facebookarchive/prepack

Fuse adjacent JOIN_GENERATORS with same path condition

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#2,565 opened on Sep 22, 2018

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Instant Renderenhancementhelp wantedlevel 2 (easy)

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Description

This...

let x = __abstract("boolean", "(x)");
if (x) console.log("Hello");
if (x) console.log(" World");

currently prepacks to

(function () {
  var _0 = x;

  if (_0) {
    console.log("Hello");
  }

  if (_0) {
    console.log(" World");
  }
})();

but should Prepack to

(function () {
  var _0 = x;

  if (_0) {
    console.log("Hello");
    console.log(" World");
  }
})();

(Seen arising from actual product code.)

Contributor guide

Research direction
Look at the Prepack IR and find where JOIN GENERATORS are generated and fused.
Tech stack
javascript
Domain
compilers
Issue type
Bug
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.
Half day
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
GitJavaScript
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50