Re: [PATCH] rtl-optimization/104686 - speedup IRA allocno conflict test

[Vladimir Makarov <vmakarov@redhat.com>]

On 2022-03-02 03:58, Richard Biener wrote:
> In this PR allocnos_conflict_p takes 90% of the compile-time via
> the calls from update_conflict_hard_regno_costs.  This is due to
> the high number of conflicts recorded in the dense bitvector
> representation.  Fortunately we can take advantage of the bitvector
> representation here and turn the O(n) conflict test into an O(1) one,
> greatly speeding up the compile of the testcase from 39s to just 4s
> (93% IRA time to 26% IRA time).
>
> While for the testcase in question the first allocno is almost always
> the nice one the patch tries a more systematic approach to finding
> the allocno to iterate object conflicts over.  That does reduce
> the actual number of compares for the testcase but it doesn't make
> a measurable difference wall-clock wise.  That's not guaranteed
> though I think so I've kept this systematic way of choosing the
> cheapest allocno.
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu.
>
> OK for trunk?
>
Yes.

Richard, thank you again for working on this issue.

> 2022-03-02  Richard Biener  <rguenther@suse.de>
>
> 	PR rtl-optimization/104686
> 	* ira-color.cc (object_conflicts_with_allocno_p): New function
> 	using a bitvector test instead of iterating when possible.
> 	(allocnos_conflict_p): Choose the best allocno to iterate over
> 	object conflicts.
> 	(update_conflict_hard_regno_costs): Do allocnos_conflict_p test
> 	last.
> other_allocno),