Re: [Qemu-devel] [PATCH 07/21] target-arm: A64: add support for 3 src data proc insns

[Peter Maydell]

On 20 December 2013 14:10, Richard Henderson <address@hidden> wrote:
> On 12/20/2013 05:18 AM, Peter Maydell wrote:
>> On 19 December 2013 19:29, Richard Henderson <address@hidden> wrote:
>>> On 12/17/2013 07:12 AM, Peter Maydell wrote:
>>>> +    tcg_gen_mul_i64(tcg_tmp, tcg_op1, tcg_op2);
>>>> +    if (is_sub) {
>>>> +        tcg_gen_sub_i64(cpu_reg(s, rd), cpu_reg(s, ra), tcg_tmp);
>>>> +    } else {
>>>> +        tcg_gen_add_i64(cpu_reg(s, rd), cpu_reg(s, ra), tcg_tmp);
>>>> +    }
>>>
>>> Perhaps worth noticing the RA=XZR special case for the MUL alias?
>>
>> Yeah, makes sense: have adjusted to:
>> +    if (ra == 31) {
>> +        /* We special-case rA == XZR as it is the standard MUL alias */
>> +        tcg_gen_mul_i64(cpu_reg(s, rd), tcg_op1, tcg_op2);
>> +    } else {
>
> You need to handle (or dismiss) is_sub.
>
> Either (ra == 31 && !is_sub) or
>
>            if (is_sub) {
>                tcg_gen_neg_i64(tcg_rd, tcg_rd);
>            }
>
> with tcg_rd pre-loaded along with tcg_op1 and tcg_op2.
>
> That said, unlike MUL I don't expect MNEG to be common at all.

Oops. Yes, let's just have (ra == 31 && !is_sub).

thanks
-- PMM