pitrou commented on code in PR #45108:
URL: https://github.com/apache/arrow/pull/45108#discussion_r1912992330
##########
cpp/src/arrow/compute/key_map_internal_avx2.cc:
##########
@@ -392,16 +387,30 @@ int SwissTable::extract_group_ids_avx2(const int
num_keys, const uint32_t* hashe
} else {
for (int i = 0; i < num_keys / unroll; ++i) {
__m256i hash = _mm256_loadu_si256(reinterpret_cast<const
__m256i*>(hashes) + i);
+ // Extend hash and local_slot to 64-bit to compute 64-bit group id
offsets to
+ // gather from. This is to prevent index overflow issues in GH-44513.
+ // NB: Use zero-extend conversion for unsigned hash.
+ __m256i hash_lo = _mm256_cvtepu32_epi64(_mm256_castsi256_si128(hash));
+ __m256i hash_hi = _mm256_cvtepu32_epi64(_mm256_extracti128_si256(hash,
1));
__m256i local_slot =
_mm256_set1_epi64x(reinterpret_cast<const
uint64_t*>(local_slots)[i]);
- local_slot = _mm256_shuffle_epi8(
- local_slot, _mm256_setr_epi32(0x80808000, 0x80808001, 0x80808002,
0x80808003,
- 0x80808004, 0x80808005, 0x80808006,
0x80808007));
- local_slot = _mm256_mullo_epi32(local_slot,
_mm256_set1_epi32(byte_size));
- __m256i pos = _mm256_srlv_epi32(hash, _mm256_set1_epi32(bits_hash_ -
log_blocks_));
- pos = _mm256_mullo_epi32(pos, _mm256_set1_epi32(byte_multiplier));
- pos = _mm256_add_epi32(pos, local_slot);
- __m256i group_id = _mm256_i32gather_epi32(elements, pos, 1);
+ __m256i local_slot_lo = _mm256_shuffle_epi8(
+ local_slot, _mm256_setr_epi32(0x80808000, 0x80808080, 0x80808001,
0x80808080,
+ 0x80808002, 0x80808080, 0x80808003,
0x80808080));
+ __m256i local_slot_hi = _mm256_shuffle_epi8(
+ local_slot, _mm256_setr_epi32(0x80808004, 0x80808080, 0x80808005,
0x80808080,
+ 0x80808006, 0x80808080, 0x80808007,
0x80808080));
+ local_slot_lo = _mm256_mul_epu32(local_slot_lo,
_mm256_set1_epi32(byte_size));
+ local_slot_lo = _mm256_mul_epu32(local_slot_hi,
_mm256_set1_epi32(byte_size));
Review Comment:
Isn't there a typo here (how come this doesn't trigger a failing test)?
```suggestion
local_slot_hi = _mm256_mul_epu32(local_slot_hi,
_mm256_set1_epi32(byte_size));
```
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