Implement both -isEqual: and -isEqualToString: to directly call the internal _isEqual, to avoid a redundant ObjC message send + type check

[Catfish-Man]

No description provided.

[Catfish-Man]

@swift-ci please smoke test

[Catfish-Man]

@swift-ci please smoke benchmark

[Catfish-Man]

@lorentey reviewed in person :)

[swift-ci]

Performance: -O

Code size: -O

Performance: -Osize

Regression	OLD	NEW	DELTA	RATIO
StringBuilderWithLongSubstring	1480	1600	+8.1%	0.93x (?)

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 mini
  Model Identifier: Macmini7,1
  Processor Name: Intel Core i5
  Processor Speed: 2.8 GHz
  Number of Processors: 1
  Total Number of Cores: 2
  L2 Cache (per Core): 256 KB
  L3 Cache: 3 MB
  Memory: 16 GB

[jrose-apple]

I feel like you could do a bit better on the Swift name here :-P

[Catfish-Man]

lmao good point