https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57534
--- Comment #15 from Aldy Hernandez <aldyh at gcc dot gnu.org> --- (In reply to Jeffrey A. Law from comment #14) > I wonder if this could be addressed with a more reasonable address > computation reassociation. > ISTM that we associating as (x + (y + c)) which seems like a mistake in this > case. > > If we associated as (x + y) + c, then the (x + y) would become a common > subexpression eliminating a bunch of unnecessary address computations. Coming out of SSA for hand_benchmark_cache_ronly(), we seem to be calculating: ((index + 1) * 8) + x ((index + 2) * 8) + x ((index + 3) * 8) + x etc After slsr we have: (index * 8) + x (((index * 8) + 8) + x) ((((index * 8) + 8) + 8) + x) And finally after forwprop4: (index * 8) + x (((index * 8) + 8) + x) (((index * 8) + 16) + x) Are you suggesting we reassociate the above as: ((index * 8) + CONSTANT) + x Is there a preferred place to put this kind of transformation? A separate pass after forwprop4? Much earlier? Is there a pass that already does this kind of juggling? BTW, it seems like a pass like tree-ssa-reassoc, tries to precisely convert: x + (y + constant) INTO (x + CONSTANT) + y which is the opposite of what we want.
