dex2oat源码流程分析

dex2oat是ART运行模式下虚拟机必备的一个组件，主要用来把安装的apk和动态加载的dex等文件转换成oat文件，方便下一步的加载解析，获得其中的类并执行相关方法，所以本文以Android 6.0源码为例，对dex的处理流程尝试做一下分析，了解其中的处理情况。

dex2oat源码位于art\dex2oat\Dex2oat.cc，入口函数为main：

int main(int argc, char** argv) {
  int result = art::dex2oat(argc, argv);
  if (!art::kIsDebugBuild && (RUNNING_ON_VALGRIND == 0)) {
    exit(result);
  }
  return result;
}

这里的整体流程如下图所示（图片来自参考文献），后边也主要分析的这个流程上的代码：

直接调用了同文件art 命名空间下的 dex2oat 函数，做下一步的处理：

static int dex2oat(int argc, char** argv) {
  b13564922();

  TimingLogger timings("compiler", false, false);

  Dex2Oat dex2oat(&timings);

  // Parse arguments. Argument mistakes will lead to exit(EXIT_FAILURE) in UsageError.
  dex2oat.ParseArgs(argc, argv);

  // Check early that the result of compilation can be written
  if (!dex2oat.OpenFile()) {
    return EXIT_FAILURE;
  }

  // Print the complete line when any of the following is true:
  //   1) Debug build
  //   2) Compiling an image
  //   3) Compiling with --host
  //   4) Compiling on the host (not a target build)
  // Otherwise, print a stripped command line.
  if (kIsDebugBuild || dex2oat.IsImage() || dex2oat.IsHost() || !kIsTargetBuild) {
    LOG(INFO) << CommandLine();
  } else {
    LOG(INFO) << StrippedCommandLine();
  }

  if (!dex2oat.Setup()) {
    dex2oat.EraseOatFile();
    return EXIT_FAILURE;
  }

  if (dex2oat.IsImage()) {
    return CompileImage(dex2oat);
  } else {
    return CompileApp(dex2oat);
  }
}

dex2oat的整个逻辑是很清晰的：
1. 做一个arm上的workaround，这个与我们分析的主线暂时无关，了解一下就可以了。
2. 构造Dex2oat对象
3. 处理命令行参数
4. 先行判断对于文件是否有写的权限
5. 打印命令行参数
6. 判断dex2oat的setup是否完成
7. 根据是否image分别调用CompileImage或CompileApp的处理
这里放一张来自参考文献的总体流程图：

CompileImage

基本上还是对于dex2oat.Compile的封装，后面都是对写文件和计时的处理：

static int CompileImage(Dex2Oat& dex2oat) {
  dex2oat.Compile();

  // Create the boot.oat.
  if (!dex2oat.CreateOatFile()) {
    dex2oat.EraseOatFile();
    return EXIT_FAILURE;
  }

  // Flush and close the boot.oat. We always expect the output file by name, and it will be
  // re-opened from the unstripped name.
  if (!dex2oat.FlushCloseOatFile()) {
    return EXIT_FAILURE;
  }

  // Creates the boot.art and patches the boot.oat.
  if (!dex2oat.HandleImage()) {
    return EXIT_FAILURE;
  }

  // When given --host, finish early without stripping.
  if (dex2oat.IsHost()) {
    dex2oat.DumpTiming();
    return EXIT_SUCCESS;
  }

  // Copy unstripped to stripped location, if necessary.
  if (!dex2oat.CopyUnstrippedToStripped()) {
    return EXIT_FAILURE;
  }

  // FlushClose again, as stripping might have re-opened the oat file.
  if (!dex2oat.FlushCloseOatFile()) {
    return EXIT_FAILURE;
  }

  dex2oat.DumpTiming();
  return EXIT_SUCCESS;
}

CompileApp

然后我们再看一下基本一模一样的CompileApp.

static int CompileApp(Dex2Oat& dex2oat) {
  dex2oat.Compile();

  // Create the app oat.
  if (!dex2oat.CreateOatFile()) {
    dex2oat.EraseOatFile();
    return EXIT_FAILURE;
  }

  // Do not close the oat file here. We might haven gotten the output file by file descriptor,
  // which we would lose.
  if (!dex2oat.FlushOatFile()) {
    return EXIT_FAILURE;
  }

