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From: Alex =?utf-8?Q?Benn=C3=A9e?= <alex.bennee@linaro.org>
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Date: Sat, 11 Jan 2014 08:30:10 +0000
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Subject: Re: [Qemu-devel] [PATCH 06/10] target-arm: A64: Add SIMD ZIP/UZP/TRN
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To: Richard Henderson <rth@twiddle.net>
Cc: Peter Maydell <peter.maydell@linaro.org>, Laurent Desnogues <laurent.desnogues@gmail.com>, patches@linaro.org, Michael Matz <matz@suse.de>, Alexander Graf <agraf@suse.de>, qemu-devel@nongnu.org, Claudio Fontana <claudio.fontana@linaro.org>, Dirk Mueller <dmueller@suse.de>, Will Newton <will.newton@linaro.org>, Alex =?utf-8?Q?Benn=C3=A9e?= <alex.bennee@linaro.org>, kvmarm@lists.cs.columbia.edu, Christoffer Dall <christoffer.dall@linaro.org>


rth@twiddle.net writes:

> On 01/10/2014 09:12 AM, Peter Maydell wrote:
>> +    for (i = 0; i < elements; i++) {
>> +        switch (opcode) {
>> +        case 1: /* UZP1/2 */
>> +        {
>> +            int midpoint = elements / 2;
>> +            if (i < midpoint) {
>> +                read_vec_element(s, tcg_res, rn, 2 * i + part, size);
>> +            } else {
>> +                read_vec_element(s, tcg_res, rm,
>> +                                 2 * (i - midpoint) + part, size);
>> +            }
>> +            break;
>> +        }
>
> You're generating up to 16 * 3 + 2 = 50 opcodes here.  I do wonder if it
> wouldn't be better to implement these as helpers.  But,

What's the hit in terms of opcodes for calling a helper function? I
would have thought you spend 10s of opcodes with messing around with
stack frames and the like before you get to the helper.

I was wondering if there is a demand for more SIMD like TCG opcodes but
I suspect all the arches are subtly different enough to make it a pain
to abstract.

>
> Reviewed-by: Richard Henderson <rth@twiddle.net>
>
>
> r~

-- 
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