Alignment of struct containing SIMD field - GDC
Cecil Ward via Digitalmars-d-learn
digitalmars-d-learn at puremagic.com
Wed Mar 1 17:17:41 PST 2017
On Wednesday, 1 March 2017 at 22:15:59 UTC, Iain Buclaw wrote:
> On Wednesday, 1 March 2017 at 19:09:24 UTC, Johan Engelen wrote:
>> On Wednesday, 1 March 2017 at 18:34:16 UTC, Iain Buclaw wrote:
>>>
>>> Simple test case would be:
>>>
>>> struct vec_struct {
>>> bool b2;
>>> struct {
>>> bool b;
>>> int8 field;
>>> }
>>> }
>>>
>>> static assert(vec_struct.b.offsetof == 32);
>>> static assert(vec_struct.field.offsetof == 64);
>>
>> With explicit align(32), it works:
>> https://godbolt.org/g/3GjOHW
>>
>> - Johan
>
> Well obviously, because it adheres to explicit alignment. The
> compiler just has the wrong idea of how default alignment
> should work.
>
> Raised bug here, and I'm raising a PR now also.
> https://issues.dlang.org/show_bug.cgi?id=17237
Thanks for your help Iain. And many thanks btw for all the
general good work which is very much appreciated by this
particular geriatric asm programmer.
I checked the case of XMM alignment, and it's fine.
I presume D does not yet support 512-bit zmm vector objects? (I
have seen GDC doing a nice job generating auto-vectorised AVX512
code though - thanks.) The same bug would presumably bite again
in that case otherwise?
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