Fix an issue where LSR would miss rewriting a use of an IV expression by a PHI node that is not the original PHI.
Fix an issue where LSR would miss rewriting a use of an IV expression by a PHI node that is not the original PHI.

This fixes up a dot-product loop in galgel, speeding it up from 18.47s to
16.13s.


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@23327 91177308-0d34-0410-b5e6-96231b3b80d8

dslab-epfl/asap,llvm-mirror/llvm,dslab-epfl/asap,dslab-epfl/asap,chubbymaggie/asap,apple/swift-llvm,dslab-epfl/asap,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,dslab-epfl/asap,chubbymaggie/asap,chubbymaggie/asap,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,dslab-epfl/asap,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,chubbymaggie/asap,dslab-epfl/asap,apple/swift-llvm,chubbymaggie/asap,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,chubbymaggie/asap,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm