[Bug tree-optimization/54985] [4.7/4.8 Regression] dom optimization erroneous remove conditional goto.

[law at redhat dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54985

--- Comment #6 from Jeffrey A. Law <law at redhat dot com> 2012-10-19 22:00:45 UTC ---
This is definitely something introduced when I extended the threading code last
year.

When threading across a backedge in the CFG we run the risk of simplifying a
conditional using equivalences which are valid for one loop iteration, but not
the next iteration.

There's a bit of special casing done to handle this. We either need to add
another case or actually invalidate the temporary equivalences we made for the
statements in the loop.  The first is pretty trivial, but I want to ponder the
special case code over the weekend for it's overall safety/correctness.

I don't see any difficulty wrapping this up early next week.

Jeff