On Mon, Aug 29, 2022 at 11:25:50AM +0700, John Naylor wrote:
> + uint32 nelem_per_vector = sizeof(Vector32) / sizeof(uint32);
> + uint32 nelem_per_iteration = 4 * nelem_per_vector;
>
> Using local #defines would be my style. I don't have a reason to
> object to this way, but adding const makes these vars more clear.
I added const.
> Speaking of const:
>
> - const __m128i tmp1 = _mm_or_si128(result1, result2);
> - const __m128i tmp2 = _mm_or_si128(result3, result4);
> - const __m128i result = _mm_or_si128(tmp1, tmp2);
> + tmp1 = vector32_or(result1, result2);
> + tmp2 = vector32_or(result3, result4);
> + result = vector32_or(tmp1, tmp2);
>
> Any reason to throw away the const declarations?
The only reason is because I had to move the declarations to before the
vector32_load() calls.
> +static inline bool
> +vector32_is_highbit_set(const Vector32 v)
> +{
> +#ifdef USE_SSE2
> + return (_mm_movemask_epi8(v) & 0x8888) != 0;
> +#endif
> +}
>
> I'm not sure why we need this function -- AFAICS it just adds more
> work on x86 for zero benefit. For our present application, can we just
> cast to Vector8 (for Arm's sake) and call the 8-bit version?
Good idea.
> - * operations using bitwise operations on unsigned integers.
> + * operations using bitwise operations on unsigned integers. Note that many
> + * of the functions in this file presently do not have non-SIMD
> + * implementations.
>
> It's unclear to the reader whether this is a matter of 'round-to-it's.
> I'd like to document what I asserted in this thread, that it's likely
> not worthwhile to do anything with a uint64 representing two 32-bit
> ints. (It *is* demonstrably worth it for handling 8 byte-values at a
> time)
Done.
> * Use saturating subtraction to find bytes <= c, which will present as
> - * NUL bytes in 'sub'.
> + * NUL bytes.
>
> I'd like to to point out that the reason to do it this way is to
> workaround SIMD architectures frequent lack of unsigned comparison.
Done.
> + * Return the result of subtracting the respective elements of the input
> + * vectors using saturation.
>
> I wonder if we should explain briefly what saturating arithmetic is. I
> had never encountered it outside of a SIMD programming context.
Done.
--
Nathan Bossart
Amazon Web Services: https://aws.amazon.com
>From 567c5309f3caa87c8cd7fe2de62309eea429d8c5 Mon Sep 17 00:00:00 2001
From: Nathan Bossart <[email protected]>
Date: Thu, 25 Aug 2022 22:18:30 -0700
Subject: [PATCH v6 1/2] abstract architecture-specific implementation details
from pg_lfind32()
---
src/include/port/pg_lfind.h | 55 ++++++++++++-----------
src/include/port/simd.h | 88 +++++++++++++++++++++++++++++++------
2 files changed, 104 insertions(+), 39 deletions(-)
diff --git a/src/include/port/pg_lfind.h b/src/include/port/pg_lfind.h
index a4e13dffec..1d9be4eb36 100644
--- a/src/include/port/pg_lfind.h
+++ b/src/include/port/pg_lfind.h
@@ -91,16 +91,19 @@ pg_lfind32(uint32 key, uint32 *base, uint32 nelem)
{
uint32 i = 0;
-#ifdef USE_SSE2
+#ifndef USE_NO_SIMD
/*
- * A 16-byte register only has four 4-byte lanes. For better
- * instruction-level parallelism, each loop iteration operates on a block
- * of four registers. Testing has showed this is ~40% faster than using a
- * block of two registers.
+ * For better instruction-level parallelism, each loop iteration operates
+ * on a block of four registers. Testing for SSE2 has showed this is ~40%
+ * faster than using a block of two registers.
