Commit 18be4ca5 authored by Feng Jiang's avatar Feng Jiang Committed by Paul Walmsley
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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: default avatarFeng Jiang <jiangfeng@kylinos.cn>
Link: https://patch.msgid.link/20251218032614.57356-1-jiangfeng@kylinos.cn


Signed-off-by: default avatarPaul Walmsley <pjw@kernel.org>
parent 098921ec

arch/riscv/lib/strlen.S

+3 −5
Original line number Diff line number Diff line
@@ -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