perf(common): Fix perf bug of sourcemap for inputs with multi-byte ch…

…ars (#6523)

**Description:**

This PR makes the source map generator cache the previous position instead of searching it from 0 every time.

**Related issue:**

 - Closes #6411.

crates/swc/benches/minify.rs

@@ -46,7 +46,7 @@ fn bench_minify(b: &mut Bencher, filename: &str) {
                         module: Default::default(),
                         safari10: Default::default(),
                         toplevel: true,
-                        source_map: Default::default(),
+                        source_map: BoolOrDataConfig::from_bool(true),
                         output_path: Default::default(),
                         inline_sources_content: true,
                         emit_source_map_columns: true,
@@ -56,9 +56,9 @@ fn bench_minify(b: &mut Bencher, filename: &str) {
         })
         .unwrap();
 
-        let res = black_box(res);
+        black_box(res);
 
-        assert_eq!(res.map, None);
+        // assert_eq!(res.map, None);
     })
 }
 
@@ -84,6 +84,7 @@ fn files_group(c: &mut Criterion) {
     bench_file("typescript");
     bench_file("victory");
     bench_file("vue");
+    // bench_file("large");
 }
 
 criterion_group!(benches, files_group);

crates/swc/scripts/instrument.sh

@@ -1,5 +1,7 @@
 #!/usr/bin/env bash
 set -eu
 
-cargo profile instruments --release -t time --bench typescript --features tracing/release_max_level_info -- --bench $@
+export RUST_LOG=off
+
+cargo profile instruments --release -t time --bench minify --features tracing/release_max_level_info -- --bench $@
 # MINIFY=1 cargo profile instruments --release -t time --bench typescript --features concurrent,tracing/release_max_level_info $@

crates/swc_common/src/lib.rs

@@ -32,7 +32,6 @@
 //!
 //! Use `fxhash` instead of `ahash` for `AHashMap` and `AHashSet`.
 #![deny(clippy::all)]
-#![deny(unused)]
 #![cfg_attr(docsrs, feature(doc_cfg))]
 
 use std::fmt::Debug;

crates/swc_common/src/source_map.rs

@@ -954,7 +954,7 @@ impl SourceMap {
     }
 
     fn bytepos_to_file_charpos_with(&self, map: &SourceFile, bpos: BytePos) -> CharPos {
-        let total_extra_bytes = self.calc_extra_bytes(map, &mut 0, bpos);
+        let total_extra_bytes = self.calc_extra_bytes(map, &mut 0, &mut 0, bpos);
         assert!(
             map.start_pos.to_u32() + total_extra_bytes <= bpos.to_u32(),
             "map.start_pos = {:?}; total_extra_bytes = {}; bpos = {:?}",
@@ -966,9 +966,15 @@ impl SourceMap {
     }
 
     /// Converts an absolute BytePos to a CharPos relative to the source_file.
-    fn calc_extra_bytes(&self, map: &SourceFile, start: &mut usize, bpos: BytePos) -> u32 {
+    fn calc_extra_bytes(
+        &self,
+        map: &SourceFile,
+        prev_total_extra_bytes: &mut u32,
+        start: &mut usize,
+        bpos: BytePos,
+    ) -> u32 {
         // The number of extra bytes due to multibyte chars in the SourceFile
-        let mut total_extra_bytes = 0;
+        let mut total_extra_bytes = *prev_total_extra_bytes;
 
         for (i, &mbc) in map.multibyte_chars[*start..].iter().enumerate() {
             debug!("{}-byte char at {:?}", mbc.bytes, mbc.pos);
@@ -991,6 +997,8 @@ impl SourceMap {
             }
         }
 
+        *prev_total_extra_bytes = total_extra_bytes;
+
         total_extra_bytes
     }
 
@@ -1183,6 +1191,11 @@ impl SourceMap {
 
         let mut prev_dst_line = u32::MAX;
 
+        let mut prev_extra_bytes = 0;
+        let mut ch_start = 0;
+        let mut line_prev_extra_bytes = 0;
+        let mut line_ch_start = 0;
+
         for (pos, lc) in mappings.iter() {
             let pos = *pos;
 
@@ -1214,6 +1227,12 @@ impl SourceMap {
                         builder.set_source_contents(src_id, Some(&f.src));
                     }
 
+                    prev_extra_bytes = 0;
+                    ch_start = 0;
+
+                    line_prev_extra_bytes = 0;
+                    line_ch_start = 0;
+
                     cur_file = Some(f.clone());
                     &f
                 }
@@ -1240,6 +1259,7 @@ impl SourceMap {
             }
 
             let mut line = a + 1; // Line numbers start at 1
+
             let linebpos = f.lines[a as usize];
             debug_assert!(
                 pos >= linebpos,
@@ -1248,8 +1268,15 @@ impl SourceMap {
                 pos,
                 linebpos,
             );
-            let chpos = pos.to_u32() - self.calc_extra_bytes(f, &mut 0, pos);
-            let linechpos = linebpos.to_u32() - self.calc_extra_bytes(f, &mut 0, linebpos);
+            let chpos =
+                pos.to_u32() - self.calc_extra_bytes(f, &mut prev_extra_bytes, &mut ch_start, pos);
+            let linechpos = linebpos.to_u32()
+                - self.calc_extra_bytes(
+                    f,
+                    &mut line_prev_extra_bytes,
+                    &mut line_ch_start,
+                    linebpos,
+                );
 
             let mut col = max(chpos, linechpos) - min(chpos, linechpos);