[ConstraintSystem] Shrink: If root expression is assignment always co…

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…nsider it as a candidate

If assignment expression is not considered as a top-level candidate
it would mean that other candidates would be allowed to produce
types inconsistent with destination type of the assignment.

Resolves: rdar://problem/51413254

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@swift-ci please smoke test compiler performance

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@swift-ci please test source compatibility

[swift-ci]

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) (3)

name	old	new	delta	delta_pct
Frontend.NumInstructionsExecuted	95,127,520,918	95,165,017,842	37,496,924	0.04%
LLVM.NumLLVMBytesOutput	6,166,516	6,166,576	60	0.0%
time.swift-driver.wall	8.3s	8.2s	-43.2ms	-0.52%

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) (21)

name	old	new	delta	delta_pct
AST.NumLoadedModules	660	660	0	0.0%
AST.NumTotalClangImportedEntities	3,832	3,832	0	0.0%
IRModule.NumIRBasicBlocks	18,754	18,754	0	0.0%
IRModule.NumIRFunctions	10,616	10,616	0	0.0%
IRModule.NumIRGlobals	8,111	8,111	0	0.0%
IRModule.NumIRInsts	313,674	313,674	0	0.0%
IRModule.NumIRValueSymbols	17,790	17,790	0	0.0%
LLVM.NumLLVMBytesOutput	6,166,516	6,166,576	60	0.0%
SILModule.NumSILGenFunctions	5,372	5,372	0	0.0%
SILModule.NumSILOptFunctions	7,018	7,018	0	0.0%
Sema.NumConformancesDeserialized	13,787	13,787	0	0.0%
Sema.NumConstraintScopes	38,122	38,122	0	0.0%
Sema.NumDeclsDeserialized	116,778	116,778	0	0.0%
Sema.NumDeclsValidated	10,764	10,764	0	0.0%
Sema.NumFunctionsTypechecked	1,516	1,516	0	0.0%
Sema.NumGenericSignatureBuilders	4,321	4,321	0	0.0%
Sema.NumLazyGenericEnvironments	26,037	26,037	0	0.0%
Sema.NumLazyGenericEnvironmentsLoaded	1,980	1,980	0	0.0%
Sema.NumLazyIterableDeclContexts	18,951	18,951	0	0.0%
Sema.NumTypesDeserialized	49,808	49,808	0	0.0%
Sema.NumTypesValidated	11,624	11,624	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	141,540,447,279	141,586,817,579	46,370,300	0.03%
LLVM.NumLLVMBytesOutput	7,187,016	7,186,932	-84	-0.0%
time.swift-driver.wall	16.0s	16.1s	123.9ms	0.77%

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) (21)

name	old	new	delta	delta_pct
AST.NumLoadedModules	76	76	0	0.0%
AST.NumTotalClangImportedEntities	2,226	2,226	0	0.0%
IRModule.NumIRBasicBlocks	21,185	21,185	0	0.0%
IRModule.NumIRFunctions	10,102	10,102	0	0.0%
IRModule.NumIRGlobals	8,129	8,129	0	0.0%
IRModule.NumIRInsts	224,200	224,200	0	0.0%
IRModule.NumIRValueSymbols	17,405	17,405	0	0.0%
LLVM.NumLLVMBytesOutput	7,187,016	7,186,932	-84	-0.0%
SILModule.NumSILGenFunctions	4,178	4,178	0	0.0%
SILModule.NumSILOptFunctions	5,852	5,852	0	0.0%
Sema.NumConformancesDeserialized	12,333	12,333	0	0.0%
Sema.NumConstraintScopes	37,940	37,940	0	0.0%
Sema.NumDeclsDeserialized	31,955	31,955	0	0.0%
Sema.NumDeclsValidated	7,784	7,784	0	0.0%
Sema.NumFunctionsTypechecked	1,526	1,526	0	0.0%
Sema.NumGenericSignatureBuilders	1,710	1,710	0	0.0%
Sema.NumLazyGenericEnvironments	6,593	6,593	0	0.0%
Sema.NumLazyGenericEnvironmentsLoaded	130	130	0	0.0%
Sema.NumLazyIterableDeclContexts	4,267	4,267	0	0.0%
Sema.NumTypesDeserialized	17,699	17,699	0	0.0%
Sema.NumTypesValidated	6,954	6,954	0	0.0%

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@swift-ci please test