Enable COWArrayOpts on OSSA

[meg-gupta]

Additional handling of copy_value/destroy_value/load[copy]/
begin_borrow/end_borrow is needed to support OSSA.

TODO: Support handling of 2d array in the pass for OSSA.
Currently hoisting of loads and borrows are not supported in OSSA

[meg-gupta]

@swift-ci test

[meg-gupta]

@swift-ci benchmark

[swift-ci]

Performance: -O

Regression	OLD	NEW	DELTA	RATIO
DataCreateMediumArray	2840	3100	+9.2%	0.92x (?)

Code size: -O

Performance: -Osize

Regression	OLD	NEW	DELTA	RATIO
FlattenListFlatMap	5920	6993	+18.1%	0.85x (?)

Code size: -Osize

Performance: -Onone

Code size: -swiftlibs

How to read the data

The tables contain differences in performance which are larger than 8% and differences in code size which are larger than 1%.

If you see any unexpected regressions, you should consider fixing the
regressions before you merge the PR.

Noise: Sometimes the performance results (not code size!) contain false
alarms. Unexpected regressions which are marked with '(?)' are probably noise.
If you see regressions which you cannot explain you can try to run the
benchmarks again. If regressions still show up, please consult with the
performance team (@eeckstein).

Hardware Overview

  Model Name: Mac Pro
  Model Identifier: MacPro6,1
  Processor Name: 12-Core Intel Xeon E5
  Processor Speed: 2.7 GHz
  Number of Processors: 1
  Total Number of Cores: 12
  L2 Cache (per Core): 256 KB
  L3 Cache: 30 MB
  Memory: 64 GB

[atrick]

LGTM. I just want to point out that the TODO's are actually regressions so they need to be tracked somehow.