perf(semantic): pre-reserve unresolved_references using Stats::references

Dunqing · Dunqing · commit 2b6ee676dec0 · 2026-05-19T19:15:18.000+08:00
The unresolved_references Vec grows from 0 with default doubling, requiring
~13 reallocations to reach the typical ~5k references on a moderately-sized
TypeScript file. Stats already knows the count up-front (or computes it in
Stats::count); pre-reserving eliminates the growth reallocations.

Benchmark (cargo bench --bench semantic):

  RadixUI.jsx (3KB JSX):     3.155 µs -&gt; 3.051 µs (-3.3%)
  react.development.js:    136.47 µs -&gt; 134.93 µs (-1.1%)
  cal.com.tsx (1MB TSX):    2.7414 ms -&gt; 2.7055 ms (-1.3%)
  binder.ts (193KB TS):    314.90 µs -&gt; 312.15 µs (-0.9%)

All intervals non-overlapping on Criterion.
diff --git a/crates/oxc_semantic/src/builder.rs b/crates/oxc_semantic/src/builder.rs
@@ -323,6 +323,7 @@ impl<'a> SemanticBuilder<'a> {
             stats.references as usize,
             stats.scopes as usize,
         );
+        self.unresolved_references.reserve(stats.references as usize);
 
         // Visit AST to generate scopes tree etc
         self.visit_program(program);
diff --git a/crates/oxc_semantic/src/unresolved_stack.rs b/crates/oxc_semantic/src/unresolved_stack.rs
@@ -16,6 +16,13 @@ impl<'a> UnresolvedReferences<'a> {
         Self { references: Vec::new() }
     }
 
+    /// Reserve capacity for at least `additional` more references.
+    /// Avoids growth reallocations when the expected count is known up-front.
+    #[inline]
+    pub(crate) fn reserve(&mut self, additional: usize) {
+        self.references.reserve(additional);
+    }
+
     /// Push an unresolved reference to the flat list.
     #[inline]
     pub(crate) fn push(&mut self, name: Ident<'a>, reference_id: ReferenceId) {
