remove switch statement in vector8_shift_{left,right}

[Nathan Bossart]

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 <nat...@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.h
index 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)