path: root/src/tools/wasm-split.cpp

/*
 * Copyright 2020 WebAssembly Community Group participants
 *
 * 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.
 */

// wasm-split: Split a module in two or instrument a module to inform future
// splitting.

#include "ir/module-splitting.h"
#include "ir/module-utils.h"
#include "ir/names.h"
#include "pass.h"
#include "support/file.h"
#include "support/name.h"
#include "support/path.h"
#include "support/utilities.h"
#include "tool-options.h"
#include "wasm-binary.h"
#include "wasm-builder.h"
#include "wasm-io.h"
#include "wasm-type.h"
#include "wasm-validator.h"
#include <sstream>

using namespace wasm;

namespace {

const std::string DEFAULT_PROFILE_EXPORT("__write_profile");

std::set<Name> parseNameList(const std::string& list) {
  std::set<Name> names;
  std::istringstream stream(list);
  for (std::string name; std::getline(stream, name, ',');) {
    names.insert(name);
  }
  return names;
}

struct WasmSplitOptions : ToolOptions {
  enum class Mode : unsigned {
    Split,
    Instrument,
    MergeProfiles,
  };
  Mode mode = Mode::Split;
  constexpr static size_t NumModes =
    static_cast<unsigned>(Mode::MergeProfiles) + 1;

  bool verbose = false;
  bool emitBinary = true;
  bool symbolMap = false;
  bool placeholderMap = false;

  // TODO: Remove this. See the comment in wasm-binary.h.
  bool emitModuleNames = false;

  std::string profileFile;
  std::string profileExport = DEFAULT_PROFILE_EXPORT;

  std::set<Name> keepFuncs;
  std::set<Name> splitFuncs;

  std::vector<std::string> inputFiles;
  std::string output;
  std::string primaryOutput;
  std::string secondaryOutput;

  std::string importNamespace;
  std::string placeholderNamespace;
  std::string exportPrefix;

  // A hack to ensure the split and instrumented modules have the same table
  // size when using Emscripten's SPLIT_MODULE mode with dynamic linking. TODO:
  // Figure out a more elegant solution for that use case and remove this.
  int initialTableSize = -1;

  // The options that are valid for each mode.
  std::array<std::unordered_set<std::string>, NumModes> validOptions;
  std::vector<std::string> usedOptions;

  WasmSplitOptions();
  WasmSplitOptions& add(const std::string& longName,
                        const std::string& shortName,
                        const std::string& description,
                        std::vector<Mode>&& modes,
                        Arguments arguments,
                        const Action& action);
  WasmSplitOptions& add(const std::string& longName,
                        const std::string& shortName,
                        const std::string& description,
                        Arguments arguments,
                        const Action& action);
  bool validate();
  void parse(int argc, const char* argv[]);
};

