What should happen here?

[max haughton]

On Sunday, 26 September 2021 at 20:39:48 UTC, Steven 
Schveighoffer wrote:
> On 9/26/21 3:13 PM, deadalnix wrote:
>> On Friday, 24 September 2021 at 15:31:46 UTC, Steven 
>> Schveighoffer wrote:
>>> On 9/24/21 11:25 AM, deadalnix wrote:
>>>>[...]
>>>
>>> You think pushing on the stack is going be 2x slower than 
>>> calling `GC.addRoot`?
>> 
>> If the optimizer isn't free to optimize thing away from the 
>> stack, yes, it's pretty much guaranteed.
>
> You realize what `GC.addRoot` does? It adds a pointer to a 
> treap, through a virtual function call after taking a global 
> lock. Pushing a stack item is going to be at least 10x faster, 
> probably more compared to that. In the function call alone, 
> there are a few stack pushes.
>
> -Steve

I think Amaury means that the code would be slower if the 
compiler is unable to register allocate at all vs. just for 
things returned by the allocator.