Removes redundant buffer zeroing in StringGraphemeBreaking.swift by using `init(unsafeUninitializedCapacity:initializingWith:)

[valeriyvan]

Removes redundant buffer zeroing by using init(unsafeUninitializedCapacity:initializingWith:) instead of init(repeating:count:)

[milseman]

Nice!

[milseman]

@swift-ci please test

[milseman]

@swift-ci please benchmark

[swift-ci]

Performance: -O

Regression	OLD	NEW	DELTA	RATIO
EqualSubstringSubstring	22	28	+27.3%	0.79x
LessSubstringSubstring	22	28	+27.3%	0.79x
EqualSubstringSubstringGenericEquatable	22	28	+27.3%	0.79x
LessSubstringSubstringGenericComparable	22	28	+27.3%	0.79x
EqualStringSubstring	23	29	+26.1%	0.79x
EqualSubstringString	23	29	+26.1%	0.79x (?)
NSStringConversion.Long	490	569	+16.1%	0.86x
StringComparison_longSharedPrefix	314	351	+11.8%	0.89x (?)
NSStringConversion.Medium	237	260	+9.7%	0.91x (?)
Improvement	OLD	NEW	DELTA	RATIO
FlattenListFlatMap	5776	4487	-22.3%	1.29x (?)
UTF8Decode_InitDecoding	161	134	-16.8%	1.20x
ArrayPlusEqualSingleElementCollection	470	423	-10.0%	1.11x (?)
UTF8Decode_InitFromBytes_ascii	222	202	-9.0%	1.10x (?)
DictionarySubscriptDefaultMutation	175	160	-8.6%	1.09x (?)

Code size: -O

Performance: -Osize

Regression	OLD	NEW	DELTA	RATIO
EqualSubstringSubstring	22	28	+27.3%	0.79x
LessSubstringSubstring	22	28	+27.3%	0.79x
EqualStringSubstring	22	28	+27.3%	0.79x (?)
EqualSubstringSubstringGenericEquatable	22	28	+27.3%	0.79x (?)
EqualSubstringString	22	28	+27.3%	0.79x
LessSubstringSubstringGenericComparable	22	28	+27.3%	0.79x
NSStringConversion.Long	499	568	+13.8%	0.88x
StringComparison_longSharedPrefix	314	351	+11.8%	0.89x (?)
NSStringConversion.Medium	241	267	+10.8%	0.90x (?)
Improvement	OLD	NEW	DELTA	RATIO
UTF8Decode_InitDecoding	161	135	-16.1%	1.19x
FlattenListFlatMap	5053	4689	-7.2%	1.08x (?)

Code size: -Osize

Regression	OLD	NEW	DELTA	RATIO
ReversedCollections.o	8689	8809	+1.4%	0.99x

Performance: -Onone

Regression	OLD	NEW	DELTA	RATIO
EqualSubstringSubstringGenericEquatable	26	32	+23.1%	0.81x
LessSubstringSubstringGenericComparable	26	32	+23.1%	0.81x
LessSubstringSubstring	27	33	+22.2%	0.82x
EqualSubstringSubstring	28	33	+17.9%	0.85x (?)
EqualStringSubstring	28	33	+17.9%	0.85x
EqualSubstringString	28	33	+17.9%	0.85x
Improvement	OLD	NEW	DELTA	RATIO
UTF8Decode_InitDecoding	182	156	-14.3%	1.17x (?)
ArrayOfPOD	726	648	-10.7%	1.12x (?)

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: 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