Ret = Runner->evaluate<int64_t>();
  assert(Ret >= 0);
  assert(Ret <= CandidateVirtRegPos);
  return Ret;
}

bool MLEvictAdvisor::loadInterferenceFeatures(
    const LiveInterval &VirtReg, MCRegister PhysReg, bool IsHint,
    const SmallVirtRegSet &FixedRegisters,
    llvm::SmallVectorImpl<float> &Largest, size_t Pos,
    llvm::SmallVectorImpl<LRStartEndInfo> &LRPosInfo) const {
  // It is only possible to evict virtual register interference.
  if (Matrix->checkInterference(VirtReg, PhysReg) > LiveRegMatrix::IK_VirtReg) {
    // leave unavailable
    return false;
  }

  const bool IsLocal = LIS->intervalIsInOneMBB(VirtReg);
  int64_t LocalIntfs = 0;
  float NrUrgent = 0.0f;

  // The cascade tracking is the same as in the default advisor
  unsigned Cascade = RA.getExtraInfo().getCascadeOrCurrentNext(VirtReg.reg());

  SmallVector<const LiveInterval *, MaxInterferences> InterferingIntervals;
  for (MCRegUnit Unit : TRI->regunits(PhysReg)) {
    LiveIntervalUnion::Query &Q = Matrix->query(VirtReg, Unit);
    // Different from the default heuristic, we don't make any assumptions
    // about what having more than 10 results in the query may mean.
    const auto &IFIntervals = Q.interferingVRegs(EvictInterferenceCutoff);
    if (IFIntervals.empty() && InterferingIntervals.empty())
      continue;
    if (IFIntervals.size() >= EvictInterferenceCutoff)
      return false;
    InterferingIntervals.append(IFIntervals.begin(), IFIntervals.end());
    for (const LiveInterval *Intf : reverse(IFIntervals)) {
      assert(Intf->reg().isVirtual() &&
             "Only expecting virtual register interference from query");
      // This is the same set of legality checks as in the default case: don't
      // try to evict fixed regs or 'done' ones. Also don't break cascades,
      // except in the urgent case, with the same nuances used in the default
      // heuristic.
      // We could try sharing this between the advisors, but it may end up
      // more complex than it is right now.
      if (FixedRegisters.count(Intf->reg()))
        return false;
      if (RA.getExtraInfo().getStage(*Intf) == RS_Done)
        return false;
      bool Urgent =
          !VirtReg.isSpillable() &&
          (Intf->isSpillable() ||
           RegClassInfo.getNumAllocatableRegs(MRI->getRegClass(VirtReg.reg())) <
               RegClassInfo.getNumAllocatableRegs(
                   MRI->getRegClass(Intf->reg())));
      // Only evict older cascades or live ranges without a cascade.
      unsigned IntfCascade = RA.getExtraInfo().getCascade(Intf->reg());
      if (Cascade <= IntfCascade) {
        if (!Urgent)
          return false;
        ++NrUrgent;
      }

      LocalIntfs += (IsLocal && LIS->intervalIsInOneMBB(*Intf) &&
                     (!EnableLocalReassign || !canReassign(*Intf, PhysReg)));
    }
  }
  // OK, so if we made it this far, this LR is an eviction candidate, load its
  // features.
  extractFeatures(InterferingIntervals, Largest, Pos, IsHint, LocalIntfs,
                  NrUrgent, LRPosInfo);
  return true;
}

MCRegister MLEvictAdvisor::tryFindEvictionCandidate(
    const LiveInterval &VirtReg, const AllocationOrder &Order,
    uint8_t CostPerUseLimit, const SmallVirtRegSet &FixedRegisters) const {
  auto MaybeOrderLimit = getOrderLimit(VirtReg, Order, CostPerUseLimit);
  if (!MaybeOrderLimit)
    return MCRegister::NoRegister;
  unsigned OrderLimit = *MaybeOrderLimit;

