[llvm] [ctxprof] Scale up everything under a root by its `TotalRootEntryCount` (PR #136015)

[Snehasish Kumar via llvm-commits]

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@@ -683,40 +689,46 @@ void PGOContextualProfile::visit(ConstVisitor V, const Function *F) const {
 const CtxProfFlatProfile PGOContextualProfile::flatten() const {
   CtxProfFlatProfile Flat;
   auto Accummulate = [](SmallVectorImpl<uint64_t> &Into,
-                        const SmallVectorImpl<uint64_t> &From) {
+                        const SmallVectorImpl<uint64_t> &From,
+                        uint64_t SamplingRate) {
     if (Into.empty())
       Into.resize(From.size());
     assert(Into.size() == From.size() &&
            "All contexts corresponding to a function should have the exact "
            "same number of counters.");
     for (size_t I = 0, E = Into.size(); I < E; ++I)
-      Into[I] += From[I];
+      Into[I] += From[I] * SamplingRate;
   };
 
-  preorderVisit<const PGOCtxProfContext::CallTargetMapTy,
-                const PGOCtxProfContext>(
-      Profiles.Contexts, [&](const PGOCtxProfContext &Ctx) {
-        Accummulate(Flat[Ctx.guid()], Ctx.counters());
-      });
-  for (const auto &[_, RC] : Profiles.Contexts)
-    for (const auto &[G, Unh] : RC.getUnhandled())
-      Accummulate(Flat[G], Unh);
+  for (const auto &[_, CtxRoot] : Profiles.Contexts) {
+    const uint64_t SamplingFactor = CtxRoot.getTotalRootEntryCount();
+    preorderVisitOneRoot<const PGOCtxProfContext>(
+        CtxRoot, [&](const PGOCtxProfContext &Ctx) {
+          Accummulate(Flat[Ctx.guid()], Ctx.counters(), SamplingFactor);
+        });
+
+    for (const auto &[G, Unh] : CtxRoot.getUnhandled())
+      Accummulate(Flat[G], Unh, SamplingFactor);
+  }
   for (const auto &[G, FC] : Profiles.FlatProfiles)
-    Accummulate(Flat[G], FC);
+    Accummulate(Flat[G], FC, /*SamplingRate=*/1);
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snehasish wrote:

Why is this hardcoded to 1?

https://github.com/llvm/llvm-project/pull/136015