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

[Paul Kirth via cfe-commits]

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@@ -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();
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ilovepi wrote:

I'm not sure I understand the logic here. We're using `SmallString<128>` above, but now you're memoizing a copy of the USR string contents in a Set, using an `std::string`. Is there a reason we need 2 string types?

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