[HotColdSplit] Describe the pass in more detail, NFC
[HotColdSplit] Describe the pass in more detail, NFC

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@352161 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit 03b0e5dcc51ea2cb76f0b5162777e77cd437f94a)

apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm