[llvm] [ADT] Simplify SparseBitVectorIterator. NFCI. (PR #143885)

[Jakub Kuderski via llvm-commits]

kuhar wrote:

> I don't know, and I'm not sure I have the time or energy to gather that kind of data.

I usually measure these things by adding an `fprintf(stderr, ...);` in the destructor, running on any bitcode laying around and then copying to a spreadsheet


https://github.com/llvm/llvm-project/pull/143885