// Copyright (c) 2017 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "stats_analyzer.h"

#include <algorithm>
#include <cassert>
#include <cstring>
#include <iostream>
#include <sstream>
#include <unordered_map>
#include <unordered_set>
#include <vector>

#include "spirv/1.2/spirv.h"
#include "source/enum_string_mapping.h"
#include "source/comp/markv_model.h"
#include "source/opcode.h"
#include "source/operand.h"
#include "source/spirv_constant.h"
#include "source/util/huffman_codec.h"

using libspirv::SpirvStats;
using spvutils::HuffmanCodec;

namespace {

// Signals that the value is not in the coding scheme and a fallback method
// needs to be used.
const uint64_t kMarkvNoneOfTheAbove =
    spvtools::MarkvModel::GetMarkvNoneOfTheAbove();

inline uint32_t CombineOpcodeAndNumOperands(uint32_t opcode,
                                            uint32_t num_operands) {
  return opcode | (num_operands << 16);
}

// Returns all SPIR-V v1.2 opcodes.
std::vector<uint32_t> GetAllOpcodes() {
  return std::vector<uint32_t>({
    SpvOpNop,
    SpvOpUndef,
    SpvOpSourceContinued,
    SpvOpSource,
    SpvOpSourceExtension,
    SpvOpName,
    SpvOpMemberName,
    SpvOpString,
    SpvOpLine,
    SpvOpExtension,
    SpvOpExtInstImport,
    SpvOpExtInst,
    SpvOpMemoryModel,
    SpvOpEntryPoint,
    SpvOpExecutionMode,
    SpvOpCapability,
    SpvOpTypeVoid,
    SpvOpTypeBool,
    SpvOpTypeInt,
    SpvOpTypeFloat,
    SpvOpTypeVector,
    SpvOpTypeMatrix,
    SpvOpTypeImage,
    SpvOpTypeSampler,
    SpvOpTypeSampledImage,
    SpvOpTypeArray,
    SpvOpTypeRuntimeArray,
    SpvOpTypeStruct,
    SpvOpTypeOpaque,
    SpvOpTypePointer,
    SpvOpTypeFunction,
    SpvOpTypeEvent,
    SpvOpTypeDeviceEvent,
    SpvOpTypeReserveId,
    SpvOpTypeQueue,
    SpvOpTypePipe,
    SpvOpTypeForwardPointer,
    SpvOpConstantTrue,
    SpvOpConstantFalse,
    SpvOpConstant,
    SpvOpConstantComposite,
    SpvOpConstantSampler,
    SpvOpConstantNull,
    SpvOpSpecConstantTrue,
    SpvOpSpecConstantFalse,
    SpvOpSpecConstant,
    SpvOpSpecConstantComposite,
    SpvOpSpecConstantOp,
    SpvOpFunction,
    SpvOpFunctionParameter,
    SpvOpFunctionEnd,
    SpvOpFunctionCall,
    SpvOpVariable,
    SpvOpImageTexelPointer,
    SpvOpLoad,
    SpvOpStore,
    SpvOpCopyMemory,
    SpvOpCopyMemorySized,
    SpvOpAccessChain,
    SpvOpInBoundsAccessChain,
    SpvOpPtrAccessChain,
    SpvOpArrayLength,
    SpvOpGenericPtrMemSemantics,
    SpvOpInBoundsPtrAccessChain,
    SpvOpDecorate,
    SpvOpMemberDecorate,
    SpvOpDecorationGroup,
    SpvOpGroupDecorate,
    SpvOpGroupMemberDecorate,
    SpvOpVectorExtractDynamic,
    SpvOpVectorInsertDynamic,
    SpvOpVectorShuffle,
    SpvOpCompositeConstruct,
    SpvOpCompositeExtract,
    SpvOpCompositeInsert,
    SpvOpCopyObject,
    SpvOpTranspose,
    SpvOpSampledImage,
    SpvOpImageSampleImplicitLod,
    SpvOpImageSampleExplicitLod,