  // The heuristic sets initial costs such as, if CostPerUseLimit is
  // max<uint8_t>, then any of the costs of the legally-evictable intervals
  // would be lower. When that happens, one of those will be selected.
  // Therefore, we allow the candidate be selected, unless the candidate is
  // unspillable, in which case it would be incorrect to not find a register
  // for it.
  const bool MustFindEviction =
      (!VirtReg.isSpillable() && CostPerUseLimit == static_cast<uint8_t>(~0u));
  // Number of available candidates - if 0, no need to continue.
  size_t Available = 0;
  // Make sure we don't have leftover partial state from an attempt where we
  // had no available candidates and bailed out early.
  resetInputs(*Runner);

  // Track the index->register mapping because AllocationOrder doesn't do that
  // and we'd have to scan it.
  // Also track their mask, to write asserts/debug.
  CandidateRegList Regs;
  Regs.fill({0, false});

  // Track the largest value of features seen during this eviction session. We
  // only normalize (some of) the float features, but it's just simpler to
  // dimension 'Largest' to all the features, especially since we have the
  // 'DoNotNormalize' list.
  FeaturesListNormalizer Largest(FeatureIDs::FeatureCount, 0.0);

  // Same overal idea as in the default eviction policy - we visit the values
  // of AllocationOrder one at a time. If it's not legally available, we mask
  // off the corresponding feature column (==do nothing because we already
  // reset all the features to 0) Use Pos to capture the column we load
  // features at - in AllocationOrder order.
  size_t Pos = 0;
  SmallVector<LRStartEndInfo, NumberOfInterferences> LRPosInfo;
  for (auto I = Order.begin(), E = Order.getOrderLimitEnd(OrderLimit); I != E;
       ++I, ++Pos) {
    MCRegister PhysReg = *I;
    assert(!Regs[Pos].second);
    assert(PhysReg);
    if (!canAllocatePhysReg(CostPerUseLimit, PhysReg)) {
      continue;
    }
    if (loadInterferenceFeatures(VirtReg, PhysReg, I.isHint(), FixedRegisters,
                                 Largest, Pos, LRPosInfo)) {
      ++Available;
      Regs[Pos] = std::make_pair(PhysReg, true);
    }
  }
  if (Available == 0) {
    // Nothing to decide, nothing to learn.
    assert(!MustFindEviction);
    return MCRegister::NoRegister;
  }
  const size_t ValidPosLimit = Pos;
  // If we must find eviction, the candidate should be masked out of the
  // decision making process.
  Regs[CandidateVirtRegPos].second = !MustFindEviction;
  if (!MustFindEviction)
    extractFeatures(SmallVector<const LiveInterval *, 1>(1, &VirtReg), Largest,
                    CandidateVirtRegPos, /*IsHint*/ 0,
                    /*LocalIntfsCount*/ 0,
                    /*NrUrgent*/ 0.0, LRPosInfo);
  assert(InitialQSize > 0.0 && "We couldn't have gotten here if we had "
                               "nothing to allocate initially.");
#ifdef LLVM_HAVE_TFLITE
  if (EnableDevelopmentFeatures) {
    extractInstructionFeatures(
        LRPosInfo, Runner,
        [this](SlotIndex InputIndex) -> int {
          auto *CurrentMachineInstruction =
              LIS->getInstructionFromIndex(InputIndex);
          if (!CurrentMachineInstruction) {
            return -1;
          }
          return CurrentMachineInstruction->getOpcode();
        },
        [this](SlotIndex InputIndex) -> float {
          auto *CurrentMachineInstruction =
              LIS->getInstructionFromIndex(InputIndex);
          return MBFI.getBlockFreqRelativeToEntryBlock(
              CurrentMachineInstruction->getParent());
        },
        [this](SlotIndex InputIndex) -> MachineBasicBlock * {
          auto *CurrentMachineInstruction =
              LIS->getInstructionFromIndex(InputIndex);
          return CurrentMachineInstruction->getParent();
        },
        FeatureIDs::instructions, FeatureIDs::instructions_mapping,
        FeatureIDs::mbb_frequencies, FeatureIDs::mbb_mapping,
        LIS->getSlotIndexes()->getLastIndex());
  }
#endif // #ifdef LLVM_HAVE_TFLITE
  // Normalize the features.
  for (auto &V : Largest)
    V = V ? V : 1.0;
  for (size_t FeatureIndex = 0; FeatureIndex < FeatureIDs::FeatureCount;
       ++FeatureIndex) {
    if (DoNotNormalize.test(FeatureIndex))
      continue;
    for (size_t Pos = 0; Pos < NumberOfInterferences; ++Pos) {
      Runner->getTensor<float>(FeatureIndex)[Pos] /= Largest[FeatureIndex];
    }
  }
  *Runner->getTensor<float>(FeatureIDs::progress) =
      static_cast<float>(RA.getQueueSize()) / InitialQSize;

