From 18be4ca5cb4e5a86833de97d331f5bc14a6c5a6d Mon Sep 17 00:00:00 2001 From: Feng Jiang Date: Sun, 25 Jan 2026 21:09:58 -0700 Subject: [PATCH] riscv: lib: optimize strlen loop efficiency Optimize the generic strlen implementation by using a pre-decrement pointer. This reduces the loop body from 4 instructions to 3 and eliminates the unconditional jump ('j'). Old loop (4 instructions, 2 branches): 1: lbu t0, 0(t1); beqz t0, 2f; addi t1, t1, 1; j 1b New loop (3 instructions, 1 branch): 1: addi t1, t1, 1; lbu t0, 0(t1); bnez t0, 1b This change improves execution efficiency and reduces branch pressure for systems without the Zbb extension. Signed-off-by: Feng Jiang Link: https://patch.msgid.link/20251218032614.57356-1-jiangfeng@kylinos.cn Signed-off-by: Paul Walmsley --- arch/riscv/lib/strlen.S | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/arch/riscv/lib/strlen.S b/arch/riscv/lib/strlen.S index eb4d2b7ed22b..e7736ccda514 100644 --- a/arch/riscv/lib/strlen.S +++ b/arch/riscv/lib/strlen.S @@ -21,13 +21,11 @@ SYM_FUNC_START(strlen) * Clobbers: * t0, t1 */ - mv t1, a0 + addi t1, a0, -1 1: - lbu t0, 0(t1) - beqz t0, 2f addi t1, t1, 1 - j 1b -2: + lbu t0, 0(t1) + bnez t0, 1b sub a0, t1, a0 ret -- 2.47.3