[libcxx-commits] [libcxx] [lldb] [libcxx] adds a size-based representation for `vector`'s unstable ABI (PR #155330)

[Christopher Di Bella via libcxx-commits]

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@@ -196,6 +197,57 @@ public:
     swap(__back_cap_, __back_capacity);
   }
 
+  /// Relocates the objects in the range `[__first, __last)` to the front of the buffer, then swaps
+  /// `__first`, `__last`, and `__capacity` with `__begin_`, `__end_`, and `__back_cap_`,
+  /// respectively.
+  ///
+  /// Precondition: `__front_spare() == __last - __first`.
+  /// Exceptions: This function has a strong exception guarantee.
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void
+  __relocate(pointer& __first, pointer& __last, pointer& __capacity) {
+    auto __size      = __last - __first;
+    auto __new_begin = __begin_ - __size;
+    std::__uninitialized_allocator_relocate(
+        __alloc_, std::__to_address(__first), std::__to_address(__last), std::__to_address(__new_begin));
+    __begin_ = __new_begin;
+    __last   = __first;
+
+    __swap_layouts(__first, __last, __capacity);
+    __front_cap_ = __begin_;
+  }
+
+  /// Relocates the objects in the range `[__first, __pivot)` to the front of the buffer, the
+  /// objects in `[__pivot, __last)` into the back of the buffer, then swaps `__first`, `__last`,
+  /// and `__capacity` with `__begin_`, `__end_`, and `__back_cap_`, respectively.
+  ///
+  /// Preconditions:
+  ///   * `__front_spare() == __pivot - __first`
+  ///   * `__back_spare() == __last - __pivot`
+  /// Exceptions: This function has a strong exception guarantee if `__first == __pivot` or
+  /// `__last - __first == __pivot`.
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cjdb wrote:

Yeah, it looks like that's correct. I think a previous iteration might've been `__last - __first == size()`, and I didn't properly update the docs.

https://github.com/llvm/llvm-project/pull/155330