[InstCombine] fix comments to match code; NFC
[InstCombine] fix comments to match code; NFC

This blob was written before match() existed, so it
could probably be reduced significantly.

But I suspect it isn't well tested, so tests would have
to be added to reduce risk from logic changes.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@371978 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm