[clang-tools-extra] [clang-doc] Improve performance by adding a short circuit (PR #96809)

[Paul Kirth via cfe-commits]

================
@@ -34,13 +43,26 @@ template <typename T> bool MapASTVisitor::mapDecl(const T *D) {
   // If there is an error generating a USR for the decl, skip this decl.
   if (index::generateUSRForDecl(D, USR))
     return true;
+
+  // Prevent Visiting USR twice
+  {
+    std::lock_guard<llvm::sys::Mutex> Guard(USRVisitedGuard);
+    std::string Visited = USR.str().str();
+    if (USRVisited.count(Visited))
+      return true;
+    // We considered a USR to be visited only when its defined
+    if (IsDefinition)
+      USRVisited.insert(Visited);
----------------
ilovepi wrote:

I don't think this logic makes sense. Why is it unreasonable to expect a USR to be valid only when its a definition? Is there some logic that prevents things that aren't definitions from being able to hold documentation? What I'm worried about, is the case where we have several USRs that contain different documentation bits that would have been merged in the past, but now wont.

If there is a concrete reason, please document that here in the comments, and in the commit message.

https://github.com/llvm/llvm-project/pull/96809