[llvm-branch-commits] [compiler-rt] [llvm] [ctxprof] Track unhandled call targets (PR #131417)

[Snehasish Kumar via llvm-branch-commits]

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@@ -246,22 +246,37 @@ ContextNode *getFlatProfile(FunctionData &Data, GUID Guid,
 
 ContextNode *getUnhandledContext(FunctionData &Data, GUID Guid,
                                  uint32_t NumCounters) {
-  // 1) if we are under a root (regardless if this thread is collecting or not a
+
+  // 1) if we are currently collecting a contextual profile, fetch a ContextNode
+  // in the `Unhandled` set. We want to do this regardless of `ProfilingStarted`
+  // to (hopefully) offset the penalty of creating these contexts to before
+  // profiling.
+  //
+  // 2) if we are under a root (regardless if this thread is collecting or not a
   // contextual profile for that root), do not collect a flat profile. We want
   // to keep flat profiles only for activations that can't happen under a root,
   // to avoid confusing profiles. We can, for example, combine flattened and
   // flat profiles meaningfully, as we wouldn't double-count anything.
   //
-  // 2) to avoid lengthy startup, don't bother with flat profiles until the
+  // 3) to avoid lengthy startup, don't bother with flat profiles until the
   // profiling started. We would reset them anyway when profiling starts.
   // HOWEVER. This does lose profiling for message pumps: those functions are
   // entered once and never exit. They should be assumed to be entered before
   // profiling starts - because profiling should start after the server is up
   // and running (which is equivalent to "message pumps are set up").
-  if (IsUnderContext || !__sanitizer::atomic_load_relaxed(&ProfilingStarted))
-    return TheScratchContext;
-  return markAsScratch(
-      onContextEnter(*getFlatProfile(Data, Guid, NumCounters)));
+  ContextRoot *R = __llvm_ctx_profile_current_context_root;
+  if (!R) {
+    if (IsUnderContext || !__sanitizer::atomic_load_relaxed(&ProfilingStarted))
+      return TheScratchContext;
+    else
+      return markAsScratch(
+          onContextEnter(*getFlatProfile(Data, Guid, NumCounters)));
+  }
+  auto It = R->Unhandled.insert({Guid, nullptr});
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snehasish wrote:

`auto& [Iter, Inserted] = R->Unhandled.insert(...)`
So that we can make the first second usage below a bit more readable.

https://github.com/llvm/llvm-project/pull/131417