Optimize visibilitymap_count() with AVX-512 instructions.
Commit 792752af4e
added infrastructure for using AVX-512 intrinsic
functions, and this commit uses that infrastructure to optimize
visibilitymap_count(). Specificially, a new pg_popcount_masked()
function is introduced that applies a bitmask to every byte in the
buffer prior to calculating the population count, which is used to
filter out the all-visible or all-frozen bits as needed. Platforms
without AVX-512 support should also see a nice speedup due to the
reduced number of calls to a function pointer.
Co-authored-by: Ants Aasma
Discussion: https://postgr.es/m/BL1PR11MB5304097DF7EA81D04C33F3D1DCA6A%40BL1PR11MB5304.namprd11.prod.outlook.com
This commit is contained in:
parent
792752af4e
commit
41c51f0c68
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@ -119,10 +119,8 @@
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#define HEAPBLK_TO_OFFSET(x) (((x) % HEAPBLOCKS_PER_BYTE) * BITS_PER_HEAPBLOCK)
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/* Masks for counting subsets of bits in the visibility map. */
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#define VISIBLE_MASK64 UINT64CONST(0x5555555555555555) /* The lower bit of each
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* bit pair */
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#define FROZEN_MASK64 UINT64CONST(0xaaaaaaaaaaaaaaaa) /* The upper bit of each
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* bit pair */
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#define VISIBLE_MASK8 (0x55) /* The lower bit of each bit pair */
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#define FROZEN_MASK8 (0xaa) /* The upper bit of each bit pair */
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/* prototypes for internal routines */
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static Buffer vm_readbuf(Relation rel, BlockNumber blkno, bool extend);
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@ -396,7 +394,6 @@ visibilitymap_count(Relation rel, BlockNumber *all_visible, BlockNumber *all_fro
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{
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Buffer mapBuffer;
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uint64 *map;
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int i;
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/*
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* Read till we fall off the end of the map. We assume that any extra
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@ -414,21 +411,9 @@ visibilitymap_count(Relation rel, BlockNumber *all_visible, BlockNumber *all_fro
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*/
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map = (uint64 *) PageGetContents(BufferGetPage(mapBuffer));
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StaticAssertStmt(MAPSIZE % sizeof(uint64) == 0,
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"unsupported MAPSIZE");
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if (all_frozen == NULL)
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{
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for (i = 0; i < MAPSIZE / sizeof(uint64); i++)
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nvisible += pg_popcount64(map[i] & VISIBLE_MASK64);
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}
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else
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{
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for (i = 0; i < MAPSIZE / sizeof(uint64); i++)
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{
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nvisible += pg_popcount64(map[i] & VISIBLE_MASK64);
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nfrozen += pg_popcount64(map[i] & FROZEN_MASK64);
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}
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}
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nvisible += pg_popcount_masked((const char *) map, MAPSIZE, VISIBLE_MASK8);
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if (all_frozen)
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nfrozen += pg_popcount_masked((const char *) map, MAPSIZE, FROZEN_MASK8);
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ReleaseBuffer(mapBuffer);
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}
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@ -303,6 +303,7 @@ pg_ceil_log2_64(uint64 num)
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extern PGDLLIMPORT int (*pg_popcount32) (uint32 word);
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extern PGDLLIMPORT int (*pg_popcount64) (uint64 word);
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extern PGDLLIMPORT uint64 (*pg_popcount_optimized) (const char *buf, int bytes);
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extern PGDLLIMPORT uint64 (*pg_popcount_masked_optimized) (const char *buf, int bytes, bits8 mask);
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/*
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* We can also try to use the AVX-512 popcount instruction on some systems.
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@ -313,6 +314,7 @@ extern PGDLLIMPORT uint64 (*pg_popcount_optimized) (const char *buf, int bytes);
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#ifdef USE_AVX512_POPCNT_WITH_RUNTIME_CHECK
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extern bool pg_popcount_avx512_available(void);
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extern uint64 pg_popcount_avx512(const char *buf, int bytes);
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extern uint64 pg_popcount_masked_avx512(const char *buf, int bytes, bits8 mask);
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#endif
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#else
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@ -320,6 +322,7 @@ extern uint64 pg_popcount_avx512(const char *buf, int bytes);
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extern int pg_popcount32(uint32 word);
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extern int pg_popcount64(uint64 word);
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extern uint64 pg_popcount_optimized(const char *buf, int bytes);
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extern uint64 pg_popcount_masked_optimized(const char *buf, int bytes, bits8 mask);
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#endif /* TRY_POPCNT_FAST */
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@ -357,6 +360,37 @@ pg_popcount(const char *buf, int bytes)
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return pg_popcount_optimized(buf, bytes);
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}
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/*
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* Returns the number of 1-bits in buf after applying the mask to each byte.
