is this an instance of the 16-byte struct bug

[deadalnix]

On Monday, 4 November 2013 at 23:14:08 UTC, jerro wrote:
> On Monday, 4 November 2013 at 23:07:27 UTC, deadalnix wrote:
>> On Monday, 4 November 2013 at 22:56:48 UTC, jerro wrote:
>>>> Then it look like a dmd backend bug. Can you post the 
>>>> generated assembly ?
>>>
>>> 000000000043050c <_Dmain>:
>>>  43050c:       push   %rbp
>>>  43050d:       mov    %rsp,%rbp
>>>  430510:       sub    $0x40,%rsp
>>>  430514:       movabs $0x3ff0000000000000,%rax
>>>  43051b:
>>>  43051e:       mov    %rax,-0x40(%rbp)
>>>  430522:       movsd  -0x40(%rbp),%xmm0
>>>  430527:       rex.W movsd %xmm0,-0x30(%rbp)
>>>  43052d:       xor    %edx,%edx
>>>  43052f:       mov    %rax,-0x10(%rbp)
>>>  430533:       mov    %rdx,-0x8(%rbp)
>>>  430537:       mov    %rax,-0x28(%rbp)
>>>  43053b:       mov    %rdx,-0x20(%rbp)
>>
>>>  43053f:       mov    0x28022(%rip),%rdx
>>>  430546:       mov    0x28013(%rip),%rsi
>>
>> What are these ? What are they referering to
>
> My guess is they are refering to length and
> ptr for "%x" string literal, which is passed to writefln.
>
>>
>>>  43054d:       mov    -0x28(%rbp),%rdi
>>>  430551:       callq  430874 <void
>>> std.stdio.writefln!(immutable(char)[],
>>> ulong).writefln(immutable(char)[], ulong)>
>>>  430556:       xor    %eax,%eax
>>>  430558:       leaveq
>>>  430559:       retq
>>
>> This calls writefln, this is not what your code does just 
>> above. Are you sure you are posting the right assembly ? Do 
>> you use the inline flag ?
>
> I think you are confusing my post with some other post (I am not
> OP).

OK, my mistake.

> My code sample was:
>
> import std.stdio;
>
> struct Y {
>       int[] _data;
> }
>
> struct CFS {
>       double x;
>       Y growth;
> }
>
> void main() {
>       auto s = CFS(1.0);
>       writefln("%x", s.growth._data.length); // prints
> 3ff0000000000000
> }
>
> The constructor's argument was 2.0 in my previous sample, but it
> should have been 1.0.

I'm not sure what DMD is trying to do, but the function call to 
writefln is clearly wrong.