[InstCombine] add test corresponding to r324252 (PR36225); NFC
[InstCombine] add test corresponding to r324252 (PR36225); NFC

As PR36225 shows, we definitely don't want to enable the
canEvaluate* logic with phis. 

There's still a question of whether we should just revert 
r324014 completely because it exposes a compile-time sinkhole
(although that problem might exist independently).


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@324266 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm