Dave Abrahams 1fb11d623b [stdlib] Remove _buffer requirement from ArrayType ...

Until we get an optimizer pass to remove get/set pairs, passing a
property that is a protocol requirement as inout from generic code is
always going to cause an extra retain, causing many unintended Array
copies.

Because this dropped reference counts to 1 in some cases, it exercised
previously-untested code paths and uncovered bugs, particularly in the
handling of subrange replacement on Slice<T>.

There are still differences in speed for short arrays of CGPoint that bear
investigation, but at least as things scale up, the ratio of time goes
to 1.

Fixes <rdar://problem/17040913> append and += on an array have
completely different performance

Swift SVN r19228

2014-06-26 08:54:07 +00:00

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