https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78684
--- Comment #8 from amker at gcc dot gnu.org --- (In reply to Jakub Jelinek from comment #7) > (In reply to amker from comment #6) > > Ok, in this case I need to check idx_step is negative if it's signed type; > > or idx_step has sign bit if it's unsigned type (negative step in effect). > > tree_int_cst_sgn always returning 1 for (sizetype)-1 looks not working here? > > tree_int_cst_compare (idx_step, size_zero_node) < 0 would be also always > false for unsigned types. Perhaps you can use wi::neg_p (idx_step) then, Yes, I made this mistake which causes this ICE. > that will return true whenever idx_step in corresponding signed type (with > the same precision as idx_step's type) is negative. > > But, is it right to consider those as negative steps? > I mean, say > for (unsigned long long c = 0; c < 0x8000000000000005ULL; c += > 0x8000000000000001ULL) > is actually positive step, not negative one. It's safe? The loop is equal to below one, right? for (unsigned long long c = 0; c < 0x8000000000000005ULL; c -= 0x7fffffffffffffffULL)
