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Joe Savona
d2e5c31fc6
This demonstrates a situation we don't handle well today. The basic structure is
that you have some variable defined at the top level, then some control flow
like if/switch where _all_ branches reassign the variable, then some code after
that references the resulting phi node:
```javascript
let x1;
// ... mutate/read x1
if (cond) {
x2 = {};
} else {
x3 = {};
}
x4 = phi(x2, x3);
```
We currently group x3, x3, and x4 into a scope together, but note that...there's
no `let` declaration for any of those! This means that it looks like the scope
for x2 and x3 start in the consequent/alternate, but the true scope spans from
before-after the if. I'm inclined to say that LeaveSSA should run _before_ scope
analysis, and produce something like the following in this case:
```javascript
let x1;
// ...mutate/read x1
let x2; // new variable declaration for the new version of x
if (cond) {
x2 = {};
} else {
x2 = {};
}
x2;
```
This then allows us to construct a correct range for x2, which starts in the
other block.