zanmato1984 commented on code in PR #45108:
URL: https://github.com/apache/arrow/pull/45108#discussion_r1908132326
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cpp/src/arrow/compute/key_map_internal_avx2.cc:
##########
@@ -392,16 +392,32 @@ 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.
+ // 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_cvtepi32_epi64(_mm256_castsi256_si128(local_slot));
+ __m256i local_slot_hi =
+ _mm256_cvtepi32_epi64(_mm256_extracti128_si256(local_slot, 1));
+ __m256i pos_lo =
+ _mm256_srlv_epi64(hash_lo, _mm256_set1_epi64x(bits_hash_ -
log_blocks_));
+ __m256i pos_hi =
+ _mm256_srlv_epi64(hash_hi, _mm256_set1_epi64x(bits_hash_ -
log_blocks_));
+ pos_lo = _mm256_mul_epi32(pos_lo, _mm256_set1_epi32(byte_multiplier));
+ pos_hi = _mm256_mul_epi32(pos_hi, _mm256_set1_epi32(byte_multiplier));
+ pos_lo = _mm256_add_epi64(pos_lo, local_slot_lo);
+ pos_hi = _mm256_add_epi64(pos_hi, local_slot_hi);
+ __m128i group_id_lo = _mm256_i64gather_epi32(elements, pos_lo, 1);
+ __m128i group_id_hi = _mm256_i64gather_epi32(elements, pos_hi, 1);
+ __m256i group_id = _mm256_set_m128i(group_id_hi, group_id_lo);
Review Comment:
I was hoping conbench can tell about the performance but it seems not (and
I'm not planning to dig into why). I'll just run some related benchmark in my
local and get the rough numbers. My hunch is that even if there is some
(supposedly small) regression, it won't be worth the complexity. Will update
later.
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