Re: [PATCH v1 1/2] s390x/tcg: Implement Vector-Enhancements Facility 2 for s390x

[Richard Henderson]

On 3/2/22 17:22, David Miller wrote:
> resolves: https://gitlab.com/qemu-project/qemu/-/issues/738
>
> implements:
> VECTOR LOAD ELEMENTS REVERSED               (VLER)
> VECTOR LOAD BYTE REVERSED ELEMENTS          (VLBR)
> VECTOR LOAD BYTE REVERSED ELEMENT           (VLEBRH, VLEBRF, VLEBRG)
> VECTOR LOAD BYTE REVERSED ELEMENT AND ZERO  (VLLEBRZ)
> VECTOR LOAD BYTE REVERSED ELEMENT AND REPLOCATE (VLBRREP)
> VECTOR STORE ELEMENTS REVERSED              (VSTER)
> VECTOR STORE BYTE REVERSED ELEMENTS         (VSTBR)
> VECTOR STORE BYTE REVERSED ELEMENTS         (VSTEBRH, VSTEBRF, VSTEBRG)
> VECTOR SHIFT LEFT DOUBLE BY BIT             (VSLD)
> VECTOR SHIFT RIGHT DOUBLE BY BIT            (VSRD)
> VECTOR STRING SEARCH                        (VSTRS)
>
> modifies:
> VECTOR FP CONVERT FROM FIXED                (VCFPS)
> VECTOR FP CONVERT FROM LOGICAL              (VCFPL)
> VECTOR FP CONVERT TO FIXED                  (VCSFP)
> VECTOR FP CONVERT TO LOGICAL                (VCLFP)
> VECTOR SHIFT LEFT                           (VSL)
> VECTOR SHIFT RIGHT ARITHMETIC               (VSRA)
> VECTOR SHIFT RIGHT LOGICAL                  (VSRL)
>
> Signed-off-by: David Miller <dmiller423@gmail.com>

Too many changes in one patch.
You need to split these into smaller, logical units.

> +/* VECTOR LOAD BYTE REVERSED ELEMENT AND ZERO */
> +    F(0xe604, VLLEBRZ, VRX,   VE2, la2, 0, 0, 0, vllebrz, 0, IF_VEC)
> +/* VECTOR LOAD BYTE REVERSED ELEMENTS */
> +       F(0xe606, VLBR,    VRX,   VE2, la2, 0, 0, 0, vlbr, 0, IF_VEC)
> +/* VECTOR LOAD ELEMENTS REVERSED */
> +       F(0xe607, VLER,    VRX,   VE2, la2, 0, 0, 0, vler, 0, IF_VEC)

Tabs, and more later.

> @@ -457,6 +457,9 @@ static DisasJumpType op_vlrep(DisasContext *s, DisasOps *o)
>       return DISAS_NEXT;
>   }
>   
> +
> +
> +
>   static DisasJumpType op_vle(DisasContext *s, DisasOps *o)

Do not add pointless whitespace.

> +static DisasJumpType op_vlebr(DisasContext *s, DisasOps *o)
> +{
> +    const uint8_t es = (1 == s->fields.op2) ? 1 : (1 ^ s->fields.op2);
> +    const uint8_t enr = get_field(s, m3);
> +    TCGv_i64 tmp;
> +
> +    if (es < ES_16 || es > ES_64 || !valid_vec_element(enr, es)) {
> +        gen_program_exception(s, PGM_SPECIFICATION);
> +        return DISAS_NORETURN;
> +    }
> +
> +    tmp = tcg_temp_new_i64();
> +    tcg_gen_qemu_ld_i64(tmp, o->addr1, get_mem_index(s), MO_TE | es);

Just use a little-endian load: MO_LE | es.
While we use MO_TE all over, it's no secret that it's always big-endian.

And everywhere else you do load then swap, or swap then store.

> +}
> +
> +
> +
> +static DisasJumpType op_vsteb(DisasContext *s, DisasOps *o)

More care with spacing.

> +static inline void s390_vec_reverse(S390Vector *vdst,
> +                                    S390Vector *vsrc, uint8_t es)
> +{
> +    const uint8_t elems = 1 << (4 - es);
> +    uint32_t enr;
> +
> +    for (enr = 0; enr < elems; enr++) {
> +        switch (es) {
> +        case MO_8:
> +            s390_vec_write_element8(vdst, enr,
> +                           s390_vec_read_element8(vsrc, 15 ^ enr));
> +            break;
> +        case MO_16:
> +            s390_vec_write_element16(vdst, enr,
> +                           s390_vec_read_element16(vsrc, 7 ^ enr));
> +            break;
> +        case MO_32:
> +            s390_vec_write_element32(vdst, enr,
> +                           s390_vec_read_element32(vsrc, 3 ^ enr));
> +            break;
> +        case MO_64:
> +            s390_vec_write_element64(vdst, enr,
> +                           s390_vec_read_element64(vsrc, 1 ^ enr));
> +            break;
> +        default:
> +            g_assert_not_reached();
> +        }
> +    }
> +}

This seems likely to go wrong for vdst == vsrc.
In addition, swapping the order of elements is something that can be done in 
parallel.

    l = src[lo], h = src[hi];
    switch (es) {
    case MO_64:
        dst[hi] = l, dst[lo] = h;
        break;
    case MO_8:
        dst[hi] = bswap64(l);
        dst[lo] = bswap64(h);
        break;
    case MO_16:
        dst[hi] = hswap64(l);
        dst[lo] = hswap64(h);
        break;
    case MO_32:
        dst[hi] = wswap64(l);
        dst[hi] = wswap64(h);
        break;
    }

which, really, can all be generated inline.


r~