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Mofei Zhang
4aa60d32b9
---
Previously, our logic was something like:
```js
fixed-point-loop {
foreach instruction {
mark referenced identifiers
// assume that usages are always visited before declarations
if (instruction is decl) {
prune(instruction);
}
}
foreach instruction {
if not referenced {
delete(instruction);
}
}
```
This contained a bug, as not all usages of a variable are guaranteed to be
visited before its declaration.
```js
// input
let x = 0;
while(x < 10) {
x += 2;
}
return x;
// hir
entry:
x$0 = 0
goto loop-test
loop-test:
x$1 = phi(x$0, x$2)
if ... goto loop-body else goto fallthrough
loop-body:
x$2 = x$1 ...
goto loop-test
fallthrough:
return x$1
```
In this example,`x$2` is defined by `loop-body` and used by `loop-test`.
Similarly, `x$1` is defined by `loop-test` and used by `loop-body`.
---
TODO: trying to come up with more test fixtures