Re: patch to fix PR82353

[Vladimir Makarov <vmakarov@redhat.com>]

On 12/13/2017 07:34 AM, Tom de Vries wrote:
> On 10/16/2017 10:38 PM, Vladimir Makarov wrote:
>> This is another version of the patch to fix
>>
>>     https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82353
>>
>> The patch was successfully bootstrapped on x86-64 with Go and Ada.
>>
>> Committed as rev. 253796.
>
> Hi Vladimir,
>
> AFAIU this bit of the patch makes sure that the flags register show up 
> in the bb_livein of the bb in which it's used (and not defined before 
> the use), but not in the bb_liveout of the predecessors of that bb.
>
> I wonder if that's a compile-speed optimization, or an oversight.
>
Hi, Tom.  It was just a minimal fix.  I prefer minimal fixes for LRA 
because even for me it is hard to predict in many cases how the patch 
will affect all the targets.  Therefore many LRA patches have a few 
iterations before to be final.

I remember that I had some serious problems in the past when I tried to 
implement fixed hard reg liveness propagation in LRA.  It was long ago 
so we could try it again.  If you send patch you mentioned to gcc 
mailing list, I'll review and approve it.  But we need to be ready to 
revert it if some problems occur again.