mirror/coreutils
1
0
Fork 0
mirror of https://https.git.savannah.gnu.org/git/coreutils.git synced 2026-01-26 15:29:07 +00:00
Code Issues Packages Projects Releases Wiki Activity

wc: simplify and generalize AVX code

Browse Source 
* src/wc_avx2.c (wc_lines_avx2): Change from
_mm256_sub_epi8() + _mm256_sad_epu8() to
_mm256_movemask_epi8() + __builtin_popcount().
This will allow adjusting the I/O size above 16KiB.
* configure.ac: Align check with routines used in wc_avx2.c.
This commit is contained in:
Evgeny Nizhibitsky 2024-03-31 12:23:32 +01:00 committed by Pádraig Brady
parent 6480d59263
commit dd976cae23
2 changed files with 13 additions and 46 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
configure.ac
View File

@ -658,8 +658,9 @@ AC_LINK_IFELSE(
int
main (void)
{
__m256i a, b;
a = _mm256_sad_epu8 (a, b);
__m256i matches = _mm256_setzero_si256 ();
int mask = _mm256_movemask_epi8 (matches);
int lines = __builtin_popcount (mask);
return __builtin_cpu_supports ("avx2");
}
]])

54
src/wc_avx2.c
View File

@ -22,10 +22,7 @@
#include <x86intrin.h>
/* This must be below 16 KB (16384) or else the accumulators can
theoretically overflow, producing wrong result. This is 2*32 bytes below,
so there is no single bytes in the optimal case. */
#define BUFSIZE (16320)
#define BUFSIZE 16384
/* Read FD and return a summary. */
extern struct wc_lines
@ -34,21 +31,11 @@ wc_lines_avx2 (int fd)
intmax_t lines = 0;
intmax_t bytes = 0;
__m256i
zeroes = _mm256_setzero_si256 (),
endlines = _mm256_set1_epi8 ('\n');
__m256i endlines = _mm256_set1_epi8 ('\n');
while (true)
{
/* Using two parallel accumulators gave a good performance increase.
Adding a third gave no additional benefit, at least on an
Intel Xeon E3-1231v3. Maybe on a newer CPU with additional vector
execution engines it would be a win. */
__m256i
accumulator = _mm256_setzero_si256 (),
accumulator2 = _mm256_setzero_si256 (),
avx_buf[BUFSIZE / sizeof (__m256i)];
__m256i avx_buf[BUFSIZE / sizeof (__m256i)];
ssize_t bytes_read = read (fd, avx_buf, sizeof avx_buf);
if (bytes_read <= 0)
return (struct wc_lines) { bytes_read == 0 ? 0 : errno, lines, bytes };
@ -56,37 +43,16 @@ wc_lines_avx2 (int fd)
bytes += bytes_read;
__m256i *datap = avx_buf;
while (bytes_read >= 64)
while (bytes_read >= 32)
{
__m256i
to_match = _mm256_load_si256 (datap),
to_match2 = _mm256_load_si256 (datap + 1),
matches = _mm256_cmpeq_epi8 (to_match, endlines),
matches2 = _mm256_cmpeq_epi8 (to_match2, endlines);
/* Compare will set each 8 bit integer in the register to 0xFF
on match. When we subtract it the 8 bit accumulators
will underflow, so this is equal to adding 1. */
accumulator = _mm256_sub_epi8 (accumulator, matches);
accumulator2 = _mm256_sub_epi8 (accumulator2, matches2);
datap += 2;
bytes_read -= 64;
__m256i to_match = _mm256_load_si256 (datap);
__m256i matches = _mm256_cmpeq_epi8 (to_match, endlines);
int mask = _mm256_movemask_epi8 (matches);
lines += __builtin_popcount (mask);
datap += 1;
bytes_read -= 32;
}
/* Horizontally add all 8 bit integers in the register. */
accumulator = _mm256_sad_epu8 (accumulator, zeroes);
lines += _mm256_extract_epi16 (accumulator, 0)
+ _mm256_extract_epi16 (accumulator, 4)
+ _mm256_extract_epi16 (accumulator, 8)
+ _mm256_extract_epi16 (accumulator, 12);
accumulator2 = _mm256_sad_epu8 (accumulator2, zeroes);
lines += _mm256_extract_epi16 (accumulator2, 0)
+ _mm256_extract_epi16 (accumulator2, 4)
+ _mm256_extract_epi16 (accumulator2, 8)
+ _mm256_extract_epi16 (accumulator2, 12);
/* Finish up any left over bytes */
char *end = (char *) datap + bytes_read;
for (char *p = (char *) datap; p < end; p++)