[Bug tree-optimization/61607] DOM missed jump threading and destroyed loops

[law at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61607

--- Comment #8 from Jeffrey A. Law <law at redhat dot com> ---
FWIW, I vaguely recall experimenting with following the SSA_NAME_VALUE chains
in the past and having problems with cycles.  IIRC we can get cycles from
things like recording equivalences created by equality tests.

We could put a (small) upper limit on the number of SSA_NAME_VALUEs we walk. 
I'd expect the vast majority of the time we'd be walking just one node.  I
guess that's worth investigating.