[Bug tree-optimization/81489] invalid phi argument used in find_implicit_erroneous_behavior

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81489

--- Comment #1 from Tom de Vries <vries at gcc dot gnu.org> ---
Created attachment 41795
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41795&action=edit
trigger and assert patch

This patch uses the bit that makes the bug easier to trigger, and adds an
assert demonstrating that we're not picking up the correct location.

Using this patch, we hit the assert:
...
FAIL: gcc.dg/tree-ssa/isolate-1.c (internal compiler error)
FAIL: gcc.dg/tree-ssa/isolate-5.c (internal compiler error)
...