[clang] Analyze only potential scopes for NRVO

[Izaron]

The current algorithm for calculating the scope's NRVO candidate looks at the whole scope. But the paper [p2025] shows that we only need to look at the variable's potential scope. It will increase the number of cases where we optimize code.

I pushed a patch and explained how it works - https://reviews.llvm.org/D119792#3321293

Now I'm looking for people who can review this patch =) Therefore I created this issue. Any comments on the topic are welcome!

[llvmbot]

@llvm/issue-subscribers-clang-frontend

[firewave]

If I understand it correctly (I am a bot confused since the creator of this ticket only provided comments but not the actual patch) this has landed in fec5ff2 and thus this issue can be closed.