// Copyright (c) 2016, 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.optimize;

import static com.android.tools.r8.ir.analysis.ClassInitializationAnalysis.Query.DIRECTLY;
import static com.android.tools.r8.ir.analysis.type.Nullability.definitelyNotNull;
import static com.android.tools.r8.ir.analysis.type.Nullability.maybeNull;

import com.android.tools.r8.dex.Constants;
import com.android.tools.r8.errors.CompilationError;
import com.android.tools.r8.errors.Unreachable;
import com.android.tools.r8.graph.AppInfo;
import com.android.tools.r8.graph.AppView;
import com.android.tools.r8.graph.DebugLocalInfo;
import com.android.tools.r8.graph.DexClass;
import com.android.tools.r8.graph.DexEncodedField;
import com.android.tools.r8.graph.DexEncodedMethod;
import com.android.tools.r8.graph.DexEncodedMethod.ClassInlinerEligibility;
import com.android.tools.r8.graph.DexEncodedMethod.TrivialInitializer;
import com.android.tools.r8.graph.DexEncodedMethod.TrivialInitializer.TrivialClassInitializer;
import com.android.tools.r8.graph.DexEncodedMethod.TrivialInitializer.TrivialInstanceInitializer;
import com.android.tools.r8.graph.DexField;
import com.android.tools.r8.graph.DexItemFactory;
import com.android.tools.r8.graph.DexItemFactory.ThrowableMethods;
import com.android.tools.r8.graph.DexMethod;
import com.android.tools.r8.graph.DexProto;
import com.android.tools.r8.graph.DexString;
import com.android.tools.r8.graph.DexType;
import com.android.tools.r8.graph.ParameterUsagesInfo;
import com.android.tools.r8.graph.ParameterUsagesInfo.ParameterUsage;
import com.android.tools.r8.graph.ParameterUsagesInfo.ParameterUsageBuilder;
import com.android.tools.r8.ir.analysis.ClassInitializationAnalysis.AnalysisAssumption;
import com.android.tools.r8.ir.analysis.type.Nullability;
import com.android.tools.r8.ir.analysis.type.TypeAnalysis;
import com.android.tools.r8.ir.analysis.type.TypeLatticeElement;
import com.android.tools.r8.ir.code.AlwaysMaterializingNop;
import com.android.tools.r8.ir.code.ArrayPut;
import com.android.tools.r8.ir.code.BasicBlock;
import com.android.tools.r8.ir.code.BasicBlock.ThrowingInfo;
import com.android.tools.r8.ir.code.Binop;
import com.android.tools.r8.ir.code.CatchHandlers;
import com.android.tools.r8.ir.code.CheckCast;
import com.android.tools.r8.ir.code.Cmp;
import com.android.tools.r8.ir.code.Cmp.Bias;
import com.android.tools.r8.ir.code.ConstInstruction;
import com.android.tools.r8.ir.code.ConstNumber;
import com.android.tools.r8.ir.code.ConstString;
import com.android.tools.r8.ir.code.DebugLocalWrite;
import com.android.tools.r8.ir.code.DebugLocalsChange;
import com.android.tools.r8.ir.code.DominatorTree;
import com.android.tools.r8.ir.code.Goto;
import com.android.tools.r8.ir.code.IRCode;
import com.android.tools.r8.ir.code.If;
import com.android.tools.r8.ir.code.If.Type;
import com.android.tools.r8.ir.code.InstanceOf;
import com.android.tools.r8.ir.code.InstancePut;
import com.android.tools.r8.ir.code.Instruction;
import com.android.tools.r8.ir.code.InstructionIterator;
import com.android.tools.r8.ir.code.InstructionListIterator;
import com.android.tools.r8.ir.code.Invoke;
import com.android.tools.r8.ir.code.InvokeDirect;
import com.android.tools.r8.ir.code.InvokeMethod;
import com.android.tools.r8.ir.code.InvokeNewArray;
import com.android.tools.r8.ir.code.InvokeStatic;
import com.android.tools.r8.ir.code.InvokeVirtual;
import com.android.tools.r8.ir.code.Move;
import com.android.tools.r8.ir.code.NewArrayEmpty;
import com.android.tools.r8.ir.code.NewArrayFilledData;
import com.android.tools.r8.ir.code.NewInstance;
import com.android.tools.r8.ir.code.NumericType;
import com.android.tools.r8.ir.code.Phi;
import com.android.tools.r8.ir.code.Position;
import com.android.tools.r8.ir.code.Return;
import com.android.tools.r8.ir.code.StaticGet;
import com.android.tools.r8.ir.code.StaticPut;
import com.android.tools.r8.ir.code.Switch;
import com.android.tools.r8.ir.code.Throw;
import com.android.tools.r8.ir.code.Value;
import com.android.tools.r8.ir.code.ValueType;
import com.android.tools.r8.ir.code.Xor;
import com.android.tools.r8.ir.conversion.IRConverter;
import com.android.tools.r8.ir.conversion.OptimizationFeedback;
import com.android.tools.r8.ir.optimize.Inliner.ConstraintWithTarget;
import com.android.tools.r8.ir.optimize.SwitchUtils.EnumSwitchInfo;
import com.android.tools.r8.ir.regalloc.LinearScanRegisterAllocator;
import com.android.tools.r8.kotlin.Kotlin;
import com.android.tools.r8.shaking.AppInfoWithLiveness;
import com.android.tools.r8.utils.InternalOptions;
import com.android.tools.r8.utils.InternalOutputMode;
import com.android.tools.r8.utils.LongInterval;
import com.android.tools.r8.utils.MethodSignatureEquivalence;
import com.google.common.base.Equivalence;
import com.google.common.base.Equivalence.Wrapper;
import com.google.common.base.Supplier;
import com.google.common.base.Suppliers;
import com.google.common.collect.ArrayListMultimap;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterables;
import com.google.common.collect.ListMultimap;
import com.google.common.collect.Sets;
import it.unimi.dsi.fastutil.ints.Int2IntArrayMap;
import it.unimi.dsi.fastutil.ints.Int2IntMap;
import it.unimi.dsi.fastutil.ints.Int2IntOpenHashMap;
import it.unimi.dsi.fastutil.ints.Int2ObjectAVLTreeMap;
import it.unimi.dsi.fastutil.ints.Int2ObjectSortedMap;
import it.unimi.dsi.fastutil.ints.Int2ReferenceMap;
import it.unimi.dsi.fastutil.ints.Int2ReferenceMap.Entry;
import it.unimi.dsi.fastutil.ints.Int2ReferenceOpenHashMap;
import it.unimi.dsi.fastutil.ints.Int2ReferenceSortedMap;
import it.unimi.dsi.fastutil.ints.IntArrayList;
import it.unimi.dsi.fastutil.ints.IntIterator;
import it.unimi.dsi.fastutil.ints.IntList;
import it.unimi.dsi.fastutil.ints.IntOpenHashSet;
import it.unimi.dsi.fastutil.ints.IntSet;
import it.unimi.dsi.fastutil.longs.Long2ReferenceMap;
import it.unimi.dsi.fastutil.longs.Long2ReferenceOpenHashMap;
import it.unimi.dsi.fastutil.objects.Object2IntLinkedOpenHashMap;
import it.unimi.dsi.fastutil.objects.Object2IntMap;
import it.unimi.dsi.fastutil.objects.Reference2IntMap;
import it.unimi.dsi.fastutil.objects.Reference2IntOpenHashMap;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Comparator;
import java.util.Deque;
import java.util.HashMap;
import java.util.HashSet;
import java.util.IdentityHashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
import java.util.Map;
import java.util.PriorityQueue;
import java.util.Set;
import java.util.function.BiFunction;
import java.util.function.Function;
import java.util.function.Predicate;

public class CodeRewriter {

  private enum InstanceOfResult {
    UNKNOWN,
    TRUE,
    FALSE
  }

  private static final int MAX_FILL_ARRAY_SIZE = 8 * Constants.KILOBYTE;
  // This constant was determined by experimentation.
  private static final int STOP_SHARED_CONSTANT_THRESHOLD = 50;
  private static final int SELF_RECURSION_LIMIT = 4;

  public final IRConverter converter;

  private final AppView<? extends AppInfo> appView;
  private final DexItemFactory dexItemFactory;
  private final InternalOptions options;

  public CodeRewriter(AppView<? extends AppInfo> appView, IRConverter converter) {
    this.appView = appView;
    this.converter = converter;
    this.options = appView.options();
    this.dexItemFactory = appView.dexItemFactory();
  }

  private static boolean removedTrivialGotos(IRCode code) {
    ListIterator<BasicBlock> iterator = code.listIterator();
    assert iterator.hasNext();
    BasicBlock block = iterator.next();
    BasicBlock nextBlock;
    do {
      nextBlock = iterator.hasNext() ? iterator.next() : null;
      // Trivial goto block are only kept if they are self-targeting or are targeted by
      // fallthroughs.
      BasicBlock blk = block;  // Additional local for lambda below.
      assert !block.isTrivialGoto()
          || block.exit().asGoto().getTarget() == block
          || code.entryBlock() == block
          || block.getPredecessors().stream().anyMatch((b) -> b.exit().fallthroughBlock() == blk);
      // Trivial goto blocks never target the next block (in that case there should just be a
      // fallthrough).
      assert !block.isTrivialGoto() || block.exit().asGoto().getTarget() != nextBlock;
      block = nextBlock;
    } while (block != null);
    return true;
  }

  public static boolean isFallthroughBlock(BasicBlock block) {
    for (BasicBlock pred : block.getPredecessors()) {
      if (pred.exit().fallthroughBlock() == block) {
        return true;
      }
    }
    return false;
  }

  private static void collapseTrivialGoto(
      IRCode code, BasicBlock block, BasicBlock nextBlock, List<BasicBlock> blocksToRemove) {

    // This is the base case for GOTO loops.
    if (block.exit().asGoto().getTarget() == block) {
      return;
    }

    BasicBlock target = block.endOfGotoChain();

    boolean needed = false;

    if (target == null) {
      // This implies we are in a loop of GOTOs. In that case, we will iteratively remove each
      // trivial GOTO one-by-one until the above base case (one block targeting itself) is left.
      target = block.exit().asGoto().getTarget();
    }

    if (target != nextBlock) {
      // Not targeting the fallthrough block, determine if we need this goto. We need it if
      // a fallthrough can hit this block. That is the case if the block is the entry block
      // or if one of the predecessors fall through to the block.
      needed = code.entryBlock() == block || isFallthroughBlock(block);
    }

    if (!needed) {
      blocksToRemove.add(block);
      unlinkTrivialGotoBlock(block, target);
    }
  }

  public static void unlinkTrivialGotoBlock(BasicBlock block, BasicBlock target) {
    assert block.isTrivialGoto();
    for (BasicBlock pred : block.getPredecessors()) {
      pred.replaceSuccessor(block, target);
    }
    for (BasicBlock succ : block.getSuccessors()) {
      succ.getMutablePredecessors().remove(block);
    }
    for (BasicBlock pred : block.getPredecessors()) {
      if (!target.getPredecessors().contains(pred)) {
        target.getMutablePredecessors().add(pred);
      }
    }
  }

  private static void collapseIfTrueTarget(BasicBlock block) {
    If insn = block.exit().asIf();
    BasicBlock target = insn.getTrueTarget();
    BasicBlock newTarget = target.endOfGotoChain();
    BasicBlock fallthrough = insn.fallthroughBlock();
    BasicBlock newFallthrough = fallthrough.endOfGotoChain();
    if (newTarget != null && target != newTarget) {
      insn.getBlock().replaceSuccessor(target, newTarget);
      target.getMutablePredecessors().remove(block);
      if (!newTarget.getPredecessors().contains(block)) {
        newTarget.getMutablePredecessors().add(block);
      }
    }
    if (block.exit().isIf()) {
      insn = block.exit().asIf();
      if (insn.getTrueTarget() == newFallthrough) {
        // Replace if with the same true and fallthrough target with a goto to the fallthrough.
        block.replaceSuccessor(insn.getTrueTarget(), fallthrough);
        assert block.exit().isGoto();
        assert block.exit().asGoto().getTarget() == fallthrough;
      }
    }
  }

  private static void collapseNonFallthroughSwitchTargets(BasicBlock block) {
    Switch insn = block.exit().asSwitch();
    BasicBlock fallthroughBlock = insn.fallthroughBlock();
    Set<BasicBlock> replacedBlocks = new HashSet<>();
    for (int j = 0; j < insn.targetBlockIndices().length; j++) {
      BasicBlock target = insn.targetBlock(j);
      if (target != fallthroughBlock) {
        BasicBlock newTarget = target.endOfGotoChain();
        if (newTarget != null && target != newTarget && !replacedBlocks.contains(target)) {
          insn.getBlock().replaceSuccessor(target, newTarget);
          target.getMutablePredecessors().remove(block);
          if (!newTarget.getPredecessors().contains(block)) {
            newTarget.getMutablePredecessors().add(block);
          }
          replacedBlocks.add(target);
        }
      }
    }
  }

  // For method with many self-recursive calls, insert a try-catch to disable inlining.
  // Marshmallow dex2oat aggressively inlines and eats up all the memory on devices.
  public static void disableDex2OatInliningForSelfRecursiveMethods(
      AppView<? extends AppInfo> appView, IRCode code) {
    if (!appView.options().canHaveDex2OatInliningIssue() || code.hasCatchHandlers()) {
      // Catch handlers disables inlining, so if the method already has catch handlers
      // there is nothing to do.
      return;
    }
    InstructionIterator it = code.instructionIterator();
    int selfRecursionFanOut = 0;
    Instruction lastSelfRecursiveCall = null;
    while (it.hasNext()) {
      Instruction i = it.next();
      if (i.isInvokeMethod() && i.asInvokeMethod().getInvokedMethod() == code.method.method) {
        selfRecursionFanOut++;
        lastSelfRecursiveCall = i;
      }
    }
    if (selfRecursionFanOut > SELF_RECURSION_LIMIT) {
      assert lastSelfRecursiveCall != null;
      // Split out the last recursive call in its own block.
      InstructionListIterator splitIterator =
          lastSelfRecursiveCall.getBlock().listIterator(lastSelfRecursiveCall);
      splitIterator.previous();
      BasicBlock newBlock = splitIterator.split(code, 1);
      // Generate rethrow block.
      DexType guard = appView.dexItemFactory().throwableType;
      BasicBlock rethrowBlock =
          BasicBlock.createRethrowBlock(code, lastSelfRecursiveCall.getPosition(), guard, appView);
      code.blocks.add(rethrowBlock);
      // Add catch handler to the block containing the last recursive call.
      newBlock.addCatchHandler(rethrowBlock, guard);
    }
  }

  // TODO(sgjesse); Move this somewhere else, and reuse it for some of the other switch rewritings.
  public abstract static class InstructionBuilder<T> {
    protected int blockNumber;
    protected final Position position;

    protected InstructionBuilder(Position position) {
      this.position = position;
    }

    public abstract T self();

    public T setBlockNumber(int blockNumber) {
      this.blockNumber = blockNumber;
      return self();
    }
  }

  public static class SwitchBuilder extends InstructionBuilder<SwitchBuilder> {
    private Value value;
    private final Int2ObjectSortedMap<BasicBlock> keyToTarget = new Int2ObjectAVLTreeMap<>();
    private BasicBlock fallthrough;

    public SwitchBuilder(Position position) {
      super(position);
    }

    @Override
    public SwitchBuilder self() {
      return this;
    }

    public SwitchBuilder setValue(Value value) {
      this.value = value;
      return  this;
    }

    public SwitchBuilder addKeyAndTarget(int key, BasicBlock target) {
      keyToTarget.put(key, target);
      return this;
    }

    public SwitchBuilder setFallthrough(BasicBlock fallthrough) {
      this.fallthrough = fallthrough;
      return this;
    }

    public BasicBlock build() {
      final int NOT_FOUND = -1;
      Object2IntMap<BasicBlock> targetToSuccessorIndex = new Object2IntLinkedOpenHashMap<>();
      targetToSuccessorIndex.defaultReturnValue(NOT_FOUND);

      int[] keys = new int[keyToTarget.size()];
      int[] targetBlockIndices = new int[keyToTarget.size()];
      // Sort keys descending.
      int count = 0;
      IntIterator iter = keyToTarget.keySet().iterator();
      while (iter.hasNext()) {
        int key = iter.nextInt();
        BasicBlock target = keyToTarget.get(key);
        Integer targetIndex =
            targetToSuccessorIndex.computeIfAbsent(target, b -> targetToSuccessorIndex.size());
        keys[count] = key;
        targetBlockIndices[count] = targetIndex;
        count++;
      }
      Integer fallthroughIndex =
          targetToSuccessorIndex.computeIfAbsent(fallthrough, b -> targetToSuccessorIndex.size());
      Switch newSwitch = new Switch(value, keys, targetBlockIndices, fallthroughIndex);
      newSwitch.setPosition(position);
      BasicBlock newSwitchBlock = BasicBlock.createSwitchBlock(blockNumber, newSwitch);
      for (BasicBlock successor : targetToSuccessorIndex.keySet()) {
        newSwitchBlock.link(successor);
      }
      return newSwitchBlock;
    }
  }

  public static class IfBuilder extends InstructionBuilder<IfBuilder> {
    private final IRCode code;
    private Value left;
    private int right;
    private BasicBlock target;
    private BasicBlock fallthrough;

    public IfBuilder(Position position, IRCode code) {
      super(position);
      this.code = code;
    }

    @Override
    public IfBuilder self() {
      return this;
    }

    public IfBuilder setLeft(Value left) {
      this.left = left;
      return  this;
    }

    public IfBuilder setRight(int right) {
      this.right = right;
      return  this;
    }

    public IfBuilder setTarget(BasicBlock target) {
      this.target = target;
      return this;
    }

    public IfBuilder setFallthrough(BasicBlock fallthrough) {
      this.fallthrough = fallthrough;
      return this;
    }

    public BasicBlock build() {
      assert target != null;
      assert fallthrough != null;
      If newIf;
      BasicBlock ifBlock;
      if (right != 0) {
        ConstNumber rightConst = code.createIntConstant(right);
        rightConst.setPosition(position);
        newIf = new If(Type.EQ, ImmutableList.of(left, rightConst.dest()));
        ifBlock = BasicBlock.createIfBlock(blockNumber, newIf, rightConst);
      } else {
        newIf = new If(Type.EQ, left);
        ifBlock = BasicBlock.createIfBlock(blockNumber, newIf);
      }
      newIf.setPosition(position);
      ifBlock.link(target);
      ifBlock.link(fallthrough);
      return ifBlock;
    }
  }

  /**
   * Covert the switch instruction to a sequence of if instructions checking for a specified
   * set of keys, followed by a new switch with the remaining keys.
   */
  private void convertSwitchToSwitchAndIfs(
      IRCode code, ListIterator<BasicBlock> blocksIterator, BasicBlock originalBlock,
      InstructionListIterator iterator, Switch theSwitch,
      List<IntList> switches, IntList keysToRemove) {

    Position position = theSwitch.getPosition();

    // Extract the information from the switch before removing it.
    Int2ReferenceSortedMap<BasicBlock> keyToTarget = theSwitch.getKeyToTargetMap();

    // Keep track of the current fallthrough, starting with the original.
    BasicBlock fallthroughBlock = theSwitch.fallthroughBlock();

