8221307: String.substring() OOB exception on start index reports improper information

Reviewed-by: rriggs, redestad

src/java.base/share/classes/java/lang/String.java

@@ -1868,18 +1868,7 @@ public final class String
      *             length of this {@code String} object.
      */
     public String substring(int beginIndex) {
-        if (beginIndex < 0) {
+        return substring(beginIndex, length());
-            throw new StringIndexOutOfBoundsException(beginIndex);
-        }
-        int subLen = length() - beginIndex;
-        if (subLen < 0) {
-            throw new StringIndexOutOfBoundsException(subLen);
-        }
-        if (beginIndex == 0) {
-            return this;
-        }
-        return isLatin1() ? StringLatin1.newString(value, beginIndex, subLen)
-                          : StringUTF16.newString(value, beginIndex, subLen);
     }
 
     /**

src/java.base/share/classes/java/lang/StringUTF16.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2015, 2019, 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

test/micro/org/openjdk/bench/java/lang/StringSubstring.java

@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2019, 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.openjdk.bench.java.lang;
+
+import org.openjdk.jmh.annotations.*;
+import java.util.concurrent.TimeUnit;
+
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@State(Scope.Benchmark)
+public class StringSubstring {
+
+    public String s = new String("An arbitrary string that happened to be of length 52");
+
+    @Benchmark
+    public String from26toEnd0() {
+        return s.substring(26);
+    }
+
+    @Benchmark
+    public String from26toEnd1() {
+        return s.substring(26, s.length());
+    }
+}