[SILGen] Add SILDeclRef for main entry-point

Allow SILDeclRef to refer to the main program
entry-point, which will either be for a main
SourceFile, or a synthetic main such as an `@main`
decl. Adjust the various SILDeclRef related
functions to handle this new case, and change the
emission to go through `emitFunctionDefinition`.

This change will allow the entry-point for an `@main`
decl (and eventually a main SourceFile) to be
emitted on-demand from its symbol name.

Author: hamishknight

include/swift/SIL/SILDeclRef.h

@@ -144,6 +144,10 @@ struct SILDeclRef {
     /// References the function used to initialize a property wrapper storage
     /// instance from a projected value.
     PropertyWrapperInitFromProjectedValue,
+
+    /// The main entry-point function. This may reference a SourceFile for a
+    /// top-level main, or a decl for e.g an @main decl.
+    EntryPoint,
   };
 
   /// The ValueDecl or AbstractClosureExpr represented by this SILDeclRef.
@@ -201,6 +205,12 @@ struct SILDeclRef {
   /// Produce a SIL constant for a default argument generator.
   static SILDeclRef getDefaultArgGenerator(Loc loc, unsigned defaultArgIndex);
 
+  /// Produces a SILDeclRef for a synthetic main entry-point such as @main.
+  static SILDeclRef getMainDeclEntryPoint(ValueDecl *decl);
+
+  /// Produces a SILDeclRef for the entry-point of a main FileUnit.
+  static SILDeclRef getMainFileEntryPoint(FileUnit *file);
+
   bool isNull() const { return loc.isNull(); }
   explicit operator bool() const { return !isNull(); }
 
@@ -217,7 +227,13 @@ struct SILDeclRef {
   AutoClosureExpr *getAutoClosureExpr() const;
   FuncDecl *getFuncDecl() const;
   AbstractFunctionDecl *getAbstractFunctionDecl() const;
-  
+  FileUnit *getFileUnit() const {
+    return loc.get<FileUnit *>();
+  }
+
+  /// Retrieves the ASTContext from the underlying AST node being stored.
+  ASTContext &getASTContext() const;
+
   llvm::Optional<AnyFunctionRef> getAnyFunctionRef() const;
 
   SILLocation getAsRegularLocation() const;

lib/IRGen/GenObjC.cpp

@@ -473,6 +473,7 @@ namespace {
       case SILDeclRef::Kind::GlobalAccessor:
       case SILDeclRef::Kind::PropertyWrapperBackingInitializer:
       case SILDeclRef::Kind::PropertyWrapperInitFromProjectedValue:
+      case SILDeclRef::Kind::EntryPoint:
         llvm_unreachable("Method does not have a selector");
 
       case SILDeclRef::Kind::Destroyer:

lib/SIL/IR/SILDeclRef.cpp

@@ -16,6 +16,7 @@
 #include "swift/AST/AnyFunctionRef.h"
 #include "swift/AST/Initializer.h"
 #include "swift/AST/ParameterList.h"
+#include "swift/AST/SourceFile.h"
 #include "swift/ClangImporter/ClangImporter.h"
 #include "swift/ClangImporter/ClangModule.h"
 #include "swift/SIL/SILLinkage.h"
@@ -180,6 +181,18 @@ Optional<AnyFunctionRef> SILDeclRef::getAnyFunctionRef() const {
   return AnyFunctionRef(loc.get<AbstractClosureExpr*>());
 }
 
+ASTContext &SILDeclRef::getASTContext() const {
+  switch (getLocKind()) {
+  case LocKind::Decl:
+    return getDecl()->getASTContext();
+  case LocKind::Closure:
+    return getAbstractClosureExpr()->getASTContext();
+  case LocKind::File:
+    return getFileUnit()->getASTContext();
+  }
+  llvm_unreachable("Unhandled case in switch");
+}
+
 bool SILDeclRef::isThunk() const {
   return isForeignToNativeThunk() || isNativeToForeignThunk();
 }
@@ -242,6 +255,10 @@ SILLinkage SILDeclRef::getLinkage(ForDefinition_t forDefinition) const {
     return isSerialized() ? SILLinkage::Shared : SILLinkage::Private;
   }
 