    // Split the switch instruction into its own block and remove it.
    iterator.previous();
    BasicBlock originalSwitchBlock = iterator.split(code, blocksIterator);
    assert !originalSwitchBlock.hasCatchHandlers();
    assert originalSwitchBlock.getInstructions().size() == 1;
    assert originalBlock.exit().isGoto();
    theSwitch.moveDebugValues(originalBlock.exit());
    blocksIterator.remove();
    theSwitch.getBlock().detachAllSuccessors();
    BasicBlock block = theSwitch.getBlock().unlinkSinglePredecessor();
    assert theSwitch.getBlock().getPredecessors().size() == 0;
    assert theSwitch.getBlock().getSuccessors().size() == 0;
    assert block == originalBlock;

    // Collect the new blocks for adding to the block list.
    int nextBlockNumber = code.getHighestBlockNumber() + 1;
    LinkedList<BasicBlock> newBlocks = new LinkedList<>();

    // Build the switch-blocks backwards, to always have the fallthrough block in hand.
    for (int i = switches.size() - 1; i >= 0; i--) {
      SwitchBuilder switchBuilder = new SwitchBuilder(position);
      switchBuilder.setValue(theSwitch.value());
      IntList keys = switches.get(i);
      for (int j = 0; j < keys.size(); j++) {
        int key = keys.getInt(j);
        switchBuilder.addKeyAndTarget(key, keyToTarget.get(key));
      }
      switchBuilder
          .setFallthrough(fallthroughBlock)
          .setBlockNumber(nextBlockNumber++);
      BasicBlock newSwitchBlock = switchBuilder.build();
      newBlocks.addFirst(newSwitchBlock);
      fallthroughBlock = newSwitchBlock;
    }

    // Build the if-blocks backwards, to always have the fallthrough block in hand.
    for (int i = keysToRemove.size() - 1; i >= 0; i--) {
      int key = keysToRemove.getInt(i);
      BasicBlock peeledOffTarget = keyToTarget.get(key);
      IfBuilder ifBuilder = new IfBuilder(position, code);
      ifBuilder
          .setLeft(theSwitch.value())
          .setRight(key)
          .setTarget(peeledOffTarget)
          .setFallthrough(fallthroughBlock)
          .setBlockNumber(nextBlockNumber++);
      BasicBlock ifBlock = ifBuilder.build();
      newBlocks.addFirst(ifBlock);
      fallthroughBlock = ifBlock;
    }

    // Finally link the block before the original switch to the new block sequence.
    originalBlock.link(fallthroughBlock);

    // Finally add the blocks.
    newBlocks.forEach(blocksIterator::add);
  }

  private static class Interval {

    private final IntList keys = new IntArrayList();

    public Interval(IntList... allKeys) {
      assert allKeys.length > 0;
      for (IntList keys : allKeys) {
        assert keys.size() > 0;
        this.keys.addAll(keys);
      }
    }

    public int getMin() {
      return keys.getInt(0);
    }

    public int getMax() {
      return keys.getInt(keys.size() - 1);
    }

    public void addInterval(Interval other) {
      assert getMax() < other.getMin();
      keys.addAll(other.keys);
    }

    public long packedSavings(InternalOutputMode mode) {
      long packedTargets = (long) getMax() - (long) getMin() + 1;
      if (!Switch.canBePacked(mode, packedTargets)) {
        return Long.MIN_VALUE + 1;
      }
      long sparseCost = Switch.baseSparseSize(mode) + Switch.sparsePayloadSize(mode, keys.size());
      long packedCost = Switch.basePackedSize(mode) + Switch.packedPayloadSize(mode, packedTargets);
      return sparseCost - packedCost;
    }

    public long estimatedSize(InternalOutputMode mode) {
      return Switch.estimatedSize(mode, keys.toIntArray());
    }
  }

  private Interval combineOrAddInterval(
      List<Interval> intervals, Interval previous, Interval current) {
    // As a first iteration, we only combine intervals if their packed size is less than their
    // sparse counterpart. In CF we will have to add a load and a jump which add to the
    // stack map table (1 is the size of a same entry).
    InternalOutputMode mode = options.getInternalOutputMode();
    int penalty = mode.isGeneratingClassFiles() ? 3 + 1 : 0;
    if (previous == null) {
      intervals.add(current);
      return current;
    }
    Interval combined = new Interval(previous.keys, current.keys);
    long packedSavings = combined.packedSavings(mode);
    if (packedSavings <= 0
        || packedSavings < previous.estimatedSize(mode) + current.estimatedSize(mode) - penalty) {
      intervals.add(current);
      return current;
    } else {
      intervals.set(intervals.size() - 1, combined);
      return combined;
    }
  }

  private void tryAddToBiggestSavings(
      Set<Interval> biggestPackedSet,
      PriorityQueue<Interval> intervals,
      Interval toAdd,
      int maximumNumberOfSwitches) {
    assert !biggestPackedSet.contains(toAdd);
    long savings = toAdd.packedSavings(options.getInternalOutputMode());
    if (savings <= 0) {
      return;
    }
    if (intervals.size() < maximumNumberOfSwitches) {
      intervals.add(toAdd);
      biggestPackedSet.add(toAdd);
    } else if (savings > intervals.peek().packedSavings(options.getInternalOutputMode())) {
      intervals.add(toAdd);
      biggestPackedSet.add(toAdd);
      biggestPackedSet.remove(intervals.poll());
    }
  }

  private int sizeForKeysWrittenAsIfs(ValueType type, Collection<Integer> keys) {
    int ifsSize = If.estimatedSize(options.getInternalOutputMode()) * keys.size();
    // In Cf we also require a load as well (and a stack map entry)
    if (options.getInternalOutputMode().isGeneratingClassFiles()) {
      ifsSize += keys.size() * (3 + 1);
    }
    for (int k : keys) {
      if (k != 0) {
        ifsSize += ConstNumber.estimatedSize(options.getInternalOutputMode(), type, k);
      }
    }
    return ifsSize;
  }

  private int codeUnitMargin() {
    return options.getInternalOutputMode().isGeneratingClassFiles() ? 3 : 1;
  }

  private int findIfsForCandidates(List<Interval> newSwitches, Switch theSwitch, IntList outliers) {
    Set<Interval> switchesToRemove = new HashSet<>();
    InternalOutputMode mode = options.getInternalOutputMode();
    int outliersAsIfSize = 0;
    // The candidateForIfs is either an index to a switch that can be eliminated totally or a sparse
    // where removing a key may produce a greater saving. It is only if keys are small in the packed
    // switch that removing the keys makes sense (size wise).
    for (Interval candidate : newSwitches) {
      int maxIfBudget = 10;
      long switchSize = candidate.estimatedSize(mode);
      int sizeOfAllKeysAsIf = sizeForKeysWrittenAsIfs(theSwitch.value().outType(), candidate.keys);
      if (candidate.keys.size() <= maxIfBudget
          && sizeOfAllKeysAsIf < switchSize - codeUnitMargin()) {
        outliersAsIfSize += sizeOfAllKeysAsIf;
        switchesToRemove.add(candidate);
        outliers.addAll(candidate.keys);
        continue;
      }
      // One could do something clever here, but we use a simple algorithm that use the fact that
      // all keys are sorted in ascending order and that the smallest absolute value will give the
      // best saving.
      IntList candidateKeys = candidate.keys;
      int smallestPosition = -1;
      long smallest = Long.MAX_VALUE;
      for (int i = 0; i < candidateKeys.size(); i++) {
        long current = Math.abs((long) candidateKeys.getInt(i));
        if (current < smallest) {
          smallestPosition = i;
          smallest = current;
        }
      }
      // Add as many keys forward and backward as we have budget and we decrease in size.
      IntList ifKeys = new IntArrayList();
      ifKeys.add(candidateKeys.getInt(smallestPosition));
      long previousSavings = 0;
      long currentSavings =
          switchSize
              - sizeForKeysWrittenAsIfs(theSwitch.value().outType(), ifKeys)
              - Switch.estimatedSparseSize(mode, candidateKeys.size() - ifKeys.size());
      int minIndex = smallestPosition - 1;
      int maxIndex = smallestPosition + 1;
      while (ifKeys.size() < maxIfBudget && currentSavings > previousSavings) {
        if (minIndex >= 0 && maxIndex < candidateKeys.size()) {
          long valMin = Math.abs((long) candidateKeys.getInt(minIndex));
          int valMax = Math.abs(candidateKeys.getInt(maxIndex));
          if (valMax <= valMin) {
            ifKeys.add(candidateKeys.getInt(maxIndex++));
          } else {
            ifKeys.add(candidateKeys.getInt(minIndex--));
          }
        } else if (minIndex >= 0) {
          ifKeys.add(candidateKeys.getInt(minIndex--));
        } else if (maxIndex < candidateKeys.size()) {
          ifKeys.add(candidateKeys.getInt(maxIndex++));
        } else {
          // No more elements to add as if's.
          break;
        }
        previousSavings = currentSavings;
        currentSavings =
            switchSize
                - sizeForKeysWrittenAsIfs(theSwitch.value().outType(), ifKeys)
                - Switch.estimatedSparseSize(mode, candidateKeys.size() - ifKeys.size());
      }
      if (previousSavings >= currentSavings) {
        // Remove the last added key since it did not contribute to savings.
        int lastKey = ifKeys.getInt(ifKeys.size() - 1);
        ifKeys.removeInt(ifKeys.size() - 1);
        if (lastKey == candidateKeys.getInt(minIndex + 1)) {
          minIndex++;
        } else {
          maxIndex--;
        }
      }
      // Adjust pointers into the candidate keys.
      minIndex++;
      maxIndex--;
      if (ifKeys.size() > 0) {
        int ifsSize = sizeForKeysWrittenAsIfs(theSwitch.value().outType(), ifKeys);
        long newSwitchSize = Switch.estimatedSparseSize(mode, candidateKeys.size() - ifKeys.size());
        if (newSwitchSize + ifsSize + codeUnitMargin() < switchSize) {
          candidateKeys.removeElements(minIndex, maxIndex);
          outliers.addAll(ifKeys);
          outliersAsIfSize += ifsSize;
        }
      }
    }
    newSwitches.removeAll(switchesToRemove);
    return outliersAsIfSize;
  }

  public void rewriteSwitch(IRCode code) {
    ListIterator<BasicBlock> blocksIterator = code.listIterator();
    while (blocksIterator.hasNext()) {
      BasicBlock block = blocksIterator.next();
      InstructionListIterator iterator = block.listIterator();
      while (iterator.hasNext()) {
        Instruction instruction = iterator.next();
        if (instruction.isSwitch()) {
          Switch theSwitch = instruction.asSwitch();
          if (theSwitch.numberOfKeys() == 1) {
            // Rewrite the switch to an if.
            int fallthroughBlockIndex = theSwitch.getFallthroughBlockIndex();
            int caseBlockIndex = theSwitch.targetBlockIndices()[0];
            if (fallthroughBlockIndex < caseBlockIndex) {
              block.swapSuccessorsByIndex(fallthroughBlockIndex, caseBlockIndex);
            }
            if (theSwitch.getFirstKey() == 0) {
              iterator.replaceCurrentInstruction(new If(Type.EQ, theSwitch.value()));
            } else {
              ConstNumber labelConst = code.createIntConstant(theSwitch.getFirstKey());
              labelConst.setPosition(theSwitch.getPosition());
              iterator.previous();
              iterator.add(labelConst);
              Instruction dummy = iterator.next();
              assert dummy == theSwitch;
              If theIf = new If(Type.EQ, ImmutableList.of(theSwitch.value(), labelConst.dest()));
              iterator.replaceCurrentInstruction(theIf);
            }
          } else {
            // If there are more than 1 key, we use the following algorithm to find keys to combine.
            // First, scan through the keys forward and combine each packed interval with the
            // previous interval if it gives a net saving.
            // Secondly, go through all created intervals and combine the ones without a saving into
            // a single interval and keep a max number of packed switches.
            // Finally, go through all intervals and check if the switch or part of the switch
            // should be transformed to ifs.

            // Phase 1: Combine packed intervals.
            InternalOutputMode mode = options.getInternalOutputMode();
            int[] keys = theSwitch.getKeys();
            int maxNumberOfIfsOrSwitches = 10;
            PriorityQueue<Interval> biggestPackedSavings =
                new PriorityQueue<>(
                    (x, y) -> Long.compare(y.packedSavings(mode), x.packedSavings(mode)));
            Set<Interval> biggestPackedSet = new HashSet<>();
            List<Interval> intervals = new ArrayList<>();
            int previousKey = keys[0];
            IntList currentKeys = new IntArrayList();
            currentKeys.add(previousKey);
            Interval previousInterval = null;
            for (int i = 1; i < keys.length; i++) {
              int key = keys[i];
              if (((long) key - (long) previousKey) > 1) {
                Interval current = new Interval(currentKeys);
                Interval added = combineOrAddInterval(intervals, previousInterval, current);
                if (added != current && biggestPackedSet.contains(previousInterval)) {
                  biggestPackedSet.remove(previousInterval);
                  biggestPackedSavings.remove(previousInterval);
                }
                tryAddToBiggestSavings(
                    biggestPackedSet, biggestPackedSavings, added, maxNumberOfIfsOrSwitches);
                previousInterval = added;
                currentKeys = new IntArrayList();
              }
              currentKeys.add(key);
              previousKey = key;
            }
            Interval current = new Interval(currentKeys);
            Interval added = combineOrAddInterval(intervals, previousInterval, current);
            if (added != current && biggestPackedSet.contains(previousInterval)) {
              biggestPackedSet.remove(previousInterval);
              biggestPackedSavings.remove(previousInterval);
            }
            tryAddToBiggestSavings(
                biggestPackedSet, biggestPackedSavings, added, maxNumberOfIfsOrSwitches);

            // Phase 2: combine sparse intervals into a single bin.
            // Check if we should save a space for a sparse switch, if so, remove the switch with
            // the smallest savings.
            if (biggestPackedSet.size() == maxNumberOfIfsOrSwitches
                && maxNumberOfIfsOrSwitches < intervals.size()) {
              biggestPackedSet.remove(biggestPackedSavings.poll());
            }
            Interval sparse = null;
            List<Interval> newSwitches = new ArrayList<>(maxNumberOfIfsOrSwitches);
            for (int i = 0; i < intervals.size(); i++) {
              Interval interval = intervals.get(i);
              if (biggestPackedSet.contains(interval)) {
                newSwitches.add(interval);
              } else if (sparse == null) {
                sparse = interval;
                newSwitches.add(sparse);
              } else {
                sparse.addInterval(interval);
              }
            }

            // Phase 3: at this point we are guaranteed to have the biggest saving switches
            // in newIntervals, potentially with a switch combining the remaining intervals.
            // Now we check to see if we can create any if's to reduce size.
            IntList outliers = new IntArrayList();
            int outliersAsIfSize = findIfsForCandidates(newSwitches, theSwitch, outliers);

            long newSwitchesSize = 0;
            List<IntList> newSwitchSequences = new ArrayList<>(newSwitches.size());
            for (Interval interval : newSwitches) {
              newSwitchesSize += interval.estimatedSize(mode);
              newSwitchSequences.add(interval.keys);
            }

            long currentSize = Switch.estimatedSize(mode, theSwitch.getKeys());
            if (newSwitchesSize + outliersAsIfSize + codeUnitMargin() < currentSize) {
              convertSwitchToSwitchAndIfs(
                  code, blocksIterator, block, iterator, theSwitch, newSwitchSequences, outliers);
            }
          }
        }
      }
    }
    // Rewriting of switches introduces new branching structure. It relies on critical edges
    // being split on the way in but does not maintain this property. We therefore split
    // critical edges at exit.
    code.splitCriticalEdges();
    assert code.isConsistentSSA();
  }

  /**
   * Inline the indirection of switch maps into the switch statement.
   * <p>
   * To ensure binary compatibility, javac generated code does not use ordinal values of enums
   * directly in switch statements but instead generates a companion class that computes a mapping
   * from switch branches to ordinals at runtime. As we have whole-program knowledge, we can
   * analyze these maps and inline the indirection into the switch map again.
   * <p>
   * In particular, we look for code of the form
   *
   * <blockquote><pre>
   * switch(CompanionClass.$switchmap$field[enumValue.ordinal()]) {
   *   ...
   * }
   * </pre></blockquote>
   */
  public void removeSwitchMaps(IRCode code) {
    for (BasicBlock block : code.blocks) {
      InstructionListIterator it = block.listIterator();
      while (it.hasNext()) {
        Instruction insn = it.next();
        // Pattern match a switch on a switch map as input.
        if (insn.isSwitch()) {
          Switch switchInsn = insn.asSwitch();
          EnumSwitchInfo info =
              SwitchUtils.analyzeSwitchOverEnum(switchInsn, appView.withLiveness());
          if (info != null) {
            Int2IntMap targetMap = new Int2IntArrayMap();
            IntList keys = new IntArrayList(switchInsn.numberOfKeys());
            for (int i = 0; i < switchInsn.numberOfKeys(); i++) {
              assert switchInsn.targetBlockIndices()[i] != switchInsn.getFallthroughBlockIndex();
              int key = info.ordinalsMap.getInt(info.indexMap.get(switchInsn.getKey(i)));
              keys.add(key);
              targetMap.put(key, switchInsn.targetBlockIndices()[i]);
            }
            keys.sort(Comparator.naturalOrder());
            int[] targets = new int[keys.size()];
            for (int i = 0; i < keys.size(); i++) {
              targets[i] = targetMap.get(keys.getInt(i));
            }

            Switch newSwitch = new Switch(info.ordinalInvoke.outValue(), keys.toIntArray(),
                targets, switchInsn.getFallthroughBlockIndex());
            // Replace the switch itself.
            it.replaceCurrentInstruction(newSwitch);
            // If the original input to the switch is now unused, remove it too. It is not dead
            // as it might have side-effects but we ignore these here.
            Instruction arrayGet = info.arrayGet;
            if (arrayGet.outValue().numberOfUsers() == 0) {
              arrayGet.inValues().forEach(v -> v.removeUser(arrayGet));
              arrayGet.getBlock().removeInstruction(arrayGet);
            }
            Instruction staticGet = info.staticGet;
            if (staticGet.outValue().numberOfUsers() == 0) {
              assert staticGet.inValues().isEmpty();
              staticGet.getBlock().removeInstruction(staticGet);
            }
          }
        }
      }
    }
  }

