**Description:**
This issue is more severe than I originally thought. It raises not in
array indexing, but in function calls and property mutation. We should
treat all function arguments as potentially be property mutated,
otherwise following example
```js
class A {
a = 1
toString() {
return this.a
}
}
const a = new A()
function foo(x) {
x.a++
}
const b = a + 1
foo(a)
console.log(b)
```
would be error(It should log 2, but logs 3 after compress).
As the result, massive regressions is unavoidable, since some of these
optimizations may indeed cause error. Part of them can be mitigated with
following optimization -- allow inline of ident even if its original
value is mutated. Consider
```js
export function foo(x) {
const y = x
x.a = 1
y.b = 2
}
```
If x is a primitive value, all mutations to its properties are ignored;
if x is a object, then y refers to the same object no matter what
mutation is performed.
And there's still room for more, currently following code
```js
export function foo(x) {
const y = Math.floor(x);
g(y);
}
```
But I'd rather do it in a separate PR.
**Related issue:**
- Closes#7402.
**Description:**
And optimize the following situation
```js
export function genElement(el, state) {
if ('slot' === el.tag) return el1 = el, genChildren(el1);
if (el.component) {
var el1
return 999;
}
}
```
which rarely happens in hand written JS, but is often generated by swc merge variable pass.
**Description:**
This is the groundwork for a parallel analyzer. This PR fixes the ordering issue of the analyzer so that the analyzer works identically regardless of the visit order. This patch contains some improvements because previously, we mixed `.and_modify()` and `.or_default()`.
**Description:**
This PR improves the alias analyzer by distinguishing call and reference, thus reducing the number of identifiers.
---
Co-authored-by: Justin Ridgewell <justin@ridgewell.name>
**Description:**
As we are not using the return value of the function, we can call `ignore_return_value` on the argument of the return statements of IIFE.
**Description:**
This PR renames `CloningMultiReplacer` to `Finalizer` and makes it handle the removal of unused variables. Also, this PR improves the sequential inliner so we can drop variables within a single pass.
**Description:**
We had two passes for joining variables. This PR removes one in the full optimizer, which is wrong.
**Related issue:**
- Closes https://github.com/swc-project/swc/issues/5989.
**Description:**
Invoke DCE only before the first compression. I verified that this patch does not affect the compression rate of the real-world inputs greatly.
