[Bug debug/70935] [6/7 Regression] ICE: verify_ssa failed (error: definition in block 9 does not dominate use in block 12) w/ -O3 -g

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70935

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
This is tree_unswitch_outer_loop -> hoist_guard not resetting debug stmts that
have some uses of SSA_NAMEs defined in the inner loop.
But the transformation is really weird.
We have:
loop7==================
  bb10
    |
    v
loop2 =============
 />bb8
| inv test
| /  |
| | something
| \  | \
|  v v  \
|   bb7  +
|   |    |
+---+    |
loop2 end =========
         |
         v
        bb13
        DEBUG pm = defined_in_something

And we move the inv test to bb 10, with one edge going to loop2, and the other
to bb13 (newly added edge).  If I understand the cfg right though, we've thus
changed an endless loop (if inv test is false, bb8 not really having any
side-effects just jumped to bb7 and back to bb8 forever) into no loop, and in
addition the newly added edge from bb10 to bb13 of course means any SSA_NAMEs
defined in loop2 can't be used.