2024-05-27 09:25:03

by Qingfang Deng

Subject: [PATCH v2] riscv: lib: relax assembly constraints in hweight

From: Qingfang Deng <[email protected]>

rd and rs don't have to be the same. In some cases where rs needs to be
saved for later usage, this will save us some mv instructions.

Signed-off-by: Qingfang Deng <[email protected]>
---
v2: updated title as suggested by Xiao.

arch/riscv/include/asm/arch_hweight.h | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/include/asm/arch_hweight.h b/arch/riscv/include/asm/arch_hweight.h
index 85b2c443823e..613769b9cdc9 100644
--- a/arch/riscv/include/asm/arch_hweight.h
+++ b/arch/riscv/include/asm/arch_hweight.h
@@ -26,9 +26,9 @@ static __always_inline unsigned int __arch_hweight32(unsigned int w)

asm (".option push\n"
".option arch,+zbb\n"
- CPOPW "%0, %0\n"
+ CPOPW "%0, %1\n"
".option pop\n"
- : "+r" (w) : :);
+ : "=r" (w) : "r" (w) :);

return w;

@@ -57,9 +57,9 @@ static __always_inline unsigned long __arch_hweight64(__u64 w)

asm (".option push\n"
".option arch,+zbb\n"
- "cpop %0, %0\n"
+ "cpop %0, %1\n"
".option pop\n"
- : "+r" (w) : :);
+ : "=r" (w) : "r" (w) :);

return w;

--
2.34.1

2024-05-27 10:29:32

by Wang, Xiao W

Subject: RE: [PATCH v2] riscv: lib: relax assembly constraints in hweight

> -----Original Message-----
> From: Qingfang Deng <[email protected]>
> Sent: Monday, May 27, 2024 5:24 PM
> To: Paul Walmsley <[email protected]>; Palmer Dabbelt
> <[email protected]>; Albert Ou <[email protected]>; linux-
> [email protected]; [email protected]
> Cc: Wang, Xiao W <[email protected]>; Qingfang Deng
> <[email protected]>
> Subject: [PATCH v2] riscv: lib: relax assembly constraints in hweight
>
> From: Qingfang Deng <[email protected]>
>
> rd and rs don't have to be the same. In some cases where rs needs to be
> saved for later usage, this will save us some mv instructions.
>
> Signed-off-by: Qingfang Deng <[email protected]>
> ---
> v2: updated title as suggested by Xiao.
>
> arch/riscv/include/asm/arch_hweight.h | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/riscv/include/asm/arch_hweight.h
> b/arch/riscv/include/asm/arch_hweight.h
> index 85b2c443823e..613769b9cdc9 100644
> --- a/arch/riscv/include/asm/arch_hweight.h
> +++ b/arch/riscv/include/asm/arch_hweight.h
> @@ -26,9 +26,9 @@ static __always_inline unsigned int
> __arch_hweight32(unsigned int w)
>
> asm (".option push\n"
> ".option arch,+zbb\n"
> - CPOPW "%0, %0\n"
> + CPOPW "%0, %1\n"
> ".option pop\n"
> - : "+r" (w) : :);
> + : "=r" (w) : "r" (w) :);
>
> return w;
>
> @@ -57,9 +57,9 @@ static __always_inline unsigned long
> __arch_hweight64(__u64 w)
>
> asm (".option push\n"
> ".option arch,+zbb\n"
> - "cpop %0, %0\n"
> + "cpop %0, %1\n"
> ".option pop\n"
> - : "+r" (w) : :);
> + : "=r" (w) : "r" (w) :);
>
> return w;
>
> --
> 2.34.1

Reviewed-by: Xiao Wang <[email protected]>