The patch introduces new way of narrowing complex (>UINT16 variants) solutions.

The patch introduces new way of narrowing complex (>UINT16 variants) solutions.
The new method introduced under "-lsr-exp-narrow" option (currenlty set to true).

Summary:

The method is based on registers number mathematical expectation and should be
 generally closer to optimal solution.
Please see details in comments to
 "LSRInstance::NarrowSearchSpaceByDeletingCostlyFormulas()" function
 (in lib/Transforms/Scalar/LoopStrengthReduce.cpp).

Reviewers: qcolombet

Differential Revision: http://reviews.llvm.org/D29862

From: Evgeny Stupachenko <evstupac@gmail.com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@295704 91177308-0d34-0410-b5e6-96231b3b80d8