pg_popcount_avx512.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * pg_popcount_avx512.c
 *    Holds the AVX-512 pg_popcount() implementation.
 *
 * Copyright (c) 2024, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/port/pg_popcount_avx512.c
 *
 *-------------------------------------------------------------------------
 */
#include "c.h"
 
#include <immintrin.h>
 
#include "port/pg_bitutils.h"
 
/*
 * It's probably unlikely that TRY_POPCNT_FAST won't be set if we are able to
 * use AVX-512 intrinsics, but we check it anyway to be sure.  We piggy-back on
 * the function pointers that are only used when TRY_POPCNT_FAST is set.
 */
#ifdef TRY_POPCNT_FAST
 
/*
 * pg_popcount_avx512
 *      Returns the number of 1-bits in buf
 */
uint64
pg_popcount_avx512(const char *buf, int bytes)
{
    __m512i     val,
                cnt;
    __m512i     accum = _mm512_setzero_si512();
    const char *final;
    int         tail_idx;
    __mmask64   mask = ~UINT64CONST(0);
 
    /*
     * Align buffer down to avoid double load overhead from unaligned access.
     * Calculate a mask to ignore preceding bytes.  Find start offset of final
     * iteration and ensure it is not empty.
     */
    mask <<= ((uintptr_t) buf) % sizeof(__m512i);
    tail_idx = (((uintptr_t) buf + bytes - 1) % sizeof(__m512i)) + 1;
    final = (const char *) TYPEALIGN_DOWN(sizeof(__m512i), buf + bytes - 1);
    buf = (const char *) TYPEALIGN_DOWN(sizeof(__m512i), buf);
 
    /*
     * Iterate through all but the final iteration.  Starting from the second
     * iteration, the mask is ignored.
     */
    if (buf < final)
    {
        val = _mm512_maskz_loadu_epi8(mask, (const __m512i *) buf);
        cnt = _mm512_popcnt_epi64(val);
        accum = _mm512_add_epi64(accum, cnt);
 
        buf += sizeof(__m512i);
        mask = ~UINT64CONST(0);
 
        for (; buf < final; buf += sizeof(__m512i))
        {
            val = _mm512_load_si512((const __m512i *) buf);
            cnt = _mm512_popcnt_epi64(val);
            accum = _mm512_add_epi64(accum, cnt);
        }
    }
 
    /* Final iteration needs to ignore bytes that are not within the length */
    mask &= (~UINT64CONST(0) >> (sizeof(__m512i) - tail_idx));
 
    val = _mm512_maskz_loadu_epi8(mask, (const __m512i *) buf);
    cnt = _mm512_popcnt_epi64(val);
    accum = _mm512_add_epi64(accum, cnt);
 
    return _mm512_reduce_add_epi64(accum);
}
 
/*
 * pg_popcount_masked_avx512
 *      Returns the number of 1-bits in buf after applying the mask to each byte
 */
uint64
pg_popcount_masked_avx512(const char *buf, int bytes, bits8 mask)
{
    __m512i     val,
                vmasked,
                cnt;
    __m512i     accum = _mm512_setzero_si512();
    const char *final;
    int         tail_idx;
    __mmask64   bmask = ~UINT64CONST(0);
    const       __m512i maskv = _mm512_set1_epi8(mask);
 
    /*
     * Align buffer down to avoid double load overhead from unaligned access.
     * Calculate a mask to ignore preceding bytes.  Find start offset of final
     * iteration and ensure it is not empty.
     */
    bmask <<= ((uintptr_t) buf) % sizeof(__m512i);
    tail_idx = (((uintptr_t) buf + bytes - 1) % sizeof(__m512i)) + 1;
    final = (const char *) TYPEALIGN_DOWN(sizeof(__m512i), buf + bytes - 1);
    buf = (const char *) TYPEALIGN_DOWN(sizeof(__m512i), buf);
 
    /*
     * Iterate through all but the final iteration.  Starting from the second
     * iteration, the mask is ignored.
     */
    if (buf < final)
    {
        val = _mm512_maskz_loadu_epi8(bmask, (const __m512i *) buf);
        vmasked = _mm512_and_si512(val, maskv);
        cnt = _mm512_popcnt_epi64(vmasked);
        accum = _mm512_add_epi64(accum, cnt);
 
        buf += sizeof(__m512i);
        bmask = ~UINT64CONST(0);
 
        for (; buf < final; buf += sizeof(__m512i))
        {
            val = _mm512_load_si512((const __m512i *) buf);
            vmasked = _mm512_and_si512(val, maskv);
            cnt = _mm512_popcnt_epi64(vmasked);
            accum = _mm512_add_epi64(accum, cnt);
        }
    }
 
    /* Final iteration needs to ignore bytes that are not within the length */
    bmask &= (~UINT64CONST(0) >> (sizeof(__m512i) - tail_idx));
 
    val = _mm512_maskz_loadu_epi8(bmask, (const __m512i *) buf);
    vmasked = _mm512_and_si512(val, maskv);
    cnt = _mm512_popcnt_epi64(vmasked);
    accum = _mm512_add_epi64(accum, cnt);
 
    return _mm512_reduce_add_epi64(accum);
}
 
#endif                          /* TRY_POPCNT_FAST */