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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libgcc/114327] `-CST % 1` is wrong for _BitInt()
Date: Thu, 14 Mar 2024 00:10:29 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114327

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
For (ignore the strict aliasing issue):
```
typedef signed _BitInt(256) B;

[[gnu::noinline]]
B
foo (signed char c, B b)
{
  return b % c;
}

int
main (void)
{
  B x =3D foo (1, -3); // -3 % 1 -> 0
 // if (x)
 //   __builtin_abort();
    signed long *t =3D (signed long *)&x;
  for(int i =3D 0;i < sizeof(B)/sizeof(long); i++ )
  {
    __builtin_printf("%lx\n", t[i]);
  }
  return 0;
}
```
We get:
```
0
ffffffffffffffff
ffffffffffffffff
ffffffffffffffff
```

Which makes it seem like we are doing the sign extend when the value was the
result was 0.

Even:
> B x =3D foo (3, -3); // -3 % 3 -> 0

Gives the wrong similar result.=