Ensure slow properties for simple {__proto__:null} literals.

test/mjsunit/object-literal.js

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+// Flags: --allow-natives-syntax
+
 var obj = {
     a: 7,
     b: { x: 12, y: 24 },
     c: 'Zebra'
 }
 
 assertEquals(7, obj.a);
 assertEquals(12, obj.b.x);
 assertEquals(24, obj.b.y);
 assertEquals('Zebra', obj.c);
@@ skipping 256 matching lines @@
   const prop = 'a';
 
   var p = new Proxy({}, handler);
   p[prop] = 'my value';
   assertEquals(undefined, p[prop]);
 
 
   var l = new Proxy({[prop]: 'my value'}, handler);
   assertEquals('my value', l[prop]);
 })();
+
+(function TestLiteralWithNullProto() {
+  // Assume dictionary usage for simple null prototype literal objects,
+  // this is equivalent to Object.create(null).
+  var obj = {__proto__:null};
+  assertFalse(%HasFastProperties(obj));
+  assertEquals(Object.getPrototypeOf(obj), null);
+  // Once we add inline properties we probably don't want slow properties
+  // anymore.
+  obj = {__proto__:null, a:1, b:2};
+  assertFalse(%HasFastProperties(obj));
+  assertEquals(Object.getPrototypeOf(obj), null);
+
+  obj = {__proto__: null, ["a"]: 1};
+  assertFalse(%HasFastProperties(obj));
+  assertEquals(Object.getPrototypeOf(obj), null);
+
+  obj = {__proto__: null, a: obj};
+  assertFalse(%HasFastProperties(obj));
+  assertEquals(Object.getPrototypeOf(obj), null);
+
+  obj = {a:1, b:2, __proto__:null};
+  assertFalse(%HasFastProperties(obj));
+  assertEquals(Object.getPrototypeOf(obj), null);
+
+  obj = {["a"]: 1, __proto__: null};
+  assertFalse(%HasFastProperties(obj));
+  assertEquals(Object.getPrototypeOf(obj), null);
+
+  obj = {a: obj, __proto__: null};
+  assertFalse(%HasFastProperties(obj));
+  assertEquals(Object.getPrototypeOf(obj), null);
+})();
+
+(function TestSlowLiteralOptimized() {
+  function f() {
+    return {__proto__:null};
+  }
+  let obj = f();
+  assertFalse(%HasFastProperties(obj));
+  assertEquals(Object.getPrototypeOf(obj), null);
+
+  %OptimizeFunctionOnNextCall(f);
+  obj = f();
+  assertFalse(%HasFastProperties(obj));
+  assertEquals(Object.getPrototypeOf(obj), null);
+})();