Error: llroundl cannot be interpreted at compile time, because it has no available source code

[mw]

On Monday, 8 June 2020 at 18:43:58 UTC, Stanislav Blinov wrote:
> On Monday, 8 June 2020 at 18:08:57 UTC, mw wrote:
>
>> 2) even it does so, but why such simple function as lroundl 
>> cannot be CTFE-ed?
>
> Because, as the error message states, there's no source for it 
> :) std.math calls into C math library.

OK, but the compiler knows it's external C func:

   return core.stdc.math.llroundl(x);

And with a symbol-to-c-func table, it should be able to just call 
that C func.

This is dramatically enhance CTFE's eval ability, esp for math 
funcs.