Fastest Way of Accessing Entries in an AA

["Nordlöw" via Digitalmars-d-learn]

On Thursday, 8 January 2015 at 16:11:07 UTC, ketmar via 
Digitalmars-d-learn wrote:
> how can it? compiler doesn't know what the code is supposed to 
> do. if
> compilers will know such things someday, we can stop writing 
> programs
> altogether, as compilers will be able to write any program for 
> us. ;-)

Correction:

I thought it would be nice if the compiler explained to me that

     key in aa ? aa[key]

is a sub-optimal performance-wise.