pg_popcount_x86.c

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/*-------------------------------------------------------------------------
 *
 * pg_popcount_x86.c
 *    Holds the x86-64 pg_popcount() implementations.
 *
 * Copyright (c) 2024-2026, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/port/pg_popcount_x86.c
 *
 *-------------------------------------------------------------------------
 */
#include "c.h"
 
#ifdef HAVE_X86_64_POPCNTQ
 
#ifdef USE_AVX512_POPCNT_WITH_RUNTIME_CHECK
#include <immintrin.h>
#endif
 
#include "port/pg_bitutils.h"
#include "port/pg_cpu.h"
 
/*
 * The SSE4.2 versions are built regardless of whether we are building the
 * AVX-512 versions.
 *
 * Technically, POPCNT is not part of SSE4.2, and isn't even a vector
 * operation, but in practice this is close enough, and "sse42" seems easier to
 * follow than "popcnt" for these names.
 */
static uint64 pg_popcount_sse42(const char *buf, int bytes);
static uint64 pg_popcount_masked_sse42(const char *buf, int bytes, bits8 mask);
 
/*
 * These are the AVX-512 implementations of the popcount functions.
 */
#ifdef USE_AVX512_POPCNT_WITH_RUNTIME_CHECK
static uint64 pg_popcount_avx512(const char *buf, int bytes);
static uint64 pg_popcount_masked_avx512(const char *buf, int bytes, bits8 mask);
#endif                          /* USE_AVX512_POPCNT_WITH_RUNTIME_CHECK */
 
/*
 * The function pointers are initially set to "choose" functions.  These
 * functions will first set the pointers to the right implementations (base on
 * what the current CPU supports) and then will call the pointer to fulfill the
 * caller's request.
 */
static uint64 pg_popcount_choose(const char *buf, int bytes);
static uint64 pg_popcount_masked_choose(const char *buf, int bytes, bits8 mask);
uint64      (*pg_popcount_optimized) (const char *buf, int bytes) = pg_popcount_choose;
uint64      (*pg_popcount_masked_optimized) (const char *buf, int bytes, bits8 mask) = pg_popcount_masked_choose;
 
 
#ifdef USE_AVX512_POPCNT_WITH_RUNTIME_CHECK
 
/*
 * Returns true if the CPU supports the instructions required for the AVX-512
 * pg_popcount() implementation.
 */
static bool
pg_popcount_avx512_available(void)
{
    return x86_feature_available(PG_AVX512_BW) &&
        x86_feature_available(PG_AVX512_VPOPCNTDQ);
}
 
#endif                          /* USE_AVX512_POPCNT_WITH_RUNTIME_CHECK */
 
/*
 * These functions get called on the first call to pg_popcount(), etc.
 * They detect whether we can use the asm implementations, and replace
 * the function pointers so that subsequent calls are routed directly to
 * the chosen implementation.
 */
static inline void
choose_popcount_functions(void)
{
    if (x86_feature_available(PG_POPCNT))
    {
        pg_popcount_optimized = pg_popcount_sse42;
        pg_popcount_masked_optimized = pg_popcount_masked_sse42;
    }
    else
    {
        pg_popcount_optimized = pg_popcount_portable;
        pg_popcount_masked_optimized = pg_popcount_masked_portable;
    }
 
#ifdef USE_AVX512_POPCNT_WITH_RUNTIME_CHECK
    if (pg_popcount_avx512_available())
    {
        pg_popcount_optimized = pg_popcount_avx512;
        pg_popcount_masked_optimized = pg_popcount_masked_avx512;
    }
#endif
}
 
static uint64
pg_popcount_choose(const char *buf, int bytes)
{
    choose_popcount_functions();
    return pg_popcount_optimized(buf, bytes);
}
 
static uint64
pg_popcount_masked_choose(const char *buf, int bytes, bits8 mask)
{
    choose_popcount_functions();
    return pg_popcount_masked(buf, bytes, mask);
}
 
#ifdef USE_AVX512_POPCNT_WITH_RUNTIME_CHECK
 
/*
 * pg_popcount_avx512
 *      Returns the number of 1-bits in buf
 */
pg_attribute_target("avx512vpopcntdq,avx512bw")
static 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")
static 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                          /* USE_AVX512_POPCNT_WITH_RUNTIME_CHECK */
 
/*
 * pg_popcount64_sse42
 *      Return the number of 1 bits set in word
 */
static inline int
pg_popcount64_sse42(uint64 word)
{
#ifdef _MSC_VER
    return __popcnt64(word);
#else
    uint64      res;
 
__asm__ __volatile__(" popcntq %1,%0\n":"=q"(res):"rm"(word):"cc");
    return (int) res;
#endif
}
 
/*
 * pg_popcount_sse42
 *      Returns the number of 1-bits in buf
 */
pg_attribute_no_sanitize_alignment()
static uint64
pg_popcount_sse42(const char *buf, int bytes)
{
    uint64      popcnt = 0;
    const uint64 *words = (const uint64 *) buf;
 
    while (bytes >= 8)
    {
        popcnt += pg_popcount64_sse42(*words++);
        bytes -= 8;
    }
 
    buf = (const char *) words;
 
    /* Process any remaining bytes */
    while (bytes--)
        popcnt += pg_number_of_ones[(unsigned char) *buf++];
 
    return popcnt;
}
 
/*
 * pg_popcount_masked_sse42
 *      Returns the number of 1-bits in buf after applying the mask to each byte
 */
pg_attribute_no_sanitize_alignment()
static uint64
pg_popcount_masked_sse42(const char *buf, int bytes, bits8 mask)
{
    uint64      popcnt = 0;
    uint64      maskv = ~UINT64CONST(0) / 0xFF * mask;
    const uint64 *words = (const uint64 *) buf;
 
    while (bytes >= 8)
    {
        popcnt += pg_popcount64_sse42(*words++ & maskv);
        bytes -= 8;
    }
 
    buf = (const char *) words;
 
    /* Process any remaining bytes */
    while (bytes--)
        popcnt += pg_number_of_ones[(unsigned char) *buf++ & mask];
 
    return popcnt;
}
 
#endif                          /* HAVE_X86_64_POPCNTQ */