linux-kernel - Re: [PATCH] LoongArch: BPF: Optimize sign-extention mov instructions

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Message-ID: <CAEyhmHQJcCvy2TPv7nwT87yS6y698WrECwd+xA9RjsCVmrVXvw@mail.gmail.com>
Date: Wed, 27 Aug 2025 09:27:32 +0800
From: Hengqi Chen <hengqi.chen@...il.com>
To: Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc: Huacai Chen <chenhuacai@...nel.org>, bpf@...r.kernel.org, loongarch@...ts.linux.dev, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] LoongArch: BPF: Optimize sign-extention mov instructions

On Tue, Aug 26, 2025 at 2:49 PM Tiezhu Yang <yangtiezhu@...ngson.cn> wrote:
>
> For 8-bit and 16-bit sign-extention mov instructions, it can use the native
> instructions ext.w.b and ext.w.h directly, no need to use the temporary t1
> register, just remove the redundant operations.
>
> Here are the test results:
>
>   # modprobe test_bpf test_range=81,84
>   # dmesg -t | tail -5
>   test_bpf: #81 ALU_MOVSX | BPF_B jited:1 5 PASS
>   test_bpf: #82 ALU_MOVSX | BPF_H jited:1 5 PASS
>   test_bpf: #83 ALU64_MOVSX | BPF_B jited:1 5 PASS
>   test_bpf: #84 ALU64_MOVSX | BPF_H jited:1 5 PASS
>   test_bpf: Summary: 4 PASSED, 0 FAILED, [4/4 JIT'ed]
>
> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
> ---
>  arch/loongarch/net/bpf_jit.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
> index abfdb6bb5c38..7072db18c6cd 100644
> --- a/arch/loongarch/net/bpf_jit.c
> +++ b/arch/loongarch/net/bpf_jit.c
> @@ -527,13 +527,11 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx, bool ext
>                         emit_zext_32(ctx, dst, is32);
>                         break;
>                 case 8:
> -                       move_reg(ctx, t1, src);
> -                       emit_insn(ctx, extwb, dst, t1);
> +                       emit_insn(ctx, extwb, dst, src);
>                         emit_zext_32(ctx, dst, is32);
>                         break;
>                 case 16:
> -                       move_reg(ctx, t1, src);
> -                       emit_insn(ctx, extwh, dst, t1);
> +                       emit_insn(ctx, extwh, dst, src);
>                         emit_zext_32(ctx, dst, is32);
>                         break;
>                 case 32:
> --

Acked-by: Hengqi Chen <hengqi.chen@...il.com>

> 2.42.0
>