From f8829cd544aebb667f46ce0a6f4962530fd4bba2 Mon Sep 17 00:00:00 2001
From: overlookmotel <theoverlookmotel@gmail.com>
Date: Fri, 12 Jul 2024 19:21:24 +0100
Subject: [PATCH 01/15] perf(semantic): avoid repeated hashing resolving
 bindings

---
 Cargo.lock                         |  1 +
 Cargo.toml                         |  1 +
 crates/oxc_semantic/Cargo.toml     |  1 +
 crates/oxc_semantic/src/builder.rs | 37 ++++++------
 crates/oxc_semantic/src/hash.rs    | 90 ++++++++++++++++++++++++++++++
 crates/oxc_semantic/src/lib.rs     |  1 +
 6 files changed, 112 insertions(+), 19 deletions(-)
 create mode 100644 crates/oxc_semantic/src/hash.rs

diff --git a/Cargo.lock b/Cargo.lock
index 9cd9083730ff5..71caf06976e93 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1704,6 +1704,7 @@ dependencies = [
 name = "oxc_semantic"
 version = "0.20.0"
 dependencies = [
+ "hashbrown",
  "indexmap",
  "insta",
  "itertools 0.13.0",
diff --git a/Cargo.toml b/Cargo.toml
index 49810d486c709..c7fd7850e7a1e 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -115,6 +115,7 @@ dashmap             = "6.0.0"
 flate2              = "1.0.30"
 futures             = "0.3.30"
 glob                = "0.3.1"
+hashbrown           = "0.14.5"
 ignore              = "0.4.22"
 itertools           = "0.13.0"
 jemallocator        = "0.5.4"
diff --git a/crates/oxc_semantic/Cargo.toml b/crates/oxc_semantic/Cargo.toml
index 8118711a26b2b..995aa8af87d18 100644
--- a/crates/oxc_semantic/Cargo.toml
+++ b/crates/oxc_semantic/Cargo.toml
@@ -27,6 +27,7 @@ oxc_diagnostics = { workspace = true }
 oxc_index       = { workspace = true }
 oxc_allocator   = { workspace = true }
 
+hashbrown  = { workspace = true }
 indexmap   = { workspace = true }
 phf        = { workspace = true, features = ["macros"] }
 rustc-hash = { workspace = true }
diff --git a/crates/oxc_semantic/src/builder.rs b/crates/oxc_semantic/src/builder.rs
index ca19d1258812b..7d0f823524e1c 100644
--- a/crates/oxc_semantic/src/builder.rs
+++ b/crates/oxc_semantic/src/builder.rs
@@ -21,12 +21,13 @@ use crate::{
     checker,
     class::ClassTableBuilder,
     diagnostics::redeclaration,
+    hash::TempUnresolvedReferences,
     jsdoc::JSDocBuilder,
     label::LabelBuilder,
     module_record::ModuleRecordBuilder,
     node::{AstNodeId, AstNodes, NodeFlags},
     reference::{Reference, ReferenceFlag, ReferenceId},
-    scope::{ScopeFlags, ScopeId, ScopeTree, UnresolvedReferences},
+    scope::{ScopeFlags, ScopeId, ScopeTree},
     symbol::{SymbolFlags, SymbolId, SymbolTable},
     JSDocFinder, Semantic,
 };
@@ -74,10 +75,10 @@ pub struct SemanticBuilder<'a> {
     pub symbols: SymbolTable,
 
     // Stack used to accumulate unresolved refs while traversing scopes.
-    // Indexed by scope depth. We recycle `UnresolvedReferences` instances during traversal
+    // Indexed by scope depth. We recycle `TempUnresolvedReferences` instances during traversal
     // to reduce allocations, so the stack grows to maximum scope depth, but never shrinks.
     // See: <https://github.com/oxc-project/oxc/issues/4169>
-    unresolved_references: Vec<UnresolvedReferences>,
+    unresolved_references: Vec<TempUnresolvedReferences>,
 
     pub(crate) module_record: Arc<ModuleRecord>,
 
@@ -198,11 +199,14 @@ impl<'a> SemanticBuilder<'a> {
             if self.check_syntax_error {
                 checker::check_module_record(&self);
             }
-        }
 
-        debug_assert_eq!(self.current_scope_depth, 0);
-        self.scope.root_unresolved_references =
-            self.unresolved_references.into_iter().next().unwrap();
+            // Convert remaining unresolved references to a standard hash map
+            debug_assert_eq!(self.current_scope_depth, 0);
+            let mut unresolved_references = self.unresolved_references.into_iter().next().unwrap();
+            for line in unresolved_references.drain() {
+                self.scope.root_unresolved_references.insert(line.name, line.reference_ids);
+            }
+        }
 
         let jsdoc = if self.build_jsdoc { self.jsdoc.build() } else { JSDocFinder::default() };
 
@@ -339,10 +343,7 @@ impl<'a> SemanticBuilder<'a> {
         let reference_name = reference.name().clone();
         let reference_id = self.symbols.create_reference(reference);
 
-        self.unresolved_references[self.current_scope_depth]
-            .entry(reference_name)
-            .or_default()
-            .push(reference_id);
+        self.unresolved_references[self.current_scope_depth].insert(reference_name, reference_id);
         reference_id
     }
 