WasmSplitOptions::WasmSplitOptions()
  : ToolOptions("wasm-split",
                "Split a module into a primary module and a secondary "
                "module, or instrument a module to gather a profile that "
                "can inform future splitting, or manage such profiles. Options "
                "that are only accepted in particular modes are marked with "
                "the accepted \"[<modes>]\" in their descriptions.") {
  (*this)
    .add("--split",
         "",
         "Split an input module into two output modules. The default mode.",
         Options::Arguments::Zero,
         [&](Options* o, const std::string& arugment) { mode = Mode::Split; })
    .add(
      "--instrument",
      "",
      "Instrument an input module to allow it to generate a profile that can"
      " be used to guide splitting.",
      Options::Arguments::Zero,
      [&](Options* o, const std::string& argument) { mode = Mode::Instrument; })
    .add("--merge-profiles",
         "",
         "Merge multiple profiles for the same module into a single profile.",
         Options::Arguments::Zero,
         [&](Options* o, const std::string& argument) {
           mode = Mode::MergeProfiles;
         })
    .add(
      "--profile",
      "",
      "The profile to use to guide splitting.",
      {Mode::Split},
      Options::Arguments::One,
      [&](Options* o, const std::string& argument) { profileFile = argument; })
    .add("--keep-funcs",
         "",
         "Comma-separated list of functions to keep in the primary module, "
         "regardless of any profile.",
         {Mode::Split},
         Options::Arguments::One,
         [&](Options* o, const std::string& argument) {
           keepFuncs = parseNameList(argument);
         })
    .add("--split-funcs",
         "",
         "Comma-separated list of functions to split into the secondary "
         "module, regardless of any profile. If there is no profile, then "
         "this defaults to all functions defined in the module.",
         {Mode::Split},
         Options::Arguments::One,
         [&](Options* o, const std::string& argument) {
           splitFuncs = parseNameList(argument);
         })
    .add("--primary-output",
         "-o1",
         "Output file for the primary module.",
         {Mode::Split},
         Options::Arguments::One,
         [&](Options* o, const std::string& argument) {
           primaryOutput = argument;
         })
    .add("--secondary-output",
         "-o2",
         "Output file for the secondary module.",
         {Mode::Split},
         Options::Arguments::One,
         [&](Options* o, const std::string& argument) {
           secondaryOutput = argument;
         })
    .add("--symbolmap",
         "",
         "Write a symbol map file for each of the output modules.",
         {Mode::Split},
         Options::Arguments::Zero,
         [&](Options* o, const std::string& argument) { symbolMap = true; })
    .add(
      "--placeholdermap",
      "",
      "Write a file mapping placeholder indices to the function names.",
      {Mode::Split},
      Options::Arguments::Zero,
      [&](Options* o, const std::string& argument) { placeholderMap = true; })
    .add("--import-namespace",
         "",
         "The namespace from which to import objects from the primary "
         "module into the secondary module.",
         {Mode::Split},
         Options::Arguments::One,
         [&](Options* o, const std::string& argument) {
           importNamespace = argument;
         })
    .add("--placeholder-namespace",
         "",
         "The namespace from which to import placeholder functions into "
         "the primary module.",
         {Mode::Split},
         Options::Arguments::One,
         [&](Options* o, const std::string& argument) {
           placeholderNamespace = argument;
         })
    .add(
      "--export-prefix",
      "",
      "An identifying prefix to prepend to new export names created "
      "by module splitting.",
      {Mode::Split},
      Options::Arguments::One,
      [&](Options* o, const std::string& argument) { exportPrefix = argument; })
    .add("--profile-export",
         "",
         "The export name of the function the embedder calls to write the "
         "profile into memory. Defaults to `__write_profile`.",
         {Mode::Instrument},
         Options::Arguments::One,
         [&](Options* o, const std::string& argument) {
           profileExport = argument;
         })
    .add(
      "--emit-module-names",
      "",
      "Emit module names, even if not emitting the rest of the names section. "
      "Can help differentiate the modules in stack traces. This option will be "
      "removed once simpler ways of naming modules are widely available. See "
      "https://bugs.chromium.org/p/v8/issues/detail?id=11808.",
      {Mode::Split, Mode::Instrument},
      Options::Arguments::Zero,
      [&](Options* o, const std::string& arguments) { emitModuleNames = true; })
    .add("--initial-table",
         "",
         "A hack to ensure the split and instrumented modules have the same "
         "table size when using Emscripten's SPLIT_MODULE mode with dynamic "
         "linking. TODO: Figure out a more elegant solution for that use "
         "case and remove this.",
         {Mode::Split, Mode::Instrument},
         Options::Arguments::One,
         [&](Options* o, const std::string& argument) {
           initialTableSize = std::stoi(argument);
         })
    .add("--emit-text",
         "-S",
         "Emit text instead of binary for the output file or files.",
         {Mode::Split, Mode::Instrument},
         Options::Arguments::Zero,
         [&](Options* o, const std::string& argument) { emitBinary = false; })
    .add("--debuginfo",
         "-g",
         "Emit names section in wasm binary (or full debuginfo in wast)",
         {Mode::Split, Mode::Instrument},
         Options::Arguments::Zero,
         [&](Options* o, const std::string& arguments) {
           passOptions.debugInfo = true;
         })
    .add("--output",
         "-o",
         "Output file.",
         {Mode::Instrument, Mode::MergeProfiles},
         Options::Arguments::One,
         [&](Options* o, const std::string& argument) { output = argument; })
    .add("--verbose",
         "-v",
         "Verbose output mode. Prints the functions that will be kept "
         "and split out when splitting a module.",
         Options::Arguments::Zero,
         [&](Options* o, const std::string& argument) {
           verbose = true;
           quiet = false;
         })
    .add_positional("INFILES",
                    Options::Arguments::N,
                    [&](Options* o, const std::string& argument) {
                      inputFiles.push_back(argument);
                    });
}

std::ostream& operator<<(std::ostream& o, WasmSplitOptions::Mode& mode) {
  switch (mode) {
    case WasmSplitOptions::Mode::Split:
      o << "split";
      break;
    case WasmSplitOptions::Mode::Instrument:
      o << "instrument";
      break;
    case WasmSplitOptions::Mode::MergeProfiles:
      o << "merge-profiles";
      break;
  }
  return o;
}

