Internalize strings in-place

test/mjsunit/thin-strings.js

Index: test/mjsunit/thin-strings.js
diff --git a/test/mjsunit/thin-strings.js b/test/mjsunit/thin-strings.js
new file mode 100644
index 0000000000000000000000000000000000000000..817570de11084b032d47fb8d1146ec7bd90d67bf
--- /dev/null
+++ b/test/mjsunit/thin-strings.js
@@ -0,0 +1,38 @@
+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --allow-natives-syntax
+
+function get_thin_string(a, b) {
+  var str = a + b;  // Make a ConsString.
+  var o = {};
+  o[str];  // Turn it into a ThinString.
+  return str;
+}
+
+var str = get_thin_string("foo", "bar");
+
+var re = /.o+ba./;
+assertEquals(["foobar"], re.exec(str));
+assertEquals(["foobar"], re.exec(str));
+assertEquals(["foobar"], re.exec(str));
+
+function CheckCS() {
+  assertEquals("o", str.substring(1, 2));
+  assertEquals("f".charCodeAt(0), str.charCodeAt(0));
+  assertEquals("f", str.split(/oo/)[0]);
+}
+CheckCS();
+%OptimizeFunctionOnNextCall(CheckCS);
+CheckCS();
+
+function CheckTF() {
+  try {} catch(e) {}  // Turbofan.
+  assertEquals("o", str.substring(1, 2));
+  assertEquals("f".charCodeAt(0), str.charCodeAt(0));
+  assertEquals("f", str.split(/oo/)[0]);
+}
+CheckTF();
+%OptimizeFunctionOnNextCall(CheckTF);
+CheckTF();