Use non-nullable ref.cast for non-nullable input (#5335)

We switched from emitting the legacy `ref.cast_static` instruction to emitting
`ref.cast null` in #5331, but that wasn't quite correct. The legacy instruction
had polymorphic typing so that its output type was nullable if and only if its
input type was nullable. In contrast, `ref.cast null` always has a a nullable
output type.

Fix our output by instead emitting non-nullable `ref.cast` if the output should
be non-nullable. Parse `ref.cast` in binary and text forms as well. Since the IR
can only represent the legacy polymorphic semantics, disallow unsupported casts
from nullable to non-nullable references or vice versa for now.

0 files changed, 0 insertions, 0 deletions