@@ -370,18 +371,16 @@ impl<'a> SemanticBuilder<'a> {
         let current_refs = iter.next().unwrap();
 
         let bindings = self.scope.get_bindings(self.current_scope_id);
-        for (name, reference_ids) in current_refs.drain() {
+        for line in current_refs.drain() {
             // Try to resolve a reference.
             // If unresolved, transfer it to parent scope's unresolved references.
-            if let Some(symbol_id) = bindings.get(&name).copied() {
-                for reference_id in &reference_ids {
+            if let Some(symbol_id) = bindings.get(&line.name).copied() {
+                for reference_id in &line.reference_ids {
                     self.symbols.references[*reference_id].set_symbol_id(symbol_id);
                 }
-                self.symbols.resolved_references[symbol_id].extend(reference_ids);
-            } else if let Some(parent_reference_ids) = parent_refs.get_mut(&name) {
-                parent_reference_ids.extend(reference_ids);
+                self.symbols.resolved_references[symbol_id].extend(line.reference_ids);
             } else {
-                parent_refs.insert(name, reference_ids);
+                parent_refs.extend(line.name, line.hash, line.reference_ids);
             }
         }
     }
@@ -442,7 +441,7 @@ impl<'a> Visit<'a> for SemanticBuilder<'a> {
         // `self.unresolved_references[self.current_scope_depth]` is initialized
         self.current_scope_depth += 1;
         if self.unresolved_references.len() <= self.current_scope_depth {
-            self.unresolved_references.push(UnresolvedReferences::default());
+            self.unresolved_references.push(TempUnresolvedReferences::default());
         }
     }
 
diff --git a/crates/oxc_semantic/src/hash.rs b/crates/oxc_semantic/src/hash.rs
new file mode 100644
index 0000000000000..602fbd6e5ef9e
--- /dev/null
+++ b/crates/oxc_semantic/src/hash.rs
@@ -0,0 +1,90 @@
+use std::hash::Hash;
+use std::hash::Hasher;
+
+use hashbrown::hash_table::{Drain, Entry, HashTable};
+use rustc_hash::FxHasher;
+
+use oxc_span::CompactStr;
+
+use crate::reference::ReferenceId;
+
+#[derive(Clone, Copy, PartialEq)]
+pub struct IdentifierHash(u64);
+
+impl IdentifierHash {
+    fn new(name: &str) -> Self {
+        let mut hasher = FxHasher::default();
+        name.hash(&mut hasher);
+        let hash = hasher.finish();
+        Self(hash)
+    }
+}
+
+pub struct Line {
+    pub name: CompactStr,
+    pub hash: IdentifierHash,
+    pub reference_ids: Vec<ReferenceId>,
+}
+
+#[derive(Default)]
+pub struct TempUnresolvedReferences {
+    inner: HashTable<Line>,
+}
+
+impl TempUnresolvedReferences {
+    #[allow(dead_code)]
+    pub fn get(&self, name: &str, hash: IdentifierHash) -> Option<&Vec<ReferenceId>> {
+        self.inner
+            .find(hash.0, |entry| entry.hash == hash && entry.name.as_ref() == name)
+            .map(|entry| &entry.reference_ids)
+    }
+
+    #[allow(dead_code)]
+    pub fn get_mut(&mut self, name: &str, hash: IdentifierHash) -> Option<&mut Vec<ReferenceId>> {
+        self.inner
+            .find_mut(hash.0, |entry| entry.hash == hash && entry.name.as_ref() == name)
+            .map(|entry| &mut entry.reference_ids)
+    }
+
+    pub fn insert(&mut self, name: CompactStr, reference_id: ReferenceId) {
+        let hash = IdentifierHash::new(&name);
+        let entry = self.inner.entry(
+            hash.0,
+            |entry| entry.hash == hash && entry.name.as_ref() == name,
+            |entry| entry.hash.0,
+        );
+        match entry {
+            Entry::Occupied(mut entry) => {
+                entry.get_mut().reference_ids.push(reference_id);
+            }
+            Entry::Vacant(entry) => {
+                entry.insert(Line { name, hash, reference_ids: vec![reference_id] });
+            }
+        }
+    }
+
+    pub fn extend(
+        &mut self,
+        name: CompactStr,
+        hash: IdentifierHash,
+        reference_ids: Vec<ReferenceId>,
+    ) {
+        let entry = self.inner.entry(
+            hash.0,
+            |entry| entry.hash == hash && entry.name.as_ref() == name,
+            |entry| entry.hash.0,
+        );
+        match entry {
+            Entry::Occupied(mut entry) => {
+                entry.get_mut().reference_ids.extend(reference_ids);
+            }
+            Entry::Vacant(entry) => {
+                entry.insert(Line { name, hash, reference_ids });
+            }
+        }
+    }
+
+    pub fn drain(&mut self) -> Drain<Line> {
+        self.inner.drain()
+    }
+}
diff --git a/crates/oxc_semantic/src/lib.rs b/crates/oxc_semantic/src/lib.rs
index 52376d4ff4974..d5461670bde8d 100644
--- a/crates/oxc_semantic/src/lib.rs
+++ b/crates/oxc_semantic/src/lib.rs
@@ -3,6 +3,7 @@ mod builder;
 mod checker;
 mod class;
 mod diagnostics;
+mod hash;
 mod jsdoc;
 mod label;
 mod module_record;

From 04b2acb9eac1d147c190aac866d46a06b295e87c Mon Sep 17 00:00:00 2001
From: overlookmotel <theoverlookmotel@gmail.com>
Date: Fri, 12 Jul 2024 20:01:05 +0100
Subject: [PATCH 02/15] Simpler hash function

