[libcxx-commits] [libcxx] [libc++] Document how __tree is layed out and how we iterate through it (PR #152453)

[Louis Dionne via libcxx-commits]

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@@ -183,6 +204,11 @@ _LIBCPP_HIDE_FROM_ABI _NodePtr __tree_next(_NodePtr __x) _NOEXCEPT {
   return __x->__parent_unsafe();
 }
 
+// __tree_next_iter and __tree_prev_iter implement iteration through the tree. The order is as follows:
+// left sub-tree -> node -> right sub-tree. When the right-most node of a sub-tree is reached, we walk up the tree until
+// we find a node where we were in the left sub-tree. We are _always_ in a left sub-tree, since the __end_node_ points
+// to the actual root of the tree through a __left_ pointer. incrementing the end() pointer is UB, so we can assume that
----------------
ldionne wrote:

```suggestion
// to the actual root of the tree through a __left_ pointer. Incrementing the end() pointer is UB, so we can assume that
```

https://github.com/llvm/llvm-project/pull/152453