[Bug tree-optimization/113237] [14 Regression] ICE verify_ssa failed when building 500.perlbench_r since r14-6822-g01f4251b8775c8

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113237

Tamar Christina <tnfchris at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P1
   Last reconfirmed|                            |2024-01-04
     Ever confirmed|0                           |1
           Assignee|unassigned at gcc dot gnu.org      |tnfchris at gcc dot gnu.org
             Status|UNCONFIRMED                 |ASSIGNED

--- Comment #3 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
Thanks,

Indeed the patch for PR 113137 won't fix this one as it looks like the peeling
code has gotten confused about which exit is which when adjusting
virtual_operands.

It looks like it's swapped them, and this happens because non of the loop exits
are counting one so it just picks a random one.

Looks the one it picks is not the latch connected one:

perl.c:10:8: note:   using as main loop exit: 11 -> 7 [AUX: (nil)]
perl.c:10:8: note:    === get_loop_niters ===
perl.c:10:8: note:    Loop has 2 exits.
perl.c:10:8: note:    Analyzing exit 0...
perl.c:10:8: note:    Analyzing exit 1...

which then incorrectly peels:

 # iters_46 = PHI <iters_12(21), iters_4(26)>

which should be:

 # iters_46 = PHI <iters_4(21), iters_12(26)>

I started implemented a fix for this same situation earlier for PR 113178 but
didn't finish it because I didn't think we'd get this far with a legit loop.

I'll finish that part.  Thanks for the testcase!