SIL optimizer: propagate count and capacity from empty Array/Set/Dictionary singletons.

[eeckstein]

Constant-propagate the 0 value when loading "count" or "capacity" from the empty Array, Set or Dictionary storage.
On high-level SIL this optimization is also done by the ArrayCountPropagation pass, but only for Array.
And even for Array it's sometimes needed to propagate the empty-array count when high-level semantics function are already inlined.

Fixes an optimization deficiency for empty OptionSet literals.

https://bugs.swift.org/browse/SR-12046
rdar://problem/58861171

[eeckstein]

@swift-ci test

[eeckstein]

@swift-ci benchmark

[swift-ci]

Performance: -O

Regression	OLD	NEW	DELTA	RATIO
Set.isSuperset.Seq.Empty.Int	46	52	+13.0%	0.88x (?)
SortIntPyramid	425	465	+9.4%	0.91x (?)
ParseInt.Small.Decimal	177	193	+9.0%	0.92x (?)
IterateData	874	948	+8.5%	0.92x (?)
Improvement	OLD	NEW	DELTA	RATIO
SuffixArrayLazy	9	4	-55.5%	2.25x
Set.isSubset.Int.Empty	52	46	-11.5%	1.13x (?)
Set.isDisjoint.Seq.Box.Empty	87	80	-8.0%	1.09x (?)

Code size: -O

Improvement	OLD	NEW	DELTA	RATIO
DictTest.o	16124	14716	-8.7%	1.10x
DictTest3.o	18461	17117	-7.3%	1.08x
DictTest2.o	11757	11309	-3.8%	1.04x

Performance: -Osize

Regression	OLD	NEW	DELTA	RATIO
Set.isDisjoint.Seq.Int.Empty	45	50	+11.1%	0.90x (?)
Improvement	OLD	NEW	DELTA	RATIO
SuffixArrayLazy	9	4	-55.5%	2.25x
ArrayAppendSequence	870	680	-21.8%	1.28x (?)
Set.isSubset.Int.Empty	49	45	-8.2%	1.09x (?)

Code size: -Osize

Performance: -Onone

Regression	OLD	NEW	DELTA	RATIO
ArrayOfGenericPOD2	713	836	+17.3%	0.85x (?)

Code size: -swiftlibs

Improvement	OLD	NEW	DELTA	RATIO
libswiftFoundation.dylib	1445888	1421312	-1.7%	1.02x

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

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 966d617

[eeckstein]

@swift-ci smoke test

[eeckstein]

@swift-ci smoke test macOS

[eeckstein]

@swift-ci smoke test macOS