proposed @noreturn attribute

[Nicholas Wilson 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.

On the contrary I think attributes are wonderful, and I have a 
DIP in the pipeline to address some the the problems 
(https://github.com/dlang/DIPs/pull/75)

>
> 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();

consider that GDC and LDC already both have that attribute 
courtesy of their backends (@attribute("noreturn") and 
@llvmAttr("noreturn") respectively).

While it may seem a good idea to unify them, if people want 
performance then they will use either GDC or LDC, which already 
have that attribute. So I would question the usefulness of such 
an attribute but won't go so far as to discourage anyone from 
trying. However it should be a compiler dependant alias in 
core.attribute if it is to become a thing.