This commit decouples StdlibUnittest from many details of
[Contiguous]Array, so tests can give useful feedback even in the
presence of a broken [Contiguous]Array implementation while we refactor.
Unfortunately, it wasn't practical to make _UnitTestArray use a
storage class other than _ContiguousArrayStorage[Base], so we still have
to watch out when making changes there.
Swift SVN r22875
This function mixes the bits in the hash value, which improves Dictionary
performance for keys with bad hashes.
PrecommitBenchmark changes with greater than 7% difference:
``````````Dictionary2`,```1456.00`,```1508.00`,```1502.00`,````624.00`,````607.00`,````592.00`,`864.00`,``145.9%
``````````Dictionary3`,```1379.00`,```1439.00`,```1408.00`,````585.00`,````567.00`,````552.00`,`827.00`,``149.8%
````````````Histogram`,````850.00`,````849.00`,````851.00`,```1053.00`,```1049.00`,```1048.00`,`199.00`,``-19.0%
````````````````Prims`,```1999.00`,```2005.00`,```2018.00`,```1734.00`,```1689.00`,```1701.00`,`310.00`,```18.4%
``````````StrSplitter`,```2365.00`,```2334.00`,```2316.00`,```1979.00`,```1997.00`,```2000.00`,`337.00`,```17.0%
```````````````TwoSum`,```1551.00`,```1568.00`,```1556.00`,```1771.00`,```1741.00`,```1716.00`,`165.00`,```-9.6%
Regressions are in benchmarks that use `Int` as dictionary key: we are just
doing more work than previously (hashing an `Int` was an identity function).
rdar://17962402
Swift SVN r21142
