https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104334
--- Comment #10 from rguenther at suse dot de <rguenther at suse dot de> --- On Wed, 2 Feb 2022, rsandifo at gcc dot gnu.org wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104334 > > --- Comment #9 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> > --- > (In reply to Jakub Jelinek from comment #7) > > The difference might be in: > > 1938 /* Optimize comparisons with constants. */ > > 1939 if (STATIC_CONSTANT_P (yi.len == 1 && yi.val[0] >= 0)) > > 1940 return xi.len == 1 && xi.to_uhwi () < (unsigned > > HOST_WIDE_INT) > > yi.val[0]; > > 1941 if (STATIC_CONSTANT_P (xi.len == 1 && xi.val[0] >= 0)) > > 1942 return yi.len != 1 || yi.to_uhwi () > (unsigned > > HOST_WIDE_INT) > > xi.val[0]; > > 1943 /* Optimize the case of two HWIs. The HWIs are implicitly > > sign-extended > > 1944 for precisions greater than HOST_BITS_WIDE_INT, but > > sign-extending > > both > > 1945 values does not change the result. */ > > 1946 if (__builtin_expect (xi.len + yi.len == 2, true)) > > 1947 { > > 1948 unsigned HOST_WIDE_INT xl = xi.to_uhwi (); > > 1949 unsigned HOST_WIDE_INT yl = yi.to_uhwi (); > > 1950 return xl < yl; > > 1951 } > > Perhaps with LTO STATIC_CONSTANT_P (yi.len && iy.val[0] >= 0) is true while > > without LTO it is false. > > I'll verify that. Though, xi.len == 1, xi.to_uhwi () is 3, yi.val[0] is 4 > > and yi.to_uhwi () is 0. > > So I think if STATIC_CONSTANT_P is true, it will return 3 < 4, while if it > > is false, it will return 3 < 0. > > > > Now, the question is, do we consider those wi::lt_p (x, 4, sign) calls > > invalid if 4 is not representable in type, > > or does the STATIC_CONSTANT_P case need to also check precision, or mask > > Xi.val[0]? > At the moment I think they're invalid. If we want to change that, > and have the value be implicitly truncated, we should probably do > it by setting primitive_int_traits::is_sign_extended to false. I also think they are invalid. I guess primitive_int_traits always produce "widest_ints", but I don't know whether we can reasonably reject the wi:lt_p (x, 4, sign) calls in favor of requiring wi::lt_p (wi::to_widest (x), 4, sign) at compile-time ... I don't think we want to silenlty truncate the literal '4', instead if we really want, we could ICE with checking enabled ...
