[llvm] Reapply "[MemProf] Streamline and avoid unnecessary context id duplication (#107918)" (PR #110036)

[Teresa Johnson via llvm-commits]

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@@ -1377,9 +1377,16 @@ void CallsiteContextGraph<DerivedCCG, FuncTy, CallTy>::
   // Compute the last node's context ids once, as it is shared by all calls in
   // this entry.
   DenseSet<uint32_t> LastNodeContextIds = LastNode->getContextIds();
-  assert(!LastNodeContextIds.empty());
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teresajohnson wrote:

I had rebased my client right before mailing this PR and a retest showed this new code from #109857 asserted with the test case from this PR. The assert is too strict at this point because we may have already reassigned the context ids on this last node to a different stack node (the same reason why we need to recompute the stack nodes for each call below).

https://github.com/llvm/llvm-project/pull/110036