Re: [PATCH] target/mips: Fix loongson multimedia condition instructions

[Aleksandar Markovic]

5:58 AM Sub, 21.03.2020. Jiaxun Yang <address@hidden> је написао/ла:
>
> Loongson multimedia condition instructions were previously implemented as
> write 0 to rd due to lack of documentation. So I just confirmed with Loongson
> about their encoding and implemented them correctly.
>
> Signed-off-by: Jiaxun Yang <address@hidden>
> ---

Thanks, Jiaxun!

I feel relieved that this "mistery" is about to be solved. This patch actually deals with a long-standing known bug, and, on that basis, it is eligible to be integrated into QEMU 5.0 after soft-freeze.

I'll take a closer look at the details and their possible improvements in next few days. But, again, in general, I salute this patch.

Yours,
Aleksansdar

>  target/mips/translate.c | 40 ++++++++++++++++++++++++++++++++++------
>  1 file changed, 34 insertions(+), 6 deletions(-)
>
> diff --git a/target/mips/translate.c b/target/mips/translate.c
> index d745bd2803..43be8d27b5 100644
> --- a/target/mips/translate.c
> +++ b/target/mips/translate.c
> @@ -5529,6 +5529,8 @@ static void gen_loongson_multimedia(DisasContext *ctx, int rd, int rs, int rt)
>  {
>      uint32_t opc, shift_max;
>      TCGv_i64 t0, t1;
> +    TCGCond cond;
> +    TCGLabel *lab;
>
>      opc = MASK_LMI(ctx->opcode);
>      switch (opc) {
> @@ -5816,7 +5818,7 @@ static void gen_loongson_multimedia(DisasContext *ctx, int rd, int rs, int rt)
>      case OPC_DADD_CP2:
>          {
>              TCGv_i64 t2 = tcg_temp_new_i64();
> -            TCGLabel *lab = gen_new_label();
> +            lab = gen_new_label();
>
>              tcg_gen_mov_i64(t2, t0);
>              tcg_gen_add_i64(t0, t1, t2);
> @@ -5837,7 +5839,7 @@ static void gen_loongson_multimedia(DisasContext *ctx, int rd, int rs, int rt)
>      case OPC_DSUB_CP2:
>          {
>              TCGv_i64 t2 = tcg_temp_new_i64();
> -            TCGLabel *lab = gen_new_label();
> +            lab = gen_new_label();
>
>              tcg_gen_mov_i64(t2, t0);
>              tcg_gen_sub_i64(t0, t1, t2);
> @@ -5862,14 +5864,39 @@ static void gen_loongson_multimedia(DisasContext *ctx, int rd, int rs, int rt)
>
>      case OPC_SEQU_CP2:
>      case OPC_SEQ_CP2:
> +        cond = TCG_COND_EQ;
> +        goto do_cc_cond;
> +        break;
> +
>      case OPC_SLTU_CP2:
> +        cond = TCG_COND_LTU;
> +        goto do_cc_cond;
> +        break;
> +
>      case OPC_SLT_CP2:
> +        cond = TCG_COND_LT;
> +        goto do_cc_cond;
> +        break;
> +
>      case OPC_SLEU_CP2:
> +        cond = TCG_COND_LEU;
> +        goto do_cc_cond;
> +        break;
> +
>      case OPC_SLE_CP2:
> -        /*
> -         * ??? Document is unclear: Set FCC[CC].  Does that mean the
> -         * FD field is the CC field?
> -         */
> +        cond = TCG_COND_LE;
> +    do_cc_cond:
> +        {
> +            int cc = (ctx->opcode >> 8) & 0x7;
> +            lab = gen_new_label();
> +            tcg_gen_ori_i32(fpu_fcr31, fpu_fcr31, 1 << get_fp_bit(cc));
> +            tcg_gen_brcond_i64(cond, t0, t1, lab);
> +            tcg_gen_xori_i32(fpu_fcr31, fpu_fcr31, 1 << get_fp_bit(cc));
> +            gen_set_label(lab);
> +        }
> +        goto no_rd;
> +        break;
> +
>      default:
>          MIPS_INVAL("loongson_cp2");
>          generate_exception_end(ctx, EXCP_RI);
> @@ -5878,6 +5905,7 @@ static void gen_loongson_multimedia(DisasContext *ctx, int rd, int rs, int rt)
>
>      gen_store_fpr64(ctx, t0, rd);
>
> +no_rd:
>      tcg_temp_free_i64(t0);
>      tcg_temp_free_i64(t1);
>  }
> --
> 2.26.0.rc2
>
>
>