[Bug rtl-optimization/64081] [5/6/7 Regression] r217827 prevents RTL loop unroll

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64081

--- Comment #54 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Thanks Aldy, this makes it clear what happens, and it is actually
pretty simple.

The patch changes check_simple_exit to also return true if
check_complex_exit is true (as well as some other conditions).
But the call in doloop_optimize (via get_simple_loop_desc) really
does need to check for only simple exits.  With the patch, the loop
in the testcase gets one of its two identical exits replaced by a
doloop pattern, which is incorrect (replacing both would work in
this case though).