Re: Patch 0/9: IRA cleanups and preparations for tracking subwords of DImode

["Vladimir N. Makarov" <vmakarov@redhat.com>]

On 06/18/2010 09:59 AM, Bernd Schmidt wrote:
> I will post a series of patches as a followups to this message; the goal
> of it is to eventually enable us to accurately track lifetimes of
> subwords of DImode values in IRA.  For an example, see PR42502.  That
> testcase has one remaining problem: we generate unnecessary moves, since
> IRA thinks a hard reg conflicts with a DImode value when in fact it only
> conflicts with one subword.
>
> The problem goes back to
>    http://gcc.gnu.org/ml/gcc-patches/2008-04/msg01990.html
> where Kenneth removed REG_NO_CONFLICT blocks, acknowledging that this
> would cause codegen regressions, but without providing any kind of
> replacement for the functionality other than a promise that Vlad would
> fix it in IRA.  IMO that should never have been approved, but we'd
> probably have lost the functionality with the conversion to IRA anyway.
>
> The idea behind these patches is to create a new ira_object structure
> which tracks live ranges and conflicts.  In a first step, there is one
> such object per allocno; the final patch will add two of them for
> suitable multiword allocnos.
>
> This patch queue is unfinished for now: the final piece, which adds
> ALLOCNO_NUM_OBJECTS and the possiblity of having more than one object
> per allocno, seems to be working, but I haven't tested it very much yet
> and I don't think I'll get it sufficiently cleaned up before the
> weekend.  So I'm posting the patches that are already done for initial
> review now.
>
> I think the initial few cleanup patches should go in in any case so I'm
> asking for approval for them.  The final three patches in this
> submission perform the conversion to use ira_objects and probably don't
> qualify on their own, but neither do they have any significant negative
> impact - only a few additional ALLOCNO_OBJECT/OBJECT_ALLOCNO
> conversions.  It would be good to know if there are any objections in
> principle against the approach.
>
>    
Thanks for addressing the problem, Bernd.

Personally I have no principle objections to the approach.  I am only 
not sure that it will help benchmarks a lot (after Ian introduced 
lowering subreg pass although it is a bit conservative)  and I am a bit 
afraid that it makes IRA even more complicated.  But in any case we 
should try this patch may be it will work very well and will be not so 
complicated as Ken's one.

> None of these preliminary patches have been observed to change code
> generation in any way.  With the whole set applied I've bootstrapped and
> regression tested on i686-linux.
>
>    
Bernd, I'll be on vacation next week and could start to review all 
patches then if Jeff does not approve them when I am back.

As for patches already approved by Jeff.  They are ok to me too.