[AST] Add a convenient getter from QualType to RecordDecl

Differential Revision: https://reviews.llvm.org/D49951

llvm-svn: 338187
diff --git a/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp b/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
index 4ee6c8e..a38df50 100644
--- a/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
+++ b/clang/lib/CodeGen/CGRecordLayoutBuilder.cpp
@@ -313,9 +313,8 @@
     if (!SeenNamedMember) {
       SeenNamedMember = Field->getIdentifier();
       if (!SeenNamedMember)
-        if (const auto *FieldRD =
-                dyn_cast_or_null<RecordDecl>(Field->getType()->getAsTagDecl()))
-        SeenNamedMember = FieldRD->findFirstNamedDataMember();
+        if (const auto *FieldRD = Field->getType()->getAsRecordDecl())
+          SeenNamedMember = FieldRD->findFirstNamedDataMember();
       if (SeenNamedMember && !isZeroInitializable(Field)) {
         IsZeroInitializable = IsZeroInitializableAsBase = false;
         StorageType = FieldType;