Minor unroll pass refacoring.

Summary:
Unrolled Loop Size calculations moved to a function.
Constant representing number of optimized instructions
 when "back edge" becomes "fall through" replaced with
 variable.
Some comments added.

Reviewers: mzolotukhin

Differential Revision: http://reviews.llvm.org/D21719

From: Evgeny Stupachenko <evstupac@gmail.com>


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@286389 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed