How to get to 100% precise tracing GC?

[Ola Fosheim Grøstad]

On Saturday, 14 November 2020 at 12:39:25 UTC, Rainer Schuetze 
wrote:
>
> On 12/11/2020 09:43, Ola Fosheim Grøstad wrote:
> These are not a problem with the current implementation, 
> because precise scanning is not done by the pointer type, but 
> the type used for the allocation. Pointer types don't contain 
> enough information for polymorphic classes or pointers to 
> fields of structs.

The docs says that one can allocate arrays of void pointers to 
emplace in, which makes the collector less precise though. If 
destuctors on structs arent called then it should be ok to only 
keep the struct field alive?

> It's mostly untyped allocations. For example delegate closures 
> don't come with type information.

If the gc involves a modified compiler then this could change,

> Another problem is precise scanning of the stack. There is no 
> info generated by the compiler. It could be implemented similar 
> to exception unwinding data, but would have to be more precise 
> as a thread can get suspended by a GC at any instruction.

Maybe the LLVM GC infrastucture can help? I haven't looked on the 
details, but that seems like a possibility.