  // When given --host, finish early without stripping.
  if (dex2oat.IsHost()) {
    if (!dex2oat.FlushCloseOatFile()) {
      return EXIT_FAILURE;
    }

    dex2oat.DumpTiming();
    return EXIT_SUCCESS;
  }

  // Copy unstripped to stripped location, if necessary. This will implicitly flush & close the
  // unstripped version. If this is given, we expect to be able to open writable files by name.
  if (!dex2oat.CopyUnstrippedToStripped()) {
    return EXIT_FAILURE;
  }

  // Flush and close the file.
  if (!dex2oat.FlushCloseOatFile()) {
    return EXIT_FAILURE;
  }

  dex2oat.DumpTiming();
  return EXIT_SUCCESS;
}

Compile

CompileImage和CompileApp都调用了dex2oat.Compile()函数：

  // Create and invoke the compiler driver. This will compile all the dex files.
  void Compile() {
    TimingLogger::ScopedTiming t("dex2oat Compile", timings_);
    compiler_phases_timings_.reset(new CumulativeLogger("compilation times"));

    // Handle and ClassLoader creation needs to come after Runtime::Create
    jobject class_loader = nullptr;
    Thread* self = Thread::Current();
    if (!boot_image_option_.empty()) {
      ClassLinker* class_linker = Runtime::Current()->GetClassLinker();
      OpenClassPathFiles(runtime_->GetClassPathString(), dex_files_, &class_path_files_);
      ScopedObjectAccess soa(self);

      // Classpath: first the class-path given.
      std::vector<const DexFile*> class_path_files;
      for (auto& class_path_file : class_path_files_) {
        class_path_files.push_back(class_path_file.get());
      }

      // Store the classpath we have right now.
      key_value_store_->Put(OatHeader::kClassPathKey,
                            OatFile::EncodeDexFileDependencies(class_path_files));

      // Then the dex files we'll compile. Thus we'll resolve the class-path first.
      class_path_files.insert(class_path_files.end(), dex_files_.begin(), dex_files_.end());

      class_loader = class_linker->CreatePathClassLoader(self, class_path_files);
    }

    driver_.reset(new CompilerDriver(compiler_options_.get(),
                                     verification_results_.get(),
                                     &method_inliner_map_,
                                     compiler_kind_,
                                     instruction_set_,
                                     instruction_set_features_.get(),
                                     image_,
                                     image_classes_.release(),
                                     compiled_classes_.release(),
                                     nullptr,
                                     thread_count_,
                                     dump_stats_,
                                     dump_passes_,
                                     dump_cfg_file_name_,
                                     compiler_phases_timings_.get(),
                                     swap_fd_,
                                     profile_file_));

    driver_->CompileAll(class_loader, dex_files_, timings_);
  }

Java不同于其它很多编译型语言的一点是在于它有ClassLoader。在做编译之前，先要对ClassLoader进行预处理。
然后，就创建一个CompilerDriver对象，并调用driver的ComileAll来完成编译。

CompilerDriver的构造函数

核心逻辑还是compiler_的初始化。看到构造需要这么多参数，我们需要对于dex2oat的命令行参数了解(art\compiler\driver\Compiler_driver.cc)：

