Re: [RFC PATCH] target/ppc: Move add and subf type fixed-point arithmetic instructions to decodetree

[Chinmay Rath <rathc@linux.vnet.ibm.com>]

Hi Richard,

On 2/13/24 03:51, Richard Henderson wrote:
> On 2/9/24 01:35, Chinmay Rath wrote:
>> +&Z23_tab_cy     rt ra rb cy
>> +@Z23_tab_cy     ...... rt:5 ra:5 rb:5 cy:2 ........ . &Z23_tab_cy
> ...
>> +ADDEX           011111 ..... ..... ..... .. 10101010 -  @Z23_tab_cy
> ...
>> +static bool trans_ADDEX(DisasContext *ctx, arg_Z23_tab_cy *a)
>> +{
>> +    gen_op_arith_add(ctx, cpu_gpr[a->rt], cpu_gpr[a->ra], 
>> cpu_gpr[a->rb],
>> +                     cpu_ov, cpu_ov32, true, true, false, false);
>> +    return true;
>> +}
>
> CY != 0 is reserved.
>
> While you could diagnose this in trans_ADDEX, it seems cleaner to 
> simply match 00 in the CY field until a future ISA defines something 
> else.  All that is required is a comment in the decodetree entry.
>
> # Z23-form, with CY=0; all other values for CY are reserved.
> # This works out the same as X-form.
> ADDEX    011111 ..... ..... ..... 00 10101010 -   @X
>
Thanks for your review comments.

I shall update as suggested in v2.

Regards,

Chinmay

>
> r~