perf(python): a module variable holding an instance is stored as the instance

The global slot holds the pointer, as a field does, instead of a box
opened at every read.

Author: darmie

crates/zyntax_python/src/lib.rs

@@ -582,10 +582,7 @@ pub fn parse_program_with(
         Span::new(0, 0),
     ));
     for (name, ty) in &inferred.globals {
-        let stored = match ty {
-            types::Ty::Int | types::Ty::Float | types::Ty::Bool | types::Ty::Str => *ty,
-            _ => types::Ty::Object,
-        };
+        let stored = lower::Lowerer::storage(*ty);
         declarations.push(TypedNode::new(
             TypedDeclaration::Variable(TypedVariable {
                 name: intern(name),

crates/zyntax_python/src/lower.rs

@@ -1282,9 +1282,11 @@ impl<'m> Lowerer<'m> {
 
     /// A global holds its own scalar type; anything else is stored boxed,
     /// so a list global is one heap header shared by every reader.
-    fn storage(ty: Ty) -> Ty {
+    /// How a module variable of type `ty` is stored: primitives,
+    /// strings and instances as themselves, the rest boxed.
+    pub(crate) fn storage(ty: Ty) -> Ty {
         match ty {
-            Ty::Int | Ty::Float | Ty::Bool | Ty::Str => ty,
+            Ty::Int | Ty::Float | Ty::Bool | Ty::Str | Ty::Class(_) => ty,
             _ => Ty::Object,
         }
     }