linux-kernel - [PATCH 4/6] riscv: hweight: Convert to use_alternative

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Message-Id: <20250820-riscv-altn-helper-wip-v1-4-c3c626c1f7e6@iscas.ac.cn>
Date: Wed, 20 Aug 2025 21:44:48 +0800
From: Vivian Wang <wangruikang@...as.ac.cn>
To: Paul Walmsley <paul.walmsley@...ive.com>, 
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
 Alexandre Ghiti <alex@...ti.fr>, Yury Norov <yury.norov@...il.com>, 
 Rasmus Villemoes <linux@...musvillemoes.dk>
Cc: Vivian Wang <wangruikang@...as.ac.cn>, Vivian Wang <uwu@...m.page>, 
 linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH 4/6] riscv: hweight: Convert to use_alternative_likely

Use use_alternative_likely() to check for RISCV_ISA_EXT_ZBB, replacing
the use of asm goto with ALTERNATIVE.

The "likely" variant is used to match the behavior of the original
implementation using ALTERNATIVE("j %l[legacy]", "nop", ...).

Signed-off-by: Vivian Wang <wangruikang@...as.ac.cn>
---
 arch/riscv/include/asm/arch_hweight.h | 42 +++++++++++++++--------------------
 1 file changed, 18 insertions(+), 24 deletions(-)

diff --git a/arch/riscv/include/asm/arch_hweight.h b/arch/riscv/include/asm/arch_hweight.h
index 0e7cdbbec8efd3c293da2fa96a8c6d0a93faf56f..58ed7a3b2d7882f6a7913c4bfdb9bce4a4394956 100644
--- a/arch/riscv/include/asm/arch_hweight.h
+++ b/arch/riscv/include/asm/arch_hweight.h
@@ -20,20 +20,17 @@
 static __always_inline unsigned int __arch_hweight32(unsigned int w)
 {
 #if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB)
-	asm goto(ALTERNATIVE("j %l[legacy]", "nop", 0,
-				      RISCV_ISA_EXT_ZBB, 1)
-			  : : : : legacy);
+	if (use_alternative_likely(0, RISCV_ISA_EXT_ZBB)) {
+		asm (".option push\n"
+		     ".option arch,+zbb\n"
+		     CPOPW "%0, %1\n"
+		     ".option pop\n"
+		     : "=r" (w) : "r" (w) :);
 
-	asm (".option push\n"
-	     ".option arch,+zbb\n"
-	     CPOPW "%0, %1\n"
-	     ".option pop\n"
-	     : "=r" (w) : "r" (w) :);
-
-	return w;
-
-legacy:
+		return w;
+	}
 #endif
+
 	return __sw_hweight32(w);
 }
 
@@ -51,20 +48,17 @@ static inline unsigned int __arch_hweight8(unsigned int w)
 static __always_inline unsigned long __arch_hweight64(__u64 w)
 {
 #if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB)
-	asm goto(ALTERNATIVE("j %l[legacy]", "nop", 0,
-				      RISCV_ISA_EXT_ZBB, 1)
-			  : : : : legacy);
+	if (use_alternative_likely(0, RISCV_ISA_EXT_ZBB)) {
+		asm (".option push\n"
+		     ".option arch,+zbb\n"
+		     "cpop %0, %1\n"
+		     ".option pop\n"
+		     : "=r" (w) : "r" (w) :);
 
-	asm (".option push\n"
-	     ".option arch,+zbb\n"
-	     "cpop %0, %1\n"
-	     ".option pop\n"
-	     : "=r" (w) : "r" (w) :);
-
-	return w;
-
-legacy:
+		return w;
+	}
 #endif
+
 	return __sw_hweight64(w);
 }
 #else /* BITS_PER_LONG == 64 */

-- 
2.50.1