Does D use zero-cost exceptions?

[Steven Schveighoffer]

On 4/15/19 4:24 PM, Andrei Alexandrescu wrote:
> On 4/15/19 3:36 PM, Nicholas Wilson wrote:
>> On Monday, 15 April 2019 at 19:25:24 UTC, A wrote:
>>> It is well known that exceptions are much slower than their 
>>> alternatives, but is there a performance cost for using try/catch, 
>>> even when no Exception/Error is being thrown?
>>
>> There is a space cost for the unwind tables, but exceptions are faster 
>> than checking error codes all over the place (you do check them right? 
>> ;) ).
> 
> Sadly that's not quite the case... we've run a bunch of test at Facebook 
> back in the day and the sheer presence of unwinding disables a bunch of 
> optimizations, notably code motion and everything enabled by it. The 
> bottom line effect is quite unpleasant, in the single digits.

It would be important to know what "the day" was. Because there have 
been a lot of improvements on LLVM. I wonder if some of this has been 
mitigated for LDC at least.

> This is a problem important enough for C++ that they added a keyword 
> dedicated to it (noexcept).

Don't we have nothrow for this?

-Steve