[x86] Hoist a function up to the rest of the non-type-specific lowering helpers, and re-flow the logic to use early exit and be a bit more readable.
[x86] Hoist a function up to the rest of the non-type-specific lowering
helpers, and re-flow the logic to use early exit and be a bit more
readable.

No functionality changed.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@218155 91177308-0d34-0410-b5e6-96231b3b80d8

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