[dmd-internals] non-PODs again

[Walter Bright]

On 3/7/2013 9:36 AM, Johannes Pfau wrote:
> I'm sorry I have to pester you with this again, but I still have some 
> questions regarding POD types and I'd like to fix this in GDC.
>
> So from last discussion:
> >> Wouldn't it be legal to still pass non-PODs in registers when calling 
> functions and only copying them back to
> >> the stack if the address is needed? As we pass structs by value anyway, how 
> could this be problematic?
> >
> > No, not allowed. Consider why there are copy constructors, and what they do.
>
> I compiled some test programs with dmd and dmd _does_ pass non-POD values in 
> registers as I suggested above.
> See this example:
> https://gist.github.com/jpf91/5064703 (D)
> https://gist.github.com/jpf91/5064764 (ASM)

That's because objects with constructors are now regarded as POD.

>
> I also don't understand how a copy ctor could break this.

Because a copy ctor executes arbitrary code, and this just does not work in the 
general case if a value is in a register.