test/mjsunit/fast-prototype.js

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// Flags: --allow-natives-syntax --expose-gc
// Flags: --noincremental-marking

// Check that objects that are used for prototypes are in the fast mode.

function Super() {
}


function Sub() {
}


function AddProps(obj) {
  for (var i = 0; i < 26; i++) {
    obj["x" + i] = 0;
  }
}


function DoProtoMagic(proto, set__proto__) {
  if (set__proto__) {
    (new Sub()).__proto__ = proto;
  } else {
    Sub.prototype = proto;
    // Need to instantiate Sub to mark .prototype as prototype. Make sure the
    // instantiated object is used so that the allocation is not optimized away.
    %DebugPrint(new Sub());
  }
}


function test(use_new, add_first, set__proto__) {
  var proto = use_new ? new Super() : {};

  // New object is fast.
  assertTrue(%HasFastProperties(proto));

  if (add_first) {
    AddProps(proto);
    // Adding this many properties makes it slow.
    assertFalse(%HasFastProperties(proto));
    DoProtoMagic(proto, set__proto__);
    // Making it a prototype makes it fast again.
    assertTrue(%HasFastProperties(proto));
  } else {
    DoProtoMagic(proto, set__proto__);
    // Still fast
    assertTrue(%HasFastProperties(proto));
    AddProps(proto);
    // Still fast.
    assertTrue(%HasFastProperties(proto));
  }
  return proto;
}

// TODO(mstarzinger): This test fails easily if gc happens at the wrong time.
gc();

for (var i = 0; i < 4; i++) {
  var set__proto__ = ((i & 1) != 0);
  var use_new = ((i & 2) != 0);

  test(use_new, true, set__proto__);
  test(use_new, false, set__proto__);
}


var x = {a: 1, b: 2, c: 3};
var o = { __proto__: x };
assertTrue(%HasFastProperties(x));
for (key in x) {
  assertTrue(key == 'a');
  break;
}
delete x.b;
for (key in x) {
  assertTrue(key == 'a');
  break;
}
assertTrue(%HasFastProperties(x));
x.d = 4;
assertTrue(%HasFastProperties(x));
for (key in x) {
  assertTrue(key == 'a');
  break;
}