pg_popcount_aarch64.c

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/*-------------------------------------------------------------------------
 *
 * pg_popcount_aarch64.c
 *    Holds the AArch64 popcount implementations.
 *
 * Copyright (c) 2025-2026, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *    src/port/pg_popcount_aarch64.c
 *
 *-------------------------------------------------------------------------
 */
#include "c.h"
 
#ifdef USE_NEON
 
#include <arm_neon.h>
 
#ifdef USE_SVE_POPCNT_WITH_RUNTIME_CHECK
#include <arm_sve.h>
 
#if defined(HAVE_ELF_AUX_INFO) || defined(HAVE_GETAUXVAL)
#include <sys/auxv.h>
/* Ancient glibc releases don't include the HWCAPxxx macros in sys/auxv.h */
#if defined(__linux__) && !defined(HWCAP_SVE)
#include <asm/hwcap.h>
#endif
#endif
#endif
 
#include "port/pg_bitutils.h"
 
/*
 * The Neon versions are built regardless of whether we are building the SVE
 * versions.
 */
static uint64 pg_popcount_neon(const char *buf, int bytes);
static uint64 pg_popcount_masked_neon(const char *buf, int bytes, uint8 mask);
 
#ifdef USE_SVE_POPCNT_WITH_RUNTIME_CHECK
 
/*
 * These are the SVE implementations of the popcount functions.
 */
static uint64 pg_popcount_sve(const char *buf, int bytes);
static uint64 pg_popcount_masked_sve(const char *buf, int bytes, uint8 mask);
 
/*
 * The function pointers are initially set to "choose" functions.  These
 * functions will first set the pointers to the right implementations (based 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, uint8 mask);
uint64      (*pg_popcount_optimized) (const char *buf, int bytes) = pg_popcount_choose;
uint64      (*pg_popcount_masked_optimized) (const char *buf, int bytes, uint8 mask) = pg_popcount_masked_choose;
 
static inline bool
pg_popcount_sve_available(void)
{
#ifdef HAVE_ELF_AUX_INFO
    unsigned long value;
 
    return elf_aux_info(AT_HWCAP, &value, sizeof(value)) == 0 &&
        (value & HWCAP_SVE) != 0;
#elif defined(HAVE_GETAUXVAL)
    return (getauxval(AT_HWCAP) & HWCAP_SVE) != 0;
#else
    return false;
#endif
}
 
static inline void
choose_popcount_functions(void)
{
    if (pg_popcount_sve_available())
    {
        pg_popcount_optimized = pg_popcount_sve;
        pg_popcount_masked_optimized = pg_popcount_masked_sve;
    }
    else
    {
        pg_popcount_optimized = pg_popcount_neon;
        pg_popcount_masked_optimized = pg_popcount_masked_neon;
    }
}
 
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, uint8 mask)
{
    choose_popcount_functions();
    return pg_popcount_masked_optimized(buf, bytes, mask);
}
 
/*
 * pg_popcount_sve
 *      Returns number of 1 bits in buf
 */
pg_attribute_target("arch=armv8-a+sve")
static uint64
pg_popcount_sve(const char *buf, int bytes)
{
    svbool_t    pred = svptrue_b64();
    svuint64_t  accum1 = svdup_u64(0),
                accum2 = svdup_u64(0),
                accum3 = svdup_u64(0),
                accum4 = svdup_u64(0);
    uint32      vec_len = svcntb(),
                bytes_per_iteration = 4 * vec_len;
    uint64      popcnt = 0;
 
    /*
     * For better instruction-level parallelism, each loop iteration operates
     * on a block of four registers.
     */
    for (; bytes >= bytes_per_iteration; bytes -= bytes_per_iteration)
    {
        svuint64_t  vec;
 
        vec = svld1_u64(pred, (const uint64 *) buf);
        accum1 = svadd_u64_x(pred, accum1, svcnt_u64_x(pred, vec));
        buf += vec_len;
 
        vec = svld1_u64(pred, (const uint64 *) buf);
        accum2 = svadd_u64_x(pred, accum2, svcnt_u64_x(pred, vec));
        buf += vec_len;
 
        vec = svld1_u64(pred, (const uint64 *) buf);
        accum3 = svadd_u64_x(pred, accum3, svcnt_u64_x(pred, vec));
        buf += vec_len;
 
        vec = svld1_u64(pred, (const uint64 *) buf);
        accum4 = svadd_u64_x(pred, accum4, svcnt_u64_x(pred, vec));
        buf += vec_len;
    }
 