  /**
   * Rewrite all branch targets to the destination of trivial goto chains when possible.
   * Does not rewrite fallthrough targets as that would require block reordering and the
   * transformation only makes sense after SSA destruction where there are no phis.
   */
  public static void collapseTrivialGotos(DexEncodedMethod method, IRCode code) {
    assert code.isConsistentGraph();
    List<BasicBlock> blocksToRemove = new ArrayList<>();
    // Rewrite all non-fallthrough targets to the end of trivial goto chains and remove
    // first round of trivial goto blocks.
    ListIterator<BasicBlock> iterator = code.listIterator();
    assert iterator.hasNext();
    BasicBlock block = iterator.next();
    BasicBlock nextBlock;

    do {
      nextBlock = iterator.hasNext() ? iterator.next() : null;
      if (block.isTrivialGoto()) {
        collapseTrivialGoto(code, block, nextBlock, blocksToRemove);
      }
      if (block.exit().isIf()) {
        collapseIfTrueTarget(block);
      }
      if (block.exit().isSwitch()) {
        collapseNonFallthroughSwitchTargets(block);
      }
      block = nextBlock;
    } while (nextBlock != null);
    code.removeBlocks(blocksToRemove);
    // Get rid of gotos to the next block.
    while (!blocksToRemove.isEmpty()) {
      blocksToRemove = new ArrayList<>();
      iterator = code.listIterator();
      block = iterator.next();
      do {
        nextBlock = iterator.hasNext() ? iterator.next() : null;
        if (block.isTrivialGoto()) {
          collapseTrivialGoto(code, block, nextBlock, blocksToRemove);
        }
        block = nextBlock;
      } while (block != null);
      code.removeBlocks(blocksToRemove);
    }
    assert removedTrivialGotos(code);
    assert code.isConsistentGraph();
  }

  public void identifyReturnsArgument(
      DexEncodedMethod method, IRCode code, OptimizationFeedback feedback) {
    List<BasicBlock> normalExits = code.computeNormalExitBlocks();
    if (normalExits.isEmpty()) {
      feedback.methodNeverReturnsNormally(method);
      return;
    }
    Return firstExit = normalExits.get(0).exit().asReturn();
    if (firstExit.isReturnVoid()) {
      return;
    }
    Value returnValue = firstExit.returnValue();
    boolean isNeverNull = returnValue.getTypeLattice().isReference() && returnValue.isNeverNull();
    for (int i = 1; i < normalExits.size(); i++) {
      Return exit = normalExits.get(i).exit().asReturn();
      Value value = exit.returnValue();
      if (value != returnValue) {
        returnValue = null;
      }
      isNeverNull &= value.getTypeLattice().isReference() && value.isNeverNull();
    }
    if (returnValue != null) {
      if (returnValue.isArgument()) {
        // Find the argument number.
        int index = code.collectArguments().indexOf(returnValue);
        assert index != -1;
        feedback.methodReturnsArgument(method, index);
      }
      if (returnValue.isConstant()) {
        if (returnValue.definition.isConstNumber()) {
          long value = returnValue.definition.asConstNumber().getRawValue();
          feedback.methodReturnsConstantNumber(method, value);
        } else if (returnValue.definition.isConstString()) {
          ConstString constStringInstruction = returnValue.definition.asConstString();
          if (!constStringInstruction.instructionInstanceCanThrow()) {
            feedback.methodReturnsConstantString(method, constStringInstruction.getValue());
          }
        }
      }
    }
    if (isNeverNull) {
      feedback.methodNeverReturnsNull(method);
    }
  }

  public void identifyInvokeSemanticsForInlining(
      DexEncodedMethod method,
      IRCode code,
      AppView<? extends AppInfo> appView,
      OptimizationFeedback feedback) {
    if (method.isStatic()) {
      // Identifies if the method preserves class initialization after inlining.
      feedback.markTriggerClassInitBeforeAnySideEffect(
          method, triggersClassInitializationBeforeSideEffect(method.method.holder, code, appView));
    } else {
      // Identifies if the method preserves null check of the receiver after inlining.
      final Value receiver = code.getThis();
      feedback.markCheckNullReceiverBeforeAnySideEffect(
          method, receiver.isUsed() && checksNullBeforeSideEffect(code, receiver, appView));
    }
  }

  public void identifyClassInlinerEligibility(
      DexEncodedMethod method, IRCode code, OptimizationFeedback feedback) {
    // Method eligibility is calculated in similar way for regular method
    // and for the constructor. To be eligible method should only be using its
    // receiver in the following ways:
    //
    //  (1) as a receiver of reads/writes of instance fields of the holder class
    //  (2) as a return value
    //  (3) as a receiver of a call to the superclass initializer. Note that we don't
    //      check what is passed to superclass initializer as arguments, only check
    //      that it is not the instance being initialized.
    //
    boolean instanceInitializer = method.isInstanceInitializer();
    if (method.accessFlags.isNative()
        || (!method.isNonAbstractVirtualMethod() && !instanceInitializer)
        || method.accessFlags.isSynchronized()) {
      return;
    }

    feedback.setClassInlinerEligibility(method, null);  // To allow returns below.

    Value receiver = code.getThis();
    if (receiver.numberOfPhiUsers() > 0) {
      return;
    }

    DexClass clazz = appView.definitionFor(method.method.holder);
    if (clazz == null) {
      return;
    }

    boolean receiverUsedAsReturnValue = false;
    boolean seenSuperInitCall = false;
    for (Instruction insn : receiver.uniqueUsers()) {
      if (insn.isReturn()) {
        receiverUsedAsReturnValue = true;
        continue;
      }

      if (insn.isInstanceGet() || insn.isInstancePut()) {
        if (insn.isInstancePut()) {
          InstancePut instancePutInstruction = insn.asInstancePut();
          // Only allow field writes to the receiver.
          if (instancePutInstruction.object() != receiver) {
            return;
          }
          // Do not allow the receiver to escape via a field write.
          if (instancePutInstruction.value() == receiver) {
            return;
          }
        }
        DexField field = insn.asFieldInstruction().getField();
        if (field.holder == clazz.type && clazz.lookupInstanceField(field) != null) {
          // Require only accessing instance fields of the *current* class.
          continue;
        }
        return;
      }

      // If this is an instance initializer allow one call to superclass instance initializer.
      if (insn.isInvokeDirect()) {
        InvokeDirect invokedDirect = insn.asInvokeDirect();
        DexMethod invokedMethod = invokedDirect.getInvokedMethod();
        if (dexItemFactory.isConstructor(invokedMethod) &&
            invokedMethod.holder == clazz.superType &&
            invokedDirect.inValues().lastIndexOf(receiver) == 0 &&
            !seenSuperInitCall &&
            instanceInitializer) {
          seenSuperInitCall = true;
          continue;
        }
        // We don't support other direct calls yet.
        return;
      }

      // Other receiver usages make the method not eligible.
      return;
    }

    if (instanceInitializer && !seenSuperInitCall) {
      // Call to super constructor not found?
      return;
    }

    feedback.setClassInlinerEligibility(
        method, new ClassInlinerEligibility(receiverUsedAsReturnValue));
  }

  public void identifyTrivialInitializer(
      DexEncodedMethod method, IRCode code, OptimizationFeedback feedback) {
    boolean isInstanceInitializer = method.isInstanceInitializer();
    boolean isClassInitializer = method.isClassInitializer();
    assert isInstanceInitializer || isClassInitializer;
    if (method.accessFlags.isNative()) {
      return;
    }

    AppInfo appInfo = appView.appInfo();
    DexClass clazz = appInfo.definitionFor(method.method.holder);
    if (clazz == null) {
      return;
    }

    feedback.setTrivialInitializer(method,
        isInstanceInitializer
            ? computeInstanceInitializerInfo(code, clazz, appInfo::definitionFor)
            : computeClassInitializerInfo(code, clazz));
  }

  public void identifyParameterUsages(
      DexEncodedMethod method, IRCode code, OptimizationFeedback feedback) {
    List<ParameterUsage> usages = new ArrayList<>();
    List<Value> values = code.collectArguments();
    for (int i = 0; i < values.size(); i++) {
      Value value = values.get(i);
      if (value.numberOfPhiUsers() > 0) {
        continue;
      }
      ParameterUsage usage = collectParameterUsages(i, value);
      if (usage != null) {
        usages.add(usage);
      }
    }
    feedback.setParameterUsages(method, usages.isEmpty() ? null : new ParameterUsagesInfo(usages));
  }

  private ParameterUsage collectParameterUsages(int i, Value value) {
    ParameterUsageBuilder builder = new ParameterUsageBuilder(value, i);
    for (Instruction user : value.uniqueUsers()) {
      if (!builder.note(user)) {
        return null;
      }
    }
    return builder.build();
  }

  // This method defines trivial instance initializer as follows:
  //
  // ** The initializer may call the initializer of the base class, which
  //    itself must be trivial.
  //
  // ** java.lang.Object.<init>() is considered trivial.
  //
  // ** all arguments passed to a super-class initializer must be non-throwing
  //    constants or arguments.
  //
  // ** Assigns arguments or non-throwing constants to fields of this class.
  //
  // (Note that this initializer does not have to have zero arguments.)
  private TrivialInitializer computeInstanceInitializerInfo(
      IRCode code, DexClass clazz, Function<DexType, DexClass> typeToClass) {
    Value receiver = code.getThis();

    InstructionIterator it = code.instructionIterator();
    while (it.hasNext()) {
      Instruction insn = it.next();

      if (insn.isReturn()) {
        continue;
      }

      if (insn.isArgument()) {
        continue;
      }

      if (insn.isConstInstruction()) {
        if (insn.instructionInstanceCanThrow()) {
          return null;
        } else {
          continue;
        }
      }

      if (insn.isInvokeDirect()) {
        InvokeDirect invokedDirect = insn.asInvokeDirect();
        DexMethod invokedMethod = invokedDirect.getInvokedMethod();

        if (invokedMethod.holder != clazz.superType) {
          return null;
        }

        // java.lang.Object.<init>() is considered trivial.
        if (invokedMethod == dexItemFactory.objectMethods.constructor) {
          continue;
        }

        DexClass holder = typeToClass.apply(invokedMethod.holder);
        if (holder == null) {
          return null;
        }

        DexEncodedMethod callTarget = holder.lookupDirectMethod(invokedMethod);
        if (callTarget == null ||
            !callTarget.isInstanceInitializer() ||
            callTarget.getOptimizationInfo().getTrivialInitializerInfo() == null ||
            invokedDirect.getReceiver() != receiver) {
          return null;
        }

        for (Value value : invokedDirect.inValues()) {
          if (value != receiver && !(value.isConstant() || value.isArgument())) {
            return null;
          }
        }
        continue;
      }

      if (insn.isInstancePut()) {
        InstancePut instancePut = insn.asInstancePut();
        DexEncodedField field = clazz.lookupInstanceField(instancePut.getField());
        if (field == null ||
            instancePut.object() != receiver ||
            (instancePut.value() != receiver && !instancePut.value().isArgument())) {
          return null;
        }
        continue;
      }

      if (insn.isGoto()) {
        // Trivial goto to the next block.
        if (insn.asGoto().isTrivialGotoToTheNextBlock(code)) {
          continue;
        }
        return null;
      }

      // Other instructions make the instance initializer not eligible.
      return null;
    }

    return TrivialInstanceInitializer.INSTANCE;
  }

  // This method defines trivial class initializer as follows:
  //
  // ** The initializer may only instantiate an instance of the same class,
  //    initialize it with a call to a trivial constructor *without* arguments,
  //    and assign this instance to a static final field of the same class.
  //
  private synchronized TrivialInitializer computeClassInitializerInfo(IRCode code, DexClass clazz) {
    InstructionIterator it = code.instructionIterator();

    Value createdSingletonInstance = null;
    DexField singletonField = null;

    while (it.hasNext()) {
      Instruction insn = it.next();

      if (insn.isConstNumber()) {
        continue;
      }

      if (insn.isConstString()) {
        if (insn.instructionInstanceCanThrow()) {
          return null;
        }
        continue;
      }

      if (insn.isReturn()) {
        continue;
      }

      if (insn.isNewInstance()) {
        NewInstance newInstance = insn.asNewInstance();
        if (createdSingletonInstance != null ||
            newInstance.clazz != clazz.type ||
            insn.outValue() == null) {
          return null;
        }
        createdSingletonInstance = insn.outValue();
        continue;
      }

      if (insn.isInvokeDirect()) {
        InvokeDirect invokedDirect = insn.asInvokeDirect();
        if (createdSingletonInstance == null ||
            invokedDirect.getReceiver() != createdSingletonInstance) {
          return null;
        }

        DexEncodedMethod callTarget = clazz.lookupDirectMethod(invokedDirect.getInvokedMethod());
        if (callTarget == null ||
            !callTarget.isInstanceInitializer() ||
            !callTarget.method.proto.parameters.isEmpty() ||
            callTarget.getOptimizationInfo().getTrivialInitializerInfo() == null) {
          return null;
        }
        continue;
      }

      if (insn.isStaticPut()) {
        StaticPut staticPut = insn.asStaticPut();
        if (singletonField != null ||
            createdSingletonInstance == null ||
            staticPut.inValue() != createdSingletonInstance) {
          return null;
        }

        DexEncodedField field = clazz.lookupStaticField(staticPut.getField());
        if (field == null ||
            !field.accessFlags.isStatic() ||
            !field.accessFlags.isFinal()) {
          return null;
        }
        singletonField = field.field;
        continue;
      }

      // Other instructions make the class initializer not eligible.
      return null;
    }

    return singletonField == null ? null : new TrivialClassInitializer(singletonField);
  }

  /**
   * An enum used to classify instructions according to a particular effect that they produce.
   *
   * The "effect" of an instruction can be seen as a program state change (or semantic change) at
   * runtime execution. For example, an instruction could cause the initialization of a class,
   * change the value of a field, ... while other instructions do not.
   *
   * This classification also depends on the type of analysis that is using it. For instance, an
   * analysis can look for instructions that cause class initialization while another look for
   * instructions that check nullness of a particular object.
   *
   * On the other hand, some instructions may provide a non desired effect which is a signal for
   * the analysis to stop.
   */
  private enum InstructionEffect {
    DESIRED_EFFECT,
    CONDITIONAL_EFFECT,
    OTHER_EFFECT,
    NO_EFFECT
  }

  /**
   * Returns true if the given code unconditionally throws if value is null before any other side
   * effect instruction.
   *
   * <p>Note: we do not track phis so we may return false negative. This is a conservative approach.
   */
  public static boolean checksNullBeforeSideEffect(
      IRCode code, Value value, AppView<? extends AppInfo> appView) {
    return alwaysTriggerExpectedEffectBeforeAnythingElse(
        code,
        (instr, it) -> {
          BasicBlock currentBlock = instr.getBlock();
          // If the code explicitly checks the nullability of the value, we should visit the next
          // block that corresponds to the null value where NPE semantic could be preserved.
          if (!currentBlock.hasCatchHandlers() && isNullCheck(instr, value)) {
            return InstructionEffect.CONDITIONAL_EFFECT;
          }
          if (isKotlinNullCheck(instr, value, appView)) {
            DexMethod invokedMethod = instr.asInvokeStatic().getInvokedMethod();
            // Kotlin specific way of throwing NPE: throwParameterIsNullException.
            // Similarly, combined with the above CONDITIONAL_EFFECT, the code checks on NPE on
            // the value.
            if (invokedMethod.name
                == appView.dexItemFactory().kotlin.intrinsics.throwParameterIsNullException.name) {
              // We found a NPE (or similar exception) throwing code.
              // Combined with the above CONDITIONAL_EFFECT, the code checks NPE on the value.
              for (BasicBlock predecessor : currentBlock.getPredecessors()) {
                Instruction last =
                    predecessor.listIterator(predecessor.getInstructions().size()).previous();
                if (isNullCheck(last, value)) {
                  return InstructionEffect.DESIRED_EFFECT;
                }
              }
              // Hitting here means that this call might be used for other parameters. If we don't
              // bail out, it will be regarded as side effects for the current value.
              return InstructionEffect.NO_EFFECT;
            } else {
              // Kotlin specific way of checking parameter nullness: checkParameterIsNotNull.
              assert invokedMethod.name
                  == appView.dexItemFactory().kotlin.intrinsics.checkParameterIsNotNull.name;
              return InstructionEffect.DESIRED_EFFECT;
            }
          }
          if (isInstantiationOfNullPointerException(instr, it, appView.dexItemFactory())) {
            it.next(); // Skip call to NullPointerException.<init>.
            return InstructionEffect.NO_EFFECT;
          } else if (instr.throwsNpeIfValueIsNull(value, appView.dexItemFactory())) {
            // In order to preserve NPE semantic, the exception must not be caught by any handler.
            // Therefore, we must ignore this instruction if it is covered by a catch handler.
            // Note: this is a conservative approach where we consider that any catch handler could
            // catch the exception, even if it cannot catch a NullPointerException.
            if (!currentBlock.hasCatchHandlers()) {
              // We found a NPE check on the value.
              return InstructionEffect.DESIRED_EFFECT;
            }
          } else if (instr.instructionMayHaveSideEffects(appView, code.method.method.holder)) {
            // If the current instruction is const-string, this could load the parameter name.
            // Just make sure it is indeed not throwing.
            if (instr.isConstString() && !instr.instructionInstanceCanThrow()) {
              return InstructionEffect.NO_EFFECT;
            }
            // We found a side effect before a NPE check.
            return InstructionEffect.OTHER_EFFECT;
          }
          return InstructionEffect.NO_EFFECT;
        });
  }

  // Note that this method may have false positives, since the application could in principle
  // declare a method called checkParameterIsNotNull(parameter, message) or
  // throwParameterIsNullException(parameterName) in a package that starts with "kotlin".
  private static boolean isKotlinNullCheck(
      Instruction instr, Value value, AppView<? extends AppInfo> appView) {
    if (!instr.isInvokeStatic()) {
      return false;
    }
    // We need to strip the holder, since Kotlin adds different versions of null-check machinery,
    // e.g., kotlin.collections.ArraysKt___ArraysKt... or kotlin.jvm.internal.ArrayIteratorKt...
    MethodSignatureEquivalence wrapper = MethodSignatureEquivalence.get();
    Wrapper<DexMethod> checkParameterIsNotNull =
        wrapper.wrap(appView.dexItemFactory().kotlin.intrinsics.checkParameterIsNotNull);
    Wrapper<DexMethod> throwParamIsNullException =
        wrapper.wrap(appView.dexItemFactory().kotlin.intrinsics.throwParameterIsNullException);
    DexMethod invokedMethod =
        appView.graphLense().getOriginalMethodSignature(instr.asInvokeStatic().getInvokedMethod());
    Wrapper<DexMethod> methodWrap = wrapper.wrap(invokedMethod);
    if (methodWrap.equals(throwParamIsNullException)
        || (methodWrap.equals(checkParameterIsNotNull) && instr.inValues().get(0).equals(value))) {
      if (invokedMethod.holder.getPackageDescriptor().startsWith(Kotlin.NAME)) {
        return true;
      }
    }
    return false;
  }

  private static boolean isNullCheck(Instruction instr, Value value) {
    return instr.isIf() && instr.asIf().isZeroTest()
        && instr.inValues().get(0).equals(value)
        && (instr.asIf().getType() == Type.EQ || instr.asIf().getType() == Type.NE);
  }

  /**
   * Returns true if the given instruction is {@code v <- new-instance NullPointerException},
   * and the next instruction is {@code invoke-direct v, NullPointerException.<init>()}.
   */
  private static boolean isInstantiationOfNullPointerException(
      Instruction instruction, InstructionListIterator it, DexItemFactory dexItemFactory) {
    if (!instruction.isNewInstance()
        || instruction.asNewInstance().clazz != dexItemFactory.npeType) {
      return false;
    }
    Instruction next = it.peekNext();
    if (next == null
        || !next.isInvokeDirect()
        || next.asInvokeDirect().getInvokedMethod() != dexItemFactory.npeMethods.init) {
      return false;
    }
    return true;
  }

  /**
   * Returns true if the given code unconditionally triggers class initialization before any other
   * side effecting instruction.
   *
   * <p>Note: we do not track phis so we may return false negative. This is a conservative approach.
   */
  private static boolean triggersClassInitializationBeforeSideEffect(
      DexType clazz, IRCode code, AppView<? extends AppInfo> appView) {
    return alwaysTriggerExpectedEffectBeforeAnythingElse(
        code,
        (instruction, it) -> {
          if (instruction.definitelyTriggersClassInitialization(
              clazz, appView, DIRECTLY, AnalysisAssumption.INSTRUCTION_DOES_NOT_THROW)) {
            // In order to preserve class initialization semantic, the exception must not be caught
            // by any handler. Therefore, we must ignore this instruction if it is covered by a
            // catch handler.
            // Note: this is a conservative approach where we consider that any catch handler could
            // catch the exception, even if it cannot catch an ExceptionInInitializerError.
            if (!instruction.getBlock().hasCatchHandlers()) {
              // We found an instruction that preserves initialization of the class.
              return InstructionEffect.DESIRED_EFFECT;
            }
          } else if (instruction.instructionMayHaveSideEffects(appView, clazz)) {
            // We found a side effect before class initialization.
            return InstructionEffect.OTHER_EFFECT;
          }
          return InstructionEffect.NO_EFFECT;
        });
  }

