https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99830
--- Comment #11 from Jakub Jelinek <jakub at gcc dot gnu.org> --- I don't understand what is wrong about that. (clobber:TI (const_int 0 [0])) in there stands for couldn't figure out what this value is or how to represent it, so it is wildcard for I don't know what the value is. I'd think if one has say (and:TI (clobber:TI (const_int 0 [0])) (const_int 0 [0])) one should be able to still simplify it into 0, etc., and what happens here is the same thing, the clobber value, whatever it is, doesn't influence in any way the whole expression value, therefore it is optimized away. If it remained there, sure, the instruction would fail recog_for_combine.