  // Get a decision.
  size_t CandidatePos = tryFindEvictionCandidatePosition(
      VirtReg, Order, OrderLimit, CostPerUseLimit, FixedRegisters);
  // The contract with the ML side is that CandidatePos is mask == 1 (i.e.
  // Regs[CandidatePos].second)
  assert(Regs[CandidatePos].second);
  if (CandidatePos == CandidateVirtRegPos) {
    assert(!MustFindEviction);
    return MCRegister::NoRegister;
  }
  assert(CandidatePos < ValidPosLimit);
  (void)ValidPosLimit;
  return Regs[CandidatePos].first;
}

const LIFeatureComponents &
MLEvictAdvisor::getLIFeatureComponents(const LiveInterval &LI) const {
  RegID ID = LI.reg().id();
  LIFeatureComponents Empty;
  auto I = CachedFeatures.insert(std::make_pair(ID, Empty));
  LIFeatureComponents &Ret = I.first->getSecond();
  if (!I.second)
    return Ret;

  SmallPtrSet<MachineInstr *, 8> Visited;
  const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();

  for (MachineRegisterInfo::reg_instr_nodbg_iterator
           I = MRI->reg_instr_nodbg_begin(LI.reg()),
           E = MRI->reg_instr_nodbg_end();
       I != E;) {
    MachineInstr *MI = &*(I++);

    ++Ret.NrDefsAndUses;
    if (!Visited.insert(MI).second)
      continue;

    if (MI->isIdentityCopy() || MI->isImplicitDef())
      continue;

    bool Reads, Writes;
    std::tie(Reads, Writes) = MI->readsWritesVirtualRegister(LI.reg());

    float Freq = MBFI.getBlockFreqRelativeToEntryBlock(MI->getParent());
    Ret.HottestBlockFreq = std::max(Freq, Ret.HottestBlockFreq);

    Ret.R += (Reads && !Writes) * Freq;
    Ret.W += (!Reads && Writes) * Freq;
    Ret.RW += (Reads && Writes) * Freq;

    auto *MBB = MI->getParent();
    auto *Loop = Loops.getLoopFor(MBB);
    bool IsExiting = Loop ? Loop->isLoopExiting(MBB) : false;

    if (Writes && IsExiting && LIS->isLiveOutOfMBB(LI, MBB))
      Ret.IndVarUpdates += Freq;

    if (MI->isCopy() && VirtRegAuxInfo::copyHint(MI, LI.reg(), TRI, *MRI))
      Ret.HintWeights += Freq;
  }
  Ret.IsRemat = VirtRegAuxInfo::isRematerializable(
      LI, *LIS, *VRM, *MF.getSubtarget().getInstrInfo());
  return Ret;
}

