__vector(ubyte[32]) misalignment

[Bruce Carneal]

On Sunday, 9 August 2020 at 09:58:18 UTC, Johan wrote:
> On Sunday, 9 August 2020 at 01:03:51 UTC, Bruce Carneal wrote:
>> The .alignof attribute of __vector(ubyte[32]) is 32 but 
>> initializing an array of such vectors via an assignment to 
>> .length has given me 16 byte alignment (and subsequent seg 
>> faults which I suspect are related).
>>
>> Is sub .alignof alignment expected here?  IOW, do I have to 
>> manually manage memory if I want alignments above 16?
>
> Do you have a code example?
> And what compiler are you using?
>
> -Johan

At run.dlang.io recent runs of both dmd and lcd compilations of 
the below revealed misalignment.

import std;

void main() @safe
{
     alias V = __vector(ubyte[32]); // requires -mcpu=native or 
other on cmd line
     V[] va;
     size_t misalignments;
     foreach(N; 1..101) {
     	va.length = N;
     	const uptr = cast(ulong)va.ptr;
         misalignments += (uptr % V.alignof) != 0;
     }
     writefln("misaligned %s per cent of the time", misalignments);
}