[ConstraintSystem] Mark generic parameter bindings as potentially inc…

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…omplete by default

This helps to postpone attempting bindings related to generic
parameters with all else being equal.

Consider situation when function has class requirement on its
generic parameter. Without such requirement solver would infer
sub-class for T. But currently when requirement is present base
class is inferred instead, because when bindings for such generic
parameter are attempted early single available binding at that
point comes from the requirement.

class BaseClass {}
class SubClass: BaseClass {}

struct Box<T> { init(_: T.Type) {} }

func test<T: BaseClass>(box: Box<T>) -> T.Type {
  return T.self
}

test(box: .init(SubClass.self)) // `T` expected to be `SubClass`

Resolves: SR-9626
Resolves: rdar://problem/47324309

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@swift-ci please smoke test compiler performance

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@swift-ci please test source compatibility

[swift-ci]

Build comment file:

Summary for master smoketest

Unexpected test results, excluded stats for Kingfisher, Alamofire, 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) (3)

name	old	new	delta	delta_pct
Frontend.NumInstructionsExecuted	124,641,163,618	124,546,931,567	-94,232,051	-0.08%
LLVM.NumLLVMBytesOutput	6,591,628	6,591,616	-12	-0.0%
time.swift-driver.wall	16.8s	16.8s	-68.6ms	-0.41%

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	1,110	1,110	0	0.0%
AST.NumLoadedModules	1,038	1,038	0	0.0%
AST.NumTotalClangImportedEntities	4,462	4,462	0	0.0%
AST.NumUsedConformances	886	886	0	0.0%
IRModule.NumIRBasicBlocks	18,386	18,386	0	0.0%
IRModule.NumIRFunctions	10,964	10,964	0	0.0%
IRModule.NumIRGlobals	9,261	9,261	0	0.0%
IRModule.NumIRInsts	320,414	320,414	0	0.0%
IRModule.NumIRValueSymbols	19,344	19,344	0	0.0%
LLVM.NumLLVMBytesOutput	6,591,628	6,591,616	-12	-0.0%
SILModule.NumSILGenFunctions	5,384	5,384	0	0.0%
SILModule.NumSILOptFunctions	7,062	7,062	0	0.0%
Sema.NumConformancesDeserialized	17,055	17,055	0	0.0%
Sema.NumConstraintScopes	41,636	41,978	342	0.82%
Sema.NumDeclsDeserialized	148,779	148,779	0	0.0%
Sema.NumDeclsValidated	11,580	11,580	0	0.0%
Sema.NumFunctionsTypechecked	2,540	2,540	0	0.0%
Sema.NumGenericSignatureBuilders	5,026	5,026	0	0.0%
Sema.NumLazyGenericEnvironments	33,373	33,373	0	0.0%
Sema.NumLazyGenericEnvironmentsLoaded	2,036	2,036	0	0.0%
Sema.NumLazyIterableDeclContexts	27,384	27,384	0	0.0%
Sema.NumTypesDeserialized	68,141	68,141	0	0.0%
Sema.NumTypesValidated	11,180	11,180	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) (3)

name	old	new	delta	delta_pct
Frontend.NumInstructionsExecuted	144,107,464,004	144,182,947,437	75,483,433	0.05%
LLVM.NumLLVMBytesOutput	7,562,480	7,562,308	-172	-0.0%
time.swift-driver.wall	27.5s	27.6s	112.5ms	0.41%

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	402	402	0	0.0%
AST.NumLoadedModules	76	76	0	0.0%
AST.NumTotalClangImportedEntities	2,113	2,113	0	0.0%
AST.NumUsedConformances	886	886	0	0.0%
IRModule.NumIRBasicBlocks	21,408	21,408	0	0.0%
IRModule.NumIRFunctions	10,630	10,630	0	0.0%
IRModule.NumIRGlobals	9,162	9,162	0	0.0%
IRModule.NumIRInsts	221,117	221,117	0	0.0%
IRModule.NumIRValueSymbols	18,992	18,992	0	0.0%
LLVM.NumLLVMBytesOutput	7,562,480	7,562,308	-172	-0.0%
SILModule.NumSILGenFunctions	4,180	4,180	0	0.0%
SILModule.NumSILOptFunctions	5,852	5,852	0	0.0%
Sema.NumConformancesDeserialized	12,287	12,287	0	0.0%
Sema.NumConstraintScopes	40,308	40,650	342	0.85%
Sema.NumDeclsDeserialized	32,498	32,498	0	0.0%
Sema.NumDeclsValidated	7,874	7,874	0	0.0%
Sema.NumFunctionsTypechecked	2,204	2,204	0	0.0%
Sema.NumGenericSignatureBuilders	1,710	1,710	0	0.0%
Sema.NumLazyGenericEnvironments	6,825	6,825	0	0.0%
Sema.NumLazyGenericEnvironmentsLoaded	130	130	0	0.0%
Sema.NumLazyIterableDeclContexts	4,174	4,174	0	0.0%
Sema.NumTypesDeserialized	18,176	18,176	0	0.0%
Sema.NumTypesValidated	5,972	5,972	0	0.0%

---

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@swift-ci please test

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Build failed
Swift Test OS X Platform
Git Sha - 3fdee3869740f0fee8675e8bc7a929bb9281fae1

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Build failed
Swift Test Linux Platform
Git Sha - 3fdee3869740f0fee8675e8bc7a929bb9281fae1