[NFC] Distinguish references to names from declarations of those names by type

[beccadax]

This is a refactoring in support of the module qualification feature I've previously pitched on Evolution.

The eventual goal for that feature is to allow any place that uses a name for a declaration defined elsewhere to qualify it with a module name. That is, all of these should allow modules:

print(SomeModule::x)   // The `x` visible from SomeModule
({ () -> SomeModule::T in ... })(x)   // The `T` from SomeModule
T.SomeModule::init()   // The `T.init()` declared in SomeModule

But things like this should not:

func SomeModule::fn() { ... }   // defining a function in a different module???
let SomeModule::x = 1    // defining a constant in another module???

To support this distinction, this PR adds a DeclNameRef type to the compiler. This type currently just wraps DeclName, but in the future it will also be able to store a module name when the user module-qualifies a name. Declarations will continue to store a DeclName or Identifier for their own names, but name lookup entry points—and therefore many other AST nodes like UnresolvedDeclRefExprs and TypeReprs—will switch over to using DeclNameRef. Thus, this PR will establish the pathways through which module qualification information will flow without actually making any functional changes to the compiler. This will reduce the amount of merge conflicts during the feature's design and review.

While this PR is in progress, DeclNameRef's constructors will be implicit but deprecated, and a DeclNameRef_ function is used whenever we want to explicitly construct a DeclNameRef. Before I merge this commit, I will make the DeclNameRef constructors explicit, rename all DeclNameRef_s to DeclNameRef, and delete the DeclNameRef function.

[beccadax]

I'm going to try running tests from the llvm-project side in swiftlang/llvm-project#430.

[beccadax]

With swiftlang/llvm-project#430

@swift-ci please test

[swift-ci]

Build failed
Swift Test Linux Platform
Git Sha - e9f61145b10edd43c1d6893e88193a1346b11e0d

[beccadax]

Notes for reviewers:

• This is mostly boring NFC type name changes.

• In general, DeclNameRef should be used where the developer has written the name of a type that is declared elsewhere. However, at various points we need to take a name from a declaration and look it up as though the user wrote it, and at other points we need to strip away the distinction between names and references to names so we can work with them as equals, and there are some places in constraint solving particularly where we end up losing the original names, so you'll sometimes see conversions back and forth.

• In many of the commits, you'll see DeclNameRef_. These mark places where I eventually inserted an explicit conversion. There are no DeclNameRef_s left in the final commit, and the function they used to call is gone.

• The easiest thing to do might be to read the smaller commits in more detail and skim the large commits for parts that look non-trivial.

[CodaFi]

I can't spot anything wrong, but then again this is a lot of code. Can the smaller refactorings be merged off separately? Ideally this patch would just be the renaming and the type plumbing afterwards.

[beccadax]

@CodaFi I could pull b1fbdbfe (Miscellaneous improvements to Playground and PCMacro transforms) into a separate followup PR; that part is +84 -88 and nothing else needs it. I don't know if there's anything else I can easily extract, though. Any suggestions?

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - e9f61145b10edd43c1d6893e88193a1346b11e0d

[beccadax]

With swiftlang/llvm-project#430

@swift-ci please test

[beccadax]

Needed yet another rebase.

With swiftlang/llvm-project#430

@swift-ci please smoke test

[beccadax]

With swiftlang/llvm-project#430

@swift-ci please test compiler performance

[beccadax]

With swiftlang/llvm-project#430

@swift-ci please test source compatibility

[beccadax]

With swiftlang/llvm-project#430

@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 (0)

name	old	new	delta	delta_pct

Unchanged (delta < 1.0% or delta < 100.0ms) (3)

name	old	new	delta	delta_pct
Frontend.NumInstructionsExecuted	105,231,041,153	105,177,753,206	-53,287,947	-0.05%
LLVM.NumLLVMBytesOutput	6,147,372	6,147,372	0	0.0%
time.swift-driver.wall	8.9s	9.0s	66.9ms	0.75%

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) (18)

name	old	new	delta	delta_pct
AST.NumLoadedModules	660	660	0	0.0%
AST.NumTotalClangImportedEntities	3,666	3,666	0	0.0%
IRModule.NumIRBasicBlocks	17,929	17,929	0	0.0%
IRModule.NumIRFunctions	10,597	10,597	0	0.0%
IRModule.NumIRGlobals	8,820	8,820	0	0.0%
IRModule.NumIRInsts	309,125	309,125	0	0.0%
IRModule.NumIRValueSymbols	18,441	18,441	0	0.0%
LLVM.NumLLVMBytesOutput	6,147,372	6,147,372	0	0.0%
SILModule.NumSILGenFunctions	5,372	5,372	0	0.0%
SILModule.NumSILOptFunctions	7,270	7,270	0	0.0%
Sema.NumConformancesDeserialized	11,782	11,782	0	0.0%
Sema.NumConstraintScopes	38,998	38,998	0	0.0%
Sema.NumDeclsDeserialized	115,226	115,226	0	0.0%
Sema.NumFunctionsTypechecked	2,034	2,034	0	0.0%
Sema.NumGenericSignatureBuilders	4,068	4,068	0	0.0%
Sema.NumLazyIterableDeclContexts	18,531	18,531	0	0.0%
Sema.NumTypesDeserialized	45,676	45,676	0	0.0%
Sema.NumTypesValidated	5,918	5,918	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	147,629,646,984	147,643,148,408	13,501,424	0.01%
LLVM.NumLLVMBytesOutput	6,863,584	6,863,576	-8	-0.0%
time.swift-driver.wall	17.0s	17.1s	121.4ms	0.71%

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) (18)

name	old	new	delta	delta_pct
AST.NumLoadedModules	76	76	0	0.0%
AST.NumTotalClangImportedEntities	2,136	2,136	0	0.0%
IRModule.NumIRBasicBlocks	17,957	17,957	0	0.0%
IRModule.NumIRFunctions	9,912	9,912	0	0.0%
IRModule.NumIRGlobals	8,921	8,921	0	0.0%
IRModule.NumIRInsts	200,046	200,046	0	0.0%
IRModule.NumIRValueSymbols	18,011	18,011	0	0.0%
LLVM.NumLLVMBytesOutput	6,863,584	6,863,576	-8	-0.0%
SILModule.NumSILGenFunctions	4,178	4,178	0	0.0%
SILModule.NumSILOptFunctions	6,229	6,229	0	0.0%
Sema.NumConformancesDeserialized	11,521	11,521	0	0.0%
Sema.NumConstraintScopes	38,800	38,800	0	0.0%
Sema.NumDeclsDeserialized	32,115	32,115	0	0.0%
Sema.NumFunctionsTypechecked	2,034	2,034	0	0.0%
Sema.NumGenericSignatureBuilders	1,579	1,579	0	0.0%
Sema.NumLazyIterableDeclContexts	4,267	4,267	0	0.0%
Sema.NumTypesDeserialized	16,745	16,745	0	0.0%
Sema.NumTypesValidated	3,914	3,914	0	0.0%