[Bug tree-optimization/110731] [11/12/13/14 Regression] Wrong-code because of wide-int division since r5-424

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110731

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I think the problem is earlier.
If I divide the same values unsigned, while the representation of the wide_int
values
is the same, i.e.
val = {0, -18014398509481984}, len = 2, precision = 119
for x, when divmod_internal_2 is called, in the signed case it sees
x/4wx b_dividend
0x7fffffffc0b0: 0x00000000      0x00000000      0x00000000      0xffc00000
while in the unsigned one
x/4wx b_dividend
0x7fffffffc0b0: 0x00000000      0x00000000      0x00000000      0x00400000
and I think the latter is what should be used in both cases, divmod_internal_2
performs
unsigned division.

So, I think the right fix is:
--- gcc/wide-int.cc.jj  2023-06-12 15:47:22.461502821 +0200
+++ gcc/wide-int.cc     2023-07-19 09:52:40.241661869 +0200
@@ -1911,9 +1911,9 @@ wi::divmod_internal (HOST_WIDE_INT *quot
     }

   wi_unpack (b_dividend, dividend.get_val (), dividend.get_len (),
-            dividend_blocks_needed, dividend_prec, sgn);
+            dividend_blocks_needed, dividend_prec, UNSIGNED);
   wi_unpack (b_divisor, divisor.get_val (), divisor.get_len (),
-            divisor_blocks_needed, divisor_prec, sgn);
+            divisor_blocks_needed, divisor_prec, UNSIGNED);

   m = dividend_blocks_needed;
   b_dividend[m] = 0;
because at this point we are after the
  /* Make the divisor and dividend positive and remember what we
     did.  */
  if (sgn == SIGNED)
    {
      if (wi::neg_p (dividend))
        {
          neg_dividend = -dividend;
          dividend = neg_dividend;
          dividend_neg = true;
        }
      if (wi::neg_p (divisor))
        {
          neg_divisor = -divisor;
          divisor = neg_divisor;
          divisor_neg = true;
        }
    }
hunk.  Of course, this makes a difference only if either the dividend or
divisor are the smallest negative value of a type.