// Overall, this currently mimics what we do for weight calculation, but instead
// of accummulating the various features, we keep them separate.
void MLEvictAdvisor::extractFeatures(
    const SmallVectorImpl<const LiveInterval *> &Intervals,
    llvm::SmallVectorImpl<float> &Largest, size_t Pos, int64_t IsHint,
    int64_t LocalIntfsCount, float NrUrgent,
    SmallVectorImpl<LRStartEndInfo> &LRPosInfo) const {
  int64_t NrDefsAndUses = 0;
  int64_t NrBrokenHints = 0;
  double R = 0.0;
  double W = 0.0;
  double RW = 0.0;
  double IndVarUpdates = 0.0;
  double HintWeights = 0.0;
  float StartBBFreq = 0.0;
  float EndBBFreq = 0.0;
  float HottestBlockFreq = 0.0;
  int32_t NrRematerializable = 0;
  float TotalWeight = 0.0;

  SlotIndex EndSI = LIS->getSlotIndexes()->getZeroIndex();
  SlotIndex StartSI = LIS->getSlotIndexes()->getLastIndex();
  int64_t MaxStage = 0;
  int64_t MinStage =
      Intervals.empty() ? 0 : std::numeric_limits<int64_t>::max();

  for (const auto *L : Intervals) {
    const LiveInterval &LI = *L;
    MaxStage = std::max<int64_t>(
        MaxStage, static_cast<int64_t>(RA.getExtraInfo().getStage(LI)));
    MinStage = std::min<int64_t>(
        MinStage, static_cast<int64_t>(RA.getExtraInfo().getStage(LI)));

    TotalWeight = std::max(TotalWeight, LI.weight());

    if (LI.beginIndex() < StartSI)
      StartSI = LI.beginIndex();

    if (LI.endIndex() > EndSI)
      EndSI = LI.endIndex();
    const LIFeatureComponents &LIFC = getLIFeatureComponents(LI);
    NrBrokenHints += VRM->hasPreferredPhys(LI.reg());

    NrDefsAndUses += LIFC.NrDefsAndUses;
    HottestBlockFreq = std::max(HottestBlockFreq, LIFC.HottestBlockFreq);
    R += LIFC.R;
    W += LIFC.W;
    RW += LIFC.RW;

    IndVarUpdates += LIFC.IndVarUpdates;

    HintWeights += LIFC.HintWeights;
    NrRematerializable += LIFC.IsRemat;

    if (EnableDevelopmentFeatures) {
      for (auto CurrentSegment : LI) {
        LRPosInfo.push_back(
            LRStartEndInfo{CurrentSegment.start, CurrentSegment.end, Pos});
      }
    }
  }
  size_t Size = 0;
  if (!Intervals.empty()) {
    StartBBFreq =
        MBFI.getBlockFreqRelativeToEntryBlock(LIS->getMBBFromIndex(StartSI));
    if (EndSI >= LIS->getSlotIndexes()->getLastIndex())
      EndSI = LIS->getSlotIndexes()->getLastIndex().getPrevIndex();
    EndBBFreq =
        MBFI.getBlockFreqRelativeToEntryBlock(LIS->getMBBFromIndex(EndSI));
    Size = StartSI.distance(EndSI);
  }
  // Set the features at the column 'Pos'.
#define SET(ID, TYPE, VAL)                                                     \
  do {                                                                         \
    Runner->getTensor<TYPE>(FeatureIDs::ID)[Pos] = static_cast<TYPE>(VAL);     \
    if (!DoNotNormalize.test(FeatureIDs::ID))                                  \
      Largest[FeatureIDs::ID] =                                                \
          std::max(Largest[FeatureIDs::ID], static_cast<float>(VAL));          \
  } while (false)
  SET(mask, int64_t, 1);
  SET(is_free, int64_t, Intervals.empty());
  SET(nr_urgent, float, NrUrgent);
  SET(nr_broken_hints, float, NrBrokenHints);
  SET(is_hint, int64_t, IsHint);
  SET(is_local, int64_t, LocalIntfsCount);
  SET(nr_rematerializable, float, NrRematerializable);
  SET(nr_defs_and_uses, float, NrDefsAndUses);
  SET(weighed_reads_by_max, float, R);
  SET(weighed_writes_by_max, float, W);
  SET(weighed_read_writes_by_max, float, RW);
  SET(weighed_indvars_by_max, float, IndVarUpdates);
  SET(hint_weights_by_max, float, HintWeights);
  SET(start_bb_freq_by_max, float, StartBBFreq);
  SET(end_bb_freq_by_max, float, EndBBFreq);
  SET(hottest_bb_freq_by_max, float, HottestBlockFreq);
  SET(liverange_size, float, Size);
  SET(use_def_density, float, TotalWeight);
  SET(max_stage, int64_t, MaxStage);
  SET(min_stage, int64_t, MinStage);
#undef SET
}

