[Bug tree-optimization/104334] [12 Regression] Ranger/dom miscompilation

["rsandifo at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

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.