Re: [qemu-s390x] [Qemu-devel] [PATCH v1 37/41] s390x/tcg: Implement VECTOR SUBTRACT WITH BORROW COMPUTE BORROW INDICATION

[Richard Henderson]

On 4/11/19 12:08 AM, David Hildenbrand wrote:
> +static DisasJumpType op_vsbcbi(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_vsbcbi128);
> +    return DISAS_NEXT;
> +}


Reviewed-by: Richard Henderson <address@hidden>

I'm sure this can be done similarly to add with carry compute carry, but it's
harder to reason with sub2.  Something like

        tcg_gen_andi_i64(tl, cl, 1);
        tcg_gen_sub2_i64(tl, th, al, zero, tl, zero);
        tcg_gen_sub2_i64(tl, th, tl, th, bl, zero);
        tcg_gen_andi_i64(tl, th, 1);
        tcg_gen_sub2_i64(tl, th, ah, zero, tl, zero);
        tcg_gen_sub2_i64(tl, th, tl, th, bh, zero);
        tcg_gen_andi_i64(tl, th, 1);
        /* result in tl */


r~