+  // The main entry-point is public.
+  if (kind == Kind::EntryPoint)
+    return SILLinkage::Public;
+
   // Add External to the linkage (e.g. Public -> PublicExternal) if this is a
   // declaration not a definition.
   auto maybeAddExternal = [&](SILLinkage linkage) {
@@ -407,6 +424,23 @@ SILDeclRef SILDeclRef::getDefaultArgGenerator(Loc loc,
   return result;
 }
 
+SILDeclRef SILDeclRef::getMainDeclEntryPoint(ValueDecl *decl) {
+  auto *file = cast<FileUnit>(decl->getDeclContext()->getModuleScopeContext());
+  assert(file->getMainDecl() == decl);
+  SILDeclRef result;
+  result.loc = decl;
+  result.kind = Kind::EntryPoint;
+  return result;
+}
+
+SILDeclRef SILDeclRef::getMainFileEntryPoint(FileUnit *file) {
+  assert(file->hasEntryPoint() && !file->getMainDecl());
+  SILDeclRef result;
+  result.loc = file;
+  result.kind = Kind::EntryPoint;
+  return result;
+}
+
 bool SILDeclRef::hasClosureExpr() const {
   return loc.is<AbstractClosureExpr *>()
     && isa<ClosureExpr>(getAbstractClosureExpr());
@@ -490,6 +524,9 @@ IsSerialized_t SILDeclRef::isSerialized() const {
     return IsNotSerialized;
   }
 
+  if (kind == Kind::EntryPoint)
+    return IsNotSerialized;
+
   if (isIVarInitializerOrDestroyer())
     return IsNotSerialized;
 
@@ -856,6 +893,10 @@ std::string SILDeclRef::mangle(ManglingKind MKind) const {
   case SILDeclRef::Kind::PropertyWrapperInitFromProjectedValue:
     return mangler.mangleInitFromProjectedValueEntity(cast<VarDecl>(getDecl()),
                                                       SKind);
+
+  case SILDeclRef::Kind::EntryPoint: {
+    return getASTContext().getEntryPointFunctionName();
+  }
   }
 
   llvm_unreachable("bad entity kind!");
@@ -1168,7 +1209,12 @@ SubclassScope SILDeclRef::getSubclassScope() const {
 }
 
 unsigned SILDeclRef::getParameterListCount() const {
-  if (!hasDecl() || kind == Kind::DefaultArgGenerator)
+  // Only decls can introduce currying.
+  if (!hasDecl())
+    return 1;
+
+  // Always uncurried even if the underlying function is curried.
+  if (kind == Kind::DefaultArgGenerator || kind == Kind::EntryPoint)
     return 1;
 
   auto *vd = getDecl();

lib/SIL/IR/SILFunctionType.cpp

@@ -2496,6 +2496,9 @@ static CanSILFunctionType getNativeSILFunctionType(
           DefaultConventions(NormalParameterConvention::Guaranteed));
     case SILDeclRef::Kind::Deallocator:
       return getSILFunctionTypeForConventions(DeallocatorConventions());
+
+    case SILDeclRef::Kind::EntryPoint:
+      llvm_unreachable("Handled by getSILFunctionTypeForAbstractCFunction");
     }
   }
   }
@@ -3023,6 +3026,7 @@ static ObjCSelectorFamily getObjCSelectorFamily(SILDeclRef c) {
   case SILDeclRef::Kind::StoredPropertyInitializer:
   case SILDeclRef::Kind::PropertyWrapperBackingInitializer:
   case SILDeclRef::Kind::PropertyWrapperInitFromProjectedValue:
+  case SILDeclRef::Kind::EntryPoint:
     llvm_unreachable("Unexpected Kind of foreign SILDeclRef");
   }
 
