[NFC] Make TrailingObjects non-copyable/non-movable

[erichkeane]

Summary

This got me pretty recently... TrailingObjects cannot be copied or
moved, since they need to be pre-allocated. This patch deletes the copy
and move operations (plus re-adds the default ctor).

[jyknight]

I can imagine there being some cases where these could theoretically be useful.

But if you've tested this change and it doesn't cause build failures with any existing uses of TrailingObjects in llvm-project, then LGTM.

[erichkeane]

In D97324#2583286, @jyknight wrote:

I can imagine there being some cases where these could theoretically be useful.

But if you've tested this change and it doesn't cause build failures with any existing uses of TrailingObjects in llvm-project, then LGTM.

Thanks! I ran into the problem because I had a function that returned by reference, and stored a copy, which worked silently. Then, during runtime, I obviously got nonsense.

Hopefully these are sufficient to prevent that from being a problem for others in the future. I'd built ahead of time (and done check-all), so I'm quite confident that this won't cause issues.

llvm/include/llvm/Support/TrailingObjects.h

#endif
   template <typename... Tys>
   static constexpr std::enable_if_t<
       std::is_same<Foo<TrailingTys...>, Foo<Tys...>>::value, size_t>
   totalSizeToAlloc(typename trailing_objects_internal::ExtractSecondType<
                    TrailingTys, size_t>::type... Counts) {
     return sizeof(BaseTy) + ParentType::additionalSizeToAllocImpl(0, Counts...);
   }
 
+  TrailingObjects() = default;
+  TrailingObjects(const TrailingObjects &) = delete;
+  TrailingObjects(TrailingObjects &&) = delete;
+  TrailingObjects &operator=(const TrailingObjects &) = delete;
+  TrailingObjects &operator=(TrailingObjects &&) = delete;
+
   /// A type where its ::with_counts template member has a ::type member
   /// suitable for use as uninitialized storage for an object with the given
   /// trailing object counts. The template arguments are similar to those
   /// of additionalSizeToAlloc.
   ///
   /// Use with FixedSizeStorageOwner, e.g.:
   ///
   /// \code{.cpp}