void extractInstructionFeatures(
    SmallVectorImpl<LRStartEndInfo> &LRPosInfo, MLModelRunner *RegallocRunner,
    function_ref<int(SlotIndex)> GetOpcode,
    function_ref<float(SlotIndex)> GetMBBFreq,
    function_ref<MachineBasicBlock *(SlotIndex)> GetMBBReference,
    const int InstructionsIndex, const int InstructionsMappingIndex,
    const int MBBFreqIndex, const int MBBMappingIndex,
    const SlotIndex LastIndex) {
  // This function extracts instruction based features relevant to the eviction
  // problem currently being solved. This function ends up extracting two
  // tensors.
  // 1 - A vector of size max instruction count. It contains the opcodes of the
  // instructions spanned by all the intervals in the current instance of the
  // eviction problem.
  // 2 - A binary mapping matrix of size (LR count * max
  // instruction count) which maps where the LRs are live to the actual opcodes
  // for which they are live.
  // 3 - A vector of size max supported MBB count storing MBB frequencies,
  // encompassing all of the MBBs covered by the eviction problem.
  // 4 - A vector of size max instruction count of indices to members of the MBB
  // frequency vector, mapping each instruction to its associated MBB.

  // Start off by sorting the segments based on the beginning slot index.
  std::sort(
      LRPosInfo.begin(), LRPosInfo.end(),
      [](LRStartEndInfo A, LRStartEndInfo B) { return A.Begin < B.Begin; });
  size_t InstructionIndex = 0;
  size_t CurrentSegmentIndex = 0;
  SlotIndex CurrentIndex = LRPosInfo[0].Begin;
  std::map<MachineBasicBlock *, size_t> VisitedMBBs;
  size_t CurrentMBBIndex = 0;
  // This loop processes all the segments sequentially by starting at the
  // beginning slot index of the first segment, iterating through all the slot
  // indices before the end slot index of that segment (while checking for
  // overlaps with segments that start at greater slot indices). After hitting
  // that end index, the current segment being processed gets bumped until they
  // are all processed or the max instruction count is hit, where everything is
  // just truncated.
  while (true) {
    // If the index that we are currently at is within the current segment and
    // we haven't hit the max instruction count, continue processing the current
    // segment.
    while (CurrentIndex <= LRPosInfo[CurrentSegmentIndex].End &&
           InstructionIndex < ModelMaxSupportedInstructionCount) {
      int CurrentOpcode = GetOpcode(CurrentIndex);
      // If the current machine instruction is null, skip it
      if (CurrentOpcode == -1) {
        // If we're currently at the last index in the SlotIndex analysis,
        // we can't go any further, so return from the function
        if (CurrentIndex >= LastIndex) {
          return;
        }
        CurrentIndex = CurrentIndex.getNextIndex();
        continue;
      }
      MachineBasicBlock *CurrentMBBReference = GetMBBReference(CurrentIndex);
      if (VisitedMBBs.count(CurrentMBBReference) == 0) {
        VisitedMBBs[CurrentMBBReference] = CurrentMBBIndex;
        ++CurrentMBBIndex;
      }
      extractMBBFrequency(CurrentIndex, InstructionIndex, VisitedMBBs,
                          GetMBBFreq, CurrentMBBReference, RegallocRunner,
                          MBBFreqIndex, MBBMappingIndex);
      // Current code assumes we're not going to get any disjointed segments
      assert(LRPosInfo[CurrentSegmentIndex].Begin <= CurrentIndex);
