src/main/java/com/android/tools/r8/horizontalclassmerging/policies/FinalizeMergeGroup.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.policies;

import com.android.tools.r8.graph.AppInfoWithClassHierarchy;
import com.android.tools.r8.graph.AppView;
import com.android.tools.r8.graph.DexType;
import com.android.tools.r8.horizontalclassmerging.HorizontalClassMerger.Mode;
import com.android.tools.r8.horizontalclassmerging.MergeGroup;
import com.android.tools.r8.horizontalclassmerging.MultiClassPolicy;
import com.android.tools.r8.utils.ListUtils;
import com.android.tools.r8.utils.SetUtils;
import java.util.Collection;
import java.util.Set;

/**
 * Identifies when instance initializer merging is required and bails out. This is needed to ensure
 * that we don't need to append extra null arguments at constructor call sites, such that the result
 * of the final round of class merging can be described as a renaming only.
 *
 * <p>This policy requires that all instance initializers with the same signature (relaxed, by
 * converting references types to java.lang.Object) have the same behavior.
 */
public class FinalizeMergeGroup extends MultiClassPolicy {

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

  public FinalizeMergeGroup(AppView<? extends AppInfoWithClassHierarchy> appView, Mode mode) {
    this.appView = appView;
    this.mode = mode;
  }

  @Override
  public Collection<MergeGroup> apply(MergeGroup group) {
    if (mode.isInitial() || group.isInterfaceGroup()) {
      group.selectTarget(appView);
      group.selectInstanceFieldMap(appView);
    } else {
      // In the final round of merging each group should be finalized by the
      // NoInstanceInitializerMerging policy.
      assert verifyAlreadyFinalized(group);
    }
    return ListUtils.newLinkedList(group);
  }

  @Override
  public String getName() {
    return "FinalizeMergeGroup";
  }

  @Override
  public boolean isIdentityForInterfaceGroups() {
    return true;
  }

  private boolean verifyAlreadyFinalized(MergeGroup group) {
    assert group.hasTarget();
    assert group.getClasses().contains(group.getTarget());
    assert group.hasInstanceFieldMap();
    Set<DexType> types =
        SetUtils.newIdentityHashSet(
            builder -> group.forEach(clazz -> builder.accept(clazz.getType())));
    group
        .getInstanceFieldMap()
        .forEach(
            (sourceField, targetField) -> {
              assert types.contains(sourceField.getHolderType());
              assert types.contains(targetField.getHolderType());
            });
    return true;
  }
}