[polly] r281052 - FlattenAlgo: Ensure we _really_ obtain a param space

[Tobias Grosser via llvm-commits]

On Fri, Sep 9, 2016, at 06:50 PM, Tobias Grosser via llvm-commits wrote:
> On Fri, Sep 9, 2016, at 06:37 PM, Michael Kruse via llvm-commits wrote:
> > Thank you for finding a fix.
> > 
> > This is somewhat strange. Isn't isl_union_map_get_space defined to
> > return a parameter space?
> 
> Right.
> 
> > What is different on those machines where it
> > happened?
> 
> They are owned by me. Seriously, I have no idea. This is very strange. I
> spent 30 minutes to look into this but was not able to find anything
> useful. :(

OK. I spent a couple of hours to look into this. No idea what is going
on still. I was first suspecting the new C++ interface to incorrectly
free/deallocate memory. However, I could not find any issue and valgrind
also does not report anything.

Then I just went to printf debugging. I attach you both my patch and the
typescript.

The interesting piece is this:

checkFlatten - SPtr: 18302032
checkFlatten - isParams :  is_params: space 18298960
 a
 b
space->tuple_id[0] 8021840
isl_id_none 8021840
 c
 d
1
copy
Take ownership: 0
Move That2
copy
flattenSchedule - SchedulePtr: 18302032
flattenSchedule - isParams:  is_params: space 18298960
 a
 b
space->tuple_id[0] 8021840
isl_id_none 140647671602904

The schedule remains the same when moving into flattenSchedule and the
space as well, even the id in space->tuple_id[0]. However, it seems the
address of the global isl_id_none changes. I tried to run this in gdb
and run 'watch  isl_id_none', but do not observe any change. I would
expect this address to stay constant at all times. I feel as if I missed
something very basic. Any idea what is going on?

Best,
Tobias
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