Optimizing Immutable Data?

[Jack Stouffer via digitalmars-d-ldc]

At Dconf, one of the speakers made an off-hand comment that LDC 
could use an LLVM feature to optimize immutable variables by 
storing them differently than mutable data. The LDC developer 
that was there made a response, but the mic didn't pick it up.

Is this something that has already been done? Should a bug report 
be filed so this is tracked?