I was originally hoping to reuse mark_must_check for multiple types of checkers.
In practice, this is not what happened... so giving it a name specifically to do
with non copyable types makes more sense and makes the code clearer.
Just a pure rename.
Vars of such types should be given lexical `alloc_stack`s by
`AllocBoxToStack` which requires that the `alloc_box` insts formed for
them have an associated borrow scope which in turn requires that type
lowering for move only structs and enums have their lexical bits set.
rdar://110901430
Code can only locally interact with a mutable memory location within a
formal access, and is only responsible for maintaining its invariants
during that access, so the move-only address checker does not need to,
and should not, observe operations that occur outside of the access
marked with the `mark_must_check` instruction. And for immutable
memory locations, although there are no explicit formal accesses, that's
because every access must be read-only, so although individual
accesses are not delimited, they are all compatible as far as
move-only checking is concerned. So we can back out the changes to SILGen
to re-project a memory location from its origin on every access, a
change which breaks invariants assumed by other SIL passes.
the main things still left behind the experimental flag(s) are
- move-only classes (guarded by MoveOnlyClasses feature)
- noimplicitcopy
- the _borrow operator
Some notes:
1. This ensures that if we capture them, we just capture the box by reference.
2. We are still using the old incorrect semantics for captures. I am doing this
so I can bring this up in separate easy to understand patches all of which
pass all of the moveonly tests.
3. Most of the test edits are due to small differences in error messages in
between the object and address checker.
4. I had to add a little support to the move only address checker for a small
pattern that doesn't occur with vars but do es occur for lets when we codegen
like this, specifically around enums. The pattern is we perform a load_borrow
and then copy_value and then use the result of the copy_value. Rather than fight
SILGen pattern I introduced a small canonicalization into the address checker which
transforms that pattern into a load [copy] + begin_borrow to restore the codegen
to a pattern the checker expects.
5. I left noimplicitcopy alone for now. But we should come back around and fix
it in a similar way. I just did not have time to do so.
This fits the name of the check better. The reason I am doing this renaming is
b/c I am going to add a nonconsumable but assignable check for
global_addr/ref_element_addr/captures with var semantics.
