Does D use zero-cost exceptions?

Andrei Alexandrescu SeeWebsiteForEmail at erdani.org
Mon Apr 15 20:24:27 UTC 2019


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.

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


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