[Constant Evaluator] Move "string.append" semantics attribute from String.+= function to String.append function.

[ravikandhadai]

String.+= is given a new semantics attribute "string.plusequals".

Teach the constant evaluator about String.append instead of String.+=.

With this change, String.append is the primitive whose semantics is built into the constant evaluator. This makes the evaluator a bit more general as String.append is also used by String.+ (string concatenation).

[ravikandhadai]

@swift-ci Please smoke test

[eeckstein]

@swift-ci benchmark

[swift-ci]

Performance: -O

TEST	OLD	NEW	DELTA	RATIO
Improvement
StringBuilderWithLongSubstring	1010	930	-7.9%	1.09x (?)

Performance: -Osize

TEST	OLD	NEW	DELTA	RATIO
Improvement
DataAppendDataLargeToLarge	24000	17400	-27.5%	1.38x (?)
PrefixCountableRange	15	14	-6.7%	1.07x (?)

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

[ravikandhadai]

@swift-ci benchmark

[swift-ci]

Performance: -O

TEST	OLD	NEW	DELTA	RATIO
Regression
SortLettersInPlace	385	416	+8.1%	0.93x (?)

Performance: -Osize

TEST	OLD	NEW	DELTA	RATIO
Regression
PrefixCountableRangeLazy	15	17	+13.3%	0.88x (?)
MapReduceShortString	12	13	+8.3%	0.92x (?)
Improvement
StringBuilderLong	920	840	-8.7%	1.10x (?)

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

[ravikandhadai]

Doesn't look like the regressing benchmarks are using String append (except for StringBuilderLong). I think this is just noise, considering the last two results.

[ravikandhadai]

@swift-ci benchmark

[swift-ci]

Performance: -Osize

TEST	OLD	NEW	DELTA	RATIO
Regression
DropFirstCountableRangeLazy	13	14	+7.7%	0.93x (?)

Performance: -Onone

TEST	OLD	NEW	DELTA	RATIO
Regression
SubstringFromLongString	9	10	+11.1%	0.90x (?)
Improvement
ObjectiveCBridgeStubFromNSDate	3320	2910	-12.3%	1.14x (?)

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

[eeckstein]

lgtm

[ravikandhadai]

@swift-ci Please test and merge