CompilerDriver::CompilerDriver(const CompilerOptions* compiler_options,
                               VerificationResults* verification_results,
                               DexFileToMethodInlinerMap* method_inliner_map,
                               Compiler::Kind compiler_kind,
                               InstructionSet instruction_set,
                               const InstructionSetFeatures* instruction_set_features,
                               bool image, std::unordered_set<std::string>* image_classes,
                               std::unordered_set<std::string>* compiled_classes,
                               std::unordered_set<std::string>* compiled_methods,
                               size_t thread_count, bool dump_stats, bool dump_passes,
                               const std::string& dump_cfg_file_name, CumulativeLogger* timer,
                               int swap_fd, const std::string& profile_file)
    : swap_space_(swap_fd == -1 ? nullptr : new SwapSpace(swap_fd, 10 * MB)),
      swap_space_allocator_(new SwapAllocator<void>(swap_space_.get())),
      profile_present_(false), compiler_options_(compiler_options),
      verification_results_(verification_results),
      method_inliner_map_(method_inliner_map),
      compiler_(Compiler::Create(this, compiler_kind)),
      compiler_kind_(compiler_kind),
      instruction_set_(instruction_set),
      instruction_set_features_(instruction_set_features),
      freezing_constructor_lock_("freezing constructor lock"),
      compiled_classes_lock_("compiled classes lock"),
      compiled_methods_lock_("compiled method lock"),
      compiled_methods_(MethodTable::key_compare()),
      non_relative_linker_patch_count_(0u),
      image_(image),
      image_classes_(image_classes),
      classes_to_compile_(compiled_classes),
      methods_to_compile_(compiled_methods),
      had_hard_verifier_failure_(false),
      thread_count_(thread_count),
      stats_(new AOTCompilationStats),
      dedupe_enabled_(true),
      dump_stats_(dump_stats),
      dump_passes_(dump_passes),
      dump_cfg_file_name_(dump_cfg_file_name),
      timings_logger_(timer),
      compiler_context_(nullptr),
      support_boot_image_fixup_(instruction_set != kMips && instruction_set != kMips64),
      dedupe_code_("dedupe code", *swap_space_allocator_),
      dedupe_src_mapping_table_("dedupe source mapping table", *swap_space_allocator_),
      dedupe_mapping_table_("dedupe mapping table", *swap_space_allocator_),
      dedupe_vmap_table_("dedupe vmap table", *swap_space_allocator_),
      dedupe_gc_map_("dedupe gc map", *swap_space_allocator_),
      dedupe_cfi_info_("dedupe cfi info", *swap_space_allocator_) {
  DCHECK(compiler_options_ != nullptr);
  DCHECK(verification_results_ != nullptr);
  DCHECK(method_inliner_map_ != nullptr);

  dex_to_dex_compiler_ = reinterpret_cast(ArtCompileDEX);

  compiler_->Init();

  CHECK_EQ(image_, image_classes_.get() != nullptr);

  // Read the profile file if one is provided.
  if (!profile_file.empty()) {
    profile_present_ = profile_file_.LoadFile(profile_file);
    if (profile_present_) {
      LOG(INFO) << "Using profile data form file " << profile_file;
    } else {
      LOG(INFO) << "Failed to load profile file " << profile_file;
    }
  }
}

CompilerDriver::CompileAll

CompilerDriver为编译线程构造了一个线程池。
在CompilerDriver进行编译的时候，分成了两个步骤：

• PreCompile
• Compile

void CompilerDriver::CompileAll(jobject class_loader,
                                const std::vector<const DexFile*>& dex_files,
                                TimingLogger* timings) {
  DCHECK(!Runtime::Current()->IsStarted());
  std::unique_ptr<ThreadPool> thread_pool(
      new ThreadPool("Compiler driver thread pool", thread_count_ - 1));
  VLOG(compiler) << "Before precompile " << GetMemoryUsageString(false);
  PreCompile(class_loader, dex_files, thread_pool.get(), timings);
  Compile(class_loader, dex_files, thread_pool.get(), timings);
  if (dump_stats_) {
    stats_->Dump();
  }
}

CompilerDriver::PreCompile

PreCompile的步骤主要就是两个：
- 做校验
- 做类的初始化
我们将前面判断是否要做校验的部分先略过，这个PreCompile的逻辑看起来就清晰得多。

void CompilerDriver::PreCompile(jobject class_loader, const std::vector<const DexFile*>& dex_files,
                                ThreadPool* thread_pool, TimingLogger* timings) {
  LoadImageClasses(timings);
  VLOG(compiler) << "LoadImageClasses: " << GetMemoryUsageString(false);

  const bool verification_enabled = compiler_options_->IsVerificationEnabled();
  const bool never_verify = compiler_options_->NeverVerify();

  // We need to resolve for never_verify since it needs to run dex to dex to add the
  // RETURN_VOID_NO_BARRIER.
  if (never_verify || verification_enabled) {
    Resolve(class_loader, dex_files, thread_pool, timings);
    VLOG(compiler) << "Resolve: " << GetMemoryUsageString(false);
  }

  if (never_verify) {
    VLOG(compiler) << "Verify none mode specified, skipping verification.";
    SetVerified(class_loader, dex_files, thread_pool, timings);
  }

  if (!verification_enabled) {
    return;
  }

  Verify(class_loader, dex_files, thread_pool, timings);
  VLOG(compiler) << "Verify: " << GetMemoryUsageString(false);

  if (had_hard_verifier_failure_ && GetCompilerOptions().AbortOnHardVerifierFailure()) {
    LOG(FATAL) << "Had a hard failure verifying all classes, and was asked to abort in such "
               << "situations. Please check the log.";
  }

