https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84037
--- Comment #26 from amker at gcc dot gnu.org --- (In reply to amker from comment #25) > I tend to believe this is an register pressure based strength-reduction + > lim problem than ivopts. > > So given class of memory references like: > > reg = ... > Loop: > MEM[iv_base + reg * 0]; > MEM[iv_base + reg * 1]; > MEM[iv_base + reg * 2]; > MEM[iv_base + reg * 3]; > MEM[iv_base + reg * 4]; > MEM[iv_base + reg * 5]; > MEM[iv_base + reg * 6]; > MEM[iv_base + reg * 7]; > > The best arrangement probably would be: > > reg = ... > regX = reg * 3; > Loop: > MEM[iv_base + reg * 0]; > MEM[iv_base + reg * 1]; > MEM[iv_base + reg * 2]; > t = iv_base + regX; > MEM[t]; > MEM[iv_base + reg * 4]; > MEM[t + reg * 2]; > MEM[iv_base + regX * 2]; > MEM[t + reg * 4]; > > Depending on the register pressure, regX should be re-materialized in loop > or hoisted as invariant. Of course supported scales in addressing modes should be considered, but I guess most targets only (if) support [base + reg * 2^x]?