    SpvOpImageSampleDrefImplicitLod,
    SpvOpImageSampleDrefExplicitLod,
    SpvOpImageSampleProjImplicitLod,
    SpvOpImageSampleProjExplicitLod,
    SpvOpImageSampleProjDrefImplicitLod,
    SpvOpImageSampleProjDrefExplicitLod,
    SpvOpImageFetch,
    SpvOpImageGather,
    SpvOpImageDrefGather,
    SpvOpImageRead,
    SpvOpImageWrite,
    SpvOpImage,
    SpvOpImageQueryFormat,
    SpvOpImageQueryOrder,
    SpvOpImageQuerySizeLod,
    SpvOpImageQuerySize,
    SpvOpImageQueryLod,
    SpvOpImageQueryLevels,
    SpvOpImageQuerySamples,
    SpvOpConvertFToU,
    SpvOpConvertFToS,
    SpvOpConvertSToF,
    SpvOpConvertUToF,
    SpvOpUConvert,
    SpvOpSConvert,
    SpvOpFConvert,
    SpvOpQuantizeToF16,
    SpvOpConvertPtrToU,
    SpvOpSatConvertSToU,
    SpvOpSatConvertUToS,
    SpvOpConvertUToPtr,
    SpvOpPtrCastToGeneric,
    SpvOpGenericCastToPtr,
    SpvOpGenericCastToPtrExplicit,
    SpvOpBitcast,
    SpvOpSNegate,
    SpvOpFNegate,
    SpvOpIAdd,
    SpvOpFAdd,
    SpvOpISub,
    SpvOpFSub,
    SpvOpIMul,
    SpvOpFMul,
    SpvOpUDiv,
    SpvOpSDiv,
    SpvOpFDiv,
    SpvOpUMod,
    SpvOpSRem,
    SpvOpSMod,
    SpvOpFRem,
    SpvOpFMod,
    SpvOpVectorTimesScalar,
    SpvOpMatrixTimesScalar,
    SpvOpVectorTimesMatrix,
    SpvOpMatrixTimesVector,
    SpvOpMatrixTimesMatrix,
    SpvOpOuterProduct,
    SpvOpDot,
    SpvOpIAddCarry,
    SpvOpISubBorrow,
    SpvOpUMulExtended,
    SpvOpSMulExtended,
    SpvOpAny,
    SpvOpAll,
    SpvOpIsNan,
    SpvOpIsInf,
    SpvOpIsFinite,
    SpvOpIsNormal,
    SpvOpSignBitSet,
    SpvOpLessOrGreater,
    SpvOpOrdered,
    SpvOpUnordered,
    SpvOpLogicalEqual,
    SpvOpLogicalNotEqual,
    SpvOpLogicalOr,
    SpvOpLogicalAnd,
    SpvOpLogicalNot,
    SpvOpSelect,
    SpvOpIEqual,
    SpvOpINotEqual,
    SpvOpUGreaterThan,
    SpvOpSGreaterThan,
    SpvOpUGreaterThanEqual,
    SpvOpSGreaterThanEqual,
    SpvOpULessThan,
    SpvOpSLessThan,
    SpvOpULessThanEqual,
    SpvOpSLessThanEqual,
    SpvOpFOrdEqual,
    SpvOpFUnordEqual,
    SpvOpFOrdNotEqual,
    SpvOpFUnordNotEqual,
    SpvOpFOrdLessThan,
    SpvOpFUnordLessThan,
    SpvOpFOrdGreaterThan,
    SpvOpFUnordGreaterThan,
    SpvOpFOrdLessThanEqual,
    SpvOpFUnordLessThanEqual,
    SpvOpFOrdGreaterThanEqual,
    SpvOpFUnordGreaterThanEqual,
    SpvOpShiftRightLogical,
    SpvOpShiftRightArithmetic,
    SpvOpShiftLeftLogical,
    SpvOpBitwiseOr,
    SpvOpBitwiseXor,
    SpvOpBitwiseAnd,
    SpvOpNot,
    SpvOpBitFieldInsert,
    SpvOpBitFieldSExtract,
    SpvOpBitFieldUExtract,
    SpvOpBitReverse,
    SpvOpBitCount,
    SpvOpDPdx,
    SpvOpDPdy,
    SpvOpFwidth,
    SpvOpDPdxFine,
    SpvOpDPdyFine,
    SpvOpFwidthFine,
    SpvOpDPdxCoarse,
    SpvOpDPdyCoarse,
    SpvOpFwidthCoarse,
    SpvOpEmitVertex,
    SpvOpEndPrimitive,
    SpvOpEmitStreamVertex,
    SpvOpEndStreamPrimitive,
    SpvOpControlBarrier,
    SpvOpMemoryBarrier,
