[Bug tree-optimization/61964] [4.8/4.9 regression] krb5 database propagation enters infinite loop; reduced test case

["rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61964

--- Comment #13 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to vries from comment #12)
> Created attachment 33220 [details]
> Alternative patch
> 
> > But that line is never executed at runtime (well, unless tail
> > merging comes along and makes it the only version present).
> 
> Ah, right, we consider a program with dead type-unsafe code valid.
> 
> This follow-up patch attempts to fix things less conservatively on trunk.
> Shall I put this through testing or do you see a problem with this approach?

Hum.  I don't like guarding optimizations with !flag_strict_aliasing, that is,
-fno-strict-aliasing shouldn't get us more optimization.

Also on trunk I'd like to rip out the use of the SCCVN lattice from
tail-merging as there FRE/PRE value-replace every SSA name which means
we don't need it.  The tight entanglement between PRE and tail-merge has
given me more headaches recently.

> Furthermore, I suspect that a similar issue exists for loads, I'll look into
> that.

I don't think so.