  InitializeClasses(class_loader, dex_files, thread_pool, timings);
  VLOG(compiler) << "InitializeClasses: " << GetMemoryUsageString(false);

  UpdateImageClasses(timings);
  VLOG(compiler) << "UpdateImageClasses: " << GetMemoryUsageString(false);
}

CompilerDriver::Compile

针对每一个dex，调用CompileDexFile去编译：

void CompilerDriver::Compile(jobject class_loader, const std::vector<const DexFile*>& dex_files,
                             ThreadPool* thread_pool, TimingLogger* timings) {
  for (size_t i = 0; i != dex_files.size(); ++i) {
    const DexFile* dex_file = dex_files[i];
    CHECK(dex_file != nullptr);
    CompileDexFile(class_loader, *dex_file, dex_files, thread_pool, timings);
  }
  VLOG(compiler) << "Compile: " << GetMemoryUsageString(false);
}

CompilerDriver::CompileDexFile

上面的Compile函数是将多个dex拆成每一个dex文件的粒度，而CompileDexFile再将其拆成每个类的粒度，针对每个类再调用CompileClass来进行编译：

void CompilerDriver::CompileDexFile(jobject class_loader, const DexFile& dex_file,
                                    const std::vector<const DexFile*>& dex_files,
                                    ThreadPool* thread_pool, TimingLogger* timings) {
  TimingLogger::ScopedTiming t("Compile Dex File", timings);
  ParallelCompilationManager context(Runtime::Current()->GetClassLinker(), class_loader, this,
                                     &dex_file, dex_files, thread_pool);
  context.ForAll(0, dex_file.NumClassDefs(), CompilerDriver::CompileClass, thread_count_);
}

context.ForAll(0, dex_file.NumClassDefs(), CompilerDriver::CompileClass, thread_count_);这条语句中重要的是CompilerDriver::CompileClass，CompilerDriver::CompileClass代表一个回调函数，这个回调函数将一个dex中的类进行编译。

void CompilerDriver::CompileClass(const ParallelCompilationManager* manager,
                                  size_t class_def_index) {
  ATRACE_CALL();
  const DexFile& dex_file = *manager->GetDexFile();
  const DexFile::ClassDef& class_def = dex_file.GetClassDef(class_def_index);
  ClassLinker* class_linker = manager->GetClassLinker();
  jobject jclass_loader = manager->GetClassLoader();
  Thread* self = Thread::Current();
  {
    // Use a scoped object access to perform to the quick SkipClass check.
    const char* descriptor = dex_file.GetClassDescriptor(class_def);
    ScopedObjectAccess soa(self);
    StackHandleScope<3> hs(soa.Self());
    Handle<mirror::ClassLoader> class_loader(
        hs.NewHandle(soa.Decode<mirror::ClassLoader*>(jclass_loader)));
    Handle<mirror::Class> klass(
        hs.NewHandle(class_linker->FindClass(soa.Self(), descriptor, class_loader)));
    if (klass.Get() == nullptr) {
      CHECK(soa.Self()->IsExceptionPending());
      soa.Self()->ClearException();
    } else if (SkipClass(jclass_loader, dex_file, klass.Get())) {
      return;
    }
  }
  ClassReference ref(&dex_file, class_def_index);
  // Skip compiling classes with generic verifier failures since they will still fail at runtime
  if (manager->GetCompiler()->verification_results_->IsClassRejected(ref)) {
    return;
  }
  const uint8_t* class_data = dex_file.GetClassData(class_def);
  if (class_data == nullptr) {
    // empty class, probably a marker interface
    return;
  }

  CompilerDriver* const driver = manager->GetCompiler();

