[libcxx-commits] [libcxx] [libcxx] adds size-based `__split_buffer` representation to unstable ABI (PR #139632)

[Christopher Di Bella via libcxx-commits]

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@@ -78,23 +80,260 @@ public:
                       __split_buffer,
                       void>;
 
-  pointer __first_;
-  pointer __begin_;
-  pointer __end_;
-  _LIBCPP_COMPRESSED_PAIR(pointer, __cap_, allocator_type, __alloc_);
+  struct __data {
+    pointer __first_ = nullptr;
+    pointer __begin_ = nullptr;
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cjdb wrote:

I don't think so, or at least, not while `vector` uses it. `vector` uses `__begin_` for its operations, and only refers to `__first` in two places (both swaps). It would be an interesting thing to explore as a potential `deque` optimisation, if we were to drop the `vector` dependency.

https://github.com/llvm/llvm-project/pull/139632