@@ -3283,6 +3287,9 @@ TypeConverter::getDeclRefRepresentation(SILDeclRef c) {
     case SILDeclRef::Kind::IVarInitializer:
     case SILDeclRef::Kind::IVarDestroyer:
       return SILFunctionTypeRepresentation::Method;
+
+    case SILDeclRef::Kind::EntryPoint:
+      return SILFunctionTypeRepresentation::CFunctionPointer;
   }
 
   llvm_unreachable("Unhandled SILDeclRefKind in switch.");
@@ -4110,6 +4117,7 @@ static AbstractFunctionDecl *getBridgedFunction(SILDeclRef declRef) {
   case SILDeclRef::Kind::PropertyWrapperInitFromProjectedValue:
   case SILDeclRef::Kind::IVarInitializer:
   case SILDeclRef::Kind::IVarDestroyer:
+  case SILDeclRef::Kind::EntryPoint:
     return nullptr;
   }
   llvm_unreachable("bad SILDeclRef kind");

lib/SIL/IR/SILPrinter.cpp

@@ -311,6 +311,7 @@ void SILDeclRef::print(raw_ostream &OS) const {
   }
   switch (kind) {
   case SILDeclRef::Kind::Func:
+  case SILDeclRef::Kind::EntryPoint:
     break;
   case SILDeclRef::Kind::Allocator:
     OS << "!allocator";

lib/SIL/IR/TypeLowering.cpp

@@ -2553,6 +2553,45 @@ getFunctionInterfaceTypeWithCaptures(TypeConverter &TC,
       innerExtInfo);
 }
 
+static CanAnyFunctionType getEntryPointInterfaceType(ASTContext &C) {
+  // Use standard library types if we have them; otherwise, fall back to
+  // builtins.
+  CanType Int32Ty;
+  if (auto Int32Decl = C.getInt32Decl()) {
+    Int32Ty = Int32Decl->getDeclaredInterfaceType()->getCanonicalType();
+  } else {
+    Int32Ty = CanType(BuiltinIntegerType::get(32, C));
+  }
+
+  CanType PtrPtrInt8Ty = C.TheRawPointerType;
+  if (auto PointerDecl = C.getUnsafeMutablePointerDecl()) {
+    if (auto Int8Decl = C.getInt8Decl()) {
+      Type Int8Ty = Int8Decl->getDeclaredInterfaceType();
+      Type PointerInt8Ty = BoundGenericType::get(PointerDecl,
+                                                 nullptr,
+                                                 Int8Ty);
+      Type OptPointerInt8Ty = OptionalType::get(PointerInt8Ty);
+      PtrPtrInt8Ty = BoundGenericType::get(PointerDecl,
+                                           nullptr,
+                                           OptPointerInt8Ty)
+        ->getCanonicalType();
+    }
+  }
+
+  using Param = FunctionType::Param;
+  Param params[] = {Param(Int32Ty), Param(PtrPtrInt8Ty)};
+
+  auto rep = FunctionTypeRepresentation::CFunctionPointer;
+  auto *clangTy = C.getClangFunctionType(params, Int32Ty, rep);
+  auto extInfo = FunctionType::ExtInfoBuilder()
+                     .withRepresentation(rep)
+                     .withClangFunctionType(clangTy)
+                     .build();
+
+  return CanAnyFunctionType::get(/*genericSig*/ nullptr,
+                                 llvm::makeArrayRef(params), Int32Ty, extInfo);
+}
+
 CanAnyFunctionType TypeConverter::makeConstantInterfaceType(SILDeclRef c) {
   if (auto *derivativeId = c.getDerivativeFunctionIdentifier()) {
     auto originalFnTy =
@@ -2627,6 +2666,8 @@ CanAnyFunctionType TypeConverter::makeConstantInterfaceType(SILDeclRef c) {
   case SILDeclRef::Kind::IVarDestroyer:
     return getIVarInitDestroyerInterfaceType(cast<ClassDecl>(vd),
                                              c.isForeign, true);
+  case SILDeclRef::Kind::EntryPoint:
+    return getEntryPointInterfaceType(Context);
   }
 
   llvm_unreachable("Unhandled SILDeclRefKind in switch.");
@@ -2678,6 +2719,8 @@ TypeConverter::getConstantGenericSignature(SILDeclRef c) {
   case SILDeclRef::Kind::GlobalAccessor:
   case SILDeclRef::Kind::StoredPropertyInitializer:
     return vd->getDeclContext()->getGenericSignatureOfContext();
+  case SILDeclRef::Kind::EntryPoint:
+    llvm_unreachable("Doesn't have generic signature");
   }
 
   llvm_unreachable("Unhandled SILDeclRefKind in switch.");