[Beignet] [PATCH v2 1/2] GBE: continue to refine interfering check.

[Song, Ruiling]

> -----Original Message-----
> From: Zhigang Gong [mailto:zhigang.gong at linux.intel.com]
> Sent: Wednesday, September 23, 2015 9:44 AM
> To: Song, Ruiling
> Cc: Gong, Zhigang; beignet at lists.freedesktop.org
> Subject: Re: [Beignet] [PATCH v2 1/2] GBE: continue to refine interfering check.
> 
> On Wed, Sep 23, 2015 at 02:33:43AM +0000, Song, Ruiling wrote:
> >
> >
> > > -----Original Message-----
> > > From: Beignet [mailto:beignet-bounces at lists.freedesktop.org] On
> > > Behalf Of Zhigang Gong
> > > Sent: Monday, September 7, 2015 8:20 AM
> > > To: beignet at lists.freedesktop.org
> > > Cc: Gong, Zhigang
> > > Subject: [Beignet] [PATCH v2 1/2] GBE: continue to refine interfering check.
> > >
> > > More aggresive interfering check, even if both registers are in
> > > Livein set or Liveout set, they are still possible not interfering to each other.
> > >
> > > v2:
> > > Liveout interfering check need to take care those BBs which has only
> > > one register defined.
> > >
> > > For example:
> > >
> > > BBn:
> > >   ...
> > >   MOV %r1, %src
> > >   ...
> > >
> > > Both %r1 and %r2 are in the BBn's liveout set, but %r2 is not
> > > defined or used in BBn. The previous implementation ignore this BB
> > > which is incorrect. As %r1 was modified to a different value, it
> > > means %r1 could not be replaced with %r2 in this case.
> > I thought of another one: (r0, r1 contain different values)
> > BB0:
> >   def r0
> >
> > BB1:
> >   def r1
> >   use r1
> >   use r0
> >
> > How could the algorithm deal with it?
> If r1 is a local value in BB1, then it is just ignored in these analysis including DAG
> and liveness. Don't worry about the correctness of this case, as in
> gen_reg_allocation we will calculate correct interval for it.

r1 was only defined and used in BB1. 
Ignored? the interfere() would return false if I call interfere() with r0 and r1 as arguments. But it should return true, as their live-ranges interfere.

> If r1 is not a local value of BB1, then it's either in live in of liveout set of BB1.
> Either case, this algorithm could deal it correctly.
> 
> > And looks like the algorithm is converting the "live-range
> > interference problem" into "checking the interference in live-In, live-Out set".
> > Any paper talking on this method?
> Actually, most of the paper just talk about to use liveness and DAg information
> to check interference between the phi and phi copy values to determin whether
> to coalesce. Not too much details. I just use our liveness information and DAG to
> do the job.
> 
> >
> > And for same BB interference (r0, r1 defined and used in same BB), although
> we don't need to support it yet, I think if we can put an assert, it would be better.
> Could you describe more detail of this case? local variable or not local variable?
> Are they in live in set or live out set?
Not in liveout or livein set. They are only defined and used in same Basic Block. But there live-range interfere.

> 
> Thanks for the comments,
> Zhigang Gong.
> 
> >
> > Thanks!
> > Ruiling
> >
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