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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/108992] Regression: Branch direction
 canonicalization leads to pointless tail duplication / CSE/sinking by
 inverting branch
Date: Thu, 02 Mar 2023 22:46:34 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108992

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I suspect this is not a bug, GCC tries to optimze the fast path into straig=
ht
line code without any waste of space.
In the first case GCC predicts that the cond is going to be true 66% of the
time because there is comparison against 0 prediction going in the heurstic=
s.

For the first testcase if you do:
void use(int *);
void use2(int *);

void foo(bool cond, int * p)
{
    if (__builtin_expect(cond, 1)) {
        use(p);
    }
    use2(p);
}

Then you get the result you want.
Adding the builtin_expect for the second case you get the same too.
Basically GCC is pushing what it thinks as cold code away from the original
path.=