[builtins] Migrate Object.keys to CodeStubAssembler builtin.

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 cdf9d9026630b36d3e50452b6f2b09c1cbecbc6f..6f03d613e6690c4fd5cf2c85965f80a5f9f16b3a 100644
--- a/src/builtins/builtins-object-gen.cc
+++ b/src/builtins/builtins-object-gen.cc
@@ -104,6 +104,88 @@ TF_BUILTIN(ObjectHasOwnProperty, ObjectBuiltinsAssembler) {
   Return(CallRuntime(Runtime::kObjectHasOwnProperty, context, object, key));
 }
 
+// ES #sec-object.keys
+TF_BUILTIN(ObjectKeys, ObjectBuiltinsAssembler) {
+  Node* object = Parameter(Descriptor::kObject);
+  Node* context = Parameter(Descriptor::kContext);
+
+  VARIABLE(var_length, MachineRepresentation::kTagged);
+  VARIABLE(var_elements, MachineRepresentation::kTagged);
+  Label if_empty(this, Label::kDeferred), if_fast(this),
+      if_slow(this, Label::kDeferred), if_join(this);
+
+  // Check if the {object} has a usable enum cache.
+  GotoIf(TaggedIsSmi(object), &if_slow);
+  Node* object_map = LoadMap(object);
+  Node* object_bit_field3 = LoadMapBitField3(object_map);
+  Node* object_enum_length =
+      DecodeWordFromWord32<Map::EnumLengthBits>(object_bit_field3);
+  GotoIf(
+      WordEqual(object_enum_length, IntPtrConstant(kInvalidEnumCacheSentinel)),
+      &if_slow);
+
+  // Ensure that the {object} doesn't have any elements.
+  CSA_ASSERT(this, IsJSObjectMap(object_map));
+  Node* object_elements = LoadObjectField(object, JSObject::kElementsOffset);
+  GotoIfNot(IsEmptyFixedArray(object_elements), &if_slow);
+  Branch(WordEqual(object_enum_length, IntPtrConstant(0)), &if_empty, &if_fast);
+
+  BIND(&if_fast);
+  {
+    // The {object} has a usable enum cache, use that.
+    Node* object_descriptors = LoadMapDescriptors(object_map);
+    Node* object_enum_cache_bridge = LoadObjectField(
+        object_descriptors, DescriptorArray::kEnumCacheBridgeOffset);
+    Node* object_enum_cache = LoadObjectField(
+        object_enum_cache_bridge, DescriptorArray::kEnumCacheBridgeCacheOffset);
+
+    // Allocate a JSArray and copy the elements from the {object_enum_cache}.
+    Node* array = nullptr;
+    Node* elements = nullptr;
+    Node* native_context = LoadNativeContext(context);
+    Node* array_map = LoadJSArrayElementsMap(FAST_ELEMENTS, native_context);
+    Node* array_length = SmiTag(object_enum_length);
+    std::tie(array, elements) = AllocateUninitializedJSArrayWithElements(
+        FAST_ELEMENTS, array_map, array_length, nullptr, object_enum_length,
+        INTPTR_PARAMETERS);
+    StoreMapNoWriteBarrier(elements, Heap::kFixedArrayMapRootIndex);
+    StoreObjectFieldNoWriteBarrier(elements, FixedArray::kLengthOffset,
+                                   array_length);
+    CopyFixedArrayElements(FAST_ELEMENTS, object_enum_cache, elements,
+                           object_enum_length, SKIP_WRITE_BARRIER);
+    Return(array);
+  }
+
+  BIND(&if_empty);
+  {
+    // The {object} doesn't have any enumerable keys.
+    var_length.Bind(SmiConstant(0));
+    var_elements.Bind(EmptyFixedArrayConstant());
+    Goto(&if_join);
+  }
+
+  BIND(&if_slow);
+  {
+    // Let the runtime compute the elements.
+    Node* elements = CallRuntime(Runtime::kObjectKeys, context, object);
+    var_length.Bind(LoadObjectField(elements, FixedArray::kLengthOffset));
+    var_elements.Bind(elements);
+    Goto(&if_join);
+  }
+
+  BIND(&if_join);
+  {
+    // Wrap the elements into a proper JSArray and return that.
+    Node* native_context = LoadNativeContext(context);
+    Node* array_map = LoadJSArrayElementsMap(FAST_ELEMENTS, native_context);
+    Node* array = AllocateUninitializedJSArrayWithoutElements(
+        FAST_ELEMENTS, array_map, var_length.value(), nullptr);
+    StoreObjectFieldNoWriteBarrier(array, JSArray::kElementsOffset,
+                                   var_elements.value());
+    Return(array);
+  }
+}
+
 // ES6 #sec-object.prototype.tostring
 TF_BUILTIN(ObjectProtoToString, ObjectBuiltinsAssembler) {
   Label return_undefined(this, Label::kDeferred),