[Mesa-dev] More loop unrolling

[Timothy Arceri]

This is three series combined. I've sent the first two previously
(patch 1-11 & patch 12-15) and they have been partially reviewed
by Thomas. Please see the previous sends of those series for cover
letters.

There is a small bug fix in patch 11 that was discovered by some
new piglit tests [1]. Otherwise those series only contain small
changes suggested by Thomas during review.

Patches 16-20 are new and improve loop analysis so we can unroll
more loops with the unroll function introduced in patch 11.

[1] https://patchwork.freedesktop.org/series/53712/