[lldb][TypeSystemClang][NFC] Clean up TypeSystemClang::DeclGetMangledName to LLVM-style

Will make upcoming changes in this area easier to read.

Author: Michael137

lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp

@@ -9164,33 +9164,36 @@ ConstString TypeSystemClang::DeclGetName(void *opaque_decl) {
 }
 
 ConstString TypeSystemClang::DeclGetMangledName(void *opaque_decl) {
-  if (opaque_decl) {
-    clang::NamedDecl *nd =
-        llvm::dyn_cast<clang::NamedDecl>((clang::Decl *)opaque_decl);
-    if (nd != nullptr && !llvm::isa<clang::ObjCMethodDecl>(nd)) {
-      clang::MangleContext *mc = getMangleContext();
-      if (mc && mc->shouldMangleCXXName(nd)) {
-        llvm::SmallVector<char, 1024> buf;
-        llvm::raw_svector_ostream llvm_ostrm(buf);
-        if (llvm::isa<clang::CXXConstructorDecl>(nd)) {
-          mc->mangleName(
-              clang::GlobalDecl(llvm::dyn_cast<clang::CXXConstructorDecl>(nd),
-                                Ctor_Complete),
-              llvm_ostrm);
-        } else if (llvm::isa<clang::CXXDestructorDecl>(nd)) {
-          mc->mangleName(
-              clang::GlobalDecl(llvm::dyn_cast<clang::CXXDestructorDecl>(nd),
-                                Dtor_Complete),
-              llvm_ostrm);
-        } else {
-          mc->mangleName(nd, llvm_ostrm);
-        }
-        if (buf.size() > 0)
-          return ConstString(buf.data(), buf.size());
-      }
-    }
+  clang::NamedDecl *nd = llvm::dyn_cast_or_null<clang::NamedDecl>(
+      static_cast<clang::Decl *>(opaque_decl));
+
+  if (!nd || llvm::isa<clang::ObjCMethodDecl>(nd))
+    return {};
+
+  clang::MangleContext *mc = getMangleContext();
+  if (!mc || !mc->shouldMangleCXXName(nd))
+    return {};
+
+  llvm::SmallVector<char, 1024> buf;
+  llvm::raw_svector_ostream llvm_ostrm(buf);
+  if (llvm::isa<clang::CXXConstructorDecl>(nd)) {
+    mc->mangleName(
+        clang::GlobalDecl(llvm::dyn_cast<clang::CXXConstructorDecl>(nd),
+                          Ctor_Complete),
+        llvm_ostrm);
+  } else if (llvm::isa<clang::CXXDestructorDecl>(nd)) {
+    mc->mangleName(
+        clang::GlobalDecl(llvm::dyn_cast<clang::CXXDestructorDecl>(nd),
+                          Dtor_Complete),
+        llvm_ostrm);
+  } else {
+    mc->mangleName(nd, llvm_ostrm);
   }
-  return ConstString();
+
+  if (buf.size() > 0)
+    return ConstString(buf.data(), buf.size());
+
+  return {};
 }
 
 CompilerDeclContext TypeSystemClang::DeclGetDeclContext(void *opaque_decl) {