[clang][dataflow][NFC] Fix outdated comment on getStableStorageLocation

[li.zhe.hua]

Summary

Follow-up to D129097.

It is no longer a requirement that the QualType passed to to
DataflowAnalysisContext::getStableStorageLocation() is not null. A
null type pass as an argument is only applicable as the pointee type
of a std::nullptr_t pointer.

[ymandel]

thanks!

[sgatev]

Thanks!

clang/include/clang/Analysis/FlowSensitive/DataflowAnalysisContext.h

public:
   takeOwnership(std::unique_ptr<T> Val) {
     assert(Val != nullptr);
     Vals.push_back(std::move(Val));
     return *cast<T>(Vals.back().get());
   }
 
   /// Returns a new storage location appropriate for `Type`.
   ///
-  /// Requirements:
-  ///
-  ///  `Type` must not be null.
+  /// A null `Type` is interpreted as the pointee type of `std::nullptr_t`.
   StorageLocation &createStorageLocation(QualType Type);
 
   /// Returns a stable storage location for `D`.
   StorageLocation &getStableStorageLocation(const VarDecl &D);
 
   /// Returns a stable storage location for `E`.
   StorageLocation &getStableStorageLocation(const Expr &E);