In response to [SR-3334], which pointed out a large cost to iteration over
ReversedRandomAccessCollections at optimization level -Onone. By adding
iteration through a.reversed() in the _Prespecialize struct, we can get to
about the same performance as forward iteration.
withoutActuallyEscaping has a signature like `<T..., U, V, W> (@nonescaping (T...) throws<U> -> V, (@escaping (T...) throws<U> -> V) -> W) -> W, but our type system for functions unfortunately isn't quite that expressive yet, so we need to special-case it. Set up the necessary type system when resolving an overload set to reference withoutActuallyEscaping, and if a type check succeeds, build a MakeTemporarilyEscapableExpr to represent it in the type-checked AST.
`type(of:)` has behavior whose type isn't directly representable in Swift's type system, since it produces both concrete and existential metatypes. In Swift 3 we put in a parser hack to turn `type(of: <expr>)` into a DynamicTypeExpr, but this effectively made `type(of:)` a reserved name. It's a bit more principled to put `Swift.type(of:)` on the same level as other declarations, even with its special-case type system behavior, and we can do this by special-casing the type system we produce during overload resolution if `Swift.type(of:)` shows up in an overload set. This also lays groundwork for handling other declarations we want to ostensibly behave like normal declarations but with otherwise inexpressible types, viz. `withoutActuallyEscaping` from SE-0110.
Swift 3 unintentionally allowed collection casts from, e.g.,
Set<AnyHashable> to Set<NSObject>, when in fact the object
representation of the AnyHashable might not be an NSObject. Fix up our
tests and overlays that ran afoul of this rule.
This modifies the _partition function used during sorting to select
the median of the first, middle, and last elements in the range to
be partitioned. Before partitioning begins, those three elements are
sorted, after which the middle element is selected as the pivot. This
change improves performance for sorted or nearly-sorted data.
For a value of an opaque generic type `<T> x: T`, the language currently defines `type(of: x)` and `T.self` as both producing a type `T.Type`, and the result of substituting an existential type by `T == P` gives `P.Protocol`, so the `type(of:)` operation on `x` can only give the concrete protocol metatype when `x` is an existential in this case. The optimizer understood this rule, but the runtime did not, causing SR-3304.
for sib/sibgen files for libraries without building them by default.
This will let engineers just cd into the build directory and type:
ninja swift-stdlib-sib
ninja swift-stdlib-sibgen
To generate sib and sibgen files respectively.
There are still some dependency issues in between the sib targets, so to get
this to work well, I would suggest doing a full build and then using these
targets.
Changes:
* Terminate all namespaces with the correct closing comment.
* Make sure argument names in comments match the corresponding parameter name.
* Remove redundant get() calls on smart pointers.
* Prefer using "override" or "final" instead of "virtual". Remove "virtual" where appropriate.