    SpvOpAtomicLoad,
    SpvOpAtomicStore,
    SpvOpAtomicExchange,
    SpvOpAtomicCompareExchange,
    SpvOpAtomicCompareExchangeWeak,
    SpvOpAtomicIIncrement,
    SpvOpAtomicIDecrement,
    SpvOpAtomicIAdd,
    SpvOpAtomicISub,
    SpvOpAtomicSMin,
    SpvOpAtomicUMin,
    SpvOpAtomicSMax,
    SpvOpAtomicUMax,
    SpvOpAtomicAnd,
    SpvOpAtomicOr,
    SpvOpAtomicXor,
    SpvOpPhi,
    SpvOpLoopMerge,
    SpvOpSelectionMerge,
    SpvOpLabel,
    SpvOpBranch,
    SpvOpBranchConditional,
    SpvOpSwitch,
    SpvOpKill,
    SpvOpReturn,
    SpvOpReturnValue,
    SpvOpUnreachable,
    SpvOpLifetimeStart,
    SpvOpLifetimeStop,
    SpvOpGroupAsyncCopy,
    SpvOpGroupWaitEvents,
    SpvOpGroupAll,
    SpvOpGroupAny,
    SpvOpGroupBroadcast,
    SpvOpGroupIAdd,
    SpvOpGroupFAdd,
    SpvOpGroupFMin,
    SpvOpGroupUMin,
    SpvOpGroupSMin,
    SpvOpGroupFMax,
    SpvOpGroupUMax,
    SpvOpGroupSMax,
    SpvOpReadPipe,
    SpvOpWritePipe,
    SpvOpReservedReadPipe,
    SpvOpReservedWritePipe,
    SpvOpReserveReadPipePackets,
    SpvOpReserveWritePipePackets,
    SpvOpCommitReadPipe,
    SpvOpCommitWritePipe,
    SpvOpIsValidReserveId,
    SpvOpGetNumPipePackets,
    SpvOpGetMaxPipePackets,
    SpvOpGroupReserveReadPipePackets,
    SpvOpGroupReserveWritePipePackets,
    SpvOpGroupCommitReadPipe,
    SpvOpGroupCommitWritePipe,
    SpvOpEnqueueMarker,
    SpvOpEnqueueKernel,
    SpvOpGetKernelNDrangeSubGroupCount,
    SpvOpGetKernelNDrangeMaxSubGroupSize,
    SpvOpGetKernelWorkGroupSize,
    SpvOpGetKernelPreferredWorkGroupSizeMultiple,
    SpvOpRetainEvent,
    SpvOpReleaseEvent,
    SpvOpCreateUserEvent,
    SpvOpIsValidEvent,
    SpvOpSetUserEventStatus,
    SpvOpCaptureEventProfilingInfo,
    SpvOpGetDefaultQueue,
    SpvOpBuildNDRange,
    SpvOpImageSparseSampleImplicitLod,
    SpvOpImageSparseSampleExplicitLod,
    SpvOpImageSparseSampleDrefImplicitLod,
    SpvOpImageSparseSampleDrefExplicitLod,
    SpvOpImageSparseSampleProjImplicitLod,
    SpvOpImageSparseSampleProjExplicitLod,
    SpvOpImageSparseSampleProjDrefImplicitLod,
    SpvOpImageSparseSampleProjDrefExplicitLod,
    SpvOpImageSparseFetch,
    SpvOpImageSparseGather,
    SpvOpImageSparseDrefGather,
    SpvOpImageSparseTexelsResident,
    SpvOpNoLine,
    SpvOpAtomicFlagTestAndSet,
    SpvOpAtomicFlagClear,
    SpvOpImageSparseRead,
    SpvOpSizeOf,
    SpvOpTypePipeStorage,
    SpvOpConstantPipeStorage,
    SpvOpCreatePipeFromPipeStorage,
    SpvOpGetKernelLocalSizeForSubgroupCount,
    SpvOpGetKernelMaxNumSubgroups,
    SpvOpTypeNamedBarrier,
    SpvOpNamedBarrierInitialize,
    SpvOpMemoryNamedBarrier,
    SpvOpModuleProcessed,
    SpvOpExecutionModeId,
    SpvOpDecorateId,
    SpvOpSubgroupBallotKHR,
    SpvOpSubgroupFirstInvocationKHR,
    SpvOpSubgroupAllKHR,
    SpvOpSubgroupAnyKHR,
    SpvOpSubgroupAllEqualKHR,
    SpvOpSubgroupReadInvocationKHR,
  });
}

