pg_popcount_avx512.c

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/*-------------------------------------------------------------------------
 *
 * 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"
 
#ifdef USE_AVX512_POPCNT_WITH_RUNTIME_CHECK
 
#if defined(HAVE__GET_CPUID) || defined(HAVE__GET_CPUID_COUNT)
#include <cpuid.h>
#endif
 
#include <immintrin.h>
 
#if defined(HAVE__CPUID) || defined(HAVE__CPUIDEX)
#include <intrin.h>
#endif
 
#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
 
/*
 * Does CPUID say there's support for XSAVE instructions?
 */
static inline bool
xsave_available(void)
{
    unsigned int exx[4] = {0, 0, 0, 0};
 
#if defined(HAVE__GET_CPUID)
    __get_cpuid(1, &exx[0], &exx[1], &exx[2], &exx[3]);
#elif defined(HAVE__CPUID)
    __cpuid(exx, 1);
#else
#error cpuid instruction not available
#endif
    return (exx[2] & (1 << 27)) != 0;   /* osxsave */
}
 
/*
 * Does XGETBV say the ZMM registers are enabled?
 *
 * NB: Caller is responsible for verifying that xsave_available() returns true
 * before calling this.
 */
#ifdef HAVE_XSAVE_INTRINSICS
pg_attribute_target("xsave")
#endif
static inline bool
zmm_regs_available(void)
{
#ifdef HAVE_XSAVE_INTRINSICS
    return (_xgetbv(0) & 0xe6) == 0xe6;
#else
    return false;
#endif
}
 
/*
 * Does CPUID say there's support for AVX-512 popcount and byte-and-word
 * instructions?
 */
static inline bool
avx512_popcnt_available(void)
{
    unsigned int exx[4] = {0, 0, 0, 0};
 
#if defined(HAVE__GET_CPUID_COUNT)
    __get_cpuid_count(7, 0, &exx[0], &exx[1], &exx[2], &exx[3]);
#elif defined(HAVE__CPUIDEX)
    __cpuidex(exx, 7, 0);
#else
#error cpuid instruction not available
#endif
    return (exx[2] & (1 << 14)) != 0 && /* avx512-vpopcntdq */
        (exx[1] & (1 << 30)) != 0;  /* avx512-bw */
}
 
/*
 * Returns true if the CPU supports the instructions required for the AVX-512
 * pg_popcount() implementation.
 */
bool
pg_popcount_avx512_available(void)
{
    return xsave_available() &&
        zmm_regs_available() &&
        avx512_popcnt_available();
}
 
/*
 * pg_popcount_avx512
 *      Returns the number of 1-bits in buf
 */
pg_attribute_target("avx512vpopcntdq,avx512bw")
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
 */
pg_attribute_target("avx512vpopcntdq,avx512bw")
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 */
#endif                          /* USE_AVX512_POPCNT_WITH_RUNTIME_CHECK */