Refactor assignment handling #1740
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* Re-add tests cases that were previously removed
kzc
reviewed
Nov 18, 2017
| @@ -0,0 +1,3 @@ | |||
| module.exports = { | |||
| description: 'does not fail fo cyclic assignments' | |||
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This pull requests profoundly improves rollup performance and will probably
It does so by radically simplifying how reassignments are handled.
Previously, reassigning a variable or a member of a variable would store the new assignment together with the variable and check all applicable assignments when determining if an operation on the variable has a relevant effect and should be retained in the bundle. This could lead to an exponential performance degradation in certain scenarios which could cause the impression that "rollup hangs".
Now for each variable we only track which keys have been reassigned. Once a variable or a relevant key is reassigned, we assume we no longer know what is assigned at that key and treat it as such when detecting effects.
This massively improves performance while keeping up the quality of the algorithm in most relevant situations. If you only use assignments inside
const variable = …statements (and use object literals to assign object members, e.g.const variable1 = {y: variable2}) the algorithm will be able to track this properly with regard to treeshaking.