llvm-project

b3411b89 - [FoldingSet] Switch to linear probing and Algorithm R deletion (#218190)

[FoldingSet] Switch to linear probing and Algorithm R deletion (#218190) FoldingSet uses an inefficient chaining hash table. Switch to linear-probing open addressing: the bucket array holds node pointers, with null marking an empty slot. Deletion uses Knuth TAOCP 6.4 Algorithm R, as DenseMap/StringMap do, so erase invalidates iterators while leaving pointers to nodes valid. The next-in-bucket pointer becomes a cached 32-bit hash, halving FoldingSetNode. A probe compares it before the profile compare, and FindNodeOrInsertPos returns it instead of a bucket address, so an InsertPos survives intervening insertions. https://discourse.llvm.org/t/rfc-modernizing-llvms-foldingset-open-addressing-with-swiss-table-and-algorithm-r/91637 LLM-aided Co-authored-by: Kazu Hirata <kazu@google.com>