[stdlib] Some cleanup enabled by _alwaysEmitIntoClient.

[milseman]

Refactor some copy-pasted code into a helper computed variable and
outline some cold paths.

[milseman]

@swift-ci please test

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 8c6b9c0

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - 8c6b9c0

[slavapestov]

You can remove this TODO and the one below no?

[milseman]

@swift-ci please test

[milseman]

@swift-ci please benchmark

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 8c6b9c0

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - 8c6b9c0

[swift-ci]

Performance: -O

TEST	OLD	NEW	DELTA	RATIO
Improvement
DictionaryBridgeToObjC_Access	1095	919	-16.1%	1.19x (?)
StringFromLongWholeSubstring	11	10	-9.1%	1.10x (?)
FlattenListLoop	4336	3975	-8.3%	1.09x (?)
Array2D	7520	6912	-8.1%	1.09x (?)
MapReduce	397	368	-7.3%	1.08x
FlattenListFlatMap	6542	6076	-7.1%	1.08x (?)
MapReduceAnyCollection	397	369	-7.1%	1.08x (?)

Code size: -O

TEST	OLD	NEW	DELTA	RATIO
Regression
UTF8Decode.o	12746	13338	+4.6%	0.96x
WordCount.o	44939	45523	+1.3%	0.99x

Performance: -Osize

TEST	OLD	NEW	DELTA	RATIO
Improvement
DictionaryBridgeToObjC_Access	1031	932	-9.6%	1.11x (?)
StringFromLongWholeSubstring	11	10	-9.1%	1.10x (?)
FlattenListLoop	4431	4069	-8.2%	1.09x (?)
Array2D	7520	6912	-8.1%	1.09x (?)

Code size: -Osize

TEST	OLD	NEW	DELTA	RATIO
Regression
WordCount.o	40660	41220	+1.4%	0.99x
UTF8Decode.o	11025	11137	+1.0%	0.99x
Improvement
RC4.o	3878	3721	-4.0%	1.04x

Performance: -Onone

TEST	OLD	NEW	DELTA	RATIO
Regression
ArrayOfGenericPOD2	1065	1236	+16.1%	0.86x (?)
SubstringEquatable	7511	8557	+13.9%	0.88x (?)
ArrayOfPOD	777	856	+10.2%	0.91x (?)
SubstringFromLongString	11	12	+9.1%	0.92x (?)
Improvement
RemoveWhereFilterStrings	4570	4072	-10.9%	1.12x (?)
StrComplexWalk	7280	6560	-9.9%	1.11x
CharIteration_korean_unicodeScalars_Backwards	390240	357520	-8.4%	1.09x (?)
CharIteration_punctuated_unicodeScalars_Backwards	87480	80160	-8.4%	1.09x (?)
CharIteration_chinese_unicodeScalars_Backwards	302840	277520	-8.4%	1.09x (?)
CharIteration_japanese_unicodeScalars_Backwards	481920	442560	-8.2%	1.09x (?)
CharIteration_ascii_unicodeScalars_Backwards	398120	367280	-7.7%	1.08x (?)
CharIteration_punctuatedJapanese_unicodeScalars_Backwards	68600	63480	-7.5%	1.08x (?)

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