Re: [Qemu-devel] [PATCH v1 05/41] s390x/tcg: Implement VECTOR ADD WITH CARRY COMPUTE CARRY

[David Hildenbrand]

On 12.04.19 23:58, Richard Henderson wrote:
> On 4/11/19 12:08 AM, David Hildenbrand wrote:
>> +static DisasJumpType op_vaccc(DisasContext *s, DisasOps *o)
>> +{
>> +    if (get_field(s->fields, m5) != ES_128) {
>> +        gen_program_exception(s, PGM_SPECIFICATION);
>> +        return DISAS_NORETURN;
>> +    }
>> +
>> +    gen_gvec_4_ool(get_field(s->fields, v1), get_field(s->fields, v2),
>> +                   get_field(s->fields, v3), get_field(s->fields, v4), 0,
>> +                   gen_helper_gvec_vaccc128);
>> +    return DISAS_NEXT;
>> +}
> 
> An inline expansion could be
> 
> One possible expansion is
> 
>   tcg_gen_andi_i64(tl, cl, 1);
>   tcg_gen_add2_i64(tl, th, tl, zero, al, zero);
>   tcg_gen_add2_i64(tl, th, tl, th, bl, zero);
>   tcg_gen_add2_i64(tl, th, th, zero, ah, zero);
>   tcg_gen_add2_i64(tl, th, tl, th, bl, zero);
>   /* carry out in th */
> 
> This is 8 insns for the addition vs the hw optimal 6, but we're not exactly an
> optimizing compiler either.  ;-)
> 

Yes, very nice! Thanks!

> 
> r~
> 


-- 

Thanks,

David / dhildenb