[llvm] [MemProf] Make sure call clones without callsite node clones get updated (PR #159861)

[Snehasish Kumar via llvm-commits]

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@@ -4553,6 +4553,34 @@ bool CallsiteContextGraph<DerivedCCG, FuncTy, CallTy>::assignFunctions() {
     DenseMap<CallInfo, CallInfo> CallMap;
   };
 
+  // Map to keep track of information needed to update calls in function clones
+  // when their corresponding callsite node was not itself cloned for that
+  // function clone. Because of call context pruning (i.e. we only keep as much
+  // caller information as needed to distinguish hot vs cold), we may not have
+  // caller edges coming to each callsite node from all possible function
+  // callers. A function clone may get created for other callsites in the
+  // function for which there are caller edges that were not pruned. Any other
+  // callsites in that function clone, which were not themselved cloned for
+  // that function clone, should get updated the same way as the corresponding
+  // callsite in the original function (which may call a clone of its callee).
+  //
+  // We build this map after completing function cloning for each function, so
+  // that we can record the information from its call maps before they are
+  // destructed. The map will be used as we update calls to update any still
+  // unassigned call clones. Note that we may create new node clones as we clone
+  // other functions, so later on we check which node clones were still not
+  // created. To this end, the inner map is a map from function clone number to
+  // the list of calls cloned for that function (can be more than one due to the
+  // Node's MatchingCalls array).
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snehasish wrote:

Does it make sense to enhance the pseudo-code in the function comment with this detail?

https://github.com/llvm/llvm-project/pull/159861