3.6.1 patch nomination: r232189 - [SCEV] Fix PR22856

[Andrew Trick]

Ok for release.
-Andy

> On Mar 13, 2015, at 1:36 PM, Sanjoy Das <sanjoy at playingwithpointers.com> wrote:
> 
> This change fixes https://llvm.org/bugs/show_bug.cgi?id=22856.
> 
> Commit message:
> 
> Summary:
> ScalarEvolutionExpander assumes that the header block of a loop is a
> legal place to have a use for a phi node.  This is true only for phis
> that are either in the header or dominate the header block, but it is
> not true for phi nodes that are strictly internal to the loop body.
> 
> This change teaches ScalarEvolutionExpander to place uses of PHI nodes
> in the basic block the PHI nodes belong to.  This is always legal, and
> `hoistIVInc` ensures that the said position dominates `IsomorphicInc`.
> 
> Reviewers: atrick
> 
> Subscribers: llvm-commits
> 
> Differential Revision: http://reviews.llvm.org/D8311