std::string GetVersionString(uint32_t word) {
  std::stringstream ss;
  ss << "Version " << SPV_SPIRV_VERSION_MAJOR_PART(word)
     << "." << SPV_SPIRV_VERSION_MINOR_PART(word);
  return ss.str();
}

std::string GetGeneratorString(uint32_t word) {
  return spvGeneratorStr(SPV_GENERATOR_TOOL_PART(word));
}

std::string GetOpcodeString(uint32_t word) {
  return spvOpcodeString(static_cast<SpvOp>(word));
}

std::string GetCapabilityString(uint32_t word) {
  return libspirv::CapabilityToString(static_cast<SpvCapability>(word));
}

template <class T>
std::string KeyIsLabel(T key) {
  std::stringstream ss;
  ss << key;
  return ss.str();
}

template <class Key>
std::unordered_map<Key, double> GetRecall(
    const std::unordered_map<Key, uint32_t>& hist, uint64_t total) {
  std::unordered_map<Key, double> freq;
  for (const auto& pair : hist) {
    const double frequency =
        static_cast<double>(pair.second) / static_cast<double>(total);
    freq.emplace(pair.first, frequency);
  }
  return freq;
}

template <class Key>
std::unordered_map<Key, double> GetPrevalence(
    const std::unordered_map<Key, uint32_t>& hist) {
  uint64_t total = 0;
  for (const auto& pair : hist) {
    total += pair.second;
  }

  return GetRecall(hist, total);
}

// Writes |freq| to |out| sorted by frequency in the following format:
// LABEL3 70%
// LABEL1 20%
// LABEL2 10%
// |label_from_key| is used to convert |Key| to label.
template <class Key>
void WriteFreq(std::ostream& out, const std::unordered_map<Key, double>& freq,
               std::string (*label_from_key)(Key), double threshold = 0.001) {
  std::vector<std::pair<Key, double>> sorted_freq(freq.begin(), freq.end());
  std::sort(sorted_freq.begin(), sorted_freq.end(),
            [](const std::pair<Key, double>& left,
               const std::pair<Key, double>& right) {
              return left.second > right.second;
            });

  for (const auto& pair : sorted_freq) {
    if (pair.second < threshold)
      break;
    out << label_from_key(pair.first) << " " << pair.second * 100.0
        << "%" << std::endl;
  }
}

// Writes |hist| to |out| sorted by count in the following format:
// LABEL3 100
// LABEL1 50
// LABEL2 10
// |label_from_key| is used to convert |Key| to label.
template <class Key>
void WriteHist(std::ostream& out, const std::unordered_map<Key, uint32_t>& hist,
               std::string (*label_from_key)(Key)) {
  std::vector<std::pair<Key, uint32_t>> sorted_hist(hist.begin(), hist.end());
  std::sort(sorted_hist.begin(), sorted_hist.end(),
            [](const std::pair<Key, uint32_t>& left,
               const std::pair<Key, uint32_t>& right) {
              return left.second > right.second;
            });

  for (const auto& pair : sorted_hist) {
    out << label_from_key(pair.first) << " " << pair.second << std::endl;
  }
}

