[IRGen] IRGen fixes for SE-0033.

Teach IRGen's type lowering to cope with swift_newtype'd types.

Author: DougGregor

lib/IRGen/GenStruct.cpp

@@ -805,7 +805,12 @@ const TypeInfo *TypeConverter::convertStructType(TypeBase *key, CanType type,
       assert(std::distance(D->getStoredProperties().begin(),
                            D->getStoredProperties().end()) == 1 &&
              "Struct representation of a Clang enum should wrap one value");
-
+    } else if (clangDecl->hasAttr<clang::SwiftNewtypeAttr>()) {
+      // Fall back to Swift lowering for the underlying type's
+      // representation as a struct member.
+      assert(std::distance(D->getStoredProperties().begin(),
+                           D->getStoredProperties().end()) == 1 &&
+             "Struct representation of a swift_newtype should wrap one value");
     } else {
       llvm_unreachable("Swift struct represents unexpected imported type");
     }

test/IRGen/newtype.swift

@@ -0,0 +1,9 @@
+// RUN// RUN: %target-swift-frontend -I %S/../IDE/Inputs/custom-modules %s -emit-ir | FileCheck %s
+import Newtype
+
+// CHECK-LABEL: define %CSo8NSString* @_TF7newtype14getErrorDomainFT_VSC11ErrorDomain()
+public func getErrorDomain() -> ErrorDomain {
+  // CHECK: load %CSo8NSString*, %CSo8NSString** getelementptr inbounds (%VSC11ErrorDomain, %VSC11ErrorDomain* @SNTErrOne
+  return .one
+}
+