  // Can we run DEX-to-DEX compiler on this class ?
  DexToDexCompilationLevel dex_to_dex_compilation_level = kDontDexToDexCompile;
  {
    ScopedObjectAccess soa(self);
    StackHandleScope<1> hs(soa.Self());
    Handle<mirror::ClassLoader> class_loader(
        hs.NewHandle(soa.Decode<mirror::ClassLoader*>(jclass_loader)));
    dex_to_dex_compilation_level = driver->GetDexToDexCompilationlevel(
        soa.Self(), class_loader, dex_file, class_def);
  }
  ClassDataItemIterator it(dex_file, class_data);
  // Skip fields
  while (it.HasNextStaticField()) {
    it.Next();
  }
  while (it.HasNextInstanceField()) {
    it.Next();
  }

  bool compilation_enabled = driver->IsClassToCompile(
      dex_file.StringByTypeIdx(class_def.class_idx_));

  // Compile direct methods
  int64_t previous_direct_method_idx = -1;
  while (it.HasNextDirectMethod()) {
    uint32_t method_idx = it.GetMemberIndex();
    if (method_idx == previous_direct_method_idx) {
      // smali can create dex files with two encoded_methods sharing the same method_idx
      // http://code.google.com/p/smali/issues/detail?id=119
      it.Next();
      continue;
    }
    previous_direct_method_idx = method_idx;
    driver->CompileMethod(self, it.GetMethodCodeItem(), it.GetMethodAccessFlags(),
                          it.GetMethodInvokeType(class_def), class_def_index,
                          method_idx, jclass_loader, dex_file, dex_to_dex_compilation_level,
                          compilation_enabled);
    it.Next();
  }
  // Compile virtual methods
  int64_t previous_virtual_method_idx = -1;
  while (it.HasNextVirtualMethod()) {
    uint32_t method_idx = it.GetMemberIndex();
    if (method_idx == previous_virtual_method_idx) {
      // smali can create dex files with two encoded_methods sharing the same method_idx
      // http://code.google.com/p/smali/issues/detail?id=119
      it.Next();
      continue;
    }
    previous_virtual_method_idx = method_idx;
    driver->CompileMethod(self, it.GetMethodCodeItem(), it.GetMethodAccessFlags(),
                          it.GetMethodInvokeType(class_def), class_def_index,
                          method_idx, jclass_loader, dex_file, dex_to_dex_compilation_level,
                          compilation_enabled);
    it.Next();
  }
  DCHECK(!it.HasNext());
}

前面的代码都在构造编译环境，初始化一些driver等，然后调用了CompileMethod函数将一个方法进行编译：

void CompilerDriver::CompileMethod(Thread* self, const DexFile::CodeItem* code_item,
                                   uint32_t access_flags, InvokeType invoke_type,
                                   uint16_t class_def_idx, uint32_t method_idx,
                                   jobject class_loader, const DexFile& dex_file,
                                   DexToDexCompilationLevel dex_to_dex_compilation_level,
                                   bool compilation_enabled) {
  CompiledMethod* compiled_method = nullptr;
  uint64_t start_ns = kTimeCompileMethod ? NanoTime() : 0;
  MethodReference method_ref(&dex_file, method_idx);

  if ((access_flags & kAccNative) != 0) {
    // Are we interpreting only and have support for generic JNI down calls?
    if (!compiler_options_->IsCompilationEnabled() &&
        InstructionSetHasGenericJniStub(instruction_set_)) {
      // Leaving this empty will trigger the generic JNI version
    } else {
      compiled_method = compiler_->JniCompile(access_flags, method_idx, dex_file);
      CHECK(compiled_method != nullptr);
    }
  } else if ((access_flags & kAccAbstract) != 0) {
    // Abstract methods don't have code.
  } else {
    bool has_verified_method = verification_results_->GetVerifiedMethod(method_ref) != nullptr;
    bool compile = compilation_enabled &&
                   // Basic checks, e.g., not .
                   verification_results_->IsCandidateForCompilation(method_ref, access_flags) &&
                   // Did not fail to create VerifiedMethod metadata.
                   has_verified_method &&
                   // Is eligable for compilation by methods-to-compile filter.
                   IsMethodToCompile(method_ref);
    if (compile) {
      // NOTE: if compiler declines to compile this method, it will return null.
      compiled_method = compiler_->Compile(code_item, access_flags, invoke_type, class_def_idx,
                                           method_idx, class_loader, dex_file);
    }
    if (compiled_method == nullptr && dex_to_dex_compilation_level != kDontDexToDexCompile) {
      // TODO: add a command-line option to disable DEX-to-DEX compilation ?
      // Do not optimize if a VerifiedMethod is missing. SafeCast elision, for example, relies on
      // it.
      (*dex_to_dex_compiler_)(*this, code_item, access_flags,
                              invoke_type, class_def_idx,
                              method_idx, class_loader, dex_file,
                              has_verified_method ? dex_to_dex_compilation_level : kRequired);
    }
  }
  if (kTimeCompileMethod) {
    uint64_t duration_ns = NanoTime() - start_ns;
    if (duration_ns > MsToNs(compiler_->GetMaximumCompilationTimeBeforeWarning())) {
      LOG(WARNING) << "Compilation of " << PrettyMethod(method_idx, dex_file)
                   << " took " << PrettyDuration(duration_ns);
    }
  }

