[NFC] Pre-calculate basic block IR counts in size remarks.
[NFC] Pre-calculate basic block IR counts in size remarks.

Size remarks are slow due to lots of recalculation of the module.

This is similar to the previous commit. Cache the size of the module and
update counts in basic block passes based off a less-expensive delta.

2/6

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@341246 91177308-0d34-0410-b5e6-96231b3b80d8

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