}  // namespace

StatsAnalyzer::StatsAnalyzer(const SpirvStats& stats) : stats_(stats) {
  num_modules_ = 0;
  for (const auto& pair : stats_.version_hist) {
    num_modules_ += pair.second;
  }

  version_freq_ = GetRecall(stats_.version_hist, num_modules_);
  generator_freq_ = GetRecall(stats_.generator_hist, num_modules_);
  capability_freq_ = GetRecall(stats_.capability_hist, num_modules_);
  extension_freq_ = GetRecall(stats_.extension_hist, num_modules_);
  opcode_freq_ = GetPrevalence(stats_.opcode_hist);
}

void StatsAnalyzer::WriteVersion(std::ostream& out) {
  WriteFreq(out, version_freq_, GetVersionString);
}

void StatsAnalyzer::WriteGenerator(std::ostream& out) {
  WriteFreq(out, generator_freq_, GetGeneratorString);
}

void StatsAnalyzer::WriteCapability(std::ostream& out) {
  WriteFreq(out, capability_freq_, GetCapabilityString);
}

void StatsAnalyzer::WriteExtension(std::ostream& out) {
  WriteFreq(out, extension_freq_, KeyIsLabel);
}

void StatsAnalyzer::WriteOpcode(std::ostream& out) {
  out << "Total unique opcodes used: " << opcode_freq_.size() << std::endl;
  WriteFreq(out, opcode_freq_, GetOpcodeString);
}

void StatsAnalyzer::WriteConstantLiterals(std::ostream& out) {
  out << "Constant literals" << std::endl;

  out << "Float 32" << std::endl;
  WriteFreq(out, GetPrevalence(stats_.f32_constant_hist), KeyIsLabel);

  out << std::endl << "Float 64" << std::endl;
  WriteFreq(out, GetPrevalence(stats_.f64_constant_hist), KeyIsLabel);

  out << std::endl << "Unsigned int 16" << std::endl;
  WriteFreq(out, GetPrevalence(stats_.u16_constant_hist), KeyIsLabel);

  out << std::endl << "Signed int 16" << std::endl;
  WriteFreq(out, GetPrevalence(stats_.s16_constant_hist), KeyIsLabel);

  out << std::endl << "Unsigned int 32" << std::endl;
  WriteFreq(out, GetPrevalence(stats_.u32_constant_hist), KeyIsLabel);

  out << std::endl << "Signed int 32" << std::endl;
  WriteFreq(out, GetPrevalence(stats_.s32_constant_hist), KeyIsLabel);

  out << std::endl << "Unsigned int 64" << std::endl;
  WriteFreq(out, GetPrevalence(stats_.u64_constant_hist), KeyIsLabel);

  out << std::endl << "Signed int 64" << std::endl;
  WriteFreq(out, GetPrevalence(stats_.s64_constant_hist), KeyIsLabel);
}

void StatsAnalyzer::WriteOpcodeMarkov(std::ostream& out) {
  if (stats_.opcode_markov_hist.empty())
    return;

  const std::unordered_map<uint32_t, std::unordered_map<uint32_t, uint32_t>>&
      cue_to_hist = stats_.opcode_markov_hist[0];

  // Sort by prevalence of the opcodes in opcode_freq_ (descending).
  std::vector<std::pair<uint32_t, std::unordered_map<uint32_t, uint32_t>>>
      sorted_cue_to_hist(cue_to_hist.begin(), cue_to_hist.end());
  std::sort(sorted_cue_to_hist.begin(), sorted_cue_to_hist.end(),
            [this](
                const std::pair<uint32_t,
                std::unordered_map<uint32_t, uint32_t>>& left,
                const std::pair<uint32_t,
                std::unordered_map<uint32_t, uint32_t>>& right) {
              const double lf = opcode_freq_[left.first];
              const double rf = opcode_freq_[right.first];
              if (lf == rf)
                return right.first > left.first;
              return lf > rf;
            });

  for (const auto& kv : sorted_cue_to_hist) {
    const uint32_t cue = kv.first;
    const double kFrequentEnoughToAnalyze = 0.0001;
    if (opcode_freq_[cue] < kFrequentEnoughToAnalyze) continue;

    const std::unordered_map<uint32_t, uint32_t>& hist = kv.second;

    uint32_t total = 0;
    for (const auto& pair : hist) {
      total += pair.second;
    }

    std::vector<std::pair<uint32_t, uint32_t>>
        sorted_hist(hist.begin(), hist.end());
    std::sort(sorted_hist.begin(), sorted_hist.end(),
              [](const std::pair<uint32_t, uint32_t>& left,
                 const std::pair<uint32_t, uint32_t>& right) {
                if (left.second == right.second)
                  return right.first > left.first;
                return left.second > right.second;
              });

    for (const auto& pair : sorted_hist) {
      const double prior = opcode_freq_[pair.first];
      const double posterior =
          static_cast<double>(pair.second) / static_cast<double>(total);
      out << GetOpcodeString(cue) << " -> " << GetOpcodeString(pair.first)
          << " " << posterior * 100 << "% (base rate " << prior * 100
          << "%, pair occurrences " << pair.second << ")" << std::endl;
    }
  }
}

void StatsAnalyzer::WriteCodegenOpcodeHist(std::ostream& out) {
  auto all_opcodes = GetAllOpcodes();

