test/mjsunit/regress/regress-1708.js

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// 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];
  }
})();