[llvm] [MemProf] Prune unneeded non-cold contexts (PR #124823)

[Teresa Johnson via llvm-commits]

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@@ -243,14 +256,35 @@ void CallStackTrie::convertHotToNotCold(CallStackTrieNode *Node) {
 bool CallStackTrie::buildMIBNodes(CallStackTrieNode *Node, LLVMContext &Ctx,
                                   std::vector<uint64_t> &MIBCallStack,
                                   std::vector<Metadata *> &MIBNodes,
-                                  bool CalleeHasAmbiguousCallerContext) {
+                                  bool CalleeHasAmbiguousCallerContext,
+                                  bool &CalleeDeepestAmbiguousAllocType) {
   // Trim context below the first node in a prefix with a single alloc type.
   // Add an MIB record for the current call stack prefix.
   if (hasSingleAllocType(Node->AllocTypes)) {
-    std::vector<ContextTotalSize> ContextSizeInfo;
-    collectContextSizeInfo(Node, ContextSizeInfo);
-    MIBNodes.push_back(createMIBNode(
-        Ctx, MIBCallStack, (AllocationType)Node->AllocTypes, ContextSizeInfo));
+    // Because we only clone cold contexts (we don't clone for exposing NotCold
+    // contexts as that is the default allocation behavior), we create MIB
+    // metadata for this context if any of the following are true:
+    // 1) It is cold.
+    // 2) The immediate callee is the deepest point where we have an ambiguous
+    //    allocation type (i.e. the other callers that are cold need to know
+    //    that we have a not cold context overlapping to this point so that we
+    //    know how deep to clone).
+    // 3) MemProfKeepAllNotColdContexts is enabled, which is useful if we are
+    //    reporting hinted sizes, and want to get information from the indexing
+    //    step for all contexts, or have specified a value less than 100% for
+    //    -memprof-cloning-cold-threshold.
+    if ((AllocationType)Node->AllocTypes == AllocationType::Cold ||
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teresajohnson wrote:

ack

https://github.com/llvm/llvm-project/pull/124823