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Optimize vector8_has_le() on AArch64.

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Presently, the SIMD implementation of this function uses unsigned
saturating subtraction to find bytes less than or equal to the
given value, which is a workaround for the lack of unsigned
comparison instructions on some architectures.  However, Neon
offers vminvq_u8(), which returns the minimum (unsigned) value in
the vector.  This commit adds a Neon-specific implementation that
uses vminvq_u8() to optimize vector8_has_le() on AArch64.

In passing, adjust the SSE2 implementation to use vector8_min() and
vector8_eq() to find values less than or equal to the given value.
This was the only use of vector8_ssub(), so it has been removed.

Reviewed-by: John Naylor <johncnaylorls@gmail.com>
Discussion: https://postgr.es/m/aNHDNDSHleq0ogC_%40nathan
This commit is contained in:
Nathan Bossart
2025-10-03 14:02:47 -05:00
parent 74b41f5a77
commit f8f4afe751
1 changed files with 10 additions and 27 deletions
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37
src/include/port/simd.h
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@@ -86,7 +86,6 @@ static inline uint32 vector8_highbit_mask(const Vector8 v);
static inline Vector8 vector8_or(const Vector8 v1, const Vector8 v2);
#ifndef USE_NO_SIMD
static inline Vector32 vector32_or(const Vector32 v1, const Vector32 v2);
static inline Vector8 vector8_ssub(const Vector8 v1, const Vector8 v2);
#endif
/*
@@ -213,6 +212,10 @@ static inline bool
vector8_has_le(const Vector8 v, const uint8 c)
{
bool result = false;
#ifdef USE_SSE2
Vector8 umin;
Vector8 cmpe;
#endif
/* pre-compute the result for assert checking */
#ifdef USE_ASSERT_CHECKING
@@ -250,14 +253,12 @@ vector8_has_le(const Vector8 v, const uint8 c)
}
}
}
#else
/*
* Use saturating subtraction to find bytes <= c, which will present as
* NUL bytes. This approach is a workaround for the lack of unsigned
* comparison instructions on some architectures.
*/
result = vector8_has_zero(vector8_ssub(v, vector8_broadcast(c)));
#elif defined(USE_SSE2)
umin = vector8_min(v, vector8_broadcast(c));
cmpe = vector8_eq(umin, v);
result = vector8_is_highbit_set(cmpe);
#elif defined(USE_NEON)
result = vminvq_u8(v) <= c;
#endif
Assert(assert_result == result);
@@ -358,24 +359,6 @@ vector32_or(const Vector32 v1, const Vector32 v2)
}
#endif /* ! USE_NO_SIMD */
/*
* Return the result of subtracting the respective elements of the input
* vectors using saturation (i.e., if the operation would yield a value less
* than zero, zero is returned instead). For more information on saturation
* arithmetic, see https://en.wikipedia.org/wiki/Saturation_arithmetic
*/
#ifndef USE_NO_SIMD
static inline Vector8
vector8_ssub(const Vector8 v1, const Vector8 v2)
{
#ifdef USE_SSE2
return _mm_subs_epu8(v1, v2);
#elif defined(USE_NEON)
return vqsubq_u8(v1, v2);
#endif
}
#endif /* ! USE_NO_SIMD */
/*
* Return a vector with all bits set in each lane where the corresponding
* lanes in the inputs are equal.