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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/19832] don't remove an if when we know the
 value is the same as with the if (subtraction)
Date: Thu, 31 Aug 2023 01:03:16 +0000
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X-Bugzilla-Component: tree-optimization
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X-Bugzilla-Keywords: missed-optimization
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D19832

--- Comment #8 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Xor should be handled too:
```
int f_xor(int i, int j)
{
  if (i!=3Dj)
    return i ^ j;
  return 0;
}
``

ior and and should be handled
```
int f_or(int i, int j)
{
  if (i!=3Dj)
    return i | j;
  return i; // could be j not just i
}

int f_and(int i, int j)
{
  if (i!=3Dj)
    return i & j;
  return i; // could be j not just i
}
```

So can plus and multiply:
```
int f_add(int i, int j)
{
  if (i!=3Dj)
    return i + j;
  return i+i;
}
int f_mult(int i, int j)
{
  if (i!=3Dj)
    return i * j;
  return i*i;
}
```


Note clang handles all of these except for f_add. f_mult might be handled v=
ia
the pull `i*` out of the conditional and then you have `i!=3Dj?j:i` which t=
hen
will be reduced to j (that is they don't pattern match f_mult). They don't =
have
pattern matching for f_add either and `i+i` will change to `i*2` and not pu=
lled
out of the condition.=