[TypeChecker] Simplify for ... in ... type checking

[xedin]

Based on #21811 with diagnostic improvements.

[xedin]

@slavapestov I have rebased your changes with the latest master and fixed diagnostic, if you want you can cherry-pick my commit to your original PR too.

[slavapestov]

Thanks! I think the first two commits (simplify Optional/pointer conversions) were bogus. Let’s drop them for now

[xedin]

@slavapestov Will do!

[xedin]

@swift-ci please test

[xedin]

@swift-ci please test source compatibility

[xedin]

@swift-ci please smoke test compiler performance

[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 (1)

name	old	new	delta	delta_pct
time.swift-driver.wall	13.2s	12.9s	-272.1ms	-2.06% ✅

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

name	old	new	delta	delta_pct
Frontend.NumInstructionsExecuted	101,840,792,414	101,674,643,428	-166,148,986	-0.16%
LLVM.NumLLVMBytesOutput	6,147,468	6,147,468	0	0.0%

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) (22)

name	old	new	delta	delta_pct
AST.NumImportedExternalDefinitions	1,028	1,028	0	0.0%
AST.NumLoadedModules	828	828	0	0.0%
AST.NumTotalClangImportedEntities	4,282	4,282	0	0.0%
IRModule.NumIRBasicBlocks	18,752	18,752	0	0.0%
IRModule.NumIRFunctions	10,522	10,522	0	0.0%
IRModule.NumIRGlobals	8,019	8,019	0	0.0%
IRModule.NumIRInsts	313,670	313,670	0	0.0%
IRModule.NumIRValueSymbols	17,602	17,602	0	0.0%
LLVM.NumLLVMBytesOutput	6,147,468	6,147,468	0	0.0%
SILModule.NumSILGenFunctions	5,370	5,370	0	0.0%
SILModule.NumSILOptFunctions	7,016	7,016	0	0.0%
Sema.NumConformancesDeserialized	15,661	15,647	-14	-0.09%
Sema.NumConstraintScopes	39,312	39,250	-62	-0.16%
Sema.NumDeclsDeserialized	134,316	134,218	-98	-0.07%
Sema.NumDeclsValidated	11,074	11,074	0	0.0%
Sema.NumFunctionsTypechecked	2,058	2,058	0	0.0%
Sema.NumGenericSignatureBuilders	4,308	4,308	0	0.0%
Sema.NumLazyGenericEnvironments	29,727	29,683	-44	-0.15%
Sema.NumLazyGenericEnvironmentsLoaded	2,012	2,012	0	0.0%
Sema.NumLazyIterableDeclContexts	23,524	23,524	0	0.0%
Sema.NumTypesDeserialized	56,945	56,935	-10	-0.02%
Sema.NumTypesValidated	11,858	11,858	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	143,262,884,674	143,165,317,600	-97,567,074	-0.07%
LLVM.NumLLVMBytesOutput	7,155,912	7,155,812	-100	-0.0%
time.swift-driver.wall	23.7s	23.6s	-31.5ms	-0.13%

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) (22)

name	old	new	delta	delta_pct
AST.NumImportedExternalDefinitions	398	398	0	0.0%
AST.NumLoadedModules	76	76	0	0.0%
AST.NumTotalClangImportedEntities	2,196	2,196	0	0.0%
IRModule.NumIRBasicBlocks	21,144	21,144	0	0.0%
IRModule.NumIRFunctions	10,004	10,004	0	0.0%
IRModule.NumIRGlobals	8,031	8,031	0	0.0%
IRModule.NumIRInsts	223,874	223,874	0	0.0%
IRModule.NumIRValueSymbols	17,207	17,207	0	0.0%
LLVM.NumLLVMBytesOutput	7,155,912	7,155,812	-100	-0.0%
SILModule.NumSILGenFunctions	4,176	4,176	0	0.0%
SILModule.NumSILOptFunctions	5,844	5,844	0	0.0%
Sema.NumConformancesDeserialized	12,433	12,433	0	0.0%
Sema.NumConstraintScopes	38,386	38,324	-62	-0.16%
Sema.NumDeclsDeserialized	32,677	32,677	0	0.0%
Sema.NumDeclsValidated	7,784	7,784	0	0.0%
Sema.NumFunctionsTypechecked	1,750	1,750	0	0.0%
Sema.NumGenericSignatureBuilders	1,640	1,640	0	0.0%
Sema.NumLazyGenericEnvironments	6,871	6,871	0	0.0%
Sema.NumLazyGenericEnvironmentsLoaded	130	130	0	0.0%
Sema.NumLazyIterableDeclContexts	4,359	4,359	0	0.0%
Sema.NumTypesDeserialized	17,841	17,841	0	0.0%
Sema.NumTypesValidated	6,942	6,942	0	0.0%