[llvm] [ReachingDefAnalysis] Extend the analysis to stack objects. (PR #118097)

[Mikhail Gudim via llvm-commits]

mgudim wrote:

> Here is a suggestion on how to rework the MBBFrameObjsReachingDefsInfo data structure [here](https://github.com/llvm/llvm-project/compare/main...michaelmaitland:llvm-project:perf/mmaitland-rda-ss?expand=1)
> 
> You can see that it does not have the "catastrophic memory usage regressions" [here](https://llvm-compile-time-tracker.com/compare.php?from=beba4b08f72152abbb7d26df024f0d9338a7038b&to=a51148b62cee5f01e3bbb6dd3e7608a1ea274388&stat=max-rss)
> 
> Feel free to take it verbatim or make your own modifications to it.

@michaelmaitland 
Thanks for fixing the regression! I think you can commit your change in a separate PR. Right now the `AllReachingDefs` uses `std::vector`s. Can you modify that to use `DenseMap` like you suggested?  Then I can rebase my PR on yours and I'll get rid of the `MBBFrameObjsReachingDefsInfo` so both physical registers and stack slots use the same data structure.

https://github.com/llvm/llvm-project/pull/118097