Re-apply r238452, the bug was in clang and was fixed in r260567.

Original commit message:
[InstCombine] Fold IntToPtr and PtrToInt into preceding loads.

Currently we only fold a BitCast into a Load when the BitCast is its
only user.

Do the same for any no-op cast.

Patch by Philip Pfaffe!

Differential Revision: http://reviews.llvm.org/D9152

llvm-svn: 260612