WasmSplitOptions& WasmSplitOptions::add(const std::string& longName,
                                        const std::string& shortName,
                                        const std::string& description,
                                        std::vector<Mode>&& modes,
                                        Arguments arguments,
                                        const Action& action) {
  // Insert the valid modes at the beginning of the description.
  std::stringstream desc;
  if (modes.size()) {
    desc << '[';
    std::string sep = "";
    for (Mode m : modes) {
      validOptions[static_cast<unsigned>(m)].insert(longName);
      desc << sep << m;
      sep = ", ";
    }
    desc << "] ";
  }
  desc << description;
  ToolOptions::add(
    longName,
    shortName,
    desc.str(),
    arguments,
    [&, action, longName](Options* o, const std::string& argument) {
      usedOptions.push_back(longName);
      action(o, argument);
    });
  return *this;
}

WasmSplitOptions& WasmSplitOptions::add(const std::string& longName,
                                        const std::string& shortName,
                                        const std::string& description,
                                        Arguments arguments,
                                        const Action& action) {
  // Add an option valid in all modes.
  for (unsigned i = 0; i < NumModes; ++i) {
    validOptions[i].insert(longName);
  }
  return add(longName, shortName, description, {}, arguments, action);
}

bool WasmSplitOptions::validate() {
  bool valid = true;
  auto fail = [&](auto msg) {
    std::cerr << "error: " << msg << "\n";
    valid = false;
  };

  // Validate the positional arguments.
  if (inputFiles.size() == 0) {
    fail("no input file");
  }
  switch (mode) {
    case Mode::Split:
    case Mode::Instrument:
      if (inputFiles.size() > 1) {
        fail("Cannot have more than one input file.");
      }
      break;
    case Mode::MergeProfiles:
      // Any number >= 1 allowed.
      break;
  }

  // Validate that all used options are allowed in the current mode.
  for (std::string& opt : usedOptions) {
    if (!validOptions[static_cast<unsigned>(mode)].count(opt)) {
      std::stringstream msg;
      msg << "Option " << opt << " cannot be used in " << mode << " mode.";
      fail(msg.str());
    }
  }

  if (mode == Mode::Split) {
    std::vector<Name> impossible;
    std::set_intersection(keepFuncs.begin(),
                          keepFuncs.end(),
                          splitFuncs.begin(),
                          splitFuncs.end(),
                          std::inserter(impossible, impossible.end()));
    for (auto& func : impossible) {
      fail(std::string("Cannot both keep and split out function ") +
           func.c_str());
    }
  }

  return valid;
}

void WasmSplitOptions::parse(int argc, const char* argv[]) {
  ToolOptions::parse(argc, argv);
  // Since --quiet is defined in ToolOptions but --verbose is defined here,
  // --quiet doesn't know to unset --verbose. Fix it up here.
  if (quiet && verbose) {
    verbose = false;
  }
}

void parseInput(Module& wasm, const WasmSplitOptions& options) {
  options.applyFeatures(wasm);
  ModuleReader reader;
  reader.setProfile(options.profile);
  try {
    reader.read(options.inputFiles[0], wasm);
  } catch (ParseException& p) {
    p.dump(std::cerr);
    std::cerr << '\n';
    Fatal() << "error parsing wasm";
  } catch (std::bad_alloc&) {
    Fatal() << "error building module, std::bad_alloc (possibly invalid "
               "request for silly amounts of memory)";
  }

  if (options.passOptions.validate && !WasmValidator().validate(wasm)) {
    Fatal() << "error validating input";
  }
}

// Add a global monotonic counter and a timestamp global for each function, code
// at the beginning of each function to set its timestamp, and a new exported
// function for dumping the profile data.
struct Instrumenter : public Pass {
  PassRunner* runner = nullptr;
  Module* wasm = nullptr;

  const std::string& profileExport;
  uint64_t moduleHash;

