[Bug tree-optimization/68013] [6 Regression] ICE on valid code at -O2 on x86_64-linux-gnu in duplicate_thread_path, at tree-ssa-threadupdate.c:2469

[law at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68013

Jeffrey A. Law <law at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2015-10-26
     Ever confirmed|0                           |1

--- Comment #1 from Jeffrey A. Law <law at redhat dot com> ---
The problem here is the first block in an FSM path may not be added to
VISITED_BBs.  That in turn results in the threader finding a path which passes
through that initial block a second time, reaching a different destination the
second time through.

This is caught by the assertion (to avoid generating incorrect code).  Fixing
is simple.  But...

I'm not real happy with how the affected code is structured, but I'm at a loss
right now how to reorganize it in the immediate term.  I'm hoping to get some
clarity as I continue to look to replace the EDGE_DFS_BACK support in the old
threader with the FSM threader.

Anyway, I'll be committing a fix shortly.