The forward transition cache in Shape uses WeakPtr<Shape> to learn when
a cached transition has been garbage collected.
When running in zombification mode, we have to explicitly revoke any
outstanding WeakPtrs to a Shape when it becomes a zombie. That ensures
that it gets pruned from transition caches.
We were doing a *lot* of string-to-int conversion while creating a new
global object. This happened because Object::put() would try to convert
the property name (string) to an integer to see if it refers to an
indexed property.
Sidestep this issue by using PropertyName for the CommonPropertyNames
struct on VM (vm.names.foo), and giving PropertyName a flag that tells
us whether it's a string that *may be* a number.
All CommonPropertyNames are set up so they are known to not be numbers.
Before this patch, every shape would permanently remember every other
shape it had ever transitioned to. This could lead to pathological
accumulation of unused shape objects in some cases.
Fix this by using WeakPtr instead of a strongly visited Shape* in the
the forward transition chain map. This means that we will now miss out
on some shape sharing opportunities, but since this is not required
for correctness it doesn't matter.
Note that the backward transition chain is still strongly cached,
as it's necessary for the reification of property tables.
An interesting future optimization could be to allow property tables
to get garbage collected (by detaching them from the shape object)
and then reconstituted from the backwards transition chain (if needed.)
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
