shape-teleporting-invalidation.js

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// The shape teleporting optimization can be disabled for an object that's used

// as prototype when either it's involved in prototype changes or it had a property

// shadowed on another prototype object.

function changeProps(o) {

  Object.assign(o, {x: 1, y: 2, z: 3});

  o.foo = 4;

  delete o.x;

function testProtoChange() {

  var receiver = {};

  var A = Object.create(null);

  var B = Object.create(A);

  // Change |receiver|'s proto: receiver => B => A => null

  // Because |receiver| is not used as a prototype object, this doesn't affect

  // teleporting.

  Object.setPrototypeOf(receiver, B);

  assertEq(hasInvalidatedTeleporting(receiver), false);

  assertEq(hasInvalidatedTeleporting(A), false);

  assertEq(hasInvalidatedTeleporting(B), false);

  // Change B's proto to C: receiver => B => C => null

  // Because B is used as prototype object, both A and B invalidate teleporting.

  var C = Object.create(null);

  Object.setPrototypeOf(B, C);

  assertEq(hasInvalidatedTeleporting(receiver), false);

  assertEq(hasInvalidatedTeleporting(A), true);

  assertEq(hasInvalidatedTeleporting(B), true);

  assertEq(hasInvalidatedTeleporting(C), false);

  // Change B's proto a second time: receiver => B => D => null

  // Now C has teleporting invalidated too.

  var D = Object.create(null);

  Object.setPrototypeOf(B, D);

  assertEq(hasInvalidatedTeleporting(receiver), false);

  assertEq(hasInvalidatedTeleporting(A), true);

  assertEq(hasInvalidatedTeleporting(B), true);

  assertEq(hasInvalidatedTeleporting(C), true);

  assertEq(hasInvalidatedTeleporting(D), false);

  // Changing properties (without shadowing) must not affect teleporting state.

  changeProps(C);

  changeProps(D);

  assertEq(hasInvalidatedTeleporting(C), true);

  assertEq(hasInvalidatedTeleporting(D), false);

testProtoChange();

function testShadowingProp() {

  // receiver => C => B => A => null

  var A = Object.create(null);

  var B = Object.create(A);

  var C = Object.create(B);

  var receiver = Object.create(C);

  // Adding non-shadowing properties doesn't affect teleporting.

  A.a = 1;

  B.b = 1;

  C.c = 1;

  receiver.receiver = 1;

  assertEq(hasInvalidatedTeleporting(receiver), false);

  assertEq(hasInvalidatedTeleporting(C), false);

  assertEq(hasInvalidatedTeleporting(B), false);

  assertEq(hasInvalidatedTeleporting(A), false);

  // Objects not used as prototype can shadow properties without affecting

  // teleporting.

  receiver.a = 1;

  receiver.b = 2;

  receiver.c = 3;

  assertEq(hasInvalidatedTeleporting(receiver), false);

  assertEq(hasInvalidatedTeleporting(C), false);

  assertEq(hasInvalidatedTeleporting(B), false);

  assertEq(hasInvalidatedTeleporting(A), false);

  // Shadowing a property of B on C invalidates teleporting for B.

  C.b = 1;

  assertEq(hasInvalidatedTeleporting(receiver), false);

  assertEq(hasInvalidatedTeleporting(C), false);

  assertEq(hasInvalidatedTeleporting(B), true);

  assertEq(hasInvalidatedTeleporting(A), false);

  // Shadowing a property of A on C invalidates teleporting for A.

  C.a = 2;

  assertEq(hasInvalidatedTeleporting(receiver), false);

  assertEq(hasInvalidatedTeleporting(C), false);

  assertEq(hasInvalidatedTeleporting(B), true);

  assertEq(hasInvalidatedTeleporting(A), true);

  // Changing properties (without shadowing) must not affect teleporting state.

  changeProps(C);

  changeProps(B);

  assertEq(hasInvalidatedTeleporting(C), false);

  assertEq(hasInvalidatedTeleporting(B), true);

testShadowingProp();

function testShadowingPropStopsAtFirst() {

  // receiver => C => B{x,y} => A{x,y,z} => null

  var A = Object.create(null);

  A.x = 1;

  A.y = 2;

  A.z = 3;

  var B = Object.create(A);

  B.x = 1;

  B.y = 2;

  var C = Object.create(B);

  var receiver = Object.create(C);

  // Teleporting is supported.

  assertEq(hasInvalidatedTeleporting(receiver), false);

  assertEq(hasInvalidatedTeleporting(C), false);

  assertEq(hasInvalidatedTeleporting(B), false);

  assertEq(hasInvalidatedTeleporting(A), false);

  // Shadowing a property of B (and A) on C.

  // This invalidates teleporting for B but not for A, because the search stops

  // at B.

  C.x = 1;

  assertEq(hasInvalidatedTeleporting(receiver), false);

  assertEq(hasInvalidatedTeleporting(C), false);

  assertEq(hasInvalidatedTeleporting(B), true);

  assertEq(hasInvalidatedTeleporting(A), false);

  // "y" is similar.

  C.y = 2;

  assertEq(hasInvalidatedTeleporting(receiver), false);

  assertEq(hasInvalidatedTeleporting(C), false);

  assertEq(hasInvalidatedTeleporting(B), true);

  assertEq(hasInvalidatedTeleporting(A), false);

  // "z" is only defined on A, so now A is affected.

  C.z = 3;

  assertEq(hasInvalidatedTeleporting(receiver), false);

  assertEq(hasInvalidatedTeleporting(C), false);

  assertEq(hasInvalidatedTeleporting(B), true);

  assertEq(hasInvalidatedTeleporting(A), true);

testShadowingPropStopsAtFirst();

// Ensure teleporting properties on Object.prototype is still possible.

assertEq(hasInvalidatedTeleporting(Object.prototype), false);