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

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104334

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mrs at gcc dot gnu.org,
                   |                            |rguenth at gcc dot gnu.org,
                   |                            |rsandifo at gcc dot gnu.org

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
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]?

And another question is, the 2, 3, 4 cases handling seems like an optimization,
so wi_fold at line 192 should give the right answer, but it doesn't.