feat(minifier): fold iife arrow functions in call expressions

[armano2]

Improve folding of iife

details

• check all CallExpression if they can be collapsed
  eg. passed as arguments or in assignment
• functions without arguments and body can be collapsed to to void 0
(() => {})() or (function () { })() to void 0
• with one statement and without return will be collapsed to (c, void 0)
(() => { fn() })() to (fn(), void 0)
• FunctionExpression is not supported
  (function () { ... })()

notes

• function with arguments could be handled by first in-lining them
• empty function with arguments could be also if all arguments do not have defaults
• we should consider optimizing function definitions by removing not used arguments
• initially i added support for FunctionExpression but there is no way to track this usage, and thus we are unable to minify this

change example

code

{
  let AOT = true;
  const getAOT = /* @__NO_SIDE_EFFECTS__ */ () => AOT;
  const fn = getAOT() ? () => console.log("Hi") : () => {};
  fn();
}

currently is collapsed to

(/* @__PURE__ */ /* @__NO_SIDE_EFFECTS__ */ (() => !0)() ? () => console.log("Hi") : () => {})();

and with this change

console.log('Hi');

---

from what i can see @sapphi-red worked on this file

[codspeed-hq]

CodSpeed Performance Report

Merging #16477 will not alter performance

_{Comparing armano2:fix/remove-unused-iife-expressions (2199e89) with main (f8abd56)}

Summary

✅ 38 untouched
⏩ 7 skipped¹

Footnotes

1. 7 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[armano2]

i noticed a bug in this implementation
this is not handled inside FunctionExpression, i was hoping to used references, but it looks like they this is not defined as such

[armano2]

@sapphi-red thank you for running tests issues reported by it should be fixed

is there any guide what tests we have to run localy?

[sapphi-red]

Running the tests ran by the CI should be fine.

[armano2]

Conformance tests should be ok, its interesting that

• Object.getPrototypeOf(async function () {}()) = Promise
• Object.getPrototypeOf(async function* () {}()) = AsyncGenerator
• Object.getPrototypeOf(async function* () {}()) = Generator

i'm not sure tho if this is this is the best way to check if we can collapse pife/iife by evaluating ancesotrs and checking if they are blocks

i did some cleanup and sorry for keeping it open while it was still WIP

[armano2]

if you find some time, review would be appreciated

[armano2]

i was thinking abot expanding this logic to functions with arguments, but that is going to come as separate pr

[sapphi-red]

Thank you!

[sapphi-red]

We cannot close #13651 as it requires more optimizations.
For example, I think this PR won't fix cases like: Oxc, SWC

[armano2]

We cannot close #13651 as it requires more optimizations

this is related to what i discovered in #16964, cross scope variables that are not static are never in-lined