---
 crates/oxc_semantic/src/hash.rs | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/crates/oxc_semantic/src/hash.rs b/crates/oxc_semantic/src/hash.rs
index 602fbd6e5ef9e..c076506c752b9 100644
--- a/crates/oxc_semantic/src/hash.rs
+++ b/crates/oxc_semantic/src/hash.rs
@@ -1,4 +1,3 @@
-use std::hash::Hash;
 use std::hash::Hasher;
 
 use hashbrown::hash_table::{Drain, Entry, HashTable};
@@ -14,9 +13,8 @@ pub struct IdentifierHash(u64);
 impl IdentifierHash {
     fn new(name: &str) -> Self {
         let mut hasher = FxHasher::default();
-        name.hash(&mut hasher);
-        let hash = hasher.finish();
-        Self(hash)
+        hasher.write(name.as_bytes());
+        Self(hasher.finish())
     }
 }
 

From b48168dbb073f5d10a95796a0a827da2bf6fe0c7 Mon Sep 17 00:00:00 2001
From: overlookmotel <theoverlookmotel@gmail.com>
Date: Fri, 12 Jul 2024 20:04:44 +0100
Subject: [PATCH 03/15] Compare `CompactStr`s directly

---
 crates/oxc_semantic/src/hash.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/crates/oxc_semantic/src/hash.rs b/crates/oxc_semantic/src/hash.rs
index c076506c752b9..1e41efd19a549 100644
--- a/crates/oxc_semantic/src/hash.rs
+++ b/crates/oxc_semantic/src/hash.rs
@@ -48,7 +48,7 @@ impl TempUnresolvedReferences {
         let hash = IdentifierHash::new(&name);
         let entry = self.inner.entry(
             hash.0,
-            |entry| entry.hash == hash && entry.name.as_ref() == name,
+            |entry| entry.hash == hash && entry.name == name,
             |entry| entry.hash.0,
         );
         match entry {
@@ -69,7 +69,7 @@ impl TempUnresolvedReferences {
     ) {
         let entry = self.inner.entry(
             hash.0,
-            |entry| entry.hash == hash && entry.name.as_ref() == name,
+            |entry| entry.hash == hash && entry.name == name,
             |entry| entry.hash.0,
         );
         match entry {

From 2725a0c9aa90be7d33eec8ef3543aa6bd0ab87d5 Mon Sep 17 00:00:00 2001
From: overlookmotel <theoverlookmotel@gmail.com>
Date: Fri, 12 Jul 2024 20:47:16 +0100
Subject: [PATCH 04/15] Snapshot change

---
 .../oxc_linter/src/snapshots/no_confusing_set_timeout.snap   | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/crates/oxc_linter/src/snapshots/no_confusing_set_timeout.snap b/crates/oxc_linter/src/snapshots/no_confusing_set_timeout.snap
index eb0da15879dd6..1b2c0fe59406b 100644
--- a/crates/oxc_linter/src/snapshots/no_confusing_set_timeout.snap
+++ b/crates/oxc_linter/src/snapshots/no_confusing_set_timeout.snap
@@ -1,5 +1,6 @@
 ---
 source: crates/oxc_linter/src/tester.rs
+assertion_line: 216
 ---
   ⚠ eslint-plugin-jest(no-confusing-set-timeout)
     ╭─[no_confusing_set_timeout.tsx:10:17]
@@ -35,7 +36,7 @@ source: crates/oxc_linter/src/tester.rs
     ·                 ───────────────
  11 │             
     ╰────
-  help: Do not call `jest.setTimeout` multiple times, as only the last call will have an effect
+  help: `jest.setTimeout` should be placed before any other jest methods
 
   ⚠ eslint-plugin-jest(no-confusing-set-timeout)
     ╭─[no_confusing_set_timeout.tsx:10:17]
@@ -44,7 +45,7 @@ source: crates/oxc_linter/src/tester.rs
     ·                 ───────────────
  11 │             
     ╰────
-  help: `jest.setTimeout` should be placed before any other jest methods
+  help: Do not call `jest.setTimeout` multiple times, as only the last call will have an effect
 
   ⚠ eslint-plugin-jest(no-confusing-set-timeout)
    ╭─[no_confusing_set_timeout.tsx:3:21]

From c30dd53bee0f220d3e583b850eed234f230848f8 Mon Sep 17 00:00:00 2001
From: overlookmotel <theoverlookmotel@gmail.com>
Date: Fri, 12 Jul 2024 22:57:29 +0100
Subject: [PATCH 05/15] Collect into `root_unresolved_references`

---
 crates/oxc_semantic/src/builder.rs | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/crates/oxc_semantic/src/builder.rs b/crates/oxc_semantic/src/builder.rs
index 7d0f823524e1c..91f801857e60e 100644
--- a/crates/oxc_semantic/src/builder.rs
+++ b/crates/oxc_semantic/src/builder.rs
@@ -203,9 +203,8 @@ impl<'a> SemanticBuilder<'a> {
             // Convert remaining unresolved references to a standard hash map
             debug_assert_eq!(self.current_scope_depth, 0);
             let mut unresolved_references = self.unresolved_references.into_iter().next().unwrap();
-            for line in unresolved_references.drain() {
-                self.scope.root_unresolved_references.insert(line.name, line.reference_ids);
-            }
+            self.scope.root_unresolved_references =
+                unresolved_references.drain().map(|line| (line.name, line.reference_ids)).collect();
         }
 
         let jsdoc = if self.build_jsdoc { self.jsdoc.build() } else { JSDocFinder::default() };

