[clang] nonblocking/nonallocating attributes: 2nd pass caller/callee analysis (PR #99656)

[Erich Keane via cfe-commits]

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@@ -571,6 +571,9 @@ New features
   if class of allocation and deallocation function mismatches.
   `Documentation <https://clang.llvm.org/docs/analyzer/checkers.html#unix-mismatcheddeallocator-c-c>`__.
 
+- Function effects (the ``nonblocking`` and ``nonallocating`` "performance constraint" attributes)
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erichkeane wrote:

I think even that is a little 'requires existing knowledge'?  Basically, the audience for this is 'random redditor trying to figure out what features to use'.  So we need to make sure anything like this is sufficiently titillating while not being so long as to lose interest.  

For most bugs in release notes, we can assume that if the person cares about it, they know the details about the bug, but for features this is sort of our first chance to 'advertise' them.  So I'd like something less vague/that gives some good 'hook' as to why the person wants to use it.

Perhaps I'll make @shafik come in, read the documentation enough to understand it, and propose some text :) 

https://github.com/llvm/llvm-project/pull/99656