[llvm] [MemProf] Use radix tree for alloc contexts in bitcode summaries (PR #117066)

[Kazu Hirata via llvm-commits]

================
@@ -4735,6 +4834,39 @@ void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
     NameVals.clear();
   };
 
+  // First walk through all the functions and collect the allocation contexts in
+  // their associated summaries, for use in constructing a radix tree of
+  // contexts. Note that we need to do this in the same order as the functions
+  // are processed further below since the call stack positions in the resulting
+  // radix tree array are identified based on this order.
+  MapVector<CallStackId, llvm::SmallVector<LinearFrameId>> CallStacks;
+  forEachSummary([&](GVInfo I, bool IsAliasee) {
+    GlobalValueSummary *S = I.second;
+    assert(S);
+    auto *FS = dyn_cast<FunctionSummary>(S);
+    if (!FS)
+      return;
+    collectMemProfCallStacks(
+        FS,
+        /*GetStackIndex*/
+        [&](unsigned I) {
+          // Get the corresponding index into the list of StackIds actually
+          // being written for this combined index (which may be a subset in
+          // the case of distributed indexes).
+          assert(StackIdIndicesToIndex.contains(I));
+          return StackIdIndicesToIndex[I];
+        },
+        CallStacks);
+  });
+  // Finalize the radix tree, write it out, and get the map of positions in the
+  // linearized tree array.
+  DenseMap<CallStackId, LinearCallStackId> CallStackPos;
+  if (!CallStacks.empty())
+    CallStackPos = writeMemoryProfileRadixTree(CallStacks, Stream, RadixAbbrev);
----------------
kazutakahirata wrote:

May I suggest `std::move` here?

```suggestion
    CallStackPos = writeMemoryProfileRadixTree(std::move(CallStacks), Stream, RadixAbbrev);
```

https://github.com/llvm/llvm-project/pull/117066