    /*
     * If enough data remains, do another iteration on a block of two
     * registers.
     */
    bytes_per_iteration = 2 * vec_len;
    if (bytes >= bytes_per_iteration)
    {
        svuint64_t  vec;
 
        vec = svld1_u64(pred, (const uint64 *) buf);
        accum1 = svadd_u64_x(pred, accum1, svcnt_u64_x(pred, vec));
        buf += vec_len;
 
        vec = svld1_u64(pred, (const uint64 *) buf);
        accum2 = svadd_u64_x(pred, accum2, svcnt_u64_x(pred, vec));
        buf += vec_len;
 
        bytes -= bytes_per_iteration;
    }
 
    /*
     * Add the accumulators.
     */
    popcnt += svaddv_u64(pred, svadd_u64_x(pred, accum1, accum2));
    popcnt += svaddv_u64(pred, svadd_u64_x(pred, accum3, accum4));
 
    /*
     * Process any remaining data.
     */
    for (; bytes > 0; bytes -= vec_len)
    {
        svuint8_t   vec;
 
        pred = svwhilelt_b8_s32(0, bytes);
        vec = svld1_u8(pred, (const uint8 *) buf);
        popcnt += svaddv_u8(pred, svcnt_u8_x(pred, vec));
        buf += vec_len;
    }
 
    return popcnt;
}
 
/*
 * pg_popcount_masked_sve
 *      Returns number of 1 bits in buf after applying the mask to each byte
 */
pg_attribute_target("arch=armv8-a+sve")
static uint64
pg_popcount_masked_sve(const char *buf, int bytes, uint8 mask)
{
    svbool_t    pred = svptrue_b64();
    svuint64_t  accum1 = svdup_u64(0),
                accum2 = svdup_u64(0),
                accum3 = svdup_u64(0),
                accum4 = svdup_u64(0);
    uint32      vec_len = svcntb(),
                bytes_per_iteration = 4 * vec_len;
    uint64      popcnt = 0,
                mask64 = ~UINT64CONST(0) / 0xFF * mask;
 
    /*
     * For better instruction-level parallelism, each loop iteration operates
     * on a block of four registers.
     */
    for (; bytes >= bytes_per_iteration; bytes -= bytes_per_iteration)
    {
        svuint64_t  vec;
 
        vec = svand_n_u64_x(pred, svld1_u64(pred, (const uint64 *) buf), mask64);
        accum1 = svadd_u64_x(pred, accum1, svcnt_u64_x(pred, vec));
        buf += vec_len;
 
        vec = svand_n_u64_x(pred, svld1_u64(pred, (const uint64 *) buf), mask64);
        accum2 = svadd_u64_x(pred, accum2, svcnt_u64_x(pred, vec));
        buf += vec_len;
 
        vec = svand_n_u64_x(pred, svld1_u64(pred, (const uint64 *) buf), mask64);
        accum3 = svadd_u64_x(pred, accum3, svcnt_u64_x(pred, vec));
        buf += vec_len;
 
        vec = svand_n_u64_x(pred, svld1_u64(pred, (const uint64 *) buf), mask64);
        accum4 = svadd_u64_x(pred, accum4, svcnt_u64_x(pred, vec));
        buf += vec_len;
    }
 
    /*
     * If enough data remains, do another iteration on a block of two
     * registers.
     */
    bytes_per_iteration = 2 * vec_len;
    if (bytes >= bytes_per_iteration)
    {
        svuint64_t  vec;
 
        vec = svand_n_u64_x(pred, svld1_u64(pred, (const uint64 *) buf), mask64);
        accum1 = svadd_u64_x(pred, accum1, svcnt_u64_x(pred, vec));
        buf += vec_len;
 
        vec = svand_n_u64_x(pred, svld1_u64(pred, (const uint64 *) buf), mask64);
        accum2 = svadd_u64_x(pred, accum2, svcnt_u64_x(pred, vec));
        buf += vec_len;
 
        bytes -= bytes_per_iteration;
    }
 
    /*
     * Add the accumulators.
     */
    popcnt += svaddv_u64(pred, svadd_u64_x(pred, accum1, accum2));
    popcnt += svaddv_u64(pred, svadd_u64_x(pred, accum3, accum4));
 
