Re: Tooltips GC overhead

[Nix]

On 4 Aug 2015, Stefan Monnier told this:

>>> The problem is that it would slow down functions like `cons'.
>> I don't see why it has to.
>
> I don't see how it wouldn't have to ;-)
>
>> And we could do that only when the memory profiler is invoked.
>
> AFAICT it would require an extra test somewhere in Fcons, and that
> test will always have to be performed.

The cost you're trying to defend against here is a mispredicted branch
and corresponding pipeline stall, so if you mark it with
__builtin_expect() (or analogue in other compilers) you can make the
'profiler off' case the predicted branch, and its cost when off should
drop to nearly zero.

(Or so it seems to me.)

-- 
NULL && (void)