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*
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* Similar to pg_popcount(), we only take on the function pointer overhead when
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* it's likely to be faster.
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*/
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static inline uint64
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pg_popcount_masked(const char *buf, int bytes, bits8 mask)
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{
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/*
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* We set the threshold to the point at which we'll first use special
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* instructions in the optimized version.
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*/
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#if SIZEOF_VOID_P >= 8
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int threshold = 8;
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#else
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int threshold = 4;
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#endif
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if (bytes < threshold)
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{
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uint64 popcnt = 0;
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while (bytes--)
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popcnt += pg_number_of_ones[(unsigned char) *buf++ & mask];
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return popcnt;
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}
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return pg_popcount_masked_optimized(buf, bytes, mask);
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}
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/*
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* Rotate the bits of "word" to the right/left by n bits.
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*/
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@ -106,19 +106,23 @@ const uint8 pg_number_of_ones[256] = {
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static inline int pg_popcount32_slow(uint32 word);
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static inline int pg_popcount64_slow(uint64 word);
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static uint64 pg_popcount_slow(const char *buf, int bytes);
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static uint64 pg_popcount_masked_slow(const char *buf, int bytes, bits8 mask);
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#ifdef TRY_POPCNT_FAST
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static bool pg_popcount_available(void);
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static int pg_popcount32_choose(uint32 word);
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static int pg_popcount64_choose(uint64 word);
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static uint64 pg_popcount_choose(const char *buf, int bytes);
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static uint64 pg_popcount_masked_choose(const char *buf, int bytes, bits8 mask);
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static inline int pg_popcount32_fast(uint32 word);
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static inline int pg_popcount64_fast(uint64 word);
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static uint64 pg_popcount_fast(const char *buf, int bytes);
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static uint64 pg_popcount_masked_fast(const char *buf, int bytes, bits8 mask);
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int (*pg_popcount32) (uint32 word) = pg_popcount32_choose;
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int (*pg_popcount64) (uint64 word) = pg_popcount64_choose;
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uint64 (*pg_popcount_optimized) (const char *buf, int bytes) = pg_popcount_choose;
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uint64 (*pg_popcount_masked_optimized) (const char *buf, int bytes, bits8 mask) = pg_popcount_masked_choose;
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#endif /* TRY_POPCNT_FAST */
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#ifdef TRY_POPCNT_FAST
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@ -156,17 +160,22 @@ choose_popcount_functions(void)
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pg_popcount32 = pg_popcount32_fast;
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pg_popcount64 = pg_popcount64_fast;
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pg_popcount_optimized = pg_popcount_fast;
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pg_popcount_masked_optimized = pg_popcount_masked_fast;
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}
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else
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{
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pg_popcount32 = pg_popcount32_slow;
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pg_popcount64 = pg_popcount64_slow;
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pg_popcount_optimized = pg_popcount_slow;
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pg_popcount_masked_optimized = pg_popcount_masked_slow;
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}
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#ifdef USE_AVX512_POPCNT_WITH_RUNTIME_CHECK
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if (pg_popcount_avx512_available())
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{
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pg_popcount_optimized = pg_popcount_avx512;
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pg_popcount_masked_optimized = pg_popcount_masked_avx512;
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}
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#endif
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}
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return pg_popcount_optimized(buf, bytes);
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}
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static uint64
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pg_popcount_masked_choose(const char *buf, int bytes, bits8 mask)
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{
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choose_popcount_functions();
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return pg_popcount_masked(buf, bytes, mask);
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}
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/*
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* pg_popcount32_fast
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* Return the number of 1 bits set in word
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return popcnt;
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}
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/*
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* pg_popcount_masked_fast
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* Returns the number of 1-bits in buf after applying the mask to each byte
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*/
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static uint64
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pg_popcount_masked_fast(const char *buf, int bytes, bits8 mask)
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{
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uint64 popcnt = 0;
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#if SIZEOF_VOID_P >= 8
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/* Process in 64-bit chunks if the buffer is aligned */
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uint64 maskv = ~UINT64CONST(0) / 0xFF * mask;
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if (buf == (const char *) TYPEALIGN(8, buf))
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{
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const uint64 *words = (const uint64 *) buf;
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while (bytes >= 8)
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{
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popcnt += pg_popcount64_fast(*words++ & maskv);
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bytes -= 8;
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}
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buf = (const char *) words;
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}
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#else
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/* Process in 32-bit chunks if the buffer is aligned. */
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uint32 maskv = ~((uint32) 0) / 0xFF * mask;
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if (buf == (const char *) TYPEALIGN(4, buf))
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{
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const uint32 *words = (const uint32 *) buf;
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while (bytes >= 4)
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{
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popcnt += pg_popcount32_fast(*words++ & maskv);
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bytes -= 4;
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}
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buf = (const char *) words;