  // uint64_t is used because kMarkvNoneOfTheAbove is outside of uint32_t range.
  out << "std::map<uint64_t, uint32_t> GetOpcodeHist() {\n"
      << "  return std::map<uint64_t, uint32_t>({\n";

  uint32_t total = 0;
  for (const auto& kv : stats_.opcode_hist) {
    total += kv.second;
  }

  for (uint32_t opcode : all_opcodes) {
    const auto it = stats_.opcode_hist.find(opcode);
    const uint32_t count = it == stats_.opcode_hist.end() ? 0 : it->second;
    const double kMaxValue = 1000.0;
    uint32_t value = uint32_t(kMaxValue * double(count) / double(total));
    if (value == 0)
      value = 1;
    out << "    { SpvOp" << GetOpcodeString(opcode)
        << ", " << value << " },\n";
  }

  // Add kMarkvNoneOfTheAbove as a signal for unknown opcode.
  out << "    { kMarkvNoneOfTheAbove, " << 10 << " },\n";
  out << "  });\n}\n";
}

void StatsAnalyzer::WriteCodegenOpcodeAndNumOperandsHist(std::ostream& out) {
  out << "std::map<uint64_t, uint32_t> GetOpcodeAndNumOperandsHist() {\n"
      << "  return std::map<uint64_t, uint32_t>({\n";


  uint32_t total = 0;
  for (const auto& kv : stats_.opcode_and_num_operands_hist) {
    total += kv.second;
  }

  uint32_t left_out = 0;

  for (const auto& kv : stats_.opcode_and_num_operands_hist) {
    const uint32_t count = kv.second;
    const double kFrequentEnoughToAnalyze = 0.001;
    const uint32_t opcode_and_num_operands = kv.first;
    const uint32_t opcode = opcode_and_num_operands & 0xFFFF;
    const uint32_t num_operands = opcode_and_num_operands >> 16;

    if (opcode == SpvOpTypeStruct ||
        double(count) / double(total) < kFrequentEnoughToAnalyze) {
      left_out += count;
      continue;
    }

    out << "    { CombineOpcodeAndNumOperands(SpvOp"
        << spvOpcodeString(SpvOp(opcode))
        << ", " << num_operands << "), " << count << " },\n";
  }

  // Heuristic.
  const uint32_t none_of_the_above =
      std::max(1, int(left_out + total * 0.01));
  out << "    { kMarkvNoneOfTheAbove, " << none_of_the_above << " },\n";
  out << "  });\n}\n";
}

void StatsAnalyzer::WriteCodegenOpcodeAndNumOperandsMarkovHuffmanCodecs(
    std::ostream& out) {
  out << "std::map<uint32_t, std::unique_ptr<HuffmanCodec<uint64_t>>>\n"
      << "GetOpcodeAndNumOperandsMarkovHuffmanCodecs() {\n"
      << "  std::map<uint32_t, std::unique_ptr<HuffmanCodec<uint64_t>>> "
      << "codecs;\n";

  for (const auto& kv : stats_.opcode_and_num_operands_markov_hist) {
    const uint32_t prev_opcode = kv.first;
    const double kFrequentEnoughToAnalyze = 0.001;
    if (opcode_freq_[prev_opcode] < kFrequentEnoughToAnalyze) continue;

    const std::unordered_map<uint32_t, uint32_t>& hist = kv.second;

    uint32_t total = 0;
    for (const auto& pair : hist) {
      total += pair.second;
    }

    uint32_t left_out = 0;

    std::map<uint64_t, uint32_t> processed_hist;
    for (const auto& pair : hist) {
      const uint32_t opcode_and_num_operands = pair.first;
      const uint32_t opcode = opcode_and_num_operands & 0xFFFF;

      if (opcode == SpvOpTypeStruct)
        continue;

      const uint32_t num_operands = opcode_and_num_operands >> 16;
      const uint32_t count = pair.second;
      const double posterior_freq = double(count) / double(total);

      if (opcode_freq_[opcode] < kFrequentEnoughToAnalyze &&
          posterior_freq < kFrequentEnoughToAnalyze) {
        left_out += count;
        continue;
      }
      processed_hist.emplace(CombineOpcodeAndNumOperands(opcode, num_operands),
                             count);
    }