    /*
     * Process any remaining data.
     */
    for (; bytes > 0; bytes -= vec_len)
    {
        svuint8_t   vec;
 
        pred = svwhilelt_b8_s32(0, bytes);
        vec = svand_n_u8_x(pred, svld1_u8(pred, (const uint8 *) buf), mask);
        popcnt += svaddv_u8(pred, svcnt_u8_x(pred, vec));
        buf += vec_len;
    }
 
    return popcnt;
}
 
#else                           /* USE_SVE_POPCNT_WITH_RUNTIME_CHECK */
 
/*
 * When the SVE version isn't available, there's no point in using function
 * pointers to vary the implementation.  We instead just make these actual
 * external functions when USE_SVE_POPCNT_WITH_RUNTIME_CHECK is not defined.
 * The compiler should be able to inline the Neon versions here.
 */
uint64
pg_popcount_optimized(const char *buf, int bytes)
{
    return pg_popcount_neon(buf, bytes);
}
 
uint64
pg_popcount_masked_optimized(const char *buf, int bytes, uint8 mask)
{
    return pg_popcount_masked_neon(buf, bytes, mask);
}
 
#endif                          /* ! USE_SVE_POPCNT_WITH_RUNTIME_CHECK */
 
/*
 * pg_popcount64_neon
 *      Return number of 1 bits in word
 */
static inline int
pg_popcount64_neon(uint64 word)
{
    return vaddv_u8(vcnt_u8(vld1_u8((const uint8 *) &word)));
}
 
/*
 * pg_popcount_neon
 *      Returns number of 1 bits in buf
 */
static uint64
pg_popcount_neon(const char *buf, int bytes)
{
    uint8x16_t  vec;
    uint64x2_t  accum1 = vdupq_n_u64(0),
                accum2 = vdupq_n_u64(0),
                accum3 = vdupq_n_u64(0),
                accum4 = vdupq_n_u64(0);
    uint32      bytes_per_iteration = 4 * sizeof(uint8x16_t);
    uint64      popcnt = 0;
 
    /*
     * For better instruction-level parallelism, each loop iteration operates
     * on a block of four registers.
     */
    for (; bytes >= bytes_per_iteration; bytes -= bytes_per_iteration)
    {
        vec = vld1q_u8((const uint8 *) buf);
        accum1 = vpadalq_u32(accum1, vpaddlq_u16(vpaddlq_u8(vcntq_u8(vec))));
        buf += sizeof(uint8x16_t);
 
        vec = vld1q_u8((const uint8 *) buf);
        accum2 = vpadalq_u32(accum2, vpaddlq_u16(vpaddlq_u8(vcntq_u8(vec))));
        buf += sizeof(uint8x16_t);
 
        vec = vld1q_u8((const uint8 *) buf);
        accum3 = vpadalq_u32(accum3, vpaddlq_u16(vpaddlq_u8(vcntq_u8(vec))));
        buf += sizeof(uint8x16_t);
 
        vec = vld1q_u8((const uint8 *) buf);
        accum4 = vpadalq_u32(accum4, vpaddlq_u16(vpaddlq_u8(vcntq_u8(vec))));
        buf += sizeof(uint8x16_t);
    }
 
    /*
     * If enough data remains, do another iteration on a block of two
     * registers.
     */
    bytes_per_iteration = 2 * sizeof(uint8x16_t);
    if (bytes >= bytes_per_iteration)
    {
        vec = vld1q_u8((const uint8 *) buf);
        accum1 = vpadalq_u32(accum1, vpaddlq_u16(vpaddlq_u8(vcntq_u8(vec))));
        buf += sizeof(uint8x16_t);
 
        vec = vld1q_u8((const uint8 *) buf);
        accum2 = vpadalq_u32(accum2, vpaddlq_u16(vpaddlq_u8(vcntq_u8(vec))));
        buf += sizeof(uint8x16_t);
 
        bytes -= bytes_per_iteration;
    }
 
    /*
     * Add the accumulators.
     */
    popcnt += vaddvq_u64(vaddq_u64(accum1, accum2));
    popcnt += vaddvq_u64(vaddq_u64(accum3, accum4));
 
