Re: sparse-llvm issue with handling of phisrc instruction

[Luc Van Oostenryck <luc.vanoostenryck@gmail.com>]

On Wed, Mar 22, 2017 at 06:55:37PM +0000, Dibyendu Majumdar wrote:
> Hi Luc,
> 
> On 22 March 2017 at 18:17, Dibyendu Majumdar <mobile@majumdar.org.uk> wrote:
> >>>>> I am trying to see if sparse-llvm can handle unsimplified IR output
> >>>>> from linearizer. I think there is a problem in how it handles phisrc.
> >>>>
> >>>> Does your non-simplified sparse IR contain the liveness information?
> >>>> I think those are needed for the handling of OP_PHI & OP_PHISOURCE
> >>>> in sparse-llvm.
> >>>>
> >>>
> >>> Probably not - I commented out everything in linearize_fn() from
> >>> simplify_symbol_usage() and downwards. Please tell me if this is
> >>> incorrect.
> >>
> >> As far as I understand, sparse-llvm needs track_pseudo_liveness().
> >>
> >
> > Tried that - it made no difference.
> >
> 
> If there is a single phisrc and phi instruction then is phisrc meant
> to have the phi in its user list?

Yes but again this may depends on the simplification for
its correctness.

Also, for phi-nodes liveness is a bit different, unintuitive at first,
the PSEUDO_PHI play no role in liveness. So, in IR code like:
   .L0
	phisrc	%phi1 <- ...
	...

   .L1
	phi	%r2 <- %phi1, %phi2

the "liveness between .L0 & .L1" is not made via %phi1 but with the
"real" pseudo: %r2 (.L0 defines %r2, .L1 needs %r2).
 
-- Luc