From 463b7d1d3abd4ca290e17c6c0761cb7d4e52a960 Mon Sep 17 00:00:00 2001
From: overlookmotel <theoverlookmotel@gmail.com>
Date: Fri, 12 Jul 2024 23:13:10 +0100
Subject: [PATCH 06/15] `resolve_references_for_root_scope`

---
 crates/oxc_semantic/src/builder.rs | 36 +++++++++++++++++++++---------
 1 file changed, 25 insertions(+), 11 deletions(-)

diff --git a/crates/oxc_semantic/src/builder.rs b/crates/oxc_semantic/src/builder.rs
index 91f801857e60e..c0deeed6d6fe8 100644
--- a/crates/oxc_semantic/src/builder.rs
+++ b/crates/oxc_semantic/src/builder.rs
@@ -27,7 +27,7 @@ use crate::{
     module_record::ModuleRecordBuilder,
     node::{AstNodeId, AstNodes, NodeFlags},
     reference::{Reference, ReferenceFlag, ReferenceId},
-    scope::{ScopeFlags, ScopeId, ScopeTree},
+    scope::{ScopeFlags, ScopeId, ScopeTree, UnresolvedReferences},
     symbol::{SymbolFlags, SymbolId, SymbolTable},
     JSDocFinder, Semantic,
 };
@@ -199,12 +199,6 @@ impl<'a> SemanticBuilder<'a> {
             if self.check_syntax_error {
                 checker::check_module_record(&self);
             }
-
-            // Convert remaining unresolved references to a standard hash map
-            debug_assert_eq!(self.current_scope_depth, 0);
-            let mut unresolved_references = self.unresolved_references.into_iter().next().unwrap();
-            self.scope.root_unresolved_references =
-                unresolved_references.drain().map(|line| (line.name, line.reference_ids)).collect();
         }
 
         let jsdoc = if self.build_jsdoc { self.jsdoc.build() } else { JSDocFinder::default() };
@@ -371,8 +365,7 @@ impl<'a> SemanticBuilder<'a> {
 
         let bindings = self.scope.get_bindings(self.current_scope_id);
         for line in current_refs.drain() {
-            // Try to resolve a reference.
-            // If unresolved, transfer it to parent scope's unresolved references.
+            // Try to resolve reference. If unresolved, transfer it to parent scope's unresolved references.
             if let Some(symbol_id) = bindings.get(&line.name).copied() {
                 for reference_id in &line.reference_ids {
                     self.symbols.references[*reference_id].set_symbol_id(symbol_id);
@@ -384,6 +377,25 @@ impl<'a> SemanticBuilder<'a> {
         }
     }
 
+    fn resolve_references_for_root_scope(&mut self) {
+        let mut root_unresolved_references = UnresolvedReferences::default();
+
+        let bindings = self.scope.get_bindings(self.current_scope_id);
+        for line in self.unresolved_references[self.current_scope_depth].drain() {
+            // Try to resolve reference. If unresolved, transfer it to root unresolved references.
+            if let Some(symbol_id) = bindings.get(&line.name).copied() {
+                for reference_id in &line.reference_ids {
+                    self.symbols.references[*reference_id].set_symbol_id(symbol_id);
+                }
+                self.symbols.resolved_references[symbol_id].extend(line.reference_ids);
+            } else {
+                root_unresolved_references.insert(line.name, line.reference_ids);
+            }
+        }
+
+        self.scope.root_unresolved_references = root_unresolved_references;
+    }
+
     pub fn add_redeclare_variable(&mut self, symbol_id: SymbolId, span: Span) {
         self.symbols.add_redeclare_variable(symbol_id, span);
     }
@@ -445,11 +457,13 @@ impl<'a> Visit<'a> for SemanticBuilder<'a> {
     }
 
     fn leave_scope(&mut self) {
-        self.resolve_references_for_current_scope();
         if let Some(parent_id) = self.scope.get_parent_id(self.current_scope_id) {
+            self.resolve_references_for_current_scope();
             self.current_scope_id = parent_id;
+            self.current_scope_depth -= 1;
+        } else {
+            self.resolve_references_for_root_scope();
         }
-        self.current_scope_depth -= 1;
     }
 
     // Setup all the context for the binder.

From eb1fa4021692d9490c2e3999248f944660174b08 Mon Sep 17 00:00:00 2001
From: overlookmotel <theoverlookmotel@gmail.com>
Date: Sat, 13 Jul 2024 22:05:30 +0100
Subject: [PATCH 07/15] Rename vars

---
 crates/oxc_semantic/src/hash.rs | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/crates/oxc_semantic/src/hash.rs b/crates/oxc_semantic/src/hash.rs
index 1e41efd19a549..998c2c72b0ac7 100644
--- a/crates/oxc_semantic/src/hash.rs
+++ b/crates/oxc_semantic/src/hash.rs
@@ -33,14 +33,14 @@ impl TempUnresolvedReferences {
     #[allow(dead_code)]
     pub fn get(&self, name: &str, hash: IdentifierHash) -> Option<&Vec<ReferenceId>> {
         self.inner
-            .find(hash.0, |entry| entry.hash == hash && entry.name.as_ref() == name)
+            .find(hash.0, |line| line.hash == hash && line.name.as_ref() == name)
             .map(|entry| &entry.reference_ids)
     }
 
