[Bug tree-optimization/126876] [17 regression] ice in ssa_range_in_phi since r17-3298

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126876

--- Comment #13 from Aldy Hernandez <aldyh at gcc dot gnu.org> ---
The path ranger is being invoked reentrantly since r17-3298, so match.pd's
lookups now land back in it mid-flight. The path ranger is expecting questions
about its exit block after it has finished computing its cache. If it happens
to be asked about something while pre-computing, as is the case here, it
expects it to be about the block it's currently walking, not some random block
(even if on its path). I suppose this wasn't possible before.

We could make things more re-entrant here. Worst case scenario, ask the root
ranger.