Structs

A stack frame.
What we store about a frame in an interpreter backtrace.
State of a local variable including a memoized layout
SpanGuard 🔒

Enums

Current value of a local variable
Unwind information.

Functions

Use the already known layout if given (but sanity check in debug mode), or compute the layout.
Test if it is valid for a MIR assignment to assign src-typed place to dest-typed value. This test should be symmetric, as it is primarily about layout compatibility.