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