[cxx-interop] Fix over-releasing foreign reference members of PODs

Large POD types were copied via memcpy instead of doing a field-wise
copy. This is incorrect for types with reference fields where we also
need to bump the corresponding refcounts.

rdar://160315343

Author: Gabor Horvath

lib/IRGen/GenStruct.cpp

@@ -1319,6 +1319,10 @@ class ClangRecordLowering {
   Size NextOffset = Size(0);
   Size SubobjectAdjustment = Size(0);
   unsigned NextExplosionIndex = 0;
+  // PODs containing fields to reference types are not real PODs, they cannot be
+  // copied using memcpy as we need to do the proper retain operations.
+  bool hasReferenceField = false;
+
 public:
   ClangRecordLowering(IRGenModule &IGM, StructDecl *swiftDecl,
                       const clang::RecordDecl *clangDecl,
@@ -1359,10 +1363,11 @@ class ClangRecordLowering {
     return LoadableClangRecordTypeInfo::create(
         FieldInfos, NextExplosionIndex, llvmType, TotalStride,
         std::move(SpareBits), TotalAlignment,
-        (SwiftDecl && SwiftDecl->getValueTypeDestructor())
-          ? IsNotTriviallyDestroyable : IsTriviallyDestroyable,
-        (SwiftDecl && !SwiftDecl->canBeCopyable())
-          ? IsNotCopyable : IsCopyable,
+        (SwiftDecl &&
+         (SwiftDecl->getValueTypeDestructor() || hasReferenceField))
+            ? IsNotTriviallyDestroyable
+            : IsTriviallyDestroyable,
+        (SwiftDecl && !SwiftDecl->canBeCopyable()) ? IsNotCopyable : IsCopyable,
         ClangDecl);
   }
 
@@ -1488,6 +1493,10 @@ class ClangRecordLowering {
           SwiftType.getFieldType(swiftField, IGM.getSILModule(),
                                  IGM.getMaximalTypeExpansionContext())));
       addField(swiftField, offset, fieldTI, isZeroSized);
+      if (swiftField->getInterfaceType()
+              ->lookThroughSingleOptionalType()
+              ->isAnyClassReferenceType())
+        hasReferenceField = true;
       return;
     }
 

test/Interop/Cxx/foreign-reference/Inputs/logging-frts.h

@@ -41,3 +41,13 @@ inline void releaseSharedFRT(SharedFRT *_Nonnull x) {
   if (x->_refCount == 0)
     delete x;
 }
+
+typedef struct LargePOD {
+  void const *a;
+  void const *b;
+  unsigned long c;
+  unsigned d;
+  SharedFRT *e;
+} LargePOD;
+
+inline LargePOD getLargePod() { return {0, 0, 0, 0, new SharedFRT()}; }

test/Interop/Cxx/foreign-reference/frts-as-fields.swift

@@ -27,4 +27,15 @@ go()
 // CHECK-NEXT: RefCount: 2, message: retain
 // CHECK-NEXT: RefCount: 1, message: release
 // CHECK-NEXT: RefCount: 0, message: release
-// CHECK-NEXT: RefCount: 0, message: Dtor
+// CHECK-NEXT: RefCount: 0, message: Dtor
+
+func takesLargePod(_ x: LargePOD) {
+    var a = x
+}
+
+takesLargePod(getLargePod())
+// CHECK:      RefCount: 1, message: Ctor
+// CHECK-NEXT: RefCount: 2, message: retain
+// CHECK-NEXT: RefCount: 1, message: release
+// CHECK-NEXT: RefCount: 0, message: release
+// CHECK-NEXT: RefCount: 0, message: Dtor