This is a staging attribute that will eventually mean "fixed-contents"
for structs and "closed" for enums, as described in
docs/LibraryEvolution.rst.
This is pretty much the minimal set of types that must be fixed-layout,
because SILGen makes assumptions about their lowering.
If desired, some SILGen refactoring can allow some of these to be
resilient. For example, bridging value types could be made to work
with resilient types.
Use it for hashing and comparison.
During String's hashValue and comparison function we create a
_NSContiguousString instance to call Foundation's hash/compare function. This is
expensive because we have allocate and deallocate a short lived object on the
heap (and deallocation for Swift objects is expensive). Instead help the
optimizer to allocate this object on the stack.
Introduces two functions on the internal _NSContiguousString:
_unsafeWithNotEscapedSelfPointer and _unsafeWithNotEscapedSelfPointerPair that
pass the _NSContiguousString instance as an opaque pointer to their closure
argument. Usage of these functions asserts that the closure will not escape
objects transitively reachable from the opaque pointer.
We then use those functions to call into the runtime to call foundation
functions on the passed strings. The optimizer can promote the strings to the
stack because of the assertion this API makes.
let lhsStr = _NSContiguousString(self._core) // will be promoted to the stack.
let rhsStr = _NSContiguousString(rhs._core) // will be promoted to the stack.
let res = lhsStr._unsafeWithNotEscapedSelfPointerPair(rhsStr) {
return _stdlib_compareNSStringDeterministicUnicodeCollationPointer($0, $1)
}
Tested by existing String tests.
We should see some nice performance improvements for string comparison and
dictionary benchmarks.
Here is what I measured at -O on my machine
Name Speedup
Dictionary 2.00x
Dictionary2 1.45x
Dictionary2OfObjects 1.20x
Dictionary3 1.50x
Dictionary3OfObjects 1.45x
DictionaryOfObjects 1.40x
SuperChars 1.60x
rdar://22173647
This commit is the result of auditing the following files:
* StringBuffer.swift
* StringCharacterView.swift
* StringCore.swift
* StringInterpolation.swift.gyb
* StringLegacy.swift
This code as written is not sound and should not type check
for non-final classes conforming to SequenceType (eg, NSArray).
Instead, capture the base of the call from the preprocess closure
passed in. The closure is @noescape, so it should be equivalent.
