https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88233
--- Comment #2 from Segher Boessenkool <segher at gcc dot gnu.org> --- Currently full lower_subreg runs only after the first splitter pass. This is much too late to be effective for this testcase. Running it before combine (I put it immediately after loop2) works, for all powerpc configs (32/64, BE/LE, old and new ABI). It will need more thorough testing, of course. It also should probably be configurable when the full lower_subreg patch is run (you cannot run it twice, that generate worse code), I think some ports want it as late as it is currently?
