http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52134
--- Comment #8 from rguenther at suse dot de <rguenther at suse dot de> 2012-03-14 09:39:31 UTC --- On Tue, 13 Mar 2012, pinskia at gcc dot gnu.org wrote: > 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. Yeah, CCP and VRP can do this as well. In fact folding bit-operations with the bit-CCP lattice is an obvious improvement, best done in ccp_fold_stmt which is called at lattice substitution time. Richard.
