[interop] C++ record should use AddressOnly type layout only when it's non-trivial for purpose of calls

A record that's non trivia for purpose of calls, as defined in Itanium ABI is allowed to have non-trivial copy/move assignment operators, but it most not have non-trivial constructors or destructors. This change ensures that a C++ record with a non-trivial copy assignment operator but trivial other members can be passed/returned directly by value, so that the compiler can accept the returned value correctly when calling a C++ function.

Author: hyp

include/swift/AST/Decl.h

@@ -4294,6 +4294,12 @@ class StructDecl final : public NominalTypeDecl {
     Bits.StructDecl.HasUnreferenceableStorage = v;
   }
 
+  /// Does this struct represent a non-trivial (for the purpose of calls, as
+  /// defined by Itanium ABI) C++ record. A C++ record is considered non-trivial
+  /// for the purpose of calls if either its constructor, copy-constructor, or
+  /// destructor is non-trivial. As such, a C++ record with a non-trivial
+  /// copy-assignment operator but other trivial members is considered to be
+  /// trivial.
   bool isCxxNonTrivial() const { return Bits.StructDecl.IsCxxNonTrivial; }
 
   void setIsCxxNonTrivial(bool v) { Bits.StructDecl.IsCxxNonTrivial = v; }

lib/ClangImporter/ImportDecl.cpp

@@ -2394,9 +2394,15 @@ namespace {
       }
 
       if (cxxRecordDecl) {
+        auto isNonTrivialForPurposeOfCalls =
+            [](const clang::CXXRecordDecl *decl) -> bool {
+          return decl->hasNonTrivialCopyConstructor() ||
+                 decl->hasNonTrivialMoveConstructor() ||
+                 !decl->hasTrivialDestructor();
+        };
         if (auto structResult = dyn_cast<StructDecl>(result))
           structResult->setIsCxxNonTrivial(
-              !cxxRecordDecl->isTriviallyCopyable());
+              isNonTrivialForPurposeOfCalls(cxxRecordDecl));
 
         for (auto &getterAndSetter : Impl.GetterSetterMap) {
           auto getter = getterAndSetter.second.first;

test/Interop/Cxx/class/type-classification-loadable-silgen.swift

@@ -54,17 +54,17 @@ func pass(s: StructWithSubobjectDefaultedCopyConstructor) {
 
 // CHECK-LABEL: sil hidden [ossa] @$s4main4pass{{.*[ (]}}StructWithCopyAssignment)
 func pass(s: StructWithCopyAssignment) {
-  // CHECK: bb0(%0 : $*StructWithCopyAssignment):
+  // CHECK: bb0(%0 : $StructWithCopyAssignment):
 }
 
 // CHECK-LABEL: sil hidden [ossa] @$s4main4pass{{.*[ (]}}StructWithInheritedCopyAssignment)
 func pass(s: StructWithInheritedCopyAssignment) {
-  // CHECK: bb0(%0 : $*StructWithInheritedCopyAssignment):
+  // CHECK: bb0(%0 : $StructWithInheritedCopyAssignment):
 }
 
 // CHECK-LABEL: sil hidden [ossa] @$s4main4pass{{.*[ (]}}StructWithSubobjectCopyAssignment)
 func pass(s: StructWithSubobjectCopyAssignment) {
-  // CHECK: bb0(%0 : $*StructWithSubobjectCopyAssignment):
+  // CHECK: bb0(%0 : $StructWithSubobjectCopyAssignment):
 }
 
 // CHECK-LABEL: sil hidden [ossa] @$s4main4pass{{.*[ (]}}StructWithDestructor)