--- old/src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.core.common/src/org/graalvm/compiler/core/common/cfg/Loop.java	2019-03-09 03:55:58.704612003 +0100
+++ new/src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.core.common/src/org/graalvm/compiler/core/common/cfg/Loop.java	2019-03-09 03:55:58.340609428 +0100
@@ -25,19 +25,28 @@
 
 package org.graalvm.compiler.core.common.cfg;
 
+import static org.graalvm.compiler.core.common.cfg.AbstractBlockBase.BLOCK_ID_COMPARATOR;
+
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 
 public abstract class Loop<T extends AbstractBlockBase<T>> {
 
     private final Loop<T> parent;
-    private final List<Loop<T>> children;
+    private final ArrayList<Loop<T>> children;
 
     private final int depth;
     private final int index;
     private final T header;
-    private final List<T> blocks;
-    private final List<T> exits;
+    private final ArrayList<T> blocks;
+    private final ArrayList<T> exits;
+    /**
+     * Natural exits, ignoring LoopExitNodes.
+     *
+     * @see #getNaturalExits()
+     */
+    private final ArrayList<T> naturalExits;
 
     protected Loop(Loop<T> parent, int index, T header) {
         this.parent = parent;
@@ -51,6 +60,7 @@
         this.blocks = new ArrayList<>();
         this.children = new ArrayList<>();
         this.exits = new ArrayList<>();
+        this.naturalExits = new ArrayList<>();
     }
 
     public abstract long numBackedges();
@@ -84,12 +94,87 @@
         return blocks;
     }
 
-    public List<T> getExits() {
+    /**
+     * Returns the loop exits.
+     *
+     * This might be a conservative set: before framestate assignment it matches the LoopExitNodes
+     * even if earlier blocks could be considered as exits. After framestate assignments, this is
+     * the same as {@link #getNaturalExits()}.
+     *
+     * <p>
+     * LoopExitNodes are inserted in the control-flow during parsing and are natural exits: they are
+     * the earliest block at which we are guaranteed to have exited the loop. However, after some
+     * transformations of the graph, the natural exit might go up but the LoopExitNodes are not
+     * updated.
+     * </p>
+     *
+     * <p>
+     * For example in:
+     *
+     * <pre>
+     * for (int i = 0; i < N; i++) {
+     *     if (c) {
+     *         // Block 1
+     *         if (dummy) {
+     *             // ...
+     *         } else {
+     *             // ...
+     *         }
+     *         if (b) {
+     *             continue;
+     *         } else {
+     *             // Block 2
+     *             // LoopExitNode
+     *             break;
+     *         }
+     *     }
+     * }
+     * </pre>
+     *
+     * After parsing, the natural exits match the LoopExitNode: Block 2 is a natural exit and has a
+     * LoopExitNode. If the {@code b} condition gets canonicalized to {@code false}, the natural
+     * exit moves to Block 1 while the LoopExitNode remains in Block 2. In such a scenario,
+     * {@code getLoopExits()} will contain block 2 while {@link #getNaturalExits()} will contain
+     * block 1.
+     *
+     *
+     * @see #getNaturalExits()
+     */
+    public List<T> getLoopExits() {
         return exits;
     }
 
-    public void addExit(T t) {
-        exits.add(t);
+    public boolean isLoopExit(T block) {
+        assert isSorted(exits);
+        return Collections.binarySearch(exits, block, BLOCK_ID_COMPARATOR) >= 0;
+    }
+
+    /**
+     * Returns the natural exit points: these are the earliest block that are guaranteed to never
+     * reach a back-edge.
+     *
+     * This can not be used in the context of preserving or using loop-closed form.
+     *
+     * @see #getLoopExits()
+     */
+    public ArrayList<T> getNaturalExits() {
+        return naturalExits;
+    }
+
+    public boolean isNaturalExit(T block) {
+        assert isSorted(naturalExits);
+        return Collections.binarySearch(naturalExits, block, BLOCK_ID_COMPARATOR) >= 0;
+    }
+
+    private static <T extends AbstractBlockBase<T>> boolean isSorted(List<T> list) {
+        int lastId = Integer.MIN_VALUE;
+        for (AbstractBlockBase<?> block : list) {
+            if (block.getId() < lastId) {
+                return false;
+            }
+            lastId = block.getId();
+        }
+        return true;
     }
 
     /**
@@ -115,4 +200,9 @@
     public int hashCode() {
         return index + depth * 31;
     }
+
+    @Override
+    public boolean equals(Object obj) {
+        return super.equals(obj);
+    }
 }