i965/fs: Perform CSE on CMP(N) instructions.

i965/fs: Perform CSE on CMP(N) instructions.

Optimizes

      cmp.ge.f0(8)  null     g45<8,8,1>F  0F
(+f0) sel(8)        g50<1>F  g40<8,8,1>F  g10<8,8,1>F
      cmp.ge.f0(8)  null     g45<8,8,1>F  0F
(+f0) sel(8)        g51<1>F  g41<8,8,1>F  g11<8,8,1>F
      cmp.ge.f0(8)  null     g45<8,8,1>F  0F
(+f0) sel(8)        g52<1>F  g42<8,8,1>F  g12<8,8,1>F
      cmp.ge.f0(8)  null     g45<8,8,1>F  0F
(+f0) sel(8)        g53<1>F  g43<8,8,1>F  g13<8,8,1>F

into

      cmp.ge.f0(8)  null     g45<8,8,1>F  0F
(+f0) sel(8)        g50<1>F  g40<8,8,1>F  g10<8,8,1>F
(+f0) sel(8)        g51<1>F  g41<8,8,1>F  g11<8,8,1>F
(+f0) sel(8)        g52<1>F  g42<8,8,1>F  g12<8,8,1>F
(+f0) sel(8)        g53<1>F  g43<8,8,1>F  g13<8,8,1>F

total instructions in shared programs: 1644938 -> 1638181 (-0.41%)
instructions in affected programs:     574955 -> 568198 (-1.18%)

Two more 16-wide programs (in L4D2). Some large (-9%) decreases in
instruction count in some of Valve's Source Engine games. No
regressions.

Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Paul Berry <stereotype441@gmail.com>