    // Heuristic.
    processed_hist.emplace(kMarkvNoneOfTheAbove,
                           std::max(1, int(left_out + total * 0.01)));

    HuffmanCodec<uint64_t> codec(processed_hist);

    out << "  {\n";
    out << "    std::unique_ptr<HuffmanCodec<uint64_t>> "
        << "codec(new HuffmanCodec<uint64_t>";
    out << codec.SerializeToText(4);
    out << ");\n" << std::endl;
    out << "    codecs.emplace(SpvOp" << GetOpcodeString(prev_opcode)
        << ", std::move(codec));\n";
    out << "  }\n\n";
  }

  out << "  return codecs;\n}\n";
}

void StatsAnalyzer::WriteCodegenLiteralStringHuffmanCodecs(std::ostream& out) {
  out << "std::map<uint32_t, std::unique_ptr<HuffmanCodec<std::string>>>\n"
      << "GetLiteralStringHuffmanCodecs() {\n"
      << "  std::map<uint32_t, std::unique_ptr<HuffmanCodec<std::string>>> "
      << "codecs;\n";

  for (const auto& kv : stats_.literal_strings_hist) {
    const uint32_t opcode = kv.first;

    if (opcode == SpvOpName || opcode == SpvOpMemberName)
      continue;

    const double kOpcodeFrequentEnoughToAnalyze = 0.001;
    if (opcode_freq_[opcode] < kOpcodeFrequentEnoughToAnalyze) continue;

    const std::unordered_map<std::string, uint32_t>& hist = kv.second;

    uint32_t total = 0;
    for (const auto& pair : hist) {
      total += pair.second;
    }

    uint32_t left_out = 0;

    std::map<std::string, uint32_t> processed_hist;
    for (const auto& pair : hist) {
      const uint32_t count = pair.second;
      const double freq = double(count) / double(total);
      const double kStringFrequentEnoughToAnalyze = 0.001;
      if (freq < kStringFrequentEnoughToAnalyze) {
        left_out += count;
        continue;
      }
      processed_hist.emplace(pair.first, count);
    }

    // Heuristic.
    processed_hist.emplace("kMarkvNoneOfTheAbove",
                           std::max(1, int(left_out + total * 0.01)));

    HuffmanCodec<std::string> codec(processed_hist);

    out << "  {\n";
    out << "    std::unique_ptr<HuffmanCodec<std::string>> "
        << "codec(new HuffmanCodec<std::string>";
    out << codec.SerializeToText(4);
    out << ");\n" << std::endl;
    out << "    codecs.emplace(SpvOp" << spvOpcodeString(SpvOp(opcode))
        << ", std::move(codec));\n";
    out << "  }\n\n";
  }

  out << "  return codecs;\n}\n";
}

void StatsAnalyzer::WriteCodegenNonIdWordHuffmanCodecs(std::ostream& out) {
  out << "std::map<std::pair<uint32_t, uint32_t>, "
      << "std::unique_ptr<HuffmanCodec<uint64_t>>>\n"
      << "GetNonIdWordHuffmanCodecs() {\n"
      << "  std::map<std::pair<uint32_t, uint32_t>, "
      << "std::unique_ptr<HuffmanCodec<uint64_t>>> codecs;\n";

  for (const auto& kv : stats_.operand_slot_non_id_words_hist) {
    const auto& opcode_and_index = kv.first;
    const uint32_t opcode = opcode_and_index.first;
    const uint32_t index = opcode_and_index.second;

    const double kOpcodeFrequentEnoughToAnalyze = 0.001;
    if (opcode_freq_[opcode] < kOpcodeFrequentEnoughToAnalyze) continue;

    const std::map<uint32_t, uint32_t>& hist = kv.second;

    uint32_t total = 0;
    for (const auto& pair : hist) {
      total += pair.second;
    }

    uint32_t left_out = 0;

    std::map<uint64_t, uint32_t> processed_hist;
    for (const auto& pair : hist) {
      const uint32_t word = pair.first;
      const uint32_t count = pair.second;
      const double freq = double(count) / double(total);
      const double kWordFrequentEnoughToAnalyze = 0.003;
      if (freq < kWordFrequentEnoughToAnalyze) {
        left_out += count;
        continue;
      }
      processed_hist.emplace(word, count);
    }

