https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90249
--- Comment #7 from Richard Earnshaw <rearnsha at gcc dot gnu.org> --- (In reply to Segher Boessenkool from comment #4) > That is code *size*. Code size is expected to grow a tiny bit, because of > *better* register allocation. > > But we could not do make_more_copies at -Os, if that helps? (The hard > register > changes themselves are required for correctness). In this case, however, we get *worse* register allocation, since it is using the the expensive register more frequently than a cheaper register which is hardly used at all. In this particular case, all the uses of the "cheap" register (r7) could use the 'expensive' register at no additional cost, since the cheap register is being used only to hold a value that will be moved to another register (a cheap operation regardless of the register used).
