[llvm] [SampleFDO] Read call-graph matching recovered top-level function profile (PR #101053)

[via llvm-commits]

================
@@ -392,6 +392,11 @@ class SampleProfileReader {
   /// which doesn't support loading function profiles on demand.
   virtual bool collectFuncsFromModule() { return false; }
 
+  virtual std::error_code readOnDemand(const DenseSet<StringRef> &FuncsToUse,
+                                       SampleProfileMap &Profiles) {
+    return sampleprof_error::not_implemented;
----------------
WenleiHe wrote:

Why not use a pure virtual function here? See `readHeader`.

https://github.com/llvm/llvm-project/pull/101053