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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/114326] Missed optimization for A || B when
 !B implies A.
Date: Wed, 13 Mar 2024 21:41:47 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114326

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to ptomsich from comment #2)
> To copy the last piece of info from our internal tracker...
>=20
> LLVM learned this new trick only in the run-up to LLVM 18.
> Up until then, GCC and LLVM performed identically on this snippet.

Yes it looks like it is pattern matching what I suggested (well with and
without the and).

Note we do need another pattern, one without the bit_and:
(simplify
 (bit_ior
  (ne@n4 @0 @1)
  (cmp
   (bit_xor @0 @1)
   @2))
 (bit_ior @n4=20
  (cmp { build_zero_cst (TREE_TYPE (@0)); } @2))
)

And we need one more for bit_ior:
(simplify
 (bit_ior
  (ne@n4 @0 @1)
  (cmp
   (bit_ior
    (bit_xor @0 @1)
    @2)
   @3))
 (bit_ior @n4=20
  (cmp @2 @3))
)

Note it looks like clang does not handle non-contants that well, (they hand=
le d
=3D=3D 0 though).

E.g.:
```
int foo(void);
int cmp1(unsigned d1, unsigned d2, unsigned c, unsigned d) {
  int t =3D ((d1 ^ d2) & c ) =3D=3D (d);
  int t1 =3D d1 !=3D d2;
  int tt =3D t | t1;
  return tt;
}

```

Should be optimized to:
int foo(void);
int cmp1(unsigned d1, unsigned d2, unsigned c, unsigned d) {
  int t =3D 0 =3D=3D d;
  int t1 =3D d1 !=3D d2;
  int tt =3D t | t1;
  return tt;
}
```=