[builtins] Properly optimize Object.prototype.isPrototypeOf.

src/builtins/builtins-object-gen.cc

Index: src/builtins/builtins-object-gen.cc
diff --git a/src/builtins/builtins-object-gen.cc b/src/builtins/builtins-object-gen.cc
index 09930c21b804fff1c204d37441e72433018f1623..1f7a4ad225ed3e368e68bc795e7d2f52e5aca7af 100644
--- a/src/builtins/builtins-object-gen.cc
+++ b/src/builtins/builtins-object-gen.cc
@@ -192,6 +192,53 @@ TF_BUILTIN(ObjectKeys, ObjectBuiltinsAssembler) {
   }
 }
 
+// ES #sec-object.prototype.isprototypeof
+TF_BUILTIN(ObjectPrototypeIsPrototypeOf, ObjectBuiltinsAssembler) {
+  Node* receiver = Parameter(Descriptor::kReceiver);
+  Node* value = Parameter(Descriptor::kValue);
+  Node* context = Parameter(Descriptor::kContext);
+  Label if_receiverisnullorundefined(this, Label::kDeferred),
+      if_valueisnotreceiver(this, Label::kDeferred);
+
+  // We only check whether {value} is a Smi here, so that the
+  // prototype chain walk below can safely access the {value}s
+  // map. We don't rule out Primitive {value}s, since all of
+  // them have null as their prototype, so the chain walk below
+  // immediately aborts and returns false anyways.
+  GotoIf(TaggedIsSmi(value), &if_valueisnotreceiver);
+
+  // Check if {receiver} is either null or undefined and in that case,
+  // invoke the ToObject builtin, which raises the appropriate error.
+  // Otherwise we don't need to invoke ToObject, since {receiver} is
+  // either already a JSReceiver, in which case ToObject is a no-op,
+  // or it's a Primitive and ToObject would allocate a fresh JSValue
+  // wrapper, which wouldn't be identical to any existing JSReceiver
+  // found in the prototype chain of {value}, hence it will return
+  // false no matter if we search for the Primitive {receiver} or
+  // a newly allocated JSValue wrapper for {receiver}.
+  GotoIf(WordEqual(receiver, NullConstant()), &if_receiverisnullorundefined);

[jgruber, 2017/06/13 07:49:51]

Nit: IsNull, IsUndefined (predicates are autogenerated for everything in CSA's
HEAP_CONSTANT_LIST).

[Benedikt Meurer, 2017/06/13 18:22:44]

Done.

+  GotoIf(WordEqual(receiver, UndefinedConstant()),
+         &if_receiverisnullorundefined);
+
+  // Loop through the prototype chain looking for the {receiver}.
+  Return(HasInPrototypeChain(context, value, receiver));
+
+  BIND(&if_receiverisnullorundefined);
+  {
+    // If {value} is a primitive HeapObject, we need to return
+    // false instead of throwing an exception per order of the
+    // steps in the specification, so check that first here.
+    GotoIfNot(IsJSReceiver(value), &if_valueisnotreceiver);
+
+    // Simulate the ToObject invocation on {receiver}.
+    CallBuiltin(Builtins::kToObject, context, receiver);
+    Unreachable();
+  }
+
+  BIND(&if_valueisnotreceiver);
+  Return(BooleanConstant(false));
+}
+
 // ES6 #sec-object.prototype.tostring
 TF_BUILTIN(ObjectProtoToString, ObjectBuiltinsAssembler) {
   Label return_undefined(this, Label::kDeferred),