From d2a510b27760527563d61c9034bd8ffc1d180f50 Mon Sep 17 00:00:00 2001
From: overlookmotel <theoverlookmotel@gmail.com>
Date: Fri, 17 Jan 2025 01:36:09 +0000
Subject: [PATCH] perf(mangler): reduce hash table lookups

---
 Cargo.lock                    |  1 -
 crates/oxc_mangler/Cargo.toml |  1 -
 crates/oxc_mangler/src/lib.rs | 54 ++++++++++++++++++++++-------------
 3 files changed, 34 insertions(+), 22 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 3f0fdf03ec2cb..32222fcfaaa4a 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1844,7 +1844,6 @@ dependencies = [
  "oxc_ast",
  "oxc_index",
  "oxc_semantic",
- "oxc_span",
  "rustc-hash",
 ]
 
diff --git a/crates/oxc_mangler/Cargo.toml b/crates/oxc_mangler/Cargo.toml
index 82f7acc69d3d8..e0413f7904f1d 100644
--- a/crates/oxc_mangler/Cargo.toml
+++ b/crates/oxc_mangler/Cargo.toml
@@ -25,7 +25,6 @@ oxc_allocator = { workspace = true }
 oxc_ast = { workspace = true }
 oxc_index = { workspace = true }
 oxc_semantic = { workspace = true }
-oxc_span = { workspace = true }
 
 itertools = { workspace = true }
 rustc-hash = { workspace = true }
diff --git a/crates/oxc_mangler/src/lib.rs b/crates/oxc_mangler/src/lib.rs
index 49af1f8033a83..d5f9c405e691f 100644
--- a/crates/oxc_mangler/src/lib.rs
+++ b/crates/oxc_mangler/src/lib.rs
@@ -1,13 +1,12 @@
 use std::ops::Deref;
 
 use itertools::Itertools;
-use rustc_hash::FxHashSet;
+use rustc_hash::{FxBuildHasher, FxHashSet};
 
 use oxc_allocator::{Allocator, Vec};
 use oxc_ast::ast::{Declaration, Program, Statement};
 use oxc_index::Idx;
 use oxc_semantic::{ReferenceId, ScopeTree, SemanticBuilder, SymbolId, SymbolTable};
-use oxc_span::Atom;
 
 #[derive(Default, Debug, Clone, Copy)]
 pub struct MangleOptions {
@@ -183,9 +182,28 @@ impl Mangler {
             &allocator,
         );
 
+        // Create `HashSet` of symbol names which are unavailable
+        // (keywords, unresolved references, and top level bindings)
         let root_unresolved_references = scope_tree.root_unresolved_references();
         let root_bindings = scope_tree.get_bindings(scope_tree.root_scope_id());
 
+        let unavailable_names_count = KEYWORDS_AND_SPECIAL_NAMES.len()
+            + root_unresolved_references.len()
+            + root_bindings.len();
+        let mut unavailable_names =
+            FxHashSet::with_capacity_and_hasher(unavailable_names_count, FxBuildHasher);
+
+        unavailable_names.extend(KEYWORDS_AND_SPECIAL_NAMES);
+        unavailable_names.extend(root_unresolved_references.keys().copied());
+
+        if self.options.top_level {
+            unavailable_names
+                .extend(root_bindings.keys().copied().filter(|name| exported_names.contains(name)));
+        } else {
+            unavailable_names.extend(root_bindings.keys().copied());
+        }
+
+        // Create list of symbol names to use
         let mut reserved_names = Vec::with_capacity_in(total_number_of_slots, &allocator);
 
         let mut count = 0;
@@ -193,14 +211,7 @@ impl Mangler {
             let name = loop {
                 let name = generate_name(count);
                 count += 1;
-                // Do not mangle keywords and unresolved references
-                let n = name.as_str();
-                if !is_keyword(n)
-                    && !is_special_name(n)
-                    && !root_unresolved_references.contains_key(n)
-                    && !(root_bindings.contains_key(n)
-                        && (!self.options.top_level || exported_names.contains(n)))
-                {
+                if !unavailable_names.contains(name.as_str()) {
                     break name;
                 }
             };
@@ -298,7 +309,7 @@ impl Mangler {
 
     fn collect_exported_symbols<'a>(
         program: &Program<'a>,
-    ) -> (FxHashSet<Atom<'a>>, FxHashSet<SymbolId>) {
+    ) -> (FxHashSet<&'a str>, FxHashSet<SymbolId>) {
         program
             .body
             .iter()
@@ -317,7 +328,7 @@ impl Mangler {
                     itertools::Either::Right(decl.id().into_iter())
                 }
             })
-            .map(|id| (id.name.clone(), id.symbol_id()))
+            .map(|id| (id.name.as_str(), id.symbol_id()))
             .collect()
     }
 }
@@ -326,6 +337,17 @@ fn is_special_name(name: &str) -> bool {
     matches!(name, "exports" | "arguments")
 }
 
+#[rustfmt::skip]
+static KEYWORDS_AND_SPECIAL_NAMES: [&str; 28] = [
+    // Keywords
+    "as", "do", "if", "in", "is", "of", "any", "for", "get",
+    "let", "new", "out", "set", "try", "var", "case", "else",
+    "enum", "from", "meta", "null", "this", "true", "type",
+    "void", "with",
+    // Special names
+    "exports", "arguments",
+];
+
 #[derive(Debug)]
 struct SlotFrequency<'a> {
     pub slot: Slot,
@@ -339,14 +361,6 @@ impl<'a> SlotFrequency<'a> {
     }
 }
 
-#[rustfmt::skip]
-fn is_keyword(s: &str) -> bool {
-    matches!(s, "as" | "do" | "if" | "in" | "is" | "of" | "any" | "for" | "get"
-            | "let" | "new" | "out" | "set" | "try" | "var" | "case" | "else"
-            | "enum" | "from" | "meta" | "null" | "this" | "true" | "type"
-            | "void" | "with")
-}
-
 #[repr(C, align(64))]
 struct Aligned64([u8; 64]);