Re: Tests of gcc development beyond its testsuite (in this case, for gfortran)

[Toon Moene <toon@moene.org>]

On 5/7/24 20:35, Andrew Pinski wrote:

> On Tue, May 7, 2024 at 11:31 AM Toon Moene <toon@moene.org> wrote:
>>
>> On 5/7/24 00:02, Toon Moene wrote:
>>
>>> OK, perhaps on the aarch64 I need the following option to make the
>>> comparison fair:
>>>
>>> ‘rdma’
>>>
>>>       Enable Round Double Multiply Accumulate instructions. This is on by
>>> default for -march=armv8.1-a.
>>>
>>> I.e., -mno-rdma
>>>
>>> (I hope that's correct - I'll will try that when the Sun rises again and
>>> I have some power to run the AArch64 machine ...).
>>
>> Well, I did two independent runs with gfortran-13.2 and the following
>> options:
>>
>> -O3 -march=armv8.1-a+rdma
>>
>> and
>>
>> -O3 -march=armv8.1-a+nordma
>>
>> No difference in the number of error runs exceeding the prescribed
>> thresholds.
>>
>> So, unless I made a mistake in the option specification (or the compiler
>> silently ignored them because they were not applicable to my machine -
>> ugh), the cause of the problem lies elsewhere.
> 
> 
> AARCH64 armv8-a has FMA as part of its base ISA.
> So you want to try with `-ffp-contract=off` instead.
> RDMA turns on/off instructions which are not used by the
> auto-vectorizer (yet) and used by intrinsics for them (If I read the
> code correctly).

Ah, thanks - I'll try that tomorrow.

-- 
Toon Moene - e-mail: toon@moene.org - phone: +31 346 214290
Saturnushof 14, 3738 XG  Maartensdijk, The Netherlands