      RegallocRunner->getTensor<int64_t>(InstructionsIndex)[InstructionIndex] =
          CurrentOpcode < OpcodeValueCutoff ? CurrentOpcode : 0;
      // set value in the binary mapping matrix for the current instruction
      auto CurrentSegmentPosition = LRPosInfo[CurrentSegmentIndex].Pos;
      RegallocRunner->getTensor<int64_t>(
          InstructionsMappingIndex)[CurrentSegmentPosition *
                                        ModelMaxSupportedInstructionCount +
                                    InstructionIndex] = 1;
      // All of the segments are sorted based on the beginning slot index, but
      // this doesn't mean that the beginning slot index of the next segment is
      // after the end segment of the one being currently processed. This while
      // loop checks for overlapping segments and modifies the portion of the
      // column in the mapping matrix for the currently processed instruction
      // for the LR it is checking. Also make sure that the beginning of the
      // current segment we're checking for overlap in is less than the current
      // index, otherwise we're done checking overlaps.
      size_t OverlapCheckCurrentSegment = CurrentSegmentIndex + 1;
      while (OverlapCheckCurrentSegment < LRPosInfo.size() &&
             LRPosInfo[OverlapCheckCurrentSegment].Begin <= CurrentIndex) {
        auto OverlapCurrentSegmentPosition =
            LRPosInfo[OverlapCheckCurrentSegment].Pos;
        if (LRPosInfo[OverlapCheckCurrentSegment].End >= CurrentIndex) {
          RegallocRunner->getTensor<int64_t>(
              InstructionsMappingIndex)[OverlapCurrentSegmentPosition *
                                            ModelMaxSupportedInstructionCount +
                                        InstructionIndex] = 1;
        }
        ++OverlapCheckCurrentSegment;
      }
      ++InstructionIndex;
      if (CurrentIndex >= LastIndex) {
        return;
      }
      CurrentIndex = CurrentIndex.getNextIndex();
    }
    // if we've just finished processing through the last segment or if we've
    // hit the maximum number of instructions, break out of the loop.
    if (CurrentSegmentIndex == LRPosInfo.size() - 1 ||
        InstructionIndex >= ModelMaxSupportedInstructionCount) {
      break;
    }
    // If the segments are not overlapping, we need to move to the beginning
    // index of the next segment to avoid having instructions not attached to
    // any register.
    if (LRPosInfo[CurrentSegmentIndex + 1].Begin >
        LRPosInfo[CurrentSegmentIndex].End) {
      CurrentIndex = LRPosInfo[CurrentSegmentIndex + 1].Begin;
    }
    ++CurrentSegmentIndex;
  }
}

void extractMBBFrequency(const SlotIndex CurrentIndex,
                         const size_t CurrentInstructionIndex,
                         std::map<MachineBasicBlock *, size_t> &VisitedMBBs,
                         function_ref<float(SlotIndex)> GetMBBFreq,
                         MachineBasicBlock *CurrentMBBReference,
                         MLModelRunner *RegallocRunner, const int MBBFreqIndex,
                         const int MBBMappingIndex) {
  size_t CurrentMBBIndex = VisitedMBBs[CurrentMBBReference];
  float CurrentMBBFreq = GetMBBFreq(CurrentIndex);
  if (CurrentMBBIndex < ModelMaxSupportedMBBCount) {
    RegallocRunner->getTensor<float>(MBBFreqIndex)[CurrentMBBIndex] =
        CurrentMBBFreq;
    RegallocRunner->getTensor<int64_t>(
        MBBMappingIndex)[CurrentInstructionIndex] = CurrentMBBIndex;
  }
}