  Name counterGlobal;
  std::vector<Name> functionGlobals;

  Instrumenter(const std::string& profileExport, uint64_t moduleHash);

  void run(PassRunner* runner, Module* wasm) override;
  void addGlobals();
  void instrumentFuncs();
  void addProfileExport();
};

Instrumenter::Instrumenter(const std::string& profileExport,
                           uint64_t moduleHash)
  : profileExport(profileExport), moduleHash(moduleHash) {}

void Instrumenter::run(PassRunner* runner, Module* wasm) {
  this->runner = runner;
  this->wasm = wasm;
  addGlobals();
  instrumentFuncs();
  addProfileExport();
}

void Instrumenter::addGlobals() {
  // Create fresh global names (over-reserves, but that's ok)
  counterGlobal = Names::getValidGlobalName(*wasm, "monotonic_counter");
  functionGlobals.reserve(wasm->functions.size());
  ModuleUtils::iterDefinedFunctions(*wasm, [&](Function* func) {
    functionGlobals.push_back(Names::getValidGlobalName(
      *wasm, std::string(func->name.c_str()) + "_timestamp"));
  });

  // Create and add new globals
  auto addGlobal = [&](Name name) {
    auto global = Builder::makeGlobal(
      name,
      Type::i32,
      Builder(*wasm).makeConst(Literal::makeZero(Type::i32)),
      Builder::Mutable);
    global->hasExplicitName = true;
    wasm->addGlobal(std::move(global));
  };
  addGlobal(counterGlobal);
  for (auto& name : functionGlobals) {
    addGlobal(name);
  }
}

void Instrumenter::instrumentFuncs() {
  // Inject the following code at the beginning of each function to advance the
  // monotonic counter and set the function's timestamp if it hasn't already
  // been set.
  //
  //   (if (i32.eqz (global.get $timestamp))
  //     (block
  //       (global.set $monotonic_counter
  //         (i32.add
  //           (global.get $monotonic_counter)
  //           (i32.const 1)
  //         )
  //       )
  //       (global.set $timestamp
  //         (global.get $monotonic_counter)
  //       )
  //     )
  //   )
  Builder builder(*wasm);
  auto globalIt = functionGlobals.begin();
  ModuleUtils::iterDefinedFunctions(*wasm, [&](Function* func) {
    func->body = builder.makeSequence(
      builder.makeIf(
        builder.makeUnary(EqZInt32,
                          builder.makeGlobalGet(*globalIt, Type::i32)),
        builder.makeSequence(
          builder.makeGlobalSet(
            counterGlobal,
            builder.makeBinary(AddInt32,
                               builder.makeGlobalGet(counterGlobal, Type::i32),
                               builder.makeConst(Literal::makeOne(Type::i32)))),
          builder.makeGlobalSet(
            *globalIt, builder.makeGlobalGet(counterGlobal, Type::i32)))),
      func->body,
      func->body->type);
    ++globalIt;
  });
}

// wasm-split profile format:
//
// The wasm-split profile is a binary format designed to be simple to produce
// and consume. It is comprised of:
//
//   1. An 8-byte module hash
//
//   2. A 4-byte timestamp for each defined function
//
// The module hash is meant to guard against bugs where the module that was
// instrumented and the module that is being split are different. The timestamps
// are non-zero for functions that were called during the instrumented run and 0
// otherwise. Functions with smaller non-zero timestamps were called earlier in
// the instrumented run than funtions with larger timestamps.

void Instrumenter::addProfileExport() {
  // Create and export a function to dump the profile into a given memory
  // buffer. The function takes the available address and buffer size as
  // arguments and returns the total size of the profile. It only actually
  // writes the profile if the given space is sufficient to hold it.
  auto name = Names::getValidFunctionName(*wasm, profileExport);
  auto writeProfile = Builder::makeFunction(
    name, Signature({Type::i32, Type::i32}, Type::i32), {});
  writeProfile->hasExplicitName = true;
  writeProfile->setLocalName(0, "addr");
  writeProfile->setLocalName(1, "size");

  // Calculate the size of the profile:
  //   8 bytes module hash +
  //   4 bytes for the timestamp for each function
  const size_t profileSize = 8 + 4 * functionGlobals.size();

