[PATCH bpf-next v2 5/6] riscv, bpf: Optimize sign-extention mov insns with Zbb support

[Björn Töpel]

Pu Lehui <pulehui at huaweicloud.com> writes:

> From: Pu Lehui <pulehui at huawei.com>
>
> Add 8-bit and 16-bit sign-extention wraper with Zbb support to optimize
> sign-extension mov instructions.
>
> Signed-off-by: Pu Lehui <pulehui at huawei.com>
> ---
>  arch/riscv/net/bpf_jit.h        | 20 ++++++++++++++++++++
>  arch/riscv/net/bpf_jit_comp64.c |  5 +++--
>  2 files changed, 23 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/net/bpf_jit.h b/arch/riscv/net/bpf_jit.h
> index 4e24fb2bd..944bdd6e4 100644
> --- a/arch/riscv/net/bpf_jit.h
> +++ b/arch/riscv/net/bpf_jit.h
> @@ -1110,6 +1110,26 @@ static inline void emit_subw(u8 rd, u8 rs1, u8 rs2, struct rv_jit_context *ctx)
>  		emit(rv_subw(rd, rs1, rs2), ctx);
>  }
>  
> +static inline void emit_sextb(u8 rd, u8 rs, struct rv_jit_context *ctx)
> +{
> +	if (rvzbb_enabled()) {
> +		emit(rvzbb_sextb(rd, rs), ctx);
> +	} else {
> +		emit_slli(rd, rs, 56, ctx);
> +		emit_srai(rd, rd, 56, ctx);
> +	}
> +}
> +
> +static inline void emit_sexth(u8 rd, u8 rs, struct rv_jit_context *ctx)
> +{
> +	if (rvzbb_enabled()) {
> +		emit(rvzbb_sexth(rd, rs), ctx);
> +	} else {
> +		emit_slli(rd, rs, 48, ctx);
> +		emit_srai(rd, rd, 48, ctx);
> +	}
> +}

Nit/personal style: I really find it easier to read early-exit code,
than nested if-else.

  | if (cond) {
  |   foo();
  |   return;
  | }
  | 
  | bar();

> +
>  static inline void emit_sextw(u8 rd, u8 rs, struct rv_jit_context *ctx)
>  {
>  	emit_addiw(rd, rs, 0, ctx);
> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
> index 0c6ffe11a..f4ca6b787 100644
> --- a/arch/riscv/net/bpf_jit_comp64.c
> +++ b/arch/riscv/net/bpf_jit_comp64.c
> @@ -1027,9 +1027,10 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
>  			emit_mv(rd, rs, ctx);
>  			break;
>  		case 8:
> +			emit_sextb(rd, rs, ctx);
> +			break;
>  		case 16:
> -			emit_slli(RV_REG_T1, rs, 64 - insn->off, ctx);
> -			emit_srai(rd, RV_REG_T1, 64 - insn->off, ctx);
> +			emit_sexth(rd, rs, ctx);

Acked-by: Björn Töpel <bjorn at kernel.org>