  /**
   * Returns true if the given code unconditionally triggers an expected effect before anything
   * else, false otherwise.
   *
   * <p>Note: we do not track phis so we may return false negative. This is a conservative approach.
   */
  private static boolean alwaysTriggerExpectedEffectBeforeAnythingElse(
      IRCode code, BiFunction<Instruction, InstructionListIterator, InstructionEffect> function) {
    final int color = code.reserveMarkingColor();
    try {
      ArrayDeque<BasicBlock> worklist = new ArrayDeque<>();
      final BasicBlock entry = code.entryBlock();
      worklist.add(entry);
      entry.mark(color);

      while (!worklist.isEmpty()) {
        BasicBlock currentBlock = worklist.poll();
        assert currentBlock.isMarked(color);

        InstructionEffect result = InstructionEffect.NO_EFFECT;
        InstructionListIterator it = currentBlock.listIterator();
        while (result == InstructionEffect.NO_EFFECT && it.hasNext()) {
          result = function.apply(it.next(), it);
        }
        if (result == InstructionEffect.OTHER_EFFECT) {
          // We found an instruction that is causing an unexpected side effect.
          return false;
        } else if (result == InstructionEffect.DESIRED_EFFECT) {
          // The current path is causing the expected effect. No need to go deeper in this path,
          // go to the next block in the work list.
          continue;
        } else if (result == InstructionEffect.CONDITIONAL_EFFECT) {
          assert !currentBlock.getNormalSuccessors().isEmpty();
          Instruction lastInstruction = currentBlock.getInstructions().getLast();
          assert lastInstruction.isIf();
          // The current path is checking if the value of interest is null. Go deeper into the path
          // that corresponds to the null value.
          BasicBlock targetIfReceiverIsNull = lastInstruction.asIf().targetFromCondition(0);
          if (!targetIfReceiverIsNull.isMarked(color)) {
            worklist.add(targetIfReceiverIsNull);
            targetIfReceiverIsNull.mark(color);
          }
        } else {
          assert result == InstructionEffect.NO_EFFECT;
          // The block did not cause any particular effect.
          if (currentBlock.getNormalSuccessors().isEmpty()) {
            // This is the end of the current non-exceptional path and we did not find any expected
            // effect. It means there is at least one path where the expected effect does not
            // happen.
            Instruction lastInstruction = currentBlock.getInstructions().getLast();
            assert lastInstruction.isReturn() || lastInstruction.isThrow();
            return false;
          } else {
            // Look into successors
            for (BasicBlock successor : currentBlock.getSuccessors()) {
              if (!successor.isMarked(color)) {
                worklist.add(successor);
                successor.mark(color);
              }
            }
          }
        }
      }

      // If we reach this point, we checked that the expected effect happens in every possible path.
      return true;
    } finally {
      code.returnMarkingColor(color);
    }
  }

  private boolean checkArgumentType(InvokeMethod invoke, int argumentIndex) {
    // TODO(sgjesse): Insert cast if required.
    TypeLatticeElement returnType =
        TypeLatticeElement.fromDexType(
            invoke.getInvokedMethod().proto.returnType, maybeNull(), appView);
    TypeLatticeElement argumentType =
        TypeLatticeElement.fromDexType(
            getArgumentType(invoke, argumentIndex), maybeNull(), appView);
    return appView.enableWholeProgramOptimizations()
        ? argumentType.lessThanOrEqual(returnType, appView)
        : argumentType.equals(returnType);
  }

  private DexType getArgumentType(InvokeMethod invoke, int argumentIndex) {
    if (invoke.isInvokeStatic()) {
      return invoke.getInvokedMethod().proto.parameters.values[argumentIndex];
    }
    if (argumentIndex == 0) {
      return invoke.getInvokedMethod().holder;
    }
    return invoke.getInvokedMethod().proto.parameters.values[argumentIndex - 1];
  }

  // Replace result uses for methods where something is known about what is returned.
  public void rewriteMoveResult(IRCode code) {
    if (options.isGeneratingClassFiles()) {
      return;
    }
    AppInfoWithLiveness appInfoWithLiveness = appView.appInfo().withLiveness();
    Set<Value> needToWidenValues = Sets.newIdentityHashSet();
    Set<Value> needToNarrowValues = Sets.newIdentityHashSet();
    InstructionIterator iterator = code.instructionIterator();
    while (iterator.hasNext()) {
      Instruction current = iterator.next();
      if (current.isInvokeMethod()) {
        InvokeMethod invoke = current.asInvokeMethod();
        Value outValue = invoke.outValue();
        // TODO(b/124246610): extend to other variants that receive error messages or supplier.
        if (invoke.getInvokedMethod() == dexItemFactory.objectsMethods.requireNonNull) {
          Value obj = invoke.arguments().get(0);
          if ((outValue == null && obj.hasLocalInfo())
              || (outValue != null && !obj.hasSameOrNoLocal(outValue))) {
            continue;
          }
          Nullability nullability = obj.getTypeLattice().nullability();
          if (nullability.isDefinitelyNotNull()) {
            if (outValue != null) {
              outValue.replaceUsers(obj);
              needToNarrowValues.addAll(outValue.affectedValues());
            }
            iterator.removeOrReplaceByDebugLocalRead();
          } else if (nullability.isDefinitelyNull()) {
            // TODO(b/124246610): throw NPE.
            // Refactor UninstantiatedTypeOptimization#replaceCurrentInstructionWithThrowNull
            // and move it to iterator.
          }
        } else if (outValue != null && !outValue.hasLocalInfo()) {
          if (appView
              .dexItemFactory()
              .libraryMethodsReturningReceiver
              .contains(invoke.getInvokedMethod())) {
            if (checkArgumentType(invoke, 0)) {
              outValue.replaceUsers(invoke.arguments().get(0));
              invoke.setOutValue(null);
            }
          } else if (appInfoWithLiveness != null) {
            DexEncodedMethod target =
                invoke.lookupSingleTarget(appInfoWithLiveness, code.method.method.holder);
            if (target != null) {
              DexMethod invokedMethod = target.method;
              // Check if the invoked method is known to return one of its arguments.
              DexEncodedMethod definition = appView.definitionFor(invokedMethod);
              if (definition != null && definition.getOptimizationInfo().returnsArgument()) {
                int argumentIndex = definition.getOptimizationInfo().getReturnedArgument();
                // Replace the out value of the invoke with the argument and ignore the out value.
                if (argumentIndex >= 0 && checkArgumentType(invoke, argumentIndex)) {
                  Value argument = invoke.arguments().get(argumentIndex);
                  assert outValue.verifyCompatible(argument.outType());
                  if (argument
                      .getTypeLattice()
                      .lessThanOrEqual(outValue.getTypeLattice(), appView)) {
                    needToNarrowValues.addAll(outValue.affectedValues());
                  } else {
                    needToWidenValues.addAll(outValue.affectedValues());
                  }
                  outValue.replaceUsers(argument);
                  invoke.setOutValue(null);
                }
              }
            }
          }
        }
      }
    }
    if (!needToWidenValues.isEmpty() || !needToNarrowValues.isEmpty()) {
      TypeAnalysis analysis = new TypeAnalysis(appView, code.method);
      // If out value of invoke < argument (e.g., losing non-null info), widen users type.
      if (!needToWidenValues.isEmpty()) {
        analysis.widening(needToWidenValues);
      }
      // Otherwise, i.e., argument has more precise types, narrow users type.
      if (!needToNarrowValues.isEmpty()) {
        analysis.narrowing(needToNarrowValues);
      }
    }
    assert code.isConsistentGraph();
  }

  /**
   * For supporting assert javac adds the static field $assertionsDisabled to all classes which have
   * methods with assertions. This is used to support the Java VM -ea flag.
   *
   * <p>The class:
   *
   * <pre>
   * class A {
   *   void m() {
   *     assert xxx;
   *   }
   * }
   * </pre>
   *
   * Is compiled into:
   *
   * <pre>
   * class A {
   *   static boolean $assertionsDisabled;
   *   static {
   *     $assertionsDisabled = A.class.desiredAssertionStatus();
   *   }
   *
   *   // method with "assert xxx";
   *   void m() {
   *     if (!$assertionsDisabled) {
   *       if (xxx) {
   *         throw new AssertionError(...);
   *       }
   *     }
   *   }
   * }
   * </pre>
   *
   * With the rewriting below (and other rewritings) the resulting code is:
   *
   * <pre>
   * class A {
   *   void m() {
   *   }
   * }
   * </pre>
   */
  public void disableAssertions(
      AppView<? extends AppInfo> appView,
      DexEncodedMethod method,
      IRCode code,
      OptimizationFeedback feedback) {
    if (method.isClassInitializer()) {
      if (!hasJavacClinitAssertionCode(code)) {
        return;
      }
      // Mark the clinit as having code to turn on assertions.
      feedback.setInitializerEnablingJavaAssertions(method);
    } else {
      // If the clinit of this class did not have have code to turn on assertions don't try to
      // remove assertion code from the method.
      DexClass clazz = appView.definitionFor(method.method.holder);
      if (clazz == null) {
        return;
      }
      DexEncodedMethod clinit = clazz.getClassInitializer();
      if (clinit == null
          || !clinit.isProcessed()
          || !clinit.getOptimizationInfo().isInitializerEnablingJavaAssertions()) {
        return;
      }
    }

    InstructionIterator iterator = code.instructionIterator();
    while (iterator.hasNext()) {
      Instruction current = iterator.next();
      if (current.isInvokeMethod()) {
        InvokeMethod invoke = current.asInvokeMethod();
        if (invoke.getInvokedMethod() == dexItemFactory.classMethods.desiredAssertionStatus) {
          iterator.replaceCurrentInstruction(code.createIntConstant(0));
        }
      } else if (current.isStaticPut()) {
        StaticPut staticPut = current.asStaticPut();
        if (staticPut.getField().name == dexItemFactory.assertionsDisabled) {
          iterator.remove();
        }
      } else if (current.isStaticGet()) {
        StaticGet staticGet = current.asStaticGet();
        if (staticGet.getField().name == dexItemFactory.assertionsDisabled) {
          iterator.replaceCurrentInstruction(code.createIntConstant(1));
        }
      }
    }
  }

  private boolean isClassDesiredAssertionStatusInvoke(Instruction instruction) {
    return instruction.isInvokeMethod()
    && instruction.asInvokeMethod().getInvokedMethod()
        == dexItemFactory.classMethods.desiredAssertionStatus;
  }

  private boolean isAssertionsDisabledFieldPut(Instruction instruction) {
    return instruction.isStaticPut()
        && instruction.asStaticPut().getField().name == dexItemFactory.assertionsDisabled;
  }

  private boolean isNotDebugInstruction(Instruction instruction) {
    return !instruction.isDebugInstruction();
  }

  private Value blockWithSingleConstNumberAndGoto(BasicBlock block) {
    InstructionIterator iterator  = block.iterator();
    Instruction constNumber = iterator.nextUntil(this::isNotDebugInstruction);
    if (constNumber == null || !constNumber.isConstNumber()) {
      return null;
    }
    Instruction exit = iterator.nextUntil(this::isNotDebugInstruction);
    return exit != null && exit.isGoto() ? constNumber.outValue() : null;
  }

  private Value blockWithAssertionsDisabledFieldPut(BasicBlock block) {
    InstructionIterator iterator  = block.iterator();
    Instruction fieldPut = iterator.nextUntil(this::isNotDebugInstruction);
    return fieldPut != null
        && isAssertionsDisabledFieldPut(fieldPut) ? fieldPut.inValues().get(0) : null;
  }

  private boolean hasJavacClinitAssertionCode(IRCode code) {
    InstructionIterator iterator = code.instructionIterator();
    Instruction current = iterator.nextUntil(this::isClassDesiredAssertionStatusInvoke);
    if (current == null) {
      return false;
    }

    Value DesiredAssertionStatus = current.outValue();
    assert iterator.hasNext();
    current = iterator.next();
    if (!current.isIf()
        || !current.asIf().isZeroTest()
        || current.asIf().inValues().get(0) != DesiredAssertionStatus) {
      return false;
    }

    If theIf = current.asIf();
    BasicBlock trueTarget = theIf.getTrueTarget();
    BasicBlock falseTarget = theIf.fallthroughBlock();
    if (trueTarget == falseTarget) {
      return false;
    }

    Value trueValue = blockWithSingleConstNumberAndGoto(trueTarget);
    Value falseValue = blockWithSingleConstNumberAndGoto(falseTarget);
    if (trueValue == null
        || falseValue == null
        || (trueTarget.exit().asGoto().getTarget() != falseTarget.exit().asGoto().getTarget())) {
      return false;
    }

    BasicBlock target = trueTarget.exit().asGoto().getTarget();
    Value storeValue = blockWithAssertionsDisabledFieldPut(target);
    return storeValue != null
        && storeValue.isPhi()
        && storeValue.asPhi().getOperands().size() == 2
        && storeValue.asPhi().getOperands().contains(trueValue)
        && storeValue.asPhi().getOperands().contains(falseValue);
  }

  public void removeTrivialCheckCastAndInstanceOfInstructions(
      IRCode code, boolean enableWholeProgramOptimizations) {
    if (!enableWholeProgramOptimizations) {
      return;
    }

    InstructionIterator it = code.instructionIterator();
    boolean needToRemoveTrivialPhis = false;
    while (it.hasNext()) {
      Instruction current = it.next();
      if (current.isCheckCast()) {
        boolean hasPhiUsers = current.outValue().numberOfPhiUsers() != 0;
        if (removeCheckCastInstructionIfTrivial(current.asCheckCast(), it, code)) {
          needToRemoveTrivialPhis |= hasPhiUsers;
        }
      } else if (current.isInstanceOf()) {
        boolean hasPhiUsers = current.outValue().numberOfPhiUsers() != 0;
        if (removeInstanceOfInstructionIfTrivial(current.asInstanceOf(), it, code)) {
          needToRemoveTrivialPhis |= hasPhiUsers;
        }
      }
    }
    // ... v1
    // ...
    // v2 <- check-cast v1, T
    // v3 <- phi(v1, v2)
    // Removing check-cast may result in a trivial phi:
    // v3 <- phi(v1, v1)
    if (needToRemoveTrivialPhis) {
      code.removeAllTrivialPhis();
    }
    assert code.isConsistentSSA();
  }

  // Returns true if the given check-cast instruction was removed.
  private boolean removeCheckCastInstructionIfTrivial(
      CheckCast checkCast, InstructionIterator it, IRCode code) {
    Value inValue = checkCast.object();
    Value outValue = checkCast.outValue();
    DexType castType = checkCast.getType();

    // If the cast type is not accessible in the current context, we should not remove the cast
    // in order to preserve IllegalAccessError. Note that JVM and ART behave differently: see
    // {@link com.android.tools.r8.ir.optimize.checkcast.IllegalAccessErrorTest}.
    if (isTypeInaccessibleInCurrentContext(castType, code.method)) {
      return false;
    }

    // If the in-value is `null` and the cast-type is a float-array type, then trivial check-cast
    // elimination may lead to verification errors. See b/123269162.
    if (options.canHaveArtCheckCastVerifierBug()) {
      if (inValue.getTypeLattice().isNullType()
          && castType.isArrayType()
          && castType.toBaseType(dexItemFactory).isFloatType()) {
        return false;
      }
    }

    // We might see chains of casts on subtypes. It suffices to cast to the lowest subtype,
    // as that will fail if a cast on a supertype would have failed.
    Predicate<Instruction> isCheckcastToSubtype =
        user ->
            user.isCheckCast()
                && appView.isSubtype(user.asCheckCast().getType(), castType).isTrue();
    if (!checkCast.getBlock().hasCatchHandlers()
        && outValue.isUsed()
        && outValue.numberOfPhiUsers() == 0
        && outValue.uniqueUsers().stream().allMatch(isCheckcastToSubtype)) {
      removeOrReplaceByDebugLocalWrite(checkCast, it, inValue, outValue);
      return true;
    }

    TypeLatticeElement inTypeLattice = inValue.getTypeLattice();
    TypeLatticeElement outTypeLattice = outValue.getTypeLattice();
    TypeLatticeElement castTypeLattice =
        TypeLatticeElement.fromDexType(castType, inTypeLattice.nullability(), appView);

    assert inTypeLattice.nullability().lessThanOrEqual(outTypeLattice.nullability());

    if (inTypeLattice.lessThanOrEqual(castTypeLattice, appView)) {
      // 1) Trivial cast.
      //   A a = ...
      //   A a' = (A) a;
      // 2) Up-cast: we already have finer type info.
      //   A < B
      //   A a = ...
      //   B b = (B) a;
      assert inTypeLattice.lessThanOrEqual(outTypeLattice, appView);
      removeOrReplaceByDebugLocalWrite(checkCast, it, inValue, outValue);
      return true;
    }

    // Otherwise, keep the checkcast to preserve verification errors. E.g., down-cast:
    // A < B < C
    // c = ...        // Even though we know c is of type A,
    // a' = (B) c;    // (this could be removed, since chained below.)
    // a'' = (A) a';  // this should remain for runtime verification.
    assert !inTypeLattice.isDefinitelyNull();
    assert outTypeLattice.equalUpToNullability(castTypeLattice);
    return false;
  }

  private boolean isTypeInaccessibleInCurrentContext(DexType type, DexEncodedMethod context) {
    DexType baseType = type.toBaseType(appView.dexItemFactory());
    if (baseType.isPrimitiveType()) {
      return false;
    }
    DexClass clazz = appView.definitionFor(baseType);
    if (clazz == null) {
      // Conservatively say yes.
      return true;
    }
    ConstraintWithTarget classVisibility =
        ConstraintWithTarget.deriveConstraint(
            context.method.holder, baseType, clazz.accessFlags, appView);
    return classVisibility == ConstraintWithTarget.NEVER;
  }

  // Returns true if the given instance-of instruction was removed.
  private boolean removeInstanceOfInstructionIfTrivial(
      InstanceOf instanceOf, InstructionIterator it, IRCode code) {
    // If the instance-of type is not accessible in the current context, we should not remove the
    // instance-of instruction in order to preserve IllegalAccessError.
    if (isTypeInaccessibleInCurrentContext(instanceOf.type(), code.method)) {
      return false;
    }

    Value inValue = instanceOf.value();
    TypeLatticeElement inType = inValue.getTypeLattice();
    TypeLatticeElement instanceOfType =
        TypeLatticeElement.fromDexType(instanceOf.type(), inType.nullability(), appView);

