Add GlobalSubtyping pass (#4306)

This specializes the fields of structs based on the types written to them. That is,
if a field is of type A but in practice we always write some subtype B to it
then we can change the type of the field to that.

On j2wasm this manages to improve at least one field in 2% of types. Not a
large amount, but this does lead to further benefits in later opts (e.g. about a third
of the improvements are to turn a field non-nullable).

0 files changed, 0 insertions, 0 deletions