Segfault when using unsafe vector operations

I was working on some benchmarks and I ran into this issue. It's actually very difficult to reproduce; changing the attached file in different ways makes the bug go away quite quickly. But with the attached file, I regularly get a internal error: evacuate: strange closure type 0 message, though on more complicated versions of the code I was working on, the integer would change for each run.

Trac metadata

Trac field	Value
Version	7.8.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
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changed weight to 5

added Tbug Trac import labels

Attached file vector-bug.hs ($1013).

closed

slice is non-copying, and so unsafeFreeze on a slice freezes the underlying vector. You can't then later write to the mutable vector that has been frozen without confusing the GC.

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedInvalid

Hmm, this sounds quite restrictive. So, do I understand correctly that there is no way to freeze a part of a mutable vector? Even if I know that that part will not change?

Can you point to a relevant description of this part of the GC? I'd like to understand the situation better to figure out what kind of work-around is possible (if at all).

Thank you!

Attached file vector-bug-fixed.hs ($1014).

I've attached a new file, vector-bug-fixed.hs, which (inspired by some attoparsec code) thaws an immutable vector before writing to it, which seems to address the issue. I have not investigated the performance impact of this.

added runtime crash label

added Pnormal label