perf: small improvement to extend_sorted_vec (#21032)

crates/trie/common/src/utils.rs

@@ -2,53 +2,42 @@ use alloc::vec::Vec;
 use core::cmp::Ordering;
 
 /// Helper function to extend a sorted vector with another sorted vector.
-/// Values from `other` take precedence for duplicate keys.
 ///
-/// This function efficiently merges two sorted vectors by:
-/// 1. Iterating through the target vector with mutable references
-/// 2. Using a peekable iterator for the other vector
-/// 3. For each target item, processing other items that come before or equal to it
-/// 4. Collecting items from other that need to be inserted
-/// 5. Appending and re-sorting only if new items were added
+/// Values from `other` take precedence for duplicate keys.
 pub(crate) fn extend_sorted_vec<K, V>(target: &mut Vec<(K, V)>, other: &[(K, V)])
 where
     K: Clone + Ord,
     V: Clone,
 {
+    let cmp = |a: &(K, V), b: &(K, V)| a.0.cmp(&b.0);
+
     if other.is_empty() {
         return;
     }
 
     let mut other_iter = other.iter().peekable();
-    let mut to_insert = Vec::new();
-
-    // Iterate through target and update/collect items from other
-    for target_item in target.iter_mut() {
+    let initial_len = target.len();
+    for i in 0..initial_len {
         while let Some(other_item) = other_iter.peek() {
-            match other_item.0.cmp(&target_item.0) {
+            let target_item = &mut target[i];
+            match cmp(other_item, target_item) {
                 Ordering::Less => {
-                    // Other item comes before current target item, collect it
-                    to_insert.push(other_iter.next().unwrap().clone());
+                    target.push(other_iter.next().unwrap().clone());
                 }
                 Ordering::Equal => {
-                    // Same key, update target with other's value
                     target_item.1 = other_iter.next().unwrap().1.clone();
                     break;
                 }
                 Ordering::Greater => {
-                    // Other item comes after current target item, keep target unchanged
                     break;
                 }
             }
         }
     }
 
-    // Append collected new items, as well as any remaining from `other` which are necessarily also
-    // new, and sort if needed
-    if !to_insert.is_empty() || other_iter.peek().is_some() {
-        target.extend(to_insert);
-        target.extend(other_iter.cloned());
-        target.sort_unstable_by(|a, b| a.0.cmp(&b.0));
+    target.extend(other_iter.cloned());
+    if target.len() > initial_len {
+        target.sort_by(cmp);
     }
 }