From 69352d74c28176087829c82c31c1a8672735f8a1 Mon Sep 17 00:00:00 2001
From: Stephen Chung <schungx@live.com>
Date: Tue, 29 Jun 2021 23:22:54 +0800
Subject: [PATCH] Optimize Scope layout.

---
 src/ast.rs   |  2 +-
 src/scope.rs | 30 ++++++++++++++----------------
 2 files changed, 15 insertions(+), 17 deletions(-)

diff --git a/src/ast.rs b/src/ast.rs
index e7c92ae8..87af9821 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -2206,7 +2206,7 @@ mod tests {
                 96
             }
         );
-        assert_eq!(size_of::<Scope>(), 160);
+        assert_eq!(size_of::<Scope>(), 464);
         assert_eq!(size_of::<LexError>(), 56);
         assert_eq!(
             size_of::<ParseError>(),
diff --git a/src/scope.rs b/src/scope.rs
index 2fe9bcfb..9fa87088 100644
--- a/src/scope.rs
+++ b/src/scope.rs
@@ -49,14 +49,14 @@ const SCOPE_ENTRIES_INLINED: usize = 8;
 // look up a variable.  Variable lookup is usually via direct indexing, by-passing the name altogether.
 //
 // Since [`Dynamic`] is reasonably small, packing it tightly improves cache locality when variables are accessed.
-//
-// The alias is `Box`'ed because it occurs infrequently.
 #[derive(Debug, Clone, Hash)]
 pub struct Scope<'a> {
     /// Current value of the entry.
     values: smallvec::SmallVec<[Dynamic; SCOPE_ENTRIES_INLINED]>,
     /// (Name, aliases) of the entry.
-    names: Vec<(Cow<'a, str>, Option<Box<StaticVec<Identifier>>>)>,
+    names: smallvec::SmallVec<
+        [(Cow<'a, str>, Option<Box<StaticVec<Identifier>>>); SCOPE_ENTRIES_INLINED],
+    >,
 }
 
 impl Default for Scope<'_> {
@@ -253,7 +253,7 @@ impl<'a> Scope<'a> {
         access: AccessMode,
         mut value: Dynamic,
     ) -> &mut Self {
-        self.names.push((name.into(), None));
+        self.names.push((name.into(), Default::default()));
         value.set_access_mode(access);
         self.values.push(value.into());
         self
@@ -436,20 +436,18 @@ impl<'a> Scope<'a> {
     #[cfg(not(feature = "no_module"))]
     #[inline(always)]
     pub(crate) fn add_entry_alias(&mut self, index: usize, alias: Identifier) -> &mut Self {
-        let entry = self
+        let (_, aliases) = self
             .names
             .get_mut(index)
             .expect("never fails unless the index is out of bounds");
-        if entry.1.is_none() {
-            // Initialize the alias list if it is empty.
-            entry.1 = Some(Default::default());
-        }
-        let list = entry
-            .1
-            .as_mut()
-            .expect("never fails because the list is initialized");
-        if !list.iter().any(|a| a == &alias) {
-            list.push(alias);
+        match aliases {
+            None => {
+                let mut list = StaticVec::new();
+                list.push(alias);
+                *aliases = Some(list.into());
+            }
+            Some(aliases) if !aliases.iter().any(|a| a == &alias) => aliases.push(alias),
+            Some(_) => (),
         }
         self
     }
@@ -534,7 +532,7 @@ impl<'a, K: Into<Cow<'a, str>>> Extend<(K, Dynamic)> for Scope<'a> {
     #[inline(always)]
     fn extend<T: IntoIterator<Item = (K, Dynamic)>>(&mut self, iter: T) {
         iter.into_iter().for_each(|(name, value)| {
-            self.names.push((name.into(), None));
+            self.names.push((name.into(), Default::default()));
             self.values.push(value);
         });
     }