Reproduce performance regression of terser --compress collapse_vars=true on module with 1,000 var defs and complex object values.
yarn or npm install
./node_modules/.bin/terser --compress collapse_vars=true --output output.js index.js
This will produce a tree-shaken output bundle in about 30 seconds, depending on hardware.
Uses a current version of terser, the performance of which--in this scenario--is similar to uglify-es@3.3.9, which is the package version that webpack 4.11.0 depends upon.
./node_modules/.bin/terser --compress collapse_vars=false --output output.js index.jsThis will produce a tree-shaken output bundle in <1 second, depending on hardware.
Same version of terser.
./node_modules/.bin/uglifyjs --compress collapse_vars=true --output output.js index.jsThis will produce a tree-shaken output bundle in <1 second, depending on hardware.
This uses uglify-js@2.8.29, which is the package version that webpack 3.12.0 depends upon.
Something has changed in the processing of the collapse_vars option such that the performance in this scenario has slowed down by some 60x. I have seen real-world build times up to 80 seconds under uglify-es@3.3.9 that would have taken 0.5 seconds under uglify-js@2.8.29.
This repro is designed to simulate a bundle produced by webpack after importing icon objects from Font Awesome 5 icon packages. Our icon packages each contain hundreds of var defs with object assignments where each object represents an icon's SVG definition. Users expect to be able to import a subset of icons from multiple icon packs and have the unused icons eliminated from the final production bundles. They also expect a fast build time.
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