[Bug middle-end/18041] OR of two single-bit bitfields is inefficient

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=18041

--- Comment #10 from Segher Boessenkool <segher at gcc dot gnu.org> ---
If combine tries to split RTL into two instructions, it tries to do that
one way (and one way only).  It picked the AND here.  It did not work.

You can add some define_split to your target to help combine along.