src/main/java/com/android/tools/r8/horizontalclassmerging/HorizontalClassMerger.java

// Copyright (c) 2020, the R8 project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

package com.android.tools.r8.horizontalclassmerging;

import com.android.tools.r8.graph.AppInfoWithClassHierarchy;
import com.android.tools.r8.graph.AppView;
import com.android.tools.r8.graph.DexProgramClass;
import com.android.tools.r8.graph.DirectMappedDexApplication;
import com.android.tools.r8.graph.PrunedItems;
import com.android.tools.r8.shaking.AppInfoWithLiveness;
import com.android.tools.r8.shaking.FieldAccessInfoCollectionModifier;
import com.android.tools.r8.shaking.KeepInfoCollection;
import com.android.tools.r8.shaking.RuntimeTypeCheckInfo;
import com.android.tools.r8.utils.InternalOptions.HorizontalClassMergerOptions;
import com.android.tools.r8.utils.Timing;
import java.util.ArrayList;
import java.util.Collection;
import java.util.LinkedList;
import java.util.List;

public class HorizontalClassMerger {

  public enum Mode {
    INITIAL,
    FINAL;

    public boolean isInitial() {
      return this == INITIAL;
    }

    public boolean isFinal() {
      return this == FINAL;
    }
  }

  private final AppView<? extends AppInfoWithClassHierarchy> appView;
  private final Mode mode;
  private final HorizontalClassMergerOptions options;

  private HorizontalClassMerger(AppView<? extends AppInfoWithClassHierarchy> appView, Mode mode) {
    this.appView = appView;
    this.mode = mode;
    this.options = appView.options().horizontalClassMergerOptions();
  }

  public static HorizontalClassMerger createForInitialClassMerging(
      AppView<AppInfoWithLiveness> appView) {
    return new HorizontalClassMerger(appView, Mode.INITIAL);
  }

  public static HorizontalClassMerger createForFinalClassMerging(
      AppView<? extends AppInfoWithClassHierarchy> appView) {
    return new HorizontalClassMerger(appView, Mode.FINAL);
  }

  public void runIfNecessary(RuntimeTypeCheckInfo runtimeTypeCheckInfo, Timing timing) {
    if (options.isEnabled(mode)) {
      timing.begin("HorizontalClassMerger (" + mode.toString() + ")");
      run(runtimeTypeCheckInfo, timing);
      timing.end();
    } else {
      appView.setHorizontallyMergedClasses(HorizontallyMergedClasses.empty(), mode);
    }
  }

  private void run(RuntimeTypeCheckInfo runtimeTypeCheckInfo, Timing timing) {
    // Run the policies on all program classes to produce a final grouping.
    List<Policy> policies = PolicyScheduler.getPolicies(appView, mode, runtimeTypeCheckInfo);
    Collection<MergeGroup> groups = new PolicyExecutor().run(getInitialGroups(), policies, timing);

    // If there are no groups, then end horizontal class merging.
    if (groups.isEmpty()) {
      appView.setHorizontallyMergedClasses(HorizontallyMergedClasses.empty(), mode);
      return;
    }

    HorizontalClassMergerGraphLens.Builder lensBuilder =
        new HorizontalClassMergerGraphLens.Builder();

    // Merge the classes.
    List<ClassMerger> classMergers = initializeClassMergers(lensBuilder, groups);
    SyntheticArgumentClass syntheticArgumentClass =
        mode.isInitial()
            ? new SyntheticArgumentClass.Builder(appView.withLiveness()).build(groups)
            : null;
    applyClassMergers(classMergers, syntheticArgumentClass);

    // Generate the graph lens.
    HorizontallyMergedClasses mergedClasses =
        HorizontallyMergedClasses.builder().addMergeGroups(groups).build();
    appView.setHorizontallyMergedClasses(mergedClasses, mode);

    HorizontalClassMergerGraphLens horizontalClassMergerGraphLens =
        createLens(mergedClasses, lensBuilder, syntheticArgumentClass);

    // Prune keep info.
    KeepInfoCollection keepInfo = appView.getKeepInfo();
    keepInfo.mutate(mutator -> mutator.removeKeepInfoForPrunedItems(mergedClasses.getSources()));