    // Heuristic.
    processed_hist.emplace(kMarkvNoneOfTheAbove,
                           std::max(1, int(left_out + total * 0.01)));

    HuffmanCodec<uint64_t> codec(processed_hist);

    out << "  {\n";
    out << "    std::unique_ptr<HuffmanCodec<uint64_t>> "
        << "codec(new HuffmanCodec<uint64_t>";
    out << codec.SerializeToText(4);
    out << ");\n" << std::endl;
    out << "    codecs.emplace(std::pair<uint32_t, uint32_t>(SpvOp"
        << spvOpcodeString(SpvOp(opcode))
        << ", " << index << "), std::move(codec));\n";
    out << "  }\n\n";
  }

  out << "  return codecs;\n}\n";
}

void StatsAnalyzer::WriteCodegenIdDescriptorHuffmanCodecs(
    std::ostream& out) {
  out << "std::map<std::pair<uint32_t, uint32_t>, "
      << "std::unique_ptr<HuffmanCodec<uint64_t>>>\n"
      << "GetIdDescriptorHuffmanCodecs() {\n"
      << "  std::map<std::pair<uint32_t, uint32_t>, "
      << "std::unique_ptr<HuffmanCodec<uint64_t>>> codecs;\n";

  std::unordered_set<uint32_t> descriptors_with_coding_scheme;

  for (const auto& kv : stats_.operand_slot_id_descriptor_hist) {
    const auto& opcode_and_index = kv.first;
    const uint32_t opcode = opcode_and_index.first;
    const uint32_t index = opcode_and_index.second;

    const double kOpcodeFrequentEnoughToAnalyze = 0.003;
    if (opcode_freq_[opcode] < kOpcodeFrequentEnoughToAnalyze) continue;

    const std::map<uint32_t, uint32_t>& hist = kv.second;


    uint32_t total = 0;
    for (const auto& pair : hist) {
      total += pair.second;
    }

    uint32_t left_out = 0;

    std::map<uint64_t, uint32_t> processed_hist;
    for (const auto& pair : hist) {
      const uint32_t descriptor = pair.first;
      const uint32_t count = pair.second;
      const double freq = double(count) / double(total);
      const double kDescriptorFrequentEnoughToAnalyze = 0.003;
      if (freq < kDescriptorFrequentEnoughToAnalyze) {
        left_out += count;
        continue;
      }
      processed_hist.emplace(descriptor, count);
      descriptors_with_coding_scheme.insert(descriptor);
    }

    // Heuristic.
    processed_hist.emplace(kMarkvNoneOfTheAbove,
                           std::max(1, int(left_out + total * 0.01)));


    HuffmanCodec<uint64_t> codec(processed_hist);

    out << "  {\n";
    out << "    std::unique_ptr<HuffmanCodec<uint64_t>> "
        << "codec(new HuffmanCodec<uint64_t>";
    out << codec.SerializeToText(4);
    out << ");\n" << std::endl;
    out << "    codecs.emplace(std::pair<uint32_t, uint32_t>(SpvOp"
        << spvOpcodeString(SpvOp(opcode))
        << ", " << index << "), std::move(codec));\n";
    out << "  }\n\n";
  }

  out << "  return codecs;\n}\n";

  out << "\nstd::unordered_set<uint32_t> GetDescriptorsWithCodingScheme() {\n"
      << "  std::unordered_set<uint32_t> descriptors_with_coding_scheme = {\n";
  for (uint32_t descriptor : descriptors_with_coding_scheme) {
    out << "    " << descriptor << ",\n";
  }
  out << "  };\n";
  out << "  return descriptors_with_coding_scheme;\n}\n";
}