Am 08.03.2013 13:15, schrieb Maxim Fomin:
2013/3/8 Johannes Pfau <[email protected]
<mailto:[email protected]>>
Am 08.03.2013 05:52, schrieb Maxim Fomin:
2013/3/8 Walter Bright <[email protected]
<mailto:[email protected]>>
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.
You're right I confused this with initialization which needs the call to
the copy ctor, but a simple assignment should not call it.
--
Johannes Pfau
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