Internalize strings in-place

test/mjsunit/thin-strings.js

+// 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();
+
+// Flat cons strings can point to a thin string.
+
+function get_cons_thin_string(a, b) {
+  // Make a ConsString.
+  var s = a + b;
+  // Flatten it.
+  s.endsWith("a");
+  // Internalize the first part.
+  var o = {};
+  o[s];
+  return s;
+}
+
+var s = get_cons_thin_string("__________", "@@@@@@@@@@a");
+s.match(/.*a/);
+assertEquals("________", s.substring(0, 8));
+
+function cc1(s) {
+  assertEquals(95, s.charCodeAt(0));
+  assertEquals(95, s.codePointAt(0));
+}
+cc1(s);
+cc1(s);
+%OptimizeFunctionOnNextCall(cc1);
+cc1(s);
+
+// Sliced strings can have a thin string as their parent.
+
+function get_sliced_thin_string(a, b) {
+  // Make a long thin string.
+  var s = a + b;
+  // Slice a substring out of it.
+  var slice = s.substring(0, 20);
+  // Make the original string thin.
+  var o = {};
+  o[s];
+  return slice;
+}
+
+var t = get_sliced_thin_string("abcdefghijklmnopqrstuvwxyz",
+                               "abcdefghijklmnopqrstuvwxyz");
+assertEquals("abcdefghijklmnopqrst", decodeURI(t));
+
+function cc2(s) {
+  assertEquals(97, s.charCodeAt(0));
+  assertEquals(97, s.codePointAt(0));
+}
+cc2(t);
+cc2(t);
+%OptimizeFunctionOnNextCall(cc2);
+cc2(t);