gt:         for (Block exit : loop.getExits()) {
context: /*
   * Copyright (c) 2011, 2012, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   * or visit www.oracle.com if you need additional information or have any
   * questions.
   */
  package org.graalvm.compiler.phases.graph;
  
  import java.util.ArrayDeque;
  import java.util.ArrayList;
  import java.util.Deque;
  import java.util.List;
  import java.util.Map;
  import java.util.function.Predicate;
  
  import org.graalvm.compiler.common.RetryableBailoutException;
  import org.graalvm.compiler.core.common.cfg.Loop;
  import org.graalvm.compiler.core.common.util.CompilationAlarm;
  import org.graalvm.compiler.graph.Node;
  import org.graalvm.compiler.nodes.AbstractEndNode;
  import org.graalvm.compiler.nodes.AbstractMergeNode;
  import org.graalvm.compiler.nodes.FixedNode;
  import org.graalvm.compiler.nodes.LoopBeginNode;
  import org.graalvm.compiler.nodes.cfg.Block;
  
  public final class ReentrantBlockIterator {
  
      public static class LoopInfo<StateT> {
  
          public final List<StateT> endStates;
          public final List<StateT> exitStates;
  
          public LoopInfo(int endCount, int exitCount) {
              endStates = new ArrayList<>(endCount);
              exitStates = new ArrayList<>(exitCount);
          }
      }
  
      public abstract static class BlockIteratorClosure<StateT> {
  
          protected abstract StateT getInitialState();
  
          protected abstract StateT processBlock(Block block, StateT currentState);
  
          protected abstract StateT merge(Block merge, List<StateT> states);
  
          protected abstract StateT cloneState(StateT oldState);
  
          protected abstract List<StateT> processLoop(Loop<Block> loop, StateT initialState);
      }
  
      private ReentrantBlockIterator() {
          // no instances allowed
      }
  
      public static <StateT> LoopInfo<StateT> processLoop(BlockIteratorClosure<StateT> closure, Loop<Block> loop, StateT initialState) {
          Map<FixedNode, StateT> blockEndStates = apply(closure, loop.getHeader(), initialState, block -> !(block.getLoop() == loop || block.isLoopHeader()));
  
          Block[] predecessors = loop.getHeader().getPredecessors();
          LoopInfo<StateT> info = new LoopInfo<>(predecessors.length - 1, loop.getExits().size());
          for (int i = 1; i < predecessors.length; i++) {
              StateT endState = blockEndStates.get(predecessors[i].getEndNode());
              // make sure all end states are unique objects
              info.endStates.add(closure.cloneState(endState));
          }
          for (Block loopExit : loop.getExits()) {
              assert loopExit.getPredecessorCount() == 1;
              assert blockEndStates.containsKey(loopExit.getBeginNode()) : loopExit.getBeginNode() + " " + blockEndStates;
              StateT exitState = blockEndStates.get(loopExit.getBeginNode());
              // make sure all exit states are unique objects
              info.exitStates.add(closure.cloneState(exitState));
          }
          return info;
      }
  
      public static <StateT> void apply(BlockIteratorClosure<StateT> closure, Block start) {
          apply(closure, start, closure.getInitialState(), null);
      }
  
      public static <StateT> Map<FixedNode, StateT> apply(BlockIteratorClosure<StateT> closure, Block start, StateT initialState, Predicate<Block> stopAtBlock) {
          Deque<Block> blockQueue = new ArrayDeque<>();
          /*
           * States are stored on EndNodes before merges, and on BeginNodes after ControlSplitNodes.
           */
          Map<FixedNode, StateT> states = Node.newIdentityMap();
  
          StateT state = initialState;
          Block current = start;
  
          while (true) {
              if (CompilationAlarm.hasExpired()) {
                  throw new RetryableBailoutException("Compilation exceeded %d seconds during CFG traversal", CompilationAlarm.Options.CompilationExpirationPeriod.getValue());
              }
              Block next = null;
              if (stopAtBlock != null && stopAtBlock.test(current)) {
                  states.put(current.getBeginNode(), state);
              } else {
                  state = closure.processBlock(current, state);
  
                  Block[] successors = current.getSuccessors();
                  if (successors.length == 0) {
                      // nothing to do...
                  } else if (successors.length == 1) {
                      Block successor = successors[0];
                      if (successor.isLoopHeader()) {
                          if (current.isLoopEnd()) {
                              // nothing to do... loop ends only lead to loop begins we've already
                              // visited
                              states.put(current.getEndNode(), state);
                          } else {
                              recurseIntoLoop(closure, blockQueue, states, state, successor);
                          }
                      } else if (current.getEndNode() instanceof AbstractEndNode) {
                          AbstractEndNode end = (AbstractEndNode) current.getEndNode();
  
                          // add the end node and see if the merge is ready for processing
                          AbstractMergeNode merge = end.merge();
                          if (allEndsVisited(states, current, merge)) {
                              ArrayList<StateT> mergedStates = mergeStates(states, state, current, successor, merge);
                              state = closure.merge(successor, mergedStates);
                              next = successor;
                          } else {
                              assert !states.containsKey(end);
                              states.put(end, state);
                          }
                      } else {
                          next = successor;
                      }
                  } else {
                      next = processMultipleSuccessors(closure, blockQueue, states, state, successors);
                  }
              }
  
              // get next queued block
              if (next != null) {
                  current = next;
              } else if (blockQueue.isEmpty()) {
                  return states;
              } else {
                  current = blockQueue.removeFirst();
                  assert current.getPredecessorCount() == 1;
                  assert states.containsKey(current.getBeginNode());
                  state = states.remove(current.getBeginNode());
              }
          }
      }
  
      private static <StateT> boolean allEndsVisited(Map<FixedNode, StateT> states, Block current, AbstractMergeNode merge) {
          for (AbstractEndNode forwardEnd : merge.forwardEnds()) {
              if (forwardEnd != current.getEndNode() && !states.containsKey(forwardEnd)) {
                  return false;
              }
          }
          return true;
      }
  
      private static <StateT> Block processMultipleSuccessors(BlockIteratorClosure<StateT> closure, Deque<Block> blockQueue, Map<FixedNode, StateT> states, StateT state, Block[] successors) {
          assert successors.length > 1;
          for (int i = 1; i < successors.length; i++) {
              Block successor = successors[i];
              blockQueue.addFirst(successor);
              states.put(successor.getBeginNode(), closure.cloneState(state));
          }
          return successors[0];
      }
  
      private static <StateT> ArrayList<StateT> mergeStates(Map<FixedNode, StateT> states, StateT state, Block current, Block successor, AbstractMergeNode merge) {
          ArrayList<StateT> mergedStates = new ArrayList<>(merge.forwardEndCount());
          for (Block predecessor : successor.getPredecessors()) {
              assert predecessor == current || states.containsKey(predecessor.getEndNode());
              StateT endState = predecessor == current ? state : states.remove(predecessor.getEndNode());
              mergedStates.add(endState);
          }
          return mergedStates;
      }
  
      private static <StateT> void recurseIntoLoop(BlockIteratorClosure<StateT> closure, Deque<Block> blockQueue, Map<FixedNode, StateT> states, StateT state, Block successor) {
          // recurse into the loop
          Loop<Block> loop = successor.getLoop();
          LoopBeginNode loopBegin = (LoopBeginNode) loop.getHeader().getBeginNode();
          assert successor.getBeginNode() == loopBegin;
  
          List<StateT> exitStates = closure.processLoop(loop, state);
  
          int i = 0;
          assert loop.getExits().size() == exitStates.size();
  