Memory alignment optimization

[Anton Titov]

On 28.05.2013 12:35, Ondřej Bílka wrote:
>
> Did you tried if following gets optimized out?
>
>   (((long)atpr)%16 != 0) abort();
>
>

No, it is not, it generates:
   406eb0:       a8 0f                   test   $0xf,%al
   406eb2:       48 89 44 24 58          mov    %rax,0x58(%rsp) // unrelated
   406eb7:       0f 85 79 16 00 00       jne    408536 
<serve_file+0x16c6> // on this address there is a call to abort

However __builtin_assume_aligned fixes this and it gets optimized out:

alignedvoid *aptr__=__builtin_assume_aligned(_mp_malloc(pool, asize__), 
MP_ALIGN);
if (((long)aptr__)%16 != 0) abort();

Best,
Anton