    InstanceOfResult result = InstanceOfResult.UNKNOWN;
    if (inType.isDefinitelyNull()) {
      result = InstanceOfResult.FALSE;
    } else if (inType.lessThanOrEqual(instanceOfType, appView) && !inType.isNullable()) {
      result = InstanceOfResult.TRUE;
    } else if (!inValue.isPhi()
        && inValue.definition.isCreatingInstanceOrArray()
        && instanceOfType.strictlyLessThan(inType, appView)) {
      result = InstanceOfResult.FALSE;
    } else if (appView.appInfo().hasLiveness()) {
      if (instanceOf.type().isClassType()
          && isNeverInstantiatedDirectlyOrIndirectly(instanceOf.type())) {
        // The type of the instance-of instruction is a program class, and is never instantiated
        // directly or indirectly. Thus, the in-value must be null, meaning that the instance-of
        // instruction will always evaluate to false.
        result = InstanceOfResult.FALSE;
      }

      if (result == InstanceOfResult.UNKNOWN) {
        if (inType.isClassType()
            && isNeverInstantiatedDirectlyOrIndirectly(
                inType.asClassTypeLatticeElement().getClassType())) {
          // The type of the in-value is a program class, and is never instantiated directly or
          // indirectly. This, the in-value must be null, meaning that the instance-of instruction
          // will always evaluate to false.
          result = InstanceOfResult.FALSE;
        }
      }
    }
    if (result != InstanceOfResult.UNKNOWN) {
      it.replaceCurrentInstruction(
          new ConstNumber(
              new Value(
                  code.valueNumberGenerator.next(),
                  TypeLatticeElement.INT,
                  instanceOf.outValue().getLocalInfo()),
              result == InstanceOfResult.TRUE ? 1 : 0));
      return true;
    }
    return false;
  }

  private boolean isNeverInstantiatedDirectlyOrIndirectly(DexType type) {
    assert appView.appInfo().hasLiveness();
    assert type.isClassType();
    DexClass clazz = appView.definitionFor(type);
    return clazz != null
        && clazz.isProgramClass()
        && !appView.appInfo().withLiveness().isInstantiatedDirectlyOrIndirectly(type);
  }

  public static void removeOrReplaceByDebugLocalWrite(
      Instruction currentInstruction, InstructionIterator it, Value inValue, Value outValue) {
    if (outValue.hasLocalInfo() && outValue.getLocalInfo() != inValue.getLocalInfo()) {
      DebugLocalWrite debugLocalWrite = new DebugLocalWrite(outValue, inValue);
      it.replaceCurrentInstruction(debugLocalWrite);
    } else {
      if (outValue.hasLocalInfo()) {
        assert outValue.getLocalInfo() == inValue.getLocalInfo();
        // Should remove the end-marker before replacing the current instruction.
        currentInstruction.removeDebugValue(outValue.getLocalInfo());
      }
      outValue.replaceUsers(inValue);
      it.removeOrReplaceByDebugLocalRead();
    }
  }

  private boolean canBeFolded(Instruction instruction) {
    return (instruction.isBinop() && instruction.asBinop().canBeFolded()) ||
        (instruction.isUnop() && instruction.asUnop().canBeFolded());
  }

  // Split constants that flow into ranged invokes. This gives the register allocator more
  // freedom in assigning register to ranged invokes which can greatly reduce the number
  // of register needed (and thereby code size as well).
  public void splitRangeInvokeConstants(IRCode code) {
    for (BasicBlock block : code.blocks) {
      InstructionListIterator it = block.listIterator();
      while (it.hasNext()) {
        Instruction current = it.next();
        if (current.isInvoke() && current.asInvoke().requiredArgumentRegisters() > 5) {
          Invoke invoke = current.asInvoke();
          it.previous();
          Map<ConstNumber, ConstNumber> oldToNew = new IdentityHashMap<>();
          for (int i = 0; i < invoke.inValues().size(); i++) {
            Value value = invoke.inValues().get(i);
            if (value.isConstNumber() && value.numberOfUsers() > 1) {
              ConstNumber definition = value.getConstInstruction().asConstNumber();
              Value originalValue = definition.outValue();
              ConstNumber newNumber = oldToNew.get(definition);
              if (newNumber == null) {
                newNumber = ConstNumber.copyOf(code, definition);
                it.add(newNumber);
                newNumber.setPosition(current.getPosition());
                oldToNew.put(definition, newNumber);
              }
              invoke.inValues().set(i, newNumber.outValue());
              originalValue.removeUser(invoke);
              newNumber.outValue().addUser(invoke);
            }
          }
          it.next();
        }
      }
    }
  }

  /**
   * If an instruction is known to be a /lit8 or /lit16 instruction, update the instruction to use
   * its own constant that will be defined just before the instruction. This transformation allows
   * to decrease pressure on register allocation by defining the shortest range of constant used
   * by this kind of instruction. D8 knowns at build time that constant will be encoded
   * directly into the final Dex instruction.
   */
  public void useDedicatedConstantForLitInstruction(IRCode code) {
    for (BasicBlock block : code.blocks) {
      InstructionListIterator instructionIterator = block.listIterator();
      while (instructionIterator.hasNext()) {
        Instruction currentInstruction = instructionIterator.next();
        if (shouldBeLitInstruction(currentInstruction)) {
          assert currentInstruction.isBinop();
          Binop binop = currentInstruction.asBinop();
          Value constValue;
          if (binop.leftValue().isConstNumber()) {
            constValue = binop.leftValue();
          } else if (binop.rightValue().isConstNumber()) {
            constValue = binop.rightValue();
          } else {
            throw new Unreachable();
          }
          if (constValue.numberOfAllUsers() > 1) {
            // No need to do the transformation if the const value is already used only one time.
            ConstNumber newConstant = ConstNumber
                .copyOf(code, constValue.definition.asConstNumber());
            newConstant.setPosition(currentInstruction.getPosition());
            newConstant.setBlock(currentInstruction.getBlock());
            currentInstruction.replaceValue(constValue, newConstant.outValue());
            constValue.removeUser(currentInstruction);
            instructionIterator.previous();
            instructionIterator.add(newConstant);
            instructionIterator.next();
          }
        }
      }
    }

    assert code.isConsistentSSA();
  }

  /**
   * A /lit8 or /lit16 instruction only concerns arithmetic or logical instruction. /lit8 or /lit16
   * instructions generate bigger code than 2addr instructions, thus we favor 2addr instructions
   * rather than /lit8 or /lit16 instructions.
   */
  private static boolean shouldBeLitInstruction(Instruction instruction) {
    if (instruction.isArithmeticBinop() || instruction.isLogicalBinop()) {
      Binop binop = instruction.asBinop();
      if (!binop.needsValueInRegister(binop.leftValue()) ||
          !binop.needsValueInRegister(binop.rightValue())) {
        return !canBe2AddrInstruction(binop);
      }
    }

    return false;
  }

  /**
   * Estimate if a binary operation can be a 2addr form or not. It can be a 2addr form when an
   * argument is no longer needed after the binary operation and can be overwritten. That is
   * definitely the case if there is no path between the binary operation and all other usages.
   */
  private static boolean canBe2AddrInstruction(Binop binop) {
    Value value = null;
    if (binop.needsValueInRegister(binop.leftValue())) {
      value = binop.leftValue();
    } else if (binop.isCommutative() && binop.needsValueInRegister(binop.rightValue())) {
      value = binop.rightValue();
    }

    if (value != null) {
      Iterable<Instruction> users = value.debugUsers() != null ?
          Iterables.concat(value.uniqueUsers(), value.debugUsers()) : value.uniqueUsers();

      for (Instruction user : users) {
        if (hasPath(binop, user)) {
          return false;
        }
      }

      for (Phi user : value.uniquePhiUsers()) {
        if (binop.getBlock().hasPathTo(user.getBlock())) {
          return false;
        }
      }
    }

    return true;
  }

  /**
   * Return true if there is a path between {@code source} instruction and {@code target}
   * instruction.
   */
  private static boolean hasPath(Instruction source, Instruction target) {
    BasicBlock sourceBlock = source.getBlock();
    BasicBlock targetBlock = target.getBlock();
    if (sourceBlock == targetBlock) {
      return sourceBlock.getInstructions().indexOf(source) <
          targetBlock.getInstructions().indexOf(target);
    }

    return source.getBlock().hasPathTo(targetBlock);
  }

  public void shortenLiveRanges(IRCode code) {
    // Currently, we are only shortening the live range of ConstNumbers in the entry block
    // and ConstStrings with one user.
    // TODO(ager): Generalize this to shorten live ranges for more instructions? Currently
    // doing so seems to make things worse.
    Supplier<DominatorTree> dominatorTreeMemoization =
        Suppliers.memoize(() -> new DominatorTree(code));
    Map<BasicBlock, List<Instruction>> addConstantInBlock = new HashMap<>();
    LinkedList<BasicBlock> blocks = code.blocks;
    for (int i = 0; i < blocks.size(); i++) {
      BasicBlock block = blocks.get(i);
      if (i == 0) {
        // For the first block process all ConstNumber as well as ConstString instructions.
        shortenLiveRangesInsideBlock(
            code,
            block,
            dominatorTreeMemoization,
            addConstantInBlock,
            insn ->
                (insn.isConstNumber() && insn.outValue().numberOfAllUsers() != 0)
                    || (insn.isConstString() && insn.outValue().numberOfAllUsers() != 0));
      } else {
        // For all following blocks only process ConstString with just one use.
        shortenLiveRangesInsideBlock(
            code,
            block,
            dominatorTreeMemoization,
            addConstantInBlock,
            insn -> insn.isConstString() && insn.outValue().numberOfAllUsers() == 1);
      }
    }

    // Heuristic to decide if constant instructions are shared in dominator block
    // of usages or move to the usages.

    // Process all blocks in stable order to avoid non-determinism of hash map iterator.
    for (BasicBlock block : blocks) {
      List<Instruction> instructions = addConstantInBlock.get(block);
      if (instructions == null) {
        continue;
      }

      if (block != blocks.get(0) && instructions.size() > STOP_SHARED_CONSTANT_THRESHOLD) {
        // Too much constants in the same block, do not longer share them except if they are used
        // by phi instructions or they are a sting constants.
        for (Instruction instruction : instructions) {
          if (instruction.outValue().numberOfPhiUsers() != 0 || instruction.isConstString()) {
            // Add constant into the dominator block of usages.
            insertConstantInBlock(instruction, block);
          } else {
            assert instruction.isConstNumber();
            ConstNumber constNumber = instruction.asConstNumber();
            Value constantValue = instruction.outValue();
            assert constantValue.numberOfUsers() != 0;
            assert constantValue.numberOfUsers() == constantValue.numberOfAllUsers();
            for (Instruction user : constantValue.uniqueUsers()) {
              ConstNumber newCstNum = ConstNumber.copyOf(code, constNumber);
              newCstNum.setPosition(user.getPosition());
              InstructionListIterator iterator = user.getBlock().listIterator(user);
              iterator.previous();
              iterator.add(newCstNum);
              user.replaceValue(constantValue, newCstNum.outValue());
            }
            constantValue.clearUsers();
          }
        }
      } else {
        // Add constant into the dominator block of usages.
        for (Instruction instruction : instructions) {
          insertConstantInBlock(instruction, block);
        }
      }
    }

    assert code.isConsistentSSA();
  }

  private void shortenLiveRangesInsideBlock(
      IRCode code,
      BasicBlock block,
      Supplier<DominatorTree> dominatorTreeMemoization,
      Map<BasicBlock, List<Instruction>> addConstantInBlock,
      Predicate<ConstInstruction> selector) {

    InstructionListIterator it = block.listIterator();
    while (it.hasNext()) {
      Instruction next = it.next();
      if (!next.isConstInstruction()) {
        continue;
      }
      ConstInstruction instruction = next.asConstInstruction();
      if (!selector.test(instruction) || instruction.outValue().hasLocalInfo()) {
        continue;
      }
      // Collect the blocks for all users of the constant.
      List<BasicBlock> userBlocks = new LinkedList<>();
      for (Instruction user : instruction.outValue().uniqueUsers()) {
        userBlocks.add(user.getBlock());
      }
      for (Phi phi : instruction.outValue().uniquePhiUsers()) {
        userBlocks.add(phi.getBlock());
      }
      // Locate the closest dominator block for all user blocks.
      DominatorTree dominatorTree = dominatorTreeMemoization.get();
      BasicBlock dominator = dominatorTree.closestDominator(userBlocks);
      // If the closest dominator block is a block that uses the constant for a phi the constant
      // needs to go in the immediate dominator block so that it is available for phi moves.
      for (Phi phi : instruction.outValue().uniquePhiUsers()) {
        if (phi.getBlock() == dominator) {
          if (instruction.outValue().numberOfAllUsers() == 1 &&
              phi.usesValueOneTime(instruction.outValue())) {
            // Out value is used only one time, move the constant directly to the corresponding
            // branch rather than into the dominator to avoid to generate a const on paths which
            // does not required it.
            int predIndex = phi.getOperands().indexOf(instruction.outValue());
            dominator = dominator.getPredecessors().get(predIndex);
          } else {
            dominator = dominatorTree.immediateDominator(dominator);
          }
          break;
        }
      }

      if (instruction.instructionTypeCanThrow()) {
        if (block.hasCatchHandlers() || dominator.hasCatchHandlers()) {
          // Do not move the constant if the constant instruction can throw
          // and the dominator or the original block has catch handlers.
          continue;
        }
      }

      List<Instruction> csts =
          addConstantInBlock.computeIfAbsent(dominator, k -> new ArrayList<>());

      ConstInstruction copy = instruction.isConstNumber()
          ? ConstNumber.copyOf(code, instruction.asConstNumber())
          : ConstString.copyOf(code, instruction.asConstString());
      instruction.outValue().replaceUsers(copy.outValue());
      csts.add(copy);
    }
  }

  private void insertConstantInBlock(Instruction instruction, BasicBlock block) {
    boolean hasCatchHandlers = block.hasCatchHandlers();
    InstructionListIterator insertAt = block.listIterator();
    // Place the instruction as late in the block as we can. It needs to go before users
    // and if we have catch handlers it needs to be placed before the throwing instruction.
    insertAt.nextUntil(i ->
        i.inValues().contains(instruction.outValue())
            || i.isJumpInstruction()
            || (hasCatchHandlers && i.instructionTypeCanThrow())
            || (options.canHaveCmpIfFloatBug() && i.isCmp()));
    Instruction next = insertAt.previous();
    instruction.setPosition(next.getPosition());
    insertAt.add(instruction);
  }

  private short[] computeArrayFilledData(ConstInstruction[] values, int size, int elementSize) {
    if (values == null) {
      return null;
    }
    if (elementSize == 1) {
      short[] result = new short[(size + 1) / 2];
      for (int i = 0; i < size; i += 2) {
        short value = (short) (values[i].asConstNumber().getIntValue() & 0xFF);
        if (i + 1 < size) {
          value |= (short) ((values[i + 1].asConstNumber().getIntValue() & 0xFF) << 8);
        }
        result[i / 2] = value;
      }
      return result;
    }
    assert elementSize == 2 || elementSize == 4 || elementSize == 8;
    int shortsPerConstant = elementSize / 2;
    short[] result = new short[size * shortsPerConstant];
    for (int i = 0; i < size; i++) {
      long value = values[i].asConstNumber().getRawValue();
      for (int part = 0; part < shortsPerConstant; part++) {
        result[i * shortsPerConstant + part] = (short) ((value >> (16 * part)) & 0xFFFFL);
      }
    }
    return result;
  }

  private ConstInstruction[] computeConstantArrayValues(
      NewArrayEmpty newArray, BasicBlock block, int size) {
    if (size > MAX_FILL_ARRAY_SIZE) {
      return null;
    }
    ConstInstruction[] values = new ConstInstruction[size];
    int remaining = size;
    Set<Instruction> users = newArray.outValue().uniqueUsers();
    Set<BasicBlock> visitedBlocks = Sets.newIdentityHashSet();
    // We allow the array instantiations to cross block boundaries as long as it hasn't encountered
    // an instruction instance that can throw an exception.
    InstructionListIterator it = block.listIterator();
    it.nextUntil(i -> i == newArray);
    do {
      visitedBlocks.add(block);
      while (it.hasNext()) {
        Instruction instruction = it.next();
        // If we encounter an instruction that can throw an exception we need to bail out of the
        // optimization so that we do not transform half-initialized arrays into fully initialized
        // arrays on exceptional edges. If the block has no handlers it is not observable so
        // we perform the rewriting.
        if (block.hasCatchHandlers() && instruction.instructionInstanceCanThrow()) {
          return null;
        }
        if (!users.contains(instruction)) {
          continue;
        }
        // If the initialization sequence is broken by another use we cannot use a
        // fill-array-data instruction.
        if (!instruction.isArrayPut()) {
          return null;
        }
        ArrayPut arrayPut = instruction.asArrayPut();
        if (!(arrayPut.value().isConstant() && arrayPut.index().isConstNumber())) {
          return null;
        }
        int index = arrayPut.index().getConstInstruction().asConstNumber().getIntValue();
        if (index < 0 || index >= values.length) {
          return null;
        }
        if (values[index] != null) {
          return null;
        }
        ConstInstruction value = arrayPut.value().getConstInstruction();
        values[index] = value;
        --remaining;
        if (remaining == 0) {
          return values;
        }
      }
      BasicBlock nextBlock = block.exit().isGoto() ? block.exit().asGoto().getTarget() : null;
      block = nextBlock != null && !visitedBlocks.contains(nextBlock) ? nextBlock : null;
      it = block != null ? block.listIterator() : null;
    } while (it != null);
    return null;
  }

  private boolean allowNewFilledArrayConstruction(Instruction instruction) {
    if (!(instruction instanceof NewArrayEmpty)) {
      return false;
    }
    NewArrayEmpty newArray = instruction.asNewArrayEmpty();
    if (!newArray.size().isConstant()) {
      return false;
    }
    assert newArray.size().isConstNumber();
    int size = newArray.size().getConstInstruction().asConstNumber().getIntValue();
    if (size < 1) {
      return false;
    }
    if (newArray.type.isPrimitiveArrayType()) {
      return true;
    }
    return newArray.type == dexItemFactory.stringArrayType
        && options.canUseFilledNewArrayOfObjects();
  }

