Is the following well defined and allowed?

[ag0aep6g]

On Thursday, 1 March 2018 at 20:14:07 UTC, Steven Schveighoffer 
wrote:
> dmd -version=dosafe -noboundscheck -run testarrayoverlap.d => 
> no error, undefined behavior
> dmd -run testarrayoverlap.d => error
>
> @safe has nothing to do with it.

@safe has everything to do with. @safe guarantees that there's no 
undefined behavior. If you can trigger UB in @safe code, that's a 
bug. The guarantee must hold whether asserts are enabled or not. 
-noboundscheck does not just disable asserts, it undermines 
@safe, rendering it meaningless.

For just disabling asserts (without affecting @safe), there's 
-release. With your same code, `dmd -release` => UB, but `dmd 
-release -version=dosafe` => Error.