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

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Message-ID: <CAAhV-H5SCuXERUBbC5D+k1pjf-Pmf33LOQXL=aUP-E-DgO6+qg@mail.gmail.com>
Date: Wed, 27 Aug 2025 18:18:16 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Hengqi Chen <hengqi.chen@...il.com>
Cc: Tiezhu Yang <yangtiezhu@...ngson.cn>, bpf@...r.kernel.org, loongarch@...ts.linux.dev, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] LoongArch: BPF: Optimize sign-extention mov instructions

Applied, thanks.

Huacai

On Wed, Aug 27, 2025 at 9:27 AM Hengqi Chen <hengqi.chen@...il.com> wrote:
>
> 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
> >