From 1b62ead08293f7049cb8c4e23224c952ea76ab76 Mon Sep 17 00:00:00 2001
From: David Wendt <dcrkid@yahoo.com>
Date: Mon, 7 Oct 2019 22:08:35 -0400
Subject: [PATCH] Construct the closure scope chain in one pass, which lets us
 skip the vec allocation.

---
 core/src/avm1/scope.rs | 46 +++++++++++++++++++++++++-----------------
 1 file changed, 27 insertions(+), 19 deletions(-)

diff --git a/core/src/avm1/scope.rs b/core/src/avm1/scope.rs
index fa948326d..9680c23c5 100644
--- a/core/src/avm1/scope.rs
+++ b/core/src/avm1/scope.rs
@@ -61,15 +61,37 @@ impl<'gc> Scope<'gc> {
 
     /// Construct a closure scope to be used as the parent of all local scopes
     /// when invoking a function.
+    ///
+    /// This function filters With scopes from the scope chain. If all scopes
+    /// are filtered (somehow), this function constructs and returns a new,
+    /// single global scope with a bare object.
     pub fn new_closure_scope(
         mut parent: GcCell<'gc, Self>,
         mc: MutationContext<'gc, '_>,
     ) -> GcCell<'gc, Self> {
-        let mut closure_scope_list = Vec::new();
+        let mut bottom_scope = None;
+        let mut top_scope: Option<GcCell<'gc, Self>> = None;
 
         loop {
             if parent.read().class != ScopeClass::With {
-                closure_scope_list.push(parent);
+                let next_scope = GcCell::allocate(
+                    mc,
+                    Self {
+                        parent: None,
+                        class: parent.read().class,
+                        values: parent.read().values,
+                    },
+                );
+
+                if let None = bottom_scope {
+                    bottom_scope = Some(next_scope);
+                }
+
+                if let Some(ref scope) = top_scope {
+                    scope.write(mc).parent = Some(next_scope);
+                }
+
+                top_scope = Some(next_scope);
             }
 
             let grandparent = parent.read().parent;
@@ -80,30 +102,16 @@ impl<'gc> Scope<'gc> {
             }
         }
 
-        let mut parent_scope = None;
-        for scope in closure_scope_list.iter().rev() {
-            parent_scope = Some(GcCell::allocate(
-                mc,
-                Scope {
-                    parent: parent_scope,
-                    class: scope.read().class,
-                    values: scope.read().values,
-                },
-            ));
-        }
-
-        if let Some(parent_scope) = parent_scope {
-            parent_scope
-        } else {
+        bottom_scope.unwrap_or_else(|| {
             GcCell::allocate(
                 mc,
-                Scope {
+                Self {
                     parent: None,
                     class: ScopeClass::Global,
                     values: GcCell::allocate(mc, Object::bare_object()),
                 },
             )
-        }
+        })
     }
 
     /// Construct a scope for use with `tellTarget` code where the timeline