[self-interest] Digest Number 219

[Mario Wolczko]

Jecel wrote:
> Here is an idea that I just had to filter out useless customization (it 
> probably has lots of flaws...):
> 
> When the NIC first generates code for a given source method, all the 
> call sites are initialized with inline caches instead of PICs. 

When first generated, all call sites call the inline-cache-miss code;
a transition to a PIC takes place only when after this code has been
replaced with an inline cache, and then _that_ has missed.

> What if 
> the second time the NIC had to generate code for the same source method 
> (different receiver "type") we just made a link to the same code? This 
> code would be shared until any one of the ICs misses. Then we copy the 
> code, set its IC to the new value and let each customized version go on 
> its own path from now on.
> 
> The SIC could check this sharing as a hint that it might not want to 
> customize a given method. Obviously, any method that has aquired one or 
> more PICs must be customized.
> 
> This still generates some identical copies, but at least it doesn't 
> need more checking than we already have.

That sounds quite plausible to me.  It's an alternative to the
implementation I was pursuing, which never customizes NIC code, but
uses PICs within NIC methods.

-Mario