[llvm] [PassManager] Add pretty stack frames (PR #96078)

[Nikita Popov via llvm-commits]

nikic wrote:

> > I just realized that this _is_ available via PI -> PIC, just currently not exposed in the API. I think I'll change this PR to make use of that.
> 
> It's only available when `shouldPopulateClassToPassNames()` is true, unsure of the compile time impact of always populating the pass name map

Always initializing the map does have measurable overhead: http://llvm-compile-time-tracker.com/compare.php?from=36c6632eb43bf67e19c8a6a21981cf66e06389b4&to=22e3ed4c5dfd93dcc3684410515ee053ace2edf3&stat=instructions:u

I've put up https://github.com/llvm/llvm-project/pull/96321 to use lazy initialization instead.

https://github.com/llvm/llvm-project/pull/96078