llvm-project

71a28f3d - [ADT] Simplify DenseMapIterator with std::reverse_iterator (NFC) (#157389)

[ADT] Simplify DenseMapIterator with std::reverse_iterator (NFC) (#157389) DenseMapIterator has two tasks: - iterate the buckets in the requested direction - skip the empty and tombstone buckets These tasks are intertwined in the current implementation. This patch cleans up DenseMapIterator by separating the two tasks. Specifically, we introduce a private middleman iterator type called BucketItTy. This is the same as the pointer-based iterator in the forward direction, but it becomes std::reverse_iterator<pointer> otherwise. Now, the user-facing iterator iterates over BucketItTy while skipping the empty and tombstone buckets. This way, AdvancePastEmptyBuckets always calls BucketItTy::operator++. If the reverse iteration is requested, the underlying raw pointer gets decremented, but that logic is hidden behind std::reverse_iterator<pointer>::operator++. As a result, we can remove RetreatPastEmptyBuckets and a couple of calls to shouldReverseIterate. Here is a data point. A couple of months ago, we were calling shouldReverseIterate from 18 places in DenseMap.h. That's down to 5. This patch reduces it further down to 3.