Opportunity: Improve compiler performance by avoiding property accesses

[evanw]

TypeScript Version: 3.9.5

Search Terms: compiler performance namespace run-time property access

Code

I have looked into TypeScript compiler performance in the past and I've always wondered why the TypeScript compiler code uses namespaces heavily, since run-time property accesses are slower than statically-bound identifiers in JavaScript.

I finally got around to writing a proof of concept:

let fs = require('fs')
let tscPath = __dirname + '/node_modules/typescript/lib/tsc.js'
let tsc = fs.readFileSync(tscPath, 'utf8')

let vars = new Set()
tsc = tsc.replace(/\bts\.(\w+)/gm, (_, id) => {
  id = `ts_${id}`
  vars.add(id)
  return id
})
tsc = `var ${[...vars].join(',\n  ')};\n${tsc}`

fs.writeFileSync(tscPath, tsc)

This post-processes tsc.js to convert run-time property accesses into statically-bound identifiers. I ran this on the Rome code as a benchmark of a reasonably-large TypeScript code base and got a noticeable speed boost:

	Before	After	Difference
Time to run tsc.js	29.5s	27.5s	2s faster

Each time is the best of 5 runs, and each run was time node node_modules/typescript/lib/tsc.js -noEmit -project rome.

The TypeScript compiler is leaving some performance on the table by using run-time property accesses where it could use statically-bound identifiers instead. I'm sure you are using namespaces for code organization for good reasons, but it does come at a cost. An alternative to namespaces that might have less performance overhead could be to use ES6 modules and bundler, for example.

I'm posting this issue because I think the results of this experiment are interesting. The issue tracker seemed like the most appropriate place to post this. Feel free to just close this issue if you'd like.

[steakscience]

Gotta go fast!

[DanielRosenwasser]

@amcasey @ahejlsberg @weswigham, it'd be nice to see if https://github.com/microsoft/TypeScript/issues/38510 gives any observable performance boost.

[mohsen1]

https://github.com/microsoft/TypeScript/pull/35561 is trying to use modules instead of namespaces

[DanielRosenwasser]

Whoops, that's the right link, thanks @mohsen1.

[amcasey]

Cool! @mohsen1 I assume that if you run the tests in the other order (i.e. no-namespaces first), you get the same result? I've gotten into the habit of discarding the first run whenever I do perf testing to minimize the effects of disk caching.

[amcasey]

I did my own run against ant-design and saw a ~5% reduction in total compilation time. Pretty impressive. I have yet to compare the compiler output (i.e. to confirm it hasn't changed).

[DanielRosenwasser]

This should go hand-in-hand with the modules work for 4.6. I would hope that a bundler with scope hoisting will allow us to avoid property accesses/function calls that serve no purpose.

[jakebailey]

For those following this issue, #51387 will fix this (though it was later than 4.6 😄).