Alignment of gfortran allocated arrays

[Tim Prince]

John Travers wrote:
> On 17/08/07, Tim Prince <tprince@computer.org> wrote:
>   
>> malloc() hardly qualifies as a gfortran internal.
>>     
>
> I never meant to imply that it was.
>
>   
>> It has been around
>> since long before gfortran or SSE.  The 32-bit glibc malloc(), if that's
>> what you're discussing, is likely to continue as it has been for over 10
>> years, supporting double precision but not SSE objects. Note that
>> gfortran runs on a lot of systems besides those which depend on 32-bit
>> glibc, so if that is your world, you might clarify your posts by so
>> stating.  As there aren't any more CPUs manufactured which don't support
>> 64-bit OS, you might take into account that many of us use 64-bit.  Not
>>     
>
> Yes, my two primary systems (including the one I posted from) are 64
> bit. I thought it was clear what I was talking about as we were
> discussing getting 16-byte alignment.
>   
16-byte alignments are needed for SSE support on both 32- and 64-bit 
OS.  Various compilers for 32-bit linux handle it in incompatible ways.  
You could get into trouble calling a vectorized gcc or gfortran 
function  from ifort, for example.  malloc() gives 4-byte alignment on 
32-bit Windows (even scalar double precision performance may suffer), 
and 8-byte on linux.
Windows and linux 64-bit both adopted 16-byte alignment as a default.  
If malloc() doesn't give a 16-byte aligned pointer, that's a bug.  The 
URLs you referenced indicate that gfortran already has resolved the 
ALLOCATABLE problem as far as 64-bit linux is concerned.  Solaris is the 
only 64-bit OS I know of which has trouble here.