Refactored and updated SimplifyUsingDistributiveLaws() to 
 * Find factorization opportunities using identity values.
 * Find factorization opportunities by treating shl(X, C) as mul (X, shl(C))
 * Keep NSW flag while simplifying instruction using factorization.

This fixes PR19263.

Differential Revision: http://reviews.llvm.org/D3799



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211261 91177308-0d34-0410-b5e6-96231b3b80d8