From 67e2c4a4fd17436732099422c25d1c0d82f815dd Mon Sep 17 00:00:00 2001
From: bohan <bohan-zhang@foxmail.com>
Date: Sat, 4 Nov 2023 16:26:25 +0800
Subject: [PATCH] perf(es): Delete useless partition and extend in comments
 (#8214)
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I've used `bizcharts` as a benchmark, and:

before this PR 17s:

<img width="288" alt="image"
src="https://github.com/web-infra-dev/rspack/assets/30187863/35232863-247a-4825-a08f-977de46e7216">

after this PR 1.7s:

<img width="585" alt="image"
src="https://github.com/swc-project/swc/assets/30187863/b802abf0-d699-45c7-b9f3-2f52192f7477">


You can get more info at
https://github.com/web-infra-dev/rspack/issues/4525
---
 crates/swc/src/dropped_comments_preserver.rs | 24 ++++++++------------
 1 file changed, 10 insertions(+), 14 deletions(-)

diff --git a/crates/swc/src/dropped_comments_preserver.rs b/crates/swc/src/dropped_comments_preserver.rs
index 3899ef2f2442..b0c15a55b131 100644
--- a/crates/swc/src/dropped_comments_preserver.rs
+++ b/crates/swc/src/dropped_comments_preserver.rs
@@ -100,16 +100,14 @@ impl DroppedCommentsPreserver {
     fn shift_leading_comments(&self, comments: &SingleThreadedComments) -> CommentEntries {
         let mut existing_comments = self.collect_existing_comments(comments);
 
-        for span in self.known_spans.iter() {
-            let (comments_to_move, next_byte_positions): (CommentEntries, CommentEntries) =
-                existing_comments
-                    .drain(..)
-                    .partition(|(bp, _)| *bp <= span.lo);
-
-            existing_comments.extend(next_byte_positions);
-
-            let collected_comments = comments_to_move.into_iter().flat_map(|(_, c)| c).collect();
+        existing_comments.sort_by(|(bp_a, _), (bp_b, _)| bp_a.cmp(bp_b));
 
+        for span in self.known_spans.iter() {
+            let cut_point = existing_comments.partition_point(|(bp, _)| *bp <= span.lo);
+            let collected_comments = existing_comments
+                .drain(..cut_point)
+                .flat_map(|(_, c)| c)
+                .collect::<Vec<Comment>>();
             self.comments
                 .add_leading_comments(span.lo, collected_comments)
         }
@@ -125,11 +123,9 @@ impl DroppedCommentsPreserver {
         let last_trailing = self
             .known_spans
             .iter()
-            .copied()
-            .fold(
-                DUMMY_SP,
-                |acc, span| if span.hi > acc.hi { span } else { acc },
-            );
+            .max_by_key(|span| span.hi)
+            .cloned()
+            .unwrap_or(DUMMY_SP);
 
         self.comments.add_trailing_comments(
             last_trailing.hi,