avm1: Small optimizations for Object::is_instance_of

- don't make a copy of the `Object.interfaces` vec;
- use `SmallVec` to reduce allocations in the common case
- of empty or non-branching interface trees.

Author: moulins

core/src/avm1/object.rs

@@ -320,7 +320,7 @@ impl<'gc> Object<'gc> {
         // TODO(moulins): should we guard against infinite loops here?
         // A recursive prototype and/or interface chain will hang Flash Player.
 
-        let mut interface_stack = vec![];
+        let mut interface_stack = smallvec::SmallVec::<[_; 4]>::new();
         let mut this = self;
 
         while let Value::Object(this_proto) = this.proto(activation) {
@@ -331,7 +331,7 @@ impl<'gc> Object<'gc> {
                     return Ok(true);
                 }
 
-                interface_stack.extend(interface.interfaces());
+                interface_stack.extend(interface.interfaces().iter().cloned());
             }
 
             this = this_proto;

core/src/avm1/object/script_object.rs

@@ -13,6 +13,7 @@ use core::{fmt, mem};
 use gc_arena::lock::RefLock;
 use gc_arena::{Collect, DynamicRoot, Gc, GcWeak, Mutation, Rootable};
 use ruffle_macros::istr;
+use std::cell::Ref;
 
 use super::super_object::SuperObject;
 
@@ -800,20 +801,18 @@ impl<'gc> Object<'gc> {
     }
 
     /// Enumerate all interfaces implemented by this object.
-    pub(super) fn interfaces(self) -> Vec<Object<'gc>> {
-        if self.as_super_object().is_some() {
-            // `super` does not implement interfaces
-            return vec![];
-        }
-
-        self.0.borrow().interfaces.clone().unwrap_or_default()
+    pub(super) fn interfaces(self) -> Ref<'gc, [Object<'gc>]> {
+        Ref::map(self.0.borrow(), |this| match &this.interfaces {
+            Some(slice) => slice.as_slice(),
+            None => &[],
+        })
     }
 
     /// Set the interface list for this object. (Only useful for prototypes.)
     /// Calling this a second time will have no effect.
     pub fn set_interfaces(self, gc_context: &Mutation<'gc>, iface_list: Vec<Object<'gc>>) {
         if self.as_super_object().is_some() {
-            // `super` probably cannot have interfaces set on it
+            // `super` cannot have interfaces set on it
             return;
         }