  // Create the function body
  Builder builder(*wasm);
  auto getAddr = [&]() { return builder.makeLocalGet(0, Type::i32); };
  auto getSize = [&]() { return builder.makeLocalGet(1, Type::i32); };
  auto hashConst = [&]() { return builder.makeConst(int64_t(moduleHash)); };
  auto profileSizeConst = [&]() {
    return builder.makeConst(int32_t(profileSize));
  };

  // Write the hash followed by all the time stamps
  Expression* writeData =
    builder.makeStore(8, 0, 1, getAddr(), hashConst(), Type::i64);

  uint32_t offset = 8;
  for (const auto& global : functionGlobals) {
    writeData = builder.blockify(
      writeData,
      builder.makeStore(4,
                        offset,
                        1,
                        getAddr(),
                        builder.makeGlobalGet(global, Type::i32),
                        Type::i32));
    offset += 4;
  }

  writeProfile->body = builder.makeSequence(
    builder.makeIf(builder.makeBinary(GeUInt32, getSize(), profileSizeConst()),
                   writeData),
    profileSizeConst());

  // Create an export for the function
  wasm->addFunction(std::move(writeProfile));
  wasm->addExport(
    Builder::makeExport(profileExport, name, ExternalKind::Function));

  // Also make sure there is a memory with enough pages to write into
  size_t pages = (profileSize + Memory::kPageSize - 1) / Memory::kPageSize;
  if (!wasm->memory.exists) {
    wasm->memory.exists = true;
    wasm->memory.initial = pages;
    wasm->memory.max = pages;
  } else if (wasm->memory.initial < pages) {
    wasm->memory.initial = pages;
    if (wasm->memory.max < pages) {
      wasm->memory.max = pages;
    }
  }

  // TODO: export the memory if it is not already exported.
}

uint64_t hashFile(const std::string& filename) {
  auto contents(read_file<std::vector<char>>(filename, Flags::Binary));
  size_t digest = 0;
  // Don't use `hash` or `rehash` - they aren't deterministic between executions
  for (char c : contents) {
    hash_combine(digest, c);
  }
  return uint64_t(digest);
}

void adjustTableSize(Module& wasm, int initialSize) {
  if (initialSize < 0) {
    return;
  }
  if (wasm.tables.empty()) {
    Fatal() << "--initial-table used but there is no table";
  }

  auto& table = wasm.tables.front();

  if ((uint64_t)initialSize < table->initial) {
    Fatal() << "Specified initial table size too small, should be at least "
            << table->initial;
  }
  if ((uint64_t)initialSize > table->max) {
    Fatal() << "Specified initial table size larger than max table size "
            << table->max;
  }
  table->initial = initialSize;
}

void writeModule(Module& wasm,
                 std::string filename,
                 const WasmSplitOptions& options) {
  ModuleWriter writer;
  writer.setBinary(options.emitBinary);
  writer.setDebugInfo(options.passOptions.debugInfo);
  if (options.emitModuleNames) {
    writer.setEmitModuleName(true);
  }
  writer.write(wasm, filename);
}

void instrumentModule(const WasmSplitOptions& options) {
  Module wasm;
  parseInput(wasm, options);

  // Check that the profile export name is not already taken
  if (wasm.getExportOrNull(options.profileExport) != nullptr) {
    Fatal() << "error: Export " << options.profileExport << " already exists.";
  }

  uint64_t moduleHash = hashFile(options.inputFiles[0]);
  PassRunner runner(&wasm, options.passOptions);
  Instrumenter(options.profileExport, moduleHash).run(&runner, &wasm);

  adjustTableSize(wasm, options.initialTableSize);

  // Write the output modules
  writeModule(wasm, options.output, options);
}

struct ProfileData {
  uint64_t hash;
  std::vector<size_t> timestamps;
};

