i965: Extend compute-to-mrf pass to understand blocks of MOVs

i965: Extend compute-to-mrf pass to understand blocks of MOVs

The current compute-to-mrf pass doesn't handle blocks of MOVs.  Shaders
that end with a texture fetch follwed by an fb write are left like this:

0x00000000: pln(8)          g6<1>F          g4<0,1,0>F      g2<8,8,1>F      { align1 WE_normal 1Q compacted };
0x00000008: pln(8)          g7<1>F          g4.4<0,1,0>F    g2<8,8,1>F      { align1 WE_normal 1Q compacted };
0x00000010: send(8)         g2<1>UW         g6<8,8,1>F
                            sampler (1, 0, 0, 1) mlen 2 rlen 4              { align1 WE_normal 1Q };
0x00000020: mov(8)          g113<1>F        g2<8,8,1>F                      { align1 WE_normal 1Q compacted };
0x00000028: mov(8)          g114<1>F        g3<8,8,1>F                      { align1 WE_normal 1Q compacted };
0x00000030: mov(8)          g115<1>F        g4<8,8,1>F                      { align1 WE_normal 1Q compacted };
0x00000038: mov(8)          g116<1>F        g5<8,8,1>F                      { align1 WE_normal 1Q compacted };
0x00000040: sendc(8)        null            g113<8,8,1>F
                            render ( RT write, 0, 4, 12) mlen 4 rlen 0      { align1 WE_normal 1Q EOT };

This patch lets compute-to-mrf recognize blocks of MOVs and match them to
instructions (typically SEND) that writes multiple registers.  With this,
the above shader becomes:

0x00000000: pln(8)          g6<1>F          g4<0,1,0>F      g2<8,8,1>F      { align1 WE_normal 1Q compacted };
0x00000008: pln(8)          g7<1>F          g4.4<0,1,0>F    g2<8,8,1>F      { align1 WE_normal 1Q compacted };
0x00000010: send(8)         g113<1>UW       g6<8,8,1>F
                            sampler (1, 0, 0, 1) mlen 2 rlen 4              { align1 WE_normal 1Q };
0x00000020: sendc(8)        null            g113<8,8,1>F
                            render ( RT write, 0, 20, 12) mlen 4 rlen 0     { align1 WE_normal 1Q EOT };

which is the bulk of the shader db results:

total instructions in shared programs: 987040 -> 986720 (-0.03%)
instructions in affected programs:     844 -> 524 (-37.91%)
GAINED:                                0
LOST:                                  0

The optimization also applies to MRT shaders that write the same
color value to multiple RTs, in which case we can eliminate four MOVs in
a similar fashion.  See fbo-drawbuffers2-blend in piglit for an example.

No measurable performance impact.  No piglit regressions.

Signed-off-by: Kristian Høgsberg <krh@bitplanet.net>