From d44462a70fe5276d032f8ffee3e1d9bf9fa35aec Mon Sep 17 00:00:00 2001
From: Boshen <boshenc@gmail.com>
Date: Fri, 31 Jan 2025 16:21:50 +0800
Subject: [PATCH] perf(codegen): avoid a heap allocation when printing floats

---
 Cargo.lock                    |  1 +
 crates/oxc_codegen/Cargo.toml |  3 ++-
 crates/oxc_codegen/src/lib.rs | 31 ++++++++++++++++---------------
 3 files changed, 19 insertions(+), 16 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index b8ccdda96a7ea..8696678dfd662 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1692,6 +1692,7 @@ dependencies = [
  "oxc_syntax",
  "pico-args",
  "rustc-hash",
+ "ryu-js",
 ]
 
 [[package]]
diff --git a/crates/oxc_codegen/Cargo.toml b/crates/oxc_codegen/Cargo.toml
index f8207d39635ad..0575d7b6c9271 100644
--- a/crates/oxc_codegen/Cargo.toml
+++ b/crates/oxc_codegen/Cargo.toml
@@ -27,13 +27,14 @@ oxc_index = { workspace = true }
 oxc_mangler = { workspace = true }
 oxc_sourcemap = { workspace = true }
 oxc_span = { workspace = true }
-oxc_syntax = { workspace = true, features = ["to_js_string"] }
+oxc_syntax = { workspace = true }
 
 assert-unchecked = { workspace = true }
 bitflags = { workspace = true }
 cow-utils = { workspace = true }
 nonmax = { workspace = true }
 rustc-hash = { workspace = true }
+ryu-js = { workspace = true }
 
 [dev-dependencies]
 base64 = { workspace = true }
diff --git a/crates/oxc_codegen/src/lib.rs b/crates/oxc_codegen/src/lib.rs
index 3e672779445b2..cdf157e0173bb 100644
--- a/crates/oxc_codegen/src/lib.rs
+++ b/crates/oxc_codegen/src/lib.rs
@@ -575,12 +575,13 @@ impl<'a> Codegen<'a> {
     }
 
     fn print_non_negative_float(&mut self, num: f64) {
-        use oxc_syntax::number::ToJsString;
+        // Inline the buffer here to avoid heap allocation on `buffer.format(*self).to_string()`.
+        let mut buffer = ryu_js::Buffer::new();
         if num < 1000.0 && num.fract() == 0.0 {
-            self.print_str(&num.to_js_string());
+            self.print_str(buffer.format(num));
             self.need_space_before_dot = self.code_len();
         } else {
-            let s = Self::get_minified_number(num);
+            let s = Self::get_minified_number(num, &mut buffer);
             self.print_str(&s);
             if !s.bytes().any(|b| matches!(b, b'.' | b'e' | b'x')) {
                 self.need_space_before_dot = self.code_len();
@@ -691,25 +692,25 @@ impl<'a> Codegen<'a> {
     // `get_minified_number` from terser
     // https://github.com/terser/terser/blob/c5315c3fd6321d6b2e076af35a70ef532f498505/lib/output.js#L2418
     #[allow(clippy::cast_possible_truncation, clippy::cast_sign_loss, clippy::cast_possible_wrap)]
-    fn get_minified_number(num: f64) -> String {
+    fn get_minified_number(num: f64, buffer: &mut ryu_js::Buffer) -> Cow<'_, str> {
         use cow_utils::CowUtils;
-        use oxc_syntax::number::ToJsString;
+
         if num < 1000.0 && num.fract() == 0.0 {
-            return num.to_js_string();
+            return Cow::Borrowed(buffer.format(num));
         }
 
-        let mut s = num.to_js_string();
+        let mut s = buffer.format(num);
 
         if s.starts_with("0.") {
-            s = s[1..].to_string();
+            s = &s[1..];
         }
 
-        s = s.cow_replacen("e+", "e", 1).to_string();
+        let s = s.cow_replacen("e+", "e", 1);
 
         let mut candidates = vec![s.clone()];
 
         if num.fract() == 0.0 {
-            candidates.push(format!("0x{:x}", num as u128));
+            candidates.push(Cow::Owned(format!("0x{:x}", num as u128)));
         }
 
         // create `1e-2`
@@ -717,14 +718,14 @@ impl<'a> Codegen<'a> {
             if let Some((i, _)) = s[1..].bytes().enumerate().find(|(_, c)| *c != b'0') {
                 let len = i + 1; // `+1` to include the dot.
                 let digits = &s[len..];
-                candidates.push(format!("{digits}e-{}", digits.len() + len - 1));
+                candidates.push(Cow::Owned(format!("{digits}e-{}", digits.len() + len - 1)));
             }
         }
 
         // create 1e2
         if s.ends_with('0') {
             if let Some((len, _)) = s.bytes().rev().enumerate().find(|(_, c)| *c != b'0') {
-                candidates.push(format!("{}e{len}", &s[0..s.len() - len]));
+                candidates.push(Cow::Owned(format!("{}e{len}", &s[0..s.len() - len])));
             }
         }
 
@@ -733,13 +734,13 @@ impl<'a> Codegen<'a> {
         if let Some((integer, point, exponent)) =
             s.split_once('.').and_then(|(a, b)| b.split_once('e').map(|e| (a, e.0, e.1)))
         {
-            candidates.push(format!(
+            candidates.push(Cow::Owned(format!(
                 "{integer}{point}e{}",
                 exponent.parse::<isize>().unwrap() - point.len() as isize
-            ));
+            )));
         }
 
-        candidates.into_iter().min_by_key(String::len).unwrap()
+        candidates.into_iter().min_by_key(|c| c.len()).unwrap()
     }
 
     fn add_source_mapping(&mut self, span: Span) {