// See "wasm-split profile format" above for more information.
ProfileData readProfile(const std::string& file) {
  auto profileData = read_file<std::vector<char>>(file, Flags::Binary);
  size_t i = 0;
  auto readi32 = [&]() {
    if (i + 4 > profileData.size()) {
      Fatal() << "Unexpected end of profile data in " << file;
    }
    uint32_t i32 = 0;
    i32 |= uint32_t(uint8_t(profileData[i++]));
    i32 |= uint32_t(uint8_t(profileData[i++])) << 8;
    i32 |= uint32_t(uint8_t(profileData[i++])) << 16;
    i32 |= uint32_t(uint8_t(profileData[i++])) << 24;
    return i32;
  };

  uint64_t hash = readi32();
  hash |= uint64_t(readi32()) << 32;

  std::vector<size_t> timestamps;
  while (i < profileData.size()) {
    timestamps.push_back(readi32());
  }

  return {hash, timestamps};
}

void writeSymbolMap(Module& wasm, std::string filename) {
  PassOptions options;
  options.arguments["symbolmap"] = filename;
  PassRunner runner(&wasm, options);
  runner.add("symbolmap");
  runner.run();
}

void writePlaceholderMap(const std::map<size_t, Name> placeholderMap,
                         std::string filename) {
  Output output(filename, Flags::Text);
  auto& o = output.getStream();
  for (auto pair : placeholderMap) {
    o << pair.first << ':' << pair.second << '\n';
  }
}

void splitModule(const WasmSplitOptions& options) {
  Module wasm;
  parseInput(wasm, options);

  std::set<Name> keepFuncs;

  if (options.profileFile.size()) {
    // Use the profile to initialize `keepFuncs`.
    uint64_t hash = hashFile(options.inputFiles[0]);
    ProfileData profile = readProfile(options.profileFile);
    if (profile.hash != hash) {
      Fatal() << "error: checksum in profile does not match module checksum. "
              << "The split module must be the original module that was "
              << "instrumented to generate the profile.";
    }
    size_t i = 0;
    ModuleUtils::iterDefinedFunctions(wasm, [&](Function* func) {
      if (i >= profile.timestamps.size()) {
        Fatal() << "Unexpected end of profile data";
      }
      if (profile.timestamps[i++] > 0) {
        keepFuncs.insert(func->name);
      }
    });
    if (i != profile.timestamps.size()) {
      Fatal() << "Unexpected extra profile data";
    }
  }

  // Add in the functions specified with --keep-funcs
  for (auto& func : options.keepFuncs) {
    if (!options.quiet && wasm.getFunctionOrNull(func) == nullptr) {
      std::cerr << "warning: function " << func << " does not exist\n";
    }
    keepFuncs.insert(func);
  }

  // Remove the functions specified with --remove-funcs
  for (auto& func : options.splitFuncs) {
    auto* function = wasm.getFunctionOrNull(func);
    if (!options.quiet && function == nullptr) {
      std::cerr << "warning: function " << func << " does not exist\n";
    }
    if (function && function->imported()) {
      if (!options.quiet) {
        std::cerr << "warning: cannot split out imported function " << func
                  << "\n";
      }
    } else {
      keepFuncs.erase(func);
    }
  }

  if (!options.quiet && keepFuncs.size() == 0) {
    std::cerr << "warning: not keeping any functions in the primary module\n";
  }

  // If warnings are enabled, check that any functions are being split out.
  if (!options.quiet) {
    std::set<Name> splitFuncs;
    ModuleUtils::iterDefinedFunctions(wasm, [&](Function* func) {
      if (keepFuncs.count(func->name) == 0) {
        splitFuncs.insert(func->name);
      }
    });

    if (splitFuncs.size() == 0) {
      std::cerr
        << "warning: not splitting any functions out to the secondary module\n";
    }

    // Dump the kept and split functions if we are verbose
    if (options.verbose) {
      auto printCommaSeparated = [&](auto funcs) {
        for (auto it = funcs.begin(); it != funcs.end(); ++it) {
          if (it != funcs.begin()) {
            std::cout << ", ";
          }
          std::cout << *it;
        }
      };

      std::cout << "Keeping functions: ";
      printCommaSeparated(keepFuncs);
      std::cout << "\n";

      std::cout << "Splitting out functions: ";
      printCommaSeparated(splitFuncs);
      std::cout << "\n";
    }
  }

