[lld] r258499 - Use of llvm_unreachable instead of warning in EhFrameHeader<ELFT>::assignEhFrame().

[David Blaikie via llvm-commits]

On Fri, Jan 22, 2016 at 8:27 AM, George Rimar <grimar at accesssoftek.com>
wrote:

> >This should probably be written with an assert instead:
> >
> > assert((!this->Sec || this->Sec == Sec) && "multiple .eh_frame sections
> ....");
>
> This should never happen, and if will due to a bug or something then
> result is completely unknown, because
> code does not suppose that. So it is fatal error actually.
>

If it's never meant to happen (if it does happen, it's a programmer error)
then that's entirely appropriate for an assertion.


> That why I think unreachable fits better than assert and also there is no
> asserts in release usually.
>

That's correct - assertions are used to test for programmatic
errors/mistakes.

unreachable is roughly equivalent - if not worse, with unreachable, in an
-O0 build the unreachable behaves something like an assert (the program
will fail hard, print an error, etc) but in anything else, LLVM will
optimize assuming the condition is true. This means if the condition is not
true, the behavior may be worse than just continuing without having done
anything. LLVM will deduce that the condition /must/ be true.

- Dave
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