[Wasm GC] GlobalTypeOptimization: Remove fields from end based on subtypes (#4553)

Previously we'd remove a field from a type if that field has no uses in any
sub- or super-type. In that case we'd remove it from all the types at once.
However, there is a case where we can remove a field only from a parent
but not from its children, if the field is at the end: if A has fields {x, y, z}
and its subtype B has fields {x, y, z, w}, and A pointers only access
field y while B pointers access all the fields, then we can remove z
from A. Removing it from the end is safe, and then B will not only add
w as it did before but also add z. Note that we cannot remove x,
because it is not at the end: removing it from just A but not B would
shift the indexes, making them incompatible.

0 files changed, 0 insertions, 0 deletions