AST: Handle TopLevelCodeDecl in DeclExportabilityVisitor.

Author: tshortli

include/swift/AST/DeclExportabilityVisitor.h

@@ -149,7 +149,6 @@ class DeclExportabilityVisitor
     return true;                                                               \
   }
   UNREACHABLE(Module);
-  UNREACHABLE(TopLevelCode);
   UNREACHABLE(Missing);
   UNREACHABLE(MissingMember);
   UNREACHABLE(GenericTypeParam);
@@ -165,6 +164,7 @@ class DeclExportabilityVisitor
   // context has already been checked.
 #define UNINTERESTING(KIND)                                                    \
   bool visit##KIND##Decl(const KIND##Decl *D) { return true; }
+  UNINTERESTING(TopLevelCode);
   UNINTERESTING(IfConfig);
   UNINTERESTING(Import);
   UNINTERESTING(PoundDiagnostic);

test/SILGen/skip_non_exportable_decls_top_level.swift

@@ -0,0 +1,11 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend -emit-silgen %s -module-name Test | %FileCheck %s --check-prefixes=CHECK,CHECK-NO-SKIP
+// RUN: %target-swift-frontend -emit-silgen %s -module-name Test -experimental-skip-non-exportable-decls | %FileCheck %s --check-prefixes=CHECK,CHECK-SKIP
+
+// CHECK-NO-SKIP: sil_global hidden @$s4Test1xSivp : $Int
+// CHECK-SKIP: sil_global hidden_external @$s4Test1xSivp : $Int
+var x = foo()
+
+// CHECK-NO-SKIP: sil hidden{{.*}} @$s4Test3fooSiyF : $@convention(thin) () -> Int {
+// CHECK-SKIP: sil hidden_external @$s4Test3fooSiyF : $@convention(thin) () -> Int
+func foo() -> Int { return 1 }