8323552: AbstractMemorySegmentImpl#mismatch returns -1 when comparing…

… distinct areas of the same instance of MemorySegment

Reviewed-by: mcimadamore

src/java.base/share/classes/jdk/internal/foreign/AbstractMemorySegmentImpl.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 2024, 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
@@ -681,10 +681,6 @@ public static long mismatch(MemorySegment srcSegment, long srcFromOffset, long s
         long dstBytes = dstToOffset - dstFromOffset;
         srcImpl.checkAccess(srcFromOffset, srcBytes, true);
         dstImpl.checkAccess(dstFromOffset, dstBytes, true);
-        if (dstImpl == srcImpl) {
-            srcImpl.checkValidState();
-            return -1;
-        }
 
         long bytes = Math.min(srcBytes, dstBytes);
         long i = 0;

test/jdk/java/foreign/TestMismatch.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 2024, 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
@@ -23,6 +23,7 @@
 
 /*
  * @test
+ * @bug 8323552
  * @run testng TestMismatch
  */
 
@@ -44,7 +45,7 @@
 
 public class TestMismatch {
 
-    // stores a increasing sequence of values into the memory of the given segment
+    // stores an increasing sequence of values into the memory of the given segment
     static MemorySegment initializeSegment(MemorySegment segment) {
         for (int i = 0 ; i < segment.byteSize() ; i++) {
             segment.set(ValueLayout.JAVA_BYTE, i, (byte)i);
@@ -278,6 +279,32 @@ public void testThreadAccess() throws Exception {
         }
     }
 
+    @Test
+    public void testSameSegment() {
+        var segment = MemorySegment.ofArray(new byte[]{
+                1,2,3,4,  1,2,3,4,  1,4});
+
+        long match = MemorySegment.mismatch(
+                segment, 0L, 4L,
+                segment, 4L, 8L);
+        assertEquals(match, -1);
+
+        long noMatch = MemorySegment.mismatch(
+                segment, 0L, 4L,
+                segment, 1L, 5L);
+        assertEquals(noMatch, 0);
+
+        long noMatchEnd = MemorySegment.mismatch(
+                segment, 0L, 2L,
+                segment, 8L, 10L);
+        assertEquals(noMatchEnd, 1);
+
+        long same = MemorySegment.mismatch(
+                segment, 0L, 8L,
+                segment, 0L, 8L);
+        assertEquals(same, -1);
+    }
+
     enum SegmentKind {
         NATIVE(i -> Arena.ofAuto().allocate(i, 1)),
         ARRAY(i -> MemorySegment.ofArray(new byte[i]));