facebookarchive/prepack

Fuse adjacent JOIN_GENERATORS with same path condition

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#2,565 创建于 2018年9月22日

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 (0 评论) (0 反应) (0 负责人)JavaScript (14,268 star) (520 fork)batch import
Instant Renderenhancementhelp wantedlevel 2 (easy)

描述

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.)

贡献者指南

技术栈
javascript
领域
performance
议题类型
performance
难度面向新贡献者的预计实现难度，1 表示很小改动，5 表示专家级工作。
3
预计时间有经验贡献者完成调查、实现、测试并准备 pull request 的粗略时间范围。
under 1 hour
活动状态议题当前的可参与程度：新鲜、活跃、陈旧、阻塞或等待维护者输入。
stale
清晰度议题是否清楚说明期望改动、验收标准和下一步。
clear
前置要求
basic understanding of JavaScriptfamiliarity with Prepack internals
新手友好度1-100 的估计分数，表示该议题对首次贡献者的友好程度。
60
研究方向
Look at the Prepack source code, likely in src/ or lib/ directories, for how JOIN GENERATORS are handled. Search for the specific optimization pattern where adjacent JOIN GENERATORS with the same condition are fused. The issue shows a clear before/after transformation, so the fix involves modifying the logic that emits these generators to merge consecutive ones when the condition is identical. Examine existing tests for similar fusion optimizations to ensure correctness. No linked PRs or comments provide further guidance.