For example:
```
%1 = begin_borrow %0
%2 = br bb1(%1, %1)
bb1(%3 : @reborrow @guaranteed, %4: @guaranteed):
// %4 is a guaranteed forwarding phi without any forwarding instructions between the begin_borrow and the incoming value.
```
Also improve the comments
Compute, update and handle borrowed-from instruction in various utilities and passes.
Also, used borrowed-from to simplify `gatherBorrowIntroducers` and `gatherEnclosingValues`.
Replace those utilities by `Value.getBorrowIntroducers` and `Value.getEnclosingValues`, which return a lazily computed Sequence of borrowed/enclosing values.
Add PartialApplyInst.hasNoescapeCapture
Add PartialApplyInst.mayEscape
Refactor DiagnoseInvalidEscapingCaptures. This may change functionality because tuples containing a noescape closure are now correctly recognized. Although I'm not sure such tupes can ever be captured directly.
Compute the live range for the borrow scopes of a guaranteed value. This returns a separate instruction range for
each of the value's borrow introducers. Unioning those ranges would be incorrect. We typically want their
intersection.
This avoids a lot of confusion because the callers expect this type. Fixing it just required some redundancy and
bridging in the EnclosigValues implementation.
Key APIs necessary for using OSSA.
- BorrowingInstruction
- BeginBorrowValue
- scopeEndingOperands
- BorrowIntroducers
- EnclosingValues
- innerAdjacentPhis
These need to be complete to be correct.
