Re: [PATCH] ira: Consider save/restore costs of callee-save registers [PR110071]

[Vladimir Makarov <vmakarov@redhat.com>]

On 9/14/23 06:45, Surya Kumari Jangala wrote:
> ira: Consider save/restore costs of callee-save registers [PR110071]
>
> In improve_allocation() routine, IRA checks for each allocno if spilling
> any conflicting allocnos can improve the allocation of this allocno.
> This routine computes the cost improvement for usage of each profitable
> hard register for a given allocno. The existing code in
> improve_allocation() does not consider the save/restore costs of callee
> save registers while computing the cost improvement.
>
> This can result in a callee save register being assigned to a pseudo
> that is live in the entire function and across a call, overriding a
> non-callee save register assigned to the pseudo by graph coloring. So
> the entry basic block requires a prolog, thereby causing shrink wrap to
> fail.

Yes, that can be a problem. The general idea is ok for me and common 
sense says me that the performance should be better but I would like to 
benchmark the patch on x86-64 spec2017 first.  Real applications have 
high register pressure and results might be not what we expect.  So I'll 
do it, report the results, and give my approval if there is no big 
performance degradation.  I think the results will be ready on Monday.