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Re: Optimal Coalescing with respect to move instruction for Live range splitting

On 2015-01-18 12:37 AM, Ajit Kumar Agarwal wrote:
Register allocation with two phase approach does optimal coalescing after the spilling. Sometime Live range splitting makes
the coalescing non optimal. The splitted Live range are connected by move instruction. Thus the Live range splitting and more
specifically aggressive Live range splitting  increases the number of move instruction and making the coalescing
non optimal.

The optimal coalescing should take the frequency of the regions into consideration. The more the frequency of the region the cost
associated with the splitted live ranges will increase. If such cost increasing then we should do aggressive coalescing in this case and
remove the move instruction by associating the same color or hard registers associated with move instruction for the splitting live

I am think of adding such heuristics in the GCC Top Down Region based register allocator for the optimal coalescing, thereby reducing
the move instruction connected with the splitted Live ranges in the more frequently code.

Thoughts please ?

It is difficult for me to understand what and how you will do this exactly. If it is not a big work to implement this heuristic, I guess you should try and see the result. If it works we can add it to the RA.

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