Unpack array of all sizes in InstCombine

Summary: This is another step toward improving fca support. This unpack load of array in a series of load to array's elements.

Reviewers: chandlerc, joker.eph, majnemer, reames, hfinkel

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D15890

llvm-svn: 262521