Re: [Qemu-devel] [PATCH v14 27/33] target-tilegx: Handle mask instructions

[Peter Maydell]

On 24 August 2015 at 17:17, Richard Henderson <address@hidden> wrote:
> Signed-off-by: Richard Henderson <address@hidden>
> ---
>  target-tilegx/translate.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/target-tilegx/translate.c b/target-tilegx/translate.c
> index 51ee158..af4b34a 100644
> --- a/target-tilegx/translate.c
> +++ b/target-tilegx/translate.c
> @@ -647,11 +647,15 @@ static TileExcp gen_rrr_opcode(DisasContext *dc, 
> unsigned opext,
>      case OE_RRR(FSINGLE_MUL2, 0, X0):
>      case OE_RRR(FSINGLE_PACK2, 0, X0):
>      case OE_RRR(FSINGLE_SUB1, 0, X0):
> +        return TILEGX_EXCP_OPCODE_UNIMPLEMENTED;
>      case OE_RRR(MNZ, 0, X0):
>      case OE_RRR(MNZ, 0, X1):
>      case OE_RRR(MNZ, 4, Y0):
>      case OE_RRR(MNZ, 4, Y1):
> -        return TILEGX_EXCP_OPCODE_UNIMPLEMENTED;
> +        t0 = load_zero(dc);
> +        tcg_gen_movcond_tl(TCG_COND_NE, tdest, tsrca, t0, tsrcb, t0);
> +        mnemonic = "mnz";
> +        break;
>      case OE_RRR(MULAX, 0, X0):
>      case OE_RRR(MULAX, 3, Y0):
>          tcg_gen_mul_tl(tdest, tsrca, tsrcb);
> @@ -767,7 +771,10 @@ static TileExcp gen_rrr_opcode(DisasContext *dc, 
> unsigned opext,
>      case OE_RRR(MZ, 0, X1):
>      case OE_RRR(MZ, 4, Y0):
>      case OE_RRR(MZ, 4, Y1):
> -        return TILEGX_EXCP_OPCODE_UNIMPLEMENTED;
> +        t0 = load_zero(dc);
> +        tcg_gen_movcond_tl(TCG_COND_EQ, tdest, tsrca, t0, tsrcb, t0);
> +        mnemonic = "mz";
> +        break;
>      case OE_RRR(NOR, 0, X0):
>      case OE_RRR(NOR, 0, X1):
>      case OE_RRR(NOR, 5, Y0):
> --
> 2.4.3
>

I *think* this code is correct, but the ISA manual perplexes me
entirely. Why on earth would you describe anything as "compute
the boolean AND of something with a value of all ones", when that's
just a no-op? I can't see what I'm missing that means they
didn't just describe 'mz' as "dest = srcA ? srcB : 0".

Reviewed-by: Peter Maydell <address@hidden>

thanks
-- PMM