Keep the buffer in the invalid UTF8 handling path of String(unsafeUninitializedCapacity:initializingWith:) alive while we're using it

[Catfish-Man]

No description provided.

[Catfish-Man]

@swift-ci please test

[Catfish-Man]

@swift-ci please smoke benchmark

[swift-ci]

Performance (x86_64): -O

Regression	OLD	NEW	DELTA	RATIO
DictionaryOfAnyHashableStrings_insert	2940	5628	+91.4%	0.52x
DictionaryKeysContainsNative	21	26	+23.8%	0.81x (?)
SortStringsUnicode	2885	3110	+7.8%	0.93x (?)
EqualStringSubstring	39	42	+7.7%	0.93x
EqualSubstringString	39	42	+7.7%	0.93x (?)
Improvement	OLD	NEW	DELTA	RATIO
StringFromLongWholeSubstring	5	4	-20.0%	1.25x

Code size: -O

Performance (x86_64): -Osize

Regression	OLD	NEW	DELTA	RATIO
EqualSubstringSubstringGenericEquatable	39	43	+10.3%	0.91x (?)
LessSubstringSubstring	39	42	+7.7%	0.93x (?)
EqualSubstringSubstring	39	42	+7.7%	0.93x (?)
EqualStringSubstring	39	42	+7.7%	0.93x (?)
EqualSubstringString	39	42	+7.7%	0.93x (?)
LessSubstringSubstringGenericComparable	39	42	+7.7%	0.93x (?)
Improvement	OLD	NEW	DELTA	RATIO
StringFromLongWholeSubstring	5	4	-20.0%	1.25x
String.data.LargeUnicode	109	95	-12.8%	1.15x (?)
StringToDataLargeUnicode	3500	3200	-8.6%	1.09x (?)
ObjectiveCBridgeStubFromNSDate	6990	6450	-7.7%	1.08x (?)

Code size: -Osize

Performance (x86_64): -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 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: 16 GB

[Catfish-Man]

Looks like all noise for perf, but someone should figure out what's up with DictionaryOfAnyHashableStrings_insert, it's being weird lately

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - 4bdc8e3

[glessard]

Nit: trailing whitespace.

[Catfish-Man]

@swift-ci please smoke test

[Catfish-Man]

@swift-ci please test

[Catfish-Man]

UGH I reverted the test changes accidentally. Ok, I'm going to eat breakfast first so I can think properly, THEN fix this PR.

[Catfish-Man]

@swift-ci please smoke test

[milseman]

LGTM