  if (compiled_method != nullptr) {
    // Count non-relative linker patches.
    size_t non_relative_linker_patch_count = 0u;
    for (const LinkerPatch& patch : compiled_method->GetPatches()) {
      if (!patch.IsPcRelative()) {
        ++non_relative_linker_patch_count;
      }
    }
    bool compile_pic = GetCompilerOptions().GetCompilePic();  // Off by default
    // When compiling with PIC, there should be zero non-relative linker patches
    CHECK(!compile_pic || non_relative_linker_patch_count == 0u);

    DCHECK(GetCompiledMethod(method_ref) == nullptr) << PrettyMethod(method_idx, dex_file);
    {
      MutexLock mu(self, compiled_methods_lock_);
      compiled_methods_.Put(method_ref, compiled_method);
      non_relative_linker_patch_count_ += non_relative_linker_patch_count;
    }
    DCHECK(GetCompiledMethod(method_ref) != nullptr) << PrettyMethod(method_idx, dex_file);
  }

  // Done compiling, delete the verified method to reduce native memory usage. Do not delete in
  // optimizing compiler, which may need the verified method again for inlining.
  if (compiler_kind_ != Compiler::kOptimizing) {
    verification_results_->RemoveVerifiedMethod(method_ref);
  }

  if (self->IsExceptionPending()) {
    ScopedObjectAccess soa(self);
    LOG(FATAL) << "Unexpected exception compiling: " << PrettyMethod(method_idx, dex_file) << "\n"
        << self->GetException()->Dump();
  }
}

首先是对JNI调用的处理，我们之前曾经看到过的序列。这里会调用compiler_->JniCompile函数。抽象方法不需要生成代码，下面再开始编普通方法，通过调用compiler_->Compile方法来完成。其中还使用到了类的成员变量dex_to_dex_compiler_，这个成员变量在CompilerDriver类的构造函数中被赋值：

CompilerDriver::CompilerDriver(...){
  ......
  dex_to_dex_compiler_ = reinterpret_cast(ArtCompileDEX);
  ......
}

ArtCompileDEX的实现代码如下：

extern "C" void ArtCompileDEX(art::CompilerDriver& driver, const art::DexFile::CodeItem* code_item,
                              uint32_t access_flags, art::InvokeType invoke_type,
                              uint16_t class_def_idx, uint32_t method_idx, jobject class_loader,
                              const art::DexFile& dex_file,
                              art::DexToDexCompilationLevel dex_to_dex_compilation_level) {
  UNUSED(invoke_type);
  if (dex_to_dex_compilation_level != art::kDontDexToDexCompile) {
    art::DexCompilationUnit unit(nullptr, class_loader, art::Runtime::Current()->GetClassLinker(),
                                 dex_file, code_item, class_def_idx, method_idx, access_flags,
                                 driver.GetVerifiedMethod(&dex_file, method_idx));
    art::optimizer::DexCompiler dex_compiler(driver, unit, dex_to_dex_compilation_level);
    dex_compiler.Compile();
  }
}

而compiler_->Compile方法中，compiler_是通过Compiler的构造函数中Compiler::Create(this, compiler_kind)创建的(art\compiler\Compiler.cc)：

