[clang] Introduce paged vector (PR #66430)

[Vassil Vassilev via cfe-commits]

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@@ -1625,6 +1625,39 @@ SmallVector has grown a few other minor advantages over std::vector, causing
    and is no longer "private to the implementation". A name like
    ``SmallVectorHeader`` might be more appropriate.
 
+.. _dss_pagedvector:
+
+llvm/ADT/PagedVector.h
+^^^^^^^^^^^^^^^^^^^^^^
+
+``PagedVector<Type, PageSize>`` is a random access container that allocates
+``PageSize`` elements of type ``Type`` when the first element of a page is accessed
+via the ``operator[]``.  This is useful for cases where the number of
+elements is known in advance; their actual initialization is expensive; and they are
+sparsely used. This utility uses page-granular lazily initialization when the element is accessed. When the
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vgvassilev wrote:

Could you reflow this again to fit 80 cols?

https://github.com/llvm/llvm-project/pull/66430