[CIR][CodeGen][BugFix] use proper base type for derived class (#404)

In the original codegen a new type is created for the base class, while
in CIR we were rewriting the type being processed (due tp misused
pointers). This PR fix this, and also makes CIR codegen even with the
original one.

clang/lib/CIR/CodeGen/CIRRecordLayoutBuilder.cpp

@@ -601,15 +601,16 @@ CIRGenTypes::computeRecordLayout(const RecordDecl *D,
   builder.lower(/*nonVirtualBaseType=*/false);
 
   // If we're in C++, compute the base subobject type.
-  mlir::cir::StructType *BaseTy = nullptr;
+  mlir::cir::StructType BaseTy;
   if (llvm::isa<CXXRecordDecl>(D) && !D->isUnion() &&
       !D->hasAttr<FinalAttr>()) {
-    BaseTy = Ty;
+    BaseTy = *Ty;
     if (builder.astRecordLayout.getNonVirtualSize() !=
         builder.astRecordLayout.getSize()) {
       CIRRecordLowering baseBuilder(*this, D, /*Packed=*/builder.isPacked);
+      baseBuilder.lower(/*NonVirtualBaseType=*/true);
       auto baseIdentifier = getRecordTypeName(D, ".base");
-      *BaseTy =
+      BaseTy =
           Builder.getCompleteStructTy(baseBuilder.fieldTypes, baseIdentifier,
                                       /*packed=*/false, D);
       // TODO(cir): add something like addRecordTypeName
@@ -630,7 +631,7 @@ CIRGenTypes::computeRecordLayout(const RecordDecl *D,
 
   auto RL = std::make_unique<CIRGenRecordLayout>(
       Ty ? *Ty : mlir::cir::StructType{},
-      BaseTy ? *BaseTy : mlir::cir::StructType{},
+      BaseTy ? BaseTy : mlir::cir::StructType{},
       (bool)builder.IsZeroInitializable,
       (bool)builder.IsZeroInitializableAsBase);
 

clang/test/CIR/CodeGen/derived-to-base.cpp

@@ -77,6 +77,9 @@ void C3::Layer::Initialize() {
 
 // CHECK-DAG: !ty_22C23A3ALayer22 = !cir.struct<class "C2::Layer"
 // CHECK-DAG: !ty_22C33A3ALayer22 = !cir.struct<struct "C3::Layer"
+// CHECK-DAG: !ty_22A22 = !cir.struct<class "A"
+// CHECK-DAG: !ty_22A2Ebase22 = !cir.struct<class "A.base"
+// CHECK-DAG: !ty_22B22 = !cir.struct<class "B" {!cir.struct<class "A.base"
 
 // CHECK: cir.func @_ZN2C35Layer10InitializeEv