OSSA support for Box types. AccessedStorage Box handling. isBorrowedAddress utility.

[atrick]

These 4 commits are interdependent as far as avoiding test regressions. The two main features are

• Unify Box/Class/Tail handling in AccessedStorage/MemAccessUtils.
• Add isBorrowedAddress, which is required for OSSA-based transformations.

Add a tiny BorrowedAddress utility.

Determines whether an address might be inside a borrowed scope. If so,
then any address substitution needs to find that scope boundary to
avoid violating its basic guarantee that all uses are within scope.

MemAccessUtils: unify Box/Class/Tail storage for consistency and usability

It was originally convenient for exclusivity optimization to treat
boxes specially. We wanted to know that the 'Box' kind was always
uniquely identified. But that's not really important. And now that
AccessedStorage is being used more generally, the inconsistency is
problematic.

A consistent model is also must easier to understand and explain.

This also make the implementation of the utility simpler and more powerful.

Functional changes:

isRCIdentical will look through mark_dependence and mark_uninitialized.

findReferenceRoot is used consistently everywhere increasing analysis precision.

[atrick]

The isBorrowedAddress utility will help fix #38672 (OSSA+TempRVO fix) and is required by #38470 (OSSA utilities)

[atrick]

@swift-ci test

[atrick]

@swift-ci test source compatibility

[atrick]

@swift-ci benchmark

[swift-ci]

Performance (x86_64): -O

Regression	OLD	NEW	DELTA	RATIO
DictionaryOfAnyHashableStrings_insert	3444	5586	+62.2%	0.62x
Set.isDisjoint.Int25	263	341	+29.7%	0.77x (?)
Set.isDisjoint.Int50	263	337	+28.1%	0.78x (?)
FlattenListFlatMap	4421	5135	+16.2%	0.86x (?)
DictionaryKeysContainsNative	22	25	+13.6%	0.88x (?)
ArrayAppendOptionals	2040	2300	+12.7%	0.89x (?)
DictionaryRemove	3170	3500	+10.4%	0.91x (?)
TypeName	904	980	+8.4%	0.92x (?)

Code size: -O

Performance (x86_64): -Osize

Improvement	OLD	NEW	DELTA	RATIO
ArrayAppendGenericStructs	2010	1330	-33.8%	1.51x (?)
FlattenListLoop	4864	3976	-18.3%	1.22x (?)

Code size: -Osize

Performance (x86_64): -Onone

Regression	OLD	NEW	DELTA	RATIO
NSStringConversion.Rebridge.Long	276	314	+13.8%	0.88x (?)
NSStringConversion.Rebridge.Medium	276	313	+13.4%	0.88x (?)
Improvement	OLD	NEW	DELTA	RATIO
String.data.Small	89	83	-6.7%	1.07x (?)

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

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - f351cb4e8528e7a8f2005e0df4372a75575e575f

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - f351cb4e8528e7a8f2005e0df4372a75575e575f

[atrick]

All SCK builds passed (although I don't know how to make them build with -sil-verify-all).

[atrick]

@swift-ci test

[meg-gupta]

Thanks @atrick ! lgtm