[llvm] [ctx_prof] Profile flatterner (PR #104539)

[Snehasish Kumar via llvm-commits]

================
@@ -193,3 +201,35 @@ InstrProfCallsite *CtxProfAnalysis::getCallsiteInstrumentation(CallBase &CB) {
       return IPC;
   return nullptr;
 }
+
+static void
+preorderVisit(const PGOCtxProfContext::CallTargetMapTy &Profiles,
+              function_ref<void(const PGOCtxProfContext &)> Visitor) {
+  std::function<void(const PGOCtxProfContext &)> Traverser =
+      [&](const auto &Ctx) {
+        Visitor(Ctx);
+        for (const auto &[_, SubCtxSet] : Ctx.callsites())
+          for (const auto &[__, Subctx] : SubCtxSet)
+            Traverser(Subctx);
+      };
+  for (const auto &[_, P] : Profiles)
+    Traverser(P);
+}
+
+const CtxProfFlatProfile PGOContextualProfile::flatten() const {
+  assert(Profiles.has_value());
+  CtxProfFlatProfile Flat;
+  preorderVisit(*Profiles, [&](const PGOCtxProfContext &Ctx) {
+    auto [It, Ins] = Flat.insert({Ctx.guid(), {}});
+    if (Ins) {
+      llvm::append_range(It->second, Ctx.counters());
----------------
snehasish wrote:

if you return after this, then you can drop the nesting for the else.

https://github.com/llvm/llvm-project/pull/104539