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* [glibc] x86: Optimize strspn in strspn-c.c
@ 2022-03-25 18:18 Noah Goldstein
0 siblings, 0 replies; only message in thread
From: Noah Goldstein @ 2022-03-25 18:18 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=412d10343168b05b8cf6c3683457cf9711d28046
commit 412d10343168b05b8cf6c3683457cf9711d28046
Author: Noah Goldstein <goldstein.w.n@gmail.com>
Date: Wed Mar 23 16:57:24 2022 -0500
x86: Optimize strspn in strspn-c.c
Use _mm_cmpeq_epi8 and _mm_movemask_epi8 to get strlen instead of
_mm_cmpistri. Also change offset to unsigned to avoid unnecessary
sign extensions.
geometric_mean(N=20) of all benchmarks that dont fallback on
sse2; New / Original: .901
All string/memory tests pass.
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
Diff:
---
sysdeps/x86_64/multiarch/strspn-c.c | 86 +++++++++++++++++--------------------
1 file changed, 39 insertions(+), 47 deletions(-)
diff --git a/sysdeps/x86_64/multiarch/strspn-c.c b/sysdeps/x86_64/multiarch/strspn-c.c
index 8fb3aba64d..6124033ceb 100644
--- a/sysdeps/x86_64/multiarch/strspn-c.c
+++ b/sysdeps/x86_64/multiarch/strspn-c.c
@@ -62,81 +62,73 @@ __strspn_sse42 (const char *s, const char *a)
return 0;
const char *aligned;
- __m128i mask;
- int offset = (int) ((size_t) a & 15);
+ __m128i mask, maskz, zero;
+ unsigned int maskz_bits;
+ unsigned int offset = (int) ((size_t) a & 15);
+ zero = _mm_set1_epi8 (0);
if (offset != 0)
{
/* Load masks. */
aligned = (const char *) ((size_t) a & -16L);
__m128i mask0 = _mm_load_si128 ((__m128i *) aligned);
-
- mask = __m128i_shift_right (mask0, offset);
+ maskz = _mm_cmpeq_epi8 (mask0, zero);
/* Find where the NULL terminator is. */
- int length = _mm_cmpistri (mask, mask, 0x3a);
- if (length == 16 - offset)
- {
- /* There is no NULL terminator. */
- __m128i mask1 = _mm_load_si128 ((__m128i *) (aligned + 16));
- int index = _mm_cmpistri (mask1, mask1, 0x3a);
- length += index;
-
- /* Don't use SSE4.2 if the length of A > 16. */
- if (length > 16)
- return __strspn_sse2 (s, a);
-
- if (index != 0)
- {
- /* Combine mask0 and mask1. We could play games with
- palignr, but frankly this data should be in L1 now
- so do the merge via an unaligned load. */
- mask = _mm_loadu_si128 ((__m128i *) a);
- }
- }
+ maskz_bits = _mm_movemask_epi8 (maskz) >> offset;
+ if (maskz_bits != 0)
+ {
+ mask = __m128i_shift_right (mask0, offset);
+ offset = (unsigned int) ((size_t) s & 15);
+ if (offset)
+ goto start_unaligned;
+
+ aligned = s;
+ goto start_loop;
+ }
}
- else
- {
- /* A is aligned. */
- mask = _mm_load_si128 ((__m128i *) a);
- /* Find where the NULL terminator is. */
- int length = _mm_cmpistri (mask, mask, 0x3a);
- if (length == 16)
- {
- /* There is no NULL terminator. Don't use SSE4.2 if the length
- of A > 16. */
- if (a[16] != 0)
- return __strspn_sse2 (s, a);
- }
+ /* A is aligned. */
+ mask = _mm_loadu_si128 ((__m128i *) a);
+
+ /* Find where the NULL terminator is. */
+ maskz = _mm_cmpeq_epi8 (mask, zero);
+ maskz_bits = _mm_movemask_epi8 (maskz);
+ if (maskz_bits == 0)
+ {
+ /* There is no NULL terminator. Don't use SSE4.2 if the length
+ of A > 16. */
+ if (a[16] != 0)
+ return __strspn_sse2 (s, a);
}
+ aligned = s;
+ offset = (unsigned int) ((size_t) s & 15);
- offset = (int) ((size_t) s & 15);
if (offset != 0)
{
+ start_unaligned:
/* Check partial string. */
aligned = (const char *) ((size_t) s & -16L);
__m128i value = _mm_load_si128 ((__m128i *) aligned);
+ __m128i adj_value = __m128i_shift_right (value, offset);
- value = __m128i_shift_right (value, offset);
-
- int length = _mm_cmpistri (mask, value, 0x12);
+ unsigned int length = _mm_cmpistri (mask, adj_value, 0x12);
/* No need to check CFlag since it is always 1. */
if (length < 16 - offset)
return length;
/* Find where the NULL terminator is. */
- int index = _mm_cmpistri (value, value, 0x3a);
- if (index < 16 - offset)
+ maskz = _mm_cmpeq_epi8 (value, zero);
+ maskz_bits = _mm_movemask_epi8 (maskz) >> offset;
+ if (maskz_bits != 0)
return length;
aligned += 16;
}
- else
- aligned = s;
+start_loop:
while (1)
{
__m128i value = _mm_load_si128 ((__m128i *) aligned);
- int index = _mm_cmpistri (mask, value, 0x12);
- int cflag = _mm_cmpistrc (mask, value, 0x12);
+ unsigned int index = _mm_cmpistri (mask, value, 0x12);
+ unsigned int cflag = _mm_cmpistrc (mask, value, 0x12);
if (cflag)
return (size_t) (aligned + index - s);
aligned += 16;
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