[stdlib] Remove workaround for sort optimization

[HassanElDesouky]

Remove workaround for sort optimization. Cherry picked from #40056.

Resolves SR-14750.

cc @lorentey, @glessard, @natecook1000

[glessard]

@swift-ci please test macOS platform

[HassanElDesouky]

@glessard can you re-run the tests again. There was a merge conflict that I just resolved.

[glessard]

@swift-ci please test macOS platform

[glessard]

@swift-ci please test Linux platform

[glessard]

@natecook1000 @lorentey I'm not sure what to make of the passed tests: it seems like this should register as an ABI change. Thoughts?

[glessard]

If we don't merge this, an alternative is to at least add the JIRA bug number: #40138

[glessard]

@HassanElDesouky The addition of the SR bug number was merged to main, and we have a merge conflict again. It's preferable to solve the conflict by rebasing rather than merging (it makes for a more understandable history.) Thanks!

[HassanElDesouky]

@glessard Thank you for adding the SR bug number. I just rebased the branch and fixed the merge conflict.

[glessard]

@swift-ci Please Build Toolchain Linux Platform

[swift-ci]

Linux Toolchain (Ubuntu 16.04)
Download Toolchain
Git Sha - 4d375c9d6e85be96e9d4a25f7ab6c683bf9114a3

Install command
tar zxf swift-PR-40081-731-ubuntu16.04.tar.gz
More info

[HassanElDesouky]

@glessard any update whether we're going to land this or not?

[lorentey]

@LucianoPAlmeida's note on ABI stability isn't resolved yet! Sadly I believe we'll need to preserve the Bool return value as these functions are ABI. (Otherwise we would introduce binary compatibility issues.)

[glessard]

We could perhaps remove the workarounds without changing the ABI: simply return true, and add the @discardableResult attribute. If nothing else, it should be a minor win in code size.

[HassanElDesouky]

@glessard Nice idea! I'm just traveling now so I'll do this solution once I get back.

[glessard]

Looks good. I'll trigger a tests run.

[glessard]

@swift-ci please test

[xwu]

@swift-ci please benchmark

[swift-ci]

Performance (x86_64): -O

Regression	OLD	NEW	DELTA	RATIO
FlattenListFlatMap	3876	4233	+9.2%	0.92x (?)
Improvement	OLD	NEW	DELTA	RATIO
StringBuilder	331	305	-7.9%	1.09x (?)

Code size: -O

Improvement	OLD	NEW	DELTA	RATIO
Phonebook.o	9947	9659	-2.9%	1.03x
SortLettersInPlace.o	8896	8720	-2.0%	1.02x
RGBHistogram.o	21834	21450	-1.8%	1.02x
SortStrings.o	27523	27043	-1.7%	1.02x
SortLargeExistentials.o	20100	19860	-1.2%	1.01x

Performance (x86_64): -Osize

Improvement	OLD	NEW	DELTA	RATIO
StringBuilderSmallReservingCapacity	340	314	-7.6%	1.08x (?)
StringBuilderWithLongSubstring	1620	1510	-6.8%	1.07x (?)

Code size: -Osize

Improvement	OLD	NEW	DELTA	RATIO
SortLettersInPlace.o	8249	8033	-2.6%	1.03x
Phonebook.o	9201	8975	-2.5%	1.03x
RGBHistogram.o	20085	19692	-2.0%	1.02x
SortIntPyramids.o	8841	8669	-1.9%	1.02x
SortStrings.o	26996	26562	-1.6%	1.02x
StaticArray.o	12005	11833	-1.4%	1.01x
SortLargeExistentials.o	20824	20552	-1.3%	1.01x
NibbleSort.o	14456	14284	-1.2%	1.01x

Performance (x86_64): -Onone

Improvement	OLD	NEW	DELTA	RATIO
CharIndexing_russian_unicodeScalars_Backwards	160320	148640	-7.3%	1.08x (?)

Code size: -swiftlibs

Improvement	OLD	NEW	DELTA	RATIO
libswiftSwiftOnoneSupport.dylib	163840	147456	-10.0%	1.11x

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

[LucianoPAlmeida]

@swift-ci Please test Windows Platform

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 6316555

[glessard]

The test failure was in a test related to the move-only work. Seems to fail for a few different PRs.

[glessard]

#40806 should fix the test failure above.

[glessard]

@swift-ci please test macOS platform

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 6316555

[xwu]

@swift-ci please test macOS platform

[HassanElDesouky]

Tests passed 🎉
@glessard

[glessard]

Thanks @HassanElDesouky for working on this!