GDC optimizations bug ?

[Maor via D.gnu]

Hi,

I'm trying to compile a program using inline asm with 
optimizations and I got my inline asm functions thrown out by the 
optimizer although I declared them as having side effects (by 
stating a memory clobber).
I wrote the following toy program to demonstrate the problem:

----------------------------------------------

import std.stdio;
import gcc.attribute;

@attribute("forceinline") ulong exchangeAndAdd(shared ulong 
*counter, ulong addition) {
       ulong retVal = void; // we don't want it initialized when 
dmd is used
       asm {
         "
           mov  %2, %0             ;
           lock                    ;
           xadd %0, (%1)           ;
         ":
         "=&r"(retVal) :
         "r"(counter), "r"(addition) :
         "memory";
       }
       return retVal;
}

ulong func1() {
   shared ulong a = 9;
   exchangeAndAdd(&a, 3);
   return a;
}

void main()
{
   ulong b;
   b = func1();
   writeln(b);
}

----------------------------------------------

Compiling it with and without optimizations gives a different 
output:
> /opt/gdc/bin/gdc ./test.d -o/tmp/a.out
> /tmp/a.out
12
> /opt/gdc/bin/gdc -O3 -g ./test.d -o/tmp/a.out
> /tmp/a.out
9

using gdb we can see that the call to exchangeAndAdd() is being 
thrown out in the optimized version:

(gdb) disas _D4test5func1FZm
Dump of assembler code for function _D4test5func1FZm:
    0x0000000000406460 <+0>:	movq   $0x9,-0x8(%rsp)
    0x0000000000406469 <+9>:	mov    -0x8(%rsp),%rax
    0x000000000040646e <+14>:	retq
End of assembler dump.


Is this a compiler bug or am I doing something wrong ?
btw, I'm using gdc 4.9.0.

thanks in advance,
Maor