How to defeat the optimizer in GDC

[Mike Franklin]

I'm trying to benchmark some code, but the optimizer is basically 
removing all of it, so I'm benchmarking nothing.

I'd like to do something like what Chandler Carruth does here to 
defeat the optimizer:  
https://www.youtube.com/watch?v=nXaxk27zwlk&feature=youtu.be&t=2446

Here presents the following inline asm function to tell the 
optimizer that `p` is being used (at least that's how I 
understand it):
```
void escape(void* p)
{
     asm volatile("" : : "g"(p) : memory);
}
```

I tried to do the same thing in D with this function:
```
void use(void* p)
{
     version(LDC)
     {
         import ldc.llvmasm;
          __asm("", "r,~{memory}", p);
     }
     version(GDC)
     {
         asm { "" : : "g"(p), "memory"; }
     }
}
```

The LDC version seems to work fine:  
https://d.godbolt.org/z/qbg54J

But I can't get GDC to do the same:  
https://explore.dgnu.org/z/quCjhU

Is this currently possible in GDC?

Mike