[llvm] [Coroutines][LazyCallGraph] resumes are not really SCC (PR #116285)

[Tyler Nowicki via llvm-commits]

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@@ -1720,6 +1720,7 @@ void LazyCallGraph::addSplitRefRecursiveFunctions(
   for (Function *NewFunction : NewFunctions) {
     Node &NewN = initNode(*NewFunction);
 
+    // Make the original function reference each new function
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TylerNowicki wrote:

Identifying the RefSCCs and SCCs here may not be the right thing to do. I wanted to point out John's early comment 

> Yeah, it's probably not trivial to get that information right during splitting because the cloned functions can end up containing arbitrary subsets of the original function.

I am worried about doing this right. And also consider that the refs are not yet finalized when addSplitRefRecursiveFunctions() is called. There is some clean-up still to do, i.e. removing unreachable blocks / simplify-cfg.

https://github.com/llvm/llvm-project/pull/116285