[Bug tree-optimization/69728] [6/7/8 Regression] internal compiler error: in outer_projection_mupa, at graphite-sese-to-poly.c:1175

[rguenther at suse dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69728

--- Comment #20 from rguenther at suse dot de <rguenther at suse dot de> ---
On Tue, 19 Sep 2017, spop at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69728
> 
> --- Comment #19 from Sebastian Pop <spop at gcc dot gnu.org> ---
> > So how'd we properly handle a valid empty domain?
> 
> DCE the statement.
> 
> If the domain for a statement is empty, it means that the statement does not
> execute: it is dead code.
> 
> I think we are better enforcing the elimination of the statement as this wrong
> analysis (or translation) of the number of iterations could produce wrong code.

That was my thinking, I put it on my TODO to figure out how to "DCE"
a stmt (or in this case it's rather the whole "loop body", right?).
I've not fully found my way through initial schedule building yet
(otherwise I would have tried refactoring to not operate in pbb
vector order but more naturally follow the SESE in a CFG walk with
maintaining a BB -> pbb mapping).

> > I assume P_21 is c.7_12
> 
> the number after P_ is the ssa variable number, so P_21 is c.7_21.
> 
> > we have 0 <= i1 <= 2147483637, whereever that comes from.
> 
> you can think about i1 as a canonical induction variable: 0 <= i1
> and i1 is indexing all iterations in that loop: i.e., i1 is incremented by 1.
> 
> > Probably from the i1 <= 2147483637 constraint
> 
> this constraint is added based on the type of the induction variable that gives
> an upper bound for the iteration domain.
> 
> > 4294967296*floor((-1 - P_21)/4294967296) < -P_21 - i1
> 
> Yes, this constraint seems to be wrong.

It indeed looks like so though I wasn't able to nail down what goes wrong.
Unfortunately the extract_affine fixes didn't affect this one in a 
positive way.