Re: [PATCH] Improve profile handling in switch lowering.

[Jeff Law <jeffreyalaw@gmail.com>]

On 1/26/22 04:11, Martin Liška wrote:
> Hello.
> 
> Right now, switch lowering does not update basic_block::count values
> so that they are uninitiliazed. Moreover, I've updated probability scaling
> when a more complex expansion happens. There are still some situations 
> where
> the profile is a bit imprecise, but the patch improves rapidly the 
> current situation.
> 
> Patch can bootstrap on x86_64-linux-gnu and survives regression tests.
> 
> Ready to be installed?
> Thanks,
> Martin
> 
>      PR tree-optimization/101301
>      PR tree-optimization/103680
> 
> gcc/ChangeLog:
> 
>      * tree-switch-conversion.cc (bit_test_cluster::emit):
>      Handle correctly remaining probability.
>      (switch_decision_tree::try_switch_expansion): Fix BB's count
>      where a cluster expansion happens.
>      (switch_decision_tree::emit_cmp_and_jump_insns): Fill up also
>      BB count.
>      (switch_decision_tree::do_jump_if_equal): Likewise.
>      (switch_decision_tree::emit_case_nodes): Handle special case
>      for BT expansion which can also fallback to a default BB.
>      * tree-switch-conversion.h (cluster::cluster): Add
>      m_default_prob probability.
Funny you just ping'd this patch.  I've held it in my queue for months 
as I didn't see it get installed.

As far as I'm concerned, you know the switch conversion bits better than 
anyone.  If you think the patch significantly improves the profile 
handling for switch conversion, then I'd say go for it.  Particularly 
since it seems to fix at least two known bugs.


Keff