    // Must rewrite AppInfoWithLiveness before pruning the merged classes, to ensure that allocation
    // sites, fields accesses, etc. are correctly transferred to the target classes.
    appView.rewriteWithLensAndApplication(
        horizontalClassMergerGraphLens, getNewApplication(mergedClasses));

    // Record where the synthesized $r8$classId fields are read and written.
    if (mode.isInitial()) {
      createFieldAccessInfoCollectionModifier(groups).modify(appView.withLiveness());
    } else {
      assert groups.stream().noneMatch(MergeGroup::hasClassIdField);
    }

    appView.pruneItems(
        PrunedItems.builder()
            .setPrunedApp(appView.appInfo().app())
            .addRemovedClasses(mergedClasses.getSources())
            .addNoLongerSyntheticItems(mergedClasses.getSources())
            .build());
  }

  private FieldAccessInfoCollectionModifier createFieldAccessInfoCollectionModifier(
      Collection<MergeGroup> groups) {
    assert mode.isInitial();
    FieldAccessInfoCollectionModifier.Builder builder =
        new FieldAccessInfoCollectionModifier.Builder();
    for (MergeGroup group : groups) {
      if (group.hasClassIdField()) {
        DexProgramClass target = group.getTarget();
        target.forEachProgramInstanceInitializerMatching(
            definition -> definition.getCode().isHorizontalClassMergingCode(),
            method -> builder.recordFieldWrittenInContext(group.getClassIdField(), method));
        target.forEachProgramVirtualMethodMatching(
            definition ->
                definition.hasCode() && definition.getCode().isHorizontalClassMergingCode(),
            method -> builder.recordFieldReadInContext(group.getClassIdField(), method));
      }
    }
    return builder.build();
  }

  private DirectMappedDexApplication getNewApplication(HorizontallyMergedClasses mergedClasses) {
    // In the second round of class merging, we must forcefully remove the merged classes from the
    // application, since we won't run tree shaking before writing the application.
    DirectMappedDexApplication application = appView.appInfo().app().asDirect();
    return mode.isInitial()
        ? application
        : application
            .builder()
            .removeProgramClasses(
                clazz -> mergedClasses.hasBeenMergedIntoDifferentType(clazz.getType()))
            .build();
  }

  private List<MergeGroup> getInitialGroups() {
    MergeGroup initialClassGroup = new MergeGroup();
    MergeGroup initialInterfaceGroup = new MergeGroup();
    for (DexProgramClass clazz : appView.appInfo().classesWithDeterministicOrder()) {
      if (clazz.isInterface()) {
        initialInterfaceGroup.add(clazz);
      } else {
        initialClassGroup.add(clazz);
      }
    }
    List<MergeGroup> initialGroups = new LinkedList<>();
    initialGroups.add(initialClassGroup);
    initialGroups.add(initialInterfaceGroup);
    initialGroups.removeIf(MergeGroup::isTrivial);
    return initialGroups;
  }

  /**
   * Prepare horizontal class merging by determining which virtual methods and constructors need to
   * be merged and how the merging should be performed.
   */
  private List<ClassMerger> initializeClassMergers(
      HorizontalClassMergerGraphLens.Builder lensBuilder,
      Collection<MergeGroup> groups) {
    List<ClassMerger> classMergers = new ArrayList<>(groups.size());
    for (MergeGroup group : groups) {
      assert group.isNonTrivial();
      classMergers.add(new ClassMerger.Builder(appView, group).setMode(mode).build(lensBuilder));
    }
    return classMergers;
  }

  /** Merges all class groups using {@link ClassMerger}. */
  private void applyClassMergers(
      Collection<ClassMerger> classMergers, SyntheticArgumentClass syntheticArgumentClass) {
    for (ClassMerger merger : classMergers) {
      merger.mergeGroup(syntheticArgumentClass);
    }
  }

  /**
   * Fix all references to merged classes using the {@link TreeFixer}. Construct a graph lens
   * containing all changes performed by horizontal class merging.
   */
  private HorizontalClassMergerGraphLens createLens(
      HorizontallyMergedClasses mergedClasses,
      HorizontalClassMergerGraphLens.Builder lensBuilder,
      SyntheticArgumentClass syntheticArgumentClass) {
    return new TreeFixer(appView, mergedClasses, lensBuilder, syntheticArgumentClass)
        .fixupTypeReferences();
  }
}