From: Nathan Bossart <nathan@postgresql.org>
Date: Mon, 6 Jul 2026 16:40:02 +0000 (-0500)
Subject: Remove switch statements in vector8_shift_{left,right}.
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=763ee7ea00b02592b5fb9572d77b82a1f6f052b9;p=thirdparty%2Fpostgresql.git

Remove switch statements in vector8_shift_{left,right}.

In commit ec8719ccbf, I added switch statements with all expected
shift counts to vector8_shift_{left,right} because vshlq_n_u32()
and vshrq_n_u32() require integer literals.  But we can use
vshlq_u32() instead for both cases, which does not require an
integer literal, thereby avoiding the need for the switch
statements.  This compiles to the same machine code on newer
versions of popular compilers.

Reviewed-by: John Naylor <johncnaylorls@gmail.com>
Discussion: https://postgr.es/m/akWxkA-mszMm57cV%40nathan
---

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 */