[move-function] A few additions #40528
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… to match move checking of address only parameters.
…nts.
These are verified like a var except that the parameter will have an implicit
read use on all function exit terminators. This ensures that if a programmer
moves a value out of the inout parameter, a new value must be assigned before
function exit. This is important since otherwise the convention would be
invalidated. Example:
```
func f(_ x: inout T) {
// Move a value out of x. x does not have a value within it anymore.
let value = _move(x)
} // So we emit an error saying there is a use here since an inout must have
// a valid object within it upon function exit due to convention guarantees.
```
As an added side-effect of this, one can now use move as on self in mutating
contexts. Thus one can move the self value out of the self inout binding using
_move and if one does not replace self with a new value by end of function, you
will get a compile time error, e.x.:
```
struct S {
var buffer: Klass
mutating func doSomething() {
let b = move(self).buffer
// ... do some stuff, maybe get a different buffer ...
let maybeDifferentBuffer = maybeNewBuffer(b)
// If we do not re-initialize S with a new value by uncommenting
// the following line, we will get a compile time error.
// self = S(differentBuffer)
}
}
```
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This PR is doing a few things: