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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/99946] fail to exchange if conditions in
 terms of likely/unlikely probability
Date: Wed, 07 Apr 2021 07:33:11 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99946

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
   Last reconfirmed|                            |2021-04-07
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
There's no pass doing all of this.  There's ifcombine that could end up
turning it into

 tem =3D likely(a>0) & unlikely(b>0);
 if (tem)
   g ();

and then RTL expansion might expand it to branchy code again.

But of course __builtin_expect is long gone then and we'll lose the
likelyness of the individual tests.

Still ifcombine has analysis logic as to "collecting" a complex predicate,
what's then missing is to "re-associate" the tests according to probability.

Which means implementing it in ifcombine should be feasible.=