     #[allow(dead_code)]
     pub fn get_mut(&mut self, name: &str, hash: IdentifierHash) -> Option<&mut Vec<ReferenceId>> {
         self.inner
-            .find_mut(hash.0, |entry| entry.hash == hash && entry.name.as_ref() == name)
+            .find_mut(hash.0, |line| line.hash == hash && line.name.as_ref() == name)
             .map(|entry| &mut entry.reference_ids)
     }
 
@@ -48,7 +48,7 @@ impl TempUnresolvedReferences {
         let hash = IdentifierHash::new(&name);
         let entry = self.inner.entry(
             hash.0,
-            |entry| entry.hash == hash && entry.name == name,
+            |line| line.hash == hash && line.name == name,
             |entry| entry.hash.0,
         );
         match entry {
@@ -69,8 +69,8 @@ impl TempUnresolvedReferences {
     ) {
         let entry = self.inner.entry(
             hash.0,
-            |entry| entry.hash == hash && entry.name == name,
-            |entry| entry.hash.0,
+            |line| line.hash == hash && line.name == name,
+            |line| line.hash.0,
         );
         match entry {
             Entry::Occupied(mut entry) => {

From 59f2bd3bc167e23c8653935970c400537e3cff74 Mon Sep 17 00:00:00 2001
From: overlookmotel <theoverlookmotel@gmail.com>
Date: Sat, 13 Jul 2024 22:05:38 +0100
Subject: [PATCH 08/15] Revert "`resolve_references_for_root_scope`"

This reverts commit 463b7d1d3abd4ca290e17c6c0761cb7d4e52a960.
---
 crates/oxc_semantic/src/builder.rs | 36 +++++++++---------------------
 1 file changed, 11 insertions(+), 25 deletions(-)

diff --git a/crates/oxc_semantic/src/builder.rs b/crates/oxc_semantic/src/builder.rs
index c0deeed6d6fe8..91f801857e60e 100644
--- a/crates/oxc_semantic/src/builder.rs
+++ b/crates/oxc_semantic/src/builder.rs
@@ -27,7 +27,7 @@ use crate::{
     module_record::ModuleRecordBuilder,
     node::{AstNodeId, AstNodes, NodeFlags},
     reference::{Reference, ReferenceFlag, ReferenceId},
-    scope::{ScopeFlags, ScopeId, ScopeTree, UnresolvedReferences},
+    scope::{ScopeFlags, ScopeId, ScopeTree},
     symbol::{SymbolFlags, SymbolId, SymbolTable},
     JSDocFinder, Semantic,
 };
@@ -199,6 +199,12 @@ impl<'a> SemanticBuilder<'a> {
             if self.check_syntax_error {
                 checker::check_module_record(&self);
             }
+
+            // Convert remaining unresolved references to a standard hash map
+            debug_assert_eq!(self.current_scope_depth, 0);
+            let mut unresolved_references = self.unresolved_references.into_iter().next().unwrap();
+            self.scope.root_unresolved_references =
+                unresolved_references.drain().map(|line| (line.name, line.reference_ids)).collect();
         }
 
         let jsdoc = if self.build_jsdoc { self.jsdoc.build() } else { JSDocFinder::default() };
@@ -365,7 +371,8 @@ impl<'a> SemanticBuilder<'a> {
 
         let bindings = self.scope.get_bindings(self.current_scope_id);
         for line in current_refs.drain() {
-            // Try to resolve reference. If unresolved, transfer it to parent scope's unresolved references.
+            // Try to resolve a reference.
+            // If unresolved, transfer it to parent scope's unresolved references.
             if let Some(symbol_id) = bindings.get(&line.name).copied() {
                 for reference_id in &line.reference_ids {
                     self.symbols.references[*reference_id].set_symbol_id(symbol_id);
@@ -377,25 +384,6 @@ impl<'a> SemanticBuilder<'a> {
         }
     }
 
-    fn resolve_references_for_root_scope(&mut self) {
-        let mut root_unresolved_references = UnresolvedReferences::default();
-
-        let bindings = self.scope.get_bindings(self.current_scope_id);
-        for line in self.unresolved_references[self.current_scope_depth].drain() {
-            // Try to resolve reference. If unresolved, transfer it to root unresolved references.
-            if let Some(symbol_id) = bindings.get(&line.name).copied() {
-                for reference_id in &line.reference_ids {
-                    self.symbols.references[*reference_id].set_symbol_id(symbol_id);
-                }
-                self.symbols.resolved_references[symbol_id].extend(line.reference_ids);
-            } else {
-                root_unresolved_references.insert(line.name, line.reference_ids);
-            }
-        }
-
-        self.scope.root_unresolved_references = root_unresolved_references;
-    }
-
     pub fn add_redeclare_variable(&mut self, symbol_id: SymbolId, span: Span) {
         self.symbols.add_redeclare_variable(symbol_id, span);
     }
@@ -457,13 +445,11 @@ impl<'a> Visit<'a> for SemanticBuilder<'a> {
     }
 
     fn leave_scope(&mut self) {
+        self.resolve_references_for_current_scope();
         if let Some(parent_id) = self.scope.get_parent_id(self.current_scope_id) {
-            self.resolve_references_for_current_scope();
             self.current_scope_id = parent_id;
-            self.current_scope_depth -= 1;
-        } else {
-            self.resolve_references_for_root_scope();
         }
+        self.current_scope_depth -= 1;
     }
 
     // Setup all the context for the binder.

