[Mesa-dev] i965: more dead code elimination

[Eric Anholt]

Motivated by some troubles in register allocation on Valve's shaders, I
found a cheap (runtime and development time) way to cut some dead code.
This looked like failure due to losing 16-wide programs, until I updated
more apps in shader-db to use shader_tests (which provide more accurate
simulation, since your FS attributes are no longer demoted to undefined
temporary values).

shader-db results:
total instructions in shared programs: 1735753 -> 1731698 (-0.23%)
instructions in affected programs:     492620 -> 488565 (-0.82%)

There are also a few cleanup patches attached that have been kicking
around several optimization branches I have.

This series is on the local-dce branch of my tree.