*/
- const __m128i keys = _mm_set1_epi32(key); /* load 4 copies of key */
- uint32 iterations = nelem & ~0xF; /* round down to multiple of 16 */
+ const Vector32 keys = vector32_broadcast(key); /* load copies of key */
+ const uint32 nelem_per_vector = sizeof(Vector32) / sizeof(uint32);
+ const uint32 nelem_per_iteration = 4 * nelem_per_vector;
+
+ /* round down to multiple of elements per iteration */
+ const uint32 tail_idx = nelem & ~(nelem_per_iteration - 1);
#if defined(USE_ASSERT_CHECKING)
bool assert_result = false;
@@ -116,31 +119,33 @@ pg_lfind32(uint32 key, uint32 *base, uint32 nelem)
}
#endif
- for (i = 0; i < iterations; i += 16)
+ for (i = 0; i < tail_idx; i += nelem_per_iteration)
{
- /* load the next block into 4 registers holding 4 values each */
- const __m128i vals1 = _mm_loadu_si128((__m128i *) & base[i]);
- const __m128i vals2 = _mm_loadu_si128((__m128i *) & base[i + 4]);
- const __m128i vals3 = _mm_loadu_si128((__m128i *) & base[i + 8]);
- const __m128i vals4 = _mm_loadu_si128((__m128i *) & base[i + 12]);
+ Vector32 vals1, vals2, vals3, vals4,
+ result1, result2, result3, result4,
+ tmp1, tmp2, result;
+
+ /* load the next block into 4 registers */
+ vector32_load(&vals1, &base[i]);
+ vector32_load(&vals2, &base[i + nelem_per_vector]);
+ vector32_load(&vals3, &base[i + nelem_per_vector * 2]);
+ vector32_load(&vals4, &base[i + nelem_per_vector * 3]);
/* compare each value to the key */
- const __m128i result1 = _mm_cmpeq_epi32(keys, vals1);
- const __m128i result2 = _mm_cmpeq_epi32(keys, vals2);
- const __m128i result3 = _mm_cmpeq_epi32(keys, vals3);
- const __m128i result4 = _mm_cmpeq_epi32(keys, vals4);
+ result1 = vector32_eq(keys, vals1);
+ result2 = vector32_eq(keys, vals2);
+ result3 = vector32_eq(keys, vals3);
+ result4 = vector32_eq(keys, vals4);
/* combine the results into a single variable */
- const __m128i tmp1 = _mm_or_si128(result1, result2);
- const __m128i tmp2 = _mm_or_si128(result3, result4);
- const __m128i result = _mm_or_si128(tmp1, tmp2);
+ tmp1 = vector32_or(result1, result2);
+ tmp2 = vector32_or(result3, result4);
+ result = vector32_or(tmp1, tmp2);
/* see if there was a match */
- if (_mm_movemask_epi8(result) != 0)
+ if (vector8_is_highbit_set((Vector8) result))
{
-#if defined(USE_ASSERT_CHECKING)
Assert(assert_result == true);
-#endif
return true;
}
}
@@ -151,14 +156,14 @@ pg_lfind32(uint32 key, uint32 *base, uint32 nelem)
{
if (key == base[i])
{
-#if defined(USE_SSE2) && defined(USE_ASSERT_CHECKING)
+#ifndef USE_NO_SIMD
Assert(assert_result == true);
#endif
return true;
}
}
-#if defined(USE_SSE2) && defined(USE_ASSERT_CHECKING)
+#ifndef USE_NO_SIMD
Assert(assert_result == false);
#endif
return false;
diff --git a/src/include/port/simd.h b/src/include/port/simd.h
index a425cd887b..709408d8c6 100644
--- a/src/include/port/simd.h
+++ b/src/include/port/simd.h
@@ -31,22 +31,32 @@
#include <emmintrin.h>
#define USE_SSE2
typedef __m128i Vector8;
+typedef __m128i Vector32;
#else
/*
* If no SIMD instructions are available, we can in some cases emulate vector
- * operations using bitwise operations on unsigned integers.
+ * operations using bitwise operations on unsigned integers. Note that many
+ * of the functions in this file presently do not have non-SIMD
+ * implementations. In particular, none of the functions involving Vector32
+ * are implemented without SIMD since it's likely not worthwhile to do anything
+ * with a uint64 representing two 32-bit integers.
*/
#define USE_NO_SIMD
typedef uint64 Vector8;
#endif
-
/* load/store operations */
static inline void vector8_load(Vector8 *v, const uint8 *s);
+#ifndef USE_NO_SIMD
+static inline void vector32_load(Vector32 *v, const uint32 *s);
+#endif
/* assignment operations */
static inline Vector8 vector8_broadcast(const uint8 c);
+#ifndef USE_NO_SIMD
+static inline Vector32 vector32_broadcast(const uint32 c);
+#endif
/* element-wise comparisons to a scalar */
static inline bool vector8_has(const Vector8 v, const uint8 c);
@@ -56,14 +66,16 @@ static inline bool vector8_is_highbit_set(const Vector8 v);
/* arithmetic operations */
static inline Vector8 vector8_or(const Vector8 v1, const Vector8 v2);
-
-/* Different semantics for SIMD architectures. */
#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
/* comparisons between vectors */
+#ifndef USE_NO_SIMD
static inline Vector8 vector8_eq(const Vector8 v1, const Vector8 v2);
-
-#endif /* ! USE_NO_SIMD */
+static inline Vector32 vector32_eq(const Vector32 v1, const Vector32 v2);
+#endif
/*
* Load a chunk of memory into the given vector.
