SourceMap performance issue

[JSerFeng]

Describe the bug

Input: A large bundle generated by webpack.
minify: 2s without sourcemap, and 20s with sourcemap

When minify and transform very large file, enable source map will have huge impact on performance, very huge impact that sometimes even slower than terser.

Reprod repo here

Config

No response

Playground link

As the file is too large, I think we better download the reprod repo locally

Expected behavior

SourceMap should be slow to generate, but shouldn't be this slow

Actual behavior

2s without sourcemap
20s with sourcemap

Version

1.3.14

Additional context

No response

[JSerFeng]

Additional information.
MacOs Monterey 12.1
CPU: 2.6 GHz Intel Core i7
32 GB mem

[willstott101]

I can repro this with @swc/core but not a locally built swc...

will@will-ubuntu:~/repos/others/swc_sourcemap_perf_issue$ npm run bench

> perf_issue@1.0.0 bench
> esno bench.ts

swc: 1.861s
terser: 23.946s
swc sourcemap: 24.095s
terser sourcemap: 24.888s

will@will-ubuntu:~/repos/others/swc_sourcemap_perf_issue$ npm i ../swc/swc-core-1.3.19.tgz 
...

will@will-ubuntu:~/repos/others/swc_sourcemap_perf_issue$ npm run bench

> perf_issue@1.0.0 bench
> esno bench.ts

swc: 8.311s
terser: 24.047s
swc sourcemap: 8.592s
terser sourcemap: 24.509s

Not sure I can dig more without some additions to CONTRIBUTING.md about building the node package. Evidently I am doing something differently (npm i && npm run build && npm pack 🤷)

I did dig in pure-rust though... and as far as I got was seeing that serializing sourcemaps isn't benched in the minify benchmark.

swc/crates/swc/benches/minify.rs

Line 49 in 48bbebf

source_map: Default::default(),

should be BoolOrDataConfig::from_bool(true) I reckon.

Once it is... then the benchmark is massively slowed down (like, x10 slower or worse) by:

swc/crates/swc_common/src/source_map.rs

Line 974 in 48bbebf

debug!("{}-byte char at {:?}", mbc.bytes, mbc.pos);

Commenting that out or even using NODE_LOG=off makes the benchmark reasonable again though. So unless I can repro the @swc/core result with a local build I think I am out of ideas for resolving.

[hardfist]

@kdy1 It seems that if the sourcefile contains lots chinese characters it will have serious performance problems, most of the time are spent on

compared to asci-only file

when I remove all the chinese character from code, the sourcemap generation cost reduce from 37s to 1s

[kdy1]

@hardfist Can you share a test input?

[hardfist]

@kdy1 https://github.com/hardfist/swc-minify-perf/blob/main/BizCharts.js

[kdy1]

Let's see if #6523 fixes it.
Performance issue is fixed, but I'm not sure if all souremap tests will pass

[JSerFeng]

Thanks !

[swc-bot]

This closed issue has been automatically locked because it had no new activity for a month. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.