Subzero: Optimize live range overlaps() computation through trimming.

Subzero: Optimize live range overlaps() computation through trimming.

The main optimization is for the repeated overlaps() calls against the Inactive set, by iteratively trimming away the early sections of the Inactive live ranges that can no longer overlap with Cur.

A more minor optimization doesn't bother checking pure point-valued Inactive ranges for expiring or reactivating.

BUG= none
R=jvoung@chromium.org

Review URL: https://codereview.chromium.org/627203002