Restrict CopyForwarding (and destroy hoisting) to OSSA SIL.

[atrick]

The premise of CopyForwarding was that memory locations have their own
ownership lifetime. We knew this was unmaintainable at the time, and
that was the original incentive for SIL opaque values, aided by
OSSA. In the meantime, we've been relying on SILGen producing
reasonable SIL patterns. Unfortunately, the CopyForwarding pass is
still with us while we make major changes to SIL ownership patterns
and agressively optimize ownership. That introduces risk.

Ultimately, the entire CopyForwarding pass should be redesigned for
OSSA-only and destroy hoisting should be a simple OSSA utility where
most of the work is done by AccessPath::collectUses.

But in the meantime, we should remove the source of risk by limiting
the CopyForwarding pass to OSSA. Any performance regressions will be
recovered as OSSA moves later in the pipeline. After that, opaque
values will improve even more over the current state by handling
generic SIL using the more powerful CopyPropagation pass.

Fixes rdar://71584600 (miscompile in CopyForwarding's release hoisting)

Here's an example of the kind of SIL the CopyForwarding does not
anticipate (although it only actually miscompiles in much more obscure
scenarios, which is why it's so dangerous):

bb0(%0 : $AnyObject):
%alloc1 = alloc_stack $AnyObject
store %0 to %objaddr : $*AnyObject
%ref = load %objaddr : $*AnyObject
%alloc2 = alloc_stack $ObjWrapper

The in-memory reference is destroyed before retaining the loaded ref.

copy_addr [take] %alloc1 to [initialization] %alloc2 : $*ObjWrapper
retain_value %ref : $AnyObject

[atrick]

@swift-ci test

[atrick]

@swift-ci benchmark

[swift-ci]

Performance: -O

Regression	OLD	NEW	DELTA	RATIO
UTF8Decode_InitFromData_ascii_as_ascii	641	715	+11.5%	0.90x (?)
Array2D	6688	7216	+7.9%	0.93x (?)
Improvement	OLD	NEW	DELTA	RATIO
FlattenListFlatMap	6763	6094	-9.9%	1.11x (?)
DataToStringLargeUnicode	7600	6850	-9.9%	1.11x (?)
Data.hash.Empty	77	71	-7.8%	1.08x (?)
DataToStringMedium	5800	5400	-6.9%	1.07x (?)

Code size: -O

Regression	OLD	NEW	DELTA	RATIO
RangeOverlaps.o	5798	6038	+4.1%	0.96x
DiffingMyers.o	6085	6277	+3.2%	0.97x
DictionaryBridgeToObjC.o	4944	5064	+2.4%	0.98x
DictionaryOfAnyHashableStrings.o	7912	8040	+1.6%	0.98x
ProtocolConformance.o	3799	3847	+1.3%	0.99x
FloatingPointConversion.o	41377	41873	+1.2%	0.99x
BucketSort.o	8587	8683	+1.1%	0.99x
Improvement	OLD	NEW	DELTA	RATIO
Suffix.o	22341	21116	-5.5%	1.06x
FloatingPointParsing.o	18882	17986	-4.7%	1.05x
RandomTree.o	11943	11775	-1.4%	1.01x

Performance: -Osize

Regression	OLD	NEW	DELTA	RATIO
StringBuilderLong	1470	1700	+15.6%	0.86x (?)
DataAccessBytesMedium	91	102	+12.1%	0.89x (?)
DataCountSmall	28	31	+10.7%	0.90x (?)
UTF8Decode_InitFromBytes_ascii_as_ascii	452	494	+9.3%	0.91x (?)
SuffixArrayLazy	11	12	+9.1%	0.92x
SuffixArray	11	12	+9.1%	0.92x
SuffixCountableRangeLazy	11	12	+9.1%	0.92x
Array2D	7520	8112	+7.9%	0.93x (?)
ObjectiveCBridgeFromNSDictionaryAnyObjectForced	9000	9700	+7.8%	0.93x (?)
Improvement	OLD	NEW	DELTA	RATIO
ObjectiveCBridgeStubFromNSDate	5810	4920	-15.3%	1.18x (?)
SuffixAnyCollection	65	59	-9.2%	1.10x
DataSubscriptSmall	37	34	-8.1%	1.09x

Code size: -Osize

Regression	OLD	NEW	DELTA	RATIO
DictionaryBridgeToObjC.o	4143	4276	+3.2%	0.97x
DiffingMyers.o	6090	6216	+2.1%	0.98x
FloatingPointConversion.o	39571	40067	+1.3%	0.99x
ProtocolConformance.o	3506	3543	+1.1%	0.99x
Improvement	OLD	NEW	DELTA	RATIO
Suffix.o	21199	20113	-5.1%	1.05x
FloatingPointParsing.o	17592	17088	-2.9%	1.03x

Performance: -Onone

Regression	OLD	NEW	DELTA	RATIO
RandomIntegersLCG	43934	54630	+24.3%	0.80x
RandomDoubleLCG	57454	71046	+23.7%	0.81x
RandomDoubleDef	93000	109200	+17.4%	0.85x (?)
ErrorHandling	4550	5030	+10.5%	0.90x (?)
RandomIntegersDef	62800	69300	+10.4%	0.91x (?)
Breadcrumbs.MutatedIdxToUTF16.ASCII	12	13	+8.3%	0.92x (?)
Dict.FilterAllMatch.28k	5282	5717	+8.2%	0.92x (?)
Dict.FilterAllMatch.16k	2792	3020	+8.2%	0.92x (?)
FlattenListFlatMap	236352	254148	+7.5%	0.93x (?)
Improvement	OLD	NEW	DELTA	RATIO
SevenBoom	2331	1755	-24.7%	1.33x (?)
NSStringConversion.Mutable	6601	5764	-12.7%	1.15x (?)
Dictionary4OfObjectsLegacy	1983	1740	-12.3%	1.14x (?)
Prims.NonStrongRef.Unmanaged.Closure	1686	1517	-10.0%	1.11x (?)
FindString.Rec3.String	948	855	-9.8%	1.11x (?)
Prims.NonStrongRef.Unmanaged	1646	1489	-9.5%	1.11x (?)
MapReduceShortString	270	246	-8.9%	1.10x (?)
FindString.Rec3.Substring	895	816	-8.8%	1.10x (?)
NSError	963	888	-7.8%	1.08x (?)
ArrayOfGenericPOD2	1110	1024	-7.7%	1.08x (?)
ArrayOfPOD	1134	1049	-7.5%	1.08x (?)
StringBuilderSmallReservingCapacity	3304	3068	-7.1%	1.08x (?)
CharIndexing_russian_unicodeScalars	153480	142640	-7.1%	1.08x (?)
Set.isStrictSubset.Seq.Int.Empty	1407	1312	-6.8%	1.07x (?)

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: 64 GB

[eeckstein]

lgtm!

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 39db766

[atrick]

I've been seeing this failure a lot recently:
lldb-api :: lang/swift/unknown_self/TestSwiftUnknownSelf.py

[atrick]

@swift-ci smoke test and merge