https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106617
--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> --- We don't fold because case COMPOUND_EXPR: /* When pedantic, a compound expression can be neither an lvalue nor an integer constant expression. */ if (TREE_SIDE_EFFECTS (arg0) || TREE_CONSTANT (arg1)) return NULL_TREE; /* Don't let (0, 0) be null pointer constant. */ tem = integer_zerop (arg1) ? build1_loc (loc, NOP_EXPR, type, arg1) : fold_convert_loc (loc, type, arg1); return tem; where we chicken out because of the fear of early folding. At least the C frontend should get this correct now. Ideally the above would just return arg1 if !TREE_SIDE_EFFECTS (arg0). OTOH it's really sth for language specific folding. Of course the bug then would be still present when replacing (0, 0) with something non-constant.