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[MOD-11881] Fix HNSW undefined behavior in container access #806

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Merged
meiravgri merged 1 commit into from
Oct 16, 2025
Merged

[MOD-11881] Fix HNSW undefined behavior in container access #806

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22 changes: 19 additions & 3 deletions src/VecSim/algorithms/hnsw/hnsw.h
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Original file line number Diff line number Diff line change
Expand Up @@ -389,7 +389,8 @@ void HNSWIndex<DataType, DistType>::removeExtraLinks(
size_t removed_idx = 0;
size_t link_idx = 0;

while (orig_candidates.size() > 0) {
// candidates <= orig_candidates
while (candidates.size() > 0) {
if (orig_candidates.top().second != candidates.top().second) {
if (neighbors_bitmap[orig_candidates.top().second]) {
removed_links[removed_idx++] = orig_candidates.top().second;
Expand All @@ -401,6 +402,15 @@ void HNSWIndex<DataType, DistType>::removeExtraLinks(
orig_candidates.pop();
}
}

assert(candidates.empty() && "candidates should be empty");
// Handle remaining elements in orig_candidates that were rejected by heuristic
while (orig_candidates.size() > 0) {
if (neighbors_bitmap[orig_candidates.top().second]) {
removed_links[removed_idx++] = orig_candidates.top().second;
}
orig_candidates.pop();
}
setListCount(node_ll, link_idx);
*removed_links_num = removed_idx;
}
Expand Down Expand Up @@ -466,7 +476,10 @@ DistType HNSWIndex<DataType, DistType>::processCandidate(
}
// Pre-fetch the neighbours list of the top candidate (the one that is going
// to be processed in the next iteration) into memory cache, to improve performance.
__builtin_prefetch(get_linklist_at_level(candidate_set.top().second, layer));
if (!candidate_set.empty()) {
assert(links_num);
__builtin_prefetch(get_linklist_at_level(candidate_set.top().second, layer));
}

return lowerBound;
}
Expand Down Expand Up @@ -515,7 +528,10 @@ void HNSWIndex<DataType, DistType>::processCandidate_RangeSearch(
}
// Pre-fetch the neighbours list of the top candidate (the one that is going
// to be processed in the next iteration) into memory cache, to improve performance.
__builtin_prefetch(get_linklist_at_level(candidate_set.top().second, layer));
if (!candidate_set.empty()) {
assert(links_num);
__builtin_prefetch(get_linklist_at_level(candidate_set.top().second, layer));
}
}

template <typename DataType, typename DistType>
Expand Down
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