Re: [PATCH v2] riscv: Add helper to make NaN-boxing for FP register

[Alistair Francis <alistair23@gmail.com>]

On Mon, Jan 27, 2020 at 4:37 PM Ian Jiang <ianjiang.ict@gmail.com> wrote:
>
> The function that makes NaN-boxing when a 32-bit value is assigned
> to a 64-bit FP register is split out to a helper gen_nanbox_fpr().
> Then it is applied in translating of the FLW instruction.
>
> Signed-off-by: Ian Jiang <ianjiang.ict@gmail.com>

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
>  target/riscv/insn_trans/trans_rvf.inc.c | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/target/riscv/insn_trans/trans_rvf.inc.c b/target/riscv/insn_trans/trans_rvf.inc.c
> index e23cd639a6..3bfd8881e7 100644
> --- a/target/riscv/insn_trans/trans_rvf.inc.c
> +++ b/target/riscv/insn_trans/trans_rvf.inc.c
> @@ -23,6 +23,20 @@
>          return false;                       \
>  } while (0)
>
> +/*
> + * RISC-V requires NaN-boxing of narrower width floating
> + * point values.  This applies when a 32-bit value is
> + * assigned to a 64-bit FP register.  Thus this does not
> + * apply when the RVD extension is not present.
> + */
> +static void gen_nanbox_fpr(DisasContext *ctx, int regno)
> +{
> +    if (has_ext(ctx, RVD)) {
> +        tcg_gen_ori_i64(cpu_fpr[regno], cpu_fpr[regno],
> +                        MAKE_64BIT_MASK(32, 32));
> +    }
> +}
> +
>  static bool trans_flw(DisasContext *ctx, arg_flw *a)
>  {
>      TCGv t0 = tcg_temp_new();
> @@ -32,8 +46,7 @@ static bool trans_flw(DisasContext *ctx, arg_flw *a)
>      tcg_gen_addi_tl(t0, t0, a->imm);
>
>      tcg_gen_qemu_ld_i64(cpu_fpr[a->rd], t0, ctx->mem_idx, MO_TEUL);
> -    /* RISC-V requires NaN-boxing of narrower width floating point values */
> -    tcg_gen_ori_i64(cpu_fpr[a->rd], cpu_fpr[a->rd], 0xffffffff00000000ULL);
> +    gen_nanbox_fpr(ctx, a->rd);
>
>      tcg_temp_free(t0);
>      mark_fs_dirty(ctx);
> --
> 2.17.1
>
>