Re-wrote the inner memcpy loops so that they can be vectorized.
Also added a few inline(__always).
Since we removed some @inlineable attributes this string-append code is not code generated in the client anymore.
The code generation in the stdlib binary is different because all the precondition checks are not folded away.
Using explicit loop control statements instead of for-in-range removes the precondition-overhead for those time critical memcpy loops.
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.
Restore (un-revert) sting comparison, with fixes
More exhaustive testing of opaque strings, which consistently reproduces prior sporadic failure. Shims fixups. Some test tweaking.
* Make Range conditionally a Collection
* Convert ClosedRange to conditionally a collection
* De-gyb Range/ClosedRange, refactoring some methods.
* Remove use of Countable{Closed}Range from stdlib
* Remove Countable use from Foundation
* Fix test errors and warnings resulting from Range/CountableRange collapse
* fix prespecialize test for new mangling
* Update CoreAudio use of CountableRange
* Update SwiftSyntax use of CountableRange
* Restore ClosedRange.Index: Hashable conformance
* Move fixed typechecker slowness test for array-of-ranges from slow to fast, yay
* Apply Doug's patch to loosen test to just check for error
Include the initial implementation of _StringGuts, a 2-word
replacement for _LegacyStringCore. 64-bit Darwin supported, 32-bit and
Linux support in subsequent commits.