From 62056b5e28890a5f7ecc3de8c33caf411c9f44ab Mon Sep 17 00:00:00 2001
From: overlookmotel <theoverlookmotel@gmail.com>
Date: Sat, 13 Jul 2024 22:08:02 +0100
Subject: [PATCH 09/15] Don't compare hash

---
 crates/oxc_semantic/src/hash.rs | 18 ++++--------------
 1 file changed, 4 insertions(+), 14 deletions(-)

diff --git a/crates/oxc_semantic/src/hash.rs b/crates/oxc_semantic/src/hash.rs
index 998c2c72b0ac7..57692417b4685 100644
--- a/crates/oxc_semantic/src/hash.rs
+++ b/crates/oxc_semantic/src/hash.rs
@@ -32,25 +32,19 @@ pub struct TempUnresolvedReferences {
 impl TempUnresolvedReferences {
     #[allow(dead_code)]
     pub fn get(&self, name: &str, hash: IdentifierHash) -> Option<&Vec<ReferenceId>> {
-        self.inner
-            .find(hash.0, |line| line.hash == hash && line.name.as_ref() == name)
-            .map(|entry| &entry.reference_ids)
+        self.inner.find(hash.0, |line| line.name.as_ref() == name).map(|entry| &entry.reference_ids)
     }
 
     #[allow(dead_code)]
     pub fn get_mut(&mut self, name: &str, hash: IdentifierHash) -> Option<&mut Vec<ReferenceId>> {
         self.inner
-            .find_mut(hash.0, |line| line.hash == hash && line.name.as_ref() == name)
+            .find_mut(hash.0, |line| line.name.as_ref() == name)
             .map(|entry| &mut entry.reference_ids)
     }
 
     pub fn insert(&mut self, name: CompactStr, reference_id: ReferenceId) {
         let hash = IdentifierHash::new(&name);
-        let entry = self.inner.entry(
-            hash.0,
-            |line| line.hash == hash && line.name == name,
-            |entry| entry.hash.0,
-        );
+        let entry = self.inner.entry(hash.0, |line| line.name == name, |entry| entry.hash.0);
         match entry {
             Entry::Occupied(mut entry) => {
                 entry.get_mut().reference_ids.push(reference_id);
@@ -67,11 +61,7 @@ impl TempUnresolvedReferences {
         hash: IdentifierHash,
         reference_ids: Vec<ReferenceId>,
     ) {
-        let entry = self.inner.entry(
-            hash.0,
-            |line| line.hash == hash && line.name == name,
-            |line| line.hash.0,
-        );
+        let entry = self.inner.entry(hash.0, |line| line.name == name, |line| line.hash.0);
         match entry {
             Entry::Occupied(mut entry) => {
                 entry.get_mut().reference_ids.extend(reference_ids);

From 406d97e2552e6b20b2dcc0272e5f361ebc25e6fd Mon Sep 17 00:00:00 2001
From: overlookmotel <theoverlookmotel@gmail.com>
Date: Sat, 13 Jul 2024 22:22:14 +0100
Subject: [PATCH 10/15] Revert "Don't compare hash"

This reverts commit 62056b5e28890a5f7ecc3de8c33caf411c9f44ab.
---
 crates/oxc_semantic/src/hash.rs | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/crates/oxc_semantic/src/hash.rs b/crates/oxc_semantic/src/hash.rs
index 57692417b4685..998c2c72b0ac7 100644
--- a/crates/oxc_semantic/src/hash.rs
+++ b/crates/oxc_semantic/src/hash.rs
@@ -32,19 +32,25 @@ pub struct TempUnresolvedReferences {
 impl TempUnresolvedReferences {
     #[allow(dead_code)]
     pub fn get(&self, name: &str, hash: IdentifierHash) -> Option<&Vec<ReferenceId>> {
-        self.inner.find(hash.0, |line| line.name.as_ref() == name).map(|entry| &entry.reference_ids)
+        self.inner
+            .find(hash.0, |line| line.hash == hash && line.name.as_ref() == name)
+            .map(|entry| &entry.reference_ids)
     }
 
     #[allow(dead_code)]
     pub fn get_mut(&mut self, name: &str, hash: IdentifierHash) -> Option<&mut Vec<ReferenceId>> {
         self.inner
-            .find_mut(hash.0, |line| line.name.as_ref() == name)
+            .find_mut(hash.0, |line| line.hash == hash && line.name.as_ref() == name)
             .map(|entry| &mut entry.reference_ids)
     }
 
     pub fn insert(&mut self, name: CompactStr, reference_id: ReferenceId) {
         let hash = IdentifierHash::new(&name);
-        let entry = self.inner.entry(hash.0, |line| line.name == name, |entry| entry.hash.0);
+        let entry = self.inner.entry(
+            hash.0,
+            |line| line.hash == hash && line.name == name,
+            |entry| entry.hash.0,
+        );
         match entry {
             Entry::Occupied(mut entry) => {
                 entry.get_mut().reference_ids.push(reference_id);
@@ -61,7 +67,11 @@ impl TempUnresolvedReferences {
         hash: IdentifierHash,
         reference_ids: Vec<ReferenceId>,
     ) {
-        let entry = self.inner.entry(hash.0, |line| line.name == name, |line| line.hash.0);
+        let entry = self.inner.entry(
+            hash.0,
+            |line| line.hash == hash && line.name == name,
+            |line| line.hash.0,
+        );
         match entry {
             Entry::Occupied(mut entry) => {
                 entry.get_mut().reference_ids.extend(reference_ids);