  /**
   * Replace new-array followed by stores of constants to all entries with new-array
   * and fill-array-data / filled-new-array.
   */
  public void simplifyArrayConstruction(IRCode code) {
    if (options.isGeneratingClassFiles()) {
      return;
    }
    for (BasicBlock block : code.blocks) {
      // Map from the array value to the number of array put instruction to remove for that value.
      Map<Value, Instruction> instructionToInsertForArray = new HashMap<>();
      Map<Value, Integer> storesToRemoveForArray = new HashMap<>();
      // First pass: identify candidates and insert fill array data instruction.
      InstructionListIterator it = block.listIterator();
      while (it.hasNext()) {
        Instruction instruction = it.next();
        if (instruction.getLocalInfo() != null
            || !allowNewFilledArrayConstruction(instruction)) {
          continue;
        }
        NewArrayEmpty newArray = instruction.asNewArrayEmpty();
        int size = newArray.size().getConstInstruction().asConstNumber().getIntValue();
        ConstInstruction[] values = computeConstantArrayValues(newArray, block, size);
        if (values == null) {
          continue;
        }
        if (newArray.type == dexItemFactory.stringArrayType) {
          // Don't replace with filled-new-array if it requires more than 200 consecutive registers.
          if (size > 200) {
            continue;
          }
          List<Value> stringValues = new ArrayList<>(size);
          for (ConstInstruction value : values) {
            stringValues.add(value.outValue());
          }
          Value invokeValue = code.createValue(
              newArray.outValue().getTypeLattice(), newArray.getLocalInfo());
          InvokeNewArray invoke =
              new InvokeNewArray(dexItemFactory.stringArrayType, invokeValue, stringValues);
          for (Value value : newArray.inValues()) {
            value.removeUser(newArray);
          }
          newArray.outValue().replaceUsers(invokeValue);
          it.removeOrReplaceByDebugLocalRead();
          instructionToInsertForArray.put(invokeValue, invoke);
          storesToRemoveForArray.put(invokeValue, size);
        } else {
          // If there is only one element it is typically smaller to generate the array put
          // instruction instead of fill array data.
          if (size == 1) {
            continue;
          }
          int elementSize = newArray.type.elementSizeForPrimitiveArrayType();
          short[] contents = computeArrayFilledData(values, size, elementSize);
          if (contents == null) {
            continue;
          }
          if (block.hasCatchHandlers()) {
            continue;
          }
          int arraySize = newArray.size().getConstInstruction().asConstNumber().getIntValue();
          NewArrayFilledData fillArray =
              new NewArrayFilledData(newArray.outValue(), elementSize, arraySize, contents);
          fillArray.setPosition(newArray.getPosition());
          it.add(fillArray);
          storesToRemoveForArray.put(newArray.outValue(), size);
        }
      }
      // Second pass: remove all the array put instructions for the array for which we have
      // inserted a fill array data instruction instead.
      if (!storesToRemoveForArray.isEmpty()) {
        Set<BasicBlock> visitedBlocks = Sets.newIdentityHashSet();
        do {
          visitedBlocks.add(block);
          it = block.listIterator();
          while (it.hasNext()) {
            Instruction instruction = it.next();
            if (instruction.isArrayPut()) {
              Value array = instruction.asArrayPut().array();
              Integer toRemoveCount = storesToRemoveForArray.get(array);
              if (toRemoveCount != null) {
                if (toRemoveCount > 0) {
                  storesToRemoveForArray.put(array, --toRemoveCount);
                  it.remove();
                }
                if (toRemoveCount == 0) {
                  storesToRemoveForArray.put(array, --toRemoveCount);
                  Instruction construction = instructionToInsertForArray.get(array);
                  if (construction != null) {
                    // Set the position of the new array construction to be the position of the
                    // last removed put at which point we are now adding the construction.
                    construction.setPosition(instruction.getPosition());
                    it.add(construction);
                  }
                }
              }
            }
          }
          BasicBlock nextBlock = block.exit().isGoto() ? block.exit().asGoto().getTarget() : null;
          block = nextBlock != null && !visitedBlocks.contains(nextBlock) ? nextBlock : null;
        } while (block != null);
      }
    }
  }

  // TODO(mikaelpeltier) Manage that from and to instruction do not belong to the same block.
  private static boolean hasLocalOrLineChangeBetween(
      Instruction from, Instruction to, DexString localVar) {
    if (from.getBlock() != to.getBlock()) {
      return true;
    }
    if (from.getPosition().isSome()
        && to.getPosition().isSome()
        && !from.getPosition().equals(to.getPosition())) {
      return true;
    }
    InstructionListIterator iterator = from.getBlock().listIterator(from);
    Position position = null;
    while (iterator.hasNext()) {
      Instruction instruction = iterator.next();
      if (position == null) {
        if (instruction.getPosition().isSome()) {
          position = instruction.getPosition();
        }
      } else if (instruction.getPosition().isSome()
          && !position.equals(instruction.getPosition())) {
        return true;
      }
      if (instruction == to) {
        return false;
      }
      if (instruction.outValue() != null && instruction.outValue().hasLocalInfo()) {
        if (instruction.outValue().getLocalInfo().name == localVar) {
          return true;
        }
      }
    }
    throw new Unreachable();
  }

  public void simplifyDebugLocals(IRCode code) {
    for (BasicBlock block : code.blocks) {
      for (Phi phi : block.getPhis()) {
        if (!phi.hasLocalInfo() && phi.numberOfUsers() == 1 && phi.numberOfAllUsers() == 1) {
          Instruction instruction = phi.singleUniqueUser();
          if (instruction.isDebugLocalWrite()) {
            removeDebugWriteOfPhi(phi, instruction.asDebugLocalWrite());
          }
        }
      }

      InstructionListIterator iterator = block.listIterator();
      while (iterator.hasNext()) {
        Instruction prevInstruction = iterator.peekPrevious();
        Instruction instruction = iterator.next();
        if (instruction.isDebugLocalWrite()) {
          assert instruction.inValues().size() == 1;
          Value inValue = instruction.inValues().get(0);
          DebugLocalInfo localInfo = instruction.outValue().getLocalInfo();
          DexString localName = localInfo.name;
          if (!inValue.hasLocalInfo() &&
              inValue.numberOfAllUsers() == 1 &&
              inValue.definition != null &&
              !hasLocalOrLineChangeBetween(inValue.definition, instruction, localName)) {
            inValue.setLocalInfo(localInfo);
            instruction.outValue().replaceUsers(inValue);
            Value overwrittenLocal = instruction.removeDebugValue(localInfo);
            if (overwrittenLocal != null) {
              inValue.definition.addDebugValue(overwrittenLocal);
              overwrittenLocal.addDebugLocalEnd(inValue.definition);
            }
            if (prevInstruction != null &&
                (prevInstruction.outValue() == null
                    || !prevInstruction.outValue().hasLocalInfo()
                    || !instruction.getDebugValues().contains(prevInstruction.outValue()))) {
              instruction.moveDebugValues(prevInstruction);
            }
            iterator.removeOrReplaceByDebugLocalRead();
          }
        }
      }
    }
  }

  private void removeDebugWriteOfPhi(Phi phi, DebugLocalWrite write) {
    assert write.src() == phi;
    for (InstructionListIterator iterator = phi.getBlock().listIterator(); iterator.hasNext(); ) {
      Instruction next = iterator.next();
      if (!next.isDebugLocalWrite()) {
        // If the debug write is not in the block header bail out.
        return;
      }
      if (next == write) {
        // Associate the phi with the local.
        phi.setLocalInfo(write.getLocalInfo());
        // Replace uses of the write with the phi.
        write.outValue().replaceUsers(phi);
        // Safely remove the write.
        // TODO(zerny): Once phis become instructions, move debug values there instead of a nop.
        iterator.removeOrReplaceByDebugLocalRead();
        return;
      }
      assert next.getLocalInfo().name != write.getLocalInfo().name;
    }
  }

  private static class CSEExpressionEquivalence extends Equivalence<Instruction> {

    private final IRCode code;
    private final InternalOptions options;

    private CSEExpressionEquivalence(IRCode code, InternalOptions options) {
      this.code = code;
      this.options = options;
    }

    @Override
    protected boolean doEquivalent(Instruction a, Instruction b) {
      // Some Dalvik VMs incorrectly handle Cmp instructions which leads to a requirement
      // that we do not perform common subexpression elimination for them. See comment on
      // canHaveCmpLongBug for details.
      if (a.isCmp() && options.canHaveCmpLongBug()) {
        return false;
      }
      // Note that we don't consider positions because CSE can at most remove an instruction.
      if (!a.identicalNonValueNonPositionParts(b)) {
        return false;
      }
      // For commutative binary operations any order of in-values are equal.
      if (a.isBinop() && a.asBinop().isCommutative()) {
        Value a0 = a.inValues().get(0);
        Value a1 = a.inValues().get(1);
        Value b0 = b.inValues().get(0);
        Value b1 = b.inValues().get(1);
        return (identicalValue(a0, b0) && identicalValue(a1, b1))
            || (identicalValue(a0, b1) && identicalValue(a1, b0));
      } else {
        // Compare all in-values.
        assert a.inValues().size() == b.inValues().size();
        for (int i = 0; i < a.inValues().size(); i++) {
          if (!identicalValue(a.inValues().get(i), b.inValues().get(i))) {
            return false;
          }
        }
        return true;
      }
    }

    @Override
    protected int doHash(Instruction instruction) {
      final int prime = 29;
      int hash = instruction.getClass().hashCode();
      if (instruction.isBinop()) {
        Binop binop = instruction.asBinop();
        Value in0 = instruction.inValues().get(0);
        Value in1 = instruction.inValues().get(1);
        if (binop.isCommutative()) {
          hash += hash * prime + getHashCode(in0) * getHashCode(in1);
        } else {
          hash += hash * prime + getHashCode(in0);
          hash += hash * prime + getHashCode(in1);
        }
        return hash;
      } else {
        for (Value value : instruction.inValues()) {
          hash += hash * prime + getHashCode(value);
        }
      }
      return hash;
    }

    private static boolean identicalValue(Value a, Value b) {
      if (a.equals(b)) {
        return true;
      }
      if (a.isConstNumber() && b.isConstNumber()) {
        // Do not take assumption that constants are canonicalized.
        return a.definition.identicalNonValueNonPositionParts(b.definition);
      }
      return false;
    }

    private static int getHashCode(Value a) {
      if (a.isConstNumber()) {
        // Do not take assumption that constants are canonicalized.
        return Long.hashCode(a.definition.asConstNumber().getRawValue());
      }
      return a.hashCode();
    }
  }

  private boolean shareCatchHandlers(Instruction i0, Instruction i1) {
    if (!i0.instructionTypeCanThrow()) {
      assert !i1.instructionTypeCanThrow();
      return true;
    }
    assert i1.instructionTypeCanThrow();
    // TODO(sgjesse): This could be even better by checking for the exceptions thrown, e.g. div
    // and rem only ever throw ArithmeticException.
    CatchHandlers<BasicBlock> ch0 = i0.getBlock().getCatchHandlers();
    CatchHandlers<BasicBlock> ch1 = i1.getBlock().getCatchHandlers();
    return ch0.equals(ch1);
  }

  private boolean isCSEInstructionCandidate(Instruction instruction) {
    return (instruction.isBinop()
        || instruction.isUnop()
        || instruction.isInstanceOf()
        || instruction.isCheckCast())
        && instruction.getLocalInfo() == null
        && !instruction.hasInValueWithLocalInfo();
  }

  private boolean hasCSECandidate(IRCode code, int noCandidate) {
    for (BasicBlock block : code.blocks) {
      InstructionListIterator iterator = block.listIterator();
      while (iterator.hasNext()) {
        if (isCSEInstructionCandidate(iterator.next())) {
          return true;
        }
      }
      block.mark(noCandidate);
    }
    return false;
  }

  public void commonSubexpressionElimination(IRCode code) {
    int noCandidate = code.reserveMarkingColor();
    if (hasCSECandidate(code, noCandidate)) {
      final ListMultimap<Wrapper<Instruction>, Value> instructionToValue =
          ArrayListMultimap.create();
      final CSEExpressionEquivalence equivalence = new CSEExpressionEquivalence(code, options);
      final DominatorTree dominatorTree = new DominatorTree(code);
      for (int i = 0; i < dominatorTree.getSortedBlocks().length; i++) {
        BasicBlock block = dominatorTree.getSortedBlocks()[i];
        if (block.isMarked(noCandidate)) {
          continue;
        }
        InstructionListIterator iterator = block.listIterator();
        while (iterator.hasNext()) {
          Instruction instruction = iterator.next();
          if (isCSEInstructionCandidate(instruction)) {
            List<Value> candidates = instructionToValue.get(equivalence.wrap(instruction));
            boolean eliminated = false;
            if (candidates.size() > 0) {
              for (Value candidate : candidates) {
                if (dominatorTree.dominatedBy(block, candidate.definition.getBlock())
                    && shareCatchHandlers(instruction, candidate.definition)) {
                  instruction.outValue().replaceUsers(candidate);
                  eliminated = true;
                  iterator.removeOrReplaceByDebugLocalRead();
                  break;  // Don't try any more candidates.
                }
              }
            }
            if (!eliminated) {
              instructionToValue.put(equivalence.wrap(instruction), instruction.outValue());
            }
          }
        }
      }
    }
    code.returnMarkingColor(noCandidate);
    assert code.isConsistentSSA();
  }

  public void simplifyIf(IRCode code) {
    for (BasicBlock block : code.blocks) {
      // Skip removed (= unreachable) blocks.
      if (block.getNumber() != 0 && block.getPredecessors().isEmpty()) {
        continue;
      }
      if (block.exit().isIf()) {
        flipIfBranchesIfNeeded(block);
        rewriteIfWithConstZero(block);

        if (simplifyKnownBooleanCondition(code, block)) {
          continue;
        }

        // Simplify if conditions when possible.
        If theIf = block.exit().asIf();
        List<Value> inValues = theIf.inValues();

        if (inValues.get(0).isConstNumber()
            && (theIf.isZeroTest() || inValues.get(1).isConstNumber())) {
          // Zero test with a constant of comparison between between two constants.
          if (theIf.isZeroTest()) {
            ConstNumber cond = inValues.get(0).getConstInstruction().asConstNumber();
            BasicBlock target = theIf.targetFromCondition(cond);
            simplifyIfWithKnownCondition(code, block, theIf, target);
          } else {
            ConstNumber left = inValues.get(0).getConstInstruction().asConstNumber();
            ConstNumber right = inValues.get(1).getConstInstruction().asConstNumber();
            BasicBlock target = theIf.targetFromCondition(left, right);
            simplifyIfWithKnownCondition(code, block, theIf, target);
          }
        } else if (inValues.get(0).hasValueRange()
            && (theIf.isZeroTest() || inValues.get(1).hasValueRange())) {
          // Zero test with a value range, or comparison between between two values,
          // each with a value ranges.
          if (theIf.isZeroTest()) {
            LongInterval interval = inValues.get(0).getValueRange();
            if (!interval.containsValue(0)) {
              // Interval doesn't contain zero at all.
              int sign = Long.signum(interval.getMin());
              simplifyIfWithKnownCondition(code, block, theIf, sign);
            } else {
              // Interval contains zero.
              switch (theIf.getType()) {
                case GE:
                case LT:
                  // [a, b] >= 0 is always true if a >= 0.
                  // [a, b] < 0 is always false if a >= 0.
                  // In both cases a zero condition takes the right branch.
                  if (interval.getMin() == 0) {
                    simplifyIfWithKnownCondition(code, block, theIf, 0);
                  }
                  break;
                case LE:
                case GT:
                  // [a, b] <= 0 is always true if b <= 0.
                  // [a, b] > 0 is always false if b <= 0.
                  if (interval.getMax() == 0) {
                    simplifyIfWithKnownCondition(code, block, theIf, 0);
                  }
                  break;
                case EQ:
                case NE:
                  // Only a single element interval [0, 0] can be dealt with here.
                  // Such intervals should have been replaced by constants.
                  assert !interval.isSingleValue();
                  break;
              }
            }
          } else {
            LongInterval leftRange = inValues.get(0).getValueRange();
            LongInterval rightRange = inValues.get(1).getValueRange();
            // Two overlapping ranges. Check for single point overlap.
            if (!leftRange.overlapsWith(rightRange)) {
              // No overlap.
              int cond = Long.signum(leftRange.getMin() - rightRange.getMin());
              simplifyIfWithKnownCondition(code, block, theIf, cond);
            } else {
              // The two intervals overlap. We can simplify if they overlap at the end points.
              switch (theIf.getType()) {
                case LT:
                case GE:
                  // [a, b] < [c, d] is always false when a == d.
                  // [a, b] >= [c, d] is always true when a == d.
                  // In both cases 0 condition will choose the right branch.
                  if (leftRange.getMin() == rightRange.getMax()) {
                    simplifyIfWithKnownCondition(code, block, theIf, 0);
                  }
                  break;
                case GT:
                case LE:
                  // [a, b] > [c, d] is always false when b == c.
                  // [a, b] <= [c, d] is always true when b == c.
                  // In both cases 0 condition will choose the right branch.
                  if (leftRange.getMax() == rightRange.getMin()) {
                    simplifyIfWithKnownCondition(code, block, theIf, 0);
                  }
                  break;
                case EQ:
                case NE:
                  // Since there is overlap EQ and NE cannot be determined.
                  break;
              }
            }
          }
        } else if (theIf.isZeroTest() && !inValues.get(0).isConstNumber()
            && (theIf.getType() == Type.EQ || theIf.getType() == Type.NE)) {
          TypeLatticeElement l = inValues.get(0).getTypeLattice();
          if (l.isReference() && inValues.get(0).isNeverNull()) {
            simplifyIfWithKnownCondition(code, block, theIf, 1);
          } else {
            if (!l.isPrimitive() && !l.isNullable()) {
              simplifyIfWithKnownCondition(code, block, theIf, 1);
            }
          }
        }
      }
    }
    Set<Value> affectedValues = code.removeUnreachableBlocks();
    if (!affectedValues.isEmpty()) {
      new TypeAnalysis(appView, code.method).narrowing(affectedValues);
    }
    assert code.isConsistentSSA();
  }

  private void simplifyIfWithKnownCondition(
      IRCode code, BasicBlock block, If theIf, BasicBlock target) {
    BasicBlock deadTarget =
        target == theIf.getTrueTarget() ? theIf.fallthroughBlock() : theIf.getTrueTarget();
    rewriteIfToGoto(code, block, theIf, target, deadTarget);
  }

  private void simplifyIfWithKnownCondition(IRCode code, BasicBlock block, If theIf, int cond) {
    simplifyIfWithKnownCondition(code, block, theIf, theIf.targetFromCondition(cond));
  }

  /**
   * This optimization exploits that we can sometimes learn the constant value of an SSA value that
   * flows into an if-eq of if-neq instruction.
   *
   * <p>Consider the following example:
   *
   * <pre>
   * 1. if (obj != null) {
   * 2.  return doStuff();
   * 3. }
   * 4. return null;
   * </pre>
   *
   * <p>Since we know that `obj` is null in all blocks that are dominated by the false-target of the
   * if-instruction in line 1, we can safely replace the null-constant in line 4 by `obj`, and
   * thereby save a const-number instruction.
   */
  public void redundantConstNumberRemoval(IRCode code) {
    Supplier<Long2ReferenceMap<List<ConstNumber>>> constantsByValue =
        Suppliers.memoize(() -> getConstantsByValue(code));
    Supplier<DominatorTree> dominatorTree = Suppliers.memoize(() -> new DominatorTree(code));

    boolean changed = false;
    for (BasicBlock block : code.blocks) {
      Instruction lastInstruction = block.getInstructions().getLast();
      if (!lastInstruction.isIf()) {
        continue;
      }

      If ifInstruction = lastInstruction.asIf();
      Type type = ifInstruction.getType();

      Value lhs = ifInstruction.inValues().get(0);
      Value rhs = !ifInstruction.isZeroTest() ? ifInstruction.inValues().get(1) : null;

      if (!ifInstruction.isZeroTest() && !lhs.isConstNumber() && !rhs.isConstNumber()) {
        // We can only conclude anything from an if-instruction if it is a zero-test or if one of
        // the two operands is a constant.
        continue;
      }

      // If the type is neither EQ nor NE, we cannot conclude anything about any of the in-values
      // of the if-instruction from the outcome of the if-instruction.
      if (type != Type.EQ && type != Type.NE) {
        continue;
      }

