Compress: Dead code elimination doesn't work with const value return functions

[schardev]

Describe the bug

Ref: vercel/next.js#78955

I noticed that dead code elimination doesn’t behave as expected when using functions that return constant values, for example, when checking process.env.NODE_ENV.

Here’s a simple example:

const isDev = () => false;

function Foo() {
    let value: string = 'default';

    // This conditional check will NOT be removed by SWC, even when isDev is set to false.
    if (isDev()) value = "dev value"

    return value;
}

let x = <Foo />

console.log(x)

Output:

"use strict";
const isDev = ()=>!1;
console.log(React.createElement(function() {
    let value = 'default';
    return isDev() && (value = "dev value"), value;
}, null));

The above might work if you move the checks outside of the component (e.g., at module scope), the DCE kicks in properly.

Input code

const isDev = () => false;

function Foo() {
    let value: string = 'default';
    if (isDev()) value = "dev value"
    return value;
}

let x = <Foo />

console.log(x)

Config

Link to the code that reproduces this issue

https://play.swc.rs/?version=1.11.25-nightly-20250505.1&code=H4sIAAAAAAAAAzWPMW7DMAxFd53iI0tsoLD3pMlUdEyXXMCW6FitIhai5LgIevfSNsqBAMnPz0fLUTK8vNGEE6oapzOGLggdjRlKtNlzxDuzTp4GGoEypi4UOkBy8vGma3tHQ1dC3uvSomlbXEcvsBydXxy6ADuS%2FcLDh4DLxxU9IdGdJ3Lof3ChOTefAldWxzwS%2BuKDw3diSyIv%2F7Y0UcRj1LQh6xFRoMwbdLPq%2FIBqHVd1vbEq486pfC12G2SiXFLcWkfza8zy2azKV30X7dkYxRcO1AS%2BVXP9B9j6spIqAQAA&config=H4sIAAAAAAAAA32UzW7bMAzH732KwOcdimDoYQ%2Bw255BUCzKUSeLhkilMYq8%2B2hZSbOGzs3mjx8SSf0%2FX3a77p367tfuUz7lZ7KZIN%2F%2BxUJzYnsWS8fzBNTnMHH340qZFsS5QLVcVtCxzQPwEgS0f93%2FbAFdRCQQs7eRoNnGkIKf70v2OE4ZiO5sYpWUZYTE9H98Yxk%2FqJ3kzn5AjGDTE2IsmZAYBsha4h5jtBOBOdmsZFlOanMg1EossDA4M2WcVJ5c4IBJaj5SB9aZHh0oKGToOZxAC5NaEpZIrqfcp2IHhzIMdczfouFkY7Gs1IRzHYmcVsl6xEBsfElaC1e40YMVtuZ%2BjwzeZOCS02PcO4a0MZO%2FANKBaImSHUHLWz287NNWtH8aGZKXleVZ4bLf2i0TDNJUE4JXOrt0BjIHbZoZXOlh6WyvHafhjfZRcGDAe9kVJTV9BO6PWtHlnaNXgMzXem2rVmBur3CDLw%2FiCf4tt2R9wZrHaPm4TWkeDxifFBiBj%2BieOMgoGLdxFpU4T9u8JAeyGuBUl0IVPIqAPABGE6tePuyGPA%2FJaIaIB1UmJtnzOsT9azNebuI82jR8qcAq0C%2FNoRvRlQqb8i9TXwX7rftyumrz7TpdoD%2FXyCr7l3%2FcAhU5RQYAAA%3D%3D

SWC Info output

No response

Expected behavior

SWC should be able to remove code blocks/function with constant conditions/return values.

Actual behavior

No response

Version

1.11.25-nightly-20250505.1

Additional context

No response