From 0c6a3dc91a0e4e079981027d14a341f9b9bd6880 Mon Sep 17 00:00:00 2001
From: overlookmotel <theoverlookmotel@gmail.com>
Date: Sat, 13 Jul 2024 22:23:45 +0100
Subject: [PATCH 11/15] Rename vars

---
 crates/oxc_semantic/src/hash.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/crates/oxc_semantic/src/hash.rs b/crates/oxc_semantic/src/hash.rs
index 998c2c72b0ac7..1d7c21f63d1a7 100644
--- a/crates/oxc_semantic/src/hash.rs
+++ b/crates/oxc_semantic/src/hash.rs
@@ -49,7 +49,7 @@ impl TempUnresolvedReferences {
         let entry = self.inner.entry(
             hash.0,
             |line| line.hash == hash && line.name == name,
-            |entry| entry.hash.0,
+            |line: &Line| line.hash.0,
         );
         match entry {
             Entry::Occupied(mut entry) => {

From 44c6662468c58876f0d970ee67e62176a57fdce6 Mon Sep 17 00:00:00 2001
From: overlookmotel <theoverlookmotel@gmail.com>
Date: Sat, 13 Jul 2024 22:28:18 +0100
Subject: [PATCH 12/15] Don't use `Entry` API

---
 crates/oxc_semantic/src/hash.rs | 39 ++++++++++++---------------------
 1 file changed, 14 insertions(+), 25 deletions(-)

diff --git a/crates/oxc_semantic/src/hash.rs b/crates/oxc_semantic/src/hash.rs
index 1d7c21f63d1a7..d7ab8a1943a01 100644
--- a/crates/oxc_semantic/src/hash.rs
+++ b/crates/oxc_semantic/src/hash.rs
@@ -1,6 +1,6 @@
 use std::hash::Hasher;
 
-use hashbrown::hash_table::{Drain, Entry, HashTable};
+use hashbrown::hash_table::{Drain, HashTable};
 use rustc_hash::FxHasher;
 
 use oxc_span::CompactStr;
@@ -46,18 +46,14 @@ impl TempUnresolvedReferences {
 
     pub fn insert(&mut self, name: CompactStr, reference_id: ReferenceId) {
         let hash = IdentifierHash::new(&name);
-        let entry = self.inner.entry(
-            hash.0,
-            |line| line.hash == hash && line.name == name,
-            |line: &Line| line.hash.0,
-        );
-        match entry {
-            Entry::Occupied(mut entry) => {
-                entry.get_mut().reference_ids.push(reference_id);
-            }
-            Entry::Vacant(entry) => {
-                entry.insert(Line { name, hash, reference_ids: vec![reference_id] });
-            }
+        if let Some(line) = self.inner.find_mut(hash.0, |line| line.name == name) {
+            line.reference_ids.push(reference_id);
+        } else {
+            self.inner.insert_unique(
+                hash.0,
+                Line { name, hash, reference_ids: vec![reference_id] },
+                |line| line.hash.0,
+            );
         }
     }
 
@@ -67,18 +63,11 @@ impl TempUnresolvedReferences {
         hash: IdentifierHash,
         reference_ids: Vec<ReferenceId>,
     ) {
-        let entry = self.inner.entry(
-            hash.0,
-            |line| line.hash == hash && line.name == name,
-            |line| line.hash.0,
-        );
-        match entry {
-            Entry::Occupied(mut entry) => {
-                entry.get_mut().reference_ids.extend(reference_ids);
-            }
-            Entry::Vacant(entry) => {
-                entry.insert(Line { name, hash, reference_ids });
-            }
+        if let Some(line) = self.inner.find_mut(hash.0, |line| line.name == name) {
+            line.reference_ids.extend(reference_ids);
+        } else {
+            self.inner
+                .insert_unique(hash.0, Line { name, hash, reference_ids }, |line| line.hash.0);
         }
     }
 

From 43e0171118f455e9dd1cd4efef76158678b85f59 Mon Sep 17 00:00:00 2001
From: overlookmotel <theoverlookmotel@gmail.com>
Date: Sat, 13 Jul 2024 23:06:15 +0100
Subject: [PATCH 13/15] More explicit code

---
 crates/oxc_semantic/src/builder.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/crates/oxc_semantic/src/builder.rs b/crates/oxc_semantic/src/builder.rs
index 91f801857e60e..12c701738b14d 100644
--- a/crates/oxc_semantic/src/builder.rs
+++ b/crates/oxc_semantic/src/builder.rs
@@ -111,7 +111,7 @@ impl<'a> SemanticBuilder<'a> {
         // This is just an estimate of a good initial size, but certainly better than
         // `Vec`'s default initial capacity of 4.
         let mut unresolved_references = vec![];
-        unresolved_references.resize_with(16, Default::default);
+        unresolved_references.resize_with(16, TempUnresolvedReferences::default);
 
         let trivias = Trivias::default();
         Self {

From c18e5d28294eacc52d0af6e58fbe224905c63f5c Mon Sep 17 00:00:00 2001
From: overlookmotel <theoverlookmotel@gmail.com>
Date: Sun, 14 Jul 2024 03:33:12 +0100
Subject: [PATCH 14/15] Optimize empty hash maps