@@ -78,6 +90,15 @@ vector8_load(Vector8 *v, const uint8 *s)
#endif
}
+#ifndef USE_NO_SIMD
+static inline void
+vector32_load(Vector32 *v, const uint32 *s)
+{
+#ifdef USE_SSE2
+ *v = _mm_loadu_si128((const __m128i *) s);
+#endif
+}
+#endif /* ! USE_NO_SIMD */
/*
* Create a vector with all elements set to the same value.
@@ -92,6 +113,16 @@ vector8_broadcast(const uint8 c)
#endif
}
+#ifndef USE_NO_SIMD
+static inline Vector32
+vector32_broadcast(const uint32 c)
+{
+#ifdef USE_SSE2
+ return _mm_set1_epi32(c);
+#endif
+}
+#endif /* ! USE_NO_SIMD */
+
/*
* Return true if any elements in the vector are equal to the given scalar.
*/
@@ -118,7 +149,7 @@ vector8_has(const Vector8 v, const uint8 c)
/* any bytes in v equal to c will evaluate to zero via XOR */
result = vector8_has_zero(v ^ vector8_broadcast(c));
#elif defined(USE_SSE2)
- result = _mm_movemask_epi8(_mm_cmpeq_epi8(v, vector8_broadcast(c)));
+ result = vector8_is_highbit_set(vector8_eq(v, vector8_broadcast(c)));
#endif
Assert(assert_result == result);
@@ -150,9 +181,6 @@ static inline bool
vector8_has_le(const Vector8 v, const uint8 c)
{
bool result = false;
-#if defined(USE_SSE2)
- __m128i sub;
-#endif
/* pre-compute the result for assert checking */
#ifdef USE_ASSERT_CHECKING
@@ -194,10 +222,10 @@ vector8_has_le(const Vector8 v, const uint8 c)
/*
* Use saturating subtraction to find bytes <= c, which will present as
- * NUL bytes in 'sub'.
+ * NUL bytes. This approach is a workaround for the lack of unsigned
+ * comparison instructions on some architectures.
*/
- sub = _mm_subs_epu8(v, vector8_broadcast(c));
- result = vector8_has_zero(sub);
+ result = vector8_has_zero(vector8_ssub(v, vector8_broadcast(c)));
#endif
Assert(assert_result == result);
@@ -230,14 +258,37 @@ vector8_or(const Vector8 v1, const Vector8 v2)
#endif
}
+#ifndef USE_NO_SIMD
+static inline Vector32
+vector32_or(const Vector32 v1, const Vector32 v2)
+{
+#ifdef USE_SSE2
+ return _mm_or_si128(v1, v2);
+#endif
+}
+#endif /* ! USE_NO_SIMD */
-/* Different semantics for SIMD architectures. */
+/*
+ * 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);
+#endif
+}
+#endif /* ! USE_NO_SIMD */
/*
* Return a vector with all bits set in each lane where the the corresponding
* lanes in the inputs are equal.
*/
+#ifndef USE_NO_SIMD
static inline Vector8
vector8_eq(const Vector8 v1, const Vector8 v2)
{
@@ -245,7 +296,16 @@ vector8_eq(const Vector8 v1, const Vector8 v2)
return _mm_cmpeq_epi8(v1, v2);
#endif
}
+#endif /* ! USE_NO_SIMD */
+#ifndef USE_NO_SIMD
+static inline Vector32
+vector32_eq(const Vector32 v1, const Vector32 v2)
+{
+#ifdef USE_SSE2
+ return _mm_cmpeq_epi32(v1, v2);
+#endif
+}
#endif /* ! USE_NO_SIMD */
#endif /* SIMD_H */
--
2.32.1 (Apple Git-133)
>From 080a0223ab3c869de80f11272ffb25e940d26eff Mon Sep 17 00:00:00 2001
From: Nathan Bossart <[email protected]>
Date: Fri, 26 Aug 2022 10:47:35 -0700
Subject: [PATCH v6 2/2] use ARM Advanced SIMD intrinsic functions where
available
---
src/include/port/simd.h | 40 +++++++++++++++++++++++++++++++++++++---
1 file changed, 37 insertions(+), 3 deletions(-)
diff --git a/src/include/port/simd.h b/src/include/port/simd.h
index 709408d8c6..aeba240e2e 100644
--- a/src/include/port/simd.h
+++ b/src/include/port/simd.h
@@ -33,6 +33,20 @@
typedef __m128i Vector8;
typedef __m128i Vector32;
+#elif defined(__aarch64__) && defined(__ARM_NEON)
+/*
+ * We use the Neon instructions if the compiler provides access to them (as
+ * indicated by __ARM_NEON) and we are on aarch64. While Neon support is
+ * technically optional for aarch64, it appears that all available 64-bit
+ * hardware does have it. Neon exists in some 32-bit hardware too, but we
+ * could not realistically use it there without a run-time check, which seems
+ * not worth the trouble for now.