      BasicBlock trueTarget, falseTarget;
      if (type == Type.EQ) {
        trueTarget = ifInstruction.getTrueTarget();
        falseTarget = ifInstruction.fallthroughBlock();
      } else {
        falseTarget = ifInstruction.getTrueTarget();
        trueTarget = ifInstruction.fallthroughBlock();
      }

      if (ifInstruction.isZeroTest()) {
        changed |=
            replaceDominatedConstNumbers(0, lhs, trueTarget, constantsByValue, dominatorTree);
        if (lhs.knownToBeBoolean()) {
          changed |=
              replaceDominatedConstNumbers(1, lhs, falseTarget, constantsByValue, dominatorTree);
        }
      } else {
        assert rhs != null;
        if (lhs.isConstNumber()) {
          ConstNumber lhsAsNumber = lhs.getConstInstruction().asConstNumber();
          changed |=
              replaceDominatedConstNumbers(
                  lhsAsNumber.getRawValue(), rhs, trueTarget, constantsByValue, dominatorTree);
          if (lhs.knownToBeBoolean() && rhs.knownToBeBoolean()) {
            changed |=
                replaceDominatedConstNumbers(
                    negateBoolean(lhsAsNumber), rhs, falseTarget, constantsByValue, dominatorTree);
          }
        } else {
          assert rhs.isConstNumber();
          ConstNumber rhsAsNumber = rhs.getConstInstruction().asConstNumber();
          changed |=
              replaceDominatedConstNumbers(
                  rhsAsNumber.getRawValue(), lhs, trueTarget, constantsByValue, dominatorTree);
          if (lhs.knownToBeBoolean() && rhs.knownToBeBoolean()) {
            changed |=
                replaceDominatedConstNumbers(
                    negateBoolean(rhsAsNumber), lhs, falseTarget, constantsByValue, dominatorTree);
          }
        }
      }

      if (constantsByValue.get().isEmpty()) {
        break;
      }
    }

    if (changed) {
      code.removeAllTrivialPhis();
    }
    assert code.isConsistentSSA();
  }

  private static Long2ReferenceMap<List<ConstNumber>> getConstantsByValue(IRCode code) {
    // A map from the raw value of constants in `code` to the const number instructions that define
    // the given raw value (irrespective of the type of the raw value).
    Long2ReferenceMap<List<ConstNumber>> constantsByValue = new Long2ReferenceOpenHashMap<>();

    // Initialize `constantsByValue`.
    Iterable<Instruction> instructions = code::instructionIterator;
    for (Instruction instruction : instructions) {
      if (instruction.isConstNumber()) {
        ConstNumber constNumber = instruction.asConstNumber();
        if (constNumber.outValue().hasLocalInfo()) {
          // Not necessarily constant, because it could be changed in the debugger.
          continue;
        }
        long rawValue = constNumber.getRawValue();
        if (constantsByValue.containsKey(rawValue)) {
          constantsByValue.get(rawValue).add(constNumber);
        } else {
          List<ConstNumber> list = new ArrayList<>();
          list.add(constNumber);
          constantsByValue.put(rawValue, list);
        }
      }
    }
    return constantsByValue;
  }

  private static int negateBoolean(ConstNumber number) {
    assert number.outValue().knownToBeBoolean();
    return number.getRawValue() == 0 ? 1 : 0;
  }

  private boolean replaceDominatedConstNumbers(
      long withValue,
      Value newValue,
      BasicBlock dominator,
      Supplier<Long2ReferenceMap<List<ConstNumber>>> constantsByValueSupplier,
      Supplier<DominatorTree> dominatorTree) {
    if (newValue.hasLocalInfo()) {
      // We cannot replace a constant with a value that has local info, because that could change
      // debugging behavior.
      return false;
    }

    Long2ReferenceMap<List<ConstNumber>> constantsByValue = constantsByValueSupplier.get();
    List<ConstNumber> constantsWithValue = constantsByValue.get(withValue);
    if (constantsWithValue == null || constantsWithValue.isEmpty()) {
      return false;
    }

    boolean changed = false;

    ListIterator<ConstNumber> constantWithValueIterator = constantsWithValue.listIterator();
    while (constantWithValueIterator.hasNext()) {
      ConstNumber constNumber = constantWithValueIterator.next();
      Value value = constNumber.outValue();
      assert !value.hasLocalInfo();
      assert constNumber.getRawValue() == withValue;

      BasicBlock block = constNumber.getBlock();

      // If the following condition does not hold, then the if-instruction does not dominate the
      // block containing the constant, although the true or false target does.
      if (block == dominator && block.getPredecessors().size() != 1) {
        // This should generally not happen, but it is possible to write bytecode where it does.
        assert false;
        continue;
      }

      if (value.knownToBeBoolean() && !newValue.knownToBeBoolean()) {
        // We cannot replace a boolean by a none-boolean since that can lead to verification
        // errors. For example, the following code fails with "register v1 has type Imprecise
        // Constant: 127 but expected Boolean return-1nr".
        //
        //   public boolean convertIntToBoolean(int v1) {
        //       const/4 v0, 0x1
        //       if-eq v1, v0, :eq_true
        //       const/4 v1, 0x0
        //     :eq_true
        //       return v1
        //   }
        continue;
      }

      if (dominatorTree.get().dominatedBy(block, dominator)) {
        if (newValue.getTypeLattice().lessThanOrEqual(value.getTypeLattice(), appView)) {
          value.replaceUsers(newValue);
          block.listIterator(constNumber).removeOrReplaceByDebugLocalRead();
          constantWithValueIterator.remove();
          changed = true;
        } else if (value.getTypeLattice().isNullType()) {
          // TODO(b/120257211): Need a mechanism to determine if `newValue` can be used at all of
          // the use sites of `value` without introducing a type error.
        }
      }
    }

    if (constantsWithValue.isEmpty()) {
      constantsByValue.remove(withValue);
    }

    return changed;
  }

  // Find all method invocations that never returns normally, split the block
  // after each such invoke instruction and follow it with a block throwing a
  // null value (which should result in NPE). Note that this throw is not
  // expected to be ever reached, but is intended to satisfy verifier.
  public void processMethodsNeverReturningNormally(IRCode code) {
    AppInfoWithLiveness appInfoWithLiveness = appView.appInfo().withLiveness();
    if (appInfoWithLiveness == null) {
      return;
    }

    ListIterator<BasicBlock> blockIterator = code.listIterator();
    while (blockIterator.hasNext()) {
      BasicBlock block = blockIterator.next();
      if (block.getNumber() != 0 && block.getPredecessors().isEmpty()) {
        continue;
      }
      InstructionListIterator insnIterator = block.listIterator();
      while (insnIterator.hasNext()) {
        Instruction insn = insnIterator.next();
        if (!insn.isInvokeMethod()) {
          continue;
        }

        DexEncodedMethod singleTarget = insn.asInvokeMethod().lookupSingleTarget(
            appInfoWithLiveness, code.method.method.holder);
        if (singleTarget == null || !singleTarget.getOptimizationInfo().neverReturnsNormally()) {
          continue;
        }

        // Split the block.
        {
          BasicBlock newBlock = insnIterator.split(code, blockIterator);
          assert !insnIterator.hasNext(); // must be pointing *after* inserted GoTo.
          // Move block iterator back so current block is 'newBlock'.
          blockIterator.previous();

          newBlock.unlinkSinglePredecessorSiblingsAllowed();
        }

        // We want to follow the invoke instruction with 'throw null', which should
        // be unreachable but is needed to satisfy the verifier. Note that we have
        // to put 'throw null' into a separate block to make sure we don't get two
        // throwing instructions in the block having catch handler. This new block
        // does not need catch handlers.
        Instruction gotoInsn = insnIterator.previous();
        assert gotoInsn.isGoto();
        assert insnIterator.hasNext();
        BasicBlock throwNullBlock = insnIterator.split(code, blockIterator);
        InstructionListIterator throwNullInsnIterator = throwNullBlock.listIterator();

        // Insert 'null' constant.
        ConstNumber nullConstant = code.createConstNull(gotoInsn.getLocalInfo());
        nullConstant.setPosition(insn.getPosition());
        throwNullInsnIterator.add(nullConstant);

        // Replace Goto with Throw.
        Throw notReachableThrow = new Throw(nullConstant.outValue());
        Instruction insnGoto = throwNullInsnIterator.next();
        assert insnGoto.isGoto();
        throwNullInsnIterator.replaceCurrentInstruction(notReachableThrow);
      }
    }
    code.removeUnreachableBlocks();
    assert code.isConsistentSSA();
  }

  /* Identify simple diamond shapes converting boolean true/false to 1/0. We consider the forms:
   *
   * (1)
   *
   *      [dbg pos x]             [dbg pos x]
   *   ifeqz booleanValue       ifnez booleanValue
   *      /        \              /        \
   * [dbg pos x][dbg pos x]  [dbg pos x][dbg pos x]
   *  [const 0]  [const 1]    [const 1]  [const 0]
   *    goto      goto          goto      goto
   *      \        /              \        /
   *      phi(0, 1)                phi(1, 0)
   *
   * which can be replaced by a fallthrough and the phi value can be replaced
   * with the boolean value itself.
   *
   * (2)
   *
   *      [dbg pos x]              [dbg pos x]
   *    ifeqz booleanValue       ifnez booleanValue
   *      /        \              /        \
   * [dbg pos x][dbg pos x]  [dbg pos x][dbg pos x]
   *  [const 1]  [const 0]   [const 0]  [const 1]
   *    goto      goto          goto      goto
   *      \        /              \        /
   *      phi(1, 0)                phi(0, 1)
   *
   * which can be replaced by a fallthrough and the phi value can be replaced
   * by an xor instruction which is smaller.
   */
  private boolean simplifyKnownBooleanCondition(IRCode code, BasicBlock block) {
    If theIf = block.exit().asIf();
    Value testValue = theIf.inValues().get(0);
    if (theIf.isZeroTest() && testValue.knownToBeBoolean()) {
      BasicBlock trueBlock = theIf.getTrueTarget();
      BasicBlock falseBlock = theIf.fallthroughBlock();
      if (isBlockSupportedBySimplifyKnownBooleanCondition(trueBlock) &&
          isBlockSupportedBySimplifyKnownBooleanCondition(falseBlock) &&
          trueBlock.getSuccessors().get(0) == falseBlock.getSuccessors().get(0)) {
        BasicBlock targetBlock = trueBlock.getSuccessors().get(0);
        if (targetBlock.getPredecessors().size() == 2) {
          int trueIndex = targetBlock.getPredecessors().indexOf(trueBlock);
          int falseIndex = trueIndex == 0 ? 1 : 0;
          int deadPhis = 0;
          // Locate the phis that have the same value as the boolean and replace them
          // by the boolean in all users.
          for (Phi phi : targetBlock.getPhis()) {
            Value trueValue = phi.getOperand(trueIndex);
            Value falseValue = phi.getOperand(falseIndex);
            if (trueValue.isConstNumber() && falseValue.isConstNumber()) {
              ConstNumber trueNumber = trueValue.getConstInstruction().asConstNumber();
              ConstNumber falseNumber = falseValue.getConstInstruction().asConstNumber();
              if ((theIf.getType() == Type.EQ &&
                  trueNumber.isIntegerZero() &&
                  falseNumber.isIntegerOne()) ||
                  (theIf.getType() == Type.NE &&
                      trueNumber.isIntegerOne() &&
                      falseNumber.isIntegerZero())) {
                phi.replaceUsers(testValue);
                deadPhis++;
              } else if ((theIf.getType() == Type.NE &&
                           trueNumber.isIntegerZero() &&
                           falseNumber.isIntegerOne()) ||
                         (theIf.getType() == Type.EQ &&
                           trueNumber.isIntegerOne() &&
                           falseNumber.isIntegerZero())) {
                Value newOutValue = code.createValue(phi.getTypeLattice(), phi.getLocalInfo());
                ConstNumber cstToUse = trueNumber.isIntegerOne() ? trueNumber : falseNumber;
                BasicBlock phiBlock = phi.getBlock();
                Position phiPosition = phiBlock.getPosition();
                int insertIndex = 0;
                if (cstToUse.getBlock() == trueBlock || cstToUse.getBlock() == falseBlock) {
                  // The constant belongs to the block to remove, create a new one.
                  cstToUse = ConstNumber.copyOf(code, cstToUse);
                  cstToUse.setBlock(phiBlock);
                  cstToUse.setPosition(phiPosition);
                  phiBlock.getInstructions().add(insertIndex++, cstToUse);
                }
                phi.replaceUsers(newOutValue);
                Instruction newInstruction = new Xor(NumericType.INT, newOutValue, testValue,
                    cstToUse.outValue());
                newInstruction.setBlock(phiBlock);
                // The xor is replacing a phi so it does not have an actual position.
                newInstruction.setPosition(phiPosition);
                phiBlock.getInstructions().add(insertIndex, newInstruction);
                deadPhis++;
              }
            }
          }
          // If all phis were removed, there is no need for the diamond shape anymore
          // and it can be rewritten to a goto to one of the branches.
          if (deadPhis == targetBlock.getPhis().size()) {
            rewriteIfToGoto(code, block, theIf, trueBlock, falseBlock);
            return true;
          }
        }
      }
    }
    return false;
  }

  private boolean isBlockSupportedBySimplifyKnownBooleanCondition(BasicBlock b) {
    if (b.isTrivialGoto()) {
      return true;
    }

    int instructionSize = b.getInstructions().size();
    if (b.exit().isGoto() && (instructionSize == 2 || instructionSize == 3)) {
      Instruction constInstruction = b.getInstructions().get(instructionSize - 2);
      if (constInstruction.isConstNumber()) {
        if (!constInstruction.asConstNumber().isIntegerOne() &&
            !constInstruction.asConstNumber().isIntegerZero()) {
          return false;
        }
        if (instructionSize == 2) {
          return true;
        }
        Instruction firstInstruction = b.getInstructions().getFirst();
        if (firstInstruction.isDebugPosition()) {
          assert b.getPredecessors().size() == 1;
          BasicBlock predecessorBlock = b.getPredecessors().get(0);
          InstructionListIterator it = predecessorBlock.listIterator(predecessorBlock.exit());
          Instruction previousPosition = null;
          while (it.hasPrevious() && !(previousPosition = it.previous()).isDebugPosition());
          if (previousPosition != null) {
            return previousPosition.getPosition() == firstInstruction.getPosition();
          }
        }
      }
    }

    return false;
  }

  private void rewriteIfToGoto(
      IRCode code, BasicBlock block, If theIf, BasicBlock target, BasicBlock deadTarget) {
    deadTarget.unlinkSinglePredecessorSiblingsAllowed();
    assert theIf == block.exit();
    block.replaceLastInstruction(new Goto());
    assert block.exit().isGoto();
    assert block.exit().asGoto().getTarget() == target;
  }

  private void rewriteIfWithConstZero(BasicBlock block) {
    If theIf = block.exit().asIf();
    if (theIf.isZeroTest()) {
      return;
    }

    List<Value> inValues = theIf.inValues();
    Value leftValue = inValues.get(0);
    Value rightValue = inValues.get(1);
    if (leftValue.isConstNumber() || rightValue.isConstNumber()) {
      if (leftValue.isConstNumber()) {
        if (leftValue.getConstInstruction().asConstNumber().isZero()) {
          If ifz = new If(theIf.getType().forSwappedOperands(), rightValue);
          block.replaceLastInstruction(ifz);
          assert block.exit() == ifz;
        }
      } else {
        if (rightValue.getConstInstruction().asConstNumber().isZero()) {
          If ifz = new If(theIf.getType(), leftValue);
          block.replaceLastInstruction(ifz);
          assert block.exit() == ifz;
        }
      }
    }
  }

  private boolean flipIfBranchesIfNeeded(BasicBlock block) {
    If theIf = block.exit().asIf();
    BasicBlock trueTarget = theIf.getTrueTarget();
    BasicBlock fallthrough = theIf.fallthroughBlock();
    assert trueTarget != fallthrough;

    if (!fallthrough.isSimpleAlwaysThrowingPath() || trueTarget.isSimpleAlwaysThrowingPath()) {
      return false;
    }

    // In case fall-through block always throws there is a good chance that it
    // is created for error checks and 'trueTarget' represents most more common
    // non-error case. Flipping the if in this case may result in faster code
    // on older Android versions.
    List<Value> inValues = theIf.inValues();
    If newIf = new If(theIf.getType().inverted(), inValues);
    block.replaceLastInstruction(newIf);
    block.swapSuccessors(trueTarget, fallthrough);
    return true;
  }

  public void rewriteLongCompareAndRequireNonNull(IRCode code, InternalOptions options) {
    if (options.canUseLongCompareAndObjectsNonNull()) {
      return;
    }

    InstructionIterator iterator = code.instructionIterator();
    while (iterator.hasNext()) {
      Instruction current = iterator.next();
      if (current.isInvokeMethod()) {
        DexMethod invokedMethod = current.asInvokeMethod().getInvokedMethod();
        if (invokedMethod == dexItemFactory.longMethods.compare) {
          // Rewrite calls to Long.compare for sdk versions that do not have that method.
          List<Value> inValues = current.inValues();
          assert inValues.size() == 2;
          iterator.replaceCurrentInstruction(
              new Cmp(NumericType.LONG, Bias.NONE, current.outValue(), inValues.get(0),
                  inValues.get(1)));
        } else if (invokedMethod == dexItemFactory.objectsMethods.requireNonNull) {
          // Rewrite calls to Objects.requireNonNull(Object) because Javac 9 start to use it for
          // synthesized null checks.
          InvokeVirtual callToGetClass = new InvokeVirtual(dexItemFactory.objectMethods.getClass,
              null, current.inValues());
          if (current.outValue() != null) {
            current.outValue().replaceUsers(current.inValues().get(0));
            current.setOutValue(null);
          }
          iterator.replaceCurrentInstruction(callToGetClass);
        }
      }
    }
    assert code.isConsistentSSA();
  }

