[mlyle]

Within a single compilation unit, and only in this most trivial case.

[WalterBright]

Here's an example of a much more complex case that is detected:

https://issues.dlang.org/show_bug.cgi?id=21745

[mlyle]

Yes, sorry if my comment isn't clear. D is very capable in this regard. While gcc with C/C++ code will spot a few trivial cases... including the one in the example above.