+ */
+#include <arm_neon.h>
+#define USE_NEON
+typedef uint8x16_t Vector8;
+typedef uint32x4_t Vector32;
+
#else
/*
* If no SIMD instructions are available, we can in some cases emulate vector
@@ -85,6 +99,8 @@ vector8_load(Vector8 *v, const uint8 *s)
{
#if defined(USE_SSE2)
*v = _mm_loadu_si128((const __m128i *) s);
+#elif defined(USE_NEON)
+ *v = vld1q_u8(s);
#else
memcpy(v, s, sizeof(Vector8));
#endif
@@ -96,6 +112,8 @@ vector32_load(Vector32 *v, const uint32 *s)
{
#ifdef USE_SSE2
*v = _mm_loadu_si128((const __m128i *) s);
+#elif defined(USE_NEON)
+ *v = vld1q_u32(s);
#endif
}
#endif /* ! USE_NO_SIMD */
@@ -108,6 +126,8 @@ vector8_broadcast(const uint8 c)
{
#if defined(USE_SSE2)
return _mm_set1_epi8(c);
+#elif defined(USE_NEON)
+ return vdupq_n_u8(c);
#else
return ~UINT64CONST(0) / 0xFF * c;
#endif
@@ -119,6 +139,8 @@ vector32_broadcast(const uint32 c)
{
#ifdef USE_SSE2
return _mm_set1_epi32(c);
+#elif defined(USE_NEON)
+ return vdupq_n_u32(c);
#endif
}
#endif /* ! USE_NO_SIMD */
@@ -148,7 +170,7 @@ vector8_has(const Vector8 v, const uint8 c)
#if defined(USE_NO_SIMD)
/* any bytes in v equal to c will evaluate to zero via XOR */
result = vector8_has_zero(v ^ vector8_broadcast(c));
-#elif defined(USE_SSE2)
+#else
result = vector8_is_highbit_set(vector8_eq(v, vector8_broadcast(c)));
#endif
@@ -168,7 +190,7 @@ vector8_has_zero(const Vector8 v)
* definition.
*/
return vector8_has_le(v, 0);
-#elif defined(USE_SSE2)
+#else
return vector8_has(v, 0);
#endif
}
@@ -218,7 +240,7 @@ vector8_has_le(const Vector8 v, const uint8 c)
}
}
}
-#elif defined(USE_SSE2)
+#else
/*
* Use saturating subtraction to find bytes <= c, which will present as
@@ -240,6 +262,8 @@ vector8_is_highbit_set(const Vector8 v)
{
#ifdef USE_SSE2
return _mm_movemask_epi8(v) != 0;
+#elif defined(USE_NEON)
+ return vmaxvq_u8(v) > 0x7F;
#else
return v & vector8_broadcast(0x80);
#endif
@@ -253,6 +277,8 @@ vector8_or(const Vector8 v1, const Vector8 v2)
{
#ifdef USE_SSE2
return _mm_or_si128(v1, v2);
+#elif defined(USE_NEON)
+ return vorrq_u8(v1, v2);
#else
return v1 | v2;
#endif
@@ -264,6 +290,8 @@ vector32_or(const Vector32 v1, const Vector32 v2)
{
#ifdef USE_SSE2
return _mm_or_si128(v1, v2);
+#elif defined(USE_NEON)
+ return vorrq_u32(v1, v2);
#endif
}
#endif /* ! USE_NO_SIMD */
@@ -280,6 +308,8 @@ 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 */
@@ -294,6 +324,8 @@ vector8_eq(const Vector8 v1, const Vector8 v2)
{
#ifdef USE_SSE2
return _mm_cmpeq_epi8(v1, v2);
+#elif defined(USE_NEON)
+ return vceqq_u8(v1, v2);
#endif
}
#endif /* ! USE_NO_SIMD */
@@ -304,6 +336,8 @@ vector32_eq(const Vector32 v1, const Vector32 v2)
{
#ifdef USE_SSE2
return _mm_cmpeq_epi32(v1, v2);
+#elif defined(USE_NEON)
+ return vceqq_u32(v1, v2);
#endif
}
#endif /* ! USE_NO_SIMD */
--
2.32.1 (Apple Git-133)
