Use the new builtins for COW representation in Array, ContiguousArray and ArraySlice.
The basic idea is to strictly separate code which mutates an array buffer from code which reads from an array.
The concept is explained in more detail in docs/SIL.rst, section "Copy-on-Write Representation".
The main change is to use beginCOWMutation() instead of isUniquelyReferenced() and insert endCOWMutation() at the end of all mutating functions. Also, reading from the array buffer must be done differently, depending on if the buffer is in a mutable or immutable state.
All the required invariants are enforced by runtime checks - but only in an assert-build of the library: a bit in the buffer object side-table indicates if the buffer is mutable or not.
Along with the library changes, also two optimizations needed to be updated: COWArrayOpt and ObjectOutliner.
test/SILOptimizer/pointer_conversion.swift’s arrayLiteralPromotion() subtest uses integer literals for 41, 42, 43, and 44. If swift-evolve shuffles a particular _internalInvariant() call in stdlib/public/core/BridgeStorage.swift to lines 41-44, the compiler will generate code which reuses the integer_literal instruction for the line number later in the test, causing this test to fail. This happens about once per 45 runs of swift-evolve.
This change negates the integer literals so they will never match a line number.
* Implement a few silcombine transformations for arrays
- Useless existential_ref <-> class conversions.
- mark_dependence_inst depending on uninteresting instructions.
- release(init_existential_ref(x)) -> release(x) when hasOneUse(x)
- Update COWArrayOpt to handle the new forms generated by this.
these aren't massive performance wins, but do shrink the size of SIL when
dealing with arrays.
* Generalize testcase to work on linux and on mac when checking stdlib is enabled.
I looked at trying to make the matches more flexible, but there are
actually some suspicious bits that I'm not so sure about. I'll just
disable the test for now.
rdar://problem/33531741
The array or string has to be kept alive past the call. John fixed
this back in 733915f but I want to make sure it doesn't regress.
rdar://problem/31325077 (originally fixed as rdar://problem/31542269,
also reported as SR-3231)
