Fix transferal of marking bits on array trimming.

test/mjsunit/regress/regress-1708.js

Index: test/mjsunit/regress/regress-1708.js
diff --git a/test/mjsunit/regress/regress-1708.js b/test/mjsunit/regress/regress-1708.js
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+// Copyright 2011 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Regression test of a very rare corner case where left-trimming an
+// array caused invalid marking bit patterns on lazily swept pages.
+
+// Flags: --expose-gc --noincremental-marking --max-new-space-size 1000
+
+(function() {
+  var head = new Array(1);
+  var tail = head;
+
+  // Fill heap to increase old-space size and trigger lazy sweeping on
+  // some of the old-space pages.
+  for (var i = 0; i < 200; i++) {
+    tail[1] = new Array(1000);
+    tail = tail[1];
+  }
+  array = new Array(100);
+  gc(); gc();
+
+  // At this point "array" should have been promoted to old-space and be
+  // located in a lazy swept page with intact marking bits. Now shift
+  // the array to trigger left-trimming operations.
+  assertEquals(100, array.length);
+  for (var i = 0; i < 50; i++) {
+    array.shift();
+  }
+  assertEquals(50, array.length);
+
+  // At this point "array" should have been trimmed from the left with
+  // marking bits being correctly transfered to the new object start.
+  // Scavenging operations cause lazy sweeping to advance and verify
+  // that marking bit patterns are still sane.
+  for (var i = 0; i < 200; i++) {
+    tail[1] = new Array(1000);
+    tail = tail[1];
+  }
+})();