[Mesa-dev] Partial loop unrolling support

[Timothy Arceri]

This series add support for partial loop unrolling for loops with an
unknown trip count. The new partial_unroll function allows the caller
to specifiy how may times the loop should be unrolled and then the
loop is inserted in the innermost continue branch of the unrolled loop.

For now we only do partial unrolling for loops where we can guess the
iteration count based on array access that uses an induction variable
as its index (see patch 7).

Patches 1-6 are tidy-ups/refactors.

Patch 7 adds a method for guessing the trip count for the loop.

Patch 8 adds partial unrolling support and also support for removing
redundant load/stores from the remaining loop when considering if
we would be accessing an array out bounds.