[llvm] [DenseMap] Store occupancy in a packed used-bit array (PR #201281)

[Fangrui Song via llvm-commits]

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@@ -53,6 +61,53 @@ struct DenseMapPair : std::pair<KeyT, ValueT> {
 
 } // end namespace detail
 
+namespace densemap::detail {
+using used_t = uint32_t;
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MaskRay wrote:

Changed to `UsedT`

https://github.com/llvm/llvm-project/pull/201281