[PATCH] Added instruction combine to transform few more negative values addition to subtraction (Part 2)

[Dinesh Dwivedi]

Hi Jingyue,

Added code can handle both cases. Basically it checks operands of OR and can deal with
both cases if it is just 'y' or '(y >> z). Now if I think, I should not have mentioned it as separate
pattern.

When I coded for this, I was looking at PR14365 and it has both pattern for XOR(AND()) and I
mentioned both pattern in my first patch for this (part 1) and just copied same for this and next 
patch.

Sorry for confusing comment.

http://reviews.llvm.org/D4209