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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/103359] [12 Regression] Dead Code Elimination
 Regression at -O3 (trunk vs 11.2.0)
Date: Mon, 22 Nov 2021 22:04:13 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103359

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2021-11-22
           Keywords|                            |missed-optimization
   Target Milestone|---                         |12.0

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.

In CCP1 on the trunk:
Visiting statement:
f_18 =3D (short intD.25) _6;
which is likely CONSTANT
Lattice value changed to CONSTANT 0x4 (0x1).  Adding SSA edges to worklist.



In ccp1 on the trunk with -fno-tree-bit-ccp:
Visiting statement:
f_18 =3D (short intD.25) _6;
which is likely CONSTANT
Applying pattern match.pd:3663, gimple-match.c:42920
Applying pattern match.pd:3580, gimple-match.c:42859
Match-and-simplified (short int) _6 to _5
Lattice value changed to CONSTANT _5.  Adding SSA edges to worklist.
marking stmt to be not simulated again

So ccp1 sometimes applies match and simplify and sometimes does not ....=