https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67260
--- Comment #2 from Alexander Monakov <amonakov at gcc dot gnu.org> --- (added SH maintainers, Oleg Endo and Kaz Kojima to Cc) In response to the last sentence in my analysis, on IRC Rich pointed out that using r1/r2/r3 should be better that r0 because some instruction can operate only on r0 so that would constrain scheduling.
