[CIR] Add support for base classes in type conversion safety check (llvm#154385)

This patch enables the record layout computation of types that are
derived more than once.

Author: mmha

clang/lib/CIR/CodeGen/CIRGenTypes.cpp

@@ -155,13 +155,14 @@ isSafeToConvert(const RecordDecl *rd, CIRGenTypes &cgt,
   // out, don't do it.  This includes virtual base classes which get laid out
   // when a class is translated, even though they aren't embedded by-value into
   // the class.
-  if (auto *crd = dyn_cast<CXXRecordDecl>(rd)) {
-    if (crd->getNumBases() > 0) {
-      assert(!cir::MissingFeatures::cxxSupport());
-      cgt.getCGModule().errorNYI(rd->getSourceRange(),
-                                 "isSafeToConvert: CXXRecordDecl with bases");
-      return false;
-    }
+  if (const CXXRecordDecl *crd = dyn_cast<CXXRecordDecl>(rd)) {
+    for (const clang::CXXBaseSpecifier &i : crd->bases())
+      if (!isSafeToConvert(i.getType()
+                               ->castAs<RecordType>()
+                               ->getOriginalDecl()
+                               ->getDefinitionOrSelf(),
+                           cgt, alreadyChecked))
+        return false;
   }
 
   // If this type would require laying out members that are currently being laid

clang/test/CIR/CodeGen/class.cpp

@@ -100,3 +100,22 @@ int use_base_via_pointer(Derived *d) {
 
 // OGCG: define{{.*}} i32 @_Z20use_base_via_pointerP7Derived
 // OGCG:   %[[D_A_ADDR:.*]] = getelementptr inbounds nuw %class.Base, ptr %{{.*}}, i32 0, i32 0
+
+struct EmptyDerived : Base {};
+struct EmptyDerived2 : EmptyDerived {};
+
+void use_empty_derived2() {
+  EmptyDerived2 d2;
+}
+
+// CIR: cir.func{{.*}} @_Z18use_empty_derived2v()
+// CIR:   %0 = cir.alloca !rec_EmptyDerived2, !cir.ptr<!rec_EmptyDerived2>, ["d2"]
+// CIR:   cir.return
+
+// LLVM: define{{.*}} void @_Z18use_empty_derived2v
+// LLVM:   alloca %struct.EmptyDerived2
+// LLVM:   ret void
+
+// OGCG: define{{.*}} void @_Z18use_empty_derived2v
+// OGCG:   alloca %struct.EmptyDerived2
+// OGCG:   ret void