Incorrect code generation -O2 gdc

[Johan Granberg]

The following code generates an assert error when compiling with gdc and 
-O2 on my iBook G3 800mhz OS X 10.4.7

gdc (GCC) 4.0.1 (gdc 0.19, using dmd 0.162)
Copyright (C) 2005 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

It looks like something goes wrong when copying structs (or I'm 
incorrect in believing structs is just binary copied)

<code>
struct SigeCallback
{
	union
	{
		void delegate(uint) del;
		void function(uint) dfp;
	}
	static SigeCallback opCall(void function(uint) c,uint i)
	{
		SigeCallback a;
		a.dfp=c;
		return a;
	}
}
SigeCallback f;
static this()
{
	f=SigeCallback(&sigeFpNull,0);//this line causes an assert error
	//f.dfp=&sigeFpNull;//this line works ok
}
void sigeFpNull(uint i){}
void main()
{
	sigeFpNull(0);
	assert(f.dfp);f.dfp(0);//line 26
}
/* output from running this
$ ./test
Error: AssertError Failure test.d(26)
*/
</code>