1866002 - Investigate adding common infrastructure for handling tagged pointers

Status: NEW

(Core :: JavaScript: GC, task, P3)

Description

[Jon Coppeard (:jonco)]

Currently there are at least the following tagged pointer types which use the low bits of the pointer to store some extra information: jsid, GCCellPtr, CalleeToken, TaggedProto, wasm::AnyRef

We could perhaps common up the infrastructure for implementing these and make it easier to add new kinds of tagged pointer in the future. For example, we might add a base class and make our tracing and barrier code handle subtypes automatically.

Possibly the concrete tagged pointer type would have to provide a way to tell the GC the kind of pointer contained, or possibly these are rare enough that we could get away with working it out in other ways.

Comment 1

[Iain Ireland [:iain]]

I wrote up a case study for one case where I couldn't figure out how to make the current machinery work cleanly for bug 1868857. I'll put up WIP patches there.