2013/3/8 Johannes Pfau <johannespfau@googlemail.com>

Am 08.03.2013 05:52, schrieb Maxim Fomin:

2013/3/8 Walter Bright <walter@digitalmars.com>

On 3/7/2013 12:19 PM, Johannes Pfau wrote:

Am 07.03.2013 20:45, schrieb 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.

This example uses a postblit to make sure the type is not a POD. It's obvious in the ASM that the copy ctor is called,

Oops, I missed that. It's a bug in dmd.

Isn't there another bug with struct parameter which is copied twice - on caller and callee side?

function  D main
Date d = _D1e4Date6__initZ;
setDate((Date __cpcttmp7 = __cpcttmp7.__cpctor(d); , __cpcttmp7))

function  e.setDate
x.opAssign((Date __cpcttmp6 = __cpcttmp6.__cpctor(d); , __cpcttmp6))

setDate assigns d to the global variable x so the second call to the cpctor seems to be caused by that and valid.

-- 
Johannes Pfau

DMD still generates double copy if variable is changed to local

void setDate(Date d)
{
Date x;
x = d;
}

function  e.setDate
Date x = _D1e4Date6__initZ;
x.opAssign((Date __cpcttmp6 = __cpcttmp6.__cpctor(d); , __cpcttmp6))

function  D main
Date d = _D1e4Date6__initZ;
setDate((Date __cpcttmp7 = __cpcttmp7.__cpctor(d); , __cpcttmp7))

Anyway whether variable is tls or not is irrelevant. Compiler should not make a copy when assigning.

-- 
Johannes Pfau