After rebasing on master and incorporating more 32-bit support,
perform a bunch of cleanup, documentation updates, comments, move code
back to String declaration, etc.
This is a giant squashing of a lot of individual changes prototyping a
switch of String in Swift 5 to be natively encoded as UTF-8. It
includes what's necessary for a functional prototype, dropping some
history, but still leaves plenty of history available for future
commits.
My apologies to anyone trying to do code archeology between this
commit and the one prior. This was the lesser of evils.
The functions in LibcShims are used externally, some directly and some through @inlineable functions. These are changed to SWIFT_RUNTIME_STDLIB_SPI to better match their actual usage. Their names are also changed to add "_swift" to the front to match our naming conventions.
Three functions from SwiftObject.mm are changed to SPI and get a _swift prefix.
A few other support functions are also changed to SPI. They already had a prefix and look like they were meant to be SPI anyway. It was just hard to notice any mixup when they were #defined to the same thing.
rdar://problem/35863717
Beside the general goal to remove inlinable functions, this reduces code size and also improves performance for several benchmarks.
The performance problem was that by inlining top-level String API functions into client code (like String.count) it ended up calling non-inlinable internal String functions eventually.
This is much slower than to make a single call at the top-level API boundary into the library. Inside the library all the internal String functions can be specialized and inlined.
rdar://problem/39921548
Switch StringObject and StringGuts from opaquely storing tagged cocoa
strings into storing small strings. Plumb small string support
throughout the standard library's routines.
Streamline internal String creation. Previously, everything funneled
into a single generic function, however, every single call of the
generic funnel had relevant specific information that could be used
for a more efficient algorithm.
In preparation for efficiently forming small strings, refactor this
logic into a handful of more specialized subroutines to preserve more
specific information from the callers.
Use the visitor pattern in most of the opaque-by-hand call
sites. Inspecting the compiler output does not show excessive and
unanticipated ARC, but there may need to be further tweaks.
One downside of the visitor pattern as written is that there's extra
shuffling around of registers for the closure CC. Hopefully this will
also be fixed soon.
Stop inlining _asOpaque into user code. Inlining it bloats user code
as there's a bit-test-and-branch to a block containing the _asOpaque
call, followed up some operations to e.g. manipulate the range or
re-align the calling convention, etc., followed by a final branch to
opaque stdlib code.
Instead, branch directly into opaque stdlib code. In theory, this
means that supporting all opaque patterns can be done with minimal
bloat. On ARM, this is a single tbnz instruction.
In preparation for small strings optimizations, bifurcate StringGuts's
inits to denote when the caller is choosing to skip any checks for is
small. In the majority of cases, the caller has more local information
to guide the decision.
Adds todos and comments as well:
* TODO(SSO) denotes any task that should be done simultaneously with
the introduction of small strings.
* TODO(TODO: JIRA) denotes tasks that should eventually happen
later (and will have corresponding JIRAs filed for).
* TODO(Comparison) denotes tasks when the new string comparison
lands.
Include the initial implementation of _StringGuts, a 2-word
replacement for _LegacyStringCore. 64-bit Darwin supported, 32-bit and
Linux support in subsequent commits.
- Revise Equatable and Hashable for synthesized requirements
- Complete Strideable and stride(from:...:by:) documentation
- Revise DoubleWidth type docs
- Add complexity notes for Set.index(of:) and .contains(_:)
- Fix typos in Set.formUnion docs
- Add missing axioms for SetAlgebra (SR-6319)
- Improve guidance for description and debugDescription
- Add note about the result of passing duplicate keys to
Dictionary(uniqueKeysWithValues:)
- Fix typo in BinaryInteger docs
- Update Substring docs with better conversion example
- Improve docs for withMemoryRebound and isKnownUniquelyReferenced
- Add missing docs not propagated from protocols
- remove additional 'characters' references from String docs
- improved language around escaping pointer arguments
- key path type abstracts
- codable type abstract revisions
- a few more NSString API fixes
* removing .characters from examples
* beginning new String doc revisions
* improvements to the String Foundation overlay docs
* minor revisions elsewhere
* [stdlib] String : RangeReplaceableCollection & BidirectionalCollection
* Add source compatibility hack for Swift.max
* Add source compatibility hack for Swift.min
* Remove redundant conformance in benchmarks
* Fix stupid typo I thought I'd already pushed
* XFAIL testing now-redundant conformance
* XFAIL an IDE test for now
