forget
Forget only the BOXED_KIND register definitions for this synonym. Keep the synonym around in all circumstances, even if there are no remaining definitions. Also, do not alter the synonym's restriction.
This mechanism is used by L2_MAKE_IMMUTABLE to ensure registers holding the mutable form aren't still accessible, which under code motion could lead to the makeImmutable being bypassed, or a value being incorrectly modified in place prior to becoming immutable.
Parameters
synonym
The L2Synonym for which to forget all boxed definitions.