src/main/java/com/android/tools/r8/ir/analysis/fieldvalueanalysis/InstanceFieldValueAnalysis.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.ir.analysis.fieldvalueanalysis;

import static com.android.tools.r8.ir.analysis.type.Nullability.maybeNull;

import com.android.tools.r8.graph.AppView;
import com.android.tools.r8.graph.DexEncodedField;
import com.android.tools.r8.graph.DexEncodedMethod;
import com.android.tools.r8.graph.DexProgramClass;
import com.android.tools.r8.graph.DexType;
import com.android.tools.r8.ir.analysis.type.ClassTypeLatticeElement;
import com.android.tools.r8.ir.analysis.type.TypeLatticeElement;
import com.android.tools.r8.ir.analysis.value.AbstractValue;
import com.android.tools.r8.ir.code.Argument;
import com.android.tools.r8.ir.code.FieldInstruction;
import com.android.tools.r8.ir.code.IRCode;
import com.android.tools.r8.ir.code.Instruction;
import com.android.tools.r8.ir.code.Value;
import com.android.tools.r8.ir.optimize.ClassInitializerDefaultsOptimization.ClassInitializerDefaultsResult;
import com.android.tools.r8.ir.optimize.info.OptimizationFeedback;
import com.android.tools.r8.ir.optimize.info.field.EmptyInstanceFieldInitializationInfoCollection;
import com.android.tools.r8.ir.optimize.info.field.InstanceFieldInitializationInfoCollection;
import com.android.tools.r8.ir.optimize.info.field.InstanceFieldInitializationInfoFactory;
import com.android.tools.r8.shaking.AppInfoWithLiveness;

public class InstanceFieldValueAnalysis extends FieldValueAnalysis {

  // Information about how this instance constructor initializes the fields on the newly created
  // instance.
  private final InstanceFieldInitializationInfoCollection.Builder builder =
      InstanceFieldInitializationInfoCollection.builder();

  private final InstanceFieldInitializationInfoFactory factory;

  private InstanceFieldValueAnalysis(
      AppView<AppInfoWithLiveness> appView,
      IRCode code,
      OptimizationFeedback feedback,
      DexProgramClass clazz,
      DexEncodedMethod method) {
    super(appView, code, feedback, clazz, method);
    factory = appView.instanceFieldInitializationInfoFactory();
  }

  /**
   * Returns information about how this instance constructor initializes the fields on the newly
   * created instance.
   */
  public static InstanceFieldInitializationInfoCollection run(
      AppView<?> appView,
      IRCode code,
      ClassInitializerDefaultsResult classInitializerDefaultsResult,
      OptimizationFeedback feedback,
      DexEncodedMethod method) {
    assert appView.appInfo().hasLiveness();
    assert appView.enableWholeProgramOptimizations();
    assert method.isInstanceInitializer();
    DexProgramClass clazz = appView.definitionFor(method.method.holder).asProgramClass();
    if (!appView.options().enableValuePropagationForInstanceFields) {
      return EmptyInstanceFieldInitializationInfoCollection.getInstance();
    }
    InstanceFieldValueAnalysis analysis =
        new InstanceFieldValueAnalysis(appView.withLiveness(), code, feedback, clazz, method);
    analysis.computeFieldOptimizationInfo(classInitializerDefaultsResult);
    return analysis.builder.build();
  }

  @Override
  boolean isSubjectToOptimization(DexEncodedField field) {
    return !field.isStatic() && field.holder() == clazz.type;
  }

  @Override
  void updateFieldOptimizationInfo(DexEncodedField field, FieldInstruction fieldPut, Value value) {
    if (fieldMaybeWrittenBetweenInstructionAndMethodExit(field, fieldPut)) {
      return;
    }

    // If this instance field is initialized with an argument or a constant, then record this in the
    // instance field initialization info.
    Value root = value.getAliasedValue();
    if (root.isDefinedByInstructionSatisfying(Instruction::isArgument)) {
      Argument argument = root.definition.asArgument();
      builder.recordInitializationInfo(
          field, factory.createArgumentInitializationInfo(argument.getIndex()));
      return;
    }

    AbstractValue abstractValue = value.getAbstractValue(appView, clazz.type);
    if (abstractValue.isSingleValue()) {
      builder.recordInitializationInfo(field, abstractValue.asSingleValue());
      return;
    }

    DexType fieldType = field.field.type;
    if (fieldType.isClassType()) {
      ClassTypeLatticeElement dynamicLowerBoundType = value.getDynamicLowerBoundType(appView);
      TypeLatticeElement dynamicUpperBoundType = value.getDynamicUpperBoundType(appView);
      TypeLatticeElement staticFieldType =
          TypeLatticeElement.fromDexType(fieldType, maybeNull(), appView);
      if (dynamicLowerBoundType != null || !dynamicUpperBoundType.equals(staticFieldType)) {
        builder.recordInitializationInfo(
            field,
            factory.createTypeInitializationInfo(dynamicLowerBoundType, dynamicUpperBoundType));
      }
    }
  }

  private boolean fieldMaybeWrittenBetweenInstructionAndMethodExit(
      DexEncodedField field, FieldInstruction fieldPut) {
    if (field.isFinal()
        || appView.appInfo().isInstanceFieldWrittenOnlyInInstanceInitializers(field)) {
      return false;
    }
    // Otherwise, conservatively return true.
    return true;
  }
}