fix(compiler): Correct mutation bug in dead branch optimization - #2400
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spotandjake wants to merge 1 commit into
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fix(compiler): Correct mutation bug in dead branch optimization#2400spotandjake wants to merge 1 commit into
spotandjake wants to merge 1 commit into
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This pr corrects a small bug related to our dead branch optimization. Programs that contained a `let` bind inside of constant `if` statement, inside of another `let mut` bind would lose the mut_flag of the outer binding. This pr corrects that by properly propagating the mut_flag. Issue: grain-lang#2399
spotandjake
requested review from
alex-snezhko,
marcusroberts,
ospencer,
peblair and
phated
as code owners
August 16, 2026 02:12
Kara-Zor-El
suggested changes
Aug 16, 2026
Comment on lines
53
to
62
| @@ -59,7 +58,7 @@ module BranchArg: Anf_mapper.MapArgument = { | |||
| recursive, | |||
| mutable_, | |||
| binds, | |||
| relinearize(id, global, body, cont), | |||
| relinearize(id, global, body, mut_flag, cont), | |||
| ), | |||
Contributor
There was a problem hiding this comment.
Tested and it seems to fix the issue reported. However, turns out that there's another where:
let mut x = if (true) {
let mut y = 1
y
} else {
2
}
let z = () => x
x = 3
print(z())
produces 1 instead of 3.
This should fix be:
- | AELet(global, recursive, mutable_, binds, body) => {
+ | AELet(inner_global, recursive, mutable_, binds, body) => {
...a,
anf_desc:
AELet(
- global,
+ inner_global,
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This pr corrects a small bug related to our dead branch optimization.
Programs that contained a
letbind inside of constantifstatement, inside of anotherlet mutbind would lose the mut_flag of the outer binding.This pr corrects that by properly propagating the mut_flag.
Issue: #2399
Thanks to @Kara-Zor-El for the help.