Cleverness of GC Scanning

[deadalnix via Digitalmars-d]

On Friday, 7 August 2015 at 12:17:19 UTC, David Nadlinger wrote:
> On Friday, 7 August 2015 at 12:05:01 UTC, Per Nordlöw wrote:
>> Is the current Phobos GC smart enough to *not* scan 
>> GC-allocated arrays when the elements don't contain any 
>> indirections (references/pointers).
>
> Yes (mostly). Have a look at the NO_SCAN attribute (and 
> similar) in the druntime docs.
>
>  — David

This attribute exists, but how much grinding in the type system 
dmd and the runtime are doing ?