https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109564
--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> --- (In reply to Richard Biener from comment #8) > I fear something more fundamental is broken here and we > possibly should play safe and not register any equivalence relation > from PHIs. > > diff --git a/gcc/gimple-range-fold.cc b/gcc/gimple-range-fold.cc > index 429734f954a..0c4ffbf3b57 100644 > --- a/gcc/gimple-range-fold.cc > +++ b/gcc/gimple-range-fold.cc > @@ -743,6 +744,7 @@ fold_using_range::range_of_phi (vrange &r, gphi *phi, > fur_source &src) > // Track if all executable arguments are the same. > tree single_arg = NULL_TREE; > bool seen_arg = false; > + bool seen_undefined = false; > > // Start with an empty range, unioning in each argument's range. > r.set_undefined (); > @@ -781,6 +783,8 @@ fold_using_range::range_of_phi (vrange &r, gphi *phi, > fur_source &src) > else if (single_arg != arg) > single_arg = NULL_TREE; > } > + else > + seen_undefined = true; > > // Once the value reaches varying, stop looking. > if (r.varying_p () && single_arg == NULL_TREE) > @@ -802,7 +806,8 @@ fold_using_range::range_of_phi (vrange &r, gphi *phi, > fur_source &src) > // dominate any incoming edge for SINGLE_ARG. > // See PR 108139 and 109462. > basic_block bb = gimple_bb (phi); > - if (!dom_info_available_p (CDI_DOMINATORS)) > + if (seen_undefined > + || !dom_info_available_p (CDI_DOMINATORS)) > single_arg = NULL; > else > for (x = 0; x < gimple_phi_num_args (phi); x++) So on a second thought since with the above we only register equality for PHIs with all arguments comparing pointer equal that case should be OK in _all_ cases (including the backedge one). But it's of course very rare in the end. It's btw similar for not executable edges in case arg_range gets undefined_p in that case. So I don't think we can allow that case either.
