Add AccessedStorage::Tail access kind and remove more exclusivity checks.

[atrick]

Distinguish ref_tail_addr storage from the other storage classes.

We didn't have this originally because be don't expect a begin_access
to directly operate on tail storage. It could occur after inlining, at
least with static access markers. More importantly it helps ditinguish
regular formal accesses from other unidentified access, so we probably
should have always had this.

At any rate, it's particularly important when AccessedStorage is
generalized to arbitrary memory access.

The immediate motivation is to add an AccessPath utility, which will
need to distinguish tail storage.

In the process, rewrite AccessedStorage::isDistinct. This could have a
large positive impact on exclusivity performance.

[atrick]

@swift-ci test

[atrick]

@swift-ci test source compatibility

[atrick]

@swift-ci benchmark

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@swift-ci test

[atrick]

@swift-ci benchmark

[atrick]

@swift-ci test source compatibility

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - d3705db7a6c0d3030618cf210c18f588fa209982

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - d3705db7a6c0d3030618cf210c18f588fa209982

[swift-ci]

Performance: -O

Regression	OLD	NEW	DELTA	RATIO
FlattenListFlatMap	3599	3903	+8.4%	0.92x (?)
Improvement	OLD	NEW	DELTA	RATIO
FlattenListLoop	1508	1250	-17.1%	1.21x (?)
ObjectiveCBridgeStubToNSDateRef	2340	2120	-9.4%	1.10x (?)

Code size: -O

Performance: -Osize

Improvement	OLD	NEW	DELTA	RATIO
FlattenListLoop	1519	927	-39.0%	1.64x (?)
FlattenListFlatMap	4432	3846	-13.2%	1.15x (?)

Code size: -Osize

Performance: -Onone

Regression	OLD	NEW	DELTA	RATIO
ObjectiveCBridgeStubNSDateRefAccess	4284	4766	+11.3%	0.90x (?)

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 mini
  Model Identifier: Macmini8,1
  Processor Name: 6-Core Intel Core i7
  Processor Speed: 3.2 GHz
  Number of Processors: 1
  Total Number of Cores: 6
  L2 Cache (per Core): 256 KB
  L3 Cache: 12 MB
  Memory: 64 GB

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@swift-ci test macOS

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 6ecbeef

[atrick]

@swift-ci test macOS

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 6ecbeef

[atrick]

This PR repeatedly fails with

/Applications/Xcode-beta.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator14.0.sdk/usr/include/objc/runtime.h:27:10: fatal error: cannot open file '/Applications/Xcode-beta.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator14.0.sdk/usr/include/objc/objc.h': Operation not permitted
23:49:12 #include <objc/objc.h>
23:49:12          ^
23:49:12 1 error generated.

[atrick]

@swift-ci test macOS