src/main/java/com/android/tools/r8/ir/conversion/CallGraph.java

// Copyright (c) 2017, 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.conversion;

import com.android.tools.r8.graph.AppView;
import com.android.tools.r8.graph.DexEncodedMethod;
import com.android.tools.r8.ir.conversion.CallGraphBuilder.CycleEliminator;
import com.android.tools.r8.ir.conversion.CallSiteInformation.CallGraphBasedCallSiteInformation;
import com.android.tools.r8.shaking.AppInfoWithLiveness;
import java.util.Set;
import java.util.TreeSet;

/**
 * Call graph representation.
 *
 * <p>Each node in the graph contain the methods called and the calling methods. For virtual and
 * interface calls all potential calls from subtypes are recorded.
 *
 * <p>Only methods in the program - not library methods - are represented.
 *
 * <p>The directional edges are represented as sets of nodes in each node (called methods and
 * callees).
 *
 * <p>A call from method <code>a</code> to method <code>b</code> is only present once no matter how
 * many calls of <code>a</code> there are in <code>a</code>.
 *
 * <p>Recursive calls are not present.
 */
public class CallGraph {

  public static class Node implements Comparable<Node> {

    public static Node[] EMPTY_ARRAY = {};

    public final DexEncodedMethod method;
    private int numberOfCallSites = 0;

    // Outgoing calls from this method.
    private final Set<Node> callees = new TreeSet<>();

    // Incoming calls to this method.
    private final Set<Node> callers = new TreeSet<>();

    public Node(DexEncodedMethod method) {
      this.method = method;
    }

    public void addCallerConcurrently(Node caller) {
      addCallerConcurrently(caller, false);
    }

    public void addCallerConcurrently(Node caller, boolean likelySpuriousCallEdge) {
      if (caller != this && !likelySpuriousCallEdge) {
        synchronized (callers) {
          callers.add(caller);
          numberOfCallSites++;
        }
        synchronized (caller.callees) {
          caller.callees.add(this);
        }
      } else {
        synchronized (callers) {
          numberOfCallSites++;
        }
      }
    }

    public void removeCaller(Node caller) {
      callers.remove(caller);
      caller.callees.remove(this);
    }

    public void cleanForRemoval() {
      assert callees.isEmpty();
      for (Node caller : callers) {
        caller.callees.remove(this);
      }
    }

    public Set<Node> getCallersWithDeterministicOrder() {
      return callers;
    }

    public Set<Node> getCalleesWithDeterministicOrder() {
      return callees;
    }

    public int getNumberOfCallSites() {
      return numberOfCallSites;
    }

    public boolean hasCallee(Node method) {
      return callees.contains(method);
    }

    public boolean hasCaller(Node method) {
      return callers.contains(method);
    }

    public boolean isLeaf() {
      return callees.isEmpty();
    }

    @Override
    public int compareTo(Node other) {
      return method.method.slowCompareTo(other.method.method);
    }

    @Override
    public String toString() {
      StringBuilder builder = new StringBuilder();
      builder.append("MethodNode for: ");
      builder.append(method.toSourceString());
      builder.append(" (");
      builder.append(callees.size());
      builder.append(" callees, ");
      builder.append(callers.size());
      builder.append(" callers");
      builder.append(", invoke count ").append(numberOfCallSites);
      builder.append(").\n");
      if (callees.size() > 0) {
        builder.append("Callees:\n");
        for (Node call : callees) {
          builder.append("  ");
          builder.append(call.method.toSourceString());
          builder.append("\n");
        }
      }
      if (callers.size() > 0) {
        builder.append("Callers:\n");
        for (Node caller : callers) {
          builder.append("  ");
          builder.append(caller.method.toSourceString());
          builder.append("\n");
        }
      }
      return builder.toString();
    }
  }

  final Set<Node> nodes;

  CallGraph(Set<Node> nodes) {
    this.nodes = nodes;
  }

  public static CallGraphBuilder builder(AppView<AppInfoWithLiveness> appView) {
    return new CallGraphBuilder(appView);
  }

  CallSiteInformation createCallSiteInformation(AppView<AppInfoWithLiveness> appView) {
    // Don't leverage single/dual call site information when we are not tree shaking.
    return appView.options().isShrinking()
        ? new CallGraphBasedCallSiteInformation(appView, this)
        : CallSiteInformation.empty();
  }

  /**
   * Extract the next set of leaves (nodes with an call (outgoing) degree of 0) if any.
   *
   * <p>All nodes in the graph are extracted if called repeatedly until null is returned. Please
   * note that there are no cycles in this graph (see {@link CycleEliminator#breakCycles}).
   *
   * <p>
   */
  MethodProcessingOrder createMethodProcessingOrder(AppView<?> appView) {
    return new MethodProcessingOrder(appView, this);
  }
}