Compiler* Compiler::Create(CompilerDriver* driver, Compiler::Kind kind) {
  switch (kind) {
    case kQuick:
      return CreateQuickCompiler(driver);

    case kOptimizing:
      return CreateOptimizingCompiler(driver);

    default:
      LOG(FATAL) << "UNREACHABLE";
      UNREACHABLE();
  }
}

举例说明CreateQuickCompiler函数(art\compiler\dex\quick\Quick_compiler.cc)：

Compiler* CreateQuickCompiler(CompilerDriver* driver) {
  return QuickCompiler::Create(driver);
}

Compiler* QuickCompiler::Create(CompilerDriver* driver) {
  return new QuickCompiler(driver);
}

所以如果编译类型为QuickCompile的话，compiler_->Compile方法就调用了QuickCompiler的Compile方法：

CompiledMethod* QuickCompiler::Compile(const DexFile::CodeItem* code_item,
                                       uint32_t access_flags,
                                       InvokeType invoke_type,
                                       uint16_t class_def_idx,
                                       uint32_t method_idx,
                                       jobject class_loader,
                                       const DexFile& dex_file) const {
  // TODO: check method fingerprint here to determine appropriate backend type.  Until then, use
  // build default.
  CompilerDriver* driver = GetCompilerDriver();

  VLOG(compiler) << "Compiling " << PrettyMethod(method_idx, dex_file) << "...";
  if (Compiler::IsPathologicalCase(*code_item, method_idx, dex_file)) {
    return nullptr;
  }

  if (driver->GetVerifiedMethod(&dex_file, method_idx)->HasRuntimeThrow()) {
    return nullptr;
  }

  DCHECK(driver->GetCompilerOptions().IsCompilationEnabled());

  Runtime* const runtime = Runtime::Current();
  ClassLinker* const class_linker = runtime->GetClassLinker();
  InstructionSet instruction_set = driver->GetInstructionSet();
  if (instruction_set == kArm) {
    instruction_set = kThumb2;
  }
  CompilationUnit cu(runtime->GetArenaPool(), instruction_set, driver, class_linker);
  cu.dex_file = &dex_file;
  cu.class_def_idx = class_def_idx;
  cu.method_idx = method_idx;
  cu.access_flags = access_flags;
  cu.invoke_type = invoke_type;
  cu.shorty = dex_file.GetMethodShorty(dex_file.GetMethodId(method_idx));

  CHECK((cu.instruction_set == kThumb2) ||
        (cu.instruction_set == kArm64) ||
        (cu.instruction_set == kX86) ||
        (cu.instruction_set == kX86_64) ||
        (cu.instruction_set == kMips) ||
        (cu.instruction_set == kMips64));

  // TODO: set this from command line
  constexpr bool compiler_flip_match = false;
  const std::string compiler_method_match = "";

  bool use_match = !compiler_method_match.empty();
  bool match = use_match && (compiler_flip_match ^
      (PrettyMethod(method_idx, dex_file).find(compiler_method_match) != std::string::npos));
  if (!use_match || match) {
    cu.disable_opt = kCompilerOptimizerDisableFlags;
    cu.enable_debug = kCompilerDebugFlags;
    cu.verbose = VLOG_IS_ON(compiler) ||
        (cu.enable_debug & (1 << kDebugVerbose));
  }

  if (driver->GetCompilerOptions().HasVerboseMethods()) {
    cu.verbose = driver->GetCompilerOptions().IsVerboseMethod(PrettyMethod(method_idx, dex_file));
  }

  if (cu.verbose) {
    cu.enable_debug |= (1 << kDebugCodegenDump);
  }

  /*
   * TODO: rework handling of optimization and debug flags.  Should we split out
   * MIR and backend flags?  Need command-line setting as well.
   */

  InitCompilationUnit(cu);

  cu.StartTimingSplit("BuildMIRGraph");
  cu.mir_graph.reset(new MIRGraph(&cu, &cu.arena));

  /*
   * After creation of the MIR graph, also create the code generator.
   * The reason we do this is that optimizations on the MIR graph may need to get information
   * that is only available if a CG exists.
   */
  cu.cg.reset(GetCodeGenerator(&cu, nullptr));

  /* Gathering opcode stats? */
  if (kCompilerDebugFlags & (1 << kDebugCountOpcodes)) {
    cu.mir_graph->EnableOpcodeCounting();
  }

