Process a slice of equivalent values by setting replaced values to nil
instead of removing them from the slice to eliminate copying. Also take
advantage of the entry number sort to break early once we reach a value
in a block that is not dominated.
For the code in issue #15112:
Before:
real 0m52.603s
user 0m56.957s
sys 0m1.213s
After:
real 0m22.048s
user 0m26.445s
sys 0m0.939s
Updates #15112
Change-Id: I06d9e1e1f1ad85d7fa196c5d51f0dc163907376d
Reviewed-on: https://go-review.googlesource.com/22068 Reviewed-by: David Chase <drchase@google.com>