  /**
   * Remove moves that are not actually used by instructions in exiting paths. These moves can arise
   * due to debug local info needing a particular value and the live-interval for it then moves it
   * back into the properly assigned register. If the register is only used for debug purposes, it
   * is safe to just remove the move and update the local information accordingly.
   */
  public static void removeUnneededMovesOnExitingPaths(
      IRCode code, LinearScanRegisterAllocator allocator) {
    if (!allocator.options().debug) {
      return;
    }
    for (BasicBlock block : code.blocks) {
      // Skip non-exit blocks.
      if (!block.getSuccessors().isEmpty()) {
        continue;
      }
      // Skip blocks with no locals at entry.
      Int2ReferenceMap<DebugLocalInfo> localsAtEntry = block.getLocalsAtEntry();
      if (localsAtEntry == null || localsAtEntry.isEmpty()) {
        continue;
      }
      // Find the locals state after spill moves.
      DebugLocalsChange postSpillLocalsChange = null;
      for (Instruction instruction : block.getInstructions()) {
        if (instruction.getNumber() != -1 || postSpillLocalsChange != null) {
          break;
        }
        postSpillLocalsChange = instruction.asDebugLocalsChange();
      }
      // Skip if the locals state did not change.
      if (postSpillLocalsChange == null
          || !postSpillLocalsChange.apply(new Int2ReferenceOpenHashMap<>(localsAtEntry))) {
        continue;
      }
      // Collect the moves that can safely be removed.
      Set<Move> unneededMoves = computeUnneededMoves(block, postSpillLocalsChange, allocator);
      if (unneededMoves.isEmpty()) {
        continue;
      }
      Int2IntMap previousMapping = new Int2IntOpenHashMap();
      Int2IntMap mapping = new Int2IntOpenHashMap();
      ListIterator<Instruction> it = block.getInstructions().listIterator();
      while (it.hasNext()) {
        Instruction instruction = it.next();
        if (instruction.isMove()) {
          Move move = instruction.asMove();
          if (unneededMoves.contains(move)) {
            int dst = allocator.getRegisterForValue(move.dest(), move.getNumber());
            int src = allocator.getRegisterForValue(move.src(), move.getNumber());
            int mappedSrc = mapping.getOrDefault(src, src);
            mapping.put(dst, mappedSrc);
            it.remove();
          }
        } else if (instruction.isDebugLocalsChange()) {
          DebugLocalsChange change = instruction.asDebugLocalsChange();
          updateDebugLocalsRegisterMap(previousMapping, change.getEnding());
          updateDebugLocalsRegisterMap(mapping, change.getStarting());
          previousMapping = mapping;
          mapping = new Int2IntOpenHashMap(previousMapping);
        }
      }
    }
  }

  private static Set<Move> computeUnneededMoves(
      BasicBlock block,
      DebugLocalsChange postSpillLocalsChange,
      LinearScanRegisterAllocator allocator) {
    Set<Move> unneededMoves = Sets.newIdentityHashSet();
    IntSet usedRegisters = new IntOpenHashSet();
    IntSet clobberedRegisters = new IntOpenHashSet();
    // Backwards instruction scan collecting the registers used by actual instructions.
    boolean inEntrySpillMoves = false;
    InstructionListIterator it = block.listIterator(block.getInstructions().size());
    while (it.hasPrevious()) {
      Instruction instruction = it.previous();
      if (instruction == postSpillLocalsChange) {
        inEntrySpillMoves = true;
      }
      // If this is a move in the block-entry spill moves check if it is unneeded.
      if (inEntrySpillMoves && instruction.isMove()) {
        Move move = instruction.asMove();
        int dst = allocator.getRegisterForValue(move.dest(), move.getNumber());
        int src = allocator.getRegisterForValue(move.src(), move.getNumber());
        if (!usedRegisters.contains(dst) && !clobberedRegisters.contains(src)) {
          unneededMoves.add(move);
          continue;
        }
      }
      if (instruction.outValue() != null && instruction.outValue().needsRegister()) {
        int register =
            allocator.getRegisterForValue(instruction.outValue(), instruction.getNumber());
        // The register is defined anew, so uses before this are on distinct values.
        usedRegisters.remove(register);
        // Mark it clobbered to avoid any uses in locals after this point to become invalid.
        clobberedRegisters.add(register);
      }
      if (!instruction.inValues().isEmpty()) {
        for (Value inValue : instruction.inValues()) {
          if (inValue.needsRegister()) {
            int register = allocator.getRegisterForValue(inValue, instruction.getNumber());
            // Record the register as being used.
            usedRegisters.add(register);
          }
        }
      }
    }
    return unneededMoves;
  }

  private static void updateDebugLocalsRegisterMap(
      Int2IntMap mapping, Int2ReferenceMap<DebugLocalInfo> locals) {
    // If nothing is mapped nothing needs to be changed.
    if (mapping.isEmpty()) {
      return;
    }
    // Locals is final, so we copy and clear it during update.
    Int2ReferenceMap<DebugLocalInfo> copy = new Int2ReferenceOpenHashMap<>(locals);
    locals.clear();
    for (Entry<DebugLocalInfo> entry : copy.int2ReferenceEntrySet()) {
      int oldRegister = entry.getIntKey();
      int newRegister = mapping.getOrDefault(oldRegister, oldRegister);
      locals.put(newRegister, entry.getValue());
    }
  }

  // Removes calls to Throwable.addSuppressed(Throwable) and rewrites
  // Throwable.getSuppressed() into new Throwable[0].
  //
  // Note that addSuppressed() and getSuppressed() methods are final in
  // Throwable, so these changes don't have to worry about overrides.
  public void rewriteThrowableAddAndGetSuppressed(IRCode code) {
    ThrowableMethods throwableMethods = dexItemFactory.throwableMethods;

    for (BasicBlock block : code.blocks) {
      InstructionListIterator iterator = block.listIterator();
      while (iterator.hasNext()) {
        Instruction current = iterator.next();
        if (current.isInvokeMethod()) {
          DexMethod invokedMethod = current.asInvokeMethod().getInvokedMethod();
          if (matchesMethodOfThrowable(invokedMethod, throwableMethods.addSuppressed)) {
            // Remove Throwable::addSuppressed(Throwable) call.
            iterator.removeOrReplaceByDebugLocalRead();
          } else if (matchesMethodOfThrowable(invokedMethod, throwableMethods.getSuppressed)) {
            Value destValue = current.outValue();
            if (destValue == null) {
              // If the result of the call was not used we don't create
              // an empty array and just remove the call.
              iterator.removeOrReplaceByDebugLocalRead();
              continue;
            }

            // Replace call to Throwable::getSuppressed() with new Throwable[0].

            // First insert the constant value *before* the current instruction.
            ConstNumber zero = code.createIntConstant(0);
            zero.setPosition(current.getPosition());
            assert iterator.hasPrevious();
            iterator.previous();
            iterator.add(zero);

            // Then replace the invoke instruction with new-array instruction.
            Instruction next = iterator.next();
            assert current == next;
            NewArrayEmpty newArray = new NewArrayEmpty(destValue, zero.outValue(),
                dexItemFactory.createType(dexItemFactory.throwableArrayDescriptor));
            iterator.replaceCurrentInstruction(newArray);
          }
        }
      }
    }
    assert code.isConsistentSSA();
  }

  private boolean matchesMethodOfThrowable(DexMethod invoked, DexMethod expected) {
    return invoked.name == expected.name
        && invoked.proto == expected.proto
        && isSubtypeOfThrowable(invoked.holder);
  }

  private boolean isSubtypeOfThrowable(DexType type) {
    while (type != null && type != dexItemFactory.objectType) {
      if (type == dexItemFactory.throwableType) {
        return true;
      }
      DexClass dexClass = appView.definitionFor(type);
      if (dexClass == null) {
        throw new CompilationError("Class or interface " + type.toSourceString() +
            " required for desugaring of try-with-resources is not found.");
      }
      type = dexClass.superType;
    }
    return false;
  }

  private Value addConstString(IRCode code, InstructionListIterator iterator, String s) {
    TypeLatticeElement typeLattice =
        TypeLatticeElement.stringClassType(appView, definitelyNotNull());
    Value value = code.createValue(typeLattice);
    ThrowingInfo throwingInfo =
        options.isGeneratingClassFiles() ? ThrowingInfo.NO_THROW : ThrowingInfo.CAN_THROW;
    iterator.add(new ConstString(value, dexItemFactory.createString(s), throwingInfo));
    return value;
  }

  /**
   * Insert code into <code>method</code> to log the argument types to System.out.
   *
   * The type is determined by calling getClass() on the argument.
   */
  public void logArgumentTypes(DexEncodedMethod method, IRCode code) {
    List<Value> arguments = code.collectArguments();
    BasicBlock block = code.entryBlock();
    InstructionListIterator iterator = block.listIterator();

    // Attach some synthetic position to all inserted code.
    Position position = Position.synthetic(1, method.method, null);
    iterator.setInsertionPosition(position);

    // Split arguments into their own block.
    iterator.nextUntil(instruction -> !instruction.isArgument());
    iterator.previous();
    iterator.split(code);
    iterator.previous();

    // Now that the block is split there should not be any catch handlers in the block.
    assert !block.hasCatchHandlers();
    DexType javaLangSystemType = dexItemFactory.createType("Ljava/lang/System;");
    DexType javaIoPrintStreamType = dexItemFactory.createType("Ljava/io/PrintStream;");
    Value out =
        code.createValue(
            TypeLatticeElement.fromDexType(javaIoPrintStreamType, definitelyNotNull(), appView));

    DexProto proto = dexItemFactory.createProto(dexItemFactory.voidType, dexItemFactory.objectType);
    DexMethod print = dexItemFactory.createMethod(javaIoPrintStreamType, proto, "print");
    DexMethod printLn = dexItemFactory.createMethod(javaIoPrintStreamType, proto, "println");

    iterator.add(
        new StaticGet(
            out, dexItemFactory.createField(javaLangSystemType, javaIoPrintStreamType, "out")));

    Value value = addConstString(code, iterator, "INVOKE ");
    iterator.add(new InvokeVirtual(print, null, ImmutableList.of(out, value)));

    value = addConstString(code, iterator, method.method.qualifiedName());
    iterator.add(new InvokeVirtual(print, null, ImmutableList.of(out, value)));

    Value openParenthesis = addConstString(code, iterator, "(");
    Value comma = addConstString(code, iterator, ",");
    Value closeParenthesis = addConstString(code, iterator, ")");
    Value indent = addConstString(code, iterator, "  ");
    Value nul = addConstString(code, iterator, "(null)");
    Value primitive = addConstString(code, iterator, "(primitive)");
    Value empty = addConstString(code, iterator, "");

    iterator.add(new InvokeVirtual(printLn, null, ImmutableList.of(out, openParenthesis)));
    for (int i = 0; i < arguments.size(); i++) {
      iterator.add(new InvokeVirtual(print, null, ImmutableList.of(out, indent)));

      // Add a block for end-of-line printing.
      BasicBlock eol = BasicBlock.createGotoBlock(code.blocks.size(), position);
      code.blocks.add(eol);

      BasicBlock successor = block.unlinkSingleSuccessor();
      block.link(eol);
      eol.link(successor);

      Value argument = arguments.get(i);
      if (!argument.getTypeLattice().isReference()) {
        iterator.add(new InvokeVirtual(print, null, ImmutableList.of(out, primitive)));
      } else {
        // Insert "if (argument != null) ...".
        successor = block.unlinkSingleSuccessor();
        If theIf = new If(Type.NE, argument);
        theIf.setPosition(position);
        BasicBlock ifBlock = BasicBlock.createIfBlock(code.blocks.size(), theIf);
        code.blocks.add(ifBlock);
        // Fallthrough block must be added right after the if.
        BasicBlock isNullBlock = BasicBlock.createGotoBlock(code.blocks.size(), position);
        code.blocks.add(isNullBlock);
        BasicBlock isNotNullBlock = BasicBlock.createGotoBlock(code.blocks.size(), position);
        code.blocks.add(isNotNullBlock);

        // Link the added blocks together.
        block.link(ifBlock);
        ifBlock.link(isNotNullBlock);
        ifBlock.link(isNullBlock);
        isNotNullBlock.link(successor);
        isNullBlock.link(successor);

        // Fill code into the blocks.
        iterator = isNullBlock.listIterator();
        iterator.setInsertionPosition(position);
        iterator.add(new InvokeVirtual(print, null, ImmutableList.of(out, nul)));
        iterator = isNotNullBlock.listIterator();
        iterator.setInsertionPosition(position);
        value = code.createValue(TypeLatticeElement.classClassType(appView, definitelyNotNull()));
        iterator.add(new InvokeVirtual(dexItemFactory.objectMethods.getClass, value,
            ImmutableList.of(arguments.get(i))));
        iterator.add(new InvokeVirtual(print, null, ImmutableList.of(out, value)));
      }

      iterator = eol.listIterator();
      iterator.setInsertionPosition(position);
      if (i == arguments.size() - 1) {
        iterator.add(new InvokeVirtual(printLn, null, ImmutableList.of(out, closeParenthesis)));
      } else {
        iterator.add(new InvokeVirtual(printLn, null, ImmutableList.of(out, comma)));
      }
      block = eol;
    }
    // When we fall out of the loop the iterator is in the last eol block.
    iterator.add(new InvokeVirtual(printLn, null, ImmutableList.of(out, empty)));
  }

  public static void ensureDirectStringNewToInit(IRCode code, DexItemFactory dexItemFactory) {
    for (BasicBlock block : code.blocks) {
      for (InstructionListIterator it = block.listIterator(); it.hasNext(); ) {
        Instruction instruction = it.next();
        if (instruction.isInvokeDirect()) {
          InvokeDirect invoke = instruction.asInvokeDirect();
          DexMethod method = invoke.getInvokedMethod();
          if (dexItemFactory.isConstructor(method)
              && method.holder == dexItemFactory.stringType
              && invoke.getReceiver().isPhi()) {
            NewInstance newInstance = findNewInstance(invoke.getReceiver().asPhi());
            replaceTrivialNewInstancePhis(newInstance.outValue());
            if (invoke.getReceiver().isPhi()) {
              throw new CompilationError(
                  "Failed to remove trivial phis between new-instance and <init>");
            }
            newInstance.markNoSpilling();
          }
        }
      }
    }
  }

  private static NewInstance findNewInstance(Phi phi) {
    Set<Phi> seen = new HashSet<>();
    Set<Value> values = new HashSet<>();
    recursiveAddOperands(phi, seen, values);
    if (values.size() != 1) {
      throw new CompilationError("Failed to identify unique new-instance for <init>");
    }
    Value newInstanceValue = values.iterator().next();
    if (newInstanceValue.definition == null || !newInstanceValue.definition.isNewInstance()) {
      throw new CompilationError("Invalid defining value for call to <init>");
    }
    return newInstanceValue.definition.asNewInstance();
  }

  private static void recursiveAddOperands(Phi phi, Set<Phi> seen, Set<Value> values) {
    for (Value operand : phi.getOperands()) {
      if (!operand.isPhi()) {
        values.add(operand);
      } else {
        Phi phiOp = operand.asPhi();
        if (seen.add(phiOp)) {
          recursiveAddOperands(phiOp, seen, values);
        }
      }
    }
  }

  // If an <init> call takes place on a phi the code must contain an irreducible loop between the
  // new-instance and the <init>. Assuming the code is verifiable, new-instance must flow to a
  // unique <init>. Here we compute the set of strongly connected phis making use of the
  // new-instance value and replace all trivial ones by the new-instance value.
  // This is a simplified variant of the removeRedundantPhis algorithm in Section 3.2 of:
  // http://compilers.cs.uni-saarland.de/papers/bbhlmz13cc.pdf
  private static void replaceTrivialNewInstancePhis(Value newInstanceValue) {
    List<Set<Value>> components = new SCC().computeSCC(newInstanceValue);
    for (int i = components.size() - 1; i >= 0; i--) {
      Set<Value> component = components.get(i);
      if (component.size() == 1 && component.iterator().next() == newInstanceValue) {
        continue;
      }
      Set<Phi> trivialPhis = new HashSet<>();
      for (Value value : component) {
        boolean isTrivial = true;
        Phi p = value.asPhi();
        for (Value op : p.getOperands()) {
          if (op != newInstanceValue && !component.contains(op)) {
            isTrivial = false;
            break;
          }
        }
        if (isTrivial) {
          trivialPhis.add(p);
        }
      }
      for (Phi trivialPhi : trivialPhis) {
        for (Value op : trivialPhi.getOperands()) {
          op.removePhiUser(trivialPhi);
        }
        trivialPhi.replaceUsers(newInstanceValue);
        trivialPhi.getBlock().removePhi(trivialPhi);
      }
    }
  }

  // Dijkstra's path-based strongly-connected components algorithm.
  // https://en.wikipedia.org/wiki/Path-based_strong_component_algorithm
  private static class SCC {

    private int currentTime = 0;
    private final Reference2IntMap<Value> discoverTime = new Reference2IntOpenHashMap<>();
    private final Set<Value> unassignedSet = new HashSet<>();
    private final Deque<Value> unassignedStack = new ArrayDeque<>();
    private final Deque<Value> preorderStack = new ArrayDeque<>();
    private final List<Set<Value>> components = new ArrayList<>();

    public List<Set<Value>> computeSCC(Value v) {
      assert currentTime == 0;
      dfs(v);
      return components;
    }

    private void dfs(Value value) {
      discoverTime.put(value, currentTime++);
      unassignedSet.add(value);
      unassignedStack.push(value);
      preorderStack.push(value);
      for (Phi phi : value.uniquePhiUsers()) {
        if (!discoverTime.containsKey(phi)) {
          // If not seen yet, continue the search.
          dfs(phi);
        } else if (unassignedSet.contains(phi)) {
          // If seen already and the element is on the unassigned stack we have found a cycle.
          // Pop off everything discovered later than the target from the preorder stack. This may
          // not coincide with the cycle as an outer cycle may already have popped elements off.
          int discoverTimeOfPhi = discoverTime.getInt(phi);
          while (discoverTimeOfPhi < discoverTime.getInt(preorderStack.peek())) {
            preorderStack.pop();
          }
        }
      }
      if (preorderStack.peek() == value) {
        // If the current element is the top of the preorder stack, then we are at entry to a
        // strongly-connected component consisting of this element and every element above this
        // element on the stack.
        Set<Value> component = new HashSet<>(unassignedStack.size());
        while (true) {
          Value member = unassignedStack.pop();
          unassignedSet.remove(member);
          component.add(member);
          if (member == value) {
            components.add(component);
            break;
          }
        }
        preorderStack.pop();
      }
    }
  }

  // See comment for InternalOptions.canHaveNumberConversionRegisterAllocationBug().
  public void workaroundNumberConversionRegisterAllocationBug(IRCode code) {
    final Supplier<DexMethod> javaLangDoubleisNaN = Suppliers.memoize(() ->
     dexItemFactory.createMethod(
        dexItemFactory.createString("Ljava/lang/Double;"),
        dexItemFactory.createString("isNaN"),
        dexItemFactory.booleanDescriptor,
        new DexString[]{dexItemFactory.doubleDescriptor}));

    ListIterator<BasicBlock> blocks = code.listIterator();
    while (blocks.hasNext()) {
      BasicBlock block = blocks.next();
      InstructionListIterator it = block.listIterator();
      while (it.hasNext()) {
        Instruction instruction = it.next();
        if (instruction.isArithmeticBinop() || instruction.isNeg()) {
          for (Value value : instruction.inValues()) {
            // Insert a call to Double.isNaN on each value which come from a number conversion
            // to double and flows into an arithmetic instruction. This seems to break the traces
            // in the Dalvik JIT and avoid the bug where the generated ARM code can clobber float
            // values in a single-precision registers with double values written to
            // double-precision registers. See b/77496850 for examples.
            if (!value.isPhi()
                && value.definition.isNumberConversion()
                && value.definition.asNumberConversion().to == NumericType.DOUBLE) {
              InvokeStatic invokeIsNaN =
                  new InvokeStatic(javaLangDoubleisNaN.get(), null, ImmutableList.of(value));
              invokeIsNaN.setPosition(instruction.getPosition());

              // Insert the invoke before the current instruction.
              it.previous();
              BasicBlock blockWithInvokeNaN =
                  block.hasCatchHandlers() ? it.split(code, blocks) : block;
              if (blockWithInvokeNaN != block) {
                // If we split, add the invoke at the end of the original block.
                it = block.listIterator(block.getInstructions().size());
                it.previous();
                it.add(invokeIsNaN);
                // Continue iteration in the split block.
                block = blockWithInvokeNaN;
                it = block.listIterator();
              } else {
                // Otherwise, add it to the current block.
                it.add(invokeIsNaN);
              }
              // Skip over the instruction causing the invoke to be inserted.
              Instruction temp = it.next();
              assert temp == instruction;
            }
          }
        }
      }
    }
  }

  // If an exceptional edge could target a conditional-loop header ensure that we have a
  // materializing instruction on that path to work around a bug in some L x86_64 non-emulator VMs.
  // See b/111337896.
  public void workaroundExceptionTargetingLoopHeaderBug(IRCode code) {
    for (BasicBlock block : code.blocks) {
      if (block.hasCatchHandlers()) {
        for (BasicBlock handler : block.getCatchHandlers().getUniqueTargets()) {
          // We conservatively assume that a block with at least two normal predecessors is a loop
          // header. If we ever end up computing exact loop headers, use that here instead.
          // The loop is conditional if it has at least two normal successors.
          BasicBlock target = handler.endOfGotoChain();
          if (target.getPredecessors().size() > 2
              && target.getNormalPredecessors().size() > 1
              && target.getNormalSuccessors().size() > 1) {
            Instruction fixit = new AlwaysMaterializingNop();
            fixit.setBlock(handler);
            fixit.setPosition(handler.getPosition());
            handler.getInstructions().addFirst(fixit);
          }
        }
      }
    }
  }
}