facebookarchive/prepack

Prepack emits if-statements with no consequent or alternate code

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#2,220 opened on Jul 6, 2018

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 (3 comments) (0 reactions) (0 assignees)JavaScript (520 forks)batch import
Instant Renderenhancementhelp wantedlevel 1 (super easy)priority: lowserializer

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Description

This

(function () {
  let n = global.__abstract ? __abstract("number", "23") : 23;
  if (n === 42) {
    let d = Date.now(); // dead pure generator entry
  }
})();

prepacks to

if (23 === 42) {}

which is obviously suboptimal.

During its fixpoint computation, the visitor should not visit the condition until at least one generator entry cannot be omitted.

Contributor guide

Research direction
Examine the fixpoint computation in Prepack's abstract interpreter and modify the visitor to delay visiting the condition until at least one generator entry cannot be omitted.
Tech stack
javascript
Domain
developer experience
Issue type
Performance
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
JavaScript
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50