[gouyt13]

Summary

Remove dead code and redundant state. The removed code either has no callers or can never trigger, so behavior is unchanged. No public API, Python API or saved-index format changes. The private layout of HierarchicalNSW changes; its source API does not.

• HNSW
  • Remove label_op_locks_: 65536 mutexes allocated on every construct and load that protected nothing. add_point is only called by construct, which passes distinct labels within its validated capacity.
  • Turn the duplicate-label and capacity throws in add_point into asserts, since construct already guarantees both.
  • Replace four graph-traversal candidate guards with assert(cand < num_stored_points_). The guards had diverged (> max_elements_ vs. >= num_stored_points_) and could not fire: construct and add publish IDs before linking, and load validates every neighbor.
  • Remove two first-element else branches whose stores were always overwritten by the promotion that follows.
• IVF
  • Reduce the five readiness checks to !ready_; the error messages are unchanged. ready_ is set only after construct or load creates the initializer, rotator and cluster storage, and reserve already omitted two of the extra conditions.
  • Assert the internal cluster-size invariant in quantize_cluster.
  • Drop the unreachable metric branch in search; the metric is validated on construction and load.
• Dispatch / core / clustering
  • Remove the unused RABITQ_RESOLVE2 macro and the two-argument resolve_kernel.
  • Fold the single-use src/simd/excode_dispatch.hpp into dispatch.cpp with internal linkage.
  • Remove the test-only one_bit::one_bit_code. The sign-convention test now uses one_bit_code_with_factor, which is the function production code calls.
  • Drop two static_cast<void>(num_workers) in LloydKMeans where the variable is also used outside OpenMP pragmas.

Kept on purpose:

• hnsw::detail::search_knn: a documented compatibility adapter and an exported symbol.
• The remaining two num_workers casts: those variables appear only in pragmas, so the casts prevent unused-variable warnings when pragmas are ignored.

Testing

• Full portable CTest (RABITQ_ENABLE_NATIVE_OPTIMIZATION=OFF, --no-tests=error) on an AVX-512 Linux host:
  • Release: 410 passed, 1 skipped.
  • ASan/UBSan Debug, with the new asserts enabled: 410 passed, 1 skipped.
  • The skipped test is the placement test, which requires OpenMP binding.
• check-format.sh, full check-tidy.sh build-tidy and git diff --check passed.
• No test, binding or doc references the removed error messages.
• No new compiler warnings.
• Not run locally: NEON, Windows, macOS and OpenMP-off core builds.