src/v8/test/mjsunit/regress/regress-2717.js

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// Test re-initializing existing field which is already being tracked as
// having double representation.
(function() {
  function test1(a) {
    return { x: 1.5, x: a };
  };

  assertEquals({}, test1({}).x);
})();

// Test initializing new field which follows an existing transition to a
// map that tracks it as having double representation.
(function() {
  function test1(a) {
    return { y: a };
  };

  function test2(a) {
    return { y: a };
  };

  assertEquals(1.5, test1(1.5).y);
  assertEquals({}, test2({}).y);
})();