[llvm-commits] [patch] Improve register coalescing

[Rafael Ávila de Espíndola]

>> The real solution I think would be to turn the coalescing algorithm
>> upside down: instead of trying to merge registers one pair at a time,
>> start by assuming that every copy related register can be merged and
>> try to show it cannot.
>
> That sounds hard to get right.

True. The difference just reminded me of regular X strong dead code 
elimination.

>> BB1:
>> X = B
>> Y = A
>>
>> BB2:
>> A = X
>> B = Y
>>
>> A and B can be merged if X and Y can be merged and X and Y can be
>> merge if A and B can be merged.
>
> I think we already detect and remove this kind of PHI loops?

Cool. If we do then just following copy definitions should get almost 
all of the cases. I might give it a try on Firefox and see if it makes a 
difference.

> /jakob
>

Cheers,
Rafael