    /*
     * Process remaining 8-byte blocks.
     */
    for (; bytes >= sizeof(uint64); bytes -= sizeof(uint64))
    {
        popcnt += pg_popcount64_neon(*((const uint64 *) buf));
        buf += sizeof(uint64);
    }
 
    /*
     * Process any remaining data byte-by-byte.
     */
    while (bytes--)
        popcnt += pg_number_of_ones[(unsigned char) *buf++];
 
    return popcnt;
}
 
/*
 * pg_popcount_masked_neon
 *      Returns number of 1 bits in buf after applying the mask to each byte
 */
static uint64
pg_popcount_masked_neon(const char *buf, int bytes, uint8 mask)
{
    uint8x16_t  vec,
                maskv = vdupq_n_u8(mask);
    uint64x2_t  accum1 = vdupq_n_u64(0),
                accum2 = vdupq_n_u64(0),
                accum3 = vdupq_n_u64(0),
                accum4 = vdupq_n_u64(0);
    uint32      bytes_per_iteration = 4 * sizeof(uint8x16_t);
    uint64      popcnt = 0,
                mask64 = ~UINT64CONST(0) / 0xFF * mask;
 
    /*
     * For better instruction-level parallelism, each loop iteration operates
     * on a block of four registers.
     */
    for (; bytes >= bytes_per_iteration; bytes -= bytes_per_iteration)
    {
        vec = vandq_u8(vld1q_u8((const uint8 *) buf), maskv);
        accum1 = vpadalq_u32(accum1, vpaddlq_u16(vpaddlq_u8(vcntq_u8(vec))));
        buf += sizeof(uint8x16_t);
 
        vec = vandq_u8(vld1q_u8((const uint8 *) buf), maskv);
        accum2 = vpadalq_u32(accum2, vpaddlq_u16(vpaddlq_u8(vcntq_u8(vec))));
        buf += sizeof(uint8x16_t);
 
        vec = vandq_u8(vld1q_u8((const uint8 *) buf), maskv);
        accum3 = vpadalq_u32(accum3, vpaddlq_u16(vpaddlq_u8(vcntq_u8(vec))));
        buf += sizeof(uint8x16_t);
 
        vec = vandq_u8(vld1q_u8((const uint8 *) buf), maskv);
        accum4 = vpadalq_u32(accum4, vpaddlq_u16(vpaddlq_u8(vcntq_u8(vec))));
        buf += sizeof(uint8x16_t);
    }
 
    /*
     * If enough data remains, do another iteration on a block of two
     * registers.
     */
    bytes_per_iteration = 2 * sizeof(uint8x16_t);
    if (bytes >= bytes_per_iteration)
    {
        vec = vandq_u8(vld1q_u8((const uint8 *) buf), maskv);
        accum1 = vpadalq_u32(accum1, vpaddlq_u16(vpaddlq_u8(vcntq_u8(vec))));
        buf += sizeof(uint8x16_t);
 
        vec = vandq_u8(vld1q_u8((const uint8 *) buf), maskv);
        accum2 = vpadalq_u32(accum2, vpaddlq_u16(vpaddlq_u8(vcntq_u8(vec))));
        buf += sizeof(uint8x16_t);
 
        bytes -= bytes_per_iteration;
    }
 
    /*
     * Add the accumulators.
     */
    popcnt += vaddvq_u64(vaddq_u64(accum1, accum2));
    popcnt += vaddvq_u64(vaddq_u64(accum3, accum4));
 
    /*
     * Process remaining 8-byte blocks.
     */
    for (; bytes >= sizeof(uint64); bytes -= sizeof(uint64))
    {
        popcnt += pg_popcount64_neon(*((const uint64 *) buf) & mask64);
        buf += sizeof(uint64);
    }
 
    /*
     * Process any remaining data byte-by-byte.
     */
    while (bytes--)
        popcnt += pg_number_of_ones[(unsigned char) *buf++ & mask];
 
    return popcnt;
}
 
#else                           /* USE_NEON */
 
/* prevent linker complaints about empty module */
extern int  pg_popcount_aarch64_dummy_variable;
int         pg_popcount_aarch64_dummy_variable = 0;
 
#endif                          /* ! USE_NEON */