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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/52134] Does not fold (x * 4) & -4
Date: Tue, 13 Mar 2012 22:12:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52134

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-03-13 22:08:12 UTC ---
CCP could also remove the &:
Visiting statement:
D.1713_2 = t_1(D) * 4;
which is likely CONSTANT
Lattice value changed to CONSTANT Lattice value changed to CONSTANT
0x00000000000000000 (0x000000000fffffffc).  Adding SSA edges to worklist.

Visiting statement:
D.1712_3 = D.1713_2 & 4294967292;
which is likely CONSTANT
Lattice value changed to CONSTANT Lattice value changed to CONSTANT
0x00000000000000000 (0x000000000fffffffc).  Adding SSA edges to worklist.

..
Visiting statement:
D.1710_2 = t_1(D) * 4;
which is likely CONSTANT
Lattice value changed to CONSTANT Lattice value changed to CONSTANT
0x00000000000000000 (0xfffffffffffffffffffffffffffffffc).  Adding SSA edges to
worklist.

Visiting statement:
D.1709_3 = D.1710_2 & -4;
which is likely CONSTANT
Lattice value changed to CONSTANT Lattice value changed to CONSTANT
0x00000000000000000 (0xfffffffffffffffffffffffffffffffc).  Adding SSA edges to
worklist.


See how the lattice's already have its last 3 bits unset.  In fact I think we
should only do this in the ccp/vrp passes to remove the & rather than fold.