[ConstraintGraph] Fix contractEdges to gather constraints only once

[xedin]

Currently we have this non-optimal behavior in contractEdges where
for every type variable it gathers constraints for its whole equivalence
class before checking if any are "contractable", instead constraints
could be gathered/filtered once which removes a lot of useless work.

[xedin]

@swift-ci please test

[xedin]

@swift-ci please smoke test compiler performance

[xedin]

@swift-ci please test source compatibility

[rudkx]

LGTM!

How much does this speed up type checking cases like SR-7632?

[slavapestov]

Can we add a scale_test for this?

[xedin]

@slavapestov I will try, but the problem is that we don't really have a good counter right now to measure the effect at the moment...

[xedin]

FYI I've tried with 25k element array of ints e.g. let _: [Int] = [1, 2, 3, ...] without changes it takes ~45 secs. to type-check, with changes it only takes ~500 milliseconds.

[swift-ci]

Build comment file:

Summary for master smoketest

Unexpected test results, excluded stats for ReactiveCocoa

No regressions above thresholds

• Debug
  • debug brief
  • debug detailed
• Release
  • release brief
  • release detailed

Debug

debug brief

Regressed (0)

name	old	new	delta	delta_pct

Improved (0)

name	old	new	delta	delta_pct

Unchanged (delta < 1.0% or delta < 100.0ms) (2)

name	old	new	delta	delta_pct
LLVM.NumLLVMBytesOutput	41,247,170	41,251,490	4,320	0.01%
time.swift-driver.wall	70.1s	69.4s	-666.3ms	-0.95%

debug detailed

Regressed (0)

name	old	new	delta	delta_pct

Improved (0)

name	old	new	delta	delta_pct

Unchanged (delta < 1.0% or delta < 100.0ms) (23)

name	old	new	delta	delta_pct
AST.NumImportedExternalDefinitions	84,556	84,556	0	0.0%
AST.NumLoadedModules	12,956	12,956	0	0.0%
AST.NumTotalClangImportedEntities	256,399	256,399	0	0.0%
AST.NumUsedConformances	8,766	8,766	0	0.0%
IRModule.NumIRBasicBlocks	125,749	125,749	0	0.0%
IRModule.NumIRFunctions	75,153	75,153	0	0.0%
IRModule.NumIRGlobals	68,675	68,675	0	0.0%
IRModule.NumIRInsts	1,429,975	1,429,975	0	0.0%
IRModule.NumIRValueSymbols	128,737	128,737	0	0.0%
LLVM.NumLLVMBytesOutput	41,247,170	41,251,490	4,320	0.01%
SILModule.NumSILGenFunctions	42,746	42,746	0	0.0%
SILModule.NumSILOptFunctions	47,119	47,119	0	0.0%
Sema.NumConformancesDeserialized	357,780	357,780	0	0.0%
Sema.NumConstraintScopes	900,349	900,349	0	0.0%
Sema.NumDeclsDeserialized	2,105,817	2,105,817	0	0.0%
Sema.NumDeclsValidated	190,411	190,411	0	0.0%
Sema.NumFunctionsTypechecked	48,042	48,042	0	0.0%
Sema.NumGenericSignatureBuilders	81,719	81,719	0	0.0%
Sema.NumLazyGenericEnvironments	419,438	419,438	0	0.0%
Sema.NumLazyGenericEnvironmentsLoaded	39,199	39,199	0	0.0%
Sema.NumLazyIterableDeclContexts	335,845	335,845	0	0.0%
Sema.NumTypesDeserialized	2,326,130	2,326,130	0	0.0%
Sema.NumTypesValidated	211,820	211,820	0	0.0%

Release

release brief

Regressed (0)

name	old	new	delta	delta_pct

Improved (0)

name	old	new	delta	delta_pct

Unchanged (delta < 1.0% or delta < 100.0ms) (2)

name	old	new	delta	delta_pct
LLVM.NumLLVMBytesOutput	30,117,892	30,117,888	-4	-0.0%
time.swift-driver.wall	144.6s	143.8s	-818.5ms	-0.57%

release detailed

Regressed (0)

name	old	new	delta	delta_pct

Improved (0)

name	old	new	delta	delta_pct

Unchanged (delta < 1.0% or delta < 100.0ms) (23)

name	old	new	delta	delta_pct
AST.NumImportedExternalDefinitions	8,764	8,764	0	0.0%
AST.NumLoadedModules	406	406	0	0.0%
AST.NumTotalClangImportedEntities	25,373	25,373	0	0.0%
AST.NumUsedConformances	8,772	8,772	0	0.0%
IRModule.NumIRBasicBlocks	158,940	158,940	0	0.0%
IRModule.NumIRFunctions	57,180	57,180	0	0.0%
IRModule.NumIRGlobals	56,040	56,040	0	0.0%
IRModule.NumIRInsts	1,324,447	1,324,447	0	0.0%
IRModule.NumIRValueSymbols	101,904	101,904	0	0.0%
LLVM.NumLLVMBytesOutput	30,117,892	30,117,888	-4	-0.0%
SILModule.NumSILGenFunctions	22,151	22,151	0	0.0%
SILModule.NumSILOptFunctions	36,626	36,626	0	0.0%
Sema.NumConformancesDeserialized	96,575	96,575	0	0.0%
Sema.NumConstraintScopes	799,066	799,066	0	0.0%
Sema.NumDeclsDeserialized	210,458	210,458	0	0.0%
Sema.NumDeclsValidated	59,864	59,864	0	0.0%
Sema.NumFunctionsTypechecked	10,695	10,695	0	0.0%
Sema.NumGenericSignatureBuilders	9,657	9,657	0	0.0%
Sema.NumLazyGenericEnvironments	33,020	33,020	0	0.0%
Sema.NumLazyGenericEnvironmentsLoaded	4,534	4,534	0	0.0%
Sema.NumLazyIterableDeclContexts	21,143	21,143	0	0.0%
Sema.NumTypesDeserialized	277,755	277,755	0	0.0%
Sema.NumTypesValidated	34,806	34,806	0	0.0%

---

[slavapestov]

@xedin You should just add a new counter that would be quadratic without this change. I think it’s important to test this so we don’t regress in the future.

[xedin]

@slavapestov Yeah, I'm trying to figure out what might it be, maybe it should be "num constraints considered by each contraction run", that metric would grown much slower comparing to before, it would be number or scopes * total number of constraints in scope, when it used to be number of scopes * num type vars * num of constraints in scope.

[xedin]

@graydon Could you please take a look at statistics changes? I wonder why I get No data when I run new scale test I added, I did everything exactly like incrementScopeCounter...

[xedin]

I wonder if that’s because that particular test would actually never find any contractable constraints... I will try putting it in find since that actual iteration.

[xedin]

@swift-ci please source compatibility

[xedin]

@swift-ci please source compatibility

[xedin]

@swift-ci please test

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - 9a99897b5c2885becbcc0a8802dafb7896eb9047

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 9a99897b5c2885becbcc0a8802dafb7896eb9047

[xedin]

@swift-ci please smoke test macOS platform

[xedin]

@swift-ci please test macOS platform