From: Nathan Bossart <nathandbossart@gmail.com>
To: pgsql-hackers@postgresql.org
Cc: johncnaylorls@gmail.com
Subject: remove switch statement in vector8_shift_{left,right}
Date: Wed, 1 Jul 2026 19:32:16 -0500
Message-ID: <akWxkA-mszMm57cV@nathan> (raw)
In commit ec8719ccbf, I added a switch statement with all expected shift
counts for vector8_shift_{left,right} because AArch64's vshlq_n_u32 and
vshrq_n_u32 require an integer literal. I discovered that we can use
vshlq_u32 instead for both cases, which avoids the need for the switch
statement and compiles to the same machine code on recent gcc/clang.
--
nathan
From 12b9db50eed370ba94ed4a7c4c9dd2218bad5f48 Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathan@postgresql.org>
Date: Wed, 1 Jul 2026 19:30:59 -0500
Subject: [PATCH v1 1/1] remove switch statement in vector8_shift_{left,right}
---
src/include/port/simd.h | 29 +++--------------------------
1 file changed, 3 insertions(+), 26 deletions(-)
diff --git a/src/include/port/simd.h b/src/include/port/simd.hindex 50615aec7f4..25a26c81cce 100644--- a/src/include/port/simd.h+++ b/src/include/port/simd.h@@ -548,10 +548,6 @@ vector8_pack_16(const Vector8 v1, const Vector8 v2)
/*
* Unsigned shift left of each 32-bit element in the vector by "i" bits.
- *- * XXX AArch64 requires an integer literal, so we have to list all expected- * values of "i" from all callers in a switch statement. If you add a new- * caller, be sure your expected values of "i" are handled.
*/
#ifndef USE_NO_SIMD
static inline Vector8
@@ -560,24 +556,13 @@ vector8_shift_left(const Vector8 v1, int i)
#ifdef USE_SSE2
return _mm_slli_epi32(v1, i);
#elif defined(USE_NEON)
- switch (i)- {- case 4:- return (Vector8) vshlq_n_u32((Vector32) v1, 4);- default:- Assert(false);- return vector8_broadcast(0);- }+ return (Vector8) vshlq_u32((Vector32) v1, vdupq_n_s32(i));
#endif
}
#endif /* ! USE_NO_SIMD */
/*
* Unsigned shift right of each 32-bit element in the vector by "i" bits.
- *- * XXX AArch64 requires an integer literal, so we have to list all expected- * values of "i" from all callers in a switch statement. If you add a new- * caller, be sure your expected values of "i" are handled.
*/
#ifndef USE_NO_SIMD
static inline Vector8
@@ -586,16 +571,8 @@ vector8_shift_right(const Vector8 v1, int i)
#ifdef USE_SSE2
return _mm_srli_epi32(v1, i);
#elif defined(USE_NEON)
- switch (i)- {- case 4:- return (Vector8) vshrq_n_u32((Vector32) v1, 4);- case 8:- return (Vector8) vshrq_n_u32((Vector32) v1, 8);- default:- Assert(false);- return vector8_broadcast(0);- }+ /* negative shift count means right shift */+ return (Vector8) vshlq_u32((Vector32) v1, vdupq_n_s32(-i));
#endif
}
#endif /* ! USE_NO_SIMD */
--
2.50.1 (Apple Git-155)
Attachments:
[text/plain] v1-0001-remove-switch-statement-in-vector8_shift_-left-ri.patch (2.1K, ../akWxkA-mszMm57cV@nathan/2-v1-0001-remove-switch-statement-in-vector8_shift_-left-ri.patch)
download | inline diff:
From 12b9db50eed370ba94ed4a7c4c9dd2218bad5f48 Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathan@postgresql.org>
Date: Wed, 1 Jul 2026 19:30:59 -0500
Subject: [PATCH v1 1/1] remove switch statement in vector8_shift_{left,right}
---
src/include/port/simd.h | 29 +++--------------------------
1 file changed, 3 insertions(+), 26 deletions(-)
diff --git a/src/include/port/simd.h b/src/include/port/simd.hindex 50615aec7f4..25a26c81cce 100644--- a/src/include/port/simd.h+++ b/src/include/port/simd.h@@ -548,10 +548,6 @@ vector8_pack_16(const Vector8 v1, const Vector8 v2)
/*
* Unsigned shift left of each 32-bit element in the vector by "i" bits.
- *- * XXX AArch64 requires an integer literal, so we have to list all expected- * values of "i" from all callers in a switch statement. If you add a new- * caller, be sure your expected values of "i" are handled.
*/
#ifndef USE_NO_SIMD
static inline Vector8
@@ -560,24 +556,13 @@ vector8_shift_left(const Vector8 v1, int i)
#ifdef USE_SSE2
return _mm_slli_epi32(v1, i);
#elif defined(USE_NEON)
- switch (i)- {- case 4:- return (Vector8) vshlq_n_u32((Vector32) v1, 4);- default:- Assert(false);- return vector8_broadcast(0);- }+ return (Vector8) vshlq_u32((Vector32) v1, vdupq_n_s32(i));
#endif
}
#endif /* ! USE_NO_SIMD */
/*
* Unsigned shift right of each 32-bit element in the vector by "i" bits.
- *- * XXX AArch64 requires an integer literal, so we have to list all expected- * values of "i" from all callers in a switch statement. If you add a new- * caller, be sure your expected values of "i" are handled.
*/
#ifndef USE_NO_SIMD
static inline Vector8
@@ -586,16 +571,8 @@ vector8_shift_right(const Vector8 v1, int i)
#ifdef USE_SSE2
return _mm_srli_epi32(v1, i);
#elif defined(USE_NEON)
- switch (i)- {- case 4:- return (Vector8) vshrq_n_u32((Vector32) v1, 4);- case 8:- return (Vector8) vshrq_n_u32((Vector32) v1, 8);- default:- Assert(false);- return vector8_broadcast(0);- }+ /* negative shift count means right shift */+ return (Vector8) vshlq_u32((Vector32) v1, vdupq_n_s32(-i));
#endif
}
#endif /* ! USE_NO_SIMD */
--
2.50.1 (Apple Git-155)
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To: pgsql-hackers@postgresql.org
Cc: nathandbossart@gmail.com, johncnaylorls@gmail.com
Subject: Re: remove switch statement in vector8_shift_{left,right}
In-Reply-To: <akWxkA-mszMm57cV@nathan>
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