Re: [Qemu-devel] [PATCH v1 7/9] tests/tcg: add float_madds test to multiarch

[Alex Bennée]

Richard Henderson <address@hidden> writes:

> On 9/17/19 5:00 PM, Alex Bennée wrote:
>>>> +    add_f32_const(0x8p-152);
>>>> +    add_f32_const(0x8p-152);
>>>> +    add_f32_const(0x8p-152);
>>>
>>> Why are you adding 3 of the same?
>>
>> To replicate the 1841491 test case where the same number is used for
>> a/b/c
>
> Then we really ought to be more explicit about that.

I guess - I was hoping to piggy back on the general case. Maybe we
should just split that into a separate test case. We can at least re-use
the format and flag printing code and drop the behind the scenes magic
to "join" the constant table with extra test values.

> You're not doing full permutations on the sets of numbers, so does 
> incrementing
> a random index really test what you intended?

I did initially do the full permutation but for madds it all adds up
quite quickly. The shuffle we do here is a bit of a comprise, so it
shuffles the various nan forms before nans with -inf and -large and
finally a bunch of real numbers (subnormals in the middle). It gives a
reasonably broad coverage without going nuts.

>
>>>> +#if defined(__arm__)
>>>> +                r = __builtin_fmaf(a, b, c);
>>>> +#else
>>>> +                r = __builtin_fmaf(a, b, c);
>>>> +#endif
>>>
>>> Eh?
>>
>> Ahh I was going to hardcode the arm madd instruction in as the builtin
>> wasn't expanding. I tried setting -march in the CFLAGS but that didn't
>> trigger it either on my buster arm-hf compiler. Any ideas how to get the
>> compiler to do the right thing?
>
> I think you want -mfpu=neon-vfpv4.

Ahh that worked. I would have hoped that v8 would be enough to spit out
aarch32 code which has to have VFPv4 for A profile right?

Anyway I'll use that for now.

>
>
> r~


--
Alex Bennée