Faster source map generation #2062
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Excellent work @mourner, I left a couple of comments re array allocation that may or may not have any tangible effect.
| @@ -49,23 +48,20 @@ class Link { | |||
| const sourcesContent: string[] = []; | |||
| const names: string[] = []; | |||
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| const mappings = this.mappings.map(line => { | |||
| const mappings = []; | |||
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It may help performance to initialize the array length there? new Array(this.mappings.length)
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No, V8 is very good at growing arrays. Besides, new Array(length) creates a sparse array (all items are undefined), which is a perf antipattern.
| const mappings = this.mappings.map(line => { | ||
| const mappings = []; | ||
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| for (const line of this.mappings) { | ||
| const tracedLine: SourceMapSegmentVector[] = []; |
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And possibly here as well, although it may not make that much of a difference, but at least avoids possible reallocation cost.
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In my experience building computational geometry libraries that process arrays with millions of items, it's safe to initialize an empty array without worrying about performance. The only case where you want (and forced to) to preallocate is with typed arrays.
I also prefer for ... of over forEach/map because it avoids new closures. TypeScript converts them into simple for loops.
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TypeScript converts them into simple for loops
Ah right, I stumbled about this once but forgot later. Very nice, so there is no performance overhead checking the array iterator.
Removes redundant source map encoding roundtrip between
magic-stringandrollup, which should speed up source map generation by up to 40%. For example, Mapbox GL JS bundle takes ~400-500ms less time after this PR.Also contains some minor code clean up in
collapseSourcemaps.tsthat I forgot to commit separately.Fixes #2061. cc @guybedford @lukastaegert