  // Actually perform the splitting
  ModuleSplitting::Config config;
  config.primaryFuncs = std::move(keepFuncs);
  if (options.importNamespace.size()) {
    config.importNamespace = options.importNamespace;
  }
  if (options.placeholderNamespace.size()) {
    config.placeholderNamespace = options.placeholderNamespace;
  }
  if (options.exportPrefix.size()) {
    config.newExportPrefix = options.exportPrefix;
  }
  config.minimizeNewExportNames = !options.passOptions.debugInfo;
  auto splitResults = ModuleSplitting::splitFunctions(wasm, config);
  auto& secondary = splitResults.secondary;

  adjustTableSize(wasm, options.initialTableSize);
  adjustTableSize(*secondary, options.initialTableSize);

  if (options.symbolMap) {
    writeSymbolMap(wasm, options.primaryOutput + ".symbols");
    writeSymbolMap(*secondary, options.secondaryOutput + ".symbols");
  }

  if (options.placeholderMap) {
    writePlaceholderMap(splitResults.placeholderMap,
                        options.primaryOutput + ".placeholders");
  }

  // Set the names of the split modules. This can help differentiate them in
  // stack traces.
  if (options.emitModuleNames) {
    if (!wasm.name) {
      wasm.name = Path::getBaseName(options.primaryOutput);
    }
    secondary->name = Path::getBaseName(options.secondaryOutput);
  }

  // write the output modules
  writeModule(wasm, options.primaryOutput, options);
  writeModule(*secondary, options.secondaryOutput, options);
}

void mergeProfiles(const WasmSplitOptions& options) {
  // Read the initial profile. We will merge other profiles into this one.
  ProfileData data = readProfile(options.inputFiles[0]);

  // In verbose mode, we want to find profiles that don't contribute to the
  // merged profile. To do that, keep track of how many profiles each function
  // appears in. If any profile contains only functions that appear in multiple
  // profiles, it could be dropped.
  std::vector<size_t> numProfiles;
  if (options.verbose) {
    numProfiles.resize(data.timestamps.size());
    for (size_t t = 0; t < data.timestamps.size(); ++t) {
      if (data.timestamps[t]) {
        numProfiles[t] = 1;
      }
    }
  }

  // Read all the other profiles, taking the minimum nonzero timestamp for each
  // function.
  for (size_t i = 1; i < options.inputFiles.size(); ++i) {
    ProfileData newData = readProfile(options.inputFiles[i]);
    if (newData.hash != data.hash) {
      Fatal() << "Checksum in profile " << options.inputFiles[i]
              << " does not match hash in profile " << options.inputFiles[0];
    }
    if (newData.timestamps.size() != data.timestamps.size()) {
      Fatal() << "Profile " << options.inputFiles[i]
              << " incompatible with profile " << options.inputFiles[0];
    }
    for (size_t t = 0; t < data.timestamps.size(); ++t) {
      if (data.timestamps[t] && newData.timestamps[t]) {
        data.timestamps[t] =
          std::min(data.timestamps[t], newData.timestamps[t]);
      } else if (newData.timestamps[t]) {
        data.timestamps[t] = newData.timestamps[t];
      }
      if (options.verbose && newData.timestamps[t]) {
        ++numProfiles[t];
      }
    }
  }

  // Check for useless profiles.
  if (options.verbose) {
    for (const auto& file : options.inputFiles) {
      bool useless = true;
      ProfileData newData = readProfile(file);
      for (size_t t = 0; t < newData.timestamps.size(); ++t) {
        if (newData.timestamps[t] && numProfiles[t] == 1) {
          useless = false;
          break;
        }
      }
      if (useless) {
        std::cout << "Profile " << file
                  << " only includes functions included in other profiles.\n";
      }
    }
  }

  // Write the combined profile.
  BufferWithRandomAccess buffer;
  buffer << data.hash;
  for (size_t t = 0; t < data.timestamps.size(); ++t) {
    buffer << uint32_t(data.timestamps[t]);
  }
  Output out(options.output, Flags::Binary);
  buffer.writeTo(out.getStream());
}

} // anonymous namespace

int main(int argc, const char* argv[]) {
  WasmSplitOptions options;
  options.parse(argc, argv);

  if (!options.validate()) {
    Fatal() << "Invalid command line arguments";
  }

  switch (options.mode) {
    case WasmSplitOptions::Mode::Split:
      splitModule(options);
      break;
    case WasmSplitOptions::Mode::Instrument:
      instrumentModule(options);
      break;
    case WasmSplitOptions::Mode::MergeProfiles:
      mergeProfiles(options);
      break;
  }
}