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From: Richard Henderson <richard.henderson@linaro.org>
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Date: Tue, 23 Apr 2019 14:40:27 -0700
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Subject: Re: [Qemu-devel] [PATCH 12/38] tcg: Add gvec expanders for variable
 shift
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To: David Hildenbrand <david@redhat.com>, qemu-devel@nongnu.org

On 4/23/19 2:02 PM, David Hildenbrand wrote:
> On 23.04.19 21:28, Richard Henderson wrote:
>> On 4/23/19 12:04 PM, David Hildenbrand wrote:
>>> In order to use this on s390x for VECTOR ELEMENT SHIFT, like
>>>
>>> +static DisasJumpType op_vesv(DisasContext *s, DisasOps *o)
>>> +{
>>> +    const uint8_t es = get_field(s->fields, m4);
>>> +    const uint8_t v1 = get_field(s->fields, v1);
>>> +    const uint8_t v2 = get_field(s->fields, v2);
>>> +    const uint8_t v3 = get_field(s->fields, v3);
>>> +
>>> +    if (es > ES_64) {
>>> +        gen_program_exception(s, PGM_SPECIFICATION);
>>> +        return DISAS_NORETURN;
>>> +    }
>>> +
>>> +    switch (s->fields->op2) {
>>> +    case 0x70:
>>> +        gen_gvec_fn_3(shlv, es, v1, v2, v3);
>>> +        break;
>>> +    case 0x7a:
>>> +        gen_gvec_fn_3(sarv, es, v1, v2, v3);
>>> +        break;
>>> +    case 0x78:
>>> +        gen_gvec_fn_3(shrv, es, v1, v2, v3);
>>> +        break;
>>> +    default:
>>> +        g_assert_not_reached();
>>> +    }
>>> +
>>> +    return DISAS_NEXT;
>>> +}
>>>
>>> We need to mask of invalid bits from the shift. Can that be added?
>>
>> Yes, I do exactly this in patch 31 for target/ppc.
>>
>>
>> r~
>>
> 
> Got it, so not via a generic gvec expansion. Thanks!

I do wonder if I *should* make the truncating expansion the
generic gvec expansion.  It would be usable from two targets
at least...

Because the one's that *don't* truncate in hardware will
still have to have their own custom expansion code.

Thoughts?


r~