// Development mode-specific implementations
#ifdef LLVM_HAVE_TFLITE

RegAllocEvictionAdvisorAnalysis *llvm::createDevelopmentModeAdvisor() {
  return new DevelopmentModeEvictionAdvisorAnalysis();
}

int64_t DevelopmentModeEvictAdvisor::tryFindEvictionCandidatePosition(
    const LiveInterval &VirtReg, const AllocationOrder &Order,
    unsigned OrderLimit, uint8_t CostPerUseLimit,
    const SmallVirtRegSet &FixedRegisters) const {
  int64_t Ret = 0;
  if (isa<ModelUnderTrainingRunner>(getRunner())) {
    Ret = MLEvictAdvisor::tryFindEvictionCandidatePosition(
        VirtReg, Order, OrderLimit, CostPerUseLimit, FixedRegisters);
  } else {
    MCRegister PhysReg = getDefaultAdvisor().tryFindEvictionCandidate(
        VirtReg, Order, CostPerUseLimit, FixedRegisters);
    // Find the index of the selected PhysReg. We need it for logging,
    // otherwise this is wasted cycles (but so would starting development mode
    // without a model nor logging)
    if (!PhysReg)
      Ret = CandidateVirtRegPos;
    else
      for (auto I = Order.begin(), E = Order.getOrderLimitEnd(OrderLimit);
           I != E; ++I, ++Ret)
        if (*I == PhysReg)
          break;
  }
  if (TrainingLog.empty())
    return Ret;
  // TODO(mtrofin): when we support optional rewards, this can go away. In the
  // meantime, we log the "pretend" reward (0) for the previous observation
  // before starting a new one.
  if (Log->hasObservationInProgress())
    Log->logReward<float>(0.0);

  Log->startObservation();
  size_t CurrentFeature = 0;
  size_t FeatureCount = EnableDevelopmentFeatures
                            ? FeatureIDs::FeaturesWithDevelopmentCount
                            : FeatureIDs::FeatureCount;
  for (; CurrentFeature < FeatureCount; ++CurrentFeature) {
    Log->logTensorValue(CurrentFeature,
                        reinterpret_cast<const char *>(
                            getRunner().getTensorUntyped(CurrentFeature)));
  }
  if (auto *MUTR = dyn_cast<ModelUnderTrainingRunner>(&getRunner()))
    for (size_t I = 0; I < MUTR->extraOutputsForLoggingSpecs().size();
         ++I, ++CurrentFeature)
      Log->logTensorValue(
          CurrentFeature,
          reinterpret_cast<const char *>(MUTR->getUntypedExtraOutputValue(I)));
  // The output is right after the features and the extra outputs
  Log->logTensorValue(CurrentFeature, reinterpret_cast<const char *>(&Ret));
  Log->endObservation();
  return Ret;
}

bool RegAllocScoring::runOnMachineFunction(MachineFunction &MF) {
  std::optional<float> CachedReward;
  auto GetReward = [&]() {
    if (!CachedReward)
      CachedReward = static_cast<float>(
          calculateRegAllocScore(MF, getAnalysis<MachineBlockFrequencyInfo>())
              .getScore());
    return *CachedReward;
  };

  getAnalysis<RegAllocEvictionAdvisorAnalysis>().logRewardIfNeeded(MF,
                                                                   GetReward);
  getAnalysis<RegAllocPriorityAdvisorAnalysis>().logRewardIfNeeded(MF,
                                                                   GetReward);
  return false;
}
#endif // #ifdef LLVM_HAVE_TFLITE

RegAllocEvictionAdvisorAnalysis *llvm::createReleaseModeAdvisor() {
  return llvm::isEmbeddedModelEvaluatorValid<CompiledModelType>() ||
                 !InteractiveChannelBaseName.empty()
             ? new ReleaseModeEvictionAdvisorAnalysis()
             : nullptr;
}

// In all cases except development mode, we don't need scoring.
#if !defined(LLVM_HAVE_TFLITE)
bool RegAllocScoring::runOnMachineFunction(MachineFunction &) { return false; }
#endif