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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 22:23:49 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103359

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The other thing is:

-ftree-bit-ccp
Visiting statement:
_4 =3D _3 & 1;
which is likely CONSTANT
Applying pattern match.pd:1641, gimple-match.c:23146
Lattice value changed to CONSTANT 0x0 (0x1).  Adding SSA edges to worklist.
marking stmt to be not simulated again

vs

-fno-tree-bit-ccp
_4 =3D _3 & 1;
which is likely CONSTANT
Applying pattern match.pd:1641, gimple-match.c:23146
Lattice value changed to VARYING.  Adding SSA edges to worklist.

In the first case we mark the stmt as not be simulated again while in the
second case we didn't.

Someone who understands ccp better should look into this.=