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}
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#endif
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/* Process any remaining bytes */
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while (bytes--)
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popcnt += pg_number_of_ones[(unsigned char) *buf++ & mask];
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return popcnt;
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}
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#endif /* TRY_POPCNT_FAST */
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return popcnt;
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}
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/*
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* pg_popcount_masked_slow
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* Returns the number of 1-bits in buf after applying the mask to each byte
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*/
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static uint64
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pg_popcount_masked_slow(const char *buf, int bytes, bits8 mask)
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{
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uint64 popcnt = 0;
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#if SIZEOF_VOID_P >= 8
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/* Process in 64-bit chunks if the buffer is aligned */
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uint64 maskv = ~UINT64CONST(0) / 0xFF * mask;
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if (buf == (const char *) TYPEALIGN(8, buf))
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{
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const uint64 *words = (const uint64 *) buf;
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while (bytes >= 8)
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{
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popcnt += pg_popcount64_slow(*words++ & maskv);
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bytes -= 8;
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}
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buf = (const char *) words;
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}
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#else
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/* Process in 32-bit chunks if the buffer is aligned. */
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uint32 maskv = ~((uint32) 0) / 0xFF * mask;
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if (buf == (const char *) TYPEALIGN(4, buf))
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{
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const uint32 *words = (const uint32 *) buf;
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while (bytes >= 4)
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{
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popcnt += pg_popcount32_slow(*words++ & maskv);
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bytes -= 4;
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}
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buf = (const char *) words;
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}
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#endif
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/* Process any remaining bytes */
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while (bytes--)
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popcnt += pg_number_of_ones[(unsigned char) *buf++ & mask];
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return popcnt;
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}
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#ifndef TRY_POPCNT_FAST
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/*
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return pg_popcount_slow(buf, bytes);
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}
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/*
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* pg_popcount_masked_optimized
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* Returns the number of 1-bits in buf after applying the mask to each byte
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*/
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uint64
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pg_popcount_masked_optimized(const char *buf, int bytes, bits8 mask)
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{
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return pg_popcount_masked_slow(buf, bytes, mask);
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}
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#endif /* !TRY_POPCNT_FAST */
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@ -78,4 +78,64 @@ pg_popcount_avx512(const char *buf, int bytes)
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return _mm512_reduce_add_epi64(accum);
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}
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/*
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* pg_popcount_masked_avx512
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* Returns the number of 1-bits in buf after applying the mask to each byte
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*/
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uint64
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pg_popcount_masked_avx512(const char *buf, int bytes, bits8 mask)
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{
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__m512i val,
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vmasked,
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cnt;
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__m512i accum = _mm512_setzero_si512();
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const char *final;
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int tail_idx;
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__mmask64 bmask = ~UINT64CONST(0);
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const __m512i maskv = _mm512_set1_epi8(mask);
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/*
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* Align buffer down to avoid double load overhead from unaligned access.
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* Calculate a mask to ignore preceding bytes. Find start offset of final
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* iteration and ensure it is not empty.
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*/
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bmask <<= ((uintptr_t) buf) % sizeof(__m512i);
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tail_idx = (((uintptr_t) buf + bytes - 1) % sizeof(__m512i)) + 1;
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final = (const char *) TYPEALIGN_DOWN(sizeof(__m512i), buf + bytes - 1);
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buf = (const char *) TYPEALIGN_DOWN(sizeof(__m512i), buf);
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/*
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* Iterate through all but the final iteration. Starting from the second
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* iteration, the mask is ignored.
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*/
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if (buf < final)
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{
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val = _mm512_maskz_loadu_epi8(bmask, (const __m512i *) buf);
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vmasked = _mm512_and_si512(val, maskv);
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cnt = _mm512_popcnt_epi64(vmasked);
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accum = _mm512_add_epi64(accum, cnt);
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buf += sizeof(__m512i);
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bmask = ~UINT64CONST(0);
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for (; buf < final; buf += sizeof(__m512i))
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{
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val = _mm512_load_si512((const __m512i *) buf);
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vmasked = _mm512_and_si512(val, maskv);
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cnt = _mm512_popcnt_epi64(vmasked);
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accum = _mm512_add_epi64(accum, cnt);
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}
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}
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/* Final iteration needs to ignore bytes that are not within the length */
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bmask &= (~UINT64CONST(0) >> (sizeof(__m512i) - tail_idx));
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val = _mm512_maskz_loadu_epi8(bmask, (const __m512i *) buf);
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vmasked = _mm512_and_si512(val, maskv);
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cnt = _mm512_popcnt_epi64(vmasked);
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accum = _mm512_add_epi64(accum, cnt);
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return _mm512_reduce_add_epi64(accum);
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}
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#endif /* TRY_POPCNT_FAST */
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