  /* Build the raw MIR graph */
  cu.mir_graph->InlineMethod(code_item, access_flags, invoke_type, class_def_idx, method_idx,
                             class_loader, dex_file);

  if (!CanCompileMethod(method_idx, dex_file, &cu)) {
    VLOG(compiler)  << cu.instruction_set << ": Cannot compile method : "
        << PrettyMethod(method_idx, dex_file);
    cu.EndTiming();
    return nullptr;
  }

  cu.NewTimingSplit("MIROpt:CheckFilters");
  std::string skip_message;
  if (cu.mir_graph->SkipCompilation(&skip_message)) {
    VLOG(compiler) << cu.instruction_set << ": Skipping method : "
        << PrettyMethod(method_idx, dex_file) << "  Reason = " << skip_message;
    cu.EndTiming();
    return nullptr;
  }

  /* Create the pass driver and launch it */
  PassDriverMEOpts pass_driver(GetPreOptPassManager(), GetPostOptPassManager(), &cu);
  pass_driver.Launch();

  /* For non-leaf methods check if we should skip compilation when the profiler is enabled. */
  if (cu.compiler_driver->ProfilePresent()
      && !cu.mir_graph->MethodIsLeaf()
      && cu.mir_graph->SkipCompilationByName(PrettyMethod(method_idx, dex_file))) {
    cu.EndTiming();
    return nullptr;
  }

  if (cu.enable_debug & (1 << kDebugDumpCheckStats)) {
    cu.mir_graph->DumpCheckStats();
  }

  if (kCompilerDebugFlags & (1 << kDebugCountOpcodes)) {
    cu.mir_graph->ShowOpcodeStats();
  }

  /* Reassociate sreg names with original Dalvik vreg names. */
  cu.mir_graph->RemapRegLocations();

  /* Free Arenas from the cu.arena_stack for reuse by the cu.arena in the codegen. */
  if (cu.enable_debug & (1 << kDebugShowMemoryUsage)) {
    if (cu.arena_stack.PeakBytesAllocated() > 1 * 1024 * 1024) {
      MemStats stack_stats(cu.arena_stack.GetPeakStats());
      LOG(INFO) << PrettyMethod(method_idx, dex_file) << " " << Dumpable(stack_stats);
    }
  }
  cu.arena_stack.Reset();

  CompiledMethod* result = nullptr;

  if (cu.mir_graph->PuntToInterpreter()) {
    VLOG(compiler) << cu.instruction_set << ": Punted method to interpreter: "
        << PrettyMethod(method_idx, dex_file);
    cu.EndTiming();
    return nullptr;
  }

  cu.cg->Materialize();

  cu.NewTimingSplit("Dedupe");  /* deduping takes up the vast majority of time in GetCompiledMethod(). */
  result = cu.cg->GetCompiledMethod();
  cu.NewTimingSplit("Cleanup");

  if (result) {
    VLOG(compiler) << cu.instruction_set << ": Compiled " << PrettyMethod(method_idx, dex_file);
  } else {
    VLOG(compiler) << cu.instruction_set << ": Deferred " << PrettyMethod(method_idx, dex_file);
  }

  if (cu.enable_debug & (1 << kDebugShowMemoryUsage)) {
    if (cu.arena.BytesAllocated() > (1 * 1024 *1024)) {
      MemStats mem_stats(cu.arena.GetMemStats());
      LOG(INFO) << PrettyMethod(method_idx, dex_file) << " " << Dumpable(mem_stats);
    }
  }

  if (cu.enable_debug & (1 << kDebugShowSummaryMemoryUsage)) {
    LOG(INFO) << "MEMINFO " << cu.arena.BytesAllocated() << " " << cu.mir_graph->GetNumBlocks()
                    << " " << PrettyMethod(method_idx, dex_file);
  }

  cu.EndTiming();
  driver->GetTimingsLogger()->AddLogger(cu.timings);
  return result;
}

关于cu.cg->GetCompiledMethod()的不再深挖，此处暂时保留。。。

参老文献：
ART世界探险(13) - 初入dex2oat
dex2oat将dex转换为oat的执行路径概览
ART世界探险(16) - 快速编译器下的方法编译