[PATCH] Added instruction combine to transform few more negative values addition to subtraction

[Dinesh Dwivedi]

> Is this the first one? Which patch is the second one?
>
> Cheers,
> Rafael

I have broken my previous patch to reduce size of patch. As other parts are depended 
on these changes, I will put them for review once this patch is in [actually don't know 
how to submit dependent patches]

I have added TODO for those patches.

http://reviews.llvm.org/D3733