---
 crates/oxc_semantic/src/builder.rs | 24 ++++++++++++++++--------
 crates/oxc_semantic/src/hash.rs    |  5 +++++
 2 files changed, 21 insertions(+), 8 deletions(-)

diff --git a/crates/oxc_semantic/src/builder.rs b/crates/oxc_semantic/src/builder.rs
index 12c701738b14d..23e021694252b 100644
--- a/crates/oxc_semantic/src/builder.rs
+++ b/crates/oxc_semantic/src/builder.rs
@@ -370,15 +370,23 @@ impl<'a> SemanticBuilder<'a> {
         let current_refs = iter.next().unwrap();
 
         let bindings = self.scope.get_bindings(self.current_scope_id);
-        for line in current_refs.drain() {
-            // Try to resolve a reference.
-            // If unresolved, transfer it to parent scope's unresolved references.
-            if let Some(symbol_id) = bindings.get(&line.name).copied() {
-                for reference_id in &line.reference_ids {
-                    self.symbols.references[*reference_id].set_symbol_id(symbol_id);
+        if !bindings.is_empty() {
+            for line in current_refs.drain() {
+                // Try to resolve a reference.
+                // If unresolved, transfer it to parent scope's unresolved references.
+                if let Some(symbol_id) = bindings.get(&line.name).copied() {
+                    for reference_id in &line.reference_ids {
+                        self.symbols.references[*reference_id].set_symbol_id(symbol_id);
+                    }
+                    self.symbols.resolved_references[symbol_id].extend(line.reference_ids);
+                } else {
+                    parent_refs.extend(line.name, line.hash, line.reference_ids);
                 }
-                self.symbols.resolved_references[symbol_id].extend(line.reference_ids);
-            } else {
+            }
+        } else if parent_refs.is_empty() {
+            std::mem::swap(current_refs, parent_refs);
+        } else {
+            for line in current_refs.drain() {
                 parent_refs.extend(line.name, line.hash, line.reference_ids);
             }
         }
diff --git a/crates/oxc_semantic/src/hash.rs b/crates/oxc_semantic/src/hash.rs
index d7ab8a1943a01..9d1c05d3d0e9e 100644
--- a/crates/oxc_semantic/src/hash.rs
+++ b/crates/oxc_semantic/src/hash.rs
@@ -44,6 +44,11 @@ impl TempUnresolvedReferences {
             .map(|entry| &mut entry.reference_ids)
     }
 
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.inner.is_empty()
+    }
+
     pub fn insert(&mut self, name: CompactStr, reference_id: ReferenceId) {
         let hash = IdentifierHash::new(&name);
         if let Some(line) = self.inner.find_mut(hash.0, |line| line.name == name) {

From 480090ca6958b26afa41ed6e9a6ee9056b4e9331 Mon Sep 17 00:00:00 2001
From: overlookmotel <theoverlookmotel@gmail.com>
Date: Sun, 14 Jul 2024 03:45:35 +0100
Subject: [PATCH 15/15] Revert "Optimize empty hash maps"

This reverts commit c18e5d28294eacc52d0af6e58fbe224905c63f5c.
---
 crates/oxc_semantic/src/builder.rs | 24 ++++++++----------------
 crates/oxc_semantic/src/hash.rs    |  5 -----
 2 files changed, 8 insertions(+), 21 deletions(-)

diff --git a/crates/oxc_semantic/src/builder.rs b/crates/oxc_semantic/src/builder.rs
index 23e021694252b..12c701738b14d 100644
--- a/crates/oxc_semantic/src/builder.rs
+++ b/crates/oxc_semantic/src/builder.rs
@@ -370,23 +370,15 @@ impl<'a> SemanticBuilder<'a> {
         let current_refs = iter.next().unwrap();
 
         let bindings = self.scope.get_bindings(self.current_scope_id);
-        if !bindings.is_empty() {
-            for line in current_refs.drain() {
-                // Try to resolve a reference.
-                // If unresolved, transfer it to parent scope's unresolved references.
-                if let Some(symbol_id) = bindings.get(&line.name).copied() {
-                    for reference_id in &line.reference_ids {
-                        self.symbols.references[*reference_id].set_symbol_id(symbol_id);
-                    }
-                    self.symbols.resolved_references[symbol_id].extend(line.reference_ids);
-                } else {
-                    parent_refs.extend(line.name, line.hash, line.reference_ids);
+        for line in current_refs.drain() {
+            // Try to resolve a reference.
+            // If unresolved, transfer it to parent scope's unresolved references.
+            if let Some(symbol_id) = bindings.get(&line.name).copied() {
+                for reference_id in &line.reference_ids {
+                    self.symbols.references[*reference_id].set_symbol_id(symbol_id);
                 }
-            }
-        } else if parent_refs.is_empty() {
-            std::mem::swap(current_refs, parent_refs);
-        } else {
-            for line in current_refs.drain() {
+                self.symbols.resolved_references[symbol_id].extend(line.reference_ids);
+            } else {
                 parent_refs.extend(line.name, line.hash, line.reference_ids);
             }
         }
diff --git a/crates/oxc_semantic/src/hash.rs b/crates/oxc_semantic/src/hash.rs
index 9d1c05d3d0e9e..d7ab8a1943a01 100644
--- a/crates/oxc_semantic/src/hash.rs
+++ b/crates/oxc_semantic/src/hash.rs
@@ -44,11 +44,6 @@ impl TempUnresolvedReferences {
             .map(|entry| &mut entry.reference_ids)
     }
 
-    #[inline]
-    pub fn is_empty(&self) -> bool {
-        self.inner.is_empty()
-    }
-
     pub fn insert(&mut self, name: CompactStr, reference_id: ReferenceId) {
         let hash = IdentifierHash::new(&name);
         if let Some(line) = self.inner.find_mut(hash.0, |line| line.name == name) {