[LLVMdev] [patch] Pluggable Coalescers

[Evan Cheng]

On Aug 28, 2007, at 8:59 AM, David Greene wrote:

> On Monday 27 August 2007 19:02, Evan Cheng wrote:
>
>>> interfere() isn't sufficient because the allocation algorithm may
>>> place other
>>> constraints on coalescing.  George and Appel's iterated register
>>> coalescing
>>> is a prime example.  It wants to "freeze" copies that should not be
>>> coalesced
>>> because doing so might cause spilling.  You don't want the coalescer
>>> touching
>>> these because if it does the data structures will be inconsistent.
>>
>> Ok. But that means this method doesn't belong to the InterferenceData
>> class. Shouldn't the allocator query the coalescer instead?
>
> No, it's the other way around.  The coalescer needs to decide  
> whether it can
> coalesce something.  It must ask the allocator if it's ok.
>
> This is part of InterferenceData to decouple the coalescer from the  
> allocator
> so the coalescer doesn't have to keep a pointer to the allocator.   
> In my
> current implementation, InterferenceData for the graph coloring  
> allocator
> has references to all of the necessary information to return an  
> answer to
> this question.

Ok. This means InterferenceData contains more than interference  
information. Perhaps you can choose a better name? Or add another  
data structure to store this information.

Evan

>
>                                                        -Dave
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