Fix PR2496, a really nasty bug which involved sinking volatile loads  into phis.  This is actually the same bug as PR2262 / 2008-04-29-VolatileLoadDontMerge.ll, but I missed checking the first  predecessor for multiple successors.  Testcase here: InstCombine/2008-07-08-VolatileLoadMerge.ll
Fix PR2496, a really nasty bug which involved sinking volatile loads 
into phis.  This is actually the same bug as PR2262 /
2008-04-29-VolatileLoadDontMerge.ll, but I missed checking the first 
predecessor for multiple successors.  Testcase here:
InstCombine/2008-07-08-VolatileLoadMerge.ll



git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@53240 91177308-0d34-0410-b5e6-96231b3b80d8

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