swift

e1006c62 - [move-only] Add copyable_to_moveonlywrapper and moveonlywrapper_to_copyable instructions.

[move-only] Add copyable_to_moveonlywrapper and moveonlywrapper_to_copyable instructions. These instructions have the following attributes: 1. copyably_to_moveonlywrapper takes in a 'T' and maps it to a '@moveOnly T'. This is semantically used when initializing a new moveOnly binding from a copyable value. It semantically destroys its input @owned value and returns a brand new independent @owned @moveOnly value. It also is used to convert a trivial copyable value with type 'Trivial' into an owned non-trivial value of type '@moveOnly Trivial'. If one thinks of '@moveOnly' as a monad, this is how one injects a copyable value into the move only space. 2. moveonlywrapper_to_copyable takes in a '@moveOnly T' and produces a new 'T' value. This is a 'forwarding' instruction where at parse time, we only allow for one to choose it to be [owned] or [guaranteed]. * moveonlywrapper_to_copyable [owned] is used to signal the end of lifetime of the '@moveOnly' wrapper. SILGen inserts these when ever a move only value has its ownership passed to a situation where a copyable value is needed. Since it is consuming, we know that the no implicit copy checker will ensure that if we need a copy for it, the program will emit a diagnostic. * moveonlywrapper_to_copyable [guaranteed] is used to pass a @moveOnly T value as a copyable guaranteed parameter with type 'T' to a function. In the case of using no-implicit-copy checking this is always fine since no-implicit-copy is a local pattern. This would be an error when performing no escape checking. Importantly, this instruction also is where in the case of an @moveOnly trivial type, we convert from the non-trivial representation to the trivial representation. Some important notes: 1. In a forthcoming commit, I am going to rebase the no implicit copy checker on top of these instructions. By using '@moveOnly' in the type system, we can ensure that later in the SIL pipeline, we can have optimizations easily ignore the code. 2. Be aware of is that due to SILGen only emitting '@moveOnly T' along immediate accesses to the variable and always converts to a copyable representation when calling other code, we can simply eliminate from the IR all moveonly-ness from the IR using a lowering pass (that I am going to upstream). In the evil scheme we are accomplishing here, we perform lowering of trivial values right after ownership lowering and before diagnostics to simplify the pipeline. On another note, I also fixed a few things in SILParsing around getASTType() vs getRawASTType().