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Mofei Zhang
314a5cfca5
---
This PR adds LoadContext and StoreContext to handle reading and writing to
context variables.
A context variable is any variable that is declared within a Forget-compiled
function and reassigned within a closure. Conceptually, we want to treat these
variables as attributes of a `EnvironmentContext` variable (as most javascript
VMs do).
- context variables currently do not participate in type inference (i.e. we do
not produce type equations for loads from context variables). In the future, we
can try typing this as `Phi(assignment1Type, assignment2Type, ...)`.
- context variables are always treated as `Effect.Mutable`.
- context variables do not participate in SSA, or certain optimizing passes
(e.g. dead code elimination, constant propagation, etc).
There is some still follow ups:
- From my understanding, we should introduce a `DeclareContext` instruction.
- currently, declaring a context variable (without initializing it) is broken.
This is because the declaration lowers to `DeclareLocal`, which assumes it is
storing to a SSA-fied identifier.
```js
let x;
x = 4;
() => { x = {}; };
```
- DeclareContext will also make some initialization logic easier. In this PR, I
added some hack-y code to handle initializing effects / mutable ranges / other
inference state for the first StoreContext.
- Handle or bail on stores to context variables through destructuring assignment
-
~~Next PR:~~
- ~~Change closures to track reassigned identifiers (to extend mutable range of
primitives)~~