[all-commits] [llvm/llvm-project] a296bd: [StringMap] Replace tombstone deletion with TAOCP ...

[Fangrui Song via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: a296bdef76b9e9c6effbb6d052e75b3ef3670f3e
      https://github.com/llvm/llvm-project/commit/a296bdef76b9e9c6effbb6d052e75b3ef3670f3e
  Author: Fangrui Song <i at maskray.me>
  Date:   2026-06-11 (Thu, 11 Jun 2026)

  Changed paths:
    M llvm/docs/ProgrammersManual.rst
    M llvm/include/llvm/ADT/StringMap.h
    M llvm/lib/Support/StringMap.cpp
    M llvm/unittests/ADT/StringMapTest.cpp
    M llvm/utils/gdb-scripts/prettyprinters.py

  Log Message:
  -----------
  [StringMap] Replace tombstone deletion with TAOCP 6.4 Algorithm R () (#203354)

Reland #202103 after relanding "[StringMap] Invalidate iterators in
remove()" (#203249)

StringMap uses quadratic probing with lazy deletion: an erased entry
becomes a tombstone, a third bucket state alongside empty and live that
every find/insert must inspect.

Switch to linear probing with Knuth TAOCP 6.4 Algorithm R deletion,
similar to DenseMap #200595.

erase now relocates the following entries to close the hole. StringMap
buckets are pointers to heap-allocated entries, so only the pointers
(and the parallel hash array) move. References and pointers to entries
remain valid, but iterators are invalidated.

Depends on #202237 and #202520
Aided by Claude Opus 4.8



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