proposed @noreturn attribute

[Jonathan Marler via Digitalmars-d]

On Saturday, 8 July 2017 at 10:15:39 UTC, Walter Bright wrote:
> C compilers (and by extension C++ compilers) usually have an 
> extension which allows a function to be marked as one that 
> never returns. The point of this is it enables improved data 
> flow analysis and better code being generated.
>
> Noreturn functions crop up in things like assert's and 
> enforce's. DMD internally hardcodes a few functions it knows 
> about that are noreturn, and the DMD optimizer and codegen take 
> advantage of it.
>
> But when people write their own assert's and enforce's, this 
> falls apart. While the programs will still work, they won't be 
> as efficient as they could be.
>
> Having an @noreturn attribute will take care of that:
>
>    @noreturn void ThisFunctionExits();
>
> Yes, it's another builtin attribute and attributes are arguably 
> a failure in language design.
>
> Has anyone a better idea? Does anyone want to write a DIP for 
> this?
>
> Example:
>
> DMC uses a pragma to do it:
>
>     void ThisFunctionExits();
>     #pragma noreturn(ThisFunctionExits);
>
> GCC uses an attribute:
>
>     void ThisFunctionExits() __attribute__ ((__noreturn__));
>
> VC uses:
>
>     __declspec(noreturn) void ThisFunctionExits();

Some questions...

What kinds of control flow does this apply to?  My guess is that 
you consider a function to be "no-return" so long as it never 
returns control directly back to the caller.  The examples I can 
think of would be functions that prevent returning to the caller 
by calling exit, asserting, throwing or even just executing an 
infinite loop (expecting the program to exit via signal or some 
other means).  Is this right?

Another question I had was would the compiler provide control 
flow checking to make sure that the function does not return?

Also, I can imagine some optimizations that can be done with this 
information, would you mind sharing the optimization(s) you had 
in mind?